Ceramide induces mitochondrial abnormalities in insulin-secreting INS-1 cells: Potential mechanisms underlying ceramide-mediated metabolic dysfunction of the β cell

Abstract

C2-ceramide, a cell permeable analogue of ceramide [CER] markedly reduced mitochondrial membrane potential [MMP] in insulin-secreting INS cells, which was followed by a significant accumulation of cytochrome c [Cyt c] into the cytosolic compartment. In a manner akin to CER, exposure of these cells to interleukin-1beta [IL-1beta] also resulted in reduction in MMP and cytosolic accumulation of Cyt c. Further, long-term exposure of these cells to either CER [but not its inactive analogue] or IL-1beta caused a marked reduction in their metabolic viability. However, unlike IL-1beta, which increased nitric oxide [NO] release, CER-treatment of INS cells had no effects of CER on NO release were demonstrable. Together, these findings suggest that CER-induced mitochondrial effects may not be mediated via iNOS gene expression and NO production. CER also activated an okadaic acid -sensitive protein phosphatase [CAPP] in the purified mitochondrial fraction, suggesting that CAPP might represent one of the target proteins for CER in the beta cell mitochondria. Together, our findings suggest direct detrimental effects of CER on mitochondrial function in beta cells leading to their dysfunction and demise via apoptosis. Moreover, our findings provide evidence for a potential difference in the mechanisms underlying CER- and IL-1beta-induced mitochondrial defects and apoptotic demise of the effete beta cell.

Localization of a nuclear serine/threonine protein phosphatase in insulin-secreting INS-1 cells: potential regulation by IL-1β

“…They include: (i) a cytosolic glutamate and magnesium-sensitive PP2A-like activity, which we have shown to mediate the dephosphorylation and activation of acetyl CoA carboxylase in the β cell [45,46]; (ii) a mitochondrial ceramide-activated protein phosphatase, which appears to dephosphorylate and inactivate pro-apoptotic proteins, such as Bcl-2 [47,48]; (iii) a PP2A-like activity that we characterized in islet lysates which is inhibited by glycolytic and tricarboxylic acid cycle intermediates; we speculate that this form of PP2A is required for glucose-stimulated insulin secretion [16]; and (iv) the currently identified nuclear PP4, which could play regulatory roles in IL-1β-mediated metabolic dysfunction and demise. Studies are in progress to determine the precise identity and the subunit composition of these phosphatases to further decipher their novel roles in the β cell function.…”

Exendin-4 protects pancreatic beta cells from palmitate-induced apoptosis by interfering with GPR40 and the MKK4/7 stress kinase signalling pathway

“…The involvement of other NEFA-dependent signals in the promotion of beta cell dysfunction and death has also been proposed. These include activation of Erk-1/2 [32], NF-κB [33], protein-kinase C (PKC)-δ [34], endoplasmic reticulum (ER) stress [35], calpain-10 [36] and ceramide formation [37], and induction of sterol regulatory element-binding protein [38], macrophage migration inhibitory factor [39], cell death-inducing DNA fragmentation factor a-like effector A [40] and cell death-inducing DFF45-like effector b [41]. NEFA-mediated inhibition of Akt activity [42] has also been implicated.…”

“…Wollheim, University of Geneva, Geneva, Switzerland) were grown as previously described [15]. Murine glucagon-secreting alpha-TC1-6 cells (passage [35][36][37][38][39][40]; a gift from Professor F. Purrello, University of Catania, Catania, Italy) were grown in monolayer at 37°C in a humidified incubator gassed with 5% CO 2 , in DMEM containing 4 mmol/l L-glutamine supplemented with 0.02% BSA, 3 g/l glucose, 10% heat-inactivated FBS, 100 IU/ml penicillin, 100 μg/ml streptomycin, 0.1 mmol/l non-essential amino acids (all from Gibco Invitrogen, Paisley, UK) and 15 mmol/ l HEPES (pH 7.4).…”

Life and death decisions of the pancreatic β-cell: the role of fatty acids

“…Palmitate has been shown to promote ceramide formation in β-cells [113], and treatment of islet cells with ceramide analogues can lead to loss of viability [102,114], although the magnitude of this effect is often rather modest [115]. In addition, an inhibitor of ceramide synthesis, fumonisin-1B, has been reported to attenuate palmitate-induced cytotoxicity in both rodent [102,116] and human [117,118] islet cells, suggesting that ceramide formation might be involved in fatty-acid-induced death under some circumstances.…”