Immunohistochemical localization of fibroblast growth factor 18 in hair follicles of healthy beagle dogs

Abstract

Increasing emphasis is being placed on the role of fibroblast growth factors (FGFs) in hair follicle cycling. In mice, expression of FGF18 mRNA peaks during the late telogen phase, leading to the hypothesis that FGF plays a role in anagen induction. There are no data on the presence of FGF18 in dogs. The main objective of this study was to identify and locate FGF18 in the canine hair follicle. The second objective was to assess potential differences in FGF18 concentration between biopsies taken in winter and summer, shoulder and flank regions, and between different sexes. Skin tissue from 10 healthy beagle dogs (three intact females, three spayed females and four intact males) was collected from the shoulder and flank. The biopsies were collected in February and August on day 0, after which the dogs were clipped and biopsies collected again from the shoulder and flank on days 1, 3, 7 and 17. Paraffin sections (4 μm thick) of the biopsies were stained with an anti-FGF18 antibody. The FGF18-positive cells were counted in the hair follicle epithelium from seven follicular units of each biopsy. Fibroblast growth factor 18 was detected as granular cytoplasmatic staining in follicles at the level of the inner root sheath, and rarely in the outer root sheath and dermal papilla. It was also detected in the apocrine glands, in arrector pili muscles and in vascular endothelial cells. There was no statistical difference in the number of FGF18-positive cells or follicles between sexes, different anatomical locations, seasons or the consecutive days of sampling.

Immunohistochemical evaluation of fibroblast growth factor 18 in canine recurrent flank alopecia

“…These results confirm that FGF18 protein is present in anagen hair follicles, as previously reported 1 . We could not demonstrate a peak in FGF18 protein immediately prior to initiation of anagen.…”

“…We recently published a study demonstrating the presence of fibroblast growth factor 18 (FGF18) protein in the hair follicle of normal beagle dogs 1 . Kawano et al.…”

“…Immunohistochemical staining and analysis was performed as before, and the localization of FGF18 was identical to our previous study 1 . Briefly, FGF18 was detected as a fine granular cytoplasmic staining in the hair follicles at the level of the inner root sheath and occasionally in the outer root sheath and the dermal papilla.…”

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“…3 These results confirm that FGF18 protein is present in anagen hair follicles, as previously reported. 1 We could not demonstrate a peak in FGF18 protein immediately prior to initiation of anagen. As our study used an immunohistochemical method, it is possible that the presence of FGF18 protein in anagen follicles is preceded by FGF18 mRNA expression.…”

“…identical to our previous study. 1 Briefly, FGF18 was detected as a fine granular cytoplasmic staining in the hair follicles at the level of the inner root sheath and occasionally in the outer root sheath and the dermal papilla. The follicles showing positive staining were anagen follicles.…”