Tryptase/Protease-Activated Receptor 2 Interactions Induce Selective Mitogen-Activated Protein Kinase Signaling and Collagen Synthesis by Cardiac Fibroblasts

The mast cell product, tryptase, has recently been implicated in fibrosis in the hypertensive heart. Tryptase has been shown to mediate non-cardiac fibroblast function via activation of protease activated receptor-2 and subsequent activation of the mitogen-activated protein kinase pathway, including extracellular signal-regulated kinase1/2. Therefore, we hypothesized that this pathway may be a mechanism leading to fibrosis in the hypertensive heart. Isolated adult cardiac fibroblasts were treated with tryptase, which induced activation of extracellular signal-regulated kinase1/2 via protease activated receptor-2. Blockade of protease activated receptor-2 with FSLLRY (10 μM) and inhibition of the extracellular signal-regulated kinase pathway with PD98059 (10 μM) prevented collagen synthesis in isolated cardiac fibroblasts stimulated with tryptase. p38 mitogen activated protein kinase and stress-activated protein/c-Jun N-terminal kinase were not activated by tryptase. Cardiac fibroblasts isolated from spontaneously hypertensive rats showed this same pattern of activation and treatment of spontaneously hypertensive rats with FSLLRY prevented fibrosis in these animals indicating the in vivo applicability of the cultured fibroblast findings. Also, tryptase induced a myofibroblastic phenotype indicated by elevations in α smooth muscle actin and ED-A fibronectin. Thus, the results from this study demonstrate the importance of tryptase for inducing a cardiac myofibroblastic phenotype, ultimately leading to the development of cardiac fibrosis through the activation of the extracellular signal-regulated kinase pathway. Specifically, tryptase causes cardiac fibroblasts to increase collagen synthesis via a mechanism involving activation of protease activated receptor-2 and subsequent induction of extracellular signal-regulated kinase signaling.