Skin photoaging is a multifaceted dermatological disorder induced by extrinsic influences (mainly excessive/prolonged exposure to ultraviolet (UV) radiation and intrinsic factors (e.g. oxidative stress), involving progressive disruption of epidermal homeostasis and dermal extracellular matrix (ECM) integrity. This study aimed to systematically evaluate the protective effects of polysaccharides from Sargassum fusiforme (DSFP-45) against UV-induced epidermal and dermal photoaging using UVB-irradiated HaCaT cells and UVA-irradiated HSF cells at concentrations of 125-500 μg/mL, and UVA + UVB-irradiated BALB/c nude mice at oral doses of 100-200 mg/kg/day. Results showed that DSFP-45 effectively alleviated UVB-induced oxidative stress, with intracellular ROS levels reduced by approximately 75% compared with the Model group, while attenuating DNA damage, inflammatory responses, keratinocyte-derived pro-melanogenic signaling pathways and improving skin barrier function in epidermal cells. In dermal fibroblasts, DSFP-45 preserved redox balance, reduced cellular senescence, and suppressed matrix metalloproteinase expression, with MMPs expression reduced by approximately 30%-50% compared with the Model group, thereby preserving ECM homeostasis. In vivo results further confirmed protective effects of DSFP-45 against UV-induced skin damage. DSFP-45 markedly preserved skin structural integrity, reducing UV-induced epidermal thickness by approximately 50% compared with the Model group, while alleviating dermal matrix loss and preserving collagen content in photoaged mice. Accordingly, DSFP-45 effectively attenuated UV-induced skin structural abnormalities and helped preserve skin architecture during photoaging, indicating its potential as a marine-derived functional ingredient for skin health.
