bims-auttor 2021-08-22 papers

bims-auttor

Biomed News

on Autophagy and mTOR

Issue of 2021–08–22
nineteen papers selected by
Viktor Korolchuk, Newcastle University

Selective Autophagy.
AMPK: a key regulator of energy stress and calcium-induced autophagy.
Autophagy and Ciliogenesis.
TFEB phosphorylation on Serine 211 is induced by autophagy in human synovial fibroblasts and by p62/SQSTM1 overexpression in HEK293 cells.
Protein aggregation and autophagy dysfunction: new lessons from mucopolysaccharidoses.
Glyceraldehyde-3-Phosphate Dehydrogenase Facilitates Macroautophagic Degradation of Mutant Huntingtin Protein Aggregates.
Induction of Sestrin2 by pterostilbene suppresses ethanol-triggered hepatocyte senescence by degrading CCN1 via p62-dependent selective autophagy.
Vorinostat in autophagic cell death: a critical insight into autophagy-mediated, -associated and -dependent cell death for cancer prevention.
Multiple functions of autophagy in vascular calcification.
Hypo-Expression of Tuberin Promotes Adenomyosis via the mTOR1-Autophagy Axis.
Contribution of Energy Dysfunction to Impaired Protein Translation in Neurodegenerative Diseases.
Differential mitochondrial roles for α-synuclein in DRP1-dependent fission and PINK1/Parkin-mediated oxidation.
Protocol to study starvation-induced autophagy in developing rat neurons.
Pharmacological Activation of Autophagy Restores Cellular Homeostasis in Ultraviolet-(B)-Induced Skin Photodamage.
Potentials of autophagy enhancing natural products in the treatment of Parkinson disease.
Mechanisms of impaired mitochondrial homeostasis and NAD+ metabolism in a model of mitochondrial heart disease exhibiting redox active iron accumulation.
Repurposing of tamoxifen ameliorates CLN3 and CLN7 disease phenotype.
Autophagy in neuronal physiology and disease.
Torin 1 alleviates impairment of TFEB-mediated lysosomal biogenesis and autophagy in TGFBI (p.G623_H626del)-linked Thiel-Behnke corneal dystrophy.

Cancer Sci. 2021 Aug 18.

Selective Autophagy.

Mohammad Omar Faruk, Yoshinobu Ichimura, Masaaki Komatsu.

  While starvation-induced autophagy is thought to randomly degrade cellular components, under certain circumstances autophagy selectively recognizes, sequesters, and degrades specific targets via autophagosomes. This process is called selective autophagy, and it contributes to cellular homeostasis by degrading specific soluble proteins, supramolecular complexes, liquid-liquid phase-separated droplets, abnormal or excess organelles, and pathogenic invasive bacteria. This means that autophagy, like the ubiquitin-proteasome system, strictly regulates diverse cellular functions through its selectivity. In this short review, we focus on the mechanism of "selective" autophagy, which is rapidly being elucidated.

Keywords:  ; autophagy; ATG8-family proteins; liquid-liquid phase separation; selective autophagy; selective autophagy receptors

DOI:  https://doi.org/10.1111/cas.15112
J Mol Med (Berl). 2021 Aug 16.

AMPK: a key regulator of energy stress and calcium-induced autophagy.

Rimpi Saikia, Jomon Joseph.

  Autophagy is a well-known cell-survival strategy orchestrated by a conserved set of proteins. It equips the cells with mechanisms to attain homeostasis during unfavorable conditions such as stress by breaking down the cellular components and reusing them for energy as well as for building new components required for survival. A basal level of autophagy is required for achieving homeostasis under normal conditions through regular turnover of macromolecules and organelles. Initiation of autophagy is regulated by two key components of the nutrient/energy sensor pathways; mammalian target of rapamycin 1 (mTORC1) and AMP-activated kinase (AMPK). Under energy-deprived conditions, AMPK is activated triggering autophagy, whereas, in nutrient-rich conditions, the growth-promoting kinase mTORC1 is activated inhibiting autophagy. Thus, the reciprocal regulation of autophagy by AMPK and mTORC1 defines a fundamental mechanism by which cells respond to nutrient availability. Interestingly, cytoplasmic calcium is also found to be an activator of AMPK and autophagy through a calmodulin/CaMKKβ pathway. However, the physiological significance of the regulation of autophagy by cytoplasmic calcium is currently unclear. This review focuses on the current understanding of the mechanism of autophagy and its regulation by AMPK.

Keywords:  AMPK; Autophagy; CaMKKβ; Calcium; Energy homeostasis; LKB1; mTORC1

DOI:  https://doi.org/10.1007/s00109-021-02125-8
JMA J. 2021 Jul 15. 4(3): 207-215

Autophagy and Ciliogenesis.

Yasuhiro Yamamoto, Noboru Mizushima.

  Autophagy is a major intracellular degradation system and plays important roles in various physiological processes such as metabolic adaptation and intracellular homeostasis. It degrades intracellular components both randomly and selectively. Autophagic activity is tightly regulated primarily by nutrient availability, but also by other extracellular and intracellular signals. Growing evidence suggests that there are multiple links between autophagy and the primary cilium. The primary cilium is an organelle present on the cell surface and is important for keeping cellular integrity by transducing extracellular stimuli inside the cell. Recent studies have revealed that autophagy selectively degrades the ciliogenesis inhibitory proteins OFD1 and MYH9, promoting ciliogenesis. Conversely, autophagy also inhibits ciliogenesis under growth conditions. The primary cilium can also regulate autophagic activity. These findings suggest that the relationship between autophagy and the primary cilia is bidirectional, and that both are important for maintaining the normal function of various organs.

Keywords:  autophagy; ciliogenesis; ciliopathy

DOI:  https://doi.org/10.31662/jmaj.2021-0090
Biochem J. 2021 Aug 18. pii: BCJ20210174. [Epub ahead of print]

TFEB phosphorylation on Serine 211 is induced by autophagy in human synovial fibroblasts and by p62/SQSTM1 overexpression in HEK293 cells.

Biserka Relic, Celine Deroyer, Olivier Malaise, Zelda Plener, Philippe Gillet, Dominique de Seny, Michel G Malaise.

  Autophagy receptor p62/SQSTM1 signals a complex network that links autophagy-lysosomal system to proteasome. Phosphorylation of p62 on Serine 349 (P-Ser349 p62) is involved in a cell protective, antioxidant pathway. We have shown previously that P-Ser349 p62 occurs and is rapidly degraded during human synovial fibroblasts autophagy. In this work we observed that fingolimod (FTY720), used as a medication for multiple sclerosis, induced coordinated expression of p62, P-Ser349 p62 and inhibitory TFEB form, phosphorylated on Serine 211 (P-Ser211 TFEB), in human synovial fibroblasts. These effects were mimicked and potentiated by proteasome inhibitor MG132. In addition, FTY720 induced autophagic flux, LC3B-II upregulation, Akt phosphorylation inhibition on Serine 473 but downregulated TFEB, suggesting stalled autophagy. FTY720 decreased cytoplasmic fraction contained TFEB but induced TFEB in nuclear fraction. FTY720-induced P-Ser211 TFEB was mainly found in membrane fraction. Autophagy and VPS34 kinase inhibitor, autophinib, further increased FTY720-induced P-Ser349 p62 but inhibited concomitant expression of P-Ser211 TFEB. These results suggested that P-Ser211 TFEB expression depends on autophagy. Overexpression of GFP tagged TFEB in HEK293 cells showed concomitant expression of its phosphorylated form on Serine 211, that was downregulated by autophinib. These results suggested that autophagy might be autoregulated through P-Ser211 TFEB as a negative feedback loop. Of interest, overexpression of p62, p62 phosphorylation mimetic (S349E) mutant and phosphorylation deficient mutant (S349A) in HEK293 cells markedly induced P-Ser211 TFEB. These results showed that p62 is involved in regulation of TFEB phosphorylation on Serine 211 but that this involvement does not depend on p62 phosphorylation on Serine 349.

Keywords:  TFEB; autophagy; p62/SQSTM1; phosphorylation/dephosphorylation

DOI:  https://doi.org/10.1042/BCJ20210174
Autophagy. 2021 Aug 18. 1-2

Protein aggregation and autophagy dysfunction: new lessons from mucopolysaccharidoses.

Antonio Monaco, Alessandro Fraldi.

  Mucopolysaccharidoses (MPS) are inherited metabolic diseases with strong neurological involvement. MPSs are caused by defects in lysosomal enzymes involved in the degradation of glycosaminoglycans (GAGs), which consequently accumulate into the lysosomes as primary storage. Macroautophagy/autophagy impairment is well known to drive neurodegeneration in MPSs, however, mechanisms underlying such dysfunction are still poorly understood. Recently, by studying a mouse model for MPS-III (Sanfilippo syndrome) we have shown that the progressive aggregation of amyloid proteins in neuronal cell bodies occurs downstream of the GAG storage and, in turn, impairs the autophagy pathway by affecting lysosomal-dependent autophagosome clearance.

Keywords:  Autophagy; lysosomal storage diseases; lysosome; mucopolysaccharidoses; protein aggregation

DOI:  https://doi.org/10.1080/15548627.2021.1961076
Mol Neurobiol. 2021 Aug 18.

Glyceraldehyde-3-Phosphate Dehydrogenase Facilitates Macroautophagic Degradation of Mutant Huntingtin Protein Aggregates.

Surbhi Chaudhary, Asmita Dhiman, Rahul Dilawari, Gaurav Kumar Chaubey, Sharmila Talukdar, Radheshyam Modanwal, Anil Patidar, Himanshu Malhotra, Chaaya Iyengar Raje, Manoj Raje.

  Protein aggregate accumulation is a pathological hallmark of several neurodegenerative disorders. Autophagy is critical for clearance of aggregate-prone proteins. In this study, we identify a novel role of the multifunctional glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in clearance of intracellular protein aggregates. Previously, it has been reported that though clearance of wild-type huntingtin protein is mediated by chaperone-mediated autophagy (CMA), however, degradation of mutant huntingtin (mHtt with numerous poly Q repeats) remains impaired by this route as mutant Htt binds with high affinity to Hsc70 and LAMP-2A. This delays delivery of misfolded protein to lysosomes and results in accumulation of intracellular aggregates which are degraded only by macroautophagy. Earlier investigations also suggest that mHtt causes inactivation of mTOR signaling, causing upregulation of autophagy. GAPDH had earlier been reported to interact with mHtt resulting in cellular toxicity. Utilizing a cell culture model of mHtt aggregates coupled with modulation of GAPDH expression, we analyzed the formation of intracellular aggregates and correlated this with autophagy induction. We observed that GAPDH knockdown cells transfected with N-terminal mutant huntingtin (103 poly Q residues) aggregate-prone protein exhibit diminished autophagy. GAPDH was found to regulate autophagy via the mTOR pathway. Significantly more and larger-sized huntingtin protein aggregates were observed in GAPDH knockdown cells compared to empty vector-transfected control cells. This correlated with the observed decrease in autophagy. Overexpression of GAPDH had a protective effect on cells resulting in a decreased load of aggregates. Our results demonstrate that GAPDH assists in the clearance of protein aggregates by autophagy induction. These findings provide a new insight in understanding the mechanism of mutant huntingtin aggregate clearance. By studying the molecular mechanism of protein aggregate clearance via GAPDH, we hope to provide a new approach in targeting and understanding several neurodegenerative disorders.

Keywords:  Autophagy; Clearance; Multifunctional protein; Neurodegenerative disorder; mTOR pathway

DOI:  https://doi.org/10.1007/s12035-021-02532-5
Cell Biol Toxicol. 2021 Aug 17.

Induction of Sestrin2 by pterostilbene suppresses ethanol-triggered hepatocyte senescence by degrading CCN1 via p62-dependent selective autophagy.

Yiming Jiang, Ying Zhou, Wenxuan Xu, Xinqi Wang, Huanhuan Jin, Xiaofeng Bao, Chunfeng Lu.

  Hepatocyte senescence is a key event participating in the progression of alcoholic liver disease. Autophagy is a critical biological process that controls cell fates by affecting cell behaviors like senescence. Pterostilbene is a natural compound with hepatoprotective potential; however, its implication for alcoholic liver disease was not understood. This study was aimed to investigate the therapeutic effect of pterostilbene on alcoholic liver disease and elucidate the potential mechanism. Our results showed that pterostilbene alleviated ethanol-triggered hepatocyte damage and senescence. Intriguingly, pterostilbene decreased the protein abundance of cellular communication network factor 1 (CCN1) in ethanol-exposed hepatocytes, which was essential for pterostilbene to execute its anti-senescent function. In vivo studies verified the anti-senescent effect of pterostilbene on hepatocytes of alcohol-intoxicated mice. Pterostilbene also relieved senescence-associated secretory phenotype (SASP), redox imbalance, and steatosis by suppressing hepatic CCN1 expression. Mechanistically, pterostilbene-forced CCN1 reduction was dependent on posttranscriptional regulation via autophagy machinery but not transcriptional regulation. To be specific, pterostilbene restored autophagic flux in damaged hepatocytes and activated p62-mediated selective autophagy to recognize and lead CCN1 to autolysosomes for degradation. The protein abundance of Sestrin2 (SESN2), a core upstream modulator of autophagy pathway, was decreased in ethanol-administrated hepatocytes but rescued by co-treatment with pterostilbene. Induction of SESN2 protein by pterostilbene rescued ethanol-triggered autophagic dysfunction in hepatocytes, which then reduced senescence-associated markers, postponed hepatocyte senescence, and relieved alcohol-caused liver injury and inflammation. In conclusion, this work discovered a novel compound pterostilbene with therapeutic implications for alcoholic liver disease and uncover its underlying mechanism.

Keywords:  Alcoholic liver disease; Autophagy; CCN1; Hepatocyte; Pterostilbene; Senescence; Sestrin2

DOI:  https://doi.org/10.1007/s10565-021-09635-8
Drug Discov Today. 2021 Aug 13. pii: S1359-6446(21)00362-7. [Epub ahead of print]

Vorinostat in autophagic cell death: a critical insight into autophagy-mediated, -associated and -dependent cell death for cancer prevention.

Srimanta Patra, Prakash P Praharaj, Daniel J Klionsky, Sujit K Bhutia.

  Histone deacetylases (HDACs) inhibit the acetylation of crucial autophagy genes, thereby deregulating autophagy and autophagic cell death (ACD) and facilitating cancer cell survival. Vorinostat, a broad-spectrum pan-HDAC inhibitor, inhibits the deacetylation of key autophagic markers and thus interferes with ACD. Vorinostat-regulated ACD can have an autophagy-mediated, -associated or -dependent mechanism depending on the involvement of apoptosis. Molecular insights reveal that hyperactivation of the PIK3C3/VPS34-BECN1 complex increased lysosomal disparity and enhanced mitophagy. These changes were followed by reduced mitochondrial biogenesis and by secondary signals that enabled superactivated, nonselective or bulk autophagy, leading to ACD. Although the evidence is limited, this review focuses on molecular insights into vorinostat-regulated ACD and describes critical concepts for clinical translation.

Keywords:  autophagy; cancer; cell death; histone deacetylases; vorinostat

DOI:  https://doi.org/10.1016/j.drudis.2021.08.004
Cell Biosci. 2021 Aug 16. 11(1): 159

Multiple functions of autophagy in vascular calcification.

Xin Zhou, Sui-Ning Xu, Shu-Tong Yuan, Xinjuan Lei, Xiaoying Sun, Lu Xing, Hui-Jin Li, Chun-Xia He, Wei Qin, Dong Zhao, Peng-Quan Li, Edward Moharomd, Xuehong Xu, Hui-Ling Cao.

   BACKGROUND: Vascular calcification is a closely linked to cardiovascular diseases, such as atherosclerosis, chronic kidney disease, diabetes, hypertension and aging. The extent of vascular calcification is closely correlate with adverse clinical events and cardiovascular all-cause mortality. The role of autophagy in vascular calcification is complex with many mechanistic unknowns.
METHODS: In this review, we analyze the current known mechanisms of autophagy in vascular calcification and discuss the theoretical advantages of targeting autophagy as an intervention against vascular calcification.
RESULTS: Here we summarize the functional link between vascular calcification and autophagy in both animal models of and human cardiovascular disease. Firstly, autophagy can reduce calcification by inhibiting the osteogenic differentiation of VSMCs related to ANCR, ERα, β-catenin, HIF-1a/PDK4, p62, miR-30b, BECN1, mTOR, SOX9, GHSR/ERK, and AMPK signaling. Conversely, autophagy can induce osteoblast differentiation and calcification as mediated by CREB, degradation of elastin, and lncRNA H19 and DUSP5 mediated ERK signaling. Secondly, autophagy also links apoptosis and vascular calcification through AMPK/mTOR/ULK1, Wnt/β-catenin and GAS6/AXL synthesis, as apoptotic cells become the nidus for calcium-phosphate crystal deposition. The failure of mitophagy can activate Drp1, BNIP3, and NR4A1/DNA‑PKcs/p53 mediated intrinsic apoptotic pathways, which have been closely linked to the formation of vascular calcification. Additionally, autophagy also plays a role in osteogenesis by regulating vascular calcification, which in turn regulates expression of proteins related to bone development, such as osteocalcin, osteonectin, etc. and regulated by mTOR, EphrinB2 and RhoA. Furthermore, autophagy also promotes vitamin K2-induced MC3T3 E1 osteoblast differentiation and FGFR4/FGF18- and JNK/complex VPS34-beclin-1-related bone mineralization via vascular calcification.
CONCLUSION: The interaction between autophagy and vascular calcification are complicated, with their interaction affected by the disease process, anatomical location, and the surrounding microenvironment. Autophagy activation in existent cellular damage is considered protective, while defective autophagy in normal cells result in apoptotic activation. Identifying and maintaining cells at the delicate line between these two states may hold the key to reducing vascular calcification, in which autophagy associated clinical strategy could be developed.

Keywords:  AMPK/mTOR; Autophagy/mitophagy; EphrinB2; GAS6/AXL; HIF-1a/PDK4; Osteoblastic differentiation of VSMCs; Osteogenesis; Vascular calcification

DOI:  https://doi.org/10.1186/s13578-021-00639-9
Front Cell Dev Biol. 2021 ;9 710407

Hypo-Expression of Tuberin Promotes Adenomyosis via the mTOR1-Autophagy Axis.

Ni-Hao Gu, Guo-Jing Li, Bing-Xin Yang, Min You, Yu Lin, Feng Sun, Hong Xu.

  Adenomyosis (AM) is a disease in which endometrial tissue invades the myometrium and has a 10-60% prevalence in reproductive-aged women. TSC2 regulates autophagy via mTOR1 signalling in colorectal cancer and endometrial carcinoma. Dysregulation of autophagy is implicated in adenomyosis pathogenesis. However, whether TSC2 participates in adenomyosis via autophagy remains obscure. Here, we found that the expression of TSC2 in adenomyosis was significantly decreased than that in normal endometrium during the secretory phase. Moreover, TSC2 and autophagy marker expression was significantly lower in ectopic lesions than in eutopic samples. TSC2 downregulation inhibited autophagy through mTOR1 signalling pathway activation in endometrial cells, leading to excessive proliferation, migration, and EMT; TSC2 overexpression induced the opposite effects. Rapamycin treatment suppressed cell proliferation, migration and EMT in the absence of TSC2. In parallel, an autophagy-specific inhibitor (SAR-405) restored migration and EMT under rapamycin treatment in TSC2-knockdown Ishikawa cells. Finally, SAR-405 treatment promoted EMT and migration of overexpressing cells. Collectively, our results suggest that TSC2 controls endometrial epithelial cell migration and EMT by regulating mTOR1-autophagy axis activation and that hypo-expression of TSC2 in the endometrium might promote adenomyosis.

Keywords:  EMT; TSC2; adenomyosis; autophagy; endometrial cell; mTOR1; migration

DOI:  https://doi.org/10.3389/fcell.2021.710407
Front Cell Neurosci. 2021 ;15 668500

Contribution of Energy Dysfunction to Impaired Protein Translation in Neurodegenerative Diseases.

Yu-Ju Liu, Yijuang Chern.

  Impaired energy homeostasis and aberrant translational control have independently been implicated in the pathogenesis of neurodegenerative diseases. AMP kinase (AMPK), regulated by the ratio of cellular AMP and ATP, is a major gatekeeper for cellular energy homeostasis. Abnormal regulation of AMPK has been reported in several neurodegenerative diseases, including Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS). Most importantly, AMPK activation is known to suppress the translational machinery by inhibiting the mechanistic target of rapamycin complex 1 (mTORC1), activating translational regulators, and phosphorylating nuclear transporter factors. In this review, we describe recent findings on the emerging role of protein translation impairment caused by energy dysregulation in neurodegenerative diseases.

Keywords:  AMP kinase; Alzheimer’s disease; amyotrophic lateral sclerosis; protein translation; stress granules

DOI:  https://doi.org/10.3389/fncel.2021.668500
Cell Death Dis. 2021 Aug 17. 12(9): 796

Differential mitochondrial roles for α-synuclein in DRP1-dependent fission and PINK1/Parkin-mediated oxidation.

Thomas J Krzystek, Rupkatha Banerjee, Layne Thurston, JianQiao Huang, Kelsey Swinter, Saad Navid Rahman, Tomas L Falzone, Shermali Gunawardena.

Mitochondria are highly dynamic organelles with strict quality control processes that maintain cellular homeostasis. Within axons, coordinated cycles of fission-fusion mediated by dynamin related GTPase protein (DRP1) and mitofusins (MFN), together with regulated motility of healthy mitochondria anterogradely and damaged/oxidized mitochondria retrogradely, control mitochondrial shape, distribution and size. Disruption of this tight regulation has been linked to aberrant oxidative stress and mitochondrial dysfunction causing mitochondrial disease and neurodegeneration. Although pharmacological induction of Parkinson's disease (PD) in humans/animals with toxins or in mice overexpressing α-synuclein (α-syn) exhibited mitochondrial dysfunction and oxidative stress, mice lacking α-syn showed resistance to mitochondrial toxins; yet, how α-syn influences mitochondrial dynamics and turnover is unclear. Here, we isolate the mechanistic role of α-syn in mitochondrial homeostasis in vivo in a humanized Drosophila model of Parkinson's disease (PD). We show that excess α-syn causes fragmented mitochondria, which persists with either truncation of the C-terminus (α-syn1-120) or deletion of the NAC region (α-synΔNAC). Using in vivo oxidation reporters Mito-roGFP2-ORP1/GRX1 and MitoTimer, we found that α-syn-mediated fragments were oxidized/damaged, but α-syn1-120-induced fragments were healthy, suggesting that the C-terminus is required for oxidation. α-syn-mediated oxidized fragments showed biased retrograde motility, but α-syn1-120-mediated healthy fragments did not, demonstrating that the C-terminus likely mediates the retrograde motility of oxidized mitochondria. Depletion/inhibition or excess DRP1-rescued α-syn-mediated fragmentation, oxidation, and the biased retrograde motility, indicating that DRP1-mediated fragmentation is likely upstream of oxidation and motility changes. Further, excess PINK/Parkin, two PD-associated proteins that function to coordinate mitochondrial turnover via induction of selective mitophagy, rescued α-syn-mediated membrane depolarization, oxidation and cell death in a C-terminus-dependent manner, suggesting a functional interaction between α-syn and PINK/Parkin. Taken together, our findings identify distinct roles for α-syn in mitochondrial homeostasis, highlighting a previously unknown pathogenic pathway for the initiation of PD.

DOI: https://doi.org/10.1038/s41419-021-04046-3
STAR Protoc. 2021 Sep 17. 2(3): 100713

Protocol to study starvation-induced autophagy in developing rat neurons.

José Wojnacki, Sébastien Nola, Thierry Galli.

  Autophagy is being involved in an increasing number of cellular pathways. It now appears that autophagy stimulation and inhibition have complex effects in neurons. Here, we present a simple yet powerful protocol to induce autophagy in primary neurons in culture by partial nutrient deprivation, in neurons with or without transfection of plasmids encoding the Longin domain of VAMP7 or a nanobody directed against VAMP7. Although limited to cells in culture, this protocol can facilitate the study of autophagy in neurons. For complete details on the use and execution of this protocol, please refer to Wojnacki et al. (2020).

Keywords:  Antibody; Cell Biology; Cell culture; Microscopy; Neuroscience

DOI:  https://doi.org/10.1016/j.xpro.2021.100713
Front Oncol. 2021 ;11 726066

Pharmacological Activation of Autophagy Restores Cellular Homeostasis in Ultraviolet-(B)-Induced Skin Photodamage.

Sheikh Ahmad Umar, Naikoo Hussain Shahid, Lone Ahmad Nazir, Malik Ahmad Tanveer, Gupta Divya, Sajida Archoo, Sharma Rai Raghu, Sheikh Abdullah Tasduq.

  Ultraviolet (UV) exposure to the skin causes photo-damage and acts as the primary etiological agent in photo-carcinogenesis. UV-B exposure induces cellular damage and is the major factor challenging skin homeostasis. Autophagy allows the fundamental adaptation of cells to metabolic and oxidative stress. Cellular dysfunction has been observed in aged tissues and in toxic insults to cells undergoing stress. Conversely, promising anti-aging strategies aimed at inhibiting the mTOR pathway have been found to significantly improve the aging-related disorders. Recently, autophagy has been found to positively regulate skin homeostasis by enhancing DNA damage recognition. Here, we investigated the geno-protective roles of autophagy in UV-B-exposed primary human dermal fibroblasts (HDFs). We found that UV-B irradiation to HDFs impairs the autophagy response in a time- and intensity-independent manner. However, improving autophagy levels in HDFs with pharmacological activators regulates the UV-B-induced cellular stress by decreasing the induction of DNA photo-adducts, promoting the DNA repair process, alleviating oxidative and ER stress responses, and regulating the expression levels of key cell cycle regulatory proteins. Autophagy also prevents HDFs from UV-B-induced nuclear damage as is evident in TUNEL assay and Acridine Orange/Ethidium Bromide co-staining. Salubrinal (an eIF2α phosphatase inhibitor) relieves ER stress response in cells and also significantly alleviates DNA damage and promotes the repair process in UV-B-exposed HDFs. P62-silenced HDFs show enhanced DNA damage response and also disturb the tumor suppressor PTEN/pAKT signaling axis in UV-B-exposed HDFs whereas Atg7-silenced HDFs reveal an unexpected consequence by decreasing the UV-B-induced DNA damage. Taken together, these results suggest that interventional autophagy offers significant protection against UV-B radiation-induced photo-damage and holds great promise in devising it as a suitable therapeutic strategy against skin pathological disorders.

Keywords:  DNA damage response; autophagy; endoplasmic reticulum stress; genotoxicity; oxidative stress; ultraviolet radiation (UV-B)

DOI:  https://doi.org/10.3389/fonc.2021.726066
Drug Metab Pers Ther. 2021 Aug 13.

Potentials of autophagy enhancing natural products in the treatment of Parkinson disease.

Taiwo G Olubodun-Obadun, Ismail O Ishola, Olufunmilayo O Adeyemi.

  Parkinson disease (PD) is a progressive neurodegenerative movement disorder characterized by motor and non-motor symptoms due to loss of striatal dopaminergic neurons and disruption of degradation signaling leading to the formation of Lewy bodies (aggregation of α-synuclein). Presently, there are no disease modifying therapy for PD despite improvement in the understanding of the disease pathogenesis. However, the drugs currently used in PD management provide symptomatic relieve for motor symptoms without significant improvement in non-motor complications, thus, a public health burden on caregivers and healthcare systems. There is therefore the need to discover disease modifying therapy with strong potential to halt the disease progression. Recent trend has shown that the dysfunction of lysosomal-autophagy pathway is highly implicated in PD pathology, hence, making autophagy a key player owing to its involvement in degradation and clearance of misfolded α-synuclein (a major hallmark in PD pathology). In this review, we described the current drugs/strategy in the management of PD including targeting the autophagy pathway as a novel approach that could serve as potential intervention for PD management. The discovery of small molecules or natural products capable of enhancing autophagy mechanism could be a promising strategy for PD treatment.

Keywords:  Parkinson disease; lysosomal-autophagy signaling; movement disorder; non-motor features; phytochemicals; α-synuclein

DOI:  https://doi.org/10.1515/dmdi-2021-0128
Redox Biol. 2021 Jun 10. pii: S2213-2317(21)00197-X. [Epub ahead of print]46 102038

Mechanisms of impaired mitochondrial homeostasis and NAD+ metabolism in a model of mitochondrial heart disease exhibiting redox active iron accumulation.

Shannon Chiang, Nady Braidy, Sanaz Maleki, Sean Lal, Des R Richardson, Michael L-H Huang.

  Due to the high redox activity of the mitochondrion, this organelle can suffer oxidative stress. To manage energy demands while minimizing redox stress, mitochondrial homeostasis is maintained by the dynamic processes of mitochondrial biogenesis, mitochondrial network dynamics (fusion/fission), and mitochondrial clearance by mitophagy. Friedreich's ataxia (FA) is a mitochondrial disease resulting in a fatal hypertrophic cardiomyopathy due to the deficiency of the mitochondrial protein, frataxin. Our previous studies identified defective mitochondrial iron metabolism and oxidative stress potentiating cardiac pathology in FA. However, how these factors alter mitochondrial homeostasis remains uncharacterized in FA cardiomyopathy. This investigation examined the muscle creatine kinase conditional frataxin knockout mouse, which closely mimics FA cardiomyopathy, to dissect the mechanisms of dysfunctional mitochondrial homeostasis. Dysfunction of key mitochondrial homeostatic mechanisms were elucidated in the knockout hearts relative to wild-type littermates, namely: (1) mitochondrial proliferation with condensed cristae; (2) impaired NAD+ metabolism due to perturbations in Sirt1 activity and NAD+ salvage; (3) increased mitochondrial biogenesis, fusion and fission; and (4) mitochondrial accumulation of Pink1/Parkin with increased autophagic/mitophagic flux. Immunohistochemistry of FA patients' heart confirmed significantly enhanced expression of markers of mitochondrial biogenesis, fusion/fission and autophagy. These novel findings demonstrate cardiac frataxin-deficiency results in significant changes to metabolic mechanisms critical for mitochondrial homeostasis. This mechanistic dissection provides critical insight, offering the potential for maintaining mitochondrial homeostasis in FA and potentially other cardio-degenerative diseases by implementing innovative treatments targeting mitochondrial homeostasis and NAD+ metabolism.

Keywords:  Cardiomyopathy; Iron; Iron loading; Mitochondria; Mitochondrial homeostasis

DOI:  https://doi.org/10.1016/j.redox.2021.102038
EMBO Mol Med. 2021 Aug 19. e13742

Repurposing of tamoxifen ameliorates CLN3 and CLN7 disease phenotype.

Chiara Soldati, Irene Lopez-Fabuel, Luca G Wanderlingh, Marina Garcia-Macia, Jlenia Monfregola, Alessandra Esposito, Gennaro Napolitano, Marta Guevara-Ferrer, Anna Scotto Rosato, Einar K Krogsaeter, Dominik Paquet, Christian M Grimm, Sandro Montefusco, Thomas Braulke, Stephan Storch, Sara E Mole, Maria A De Matteis, Andrea Ballabio, Julio L Sampaio, Tristan McKay, Ludger Johannes, Juan P Bolaños, Diego L Medina.

  Batten diseases (BDs) are a group of lysosomal storage disorders characterized by seizure, visual loss, and cognitive and motor deterioration. We discovered increased levels of globotriaosylceramide (Gb3) in cellular and murine models of CLN3 and CLN7 diseases and used fluorescent-conjugated bacterial toxins to label Gb3 to develop a cell-based high content imaging (HCI) screening assay for the repurposing of FDA-approved compounds able to reduce this accumulation within BD cells. We found that tamoxifen reduced the lysosomal accumulation of Gb3 in CLN3 and CLN7 cell models, including neuronal progenitor cells (NPCs) from CLN7 patient-derived induced pluripotent stem cells (iPSC). Here, tamoxifen exerts its action through a mechanism that involves activation of the transcription factor EB (TFEB), a master gene of lysosomal function and autophagy. In vivo administration of tamoxifen to the CLN7Δex2 mouse model reduced the accumulation of Gb3 and SCMAS, decreased neuroinflammation, and improved motor coordination. These data strongly suggest that tamoxifen may be a suitable drug to treat some types of Batten disease.

Keywords:  CLN3; CLN7; TFEB; high content imaging screening; tamoxifen

DOI:  https://doi.org/10.15252/emmm.202013742
Curr Opin Pharmacol. 2021 Aug 17. pii: S1471-4892(21)00107-7. [Epub ahead of print]60 133-140

Autophagy in neuronal physiology and disease.

Akiko Sumitomo, Toshifumi Tomoda.

Neural circuit functions critically depend on homeostatic regulation and quality control of neuronal proteins and organelles. Emerging evidence shows that autophagy, cellular clearance machinery, selectively degrades or controls homeostasis of both pre- and post-synaptic components (e.g. synaptic proteins, organelles, neurotransmitters, and their receptors), thereby regulating synaptic remodeling, neurotransmission, and neuroplasticity. Along with its well-known role in supporting neuronal cell viability and neurodevelopment, autophagy is now implicated in a wide range of neuronal physiology throughout neuronal lifetime, including higher-order brain functions such as information processing, memory encoding, or cognitive functions. Here, we review recent literature on the roles of neuronal autophagy in homeostatic maintenance of synaptic functions and discuss how disruptions in these processes may contribute to the pathophysiology of neurodevelopmental and psychiatric disorders.

DOI: https://doi.org/10.1016/j.coph.2021.07.013
Autophagy. 2021 Aug 17. 1-18

Torin 1 alleviates impairment of TFEB-mediated lysosomal biogenesis and autophagy in TGFBI (p.G623_H626del)-linked Thiel-Behnke corneal dystrophy.

Liyuan Wang, Chuchu Zhao, Tao Zheng, Yi Zhang, Hanruo Liu, Xi Wang, Xianling Tang, Baowen Zhao, Ping Liu.

  Thiel-Behnke corneal dystrophy (TBCD) is an epithelial-stromal TGFBI dystrophy caused by mutations in the TGFBI (transforming growth factor beta induced) gene, though the underlying mechanisms and pathogenesis of TBCD are still obscure. The study identifies a novel mutation in the TGFBI gene (p.Gly623_His626del) in a TBCD pedigree. Characteristics of the typical vacuole formation, irregular corneal epithelial thickening and thinning, deposition of eosinophilic substances beneath the epithelium, and involvement of the anterior stroma were observed in this pedigree via transmission electron microscopy (TEM) and histological staining. Tgfbi-p.Gly623_Tyr626del mouse models of TBCD were subsequently generated via CRISPR/Cas9 technology, and the above characteristics were further verified via TEM and histological staining. Lysosomal dysfunction and downregulation of differential expression protein CTSD (cathepsin D) were observed using LysoTracker Green DND-26 and proteomic analysis, respectively. Hence, lysosomal dysfunction probably leads to autophagic flux obstruction in TBCD; this was supported by enhanced LC3-II and SQSTM1 levels and decreased CTSD. TFEB (transcription factor EB) was prominently decreased in TBCD corneal fibroblasts and administration of ATP-competitive MTOR inhibitor torin 1 reversed this decline, resulting in the degradation of accumulated mut-TGFBI (mutant TGFBI protein) via the ameliorative lysosomal function and autophagic flux owing to elevated TFEB activity as measured by western blot, confocal microscopy, and flow cytometry. Transfected HEK 293 cells overexpressing human full-length WT-TGFBI and mut-TGFBI were generated to further verify the results obtained in human corneal fibroblasts. Amelioration of lysosome dysfunction may therefore have therapeutic efficacy in the treatment of TBCD.

Keywords:  Autophagy; TBCD; TFEB; TGFBI; lysosome dysfunction; torin 1

DOI:  https://doi.org/10.1080/15548627.2021.1955469