Central role of fibroblast α3 nicotinic acetylcholine receptor in mediating cutaneous effects of nicotine

Abstract

Smoking is associated with aberrant cutaneous tissue remodeling, such as precocious skin aging and impaired wound healing. The mechanism is not fully understood. Dermal fibroblasts (DF) are the primary cellular component of the dermis and may provide a target for pathobiologic effects of tobacco products. The purpose of this study was to characterize a mechanism of nicotine (Nic) effects on the growth and tissue remodeling function of DF. We hypothesized that the effects of Nic on DF result from its binding to specific nicotinic acetylcholine receptors (nAChRs) expressed by these cells and that downstream signaling from the receptors alters normal cell functioning, leading to changes in skin homeostasis. Using RT-PCR and Western blotting, we found that a 24-hour exposure of human DF to 10 μm Nic causes a 1.9- to 28-fold increase of the mRNA and protein levels of the cell cycle regulators p21, cyclin D1, Ki-67, and PCNA and a 1.7- to 2-fold increase of the apoptosis regulators Bcl-2 and caspase 3. Nic exposure also up-regulated expression of the dermal matrix proteins collagen type Iα1 and elastin as well as matrix metalloproteinase-1. Mecamylamine (Mec), the specific antagonist of nAChRs, abolished Nic-induced alterations, indicating that they resulted from a pharmacologic stimulation of nAChRs expressed by DF. To establish the relevance of these findings to a specific nicotinergic pathway, we studied human DF transfected with anti-α3 antisense oligonucleotides and murine DF from α3 nAChR knockout mice. In both cases, lack of α3 was associated with alterations in fibroblast growth and function that were opposite to those observed in DF treated with Nic, suggesting that the nicotinic effects on DF were mostly mediated by α3 nAChR. In addition to α3, the nAChR subunits detected in human DF were α5, α7, β2, and β4. The exposure of DF to Nic altered the relative amounts of each of these subunits, leading to reciprocal changes in [3H]epibatidine-binding kinetics. Thus, some of the pathobiologic effects of tobacco products on extracellular matrix turnover in the skin may stem from Nic-induced alterations in the physiologic control of the unfolding of the genetically determined program of growth and the tissue remodeling function of DF as well as alterations in the structure and function of fibroblast nAChRs.