Background and PurposeThe Hippo pathway has emerged as a potential therapeutic 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 ApproachWe 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 echocardiography, qRT‐PCR and immunohistochemical methods in vivo.Key ResultsXMU‐MP‐1 treatment significantly increased activity of the Hippo pathway effector yes‐associated protein and inhibited phenylephrine‐induced hypertrophy in NRCM. XMU‐MP‐1 improved cardiomyocyte survival and reduced apoptosis 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 ImplicationsThe Hippo pathway inhibitor, XMU‐MP‐1, reduced cellular hypertrophy and improved survival in cultured cardiomyocytes and, in vivo, preserved cardiac function following pressure overload.

Diabetes mellitus (DM) is one of the major causes of death in the world. There are two types of DM—type 1 DM and type 2 DM. Type 1 DM can only be treated by insulin injection whereas type 2 DM is commonly treated using anti-hyperglycemic agents. Despite its effectiveness in controlling blood glucose level, this therapeutic approach is not able to reduce the decline in the number of functional pancreatic β cells. MST1 is a strong pro-apoptotic kinase that is expressed in pancreatic β cells. It induces β cell death and impairs insulin secretion. Recently, a potent and specific inhibitor for MST1, called XMU-MP-1, was identified and characterized. We hypothesized that treatment with XMU-MP-1 would produce beneficial effects by improving the survival and function of the pancreatic β cells. We used INS-1 cells and STZ-induced diabetic mice as in vitro and in vivo models to test the effect of XMU-MP-1 treatment. We found that XMU-MP-1 inhibited MST1/2 activity in INS-1 cells. Moreover, treatment with XMU-MP-1 produced a beneficial effect in improving glucose tolerance in the STZ-induced diabetic mouse model. Histological analysis indicated that XMU-MP-1 increased the number of pancreatic β cells and enhanced Langerhans islet area in the severe diabetic mice. Overall, this study showed that MST1 could become a promising therapeutic target for diabetes mellitus.