bims-cesemi 2024-06-16 papers

bims-cesemi

Biomed News

on Cellular senescence and mitochondria

Issue of 2024–06–16
seventeen papers selected by
Julio Cesar Cardenas, Universidad Mayor

Regulation of cell function and identity by cellular senescence.
The mitochondrial calcium uniporter: Balancing tumourigenic and anti-tumourigenic responses.
Monitoring mitochondrial calcium in cardiomyocytes during coverslip hypoxia using a fluorescent lifetime indicator.
A Fully-Automated Senescence Test (FAST) for the high-throughput quantification of senescence-associated markers.
C16ORF70/Mytho promotes healthy ageing in C. elegans and prevents cellular senescence in mammals.
Suppression of autophagy induces senescence in the heart.
Interactions between oxidative stress and senescence in cancer: Mechanisms, therapeutic implications, and future perspectives.
Calcium signaling from sarcoplasmic reticulum and mitochondria contact sites in acute myocardial infarction.
Mammalian target of differentiation-inducing factor-1 is mitochondrial malate dehydrogenase for activation of AMP-activated protein kinase and induction of mitochondrial fission.
The Bioenergetic Landscape of Cancer.
MTFP1 controls mitochondrial fusion to regulate inner membrane quality control and maintain mtDNA levels.
The miR-30-5p/TIA-1 axis directs cellular senescence by regulating mitochondrial dynamics.
IP3R2 regulates apoptosis by Ca2+ transfer through mitochondria-ER contacts in hypoxic photoreceptor injury.
HDAC4 influences the DNA damage response and counteracts senescence by assembling with HDAC1/HDAC2 to control H2BK120 acetylation and homology-directed repair.
Mitochondrial Calcium Signaling Regulates Branched-Chain Amino Acid Catabolism in Fibrolamellar Carcinoma.
Aberrant ER-mitochondria communication is a common pathomechanism in mitochondrial disease.
Age-related behavioral resilience in smartphone touchscreen interaction dynamics.

J Cell Biol. 2024 Aug 05. pii: e202401112. [Epub ahead of print]223(8):

Regulation of cell function and identity by cellular senescence.

Anda Huna, Amélie Massemin, Gabriela Makulyte, Jean-Michel Flaman, Nadine Martin, David Bernard.

During aging and in some contexts, like embryonic development, wound healing, and diseases such as cancer, senescent cells accumulate and play a key role in different pathophysiological functions. A long-held belief was that cellular senescence decreased normal cell functions, given the loss of proliferation of senescent cells. This view radically changed following the discovery of the senescence-associated secretory phenotype (SASP), factors released by senescent cells into their microenvironment. There is now accumulating evidence that cellular senescence also promotes gain-of-function effects by establishing, reinforcing, or changing cell identity, which can have a beneficial or deleterious impact on pathophysiology. These effects may involve both proliferation arrest and autocrine SASP production, although they largely remain to be defined. Here, we provide a historical overview of the first studies on senescence and an insight into emerging trends regarding the effects of senescence on cell identity.

DOI: https://doi.org/10.1083/jcb.202401112
J Physiol. 2024 Jun 10.

The mitochondrial calcium uniporter: Balancing tumourigenic and anti-tumourigenic responses.

Danielle M Colussi, Peter B Stathopulos.

  Increased malignancy and poor treatability associated with solid tumour cancers have commonly been attributed to mitochondrial calcium (Ca2+) dysregulation. The mitochondrial Ca2+ uniporter complex (mtCU) is the predominant mode of Ca2+ uptake into the mitochondrial matrix. The main components of mtCU are the pore-forming mitochondrial Ca2+ uniporter (MCU) subunit, MCU dominant-negative beta (MCUb) subunit, essential MCU regulator (EMRE) and the gatekeeping mitochondrial Ca2+ uptake 1 and 2 (MICU1 and MICU2) proteins. In this review, we describe mtCU-mediated mitochondrial Ca2+ dysregulation in solid tumour cancer types, finding enhanced mtCU activity observed in colorectal cancer, breast cancer, oral squamous cell carcinoma, pancreatic cancer, hepatocellular carcinoma and embryonal rhabdomyosarcoma. By contrast, decreased mtCU activity is associated with melanoma, whereas the nature of mtCU dysregulation remains unclear in glioblastoma. Furthermore, we show that numerous polymorphisms associated with cancer may alter phosphorylation sites on the pore forming MCU and MCUb subunits, which cluster at interfaces with EMRE. We highlight downstream/upstream biomolecular modulators of MCU and MCUb that alter mtCU-mediated mitochondrial Ca2+ uptake and may be used as biomarkers or to aid in the development of novel cancer therapeutics. Additionally, we provide an overview of the current small molecule inhibitors of mtCU that interact with the Asp residue of the critical Asp-Ile-Met-Glu motif or through other allosteric regulatory mechanisms to block Ca2+ permeation. Finally, we describe the relationship between MCU- and MCUb-mediating microRNAs and mitochondrial Ca2+ uptake that should be considered in the discovery of new treatment approaches for cancer.

Keywords:  MCU; MCU dominant negative beta subunit; MCUb; cancer; miRNA; mitochondrial calcium uniporter; mutation; phosphorylation

DOI:  https://doi.org/10.1113/JP285515
J Mol Cell Cardiol Plus. 2024 Jun;pii: 100074. [Epub ahead of print]8

Monitoring mitochondrial calcium in cardiomyocytes during coverslip hypoxia using a fluorescent lifetime indicator.

Yusuf Mastoor, Mikako Harata, Kavisha Silva, Chengyu Liu, Christian A Combs, Barbara Roman, Elizabeth Murphy.

  An increase in mitochondrial calcium via the mitochondrial calcium uniporter (MCU) has been implicated in initiating cell death in the heart during ischemia-reperfusion (I/R) injury. Measurement of calcium during I/R has been challenging due to the pH sensitivity of indicators coupled with the fall in pH during I/R. The development of a pH-insensitive indicator, mitochondrial localized Turquoise Calcium fluorescence Lifetime Sensor (mito-TqFLITS), allows for quantifying mitochondrial calcium during I/R via fluorescent lifetime imaging. Mitochondrial calcium was monitored using mito-TqFLITS, in neonatal mouse ventricular myocytes (NMVM) isolated from germline MCU-KO mice and MCUfl/fl treated with CRE-recombinase to acutely knockout MCU. To simulate ischemia, a coverslip was placed on a monolayer of NMVMs to prevent access to oxygen and nutrients. Reperfusion was induced by removing the coverslip. Mitochondrial calcium increases threefold during coverslip hypoxia in MCU-WT. There is a significant increase in mitochondrial calcium during coverslip hypoxia in germline MCU-KO, but it is significantly lower than in MCU-WT. We also found that compared to WT, acute MCU-KO resulted in no difference in mitochondrial calcium during coverslip hypoxia and reoxygenation. To determine the role of mitochondrial calcium uptake via MCU in initiating cell death, we used propidium iodide to measure cell death. We found a significant increase in cell death in both the germline MCU-KO and acute MCU-KO, but this was similar to their respective WTs. These data demonstrate the utility of mito-TqFLITS to monitor mitochondrial calcium during simulated I/R and further show that germline loss of MCU attenuates the rise in mitochondrial calcium during ischemia but does not reduce cell death.

Keywords:  calcium; cardioprotection; cell death; fluorescent lifetime imaging; ischemia-reperfusion; mitochondria

DOI:  https://doi.org/10.1016/j.jmccpl.2024.100074
Geroscience. 2024 Jun 13.

A Fully-Automated Senescence Test (FAST) for the high-throughput quantification of senescence-associated markers.

Francesco Neri, Selma N Takajjart, Chad A Lerner, Pierre-Yves Desprez, Birgit Schilling, Judith Campisi, Akos A Gerencser.

  Cellular senescence is a major driver of aging and age-related diseases. Quantification of senescent cells remains challenging due to the lack of senescence-specific markers and generalist, unbiased methodology. Here, we describe the Fully-Automated Senescence Test (FAST), an image-based method for the high-throughput, single-cell assessment of senescence in cultured cells. FAST quantifies three of the most widely adopted senescence-associated markers for each cell imaged: senescence-associated β-galactosidase activity (SA-β-Gal) using X-Gal, proliferation arrest via lack of 5-ethynyl-2'-deoxyuridine (EdU) incorporation, and enlarged morphology via increased nuclear area. The presented workflow entails microplate image acquisition, image processing, data analysis, and graphing. Standardization was achieved by (i) quantifying colorimetric SA-β-Gal via optical density; (ii) implementing staining background controls; and (iii) automating image acquisition, image processing, and data analysis. In addition to the automated threshold-based scoring, a multivariate machine learning approach is provided. We show that FAST accurately quantifies senescence burden and is agnostic to cell type and microscope setup. Moreover, it effectively mitigates false-positive senescence marker staining, a common issue arising from culturing conditions. Using FAST, we compared X-Gal with fluorescent C12FDG live-cell SA-β-Gal staining on the single-cell level. We observed only a modest correlation between the two, indicating that those stains are not trivially interchangeable. Finally, we provide proof of concept that our method is suitable for screening compounds that modify senescence burden. This method will be broadly useful to the aging field by enabling rapid, unbiased, and user-friendly quantification of senescence burden in culture, as well as facilitating large-scale experiments that were previously impractical.

Keywords:  Aging; Cellular senescence; High-content image analysis; High-throughput screening; Machine learning; Senescence-associated-β-galactosidase

DOI:  https://doi.org/10.1007/s11357-024-01167-3
J Clin Invest. 2024 Jun 13. pii: e165814. [Epub ahead of print]

C16ORF70/Mytho promotes healthy ageing in C. elegans and prevents cellular senescence in mammals.

Anais Franco-Romero, Valeria Morbidoni, Giulia Milan, Roberta Sartori, Jesper Wulff, Vanina Romanello, Andrea Armani, Leonardo Salviati, Maria Conte, Stefano Salvioli, Claudio Franceschi, Viviana Buonomo, Casey O Swoboda, Paolo Grumati, Luca Pannone, Simone Martinelli, Harold Bj Jefferies, Ivan Dikic, Jennifer van der Laan, Filipe Cabreiro, Douglas P Millay, Sharon A Tooze, Eva Trevisson, Marco Sandri.

  The identification of genes that confer either extension of lifespan or accelerate age-related decline was a step forward in understanding the mechanisms of ageing and revealed that it is partially controlled by genetics and transcriptional programs. Here we discovered that the human DNA sequence C16ORF70 encoded for a protein, named MYTHO (Macroautophagy and YouTH Optimizer), which controls life- and health-span. MYTHO protein is conserved from C. elegans to humans and its mRNA was upregulated in aged mice and elderly people. Deletion of the ortholog myt-1 gene in C. elegans dramatically shortened lifespan and decreased animal survival upon exposure to oxidative stress. Mechanistically, MYTHO is required for autophagy likely because it acts as a scaffold that binds WIPI2 and BCAS3 to recruit and assemble the conjugation system at the phagophore, the nascent autophagosome. We conclude that MYTHO is a transcriptionally regulated initiator of autophagy that is central in promoting stress resistance and healthy ageing.

Keywords:  Aging; Autophagy; Cell biology; Cellular senescence; Skeletal muscle

DOI:  https://doi.org/10.1172/JCI165814
bioRxiv. 2024 May 30. pii: 2024.05.26.595978. [Epub ahead of print]

Suppression of autophagy induces senescence in the heart.

Peiyong Zhai, Eun-Ah Sung, Yuka Shiheido-Watanabe, Koichiro Takayama, Yimin Tian, Junichi Sadoshima.

Aging is a critical risk factor for heart disease, including ischemic heart disease and heart failure. Cellular senescence, characterized by DNA damage, resistance to apoptosis and the senescence-associated secretory phenotype (SASP), occurs in many cell types, including cardiomyocytes. Senescence precipitates the aging process in surrounding cells and the organ through paracrine mechanisms. Generalized autophagy, which degrades cytosolic materials in a non-selective manner, is decreased during aging in the heart. This decrease causes deterioration of cellular quality control mechanisms, facilitates aging and negatively affects lifespan in animals, including mice. Although suppression of generalized autophagy could promote senescence, it remains unclear whether the suppression of autophagy directly stimulates senescence in cardiomyocytes, which, in turn, promotes myocardial dysfunction in the heart. We addressed this question using mouse models with a loss of autophagy function. Suppression of general autophagy in cardiac-specific Atg7 knockout ( Atg7 cKO) mice caused accumulation of senescent cardiomyocytes. Induction of senescence via downregulation of Atg7 was also observed in chimeric Atg7 cardiac-specific KO mice and cultured cardiomyocytes in vitro , suggesting that the effect of autophagy suppression upon induction of senescence is cell autonomous. ABT-263, a senolytic agent, reduced the number of senescent myocytes and improved cardiac function in Atg7 cKO mice. Suppression of autophagy and induction of senescence were also observed in doxorubicin-treated hearts, where activation of autophagy alleviated senescence in cardiomyocytes and cardiac dysfunction. These results suggest that suppression of general autophagy directly induces senescence in cardiomyocytes, which in turn promotes cardiac dysfunction.

DOI: https://doi.org/10.1101/2024.05.26.595978
Redox Biol. 2024 Jul;pii: S2213-2317(24)00186-1. [Epub ahead of print]73 103208

Interactions between oxidative stress and senescence in cancer: Mechanisms, therapeutic implications, and future perspectives.

Dengxiong Li, Qingxin Yu, Ruicheng Wu, Zhouting Tuo, Jie Wang, Luxia Ye, Fanglin Shao, Premkamon Chaipanichkul, Koo Han Yoo, Wuran Wei, Uzoamaka Adaobi Okoli, Shi Deng, Mang Ke, William C Cho, Susan Heavey, Dechao Feng.

   BACKGROUND: Recently, numerous studies have reported the interaction between senescence and oxidative stress in cancer. However, there is a lack of a comprehensive understanding of the precise mechanisms involved.
AIM: Therefore, our review aims to summarize the current findings and elucidate by presenting specific mechanisms that encompass functional pathways, target genes, and related aspects.
METHODS: Pubmed and Web of Science databases were retrieved to search studies about the interaction between senescence and oxidative stress in cancer. Relevant publications in the reference list of enrolled studies were also checked.
RESULTS: In carcinogenesis, oxidative stress-induced cellular senescence acts as a barrier against the transformation of stimulated cells into cancer cells. However, the senescence-associated secretory phenotype (SASP) is positively linked to tumorigenesis. In the cancer progression stage, targeting specific genes or pathways that promote oxidative stress-induced cellular senescence can suppress cancer progression. In terms of treatment, many current clinical therapies combine with novel drugs to overcome resistance and reduce side effects by attenuating oxidative stress-induced senescence. Notably, emerging drugs control cancer development by enhancing oxidative stress-induced senescence. These studies highlight the complacted effects of the interplay between oxidative stress and senescence at different cancer stages and among distinct cell populations. Future research should focus on characterizing the roles of distinct senescent cell types in various tumor stages and identifying the specific components of SASP.
CONCLUDSION: We've summarized the mechanisms of senescence and oxidative stress in cancer and provided illustrative figures to guide future research in this area.

Keywords:  Aging; Cancer; Oxidative stress; SASP; Senescence

DOI:  https://doi.org/10.1016/j.redox.2024.103208
J Transl Med. 2024 Jun 09. 22(1): 552

Calcium signaling from sarcoplasmic reticulum and mitochondria contact sites in acute myocardial infarction.

Esther Densu Agyapong, Gaia Pedriali, Daniela Ramaccini, Esmaa Bouhamida, Elena Tremoli, Carlotta Giorgi, Paolo Pinton, Giampaolo Morciano.

Acute myocardial infarction (AMI) is a serious condition that occurs when part of the heart is subjected to ischemia episodes, following partial or complete occlusion of the epicardial coronary arteries. The resulting damage to heart muscle cells have a significant impact on patient's health and quality of life. About that, recent research focused on the role of the sarcoplasmic reticulum (SR) and mitochondria in the physiopathology of AMI. Moreover, SR and mitochondria get in touch each other through multiple membrane contact sites giving rise to the subcellular region called mitochondria-associated membranes (MAMs). MAMs are essential for, but not limited to, bioenergetics and cell fate. Disruption of the architecture of these regions occurs during AMI although it is still unclear the cause-consequence connection and a complete overview of the pathological changes; for sure this concurs to further damage to heart muscle. The calcium ion (Ca2+) plays a pivotal role in the pathophysiology of AMI and its dynamic signaling between the SR and mitochondria holds significant importance. In this review, we tried to summarize and update the knowledge about the roles of these organelles in AMI from a Ca2+ signaling point of view. Accordingly, we also reported some possible cardioprotective targets which are directly or indirectly related at limiting the dysfunctions caused by the deregulation of the Ca2+ signaling.

DOI: https://doi.org/10.1186/s12967-024-05240-5
Life Sci. 2024 Jun 07. pii: S0024-3205(24)00397-7. [Epub ahead of print]351 122807

Mammalian target of differentiation-inducing factor-1 is mitochondrial malate dehydrogenase for activation of AMP-activated protein kinase and induction of mitochondrial fission.

Masaki Arioka, Koichi Miura, Ruzhe Han, Kazunobu Igawa, Fumi Takahashi-Yanaga, Toshiyuki Sasaguri.

   AIMS: Differentiation-inducing factor-1 (DIF-1) is a polyketide produced by Dictyostelium discoideum that inhibits growth and migration, while promoting the differentiation of Dictyostelium stalk cells through unknown mechanisms. DIF-1 localizes in stalk mitochondria. In addition to its effect on Dictyostelium, DIF-1 also inhibits growth and migration, and induces mitochondrial fission followed by mitophagy in mammalian cells, at least in part by activating AMP-activated protein kinase (AMPK). In a previous study, we found that DIF-1 binds to mitochondrial malate dehydrogenase (MDH2) and inhibits its activity in HeLa cells. In the present study, we investigated whether MDH2 serves as a pharmacological target of DIF-1 in mammalian cells.
MAIN METHODS: To examine the enzymatic activity of MDH, mitochondrial morphology, and molecular mechanisms of DIF-1 action, we conducted an MDH reverse reaction assay, immunofluorescence staining, western blotting, and RNA interference using mammalian cells such as human umbilical vein endothelial cells, human cervical cancer cells, mouse endothelial cells, and mouse breast cancer cells.
KEY FINDINGS: DIF-1 inhibited mitochondrial but not cytoplasmic MDH activity. Similar to DIF-1, LW6, an authentic MDH2 inhibitor, induced phosphorylation of AMPK, resulting in the phosphorylation of acetyl-CoA carboxylase (ACC) and the dephosphorylation of p70 S6 kinase with approximately the same potency. DIF-1 and LW6 induced mitochondrial fission. Furthermore, MDH2 knockdown using siRNA reproduced the DIF-1 action on the AMPK signaling and mitochondrial morphology. Conversely, an AMPK inhibitor prevented DIF-1-induced mitochondrial fission.
SIGNIFICANCE: We propose that MDH2 is a mammalian target of DIF-1 for the activation of AMPK and induction of mitochondrial fission.

Keywords:  AMP-activated protein kinase; Differentiation-inducing factor-1; Mitochondrial fission; Mitochondrial malate dehydrogenase

DOI:  https://doi.org/10.1016/j.lfs.2024.122807
Mol Metab. 2024 Jun 12. pii: S2212-8778(24)00097-8. [Epub ahead of print] 101966

The Bioenergetic Landscape of Cancer.

Elizabeth R M Zunica, Christopher L Axelrod, L Anne Gilmore, Erich Gnaiger, John P Kirwan.

  Bioenergetic remodeling of core energy metabolism is essential to the initiation, survival, and progression of cancer cells through exergonic supply of adenosine triphosphate (ATP) and metabolic intermediates, as well as control of redox homeostasis. Mitochondria are evolutionarily conserved organelles that mediate cell survival by conferring energetic plasticity and adaptive potential. Mitochondrial ATP synthesis is coupled to the oxidation of a variety of substrates generated through diverse metabolic pathways. As such, inhibition of the mitochondrial bioenergetic system by restricting metabolite availability, direct inhibition of the respiratory Complexes, altering organelle structure, or coupling efficiency may restrict carcinogenic potential and cancer progression. Here, we review the role of bioenergetics as the principal conductor of energetic functions and carcinogenesis while highlighting the therapeutic potential of targeting mitochondrial functions.

Keywords:  Bioenergetics; Cancer; Cell Survival; Energy Transformation; Mitochondria

DOI:  https://doi.org/10.1016/j.molmet.2024.101966
Cell. 2024 Jun 05. pii: S0092-8674(24)00526-9. [Epub ahead of print]

MTFP1 controls mitochondrial fusion to regulate inner membrane quality control and maintain mtDNA levels.

Luis Carlos Tábara, Stephen P Burr, Michele Frison, Suvagata R Chowdhury, Vincent Paupe, Yu Nie, Mark Johnson, Jara Villar-Azpillaga, Filipa Viegas, Mayuko Segawa, Hanish Anand, Kasparas Petkevicius, Patrick F Chinnery, Julien Prudent.

  Mitochondrial dynamics play a critical role in cell fate decisions and in controlling mtDNA levels and distribution. However, the molecular mechanisms linking mitochondrial membrane remodeling and quality control to mtDNA copy number (CN) regulation remain elusive. Here, we demonstrate that the inner mitochondrial membrane (IMM) protein mitochondrial fission process 1 (MTFP1) negatively regulates IMM fusion. Moreover, manipulation of mitochondrial fusion through the regulation of MTFP1 levels results in mtDNA CN modulation. Mechanistically, we found that MTFP1 inhibits mitochondrial fusion to isolate and exclude damaged IMM subdomains from the rest of the network. Subsequently, peripheral fission ensures their segregation into small MTFP1-enriched mitochondria (SMEM) that are targeted for degradation in an autophagic-dependent manner. Remarkably, MTFP1-dependent IMM quality control is essential for basal nucleoid recycling and therefore to maintain adequate mtDNA levels within the cell.

Keywords:  IMM quality control; IMM remodeling; MTFP1; autophagy; fission and fusion; mitochondria; mitochondrial dynamics; mitophagy; mtDNA

DOI:  https://doi.org/10.1016/j.cell.2024.05.017
Cell Death Dis. 2024 Jun 10. 15(6): 404

The miR-30-5p/TIA-1 axis directs cellular senescence by regulating mitochondrial dynamics.

Hyosun Tak, Seongho Cha, Youlim Hong, Myeongwoo Jung, Seungyeon Ryu, Sukyoung Han, Seung Min Jeong, Wook Kim, Eun Kyung Lee.

Senescent cells exhibit a diverse spectrum of changes in their morphology, proliferative capacity, senescence-associated secretory phenotype (SASP) production, and mitochondrial homeostasis. These cells often manifest with elongated mitochondria, a hallmark of cellular senescence. However, the precise regulatory mechanisms orchestrating this phenomenon remain predominantly unexplored. In this study, we provide compelling evidence for decreases in TIA-1, a pivotal regulator of mitochondrial dynamics, in models of both replicative senescence and ionizing radiation (IR)-induced senescence. The downregulation of TIA-1 was determined to trigger mitochondrial elongation and enhance the expression of senescence-associated β-galactosidase, a marker of cellular senescence, in human foreskin fibroblast HS27 cells and human keratinocyte HaCaT cells. Conversely, the overexpression of TIA-1 mitigated IR-induced cellular senescence. Notably, we identified the miR-30-5p family as a novel factor regulating TIA-1 expression. Augmented expression of the miR-30-5p family was responsible for driving mitochondrial elongation and promoting cellular senescence in response to IR. Taken together, our findings underscore the significance of the miR-30-5p/TIA-1 axis in governing mitochondrial dynamics and cellular senescence.

DOI: https://doi.org/10.1038/s41419-024-06797-1
Exp Eye Res. 2024 Jun 06. pii: S0014-4835(24)00186-6. [Epub ahead of print]245 109965

IP3R2 regulates apoptosis by Ca2+ transfer through mitochondria-ER contacts in hypoxic photoreceptor injury.

Li Xu, Yihua Xu, Yaoxu Jiang, Jingjing Jiang, Shimei Chen, Dandan Sun, Shenping Li, Fang Wei, Hong Zhu.

  Mitochondria-associated ER membranes (MAMs) are contact sites that enable bidirectional communication between the ER (endoplasmic reticulum) and mitochondria, including the transfer of Ca2+ signals. MAMs are essential for mitochondrial function and cellular energy metabolism. However, unrestrained Ca2+ transfer to the mitochondria can lead to mitochondria-dependent apoptosis. IP3R2 (Inositol 1,4,5-trisphosphate receptor 2) is an important intracellular Ca2+ channel. This study investigated the contribution of IP3R2-MAMs to hypoxia-induced apoptosis in photoreceptor cells. A photoreceptor hypoxia model was established by subretinal injection of hyaluronic acid (1%) in C57BL/6 mice and 1% O2 treatment in 661W cells. Transmission electron microscopy (TEM), ER-mitochondria colocalization, and the MAM reporter were utilized to evaluate MAM alterations. Cell apoptosis and mitochondrial homeostasis were evaluated using immunofluorescence (IF), flow cytometry, western blotting (WB), and ATP assays. SiRNA transfection was employed to silence IP3R2 in 661W cells. Upon hypoxia induction, MAMs were significantly increased in photoreceptors both in vivo and in vitro. This was accompanied by the activation of mitochondrial apoptosis and disruption of mitochondrial homeostasis. Elevated MAM-enriched IP3R2 protein levels induced by hypoxic injury led to mitochondrial calcium overload and subsequent photoreceptor apoptosis. Notably, IP3R2 knockdown not only improved mitochondrial morphology but also restored mitochondrial function in photoreceptors by limiting MAM formation and thereby attenuating mitochondrial calcium overload under hypoxia. Our results suggest that IP3R2-MAM-mediated mitochondrial calcium overload plays a critical role in mitochondrial dyshomeostasis, ultimately contributing to photoreceptor cell death. Targeting MAM constitutive proteins might provide an option for a therapeutic approach to mitigate photoreceptor death in retinal detachment.

Keywords:  Hypoxia; IP3R2; Mitochondria; Mitochondria-associated endoplasmic reticulum membranes (MAM); Photoreceptor

DOI:  https://doi.org/10.1016/j.exer.2024.109965
Nucleic Acids Res. 2024 Jun 14. pii: gkae501. [Epub ahead of print]

HDAC4 influences the DNA damage response and counteracts senescence by assembling with HDAC1/HDAC2 to control H2BK120 acetylation and homology-directed repair.

Eros Di Giorgio, Emiliano Dalla, Vanessa Tolotto, Francesca D'Este, Harikrishnareddy Paluvai, Liliana Ranzino, Claudio Brancolini.

Access to DNA is the first level of control in regulating gene transcription, a control that is also critical for maintaining DNA integrity. Cellular senescence is characterized by profound transcriptional rearrangements and accumulation of DNA lesions. Here, we discovered an epigenetic complex between HDAC4 and HDAC1/HDAC2 that is involved in the erase of H2BK120 acetylation. The HDAC4/HDAC1/HDAC2 complex modulates the efficiency of DNA repair by homologous recombination, through dynamic deacetylation of H2BK120. Deficiency of HDAC4 leads to accumulation of H2BK120ac, impaired recruitment of BRCA1 and CtIP to the site of lesions, accumulation of damaged DNA and senescence. In senescent cells this complex is disassembled because of increased proteasomal degradation of HDAC4. Forced expression of HDAC4 during RAS-induced senescence reduces the genomic spread of γH2AX. It also affects H2BK120ac levels, which are increased in DNA-damaged regions that accumulate during RAS-induced senescence. In summary, degradation of HDAC4 during senescence causes the accumulation of damaged DNA and contributes to the activation of the transcriptional program controlled by super-enhancers that maintains senescence.

DOI: https://doi.org/10.1093/nar/gkae501
bioRxiv. 2024 May 28. pii: 2024.05.27.596106. [Epub ahead of print]

Mitochondrial Calcium Signaling Regulates Branched-Chain Amino Acid Catabolism in Fibrolamellar Carcinoma.

Nicole M Marsh, Melissa J S MacEwen, Jane Chea, Heidi L Kenerson, Albert A Kwong, Timothy M Locke, Francisco Javier Miralles, Tanmay Sapre, Natasha Gozali, G Ekin Atilla-Gokcumen, Shao-En Ong, John D Scott, Raymond S Yeung, Yasemin Sancak.

Metabolic adaptations in response to changes in energy supply and demand are essential for survival. The mitochondrial calcium uniporter coordinates metabolic homeostasis by regulating TCA cycle activation, mitochondrial fatty acid oxidation and cellular calcium signaling. However, a comprehensive analysis of uniporter-regulated mitochondrial metabolic pathways has remained unexplored. Here, we investigate the metabolic consequences of uniporter loss- and gain-of-function, and identify a key transcriptional regulator that mediates these effects. Using gene expression profiling and proteomic, we find that loss of uniporter function increases the expression of proteins in the branched-chain amino acid (BCAA) catabolism pathway. Activity is further augmented through phosphorylation of the enzyme that catalyzes this pathway's committed step. Conversely, in the liver cancer fibrolamellar carcinoma (FLC)-which we demonstrate to have high mitochondrial calcium levels- expression of BCAA catabolism enzymes is suppressed. We also observe uniporter-dependent suppression of the transcription factor KLF15, a master regulator of liver metabolic gene expression, including those involved in BCAA catabolism. Notably, loss of uniporter activity upregulates KLF15, along with its transcriptional target ornithine transcarbamylase (OTC), a component of the urea cycle, suggesting that uniporter hyperactivation may contribute to the hyperammonemia observed in FLC patients. Collectively, we establish that FLC has increased mitochondrial calcium levels, and identify an important role for mitochondrial calcium signaling in metabolic adaptation through the transcriptional regulation of metabolism.

DOI: https://doi.org/10.1101/2024.05.27.596106
Cell Death Dis. 2024 Jun 10. 15(6): 405

Aberrant ER-mitochondria communication is a common pathomechanism in mitochondrial disease.

Patricia Morcillo, Khushbu Kabra, Kevin Velasco, Hector Cordero, Sarah Jennings, Taekyung D Yun, Delfina Larrea, H Orhan Akman, Eric A Schon.

Genetic mutations causing primary mitochondrial disease (i.e those compromising oxidative phosphorylation [OxPhos]) resulting in reduced bioenergetic output display great variability in their clinical features, but the reason for this is unknown. We hypothesized that disruption of the communication between endoplasmic reticulum (ER) and mitochondria at mitochondria-associated ER membranes (MAM) might play a role in this variability. To test this, we assayed MAM function and ER-mitochondrial communication in OxPhos-deficient cells, including cybrids from patients with selected pathogenic mtDNA mutations. Our results show that each of the various mutations studied indeed altered MAM functions, but notably, each disorder presented with a different MAM "signature". We also found that mitochondrial membrane potential is a key driver of ER-mitochondrial connectivity. Moreover, our findings demonstrate that disruption in ER-mitochondrial communication has consequences for cell survivability that go well beyond that of reduced ATP output. The findings of a "MAM-OxPhos" axis, the role of mitochondrial membrane potential in controlling this process, and the contribution of MAM dysfunction to cell death, reveal a new relationship between mitochondria and the rest of the cell, as well as providing new insights into the diagnosis and treatment of these devastating disorders.

DOI: https://doi.org/10.1038/s41419-024-06781-9
Proc Natl Acad Sci U S A. 2024 Jun 18. 121(25): e2311865121

Age-related behavioral resilience in smartphone touchscreen interaction dynamics.

Enea Ceolini, K Richard Ridderinkhof, Arko Ghosh.

  We experience a life that is full of ups and downs. The ability to bounce back after adverse life events such as the loss of a loved one or serious illness declines with age, and such isolated events can even trigger accelerated aging. How humans respond to common day-to-day perturbations is less clear. Here, we infer the aging status from smartphone behavior by using a decision tree regression model trained to accurately estimate the chronological age based on the dynamics of touchscreen interactions. Individuals (N = 280, 21 to 87 y of age) expressed smartphone behavior that appeared younger on certain days and older on other days through the observation period that lasted up to ~4 y. We captured the essence of these fluctuations by leveraging the mathematical concept of critical transitions and tipping points in complex systems. In most individuals, we find one or more alternative stable aging states separated by tipping points. The older the individual, the lower the resilience to forces that push the behavior across the tipping point into an older state. Traditional accounts of aging based on sparse longitudinal data spanning decades suggest a gradual behavioral decline with age. Taken together with our current results, we propose that the gradual age-related changes are interleaved with more complex dynamics at shorter timescales where the same individual may navigate distinct behavioral aging states from one day to the next. Real-world behavioral data modeled as a complex system can transform how we view and study aging.

Keywords:  aging; critical transitions; resilience; smartphone behavior; trajectory of aging

DOI:  https://doi.org/10.1073/pnas.2311865121