AAV-driven human BAG3 overexpression unexpectedly exacerbate heart failure in a LMNAH222P DCM mice model

Abstract

Dilated cardiomyopathy (DCM) is major cause of heart failure with myocardial systolic dysfunction and ventricular dilatation. In the 30% monogenic forms of DCM, up to 50 genes with causal mutations have been reported potentially leading to protein misfolding and structure/function alteration. One of the well-established causative genes is BAG3 , encoding a co-chaperone playing a key role in autophagy, an essential cellular mechanism involved in proteostasis. Thereby, genetic mutations associated with protein misfolding or aggregation could act through a common proteotoxic mechanism that could be balanced by BAG3-dependant autophagy. Here, our aim was to demonstrate that cardiac restricted BAG3 overexpression could be a therapeutic approach to stop or reverse the DCM phenotype observed in a mouse model knocked-in for a DCM causative LMNA mutation. Echocardiographic function assessment of two groups of LmnaH222P / H222P mice, either injected with cardiotropic AAV9 expressing the human cDNA Hs-BAG3 or GFP (control), was carried out and followed by biochemistry and immunofluorescence analysis of cardiac tissue. Hs-BAG3 overexpression was significant and specific to heart tissue at both the protein and transcript levels. Unexpectedly Hs-BAG3-injected mice present altered life expectancy with early signs of heart failure from the age of 6 weeks compare to 12 weeks for AAV-GFP injected controls. Based on the known drastic deleterious cardiac effect of Lmna KO in mice, we hypothesized an increased lamin A/C degradation in LmnaH222P/H222P mice. However, using immunoblotting and immunofluoresence, no difference in lamin A/C protein levels or localization was observable in AAV-HsBAG3 expressing mice hearts. In the LmnaH222P/H222P mouse model, we highlighted a strong adverse effect of Hs-BAG3 expression in heart tissue, but not associated with increased degradation of lamin A/C. Since BAG3 gene therapy is being evaluated to cure heart failure, it would be of particular interest to study the underlining mechanisms of this unanticipated result.