This application synergizes expertise from two groups, with one specialized in mitochondrial biology and
proteostatic signaling and the other in V-ATPase biochemistry and vacuolar/lysosomal biology. Mitochondria
are multifunctional organelles. In addition to their major role in ATP production, mitochondria are also involved
in other cellular processes including stress signaling and cell death. However, under many pathophysiological
conditions and during aging, to what extent impairment to non-bioenergetic mitochondrial functions contributes
to the decline of cell fitness is poorly understood. We found that various mitochondrial stressors can directly
induce proteostatic stress in the cytosol independent of energy metabolism, by a mechanism named
mitochondrial Precursor Overaccumulation Stress (mPOS). The mechanisms by which mPOS affects cellular
function and viability remain unknown so far. The lysosome (or vacuole in yeast) also carries out many cellular
functions in the cell, including pH control, ion and amino acid homeostasis, protein degradation, autophagy and
vesicular trafficking. Interestingly, defects in mitochondrial and lysosomal functions can both contribute to cell
aging and aging-associated degenerative disorders, including Parkinson’s disease and amyotrophic lateral
sclerosis. This odd coincidence invites the question of whether damage to mitochondria and lysosomes can
synergize, either sequentially or additively, to affect a common cellular process critical for the fitness and
survival of aged cells. To address this question, it is important to comprehensively describe how mitochondria
and lysosomes interact at the molecular level to affect cellular functions. In this application, we focus on a
novel mitochondria-to-lysosome stress signaling pathway, in which mitochondrial defects cause proteostatic
stress to the vacuole/lysosome thereby affecting cell survival. The scientific premise of this application is based
on our strong preliminary data from studies in yeast, cultured human cells and transgenic mice. More
specifically, the Aim 1 of the proposal will test the hypothesis that specific mitochondrial stress can cause
severe proteostatic damage to the yeast vacuole. The genetic amenability of the yeast system will enable us to
discover genes that suppress the mitochondria-to-vacuole stress signaling and possibly, extend cell’s lifespan.
In Aim 2, we will validate this novel mitochondria-to-lysosome stress signaling pathway in cultured mammalian
cells. In Aim 3, we will test the hypothesis that mitochondrial stress causes lysosomal damage and affects
tissue homeostasis in vivo, using a unique mouse model that we recently developed. We will determine the
mechanism of the mitochondria-induced lysosomal damage in post-mitotic tissues. Success of our experiments
may unravel a novel mechanism of cell demise that involves mitochondria-to-lysosome stress signaling. The
results may ultimately help the better understanding of many aging-associated diseases that are co-manifested
by mitochondrial and lysosomal defects.