Background and aims: Type 2 diabetes mellitus results from complex interplay between genetic predisposition and environmental factors that together promote impairment of insulin-producing β-cells. Elevated levels of glucose, fatty acid palmitate and apolipoprotein CIII (apoCIII) are implicated in this process. To delineate effects of these factors, the role of enhanced carnitine palmitoyltransferase 1 (CPT1) expression in glucolipotoxic cells, glucose-dependency of the unfolded protein response (UPR) in palmitate-induced apoptosis and activation of mitogen activated protein kinases (MAPKs) in apoCIII-induced apoptosis were evaluated. In addition, protein profiles of β-cell exposed to elevated levels of glucose or palmitate were generated to identify proteins regulated by these nutrients. Methodology: INS-1E cells were cultured at different glucose concentrations in the absence or presence of palmitate or apoCIII for up to 48 hours. CPT1 was over-expressed with a Tet-ON regulated adenovirus. In cells exposed to apoCIII, inhibitors of MAPKs p38 or ERK1/2 were included during culture. After culture, apoptosis, insulin secretion, expression of UPR-markers and MAPKs and protein profiles were determined. Results: INS-1E cells exposed to elevated levels of glucose and palmitate showed deranged insulin secretion with increased insulin secretion at non-stimulatory glucose level, enhanced apoptosis and induced expression of UPR-markers. Over-expression of CPT1 reduced basal insulin secretion and attenuated apoptosis. Palmitate-induced apoptosis was accentuated by increasing the culture glucose concentration. Markers of UPR were not modulated by the glucose concentration in INS-1E cell exposed to palmitate, however. ApoCIII-induced apoptosis in INS-1E cells was accompanied by activation of p38 and ERK1/2. Protein profiling of INS-1E cells exposed to elevated levels of glucose or palmitate revealed changes in expression of multiple β-cell proteins implicated in glucose metabolism, defence against reactive oxygen species, protein translation/folding/degradation and insulin granular trafficking. Conclusions: Over-expression of CPT1 counteracts β-cell glucolipotoxicity. Activation of UPR is not a major determinant for palmitate-induced β-cell apoptosis. ApoCIII-induced β-cell apoptosis involves activation of MAPKs. The identified differentially expressed proteins indicate a central role of altered glucose metabolism and protein synthesis in gluco- and lipotoxic β-cells and may provide specific molecular mechanisms offering new ways of treating the disease.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:uu-98367 |
| Date | January 2009 |
| Creators | Sol, E-ri Maria |
| Publisher | Uppsala universitet, Institutionen för medicinsk cellbiologi, Uppsala : Acta Universitatis Upsaliensis |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, info:eu-repo/semantics/doctoralThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, 1651-6206 ; 429 |
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