Far-infrared suppresses skin photoaging in ultraviolet B-exposed fibroblasts and hairless mice.

Hui-Wen Chiu,Yung-Ho Hsu,Yi-Jie Chen,Cheng-Hsien Chen,Ying-Jan Wang

doi:10.1371/journal.pone.0174042

Abstract

Ultraviolet (UV) induces skin photoaging, which is characterized by thickening, wrinkling, pigmentation, and dryness. Collagen, which is one of the main building blocks of human skin, is regulated by collagen synthesis and collagen breakdown. Autophagy was found to block the epidermal hyperproliferative response to UVB and may play a crucial role in preventing skin photoaging. In the present study, we investigated whether far-infrared (FIR) therapy can inhibit skin photoaging via UVB irradiation in NIH 3T3 mouse embryonic fibroblasts and SKH-1 hairless mice. We found that FIR treatment significantly increased procollagen type I through the induction of the TGF-β/Smad axis. Furthermore, UVB significantly enhanced the expression of matrix metalloproteinase-1 (MMP-1) and MMP-9. FIR inhibited UVB-induced MMP-1 and MMP-9. Treatment with FIR reversed UVB-decreased type I collagen. In addition, FIR induced autophagy by inhibiting the Akt/mTOR signaling pathway. In UVB-induced skin photoaging in a hairless mouse model, FIR treatment resulted in decreased skin thickness in UVB irradiated mice and inhibited the degradation of collagen fibers. Moreover, FIR can increase procollagen type I via the inhibition of MMP-9 and induction of TGF-β in skin tissues. Therefore, our study provides evidence for the beneficial effects of FIR exposure in a model of skin photoaging.

Highlights

Chronic exposure to ultraviolet (UV) irradiation is the major cause of skin damage that leads to premature aging of the skin, which is called photoaging
The results showed that transforming growth factor-β (TGF-β) and FIR treatment did not cause cell proliferation or cell death (Fig 1A)
These results indicated that FIR treatment induced mild collagen synthesis but did not affect the viability of fibroblasts

Summary

Introduction

Chronic exposure to ultraviolet (UV) irradiation is the major cause of skin damage that leads to premature aging of the skin, which is called photoaging. Far-infrared suppresses skin photoaging collagen molecule is characterized by amino- and carboxy-terminal propeptide sequences. These form the central triple helical structure of procollagen and collagen. UV irradiation generates increased reactive oxygen species (ROS) levels in the skin and amplifies signals, which lead to the activation of mitogen-activated protein kinases (MAPKs) and phosphatidylinositol-3-kinase (PI3K)/Akt [6, 7]. These kinases stimulate MMPs expression and can cause collagen degradation [8]

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