Mitochondrial Permeability Uncouples Elevated Autophagy and Lifespan Extension

Systemic GDF11 attenuates depression-like phenotype in aged mice via stimulation of neuronal autophagy

Cognitive decline and mood disorders increase in frequency with age. Many efforts are focused on the identification of molecules and pathways to treat these conditions. Here, we demonstrate that systemic administration of growth differentiation factor 11 (GDF11) in aged mice improves memory and alleviates senescence and depression-like symptoms in a neurogenesis-independent manner. Mechanistically, GDF11 acts directly on hippocampal neurons to enhance neuronal activity via stimulation of autophagy. Transcriptomic and biochemical analyses of these neurons reveal that GDF11 reduces the activity of mammalian target of rapamycin (mTOR), a master regulator of autophagy. Using a murine model of corticosterone-induced depression-like phenotype, we also show that GDF11 attenuates the depressive-like behavior of young mice. Analysis of sera from young adults with major depressive disorder (MDD) reveals reduced GDF11 levels. These findings identify mechanistic pathways related to GDF11 action in the brain and uncover an unknown role for GDF11 as an antidepressant candidate and biomarker.

Hallmarks of aging: An expanding universe

Aging is driven by hallmarks fulfilling the following three premises: (1) their age-associated manifestation, (2) the acceleration of aging by experimentally accentuating them, and (3) the opportunity to decelerate, stop, or reverse aging by therapeutic interventions on them. We propose the following twelve hallmarks of aging: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, disabled macroautophagy, deregulated nutrient-sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, chronic inflammation, and dysbiosis. These hallmarks are interconnected among each other, as well as to the recently proposed hallmarks of health, which include organizational features of spatial compartmentalization, maintenance of homeostasis, and adequate responses to stress.

Hepatocytes: A key role in liver inflammation

Hepatocytes, the major parenchymal cells in the liver, are responsible for a variety of cellular functions including carbohydrate, lipid and protein metabolism, detoxification and immune cell activation to maintain liver homeotasis. Recent studies show hepatocytes play a pivotal role in liver inflammation. After receiving liver insults and inflammatory signals, hepatocytes may undergo organelle damage, and further respond by releasing mediators and expressing molecules that can act in the microenvironment as well as initiate a robust inflammatory response. In this review, we summarize how the hepatic organelle damage link to liver inflammation and introduce numerous hepatocyte-derived pro-inflammatory factors in response to chronic liver injury.

Proteotoxic stress disrupts epithelial integrity by inducing MTOR sequestration and autophagy overactivation

Macroautophagy/autophagy, an evolutionarily conserved degradation system, serves to clear intracellular components through the lysosomal pathway. Mounting evidence has revealed cytoprotective roles of autophagy; however, the intracellular causes of overactivated autophagy, which has cytotoxic effects, remain elusive. Here we show that sustained proteotoxic stress induced by loss of the RING and Kelch repeat-containing protein C53A5.6/RIKE-1 induces sequestration of LET-363/MTOR complex and overactivation of autophagy, and consequently impairs epithelial integrity in C. elegans. In C53A5.6/RIKE-1-deficient animals, blocking autophagosome formation effectively prevents excessive endosomal degradation, mitigates mislocalization of intestinal membrane components and restores intestinal lumen morphology. However, autophagy inhibition does not affect LET-363/MTOR aggregation in animals with compromised C53A5.6/RIKE-1 function. Improving proteostasis capacity by reducing DAF-2 insulin/IGF1 signaling markedly relieves the aggregation of LET-363/MTOR and alleviates autophagy overactivation, which in turn reverses derailed endosomal trafficking and rescues epithelial morphogenesis defects in C53A5.6/RIKE-1-deficient animals. Hence, our studies reveal that C53A5.6/RIKE-1-mediated proteostasis is critical for maintaining the basal level of autophagy and epithelial integrity.Abbreviations: ACT-5: actin 5; ACTB: actin beta; ALs: autolysosomes; APs: autophagosomes; AJM-1: apical junction molecule; ATG: autophagy related; C. elegans: Caenorhabditis elegans; CPL-1: cathepsin L family; DAF: abnormal dauer formation; DLG-1: Drosophila discs large homolog; ERM-1: ezrin/radixin/moesin; EPG: ectopic P granule; GFP: freen fluorescent protein; HLH-30: helix loop helix; HSP: heat shock protein; LAAT-1: lysosome associated amino acid transporter; LET: lethal; LGG-1: LC3, GABARAP and GATE-16 family; LMP-1: LAMP (lysosome-associated membrane protein) homolog; MTOR: mechanistic target of rapamycin kinase; NUC-1: abnormal nuclease; PEPT-1/OPT-2: Peptide transporter family; PGP-1: P-glycoprotein related; RAB: RAB family; RIKE-1: RING and Kelch repeat-containing protein; SLCF-1: solute carrier family; SQST-1: sequestosome related; SPTL-1: serine palmitoyl transferase family.

Mechanosensitive channel MscL induces non-apoptotic cell death and its suppression of tumor growth by ultrasound

Mechanosensitive channel of large conductance (MscL) is the most thoroughly studied mechanosensitive channel in prokaryotes. Owing to its small molecular weight, clear mechanical gating mechanism, and nanopore forming ability upon opening, accumulating studies are implemented in regulating cell function by activating mechanosensitive channel of large conductance in mammalian cells. This study aimed to investigate the potentials of mechanosensitive channel of large conductance as a nanomedicine and a mechano-inducer in non-small cell lung cancer (NSCLC) A549 cells from the view of molecular pathways and acoustics. The stable cytoplasmic vacuolization model about NSCLC A549 cells was established via the targeted expression of modified mechanosensitive channel of large conductance channels in different subcellular organelles. Subsequent morphological changes in cellular component and expression levels of cell death markers are analyzed by confocal imaging and western blots. The permeability of mitochondrial inner membrane (MIM) exhibited a vital role in cytoplasmic vacuolization formation. Furthermore, mechanosensitive channel of large conductance channel can be activated by low intensity focused ultrasound (LIFU) in A549 cells, and the suppression of A549 tumors in vivo was achieved by LIFU with sound pressure as low as 0.053 MPa. These findings provide insights into the mechanisms underlying non-apoptotic cell death, and validate the nanochannel-based non-invasive ultrasonic strategy for cancer therapy.

Urolithin A reduces amyloid-beta load and improves cognitive deficits uncorrelated with plaque burden in a mouse model of Alzheimer's disease

In the present study, we investigated the effects of urolithin A (UA), a metabolite generated from ellagic acid via its metabolism by gut bacteria, as an autophagy activator with potential neuroprotective activity. WT and 3xTg-AD mice were administered long-term intermittent dietary supplementation with UA. UA was found to prevent deficits in spatial memory, cued fear response, and exploratory behavior in this model. It also decreased the Aβ plaque burden in areas of the hippocampus where these protein deposits are prominent in the model. Interestingly, correlation analyses demonstrate that Aβ plaque burden positively correlates with enhanced spatial memory in 3xTg-AD mice on a control diet but not in those supplemented with UA. In contrast, Aβ42 abundance in cortical and hippocampal homogenates negatively correlate with spatial memory in UA-fed mice. Our data suggest that plaque formation may be a protective mechanism against neurodegeneration and cognitive decline and that targeting the generation of proteotoxic Aβ species might be a more successful approach in halting disease progression. UA was also found to extend lifespan in normal aging mice. Mechanistically, we demonstrate that UA is able to induce autophagy and to increase Aβ clearance in neuronal cell lines. In summary, our studies reveal UA, likely via its actions as a autophagy inducer, is capable of removing Aβ from neurons and its dietary administration prevents the onset of cognitive deficits associated with pathological Aβ deposition in the 3xTg-AD mouse model as well as extending lifespan in normal aging mice.

Mitochondria-originated redox signalling regulates KLF-1 to promote longevity in Caenorhabditis elegans

Alternations of redox metabolism have been associated with the extension of lifespan in roundworm Caenorhabditis elegans, caused by moderate mitochondrial dysfunction, although the underlying signalling cascades are largely unknown. Previously, we identified transcriptional factor Krüppel-like factor-1 (KLF-1) as the main regulator of cytoprotective longevity-assurance pathways in the C. elegans long-lived mitochondrial mutants. Here, we show that KLF-1 translocation to the nucleus and the activation of the signalling cascade is dependent on the mitochondria-derived hydrogen peroxide (H₂O₂) produced during late developmental phases where aerobic respiration and somatic mitochondrial biogenesis peak. We further show that mitochondrial-inducible superoxide dismutase-3 (SOD-3), together with voltage-dependent anion channel-1 (VDAC-1), is required for the life-promoting H₂O₂ signalling that is further regulated by peroxiredoxin-3 (PRDX-3). Increased H₂O₂ release in the cytoplasm activates the p38 MAPK signalling cascade that induces KLF-1 translocation to the nucleus and the activation of transcription of C. elegans longevity-promoting genes, including cytoprotective cytochrome P450 oxidases. Taken together, our results underline the importance of redox-regulated signalling as the key regulator of longevity-inducing pathways in C. elegans, and position precisely timed mitochondria-derived H₂O₂ in the middle of it.

Deficiency of MST1 in endometriosis related peritoneal macrophages promoted the autophagy of ectopic endometrial stromal cells by IL-10

Changes in the function of peritoneal macrophages contribute to the homeostasis of the peritoneal immune microenvironment in endometriosis. The mechanism by which ectopic tissues escape phagocytic clearance by macrophages to achieve ectopic colonization and proliferation is unknown. The expression of CD163 in peritoneal macrophages in patients with endometriosis is increased, with the overexpression of MAPK, which can promote the M2-type polarization of macrophages and reduce their ability to phagocytose ectopic endometrial cells. As an upstream regulator of MAPK, MST1 expression is deficient in peritoneal macrophages of patients with endometriosis. This process is regulated by miR-887-5p, a noncoding RNA targeting MST1. Moreover, MST1-knockout macrophages secrete anti-inflammatory factor IL-10, which promotes autophagy of ectopic endometrial stromal cells. These results suggest that MST1 deficient macrophages may accelerate the autophagy of ectopic endometrium via IL-10 which was regulated by miR-887-5p.

Cell Death Mechanisms in Cerebral Ischemia-Reperfusion Injury

Ischemic stroke is one of the major causes of morbidity and mortality, affecting millions of people worldwide. Inevitably, the interruption of cerebral blood supply after ischemia may promote a cascade of pathophysiological processes. Moreover, the subsequent restoration of blood flow and reoxygenation may further aggravate brain tissue injury. Although recombinant tissue plasminogen activator (rt-PA) is the only approved therapy for restoring blood perfusion, the reperfusion injury and the narrow therapeutic time window restrict its application for most stroke patients. Increasing evidence indicates that multiple cell death mechanisms are relevant to cerebral ischemia-reperfusion injury, including apoptosis, necrosis, necroptosis, autophagy, pyroptosis, ferroptosis, and so on. Therefore, it is crucial to comprehend various cell death mechanisms and their interactions. In this review, we summarize the various signaling pathways underlying cerebral ischemia-reperfusion injury and elaborate on the crosstalk between the different mechanisms.

SIN-3 functions through multi-protein interaction to regulate apoptosis, autophagy, and longevity in Caenorhabditis elegans

SIN3/HDAC is a multi-protein complex that acts as a regulatory unit and functions as a co-repressor/co-activator and a general transcription factor. SIN3 acts as a scaffold in the complex, binding directly to HDAC1/2 and other proteins and plays crucial roles in regulating apoptosis, differentiation, cell proliferation, development, and cell cycle. However, its exact mechanism of action remains elusive. Using the Caenorhabditis elegans (C. elegans) model, we can surpass the challenges posed by the functional redundancy of SIN3 isoforms. In this regard, we have previously demonstrated the role of SIN-3 in uncoupling autophagy and longevity in C. elegans. In order to understand the mechanism of action of SIN3 in these processes, we carried out a comparative analysis of the SIN3 protein interactome from model organisms of different phyla. We identified conserved, expanded, and contracted gene classes. The C. elegans SIN-3 interactome -revealed the presence of  well-known proteins, such as DAF-16, SIR-2.1, SGK-1, and AKT-1/2, involved in autophagy, apoptosis, and longevity. Overall, our analyses propose  potential mechanisms by which SIN3 participates in multiple biological processes and their conservation across species and identifies candidate genes for further experimental analysis.

Small molecules as modulators of regulated cell death against ischemia/reperfusion injury

Ischemia/reperfusion (IR) injury contributes to disability and mortality worldwide. Due to the complicated mechanisms and lack of proper therapeutic targets, few interventions are available that specifically target the pathogenesis of IR injury. Regulated cell death (RCD) of endothelial and parenchymal cells is recognized as the promising intervening target. Recent advances in IR injury suggest that small molecules exhibit beneficial effects on various RCD against IR injury, including apoptosis, necroptosis, autophagy, ferroptosis, pyroptosis, and parthanatos. Here, we describe the mechanisms behind these novel promising therapeutic targets and explain the machinery powering the small molecules. These small molecules exert protection by targeting endothelial or parenchymal cells to alleviate IR injury. Therapies of the ideal combination of small molecules targeting multiple cell types have shown potent synergetic therapeutic effects, laying the foundation for novel strategies to attenuate IR injury.

Nutrition, longevity and disease: From molecular mechanisms to interventions

Diet as a whole, encompassing food composition, calorie intake, and the length and frequency of fasting periods, affects the time span in which health and functional capacity are maintained. Here, we analyze aging and nutrition studies in simple organisms, rodents, monkeys, and humans to link longevity to conserved growth and metabolic pathways and outline their role in aging and age-related disease. We focus on feasible nutritional strategies shown to delay aging and/or prevent diseases through epidemiological, model organism, clinical, and centenarian studies and underline the need to avoid malnourishment and frailty. These findings are integrated to define a longevity diet based on a multi-pillar approach adjusted for age and health status to optimize lifespan and healthspan in humans.

Molecular mechanisms and consequences of mitochondrial permeability transition

Mitochondrial permeability transition (mPT) is a phenomenon that abruptly causes the flux of low molecular weight solutes (molecular weight up to 1,500) across the generally impermeable inner mitochondrial membrane. The mPT is mediated by the so-called mitochondrial permeability transition pore (mPTP), a supramolecular entity assembled at the interface of the inner and outer mitochondrial membranes. In contrast to mitochondrial outer membrane permeabilization, which mostly activates apoptosis, mPT can trigger different cellular responses, from the physiological regulation of mitophagy to the activation of apoptosis or necrosis. Although there are several molecular candidates for the mPTP, its molecular nature remains contentious. This lack of molecular data was a significant setback that prevented mechanistic insight into the mPTP, pharmacological targeting and the generation of informative animal models. In recent years, experimental evidence has highlighted mitochondrial F₁F_o ATP synthase as a participant in mPTP formation, although a molecular model for its transition to the mPTP is still lacking. Recently, the resolution of the F₁F_o ATP synthase structure by cryogenic electron microscopy led to a model for mPTP gating. The elusive molecular nature of the mPTP is now being clarified, marking a turning point for understanding mitochondrial biology and its pathophysiological ramifications. This Review provides an up-to-date reference for the understanding of the mammalian mPTP and its cellular functions. We review current insights into the molecular mechanisms of mPT and validated observations - from studies in vivo or in artificial membranes - on mPTP activity and functions. We end with a discussion of the contribution of the mPTP to human disease. Throughout the Review, we highlight the multiple unanswered questions and, when applicable, we also provide alternative interpretations of the recent discoveries.

PPARγ/SOD2 Protects Against Mitochondrial ROS-Dependent Apoptosis via Inhibiting ATG4D-Mediated Mitophagy to Promote Pancreatic Cancer Proliferation

Pancreatic ductal adenocarcinoma (PDAC) is an extremely aggressive disease with poor prognosis. Our previous study found that peroxisome proliferator activated receptor gamma (PPARγ) was capable of enhancing glycolysis in PDAC cells. However, whether PPARγ could promote PDAC progression remains unclear. In our present study, PPARγ was positively associated with tumor size and poor prognosis in PDAC patients. Functional assays demonstrated that PPARγ could promote the proliferation of pancreatic cancer cells in vitro and in vivo. Additionally, flow cytometry results showed that PPARγ decreased mitochondrial reactive oxygen species (mitochondrial ROS) production, stabilized mitochondrial membrane potential (MMP) and inhibited cell apoptosis via up-regulating superoxide dismutase 2 (SOD2), followed by the inhibition of ATG4D-mediated mitophagy. Meanwhile, the activation of PPARγ might reduce pancreatic cancer cell stemness to improve PDAC chemosensitivity via down-regulating ATG4D. Thus, these results revealed that PPARγ/SOD2 might protect against mitochondrial ROS-dependent apoptosis via inhibiting ATG4D-mediated mitophagy to promote pancreatic cancer proliferation, further improving PDAC chemosensitivity.

Tourniquet-induced lower limb ischemia/reperfusion reduces mitochondrial function by decreasing mitochondrial biogenesis in acute kidney injury in mice

The mechanisms by which lower limb ischemia/reperfusion induces acute kidney injury (AKI) remain largely uncharacterized. We hypothesized that tourniquet-induced lower limb ischemia/reperfusion (TILLIR) would inhibit mitochondrial function in the renal cortex. We used a murine model to show that TILLIR of the high thigh regions inflicted time-dependent AKI as determined by renal function and histology. This effect was associated with decreased activities of mitochondrial complexes I, II, V and citrate synthase in the kidney cortex. Moreover, TILLIR reduced mRNA levels of a master regulator of mitochondrial biogenesis PGC-1α, and its downstream genes NDUFS1 and ATP5o in the renal cortex. TILLIR also increased serum corticosterone concentrations. TILLIR did not significantly affect protein levels of the critical regulators of mitophagy PINK1 and PARK2, mitochondrial transport proteins Tom20 and Tom70, or heat-shock protein 27. TILLIR had no significant effect on mitochondrial oxidative stress as determined by mitochondrial ability to generate reactive oxygen species, protein carbonylation, or protein levels of MnSOD and peroxiredoxin1. However, TILLIR inhibited classic autophagic flux by increasing p62 protein abundance and preventing the conversion of LC3-I to LC3-II. TILLIR increased phosphorylation of cytosolic and mitochondrial ERK1/2 and mitochondrial AKT1, as well as mitochondrial SGK1 activity. In conclusion, lower limb ischemia/reperfusion induces distal AKI by inhibiting mitochondrial function through reducing mitochondrial biogenesis. This AKI occurs without significantly affecting PINK1-PARK2-mediated mitophagy or mitochondrial oxidative stress in the kidney cortex.

SARS-CoV-2 infection enhances mitochondrial PTP complex activity to perturb cardiac energetics

SARS-CoV-2 is a newly identified coronavirus that causes the respiratory disease called coronavirus disease 2019 (COVID-19). With an urgent need for therapeutics, we lack a full understanding of the molecular basis of SARS-CoV-2-induced cellular damage and disease progression. Here, we conducted transcriptomic analysis of human PBMCs, identified significant changes in mitochondrial, ion channel, and protein quality-control gene products. SARS-CoV-2 proteins selectively target cellular organelle compartments, including the endoplasmic reticulum and mitochondria. M-protein, NSP6, ORF3A, ORF9C, and ORF10 bind to mitochondrial PTP complex components cyclophilin D, SPG-7, ANT, ATP synthase, and a previously undescribed CCDC58 (coiled-coil domain containing protein 58). Knockdown of CCDC58 or mPTP blocker cyclosporin A pretreatment enhances mitochondrial Ca2+ retention capacity and bioenergetics. SARS-CoV-2 infection exacerbates cardiomyocyte autophagy and promotes cell death that was suppressed by cyclosporin A treatment. Our findings reveal that SARS-CoV-2 viral proteins suppress cardiomyocyte mitochondrial function that disrupts cardiomyocyte Ca2+ cycling and cell viability.

Sulphenylation of CypD at Cysteine 104: A Novel Mechanism by Which SO2 Inhibits Cardiomyocyte Apoptosis

Objectives: The study was designed to explore the role of endogenous gaseous signaling molecule sulfur dioxide (SO2) in the control of cardiomyocyte apoptosis and its molecular mechanisms.

Methods: Neonatal mouse cardiac myocytes (NMCMs) and H9c2 cells were used in the cell experiments. The endogenous SO2 pathway including SO2 level and the expression of SO2-generating enzyme aspartate aminotransferase 1/2 (AAT1/2) were detected in NMCMs. The apoptosis of cardiomyocytes was examined by a TUNEL assay. The cleavage and the activity of apoptotic proteins caspase9 and caspase3 were measured. The content of ATP, the opening of mitochondrial permeability transition pore (mPTP), and the cytochrome c (cytc) leakage were detected by immunofluorescence. The sulphenylation of cyclophilin-D (CypD) was detected by biotin switch analysis. The four CypD mutant plasmids in which cysteine sites were mutated to serine were constructed to identify the SO2-affected site in vitro.

Results: ISO down-regulated the endogenous SO2/AAT pathway of cardiomyocytes in association with a significant increase in cardiomyocyte apoptosis, demonstrated by the increases in apoptosis, cleaved-caspase3/caspase3 ratio, and caspase3 activity. Furthermore, ISO significantly reduced ATP production in H9c2 cells, but the supplement of SO2 significantly restored the content of ATP. ISO stimulated mPTP opening, resulting in an increase in the release of cytc, which further increased the ratio of cleaved caspase9/caspase9 and enhanced the protein activity of caspase9. While, the supplementation of SO2 reversed the above effects. Mechanistically, SO2 did not affect CypD protein expression, but sulphenylated CypD and inhibited mPTP opening, resulting in an inhibition of cardiomyocyte apoptosis. The C104S mutation in CypD abolished SO2-induced sulphenylation of CypD, and thereby blocked the inhibitory effect of SO2 on the mPTP opening and cardiomyocyte apoptosis.

Conclusion: Endogenous SO2 sulphenylated CypD at Cys104 to inhibit mPTP opening, and thus protected against cardiomyocyte apoptosis.

Discovery of Herbacetin as a Novel SGK1 Inhibitor to Alleviate Myocardial Hypertrophy

Cardiac hypertrophy is a pivotal pathophysiological step of various cardiovascular diseases, which eventually leads to heart failure and death. Extracts of Rhodiola species (Ext.R), a class of commonly used medicinal herbs in Europe and East Asia, can attenuate cardiac hypertrophy both in vitro and in vivo. Serum/glucocorticoid regulated kinase 1 (SGK1) is identified as a potential target of Ext. R. By mass spectrometry-based kinase inhibitory assay, herbacetin (HBT) from Ext.R is identified as a novel SGK1 inhibitor with IC50 of 752 nmol. Thermal shift assay, KINOMEscan in vitro assay combined with molecular docking proves a direct binding between HBT and SGK1. Site-specific mutation of Asp177 in SGK1 completely ablates the inhibitory activity of HBT. The presence of OH groups at the C-3, C-8, C-4' positions of flavonoids is suggested to be favorable for the inhibition of SGK1 activity. Finally, HBT significantly suppresses cardiomyocyte hypertrophy in vitro and in vivo, reduces reactive oxygen species (ROS) synthesis and calcium accumulation. HBT decreases phosphorylation of SGK1 and regulates its downstream forkhead box protein O1 (FoxO1) signaling pathway. Taken together, the findings suggest that a panel of flavonoids structurally related to HBT may be novel leads for developing new therapeutics against cardiac hypertrophy.

Directly Reprogrammed Human Neurons to Understand Age-Related Energy Metabolism Impairment and Mitochondrial Dysfunction in Healthy Aging and Neurodegeneration

Brain aging is characterized by several molecular and cellular changes grouped as the hallmarks or pillars of aging, including organelle dysfunction, metabolic and nutrition-sensor changes, stem cell attrition, and macromolecular damages. Separately and collectively, these features degrade the most critical neuronal function: transmission of information in the brain. It is widely accepted that aging is the leading risk factor contributing to the onset of the most prevalent pathological conditions that affect brain functions, such as Alzheimer's, Parkinson's, and Huntington's disease. One of the limitations in understanding the molecular mechanisms involved in those diseases is the lack of an appropriate cellular model that recapitulates the “aged” context in human neurons. The advent of the cellular reprogramming of somatic cells, i.e., dermal fibroblasts, to obtain directly induced neurons (iNs) and induced pluripotent stem cell- (iPSC-) derived neurons is technical sound advances that could open the avenues to understand better the contribution of aging toward neurodegeneration. In this review, we will summarize the commonalities and singularities of these two approaches for the study of brain aging, with an emphasis on the role of mitochondrial dysfunction and redox biology. We will address the evidence showing that iNs retain age-related features in contrast to iPSC-derived neurons that lose the aging signatures during the reprogramming to pluripotency, rendering iNs a powerful strategy to deepen our knowledge of the processes driving normal cellular function decline and neurodegeneration in a human adult model. We will finally discuss the potential utilization of these novel technologies to understand the differential contribution of genetic and epigenetic factors toward neuronal aging, to identify and develop new drugs and therapeutic strategies.

Macroautophagy and aging: The impact of cellular recycling on health and longevity

Aging is associated with many deleterious changes at the cellular level, including the accumulation of potentially toxic components that can have devastating effects on health. A key protective mechanism to this end is the cellular recycling process called autophagy. During autophagy, damaged or surplus cellular components are delivered to acidic vesicles called lysosomes, that secure degradation and recycling of the components. Numerous links between autophagy and aging exist. Autophagy declines with age, and increasing evidence suggests that this reduction plays important roles in both physiological aging and the development of age-associated disorders. Studies in pharmacologically and genetically manipulated model organisms indicate that defects in autophagy promote age-related diseases, and conversely, that enhancement of autophagy has beneficial effects on both healthspan and lifespan. Here, we review our current understanding of the role of autophagy in different physiological processes and their molecular links with aging and age-related diseases. We also highlight some recent advances in the field that could accelerate the development of autophagy-based therapeutic interventions.

Autophagy in metabolic disease and ageing

Autophagy is an evolutionarily conserved, lysosome-dependent catabolic process whereby cytoplasmic components, including damaged organelles, protein aggregates and lipid droplets, are degraded and their components recycled. Autophagy has an essential role in maintaining cellular homeostasis in response to intracellular stress; however, the efficiency of autophagy declines with age and overnutrition can interfere with the autophagic process. Therefore, conditions such as sarcopenic obesity, insulin resistance and type 2 diabetes mellitus (T2DM) that are characterized by metabolic derangement and intracellular stresses (including oxidative stress, inflammation and endoplasmic reticulum stress) also involve the accumulation of damaged cellular components. These conditions are prevalent in ageing populations. For example, sarcopenia is an age-related loss of skeletal muscle mass and strength that is involved in the pathogenesis of both insulin resistance and T2DM, particularly in elderly people. Impairment of autophagy results in further aggravation of diabetes-related metabolic derangements in insulin target tissues, including the liver, skeletal muscle and adipose tissue, as well as in pancreatic β-cells. This Review summarizes the role of autophagy in the pathogenesis of metabolic diseases associated with or occurring in the context of ageing, including insulin resistance, T2DM and sarcopenic obesity, and describes its potential as a therapeutic target.

Serum- and glucocorticoid-induced kinase drives hepatic insulin resistance by directly inhibiting AMP-activated protein kinase

A hallmark of type 2 diabetes (T2D) is hepatic resistance to insulin's glucose-lowering effects. The serum- and glucocorticoid-regulated family of protein kinases (SGK) is activated downstream of mechanistic target of rapamycin complex 2 (mTORC2) in response to insulin in parallel to AKT. Surprisingly, despite an identical substrate recognition motif to AKT, which drives insulin sensitivity, pathological accumulation of SGK1 drives insulin resistance. Liver-specific Sgk1-knockout (Sgk1Lko) mice display improved glucose tolerance and insulin sensitivity and are protected from hepatic steatosis when fed a high-fat diet. Sgk1 promotes insulin resistance by inactivating AMP-activated protein kinase (AMPK) via phosphorylation on inhibitory site AMPKαSer485/491. We demonstrate that SGK1 is dominant among SGK family kinases in regulation of insulin sensitivity, as Sgk1, Sgk2, and Sgk3 triple-knockout mice have similar increases in hepatic insulin sensitivity. In aggregate, these data suggest that targeting hepatic SGK1 may have therapeutic potential in T2D.

Lily bulbs' polyphenols extract ameliorates oxidative stress and lipid accumulation in vitro and in vivo

BACKGROUND

Polyphenols have the potential to reduce the risk of many metabolic disorders. Lily bulbs are rich in polyphenols; however, their effects on lipid metabolism remain unclear. This study aimed to explore the effects of lily bulbs' polyphenols (LBPs) on oxidative stress and lipid metabolism.

RESULTS

A total of 14 polyphenolic compounds in LBPs were identified by high-performance liquid chromatography equipped with diode-array detection mass spectrometry. Total phenolic compound in LBPs was 53.76 ± 1.12 g kg^-1 dry weight. In cellular experiments, LBPs attenuated the disruption of mitochondrial membrane potential, impeded reactive oxygen species production, alleviated oxidative stress, and reduced lipid accumulation in oleic acid induced HepG2 cells. In in vivo studies, LBPs significantly inhibited body weight gain, reduced lipid levels in serum and liver, and improved oxidative damage in a dose-dependent manner in mice fed a high-fat diet. Moreover, LBPs ameliorated hepatic steatosis and suppressed the expression of hepatic-lipogenesis-related genes (SREBP-1c, FAS, ACC1, and SCD-1) and promoted lipolysis genes (SRB1 and HL) and lipid oxidation genes (PPARα and CPT-1) in mice fed a high-fat diet.

CONCLUSION

It was concluded that LBPs are a potential complementary therapeutic alternative in the development of functional foods to curb obesity and obesity-related diseases, such as metabolic syndrome. © 2021 Society of Chemical Industry.

Effects of Iron and Zinc on Mitochondria: Potential Mechanisms of Glaucomatous Injury

Glaucoma is the most substantial cause of irreversible blinding, which is accompanied by progressive retinal ganglion cell damage. Retinal ganglion cells are energy-intensive neurons that connect the brain and retina, and depend on mitochondrial homeostasis to transduce visual information through the brain. As cofactors that regulate many metabolic signals, iron and zinc have attracted increasing attention in studies on neurons and neurodegenerative diseases. Here, we summarize the research connecting iron, zinc, neuronal mitochondria, and glaucomatous injury, with the aim of updating and expanding the current view of how retinal ganglion cells degenerate in glaucoma, which can reveal novel potential targets for neuroprotection.

mTORC2: The other mTOR in autophagy regulation

The mechanistic target of rapamycin (mTOR) has gathered significant attention as a ubiquitously expressed multimeric kinase with key implications for cell growth, proliferation, and survival. This kinase forms the central core of two distinct complexes, mTORC1 and mTORC2, which share the ability of integrating environmental, nutritional, and hormonal cues but which regulate separate molecular pathways that result in different cellular responses. Particularly, mTORC1 has been described as a major negative regulator of endosomal biogenesis and autophagy, a catabolic process that degrades intracellular components and organelles within the lysosomes and is thought to play a key role in human health and disease. In contrast, the role of mTORC2 in the regulation of autophagy has been considerably less studied despite mounting evidence this complex may regulate autophagy in a different and perhaps complementary manner to that of mTORC1. Genetic ablation of unique subunits is currently being utilized to study the differential effects of the two mTOR complexes. RICTOR is the best‐described subunit specific to mTORC2 and as such has become a useful tool for investigating the specific actions of this complex. The development of complex‐specific inhibitors for mTORC2 is also an area of intense interest. Studies to date have demonstrated that mTORC1/2 complexes each signal to a variety of exclusive downstream molecules with distinct biological roles. Pinpointing the particular effects of these downstream effectors is crucial toward the development of novel therapies aimed at accurately modulating autophagy in the context of human aging and disease.

Autophagy in healthy aging and disease

Autophagy is a fundamental cellular process that eliminates molecules and subcellular elements, including nucleic acids, proteins, lipids and organelles, via lysosome-mediated degradation to promote homeostasis, differentiation, development and survival. While autophagy is intimately linked to health, the intricate relationship among autophagy, aging and disease remains unclear. This Review examines several emerging features of autophagy and postulates how they may be linked to aging as well as to the development and progression of disease. In addition, we discuss current preclinical evidence arguing for the use of autophagy modulators as suppressors of age-related pathologies such as neurodegenerative diseases. Finally, we highlight key questions and propose novel research avenues that will likely reveal new links between autophagy and the hallmarks of aging. Understanding the precise interplay between autophagy and the risk of age-related pathologies across organisms will eventually facilitate the development of clinical applications that promote long-term health.

Combinatorial Approach Using Caenorhabditis elegans and Mammalian Systems for Aging Research

Aging is associated with functional and structural declines in organisms over time. Organisms as diverse as the nematode Caenorhabditis elegans and mammals share signaling pathways that regulate aging and lifespan. In this review, we discuss recent combinatorial approach to aging research employing C. elegans and mammalian systems that have contributed to our understanding of evolutionarily conserved aging-regulating pathways. The topics covered here include insulin/IGF-1, mechanistic target of rapamycin (mTOR), and sirtuin signaling pathways; dietary restriction; autophagy; mitochondria; and the nervous system. A combinatorial approach employing high-throughput, rapid C. elegans systems, and human model mammalian systems is likely to continue providing mechanistic insights into aging biology and will help develop therapeutics against age-associated disorders.

New Insights in Mechanisms and Therapeutics for Short- and Long-Term Impacts of Hepatic Ischemia Reperfusion Injury Post Liver Transplantation

Liver transplantation has been identified as the most effective treatment for patients with end-stage liver diseases. However, hepatic ischemia reperfusion injury (IRI) is associated with poor graft function and poses a risk of adverse clinical outcomes post transplantation. Cell death, including apoptosis, necrosis, ferroptosis and pyroptosis, is induced during the acute phase of liver IRI. The release of danger-associated molecular patterns (DAPMs) and mitochondrial dysfunction resulting from the disturbance of metabolic homeostasis initiates graft inflammation. The inflammation in the short term exacerbates hepatic damage, leading to graft dysfunction and a higher incidence of acute rejection. The subsequent changes in the graft immune environment due to hepatic IRI may result in chronic rejection, cancer recurrence and fibrogenesis in the long term. In this review, we mainly focus on new mechanisms of inflammation initiated by immune activation related to metabolic alteration in the short term during liver IRI. The latest mechanisms of cancer recurrence and fibrogenesis due to the long-term impact of inflammation in hepatic IRI is also discussed. Furthermore, the development of therapeutic strategies, including ischemia preconditioning, pharmacological inhibitors and machine perfusion, for both attenuating acute inflammatory injury and preventing late-phase disease recurrence, will be summarized in the context of clinical, translational and basic research.

Mitochondrial quality control in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a common and early-onset pathogenesis in the human lifespan that can increase the risk of low back pain. More clarification of the molecular mechanisms associated with the onset and progression of IDD is likely to help establish novel preventive and therapeutic strategies. Recently, mitochondria have been increasingly recognized as participants in regulating glycolytic metabolism, which has historically been regarded as the main metabolic pathway in intervertebral discs due to their avascular properties. Indeed, mitochondrial structural and functional disruption has been observed in degenerated nucleus pulposus (NP) cells and intervertebral discs. Multilevel and well-orchestrated strategies, namely, mitochondrial quality control (MQC), are involved in the maintenance of mitochondrial integrity, mitochondrial proteostasis, the mitochondrial antioxidant system, mitochondrial dynamics, mitophagy, and mitochondrial biogenesis. Here, we address the key evidence and current knowledge of the role of mitochondrial function in the IDD process and consider how MQC strategies contribute to the protective and detrimental properties of mitochondria in NP cell function. The relevant potential therapeutic treatments targeting MQC for IDD intervention are also summarized. Further clarification of the functional and synergistic mechanisms among MQC mechanisms may provide useful clues for use in developing novel IDD treatments.

Amino Acids in Autophagy: Regulation and Function

Autophagy is a dynamic process in which the eukaryotic cells break down intracellular components by lysosomal degradation. Under the normal condition, the basal level of autophagy removes damaged organelles, misfolded proteins, or protein aggregates to keep cells in a homeostatic condition. Deprivation of nutrients (e.g., removal of amino acids) stimulates autophagy activity, promoting lysosomal degradation and the recycling of cellular components for cell survival. Importantly, insulin and amino acids are two main inhibitors of autophagy. They both activate the mTOR complex 1 (mTORC1) signaling pathway to inhibit the autophagy upstream of the uncoordinated-51 like kinase 1/2 (ULK1/2) complex that triggers autophagosome formation. In particular, insulin activates mTORC1 via the PI3K class I-AKT pathway; while amino acids activate mTORC1 either through the PI3K class III (hVps34) pathway or through a variety of amino acid sensors located in the cytosol or lysosomal membrane. These amino acid sensors control the translocation of mTORC1 from the cytosol to the lysosomal surface where mTORC1 is activated by Rheb GTPase, therefore regulating autophagy and the lysosomal protein degradation.

The Role of Voltage-Dependent Anion Channel in Mitochondrial Dysfunction and Human Disease

The voltage-dependent anion channel (VDAC) is a β-barrel membrane protein located in the outer mitochondrial membrane (OMM). VDAC has two conductance states: an open anion selective state, and a closed and slightly cation-selective state. VDAC conductance states play major roles in regulating permeability of ATP/ADP, regulation of calcium homeostasis, calcium flux within ER-mitochondria contact sites, and apoptotic signaling events. Three reported structures of VDAC provide information on the VDAC open state via X-ray crystallography and nuclear magnetic resonance (NMR). Together, these structures provide insight on how VDAC aids metabolite transport. The interaction partners of VDAC, together with the permeability of the pore, affect the molecular pathology of diseases including Parkinson’s disease (PD), Friedreich’s ataxia (FA), lupus, and cancer. To fully address the molecular role of VDAC in disease pathology, major questions must be answered on the structural conformers of VDAC. For example, further information is needed on the structure of the closed state, how binding partners or membrane potential could lead to the open/closed states, the function and mobility of the N-terminal α-helical domain of VDAC, and the physiological role of VDAC oligomers. This review covers our current understanding of the various states of VDAC, VDAC interaction partners, and the roles they play in mitochondrial regulation pertaining to human diseases.

Potential protective effect of hesperidin on hypoxia/reoxygenation-induced hepatocyte injury

Hesperidin (HDN) has been reported to have hydrogen radical- and hydrogen peroxide-removal activities and to serve an antioxidant role in biological systems. However, whether HDN protects hepatocytes (HCs) against hypoxia/reoxygenation (H/R)-induced injury remains unknown. The present study aimed to explore the role of HDN in H/R-induced injury. HCs were isolated and cultured under H/R conditions with or without HDN treatment. HC damage was markedly induced under H/R, as indicated by cell viability, supernatant lactate dehydrogenase levels and alanine aminotransferase levels; however, HDN treatment significantly reversed HC injury. Oxidative stress markers (malondialdehyde, superoxide dismutase, glutathioneand reactive oxygen species) were increased markedly during H/R in HCs; however, this effect was significantly attenuated after exposure to HDN. Compared with those of the control group, the mRNA expression levels of IL-6 and TNF-α in HCs and the concentrations of IL-6 and TNF-α in the supernatants increased significantly following H/R, and HDN significantly ameliorated these effects. Western blotting demonstrated that microtubule-associated protein 1 light chain 3α (MAP1LC3A, also known as LC3) and Beclin-1 protein expression levels increased, while sequestosome 1 levels decreased during H/R following exposure to HDN. The number of GFP-LC3 puncta in HCs following exposure to HDN was increased compared with that observed in HCs without HDN exposure under the H/R conditions after bafilomycin A1 treatment. In summary, the present study demonstrated that HDN attenuated HC oxidative stress and inflammatory responses while enhancing autophagy during H/R. HDN may have a potential protective effect on HCs during H/R-induced injury.

The mTOR-Autophagy Axis and the Control of Metabolism

The mechanistic target of rapamycin (mTOR), master regulator of cellular metabolism, exists in two distinct complexes: mTOR complex 1 and mTOR complex 2 (mTORC1 and 2). MTORC1 is a master switch for most energetically onerous processes in the cell, driving cell growth and building cellular biomass in instances of nutrient sufficiency, and conversely, allowing autophagic recycling of cellular components upon nutrient limitation. The means by which the mTOR kinase blocks autophagy include direct inhibition of the early steps of the process, and the control of the lysosomal degradative capacity of the cell by inhibiting the transactivation of genes encoding structural, regulatory, and catalytic factors. Upon inhibition of mTOR, autophagic recycling of cellular components results in the reactivation of mTORC1; thus, autophagy lies both downstream and upstream of mTOR. The functional relationship between the mTOR pathway and autophagy involves complex regulatory loops that are significantly deciphered at the cellular level, but incompletely understood at the physiological level. Nevertheless, genetic evidence stemming from the use of engineered strains of mice has provided significant insight into the overlapping and complementary metabolic effects that physiological autophagy and the control of mTOR activity exert during fasting and nutrient overload.

The mitochondrial permeability transition pore: an evolving concept critical for cell life and death

In this review, we summarize current knowledge of perhaps one of the most intriguing phenomena in cell biology: the mitochondrial permeability transition pore (mPTP). This phenomenon, which was initially observed as a sudden loss of inner mitochondrial membrane impermeability caused by excessive calcium, has been studied for almost 50 years, and still no definitive answer has been provided regarding its mechanisms. From its initial consideration as an in vitro artifact to the current notion that the mPTP is a phenomenon with physiological and pathological implications, a long road has been travelled. We here summarize the role of mitochondria in cytosolic calcium control and the evolving concepts regarding the mitochondrial permeability transition (mPT) and the mPTP. We show how the evolving mPTP models and mechanisms, which involve many proposed mitochondrial protein components, have arisen from methodological advances and more complex biological models. We describe how scientific progress and methodological advances have allowed milestone discoveries on mPTP regulation and composition and its recognition as a valid target for drug development and a critical component of mitochondrial biology.

Plasma methionine metabolic profile is associated with longevity in mammals

Methionine metabolism arises as a key target to elucidate the molecular adaptations underlying animal longevity due to the negative association between longevity and methionine content. The present study follows a comparative approach to analyse plasma methionine metabolic profile using a LC-MS/MS platform from 11 mammalian species with a longevity ranging from 3.5 to 120 years. Our findings demonstrate the existence of a species-specific plasma profile for methionine metabolism associated with longevity characterised by: i) reduced methionine, cystathionine and choline; ii) increased non-polar amino acids; iii) reduced succinate and malate; and iv) increased carnitine. Our results support the existence of plasma longevity features that might respond to an optimised energetic metabolism and intracellular structures found in long-lived species.

Mota-Martorell and colleagues use a comparative metabolomics approach to examine plasma metabolite levels associated with methionine metabolism in 11 mammalian species. They identify species specific plasma profiles indicative of a link between lifetime longevity and methionine metabolism.

Prohibitin depletion extends lifespan of a TORC2/SGK-1 mutant through autophagy and the mitochondrial UPR

Mitochondrial prohibitins (PHB) are highly conserved proteins with a peculiar effect on lifespan. While PHB depletion shortens lifespan of wild‐type animals, it enhances longevity of a plethora of metabolically compromised mutants, including target of rapamycin complex 2 (TORC2) mutants sgk‐1 and rict‐1. Here, we show that sgk‐1 mutants have impaired mitochondrial homeostasis, lipogenesis and yolk formation, plausibly due to alterations in membrane lipid and sterol homeostasis. Remarkably, all these features are suppressed by PHB depletion. Our analysis shows the requirement of SRBP1/SBP‐1 for the lifespan extension of sgk‐1 mutants and the further extension conferred by PHB depletion. Moreover, although the mitochondrial unfolded protein response (UPR^mt) and autophagy are induced in sgk‐1 mutants and upon PHB depletion, they are dispensable for lifespan. However, the enhanced longevity caused by PHB depletion in sgk‐1 mutants requires both, the UPR^mt and autophagy, but not mitophagy. We hypothesize that UPR^mt induction upon PHB depletion extends lifespan of sgk‐1 mutants through autophagy and probably modulation of lipid metabolism.

An energetics perspective on geroscience: mitochondrial protonmotive force and aging

Mitochondria are organelles that provide energy to cells through ATP production. Mitochondrial dysfunction has long been postulated to mediate cellular declines that drive biological aging. Many well-characterized hallmarks of aging may involve underlying energetic defects that stem from loss of mitochondrial function with age. Why and how mitochondrial function declines with age is an open question and one that has been difficult to answer. Mitochondria are powered by an electrochemical gradient across the inner mitochondrial membrane known as the protonmotive force (PMF). This gradient decreases with age in several experimental models. However, it is unclear if a diminished PMF is a cause or a consequence of aging. Herein, we briefly review and define mitochondrial function, we summarize how PMF changes with age in several models, and we highlight recent studies that implicate PMF in aging biology. We also identify barriers that must be addressed for the field to progress. Emerging technology permits more precise in vivo study of mitochondria that will allow better understanding of cause and effect in metabolic models of aging. Once cause and effect can be discerned more precisely, energetics approaches to combat aging may be developed to prevent or reverse functional decline.

Taurine Antagonizes Macrophages M1 Polarization by Mitophagy-Glycolysis Switch Blockage via Dragging SAM-PP2Ac Transmethylation

The excessive M1 polarization of macrophages drives the occurrence and development of inflammatory diseases. The reprogramming of macrophages from M1 to M2 can be achieved by targeting metabolic events. Taurine promotes for the balance of energy metabolism and the repair of inflammatory injury, preventing chronic diseases and complications. However, little is known about the mechanisms underlying the action of taurine modulating the macrophage polarization phenotype. In this study, we constructed a low-dose LPS/IFN-γ-induced M1 polarization model to simulate a low-grade pro-inflammatory process. Our results indicate that the taurine transporter TauT/SlC6A6 is upregulated at the transcriptional level during M1 macrophage polarization. The nutrient uptake signal on the membrane supports the high abundance of taurine in macrophages after taurine supplementation, which weakens the status of methionine metabolism, resulting in insufficient S-adenosylmethionine (SAM). The low availability of SAM is directly sensed by LCMT-1 and PME-1, hindering PP2Ac methylation. PP2Ac methylation was found to be necessary for M1 polarization, including the positive regulation of VDAC1 and PINK1. Furthermore, its activation was found to promote the elimination of mitochondria by macrophages via the mitophagy pathway for metabolic adaptation. Mechanistically, taurine inhibits SAM-dependent PP2Ac methylation to block PINK1-mediated mitophagy flux, thereby maintaining a high mitochondrial density, which ultimately hinders the conversion of energy metabolism to glycolysis required for M1. Our findings reveal a novel mechanism of taurine-coupled M1 macrophage energy metabolism, providing novel insights into the occurrence and prevention of low-grade inflammation, and propose that the sensing of taurine and SAM availability may allow communication to inflammatory response in macrophages.

Acetyl-CoA Metabolism and Histone Acetylation in the Regulation of Aging and Lifespan

Acetyl-CoA is a metabolite at the crossroads of central metabolism and the substrate of histone acetyltransferases regulating gene expression. In many tissues fasting or lifespan extending calorie restriction (CR) decreases glucose-derived metabolic flux through ATP-citrate lyase (ACLY) to reduce cytoplasmic acetyl-CoA levels to decrease activity of the p300 histone acetyltransferase (HAT) stimulating pro-longevity autophagy. Because of this, compounds that decrease cytoplasmic acetyl-CoA have been described as CR mimetics. But few authors have highlighted the potential longevity promoting roles of nuclear acetyl-CoA. For example, increasing nuclear acetyl-CoA levels increases histone acetylation and administration of class I histone deacetylase (HDAC) inhibitors increases longevity through increased histone acetylation. Therefore, increased nuclear acetyl-CoA likely plays an important role in promoting longevity. Although cytoplasmic acetyl-CoA synthetase 2 (ACSS2) promotes aging by decreasing autophagy in some peripheral tissues, increased glial AMPK activity or neuronal differentiation can stimulate ACSS2 nuclear translocation and chromatin association. ACSS2 nuclear translocation can result in increased activity of CREB binding protein (CBP), p300/CBP-associated factor (PCAF), and other HATs to increase histone acetylation on the promoter of neuroprotective genes including transcription factor EB (TFEB) target genes resulting in increased lysosomal biogenesis and autophagy. Much of what is known regarding acetyl-CoA metabolism and aging has come from pioneering studies with yeast, fruit flies, and nematodes. These studies have identified evolutionary conserved roles for histone acetylation in promoting longevity. Future studies should focus on the role of nuclear acetyl-CoA and histone acetylation in the control of hypothalamic inflammation, an important driver of organismal aging.

Hypocaloric Diet Initiated Post-Ischemia Provides Long-Term Neuroprotection and Promotes Peri-Infarct Brain Remodeling by Regulating Metabolic and Survival-Promoting Proteins

Calorie restriction confers post-ischemic neuroprotection, when administered in a defined time window before ischemic stroke. How a hypocaloric diet influences stroke recovery when initiated after stroke has not been investigated. Male C57BL6/j mice were exposed to transient intraluminal middle cerebral artery occlusion. Immediately post-ischemia, mice were randomized to two groups receiving moderately hypocaloric (2286 kcal/kg food) or normocaloric (3518 kcal/kg) diets ad libitum. Animals were sacrificed at 3 or 56 days post-ischemia (dpi). Besides increased low density lipoprotein at 3 days and reduced alanine aminotransferase and increased urea at 56 days, no alterations of plasma markers were found in ischemic mice on hypocaloric diet. Body weight mildly decreased over 56 dpi by 7.4%. Hypocaloric diet reduced infarct volume in the acute stroke phase at 3 dpi and decreased brain atrophy, increased neuronal survival and brain capillary density in peri-infarct striatum and reduced motor coordination impairment in tight rope tests in the post-acute stroke phase over up to 56 dpi. The abundance of brain-derived neurotrophic factor, the NAD-dependent deacetylase and longevity protein sirtuin-1, the anti-oxidant glutathione peroxidase-3, and the ammonium detoxifier glutamine synthetase in the peri-infarct brain tissue was increased by hypocaloric diet. This study shows that a moderately hypocaloric diet that is initiated after stroke confers long-term neuroprotection and promotes peri-infarct brain remodeling.

Molecular and Supramolecular Structure of the Mitochondrial Oxidative Phosphorylation System: Implications for Pathology

Under aerobic conditions, mitochondrial oxidative phosphorylation (OXPHOS) converts the energy released by nutrient oxidation into ATP, the currency of living organisms. The whole biochemical machinery is hosted by the inner mitochondrial membrane (mtIM) where the protonmotive force built by respiratory complexes, dynamically assembled as super-complexes, allows the F1FO-ATP synthase to make ATP from ADP + Pi. Recently mitochondria emerged not only as cell powerhouses, but also as signaling hubs by way of reactive oxygen species (ROS) production. However, when ROS removal systems and/or OXPHOS constituents are defective, the physiological ROS generation can cause ROS imbalance and oxidative stress, which in turn damages cell components. Moreover, the morphology of mitochondria rules cell fate and the formation of the mitochondrial permeability transition pore in the mtIM, which, most likely with the F1FO-ATP synthase contribution, permeabilizes mitochondria and leads to cell death. As the multiple mitochondrial functions are mutually interconnected, changes in protein composition by mutations or in supercomplex assembly and/or in membrane structures often generate a dysfunctional cascade and lead to life-incompatible diseases or severe syndromes. The known structural/functional changes in mitochondrial proteins and structures, which impact mitochondrial bioenergetics because of an impaired or defective energy transduction system, here reviewed, constitute the main biochemical damage in a variety of genetic and age-related diseases.

Targeting the Mitochondria-Proteostasis Axis to Delay Aging

Human life expectancy continues to grow globally, and so does the prevalence of age-related chronic diseases, causing a huge medical and economic burden on society. Effective therapeutic options for these disorders are scarce, and even if available, are typically limited to a single comorbidity in a multifaceted dysfunction that inevitably affects all organ systems. Thus, novel therapies that target fundamental processes of aging itself are desperately needed. In this article, we summarize current strategies that successfully delay aging and related diseases by targeting mitochondria and protein homeostasis. In particular, we focus on autophagy, as a fundamental proteostatic process that is intimately linked to mitochondrial quality control. We present genetic and pharmacological interventions that effectively extend health- and life-span by acting on specific mitochondrial and pro-autophagic molecular targets. In the end, we delve into the crosstalk between autophagy and mitochondria, in what we refer to as the mitochondria-proteostasis axis, and explore the prospect of targeting this crosstalk to harness maximal therapeutic potential of anti-aging interventions.

Mitochondrial dysfunction and mitophagy pathway activation in hepatitis E virus-infected livers of Mongolian gerbils

Recently, hepatitis E virus (HEV) has caused large outbreaks and presented a significant public health problem. Thus, the mechanism of HEV has attracted increasing research attention. Previous studies revealed that HEV infection induced hepatocyte injuries and structural and functional changes in mitochondria. These pathological changes affected the life cycle of hepatocytes. However, the precise underlying mechanism and the effector protein responsible for this process remain unclear. In the present study, mitochondrial function and the expression of mitophagy-associated mRNA transcripts and proteins were detected in an HEV- infected Mongolian gerbil model. Observation of ultrastructural changes in the liver of the inoculated group revealed the disappearance of mitochondrial cristae of mitochondrion, blurring of the bilayer structure and cavitation in the cytoplasm. The results showed that the mitochondrial transmembrane potential of decreased, mitochondrial transition pore (MPTP) opening increased, reactive oxygen species (ROS) production increased, and glutathione peroxidase (GSH-Px) activity decreased in the HEV-inoculated group. Moreover, the LC3, Beclin1, BNIP3L, Parkin, PINK1 and P62 mRNA levels were significantly increased (p < 0.05 and p < 0.01) in the inoculated group. Western blot and immunohistochemistry assay analyses detected the upregulation of the mitophagy-associated proteins LC3, Beclin1, BNIP3L, Parkin, PINK1 and P62 (p < 0.05 and p < 0.01) in HEV-infected gerbils. All these data demonstrated that HEV infection in vivo induced mitochondrial dysfunction and the activation of the mitophagy pathway, which might be one of the key factors in hepatocyte injury.

The neurosteroid allopregnanolone protects retinal neurons by effects on autophagy and GABRs/GABAA receptors in rat glaucoma models

In an ex vivo rat glaucoma model using dissected retinas, the neurosteroid allopregnanolone (AlloP) protects retinal ganglion cells (RGCs) via GABR/GABAA receptors. To determine the involvement of macroautophagy/autophagy in neuroprotection by AlloP, we examined the effects of autophagy activators, rapamycin and torin 2, and autophagy inhibitors, bafilomycin A1 and SAR405, on retinal retinal morphology and expression of MAP1 LC3B/LC3B (microtubule-associated protein 1 light chain 3 beta) and SQSTM1 (sequestosome 1). Administration of rapamycin or torin 2 exerted partial histological neuroprotection, while combined administration of AlloP with bafilomycin A1 or SAR405 induced severe degeneration in a hyperbaric condition. Electron microscopic analyses showed that the addition of AlloP significantly increased autophagosomes and degenerative autophagic vacuoles in the retinal nerve fiber layer. Immunoblotting showed that the addition of AlloP or autophagic activators increased the lipidated form of LC3B (LC3B-II) and suppressed SQSTM1. Moreover, bafilomycin A1 increased LC3B-II and SQSTM1 protein levels in the presence of AlloP without changes in corresponding mRNAs compared to AlloP-treated retinas in a hyperbaric condition. These data indicate that AlloP likely induces a protective form of autophagy in this model. In an in vivo rat model of glaucoma, we also observed neuroprotective effects of AlloP. Injection of polystyrene microbeads into the anterior chamber increased intraocular pressure about 3-fold and induced RGC apoptosis. A single intravitreal injection of AlloP or autophagy activators prevented apoptosis and protected RGCs with autophagy activation. We conclude that AlloP may serve as a potential therapeutic agent for the treatment of glaucoma via diverse mechanisms.Abbreviations: 2HBCD: 2-Hydroxypropyl)-β-cyclodextrin; 3-MA: 3-methyladenine; AlloP: allopregnanolone; AP: autophagosome; AVd: degradative autophagic vacuoles; GCL: ganglion cell layer; INL: inner nuclear layer; IOP: intraocular pressure; IPL: inner plexiform layer; LC3B-I: cytosolic form of LC3B; LCB-II: lipidated form of LC3B; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; mPTP: mitochondrial permeability transition pore; NDS: neuronal damage score; NFL: nerve fiber layer; OH: ocular hypertension; ON: optic nerve; ONL: outer nuclear layer; OPL: outer plexiform layer; p-STR: scotopic threshold response; RGC: retinal ganglion cells; RT-PCR: real-time reverse transcription polymerase chain reaction; SQSTM1: sequestosome 1; TUNEL: TdT-mediated dUTP Nick End Labeling.

Evidence and perspectives of cell senescence in neurodegenerative diseases

Increased life expectancies have significantly increased the number of individuals suffering from geriatric neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). The financial cost for current and future patients with these diseases is overwhelming, resulting in substantial economic and societal costs. Unfortunately, most recent high-profile clinical trials for neurodegenerative diseases have failed to obtain efficacious results, indicating that novel approaches are desperately needed to treat these pathologies. Cell senescence, characterized by permanent cell cycle arrest, resistance to apoptosis, mitochondrial alterations, and secretion of senescence-associated secretory phenotype (SASP) components, has been extensively studied in mitotic cells such as fibroblasts, which is considered a hallmark of aging. Furthermore, multiple cell types in the senescent state in the brain, including neurons, microglia, astrocytes, and neural stem cells, have recently been observed in the context of neurodegenerative diseases, suggesting that these senescent cells may play an essential role in the pathological processes of neurodegenerative diseases. Therefore, this review begins by outlining key aspects of cell senescence constitution followed by examining the evidence implicating senescent cells in neurodegenerative diseases. In the final section, we review how cell senescence may be targeted as novel therapeutics to treat pathologies associated with neurodegenerative diseases.

Targeting the Mitochondrial Permeability Transition Pore to Prevent Age-Associated Cell Damage and Neurodegeneration

The aging process is associated with significant alterations in mitochondrial function. These changes in mitochondrial function are thought to involve increased production of reactive oxygen species (ROS), which over time contribute to cell death, senescence, tissue degeneration, and impaired tissue repair. The mitochondrial permeability transition pore (mPTP) is likely to play a critical role in these processes, as increased ROS activates mPTP opening, which further increases ROS production. Injury and inflammation are also thought to increase mPTP opening, and chronic, low-grade inflammation is a hallmark of aging. Nicotinamide adenine dinucleotide (NAD+) can suppress the frequency and duration of mPTP opening; however, NAD+ levels are known to decline with age, further stimulating mPTP opening and increasing ROS release. Research on neurodegenerative diseases, particularly on Parkinson's disease (PD) and Alzheimer's disease (AD), has uncovered significant findings regarding mPTP openings and aging. Parkinson's disease is associated with a reduction in mitochondrial complex I activity and increased oxidative damage of DNA, both of which are linked to mPTP opening and subsequent ROS release. Similarly, AD is associated with increased mPTP openings, as evidenced by amyloid-beta (Aβ) interaction with the pore regulator cyclophilin D (CypD). Targeted therapies that can reduce the frequency and duration of mPTP opening may therefore have the potential to prevent age-related declines in cell and tissue function in various systems including the central nervous system.

Intricate role of mitochondrial calcium signalling in mitochondrial quality control for regulation of cancer cell fate

Mitochondrial quality control is crucial for sustaining cellular maintenance. Mitochondrial Ca²⁺ plays an important role in the maintenance of mitochondrial quality control through regulation of mitochondrial dynamics, mitophagy and mitochondrial biogenesis for preserving cellular homeostasis. The regulation of this dynamic interlink between these mitochondrial networks and mitochondrial Ca²⁺ appears indispensable for the adaptation of cells under external stimuli. Moreover, dysregulation of mitochondrial Ca²⁺ divulges impaired mitochondrial control that results in several pathological conditions such as cancer. Hence this review untangles the interplay between mitochondrial Ca²⁺ and quality control that govern mitochondrial health and mitochondrial coordinates in the development of cancer.

The Mitochondrial Permeability Transition: Nexus of Aging, Disease and Longevity

The activity of the mitochondrial permeability transition pore, mPTP, a highly regulated multi-component mega-channel, is enhanced in aging and in aging-driven degenerative diseases. mPTP activity accelerates aging by releasing large amounts of cell-damaging reactive oxygen species, Ca²⁺ and NAD⁺. The various pathways that control the channel activity, directly or indirectly, can therefore either inhibit or accelerate aging or retard or enhance the progression of aging-driven degenerative diseases and determine lifespan and healthspan. Autophagy, a catabolic process that removes and digests damaged proteins and organelles, protects the cell against aging and disease. However, the protective effect of autophagy depends on mTORC2/SKG1 inhibition of mPTP. Autophagy is inhibited in aging cells. Mitophagy, a specialized form of autophagy, which retards aging by removing mitochondrial fragments with activated mPTP, is also inhibited in aging cells, and this inhibition leads to increased mPTP activation, which is a major contributor to neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. The increased activity of mPTP in aging turns autophagy/mitophagy into a destructive process leading to cell aging and death. Several drugs and lifestyle modifications that enhance healthspan and lifespan enhance autophagy and inhibit the activation of mPTP. Therefore, elucidating the intricate connections between pathways that activate and inhibit mPTP, in the context of aging and degenerative diseases, could enhance the discovery of new drugs and lifestyle modifications that slow aging and degenerative disease.