Down Regulating PHGDH Affects The Lactate Production Of Sertoli Cells In Varicocele

Varicocele,the abnormal dilation and tortuosity of the pampiniform venous plexus within the spermatic cord,is present in about 15%of the male adult population and almost 40%of infertile males[1].Many factors account for male infertility in varicocele,such as hypoxia,metabolic abnormalities,hormonal dysfunction,elevated testicular temperature and spermatic veins hypertension[2].The precise mechanism by which varicocele might cause infertility is still unknown.No single factor is believed to be responsible for the negative testicular effects[3];instead the pathogenesis is believed to be complex and multifactorial,with several proposed mechanisms acting together[4].In this complex pathophysiological network,metabolic abnormalities seems to have a important role,although some studies have suggested a link between abnormal glycolysis and varicocele,the specific mechanisms are still poorly understood[5].Sertoli cells,located in the basal compartment of seminiferous tubules,are responsible for providing energy and nutritional support to developing germ cells[6].It is imperative that germ cells receive an adequate level of energy substrates,otherwise they will degenerate and enter the apoptotic pathway[7].In fact,the majority of energy required for spermatogenesis are provided by sertoli cells through glycolysis to produce lactate[8].Therefore,the glycolysis of sertoli cells defines the population size of germ cells,which is essential for the maintenance of spermatogenesis and consequently,male fertility[9].PHGDH,the first enzyme branching from glycolysis in a three-step serine biosynthetic pathway.The product is then subsequently converted into phosphoserine via transamination by PS ATI and,ultimately,to serine via phosphate ester hydrolysis and the enzyme PSPH[10],serine is also an activator of PKM2 in the glycolysis[11].The overexpression of PHGDH is often associated with progression of cancers,and the inhibitors of PHGDH reduce the glycolysis and suppress the growth of cancers[12].However,the associated investigation in the reproductive system remains limited.Methods and Results:1.The lactate on the varicocele side of the patients decreasedThe blood gas analysis results showed that compared with the peripheral venous blood,the lactate concentration in the varicocele side of the patients decreased significantly.2.Testicular protein PHGDH was down-regulated in varicocelePHGDH mRNA and protein expression was obviously reduced in the left testes from the varicocele group relative to the sham group.3.PHGDH knockdown inhibited sertoli cells glycolysis and lactate productionPHGDH knockdown significantly decreased the glucose consumption and the LDH activities of sertoli cells,inhibited the lactate production of sertoli cells.These results indicate that PHGDH knockdown inhibited the glycolysis of sertoli cells and resulted in the reduction of lactate production.4.PHGDH regulates the expression of PSPH and PKM2 expression in sertoli cellsWe constructed a PPI network using the STRING database,It was verified that PSPH,PSAT1 and PKM2 were indeed related to PHGDH.Our results showed that knockdown of PHGDH remarkably decreased the expression of PSPH and PKM2.5.PHGDH knockdown inhibited sertoli cells growthPHGDH knockdown decreased the proportion of cells in S-phase and increased the percentage of apoptotic cells in sertoli cells compared with control groups.These results indicate that PHGDH might play a key role in sertoli cells growth.Conclusion:our current findings indicate that varicocele lead to the low expression of PHGDH in sertoli cells and the low expression of PHGDH ultimately led to a decrease in lactate production by affecting the glycolysis pathway.Moreover,PHGDH knockdown can promote apoptosis and inhibit cell cycle to affect cell growth.That may be one of the important causes of impairment of spermatogenesis and male infertility.