Mechanism Of Action Of Adipose Tissue In LPL Mutation Leading To Abnormal Glucose Metabolism

OBJECTIVE:In the previous study,a LPL gene mutation was found and a gene knock-in animal model of the mutation was established.It was found that the knock-in model mutant mice showed significant impaired glucose tolerance.Previous studies found that the mutant group had myocardial tissue and Endoplasmic reticulum stress and disorders of the insulin signaling pathway occur in skeletal muscle tissue.Adipose tissue plays an important role in glycolipid metabolism,and adipose tissue is the organ that mainly expresses LPL in the body,and is also the main target organ of insulin.This study is to investigate the molecular mechanism of adipose tissue-induced metabolic abnormalities in mice.Methods:Tissue extraction and DNA detection were performed on mouse tissues,and genotypes were identified by one-generation sequencing.Mice were divided into two groups,wild type and mutant type.Wild-type and mutant mice were fed a normal diet.The biochemical parameters of basal glycolipid metabolism were measured by extracting mouse serum;the glucose tolerance of mice was evaluated by OGTT assay;the expression of bip,akt,Glut4,SAPK\JUNK protein in adipose tissue was detected by western blot,and adipose tissue was observed by light microscopy.The morphology and structure of HE were stained.The ultrastructure of adipose tissue was observed by transmission electron microscopy.The transcriptome sequencing of adipose tissue was used to observe the changes of gene expression in adipose tissue.Results: Mouse genotypes were identified by one generation sequencing to distinguish between wild-type and mutant mice.There was no significant change in serum lipid metabolism index and glucose metabolism index in the two groups.OGTT results showed that the glucose tolerance of the mutant group was abnormal,the blood glucose peak was advanced,and the blood glucose peak was significantly higher than that of the wild group.Furthermore,it was found that the serum insulin levels of the mutant mice were elevated.Western bolt results showed that in adipose tissue,the expression of Bip protein in the mutant group increased,indicating that endoplasmic reticulum stress occurred in the adipose tissue of the mutant group.There was no difference in total Akt levels between the two groups of mice,but the expression level of phosphorylated Akt in the mutant group decreased,indicating the occurrence of insulin resistance.Endoplasmic reticulum stress can inhibit insulin signaling by promoting SAPK/JNK phosphorylation.There was no difference in total SAPK/JNK protein in adipose tissue between the two groups,but the expression levels of phosphorylated SAPK/JNK in adipose tissue of the two groups were different.The phosphorylation level of SAPK/JNK in the mutant group increased,eventually leading to Abnormal insulin signaling.Compared with wild type mice,the expression level of GLUT4 in the mutant group decreased,indicating that the glucosaccharide transport ability of the mutant group was decreased.After HE staining,macrophage infiltration was observed in the adipose tissue of the mutant mice under light microscope,indicating the occurrence of inflammatory reaction.Electron microscopy showed changes in mitochondria and endoplasmic reticulum in adipose tissue of mutant mice,affecting protein processing and secretion and energy metabolism.Electron microscopy showed the formation of autophagosomes and lysosomes in the adipose tissue of the mutant mice.Conclusion:Our previous study found that the LPL C310 R mutation caused abnormal glucose tolerance in mice and pathological changes in both skeletal muscle and myocardial tissue.Through our further research,we found that LPL mutations lead to endoplasmic reticulum stress,inflammatory cell infiltration,oxidative stress,decreased glucose transport capacity,changes in insulin signaling,insulin resistance,and mitochondrial swelling.A series of pathological changes such as damage and destruction of the endoplasmic reticulum structure,so adipose tissue also plays an important role in the metabolic abnormalities caused by LPL mutations.This may be an important cause of abnormal glucose tolerance.