BAG family molecular chaperone regulator 3

BAG3 (BAG family molecular chaperone regulator 3) is a co-chaperone and adapter protein that coordinates different classes of heat shock proteins, including HSP70s and small heat shock proteins like HSPB8 (UniProt: O95817). It functions as a nucleotide-exchange factor promoting ADP release from HSP70s and subsequent client protein release, and exhibits anti-apoptotic activity through binding to both the nucleotide-binding and substrate-binding domains of HSP70 proteins.

BAG3 is broadly expressed and has roles in protein quality control and cellular stress responses. Beyond its general cellular functions, mutations in BAG3 are associated with several neuromuscular and cardiac disorders including myofibrillar myopathy 6 (MFM6), dilated cardiomyopathy (CMD1HH), distal hereditary motor neuronopathy 15 (HMND15), and Charcot-Marie-Tooth disease type 2JJ (CMT2JJ), reflecting its importance in maintaining muscle and neuronal function (UniProt: O95817).

BAG3 is significantly upregulated in Alzheimer's disease brain tissue compared to age-matched controls, with a mean log2 fold-change of 1.15 in post-mortem AD brain proteomics data (Chaparral AD proteomics). This upregulation suggests BAG3 may play a role in AD-related pathology, potentially reflecting compensatory stress response mechanisms or involvement in protein misfolding processes characteristic of neurodegeneration.