Mitochondrial Dysfunction Is Involved in Apoptosis Induced by Serum Withdrawal and Fatty Acids in the β-Cell Line Ins-1

Abstract

The potential toxic effects of high extracellular concentrations of fatty acids were tested in beta(INS-1)-cells cultured in the absence of serum, a condition known to alter cell survival in various systems. This may in part mimic the situation in type 1 or 2 diabetes where beta-cells are already insulted by various stressful conditions, such as cytokines and oxidative stress. Serum removal caused, over a 36-h period, oxidative stress and an early impairment of mitochondrial function, as revealed by increased superoxide production and markedly reduced mitochondrial membrane potential, but a lack of cytochrome c and apoptosis-inducing factor release in the cytosol. The fatty acids palmitate and oleate considerably accelerated the apoptosis process in serum-starved cells, as revealed by fluorescence-activated cell sorting analysis, morphological changes, chromatin condensation, DNA laddering, poly(ADP-ribose) polymerase cleavage, cytochrome c and apoptosis-inducing factor release, and increased levels of Bax and cytosolic caspase-2. The fatty acids also increased nitric oxide production, apparently independently of inducible nitric oxide synthase induction. Under the same experimental conditions, elevated glucose alone had only a marginal effect on beta-cell apoptosis. Together the results indicate that elevated concentrations of fatty acids are particularly efficient in accelerating the rate of apoptosis of already stressed beta(INS-1)-cells displaying altered mitochondrial function, and that the mitochondrial arm of the apoptosis process is involved in beta-cell lipotoxicity.

An immune origin of type 2 diabetes?

“…The toxic actions of NEFA on beta cell function may be mediated by similar pathways; several lines of evidence point to this. Exposure to NEFA causes oxidative stress [76,125,127,[138][139][140][141] followed by apoptosis [142], and IL-1 potentiates NEFA toxicity [143]. Exogenous IL-1 or other toxic immune mediators from the islet endothelium [144][145][146][147] or from the circulation may act in concert with dietary fatty acids to damage beta cells, although the signalling pathways involved may differ in some respects.…”

Loss of Stearoyl-CoA Desaturase-1 Improves Insulin Sensitivity in Lean Mice but Worsens Diabetes in Leptin-Deficient Obese Mice

“…Chronic exposure of ␤-cells to high levels of fatty acids, particularly saturated fatty acids, is associated with impaired glucose-stimulated insulin secretion and eventually ␤-cell death (22)(23)(24)(25)(26)(27)(28) (Fig. 4A), whereas the concentration of stearate (18:0) was significantly elevated (Fig.…”

“…Hyperglycemia and islet fatty acid and cholesterol accumulation have been previously associated with impaired ␤-cell function and cell death (22,24,25,29,30,(41)(42)(43). Consistent with altered ␤-cell function, GLUT2 (Slc2a2), insulin (Ins2), insulin promoter factor 1 (Ipf1/ Pdx1), glucokinase (Gck), and insulin receptor substrate 2 (Irs2) were all dramatically (Ͼ90%; Table 2) downregulated in type B islets from Scd1 Ϫ/Ϫ leptin ob/ob mice.…”

Glucagon-like peptide-1 prevents beta cell glucolipotoxicity

“…However, chronic hyperglycaemia causes beta cell dysfunction characterised by reduced insulin biosynthesis [6] and increased levels of apoptosis (glucotoxicity) [7,8,9,10,11]. Similarly, acute exposure to NEFA potentiates glucose-induced insulin secretion by beta cells [12], whereas prolonged exposure to high concentrations of NEFA triggers beta cell apoptosis (lipotoxicity) [13,14,15,16,17]. A recent study showed that protein kinase B (PKB) activation can rescue MIN6 cells from oleate cytotoxicity [18].…”