Pignalosa, Francesca Chiara (2022) MOLECULAR MECHANISMS OF DIABETES-ASSOCIATED DOPAMINERGIC DYSFUNCTION IN NEURONAL CELLS. [Tesi di dottorato]

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Abstract

DA is a catecholamine that regulates several relevant body functions, including cognition. Interestingly, dopaminergic dysfunction and cognitive decline are both associated to diabetes mellitus, an heterogenic disorder characterized by alterations in glucose, lipid and protein metabolism. An interplay between glucose metabolism and dopaminergic function has been evidenced and it has been shown that relative insulin deficiency and chronic hyperglycemia, the two major players of diabetes, can affect the dopaminergic system, altering DA content and turnover. In particular, pathological states characterized by impaired insulin signaling are associated with alterations in expression and/or activity of TH, the rate limiting enzyme for DA synthesis, suggesting that insulin is able to modulate TH expression and thus DA synthesis. On the other hand, the hyperglycemia typical of DM leads to the intracellular accumulation of MGO, a reactive dicarbonyl, able to induce the non-enzymatic glycosylation of proteins and lipids and nucleic acids, contributing to glucotoxicity. MGO plays a key role in cognitive decline and in dopaminergic dysfunction. In particular, repeated intraperitoneal injection of MGO in mice reduces DA content in the prefrontal cortex and in neuronal cells MGO modulates the expression of genes involved in the metabolism of DA. However, the molecular mechanisms underlying insulin regulation of TH and MGO modulation of dopaminergic genes are still unknown. This work aims: 1) to clarify the molecular basis of insulin action on TH expression, identifying the transcription factors involved 2) to investigate MGO ability to induce dopaminergic dysfunction and to unveil the molecular mechanisms of MGO regulation of dopaminergic genes. Since in endothelial cells MGO regulates gene expression modulating levels of specific miRNA, a particular effort has been focused on the investigation of miRNA role in MGO modulation of dopaminergic genes. The results obtained show that: 1) Insulin modulates TH mRNA and protein levels in a biphasic manner in PC12 cells. The activation of insulin receptor and of insulin effectors PI3K and ERK1/2 are required for insulin-induced increase of TH expression. The transcription factors involved downstream insulin action are HIF-1alpha and Nur77. 2) MGO induces dopaminergic dysfunction reducing dopamine levels in SHSY5Y cells. This reduction is paralleled by an increased expression of genes involved in DA degradation (MAO A and COMT) and of SNCA gene, codifying for alpha synuclein, a protein involved in neurodegeneration and known to modulate DA amount. miR-214 and miR-190a are involved in MGO induced dopaminergic dysfunction and mediate MGO effect on the expression of COMT and SNCA. In conclusion, the results showed in my PhD thesis shed light on the molecular mechanisms underlying diabetes associated dopaminergic dysfunction and represent the first step for the identification of innovative pharmacological targets potentially useful for treatment of diabetes associated dopaminergic dysfunction and cognitive decline.

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