AN IMMUNOHISTOCHEMICAL STUDY EVIDENCES GHRELIN AND ITS RECEPTOR IN THE HAIR FOLLICLE OF THE SHEEP

Ghrelin is a peptide hormone discovered in 1999. It is mainly secreted by the endocrine cells of the gastrointestinal tract and acts by binding to a specific receptor. Ghrelin presents a wide tissue distribution and is involved in numerous central and peripheral actions including hormonal, orexigenic, neurological, cardiovascular, and immunological activities (1).In this work, the expression and localization of ghrelin and its receptor was investigated in the skin of sheep by means of immunohistochemistry. The immunohistochemical reaction was performed on ovine skin samples collected from the neck ventral region of healthy animals regularly slaughtered at the abattoir. Samples were fixed in formalin and embedded in paraffin. Dewaxed sections were incubated with 3% peroxidase-blocking solution and with normal goat serum to block the endogenous peroxidase activity and non-specific binding respectively. Successively, serial sections were incubated overnight with polyclonal anti-Ghrelin and anti-Ghrelin receptor antibodies (Abcam Cambridge UK). The reaction was visualized using Vectastain ABC kit and DAB (Vector Laboratories, Burlingame, CA, USA). The analyses performed evidenced a clear and intense immunostaining for both ghrelin and its receptor in the ovine skin. Staining was mainly localized in the hair follicles (HF). Positivity to ghrelin was observed in a short area of the HF at the level of the soprabulbar region; it involved the inner cells of the outer root sheath, including the companion layer, and the cells of the inner root sheath. The receptor, instead, was observed in all cell layers of the outer root sheath and extended more than ghrelin, from the soprabulbar region to the isthmus. Other than HF, ghrelin showed a weak positivity in the soprabasal layers of the epidermis which nevertheless were negative to the receptor. Finally, the receptor was clearly expressed by the cells of the sweat glands. At present, the skin is described as an endocrine organ since it is the target of several endocrine signals and, at the same time, it is itself capable of producing substances with hormone-like activity (2). The study of ghrelin and, more in general, of adipokines at the skin level represent an interesting and current topic for domestic animals including sheep. It was shown that some adipokines, such as leptin and adiponectin, are widely involved in the metabolism of the skin, and, more specifically, of the HF in both physiological and pathological conditions (3, 4). Ghrelin is a recently discovered molecule and there are until now a few surveys on ghrelin at the skin level. However the strong immunohistochemical expression of ghrelin and its receptor evidenced in the HF of the sheep let us to suppose that ghrelin may have a role in the HF activity probably acting through a paracrine or autocrine mechanism