Silencing Mitogen-activated Protein 4 Kinase 4 (MAP4K4) Protects Beta Cells from Tumor Necrosis Factor-α-induced Decrease of IRS-2 and Inhibition of Glucose-stimulated Insulin Secretion

Abstract

Obesity and type 2 diabetes present partially overlapping phenotypes with systemic inflammation as a common feature, raising the hypothesis that elevated cytokine levels may contribute to peripheral insulin resistance as well as the decreased beta cell functional mass observed in type 2 diabetes. In healthy humans, TNF-␣ infusion induces skeletal muscle insulin resistance. We now explore the impact of TNF-␣ on primary beta cell function and the underlying signaling pathways. Human and rat primary beta cells were sorted by FACS and cultured for 24 h ؎ 20 ng/ml TNF-␣ to explore the impact on apoptosis, proliferation, and short-term insulin secretion (1 h, 2.8 mM glucose followed by 1 h, 16.7 mM glucose at the end of the 24-h culture period) as well as key signaling protein phosphorylation and expression. Prior exposure to TNF-␣ for 24 h inhibits glucose-stimulated insulin secretion from primary beta cells. This is associated with a decrease in glucose-stimulated phosphorylation of key proteins in the insulin signaling pathway including Akt, AS160, and other Akt substrates, ERK as well as the insulin receptor. Strikingly, TNF-␣ treatment decreased IRS-2 protein level by 46 ؎ 7% versus control, although mRNA expression was unchanged. While TNF-␣ treatment increased MAP4K4 mRNA expression by 33 ؎ 5%, knockdown of MAP4K4 by siRNA-protected beta cells against the detrimental effects of TNF-␣ on both insulin secretion and signaling. We thus identify MAP4K4 as a key upstream mediator of TNF-␣ action on the beta cell, making it a potential therapeutic target for preservation of beta cell function in type 2 diabetes.

MicroRNA-30d Induces Insulin Transcription Factor MafA and Insulin Production by Targeting Mitogen-activated Protein 4 Kinase 4 (MAP4K4) in Pancreatic β-Cells

“…silencing has reproduced that reported earlier in rat primary ␤-cells (30). MafA is a highly phosphorylated protein and tightly controlled by the coordinated action of multiple kinase pathways (36 -39).…”

“…Of interest, knockdown of MAP4K4 by siRNA prevented the inhibitory effect of TNF-␣ on IRS2 expression in Min6 cells (Fig. 6C), an observation consistent with a previous study in rat primary islets (30). Taken together, the data presented here demonstrated unequivocally that MAP4K4 negatively regulates insulin gene transcription and signaling and that silencing of MAP4K4 essentially mimicked miR-30d-targeted down-regulation of MAP4K4 in protecting ␤-cells from TNF-␣-induced inhibition.…”

Mixed Lineage Kinase-3 Stabilizes and Functionally Cooperates with TRIBBLES-3 to Compromise Mitochondrial Integrity in Cytokine-induced Death of Pancreatic Beta Cells

“…Other studies have shown that Akt activity can be inhibited by proinflammatory cytokines (42,43). We therefore examined whether TRB3 knockdown attenuated the ability of cytokines to inhibit Akt Ser 473 phosphorylation (Fig.…”

Structure-Based Design of GNE-495, a Potent and Selective MAP4K4 Inhibitor with Efficacy in Retinal Angiogenesis

“…M itogen-activated protein kinase kinase kinase kinase 4 (MAP4K4, or HGK), and its homologues Misshapen and MIG-15 have been shown to regulate a multitude of biological processes, including embryonic development, 1,2 metabolism, 3,4 inflammation, 5 neural regeneration, 6 angiogenesis, 7 and cancer. 8,9 Given its diverse roles in these processes, we became interested in the therapeutic potential of MAP4K4 inhibition and began an endeavor to identify an inhibitor that would function in vivo.…”