Explore the vast range of titles available.

Cellular systems governing protein folding depend on functional redundancy and diversification to maintain proteostasis. Here, using Caenorhabditis elegans , we show two homologous ER-resident HSP70 chaperones, HSP-3 and HSP-4, have overlapping and distinct roles in ER proteostasis and organismal physiology. Their expression and function vary by tissue, age, and stress, impacting ER stress resistance, reproduction, body size, and lifespan. We also find HSP-3 and HSP-4 uniquely regulate dietary restriction and reduced insulin signaling-mediated longevity in C. elegans . Notably, knockdown of hsp-4 , but not hsp-3 , induces autophagy and enhances tolerance to protein aggregation stress; this process requires the ortholog of ER-Phagy receptor Sec-62 (C18E9.2) and IRE-1. Finally, human cell data suggests that the dissociation of chaperone Binding Immunoglobulin Protein (BiP) from IRE-1 during times of ER stress promotes autophagy by enhancing the interaction of IRE-1 and Sec-62. These findings reveal how ER chaperone diversification maximizes stress resilience and suggest a BiP-dependent regulation of autophagy. Cells rely on diversification and redundancy of protein chaperones to maintain proteostasis. Here, the authors show that two C. elegans orthologs of a chaperone have distinct roles in stress resistance, aging, and autophagy through an ER-phagy receptor-dependent pathway.

The mitochondrial unfolded protein response (UPR mt ) has emerged as a predominant mechanism that preserves mitochondrial function. Consequently, multiple pathways likely exist to modulate UPR mt . We discovered that the tRNA processing enzyme, homolog of ELAC2 (HOE-1), is key to UPR mt regulation in Caenorhabditis elegans . We find that nuclear HOE-1 is necessary and sufficient to robustly activate UPR mt . We show that HOE-1 acts via transcription factors ATFS-1 and DVE-1 that are crucial for UPR mt . Mechanistically, we show that HOE-1 likely mediates its effects via tRNAs, as blocking tRNA export prevents HOE-1-induced UPR mt . Interestingly, we find that HOE-1 does not act via the integrated stress response, which can be activated by uncharged tRNAs, pointing toward its reliance on a new mechanism. Finally, we show that the subcellular localization of HOE-1 is responsive to mitochondrial stress and is subject to negative regulation via ATFS-1. Together, we have discovered a novel RNA-based cellular pathway that modulates UPR mt .

Metabolic homeostasis requires engagement of catabolic and anabolic pathways consuming nutrients that generate and consume energy and biomass. Our current understanding of cell homeostasis and metabolism, including how cells utilize nutrients, comes largely from tissue and cell models analyzed after fractionation, and that fail to reveal the spatial characteristics of cell metabolism, and how these aspects relate to the location of cells and organelles within tissue microenvironments. Here we show the application of multi-scale microscopy, machine learning-based image segmentation, and spatial analysis tools to quantitatively map the fate of nutrient-derived 13 C atoms across spatiotemporal scales. This approach reveals the cellular and organellar features underlying the spatial pattern of glucose 13 C flux in hepatocytes in situ, including the timeline of mitochondria-ER contact dynamics in response to changes in blood glucose levels, and the discovery of the ultrastructural relationship between glycogenesis and lipid droplets. Most metabolic studies using traditional procedures fail to reveal the spatial patterning associated with metabolic flux and cellular metabolism within tissue microenvironments. Here, the authors show the application of multi-scale microscopy, machine learning-based image segmentation and spatial analysis to map the fate of nutrient-derived 13 C across spatiotemporal scales.

Abstract Inter-organelle communication is a critical determinant of cellular metabolic homeostasis, and defects in the interactions between organelles are increasingly correlated with age-dependent diseases. Despite these promising links, exploration of how inter-organelle signaling pathways can be targeted to promote healthy organismal aging is a nascent area of research. We have established a foundation in C. elegans to investigate how the communication between endoplasmic reticulum (ER) and mitochondria, two of the most central metabolic hubs in cells, controls the aging process. Combining electron microscopy, live-imaging and biochemical approaches, we provide evidence that C. elegans forms ER-mitochondrial contacts and that through molecular mechanisms conserved to mammals, ER calcium flux potently stimulates mitochondrial bioenergetics. Furthermore, genetic manipulation of the ER inositol triphosphate receptor (InsP3R) reveals that ER calcium signaling promotes mitochondrial homeostasis at multiple other levels, including mitochondrial gene expression and dynamics. Building on this foundation, we now reveal that ER calcium signaling is essential for longevity in contexts of mitochondrial reprogramming. Surprisingly, InsP3R-stimulated mitochondrial bioenergetics do not appear to be the key mechanism of longevity in these contexts, but rather the underappreciated roles of the ER in tuning mitochondrial gene expression and morphology. Our results thus highlight the InsP3R as a potent and central regulator of diverse mitochondrial properties and reveal that the connections between ER and mitochondria are deeper and more complex than current models suggest. Overall, we reveal that inter-organelle communication between ER and mitochondria is an essential mechanism of longevity in paradigms involving mitochondrial reprogramming.

Exposure of C. elegans to hypertonic stress-induced water loss causes rapid and widespread cellular protein damage. Survival in hypertonic environments depends critically on the ability of worm cells to detect and degrade misfolded and aggregated proteins. Acclimation of C. elegans to mild hypertonic stress suppresses protein damage and increases survival under more extreme hypertonic conditions. Suppression of protein damage in acclimated worms could be due to 1) accumulation of the chemical chaperone glycerol, 2) upregulation of protein degradation activity, and/or 3) increases in molecular chaperoning capacity of the cell. Glycerol and other chemical chaperones are widely thought to protect proteins from hypertonicity-induced damage. However, protein damage is unaffected by gene mutations that inhibit glycerol accumulation or that cause dramatic constitutive elevation of glycerol levels. Pharmacological or RNAi inhibition of proteasome and lyosome function and measurements of cellular protein degradation activity demonstrated that upregulation of protein degradation mechanisms plays no role in acclimation. Thus, changes in molecular chaperone capacity must be responsible for suppressing protein damage in acclimated worms. Transcriptional changes in chaperone expression have not been detected in C. elegans exposed to hypertonic stress. However, acclimation to mild hypertonicity inhibits protein synthesis 50-70%, which is expected to increase chaperone availability for coping with damage to existing proteins. Consistent with this idea, we found that RNAi silencing of essential translational components or acute exposure to cycloheximide results in a 50-80% suppression of hypertonicity-induced aggregation of polyglutamine-YFP (Q35::YFP). Dietary changes that increase protein production also increase Q35::YFP aggregation 70-180%. Our results demonstrate directly for the first time that inhibition of protein translation protects extant proteins from damage brought about by an environmental stressor, demonstrate important differences in aging- versus stress-induced protein damage, and challenge the widely held view that chemical chaperones are accumulated during hypertonic stress to protect protein structure/function.

Under adverse environmental conditions the nematode Caenorhabditis elegans can enter an alternate developmental stage called the dauer larva. To identify lipophilic signaling molecules that influence this process, we screened a library of bioactive lipids and found that AM251, an antagonist of the human cannabinoid (CB) receptor, suppresses dauer entry in daf-2 insulin receptor mutants. AM251 acted synergistically with glucose supplementation indicating that the metabolic status of the animal influenced the activity of this compound. Similarly, loss of function mutations in the energy-sensing AMP-activated kinase subunit, aak-2, enhanced the dauer-suppressing effects of AM251, while constitutive activation of aak-2 in neurons was sufficient to inhibit AM251 activity. Chemical epistasis experiments indicated that AM251 acts via G-protein signaling and requires the TGF-β ligand DAF-7, the insulin peptides DAF-28 and INS-6, and a functional ASI neuron to promote reproductive growth. AM251 also required the presence of the SER-5 serotonin receptor, but in vitro experiments suggest that this may not be via a direct interaction. Interestingly, we found that other antagonists of mammalian CB receptors also suppress dauer entry, while the nonselective CB receptor agonist, O-2545, not only inhibited the activity of AM251, but also was able to promote dauer entry when administered alone. Since worms do not have obvious orthologs of CB receptors, the effects of synthetic CBs on neuroendocrine signaling in C. elegans are likely to be mediated via another, as yet unknown, receptor mechanism. However, we cannot exclude the existence of a noncanonical CB receptor in C. elegans.

Mitochondrial morphology is dynamically regulated through remodeling processes essential for maintaining mitochondrial function and ensuring cellular and metabolic homeostasis. While classical models of mitochondrial dynamics center on cycles of fragmentation and elongation, emerging evidence highlights additional membrane remodeling mechanisms, including the formation of mitochondrial-derived vesicles (MDVs) and mitochondrial-derived compartments (MDCs). These mitochondrial-derived structures, however, have been predominantly characterized in cultured cells and unicellular organisms, leaving their relevance in multicellular systems largely unexplored. Here, we identify a previously uncharacterized class of mitochondrial-derived structures in muscle cells that are induced in response to intermittent fasting. We show that these structures appear specifically during the refeeding phase- coinciding with mitochondrial elongation -and are absent during fasting. Consistent with MDCs, the structures, approximately 1 µm in size, are enriched in outer mitochondrial membrane markers such as TOMM-20 and TOMM-70, but notably lack components of the inner mitochondrial membrane. Their formation requires the microtubule-associated MIRO-1/2 proteins, and their size is modulated by the mitochondrial dynamics machinery. Together, our findings reveal a nutritionally regulated mitochondrial remodeling event in muscle that may play a role in mitochondrial quality control and adaptation to metabolic cues.

The neuronal endoplasmic reticulum (ER) extends from the soma into axons and dendrites to coordinate protein trafficking, lipid metabolism, inter-organelle organization, and calcium homeostasis. Conserved genes involved in shaping the tubular ER are implicated in neurodevelopment and neurodegeneration, suggesting that ER structure and dynamics influence neuronal health and drive pathogenesis. However, the links between ER morphology and neuronal function and resilience remain incompletely understood. While models typically depict the neuronal ER as a fully continuous network, here we show that micron-scale ER discontinuities in neurites are unexpectedly common in young, unstressed . These discontinuities occur in both axonal and dendritic compartments with a consistent frequency that varies between motor and mechanosensory neuron types. Using live imaging and photokinetic assays of endogenously tagged markers of the ER, we confirm that these gaps reflect true loss of ultrastructural continuity. Subpopulations of ER tubule tips are highly motile, and the majority of ER discontinuities are resolved in less than an hour. Suggesting the formation of discontinuities is linked to cellular damage, their frequency increases with both age and environmental stress. Finally, in agreement with prior observations across models, discontinuities are exacerbated by impairment of certain ER shaping factors involved in hereditary spastic paraplegia, such as reticulon. These findings reveal a model where ER discontinuities are not uncommon in healthy animals, and provide a tractable system in to dissect the molecular mechanisms maintaining ER structural homeostasis in vivo.

Certain forms of mitochondrial impairment confer longevity, while mitochondrial dysfunction arising from aging and disease-associated mutations triggers severe pathogenesis. The adaptive pathways that distinguish benefit from pathology remain unclear. Here we reveal that longevity induced by mitochondrial Complex I/ mutation in is dependent on the endoplasmic reticulum (ER) Ca channel, InsP3R. We find that the InsP3R promotes mitochondrial respiration, but the mitochondrial calcium uniporter is dispensable for both respiration and lifespan extension in Complex I mutants, suggesting InsP3R action is independent of matrix Ca flux. Transcriptomic profiling and imaging reveal a previously unrecognized role for the InsP3R in regulating mitochondrial scaling, where InsP3R impairment results in maladaptive hyper-expansion of dysfunctional mitochondrial networks. We reveal a conserved InsP3R signaling axis through which calmodulin and actomyosin remodeling machineries, including Arp2/3, formin FHOD-1, and MLCK, constrain mitochondrial expansion and promote longevity. Disruption of actin remodeling or autophagy mimics InsP3R loss. Conversely, driving fragmentation ameliorates mitochondrial expansion and rescues longevity, supporting a model in which InsP3R-dependent actin remodeling sustains mitochondrial turnover. These findings establish an inter-organelle signaling axis by which ER calcium release orchestrates mitochondrial-based longevity through cytoskeletal effectors.