M1/M2 Macrophage Skewing is Related to Reduction in Types I, V, and VI Collagens with Aging in Sun-Exposed Human Skin.

Sun-exposed, aged human skin is fragile because of collagen fragmentation and loss. We recently reported that the balance of M1 and M2 macrophages is associated with chronic inflammation and related inflammaging in sun-exposed human skin. In this study, we analyzed its role in the maintenance of collagen matrix formation by performing histological analyses of human facial skin.

IL-34 Downregulation‒Associated M1/M2 Macrophage Imbalance Is Related to Inflammaging in Sun-Exposed Human Skin.

Macrophages can be polarized into two subsets: a proinflammatory (M1) or an anti-inflammatory (M2) phenotype. In this study, we show that an increased M1-to-M2 ratio associated with a decrease in IL-34 induces skin inflammaging. The total number of macrophages in the dermis did not change, but the number of M2 macrophages was significantly decreased.

Regeneration of collagen fibrils at the papillary dermis by reconstructing basement membrane at the dermal-epidermal junction.

The epidermal basement membrane deteriorates with aging. We previously reported that basement membrane reconstruction not only serves to maintain epidermal stem/progenitor cells in the epidermis, but also increases collagen fibrils in the papillary dermis. Here, we investigated the mechanism of the latter action.

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

Daily sunlight exposure damages the epidermal basement membrane (BM) and disrupts epidermal homeostasis. Inter-follicular epidermal stem cells (IFE-SCs) regulate epidermal proliferation and differentiation, which supports epidermal homeostasis. Here, we examine how photoaging affects the function of IFE-SCs and we identify key components in their cellular environment (niche).