Morphogenesis- and hair cycle-dependent expression of trichohyalin, peptidylarginine deiminase type III and deiminated trichohyalin in rat dorsal skin hair follicles

Previously, we have reported the localizations of trichohyalin (THH), peptidylarginine deiminase (PAD; EC 3.5.3.15) type III and deiminated THH in the inner root sheath and medulla cells of infant rat dorsal skin hair follicles, showing the functional involvement of PAD in the formation of the rigid structures of the inner root sheath and medulla of the hair follicle. To further elucidate the function of PAD type III in the formation of the rigid structure, we performed immunocytochemical studies on its expression during the first and second hair cycle of the rat dorsal skin hair follicle. During the first hair cycle, THH and PAD type III appeared coincidently in the cone-shaped inner root sheath of the developing hair follicle before the appearance of the deiminated THH. In the catagen of the first hair follicle, the immunoreactivities of THH and deiminated THH were deteriorated and completely disappeared in the telogen. During the second hair cycle, big hair was developed, the cortex of which was about four-fold thicker and the follicle was about 1.5-fold longer than those of the small hairs developed during the first hair cycle. In the matured big hair follicle, THH was detected in the inner root sheath and in the medulla from the bulb region to the middle follicle region. In contrast, deiminated THH was intensely detected in the inner root sheath and medulla from the middle follicle region to the end of the follicle or hair shaft, although it was also detected faintly in Henle's layer of the inner root sheath from the upper bulb region to the middle follicle region. PAD type III in the second hair cycle was detected in the inner root sheath from the lower bulb region and in the medulla cells from the region in contact with the dermal papilla, and also in the cortex cells from the lower bulb region, but not in the outer root sheath. These observations indicate that THH and PAD type III are expressed coincidentally at the early stage of the anagen, but the deimination of THH occurs later after a time-lag, suggesting that the additional factor might be involved in triggering the reaction.