S. R. Hamarneh1, J. M. Ramirez Decrescenzo1, F. M. Kuehn1, A. R. Munoz1, S. Morrison1, F. Adiliaghdam1, R. A. Hodin1 1Massachusetts General Hospital,Department Of Surgery, General & Gastrointestinal Surgery,Boston, MA, USA
Introduction: Type 2 diabetes is characterized by insulin resistance, inadequate insulin secretion and declined pancreatic β-cell mass. EI24 is a tumor suppressor gene and has emerged as a regulator of autophagy and inflammatory pathways. We sought to explore the role that EI24 plays in insulin production and β-cell proliferation.
Methods: We performed expression analysis of the EI24 gene using Gene-ontology data from patients with or without diabetes. To study the role of Ei24 in β-cell function, rat insulinoma cell line INS-1 was incubated with different inflammatory mediators and under nutrient deprivation conditions to study the effect of these stressors on Ei24 levels. Additionally, we studied the effect of Ei24 deletion or activation on inflammation levels, autophagy influx and insulin production in β-cells in vitro. Furthermore, functional analysis was performed after immunoprecipitation of Ei24 protein complexes to elucidate the plausible cellular pathways affected by Ei24 in pancreatic β-cells.
Results: Ei24 expression levels were lower in human β-cells from diabetic compared to non-diabetic patients (-1.27 vs. 1, p=0.0004). In INS-1 cells, inflammatory mediators such as TNF-α, LPS and bacterial contents suppressed Ei24 levels. Furthermore, the Ei24 expression was induced by nutrient availability. Overexpression of Ei24 increased insulin levels (Ei24 WT vs. Ei24-overexpressing Cells, 1.0 ± 0.3 Vs. 2.8 ± 0.45 Relative Expression, p< 0.01) in INS-1 cells in vitro. Ei24 deletion in β-cells altered the expression of genes involved in β-cell activity such as Ppar-α (Ei24 WT vs. Ei24-KO Cells, 1.0 ± 0.24 vs. 0.4 ± 0.056 Relative Expression, p< 0.05), Ppar-γ (Ei24 WT vs. Ei24-KO Cells, 1.0 ± 0.16 Vs. 7.2 ± 1.0 Relative Expression, p< 0.01) and Pgc1-α (Ei24 WT vs. Ei24-KO Cells, 1.0 ± 0.18 Vs. 3.7 ± 0.68 Relative Expression, p< 0.01). Also, EI24 deletion increased inflammatory cytokine levels: TNF-α (Ei24 WT vs. Ei24-KO Cells, 1.0 ± 0.08 vs. 63 ± 7.8 Relative Expression, p< 0.001), IL-1β (Ei24 WT vs. Ei24-KO Cells, 1.0 ± 0.23 Vs. 57 ± 5.5 Relative Expression, p< 0.001) and IL-6 (Ei24 WT vs. Ei24-KO Cells, 1.0 ± 0.1 Vs. 42 ± 3.8 Relative Expression, p< 0.001) and impaired autophagic flux in β cells in vitro. Functional analysis demonstrated an extended role for Ei24 in β-cell function.
Conclusion: EI24 plays a major role in β-cell function and homeostasis. The EI24 pathway in pancreatic β-cells may represent an important therapeutic target to prevent or treat diabetes in humans.