AbstractsBiology & Animal Science

Dissecting the microRNA pathway in the pancreatic β-cell during insulin resistance


by Sudhir Gopal Tattikota




Institution: Freie Universität Berlin
Department: FB Biologie, Chemie, Pharmazie
Degree: PhD
Year: 2015
Record ID: 1114023
Full text PDF: http://edocs.fu-berlin.de/diss/receive/FUDISS_thesis_000000098970


Abstract

In summary, two critical aspects of the β-cell biology have been addressed in this thesis. We have shown that loss of Ago2 from β-cells potentiated the release of β-cell secretome, besides insulin, as a result of de-repression of miR-375-targeted genes. The β-cell secretome led to the identification of several proteins that are important for optimal β-cell function. Interestingly, several proteins within the β-cell secretome were previously shown to be associated with bone physiology. Their release by the β-cells is intriguing and future investigations could shed novel light on the β-cell-bone interactions. On the other hand, we also established that silencing of miR-184 in vivo promoted the expression of its target Ago2 in the islets of several mouse models of insulin resistance. In mouse models that overexpress Ago2 (dox-Ago2) or mice genetically ablated for miR-184 (miR-184KO), increased expression of Ago2 resulted in increased β-cell proliferation. Elevated levels of Ago2 in the islets of ob/ob mice enhanced miRNA function via increased suppression of genes targeted by miR-375 such as Cadm1, Gphn, Rasd1, Ywhaz, and HuD. These target genes are implicated in cellular growth and insulin secretion pathways. Importantly, the miRNA pathway in the β-cell is able to effectively sense nutrient changes and adjusts its activity accordingly. This is demonstrated by the fact that restoration of insulin sensitivity by ketogenic diet in ob/ob mice promoted the expression of miR-184 in the islets. This in turn restored the levels of Ago2, Cadm1, and ultimately the β-cell mass. Lastly, the levels of miR-184 were found to be downregulated in the islets of T2D human donors, demonstrating the functional relevance of miR-184 in human disease. In addition, the expression of Ago2 inversely correlated to that of miR-184 in islets across the entire cohort of human subjects. These observations clearly indicate that feedback mechanisms exist within the miRNA pathway so as to adjust the optimal release of β-cell secretome, besides insulin, and β-cell proliferation according to insulin sensitivity. Future studies to further dissect this pathway in the β-cell would shed novel light into mechanisms of T2D in humans. Die hier vorgelegte Arbeit adressiert zwei kritische funktionelle Aspekte der β-Zellbiologie. Wir konnten zeigen, dass der Verlust von Ago2 in β-Zellen zur verstärkten Freisetzung von Insulin führt, bedingt durch die Derepression von miR-375-Zielgenen. Außerdem konnte gezeigt werden, dass Ago2 auch das β-Zell-Sekretom reguliert. Durch die erstmalige Identifizierung aller von β-Zellen freigesetzter/sezernierter Proteine, waren wir auch in der Lage, einige Proteine zu identifizieren, die eine wichtige Rolle für die normale Funktion von β-Zellen spielen. Besonders interessant dabei ist, dass eine Reihe von Proteinen, die von β-Zellen freigesetzt werden auch in der Physiologie von Knochenzellen eine Rolle spielen. Dieser Umstand ist überraschend und zusätzliche Untersuchungen könnten bisher unbekannte Verbindungen zwischen…