Type 1 diabetes (T1D) is a chronic metabolic disorder that is characterized by immune-mediated β cell destruction, resulting in the lifelong need for exogenous insulin therapy. Historically, T1D has been considered a disease of β cell homicide. However, recent evidence suggests that the β cell actively contributes to its own demise in T1D through engagement of cell intrinsic stress pathways that both hasten cell death and exacerbate autoimmunity. microRNAs (miRNAs, 18-25 nt) are a class of small non-coding RNAs that post transcriptionally modulate gene expression by binding the 3’untranslated region of a target mRNA to either inhibit mRNA translation or cause mRNA degradation. In addition to these regulatory roles within their cells of origin, miRNAs can be packaged and released within extracellular vesicles (EVs), which can be transferred to recipient cells to both facilitate intercellular communication and promote disease pathogenesis. While miRNAs have been shown to regulate several key processes within the β cell and have been implicated as potential mediators of a dialogue between the immune system and the β cell in diabetes, a full understanding of the role of miRNAs in T1D pathophysiology remains elusive. To this end, we profiled changes in miRNA expression patterns in human islets and islet-derived extracellular vesicles (EV’s) in response to IL-1β and IFN-γ, two cytokines selected to model the inflammatory intra-islet milieu observed in T1D. Our initial small RNA sequencing and additional preliminary data has shown that islet miRNA expression patterns are responsive to inflammatory extrinsic cues and that miRNAs appear to be selectively packaged into islet-derived EV’s in response to cytokine treatment. Moreover, islet and islet-derived EV miRNAs exhibited striking sexually dimorphic expression patterns under basal conditions and following cytokine treatment. Interestingly, miR-155-5p and miR-146-5p were the only two miRNAs that were coordinately upregulated in cytokine-treated islets and islet-derived EVs from both male and female donors, and upregulation of these miRNAs was associated with detrimental changes in β cell function and survival. Based on these findings, we hypothesize that β cell miR-155-5p and miR-146-5p function as key molecular hubs during the evolution of T1D, playing a role in disease pathogenesis, while also having potential utility as diabetes biomarkers. To test this hypothesis, we aim to: 1) define how miRNA signatures change in human β cells during T1D progression using state-of-the art smFISH imaging approaches, focused on miR-155 and 146 and a panel of additional miRNAs predicted to have either common or distinct expression patterns in males and females; 2) elucidate the mechanisms underlying miR-155-5p and miR-146-5p upregulation under inflammatory conditions; 3) define how miR-146 and miR-155 regulate β cell function and survival, leveraging both ex vivo human islet models and novel mouse models of β cell specific deletion of miR-155; and 4) test the utility of EV miRNA signatures informed from islet RNA sequencing as clinical biomarkers using plasma EVs and β cell enriched plasma EVs collected from pediatric subjects with recent onset T1D or autoantibody positivity.

Type 1 diabetes develops as a result of a complex dialogue that is established between immune cells that infiltrate the pancreatic islet and injured and dying β cells. miRNAs are small noncoding RNAs that modulate expression of genes, and accumulating data suggest that β cell miRNA expression patterns are dynamically modulated during the evolution of type 1 diabetes. This proposal seeks to define the role of inflammatory-induced miRNAs in β cell death and diabetes pathophysiology and will test the idea that detection of β cell-derived miRNAs can serve as biomarkers of type 1 diabetes risk.