Identification of Merkel cells associated with neurons in engineered skin substitutes after grafting to full thickness wounds

• Published in: PloS one Vol. 14; no. 3; p. e0213325
• Main Authors: Hahn, Jennifer M, Combs, Kelly A, Lloyd, Christopher M, McFarland, Kevin L, Boyce, Steven T, Supp, Dorothy M
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 05.03.2019; Public Library of Science (PLoS)
• Subjects: Adolescent; Animals; Antigens; Artificial skin; B cells; Biology and Life Sciences; Biopolymers; Burns; Cells (Biology); Cells, Cultured; Composition; E-cadherin; EDTA; Epidermis; Fibroblasts; Fibroblasts - cytology; Fibroblasts - physiology; Grafting; Grafts; Health aspects; Histocompatibility antigen HLA; HLA antigens; Humans; Identification and classification; Innervation; Keratin; Keratinocytes; Keratinocytes - cytology; Keratinocytes - physiology; Leukocytes; Localization; Markers; Medicine and Health Sciences; Merkel cells; Merkel Cells - cytology; Merkel Cells - physiology; Mice; Mice, SCID; Mortality; Neurons; Neurons - cytology; Neurons - physiology; Patient outcomes; Patients; Pediatrics; Physiological aspects; Polymers; Quality of life; Research and Analysis Methods; Scars; Sensory receptors; Skin; Skin & tissue grafts; Skin grafts; Skin Transplantation - methods; Skin, Artificial; Substitutes; Surgery; Synaptophysin; Tissue Engineering - methods; Touch; Touch - physiology; Transplantation; Wound Healing; United States > US; Ohio
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0213325

Engineered skin substitutes (ESS), prepared using primary human fibroblasts and keratinocytes with a biopolymer scaffold, were shown to provide stable closure of excised burns, but relatively little is known about innervation of ESS after grafting. This study investigated innervation of ESS and, specifically, whether Merkel cells are present in healed grafts. Merkel cells are specialized neuroendocrine cells required for fine touch sensation in skin. We discovered cells positive for keratin 20 (KRT20), a general marker for Merkel cells, in the basal epidermis of ESS after transplantation to mice, suggesting the presence of Merkel cells. Cells expressing KRT20 were not observed in ESS in vitro. However, widely separated KRT20-positive cells were observed in basal epidermis of ESS by 2 weeks after grafting. By 4 weeks, these cells increased in number and expressed keratins 18 and 19, additional Merkel cells markers. Putative Merkel cell numbers increased further between weeks 6 and 14; their densities varied widely and no specific pattern of organization was observed, similar to Merkel cell localization in human skin. KRT20-positive cells co-expressed epidermal markers E-cadherin and keratin 15, suggesting derivation from the epidermal lineage, and neuroendocrine markers synaptophysin and chromogranin A, consistent with their identification as Merkel cells. By 4 weeks after grafting, some Merkel cells in engineered skin were associated with immature afferents expressing neurofilament-medium. By 8 weeks, Merkel cells were complexed with more mature neurons expressing neurofilament-heavy. Positive staining for human leukocyte antigen demonstrated that the Merkel cells in ESS were derived from grafted human cells. The results identify, for the first time, Merkel cell-neurite complexes in engineered skin in vivo. This suggests that fine touch sensation may be restored in ESS after grafting, although this must be confirmed with future functional studies.