Browsing by Subject "β cell dysfunction"

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    OR05-3 Mir-21 Contributes to Cytokine-Induced Beta Cell Dysfunction via Inhibition of mRNAs Regulating Beta Cell Identity
    (Oxford University Press, 2019-04-15) Ibrahim, Sara; Anderson, Ryan; Mirmira, Raghavendra; Sims, Emily; Medicine, School of Medicine
    A hallmark of diabetes is the loss of physical or functional β cell mass. Alterations in β cell microRNA (miRNA) profiles have been described in diabetes. MiRNAs have also been shown to serve as important regulators of β cell development and function, implicating them in β cell dysfunction during diabetes development. Our lab has previously demonstrated that β cell microRNA 21 (miR-21) is increased in models of diabetes. However, a comprehensive analysis of the β cell effects of miR-21 remain poorly defined, and the effects of miR-21 on in vivo glucose homeostasis have never been explored. To this end, we performed a comprehensive in silico analysis of bioinformatics databases to identify potential β cell targets of miR-21, which yielded multiple targets in the Transforming Growth Factor Beta 2 (Tgfb2) and Fibroblast Growth Factor Receptor 3 (Fgfr3) pathways associated with regulation of differentiation. We hypothesize that β cell miR-21 plays a critical role in inhibiting β cell function and inducing loss of β cell identity. To validate targets in vitro, we developed a model whereby miR-21 is upregulated using a dose dependent lentiviral Tetracycline-on system in INS1 cells. Overexpression of miR-21 led to a reduction in expression levels of several members of the Tgfb2 and Fgfr3 pathways as well as multiple transcription factors associated with β cell function and identity, and an increase in aldehyde dehydrogenase transcripts, consistent with β cell dedifferentiation. To verify direct interactions between miR-21 and candidate target mRNAs, a biotin pulldown experiment was performed using a 3’ biotinylated mature miR-21 construct and a 3’ biotinylated cel-miR-67 control construct. Several mRNAs associated with β cell identity were enriched in the pulldown, indicating a direct interaction with miR-21. Lineage tracing was performed within an in vivo zebrafish model of β cell specific oxidative stress in which β cells expressed a nuclear GFP signal. Whole body knock down of miR-21 by morpholino microinjection showed a protective effect in stressed β cells and rescued against a dedifferentiated phenotype. To test the effect of miR-21 on glucose tolerance in vivo, inducible β cell specific knockout (βmiR-21KO) and overexpression (βmiR-21) mice were generated by crossing Ins1tm1(CreERT2)Thor mice with miR-21 floxed mice and miR-21-CAG-Z-EGFP mice, respectively. When compared to littermate controls, intraperitoneal glucose tolerance tests (IPGTT) exhibited hyperglycemia in βmiR-21 mice and euglycemia in βmiR-21KO mice. Metabolic studies, including glucose stimulated insulin secretion (GSIS) and insulin tolerance tests (ITT) are ongoing in our mouse models. Our results implicate miR-21 as a regulator of β cell dedifferentiation during diabetes development.
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    The Role of Beta Cell Dysfunction in Early Type 1 Diabetes
    (Wolters Kluwer, 2020-08) Sims, Emily K.; Mirmira, Raghavendra G.; Evans-Molina, Carmella; Pediatrics, School of Medicine
    Purpose of review: Emerging data have suggested that β-cell dysfunction may exacerbate the development and progression of type 1 diabetes (T1D). In this review, we highlight clinical and preclinical studies suggesting a role for β-cell dysfunction during the evolution of T1D and suggest agents that may promote β-cell health in T1D. Recent findings: Metabolic abnormalities exist years before development of hyperglycemia and exhibit a reproducible pattern reflecting progressive deterioration of β-cell function and increases in β-cell stress and death. Preclinical studies indicate that T1D may be prevented by modification of pathways impacting intrinsic β-cell stress and antigen presentation. Recent findings suggest that differences in metabolic phenotypes and β-cell stress may reflect differing endotypes of T1D. Multiple pathways representing potential drug targets have been identified, but most remain to be tested in human populations with preclinical disease. Summary: This cumulative body of work shows clear evidence that β-cell stress, dysfunction, and death are harbingers of impending T1D and likely contribute to progression of disease and insulin deficiency. Treatment with agents targeting β-cell health could augment interventions with immunomodulatory therapies but will need to be tested in intervention studies with endpoints carefully designed to capture changes in β-cell function and health.