The very early phase of Type 1 Diabetes is driven by neolymphangiogenesis.

Background: Before adaptive immune infiltration, inflammation and innate response remodels the islet to allow insulitis. The understanding of the cellular and molecular basis for the initial events would define new potential therapeutic targets. A single cell dissection of the very early phase of disease in mice has allowed us to dissect the mechanisms supporting peri-islet lymphangiogenesis and initial CD4 T cell recruitment.

Method: 4-8 week old NOD pancreas were examined for the presence of lymphatic vasculature by immunocytochemistry. Single islet macrophages were sorted by cytometry and examined for targeted gene expression. Upregulated genes identified in transcriptomic profiling were confirmed in tissue section. In vivo blockade of molecules identified in this study was monitored on glycemia and disease onset.

Results: Macrophages appear to be the drivers of lymphangiogenesis through the expression of the master transcription factor Prox1. Through epigenetic modifications, Prox1 drives the expression of the trophic factor of lymphatic vessels, VEGF-C, and its receptor VEGFR3. This signaling loop induces the expression of LYVE-1 and podoplanin on endothelial cells and the building of new lymphatic structures within lymphokin islands, another soluble factor expressed during inflammation. Prox1, VEGF-C, VEGFR3, LYVE-1, podoplanin, and midkine are expressed at a very early stage of disease, and are all potential targets for therapeutic intervention. In a proof-of-concept experiment, blocking podoplanin with antibodies delayed the onset of diabetes. Blockade of VEGF-C/VEGFR3 signaling with VEGF traps, inhibition of Prox1 activity through pharmacologic inhibition of CPT1A, and anti-podoplanin antibodies are all used to evaluate the most effective approach to prevent anti-islet immunity. A therapeutic intervention at a pre-T cell phase of disease appears within reach.