Normal Human Merkel Cells are Present in Epidermal Cell Populations Isolated and Cultured from Glabrous and Hairy Skin Sites

Abstract

The Merkel cell is a highly specialized cell that primarily acts as a slowly adapting mechanoreceptor. Merkel cells are scarce in normal skin but can be identified by the expression of distinct keratin filaments. Merkel cells constitute a very unique population and many questions still remain as to their origin, number, proliferative capacity, and functions in cutaneous biology. The dissociation of epidermal cells from skin is a widely used technique to extract and culture keratinocytes. We took advantage of a two-step extraction method to quantify keratin-20-expressing Merkel cells among total cutaneous cells obtained from either hairy or glabrous skin biopsies. Flow cytometry analysis revealed that keratin-20-labeled Merkel cells represent between 3.6% and 5.7% of freshly dissociated basal epidermal cells. No significant differences were seen between samples derived from glabrous palmar and hairy anatomic sites, from children and adult, respectively. We also report on the presence of Merkel cells in primary and first subcultures of epidermal cells indicating their capacity to remain viable after extraction from skin of various anatomic sites. To our knowledge, this is the first demonstration of nontumorigenic human Merkel cells in culture in vitro. The persistence of a small number of Merkel cells in culture suggests that, with the development of appropriate culture conditions, these cells could be amplified and further studied to unravel long-standing questions relative to their paracrine function or epithelial origin.

Intercellular adhering junctions with an asymmetric molecular composition: desmosomes connecting Merkel cells and keratinocytes

“…Within the confinements of the epidermis, MCs can be recognized by their specific neuroendocrine vesicles (for reviews see, e.g., Cheng Chew and Leung 1994;Eispert et al 2009;Fantini and Johansson 1995;Hartschuh et al 1989a, b;Tachibana 1995), by their IFs containing certain simple epithelium keratins, of which keratin 20 is the most distinctive (for references see Introduction and Fradette et al 2003) and by their special junctions with each other and with keratinocytes. In the present study we have shown that the MC-halves of the desmosomes connecting MCs and keratinocytes generally differ by the presence of plakophilin Pkp2 as the only plakophilin present, irrespective of whether the specific MCs occur in basal or suprabasal epidermal cell layers.…”

Merkel Cell-Nerve Cell Interaction Undergoes Formation of a Synapse-like Structure in a Primary Culture

“…In fact, our previous study and others have immunohistochemically suggested that Merkel cells in vivo are closely associated with nerve terminals (Kim et al, 2001;Narisawa et al, 1991;Pasche et al, 1990). However, there has been little in vitro evidence that supports this hypothesis, because there is no suitable culture system for investigating Merkel cellnerve cell interaction (Fradette et al, 2003;Fukuda et al, 1996;Yamashita et al, 1993;Vos et al, 1991).…”

Merkel cells

“…In the presence of 10% fetal calf serum, adult MCs from human hairy skin biopsies survive for more than 1 week on a 3T3 feeder layer without a neuronal component. 52 One study describes a primary culture enriched in rat MCs after enzymatic treatment of the epidermis, followed by a coculture with neural cells. In Dulbecco's modified eagle's medium Ham's F12 medium, only sensory neurons grow their neurites toward MCs, while sympathetic neurons fail to grow onto MC clusters.…”

“…52,67 Although they are localized in the basal layer of the epidermis, their density varies between anatomical sites. 4,68 MCs are mainly found in hairy skin, 69,70 tactile areas of glabrous skin, 49 whisker pads, 62 taste buds, 71 the anal canal, 72 foot pads, 57 in eccrine glands, 73 sweat glands, 74 and in the labial epithelium and palatine mucosa.…”