Wound Induced Hair Neogenesis - A Novel Paradigm for Studying Regeneration and Aging.

Myan Bhoopalam,Luis A Garza,Sashank K Reddy

doi:10.3389/fcell.2020.582346

Myan Bhoopalam, Luis A Garza + Show 1 more

Open Access

https://doi.org/10.3389/fcell.2020.582346

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Abstract

Hair follicles are the signature dermal appendage of mammals. They can be thought of as mini-organs with defined polarity, distinct constituent cell types, dedicated neurovascular supply, and specific stem cell compartments. Strikingly, some mammals show a capacity for adult hair follicle regeneration in a phenomenon known as wound-induced hair neogenesis (WIHN). In WIHN functional hair follicles reemerge during healing of large cutaneous wounds, and they can be counted to provide an index of regeneration. While age-related decline in hair follicle number and cycling are widely appreciated in normal physiology, it is less clear whether hair follicle regeneration also diminishes with age. WIHN provides an extraordinary quantitative system to address questions of mammalian regeneration and aging. Here we review cellular and molecular underpinnings of WIHN, explore known age-related changes to these elements, and present unanswered questions for future exploration.

Highlights

Regeneration in mammalian systems is limited when compared to those of other phyla
Since some of these same hair follicle stem cells (HFSCs) are involved in hair follicle neogenesis, it will be interesting to examine whether similar abortive regeneration occurs in response to full thickness wounds that normally produce wound induced hair neogenesis (WIHN)
The bulge is the area of the hair follicle that contains long-lived HFSCs responsible for hair renewal throughout life – cycles of anagen, catagen, and telogen (Cotsarelis et al, 1990; Blanpain and Fuchs, 2006). Given their key early role in healing of the intrafollicular epidermis, it was surprising that Krt15+ bulge stem cells from adjacent HFs were shown to be insignificant contributors to hair follicle regeneration in WIHN (Ito et al, 2005, 2007). As these cells are critical for normal hair follicle cycling, their lack of contribution to WIHN reveals an important difference between physiologic renewal and damage-induced regeneration

Summary

Introduction

Regeneration in mammalian systems is limited when compared to those of other phyla. In making this comparison, we distinguish between renewal and regeneration. While hair follicle stem cells (HFSCs) were found to be present in near normal numbers in the old mice and had retained their identity, they engaged in aberrant cycles of hair follicle renewal in response to wounding. Since some of these same HFSCs are involved in hair follicle neogenesis, it will be interesting to examine whether similar abortive regeneration occurs in response to full thickness wounds that normally produce WIHN.

Results

Conclusion