GluN2B suppression restores phenylalanine-induced neuroplasticity and cognition impairments in a mouse model of phenylketonuria
Woo Seok Song, … , Jae Min Lim, Myoung-Hwan Kim
Woo Seok Song, … , Jae Min Lim, Myoung-Hwan Kim
Published May 8, 2025
Citation Information: J Clin Invest. 2025;135(13):e184299. https://doi.org/10.1172/JCI184299.
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Research Article Metabolism Neuroscience

GluN2B suppression restores phenylalanine-induced neuroplasticity and cognition impairments in a mouse model of phenylketonuria

Abstract

Phenylketonuria (PKU), an inborn error of phenylalanine (Phe) metabolism, is a common cause of intellectual disability. However, the mechanisms by which elevated Phe levels cause cognitive impairment remain unclear. Here, we show that submillimolar Phe perturbs synaptic plasticity through the hyperactivation of GluN2B-containing NMDARs. PahEnu2 PKU model mice exhibited submillimolar and supramillimolar concentrations of Phe in the cerebrospinal fluid (CSF) and serum, respectively. l-Phe produced concentration-dependent bidirectional effects on NMDA-induced currents, without affecting synaptic NMDA receptors (NMDARs) in hippocampal CA1 neurons. l-Phe-induced hyperactivation of extrasynaptic GluN2B resulted in activity-dependent downregulation of AMPA receptors during burst or sustained synaptic activity. Administration of l-Phe in mice decreased neural activity and impaired memory, which were blocked by pretreatment with GluN2B inhibitors. Furthermore, pharmacological and virus-mediated suppression of GluN2B reversed the impaired learning in PahEnu2 mice. Collectively, these results suggest the concentration of Phe in the CSF of patients with PKU perturbs extrasynaptic NMDARs and synaptic plasticity and that suppression of GluN2B may have the potential to improve cognitive function in patients with PKU.

Authors

Woo Seok Song, Young Sook Kim, Young-Soo Bae, Sang Ho Yoon, Jae Min Lim, Myoung-Hwan Kim

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Figure 1

Submillimolar l-Phe increases GluN2B-NMDAR activity.

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Submillimolar l-Phe increases GluN2B-NMDAR activity. (A and B) Increased...
(A and B) Increased Phe concentration in the serum (A) and CSF (B) of adult PahEnu2 mouse. (C) Experimental design for NMDAR-EPSC (top) and INMDA (bottom) recordings. Stim., stimulating electrode; Rec., recording electrode. (D) Representative traces of NMDAR-EPSCs (top) obtained at the indicated time points (1, 2), and the time course of the peak amplitudes (bottom left) of NMDAR-EPSCs measured at −40 mV in CA1 neurons. Bottom right: l-Phe had no effect on the peak amplitudes of NMDAR-EPSCs. (E) In the presence of NBQX and picrotoxin, INMDA was induced by bath application of NMDA (5−10 μM). Different concentrations of l-Phe were perfused with NMDA for 5 minutes. (F) l-Phe exhibits concentration-dependent bidirectional effects on INMDA. (G) INMDA was induced by 3−12 μM NMDA in the presence of GluN2A or GluN2B blockers. (H) l-Phe-induced facilitation of INMDA was blocked by Ro (2 μM) or ifen (6 μM) but not by PEAQX (0.5 μM). (I and J) A sample trace (left) and summary (right) of INMDA measured before and during l-Phe perfusion in HEK293 cells expressing GluN2A (I) or GluN2B (J). (K) Representative traces (top) and the peak amplitudes (bottom left) of NMDAR-EPSCs measured in the presence of TBOA (10 μM). l-Phe induced facilitation of NMDAR-EPSCs in each condition (bottom right). (L) Addition of 5, 10, and 20 μM glycine attenuated l-Phe-induced INMDA facilitation. INMDA was induced by 5 μM NMDA. (M) The concentration relationship between l-Phe-induced facilitation of INMDA and added glycine (Gly) concentration. A Student’s t test (A, B, D, F, I, and J) or a 1-way ANOVA with a post hoc Tukey’s test (H and K) was used for statistical analysis. *P < 0.05, **P < 0.01, ***P < 0.001, and NS, P ≥ 0.05. Scale bars: 50 ms and 50 pA (D and K) Veh, vehicle.