Low-Dose Streptozocin-Induced Diabetes in Mice: Electron Microscopy Reveals Single-Cell Insulitis Before Diabetes Onset

Abstract

We investigated the morphology of mouse islets 5 days after completion of low-dose streptozocin treatment of C57BL/6 mice by electron microscopy. At this stage, mice were still normoglycemic and light microscopy did not reveal massive islet infiltration. The electron-microscopic investigation revealed two characteristics indicative of ongoing islet cell destruction. In all islets investigated, lysed islet beta-cells were recognized by disrupted plasma membranes and concomitantly decreased plasma contrast. Many of the lysed islet beta-cells still contained numerous insulin granules. We also found immunocytes scattered throughout the islets, most of which could be identified as macrophages. Some were found engaged in phagocytosis of islet beta-cell debris. This early stage of islet lesion termed single-cell insulitis is followed by the well-known later stage of massive infiltration easily recognized in light microscopy. Administration of silica particles to mice treated with low-dose streptozocin inhibited macrophage infiltration of islets as shown by immunocytochemistry with macrophage-specific monoclonal antibody F4/80. In parallel, the development of hyperglycemia was suppressed. The observations favor a pathogenic role of macrophages in islet destruction.

Immunophenotyping of insulitis in control and essential fatty acid deficient mice treated with multiple low-dose streptozotocin

“…The results of our current study confirm the findings of others who have reported that LDS-induced insulitis is characterized by both lymphocytic and histiocytic infiltrates and that the latter precedes the former [16][17][18]. Our study also confirms our previous observation that EFA deficiency decreased the severity of lymphocytic insulitis in LDS-treated mice [10,11,12].…”

“…Herald et al [16] and Kantwerk et al [17] demonstrated with immunohistochemistry large numbers of CD4-positive and CD8-positive cells. Later, Kolb-Bachofen et al [18] demonstrated that, prior to onset of insulitis and diabetes, macrophages infiltrated the islets and they termed this "single cell insulitis". The same group also demonstrated that single cell insulitis played an important role in the onset of LDS diabetes by demonstrating that treatment with silica, a macrophage toxin, was more protective than T-cell depletion [19].…”

DsAAV8-mediated expression of glucagon-like peptide-1 in pancreatic beta-cells ameliorates streptozotocin-induced diabetes

“…Beta-cell destruction following multiple low-dose STZ treatment has been shown to involve islet infiltration by both macrophages and lymphocytes, 31,32 thus recapitulating, in part, the known etiology of type-1 diabetes. As shown in Figure 3c, mice receiving either DsAAV-MIP-eGFP or vehicle alone had AAV-mediated expression of GLP-1 in beta-cells MJ Riedel et al significantly higher blood glucose levels than those receiving DsAAV8-MIP-GLP-1 as measured by twoway, repeated-measures analysis of variance.…”

Cytotoxic action of IL‐1β against pancreatic islets is mediated via nitric oxide formation and is inhibited by NG‐monomethyl‐l‐arginine

“…Macrophages have been repeatedly shown to play a crucial role in early phases of disease development in animal models: they constitute the major infiltrating cell type during early insulitis in BB rats [1], NOD mice [2] and low-dose streptozotocintreated mice [3]. Impairment of maerophage function prevents disease manifestation in these animals [3][4][5]. Activated but not resident macrophages were found to rapidly and effectively kill islet ceils but not hepatocytes or thyroeytes [6].…”