GSE135296
Hippo Pathway Deletion in Adult Resting Cardiac Fibroblasts Initiates a Cell State Transition with Spontaneous and Self-Sustaining Fibrosis
Cardiac fibroblasts (CFs) respond to injury by transitioning through multiple cell states, including resting CFs, activated CFs, and myofibroblasts. We report here that Hippo signaling cell-autonomously regulates CF fate transitions and proliferation, and non-cell-autonomously regulates both myeloid and CF activation in the heart. Conditional deletion of Hippo pathway kinases, Lats1 and Lats2, in uninjured CFs initiated a self-perpetuating fibrotic response in the adult heart that was lethally exacerbated by myocardial infarction (MI). Single cell transcriptomics showed that uninjured Lats1/2 mutant CFs spontaneously transitioned to a myofibroblast cell state. Through gene regulatory network reconstruction, we found that Hippo-deficient myofibroblasts deployed a network of transcriptional regulators of endoplasmic reticulum (ER) stress, and the unfolded protein response (UPR) consistent with elevated secretory activity. Moreover, we observed an expansion of myeloid cell heterogeneity in uninjured Lats1/2 CKO hearts with a striking similarity to cells recovered from infarcted control hearts. Integrated genome-wide analysis of Yap chromatin occupancy revealed that Yap directly activates myofibroblast cell identity genes, the proto-oncogene Myc, and an array of genes encoding pro-inflammatory factors through enhancer-promoter looping. Thus, our data indicate that Lats1/2 maintain the resting CF cell state through restricting the Yap-induced injury response. Overall design: Using unbiased genomic approaches including high throughput single-cell transcriptomics, enhancer connectome profiling (H3K27ac HiChIP), CUT&RUN, and computational analysis to characterize CFs and myofibroblasts in unprecedented detail, we discovered that the Hippo signaling pathway acts as a repressor of pro-inflammatory signaling cascades, myofibroblast identity, and the global cardiac injury response. Remarkably, after deletion of the core Hippo signaling kinase components, Lats1 and Lats2, in uninjured mouse CFs, we observed massive organ-wide fibrosis that resembled, at the molecular and phenotypic levels, the control heart after MI. Furthermore, Hippo-deficient CFs challenged with myocardial infarction were unable to differentiate and generate a mature scar. Our data highlight an essential role for Lats kinases in cardiac tissue homeostasis and the regulation of the wound response through repression of the downstream effector Yap.