Distinct mechanisms of non-autonomous UPR ER mediated by GABAergic, glutamatergic, and octopaminergic neurons.

The capacity to deal with stress declines during the aging process, and preservation of cellular stress responses is critical to healthy aging. The unfolded protein response of the endoplasmic reticulum (UPR ER ) is one such conserved mechanism, which is critical for the maintenance of several major functions of the ER during stress, including protein folding and lipid metabolism. Hyperactivation of the UPR ER by overexpression of the major transcription factor, xbp-1s , solely in neurons drives lifespan extension as neurons send a neurotransmitter-based signal to other tissue to activate UPR ER in a non-autonomous fashion. Previous work identified serotonergic and dopaminergic neurons in this signaling paradigm. To further expand our understanding of the neural circuitry that underlies the non-autonomous signaling of ER stress, we activated UPR ER solely in glutamatergic, octopaminergic, and GABAergic neurons in C. elegans and paired whole-body transcriptomic analysis with functional assays. We found that UPR ER -induced signals from glutamatergic neurons increased expression of canonical protein homeostasis pathways and octopaminergic neurons promoted pathogen response pathways, while minor, but statistically significant changes were observed in lipid metabolism-related genes with GABAergic UPR ER activation. These findings provide further evidence for the distinct role neuronal subtypes play in driving the diverse response to ER stress.

A metabolic atlas of mouse aging.

Humans are living longer, but this is accompanied by an increased incidence of age-related chronic diseases. Many of these diseases are influenced by age-associated metabolic dysregulation, but how metabolism changes in multiple organs during aging in males and females is not known. Answering this could reveal new mechanisms of aging and age-targeted therapeutics. In this study, we describe how metabolism changes in 12 organs in male and female mice at 5 different ages. Organs show distinct patterns of metabolic aging that are affected by sex differently. Hydroxyproline shows the most consistent change across the dataset, decreasing with age in 11 out of 12 organs investigated. We also developed a metabolic aging clock that predicts biological age and identified alpha-ketoglutarate, previously shown to extend lifespan in mice, as a key predictor of age. Our results reveal fundamental insights into the aging process and identify new therapeutic targets to maintain organ health.

Mechanical stress through growth on stiffer substrates impacts animal health and longevity in C. elegans.

Mechanical stress is a measure of internal resistance exhibited by a body or material when external forces, such as compression, tension, bending, etc. are applied. The study of mechanical stress on health and aging is a continuously growing field, as major changes to the extracellular matrix and cell-to-cell adhesions can result in dramatic changes to tissue stiffness during aging and diseased conditions. For example, during normal aging, many tissues including the ovaries, skin, blood vessels, and heart exhibit increased stiffness, which can result in a significant reduction in function of that organ. As such, numerous model systems have recently emerged to study the impact of mechanical and physical stress on cell and tissue health, including cell-culture conditions with matrigels and other surfaces that alter substrate stiffness and ex vivo tissue models that can apply stress directly to organs like muscle or tendons. Here, we sought to develop a novel method in an in vivo, model organism setting to study the impact of mechanical stress on aging, by increasing substrate stiffness in solid agar medium of C. elegans. To our surprise, we found shockingly limited impact of growth of C. elegans on stiffer substrates, including limited effects on cellular health, gene expression, organismal health, stress resilience, and longevity. Overall, our studies reveal that altering substrate stiffness of growth medium for C. elegans have only mild impact on animal health and longevity; however, these impacts were not nominal and open up important considerations for C. elegans biologists in standardizing agar medium choice for experimental assays.

Surveying Low-Cost Methods to Measure Lifespan and Healthspan in Caenorhabditis elegans.

The discovery and development of Caenorhabditis elegans as a model organism was influential in biology, particularly in the field of aging. Many historical and contemporary studies have identified thousands of lifespan-altering paradigms, including genetic mutations, transgenic gene expression, and hormesis, a beneficial, low-grade exposure to stress. With its many advantages, including a short lifespan, easy and low-cost maintenance, and fully sequenced genome with homology to almost two-thirds of all human genes, C. elegans has quickly been adopted as an outstanding model for stress and aging biology. Here, several standardized methods are surveyed for measuring lifespan and healthspan that can be easily adapted into almost any research environment, especially those with limited equipment and funds. The incredible utility of C. elegans is featured, highlighting the capacity to perform powerful genetic analyses in aging biology without the necessity of extensive infrastructure. Finally, the limitations of each analysis and alternative approaches are discussed for consideration.

ß-Cell-specific ablation of sirtuin 4 does not affect nutrient-stimulated insulin secretion in mice.

Sirtuins are a family of proteins that regulate biological processes such as cellular stress and aging by removing posttranslational modifications (PTMs). We recently identified several novel PTMs that can be removed by sirtuin 4 (SIRT4), which is found in mitochondria. We showed that mice with a global loss of SIRT4 [SIRT4-knockout (KO) mice] developed an increase in glucose- and leucine-stimulated insulin secretion, and this was followed by accelerated age-induced glucose intolerance and insulin resistance. Because whole body SIRT4-KO mice had alterations to nutrient-stimulated insulin secretion, we hypothesized that SIRT4 plays a direct role in regulating pancreatic ß-cell function. Thus, we tested whether ß-cell-specific ablation of SIRT4 would recapitulate the elevated insulin secretion seen in mice with a global loss of SIRT4. Tamoxifen-inducible ß-cell-specific SIRT4-KO mice were generated, and their glucose tolerance and glucose- and leucine-stimulated insulin secretion were measured over time. These mice exhibited normal glucose- and leucine-stimulated insulin secretion and maintained normal glucose tolerance even as they aged. Furthermore, 832/13 ß-cells with a CRISPR/Cas9n-mediated loss of SIRT4 did not show any alterations in nutrient-stimulated insulin secretion. Despite the fact that whole body SIRT4-KO mice demonstrated an age-induced increase in glucose- and leucine-stimulated insulin secretion, our current data indicate that the loss of SIRT4 specifically in pancreatic ß-cells, both in vivo and in vitro, does not have a significant impact on nutrient-stimulated insulin secretion. These data suggest that SIRT4 controls nutrient-stimulated insulin secretion during aging by acting on tissues external to the ß-cell, which warrants further study.