P209L Mutation in BAG3 Does Not Cause Cardiomyopathy in Mice

Bcl2-associated athanogene 3 (BAG3) is a co-chaperone protein and a central player of the cellular protein quality control system. BAG3 is prominently expressed in the heart and plays an essential role in cardiac protein homeostasis by interacting with chaperone heat shock proteins (HSPs) in large, functionally distinct multi-chaperone complexes. The BAG3 mutation of proline 209 to leucine (P209L), which resides in a critical region that mediates the direct interaction between BAG3 and small heat shock proteins (sHSPS), is associated with cardiomyopathy in humans. However, the mechanism by which the BAG3 P209L missense mutation leads to cardiomyopathy remains unknown. To determine the molecular basis underlying the cardiomyopathy caused by the BAG3 P209L mutation, we generated a knock-in (KI) mouse model in which the endogenous Bag3 gene was replaced with mutant Bag3 containing the P215L mutation, which is equivalent to the human P209L mutation. We performed physiological, histological, and biochemical analyses of Bag3 P209L-KI mice to determine the functional, morphological, and molecular consequences of the P209L mutation. We found that Bag3 P209L-KI mice exhibited normal cardiac function and morphology up to 16 months of age. Western blot analysis further revealed that levels of sHSPs, stress-inducible HSPs, ubiquitinated proteins, and autophagy were unaffected in P209L mutant mouse hearts. In conclusion, P209L mutation in Bag3 does not cause cardiomyopathy in mice up to 16 months of age at baseline conditions.