Up-regulation of cholesterol synthesis by lysosomal defects requires a functional mitochondrial respiratory chain.

Mitochondria and lysosomes are two organelles that carry out both signaling and metabolic roles in the cells. Recent evidence has shown that mitochondria and lysosomes are dependent on one another, as primary defects in one cause secondary defects in the other. Nevertheless, the signaling consequences of primary mitochondrial malfunction and of primary lysosomal defects are not similar, despite in both cases there are impairments of mitochondria and of lysosomes. Here, we used RNA sequencing to obtain transcriptomes from cells with primary mitochondrial or lysosomal defects, to identify what are the global cellular consequences that are associated with malfunction of mitochondria or lysosomes. We used these data to determine what are the pathways that are affected by defects in both organelles, which revealed a prominent role for the cholesterol synthesis pathway. This pathway is transcriptionally up-regulated in cellular and mouse models of lysosomal defects and is transcriptionally down-regulated in cellular and mouse models of mitochondrial defects. We identified a role for post-transcriptional regulation of the transcription factor SREBF1, a master regulator of cholesterol and lipid biosynthesis, in models of mitochondrial respiratory chain deficiency. Furthermore, the retention of Ca 2+ in the lysosomes of cells with mitochondrial respiratory chain defects contributes to the differential regulation of the cholesterol synthesis pathway in the mitochondrial and lysosomal defects tested. Finally, we verified in vivo , using models of mitochondria-associated diseases in C. elegans , that normalization of lysosomal Ca 2+ levels results in partial rescue of the developmental arrest induced by the respiratory chain deficiency.

Abl depletion via autophagy mediates the beneficial effects of quercetin against Alzheimer pathology across species.

Alzheimer's disease is the most common age-associated neurodegenerative disorder and the most frequent form of dementia in our society. Aging is a complex biological process concurrently shaped by genetic, dietary and environmental factors and natural compounds are emerging for their beneficial effects against age-related disorders. Besides their antioxidant activity often described in simple model organisms, the molecular mechanisms underlying the beneficial effects of different dietary compounds remain however largely unknown. In the present study, we exploit the nematode Caenorhabditis elegans as a widely established model for aging studies, to test the effects of different natural compounds in vivo and focused on mechanistic aspects of one of them, quercetin, using complementary systems and assays. We show that quercetin has evolutionarily conserved beneficial effects against Alzheimer's disease (AD) pathology: it prevents Amyloid beta (Aß)-induced detrimental effects in different C. elegans AD models and it reduces Aß-secretion in mammalian cells. Mechanistically, we found that the beneficial effects of quercetin are mediated by autophagy-dependent reduced expression of Abl tyrosine kinase. In turn, autophagy is required upon Abl suppression to mediate quercetin's protective effects against Aß toxicity. Our data support the power of C. elegans as an in vivo model to investigate therapeutic options for AD.

Mitochondria hormesis delays aging and associated diseases in Caenorhabditis elegans impacting on key ferroptosis players.

Excessive iron accumulation or deficiency leads to a variety of pathologies in humans and developmental arrest in the nematode Caenorhabditis elegans. Instead, sub-lethal iron depletion extends C. elegans lifespan. Hypoxia preconditioning protects against severe hypoxia-induced neuromuscular damage across species but it has low feasible application. In this study, we assessed the potential beneficial effects of genetic and chemical interventions acting via mild iron instead of oxygen depletion. We show that limiting iron availability in C. elegans through frataxin silencing or the iron chelator bipyridine, similar to hypoxia preconditioning, protects against hypoxia-, age-, and proteotoxicity-induced neuromuscular deficits. Mechanistically, our data suggest that the beneficial effects elicited by frataxin silencing are in part mediated by counteracting ferroptosis, a form of non-apoptotic cell death mediated by iron-induced lipid peroxidation. This is achieved by impacting on different key ferroptosis players and likely via gpx-independent redox systems. We thus point to ferroptosis inhibition as a novel potential strategy to promote healthy aging.

Cobalt chloride has beneficial effects across species through a hormetic mechanism.

Severe oxygen and iron deficiencies have evolutionarily conserved detrimental effects, leading to pathologies in mammals and developmental arrest as well as neuromuscular degeneration in the nematode Caenorhabditis elegans. Yet, similar to the beneficial effects of mild hypoxia, non-toxic levels of iron depletion, achieved with the iron chelator bipyridine or through frataxin silencing, extend C. elegans lifespan through hypoxia-like induction of mitophagy. While the positive health outcomes of hypoxia preconditioning are evident, its practical application is rather challenging. Here, we thus test the potential beneficial effects of non-toxic, preconditioning interventions acting on iron instead of oxygen availability. We find that limiting iron availability through the iron competing agent cobalt chloride has evolutionarily conserved dose-dependent beneficial effects: while high doses of cobalt chloride have toxic effects in mammalian cells, iPS-derived neurospheres, and in C. elegans, sub-lethal doses protect against hypoxia- or cobalt chloride-induced death in mammalian cells and extend lifespan and delay age-associated neuromuscular alterations in C. elegans. The beneficial effects of cobalt chloride are accompanied by the activation of protective mitochondrial stress response pathways.

Neuroligin-mediated neurodevelopmental defects are induced by mitochondrial dysfunction and prevented by lutein in C. elegans.

Complex-I-deficiency represents the most frequent pathogenetic cause of human mitochondriopathies. Therapeutic options for these neurodevelopmental life-threating disorders do not exist, partly due to the scarcity of appropriate model systems to study them. Caenorhabditis elegans is a genetically tractable model organism widely used to investigate neuronal pathologies. Here, we generate C. elegans models for mitochondriopathies and show that depletion of complex I subunits recapitulates biochemical, cellular and neurodevelopmental aspects of the human diseases. We exploit two models, nuo-5/NDUFS1- and lpd-5/NDUFS4-depleted animals, for a suppressor screening that identifies lutein for its ability to rescue animals' neurodevelopmental deficits. We uncover overexpression of synaptic neuroligin as an evolutionarily conserved consequence of mitochondrial dysfunction, which we find to mediate an early cholinergic defect in C. elegans. We show lutein exerts its beneficial effects by restoring neuroligin expression independently from its antioxidant activity, thus pointing to a possible novel pathogenetic target for the human disease.

Aryl Hydrocarbon Receptor-Dependent and -Independent Pathways Mediate Curcumin Anti-Aging Effects.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor whose activity can be modulated by polyphenols, such as curcumin. AhR and curcumin have evolutionarily conserved effects on aging. Here, we investigated whether and how the AhR mediates the anti-aging effects of curcumin across species. Using a combination of in vivo, in vitro, and in silico analyses, we demonstrated that curcumin has AhR-dependent or -independent effects in a context-specific manner. We found that in Caenorhabditis elegans, AhR mediates curcumin-induced lifespan extension, most likely through a ligand-independent inhibitory mechanism related to its antioxidant activity. Curcumin also showed AhR-independent anti-aging activities, such as protection against aggregation-prone proteins and oxidative stress in C. elegans and promotion of the migratory capacity of human primary endothelial cells. These AhR-independent effects are largely mediated by the Nrf2/SKN-1 pathway.

Insights into cisplatin-induced neurotoxicity and mitochondrial dysfunction in Caenorhabditis elegans.

Cisplatin is the most common drug in first-line chemotherapy against solid tumors. We and others have previously used the nematode Caenorhabditis elegans to identify genetic factors influencing the sensitivity and resistance to cisplatin. In this study, we used C. elegans to explore cisplatin effects on mitochondrial functions and investigate cisplatin-induced neurotoxicity through a high-resolution system for evaluating locomotion. First, we report that a high-glucose diet sensitizes C. elegans to cisplatin at the physiological level and that mitochondrial CED-13 protects the cell from cisplatin-induced oxidative stress. Additionally, by assessing mitochondrial function with a Seahorse XFe96 Analyzer, we observed a detrimental effect of cisplatin and glucose on mitochondrial respiration. Second, because catechol-O-methyltransferases (involved in dopamine degradation) are upregulated upon cisplatin exposure, we studied the protective role of dopamine against cisplatin-induced neurotoxicity. Using a Tierpsy Tracker system for measuring neurotoxicity, we showed that abnormal displacements and body postures in cat-2 mutants, which have dopamine synthesis disrupted, can be rescued by adding dopamine. Then, we demonstrated that dopamine treatment protects against the dose-dependent neurotoxicity caused by cisplatin.

High-Content C. elegans Screen Identifies Natural Compounds Impacting Mitochondria-Lipid Homeostasis and Promoting Healthspan.

The aging process is concurrently shaped by genetic and extrinsic factors. In this work, we screened a small library of natural compounds, many of marine origin, to identify novel possible anti-aging interventions in Caenorhabditis elegans, a powerful model organism for aging studies. To this aim, we exploited a high-content microscopy platform to search for interventions able to induce phenotypes associated with mild mitochondrial stress, which is known to promote animal's health- and lifespan. Worms were initially exposed to three different concentrations of the drugs in liquid culture, in search of those affecting animal size and expression of mitochondrial stress response genes. This was followed by a validation step with nine compounds on solid media to refine compounds concentration, which led to the identification of four compounds (namely isobavachalcone, manzamine A, kahalalide F and lutein) consistently affecting development, fertility, size and lipid content of the nematodes. Treatment of Drosophila cells with the four hits confirmed their effects on mitochondria activity and lipid content. Out of these four, two were specifically chosen for analysis of age-related parameters, kahalalide F and lutein, which conferred increased resistance to heat and oxidative stress and extended animals' healthspan. We also found that, out of different mitochondrial stress response genes, only the C. elegans ortholog of the synaptic regulatory proteins neuroligins, nlg-1, was consistently induced by the two compounds and mediated lutein healthspan effects.

Dietary and environmental factors have opposite AhR-dependent effects on C. elegans healthspan.

Genetic, dietary, and environmental factors concurrently shape the aging process. The aryl hydrocarbon receptor (AhR) was discovered as a dioxin-binding transcription factor involved in the metabolism of different environmental toxicants in vertebrates. Since then, the variety of pathophysiological processes regulated by the AhR has grown, ranging from immune response, metabolic pathways, and aging. Many modulators of AhR activity may impact on aging and age-associated pathologies, but, whether their effects are AhR-dependent has never been explored. Here, using Caenorhabditis elegans, as an elective model organism for aging studies, we show for the first time that lack of CeAHR-1 can have opposite effects on health and lifespan in a context-dependent manner. Using known mammalian AhR modulators we found that, ahr-1 protects against environmental insults (benzo(a)pyrene and UVB light) and identified a new role for AhR-bacterial diet interaction in animal lifespan, stress resistance, and age-associated pathologies. We narrowed down the dietary factor to a bacterially extruded metabolite likely involved in tryptophan metabolism. This is the first study clearly establishing C. elegans as a good model organism to investigate evolutionarily conserved functions of AhR-modulators and -regulated processes, indicating it can be exploited to contribute to the discovery of novel information about AhR in mammals.

Mitophagy and iron: two actors sharing the stage in age-associated neuronal pathologies.

Aging is characterized by the deterioration of different cellular and organismal structures and functions. A typical hallmark of the aging process is the accumulation of dysfunctional mitochondria and excess iron, leading to a vicious cycle that promotes cell and tissue damage, which ultimately contribute to organismal aging. Accordingly, altered mitochondrial quality control pathways such as mitochondrial autophagy (mitophagy) as well as altered iron homeostasis, with consequent iron overload, can accelerate the aging process and the development and progression of different age-associated disorders. In this review we first briefly introduce the aging process and summarize molecular mechanisms regulating mitophagy and iron homeostasis. We then provide an overview on how dysfunction of these two processes impact on aging and age-associated neurodegenerative disorders with a focus on Alzheimer's disease, Parkinson's disease and Amyotrophic Lateral Sclerosis. Finally, we summarize some recent evidence showing mechanistic links between iron metabolism and mitophagy and speculate on how regulating the crosstalk between the two processes may provide protective effects against aging and age-associated neuronal pathologies.

AHR Signaling Dampens Inflammatory Signature in Neonatal Skin γδ T Cells.

Background Aryl hydrocarbon receptor (AHR)-deficient mice do not support the expansion of dendritic epidermal T cells (DETC), a resident immune cell population in the murine epidermis, which immigrates from the fetal thymus to the skin around birth. Material and Methods In order to identify the gene expression changes underlying the DETC disappearance in AHR-deficient mice, we analyzed microarray RNA-profiles of DETC, sorted from the skin of two-week-old AHR-deficient mice and their heterozygous littermates. In vitro studies were done for verification, and IL-10, AHR repressor (AHRR), and c-Kit deficient mice analyzed for DETC frequency. Results We identified 434 annotated differentially expressed genes. Gene set enrichment analysis demonstrated that the expression of genes related to proliferation, ion homeostasis and morphology differed between the two mouse genotypes. Importantly, with 1767 pathways the cluster-group "inflammation" contained the majority of AHR-dependently regulated pathways. The most abundant cluster of differentially expressed genes was "inflammation." DETC of AHR-deficient mice were inflammatory active and had altered calcium and F-actin levels. Extending the study to the AHRR, an enigmatic modulator of AHR-activity, we found approximately 50% less DETC in AHRR-deficient mice than in wild-type-littermates. Conclusion AHR-signaling in DETC dampens their inflammatory default potential and supports their homeostasis in the skin.

Mitochondrial bioenergetic changes during development as an indicator of C. elegans health-span.

Mild suppression of mitochondrial activity has beneficial effects across species. The nematode Caenorhabditis elegans is a versatile, genetically tractable model organism widely employed for aging studies, which has led to the identification of many of the known evolutionarily conserved mechanisms regulating lifespan. In C. elegans the pro-longevity effect of reducing mitochondrial function, for example by RNA interference, is only achieved if mitochondrial stress is applied during larval development. Surprisingly, a careful analysis of changes in mitochondrial functions resulting from such treatments during the developmental windows in which pro-longevity signals are programmed has never been carried out. Thus, although the powerful C. elegans genetics have led to the identification of different molecular mechanisms causally involved in mitochondrial stress control of longevity, specific functional mitochondrial biomarkers indicative or predictive of lifespan remain to be identified. To fill this gap, we systematically characterized multiple mitochondrial functional parameters at an early developmental stage in animals that are long-lived due to mild knockdown of twelve different mitochondrial proteins and correlated these parameters with animals' lifespan. We found that basal oxygen consumption rate and ATP-linked respiration positively correlate with lifespan extension and propose the testable hypothesis that the Bioenergetic Health Index can be used as a proxy to predict health-span outcomes.

The flavonoid 4,4'-dimethoxychalcone promotes autophagy-dependent longevity across species.

Ageing constitutes the most important risk factor for all major chronic ailments, including malignant, cardiovascular and neurodegenerative diseases. However, behavioural and pharmacological interventions with feasible potential to promote health upon ageing remain rare. Here we report the identification of the flavonoid 4,4'-dimethoxychalcone (DMC) as a natural compound with anti-ageing properties. External DMC administration extends the lifespan of yeast, worms and flies, decelerates senescence of human cell cultures, and protects mice from prolonged myocardial ischaemia. Concomitantly, DMC induces autophagy, which is essential for its cytoprotective effects from yeast to mice. This pro-autophagic response induces a conserved systemic change in metabolism, operates independently of TORC1 signalling and depends on specific GATA transcription factors. Notably, we identify DMC in the plant Angelica keiskei koidzumi, to which longevity- and health-promoting effects are ascribed in Asian traditional medicine. In summary, we have identified and mechanistically characterised the conserved longevity-promoting effects of a natural anti-ageing drug.

BRCA1 and BARD1 mediate apoptotic resistance but not longevity upon mitochondrial stress in Caenorhabditis elegans.

Interventions that promote healthy aging are typically associated with increased stress resistance. Paradoxically, reducing the activity of core biological processes such as mitochondrial or insulin metabolism promotes the expression of adaptive responses, which in turn increase animal longevity and resistance to stress. In this study, we investigated the relation between the extended Caenorhabditis elegans lifespan elicited by reduction in mitochondrial functionality and resistance to genotoxic stress. We find that reducing mitochondrial activity during development confers germline resistance to DNA damage-induced cell cycle arrest and apoptosis in a cell-non-autonomous manner. We identified the C. elegans homologs of the BRCA1/BARD1 tumor suppressor genes, brc-1/brd-1, as mediators of the anti-apoptotic effect but dispensable for lifespan extension upon mitochondrial stress. Unexpectedly, while reduced mitochondrial activity only in the soma was not sufficient to promote longevity, its reduction only in the germline or in germline-less strains still prolonged lifespan. Thus, in animals with partial reduction in mitochondrial functionality, the mechanisms activated during development to safeguard the germline against genotoxic stress are uncoupled from those required for somatic robustness and animal longevity.

HDAC inhibition improves autophagic and lysosomal function to prevent loss of subcutaneous fat in a mouse model of Cockayne syndrome.

Cockayne syndrome (CS), a hereditary form of premature aging predominantly caused by mutations in the csb gene, affects multiple organs including skin where it manifests with hypersensitivity toward ultraviolet (UV) radiation and loss of subcutaneous fat. There is no curative treatment for CS, and its pathogenesis is only partially understood. Originally considered for its role in DNA repair, Cockayne syndrome group B (CSB) protein most likely serves additional functions. Using CSB-deficient human fibroblasts, Caenorhabditiselegans, and mice, we show that CSB promotes acetylation of α-tubulin and thereby regulates autophagy. At the organ level, chronic exposure of csbm/m mice to UVA radiation caused a severe skin phenotype with loss of subcutaneous fat, inflammation, and fibrosis. These changes in skin tissue were associated with an accumulation of autophagic/lysosomal proteins and reduced amounts of acetylated α-tubulin. At the cellular level, we found that CSB directly interacts with the histone deacetylase 6 (HDAC6) and the α-tubulin acetyltransferase MEC-17. Upon UVA irradiation, CSB is recruited to the centrosome where it colocalizes with dynein and HDAC6. Administration of the pan-HDAC inhibitor SAHA (suberoylanilide hydroxamic acid) enhanced α-tubulin acetylation, improved autophagic function in CSB-deficient models from all three species, and rescued the skin phenotype in csbm/m mice. HDAC inhibition may thus represent a therapeutic option for CS.

Constitutive MAP-kinase activation suppresses germline apoptosis in NTH-1 DNA glycosylase deficient C. elegans.

Oxidation of DNA bases, an inevitable consequence of oxidative stress, requires the base excision repair (BER) pathway for repair. Caenorhabditis elegans is a well-established model to study phenotypic consequences and cellular responses to oxidative stress. To better understand how BER affects phenotypes associated with oxidative stress, we characterised the C. elegans nth-1 mutant, which lack the only DNA glycosylase dedicated to repair of oxidative DNA base damage, the NTH-1 DNA glycosylase. We show that nth-1 mutants have mitochondrial dysfunction characterised by lower mitochondrial DNA copy number, reduced mitochondrial membrane potential, and increased steady-state levels of reactive oxygen species. Consistently, nth-1 mutants express markers of chronic oxidative stress with high basal phosphorylation of MAP-kinases (MAPK) but further activation of MAPK in response to the superoxide generator paraquat is attenuated. Surprisingly, nth-1 mutants also failed to induce apoptosis in response to paraquat. The ability to induce apoptosis in response to paraquat was regained when basal MAPK activation was restored to wild type levels. In conclusion, the failure of nth-1 mutants to induce apoptosis in response to paraquat is not a direct effect of the DNA repair deficiency but an indirect consequence of the compensatory cellular stress response that includes MAPK activation.

Crosstalk of clock gene expression and autophagy in aging.

Autophagy and the circadian clock counteract tissue degeneration and support longevity in many organisms. Accumulating evidence indicates that aging compromises both the circadian clock and autophagy but the mechanisms involved are unknown. Here we show that the expression levels of transcriptional repressor components of the circadian oscillator, most prominently the human Period homologue PER2, are strongly reduced in primary dermal fibroblasts from aged humans, while raising the expression of PER2 in the same cells partially restores diminished autophagy levels. The link between clock gene expression and autophagy is corroborated by the finding that the circadian clock drives cell-autonomous, rhythmic autophagy levels in immortalized murine fibroblasts, and that siRNA-mediated downregulation of PER2 decreases autophagy levels while leaving core clock oscillations intact. Moreover, the Period homologue lin-42 regulates autophagy and life span in the nematode Caenorhabditis elegans, suggesting an evolutionarily conserved role for Period proteins in autophagy control and aging. Taken together, this study identifies circadian clock proteins as set-point regulators of autophagy and puts forward a model, in which age-related changes of clock gene expression promote declining autophagy levels.

Iron-Starvation-Induced Mitophagy Mediates Lifespan Extension upon Mitochondrial Stress in C. elegans.

Frataxin is a nuclear-encoded mitochondrial protein involved in the biogenesis of Fe-S-cluster-containing proteins and consequently in the functionality of the mitochondrial respiratory chain. Similar to other proteins that regulate mitochondrial respiration, severe frataxin deficiency leads to pathology in humans--Friedreich's ataxia, a life-threatening neurodegenerative disorder--and to developmental arrest in the nematode C. elegans. Interestingly, partial frataxin depletion extends C. elegans lifespan, and a similar anti-aging effect is prompted by reduced expression of other mitochondrial regulatory proteins from yeast to mammals. The beneficial adaptive responses to mild mitochondrial stress are still largely unknown and, if characterized, may suggest novel potential targets for the treatment of human mitochondria-associated, age-related disorders. Here we identify mitochondrial autophagy as an evolutionarily conserved response to frataxin silencing, and show for the first time that, similar to mammals, mitophagy is activated in C. elegans in response to mitochondrial stress in a pdr-1/Parkin-, pink-1/Pink-, and dct-1/Bnip3-dependent manner. The induction of mitophagy is part of a hypoxia-like, iron starvation response triggered upon frataxin depletion and causally involved in animal lifespan extension. We also identify non-overlapping hif-1 upstream (HIF-1-prolyl-hydroxylase) and downstream (globins) regulatory genes mediating lifespan extension upon frataxin and iron depletion. Our findings indicate that mitophagy induction is part of an adaptive iron starvation response induced as a protective mechanism against mitochondrial stress, thus suggesting novel potential therapeutic strategies for the treatment of mitochondrial-associated, age-related disorders.

Mitochondrial stress extends lifespan in C. elegans through neuronal hormesis.

Progressive neuronal deterioration accompanied by sensory functions decline is typically observed during aging. On the other hand, structural or functional alterations of specific sensory neurons extend lifespan in the nematode Caenorhabditis elegans. Hormesis is a phenomenon by which the body benefits from moderate stress of various kinds which at high doses are harmful. Several studies indicate that different stressors can hormetically extend lifespan in C. elegans and suggest that hormetic effects could be exploited as a strategy to slow down aging and the development of age-associated (neuronal) diseases in humans. Mitochondria play a central role in the aging process and hormetic-like bimodal dose-response effects on C. elegans lifespan have been observed following different levels of mitochondrial stress. Here we tested the hypothesis that mitochondrial stress may hormetically extend C. elegans lifespan through subtle neuronal alterations. In support of our hypothesis we find that life-lengthening dose of mitochondrial stress reduces the functionality of a subset of ciliated sensory neurons in young animals. Notably, the same pro-longevity mitochondrial treatments rescue the sensory deficits in old animals. We also show that mitochondrial stress extends C. elegans lifespan acting in part through genes required for the functionality of those neurons. To our knowledge this is the first study describing a direct causal connection between sensory neuron dysfunction and extended longevity following mitochondrial stress. Our work supports the potential anti-aging effect of neuronal hormesis and open interesting possibility for the development of therapeutic strategy for age-associated neurodegenerative disorders.