Protective effect and mechanism of lycium barbarum polysaccharide against UVB-induced skin photoaging.

Background: Cellular senescence can be categorized into two main types, including exogenous and endogenous aging. Photoaging, which is aging induced by ultraviolet (UV) radiation, significantly contributes to exogenous aging, accounting for approximately 80% of such cases. Superoxide Dismutase (SOD) is a class of antioxidant enzymes, with SOD2 being predominantly localized in the mitochondrial matrix. Ultraviolet radiation (UVR) inhibits SOD2 activity by acetylating the key lysine residues on SOD2. Sirtuin3 (SIRT3), the principal mitochondrial deacetylase, enhances the anti-oxidant capacity of SOD2 by deacetylating. Lycium barbarum polysaccharide (LBP) is the main bioactive component extracted from Lycium barbarum (LB). It has been reported to have numerous potential health benefits, such as anti-oxidation, anti-aging, anti-inflammatory and anti-apoptotic properties. Furthermore, LBP has been shown to regulate hepatic oxidative stress via the SIRT3-SOD2 pathway. The aim of this study was to construct a UVB-Stress-induced Premature Senescence (UVB-SIPS) model to investigate the protective effects and underlying mechanisms of LBP against UVB-induced skin photoaging.

Methods: Irradiated with different UVB doses to select the suitable dose for constructing the UVB-SIPS model. Cell morphology was observed using a microscope. The proportion of senescent cells was assessed by senescence-associated β-galactosidase (SA-β-gal) staining. Cell viability was studied using the Cell Counting Kit-8 (CCK-8). Intracellular levels of reactive oxygen species (ROS) were observed using flow cytometry and an inverted fluorescence microscope. Expression of γ-H2AX was investigated using flow cytometry. Western blot (WB) was used to verify the expression of senescence-associated proteins (p21, p53, MMP-1, and MMP-3). Enzyme-Linked Immunosorbnent Assay (ELISA) was used to measure pro-inflammatory cytokines levels (IL-6, TNF-α). WB was also used to analyze the expression of SIRT3, SOD2, and Ac-SOD2, and a specific kit was employed to detect SOD2 activity.

Results: Our results suggested that the UVB-SIPS group pre-treated with LBP exhibited a reduced proportion of cells positive for SA-β-gal staining, mitigated production of intracellular ROS, an amelioration in γ-H2AX expression, and down-regulated expression of senescence-associated proteins and pro-inflammatory cytokines as compared to the UVB-SIPS group. Moreover, in contrast to the control group, the UVB-SIPS group showed regulated SIRT3 expression and SOD activity, elevated Ac-SOD2 expression and an increased ratio of Ac-SOD2/SOD2. However, the UVB-SIPS group pre-treated with LBP showed an upregulation of SIRT3 expression and enhanced SOD activity, a reduction in AC-SOD2 expression, and a decreased ratio of AC-SOD2/SOD2, compared to the untreated UVB-SIPS group. Additionally, the photo-protective effect of LBP was diminished following treatment with 3-TYP, a SIRT3-specific inhibitor. This study suggested that LBP, a natural component, exhibits anti-oxidant and anti-photoaging properties, potentially mediated through the SIRT3-SOD2 pathway.