Targeting organogenesis and beta cell survivalrole of the lrh1/nr5a2-ptgs2/cox2 signaling axis in pancreatic islet physiology and pathophysiology

Laburpena

Type 1 Diabetes Mellitus (T1DM) is a disease caused by the selective destruction of pancreatic islet beta cells by aberrant activation of the immune system, characterized by a subsequent chronic unresolved proinflammatory status within the pancreas. Up to date, no effective therapies have been developed to cure this autoimmune disorder, which indeed, apart from the beta cell death and subsequent lack of insulin, leads to long-term complications that substantially impact on life quality and shorten life expectancy. However, our laboratory recently reported promising outcomes from the in vivo activation of a nuclear receptor, denoted as Liver Receptor Homolog 1 (also known as (a.k.a.) Nuclear Receptor Subfamily 5 Group A Member 2, LRH1/NR5A2), using different preclinical mouse models of autoimmune diabetes, and also in vitro, by mimicking the stress/proinflammatory conditions that characterize T1DM in both, mouse and human primary islet-cell cultures. These beneficial effects derived from the treatment with a chemical agonist of LRH1/NR5A2, codename BL001, which potentially favoured a crosstalk between the immune system and islet cells, aimed at protecting the beta cell mass via increasing its survival. Understanding the molecular signaling and consequences derived from LRH1/NR5A2 expression and activation in beta cells was the following step to exploit its therapeutic value within T1DM conditions. In this Thesis, we first uncovered the essential role of LRH1/NR5A2 expression in beta cells during neonatal development. We found that the LRH1/NR5A2 constitutive ablation in the beta cell mass caused a significant reduction of this cell type, mainly characterized by blunted proliferation, along with detrimental consequences in the metabolic and physical health of mouse pups that culminated in early death. We next demonstrated that the LRH1/NR5A2 specific activation in beta cells was the responsible of the beneficial effects observed in vivo, after BL001 treatment. Using an inducible approach, LRH1/NR5A2 ablation in adult beta cells abolished the protective effect of BL001 in streptozotocin (STZ)-treated mice, correlating with an almost complete beta cell mass destruction. In order to get insight into the mode of action of this potential anti-diabetic drug in beta cells, we next explored the molecular branches of the BL001-LRH1/NR5A2 axis, focusing on the inducible Prostaglandin Endoperoxidase Synthase-2 gene (a.k.a. Cyclooxygenase-2, Ptgs2/Cox2), previously shown to be upregulated by BL001, and which plays a role in immunomodulation. Ptgs2/Cox2 downstream signaling involves the secretion of Prostaglandin E2 (PGE2) and activation of one or several Prostaglandin G-protein coupled receptors (a.k.a. E-Prostanoid receptors, PTGERs/EPs). We found that mouse islets treated in vitro with BL001 upon a proinflammatory cytokine (CTK) challenge produced PGE2 massively. Importantly, both silencing of Ptgs2/Cox2 gene or downstream blockade of the anti-apoptotic PTGER1/EP1 receptor negated BL001-mediated increased islet-cell survival upon the CTK treatment, establishing the molecular survival signaling axis in mouse beta cells as follows: BL001-LRH1/NR5A2-Ptgs2/Cox2-PGE2-PTGER1/EP1. In parallel, we uncovered the deleterious role of the pro-apoptotic PTGER3/EP3 in an in vivo context, using the RIP-B7.1 mouse model of autoimmune diabetes. We found that PTGER3/EP3 antagonism reduced insulitis and protected the beta cell mass in these animals. Finally, as a future therapy for T1DM, it was mandatory to translate our survival cascade to a human setting. As such, we successfully recapitulated part of this pathway in human induced-Pluripotent Stem Cells (hiPSCs) derived islet-like organoids. This research work provides a complete molecular characterization of LRH1/NR5A2 activation specifically in the beta cell mass, which could be further fine-tuned to finally develop a successful therapy for T1DM.