Benedetto, A. | bioRxiv Science

bioRxiv2017

Autophagy-dependent gut-to-yolk biomass conversion generates visceral polymorbidity in aging C. elegans

Aging (senescence) is characterized by the development of numerous pathologies, some of which limit lifespan. Key to understanding aging is discovery of the mechanisms (etiologies) that cause senescent pathology. In Caenorhabditis elegans a major senescent pathology of unknown etiology is atrophy of its principal metabolic organ, the intestine. Here we identify a cause of not only this pathology, but also of yolky lipid accumulation and redistribution (a form of senescent obesity): autophagy-mediated conversion of intestinal biomass into yolk. Inhibiting intestinal autophagy or vitellogenesis rescues both visceral pathologies, and can also extend lifespan. This defines a disease syndrome leading to polymorbidity and contributing to late-life mortality. Activation of gut-to-yolk biomass conversion by insulin/IGF-1 signaling (IIS) promotes reproduction and senescence. This illustrates how major, IIS-promoted senescent pathologies in C. elegans can originate not from damage accumulation, but from continued action of a wild-type function (vitellogenesis), consistent with the recently proposed hyperfunction theory of aging.

physiology↗

bioRxiv2017

Monsters in the uterus: A parthenogenetic quasi-program causes teratoma-like tumors during aging in wild-type C. elegans

Many diseases whose frequency increases with advancing age are caused by aging (senescence), but the mechanisms of senescence remain poorly understood. According to G.C. Williams and M.V. Blagosklonny, a major etiological determinant of senescence is late-life, wild-type gene action and non-adaptive execution of biological programs (or quasi-programs). These generate a wide range of senescent pathologies causing illness and death. Here we investigate the etiology of a prominent senescent pathology in the nematode C. elegans, uterine tumors, in the light of the Williams Blagosklonny theory. Uterine tumors develop from unfertilized, immature oocytes which execute incomplete embryogenetic programs. This includes extensive endomitosis, leading to formation of chromatin masses and cellular hypertrophy. The starting point of pathogenesis is exhaustion of sperm stocks. The timing of this transition between program and quasi-program can be altered by blocking sperm production (causing earlier tumors) or supplying additional sperm by mating (delaying tumor onset). Other pathophysiological determinants are yolk consumption by tumors, and bacterial proliferation within tumors. Uterine tumors resemble mammalian ovarian teratomas (tera, Greek: monster) in that both develop from oocytes that fail to mature after meiosis I, and both are the result of quasi-programs. Moreover, older but not younger uterine tumors show expression of markers of later embryogenesis, i.e. are teratoma-like. These results show how uterine tumors in C. elegans form as the result of run-on of embryogenetic quasi-programs. They also suggest fundamental etiological equivalence between teratoma and some forms of senescent pathology, insofar as both are caused by quasi-programs.

developmental biology↗