Study On The Effect Of Mitochondrial DNA-Depleted In Apoptosis Induced By Simulated Solar Irradiation

Background:The depletion of stratospheric ozone, caused by a series ofanthropogenic activities (mainly the release of halogenated hydrocarbons), has resulted inan increase in the UV-B radiation reaching the biosphere. Solar irradiation is well proved asan important nature factor leading to both human skin cancer and skin photoaging. Themain manifestations of longtime solar irradiation impairment are premature skin aging andtumour-prone exposure. Vast accumulated mtDNA in multiple types induced by radiationdamage has been widely demonstrated,but of which does the biological sense need furtherexpound. Cell apoptosis palys an important role in skin photoaging and sunlight-relateddermatoma.On the one hand, reduction of cell ingredient in skin tissue, caused by apoptosis,results in degenerative aging. On the other hand, dermatoma might be leaded if mutatedcells couldn’t die on time. It is still unclear that whether apoptosis induced by solarirradiation is caused by changes of mtDNA. In our study, Rho°cells(Rho°206cell) andparental cells(143B cell) provided valuable cell models for investigating importantfunctions of mtDNA in apoptosis induced by simulated solar irradiation so as to explain thefunction of mtDNA in chronic light injury.Objectives:To explore the possible mechanism and effect of mtDNA in apoptosis bystudying Rho°206and143B cell lines apoptosis induced by simulated solar irradiation.Methods:1.Morphological changes were examined by TEM.2.Morphological changesof Rho°206and143B cell lines apoptosis induced by different doses(177mJ/cm~2+3.39J/cm~2,354mJ/cm~2+6.78J/cm~2,531mJ/cm~2+10.17J/cm~2and708mJ/cm~2+13.56J/cm~2) ofsimulated solar irradiation were observed under light microscopy.3.Apoptosis of Rho°206and143B cell lines induced by different doses of simulated solar UV-irradiation wasalso examined morphologically and staining the cells with Hoechst33258. The cells were observed in the dark under a fluorescence microscope.4.Apoptosis of Rho°206and143B cell lines induced by different doses of simulated solar irradiation were analyzed byflow cytometry.5.ROS production duiring Rho°206and143B cell lines apoptosis inducedby different doses of simulated solar irradiation is assayed by flow cytometer.Results:1.Morphological analysis showed that cells treated with simulated solarirradiation marked typical morphological alterations of cell apoptosis. Compared with143Bcell lines, apoptosis induced by corresponding dose of irradiation decreased in Rho°206cells. However, both143B cell and Rho°206cell lines with sham-irradiation treatmentexhibited similar morphological apoptosis.2.According to Annexin V-/7-AAD assay, therewas no significant difference between apoptotic rate(AR) of both143B cell (9.23±0.85%)and Rho°206cell lines(9.10±1.20%) in sham-irradiated group(P>0.05). RA undercorresponding irradiation dose of Rho°206cell lines were22.93±1.15%,27.26±0.91%,36.10±1.20%and39.53±1.15%respectively. RA under corresponding irradiation dose of143B cells were30.51±1.61%,39.76±1.15%,46.56±1.30%and55.86±1.81%respectively. So RA under different irradiation dose in the same group were significantlydifferent(P<0.05). In addition, RA under the same irradiation dose between different groupwere significantly different as well(P<0.05).3.Production of ROS was monitored usingflow cytometry. The intracellular ROS levels didn’t change significantly (P>0.05) withsham-irradiation treatment in both143B cells(8.25±0.86%) and Rho°206cells(8.15±0.92%). In the simulated solar irradiation group, ROS were21.41±1.04%,24.82±1.12%,28.85±1.07%and2.78±1.14%respectively in143B cells, and14.99±1.17%,18.36±1.05%,24.44±1.14%and27.61±1.11%respectively in Rho°206cells. So ROS underdifferent irradiation dose in the same group were significantly different(P<0.05). ROSunder the same irradiation dose between different group were significantly different aswell(P<0.05).Conclusions:1.Apoptosis was striking induced both in Rho°cells and parental cellsby stimulated solar irradiation in a dose-dependent manner. The more irradiation doses add,the more apoptosis occurred.2.Compared to143B cell, DNA-depleted cells can resistagainst the apoptosis induced by stimulated solar irradiation in certain dose.3.The possibility has to taken into account that the resistance of Rho°cells could be related to adecreased ROS generation.