KATP Channel Mutation Disrupts Hippocampal Network Activity and Nocturnal Gamma Wave Changes

Research Background

ATP-sensitive potassium (KATP) channels are crucial ion channels that link cellular metabolism with electrical activity. Studies have shown that high activity of KATP channels is closely related to a rare disease—Developmental delay, Epilepsy, and Neonatal Diabetes syndrome (DEND syndrome). Individuals affected by this disease usually exhibit various neurological and endocrine system disorders. However, despite our good understanding of the etiology of diabetes in DEND syndrome, the pathophysiological mechanisms of neurological symptoms remain elusive.

Research Source

This study was conducted by Marie-Elisabeth Burkart, Josephine Kurzke, Robert Jacobi, Jorge Vera, Frances M. Ashcroft, Jens Eilers, and Kristina Lippmann, belonging to Leipzig University’s Carl-Ludwig-Physiology Institute, the University of Würzburg’s Neurophysiology Department for Physiology, Albert Einstein College of Medicine in Bronx, New York City, and the Henry Wellcome Centre for Gene Function at the University of Oxford in England. The paper will be published in the journal Brain in 2024.

Research Objective

The authors hypothesized that impaired activity originating from parvalbumin-positive intermediate neurons (PV-IN) might trigger epilepsy and cognitive dysfunctions in DEND syndrome. Therefore, this study aims to investigate how a common KATP channel mutation in DEND syndrome affects neural network activity and the role of PV-IN in the hippocampal CA1 region.

Research Process

Experimental Subjects and Model Construction

Experimental subjects included wild-type mice and mice carrying the KATP channel mutation gene Kir6.2-V59M. All experiments followed the European Commission’s guidelines for animal experimentation.

To study the impact of the DEND mutation, the authors constructed genetically engineered mice, using the Cre-loxP system to specifically express the Kir6.2-V59M mutation in PV-IN. Through a series of breeding processes, they produced mouse groups carrying the Kir6.2-V59M mutation and labeled PV with red fluorescence.

Electrophysiological and Behavioral Experiments

Whole-cell patch clamp tests were used to study the intrinsic properties, synaptic transmission, and network activities of PV-IN. Local field potentials (LFP) were recorded to evaluate the impact of PV-IN on hippocampal grid activities, including sharp waves and gamma oscillations. Meanwhile, long-term wireless EEG monitoring was used to study the spontaneous epileptic activities and circadian rhythms of the DEND model mice.

Histological and Immunohistochemical Studies

Immunohistochemical staining and light sheet microscopy techniques were used to analyze the distribution and morphology of PV-IN in the hippocampal CA1 region, exploring the impact of the mutation on cellular tissue modular structure.

Research Results

Impact of KATP Channel Activation on Network Activity

By applying the KATP channel agonist diazoxide to wild-type mice, the authors found that channel activation significantly reduced the number of spontaneously generated sharp waves in the hippocampal region and decreased the peak frequency of gamma oscillations. This study suggests that channel activation significantly disrupts brain network activities.

Impact of DEND Mutation on Hippocampal Network Activity

Using the mouse model carrying the Kir6.2-V59M mutation, a significant reduction in the frequency of hippocampal sharp waves was similarly observed, and gamma oscillations were significantly impaired, unable to reach the normal frequency range, revealing the mutation’s destructive effect on hippocampal network functions.

Impact on PV Intermediate Neurons

Kir6.2-V59M mutation does not directly alter the membrane potential or intrinsic properties of PV-IN but significantly reduces the cells’ gamma oscillation characteristics, including endogenous oscillations and resonance properties. The mutation also reduces the short-term synaptic inhibitory ability between PV-IN and pyramidal neurons. All these result in the disruption of cascaded network activities.

Seizures and Loss of Nocturnal Gamma Spectrum

In vivo experiments showed that the Kir6.2-V59M mutation group mice exhibited obvious epileptic activities, occurring an average of 2.7 times daily. However, LFP data showed that during circadian rhythm transitions, the DEND model mice failed to normally activate their nocturnal gamma spectrum, indicating impaired cognitive and memory functions.

Pharmacological Antagonism by Indobutylamide

Acute slice experiments in vivo found that the number of sharp waves in brain slices of mutant mice partially recovered after adding the KATP inhibitor indobutylamide. However, gamma resonance was independent of pharmacological blockade, suggesting that the structural mutation of the channel tends to affect cell morphology and connections.

Cellular Morphological Changes in PV-IN

The study found that the Kir6.2-V59M mutation caused more clustered and locally randomly distributed PV-IN, indicating that this mutation affected the organizational layout of PV-IN in the hippocampal CA1 region. Additionally, the dendritic branching ratio of PV-IN also slightly increased, suggesting different degrees of local effects by the mutation.

Conclusion

Through targeted introduction of DEND pathogenic mutations into the PV intermediate neurons of model mice, this study systematically explains the key regulatory role of KATP channels in brain neural networks. For the first time, this study reveals how DEND mutations hinder the ability of PV-IN to normally generate and maintain gamma oscillations, leading to cognitive and network functional impairments, providing important theoretical basis for exploring its treatment methods. Furthermore, the experimental model provides a direct pathway for further research on the function of KATP channels in other neural cells.