EPIDERMIS AND HAIR FOLLICLE IN BOVINE SKIN EXPRESS THE LEPTIN HORMONE AND ITS RECEPTOR

Leptin (Ob) is a hormone that acts through the activation of the specific receptor Ob-R. It is mainly secreted by visceral and subcutaneous adipose tissue and represents the first known adipokine [1]. Ob is a pleiotropic molecule and plays an important role in the skin, where it stimulates keratinocytes to proliferate and intervenes in the regulation of wound healing processes. It also participates in the control of hair follicle morphogenesis and its cycles of growth, regression, and rest [2]. Ob may act through endocrine, paracrine and autocrine mechanisms. While it is secreted by skin structures including epidermis and hair follicles, intradermal adipose tissue also seems to have a role in Ob secretion and accordingly in the control of the hair follicle cycle in mice and humans [3]. In this work, the morphological characteristics of the skin in bovine species were evaluated by Hematoxylin-Eosin and Oil Red O staining to investigate the presence and extension of intradermal adipose tissue that may be involved in Ob secretion. Moreover, Ob and Ob-R expressions were analyzed by means of RT-PCR and immunohistochemistry. Through the morphological analysis, a high and thick dermis without adipocytes was observed. Hair follicles and glands were located in the proximal part of the skin, beneath the epidermis, while a thick layer of connective tissue, lacking adipose cells, separated these structures by subcutis. RT-PCR gave a positive outcome, evidencing the transcripts for both molecules in the bovine skin samples examined. By immunohistochemistry, Ob and its receptor were observed in the epidermis and in the outer root sheath of hair follicles during the follicular cycle. The epidermis abundantly expressed Ob; while all layers of cells were involved, the suprabasal layers expressed a stronger signal. Ob-R was observed in the cells of the basal layer. As regards hair follicles, both Ob and Ob-R were expressed by the outer root sheath of hair follicles. Staining mainly extended into the regions of the infundibulum and isthmus while the bulb was negative. Immunostaining persisted in all stages of hair follicles. The expression of Ob-R in the bovine skin proves that Ob acts on this peripheral organ. The identification of Ob in the epidermis and hair follicle epithelium attests that Ob may act through a paracrine and autocrine mechanism on these structures even if an endocrine mechanism cannot be excluded. The absence of adipocytes around hair follicles and, broadly, in all the dermis indicates that the intradermal adipose tissue does not exist in bovine and accordingly cannot exert paracrine control on the hair follicle. The identification of the Ob system in bovine skin provides important information for properly understanding the biological mechanisms that regulate skin structures, and well as for comparing animal species and highlighting their differences.