Neurodevelopmental disorders are associated with disabilities in brain function that affect a child's behavior, memory or ability to learn. Such disabilities carry devastating mental, emotional, and economic consequences for the individuals, their families, as well as society. The molecular bases for a subset of disabilities involve disease-causing mutations in various ion channel families, including NMDA receptors (NMDARs). The cation-selective NMDAR channels formed from assembly of two glycine-binding GluN1 subunits and two glutamate-binding GluN2 subunits mediate a slow, Ca2+-permeable component of excitatory synaptic currents that can trigger changes in synaptic strength, a cellular correlate of learning. NMDARs also play an important role in normal brain development. A large number of mutations (>140) have been reported in just the last three years, leading to the view that these mutations are present in a subset of patients with neurological disorders, particularly early onset intractable seizures. Surprisingly, the incidence of NMDAR mutations found in pediatric patients presenting with neurological problems is 5.7%, similar to or higher than that for Na+, K+ , Ca2+ channels and GABA receptors. Mutations in NMDAR subunits have been identified in children with a broad range of neurodevelopmental problems, including attention deficit hyperactivity disorder (ADHD), autism spectrum disorders, developmental delay, mental retardation, schizophrenia, intellectual disability, and intractable seizures. Unfortunately, virtually no functional analysis of these mutations exists, making it impossible to evaluate effects of mutations in the context of clinical phenotype. We proposed 4 lines of experimentation addressing the molecular mechanism underlying neurological diseases suggested to arise from mutations in NMDAR subunits. We will study the functional effects of mutations in the transmembrane domain (TM), linkers, and ligand binding domains (LBD) and test the ability of FDA-approved drugs to rectify the mutation-induced gain-of-function. All experiments will utilize receptors that contain 0, 1, or 2 mutant NMDAR subunits, enabling an assessment of function in heterozygous patients.
Aim 1. How do human NMDAR mutations in the TM- linker regions impact function? We will analyze 26 mutations in the transmembrane domain or associated linkers. We will collaborate on efforts to obtain crystals of the open channel configuration.
Aim 2. How do human NMDAR mutations in the ligand binding domains impact function? We will evaluate the functional effects of 36 mutations in the ligand binding domain, and collaborate to obtain crystallographic data.
Aim 3. How do human NMDAR mutations influence neuronal trafficking and function? We will analyze the properties of NMDAR-mediated synaptic current in slice cultures transfected with mutant NMDAR subunits.
Aim 4. Are NMDAR channelopathies treatable? We will evaluate the potency (IC50) of FDA-approved NMDAR antagonists at gain-of-function NMDAR mutations and evaluate the neurotoxic potential of NMDAR mutations.
NMDA receptors mediate communication between neurons and thus play important roles in normal brain functions and a wide range of neurological diseases. Genetic mutations of NMDA receptor genes have been identified in children with profound neurodevelopmental problems, including intractable seizures, attention deficit hyperactivity disorder (ADHD), autism spectrum disorders, developmental delay or mental retardation, schizophrenia, and intellectual disability. We will determine functional changes of these mutations and their pharmacological profiles, which provide the first opportunity to understand the molecular mechanism and targeted therapeutic strategies for these neurological disorders.
Showing the most recent 10 out of 15 publications
