Effect of Extracellular Citrate on Neuronal Excitability in SLC13A5 Epilepsy - Project Summary SLC13A5 Epilepsy, or developmental epileptic encephalopathy 25 (DEE25), is a genetic form of epilepsy characterized by severe multi-focal seizures within the first 24 hours of birth. This disorder is caused by bi-allelic mutations in the SLC13A5 gene, which encodes a sodium citrate co-transporter (NaCT) that mediates citrate import across the plasma membrane. Though there is currently limited understanding of the complete disease spectrum and lack of comprehensive characterization, studies have demonstrated that patients with SLC13A5 Epilepsy exhibit elevated citrate levels in both the cerebrospinal fluid and plasma. Given the function of the SLC13A5 protein in citrate import and regulation, it is hypothesized that SLC13A5 deficiency leads to the accumulation of extracellular citrate. Studies have found the liver and brain express high levels of SLC13A5, but the tissue-specific source of excess citrate and its impact on neuronal excitability, and subsequent epileptogenesis, are unknown. I will draw on years of translational neuroscience experience in my sponsor’s laboratory to understand the relationship between extracellular citrate levels and neuronal excitability. In mice, homozygous loss of SLC13A5 (SLC13A5-/-) is associated with epileptiform discharges in mouse electroencephalography. Preliminary data from our laboratory has found that increasing levels of extracellular citrate lead to increased interictal discharge events in local field potential recordings from both wild-type and SLC13A5-/- mouse brain slices. Based on this data, I hypothesize that elevated citrate levels, secondary to tissue-specific SLC13A5 deficiency, will increase overall neuronal excitability, thereby contributing to epileptogenesis. To test this hypothesis, I will examine the impact of SLC13A5 deficiency in tissues where SLC13A5 is most highly expressed by combining advanced imaging with traditional electrophysiology. In Aim 1, I will identify the tissue(s) where aberrant SLC13A5 expression leads to epileptogenesis using mouse electroencephalography and quantitative PCR. In Aim 2, I will assess the impact of elevated extracellular citrate on neuronal excitability using whole-cell patch-clamp electrophysiology and liquid chromatography-mass spectrometry of mouse bodily fluids. In Aim 3, I will quantify neurotransmitter levels secondary to SLC13A5 deficiency with high-speed glutamate imaging. Overall, these experiments will establish the role of citrate in abnormalities of neuronal excitability. My long-term goal for this award is to transition into a career as a physician-scientist studying and treating epilepsy. The sponsor team will share their expertise in translational epilepsy research, clinical evaluations, and career development. Further training will be acquired from workshops and conferences, both at and outside of Brown University, in addition to both national and international conferences. Overall, this proposal will provide research and clinical training in addition to professional development.
