Aging
It is evident that a scratch along the skin heals faster in young people and that the healing capacity and the normal cell turnover gradually decline with age. The skin is a noticeable example; however, regeneration of all regenerative tissues is slow and aberrant in the aged organism due to deteriorated function of stem cells. A major research question in our lab is why stem cell functionality declines with age is.
Aging related testis degeneration. Immunofluorescent images (in the same magnitude) of testes dissected from 1-day young, 15-days, 30-days aged old male (left-right). Asterisk (left image) marks the stem cell niche (Fas3, blue) at the apical tip of the testis, Imp-GFP (green) trap line marks mature sperms and Vasa (red) marks germ cells. Scale bar 250μm. Epstein et al., Nat Commun, 2017.
The Drosophila testis is an excellent model system to study aging-related changes in stem cell function in the whole organism mainly because aging dramatically compromises regeneration, resulting in morphological changes (significantly smaller testis with reduced stem cells and differentiated progeny), and in physiological changes that eventually arrest sperm production.
The decline in tissue regeneration with age suggests an attractive possibility whereby restoration of stem cell function in an aged tissue could rejuvenate tissue homeostasis and repair deteriorated function. However, stem cell function and maintenance relies on other cell populations that may be directly affected by aging. In particular, aging may impede niche function and differentiated progeny production in addition to intrinsic stem-cell factors. Therefore, understanding the mechanism that results in a dysfunctional, aged tissue requires a combined analysis of these distinct cell populations and the interactions among them in the context of the whole organism.