Introduction: Our lab has recently identified and characterized a novel transmembrane protein named DWORF (DWarf Open Reading Frame) that binds to SERCA2a and enhances its activity by displacing phospholamban (PLN), a potent SERCA inhibitor.
Hypothesis: Cardiac-specific overexpression of DWORF (αMHC-DWORF transgene, DwTg) can mitigate the cellular phenotype of PLN transgenic mice and rescue experimental models of heart failure.
Results: DwTg mice have a cellular phenotype that phenocopies that observed in PLN null mice, exhibiting an increase in peak Ca2+-transient amplitude, faster cytosolic Ca2+ decay rates, higher SR Ca2+ load and enhanced cardiomyocyte contractility. Previous in vitro studies indicate that DWORF activates SERCA by displacing its negative regulator, PLN. To investigate this in vivo, we crossed our DwTg mice with the well-characterized αMHC-PLN transgenic mice (PlnTg). Interestingly, double transgenic (Dw/PlnTg) animals exhibited a complete rescue of impaired Ca2+ cycling that is associated with PLN overexpression, and these mice showed enhanced Ca2+-handling similar to DwTg mice. Using a well-characterized mouse model of dilated cardiomyopathy (DCM) due to deletion of the muscle-specific LIM protein (MLP KO), crossing in the DWORF transgene resulted in a complete rescue of in vivo cardiac function and prevented the pathological remodeling, development of fibrosis and ultrastructural defects that are all characteristic features of MLP KO hearts. At the cellular level, cardiomyocytes isolated from DwTg/MLP KO displayed enhanced Ca2+-cycling and contractile properties that contrasted sharply with MLP KO cardiomyocytes, which exhibited depressed contractility. These results are reminiscent of past studies in which PLN KO mice also provided protection to the DCM phenotype associated with MLP KO mice.
Conclusions: Cardiac-specific overexpression of DWORF enhances Ca2+ cycling in PLN transgenic mice, prevents the DCM phenotype of MLP KO mice and provides an attractive candidate for a novel heart failure therapeutic.