Date of Award

2023

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Physiology

Abstract

Bcl2-associated athanogene-3 (BAG3) is a pro-autophagy co-chaperone that we havepreviously shown localizes to the cardiac sarcomere and is critical for proteostasis and maintenance of normal sarcomeric function. Indeed, BAG3 loss in heart failure (HF) results in accumulation of ubiquitinated sarcomeric proteins, and depressed maximum force generating capacity (Fmax). However, how BAG3 is regulated in the cell is not well understood, with uncertainty about its structure and proteoforms. During our analysis of human heart tissue, BAG3 appears as a “doublet”, with one band at 74 kDa (BAG3-Z) and a second at a higher 85 kDa (BAG3-FL). Previous studies hypothesized the full-length BAG3 protein is 74 kDa, and the 85 kDa proteoform was due to phosphorylation. Our results confirmed that BAG3-FL is the full-length protein with a molecular weight of 85 kDa. It also revealed that BAG3-Z is a cleavage product of BAG3-FL at the N- and C- termini, which has not been reported before. We have shown that BAG3-Z formation is stress induced and caspase dependent, likely by caspases 1, 8, and 9. The N-terminus cleavage includes ~1/3 of the WW domain, suggesting a possible loss-of-function especially regarding autophagosome formation and regulation of the lysosomal degradation pathway. Furthermore, BAG3-Z preferentially localized to the myofilament compared to the cytoplasm, where it could be competing and inhibiting the activities of BAG3-FL. Identification of the specific cleavage sites in BAG3-FL, BAG3-Z's interactome, and its effects on the cardiomyocyte protein quality control and stress response is necessary for the development of BAG3-based therapeutics for HF.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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