Hippocampus Chronic Deep Brain Stimulation Induces Transcript Changes in mTLE Model

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Hippocampus Chronic Deep Brain Stimulation Induces Reversible Transcript Changes in a Macaque Model of Mesial Temporal Lobe Epilepsy

Mesial temporal lobe epilepsy (mTLE) is the most common pharmacoresistant epilepsy syndrome, affecting approximately 30% of patients who fail to respond to antiepileptic drugs. Hippocampal deep brain stimulation (hip-DBS) has emerged as a promising therapeutic intervention for refractory mTLE, yet its molecular mechanisms remain poorly understood. This study utilized a macaque model of mTLE to systematically investigate the transcriptomic changes induced by chronic hip-DBS, revealing critical insights into its anti-epileptogenic effects.

Experimental Design and Animal Model

The study employed nine male macaques divided into three groups: a control group receiving intrahippocampal saline injections, a kainic acid (KA)-induced mTLE group, and a KA + hip-DBS group. The mTLE model was established via stereotactic KA injection into the right hippocampus, followed by continuous high-frequency hip-DBS (130 Hz, 1.5 V, 450 μs pulse width) for three months. Electrode placement was confirmed via MRI, and spontaneous seizures were monitored via video recordings. Post-stimulation, hippocampal tissues were harvested for transcriptomic and protein analyses.

High-Throughput Microarray Analysis

Microarray profiling identified 4,119 differentially expressed genes (DEGs) across the three groups. Key comparisons included:

  • Control vs. KA: 1,597 DEGs, highlighting genes upregulated during epileptogenesis.
  • KA vs. KA + hip-DBS: 1,062 DEGs, reflecting DBS-mediated reversals.
  • KA + hip-DBS vs. Control: 1,460 DEGs, indicating residual transcriptional alterations post-therapy.

Series Test of Cluster (STC) analysis categorized these DEGs into 16 expression profiles. Three profiles dominated:

  • Profile 5: Genes upregulated in KA and downregulated by hip-DBS (e.g., Col1a2, Itgb1, Fn1).
  • Profile 3: Genes upregulated in KA but unaltered by hip-DBS.
  • Profile 2: Genes progressively upregulated from KA to hip-DBS.

Pathway and Functional Enrichment

Gene Ontology (GO) analysis identified 102 significant terms (P < 0.05), emphasizing cell adhesion, extracellular matrix (ECM) organization, and integrin signaling. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed 13 enriched pathways, including:

  1. Focal adhesion (P < 0.01): Critical for ECM-receptor interactions and mechanotransduction.
  2. ECM-receptor interaction (P < 0.01): Involved in cell survival and synaptic plasticity.
  3. Calcium signaling (P < 0.001): Modulates neuronal excitability.
  4. MAPK signaling (P < 0.05): Linked to inflammation and apoptosis.

Notably, 9 genes within focal adhesion and ECM pathways (Arhgap5, Col1a2, Itgb1, Pik3r1, Lama4, Fn1, Col3a1, Itga9, Shc4) were dysregulated in mTLE and normalized by hip-DBS.

Validation of Transcriptomic Findings

qRT-PCR Validation: Six of nine tested genes (Arhgap5, Col1a2, Itgb1, Pik3r1, Lama4, Fn1) exhibited expression patterns consistent with microarray data. Col1a2 showed significant downregulation post-DBS (P < 0.001 vs. KA group).
Western Blot Validation: Protein levels of Col1a2, Itgb1, and Flna (filamin A) were elevated in KA-treated macaques (P < 0.01) and reduced by hip-DBS (P < 0.01), confirming pathway-specific reversals.

Mechanistic Insights into Hip-DBS

The study highlights hip-DBS as a modulator of ECM and focal adhesion pathways, which are pivotal in epileptogenesis. Key mechanisms include:

  1. ECM Remodeling: KA-induced overexpression of collagen isoforms (Col1a2, Col3a1) and integrins (Itgb1, Itga9) disrupts synaptic architecture. Hip-DBS reverses these changes, potentially restoring neuronal connectivity.
  2. Focal Adhesion Regulation: Dysregulated genes like Arhgap5 (Rho GTPase activator) and Pik3r1 (PI3K regulatory subunit) influence cell motility and survival. Normalization of these genes may reduce aberrant synaptic sprouting.
  3. Anti-Inflammatory Effects: MAPK pathway modulation by hip-DBS likely attenuates neuroinflammation, a known contributor to seizure progression.

Implications and Limitations

This study provides the first transcriptomic evidence of hip-DBS efficacy in a non-human primate model of mTLE. The macaque model offers translational relevance due to hippocampal homology with humans. However, small sample sizes (n=3 per group) and reliance on fold-change filtering (vs. statistical testing) for DEG identification limit robustness. Future studies should validate these pathways in larger cohorts and explore downstream effectors like MMPs and tenascins, which are implicated in ECM remodeling.

Conclusion

Chronic hip-DBS exerts anti-epileptogenic effects by reversing mTLE-induced transcriptional dysregulation, particularly in ECM-receptor interaction and focal adhesion pathways. These findings advance our understanding of DBS mechanisms and identify potential therapeutic targets for drug-resistant epilepsy.

doi.org/10.1097/CM9.0000000000001644

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