ABHD6 Drives Endocytosis of AMPA Receptors to Regulate Synaptic Plasticity and Learning Flexibility

Research Background

In the exploration of the neural system’s mechanisms, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPAR) maintain the tuning ability of neurons in both resting and active states through the regulation of AMPAR-interacting proteins. The endocytosis of AMPA receptors depends on vesicle-mediated endocytosis, which constitutes the cellular basis for long-term depression (LTD) and homeostatic downscaling. This process is regulated by multiple AMPAR-interacting proteins, such as PICK1, AP2, and BRAG2, which influence the recruitment of core termination machinery of AMPAR endocytosis and the formation of clathrin-coated pits.

Research Question

Previous studies have found that α/β-hydrolase domain-containing 6 (ABHD6), an endogenous cannabinoid (ECB) hydrolase, hydrolyzes monoacylglycerol (MAG) lipids in various tissues and regulates the ECB signaling system in the brain by controlling the levels of 2-arachidonoylglycerol (2-AG) to modulate the activity of CB1 and CB2 receptors. However, ABHD6 as an auxiliary component of the AMPAR complex shows a negative regulation on surface AMPAR trafficking, particularly preventing AMPAR tetramerization in the endoplasmic reticulum. Although ABHD6 is also present at postsynaptic sites, its interaction with AMPAR at these sites and its physiological significance in AMPAR trafficking remain unclear.

Paper Source

The article “ABHD6 drives endocytosis of AMPA receptors to regulate synaptic plasticity and learning flexibility” was written by Meng Pingcheng, Yang Lei, Su Feng, Liu Ying, Zhao Xinyi, and others from well-known research institutions such as Capital Medical University, Peking University, Nanjing University, and the Institute of Psychology, Chinese Academy of Sciences. It was published in the journal Progress in Neurobiology on December 28, 2023.

Research Process

a) Research Workflow

1. Establishment of Mouse Model: The research team used CRISPR/Cas9 technology to create ABHD6 knockout (ABHD6KO) mouse models.
2. Genotype Identification and Basic Phenotypic Observation: The complete knockout of ABHD6 in the mouse hippocampus was verified by quantitative reverse transcription PCR and Western Blot, and the birth rate and body weight were assessed.
3. Synaptic and Protein Component Analysis: The total hippocampal, synaptosomal, and postsynaptic density (PSD) fractions were purified and analyzed for proteins, confirming the presence of ABHD6 and its knockout without affecting the composition of major synaptic proteins and synaptic ultrastructure.
4. Recording Synaptic Transmission and Plasticity: Whole-cell patch-clamp techniques were used to record the AMPA/NMDA ratio, among other synaptic transmission and plasticity experiments, in the Schaffer collateral pathway of the hippocampus in ABHD6KO and wild-type (WT) mice.
5. AMPAR Endocytosis Experiments: Surface AMPAR levels were assessed using quantitative immunostaining and membrane protein biotinylation assays to study the influence of ABHD6 on surface expression and endocytosis of AMPAR.
6. Learning and Memory Behavioral Tests: Various behavioral tests such as the paw-hole test, Morris water maze, and fear conditioning experiments were conducted to analyze the learning and memory performance of ABHD6KO mice.

b) Detailed Research Results

1. Increased Baseline Synaptic Response and Surface Expression of Postsynaptic AMPAR: It was found that ABHD6 knockout significantly increased AMPAR-mediated synaptic transmission in hippocampal neurons.
2. Impaired Hippocampal LTD: Low-frequency stimulation (LFS)-induced LTD was significantly reduced in ABHD6KO mice, whereas metabotropic glutamate receptor 5 (mGluR5)-dependent LTD induced by dihydroxyphenylglycine (DHPG) showed no change.
3. Impaired Homeostatic Synaptic Downscaling: ABHD6KO mice failed to reduce the amplitude of mini excitatory postsynaptic currents (miniEPSCs) during high-activity-induced homeostatic synaptic downscaling, indicating ABHD6’s important role in this process.
4. Activity-Dependent AMPAR Endocytosis Is Blocked: NMDA-induced AMPAR endocytosis was significantly reduced in ABHD6KO mice, whereas chemically induced long-term potentiation (LTP) exhibited no significant changes, highlighting the importance of ABHD6 in AMPAR endocytosis independent of its hydrolase activity.

c) Research Conclusions and Value

Conclusion: ABHD6, as a crucial regulator of AMPAR endocytosis, plays a vital role in synaptic plasticity and learning flexibility by regulating LTD and synaptic downscaling. Its function in regulating AMPAR endocytosis is independent of its hydrolase activity.

Scientific Value: This study reveals a new mechanism of ABHD6 in neurons, providing new insights into the regulation of AMPA receptors. Application Value: The findings offer new potential targets for the treatment of neurodegenerative diseases.

d) Research Highlights

1. Discovery of a Novel Regulator: The study uncovers the significant role of ABHD6 in AMPAR endocytosis and synaptic plasticity.
2. Function Independent of Enzymatic Activity: ABHD6’s role in regulating AMPAR endocytosis is independent of its hydrolase activity, providing a new perspective on ABHD6’s function.
3. Significant Influence on Learning Flexibility: Deficits in learning flexibility in ABHD6KO mice underscore its importance in cognitive function.

e) Other Valuable Information

The study also indicates that ABHD6’s regulation of AMPAR endocytosis may involve direct interactions with the C-terminal domain of AMPAR subunits, affecting or promoting their interactions with other endocytic regulatory proteins. This lays an important foundation for further research on the mechanisms of ABHD6’s role in neural activity.