Alopecia X, cyclical flank alopecia and follicular dysplasia: expression of p63 in canine hair follicle

Skin diseases characterized by alopecia are generally associated with a deregulation of the Hair Cycle (HC) or an abnormal development of the Hair Follicle (HF), although their pathogenesis is not completely defined. Adult skin contains several reservoirs of stem cells (SCs) located in the epidermis, HFs and probably sebaceous glands. P63, a member of the p53 family of proto-oncogenes, is a transcription factor that is likely to play a key role in regulating self-renewal and long-term proliferative capacity of SCs [1]. P63 is also important in skin development and homeostasis, by promoting cell proliferation in basal and suprabasal epidermal cells, as well as in the outer root sheat (ORS) and matrix of HFs [2]. The immunohistochemical evaluation of p63 expression in the scalp of affected (frontal) and unaffected (occipital) skin of human patients with androgenetic alopecia showed that the root sheaths from occipital skin had significantly higher expression of p63 in comparison to frontal areas [3]. The aim of our study was to evaluate the immunohistochemical expression of p63 in 15 necropsy samples of canine normal skin and 16 skin biopsy samples from dogs affected by Alopecia X (n=10), Cyclical flank alopecia (n=4) and Canine follicular dysplasia (n=2), in order to determine if this molecule may be involved in the pathological mechanisms of HC arrest and if there are differences in p63 expression between the various types of canine alopecia. The number of p63-positive nuclei in HF cells for each sample was calculated in 10 randomly selected high-power (×400) fields, counting at least 1000 positive nuclei, and expressed as a percentage. P63 expression was only detectable in the ORS cells and bulbs of HFs, with a significantly higher nuclear score in canine normal skin (89.9%; +/- 2%) when compared to affected skin (76.3%; +/- 4,7) (p