Mechanisms Of Dietary Valine Deficiency Regulating Food Intake And Short-term Feeding Behaviors

Increasing food intake is a prerequisite for improving growth performance in healthy animals.Numerous studies show that dietary indispensable amino acid deficiency can reduce the food intake.Val is next limited amino acid after Lys,Met,Thr,and Trp in corn-soybean basic diet of the weaned piglets.Importantly,some researches indicated that Val deficiency led to much more decrease food intake and body weight.However,the mechanisms of decrease the food intake in dietary Val deficiency are still unclear.Thus,it is critical to elucidate the mechanisms of regulating food intake in condition of Val deficiency.The means of regulation of food intake are divided into the central and peripheral in according to body position.Gut hormones play an important role of peripheral regulation of food intake.Recently,the latest researches suggested that hepatic fibroblast growth factor-21(FGF21)regulates macronutrient intake.Hypothalamus is vital section in the brain of regulating food intake especially arcuatus nucleus(ARC)that involved in energy homeostasis,nutrients and hormones sensing and signaling transduction.On the one hand,the hypothalamus regulates food intake by manipulating the expression of neuropeptide Y(NPY)/ agouti-related peptide(Agrp)and proopiomelanocortin(POMC)/cocaine-and amphetamine-regulated transcript(CART).On the other hand,mammalian target of rapamycin(mTOR)and AMP-activated protein kinase(AMPK)signaling pathways play a critical role for the hypothalamus.Anterior piriform cortex(APC)is also able to sense indispensable amino acids deficiency and inhibit food intake via activation of the general control nonderepressible-2(GCN2)pathway.In this study,used feeding behavior analysis,measured peripheral and central appetite-related genes expression,detected activity of signaling pathways and amino acid concentration in plasma elucidate the mechanisms of regulating food intake in dietary Val deficiency.The main results are as follows:1.Diet neophobia test: In order to exclude the difference of diet composition and taste,a separate experiment was designed as follows.The selected 12 male Kunming mice with similar body weight were random Ly divided into Val deficiency(VD)group and control group after feeding the AIN93 G 5 days,and then recorded food intake at the sixth and seventh day.The results showed that the food intake of VD group was very significantly lower than control group or before switching(P <0.01).Interestingly,the food intake of VD group was markedly(P<0.05)suppressed in the first hour compared with control group.The result indicated that mice can rapid sense and refuse the diet of Val deficiency.2.Effects of Val deficiency on short-term food intake and feeding behaviors: 16 wild and 14 FGF21 heterozygous type male Kunming mice were random Ly allotted into VD group and control group,namely wild type-control diet(WT-CD),wild type-Val-deficient diet(WT-VD),heterozygous type-control diet(HT-CD),heterozygous type-Val-deficient diet(HT-VD).The feeding behaviors of the mice were observed and the food intakes at each stage were recorded after fasted 24 hours.Our results revealed that WT-VD group pronouncedly(P<0.05)declined food intake at the initial 2 hours compared with WT-CD.Nevertheless,HT-VD group prolonged the first 12 hours.There was no difference between the four groups for the first feeding behaviors after fasted 24 hours.Meal partterns data indicated that the main reason why reduce of food intake in Val-deficient diet was decrease(P<0.05)the total meal time.Compared with wild-type mice,FGF21 heterozygous mice distinctly(P<0.05)reduced the meal numbers,but significantly(P<0.05)increased average meal duration.3.The impact of Val deficiency on long-term food intake: At the end of feeding behavior experiment,raised 4 weeks,the food intake and body weight were monitored.The results indicated that both WT-VD and HT-VD groups were lower(P<0.05)average daily food intake,body weight and slaughter performance than matched control groups.4.Comparative trial: 8 similar body weight and male Kunming mice were divided into two stages.Significant reductions(P<0.05)in food intake and body weight were induced by feeding mice a Val-deficient diet in the first phase.These mice that received the Val-deficient diet for 10 days were then switched to the control diet and within one day their food intake returned to same level.Similarly,the body weight rapidly recovered to normal condition after switching to control diet 3 days.5.The effect of Val deficiency on genes expression of gastrointestinal hormones and hepatic FGF21: Val deficiency had no effect on GLP-1,PYY,and Ghrelin mRNA level in stomach or small intestine,but pronounced increase(P<0.05)CCK gene expression in small intestine.In contrast,Val deficiency very significantly reduced leptin(P<0.01)mRNA levels in the stomach compared with control groups.Both WT-VD and HT-VD groups had higher(P<0.05)FGF21 and ATF4 mRNA levels,phosphorylation of eIF? in liver and concentration of FGF21 in plasma than control groups.It is important that there was a good linear(R2=0.515,P=0.0003)and quadratic(R2=0.60,P=0.0003)regression relationship between liver FGF21 expression levels and food intake.Meanwhile,there was a negative correlation between concentration of FGF21 in plasma and food intake(R =-0.502,P=0.0047).6.The impact of Val deficiency on amino acid patterns in plasma: Both WT-VD and HT-VD groups were distinctly lower(P<0.05)Val and Met concentration in plasma.It is notable that Val deficiency significantly increased concentration of His in plasma.Concentration of Val in plasma had a linear(R2=0.79,P<0.0001)and quadratic(R2=0.794,P<0.0001)regression relationship with food intake.It is similar that concentration of Val in plasma had also a linear(R2=0.56,P<0.0001)and quadratic(R2=0.615,P=0.0002)regression relationship with FGF21 mRNA levels in liver.Meanwhile,concentration of Val in plasma was a negative(R=-0.47,P=0.008)associated with concentration of FGF21 in plasma.Finally,His level had a linear(R2=0.58,P<0.0001)regression relationship with food intake as well.7.The effects of Val deficiency on NPY and signaling pathways activity in the brain: Dietary treatment had no influence on positivity of NPY neural cells in ARC.Similarly,Val deficiency had no effect on the number of p-mTOR positive cells in ARC.It is notice that Val deficiency increased(P<0.05)the number of p-eIF? positive cells in APC.In summary,mice rapidly sense and reject Val-deficient diet.It is important that food intake and body weight are able to recover to normal levels within a short time when they receive the control diet again.Mice decreased food intake in Val-deficient groups through significantly decrease the total meal time and average meal size.Val deficiency induced CCK expression in small intestine.Moreover,long period lacking of Val increased the concentration of His and reduced the concentration of Val,Met in plasma.Subsequently,lower concentration of Val in plasma increased FGF21 expression and secretion via activation of hepatic GCN2 pathway.In addition,Val deficiency had also increase the number of positive p-e IF2? cells in APC.Eventually,these actions produce anorexia,inhibit food intake and decrease body weight.