Merkel cells as putative regulatory cells in skin disorders: an in vitro study.
Bottom Line: However, neither proliferation nor reactions to the epidermal environment have been demonstrated.Conversely, neurotrophins failed to induce cell spreading, suggesting that they do not act as a growth factor for MCs.We conclude that neuropeptide release and neurotransmitter exocytosis may be two distinct pathways that are differentially regulated.
Affiliation: University of Brest, EA4326, Brest, France.
Merkel cells (MCs) are involved in mechanoreception, but several lines of evidence suggest that they may also participate in skin disorders through the release of neuropeptides and hormones. In addition, MC hyperplasias have been reported in inflammatory skin diseases. However, neither proliferation nor reactions to the epidermal environment have been demonstrated. We established a culture model enriched in swine MCs to analyze their proliferative capability and to discover MC survival factors and modulators of MC neuroendocrine properties. In culture, MCs reacted to bFGF by extending outgrowths. Conversely, neurotrophins failed to induce cell spreading, suggesting that they do not act as a growth factor for MCs. For the first time, we provide evidence of proliferation in culture through Ki-67 immunoreactivity. We also found that MCs reacted to histamine or activation of the proton gated/osmoreceptor TRPV4 by releasing vasoactive intestinal peptide (VIP). Since VIP is involved in many pathophysiological processes, its release suggests a putative regulatory role for MCs in skin disorders. Moreover, in contrast to mechanotransduction, neuropeptide exocytosis was Ca(2+)-independent, as inhibition of Ca(2+) channels or culture in the absence of Ca(2+) failed to decrease the amount of VIP released. We conclude that neuropeptide release and neurotransmitter exocytosis may be two distinct pathways that are differentially regulated.
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Mentions: MCs of most mammalian species produce VIP . Conversely, keratinocytes do not express it under physiological conditions . In our culture conditions, MCs were immunoreactive to VIP as revealed by double immunofluorescence (Figure 6). The merge picture demonstrated that nearly all CK20-positive MCs also produced VIP, and that cells other than MCs were not found to express VIP. In addition, the synthesis of VIP was detected by western blot (WB) analysis of whole cell homogenates produced from cultures enriched in MCs (Figure 6, WB). In contrast, calcitonin gene-related peptide (CGRP) and substance P were produced by MCs and keratinocytes. Neuropeptide Y (NPY) was hardly detectable in our cultures (data not shown).