The LXRB-SREBP1 network regulates lipogenic homeostasis by controlling the synthesis of polyunsaturated fatty acids in goat mammary epithelial cells

Background:In rodents,research has revealed a role of liver X receptors(LXR) in controlling lipid homeostasis and regulating the synthesis of polyunsaturated fatty acids(PUFA).Recent data suggest that LXRB is the predominant LXR subtype in ruminant mammary cells,but its role in lipid metabolism is unknown.It was hypothesized that LXRB plays a role in lipid homeostasis via altering the synthesis of PUFA in the ruminant mammary gland.We used overexpression and knockdown of LXRB in goat primary mammary epithelial cells(GMEC) to evaluate abundance of lipogenic enzymes,fatty acid profiles,content of lipid stores and activity of the stearoyl-Co A desaturase(SCD1) promoter.Results:Overexpression of LXRB markedly upregulated the protein abundance of LXRB while incubation with si RNA targeting LXRB markedly decreased abundance of LXRB protein.Overexpression of LXRB plus T0901317(T09,a ligand for LXR) dramatically upregulated SCD1 and elongation of very long chain fatty acid-like fatty acid elongases 5–7(ELOVL 5–7),which are related to PUFA synthesis.Compared with the control,cells overexpressing LXRB and stimulated with T09 had greater concentrations of C16:0,16:1,18:1n7,18:1n9 and C18:2 as well as desaturation and elongation indices of C16:0.Furthermore,LXRB-overexpressing cells incubated with T09 had greater levels of triacylglycerol and cholesterol.Knockdown of LXRB in cells incubated with T09 led to downregulation of genes encoding elongases and desaturases.Knockdown of LXRB attenuated the increase in triacylglycerol and cholesterol that was induced by T09.In cells treated with dimethylsulfoxide,knockdown of LXRB increased the concentration of C16:0 at the expense of C18:0,while a significant decrease in C18:2 was observed in cells incubated with both si LXRB and T09.The abundance of sterol regulatory element binding transcription factor 1 precursor(p SREBP1) and its mature fragment(n SREBP1) was upregulated by T09,but not LXRB overexpression.In the cells cultured with T09,knockdown of LXRB downregulated the abundance for p SREBP1 and n SREBP1.Luciferase reporter assays revealed that the activities of wild type SCD1 promoter or fragment with SREBP1 response element(SRE) mutation were decreased markedly when LXRB was knocked down.Activity of the SCD1 promoter that was induced by T09 was blocked when the SRE mutation was introduced.Conclusion:The current study provides evidence of a physiological link between the LXRB and SREBP1 in the ruminant mammary cell.An important role was revealed for the LXRB-SREBP1 network in the synthesis of PUFA via the regulation of genes encoding elongases and desaturases.Thus,targeting this network might elicit broad effects on lipid homeostasis in ruminant mammary gland.

NH4Cl promotes apoptosis and inflammation in bovine mammary epithelial cells via the circ02771/miR-194b/TGIF1 axis

Excess ammonia(NH_(3))in the circulation of dairy animals can reduce animal health and the quality of products for human consumption.To develop effective prevention and treatment methods,it is essential to examine the molecular mechanisms through which excess NH_(3) may affect the mammary gland.The present study used bovine mammary epithelial cells(BMECs)to evaluate the effects of exogenous NH_(4)Cl on the abundance of circular RNAs(circRNAs)using high-throughput sequencing.Among the identified circRNAs,circ02771 was the most significantly upregulated by exogenous NH_(4)Cl(P<0.05),with a fold change of 4.12.The results of the apoptosis and proliferation assays,transmission electron microscopy,H&E staining,and immunohistochemistry revealed that circ02771 increased apoptosis and inflammation.A double luciferase reporter assay revealed that circ02771 targeted miR-194b,and the overexpression of circ02771(pcDNA-circ02771)reduced(P<0.05)the expression of miR-194b and led to apoptosis and inflammation.Circ02771 also enhanced the expression of transforming growth factor beta-induced factor homeobox 1(TGIF1),which is a target gene of miR-194b.Overall,this study suggests that the circ02771/miR-194b/TGIF1 axis plays a role in mediating the effects of NH_(4)Cl on BMECs.Therefore,this axis provides a novel target to help control hazards within the mammary gland from high circulating NH_(4)Cl levels.

AMPK-ChREBP axis mediates de novo milk fatty acid synthesis promoted by glucose in the mammary gland of lactating goats

To investigate the role of glucose in regulating milk fatty acid synthesis,6 lactating Guanzhong dairy goats were infused with 0,60,or 100 g/d glucose via the external pubic artery in a 33 repeated Latin square experiment.A concomitant in vitro experiment was conducted to investigate possible mechanisms whereby glucose regulates milk fatty acid synthesis.RNA sequencing was used for cellular transcriptome analysis.Drugs,MK-2206,rapamycin,and dorsomorphin were used to block cellular mammalian AMP-activated protein kinase(AMPK),AKT serine/threonine kinase 1,and mechanistic target of rapamycin kinase signaling pathways,respectively.Carbohydrate response element binding protein(ChREBP)was knockdown and overexpressed to investigate its role in regulating milk fatty acid synthesis in mammary epithelial cells.Glucose infusion linearly elevated the concentration of C8:0(P=0.039)and C10:0(P=0.041)in milk fat while it linearly decreased(P=0.049)that of C16:0.This result was in agreement with the upregulation of genes related to de novo synthesis of fatty acids and lipid droplet formation,including adipose differentiation-related protein,butyrophilin subfamily 1 member A1,fatty acid synthase(FASN)and ChREBP.Their expression increased(P<0.05)linearly in the lactating goat mammary gland.In vitro,glucose linearly stimulated the expression of genes related to de novo synthesis of fatty acids and cellular triacylglycerol in cultured mammary epithelial cells.RNA sequencing and inhibition studies revealed that glucose induced transcriptomic changes increasing lipogenic pathways,with AMPK responding to glucose by controlling ChREBP and FASN.Knockdown and overexpression of ChREBP highlighted its essential role in lipogenesis.The knockdown and overexpression of ChREBP protein also revealed an essential role in regulating the de novo synthesis of fatty acids.Collectively,our data highlight that glucose supplementation promotes de novo fatty acid synthesis via the AMPK-ChREBP axis,hence increasing milk fat yield in the goat mammary gland.Results from the current study provide possible strategies to manipulate the fatty acid composition as well as improve ruminant milk quality.