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

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

Epilepsy affects 0.5% to 1% of people worldwide, and for 30% of those with mesial temporal lobe epilepsy (mTLE)—the most common drug-resistant form—medications fail to control seizures. Deep brain stimulation (DBS) of the hippocampus, a brain region critical for memory and seizure regulation, is an emerging treatment for refractory mTLE. But while DBS reduces seizures, scientists have long struggled to understand how it works at the molecular level. A 2021 study by researchers at Beijing Tiantan Hospital, Capital Medical University, and the Chinese Institute for Brain Research sheds new light on this question by mapping how chronic hippocampal DBS alters gene expression in a macaque model of mTLE.

The Study: A Closer Look

To mimic mTLE, the team injected kainic acid (KA)—a chemical that induces seizures—into the right hippocampus of nine male macaques. Three groups were tested:

  1. Control: Macaques given saline (no KA, no DBS).
  2. mTLE: Macaques given KA (no DBS).
  3. mTLE + DBS: Macaques given KA and implanted with DBS electrodes in the hippocampus.

The DBS group received continuous high-frequency stimulation (130 Hz, 1.5 V, 450 ms pulse width) for 3 months. After treatment, the researchers analyzed gene expression in the hippocampus using high-throughput microarrays (tools that measure thousands of genes at once) and validated results with two gold-standard techniques: quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot (which measures protein levels).

Key Findings: Genes, Pathways, and DBS

The team identified 4119 differentially expressed genes—genes whose activity changed in response to mTLE or DBS. To make sense of this data, they used a tool called the Series Test of Cluster (STC) algorithm to group genes by their expression patterns across the three groups. The most significant pattern—Profile 5—included genes that were upregulated in the mTLE group (KA injection alone) but downregulated when DBS was added. This suggested these genes are linked to both mTLE and DBS’s therapeutic effects.

Further analysis revealed Profile 5 genes were heavily involved in two key biological pathways:

  1. Extracellular Matrix (ECM)-Receptor Interaction: The ECM is a “scaffold” of proteins and sugars that surrounds cells. This pathway helps cells stick to the ECM and communicate with their environment.
  2. Focal Adhesion: These are structures that connect cells to the ECM and transmit signals (like those involved in cell growth, movement, and survival).

Both pathways are known to play roles in epileptogenesis—the process by which the brain becomes prone to seizures. For example, seizures can alter ECM and focal adhesion proteins, leading to abnormal brain wiring (like mossy fiber sprouting) and increased seizure risk. The study found DBS reversed this dysregulation: genes overactive in mTLE returned to near-normal levels with treatment.

Validating the Results

To confirm their microarray findings, the team tested nine Profile 5 genes from the focal adhesion pathway using qRT-PCR. Six genes (including Col1a2, Itgb1, and Fn1) matched the microarray results—their expression rose with mTLE and fell with DBS. While only Col1a2 (a collagen gene key to ECM structure) showed statistically significant changes across all groups, Western blot analysis of three proteins (Col1a2, Flna, and Itgb1) supported the main trend: all three were overexpressed in mTLE and reduced by DBS.

What Does This Mean for Epilepsy Treatment?

The study’s biggest takeaway is that DBS likely works, in part, by correcting mTLE-induced changes to ECM and focal adhesion pathways. These pathways are critical for maintaining brain structure and communication—when they’re disrupted by seizures, the brain becomes hyper-excitable. DBS appears to “reset” this dysregulation, reducing seizure activity.

The use of macaques—animals with brain structures similar to humans—adds weight to the findings. While the microarray analysis had a small sample size (two samples per group), the consistency with prior research (e.g., human mTLE studies showing ECM pathway changes) strengthens the conclusions.

Limitations and Next Steps

Like all studies, this one has limitations. The small sample size for microarray analysis means some results need further validation, and the team notes not all qRT-PCR results aligned with expectations. However, the Western blot data— which directly measures protein levels (the end product of gene activity)—provided strong support for the ECM/focal adhesion hypothesis.

Future research will need to explore how these pathway changes translate to human patients and whether targeting specific genes (like Col1a2) could improve DBS efficacy.

The Bottom Line

For people with drug-resistant mTLE, DBS offers hope—but understanding why it works is key to making it better. This study takes a major step forward by linking DBS to molecular changes in pathways critical for brain health. By unraveling these mechanisms, researchers are moving closer to more targeted, effective treatments for epilepsy.

Original Study Citation

Chen N, Zhang JG, Han CL, Meng FG. Hippocampus chronic deep brain stimulation induces reversible transcript changes in a macaque model of mesial temporal lobe epilepsy. Chinese Medical Journal. 2021;134(15):1845–1854. doi:10.1097/CM9.0000000000001644

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