Glucolipotoxicity Alters Lipid Partitioning and Causes Mitochondrial Dysfunction, Cholesterol, and Ceramide Deposition and Reactive Oxygen Species Production in INS832/13 ß-Cells

Abstract

Elevated glucose and saturated fatty acids synergize in inducing apoptosis in INS832/13 cells and in human islet cells. In order to gain insight into the molecular mechanism(s) of glucolipotoxicity (Gltox), gene profiling and metabolic analyses were performed in INS832/13 cells cultured at 5 or 20 mm glucose in the absence or presence of palmitate. Expression changes were observed for transcripts involved in mitochondrial, lipid, and glucose metabolism. At 24 h after Gltox, increased expression of lipid partitioning genes suggested a promotion of fatty acid esterification and reduced lipid oxidation/detoxification, whereas changes in the expression of energy metabolism genes suggested mitochondrial dysfunction. These changes were associated with decreased glucose-induced insulin secretion, total insulin content, ATP levels, AMP-kinase activity, mitochondrial membrane potential and fat oxidation, unchanged de novo fatty acid synthesis, and increased reactive oxygen species, cholesterol, ceramide, and triglyceride levels. However, the synergy between elevated glucose and palmitate to cause ss-cell toxicity in term of apoptosis and reduced glucose-induced insulin secretion only correlated with triglyceride and ceramide depositions. Overexpression of endoplasmic reticulum glycerol-3-phosphate acyl transferase to enhance lipid esterification amplified Gltox at intermediate glucose (11 mm), whereas reducing acetyl-coenzyme A carboxylase 1 expression by small interfering RNA to shift lipid partitioning to fat oxidation reduced Gltox. The results suggest that Gltox entails alterations in lipid partitioning, sterol and ceramide accumulation, mitochondrial dysfunction, and reactive oxygen species production, all contributing to altering ss-cell function. The data also suggest that the early promotion of lipid esterification processes is instrumental in the Gltox process.

Coordinate Changes in Histone Modifications, mRNA Levels, and Metabolite Profiles in Clonal INS-1 832/13 β-Cells Accompany Functional Adaptations to Lipotoxicity

“…Our results are in line with previous microarray-based studies of palmitate-induced lipotoxicity in the MIN6 and INS-1 832/13 clonal ␤-cell lines (68,69). We also observed up-regulation in steroid biosynthesis and in the sterol-sensitive mRNAs Insig1, Srebf-2, Lss, Hmgcs1, Hmgcr, and Ldlr.…”

Monoacylglycerol as a Metabolic Coupling Factor in Glucose-Stimulated Insulin Secretion

“…Of special importance, the combination of high glucose and high FFA showed highest apoptosis, compared to the group with low glucose (El-Assaad et al, 2003). Further study indicates that this strong apoptosis inducing effect was closely related to lipid esterification processes, TG accumulation and ceramide deposition as well as activation cascade-3 pathway in the cells (El-Assaad et al, 2010). Similar results were also reported in dispersed rat and human islets (Buteau et al, 2004).…”

Increased Lipogenesis and Stearate Accelerate Vascular Calcification in Calcifying Vascular Cells

“…The data suggest that changes in stearate-CoA or its metabolite levels control mineralization and osteogenic differentiation in vascular cells, through a mechanism yet to be determined. In a number of previous studies using cell culture systems, saturated fatty acids have been shown to have lipotoxic effects via several cell signaling pathways including 1) endoplasmic reticulum stress (36,37), 2) Toll-like receptor activation (38 -41), 3) an increase in reactive oxygen species (42, 43), 4) de novo ceramide synthesis (44 -46), 5) modification of mitochondrial structure and function (44,47), and 6) suppression of anti-apoptotic components (46,48). In addition, unsaturated fatty acid supplementation has been known to block the lipotoxic effects of saturated fatty acids.…”