| dc.description.abstract | The epicardium, the heart’s outermost layer, contains progenitors for
essential non-cardiomyocyte lineages that support coronary vascular
development. The Hippo pathway, a conserved kinase cascade, controls organ
size in the developing heart and inhibits regeneration in the adult heart. In the first
study, using high-throughput single cell RNA-seq (scRNA-seq), we investigated
the function of Hippo pathway kinases, Lats1 and Lats2 (Lats1/2) in epicardial
development. Lats1/2 mutant cells fail to activate the fibroblast differentiation
program, but instead remain suspended in an intermediate progenitor cell state
with characteristics of epicardial cells and fibroblasts. Computational analysis and
lineage tracing revealed an arrested developmental trajectory for Lats1/2 mutant
cells that resulted in an abnormal extracellular matrix composition and an altered
extracellular growth factor milieu, leading to defective coronary vascular
remodeling.
In the second study, we focused on the minor lineage endothelial cell which
rarely comes from epicardium at normal state. Lats mutant epicardium
preferentially generated endothelial cells. Genes associated with F-actin
polymerization were upregulated in Lats mutant epicardium. Super-resolution
microscopy and atomic force microscopy indicated that Lats mutant epicardium
was stiffer with more intracellular F-actin bundles. Explant studies revealed that
epicardial progenitors cultured on stiff matrices acquired an endothelial phenotype
independently of Lats , while on softer, more physiologic matrices Lats inhibited the endothelial phenotype. Thus, Lats inhibits Wt1 derived endothelial lineage
expansion in cooperation with cytoskeletal state.
In the third study, we investigated the role of Lats1/2 in adult cardiac
fibroblast. Inactivation of Lats1/2 in fibroblasts resulted in hyper-proliferation of
cardiac fibroblast. Lats1/2CKO hearts also showed reduced collagen production
after injury, suggesting defective injury response. We compared the transcriptome
of these two groups at homeostasis without surgery. Interestingly, interferon
responding genes and genes associated with T cell activation were decreased,
suggesting common cross-talk between fibroblasts and immune cells at resting
condition. To be noted, these Lats1/2 mutant fibroblasts exhibited pronounced
Myc expression, which were accompanied with significant apoptosis in
surrounding cells, suggesting cell competition between Lats1/2 mutant cells and
neighboring “wild type” cells. Taken together, our study revealed a pivotal role of
Lats kinase in heart homeostasis maintenance and injury response. | en |
