Activation of Yap1/Taz signaling in ischemic heart disease and dilated cardiomyopathy.

Genetic manipulation of key components of the evolutionally conserved Hippo pathway has shown that the precise control of these signaling molecules is critical to cardiac development and response to stresses. However, how this pathway is involved in the progression of cardiac dysfunction in different heart diseases remains unclear. We investigated the expressional levels and subcellular localization of Yap1, Taz, and Tead1 and determined Hippo target gene expression in failing human hearts with ischemic heart disease (IHD) and idiopathic dilated cardiomyopathy (IDC) and mouse desmin-related cardiomyopathy (DES). Our results demonstrated that Yap1, Taz, and Tead1 were significantly increased in failing human and DES hearts compared with the non-failing controls (NFH) or wild type (WT) mouse hearts at both mRNA and protein levels. Interestingly, adult human and mouse hearts had more Taz than Yap1 by mRNA and protein expression and their increases in diseased hearts were proportional and did not change Yap1/Taz ratio. Yap1, Taz, and Tead1 were accumulated in the nuclear fraction and cardiomyocyte nuclei of diseased hearts. The ratio of Yap1 phosphorylated at serine 127 (human) or serine 112 (mouse) to the total Yap1 (pYap1/Yap1) was significantly lower in the nuclear fraction of diseased hearts than that in normal controls. More importantly, Hippo downstream targets Ankrd1, Ctgf, and Cyr61 were transcriptionally elevated in the diseased hearts. These results suggest that Yap1/Taz signaling is activated in human and mouse dysfunctional hearts. Further investigation with relevant animal models will determine whether this pathway is a potential target for preventing and reversing abnormal remodeling during the progression of different cardiac disorders.