InsulinSignalingWeg

InsulinSignalingWeg refers to the intracellular signaling cascade triggered by insulin binding to its receptor on target cells, coordinating glucose uptake and metabolism. In most mammalian cells, insulin binds to the insulin receptor (IR), a receptor tyrosine kinase. Binding induces autophosphorylation of tyrosine residues, creating docking sites for IRS proteins (IRS-1 and IRS-2) and other adaptors.

IRS proteins recruit and activate PI3K, catalyzing conversion of PIP2 to PIP3, which recruits PDK1 and AKT to the membrane. AKT is phosphorylated and activated; downstream actions include translocation of GLUT4 vesicles to the plasma membrane in muscle and adipose tissue, increasing glucose uptake; AKT also inhibits GSK3, promoting glycogen synthesis; stimulates lipid synthesis and protein synthesis via mTORC1. Additionally, insulin signaling activates the MAPK pathway (Ras–Raf–MEK–ERK) contributing to cell growth and gene expression.

Regulation of the pathway occurs through dephosphorylation and negative regulators: PTEN and SHIP2 dephosphorylate PIP3; PTP1B and serine kinases can attenuate IRS signaling; SOCS proteins can interfere with signaling. Insulin resistance can arise from defects at any node of this cascade, affecting metabolic and mitogenic responses.

Physiological roles include promoting glucose uptake in muscle and adipose tissue and suppressing hepatic glucose production, while in the liver insulin stimulates glycogen synthesis and lipogenesis.

Clinical relevance involves the association of impaired insulin signaling with insulin resistance and type 2 diabetes. Therapeutic approaches aiming to improve insulin sensitivity include metformin, which reduces hepatic glucose production and can enhance signaling, and thiazolidinediones, which act via PPARgamma to improve peripheral insulin sensitivity.