| Background and ObjectiveInfertility has become one of the public health problems recognized by the World Health Organization.According to statistics,9% of couples in the world have fertility problems,and 50% of the problems are caused by male factors.It is imperative to improve or solve the problem of male infertility.In recent years,with the continuous development of economy and society,the incidence of obesity is also on the rise.Obesity is closely related to the occurrence of many diseases,such as high blood pressure,diabetes and heart disease.At the same time,whether obesity will affect male reproductive ability has been widely concerned and studied.At present,the studies on obesity and male reproduction are cross-sectional studies,and the conclusions are inconsistent.In the study of sperm quality,previous studies have shown that obesity can reduce the semen quality of men,such as obesity reduces the total number of sperm,motility and so on;however,some studies have shown that there is no significant difference in semen quality between normal and overweight or obese men.In terms of mechanism exploration,the mechanism of the impact of obesity on male reproduction is not clear.Based on the prevalence of obesity and infertility,the different conclusions and mechanisms of obesity on male reproduction,and the lack of long-term dynamic research,we will carry out the following studies:(1)systematic review and meta-analysis of the effect of obesity on sperm quality in men;(2)observation and analysis of reproductive function and testicular morphology of male mice with different feeding time and obesity degree;(3)from the endocrine,cell cycle,mitochondrial membrane potential,oxidative stress and other aspects to explore the mechanism of obesity induced by high-fat diet on male reproduction.The purpose of this study is to provide theoretical basis and solutions for the reproductive problems of obese men.Methods1.To explore the effect of obesity on human sperm quality through meta-analysis.The English databases Pub Med,Embase,Medline,The Cochrane Library and Web of Science,and the Chinese databases VIP,CNKI,Wanfang and Chinese biomedical literature service system(Sino Med),were searched to find the related literatures about the effect of obesity on sperm quality.The data of the literatures meeting the standards were extracted and analyzed.2.To explore the changes of reproductive function,sperm quality and testicular morphology of male mice with different feeding time and obesity degree.The reproductive function of the male mice in each experimental group was detected by counting the pregnant rate,litter size and weight of the female mice;the changes of sperm quality related indicators were detected by sperm quality analyzer;the morphological changes of testis were observed by HE staining section with optical microscope,The changes of spermatogenesis phase were observed and analyzed by Johnson score,and the changes of cell and subcellular structure of testis were further observed by transmission electron microscope.3.A preliminary study on the mechanism of sperm quality decline and testicular function damage induced by long-term high-fat diet in mice.The changes of serum testosterone(T),estradiol(E2),follicle stimulating hormone(FSH)and luteinizing hormone(LH)in male mice of each group were detected by enzyme linked immunosorbent assay(Elisa),and the sperm membrane potential and spermatogenic cell cycle of testicular tissue were detected by flow cytometry.The expression of reactive oxygen species(ROS),malondialdehyde(MDA)and superoxide dismutase(SOD)in testicular tissue of male mice in each group was detected by multi-function enzyme labeling instrument,and the changes of mitochondrial kinetics-related proteins Drp1,Mfn1 and Mfn2,autophagy-related proteins LC3 and p62 were detected by Western blot.Result1.Meta-analysis of the effect of obesity on human sperm quality showed that obesity reduced semen volume(SMD:-0.32,95%CI:-0.52～-0.12,P=0.002)and total sperm count(SMD:-0.77,95%CI:-1.31～-0.23,P=0.005),percentage of forward progression(SMD:-0.95,95%CI:-1.7～-0.19,P = 0.014)(SMD:-0.95,95%CI:-1.7～-0.19,P=0.014)and percentage of viability(SMD:-0.812,95%CI:-1.532～-0.093,P=0.027),but had no effect on sperm density(SMD:-0.15,95%CI:-0.32～0.02,P=0.088)and percentage of normal sperm morphology(SMD:-0.17,95%CI:-0.66～0.32,P=0.487).2.The body weight of the mice in the high-fat diet group increased significantly,and the pregnancy rate and litter size of the obese mice fed with high-fat diet for 4months decreased,but the body weight of the cubs did not change.The total sperm count of obese mice fed with high-fat diet for 4 and 5 months were significantly decreased,and the sperm viability of obese mice fed with high-fat diet for 5 months decreased.3.With the extension of feeding time,the wall of seminiferous tubule in testicular tissue of obese mice fed with high fat for 4 and 5 months became thinner(the number of cell layers became less),and the proportion of lumen with sperm decreased,while in obese mice fed with high fat for 5 months,the arrangement of spermatogenic cells was loose and disordered,at the same time,large groups of spermatogenic cells protruded into the lumen,and the Johnson score was lower.There was no significant difference in the number of interstitial cells among the experimental groups.The statistics of spermatogenic phase showed that the number of seminiferous tubules decreased and increased in the early stage of spermatogenesis in obese mice fed with high-fat diet for 4 and 5 months;With the prolongation of feeding time,the number of seminiferous tubules decreased in obese mice fed with high fat for 5 months.Transmission electron microscope showed that the basement membrane of seminiferous tubule was uneven in male mice fed with high fat for 4 months.In the male mice fed with high fat for 5 months,the density of seminiferous tubule basement membrane decreased,delamination and fracture were observed,and the number of fine cell layers decreased and arranged in disorder.In the male mice fed with high fat for 4months and 5 months,the spermatogonia showed more pyknosis,the cells separated from the surroundings,the chromatin was unevenly distributed in some spermatogenic nuclei,the mitochondria swelled and vacuolated obviously,and the suspicious membrane structure appeared.4.In the obese mice fed with high fat diet,the levels of serum testosterone,follicle stimulating hormone(FSH)and luteinizing hormone(LH)increased,while the level of estrogen decreased.The decrease of sperm membrane potential in obese mice fed with high fat diet for 5 months.After 4 months of high-fat feeding,the proportion of haploid cells and the ratio of haploid to diploid and tetraploid decreased.The level of oxidative stress related index ROS and MDA increased significantly,while the level of antioxidant index SOD decreased.The expression of mitochondrial fusion protein Mfn2 was slightly decreased,but the difference was not statistically significant.The expression of other mitochondrial dynamics related proteins Mfn1,Drp1 and autophagy related proteins LC3,P62 in each experimental group was not statistically significant.Conclusion Long term hyperlipidemia may cause mitochondrial damage and dynamic changes through oxidative stress,leading to mitochondrial dysfunction,thus affecting testicular morphological abnormalities and spermatogenesis,and ultimately leading to decreased sperm quality and male fertility. |
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