Peroxisome Proliferator–Activated Receptor α Improves Pancreatic Adaptation to Insulin Resistance in Obese Mice and Reduces Lipotoxicity in Human Islets

Abstract

Peroxisome proliferator-activated receptor (PPAR) ␣ is a transcription factor controlling lipid and glucose homeostasis. PPAR␣-deficient (؊/؊) mice are protected from high-fat diet-induced insulin resistance. However, the impact of PPAR␣ in the pathophysiological setting of obesityrelated insulin resistance is unknown. Therefore, PPAR␣ ؊/؊ mice in an obese (ob/ob) background were generated. PPAR␣ deficiency did not influence the growth curves of the obese mice but surprisingly resulted in a severe, age-dependent hyperglycemia. PPAR␣ deficiency did not aggravate peripheral insulin resistance. By contrast, PPAR␣ ؊/؊ ob/ob mice developed pancreatic ␤-cell dysfunction characterized by reduced mean islet area and decreased insulin secretion in response to glucose in vitro and in vivo. In primary human pancreatic islets, PPAR␣ agonist treatment prevented fatty acid-induced impairment of glucose-stimulated insulin secretion, apoptosis, and triglyceride accumulation. These results indicate that PPAR␣ improves the adaptative response of the pancreatic ␤-cell to pathological conditions. PPAR␣ could thus represent a promising target in the prevention of type 2 diabetes.

Single Nucleotide Polymorphisms of the Peroxisome Proliferator–Activated Receptor-α Gene (PPARA) Influence the Conversion From Impaired Glucose Tolerance to Type 2 Diabetes

“…Moreover, recent studies show that PPAR-␣ deficiency decreases the mean area of the pancreatic ␤-cells and diminishes insulin secretion in response to glucose, whereas PPAR-␣ agonists reduce lipotoxicity in human islets and prevent the progression to diabetes (19). It is therefore possible that the pancreatic effects of PPAR-␣ are responsible for the results observed in our study.…”

Peroxisome proliferator-activated receptor α (PPARα) protects against oleate-induced INS-1E beta cell dysfunction by preserving carbohydrate metabolism

“…In rats, it was observed that activation of PPARα for 24 h can reverse the insulin hypersecretion induced by high-fat feeding [23]. In ob/ob mice, glucose intolerance is aggravated by the absence of PPARα, correlating with reduced glucose-stimulated insulin secretion in isolated islets [21]. The same study reported that PPARα agonists protected human islets from palmitateinduced lipotoxicity [21].…”

“…In ob/ob mice, glucose intolerance is aggravated by the absence of PPARα, correlating with reduced glucose-stimulated insulin secretion in isolated islets [21]. The same study reported that PPARα agonists protected human islets from palmitateinduced lipotoxicity [21]. In pregnant rats fed a high-fat diet, in vivo administration of a PPARα agonist has been shown to prevent loss of glucose-stimulated insulin secretion [24].…”

“…A less severe effect of fatty acids on beta cells leads to elevated basal insulin release accompanied by impaired glucosestimulated insulin secretion, a phenomenon we refer to as lipodysfunction [19,20]. Recent studies indicate a new role for PPARα in beta cells, that of protecting against fatty acid-induced dysfunction [20][21][22]. In rats, it was observed that activation of PPARα for 24 h can reverse the insulin hypersecretion induced by high-fat feeding [23].…”

Weight Loss Decreases Excess Pancreatic Triacylglycerol Specifically in Type 2 Diabetes

“…Identification of the location of triacylglycerol within the pancreas has been hampered by rapid postmortem autolysis, but a study of pancreata retrieved and not used for pancreas transplantation showed that intracellular fat droplets were widely distributed within the exocrine cells, in addition to widely scattered isolated adipocytes (23). Exposure to even modest concentrations of fatty acids causes marked triacylglycerol accumulation in human islets in vitro (7). Local lipolysis is likely to bring about interstitial and intracellular concentrations of fatty acids sufficient to inhibit b-cell function.…”