Mitochondrial damage in a Takotsubo syndrome-like mouse model mediated by activation of ß-adrenoceptor-Hippo signaling pathway.

Takotsubo syndrome (TTS) is characterized by short-term contractile dysfunction with its mechanism undefined. We showed that activation of cardiac Hippo pathway mediates mitochondrial dysfunction and that stimulation of ß-adrenoceptors (ßAR) activates Hippo pathway. Here, we investigated the role of ßAR-Hippo signaling in mediating mitochondrial dysfunction in isoproterenol (Iso)-induced TTS-like mouse model. Elderly postmenopausal female mice were administered with Iso (1.25 mg/kg/h for 23 h). Cardiac function was determined by serially echocardiography. At days 1 and 7 post-Iso exposure, mitochondrial ultrastructure and function were examined by electron microscopy and various assays. Alterations in cardiac Hippo pathway and effects of genetic inactivation of Hippo kinase (Mst1) on mitochondrial damage and dysfunction in the acute phase of TTS were investigated. Isoproterenol exposure induced acute increase in biomarkers of cardiac damage and ventricular contractile dysfunction and dilation. At day 1 post-Iso, we observed extensive abnormalities in mitochondrial ultrastructure, downregulation of mitochondrial marker proteins, and mitochondrial dysfunction evidenced by lower ATP content, increased lipid droplets, higher contents of lactate, and augmented reactive oxygen species (ROS). All changes were reversed by day 7. ßAR stimulation led to activation of cardiac Hippo pathway with enhanced expression of Hippo kinase Mst1 and inhibitory YAP phosphorylation, as well as reduced nuclear YAP-TEAD1 interaction. In mice with cardiac expression of inactive mutant Mst1 gene, acute mitochondrial damage and dysfunction were mitigated. Stimulation of cardiac ßAR activates Hippo pathway that mediates mitochondrial dysfunction with energy insufficiency and enhanced ROS, promoting acute but short-term ventricular dysfunction.NEW & NOTEWORTHY Takotsubo syndrome (TTS) is featured by activation of sympatho-ß-adrenoceptor (ßAR) system leading to acute loss of ventricular contractile performance. However, the molecular mechanism remains undefined. We demonstrated, in an isoproterenol-induced murine TTS-like model, extensive mitochondrial damage, metabolic dysfunction, and downregulated mitochondrial marker proteins, changes temporarily associated with cardiac dysfunction. Mechanistically, stimulation of ßAR activated Hippo signaling pathway and genetic inactivation of Mst1 kinase ameliorated mitochondrial damage and metabolic dysfunction at the acute phase of TTS.

Evaluation of Coenzyme Q10 (CoQ10) Deficiency and Therapy in Mouse Models of Cardiomyopathy.

ABSTRACT: Mitochondrial dysfunction plays a key role in the development of heart failure, but targeted therapeutic interventions remain elusive. Previous studies have shown coenzyme Q10 (CoQ10) insufficiency in patients with heart disease with undefined mechanism and modest effectiveness of CoQ10 supplement therapy. Using 2 transgenic mouse models of cardiomyopathy owing to cardiac overexpression of Mst1 (Mst1-TG) or ß 2 -adrenoceptor (ß 2 AR-TG), we studied changes in cardiac CoQ10 content and alterations in CoQ10 biosynthesis genes. We also studied in Mst1-TG mice effects of CoQ10, delivered by oral or injection regimens, on both cardiac CoQ10 content and cardiomyopathy phenotypes. High performance liquid chromatography and RNA sequencing revealed in both models significant reduction in cardiac content of CoQ10 and downregulation of most genes encoding CoQ10 biosynthesis enzymes. Mst1-TG mice with 70% reduction in cardiac CoQ10 were treated with CoQ10 either by oral gavage or i.p. injection for 4-8 weeks. Oral regimens failed in increasing cardiac CoQ10 content, whereas injection regimen effectively restored the cardiac CoQ10 level in a time-dependent manner. However, CoQ10 restoration in Mst1-TG mice did not correct mitochondrial dysfunction measured by energy metabolism, downregulated expression of marker proteins, and oxidative stress nor to preserve cardiac contractile function. In conclusion, mouse models of cardiomyopathy exhibited myocardial CoQ10 deficiency likely due to suppressed endogenous synthesis of CoQ10. In contrast to ineffectiveness of oral administration, CoQ10 administration by injection regimen in cardiomyopathy mice restored cardiac CoQ10 content, which, however, failed in achieving detectable efficacy at molecular and global functional levels.

Hippo pathway activation mediates chemotherapy-induced anti-cancer effect and cardiomyopathy through causing mitochondrial damage and dysfunction.

Rationale: Chemotherapy is a common clinical strategy for cancer treatment. However, the accompanied cardiomyopathy renders cancer patients under risk of another life-threatening condition. Whereas Hippo pathway is known to play key roles in both cancerogenesis and heart disease, it remains unclear whether Hippo pathway activation mediates chemotherapy-induced cardiomyopathy. Methods and Results: In human breast cancer cells, doxorubicin (DOX) significantly induced upregulation of Hippo kinase Mst1, inhibitory phosphorylation of YAP, mitochondrial damage, reduced cell viability and increased apoptosis. Hippo pathway inactivation by Mst1-siRNA transfection effectively improved cell survival and mitigated mitochondrial damage and cell apoptosis. Another anti-cancer drug YAP inhibitor verteporfin also induced lower cancer cell viability, apoptosis and mitochondrial injury. Chronic treatment with DOX in vivo (4 mg/kg/week for 6 weeks) caused mitochondrial damage and dysfunction, oxidative stress and cardiac fibrosis, while acute DOX treatment (16 mg/kg single bolus) also induced myocardial oxidative stress and mitochondrial abnormalities. Chronic treatment with verteporfin (2 months) resulted in cardiomyopathy phenotypes comparable to that by chronic DOX regimen. In transgenic mice with cardiac overexpression of kinase-dead mutant Mst1 gene, these adverse cardiac effects of DOX were significantly attenuated relative to wild-type littermates. Conclusions: Anti-cancer action of both DOX and verteporfin is associated with Hippo pathway activation. Such action on cardiac Hippo pathway mediates mitochondrial damage and cardiomyopathy.