Myocardial KRASG12D expression does not cause cardiomyopathy in mice

Aims Germ-line mutations in genes encoding components of the RAS/mitogen-activated protein kinase (MAPK) pathway cause developmental disorders called RASopathies. Hypertrophic cardiomyopathy (HCM) is the most common myocardial pathology and a leading cause of death in RASopathy patients. KRAS mutations are found in Noonan and cardio-facio-cutaneous syndromes. KRAS mutations, unlike mutations of RAF1 and HRAS, are rarely associated with HCM. This has been attributed to the fact that germ-line KRAS mutations cause only a moderate up-regulation of the MAPK pathway. Highly bioactive KRAS mutations have been hypothesized to cause severe cardiomyopathy incompatible with life. The aim of this study was to define the impact of KRASG12D expression in the heart. Methods and results To generate mice with endogenous cardiomyocyte-specific KRASG12D expression (cKRASG12D mice), we bred mice with a Cre-inducible allele expressing KRASG12D from its endogenous promoter (Kras2LSL) to mice expressing Cre under control of the cardiomyocyte-specific α-myosin heavy chain promoter (αMHC-Cre). cKRASG12D mice showed high levels of myocardial ERK and AKT signalling. However, surprisingly, cKRASG12D mice were born in Mendelian ratios, appeared healthy, and had normal function, size, and histology of the heart. Conclusion Mice with cardiomyocyte-specific KRASG12D expression do not develop heart pathology. These results challenge the view that the level of MAPK activation correlates with the severity of HCM in RASopathies and suggests that MAPK-independent strategies may be of interest in the development of new treatments for these syndromes.