My research is focused on the ionic and molecular mechanisms of neuronal cell death and neuroprotection after hypoxia and ischemia in vitro as well as in animal models. My previous investigations contributed to the identification of novel ionic and molecular mechanisms that involve voltage-gated channels and ligand-gated receptors in apoptotic and necrotic cell death. Using electrophysiological and gene modification techniques, we have examined how with some specific ion channel’s, such as Kv2.1, over-activation may contribute to apoptotic cell death, and how KCNQ3/4 may regulate neuronal differentiation of neural progenitor cells. My research has also identified novel mechanisms for promoting FAK activation and directional migration of neuronal cells. We are among the first groups to develop the concept of preconditioning transplanted stem cells and have demonstrated the multifaceted pro-survival and pro-regenerative effects of hypoxic preconditioned cells in vitro and after transplantation into the ischemic heart and brain. We have developed novel approaches involving optogenetics in stem cell transplantation therapy after ischemic stroke and traumatic brain injury (TBI). Our latest progress is the development of intranasal delivery of stem cells after stroke and TBI. This non-invasive method targets the CNS for more efficient and more clinically feasible cell delivery. Another main area of my research includes a novel investigation into pharmacologically induced hypothermia (PIH) for the treatment of stroke and TBI. We have also been carrying out innovative projects including direct conversion of glial cells to neuronal cells and receptor mechanisms of chronic pain in inflammation and cancer. Our ultimate goal is to develop effective, feasible and safe therapies for the treatment of stroke and TBI patients.

Contribution to Science

1. As one of the pioneers, 20 years ago, to cross fields from basic electrophysiology to disease oriented research, I was among the first few researchers to apply the electrophysiological approach to delineate the ionic mechanism of apoptotic cell death. Apoptosis is now regarded as a general cell death mechanism in many diseases. Although the molecular mechanism of apoptosis was extensively investigated, the concept that apoptosis could also under control by ionic mechanisms did not exist for years. Based on the unique morphological features of cell shrinkage during apoptosis, I developed and examined the hypothesis that the K+ homeostasis and excessive K+ efflux played a critical role in the initiation of apoptotic cascade. In a series of papers, I reported novel evidence that 1) excessive K+ efflux via the up-modulated K+ channels such as the Kv delayed rectifier channels mediated caspase activation, DNA damage, and apoptotic death; 2) K+ channel blockers attenuated apoptotic cell death in neuronal cultures as well as in ischemic animals. These pioneer investigations have been supported by increasing evidence by many groups on neuronal and non-neuronal cells. Maintenance of the K+ homeostasis is likely an important strategy in the treatment of brain disorders such as ischemic stroke.
a. Yu SP, Yeh CH, Sensi SL, Gwag BJ, Canzoniero LM, Farhangrazi ZS, Ying HS, Tian M, Dugan LL, Choi DW. Mediation of neuronal apoptosis by enhancement of outward potassium current. Science, 278:114-117. PubMed PMID:9311914, 1996.
b. Yu SP, Farhangrazi ZS, Ying HS, Yeh CH, Choi DW. Enhancement of outward potassium current may participate in beta-amyloid peptide-induced cortical neuronal death. Neurobiol Dis. 5(2):81-88. PubMed PMID: 9746905, 1998.
c. Yu SP, Yeh CH, Gottron F, Wang X, Grabb MC, Choi DW. Role of the outward delayed rectifier K+ current in ceramide-induced caspase activation and apoptosis in cultured cortical neurons. J Neurochem. 73(3):933-941. PubMed PMID:10461882, 1999.
d. Wei L, Yu SP, Gottron F, Snider BJ, Zipfel GJ, Choi DW. Potassium channel blockers attenuate hypoxia- and ischemia-induced neuronal death in vitro and in vivo. Stroke. 34(5):1281-1286. PubMed PMID: 12677023, 2003.

2. In searching for membrane related mechanisms for the pro-apoptotic K+ efflux, I identified significant K+ efflux mediated by NMDA receptors and its association with neuronal apoptosis. These studies provided novel information on the NMDA receptor regulation under pathological conditions and the mechanism of neuroprotective effects of NMDA receptor antagonists. For example, we reported a novel regulation of the NMDA receptor outward current mediated by a voltage-dependent, Src-mediated but Ca2+-independent mechanism. These results filled the knowledge gap of the characteristics and regulation of the NMDA receptor outward activity, suggesting that the NMDA receptor channel inward and outward activities are regulated under distinguishable cellular and molecular mechanisms.

a. Yu SP, Yeh C, Strasser U, Tian M, Choi DW. NMDA receptor-mediated K+ efflux and neuronal apoptosis. Science. 284(5412):336-339. PubMed PMID: 10195902, 1999.
b. Xiao AY, Homma M, Wang XQ, Wang X, Yu SP. Role of K+ efflux in apoptosis induced by AMPA and kainate in mouse cortical neurons. Neuroscience. 108(1):61-67. PubMed PMID: 11738131, 2001.
c. Ichinose T, Yu S, Wang XQ, Yu SP. Ca2+-independent, but voltage- and activity-dependent regulation of the NMDA receptor outward K+ current in mouse cortical neurons. J Physiol. 551(Pt 2):403-417. PubMed PMID: 12860921; PubMed Central PMCID: PMC2343239, 2003.
d. Takata T, Hood AY, Yu SP. Voltage-dependent and Src-mediated regulation of NMDA receptor single channel outward currents in cortical neurons. Cell Biochem Biophys. 47(2):257-270. PubMed PMID: 17652774, 2007.

3. For many years, it was known that blocking Na+,K+-ATPase was toxic to cells; the type of cell death, however, was unknown. Based on the discovery of the K+ mechanism of apoptosis, my research identified the unique role of Na+, K+-ATPase in the induction of neuronal apoptosis. I demonstrated that dysfunction of the Na+ pump is a key step in the apoptotic process, while the simultaneous disruption of the Ca2+ and Na+ homeostasis lead to a previously unreported hybrid cell death of concurrent apoptosis and necrosis in the same cells. In a series of investigations, my work delineated the novel regulation of the Na+ pump by a direct binding of the lyn kinase to the alpha 3 subunit of Na+,K+-ATPase. My recent research in glioblastoma cells shows that these cancer cells express significantly high levels of the pump alpha 2 and alpha 3 subunits, blocking the pump activity selectively induces hybrid cell death in cancer cells and enhances the sensitivity of these cells to chemotherapy drugs. These investigations are consistent with recent understanding of the relationship between mitochondrial damage induced metabolism failure and cell death. The unique role of the Na+ pump suggests a therapeutic target in the treatments of brain injury and cancer therapy.

a. Xiao AY, Wei L, Xia S, Rothman S, Yu SP. Ionic mechanism of ouabain-induced concurrent apoptosis and necrosis in individual cultured cortical neurons. J Neurosci. 22(4):1350-1362. PubMed PMID: 11850462, 2002.
b. Wang XQ, Yu SP. Novel regulation of Na, K-ATPase by Src tyrosine kinases in cortical neurons. J Neurochem. 93(6):1515-23. PubMed PMID: 15935067, 2005.
c. Wang XQ, Xiao AY, Sheline C, Hyrc K, Yang A, Goldberg MP, Choi DW, Yu SP.Apoptotic insults impair Na+, K+-ATPase activity as a mechanism of neuronal death mediated by concurrent ATP deficiency and oxidant stress. J Cell Sci. 116(Pt 10):2099-2110, PubMed PMID: 12679386, 2003.
d. Chen D, Song M, Mohamad O, Yu SP. Inhibition of Na+/K+-ATPase induces hybrid cell death and enhanced sensitivity to chemotherapy in human glioblastoma cells. BMC Cancer. 14:716. PubMed PMID: 25255962; PubMed Central PMCID: PMC4190379, 2014.

4. In stem cell research, my group was the first to develop the novel application of the preconditioning strategy in stem cell transplantation therapies. We demonstrated in neural progenitor cells and bone marrow mesenchymal stem cells that a hypoxic pre-treatment of cells before transplantation markedly enhanced the survival, differentiation, and migration of transplanted cells in the post-stroke brain. Transplantation of hypoxic preconditioned cells showed significantly better functional benefits after ischemic stroke. The novel idea of priming stem cells before transplantation has attracted increased attention from researchers in the fields of brain and spinal cord injury, heart ischemic injury and stem cell transplantation therapies. The preconditioning treatment provides a clinically feasible and efficient way of enhancing the clinical potential of the stem cell transplantation therapy.

a. Theus MH, Wei L, Cui L, Francis K, Hu X, Keogh C, Yu SP. In vitro hypoxic preconditioning of embryonic stem cells as a strategy of promoting cell survival and functional benefits after transplantation into the ischemic rat brain. Exp Neurol. 210(2):656-670. 2008.
b. Hu X, Yu SP, Fraser JL, Lu Z, Ogle ME, Wang JA, Wei L. Transplantation of hypoxia-preconditioned mesenchymal stem cells improves infarcted heart function via enhanced survival of implanted cells and angiogenesis. J Thorac Cardiovasc Surg. 135(4):799-808. PubMed PMID: 18374759, 2008.
c. Hu X, Wei L, Taylor TM, Wei J, Zhou X, Wang JA, Yu SP. Hypoxic preconditioning enhances bone marrow mesenchymal stem cell migration via Kv2.1 channel and FAK activation. Am J Physiol Cell Physiol. 301(2):C362-C372. PubMed Central PMCID: PMC3154562, 2011.
d. Wei L, Fraser JL, Lu ZY, Hu X, Yu SP. Transplantation of hypoxia preconditioned bone marrow mesenchymal stem cells enhances angiogenesis and neurogenesis after cerebral ischemia in rats. Neurobiol Dis. 46(3):635-645. ubMed Central PMCID: PMC3353023, 2012.

5. In addition to my previous studies on the neuroprotective drugs blocking excitotoxicity and apoptosis, through my collaboration with Dr. Thomas Dix, we have developed the novel drug-induced hypothermia therapy using the novel neurotensin receptor 1 agonists. Our novel compounds are BBB permeable, acting on the central thermoregulator and induce well controlled hypothermia in rodents and monkeys. Because the drug-induced hypothermia does not trigger the shivering response, the hypothermic treatment can be administered without the need for general anesthesia and thus avoid many associated side effects. I expect that drug-induced hypothermia will provide an efficient and safe early treatment after an ischemic or hemorrhage attack and confers global brain protection via multiple mechanisms and increases the therapeutic window for other interventions such as tPA.

a. Choi KE, Hall CL, Sun JM, Wei L, Mohamad O, Dix TA, Yu SP. A novel stroke therapy of pharmacologically induced hypothermia after focal cerebral ischemia in mice. FASEB J. 26(7):2799-2810. PubMed PMID: 22459147; PubMed Central PMCID: PMC3382100, 2012.
b. Wei S, Sun J, Li J, Wang L, Hall CL, Dix TA, Mohamad O, Wei L, Yu SP. Acute and delayed protective effects of pharmacologically induced hypothermia in an intracerebral hemorrhage stroke model of mice. Neuroscience. 252:489-500. PubMed Central PMCID: PMC3961766, 2013.
c. Lee JH, Wei L, Gu X, Wei Z, Dix TA, Yu SP. Therapeutic effects of pharmacologically induced hypothermia against traumatic brain injury in mice. J Neurotrauma. 31(16):1417-1430. PubMed PMID: 24731132; PubMed Central PMCID: PMC4132583, 2014.
d. Gu X, Wei ZZ, Espinera A, Lee JH, Ji X, Wei L, Dix TA, Yu SP. Pharmacologically induced hypothermia attenuates traumatic brain injury in neonatal rats. Exp Neurol. 267:135-142, PubMed PMID: 25725354, 2015.
e. Lee JH, Cao W, Gu X, Caslin A, Dix TA, Wei L, and Yu SP. Pharmacologically induced hypothermia reduces inflammatory responses and improved functional recovery after stroke in mice. In revision.