A Study On The Effects Of Ultraviolet Radiation On Rana Kukunoris At Different Altitudes And Its Physiological Mecanisms

With the depletion of atmospheric ozone,the ultraviolet radiation(UVBR)intensity reaching the earth’s surface increases year by year.The skin damage and other hazards caused by it has become one of the main factors threatening human health.In the typical strong ultraviolet environment,the indigenous organisms of the Qinghai-Tibet Plateau have evolved a corresponding ultraviolet adaptability.Amphibian Rana kukunoris can be used as an ideal material to study the mechanism of ultraviolet adaptation of plateau animals because its skin is sensitive to external environment and it has a wide range of distribution.Therefore,in this experiment,the Rana kukunoris of high and low altitude populations were treated with UVBR for 8 days to explore the effects of ultraviolet radiation on the morphology,body color,hematological parameters,immune system and oxidative stress system,and UVB damage repair genes of Rana kukunoris at different elevations,as well as the possible mechanism of adaptation of high altitude Rana kukunoris to ultraviolet radiation.The experimental results showed that UVBR of 1.8 m W/cm~2 significantly increased the plasma total corticosterone content of Rana kukunoris,indicating that the UVBR under experimental conditions caused stress responses in both populations.The morphological results showed that the skin color of low-altitude Rana kukunoris darkened after UV exposure,and their body condition and fat body decreased,while no significant difference was found in high-altitude populations.This suggests that low-altitude populations may need to avoid UV radiation by increasing a series of energy-consuming reactions such as pigment deposition,while high-altitude populations may have adapted to UVBR.The results of WBC and cytokine determination showed that after UV exposure,the white blood cell(WBC)and neutrophil-to-lymphocyte ratio(NLR)values in the blood,as well as the concentrations of IL-6 and TNF-αin the plasma and skin of low-altitude Rana kukunoris increased,while there was no significant difference in other indicators of high-altitude populations except for the increase in cytokine levels in the plasma.This indicates that frogs from low-altitude populations are more sensitive to UVBR,suffer more severe cell damage,and produced stronger inflammatory response.The results of basic immunology experiments showed that under no UVB treatment,compared with the low-altitude population,the high-altitude Rana kukunoris had lower Ig M and Ig Y levels in the plasma,and a lower PHA swelling response,indicating that the humoral and cellular immune capabilities of the high-altitude population were weaker.After UV exposure,the levels of Ig M and Ig Y and the degree of response to PHA of the low-altitude population were significantly reduced,while there was no significant difference in the high-altitude population.This indicates that UVBR is more likely to inhibit the cellular and humoral immune responses of low-altitude Rana kukunoris.The results of oxidative stress experiment showed that UVBR significantly increased the content of MDA and carbonyl protein in the liver of high-and low-altitude Rana kukunoris population,while the SOD activity,CAT activity and total antioxidant capacity(T-AOC)decreased significantly.This indicates that UVBR has similar effects on oxidative damage in the liver of high-and low-altitude populations.UVBR causes varying degrees of oxidative stress damage in the muscles.Without UVB treatment,compared with the low-altitude population,the T-AOC in the muscles of high-altitude population of Rana kukunoris was lower.Under the same degree of UVBR,the MDA content in the muscles of the low altitude population of Rana kukunoris significantly increased,and the T-AOC content decreased,indicating more severe lipid damage and weaker total antioxidant capacity.However,the T-AOC content in the muscles of the high altitude population of Rana kukunoris significantly increased,which meant the total antioxidant capacity was stronger in the high altitude population.The expression level of UV damage-related repair genes showed significant tissue specificity in USP1 and CPD genes in the Rana kukunoris.After UV irradiation,the relative expression levels of USP1 and CPD genes in the liver of the high altitude population were about 4 times higher than those in the low altitude population.The expression levels of USP1 and CPD genes in the skin of the high altitude population of Rana kukunoris increased as well.This means that compared with the low altitude population,the high altitude population of the Rana kukunoris has higher expression of UV repair genes and stronger UV gene repair ability,which is conducive to adapting to the harsh environments of the plateau.In conclusion,compared with the low-altitude population,the high-altitude Rana kukunoris population showed the higher expression of repair genes which basically eliminated the UV-induced DNA damage,only caused a slight inflammatory response,and did not affect the normal cellular and humoral immunity.Although it significantly caused oxidative damage to the liver,it maintained the balance of the antioxidant system in normal muscle tissue.It shows that the high-altitude Rana kukunoris population has a strong ability to adapt to strong ultraviolet radiation.The results of this study are helpful to reveal the law and mechanism of ultraviolet adaptation of plateau species,provide a scientific basis for the research and protection strategies of other amphibians,and provide clues for the medical treatment of human ultraviolet damage.