NAMPT activity plays a key role in driving autoimmune processes that characterise type 1 diabetes development in mice
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Objective
Type 1 diabetes (T1D) is characterised by destruction of pancreatic beta cells by islet-infiltrating cytotoxic lymphocytes, and elevated intra-islet secretion of pro-inflammatory cytokines. However, the underlying pathophysiological mechanisms remain incompletely understood. We hypothesise that abnormal elevation of islet NAD, via activation of NAMPT, plays a key role in driving islet autoimmune processes in T1D, and that conversely, NAMPT inhibition may be an attractive therapeutic approach for T1D.
Methods
Islets were isolated from non-diabetic CD1 mice or obtained from human islet donors and exposed to pro-inflammatory cytokine cocktail (IL-1β, TNFα and IFNγ) +/− NAMPT inhibitor. Beta-cell function was determined by static glucose-stimulated insulin secretion. Islet apoptosis was determined by caspase 3/7 activity. Islet cell differential gene expression was assessed via bulk-RNA sequencing. Diabetes was induced in CD1 mice via multiple low dose streptozotocin (MLDS) injection. MLDS mice were then administered FK866 (10 mg/kg; IP) or saline equivalent for 16 days. Ambient blood glucose was measured every 2-3 days. Beta-cell function was assessed by measurement of serum insulin and c-peptide levels. Insulin content was assessed by flow cytometry. Intra-islet immune cell infiltration, as well as immune cell proliferation and cytokine production were assessed via flow cytometry. For migration assays, islets were isolated from BALB/c mice dispersed and reaggregated into reformed islets. CD8 + cells were isolated from splenocytes derived from NY8.3 NOD mice migration of immune cells was assessed using a transwell culture protocol.
Results
NAMPT inhibition with FK866 or compound 17 protected mouse and human islets against cytokine-mediated beta cell dysfunction and death. RNAseq revealed that inhibiting NAMPT blocked pro-inflammatory cytokine-mediated gene expression linked to pro-inflammatory responses and leukocyte migration. FK866 improved glycaemic control and beta-cell function in MLDS mice. FK866 also reduced proportions of islet-residing TNFα producing CD4 + T-cells and F4/80 + macrophages, proliferation of spleen-derived CD4 + and CD8 + T-cells, and proliferation of islet-derived CD4 + T-cells and F4/80 + macrophages. Finally, FK866 was able to block pro-inflammatory cytokine-mediated migration of cytotoxic CD8 + T-cells into reformed islets.
Conclusions
This data supports a key immunomodulatory role for NAMPT in islet autoimmunity. NAMPT inhibition may represent a novel therapeutic approach for T1D.