Mechanism Of Propionate Alleviates Free Fatty Acids-induced Mitochondrial Damage And Apoptosis In Calf Hepatocytes

During the transition period,depressed feed intake renders cows unable to meet their energy needs for maintenance and lactation,leading cows entering a state of negative energy balance(NEB).NEB initiates fat mobilization to provide fatty acids as energy fuel to meet energy requirements.However,excessive fatty acids are lipotoxic,which can cause oxidative stress and apoptosis in calf hepatocytes,leading to liver metabolic dysfunction and aggravating NEB.Propionate produced by rumen fermentation is the main substrate of liver gluconeogenesis.Postpartum dairy cows are given propylene glycol(metabolic to produce propionate in the rumen)to alleviate the NEB.Besides,ketosis cows can be treated with propylene glycol to improve liver damage.It shows that propionate not only participates in liver metabolism as a substrate of gluconeogenesis but also may regulate other metabolic activities of hepatocytes.Therefore,this experiment uses the in vitro culture of dairy cow hepatocytes to simulate the experiment of high fatty acids,to determine whether propionate can improve the mitochondria damage and apoptosis of dairy cow hepatocytes caused by high fatty acids,and explore its underlying mechanism.To investigate the effect of propionate on the mitochondria of primary calf hepatocytes,hepatocytes were collected and cultured in vitro and treated with propionate at gradient concentration or gradient time.The results showed that 2 m M propionate treatment for 12 h could significantly increase the expression of mitochondrial-associated proteins PGC-1α,VDAC1,Tfam,and COXⅣ in primary calf hepatocytes.Flow cytometry results showed that propionate treatment increased the fluorescence intensity of Mitotracker,and had no effect on cell viability.Prove that propionate can promote mitochondrial biosynthesis in dairy cow hepatocytes.Previous articles have proved that high concentrations of fatty acids induce mitochondrial damage in dairy cow hepatocytes,and induce oxidative stress and apoptosis.To investigate whether propionate can alleviate fatty acid-induced cell damage,we use propionate and fatty acids co-treated hepatocytes.It was found that propionate treatment can significantly reverse the decrease of mitochondrial-associated protein expression caused by fatty acids,including hepatocytes.Propionate can also reduce cellular MDA and ROS content,increase SOD and GSH-PX activity,and enhance cellular antioxidant capacity.Besides,flow cytometry was used to detect cell apoptosis and found that propionate treatment can also alleviate fatty acid-induced cell apoptosis.Prove that propionate can improve the mitochondrial damage,oxidative stress,and apoptosis of dairy cow liver cells induced by high concentrations of fatty acids.The highly expressed PGC-1α in the liver is a key regulator of mitochondrial number and function.This study found that propioniate can enhance the expression of PGC-1α in hepatocytes.However,in hepatocytes treated with high concentrations of fatty acids,silence PGC-1α,propionate treatment could not enhance the expression of the mitochondrial-associated protein PGC-1α,VDAC1,Tfam,and COXⅣ in calf hepatocytes,inability to increase the number of mitochondria.Also,propionate could not alleviate oxidative stress and apoptosis induced by fatty acids.These results indicate that propionate plays an anti-mitochondrial damage and anti-apoptosis role through PGC-1α.In conclusion,propionate could promote mitochondrial biosynthesis by increasing the expression of PGC-1α in primary calf hepatocytes,thus reversing mitochondrial damage caused by fatty acids and alleviating oxidative stress and apoptosis.