Protection Of 4-phenylbutyric Acid Against Glucocorticoid-induced Endoplasmic Reticulum Stress In Pancreatic Islet Beta Cells And Preliminary Study On The Correlation Between FGF21 And Proinsulin

PART ONE The protective effect of 4-phenylbutyric acid on glucocorticoidinduced endoplasmic reticulum stress in MIN6 cells?Background and Objective?Glucocorticoids(GCs)can significantly reduce glucose tolerance in the body.GCs increase insulin resistance significantly,and the interference of GCs with islet function is gradually gaining attention.However,the complex mechanisms of GC-induced impairment of beta cell function have not yet been fully elucidated.Endoplasmic reticulum stress is one of the important mechanisms of islet beta cell injury.The purpose of this study was to investigate the role of GC in islet beta cell ER stress and to determine whether 4-phenylbutyric acid(4-PBA),an inhibitor of ER stress,has a protective inhibitory effect on GC-induced islet beta cells endoplasmic reticulum stress.?Methods? Pancreatic islet ?-cell line MIN6 cells were cultured in dexamethasone with different concentrations(0.1 ?mol/L and 0.5 ?mol/L)for different periods(1 hour,4 hours,12 hours,and 24 hours).Genes related to ER stress such as BIP,IRE-1,ATF6,PERK and CHOP and ? cell function-related genes GLUT2 and PDX1 expression levels.Simultaneously with 4-phenylbutyric acid(4-PBA)in combination with dexamethasone to interfere with MIN6 cells,to detect whether there are differences in the expression levels of genes related to ER and ? cell function.?Results?The expression of BIP,IRE-1,ATF6,and PERK in the unfolded protein response after dexamethasone intervention in MIN6 cells increased in both concentration and time-dependence way.Compared to the control group,after 0.5 ?mol/m L dexamethasone for 24 hours,the expressions of BIP,IRE-1,ATF6 and PERK m RNA were increased by 5.72,6.27,5.40,and 4.43 times,respectively(P<0.001).The ER stress associated CHOP gene,which is involved in the apoptotic pathway,also showed with a time-dependent increase.Compared with the control group,the expression of CHOP m RNA at 0.5 ?mol/L dexamethasone increased by 5.60 times after 24 hours intervention(P<0.001).With 4-PBA treatment,the expression of ER stressrelated genes induced by dexamethasone was significantly decreased almost to the comparable level of control(P<0.001).? cell function-related genes pancreatic duodenal homeobox gene(PDX1)and glucose transporter 2(GLUT2)decreased after high-dose 0.5 ?mmol/L dexamethasone intervention,but After 4-PDA added to MIN6 cell,There was has little effect on the expression of PDX1 and GLUT2.?Conclusion? Glucocorticoids can directly induce the high expression of apoptotic pathway-related genes mediated by endoplasmic reticulum stress and unfolded protein response in pancreatic ?-cells,while 4-PBA can significantly alleviate this effect of glucocorticoids.Glucocorticoids can reduce ? cell function-related gene expression,and whether 4-PBA has a definite role in this process remains to be further studied.PART TWO A preliminary study on the correlation between proinsulin and fibroblast growth factor 21 in newly-diagnosed type 2 diabetes mellitus?Background and Objective?In the development and progression of type 2 diabetes,the loss of islet ?-cell function and mass are accompanied by ER stress,but there is no simple and effective indicators detecting endoplasmic reticulum stress in the human body.Levels of fibroblast growth factor 21(FGF-21)and proinsulin(PI)are considered to be associated with islet ? cell stress,so we initially compared levels of peripheral blood fibroblast growth factor 21,proinsulin,insulin,Proinsulin/insulin(PI/I)ratio and proinsulin /C-peptide ratio(PI/C)in newly diagnosed type 2 diabetes and controls.and their correlations with the risk of diabetes.?Methods? We collected 37 patients with newly diagnosed type 2 diabetes and 40 normal controls,collected medical records and recorded anthropometric charactericsics,measured biochemical markers,fasting plasma glucose and fasting insulin and Cpeptide,and serum FGF-21 and PI concentration.? Results ? Compared with the control group,fasting plasma FGF-21 and PI concentrations were significantly increased in diabetic subjects(FGF21: 36.02(33.70,38.40)VS.23.38(15.46,30.67),P<0.05;PI: 116.28(65.50,263.16)VS.42.13(17.44,102.44),P<0.05).With the increased levels of FGF21 and PI,the risk of developing diabetes is significantly increased.The order of elevation of PI and FGF21 triads divides the subjects into three groups.The risk of developing diabetes increased by 15.84-fold for each quintile of FGF21.The PI risk and PI/C risk per group increases by 2.87 and 1.91 times(P<0.05).Correlation analysis showed that FGF21 was associated with PI,PI/I and PI/C.In multiple linear regression analysis,plasma FGF-21 and PI levels were possitivly correlated with Hb A1 c.After the addition of HOMAIR and HOMA-? to multiple regression analysis,there was a strong negative correlation between FGF21,PI/I and PI/C with HOMA-?.?Conclusion?The pre-diabetic patients with ?-cells may have been in stress before severe diabetes.FGF21 and proinsulin may be an index to evaluate islet ?-cell function.Combination of FGF21 and proinsulin may better predict the occurrence of diabetes.