Peroxisomes in endocrine pancreatic islets, possible protectors against lipotoxicity?

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Bonilla_MartinezRocio_2019_03_28.pdf (6.63 MB)

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2018

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DOI:
http://dx.doi.org/10.22029/jlupub-14680

Abstract

Type 2 diabetes is characterized by impaired insulin secretion paralleled by a progressive decline in ß-cell function and chronic insulin resistance. The failure in ß-cell function has been attributed to the deleterious effect of chronically elevated levels of glucose and fatty acids. These processes, known as glucolipotoxicity, are related to the generation of chronic oxidative stress and the alteration of the intracellular energy metabolism in pancreatic ß-cells.Peroxisomes are organelles involved in the degradation of a variety of lipid derivatives and in the metabolism of reactive oxygen species. To date, scarce information is available concerning the function of peroxisomes in pancreatic ß-cells, however, the abundance of this organelle in the pancreatic endocrine region suggests that the metabolic function of peroxisomes might be particularly relevant to ß-cell function. Therefore, we investigated whether the dysfunction of peroxisomes is involved in oxidative stress and intracellular lipid accumulation which in turn results in ß-cell dysfunction and death.Therefore, the main goal of this thesis was to analyse the role of peroxisomes in maintaining normal ß-cell physiology and protecting ß-cells against glucolipotoxicity induced by palmitic and phytanic acid.To this end, a peroxisomal dysfunction was induced in ß-TC3 cells by siRNA-mediated Pex13 and Abcd3 knockdown. To obtain an integral overview on the peroxisomal compartment and its enzyme composition and to analyse the molecular consequences of peroxisome deficiency as well as the induced glucolipotoxicity in the pathology of ß cells, total RNA isolation, qRT-PCR, Western blot, immunofluorescence analysis, catalase-assay, reactive oxygen species indirect measurements, laser capture microdissection and lipid droplet accumulation analysis were carried out. Further, we also assessed the capability of the ß-TC3 cells to store/secrete insulin after the induced peroxisomal defect and lipid overload.The results in this thesis stress the importance of functional peroxisomal metabolism for the detoxification of excess FA in ß-cells. Our findings support the notion that peroxisomal dysfunction, here achieved by the silencing of Pex13, leads to an increased intracellular H2O2 production and causes mitochondrial alterations in ß-TC3 cells. Furthermore, the peroxisomal dysfunction (alone or in combination with toxic lipid concentrations) alters the lipid storage capability of ß-cells.Novel evidence of the toxicity of PHY for the ß-cell (which was exacerbated by the Pex13 knockdown) was presented, which was accompanied by a decrease in insulin biosynthesis. We showed a rise in the formation of H2O2 production after PA treatment together with an increase in catalase expression and activity suggesting a positive-feedback to re-establish the redox homeostasis that was disturbed by the addition of the FA. Moreover, the treatment with PA and the Pex13 silencing (but not PHY treatment) resulted in alterations of ß-cell-specific genes involved in ß-cell function and identity (Pax6, Pax4 and Pdx1).Further elucidation of the role of this organelle in ß-cell function and disease might bring new research opportunities to find new targets and strategies in the treatment and prevention of diabetes.

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