Lamin regulates the dietary restriction response via the mTOR pathway in Caenorhabditis elegans

Chromatin: the old and young of it

Aging affects nearly all aspects of our cells, from our DNA to our proteins to how our cells handle stress and communicate with each other. Age-related chromatin changes are of particular interest because chromatin can dynamically respond to the cellular and organismal environment, and many modifications at chromatin are reversible. Changes at chromatin occur during aging, and evidence from model organisms suggests that chromatin factors could play a role in modulating the aging process itself, as altering proteins that work at chromatin often affect the lifespan of yeast, worms, flies, and mice. The field of chromatin and aging is rapidly expanding, and high-resolution genomics tools make it possible to survey the chromatin environment or track chromatin factors implicated in longevity with precision that was not previously possible. In this review, we discuss the state of chromatin and aging research. We include examples from yeast, Drosophila, mice, and humans, but we particularly focus on the commonly used aging model, the worm Caenorhabditis elegans, in which there are many examples of chromatin factors that modulate longevity. We include evidence of both age-related changes to chromatin and evidence of specific chromatin factors linked to longevity in core histones, nuclear architecture, chromatin remodeling, and histone modifications.

Somatic nuclear blebbing in Caenorhabditis elegans is not a feature of organismal aging but a potential indicator of germline proliferation in early adulthood

Abnormal nuclear morphology is suggested to be a hallmark of aging and one such abnormality is nuclear blebbing. However, little is known about whether and how nuclear blebbing participates in animal aging, and what regulates it. In this study, we show that the frequency of nuclear blebbing in the hypodermis increases during aging in wild-type C. elegans. These nuclear blebs are enveloped by the nuclear lamina, the inner and the outer nuclear membrane, and 42% of them contain chromatin. Although nuclear blebbing could lead to DNA loss if chromatin-containing blebs detach and fuse with lysosomes, we find by time-lapse imaging that nuclear blebs rarely detach, and the estimated lifetime of a nuclear bleb is 772 h or 32 days. The amount of DNA lost through nuclear blebbing is estimated to be about 0.1% of the total DNA loss by adult Day 11. Furthermore, the frequency of nuclear blebbing does not correlate with the rate of aging in C. elegans. Old age does not necessarily induce nuclear blebbing, neither does starvation, heat stress, or oxidative stress. Intriguingly, we find that proliferation of germ cells promotes nuclear blebbing.

Age-dependent nuclear lipid droplet deposition is a cellular hallmark of aging in Caenorhabditis elegans

Aging is the major risk factor for several life-threatening pathologies and impairs the function of multiple cellular compartments and organelles. Age-dependent deterioration of nuclear morphology is a common feature in evolutionarily divergent organisms. Lipid droplets have been shown to localize in most nuclear compartments, where they impinge on genome architecture and integrity. However, the significance of progressive nuclear lipid accumulation and its impact on organismal homeostasis remain obscure. Here, we implement non-linear imaging modalities to monitor and quantify age-dependent nuclear lipid deposition in Caenorhabditis elegans. We find that lipid droplets increasingly accumulate in the nuclear envelope, during aging. Longevity-promoting interventions, such as low insulin signaling and caloric restriction, abolish the rate of nuclear lipid accrual and decrease the size of lipid droplets. Suppression of lipotoxic lipid accumulation in hypodermal and intestinal nuclei is dependent on the transcription factor HLH-30/TFEB and the triglyceride lipase ATGL-1. HLH-30 regulates the expression of ATGL-1 to reduce nuclear lipid droplet abundance in response to lifespan-extending conditions. Notably, ATGL-1 localizes to the nuclear envelope and moderates lipid content in long-lived mutant nematodes during aging. Our findings indicate that the reduced ATGL-1 activity leads to excessive nuclear lipid accumulation, perturbing nuclear homeostasis and undermining organismal physiology, during aging.