Hexosamine biosynthesis impairs insulin action via a cholesterolgenic response

Area of Science:

• Cell Biology
• Metabolic Disease Research
• Molecular Endocrinology

Background:

• Plasma membrane cholesterol accumulation is linked to cellular insulin resistance.
• The hexosamine biosynthesis pathway (HBP) senses nutrient excess and contributes to insulin resistance.

Purpose of the Study:

• To investigate if excess glucose flux via HBP causes cholesterol production in response to hyperinsulinemia.
• To elucidate the molecular mechanisms linking hyperinsulinemia, HBP, and cholesterol metabolism.

Main Methods:

• Utilized 3T3-L1 adipocytes exposed to varying insulin doses.
• Measured mRNA/protein levels of 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGR).
• Assessed O-linked β-N-acetylglucosamine (O-GlcNAc) modification of Sp1, chromatin immunoprecipitation, luciferase assays, and effects of HBP/Sp1 inhibitors (DON, mithramycin).

Main Results:

• Hyperinsulinemia dose-dependently increased HMGR levels and plasma membrane cholesterol.
• Increased HBP flux and O-GlcNAc modification of Sp1 enhanced Sp1 binding to SREBP1 and HMGR promoters.
• HBP inhibition or Sp1 inhibition prevented HMGR upregulation and cholesterol accumulation.
• Sp1 inhibition restored cytoskeletal structure and insulin-stimulated glucose transport.

Conclusions:

• Increased HBP activity promotes a cholesterol synthesis program via Sp1 transcriptional activation.
• This mechanism elevates plasma membrane cholesterol, impairing insulin action by disrupting cytoskeletal function.
• Targeting HBP or Sp1 may offer therapeutic strategies for insulin resistance.