PPARγ regulates exocrine pancreas lipase.

AIM: Pancreatic lipase (triacylglycerol lipase EC 3.1.1.3) is an essential enzyme in hydrolysis of dietary fat. Dietary fat, especially polyunsaturated fatty acids (PUFA), regulate pancreatic lipase (PNLIP); however, the molecular mechanism underlying this regulation is mostly unknown. As PUFA are known to regulate expression of proliferator-activated receptor gamma (PPARγ), and as we identified in-silico putative PPARγ binding sites within the putative PNLIP promoter sequence, we hypothesized that PUFA regulation of PNLIP might be mediated by PPARγ. MATERIALS AND METHODS: We used in silico bioinformatics tools, reporter luciferase assay, PPARγ agonists and antagonists, PPARγ overexpression in exocrine pancreas AR42J and primary cells to study PPARγ regulation of PNLIP. RESULTS: Using in silico bioinformatics tools we mapped PPARγ binding sites (PPRE) to the putative promoter region of PNLIP. Reporter luciferase assay in AR42J rat exocrine pancreas acinar cells transfected with various constructs of the putative PNLIP promoter showed that PNLIP transcription is significantly enhanced by PPARγ dose-dependently, reaching maximal levels with multi PPRE sites. This effect was significantly augmented in the presence of PPARγ agonists and reduced by PPARγ antagonists or mutagenesis abrogating PPRE sites. Over-expression of PPARγ significantly elevated PNLIP transcript and protein levels in AR42J cells and in primary pancreas cells. Moreover, PNLIP expression was up-regulated by PPARγ agonists (pioglitazone and 15dPGJ2) and significantly down-regulated by PPARγ antagonists in non-transfected rat exocrine pancreas AR42J cell line cells. CONCLUSION: PPARγ transcriptionally regulates PNLIP gene expression. This transcript regulation resolves part of the missing link between dietary PUFA direct regulation of PNLIP.

GLP-1-RA Corrects Mitochondrial Labile Iron Accumulation and Improves ß-Cell Function in Type 2 Wolfram Syndrome.

CONTEXT: Type 2 Wolfram syndrome (T2-WFS) is a neuronal and ß-cell degenerative disorder caused by mutations in the CISD2 gene. The mechanisms underlying ß-cell dysfunction in T2-WFS are not known, and treatments that effectively improve diabetes in this context are lacking. OBJECTIVE: Unraveling the mechanisms of ß-cell dysfunction in T2-WFS and the effects of treatment with GLP-1 receptor agonist (GLP-1-RA). DESIGN AND SETTING: A case report and in vitro mechanistic studies. PATIENT AND METHODS: We treated an insulin-dependent T2-WFS patient with the GLP-1-RA exenatide for 9 weeks. An iv glucose/glucagon/arginine stimulation test was performed off-drug before and after intervention. We generated a cellular model of T2-WFS by shRNA knockdown of CISD2 (nutrient-deprivation autophagy factor-1 [NAF-1]) in rat insulinoma cells and studied the mechanisms of ß-cell dysfunction and the effects of GLP-1-RA. RESULTS: Treatment with exenatide resulted in a 70% reduction in daily insulin dose with improved glycemic control, as well as an off-drug 7-fold increase in maximal insulin secretion. NAF-1 repression in INS-1 cells decreased insulin content and glucose-stimulated insulin secretion, while maintaining the response to cAMP, and enhanced the accumulation of labile iron and reactive oxygen species in mitochondria. Remarkably, treatment with GLP-1-RA and/or the iron chelator deferiprone reversed these defects. CONCLUSION: NAF-1 deficiency leads to mitochondrial labile iron accumulation and oxidative stress, which may contribute to ß-cell dysfunction in T2-WFS. Treatment with GLP-1-RA and/or iron chelation improves mitochondrial function and restores ß-cell function. Treatment with GLP-1-RA, probably aided by iron chelation, should be considered in WFS and other forms of diabetes associated with iron dysregulation.