Comparison between human fetal and adult skin

Abstract

Healing of early-gestation fetal wounds results in scarless healing. Since the capacity for regeneration is probably inherent to the fetal skin itself, knowledge of the fetal skin composition may contribute to the understanding of fetal wound healing. The aim of this study was to analyze the expression profiles of different epidermal and dermal components in the human fetal and adult skin. In the human fetal skin (ranging from 13 to 22 weeks' gestation) and adult skin biopsies, the expression patterns of several epidermal proteins (K10, K14, K16, K17, SKALP, involucrin), basement membrane proteins, Ki-67, blood vessels and extracellular matrix proteins (fibronectin, chondroitin sulfate, elastin) were determined using immunohistochemistry. The expression profiles of K17, involucrin, dermal Ki-67, fibronectin and chondroitin sulfate were higher in the fetal skin than in adult skin. In the fetal skin, elastin was not present in the dermis, but it was found in the adult skin. The expression patterns of basement membrane proteins, blood vessels, K10, K14, K16 and epidermal Ki-67 were similar in human fetal skin and adult skin. In this systematic overview, most of the differences between fetal and adult skin were found at the level of dermal extracellular matrix molecules expression. This study suggests that, especially, dermal components are important in fetal scarless healing.

Fig. 1

Histology of 14 and 20 weeks’ gestation fetal skin and of adult skin. At 14 weeks, the epidermis consisted of a basal layer, an intermediate cell layer and periderm. At 20 weeks, the number of intermediate cells layers was increased and developing hair follicles were visible. The adult skin contained basal, spinous, granular and cornified layers. Scale bars 100 μm

Fig. 2

Proliferation during fetal skin development and in adult skin. a Proliferation index in the fetal and adult epidermis. The proliferation index (PI) was defined as the number of Ki-67-positive basal cells divided by the total number of basal cells × 100%. Each dot represents the mean PI of three randomly chosen regions in each section. b The total number of cells and c Ki-67-positive cells per mm² in the dermis of fetal and adult skin. Each dot represents the mean total number of cells per mm² or the mean number of Ki-67-positive cells per mm² of three randomly chosen regions in each section. The broken lines indicate the median observation in each group, except for the group of 13–14 weeks in which the mean observation of two skin samples is indicated. Statistical significance was determined by Mann–Whitney U. *P < 0.05

Fig. 3

Presence of keratin 17 (a–c) and involucrin (d–f) in 14 and 19 weeks’ gestation fetal skin and of adult skin. At 14 weeks, K17 was detected in the basal layer, some cells of the intermediate layer and in the periderm (a). At 19 weeks, K17 was visible in some cells of the basal and intermediate layers, in the periderm and in developing hair follicles (b). Adult skin was negative for K17 (c). In the fetal skin, involucrin was observed in the suprabasal layers (d, e). Involucrin was present in the granular layers of adult epidermis (f). Scale bars 100 μm

Fig. 4

Presence of blood vessels in 16 week’s gestation fetal skin (a), in 18 weeks’ gestation skin (c) and in adult skin (b, d). In fetal and adult dermis, CD31 (a, b) and α-smooth muscle actin (c, d) were detected in small blood vessels in the upper part of the dermis and in larger blood vessels in the lower part of the dermis. Scale bars 100 μm

Fig. 5

Presence of chondroitin sulfate (a, b), elastin (c, d) and fibronectin (e, f) in 18 weeks’ gestation fetal skin and in adult skin. In the fetal skin, CS was present in the upper part of the dermis (a). In the adult skin, CS was only visible around the basement membrane zone (b). Elastin was not present in early-gestation fetal skin (c), but it was observed in the adult skin (d). FN was detected in the entire fetal skin (e), but it was only present in the basement membrane zone in the adult skin (f). Scale bars 100 μm