Tubular lysosome induction couples animal starvation to healthy aging.

Dietary restriction promotes longevity in several species via autophagy activation. However, changes to lysosomes underlying this effect remain unclear. Here using the nematode Caenorhabditis elegans, we show that the induction of autophagic tubular lysosomes (TLs), which occurs upon dietary restriction or mechanistic target of rapamycin inhibition, is a critical event linking reduced food intake to lifespan extension. We find that starvation induces TLs not only in affected individuals but also in well-fed descendants, and the presence of gut TLs in well-fed progeny is predictive of enhanced lifespan. Furthermore, we demonstrate that expression of Drosophila small VCP-interacting protein, a TL activator in flies, artificially induces TLs in well-fed worms and improves C. elegans health in old age. These findings identify TLs as a new class of lysosomes that couples starvation to healthy aging.

Rbp4-Gal4, a germline driver that activates in meiosis, reveals functions for VCP in spermatid development.

Valosin-containing protein (VCP) is a versatile and ubiquitously expressed AAA+ ATPase that regulates multiple stages of Drosophila spermatogenesis. While VCP has documented roles in mitotic spermatogonia and meiotic spermatocytes, it is also highly expressed in post-meiotic spermatids, suggesting potential late-stage developmental functions as well. However, tools to assess late-stage activities of pleiotropic spermatogenesis genes such as VCP are lacking. Available germline-specific Gal4 drivers activate in stem cells or spermatogonia; consequently, knocking down VCP using one of these drivers disrupts or blocks early germ-cell development, precluding analysis of VCP in later stages. A Gal4 driver that activates later in development, such as at the meiotic spermatocyte stage, may permit functional analyses of VCP and other factors in post-meiotic stages. Here, we describe a germline-specific Gal4 driver, Rbp4-Gal4, which drives transgene expression beginning in the early spermatocyte stage. We find that Rbp4-Gal4-driven knockdown of VCP causes defects in spermatid chromatin condensation and individualization without affecting earlier developmental stages. Interestingly, the defect in chromatin condensation appears linked to errors in the histone-to-protamine transition, a key event in spermatid development. Overall, our study reveals roles for VCP in spermatid development and establishes a powerful tool to dissect the functions of pleiotropic spermatogenesis genes.

VCP promotes tTAF-target gene expression and spermatocyte differentiation by downregulating mono-ubiquitylated H2A.

Valosin-containing protein (VCP) binds and extracts ubiquitylated cargo to regulate protein homeostasis. VCP has been studied primarily in aging and disease contexts, but it also affects germline development. However, the precise molecular functions of VCP in the germline, particularly in males, are poorly understood. Using the Drosophila male germline as a model system, we find that VCP translocates from the cytosol to the nucleus as germ cells transition into the meiotic spermatocyte stage. Importantly, nuclear translocation of VCP appears to be one crucial event stimulated by testis-specific TBP-associated factors (tTAFs) to drive spermatocyte differentiation. VCP promotes the expression of several tTAF-target genes, and VCP knockdown, like tTAF loss of function, causes cells to arrest in early meiotic stages. At a molecular level, VCP activity supports spermatocyte gene expression by downregulating a repressive histone modification, mono-ubiquitylated H2A (H2Aub), during meiosis. Remarkably, experimentally blocking H2Aub in VCP-RNAi testes is sufficient to overcome the meiotic-arrest phenotype and to promote development through the spermatocyte stage. Collectively, our data highlight VCP as a downstream effector of tTAFs that downregulates H2Aub to facilitate meiotic progression.

A meiotic switch in lysosome activity supports spermatocyte development in young flies but collapses with age.

Gamete development ultimately influences animal fertility. Identifying mechanisms that direct gametogenesis, and how they deteriorate with age, may inform ways to combat infertility. Recently, we found that lysosomes acidify during oocyte maturation in Caenorhabditis elegans, suggesting that a meiotic switch in lysosome activity promotes female germ-cell health. Using Drosophila melanogaster, we report that lysosomes likewise acidify in male germ cells during meiosis. Inhibiting lysosomes in young-male testes causes E-cadherin accumulation and loss of germ-cell partitioning membranes. Notably, analogous changes occur naturally during aging; in older testes, a reduction in lysosome acidity precedes E-cadherin accumulation and membrane dissolution, suggesting one potential cause of age-related spermatocyte abnormalities. Consistent with lysosomes governing the production of mature sperm, germ cells with homozygous-null mutations in lysosome-acidifying machinery fail to survive through meiosis. Thus, lysosome activation is entrained to meiotic progression in developing sperm, as in oocytes, and lysosomal dysfunction may instigate male reproductive aging.

Degradative tubular lysosomes link pexophagy to starvation and early aging in C. elegans.

Organelle-specific autophagy directs degradation of eukaryotic organelles under certain conditions. Like other organelles, peroxisomes are subject to autophagic turnover at lysosomes. However, peroxisome autophagy (pexophagy) has yet to be analyzed in a live-animal system, limiting knowledge on its regulation during an animal's life. Here, we generated a tandem-fluorophore reporter that enabled real-time tracking of pexophagy in live Caenorhabditis elegans. We observed that pexophagy occurred at a population of non-canonical, tubular lysosomes specifically during starvation and aging. Remarkably, in these contexts, tubular lysosomes were the predominant type of lysosome in the intestine, transforming from vesicles. Though we found that peroxisomes were largely eliminated in early adulthood, they appeared restored in new generations. We identified peroxisomal genes that regulated age-dependent peroxisome loss and demonstrated that modifying this process altered animal lifespan. These findings reveal new facets of peroxisome homeostasis relevant to aging and challenge the prevailing perception of lysosome homogeneity in autophagy.Abbreviations: GFP: green fluorescent protein; SKL: serine-lysine-leucine peroxisome signal sequence; spin: spinster; TLs: tubular lysosomes.

Organelle-Specific Autophagy in Cellular Aging and Rejuvenation.

The health of a cell requires proper functioning, regulation, and quality control of its organelles, the membrane-enclosed compartments inside the cell that carry out its essential biochemical tasks. Aging commonly perturbs organelle homeostasis, causing problems to cellular health that can spur the initiation and progression of degenerative diseases and related pathologies. Here, we discuss emerging evidence indicating that age-related defects in organelle homeostasis stem in part from dysfunction of the autophagy-lysosome system, a pivotal player in cellular quality control and damage clearance. We also highlight natural examples from biology where enhanced activity of the autophagy-lysosome system might be harnessed to erase age-related organelle damage, raising potential implications for cellular rejuvenation.