Metabolic Modulation of Collagens in the Extracellular Matrix to Preserve GABAergic Inhibition After Traumatic Brain Injury
Abstract
Traumatic brain injury (TBI) disrupts brain circuits and can lead to post-traumatic epilepsy (PTE). Approximately 30% of PTE cases are refractory to treatment with anti-seizure drugs, so novel therapies are needed. Unfortunately, no treatment options exist to block the process of epileptogenesis that transforms the injured brain into an epileptic brain. Changes that may contribute include increased excitation, reduced inhibition, disrupted neuronal connectivity, and loss of GABAergic interneurons (INs) which provide critical inhibitory control of circuit function. Our work using the controlled cortical impact (CCI) model of rodent TBI shows that GABAergic INs are lost in the cerebral cortex following TBI, leading to cortical dysfunction. INs are also lost following human TBI. Preserving or replacing INs after TBI could act therapeutically to prevent PTE, but this presents challenges as there is no human source of precursor cells to transplant. We have focused on glycolytic inhibition as a therapeutic tool to increase GABAergic IN survival and improve IN function following TBI. Disrupting glycolysis is powerfully anticonvulsant, as demonstrated by the ketogenic diet (KD), which functions by switching the brain from glycolysis to ketosis as a source of energy. Although the KD has beneficial effects, clinicians struggle to maintain patient compliance. Therefore, direct inhibition of glucose metabolism may be beneficial. To mimic aspects of the KD, we have used the glucose analog 2-deoxyglucose (2DG, a clinical imaging tracer used to label glucose uptake in tissues) to inhibit hexokinase, the rate-limiting enzyme of glycolysis. Glycolysis is a fundamental way that cells generate energy by burning glucose, a common sugar. Increases in glycolysis occur in both human TBI patients and in animal models, making this a plausible therapeutic target. Importantly, inhibition of glycolysis using 2DG is neuroprotective and slows epileptogenesis in animal models. 2DG is already in use clinically and is well-tolerated during short treatment regimens. Excitingly, in work previously supported by the Department of Defense (DOD), we published that in vivo treatment with 2DG for 7 days following TBI in mice significantly reduced injury-induced loss of GABAergic INs, preserved synaptic inhibition, and attenuated cortical circuit hyperexcitability (Koenig, J, Journal of Clinical Investigation Insight, 2019). This validates 2DG treatment as a potential therapy for TBI/PTE, but much work remains to understand the mechanism of action of 2DG. Parallel to our DOD-funded studies, we also performed single nucleus RNAseq (snRNAseq) to identify the cell types most involved in PTE-related transcriptional changes and those most impacted by in vivo 2DG treatment. We found that (1) GABAergic INs show large changes in the transcriptional control of metabolism after TBI, and (2) in vivo 2DG treatment largely attenuated these metabolic changes in INs. In addition, our snRNAseq studies revealed that Collagen XIX is highly down-regulated in GABAergic INs, and furthermore this collagen was recently shown to drive the formation of GABAergic synapses. In brief, somatostatin-positive (SST+) INs release ColXIX into the extracellular space and ColXIX is cleaved by extracellular proteases to produce the NC1 domain. NC1 binds to integrins expressed by parvalbumin-positive (PV+) INs, and this drives PV+ INs to form synaptogamin2-positive (Syt2+) GABAergic synapses onto excitatory neurons. Loss of ColXIX leads to a reduced number of GABAergic synapses, dysfunction of GABAergic INs, and the development of epilepsy. Therefore, the loss of ColXIX after CCI could contribute to inhibitory dysfunction and PTE. In vivo treatment with 2DG following TBI appears to attenuate the loss of ColXIX in SST+ INs and increases Syt2 expression in PV+ INs, suggesting that glycolytic inhibition after TBI could act via ColXIX to prevent epileptogenic changes following TBI. Here, we will dete
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Dec 28, 2022
- Source ID
- W81XWH2210769
Entities
People
- Chris G Dulla
Organizations
- Tufts University School of Medicine
- United States Army