Abstract 12827: Mouse Model of LEOPARD Syndrome Reveals a Dominant Negative Function of the PTPN11 (Shp2) Mutation and a Mechanism of Regulation and Therapy for Hypertrophic Cardiomyopathy

Over 90% of cases of LEOPARD syndrome (LS), a rare autosomal dominant multi-systemic disease, are caused by mutations in the protein tyrosine phosphatase non-receptor type 11 gene ( PTPN11 ), which encodes Shp2. However, in vivo mechanisms and signlaling pathways that regulate LS in the heart remain undefined. We hypothesize that LS mutations in the heart behave as dominant negatives and aberrantly activate downstream signaling pathways to cause hypertrophic cardiomyopathy (HCM). To test this, we generated inducible knock-in mice to one of the most common Shp2 mutations in LS, Y279C. Inducible mice were crossed to EIIA-whole body deleter Cre mice to generate LS/+ mice. Viable and born at Mendelian ratios, LS/+ mice recapitulate the human disease phenotype, with abnormal facies, growth-retardation, and abnormal chest walls. Echocardiography and histopathology reveal LS/+ mice to have progressive left ventricular HCM peaking at 12-16 weeks, followed by dilation and decreased ejection fraction by 20 weeks, as compared to wildtype littermates (WT). The cardiac fetal gene program is also reactivated in LS/+, further validating the HCM observed in these mice. Biochemically, LS/+ hearts have significantly reduced Shp2 phosphatase activity in vivo . While no significant change in basal Erk/MAPK activity is observed, upon insulin stimulation, lysates from LS/+ hearts have significantly reduced Erk/MAPK response, as compared to WT. In parallel, the Akt/TSC2/S6K pathway and the cardiac stress-mediated signaling pathways (pStat3, p38 and JNK) are all significantly elevated, with concomitant increase in nuclear NFAT. To determine whether PI3K/Akt signaling facilitates the hypertrophic response in LS, we isolated LS/+ and WT primary MEFs; LS/+ MEFs were significantly larger in size and shape than WT and, importantly, overnight treatment of the LS/+ cells with the Akt/mTOR pathway inhibitor, rapamycin, reversed the hypertrophic phenotype. Indeed, in vivo, mice given a daily low-dose of rapamycin for a period of four weeks have significantly improved cardiac function, with reversal of the HCM, as observed by echocardiography. Taken together, these data reveal the first in vivo analysis for LS and identify rapamycin as a targetable therapy for HCM in LS patients.