Identification of an intracellular metabolic signature impairing beta cell function in the rat beta cell line INS-1E and human islets

Abstract

Aims/hypothesis Chronic hyperglycaemia promotes the progressive failure of pancreatic beta cells in patients with type 2 diabetes mellitus, a clinically highly relevant phenomenon known as glucotoxicity. The intracellular metabolic consequences of a chronically high availability of glucose in beta cells are, as yet, poorly understood in its full complexity. Methods An unbiased metabolite profiling analysis (GCtime-of-flight-MS) was used to identify the time course of core metabolite patterns in rat beta cell line INS-1E during exposure to high glucose concentrations and its relation to insulin expression. Results We report here that pentose phosphate pathway (PPP) metabolites accumulate remarkably during chronic but not acute glucose treatment, indicating altered processing of glucose through the pentose phosphate pathway. Subsequent functional studies in INS-1E cells and human islets revealed that a disturbance in this pathway contributes to decreases in insulin gene expression and a lack of glucose-stimulated insulin secretion. These effects were found to depend on the activation of extracellular-regulatedkinase (ERK1/2). Long-term inhibition of 6-phosphogluconic acid dehydrogenase resulted in accumulation of PPP metabolites, induced ERK1/2 activation independently of high glucose and impaired beta cell function. In turn, inhibition of ERK1/2 overstimulation during chronic glucose exposure partly inhibited metabolite accumulation and restored beta cell function. Conclusions/interpretation Based on unbiased metabolite analyses, the data presented here provide novel targets, namely the inhibition of PPP metabolite accumulation

Cocaine- and Amphetamine-regulated Transcript (CART) Protects Beta Cells against Glucotoxicity and Increases Cell Proliferation

“…Furthermore, our observation that CART activated CREB in the INS-1 (832/13) cells and rat islets is corroborated by findings from prior studies in neuronal models (15,56,57). Because glucose by itself is known to trigger these signaling pathways in the beta cells (32,58,59), we confirmed that CART indeed activates CREB by starving the cells for an additional 2 h in KRB-H with 2.8 mM glucose after 48 h of glucotoxicity before stimulating with CART. Further, evidence of this pathway being involved in beta cell proliferation comes from in vivo studies showing that beta G s knock-out mice exhibit reduced beta cell mass due to decreased cell prolifera- tion (60).…”

Urea impairs β cell glycolysis and insulin secretion in chronic kidney disease

“…Protein O-GlcNAcylation is involved in both the physiological regulation of protein function and pathological phe- decreased PFK-1 activity also leads to the diversion of glucose flux from the glycolytic pathway to the pentose phosphate (PPP) or glycogen synthesis pathway. Physiologically, the use of glucose-6-phosphate by these pathways is very limited in β cells (68), yet under pathophysiological conditions, the PPP contributes to the inhibition of β cell function (69) and, hence, could be a contributing factor to defective insulin secretion in CKD. Given that most enzymes in the glycolytic pathway are potentially O-GlcNAcylated (38,70), it is possible that other enzymes are deregulated in addition to PFK-1.…”

Chronic High Glucose and Pyruvate Levels Differentially Affect Mitochondrial Bioenergetics and Fuel-stimulated Insulin Secretion from Clonal INS-1 832/13 Cells

“…Although this does not establish a causal relationship, it still highlights a marked metabolic difference between cells cultured at low and high glucose, which perform robustly or not in response to physiological stimuli. Exactly how this comes about is unclear, but it is noteworthy that the pentose phosphate pathway has recently been implicated in glucotoxic ␤-cell dysfunction (27). Moreover, this pathway may also play a role in ␤-cell stimulus-secretion coupling (28).…”