Mosser RE, Maulis MF, Moullé VS, Dunn JC, Carboneau BA, Arasi K, Pappan K, Poitout V, Gannon M. High-fat diet-induced ␤-cell proliferation occurs prior to insulin resistance in C57Bl/6J male mice. Am J Physiol Endocrinol Metab 308: E573-E582, 2015. First published January 27, 2015; doi:10.1152/ajpendo.00460.2014.-Both short-(1 wk) and long-term (2-12 mo) high-fat diet (HFD) studies reveal enhanced ␤-cell mass due to increased ␤-cell proliferation. ␤-Cell proliferation following HFD has been postulated to occur in response to insulin resistance; however, whether HFD can induce ␤-cell proliferation independent of insulin resistance has been controversial. To examine the kinetics of HFD-induced ␤-cell proliferation and its correlation with insulin resistance, we placed 8-wk-old male C57Bl/6J mice on HFD for different lengths of time and assayed the following: glucose tolerance, insulin secretion in response to glucose, insulin tolerance, ␤-cell mass, and ␤-cell proliferation. We found that ␤-cell proliferation was significantly increased after only 3 days of HFD feeding, weeks before an increase in ␤-cell mass or peripheral insulin resistance was detected. These results were confirmed by hyperinsulinemic euglycemic clamps and measurements of ␣-hydroxybutyrate, a plasma biomarker of insulin resistance in humans. An increase in expression of key islet-proliferative genes was found in isolated islets from 1-wk HFD-fed mice compared with chow diet (CD)-fed mice. These data indicate that short-term HFD feeding enhances ␤-cell proliferation before insulin resistance becomes apparent.high-fat diet; mouse models; insulin resistance; ␤-cell proliferation; ␤-cell mass ␤-CELL COMPENSATION IN RESPONSE TO OBESITY is observed in both humans and rodent models. Human autopsy studies have revealed that nondiabetic obese individuals have 50% greater ␤-cell mass compared with lean individuals, and pancreata from type 2 diabetes patients have diminished ␤-cell mass compared with nondiabetic BMI-matched individuals (7). In mice, high-fat diet (HFD) feeding leads to increased body weight and a corresponding expansion in ␤-cell mass via increased ␤-cell proliferation (19,35,43,46). The ␤-cell response to HFD feeding in mice could enhance our understanding of the ␤-cell response to energy excess in humans and help us develop new strategies for augmenting ␤-cell mass in type 2 diabetes patients, but a key point is to discern early responses vs. compensatory responses that might occur after prolonged HFD feeding.The ␤-cell response to HFD feeding has been studied extensively; however, the data are difficult to interpret due to varying model systems and experimental designs. Studies vary in the ␤-cell characteristics measured, the composition and timing of diet, and mouse genotype, age, and, sex. Only by combining parallel measurements can a relationship between ␤-cell adaptations and the progression of dietinduced obesity be defined. The majority of studies utilize long-term HFD consumption, and the ␤-cell response is assessed after rodents...

The regulation of pancreatic β cell mass is a critical factor to help maintain normoglycemia during insulin resistance. Nutrient-sensing G protein-coupled receptors (GPCR) contribute to aspects of β cell function, including regulation of β cell mass. Nutrients such as free fatty acids (FFAs) contribute to precise regulation of β cell mass by signaling through cognate GPCRs, and considerable evidence suggests that circulating FFAs promote β cell expansion by direct and indirect mechanisms. Free Fatty Acid Receptor 2 (FFA2) is a β cell-expressed GPCR that is activated by short chain fatty acids, particularly acetate. Recent studies of FFA2 suggest that it may act as a regulator of β cell function. Here, we set out to explore what role FFA2 may play in regulation of β cell mass. Interestingly, Ffar2−/− mice exhibit diminished β cell mass at birth and throughout adulthood, and increased β cell death at adolescent time points, suggesting a role for FFA2 in establishment and maintenance of β cell mass. Additionally, activation of FFA2 with Gαq/11-biased agonists substantially increased β cell proliferation in in vitro and ex vivo proliferation assays. Collectively, these data suggest that FFA2 may be a novel therapeutic target to stimulate β cell growth and proliferation.

Current protocols for screening proliferative factors for β cells ex vivo are time-consuming, require cell lines or dissociated islets, and often entail expensive specialized screening equipment. Here we present an efficient and lower cost alternative that utilizes intact mouse islets for the initial screening of proliferative compounds and allows confirmation of β cell proliferation from the same islets. This protocol simplifies the process, saves money, and provides a way to identify β cell proliferative factors using equipment that is ubiquitous in most laboratories.

Pancreatic β-cell expansion is a highly regulated metabolic adaptation to increased somatic demands, including obesity and pregnancy; adult β-cells otherwise rarely proliferate. We previously showed that high fat diet (HFD) feeding induces mouse β-cell proliferation in less than one week in the absence of insulin resistance. Here we metabolically profiled tissues from a short-term HFD β-cell expansion mouse model to identify pathways and metabolite changes associated with β-cell proliferation. Mice fed HFD vs CD showed a 14.3% increase in body weight after 7 days; β-cell proliferation increased 1.75-fold without insulin resistance. Plasma from one-week HFD-fed mice induced β-cell proliferation ex vivo. The plasma, as well as liver, skeletal muscle, and bone, were assessed by LC and GC mass-spectrometry for global metabolite changes. Of the 1283 metabolites detected, 159 showed significant changes (FDR<0.1). The majority of changes were in liver and muscle. Pathway enrichment analysis revealed key metabolic changes in steroid synthesis and lipid metabolism, including free fatty acids and other bioactive lipids. Other important enrichments included changes in the citric acid cycle and 1-carbon metabolism pathways implicated in DNA methylation. Although the minority of changes were observed in bone and plasma (<20), increased p-cresol sulfate was increased >4 fold in plasma (the largest increase in all tissues), and pantothenate (vitamin B5) decreased >2-fold. The results suggest that HFD-mediated β-cell expansion is associated with complex, global metabolite changes. The finding could be a significant insight into Type 2 diabetes pathogenesis and potential novel drug targets.