Protease-activated receptor-2 (PAR2) in epithelial biology

Protease-activated receptor-2 is a G-protein-coupled receptor involved in inflammatory and pain responses, as well as pathogenesis in the gastrointestinal and cardiovascular systems, among others. Efforts to identify the serine protease(s) involved in activation of Par2 in vivo have so far been unsuccessful. Here we describe novel roles for Par2 in two animal models: mouse and zebrafish, as well as identify matriptase as a key activator of Par2 in vivo. We report an unexpected role for protease signaling in neural tube closure and formation of the central nervous system. Mouse embryos lacking protease-activated receptor 1 and 2 showed defective hindbrain and posterior neuropore closure and developed exencephaly and spina bifida, important human congenital anomalies. Par1 and Par2 were expressed in surface ectoderm, Par2 selectively along the line of closure. Ablation of Gi/z and Rac1 function in these Par2-expressing cells disrupted neural tube closure, further implicating G protein-coupled receptors and identifying a likely effector pathway. Cluster analysis of protease and Par2 expression patterns revealed a group of membrane-tethered proteases often co-expressed with Par2. Among these, matriptase activated Par2 with picomolar potency, and hepsin and prostasin activated matriptase. Together, our results suggest a role for protease-activated receptor signaling in neural tube closure and identify a local protease network that may trigger Par2 signaling and monitor and regulate epithelial integrity in this context. We also describe a role for Par2 in zebrafish embryos. Hai1a morphants exhibit skin defects including keratinocyte aggregation and shedding, as well as chronic inflammation and ultimately death. Co-knockdown of matriptase or Par2b rescues this phenotype. Further examination of Hai1a morphants reveals keratinocytes that are extruded from the skin, characterized by contraction of an actin-myosin ring around the ejected cell; Par2b knockdown rescues this. Cell extrusion in this context is not apoptosis dependent as extruding cells were negative for caspase-3 and TUNEL stain. Our data taken together suggests important roles for Par2 in epithelial biology as well as identifies matriptase as an important activator of Par2 in animal models