The multi‐domain structure of Bcl‐2‐associated athanogene 3 (BAG3) facilitates its interaction with many different proteins that participate in regulating a variety of biological pathways. After revisiting the BAG3 literature published over the past ten years with Citespace software, we classified the BAG3 research into several clusters, including cancer, cardiomyopathy, neurodegeneration, and viral propagation. We then highlighted recent key findings in each cluster. To gain greater insight into the roles of BAG3, we analyzed five different published mass spectrometry data sets of proteins that co‐immunoprecipitate with BAG3. These data gave us insight into universal, as well as cell‐type‐specific BAG3 interactors in cancer cells, cardiomyocytes, and neurons. Finally, we mapped variable BAG3 SNPs and also mutation data from previous publications to further explore the link between the domains and function of BAG3. We believe this review will provide a better understanding of BAG3 and direct future studies towards understanding BAG3 function in physiological and pathological conditions.

The decline in proteostasis during aging is a major contributing factor to increased susceptibility to neurodegenerative diseases such as Alzheimer’s disease. Although dysfunction of the autophagy pathway is likely one of the contributors, emerging studies implicate that impairment of the endosome-lysosome pathway is also a significant factor in the pathogenesis of these diseases. Our lab was the first to demonstrate that BAG3 facilitates phosphorylated tau clearance through autophagy. However, we did not fully define the mechanisms by which BAG3 regulates endogenous tau proteostasis. Here, we applied mass spectrometric analyses and found a major group of neuronal BAG3 interactors are in the endocytic pathway. Among them were key regulators of small GTPases. Excitingly one of these was the Rab35 GTPase activating protein, TBC1D10B. Our data demonstrate that a BAG3-HSP70-TBC1D10B complex attenuates the ability of TBC1D10B to inactivate Rab35. Thus BAG3, through its interaction with TBC1D10B supports the activation of Rab35 and recruitment of Hrs, which initiates ESCRT-mediated endosomal tau clearance. Further, intrahippocampal expression of BAG3 in P301S mice increased the co-localization of phospho-tau with the ESCRT III protein CHMP2B and reduced the levels of the mutant human tau. Overall, our data provide evidence of a novel BAG3-TBC1D10B-Rab35 regulatory axis in modulating vacuolar dependent protein degradation machinery through ESCRT. These findings expand our understanding of the role of BAG3 in neuronal proteostasis, and how dysregulation could contribute to the pathogenesis of Alzheimer’s disease, as well as other neurodegenerative diseases.

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