B56δ-related protein phosphatase 2A dysfunction identified in patients with intellectual disability

Area of Science:

• Neurogenetics
• Molecular Biology
• Biochemistry

Background:

• Intellectual disability (ID) is a complex neurodevelopmental disorder with diverse genetic etiologies.
• Protein phosphatase 2A (PP2A) is a crucial enzyme regulating numerous cellular processes through dephosphorylation.
• Dysregulation of PP2A activity has been implicated in various neurological conditions.

Purpose of the Study:

• To investigate the role of inherited protein phosphatase activity dysregulation in intellectual disability.
• To identify specific mutations in PP2A subunits causing intellectual disability and associated phenotypes.
• To elucidate the molecular mechanisms by which these mutations lead to impaired PP2A function.

Main Methods:

• Genetic analysis of individuals with intellectual disability to identify de novo missense mutations in PP2A subunits (PPP2R5D and PPP2R1A).
• Functional assays to assess the stability, subunit binding, and catalytic activity of mutant PP2A components.
• Analysis of downstream signaling pathways, including GSK3β phosphorylation, in response to mutant PP2A subunits.

Main Results:

• Identified de novo missense mutations in the B56δ (PPP2R5D) and Aα (PPP2R1A) subunits of PP2A in 16 individuals with ID.
• Mutations in the B56δ subunit (E198K) and Aα subunit (R182W) were recurrent.
• Mutant PP2A subunits exhibited impaired phosphatase activity, defective subunit interactions, and led to hyperphosphorylation of GSK3β, correlating with ID severity.

Conclusions:

• Inherited dysregulation of PP2A activity due to mutations in its subunits is a novel cause of intellectual disability.
• Mutations impair PP2A function through dominant-negative mechanisms, affecting substrate dephosphorylation.
• These findings highlight the critical role of precise PP2A regulation in neurodevelopment and provide insights into the molecular basis of ID.