PAR‐1‐dependent and PAR‐independent pro‐inflammatory signaling in human lung fibroblasts exposed to thrombin

Abstract

Proteinase-activated receptors (PARs) are crucial in orchestrating cellular responses to coagulation proteinases, such as thrombin and FXa. Four PARs have been characterized and have been shown to be differentially expressed in mice and humans and between tissues. We have previously shown that in murine lung fibroblasts, PAR-1 is solely responsible for all cellular responses to thrombin and FXa. In contrast, we report here that in primary human lung fibroblasts (pHLFs), known PARs fail to account for all of the cellular responses to thrombin, in particular in the presence of high, but physiologically achievable concentrations of thrombin. We report that pHLFs secrete CCL2 in a PAR-1-dependent manner at low thrombin concentration (∼0.3 nM). At or above 10 nM thrombin, pharmacological antagonism (RWJ-58259) fails to block thrombin-induced CCL2 release; whereas PAR-1 cleavage-blocking monoclonal antibodies (ATAP2 and WEDE15) only partially inhibit thrombin-induced CCL2 secretion. In addition, activation of PAR-3, PAR-4, and transactivation of either PAR-2 or EGFR were ruled out as being responsible for thrombin-mediated CCL2 secretion at high yet standard concentrations of the proteinase. We further provide evidence that PAR-1-dependent and PAR-independent signaling involves the rapid phosphorylation of ERK, which in turn is absolutely required for thrombin-induced CCL2 secretion at both low and standard concentration of the proteinase. Our findings suggest the existence of a PAR-independent signaling mechanism in human lung fibroblasts and have important implications for the design of therapeutic strategies aimed at blocking pro-inflammatory signaling responses associated with excessive thrombin generation.

Tissue Kallikrein Mediates Pro-Inflammatory Pathways and Activation of Protease-Activated Receptor-4 in Proximal Tubular Epithelial Cells

“…As PAR expression has been implicated in the pathogenesis of many inflammatory diseases [27]–[30] and some renal disorders [22], [23], we evaluated the expression of all PARs in renal biopsies from both DN patients and non-diabetic control subjects by immunohistochemical staining (IHC). Table 1 showed the clinical data of the study subjects and the intensity of PAR immunostaining in their kidney tissues.…”

The Coagulant Factor Xa Induces Protease-Activated Receptor-1 and Annexin A2–Dependent Airway Smooth Muscle Cytokine Production and Cell Proliferation

“…The latter is catalysed by another serine protease, plasmin, suggesting the convergence of the coagulation and plasminogen activation systems in allergic airway inflammation. Proteases of both systems also activate protease-activated receptors (PARs) in various cell types [11][12][13][14]. The PARs are a G-protein-coupled receptor family, activated…”

Thrombin induces ICAM-1 expression in human lung epithelial cells via c-Src/PDGFR/PI3K/Akt-dependent NF-κB/p300 activation

“…Thrombin-mediated cellular responses are mostly mediated by the PAR (proteaseactivated receptor) family of receptors, although some exceptions have been noted [9]. Thrombin-mediated cellular responses are mostly mediated by the PAR (proteaseactivated receptor) family of receptors, although some exceptions have been noted [9].…”