Nicotinic acetylcholine receptor alpha7 subunit is time-dependently expressed in distinct cell types during skin wound healing in mice

Recent studies have shown that nicotinic acetylcholine receptor alpha7 subunit (nAChR alpha 7) plays an important role in regulation of inflammation, angiogenesis and keratinocyte biology, but little is known about its expression after the skin is wounded. A preliminary study on time-dependent expression and distribution of nAChR alpha 7 was performed by immunohistochemistry, Western blotting and RT-PCR during skin wound healing in mice. After a 1-cm-long incision was made in the skin of the central dorsum, mice were killed at intervals ranging from 6 h to 14 days post-injury. In uninjured skin controls, nAChR alpha 7 positive staining was observed in epidermis, hair follicles, sebaceous glands, vessel endothelium and resident dermal fibroblastic cells. In wounded specimens, a small number of polymorphonuclear cells, a large number of mononuclear cells (MNCs) and fibroblastic cells (FBCs) showed positive reaction for nAChR alpha 7 in the wound zones. Simultaneously, nAChR alpha 7 immunoreactivity was evident in endothelial-like cells of regenerated vessels and neoepidermis. By morphometric analysis, an up-regulation of nAChR alpha 7 expression was verified at the inflammatory phase after skin injury and reached a peak at the proliferative phase of wound healing. The expression tendency was further confirmed by Western blotting and RT-PCR assay. By immunofluorescent staining for co-localization, the nAChR alpha 7-positive MNCs and FBCs in skin wounds were identified as macrophages, fibrocytes and myofibroblasts. A number of nAChR alpha 7-positive myofibroblasts were also CD45 positive, indicating that they originated from differentiation of fibrocytes. The results demonstrate that nAChR alpha 7 is time-dependently expressed in distinct cell types, which may be closely involved in inflammatory response and repair process during skin wound healing.