bims-mikwok 2024-03-17 papers

bims-mikwok

Biomed News

on Mitochondrial quality control

Issue of 2024–03–17
25 papers selected by
Gavin McStay, Liverpool John Moores University

GRAF1 Acts as a Downstream Mediator of Parkin to Regulate Mitophagy in Cardiomyocytes.
PKM2 interacts with and phosphorylates PHB2 to sustain mitochondrial quality control against septic cerebral-cardiac injury.
Loss of FoxO1 activates an alternate mechanism of mitochondrial quality control for healthy adipose browning.
The loss of OPA1 accelerates intervertebral disc degeneration and osteoarthritis in aged mice.
NME3 is a gatekeeper for DRP1-dependent mitophagy in hypoxia.
Study of an FBXO7 patient mutation reveals Fbxo7 and PI31 co-regulate proteasomes and mitochondria.
Yeast Bxi1/Ybh3 mediates conserved mitophagy and apoptosis in yeast and mammalian cells: convergence in Bcl-2 family.
The mitochondrial UPR induced by ATF5 attenuates intervertebral disc degeneration via cooperating with mitophagy.
MoAti1 mediates mitophagy by facilitating recruitment of MoAtg8 to promote invasive growth in Magnaporthe oryzae.
The Ubiquitin Ligase RBX2/SAG Regulates Mitochondrial Ubiquitination and Mitophagy.
Mitochondrial damage and clearance in retinal pigment epithelial cells.
Targeting PARP14 with lomitapide suppresses drug resistance through the activation of DRP1-induced mitophagy in multiple myeloma.
BAG3 localizes to mitochondria in cardiac fibroblasts and regulates mitophagy.
Drp1-dependent mitochondrial fragmentation mediates photoreceptor abnormalities in type 1 diabetic retina.
Genetic ablation of Immt induces a lethal disruption of the MICOS complex.
TDCPP and TiO2 NPs aggregates synergistically induce SH-SY5Y cell neurotoxicity by excessive mitochondrial fission and mitophagy inhibition.
Modular Assembly of Mitochondrial β-Barrel Proteins.
Mitophagy defect mediates the aging-associated hallmarks in Hutchinson-Gilford progeria syndrome.
A detailed review of pharmacology of MFN1 (mitofusion-1)-mediated mitochondrial dynamics: Implications for cellular health and diseases.
Research Progress of Mitophagy in Alzheimer's Disease.
Downregulation of Mitochondrial Fusion Protein Expression Affords Protection from Canonical Necroptosis in H9c2 Cardiomyoblasts.
Nicotinamide Mononucleotide (NMN) Works in Type 2 Diabetes through Unexpected Effects in Adipose Tissue, Not by Mitochondrial Biogenesis.
The use of NADH anisotropy to investigate mitochondrial cristae alignment.
Mitochondrial calcium uniporter promotes mitophagy by regulating the PINK1/Parkin pathway in caerulein‑treated pancreatic ductal epithelial cells in vitro.
Identification and validation of mitophagy-related signatures as a novel prognostic model for colorectal cancer.

Cells. 2024 Mar 04. pii: 448. [Epub ahead of print]13(5):

GRAF1 Acts as a Downstream Mediator of Parkin to Regulate Mitophagy in Cardiomyocytes.

Qiang Zhu, Matthew E Combs, Dawn E Bowles, Ryan T Gross, Michelle Mendiola Pla, Christopher P Mack, Joan M Taylor.

  Cardiomyocytes rely on proper mitochondrial homeostasis to maintain contractility and achieve optimal cardiac performance. Mitochondrial homeostasis is controlled by mitochondrial fission, fusion, and mitochondrial autophagy (mitophagy). Mitophagy plays a particularly important role in promoting the degradation of dysfunctional mitochondria in terminally differentiated cells. However, the precise mechanisms by which this is achieved in cardiomyocytes remain opaque. Our study identifies GRAF1 as an important mediator in PINK1-Parkin pathway-dependent mitophagy. Depletion of GRAF1 (Arhgap26) in cardiomyocytes results in actin remodeling defects, suboptimal mitochondria clustering, and clearance. Mechanistically, GRAF1 promotes Parkin-LC3 complex formation and directs autophagosomes to damaged mitochondria. Herein, we found that these functions are regulated, at least in part, by the direct binding of GRAF1 to phosphoinositides (PI(3)P, PI(4)P, and PI(5)P) on autophagosomes. In addition, PINK1-dependent phosphorylation of Parkin promotes Parkin-GRAF1-LC3 complex formation, and PINK1-dependent phosphorylation of GRAF1 (on S668 and S671) facilitates the clustering and clearance of mitochondria. Herein, we developed new phosphor-specific antibodies to these sites and showed that these post-translational modifications are differentially modified in human hypertrophic cardiomyopathy and dilated cardiomyopathy. Furthermore, our metabolic studies using serum collected from isoproterenol-treated WT and GRAF1CKO mice revealed defects in mitophagy-dependent cardiomyocyte fuel flexibility that have widespread impacts on systemic metabolism. In summary, our study reveals that GRAF1 co-regulates actin and membrane dynamics to promote cardiomyocyte mitophagy and that dysregulation of GRAF1 post-translational modifications may underlie cardiac disease pathogenesis.

Keywords:  GRAF1; PINK1-Parkin pathway; cardiomyocytes; metabolism; mitophagy

DOI:  https://doi.org/10.3390/cells13050448
Int J Med Sci. 2024 ;21(4): 633-643

PKM2 interacts with and phosphorylates PHB2 to sustain mitochondrial quality control against septic cerebral-cardiac injury.

Yuanchen Zhao, Yawen Pan, Mengyuan Chen, Ying Tan, Xing Chang, Haixia Li, Yinghao Zhi.

  Sepsis induces profound disruptions in cellular homeostasis, particularly impacting mitochondrial function in cardiovascular and cerebrovascular systems. This study elucidates the regulatory role of the Pyruvate Kinase M2 (PKM2)- Prohibitin 2 (PHB2) axis in mitochondrial quality control during septic challenges and its protective effects against myocardial and cerebral injuries. Employing LPS-induced mouse models, we demonstrate a significant downregulation of PKM2 and PHB2 in both heart and brain tissues post-sepsis, with corresponding impairments in mitochondrial dynamics, including fission, fusion, and mitophagy. Overexpression of PKM2 and PHB2 not only restores mitochondrial function, as evidenced by normalized ATP production and membrane potential but also confers resistance to oxidative stress by mitigating reactive oxygen species generation. These cellular mechanisms translate into substantial in vivo benefits, with transgenic mice overexpressing PKM2 or PHB2 displaying remarkable resistance to sepsis-induced cardiomyocyte and neuronal apoptosis, and organ dysfunction. Our findings highlight the PKM2-PHB2 interaction as a novel therapeutic target for sepsis, providing a foundation for future research into mitochondrial-based interventions to treat this condition. The study's insights into the molecular underpinnings of sepsis-induced organ failure pave the way for potential clinical applications in the management of sepsis and related pathologies.

Keywords:  PHB2; PKM2; mitochondrial quality control; septic cerebrovascular damage

DOI:  https://doi.org/10.7150/ijms.92367
Clin Sci (Lond). 2024 Mar 20. 138(6): 371-385

Loss of FoxO1 activates an alternate mechanism of mitochondrial quality control for healthy adipose browning.

Limin Shi, Jinying Yang, Zhipeng Tao, Louise Zheng, Tyler F Bui, Ramon L Alonso, Feng Yue, Zhiyong Cheng.

  Browning of white adipose tissue is hallmarked by increased mitochondrial density and metabolic improvements. However, it remains largely unknown how mitochondrial turnover and quality control are regulated during adipose browning. In the present study, we found that mice lacking adipocyte FoxO1, a transcription factor that regulates autophagy, adopted an alternate mechanism of mitophagy to maintain mitochondrial turnover and quality control during adipose browning. Post-developmental deletion of adipocyte FoxO1 (adO1KO) suppressed Bnip3 but activated Fundc1/Drp1/OPA1 cascade, concurrent with up-regulation of Atg7 and CTSL. In addition, mitochondrial biogenesis was stimulated via the Pgc1α/Tfam pathway in adO1KO mice. These changes were associated with enhanced mitochondrial homeostasis and metabolic health (e.g., improved glucose tolerance and insulin sensitivity). By contrast, silencing Fundc1 or Pgc1α reversed the changes induced by silencing FoxO1, which impaired mitochondrial quality control and function. Ablation of Atg7 suppressed mitochondrial turnover and function, causing metabolic disorder (e.g., impaired glucose tolerance and insulin sensitivity), regardless of elevated markers of adipose browning. Consistently, suppression of autophagy via CTSL by high-fat diet was associated with a reversal of adO1KO-induced benefits. Our data reveal a unique role of FoxO1 in coordinating mitophagy receptors (Bnip3 and Fundc1) for a fine-tuned mitochondrial turnover and quality control, underscoring autophagic clearance of mitochondria as a prerequisite for healthy browning of adipose tissue.

Keywords:  FoxO1; adipose browning; metabolism; mitochondrial quality control; mitophagy

DOI:  https://doi.org/10.1042/CS20230973
Res Sq. 2024 Feb 20. pii: rs.3.rs-3950044. [Epub ahead of print]

The loss of OPA1 accelerates intervertebral disc degeneration and osteoarthritis in aged mice.

Makarand Risbud, Vedavathi Madhu, Miriam Hernandez-Meadows, Ashley Coleman, Kimheak Sao, Kameron Inguito, Owen Haslam, Paige Boneski, Hiromi Sesaki, John Collins.

NP cells of the intervertebral disc and articular chondrocytes reside in avascular and hypoxic tissue niches. As a consequence of these environmental constraints the cells are primarily glycolytic in nature and were long thought to have a minimal reliance on mitochondrial function. Recent studies have challenged this long-held view and highlighted the increasingly important role of mitochondria in the physiology of these tissues. However, the foundational understanding of mechanisms governing mitochondrial dynamics and function in these tissues is lacking. We investigated the role of mitochondrial fusion protein OPA1 in maintaining the spine and knee joint health in mice. OPA1 knockdown in NP cells altered mitochondrial size and cristae shape and increased the oxygen consumption rate without affecting ATP synthesis. OPA1 governed the morphology of multiple organelles, including peroxisomes, early endosomes and cis-Golgi and its loss resulted in the dysregulation of NP cell autophagy. Metabolic profiling and 13 C-flux analyses revealed TCA cycle anaplerosis and altered metabolism in OPA1-deficient NP cells. Noteworthy, Opa1 AcanCreERT2 mice with Opa1 deletion in disc and cartilage showed age-dependent disc degeneration, osteoarthritis, and vertebral osteopenia. Our findings underscore that OPA1 regulation of mitochondrial dynamics and multi-organelle interactions is critical in preserving metabolic homeostasis of disc and cartilage.

DOI: https://doi.org/10.21203/rs.3.rs-3950044/v1
Nat Commun. 2024 Mar 13. 15(1): 2264

NME3 is a gatekeeper for DRP1-dependent mitophagy in hypoxia.

Chih-Wei Chen, Chi Su, Chang-Yu Huang, Xuan-Rong Huang, Xiaojing Cuili, Tung Chao, Chun-Hsiang Fan, Cheng-Wei Ting, Yi-Wei Tsai, Kai-Chien Yang, Ti-Yen Yeh, Sung-Tsang Hsieh, Yi-Ju Chen, Yuxi Feng, Tony Hunter, Zee-Fen Chang.

NME3 is a member of the nucleoside diphosphate kinase (NDPK) family localized on the mitochondrial outer membrane (MOM). Here, we report a role of NME3 in hypoxia-induced mitophagy dependent on its active site phosphohistidine but not the NDPK function. Mice carrying a knock-in mutation in the Nme3 gene disrupting NME3 active site histidine phosphorylation are vulnerable to ischemia/reperfusion-induced infarction and develop abnormalities in cerebellar function. Our mechanistic analysis reveals that hypoxia-induced phosphatidic acid (PA) on mitochondria is essential for mitophagy and the interaction of DRP1 with NME3. The PA binding function of MOM-localized NME3 is required for hypoxia-induced mitophagy. Further investigation demonstrates that the interaction with active NME3 prevents DRP1 susceptibility to MUL1-mediated ubiquitination, thereby allowing a sufficient amount of active DRP1 to mediate mitophagy. Furthermore, MUL1 overexpression suppresses hypoxia-induced mitophagy, which is reversed by co-expression of ubiquitin-resistant DRP1 mutant or histidine phosphorylatable NME3. Thus, the site-specific interaction with active NME3 provides DRP1 a microenvironment for stabilization to proceed the segregation process in mitophagy.

DOI: https://doi.org/10.1038/s41467-024-46385-7
FEBS J. 2024 Mar 11.

Study of an FBXO7 patient mutation reveals Fbxo7 and PI31 co-regulate proteasomes and mitochondria.

Sara Al Rawi, Lorna Simpson, Guðrún Agnarsdóttir, Neil Q McDonald, Veronika Chernuha, Orly Elpeleg, Massimo Zeviani, Roger A Barker, Ronen Spiegel, Heike Laman.

  Mutations in FBXO7 have been discovered to be associated with an atypical parkinsonism. We report here a new homozygous missense mutation in a paediatric patient that causes an L250P substitution in the dimerisation domain of Fbxo7. This alteration selectively ablates the Fbxo7-PI31 interaction and causes a significant reduction in Fbxo7 and PI31 levels in patient cells. Consistent with their association with proteasomes, patient fibroblasts have reduced proteasome activity and proteasome subunits. We also show PI31 interacts with the MiD49/51 fission adaptor proteins, and unexpectedly, PI31 acts to facilitate SCFFbxo7 -mediated ubiquitination of MiD49. The L250P mutation reduces the SCFFbxo7 ligase-mediated ubiquitination of a subset of its known substrates. Although MiD49/51 expression was reduced in patient cells, there was no effect on the mitochondrial network. However, patient cells show reduced levels of mitochondrial function and mitophagy, higher levels of ROS and are less viable under stress. Our study demonstrates that Fbxo7 and PI31 regulate proteasomes and mitochondria and reveals a new function for PI31 in enhancing the SCFFbxo7 E3 ubiquitin ligase activity.

Keywords:  E3 ubiquitin ligase; Fbxo7/PARK15; Parkinson's disease; mitochondria; proteasome

DOI:  https://doi.org/10.1111/febs.17114
Biol Chem. 2024 Mar 12.

Yeast Bxi1/Ybh3 mediates conserved mitophagy and apoptosis in yeast and mammalian cells: convergence in Bcl-2 family.

Yuying Wang, Zhiyuan Hu, Maojun Jiang, Yanxin Zhang, Linjie Yuan, Ziqian Wang, Ting Song, Zhichao Zhang.

  The process of degrading unwanted or damaged mitochondria by autophagy, called mitophagy, is essential for mitochondrial quality control together with mitochondrial apoptosis. In mammalian cells, pan-Bcl-2 family members including conical Bcl-2 members and non-conical ones are involved in and govern the two processes. We have illustrated recently the BH3 receptor Hsp70 interacts with Bim to mediate both apoptosis and mitophagy. However, whether similar pathways exist in lower eukaryotes where conical Bcl-2 members are absent remained unclear. Here, a specific inhibitor of the Hsp70-Bim PPI, S1g-10 and its analogs were used as chemical tools to explore the role of yeast Bxi1/Ybh3 in regulating mitophagy and apoptosis. Using Om45-GFP processing assay, we illustrated that yeast Ybh3 mediates a ubiquitin-related mitophagy pathway in both yeast and mammalian cells through association with Hsp70, which is in the same manner with Bim. Moreover, by using Bax/Bak double knockout MEF cells, Ybh3 was identified to induce apoptosis through forming oligomerization to trigger mitochondrial outer membrane permeabilization (MOMP) like Bax. We not only illustrated a conserved ubiquitin-related mitophagy pathway in yeast but also revealed the multi-function of Ybh3 which combines the function of BH3-only protein and multi-domain Bax protein as one.

Keywords:  Bxi1/Ybh3; Hsp70; mitophagy; ubiquitin

DOI:  https://doi.org/10.1515/hsz-2023-0359
Cell Biol Toxicol. 2024 Mar 13. 40(1): 16

The mitochondrial UPR induced by ATF5 attenuates intervertebral disc degeneration via cooperating with mitophagy.

Wen-Ning Xu, Huo-Liang Zheng, Run-Ze Yang, Yuan-Fang Sun, Bi-Rong Peng, Chun Liu, Jian Song, Sheng-Dan Jiang, Li-Xin Zhu.

  Intervertebral disc degeneration (IVDD) is an aging disease that results in a low quality of life and heavy socioeconomic burden. The mitochondrial unfolded protein response (UPRmt) take part in various aging-related diseases. Our research intents to explore the role and underlying mechanism of UPRmt in IVDD. Nucleus pulposus (NP) cells were exposed to IL-1β and nicotinamide riboside (NR) served as UPRmt inducer to treat NP cells. Detection of ATP, NAD + and NADH were used to determine the function of mitochondria. MRI, Safranin O-fast green and Immunohistochemical examination were used to determine the degree of IVDD in vivo. In this study, we discovered that UPRmt was increased markedly in the NP cells of human IVDD tissues than in healthy controls. In vitro, UPRmt and mitophagy levels were promoted in NP cells treated with IL-1β. Upregulation of UPRmt by NR and Atf5 overexpression inhibited NP cell apoptosis and further improved mitophagy. Silencing of Pink1 reversed the protective effects of NR and inhibited mitophagy induced by the UPRmt. In vivo, NR might attenuate the degree of IDD by activating the UPRmt in rats. In summary, the UPRmt was involved in IVDD by regulating Pink1-induced mitophagy. Mitophagy induced by the UPRmt might be a latent treated target for IVDD.

Keywords:  Atf5; Intervertebral disc degeneration; Mitochondrial unfolded protein response; Mitophagy; Pink1

DOI:  https://doi.org/10.1007/s10565-024-09854-9
Mol Plant Pathol. 2024 Mar;25(3): e13439

MoAti1 mediates mitophagy by facilitating recruitment of MoAtg8 to promote invasive growth in Magnaporthe oryzae.

Huanbin Shi, Shuai Meng, Jiehua Qiu, Shuwei Xie, Nan Jiang, Chaoxi Luo, Naweed I Naqvi, Yanjun Kou.

  Mitophagy is a selective autophagy for the degradation of damaged or excessive mitochondria to maintain intracellular homeostasis. In Magnaporthe oryzae, a filamentous ascomycetous fungus that causes rice blast, the most devastating disease of rice, mitophagy occurs in the invasive hyphae to promote infection. To date, only a few proteins are known to participate in mitophagy and the mechanisms of mitophagy are largely unknown in pathogenic fungi. Here, by a yeast two-hybrid screen with the core autophagy-related protein MoAtg8 as a bait, we obtained a MoAtg8 interactor MoAti1 (MoAtg8-interacting protein 1). Fluorescent observations and protease digestion analyses revealed that MoAti1 is primarily localized to the peripheral mitochondrial outer membrane and is responsible for recruiting MoAtg8 to mitochondria under mitophagy induction conditions. MoAti1 is specifically required for mitophagy, but not for macroautophagy and pexophagy. Infection assays suggested that MoAti1 is required for mitophagy in invasive hyphae during pathogenesis. Notably, no homologues of MoAti1 were found in rice and human protein databases, indicating that MoAti1 may be used as a potential target to control rice blast. By the host-induced gene silencing (HIGS) strategy, transgenic rice plants targeted to silencing MoATI1 showed enhanced resistance against M. oryzae with unchanged agronomic traits. Our results suggest that MoATI1 is required for mitophagy and pathogenicity in M. oryzae and can be used as a target for reducing rice blast.

Keywords:  Atg8; fungal pathogen; pathogenicity; rice blast; selective autophagy

DOI:  https://doi.org/10.1111/mpp.13439
bioRxiv. 2024 Feb 28. pii: 2024.02.24.581168. [Epub ahead of print]

The Ubiquitin Ligase RBX2/SAG Regulates Mitochondrial Ubiquitination and Mitophagy.

Wenjuan Wang, Ermin Li, Jianqiu Zou, Qu Chen, Juan Ayala, Yuan Wen, Md Sadikul Islam, Neal L Weintraub, David J Fulton, Qiangrong Liang, Jiliang Zhou, Jinbao Liu, Jie Li, Yi Sun, Huabo Su.

Clearance of damaged mitochondria via mitophagy is crucial for cellular homeostasis. While the role of ubiquitin (Ub) ligase PARKIN in mitophagy has been extensively studied, increasing evidence suggests the existence of PARKIN-independent mitophagy in highly metabolically active organs such as the heart. Here, we identify a crucial role for Cullin-RING Ub ligase 5 (CRL5) in basal mitochondrial turnover in cardiomyocytes. CRL5 is a multi-subunit Ub ligase comprised by the catalytic RING box protein RBX2 (also known as SAG), scaffold protein Cullin 5 (CUL5), and a substrate-recognizing receptor. Analysis of the mitochondrial outer membrane-interacting proteome uncovered a robust association of CRLs with mitochondria. Subcellular fractionation, immunostaining, and immunogold electron microscopy established that RBX2 and Cul5, two core components of CRL5, localizes to mitochondria. Depletion of RBX2 inhibited mitochondrial ubiquitination and turnover, impaired mitochondrial membrane potential and respiration, and increased cell death in cardiomyocytes. In vivo , deletion of the Rbx2 gene in adult mouse hearts suppressed mitophagic activity, provoked accumulation of damaged mitochondria in the myocardium, and disrupted myocardial metabolism, leading to rapid development of dilated cardiomyopathy and heart failure. Similarly, ablation of RBX2 in the developing heart resulted in dilated cardiomyopathy and heart failure. Notably, the action of RBX2 in mitochondria is not dependent on PARKIN, and PARKIN gene deletion had no impact on the onset and progression of cardiomyopathy in RBX2-deficient hearts. Furthermore, RBX2 controls the stability of PINK1 in mitochondria. Proteomics and biochemical analyses further revealed a global impact of RBX2 deficiency on the mitochondrial proteome and identified several mitochondrial proteins as its putative substrates. These findings identify RBX2-CRL5 as a mitochondrial Ub ligase that controls mitophagy under physiological conditions in a PARKIN-independent, PINK1-dependent manner, thereby regulating cardiac homeostasis.
Non-standard abbreviations and acronyms: RBX2, RING-Box Protein 2; SAG, Sensitive to Apoptosis Gene; Ub, Ubiquitin; pS65-Ub, phosphorylated Ub at serine 65; MAVS, mitochondrial antiviral-signaling protein; AAV, adeno-associated virus; AV, adenovirus; siRNA, Small interfering RNA; GFP, green fluorescent protein; CUL, cullin; RING, Really Interesting New Gene; CRLs, cullin-RING ligases; CSN, COP9 signalosome; APEX2, ascorbate peroxidase 2; mito, mitochondrial; cyto, cytosolic; MOM, mitochondrial outer membrane; CCCP, Carbonyl Cyanide Chlorophenylhydrazone; OMP25, Outer membrane protein 25; PK, proteinase K; HA, hemagglutinin; TMRM, Tetramethylrhodamine methyl ester perchlorate; αMHC,α-myosin heavy chain; CKO, cardiomyocyte-specific knockout; TAM, tamoxifen; TMT, tandem mass tag; KD, knockdown; CTL, control; MCM, MerCreMer; iCKO, inducible cardiomyocyte-specific knockout; BFA, bafilomycin A1; PCA, principle component analysis; MS, Mass spectrometry; DEPs, differentially expressed proteins; FC, fold change; FDR, False Discovery Rate; KEGG, Kyoto encyclopedia of genes and genomes; ER, endoplasmic reticulum; DKO, double knockout; CM, cardiomyocyte; cTnT, cardiac troponin T; NRVCs, neonatal rat ventricular cardiomyocytes; NRVMs, neonatal mouse ventricular cardiomyocytes; NMVFs, neonatal mouse ventricular fibroblasts; HF, heart failure; KO, knockout; MF, Molecular Functions; CC, Cellular Components; BP, Biological Process; TUNEL, Terminal deoxynucleotidyl transferase dUTP nick end labeling; SCF, Skp1-Cullin 1-F-box.

DOI: https://doi.org/10.1101/2024.02.24.581168
Acta Ophthalmol. 2024 Mar;102 Suppl 282 3-53

Mitochondrial damage and clearance in retinal pigment epithelial cells.

Iswariyaraja Sridevi Gurubaran.

  Age-related macular degeneration (AMD) is a devastating eye disease that causes permanent vision loss in the central part of the retina, known as the macula. Patients with such severe visual loss face a reduced quality of life and are at a 1.5 times greater risk of death compared to the general population. Currently, there is no cure for or effective treatment for dry AMD. There are several mechanisms thought to underlie the disease, for example, ageing-associated chronic oxidative stress, mitochondrial damage, harmful protein aggregation and inflammation. As a way of gaining a better understanding of the molecular mechanisms behind AMD and thus developing new therapies, we have created a peroxisome proliferator-activated receptor gamma coactivator 1-alpha and nuclear factor erythroid 2-related factor 2 (PGC1α/NFE2L2) double-knockout (dKO) mouse model that mimics many of the clinical features of dry AMD, including elevated levels of oxidative stress markers, damaged mitochondria, accumulating lysosomal lipofuscin and extracellular drusen-like structures in retinal pigment epithelial cells (RPE). In addition, a human RPE cell-based model was established to examine the impact of non-functional intracellular clearance systems on inflammasome activation. In this study, we found that there was a disturbance in the autolysosomal machinery responsible for clearing mitochondria in the RPE cells of one-year-old PGC1α/NFE2L2-deficient mice. The confocal immunohistochemical analysis revealed an increase in autophagosome marker microtubule-associated proteins 1A/1B light chain 3B (LC3B) as well as multiple mitophagy markers such as PTE-induced putative kinase 1 (PINK1) and E3 ubiquitin ligase (PARKIN), along with signs of damaged mitochondria. However, no increase in autolysosome formation was detected, nor was there a colocalization of the lysosomal marker LAMP2 or the mitochondrial marker, ATP synthase β. There was an upregulation of late autolysosomal fusion Ras-related protein (Rab7) in the perinuclear space of RPE cells, together with autofluorescent aggregates. Additionally, we observed an increase in the numbers of Toll-like receptors 3 and 9, while those of NOD-like receptor 3 were decreased in PGC1α/NFE2L2 dKO retinal specimens compared to wild-type animals. There was a trend towards increased complement component C5a and increased involvement of the serine protease enzyme, thrombin, in enhancing the terminal pathway producing C5a, independent of C3. The levels of primary acute phase C-reactive protein and receptor for advanced glycation end products were also increased in the PGC1α/NFE2L2 dKO retina. Furthermore, selective proteasome inhibition with epoxomicin promoted both nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and mitochondrial-mediated oxidative stress, leading to the release of mitochondrial DNA to the cytosol, resulting in potassium efflux-dependent activation of the absent in melanoma 2 (AIM2) inflammasome and the subsequent secretion of interleukin-1β in ARPE-19 cells. In conclusion, the data suggest that there is at least a relative decrease in mitophagy, increases in the amounts of C5 and thrombin and decreased C3 levels in this dry AMD-like model. Moreover, selective proteasome inhibition evoked mitochondrial damage and AIM2 inflammasome activation in ARPE-19 cells.

Keywords:  ageing; inflammasomes; inflammation; macular degeneration; mitochondria; mitophagy; oxidative stress; protein aggregation; retinal pigment epithelium

DOI:  https://doi.org/10.1111/aos.16661
Cancer Lett. 2024 Mar 09. pii: S0304-3835(24)00195-2. [Epub ahead of print] 216802

Targeting PARP14 with lomitapide suppresses drug resistance through the activation of DRP1-induced mitophagy in multiple myeloma.

Honghao Zhang, Hao Wang, Yuxing Hu, Yang Gao, Jianyu Chen, Yabo Meng, Yingqi Qiu, Rong Hu, Peiyun Liao, Meifang Li, Yanjie He, Zhao Liang, Xiaoling Xie, Yuhua Li.

  Multiple myeloma (MM) is a hematological malignancy that remains incurable, primarily due to the high likelihood of relapse or development of resistance to current treatments. To explore and discover new medications capable of overcoming drug resistance in MM, we conducted cell viability inhibition screens of 1504 FDA-approved drugs. Lomitapide, a cholesterol-lowering agent, was found to exhibit effective inhibition on bortezomib-resistant MM cells in vitro and in vivo. Our data also indicated that lomitapide decreases the permeability of the mitochondrial outer membrane and induces mitochondrial dysfunction in MM cells. Next, lomitapide treatment upregulated DRP1 and PINK1 expression levels, coupled with the mitochondrial translocation of Parkin, leading to MM cell mitophagy. Excessive mitophagy caused mitochondrial damage and dysfunction induced by lomitapide. Meanwhile, PARP14 was identified as a direct target of lomitapide by SPR-HPLC-MS, and we showed that DRP1-induced mitophagy was crucial in the anti-MM activity mediated by PARP14. Furthermore, PARP14 is overexpressed in MM patients, implying that it is a novel therapeutic target in MM. Collectively, our results demonstrate that DRP1-mediated mitophagy induced by PARP14 may be the cause for mitochondrial dysfunction and damage in response to lomitapide treatment.

Keywords:  Drug resistance; Lomitapide; Mitophagy; Multiple myeloma; PARP14

DOI:  https://doi.org/10.1016/j.canlet.2024.216802
Am J Physiol Heart Circ Physiol. 2024 Mar 15.

BAG3 localizes to mitochondria in cardiac fibroblasts and regulates mitophagy.

Thomas G Martin, Laura A Sherer, Jonathan A Kirk.

  The co-chaperone BAG3 is a central node in protein quality control in the heart. In humans and animal models, decreased BAG3 expression is associated with cardiac dysfunction and dilated cardiomyopathy. While previous studies focused on BAG3 in cardiomyocytes, cardiac fibroblasts are also critical drivers of pathologic remodeling. Yet, BAG3's role in cardiac fibroblasts is almost completely unexplored. Here, we show BAG3 is expressed in primary rat neonatal cardiac fibroblasts and preferentially localizes to mitochondria. Knockdown of BAG3 reduces mitophagy and enhances fibroblast activation, which is associated with fibrotic remodeling. Hsp70 is a critical binding partner for BAG3 and inhibiting this interaction in fibroblasts using the drug JG-98 decreased autophagy, decreased mitofusin-2 expression, and disrupted mitochondrial morphology. Together, this data indicates that BAG3 is expressed in cardiac fibroblasts, where it facilitates mitophagy and promotes fibroblast quiescence. This suggests that depressed BAG3 levels in heart failure may exacerbate fibrotic pathology, thus contributing to myocardial dysfunction through sarcomere-independent pathways.

Keywords:  BAG3; cardiac fibroblasts; heart; mitophagy

DOI:  https://doi.org/10.1152/ajpheart.00736.2023
Exp Eye Res. 2024 Mar 09. pii: S0014-4835(24)00081-2. [Epub ahead of print] 109860

Drp1-dependent mitochondrial fragmentation mediates photoreceptor abnormalities in type 1 diabetic retina.

Shuyu Tang, Mengling Huang, Ruixuan Wang, Ming Li, Ning Dong, Ronghan Wu, Zailong Chi, Ling Gao.

  Recent studies have highlighted that retinal neurodegeneration precedes microvascular changes in diabetic retinopathy (DR), but the specific mechanisms remain unclear. Given the pivotal role of dysfunctional mitochondria and oxidative stress in early DR, our objective was to observe mitochondria-related alterations in the neural retina of type one diabetic mellitus mice with no evidence of DR (T1DM-NDR). We aimed to identify the key mitochondrial-related proteins contributing to mitochondrial injury. Our study revealed that T1DM-NDR mice exhibited outer retina thinning, including the ellipsoid zone, inner segment, and outer segment. Additionally, there was an impaired amplitude of the b-wave in electroretinogram (ERG) and a disorganized arrangement of the photoreceptor layer. In both the retina of DM mice and high glucose (HG)-treated 661w cells, mitochondria appeared swollen and fragmented, with disrupted cristae, disorganized or shortened branches in the mitochondrial network, and decreased mitochondrial membrane potential. Among the mitochondrial-related proteins, dynamin-related protein 1 (Drp1) was upregulated, and the ratio of phosphorylated Drp1 protein at serine 616 (S616) and serine 637 (S637) sites significantly increased in the retina of DM mice. The administration of Mdivi-1 ameliorated high-glucose-induced dysfunctional mitochondria, thereby protecting T1DM-NDR mice retina from morphological and functional injuries. Our findings suggest that hyperglycemia promotes Drp1-mediated mitochondrial dysfunction, which may be a significant factor in the development of DR. The inhibition of high-glucose-induced mitochondrial fission emerges as a potential and innovative intervention strategy for preventing DR.

Keywords:  Diabetic retinopathy; Drp1; Mitochondria; Photoreceptor; T1DM

DOI:  https://doi.org/10.1016/j.exer.2024.109860
Life Sci Alliance. 2024 Jun;pii: e202302329. [Epub ahead of print]7(6):

Genetic ablation of Immt induces a lethal disruption of the MICOS complex.

Stephanie M Rockfield, Meghan E Turnis, Ricardo Rodriguez-Enriquez, Madhavi Bathina, Seng Kah Ng, Nathan Kurtz, Nathalie Becerra Mora, Stephane Pelletier, Camenzind G Robinson, Peter Vogel, Joseph T Opferman.

The mitochondrial contact site and cristae organizing system (MICOS) is important for crista junction formation and for maintaining inner mitochondrial membrane architecture. A key component of the MICOS complex is MIC60, which has been well studied in yeast and cell culture models. However, only one recent study has demonstrated the embryonic lethality of losing Immt (the gene encoding MIC60) expression. Tamoxifen-inducible ROSA-CreERT2-mediated deletion of Immt in adult mice disrupted the MICOS complex, increased mitochondria size, altered cristae morphology, and was lethal within 12 d. Pathologically, these mice displayed defective intestinal muscle function (paralytic ileus) culminating in dehydration. We also identified bone marrow (BM) hypocellularity in Immt-deleted mice, although BM transplants from wild-type mice did not improve survival. Altogether, this inducible mouse model demonstrates the importance of MIC60 in vivo, in both hematopoietic and non-hematopoietic tissues, and provides a valuable resource for future mechanistic investigations into the MICOS complex.

DOI: https://doi.org/10.26508/lsa.202302329
Environ Pollut. 2024 Mar 08. pii: S0269-7491(24)00454-8. [Epub ahead of print] 123740

TDCPP and TiO2 NPs aggregates synergistically induce SH-SY5Y cell neurotoxicity by excessive mitochondrial fission and mitophagy inhibition.

Ling Wang, Binquan Wang, Xiaoyan Zhang, Ziyi Yang, Xing Zhang, Hongyang Gong, Yuanyuan Song, Ke Zhang, Mingkuan Sun.

  Tris (1,3-dichloro-2-propyl) phosphate (TDCPP), a halogen-containing phosphorus flame retardant, is widely used and has been shown to possess health risks to humans. The sustained release of artificial nanomaterials into the environment increases the toxicological risks of their coexisting pollutants. Nanomaterials may seriously change the environmental behavior and fate of pollutants. In this study, we investigated this combined toxicity and the potential mechanisms of toxicity of TDCPP and titanium dioxide nanoparticles (TiO2 NPs) aggregates on human neuroblastoma SH-SY5Y cells. TDCPP and TiO2 NPs aggregates were exposed in various concentration combinations, revealing that TDCPP (25 μg/mL) reduced cell viability, while synergistic exposure to TiO2 NPs aggregates exacerbated cytotoxicity. This combined exposure also disrupted mitochondrial function, leading to dysregulation in the expression of mitochondrial fission proteins (DRP1 and FIS1) and fusion proteins (OPA1 and MFN1). Consequently, excessive mitochondrial fission occurred, facilitating the translocation of cytochrome C from mitochondria to activate apoptotic signaling pathways. Furthermore, exposure of the combination of TDCPP and TiO2 NPs aggregates activated upstream mitochondrial autophagy but disrupted downstream Parkin recruitment to damaged mitochondria, preventing autophagosome-lysosome fusion and thereby disrupting mitochondrial autophagy. Altogether, our findings suggest that TDCPP and TiO2 NPs aggregates may stimulate apoptosis in neuronal SH-SY5Y cells by inducing mitochondrial hyperfission and inhibiting mitochondrial autophagy.

Keywords:  Apoptosis; Autophagic flux; Mitochondrial dysfunction; Neurotoxic effects; TDCPP; TiO(2) NPs aggregates

DOI:  https://doi.org/10.1016/j.envpol.2024.123740
Methods Mol Biol. 2024 ;2778 201-220

Modular Assembly of Mitochondrial β-Barrel Proteins.

Rituparna Bhowmik, Fabian den Brave, Thomas Becker.

  Mitochondrial β-barrel proteins fulfill crucial roles in the biogenesis and function of the cell organelle. They mediate the import and membrane insertion of proteins and transport of small metabolites and ions. All β-barrel proteins are made as precursors on cytosolic ribosomes and are imported into mitochondria. The β-barrel proteins fold and assemble with partner proteins in the outer membrane. The in vitro import of radiolabelled proteins into isolated mitochondria is a powerful tool to investigate the import of β-barrel proteins, the folding of the β-barrel proteins, and their assembly into protein complexes. Altogether, the in vitro import assay is a versatile and crucial assay to analyze the mechanisms of the biogenesis of mitochondrial β-barrel proteins.

Keywords:  Blue native electrophoresis; Mitochondria; Protein import assay; SAM complex; TOM complex; β-barrel proteins

DOI:  https://doi.org/10.1007/978-1-0716-3734-0_13
Aging Cell. 2024 Mar 14. e14143

Mitophagy defect mediates the aging-associated hallmarks in Hutchinson-Gilford progeria syndrome.

Yingying Sun, Le Xu, Yi Li, Shunze Jia, Gang Wang, Xufeng Cen, Yuyan Xu, Zhongkai Cao, Jingjing Wang, Ning Shen, Lidan Hu, Jin Zhang, Jianhua Mao, Hongguang Xia, Zhihong Liu, Xudong Fu.

  Hutchinson-Gilford progeria syndrome (HGPS) is a rare and fatal disease manifested by premature aging and aging-related phenotypes, making it a disease model for aging. The cellular machinery mediating age-associated phenotypes in HGPS remains largely unknown, resulting in limited therapeutic targets for HGPS. In this study, we showed that mitophagy defects impaired mitochondrial function and contributed to cellular markers associated with aging in mesenchymal stem cells derived from HGPS patients (HGPS-MSCs). Mechanistically, we discovered that mitophagy affected the aging-associated phenotypes of HGPS-MSCs by inhibiting the STING-NF-ĸB pathway and the downstream transcription of senescence-associated secretory phenotypes (SASPs). Furthermore, by utilizing UMI-77, an effective mitophagy inducer, we showed that mitophagy induction alleviated aging-associated phenotypes in HGPS and naturally aged mice. Collectively, our results uncovered that mitophagy defects mediated the aging-associated markers in HGPS, highlighted the function of mitochondrial homeostasis in HGPS progression, and suggested mitophagy as an intervention target for HGPS and aging.

Keywords:  HGPS; UMI-77; aging; mitophagy

DOI:  https://doi.org/10.1111/acel.14143
Saudi Pharm J. 2024 Apr;32(4): 102012

A detailed review of pharmacology of MFN1 (mitofusion-1)-mediated mitochondrial dynamics: Implications for cellular health and diseases.

Adel Alghamdi.

  The mitochondria are responsible for the production of cellular ATP, the regulation of cytosolic calcium levels, and the organization of numerous apoptotic proteins through the release of cofactors necessary for the activation of caspases. This level of functional adaptability can only be attained by sophisticated structural alignment. The morphology of the mitochondria does not remain unchanged throughout time; rather, it undergoes change as a result of processes known as fusion and fission. Fzo in flies, Fzo1 in yeast, and mitofusins in mammals are responsible for managing the outer mitochondrial membrane fusion process, whereas Mgm1 in yeast and optic atrophy 1 in mammals are responsible for managing the inner mitochondrial membrane fusion process. The fusion process is composed of two phases. MFN1, a GTPase that is located on the outer membrane of the mitochondria, is involved in the process of linking nearby mitochondria, maintaining the potential of the mitochondrial membrane, and apoptosis. This article offers specific information regarding the functions of MFN1 in a variety of cells and organs found in living creatures. According to the findings of the literature review, MFN1 plays an important part in a number of diseases and organ systems; nevertheless, the protein's function in other disease models and cell types has to be investigated in the near future so that it can be chosen as a promising marker for the therapeutic and diagnostic potentials it possesses. Overall, the major findings of this review highlight the pivotal role of mitofusin (MFN1) in regulating mitochondrial dynamics and its implications across various diseases, including neurodegenerative disorders, cardiovascular diseases, and metabolic syndromes. Our review identifies novel therapeutic targets within the MFN1 signaling pathways and underscores the potential of MFN1 modulation as a promising strategy for treating mitochondrial-related diseases. Additionally, the review calls for further research into MFN1's molecular mechanisms to unlock new avenues for clinical interventions, emphasizing the need for targeted therapies that address MFN1 dysfunction.

Keywords:  Apoptosis; MFN1; Mitochondria; Mitochondrial energetics; Mitochondrial fusion; Mitochondrial membrane potential

DOI:  https://doi.org/10.1016/j.jsps.2024.102012
Curr Alzheimer Res. 2024 Mar 12.

Research Progress of Mitophagy in Alzheimer's Disease.

Jinglin Yao, Bohong Kan, Zhengjia Dong, Zhenyu Tang.

  The prevalence of Alzheimer's disease (AD) is increasing as the elderly population, which hurts elderly people's cognition and capacity for self-care. The process of mitophagy involves the selective clearance of ageing and impaired mitochondria, which is required to preserve intracellular homeostasis and energy metabolism. Currently, it has been discovered that mitophagy abnormalities are intimately linked to the beginning and progression of AD. This article discusses the mechanism of mitophagy, abnormal mitophagy, and therapeutic effects in AD. The purpose is to offer fresh perspectives on the causes and remedies of AD.

Keywords:  Alzheimer's disease (AD); PINK1; mitochondrial damage; mitophagy; parkin; treatment.

DOI:  https://doi.org/10.2174/0115672050300063240305074310
Int J Mol Sci. 2024 Mar 02. pii: 2905. [Epub ahead of print]25(5):

Downregulation of Mitochondrial Fusion Protein Expression Affords Protection from Canonical Necroptosis in H9c2 Cardiomyoblasts.

Yuki Toda, Sang-Bing Ong, Toshiyuki Yano, Atsushi Kuno, Hidemichi Kouzu, Tatsuya Sato, Wataru Ohwada, Yuki Tatekoshi, Toshifumi Ogawa, Masaki Shimizu, Masaya Tanno, Masato Furuhashi.

  Necroptosis, a form of necrosis, and alterations in mitochondrial dynamics, a coordinated process of mitochondrial fission and fusion, have been implicated in the pathogenesis of cardiovascular diseases. This study aimed to determine the role of mitochondrial morphology in canonical necroptosis induced by a combination of TNFα and zVAD (TNF/zVAD) in H9c2 cells, rat cardiomyoblasts. Time-course analyses of mitochondrial morphology showed that mitochondria were initially shortened after the addition of TNF/zVAD and then their length was restored, and the proportion of cells with elongated mitochondria at 12 h was larger in TNF/zVAD-treated cells than in non-treated cells (16.3 ± 0.9% vs. 8.0 ± 1.2%). The knockdown of dynamin-related protein 1 (Drp1) and fission 1, fission promoters, and treatment with Mdivi-1, a Drp-1 inhibitor, had no effect on TNF/zVAD-induced necroptosis. In contrast, TNF/zVAD-induced necroptosis was attenuated by the knockdown of mitofusin 1/2 (Mfn1/2) and optic atrophy-1 (Opa1), proteins that are indispensable for mitochondrial fusion, and the attenuation of necroptosis was not canceled by treatment with Mdivi-1. The expression of TGFβ-activated kinase (TAK1), a negative regulator of RIP1 activity, was upregulated and the TNF/zVAD-induced RIP1-Ser166 phosphorylation, an index of RIP1 activity, was mitigated by the knockdown of Mfn1/2 or Opa1. Pharmacological TAK1 inhibition attenuated the protection afforded by Mfn1/2 and Opa1 knockdown. In conclusion, the inhibition of mitochondrial fusion increases TAK1 expression, leading to the attenuation of canonical necroptosis through the suppression of RIP1 activity.

Keywords:  RIP1; TAK1; cardiomyocyte; mitochondrial fusion; necroptosis

DOI:  https://doi.org/10.3390/ijms25052905
Int J Mol Sci. 2024 Feb 23. pii: 2594. [Epub ahead of print]25(5):

Nicotinamide Mononucleotide (NMN) Works in Type 2 Diabetes through Unexpected Effects in Adipose Tissue, Not by Mitochondrial Biogenesis.

Roua Gabriela Popescu, Anca Dinischiotu, Teodoru Soare, Ene Vlase, George Cătălin Marinescu.

  Nicotinamide mononucleotide (NMN) has emerged as a promising therapeutic intervention for age-related disorders, including type 2 diabetes. In this study, we confirmed the previously observed effects of NMN treatment on glucose uptake and investigated its underlying mechanisms in various tissues and cell lines. Through the most comprehensive proteomic analysis to date, we discovered a series of novel organ-specific effects responsible for glucose uptake as measured by the IPGTT: adipose tissue growing (suggested by increased protein synthesis and degradation and mTOR proliferation signaling upregulation). Notably, we observed the upregulation of thermogenic UCP1, promoting enhanced glucose conversion to heat in intermuscular adipose tissue while showing a surprising repressive effect on mitochondrial biogenesis in muscle and the brain. Additionally, liver and muscle cells displayed a unique response, characterized by spliceosome downregulation and concurrent upregulation of chaperones, proteasomes, and ribosomes, leading to mildly impaired and energy-inefficient protein synthesis machinery. Furthermore, our findings revealed remarkable metabolic rewiring in the brain. This involved increased production of ketone bodies, downregulation of mitochondrial OXPHOS and TCA cycle components, as well as the induction of well-known fasting-associated effects. Collectively, our data elucidate the multifaceted nature of NMN action, highlighting its organ-specific effects and their role in improving glucose uptake. These findings deepen our understanding of NMN's therapeutic potential and pave the way for novel strategies in managing metabolic disorders.

Keywords:  DIA SWATH proteomics; NMN proteomics; NMN type 2 diabetes; nicotinamide mononucleotide (NMN) effects; pathway analysis; protein interaction network

DOI:  https://doi.org/10.3390/ijms25052594
Sci Rep. 2024 03 12. 14(1): 5980

The use of NADH anisotropy to investigate mitochondrial cristae alignment.

Holly E Smith, Alasdair M Mackenzie, Chloe Seddon, Rhys Mould, Ifi Kalampouka, Partha Malakar, Sarah R Needham, Konstantinos Beis, Jimmy D Bell, Alistair Nunn, Stanley W Botchway.

Life may be expressed as the flow of electrons, protons, and other ions, resulting in large potential difference. It is also highly photo-sensitive, as a large proportion of the redox capable molecules it relies on are chromophoric. It is thus suggestive that a key organelle in eukaryotes, the mitochondrion, constantly adapt their morphology as part of the homeostatic process. Studying unstained in vivo nano-scale structure in live cells is technically very challenging. One option is to study a central electron carrier in metabolism, reduced nicotinamide adenine dinucleotide (NADH), which is fluorescent and mostly located within mitochondria. Using one and two-photon absorption (340-360 nm and 730 nm, respectively), fluorescence lifetime imaging and anisotropy spectroscopy of NADH in solution and in live cells, we show that mitochondria do indeed appear to be aligned and exhibit high anisotropy (asymmetric directionality). Aqueous solution of NADH showed an anisotropy of ~ 0.20 compared to fluorescein or coumarin of < 0.1 and 0.04 in water respectively and as expected for small organic molecules. The anisotropy of NADH also increased further to 0.30 in the presence of proteins and 0.42 in glycerol (restricted environment) following two-photon excitation, suggesting more ordered structures. Two-photon NADH fluorescence imaging of Michigan Cancer Foundation-7 (MCF7) also showed strong anisotropy of 0.25 to 0.45. NADH has a quantum yield of fluorescence of 2% compared to more than 40% for photoionisation (electron generation), when exposed to light at 360 nm and below. The consequence of such highly ordered and directional NADH patterns with respect to electron ejection upon ultra-violet (UV) excitation could be very informative-especially in relation to ascertaining the extent of quantum effects in biology, including electron and photonic cascade, communication and modulation of effects such as spin and tunnelling.

DOI: https://doi.org/10.1038/s41598-024-55780-5
Exp Ther Med. 2024 Apr;27(4): 147

Mitochondrial calcium uniporter promotes mitophagy by regulating the PINK1/Parkin pathway in caerulein‑treated pancreatic ductal epithelial cells in vitro.

Yu Lei, Hui-Ying Yang, Nuo Meng, Ying-Ying Qin, Meng-Tao Xu, Xue-Lian Xiang, Li Liu, Guo-Du Tang.

  The mitochondrial calcium uniporter (MCU) is a major protein for the uptake of mitochondrial calcium to regulate intracellular energy metabolism, including processes such as mitophagy. The present study investigated the effect of the MCU on mitophagy in pancreatic ductal epithelial cells (PDECs) in acute pancreatitis (AP) in vitro. The normal human PDECs (HPDE6-C7) were treated with caerulein (CAE) to induce AP-like changes, with or without ruthenium red to inhibit the MCU. The mitochondrial membrane potentials (MMPs) and mitochondrial Ca2+ levels were analyzed by fluorescence. The expression levels of MCU, LC3, p62, and translocase of the outer mitochondrial membrane complex subunit 20 (TOMM20), putative kinase 1 (PINK1), and Parkin were measured by western blotting and immunofluorescence. Mitophagy was observed by confocal fluorescence microscopy and transmission electron microscopy. The results showed that CAE increased the MCU protein expression, mitochondrial Ca2+ levels, MMP depolarization and the protein expression of mitophagy markers including the LC3II/I ratio, PINK1, and Parkin. CAE decreased the protein expression of p62 and TOMM20, and promoted the formation of mitophagosomes in HPDE6-C7 cells. Notably, changes in these markers were reversed by inhibiting the MCU. In conclusion, an activated MCU may promote mitophagy by regulating the PINK1/Parkin pathway in PDECs in AP.

Keywords:  acute pancreatitis; mitochondrial calcium uniporter; mitophagy; pancreatic ductal epithelial cells; putative kinase 1/Parkin pathway

DOI:  https://doi.org/10.3892/etm.2024.12435
Transl Cancer Res. 2024 Feb 29. 13(2): 782-797

Identification and validation of mitophagy-related signatures as a novel prognostic model for colorectal cancer.

Qing Ke, Yun Wang, Yanyan Deng, Jinjin Wang, Mengjiao Yuan, Aifeng Liang, Jin Wang, Qian Gong.

   Background: Colorectal cancer (CRC) is one of the most commonly diagnosed cancers in the world. Mitophagy is associated with tumorigenesis and development of malignancy. However, the specific role of mitophagy has yet not been systematically explored in CRC.
Methods: The RNA-sequencing dataset of CRC from The Cancer Genome Atlas (TCGA) and microarray data of gene expression profiles of CRC from Gene Expression Omnibus (GEO) were downloaded. Mitophagy-related gene sets were obtained from the Pathway Unification database. The package "limma" was used for differential gene expression analysis. Kaplan-Meier (KM) survival analyses were utilized to evaluate the prognostic value of the mitophagy regulators. Single-sample gene set enrichment analysis (ssGSEA) was used to estimate the infiltrating immune cells and the activity of immune response. The ConsensusClusterPlus algorithm was used to determine mitophagy-related subtypes. Principal component analysis (PCA) was used to create composite measurement of mitophagy scores. The R packages "survminer" and "ReGlot" were used to plot the nomogram and calibration curves.
Results: Integrated analysis of the GEO and TCGA databases revealed some common differentially expressed genes (DEGs) in CRC. MFN2, UBB, PINK1, and PRKN were significantly downregulated in CRC samples as compared to normal samples, and other genes were significantly upregulated in CRC samples. KM survival analyses showed that high expression of ATG12 and MAP1LC3B predicted a poor prognosis, whereas high expression of TOMM22 and TOMM40 predicted a better prognosis. Mitophagy showed significant correlation with immune-related pathways in CRC samples. We identified 2 distinct CRC subtypes with different mitophagy accumulation, of which subtype B had better prognosis and immune activity. The mitophagy score may be employed as a new and efficient clinical predictor in conjunction with other clinical indicators to predict the prognosis of CRC patients.
Conclusions: We systematically investigated the CRC heterogeneity with reference to mitophagy based on bioinformatics analyses, and the findings of this study might provide some guidance for future research into potential biomarkers for diagnosis and prognosis prediction of CRC patients.

Keywords:  Colorectal cancer (CRC); immunity; mitophagy; prognosis

DOI:  https://doi.org/10.21037/tcr-23-785