Insulin resistance uncoupled from dyslipidemia due to C-terminal PIK3R1 mutations

Area of Science:

• Genetics and Molecular Biology
• Endocrinology
• Metabolic Disorders

Background:

• Obesity-related insulin resistance is linked to fatty liver, dyslipidemia, and low adiponectin.
• Insulin receptor (INSR) dysfunction causes insulin resistance without these metabolic features.
• Downstream AKT2 dysfunction phenocopies obesity-related insulin resistance.

Purpose of the Study:

• Investigate the role of C-terminal PIK3R1 mutations in insulin signaling and metabolic phenotypes.
• Characterize the specific subphenotype of insulin resistance caused by PIK3R1 mutations.
• Determine the mechanistic link between PIK3R1 mutations and components of the metabolic syndrome.

Main Methods:

• Reported clinical and genetic findings in 5 patients with SHORT syndrome and PIK3R1 mutations.
• Analyzed plasma adiponectin levels and associated metabolic parameters.
• Performed cellular studies using patient-derived cells and 3T3-L1 preadipocytes to assess insulin signaling and differentiation.

Main Results:

• Four of five patients exhibited extreme insulin resistance without dyslipidemia or hepatic steatosis.
• Plasma adiponectin was preserved in three patients, similar to INSR dysfunction.
• PIK3R1 C-terminal mutations impaired insulin signaling in specific cellular contexts, affecting IRS1 association and AKT phosphorylation.

Conclusions:

• C-terminal PIK3R1 mutations lead to a distinct insulin resistance subphenotype resembling INSR dysfunction.
• These mutations implicate phosphoinositide 3-kinase (PI3K) in the pathogenesis of key metabolic syndrome components.
• The cellular context influences the manifestation of insulin signaling defects caused by PIK3R1 mutations.