Ceramide synthase 4 and de novo production of ceramides with specific N-acyl chain lengths are involved in glucolipotoxicity-induced apoptosis of INS-1 β-cells

Abstract

Pancreatic β-cell apoptosis induced by palmitate requires high glucose concentrations. Ceramides have been suggested to be important mediators of glucolipotoxicity-induced β-cell apoptosis. In INS-1 β-cells, 0.4 mM palmitate with 5 mM glucose increased the levels of dihydrosphingosine and dihydroceramides, two lipid intermediates in the de novo biosynthesis of ceramides, without inducing apoptosis. Increasing glucose concentrations to 30 mM amplified palmitate-induced accumulation of dihydrosphingosine and the formation of (dihydro)ceramides. Of note, glucolipotoxicity specifically induced the formation of C(18:0), C(22:0) and C(24:1) (dihydro)ceramide molecular species, which was associated with the up-regulation of CerS4 (ceramide synthase 4) levels. Fumonisin-B1, a ceramide synthase inhibitor, partially blocked apoptosis induced by glucolipotoxicity. In contrast, apoptosis was potentiated in the presence of D,L-threo-1-phenyl-2-palmitoylamino-3-morpholinopropan-1-ol, an inhibitor of glucosylceramide synthase. Moreover, overexpression of CerS4 amplified ceramide production and apoptosis induced by palmitate with 30 mM glucose, whereas down-regulation of CerS4 by siRNA (short interfering RNA) reduced apoptosis. CerS4 also potentiates ceramide accumulation and apoptosis induced by another saturated fatty acid: stearate. Collectively, our results suggest that glucolipotoxicity induces β-cell apoptosis through a dual mechanism involving de novo ceramide biosynthesis and the formation of ceramides with specific N-acyl chain lengths rather than an overall increase in ceramide content.

Alteration of Endoplasmic Reticulum Lipid Rafts Contributes to Lipotoxicity in Pancreatic β-Cells

“…1E, to 112.7 Ϯ 11.2 from 209.3 Ϯ 31.6 pmol/mg protein, p ϭ 0.015) and islets (F, to 38.3 Ϯ 4.2 from 61.5 Ϯ 5.1 pmol/mg protein, p ϭ 0.0045) with palmitate treatment. Previous studies of INS-1 ␤-cells showed an increased content of the de novo Cer biosynthetic product dihydroceramide after 24 h of palmitate exposure (28). However, we did not observe this in either MIN6 cells (Fig.…”

“…Moreover, when assessed directly, palmitate did not appear to promote misfolding of a reporter protein (27). An alternative, initially proposed by us (27) and now confirmed independently (28,29), postulates that palmitate slows protein trafficking out of the ER, which would, therefore, enhance ER stress because of lumenal protein overload. Our work further linked this trafficking defect to alterations in SL metabolism, although both the exact metabolite and the underlying mechanism remained obscure (30).…”

Neutral ceramidase activity inhibition is involved in palmitate-induced apoptosis in INS-1 cells

“…Palm is a precursor of palmitoyl CoA [19], which is implicated in ceramide synthesis de novo. Accordingly, excessive Palm induced ceramide accumulation via promoting ceramide synthesis de novo and caused β cell impairment [20]. Interestingly, an in vivo animal study revealed that inhibition of NCDase activity was an underlying mechanism by which saturated fatty acid induced endogenous ceramide accumulation in rat skeletal muscle [21].…”

Deoxysphingolipids, Novel Biomarkers for Type 2 Diabetes, Are Cytotoxic for Insulin-Producing Cells

“…Our mass spectrometry and inhibitor analyses support this hypothesis. In addition, 1-deoxysphinganine increased the expression of CerS5, whereas b-cell lipotoxicity resulting from palmitate treatment stimulated the synthesis of CerS4 (31), suggesting that different lipids stimulate specific CerS isoforms. Collectively, the results suggest that some of the cytotoxic effects of 1-deoxysphinganine occur after its intracellular uptake and metabolism to 1-deoxy-dihydroceramide.…”