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Le rôle du récepteur aux LDL et de PCSK9 dans le diabète de type 2

Abstract : Statins are lipid-lowering drugs widely prescribed to prevent cardiovascular diseases. They inhibit the endogenous synthesis of cholesterol and thereby increase LDLR gene expression by activating the SREPB-2 transcription factor. The positive effects of statins regarding cardiovascular diseases are undisputable. However, their action is limited by the proprotein convertases subtilisin kexin type 9 (PCSK9), the natural inhibitor of the LDL receptor (LDLR), which is also activated by the SREBP-2 transcription factor. As a result, novel lipid-lowering strategies targeting circulating PCSK9 have emerged and have been approved recently. These are the PCSK9 inhibitors. Despite their well-established beneficial effects, the use of high doses of statins for long-term treatments induces in rare instances the onset of type 2 diabetes in predisposed individuals. In addition, “loss of function” genetic variants of PCSK9 are associated with an increased risk of type 2 diabetes. The effects of long term use of PCSK9 inhibitors on the risk of type 2 diabetes remain to be established. Thus, we hypothesized that cholesterol overload of insulin secreting pancreatic beta cells induced by the overexpression of the LDLR at their plasma membranes following treatment with statins and PCSK9 inhibitors may cause cell dysfunction, lower insulin secretion, and ultimately type 2 diabetes. The aims of my thesis were (i) to determine the circulating levels of PCSK9 and their modulation by statins in patients with type 2 diabetes, (ii) to determine if reduced circulating PCSK9 levels are predictive of new onset type 2 diabetes and finally (iii) to investigate the effect of statins, PCSK9, and PCSK9 inhibitors on beta cell function. Using three cohorts of patients, we showed that circulating PCSK9 plasma levels are increased in patients with type 2 diabetes and that reduced circulating PCSK9 levels are negatively associated with insulin resistance and elevated fasting blood glucose. In human pancreatic sections and human pancreatic beta cell lines, we showed for the first time that PCSK9 is expressed, synthesized and secreted only by beta cells in pancreatic islets. We did not find any significant effect of PCSK9 or PCSK9 inhibitors on glucose stimulated insulin secretion. Altogether, my thesis works underpin that the use of PCSK9 inhibitors in the clinic will probably not be diabetogenic. This is reassuring regarding the development of these new lipid-lowering therapies.
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Submitted on : Tuesday, September 1, 2020 - 2:34:26 PM
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Stéphane Ramin-Mangata. Le rôle du récepteur aux LDL et de PCSK9 dans le diabète de type 2. Biochimie, Biologie Moléculaire. Université de la Réunion, 2020. Français. ⟨NNT : 2020LARE0005⟩. ⟨tel-02927160⟩

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