Study On The Role Of Angptl8 On Appetite And Energy Homeostasis

Background: Obesity has become a well-known risk factor affecting public health.According to the world health organization,the incidence of obesity will reach 57.8% worldwidely by 2030.Obesity could be an etiological factor of disease onset around the body,and more than 50% of global deaths are caused by obesity-related chronic diseases.The obesity issue urgently needs to be solved.Angiopoietin-like protein 8(Angptl8)is a brain-intestinal peptide secreted by the liver,and could regulate lipid metabolism by inhibiting the activity of lipoprotein esterase.Angptl8 is also closely related to the feeding state of the body.Objective:(1)To explore the distribution of Angiopoietin-like protein 8(Angptl8)in appetite related nucleus in hypothalamus.(2)To detect the effect of intravenous and lateral cerebral ventricular injected Angptl8 on food intake.(3)To investigate the effect of intravenous and lateral cerebral ventricular injected Angptl8 on the expression of c-Fos in appetite related nuclei in hypothalamus.(4)To study the physiological role of Angptl8 in peripheral and central regulation of food intake on molecular level.(5)To observe the influence of Angptl8 in adipose tissue deposit and energy expenditure.Methods:(1)Intravenous injection was used to observe the effect of peripheral Angptl8 on food intake and long-term body weight gain of C57BL/6J mice.(2)Combination of cannulae implantation and microinjection was used to observe the effect of central Angptl8 on food intake and long-term injection on body weight gain of C57BL/6J mice.(3)Immunohistochemistry and Immunofluorescence were used to detect the effect of intravenous and lateral cerebral ventricular injected Angptl8 on the expression of c-Fos and neuropeptide Y(NPY)in appetite related nucleus in hypothalamus.(4)Hematoxylin-eosin(HE)staining was used to observe the morphology of brown adipose tissue(BAT).Western blot and real-time PCR were used to detect the uncoupling protein-1(Ucp-1)level in BAT.Results:(1)Intravenous injection of Angptl8(0.1ml)decreased the nocturnal cumulative food intake dose dependently for 12h(3 μg/ml: 5.14±0.26 g vs.5.95±0.21 g,30 μg/ml: 4.58±0.28 g vs.5.95±0.21 g,P < 0.05).Lateral cerebral ventricular injection of 0.3μg/μl Angptl8 for 2μl decreased the nocturnal cumulative food intake for 6 hours(2.00±0.28 vs. 3.82±0.25 g,P < 0.05).Intravenous injected(30 μg/ml)and lateral cerebral ventricular injected(0.3 μg/μl)Angptl8 once both decreased the 24 h body weight gain.(2)Angptl8 was expressed in appetite-related nucleus in hypothalamus such as paraventricular nucleus(PVN),dorsomedial hypothalamus(DMH),ventromedial hypothalamus(VMH)and arcuate nucleus(ARC).But immunohistochemistry and realtime PCR in nuclei mentioned above showed no statistical difference before and after fasting for 12 hours in C57BL/6J mice.(3)Intravenous injected Angptl8 significantly decreased the number of c-Fos-positive neurons in the DMH(103.70 ± 8.55 vs.73.50 ± 11.52 cells per section in normal saline(NS)and Angptl8 treated animals,respectively;P < 0.05).Lateral cerebral ventricular injected Angptl8 reduced neuron activation in the DMH(125.13 ± 8.86 vs.98.00 ± 9.02 cells per section in NS and Angptl8 treated animals,respectively;P < 0.05).In addition,this reduction in c-Fos-positive nuclei was clearly detected in the PVN(161.00 ± 5.41 vs.66.33 ± 9.65 cells per section in NS and Angptl8 treated animals,respectively;P < 0.05),but c-Fos-positive nuclei were increased in the ARC(100.80 ± 26.26 vs.154.08 ± 35.15 cells per section in NS and Angptl8 treated animals,respectively;P < 0.05).Angptl8(0.3 mg/ml)significantly decreased the coexpression of NPY-and c-Fos-positive neurons in the DMH(37.67 ± 5.69 vs.20.25 ± 7.18 cells per section in NS and Angptl8 treated animals,respectively;P < 0.05).(4)Chronic long-term injection of peripheral Angptl8 decreased body weight gain(3.69±1.10 g vs.6.88±0.64 g,P < 0.05).The proportion of epididymal adipose tissue was also decreased(0.01±0.0008 g vs.0.01±0.0031 g,P < 0.05);however,inguinal adipose tissue(0.01±0.00 g vs.0.01±0.00 g,P > 0.05)and plasma free fatty acid(FFA)levels(0.17±0.07 g vs.0.19 ± 0.03 g,P > 0.05)were unchanged.Chronic long-term injection of central Angptl8 decreased body weight gain(0.79 ± 0.60 g vs.2.64 ± 0.36 g,P < 0.05).The proportions of epididymal adipose tissue(0.11 ± 0.04 g vs.0.06 ± 0.01 g,P < 0.05)and inguinal adipose tissue(0.08 ± 0.02 g vs.0.05 ± 0.01 g,P < 0.05)were greater in the Angptl8 group.However,the plasma FFA levels(0.15 ± 0.05 g vs.0.10 ± 0.03 g,P < 0.05)were lower in the Angptl8 group.(5)Intravenous injected Angptl8 decreased the proportion of BAT but lateral cerebral ventricular injected Angptl8 increased it.Both intravenous and lateral cerebral ventricular injected Angptl8 didn’t influence the morphology of BAT and the expression of Ucp-1.Conclusion:(1)Angptl8 was widely expressed in appetite-related nuclei in hypothalamus such as PVN,VMH,DMH and ARC.(2)NPY neurons in DMH were involved in the anorexic effect of Angptl8.(3)Angptl8 had effect on adipose tissue deposit but had no impact on the energy expenditure in brown adipose tissue.This study provided experimental references for further investigation about the role of Angptl8 in regulation of obesity and energy metabolism disorders.