The Effect And Mechanism Of Bone-derived LCN2 On Regulation Of Bone-hypothalamic Axis With Different Exercise

Osteoblasts(OB)secrete lipocalin-2(LCN2),which can act on the hypothalamus and bind to melanocortin receptor-4(MC4R)to activate the MC4 R dependent appetite suppression pathway.Brain derived neurotrophic factor(BDNF),corticotropin releasing hormone(CRH),thyrotropin-releasing hormone(TRH)and single-homolog protein(Sim1)and other downstream factors were all promoted in the hypothalamus,thereby affecting appetite and participating in energy metabolism.This mechanism is a possible mechanism proposed by foreign studies that osteogenic LCN2 is involved in appetite regulation,but it is not very clear.Other studies have shown that exercise can affect the secretory function of OB.However,it is not clear whether exercise can regulate appetite and energy metabolism by changing the level of secretion of LCN2 by OB and thereby affecting its downstream signaling factors.Purposes: This study aims to verify the effect of exercise on the endocrine function of OB,and to explore the role and molecular mechanism of its endocrine factor LCN2 in the regulation of "bone-hypothalamic axis" process by exercise,so as to provide experimental basis for the effect of bone endocrine on appetite and energy metabolism.Methods: In this study,40 C57BL/6 male mice aged 4 weeks were randomly divided into the control group(group C),down-jumping group(group D),downhill running group(group R)and swimming group(group S),with 10 mice in each group.The duration of sports training is 50min/ day,6 days of training per week and 1 day of rest.The body weight,rat food and drinking water of each group were weighed every Monday.After 8 weeks of training,the lower limb bone,blood,hypothalamus,groin fat,epididymis fat and other tissues were selected in the second day,to detected the morphological,cellular and molecular indexes.Results:(1)Compared with group C,the lower limb bone length,width and femoral wet weight of mice in group R were significantly increased(P<0.01),and the wet weight of tibiofibula was significantly increased(P<0.05);Lower limb bone length and femur width were significantly increased in group D(P<0.05);The femoral width of mice in the group S was significantly increased(P<0.05).The results of cell culture showed that,compared with group C,the differentiation ability of osteoclasts in group D and R was significantly increased,while the differentiation ability of osteoclasts was significantly decreased.The results suggest that exercise can promote bone formation,inhibit bone resorption,contribute to the increase of bone secretion,and downhill running has the best effect.(2)Compared with group C,protein and mRNA expression levels of osteogenic LCN2,serum LCN2 concentration and mRNA expression levels of hypothalamic LCN2 in mice of group R were significantly increased(P<0.01),while protein expression levels of hypothalamic LCN2 were significantly increased(P<0.05);Serum LCN2 concentration and mRNA expression level of hypothalamus LCN2 in group D mice were significantly increased(P<0.05).Compared with the group S,the mRNA expression level of osteogenic LCN2 in the group R was significantly increased(P<0.05),while its protein expression was significantly increased(P=0.0653).The results of this study suggest that exercise can promote the expression of bone-derived LCN2 and cause the increase of hypothalamus LCN2 level through blood circulation.(3)Compared with group C,mRNA expression levels of MC4 R,BDNF,TRH and Sim1 in the hypothalamus of group R were significantly increased(P<0.05),mRNA expression levels of CRH were significantly increased(P<0.01),and protein expression levels of BDNF were significantly increased(P=0.057);The mRNA expression level of hypothalamic CRH was significantly increased in the group S(P<0.05).Compared with group D,the mRNA expression level of hypothalamic CRH in group R was significantly increased(P<0.01).Compared with group S,mRNA expression levels of MC4 R,BDNF and CRH in hypothalamus of group R were significantly increased(P<0.05).The results suggested that the increase of osteogenic LCN2 could to some extent up-regulate the expressions of BDNF,CRH,TRH and Sim1,and exercise could promote the expression of MC4 R in the hypothalamus and increase its role.(4)Compared with group C,the weekly average food intake and water intake of the exercise group mice were significantly reduced,and the growth was slow.The food intake of mice in group D was significantly decreased,and the water intake of mice in group S was significantly decreased.Compared with group C,the body weight of mice in group D and R decreased significantly(P<0.01),while that of mice in group S decreased significantly(P<0.05).The results showed that bone-derived LCN2 could reduce appetite and control body weight during exercise regulation.Conclusions:(1)Exercise can promote osteoblast differentiation,inhibit osteoclast differentiation,promote bone growth in mice and improve bone quality.(2)Exercise can regulate bone endocrine function,promote the expression of bone-derived LCN2,regulate the expression of MC4 R in the hypothalamus,and then regulate the expression levels of BDNF,CRH,TRH,Sim1 and other related factors,thereby regulating the appetite suppression signaling pathway.(3)Exercise can control the appetite,reduce food intake and control body weight through the LCN2-MC4 R pathway.