Effects Of Different Fatty Acids On Mammary Gland Development And Lactation Function Of Mice And Its Mechanisms

Mammary gland is an important tissue and organ of mammal lactation.During the development and reproduction of female animals,the development of mammary gland can be divided into the following five stages: embryo,puberty,pregnancy,lactation and degeneration.After sexual maturation,mammary gland development and lactation function still show dynamic changes in each reproductive cycle.The development of mammary gland and its lactation function are affected by strain,environment and nutrition,among which nutritional factors play an important role in regulating the development and lactation function of mammary gland after sexual maturity.Fatty acids are important nutrients.A large number of studies have shown that fatty acids play an important role in animal energy supply,fat deposition and inflammatory reaction.Therefore,fatty acids are widely used in animal production.Mice and pig are polythelia and multiparousanimal.There are more than 6 pairs of nipples in pig and 4 pairs in mice,which have high similarity in the development and regulation mechanism of mammary gland,and can be used for reference in developmental biology.In order to screen functional fatty acids from many fatty acids that can effectively regulate the development of mammary glands in mice and reveal their regulatory mechanisms,the following four parts of experiments were carried out in this study.Part 1: Screening of functional fatty acids on regulating mammary gland developmentForty-eight lactating female mice(12 weeks)were divided into four groups,12 mice in each group.The mice in the control group were fed with control diet,while the other groups were fed with 1% lauric acid(LA),2% stearic acid,2% linoleic acid respectively for21 days.Litter weight,maternal weight and feed intake were weighed every week.On the21 st day,the serum,mammary gland,liver,spleen,lung,kidney and other tissues of mice were collected.The viscera coefficient of the mice,the weight of litter,the weight of newborn mouse and the morphology of the HE section of the mammary gland of the mice were collected to study the effects of three different fatty acids on mammary gland development and lactation function.The results showed that 1% lauric acid,2% stearic acid and 2% linoleic acid could increase the acinar area of female mice,among which lauric acid carried the most significant effect,and lauric acid could also improve the growth performance of offspring.It was concluded that lauric acid was the most important fatty acid in mammary gland development of lactating mice.Part 2: The effects of dietary lauric acid on lactating mice mammary gland development,the growth performance of offspring and its mechanismThe addition of 1% lauric acid in diet could significantly promote the mammary gland development of lactating mice and improve the growth performance of offspring.In order to study the effect of lauric acid on lactating mice mammary gland development and its mechanism.We detected the levels of PRL and IGF-1 in serum and the expression of IGF-1gene and its related genes IGFBP1,IGFBP3,Albumin in liver and fatty acid metabolism related genes FASN,PPARγ and ACADM,FATP4 in mammary gland in lactation mice.The expression of fatty acids,protein synthesis marker protein ADRP and β-casein,JAK2/STAT5,PI3K/Akt-mTOR associated protein and Elf5,IGF-1 protein in mammary gland were detected by Western Blot.The results showed that the addition of 1% lauric acid in diet could decrease the concentration of IGF-1 in maternal serum,decreased the expression of IGF-1 gene m RNA in liver,decreased the expression of p-JAK2 protein and Elf5 protein in mammary gland,and increased the expression of β-casein.These results suggest that the addition of lauric acid in diet could increase the expression of β-casein,increase the number of mammary acinar,promote the development of mammary acinar,improve the lactating ability of mice and improve the growth performance of offspring.Part 3: Effects of lauric acid on lipid metabolism in blood of lactating miceIn order to study the effect of lauric acid on lipid metabolism in lactating mice.In the experiment,the serum samples of maternal mice were collected from the previous feeding experiment,and the lipid metabolites in the serum of mice were detected by UPLC-MS/MS,cluster analysis and principal component analysis were used to detect the lipid metabolites in the serum of mice.Differential analysis of qualitative and quantitative lipid data was carried out by orthogonal partial least square discriminant analysis,and differential metabolites were obtained by analysis.The results showed that the addition of lauric acid in diet had an effect on serum metabolites of lactating mice.There were 27 different metabolites,18 of which were down regulated,mainly arachidonic acid and PE,PC-O and TG with sn-2 bit C14 SA or MUFA.There are 9 kinds of upregulated,mainly sphingomyelin substance(sn-2 is C12 SM)and triglyceride(sn-2 site is C12:0,sn1 site is C18 PUFA TG).The results indicated that the addition of lauric acid in diet not only regulated the TG synthesis and metabolism in the serum of lactating mice,but also regulated the synthesis and metabolism of phospholipid and sphingomyelin.Although phospholipid and sphingolipid account for a relatively low proportion of fatty acids,their biological functions are very important.We found that lauric acid promoted mammary gland development and lactation performance in maternal mice,possibly because of lauric acid increased the content of SM in metabolic species and thus promoted the proliferation and differentiation of mammary gland cells.Part 4 : Effects of fatty acids on HC11 differentiation and its mechanismIn order to analyze the effects of fatty acids on mammary gland development in mice and its mechanism at the cellular level,we selected fatty acids with different carbon chains and saturated concentrations of 100μM,including lauric acid(LA),oleic acid(OA),stearic acid(SA),octanoic acid,Eicosapentaenoic acid(EPA),Palmitoleic acid(PA),linoleic acid.The differentiated HC11 cells were treated with these fatty acid for 4 days.The results showed that the addition of these fatty acids could promote the formation of lipid in the cells,but none of them enhanced the fatty acids de novo synthesis.Medium chain fatty acid octanoic acid increased the content of TG by activating the JAK2/STAT5 signaling pathway,and LA increased the TG content in the supernatant by activating the PI3K/Akt-mTOR signaling pathway.Long chain fatty acids(SA,OA,PA,EPA and linoleic acid)increase the formation of lipid droplets in cells,and the signaling pathways of each fatty acid promoting lipid droplets are different.Long-chain saturated fatty acid(SA)promotes lipid droplet formation by activating JAK2/STAT5 signaling pathway,and long-chain unsaturated fatty acid OA,PA promotes lipid droplet formation by activating PI3K/Akt-mTOR pathway.Long-chain unsaturated fatty acid linoleic acid promotes lipid droplet formation by activating JAK2/STAT5 and PI3K/Akt-mTOR signaling pathways.