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This Article Full Text Full Text (PDF) All Versions of this Article: 296/4/E690    most recent 90525.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Gwiazda, K. S. Articles by Johnson, J. D. Search for Related Content PubMed PubMed Citation Articles by Gwiazda, K. S. Articles by Johnson, J. D.

Effects of palmitate on ER and cytosolic Ca²⁺ homeostasis in β-cells

Laboratory of Molecular Signaling in Diabetes, Diabetes Research Group, Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada

Submitted 24 June 2008 ; accepted in final form 9 January 2009

There are strong links between obesity, elevated free fatty acids, and type 2 diabetes. Specifically, the saturated fatty acid palmitate has pleiotropic effects on β-cell function and survival. In the present study, we sought to determine the mechanism by which palmitate affects intracellular Ca²⁺, and in particular the role of the endoplasmic reticulum (ER). In human β-cells and MIN6 cells, palmitate rapidly increased cytosolic Ca²⁺ through a combination of Ca²⁺ store release and extracellular Ca²⁺ influx. Palmitate caused a reversible lowering of ER Ca²⁺, measured directly with the fluorescent protein-based ER Ca²⁺ sensor D1ER. Using another genetically encoded indicator, we observed long-lasting oscillations of cytosolic Ca²⁺ in palmitate-treated cells. In keeping with this observed ER Ca²⁺ depletion, palmitate induced rapid phosphorylation of the ER Ca²⁺ sensor protein kinase R-like ER kinase (PERK) and subsequently ER stress and β-cell death. We detected little palmitate-induced insulin secretion, suggesting that these Ca²⁺ signals are poorly coupled to exocytosis. In summary, we have characterized Ca²⁺-dependent mechanisms involved in altered β-cell function and survival induced by the free fatty acid palmitate. We present the first direct evidence that free fatty acids reduce ER Ca²⁺ and shed light on pathways involved in lipotoxicity and the pathogenesis of type 2 diabetes.

diabetes; free fatty acids; fluorescence resonance energy transfer; calcium homeostasis; endoplasmic reticulum