Adipose Tissue and Insulin

adipose tissue

• metabolic role in energy homeostasis

• endocrine organ

  • synthesizes and secretes hormones and adipokines

adipose mass

• determined by adipocyte number and function

• larger cells are less sensitive to insulin, higher rates of lipolysis

leptin

deficiency causes severe obesity, insulin resistance, and impaired thermogenesis

adiponectin

• increases insulin sensitivity

• expressed in mature adipocytes

• binding to receptor increases glucose uptake and fatty acid oxidation in muscle and adipose

RBP4 (retinol binding protein 4)

• specific circulating transport protein for retinol

• secreted by adipose tissue when GLUT channels don’t detect glucose

• inhibits insulin signaling (inhibits phosphoylation of insulin receptor)

resistin

• adiponectin’s Wario

• structurally similar to adiponectin

• leads to insulin resistance, decreases insulin sensitivity

visfatin

• produced by macrophages

• levels correlated with amount of visceral fat

• insulin-mimetic effects

insulin

• secreted from pancreatic beta cells

• anabolic hormone that plays a crucial role in energy store

  • conversions of precursors into storage forms

tyrosine phosphatases

enzymes that catalyze the removal of phosphate groups from tyrosine residues on proteins

• inhibit insulin signaling transduction

insulin signaling inhibitors

block the receptor IRS interaction

serine kinases

inhibit receptor activity by dephosphorylating serine rather than activation via tyrosine phosphorylation