Pharmacological inhibition of Hippo pathway, with the novel kinase inhibitor XMU‐MP‐1, protects the heart against adverse effects during pressure overload

Background and Purpose: The Hippo pathway has emerged as a potential thera- peutic target to control pathological cardiac remodelling. The core components of the Hippo pathway, mammalian Ste‐20 like kinase 1 (Mst1) and mammalian Ste‐20 like kinase 2 (Mst2), modulate cardiac hypertrophy, apoptosis, and fibrosis. Here, we study the effects of pharmacological inhibition of Mst1/2 using a novel inhibitor XMU‐MP‐1 in controlling the adverse effects of pressure overload‐induced hypertrophy. Experimental Approach: We used cultured neonatal rat cardiomyocytes (NRCM) and C57Bl/6 mice with transverse aortic constriction (TAC) as in vitro and in vivo models, respectively, to test the effects of XMU‐MP‐1 treatment. We used luciferase reporter assays, western blots and immunofluorescence assays in vitro, with echocar- diography, qRT‐PCR and immunohistochemical methods in vivo. Key Results: XMU‐MP‐1 treatment significantly increased activity of the Hippo pathway effector yes‐associated protein and inhibited phenylephrine‐induced hyper- trophy in NRCM. XMU‐MP‐1 improved cardiomyocyte survival and reduced apopto- sis following oxidative stress. In vivo, mice 3 weeks after TAC, were treated with XMU‐MP‐1 (1 mg·kg−1) every alternate day for 10 further days. XMU‐MP‐1‐treated mice showed better cardiac contractility than vehicle‐treated mice. Cardiomyocyte cross‐sectional size and expression of the hypertrophic marker, brain natriuretic peptide, were reduced in XMU‐MP‐1‐treated mice. Improved heart function in XMU‐MP‐1‐treated mice with TAC, was accompanied by fewer TUNEL positive cardiomyocytes and lower levels of fibrosis, suggesting inhibition of cardiomyocyte apoptosis and decreased fibrosis. Conclusions and Implications: The Hippo pathway inhibitor, XMU‐MP‐1, reduced cellular hypertrophy and improved survival in cultured cardiomyocytes and, in vivo, preserved cardiac function following pressure overload. Abbreviations: