CDK4 is an essential insulin effector in adipocytes

Area of Science:

• Metabolic biology
• Molecular endocrinology
• Adipose tissue physiology

Background:

• Insulin resistance is central to metabolic disorders like obesity and type 2 diabetes.
• Adipose tissue dysfunction, involving fatty acid release, adipokines, and inflammation, drives insulin resistance.
• The role of cyclin-dependent kinase 4 (CDK4) in adipose tissue biology remains underexplored.

Purpose of the Study:

• To investigate the role of cyclin-dependent kinase 4 (CDK4) in white adipose tissue (WAT) biology and insulin signaling.
• To elucidate the molecular mechanisms by which CDK4 influences adipocyte function.
• To assess the relevance of CDK4 in human obesity.

Main Methods:

• Analysis of white adipose tissue (WAT) from CDK4-deficient mice and mice expressing a hyperactive CDK4 mutant (CDK4(R24C)).
• Assessment of lipogenesis and lipolysis in adipose tissue.
• Global kinome analysis following insulin stimulation in CDK4-deficient mice.
• Investigation of insulin signaling pathways, including the CCND3-CDK4 complex and insulin receptor substrate 2 (IRS2) phosphorylation.
• Analysis of CCND3 expression and IRS2 phosphorylation in human obese subjects.

Main Results:

• CDK4 deficiency in mice impairs lipogenesis and increases lipolysis in WAT.
• Hyperactive CDK4 mutant increases lipogenesis and decreases lipolysis.
• Insulin signaling is impaired in CDK4-deficient mice.
• Insulin activates the CCND3-CDK4 complex, which phosphorylates IRS2 at serine 388, creating a positive feedback loop for insulin signaling.
• CCND3 expression and IRS2 serine 388 phosphorylation are elevated in human obesity.

Conclusions:

• CDK4 is a key regulator of insulin signaling in white adipose tissue (WAT).
• The CCND3-CDK4-IRS2 pathway represents a critical positive feedback loop for maintaining adipocyte insulin sensitivity.
• Dysregulation of CDK4 and associated pathways in WAT contributes to metabolic disorders like obesity.