PROJECT SUMMARY
Stroke is the third leading cause of death and also the leading cause of serious long-term disability in the
United States. About 87% of all strokes are classified as ischemic, which occurs as a result of an
obstruction within a blood vessel supplying oxygen-rich blood to an area of the brain. Despite the efficacy
and safety of thrombolysis (by tissue plasminogen activator, t-PA) and thrombectomy (by surgery), most
patients are ineligible for treatment due to the narrow time-window. Thus, ischemic stroke is a huge unmet
medical need; it's imperative to identify new stroke therapeutic targets. Swelling of astrocytes and neurons
is a pathological hallmark of many neurological diseases, including ischemic stroke and traumatic brain
injury. How it contributes to the pathogenesis remains unclear. Cell swelling activates the Volume-
Regulated Anion Channel (VRAC), which typically facilitates regulatory volume decrease by mediating
efflux of chloride and organic osmolytes, followed by release of osmotically obligated water. However,
persistent VRAC activation in the brain is thought to be detrimental. For example, VRAC has been
proposed to be a major pathway for the excessive glutamate release from swollen astrocytes, which over-
stimulates neuronal NMDA receptors and causes excitotoxicity. Despite intense research in 3 decades,
the molecular identity of VRAC was a longstanding mystery. Due to this gap, the previous evidence
supporting VRAC's pathological role was mainly based on nonspecific pharmacological inhibitors. We
developed an innovative high-throughput assay and through a genome-wide RNAi screen, have
successfully identified a novel membrane protein SWELL1 (LRRC8A) as the only essential VRAC subunit.
Our preliminary data showed that Swell1-dependent VRAC in astrocytes directly releases glutamate,
which enhances neuronal excitability. Importantly, Swell1 astrocyte-specific KO mice were significantly
protected from brain damage in transient middle cerebral artery occlusion (tMCAO) stroke model. This
proposed research program will combine innovative approaches including cell and acute brain slice
electrophysiology, live cell imaging, high-throughput chemical screening, cell-type specific KO mouse
models, and in vivo experimental stroke models to elucidate the important role of the cell swelling-
activated chloride channel in the pathogenesis of ischemic stroke. Completion of the proposed study will
establish Swell1 channel as a key pathological mediator in stroke and provide a new “druggable” ion
channel target for not only stroke, but also other neurological disease associated with abnormal cell
swelling.