Date of Award

7-20-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Applied Science

First Advisor

Fusheng Tang

Abstract

Yeast vacuoles (mammalian lysosomes) and their closely related organelle late endosomes (LE) play a central role in anti-aging processes since they host the target of rapamycin complex 1 (TORC1). A recent study showed that the vacuolar TORC1 stimulates protein synthesis and cell growth while the late endosomal TORC1 inhibits autophagy, an anti-aging process. This raises a question as to which membrane trafficking pathways toward LE/vacuoles are critical in controlling endosomal TORC1 and anti-aging processes. Members of the family of oxysterol-binding proteins mediate non-vesicular lipid transport between membranes and contribute to longevity in different manners. We previously found that a 2-fold up-regulation of Osh6, one of seven yeast oxysterol-binding proteins, remedies vacuolar morphology defects in mid-aged cells, partly down-regulates the target of rapamycin complex 1 (TORC1), and increases the replicative lifespan. At the molecular level, Osh6 transports phosphatidylserine (PS) and phosphatidylinositol-4- phosphate (PI4P) between the endoplasmic reticulum (ER) and the plasma membrane (PM). To decipher how an ER-PM working protein controls vacuolar morphology, we tested genetic interactions between OSH6 and DRS2, whose protein flips PS from the lumen to the cytosolic side of the Golgi, the organelle between ER and vacuoles in many pathways. Up-regulated OSH6 complemented vacuolar morphology of drs2∆ and enriched PI4P on the Golgi, indicating that Osh6 also works on the Golgi. This altered PI4P-enrichment led to a delay in the secretion of the proton ATPase Pma1 to the PM and a rerouting of Pma1 to vacuoles in a manner dependent on the trans-Golgi network (TGN) to late endosome (LE) trafficking pathway. Since the TGN-LE pathway controls endosomal and vacuolar TORC1, it may be the anti-aging pathway boosted by up-regulated Osh6. The sequestration of PI4P may decrease the availability of PI for the PI3 kinase Vps34, which stimulates TORC1. The contribution of PI4P on the early cisternae of TGN to TGN-LE trafficking and PI3P metabolism are both new to the field of longevity studies and deserve further explorations since Osh proteins and TORC1 regulations are conserved among all eukaryotic organisms, this approach can be used to study different age related disease such as neurodegenerative disease, Alzheimer, and cardiovascular disease.

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