The Hippo Pathway is Activated and is a Causal Mechanism for Adipogenesis in Arrhythmogenic Cardiomyopathy
Rationale: Mutations in the intercalated disc (ID) proteins, such as plakophilin 2 (PKP2) cause arrhythmogenic cardiomyopathy (AC). AC is characterized by the replacement of cardiac myocytes by fibro-adipocytes, cardiac dysfunction, arrhythmias and sudden death.
Objective: To delineate the molecular pathogenesis of AC.
Methods and Results: Localization and levels of selected ID proteins including signaling molecules were markedly reduced in the human hearts with AC. Altered protein constituents of IDs was associated with activation of the upstream Hippo molecules in the human hearts, Nkx2.5-Cre:DspW/F and Myh6:Jup mouse models of AC, and in the plakophilin 2 (PKP2) knock down HL-1 myocytes (HL-1PKP2:shRNA). Level of active PKC-α, which requires PKP2 for activity, was reduced. In contrast, neurofibromin (NF2 or Merlin), a molecule upstream to the Hippo pathway, which is inactivated by PKC-α, was activated. Consequently, the downstream Hippo molecules MST1/2, LATS1/2 and YAP; the latter is the effector of the pathway, were phosphorylated. Co-immunoprecipitation detected binding of pYAP, pβ-catenin, and JUP, the latter translocated from the junction. RNA sequencing, transcript qPCR and reporter assays showed suppressed activity of TEAD and TCF7L2, transcription factors of the Hippo and the canonical Wnt signaling, respectively. In contrast, adipogenesis was enhanced. Simultaneous KD of Lats1/2, molecules upstream to YAP, rescued inactivation of YAP and β-catenin and adipogenesis in the HL-1PKP2:shRNA myocytes.
Conclusions: Molecular remodeling of the IDs leads to pathogenic activation of the Hippo pathway, suppression of the canonical Wnt signaling and enhanced adipogenesis in AC. The findings offer novel mechanisms for the pathogenesis of AC.
- Received October 8, 2013.
- Revision received November 19, 2013.
- Accepted November 25, 2013.