Glycative Stress Research
Online edition : ISSN 2188-3610
Print edition : ISSN 2188-3602
Received : July 26, 2022
Accepted : August 14, 2022
Published online : September 30, 2022
doi:10.24659/gsr.9.3_126

Review article

Skin stiffness due to decreased blood vessels induces epidermal
stem cell senescence
Ryo Ichijo
Department of Biosystems Science, Institute for Frontier Life and Medical Science, Kyoto University, Kyoto, Japan

Abstract

Keratinocytes, which make up the majority of the skin epithelium, differentiate from epidermal stem cells and migrate fromthe basement membrane to the upper layers of the skin, where they are finally shed as grime. Epidermal stem cells play animportant role for skin homeostasis by proliferative capacity and flexibility in response to wound healing and physiologicalchanges. However, factors affecting epidermal stem cell proliferation remain unresolved. In this study, we focused on Piezo1, amechano-ion channel that recognizes "stiffness" and becomes activated, and clarified the mechanism by which the mechanicalenvironment induces epidermal stem cell senescence. A new mechanism of skin aging has been identified in which Ptx3
expression from dermal fibroblasts increases with aging, which induces vascular atrophy and dermal stiffening, and induces
age-related alterations in epidermal stem cells due to long-term calcium influx via Piezo1. This finding may be useful for thedevelopment of new functional ingredients with a novel mechanism “ Ptx3 regulation.”

KEY WORDS: epidermal stem cells, skin aging, dermal stiffening, vascular atrophy, Ptx3, Piezo1

Introduction
The skin has the epidermis, dermis, and hypodermis.
The epidermis is composed of multiple cell layers at different
stages of differentiation, starting from the upper layers:
stratum corneum, granular layer, spinus layer, and basallayer. Basal cells in the basal layer maintain their function
as epidermal stem cells attached to the basement membrane.
Epidermal stem cells undergo a series of metabolic processes:
they proliferate constantly, differentiate step by step bypeeling off from the basement membrane and migrating to
the upper layers, and finally peel off as grime. Epidermal
stem cells respond flexibly to wound healing and physiologicalchanges, and their proliferative capacity can be temporarily
increased 1- 3).
It is known that epidermal stem cells lose their function
with aging, their adhesion to the basement membrane
becomes weaker, and the direction of cell division becomesabnormal 4, 5). This aging-related disorders of epidermal stem
cells is thought to be caused by internal cellular changes,
i.e., DNA damage induced by oxidative stress 6). However,

the aging changes in the environment surrounding epidermal
stem cells and their effects on epidermal stem cells have notyet been elucidated.
By focusing on the "stiffness" of the dermis underthe epidermis, this study clarified the mechanism by which
age-related alterations in the mechanical environment of
epidermal stem cells induce aging 7).

Differences between young and aged skinIn the study of differences between young and aged
mouse plantar epidermis, we found that epidermal stem
cells in aged mice showed age-related alterations, including
weakening of hemidesmosomes that support adhesion tothe basement membrane, increased perpendicular division
to the basement membrane, and ectopic expression ofdifferentiation markers. To identify the cause of this aging
disorders, gene expression in epidermal stem cells wascompared between young and aged mice. The gene group

Correspondent to: Ryo Ichijo, PhD
Department of Biosystems Science, Institute for Frontier Life and Medical Science,
Kyoto University
Sakyo-ku, Kyoto 606 -8507 Japan
TEL : +81-75-751- 4040 FAX: +81-75-771-5699
e-mail: richijo@infront.kyoto-u.ac.jp_ 12 6 _Glycative Stress Research 2022; 9 (3) : 126-128(c) Society for Glycative Stress ResearchGlycative Stress Research

whose expression was elevated in aged mice was significantly
enriched in genes related to calcium signaling. Regarding
calcium, studies using cultured cells have shown that it
induces keratinocyte differentiation and hemidesmosome
disassembly 8).
Therefore, we performed calcium in vivo imaging of
epidermal stem cells in the plantar region of living mice andfound that calcium pulses of 20 seconds or longer duration
were more frequent in aged mice than in young mice. We
hypothesized that ion channels, which are activated bysensing mechanical changes in cells, may be involved in thisphenomenon, and investigated the possibility of changes intissue stiffness to find that the dermis was stiffer in aged
mice than in young mice.
Next, we focused on Piezo1, a mechano-ion channel thatrecognizes and activates substrate "stiffness" 8). When Piezo1
was knocked out specifically in epidermal basal cells, theprolonged calcium pulse induced by aging was suppressed, as
was the aging disorders of epidermal stem cells. Thus, agerelated stiffening of the dermis induces sustained activationof Piezo1 in epidermal basal cells, which in turn induces agerelated disorders of epidermal stem cells through prolonged
calcium influx.

Effects of aging on the skin dermis
We have attempted to elucidate the causes of age-relateddermal stiffening and previously clarified that blood vessels
are important for epidermal stem cell proliferation 9).
Therefore, we examined the blood vessels in the dermis ofaging mice and found that the number of blood vessels wasreduced in the dermis of aging mice. Furthermore,
artificially increasing the number of blood vessels intransgenic mice restored the age-related stiffening of thedermis and also the aging disorders of epidermal stem cells.
Conversely, genetic modification of young mice to reduce
vascularity induced a phenotype of dermal stiffening andage-related transformation of epidermal basal cells.
Next, we attempted to identify the cause of age-related
vascular atrophy. Using a single cell RNA sequencing of thedermis of young and aged mice, it revealed the increased
cluster of fibroblasts expressing high levels of Pentraxin 3(Ptx3), a secreted factor that inhibits angiogenesis 10). In Ptx3
knockout mice, age-related vascular atrophy was suppressed,dermal stiffness was improved, and age-related disorders of
epidermal stem cells were alleviated. Furthermore, analysis
of human skin samples showed that Ptx3 accumulated morein the skin dermis of older adults than that of youngeradults.

Conclusion: Decreased blood vessels anddermal stiffening
These results reveal a novel mechanism of skin aging inwhich Ptx3 expression increases with aging from fibroblasts
in the dermis, which induces vascular reduction and dermal
stiffening, thus inducing age-related disorders of epidermal
stem cells by long-term calcium influx via Piezo1 ( Fig. 1).
The results may be useful for the development of drugs andcosmetics with new mechanisms of action “Ptx3 regulation.”

Conflict of interest declaration
The authors have no conflicts of interest to declare withrespect to this study.

Acknowledgment
This work was supported by JSPS KAKENHI Grant
Number 21K16209.

Fig. 1. Schematic of the mechanism of age-associated IFESC dysregulation.

Fig. 1. Schematic of the mechanism of age-associated IFESC dysregulatio_ 127 _Skin Stiffening and Epidermal Stem Cell Aging due to Vascular Atrophy

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