Islet amyloid, formed by islet amyloid polypeptide (IAPP) aggregates, may be a trigger of islet inflammation in T2D. In vitro studies using bone marrow-derived macrophages suggest roles for Toll-like receptor 2 (TLR2), and the NLRP3 inflammasome in mediating IAPP aggregate-induced inflammatory gene expression. To assess the impact of amyloid on islet macrophages in vivo, we performed single cell RNA sequencing on sorted islet immune cells from mice which develop islet amyloid via expression of human IAPP (hIAPP-Tg mice); this uncovered robust changes in islet macrophage populations, including upregulation of TLR2 (∼3.0 fold, p=0.002) and NLRP3 (∼2.8 fold, p=0.006) in proinflammatory macrophages. To test whether these receptors mediate IAPP aggregate-induced inflammation and beta cell dysfunction in vivo, we examined if TLR2 or NLRP3 deletion attenuated islet amyloid-induced beta cell dysfunction by crossing hIAPP-Tg mice to Tlr2-/- or Nlrp3-/- mice. Loss of TLR2 did not impact beta cell dysfunction in hIAPP-Tg Tlr2-/- male or female mice compared to hIAPP-Tg Tlr2+/+ littermates, revealing that TLR2 is not necessary for islet-amyloid driven beta cell pathology. In contrast, NLRP3 knockout improved glucose tolerance in young hIAPP-Tg male mice and delayed diabetes onset on high fat diet (HFD) (10.9 vs. 4.9 weeks; p=0.02) compared to hIAPP-Tg littermates with intact NLRP3. However, hIAPP-Tg Nlrp3-/- males eventually developed diabetes and glucose intolerance on long-term HFD. In female hIAPP-Tg mice, in which islet amyloid forms more slowly, NLRP3 deletion markedly improved glucose tolerance after 18 weeks of HFD relative to hIAPP-Tg Nlrp3+/+ controls (AUC: 886 ± 207 vs. 1854 ± 296, p<0.0001). The glycemic benefit of NLRP3 knockout was not due to altered insulin sensitivity, and was absent in non-hIAPP expressing mice, which do not form amyloid. Thus, NLRP3, but not TLR2, mediates early islet amyloid-induced beta cell dysfunction, and may be a therapeutic target for islet inflammation in T2D.

Disclosure

H.C. Denroche: Advisory Panel; Self; Integrated Nanotherapeutics. N. Kim: Employee; Self; Integrated Nanotherapeutics. K. Yau: None. D. Nackiewicz: None. P.C. Orban: None. I. Suen: None. C.B. Verchere: Advisory Panel; Self; Sirona Biochem. Board Member; Self; Integrated Nanotherapeutics.

Funding

JDRF; Canadian Institutes of Health Research

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