Division of Cell Signalling and Immunology, Sir James Black Centre, College of Life Sciences, University of Dundee, Dundee, United Kingdom.
PLoS One. 2011;6(10):e25975. doi: 10.1371/journal.pone.0025975. Epub 2011 Oct 5.
Sustained exposure of pancreatic β cells to an increase in saturated fatty acids induces pleiotropic effects on β-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.
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 (~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.
Our results exclude changes in ceramide content or mitochondrial fatty acid handling as factors initiating palmitate-induced defects in insulin release from MIN6 β cells, but suggest that reduced CaMKII and ERK activation associated with palmitate overload may contribute to impaired stimulus-induced insulin secretion.
胰腺β细胞持续暴露于饱和脂肪酸增加会对β细胞功能产生多种影响，包括减少刺激诱导的胰岛素分泌。本研究的目的是研究棕榈酸的慢性过量供应对葡萄糖和氨基酸刺激的胰岛素分泌（GSIS 和 AASIS）以及自分泌依赖性胰岛素信号转导的影响，特别关注神经酰胺、ERK 和 CaMKII 信号转导的重要性。
GSIS 和 AASIS 均被刺激超过 7 倍，导致蛋白激酶 B（PKB，也称为 Akt）的自分泌依赖性激活。胰岛素释放依赖于营养物质诱导的钙/钙调蛋白依赖性蛋白激酶 II（CaMKII）和细胞外信号调节激酶（ERK）的激活，因为它们的药理抑制显著抑制了 GSIS/AASIS。慢性（48 小时，0.4mM）棕榈酸处理使葡萄糖/AA 诱导的 CaMKII 和 ERK 激活减弱，并导致 GSIS/AASIS 和自分泌依赖性 PKB 激活减少约 75%。这种抑制不能归因于增强的线粒体脂肪酸摄取/氧化或神经酰胺合成，棕榈酸对其没有影响。相反，二酰基甘油合成增加表明，增加的棕榈酸酯化而不是氧化可能导致刺激-分泌偶联受损。与此一致的是，2-溴棕榈酸，一种不可氧化的棕榈酸类似物，对 GSIS 的抑制作用与棕榈酸一样有效。
我们的结果排除了神经酰胺含量或线粒体脂肪酸处理的变化作为棕榈酸诱导 MIN6β细胞胰岛素释放缺陷的起始因素，但表明与棕榈酸过载相关的 CaMKII 和 ERK 激活减少可能导致刺激诱导的胰岛素分泌受损。
