Decrease of laminin‑511 in the basement membrane due to photoaging reduces epidermal stem/progenitor cells

Here, the authors examine how photoaging affects the function of Inter-follicular epidermal stem cells (IFE-SCs) which regulate epidermal proliferation and differentiation. It is known that daily sunlight disrupts epidermal homeostasis and the authors found that sun-exposed skin showed a decrease of MCSP-positive and β1-integrin-positive cells concomitantly with a decrease of laminin-511 at the dermal-epidermal junction (DEJ), as compared with sun-protected skin. Higher levels of laminin-511 were associated with increased colony formation efficiency, higher expression levels of MCSP as well as other stem cell markers in human skin. UVB exposure to cultured human skin impaired laminin-511 integrity at the dermal-epidermal junction and reduced MCSP-positive basal epidermal cells as well as K15-positive cells. Combined treatment with matrix metalloproteinase and heparanase inhibitors protected the integrity of laminin-511 and inhibited the reduction of MCSP-positive cells and K15-positive cells. These results suggest that photoaging may reduce the levels of MCSP-positive and K15-positive epidermal stem/ progenitor cells in the epidermis via loss of laminin-511 at the dermal-epidermal junction.