Attenuation of UV-induced skin photoaging in rats by walnut protein hydrolysates is linked to enhancement of antioxidant capacity, modulation of MAPK/AP-1/TGF-β/Samd signaling pathway, and promotion of type I procollagen synthesis

There is growing evidences that prevention of skin photoaging by oral administration of food-derived proteins hydrolysates is intricately linked to its alleviation against oxidative stress through modulation of signaling pathway. Previously, the walnut proteins hydrolysates (WPH) was prepared by enzymatic hydrolysis in our group and exhibited excellent anti-photoaging effect through regulation of extracellular matrix metabolism and NF-κB signal pathway. However, its response to oxidative stress and cascade mechanism remains unknown. In present study, Sprague-Dawley rats were exposed periodically to UV irradiation and orally administrated with WPH to further examine the effects of WPH on redox state, MAPK/AP-1/TGF-β/Samd signal pathway, type Ⅰ procollagen synthesis, and histopathological impairments in photoaging skin. Intervention with WPH for 18 weeks significantly alleviated the photoaging morphology, enhanced the antioxidant components, down-regulated the phosphorylation levels of extracellular signal-regulated kinase (ERK), C-Jun N-terminal kinase (JNK and p38 protein) in photoaging tissue, while the significant alterations of gene expression levels of ERK, JNK and p38 were not observed. Meanwhile, WPH significantly activated TGF-β/Samd signaling pathway and type Ⅰ procollagen production. Furthermore, histopathological analysis illustrated that WPH predominately attenuated epidermal hyperplasia, reduced inflammatory filtration, and promoted deposition of collagen fibers in photoaging skin. Altogether, the underlying mechanism of WPH attenuating skin photoaging might lie in the synergistic modulation by elevating antioxidant capacity, modulating MAPK/AP-1/MMP-1/TGF-β/Samd signal pathway, stimulating synthesis of type Ⅰ procollagen, and restoring impaired architecture structure. Our findings suggest that WPH is a promising agent for preventing skin photoaging.