The Anti-photoaging Effect And Mechanism Of Dietary N-3 Polyunsaturated Fatty Acid Supplementation Based On SKH-1 Hairless Mouse Model

Background As the largest organ in the human body contact with the environment,the aging of skin is easily affected by the external environment,among which Ultraviolet radiation(UVR)has the greatest influence.Photoaging caused by UVR is basically equivalent to exogenous aging.The appearance of photoaging is characterized by deep skin wrinkles,telangiectasia etc.The histological features are epidermal cell proliferation,abnormal synthesis and degradation of dermal extracellular matrix,especially collagen,and then the occurrence of AK,basal cell carcinoma,squamous cell carcinoma and other skin tumors.So delay photoaging is of great significance to the prevention and treatment of skin tumors.Dietary regulation as a convenient and safe means of disease prevention has been paid more and more attention.N-3 polyunsaturated fatty acids(n-3 PUFA)can assist treatment of rheumatoid arthritis,psoriasis,asthma,cardiovascular disease,cancer and other diseases,and on the nervous system,immune system,visual system,and the skin play a protective effect.Previous studies in this study found that dietary supplementation with n-3 PUFA could reduce acute injury and acute inflammation caused by UVR.Unlike acute UV damage,photoaging is a chronic effect of low doses of UVR accumulated over time.In this study,fish oil was used as the supplementary source of n-3 PUFA to investigate whether long-term supplementation of n-3 PUFA could delay photoaging,the lowest effective dose and the mechanism of action.Objective In this study,the long-term low-dose UV cumulated SKH-1 hairless mouse photoaging model was used to verify the delayed effect of fish oil as a dietary supplement source of n-3 PUFA on the skin photoaging of mice,and the dose-effect relationship and the mechanism were exploredMethods With herring oil(rich in EPA and DHA)as the source of n-3 PUFA,we ordered 5 kinds of special feed with different concentrations of fish oil.The proportion of fish oil in lipid was 0%,9.7%,19.4%,38.8% and 77.6%,respectively.The rest of the nutrients were the same as normal mouse feed.50 SKH-1 mice were randomly divided into 5 groups for special dietary intervention with n-3 PUFA concentration gradient.At the third week of the special diet,5 mice were randomly selected from each group to establish the UVR induced photoaging model,and the back skin of the mice was irradiated with SSO3 AB UVR therapy apparatus,and the photoaging model was completed after 8 weeks of continuous irradiation.The other 5 mice were not illuminated and were negative controls.In the process of UVR mode,dermoscopic detection and visual observation were carried out,and standard photos were retained.Indicators such as skin wrinkles,pigmentation and dryness were recorded,and photoaging was scored.At the end of the UVR modeling,the back skin of the mice was selected to retain tissue samples.GC-MS was used to detect the content of medium and long chain fatty acids in skin tissue,and the content of n-3 PUFA(such as DHA,EPA,ALA,etc.)and the relative ratio of n-3/n-6 PUFA in the skin were analyzed to determine the effect of dietary supplementation of n-3 PUFA on the skin.The structural changes of epidermis and dermis of photoaged skin were evaluated by histopathology and special staining.By immunohistochemical evaluation of different concentrations of n-3 PUFA dietary to skin immune cells(T cells,B cells)and the effect of taking enzyme-linked immunosorbent analysis(Enzyme linked immunosorbent assay,ELISA)assessment of different concentrations of n-3 PUFA dietary inflammatory factor to skin the TNF-α,IL-6,the expression of PGE2,so as to explore the n-3 PUFA optical effect of chronic inflammation in the process of aging.Therefore,the activation of MAPK pathway and the synthesis of matrix metallo proteinases(MMPs)were studied by Western Blot to explore the possible mechanism of n-3 PUFA.Results Dermoscopy and general observation showed that: photoaging performance: With the increase of n-3 PUFA content,the mice with n-3 PUFA content of 9.7%,19.4%,38.8% and 77.6% in UV-induced photoaging mice had fewer deep skin wrinkles than those with 0% of fish oil content,and the group of 77.6% had the least deep skin wrinkles.The area of dorsal erythema in group 38.8% and group 77.6% was significantly smaller than that in group 0%,group 9.7% and group 19.4%.Histopathology and special staining showed that the skin of photoaged mice was thickened,epidermal cells were overproliferated,and dermal collagen was disordered.Compared with 0% group,9.7% group and 19.4% group,the photoaged mice with n-3 PUFA content in group 38.8% and group 77%showed slight epidermal thickening and dermal collagen disorder.ELISA showed that the expression of inflammatory factors such as il-6,PGE2 and TNF-PCR in the skin of photoaged mice was significantly increased compared with normal mice,and the expression of TNF-αin the skin of photoaged mice with n-3 PUFA content of 77.6% was significantly decreased compared with that in the 0% group.However,the expression of il-6 and PGE2 did not significantly differ with the concentration of fish oil.Immunohistochemistry showed that UVR had a certain inhibitory effect on the number of T and B cells in the superficial dermis,but the number of T and B cells in the skin of mice fed with different n-3 PUFA concentrations was significantly different.The phosphorylation and activation degree of MAPK pathway gradually decreased with the increase of fish oil concentration,and matrix metalloproteinases-1(MMP-1)also showed a decreasing trend with the increase of n-3 PUFA concentration.According to research,UVR can induce the activation of MAPK pathway and promote the synthesis of MMP-1.By inhibiting the activation of MAPK pathway,it can resist the degradation of dermal extracellular matrix caused by UVR and play a protective role of photoaging.Conclusion: Dietary supplementation with n-3 PUFA can delay photoaging caused by UVR.The higher the concentration of n-3 PUFA,the stronger the protective effect.When the concentration of n-3 PUFA reached 9.7% of the lipid,the reduction of photoaging could be observed by the naked eye.When the concentration of n-3 PUFA reached 38.8%,the effect of delaying photoaging was significant.N-3 PUFA can dose-dependently reduce epidermal thickening and dermal collagen disorder caused by UVR accumulation over a long period of time,and can inhibit the production of inflammatory factors and MMP-1 to a certain extent.The mechanism of n-3 PUFA in delaying photoaging may be related to the inhibition of MAPK pathway activation.