Function And Mechanism Study Of Liver Cold-Induced RNA-Binding Protein On Adipose Tissue Browning

Obesity and its complications have become one of the major diseases threatening human health.The advantages of white fat browning to significantly increase energy consumption,resist excessive fat accumulation and improve the body’s glucolipid metabolism have become a current research hotspot in the treatment of obesity.Adipose browning is influenced by several factors and can be regulated by the intercommunication between different tissues.The effect of the liver,as the most critical metabolic organ in the body,on adipose browning and its mechanisms still need to be further investigated in current studies.In this paper,we found a correlation between cold-inducible RNA binding protein(CIRP)expression in the liver and obesity in different obese mouse models,and the phenomenon is consistent with that in human obese patients.We constructed adeno-associated virus AAV-CIRPi to knock down CIRP in a diet-induced obese mouse model,and showed that the percentage of subcutaneous adipose tissue in mice with downregulated CIRP expression in the liver decreased significantly,the cell size in subcutaneous fat was smaller,the expression of thermogenic genes was higher,the overall metabolic level of mice increased significantly,and glucose sensitivity was improved.To mimic the high expression of CIRP in obese mice,we constructed liver-specific expression of adenovirus Ad-CIRP and showed that the overall metabolic level of mice in the CIRP overexpression group decreased,the expression of thermogenic genes in subcutaneous fat was down-regulated,and glucose sensitivity was reduced.We did not find a regulatory effect of CIRP on adipose tissue browning by direct stimulation of cells and mice with recombinant protein re CIRP,ruling out the possibility that CIRP directly regulates adipose browning.Next,we searched for the target protein angiopoietin-like protein 3(ANGPTL3),a liver factor regulated by CIRP,through the screening of various known liver factors,and after RNA half-life assay and luciferase reporter assay,we found that CIRP could up-regulate the expression of ANGPTL3 protein by prolonging the stability of ANGPTL3 m RNA,thus regulating adipose tissue browning.Accoding to the studies of ANGPTL3 receptors,we demonstrated that ANGPTL3 plays a role in suppressing the expression of thermogenic genes such as UCP1 in adipose by activating the downstream JNK signaling pathway through binding to the receptor integrin αvβ3,thereby inhibiting the onset of white fat browning.In addition,experiments in mice showed that Cilengitide,an inhibitor of integrin αvβ3(the receptor for ANGPTL3),promoted the development of adipose browning.We also established the regulatory role of endoplasmic reticulum stress response-activated transcription factor 4(ATF4)on the expression of CIRP in the liver and the effect of endoplasmic reticulum stress on adipose browning in the liver by incubating adipocytes with culture supernatants from primary hepatocytes.In summary,this paper identified a regulatory mechanism based on the inhibition of adipose browning by the ATF4-CIRP-ANGPTL3 signaling axis induced by hepatic endoplasmic reticulum stress,establishing a link between hepatic endoplasmic reticulum stress and adipose browning.It revealed a potential effect between obesity-induced hepatic endoplasmic reticulum stress and adipose tissue metabolism.Meanwhile,the inhibitory effect of hepatic secretory factor ANGPTL3 on adipose browning also provides new ideas for the treatment of obesity and its related metabolic diseases.