A pig model exploring the postnatal hair follicle cycle

Abstract

Introduction: The hair follicle (HF) is a micro-organ capable of regeneration. A HF cycle consists of an anagen, catagen and telogen. Abnormalities in the HF cycle can lead to many hair disorders such as hair loss. The pig is a good biomedical model, but there are few data on their HF cycle. The aim of this study was to classify the pig HF cycle and determine the feasibility of the pig as an animal model for human HF cycle.

Methods: Skin samples from 10 different postnatal (P) days Yorkshire pigs was collected to determine the key time points of the first HF cycle in pig by H&E staining, immunofluorescence staining, q-PCR and western-blot.

Results: By morphological observation and detection of markers at different stages, pig HF cycle was classified into three main periods - the first anagen until P45, catagen (P45-P85), telogen (P85-P100), and next anagen (>P100). In addition, we examined the expression of important genes AE15, CD34, Versican, Ki67 et al. related to the HF cycle at different stages of pig HF, indicating that pig and human share similarities in morphology and marker gene expression patterns of HF cycle.

Discussion: Our findings will facilitate the study of HF cycle and offer researchers a suitable model for human hair research.

Keywords: anagen; catagen; hair follicle cycle; pig model; telogen.

FIGURE 1

The anagen and catagen phases of postnatal pig HF. The identification of anagen (P18) (A), early catagen (P45) (E), mid-Catagen (P62) (I) and late Catagen (P75) (M). The Note column summarizes simple basic parameters for the HF cycle obtained via hematoxylin and eosin staining and marker gene expression. The characteristics of the Anagen and Catagen in pig HF cycle were obtained via hematoxylin and eosin staining at P18 (B), P45 (F), P62 (J), and P75 (N). Gene expression in pig HF cycle at P18 (C, D), P45 (G, H), P62 (K, L), and P75 (O, P) via immunofluorescence. Scale bars: 100 μm.

FIGURE 2

The telogen and the second anagen phases of postnatal pig HF. The identification of telogen (P85) (A) and second anagen (P100) (E). The Note column summarizes simple basic parameters for the HF cycle obtained via hematoxylin and eosin staining and marker gene expression. The characteristic of the pig HF cycle was obtained via hematoxylin and eosin staining at P85 (B) and P100 (F). Gene expression P85 (C, D), P100 (G, H) in pig HF cycle at different stages via immunofluorescence. Scale bars: 100 μm.

FIGURE 3

Localization of expression of key genes at different stages of hair follicle cycle development. (A) Immunofluorescence merge of AE15 in different time periods. (B) Immunofluorescence merge of CD34 in different time periods. (C) Immunofluorescence merge of Versican in different time periods. (D) Immunofluorescence merge of K14 in different time periods. a, b, c, d, e, and f show different periods. The blue fluorescence is DAPI, and the red fluorescence is the target gene. Scale bars: 100 μm.

FIGURE 4

Expression of genes in the pig HF cycle. The mRNA expression of Wnt10b (A), Wnt5a (B), LEF1 (C), SHH (D), LHX2 (E), α-SMA (F) in Anagen, Catagen and Telogen of HF cycle was detected by q-PCR. Data are presented as the mean ± SEM.*P< 0.05, **P< 0.01. ***P< 0.001 (Student’s t-test, n = 3 for each group).

FIGURE 5

HF cycle development during postnatal in pigs. The first HF cycle of postnatal pigs has been summarized into three main periods. The anagen phase of postnatal pig HF is maintained up to P45; early catagen (P45–P62); mid-catagen (P62–P75); late catagen (P75–P85); telogen (P85–P100); and second anagen (> P100). Stages of the postnatal hair cycle are depicted. DP, dermal papilla; IRS, inner root sheath; ORS, outer root sheath.