ENPP1 affects insulin action and secretion: evidences from in vitro studies

Area of Science:

• Biochemistry
• Molecular Biology
• Endocrinology

Background:

• ENPP1 negatively modulates insulin receptor (IR) activation.
• Understanding ENPP1's role in insulin signaling and glucose metabolism is crucial for metabolic disease research.

Purpose of the Study:

• To investigate the mechanisms of ENPP1 in insulin signaling, insulin secretion, and glucose metabolism.
• To compare the effects of ENPP1 K121 and Q121 variants on cellular functions.

Main Methods:

• Transfection of ENPP1 cDNA (K121 or Q121 variants) into HepG2 liver, L6 skeletal muscle, and INS1E beta-cells.
• Assays for insulin-induced IR-autophosphorylation, Akt, ERK1/2, and GSK3-beta phosphorylation.
• Measurement of PEPCK mRNA, glucose uptake, GLUT 4 mRNA, insulin secretion, and caspase-3 activation.

Main Results:

• ENPP1, especially the Q121 variant, significantly reduced insulin-induced IR-autophosphorylation and downstream signaling in liver, muscle, and beta-cells.
• ENPP1 impaired insulin-mediated glucose uptake and GLUT 4 mRNA expression in muscle cells.
• ENPP1, particularly Q121, markedly reduced glucose-stimulated insulin secretion and increased beta-cell apoptosis.
• Reduced insulin secretion was observed in human islets from ENPP1 QQ donors.

Conclusions:

• ENPP1, especially the Q121 variant, is a potent pathogenic factor in insulin resistance.
• ENPP1 dysregulates insulin signaling in liver and muscle, and impairs both function and survival of pancreatic beta-cells.
• These findings highlight ENPP1 as a key player in the pathogenesis of metabolic abnormalities.