Effects of palmitate on ER and cytosolic Ca2+ homeostasis in beta-cells.
There are strong links between obesity, elevated free fatty acids, and type 2 diabetes. Specifically, the saturated fatty acid palmitate has pleiotropic effects on beta-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 beta-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 beta-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 beta-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.
Gwiazda
Kamila S
KS
Laboratory of Molecular Signaling in Diabetes, Diabetes Research Group, Department of Cellular and Physiological Sciences, University of British Columbia, 5358 Life Sciences Bldg., 2350 Health Sciences Mall, Vancouver, BC, Canada, V6T 1Z3.
Yang
Ting-Lin B
TL
Lin
Yalin
Y
Johnson
James D
JD
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D003600:Cytosol / Q000187:drug effects* / Q000378:metabolism; D003924:Diabetes Mellitus, Type 2 / Q000209:etiology / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D005230:Fatty Acids, Nonesterified / Q000378:metabolism / Q000502:physiology; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D019301:Oleic Acid / Q000494:pharmacology; D019308:Palmitic Acid / Q000494:pharmacology*
D005230:Fatty Acids, Nonesterified; D007328:Insulin; D019301:Oleic Acid; D019308:Palmitic Acid; D002118:Calcium