Analysis of protease‐activated receptor‐1 and ‐2 in human scar formation

Abstract

Protease-activated receptor (PAR)-1 and PAR-2 are reported to contribute to the fibrotic process in a number of organs, including lung, liver, pancreas, and kidney. The aim of this study was to localize expression and biological activity of PAR-1 and PAR-2 in normal and pathological cutaneous scars. First, we investigated the immunohistochemical expression of PAR-1 and PAR-2 proteins in a series of human normal scars (NS, n = 10), hypertrophic scars (HS, n = 10), and keloids (K, n = 10). Expression of PAR-1 and PAR-2 was observed in all types of scar. Specifically, in HS and K, diffuse PAR-1 and PAR-2 positivity was found in dermal cellular areas composed of myofibroblasts, while no or minor staining was observed in the scattered fibroblasts embedded in abundant extracellular matrix in the context of the more collagenous nodules, irrespective of the type of scar. The hyperplastic epidermis overlying K was also found to be strongly PAR-1 and PAR-2 positive, whilst in most NS and HS the epidermis was faintly to moderately stained. Second, ribonuclease protection assay on paraffin-embedded specimens showed overexpression of PAR-1 and PAR-2 mRNA in K compared to NS and HS. Third, cultured human fibroblasts exposed to TGF-beta1 expressed a myofibroblast phenotype associated with overexpression of PAR-2, while PAR-1 expression was unaffected. Intracellular Ca(2+) mobilization by PAR-2 agonists in myofibroblasts was increased as compared to fibroblasts, whereas the effect of PAR-1 agonists was unchanged. Our in vivo study indicates that PAR-1 and PAR-2 are expressed in cells involved in physiological and pathological scar formation and suggests that in vitro overexpression and exaggerated functional response of PAR-2 may play a role in the function of myofibroblasts in scar evolution from a physiological repair process to a pathological tissue response.

Protease-Activated Receptor-2 Induces Myofibroblast Differentiation and Tissue Factor Up-Regulation during Bleomycin-Induced Lung Injury

“…Overall, these observations further emphasize the very distinct downstream responses triggered by each receptor and are in line with the hypothesis that PAR-2 specifically elicits fibroproliferative programs. 48 In line with previous observations that aSMA and PAR-2 expression is correlated in renal fibrosis, 25 aSMA levels do not increase in PAR-2Ϫdeficient animals after bleomycin treatment. Interestingly however, PAR-2Ϫde-ficient mice still develop fibrosis, as evident from abnormal lung histology (Figure 4).…”

Protease Activated Receptor-1 Deficiency Diminishes Bleomycin-Induced Skin Fibrosis

“…The fact that we show that PAR-1 deficiency limits skin fibrosis in this model, together with the fact that PAR-1 expression is increased in the skin during human Ssc (11) and that PAR-1 activation on human cell types potentiates key profibrotic processes, suggests that PAR-1 may have clinical relevance for human scleroderma. Besides increased PAR-1 expression in scleroderma, PAR-1 also is expressed in other skin disorders such as normal and hypertrophic scars and keloid lesions (12), and PAR-1 might, consequently, also play a role in the development of these disorders. Before targeting PAR-1 in patients, one should realize, however, that PAR-1 also mediates platelet activation and targeting PAR-1 could lead to bleeding complications.…”

“…In the skin, PAR-1 is expressed on keratinocytes, endothelial cells and fibroblasts and the density of PAR-1 positive fibroblasts is increased in the skin of SSc patients compared with that of healthy controls (11). Moreover, PAR-1 is expressed in both the epidermis and dermis of normal and hypertrophic scars and in keloid lesions (12). The functional consequence of PAR-1 expression in the skin remains elusive however although accelerated wound healing in mice after topical PAR-1 activation pinpoints PAR-1 as an important receptor in the skin (13).…”

Activated Protein C Enhances Human Keratinocyte Barrier Integrity via Sequential Activation of Epidermal Growth Factor Receptor and Tie2

“…6). EPCR, PAR-1, and EGFR are expressed and co-localized in basal and suprabasal keratinocytes in human skin epidermis (15,25,26). EPCR does not signal but acts by spatially locating APC to cleave the G protein-coupled receptor, PAR-1.…”