Protective Role of ST2 Signaling in Diabetic Nephropathy

Background: Diabetic nephropathy (DN) contributes to morbidity in Diabetes patients (DM), for whom glycemic control remains the primary treatment. The IL-1 superfamily member IL1RL1 (ST2), is activated by its ligand IL-33 was identified in type 2 immune response Recent data suggests loss of IL-33 or its receptor ST2 resulted in increased susceptibility to Type-2 diabetes, increased adiposity, and worsened metabolic profile. Studies from our lab have shown that a novel hybrid cytokine IL233, bearing activity of IL-2 and IL-33, enhances T-regulatory cells (Tregs) and attenuated the loss of kidney function in diabetic Ob/Ob mice, as shown by proteinuria, urinary albumin creatinine ratio (ACR). Histopathology of kidney showed lower inflammation with attenuation of glomerular hypertrophy and mesangial expansion in IL233 treated mice. However, there is lack of knowledge for the role of ST2 signaling in DN. Methods: We investigated the difference between wild type (WT) and ST2KO mice for susceptibility to DM and DN. We also generated mice with ST2 deletion in Tregs cells (Il1rl1fl/flFoxp3YFP-Cre) to understand the role of ST2 expressing Tregs in DN. Mice were subjected to multiple low dose streptozotocin (STZ). The structure and function of pancreas and kidney were probed using flow cytometry, histology, immunohistochemistry, ELISA, quantitative PCR as well as enzymatic and biochemical analysis. Results: Histological analysis of the pancreatic tissue through hematoxylin and eosin staining indicated ST2KO mice had a lower number of islets with smaller islet diameters. Single cell RNA sequencing unraveled unique cell states in knockout islets compared to the WT counterparts. Both immunostaining and transcriptomic analysis indicated lower insulin levels in ST2KO islets compared to WT islets. In vivo studies using low dose STZ suggested ST2 deficient mice were more susceptible to diabetes compared to WT mice. In addition, Urinary ACR assay indicated both the global as well as Treg specific loss of ST2 worsened the susceptibility and severity of DN. Flow cytometry data showed increased inflammatory milieu in the pancreas and the kidneys of mice lacking ST2 expression globally or in Tregs. Conclusion: Results from our studies demonstrate a prominent role of ST2 in islet function, maintain immune homeostasis and protection from DN in a Treg-dependent manner. Funding: NIDDK Support, Private Foundation Support