Chronic effects of palmitate overload on nutrient-induced insulin secretion and autocrine signalling in pancreatic MIN6 beta cells

Maria L. Watson, Katherine Macrae, Anna E. Marley, Harinder S. Hundal

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    Abstract

    Background: Sustained exposure of pancreatic beta cells to an increase in saturated fatty acids induces pleiotropic effects on beta-cell function, including a reduction in stimulus-induced insulin secretion. The objective of this study was to investigate the effects of chronic over supply of palmitate upon glucose- and amino acid-stimulated insulin secretion (GSIS and AASIS, respectively) and autocrine-dependent insulin signalling with particular focus on the importance of ceramide, ERK and CaMKII signalling.

    Principal Findings: GSIS and AASIS were both stimulated by >7-fold resulting in autocrine-dependent activation of protein kinase B (PKB, also known as Akt). Insulin release was dependent upon nutrient-induced activation of calcium/calmodulin-dependent protein kinase II (CaMKII) and extracellular signal-regulated kinase (ERK) as their pharmacological inhibition suppressed GSIS/AASIS significantly. Chronic (48 h, 0.4 mM) palmitate treatment blunted glucose/AA-induced activation of CaMKII and ERK and caused a concomitant reduction (similar to 75%) in GSIS/AASIS and autocrine-dependent activation of PKB. This inhibition could not be attributed to enhanced mitochondrial fatty acid uptake/oxidation or ceramide synthesis, which were unaffected by palmitate. In contrast, diacylglycerol synthesis was elevated suggesting increased palmitate esterification rather than oxidation may contribute to impaired stimulus-secretion coupling. Consistent with this, 2-bromopalmitate, a non-oxidisable palmitate analogue, inhibited GSIS as effectively as palmitate.

    Conclusions: Our results exclude changes in ceramide content or mitochondrial fatty acid handling as factors initiating palmitate-induced defects in insulin release from MIN6 beta cells, but suggest that reduced CaMKII and ERK activation associated with palmitate overload may contribute to impaired stimulus-induced insulin secretion.

    Original languageEnglish
    Article numbere25975
    Pages (from-to)-
    Number of pages12
    JournalPLoS ONE
    Volume6
    Issue number10
    DOIs
    Publication statusPublished - 5 Oct 2011

    Keywords

    • FREE FATTY-ACIDS
    • SKELETAL-MUSCLE CELLS
    • LONG-TERM EXPOSURE
    • PROTEIN-KINASE-C
    • GENE-EXPRESSION
    • CERAMIDE SYNTHESIS
    • REGULATED KINASES
    • COA PATHWAY
    • MALONYL-COA
    • LINE INS-1

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