Effect of pioglitazone treatment on endoplasmic reticulum stress response in human adipose and in palmitate-induced stress in human liver and adipose cell lines.
Obesity and elevated cytokine secretion result in a chronic inflammatory state and may cause the insulin resistance observed in type 2 diabetes. Recent studies suggest a key role for endoplasmic reticulum stress in hepatocytes and adipocytes from obese mice, resulting in reduced insulin sensitivity. To address the hypothesis that thiazolidinediones, which improve peripheral insulin sensitivity, act in part by reducing the endoplasmic reticulum stress response, we tested subcutaneous adipose tissue from 20 obese volunteers treated with pioglitazone for 10 wk. We also experimentally induced endoplasmic reticulum stress using palmitate, tunicamycin, and thapsigargin in the human HepG2 liver cell line with or without pioglitazone pretreatment. We quantified endoplasmic reticulum stress response by measuring both gene expression and phosphorylation. Pioglitazone significantly improved insulin sensitivity in human volunteers (P = 0.002) but did not alter markers of endoplasmic reticulum stress. Differences in pre- and posttreatment endoplasmic reticulum stress levels were not correlated with changes in insulin sensitivity or body mass index. In vitro, palmitate, thapsigargin, and tunicamycin but not oleate induced endoplasmic reticulum stress in HepG2 cells, including increased transcripts CHOP, ERN1, GADD34, and PERK, and increased XBP1 splicing along with phosphorylation of eukaryotic initiation factor eIF2alpha, JNK1, and c-jun. Although patterns of endoplasmic reticulum stress response differed among palmitate, tunicamycin, and thapsigargin, pioglitazone pretreatment had no significant effect on any measure of endoplasmic reticulum stress, regardless of the inducer. Together, our data suggest that improved insulin sensitivity with pioglitazone is not mediated by a reduction in endoplasmic reticulum stress.
Das
Swapan K
SK
Endocrinology Section, Medicine and Research Services, Central Arkansas Veterans Healthcare System, John L. McClellan Memorial Veterans Hospital, 4300 W. 7th St., Little Rock, AR 72205, USA. skdas@uams.edu
Chu
Winston S
WS
Mondal
Ashis K
AK
Sharma
Neeraj K
NK
Kern
Philip A
PA
Rasouli
Neda
N
Elbein
Steven C
SC
D051702:Activating Transcription Factor 6 / Q000096:biosynthesis / Q000235:genetics; D000328:Adult; D000368:Aged; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D004722:Endoribonucleases / Q000096:biosynthesis / Q000235:genetics; D005260:Female; D006360:Heat-Shock Proteins / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D018832:Molecular Chaperones / Q000096:biosynthesis / Q000235:genetics; D000077205:Pioglitazone; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D000071701:Regulatory Factor X Transcription Factors; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013312:Stress, Physiological / Q000188:drug therapy / Q000378:metabolism*; D050151:Subcutaneous Fat / Q000187:drug effects* / Q000378:metabolism; D045162:Thiazolidinediones / Q000494:pharmacology*; D051742:Transcription Factor CHOP / Q000096:biosynthesis / Q000235:genetics; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics; D000071717:X-Box Binding Protein 1; D019892:eIF-2 Kinase / Q000096:biosynthesis / Q000235:genetics
C497111:ATF6 protein, human; D051702:Activating Transcription Factor 6; C497249:DDIT3 protein, human; D004268:DNA-Binding Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D007004:Hypoglycemic Agents; D018832:Molecular Chaperones; D012333:RNA, Messenger; D000071701:Regulatory Factor X Transcription Factors; D045162:Thiazolidinediones; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; C000605544:Xbp1 protein, mouse; D051742:Transcription Factor CHOP; C528229:ERN1 protein, human; D017346:Protein Serine-Threonine Kinases; D019892:eIF-2 Kinase; D004722:Endoribonucleases; D000077205:Pioglitazone