Tissue Plasminogen Activator (tPA) Expression Is Increased by Islet Amyloid Formation In Vitro

Abstract

Islet amyloid deposition is a pathologic hallmark of type 2 diabetes (T2D) resulting in β-cell loss. tPA, an activator of fibrinolysis, attenuates brain amyloid deposition associated with Alzheimer’s disease. Based on RNAseq analysis to identify genes upregulated by islet amyloid, we found tPA to be specifically increased in islets with amyloid deposition (FDR=6.23 E-40). We therefore determined whether tPA expression is explicitly regulated by islet amyloid formation and thus could impact islet pathology in T2D. Using a transgenic mouse expressing human islet amyloid polypeptide (hIAPP) in β cells, a model of islet amyloid formation, and mice expressing non-amyloidogenic mouse IAPP (mIAPP) as control, we measured tPA mRNA expression in islets during amyloid formation. Isolated islets were cultured for up to 7 days in 11.1 or 16.7 mM glucose, the latter to induce amyloid deposition in hIAPP islets. Under amyloidogenic conditions, tPA gene expression increased 2-fold after 2 days of culture and was further elevated at 7 days in hIAPP compared to mIAPP islets (7.6±1.4 vs. 1.2±0.1, n=4, p<0.001). This increase at 7 days was not observed in hIAPP islets cultured under non-amyloidogenic conditions (1.1±0.5 vs. 7.6±1.4 in 11.1 vs. 16.7 mM glucose, respectively, n=4, p<0.001). When cultured in 16.7 mM glucose with an amyloid inhibitor (200 μM Congo Red [CR]), tPA gene expression was abrogated in hIAPP transgenic islets (1.5±0.14 vs. 9.5±0.33 with or without CR, respectively, n=4, p<0.001), implying tPA gene expression is regulated downstream of amyloid formation. Immunoblot confirmed the presence of tPA protein in islets but not in a β-cell line, and islet immunohistochemistry showed it did not co-localize with insulin, suggesting it is likely that tPA is not produced in β cells. In summary, we identified the fibrinolytic activator tPA to be upregulated with amyloid formation in islets. Thus, modulating tPA expression could reduce the deleterious impact of islet amyloid on β-cell mass in T2D. Disclosure N. Esser: None. M.F. Hogan: None. A.T. Templin: None. M. Ziemann: None. A. El-Osta: None. S. Zraika: None. R.L. Hull: Research Support; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Eli Lilly and Company. S.E. Kahn: Advisory Panel; Self; Boehringer Ingelheim GmbH, Elcelyx Therapeutics, Inc., Eli Lilly and Company, Intarcia Therapeutics, Inc., Janssen Research & Development, Merck & Co., Inc., Novo Nordisk A/S.