The aim of this study was to establish reversibility of cardiac phenotypes in hypertrophic cardiomyopathy (HCM) by generating bigenic mice in which expression of the mutant transgene could be turned on and off as needed.

Advances in molecular therapeutics could ultimately lead to therapies aimed at correcting the causal mutations. However, whether cardiac phenotypes, once established, are permanent, or could be reversed, if expression of the mutant protein is turned off, is unknown.

We generated ligand-inducible bigenic mice, turned on and off expression of cardiac troponin T-Q92 (cTnT-Q92), responsible for human HCM, and characterized molecular, histologic, and functional phenotypes.

We established six lines and in dose-titration studies showed that treatment with 1,000 μg/kg of mifepristone consistently switched on cTnT-Q92 expression in the heart. Short-term (16 days) induced expression enhanced myocardial systolic function without changing myocardial cyclic adenosine monophosphate levels. Levels of PTEN, a regulator of cardiac function, phospho-protein kinase C-Ζλ-Thr538 and phosphor-protein kinase D-Ser744-748 were reduced, whereas messenger ribonucleic acid (mRNA) levels of NPPA, NPPB, and sarcoplasmic reticulum calcium adenine triphosphatase 2 (ATP2A2) (hypertrophic markers) and procollagen COL1A1, COL1A2, and COL3A1were unchanged. Long-term (70 days) induced expression increased COL1A1and COL1A3 mRNAs levels and collagen volume fraction and reduced levels of NPPAand NPPB. Switching off expression of the cTnT-Q92 reversed functional, molecular, and histologic phenotypes completely.

The initial phenotype induced by cTnT-Q92 is enhanced myocardial systolic function followed by changes in signaling kinases and interstitial fibrosis. Established phenotypes in HCM reverse upon turning off expression of the mutant protein. These findings provoke pursuing specific therapies directed at correcting the underlying the genetic defect in HCM.