Involvement Of Leptin-NPY Pathway In Feed Efficiency Regulation

Feed efficiency is critical in livestock industry for both economic and environmental reasons.An accumulation of over a decade of research in cattle has shown that genetic selection for decreased residual feed intake(RFI),defined as the difference between an animal's actual feed intake and its expected feed intake,is a viable option for improving feed efficiency and reducing the feed requirements of herds,thereby improving the profitability of cattle producers.Currently,the molecular mechanisms underlying feed efficiency are largely unknown.Hormonal regulation is one of the most important factors in feed intake.Neuropeptide Y(NPY)is constantly being modulated through inhibition by leptin-induced JAK2/STAT3(janus kinase 2/signal transducer and activator of transcription 3)signaling to affect appetite and regulate feed intake,so it is likely to influence feed efficiency.In this study,in order to explore the relationship between leptin-NPY signaling pathway and feed efficiency in dairy cattle and SD rats.Firstly,we performed gene expression profiling of jugular vein serum on hormonal regulation of Chinese Holstein cattle with low and high RFI coefficients.After the analysiswith GO and KEGG,we found that these differences may be related to the molecular regulation of the leptin-NPYsignaling pathway,insulin signaling pathway,JAK/STAT signaling pathway and so on,especially the leptin-NPY axie.Then,we explored variations in RFI by comparing the differences in body size,milk performance,feeding behavior,and serum metabolites in cows and found that substantial differences between cows with different RFI.Beside that,the levels of insulin and glucose between cattle with low and high RFI coefficients showed no difference,but NEFA,leptin and NPY levels had significant difference.As a result,we surposed that letin-NPY axie might act as an important fector for regulating feed effeiciency.Next,we wanted to deeply study the regulation process of feed efficiency.However,after considering the overspend and difficulties inanatomical operation of dairy cattle,especially the lack of standard method and location map needed for neurological test,we choose model animal,SD rats,to finish the follow-up work.In the following study,rats were ranked and grouped on RFI.The phenotypes and molecular mechanism of rat models has revealed significant and distinct roles of leptin-induced JAK2/STAT3 signaling pathway participating in the process of feed efficiency by influencing hypothalamus NPY level as well as the functional contributions of NPY receptors to this physiological process.Wediscusstheregulatory mechanismsof feed efficiency inthefollowingthreeparts:1.Gene Expression Profiling of Hormonal Regulation Related to the Residual Feed Intake of Holstein CattleTo determine the relationship between hormones and feed efficiency,we performed gene expression profiling of jugular vein serum on hormonal regulation of Chinese Holstein cattle with low and high RFI coefficients.857 differential expression genes(from 24683 genes)were found.Among these,415 genes were up-regulated and 442 genes were down-regulated in the low RFI group.The gene ontology(GO)search revealed 6 significant terms and 64 genes associated with hormonal regulation,and the Kyoto Encyclopedia of Genes and Genomes(KEGG)selected the adipocytokine signaling pathway,insulin signaling pathway.2.Differencesof milk performance,feeding behavior and serum metabolites related to residual feed intake in dairy cowsThis study explored variation in RFI by comparing the differences in body size,milk performance,feeding behavior,and serum metabolites in Holstein cows.Twenty-nine cows in mid lactation were selected from a total of 84 animals based on their RFI following feedlot tests.Selected cows were ranked into high RFI(RFI>1 SD above the mean,n=14)and low RFI(RFI<1 SD below the mean,n=15).Measurements,including body size,milk performance,feeding behavior and serum metabolites,were analyzed using the MIXED procedure.The low RFI cows(more efficient)consumed 1.59 kg/d less dry matter than the high RFI group(P<0.01),while they produced nearly equal 4%fat-corrected milk.The milk:feed ratio was higher for the low RFI group than for the high RFI group(P<0.05).The levels of milk protein(P<0.01),total solids(P<0.05),and nonfat solids(P<0.05)were also higher for the low RFI group,whereas milk urea nitrogen was lower(P<0.01).The daily feeding duration was shorter for the low RFI group than for the high RFI group(P<0.01).No significant differences were found in levels of glucose,p-hydroxybutyrate,prolactin,insulin,IGF-1,growth hormone or ghrelin,but the level of NPY was higher(P<0.01)and levels of leptin and NEFA(non-esterified fatty acid)(P<0.05)were lower for the low RFI group than for the high RFI group.3.The JAK2/STAT3 pathway participate in the process of feed efficiency regulation by influencing hypothalamus neuropeptide Y level in Sprague-Dawley ratsIn this study,we investigated the role of NPY secretions influencing by leptin-induced JAK2/STAT3 signaling through and function of NPY receptors on feed efficiency regulation.Forty one male Sprague-Dawley rats were ranked on residual feed intake(RFI;a metric for feed efficiency),and 13 were selected as the extremes in RFI(6 Low-and 7 High-).As a result,the Low-RFI group(more efficient)consumed averagely 1.63 g/d less food than the High-RFI group daily(P<0.001),and they gained nearly equal weight.The concentration of NEFA in Low-RFI group was lower than that in High-RFI group(P<0.05).Concentrations of NPY in serum were higher in the Low-RFI group than that in the High-RFI group(P<0.01).Comparing with the High-RFI group,the mRNA relative expressions and protein expressions of NPY in the Low-RFI group were also higher in hypothalamus and cortex tissues,especially in hypothalamus arcuate nucleus.Moreover,the expression levels of the LEP,LEPR(P<0.05),JAK1(P<0.05),JAK2,STAT3(P<0.01)and SCOS3(suppressor of cytokine signaling 3)(P<0.01)genes were all decreased for the Low-RFI group than for the High-RFI group.Meanwhile,Jak2(P<0.05)and Stat3(P<0.01)protein expressions were in accordance with those of the mRNA levels.In addition,the expression level of the NPY4R was increased in the low RFI samples(P<0.01);in contrast,that of NPY1R was increased in the high RFI samples in both hypothalamus(P<0.01)and cortex(P<0.05)tissues.Their protein expressions were in accordance with those of the mRNA levels(P<0.01).Besides that,in hypothalamus,NPY2R and NPY5R proteins expressed more highly in Low-RFI line than them in High-RFI line.As stated above,the conclusions are as follows:1.The study indicated that the molecular expression of genes associated with hormonal regulation differs in dairy cows,depending on their RFI coefficients,and that these differences may be related to the molecular regulation of the leptin-NPYsignaling pathway,insulin signaling pathway,JAK/STAT signaling pathway and so on.2.There were substantial differences between cows with different RFI,which might affect the efficiency of milk protein metabolism and fat mobilization.3.The phenotypes and molecular mechanism of rat models has revealed significant and distinct roles of leptin-induced JAK2/STAT3 signaling pathway participating in the process of feed efficiency by influencing hypothalamus NPY level as well as the functional contributions of NPY receptors to this physiological process.