The innate immune response in the CNS plays a critical role in disease progression in multiple sclerosis (MS)/ experimental autoimmune encephalomyelitis (EAE). Astrocytes, microglia, and pro-inflammatory monocytes actively promote neurodegeneration, demyelination and scar formation, but therapeutic strategies targeting glial cells remain elusive. Reactive astrocytes in EAE (here called the ?EAE-astrocytes? for short) in the spinal cord secrete numerous pro-inflammatory factors, with inhibition of each factor individually being beneficial in EAE. Whereas targeting pro-inflammatory factors individually may be beneficial, a more promising strategy may be to target the pro-inflammatory secretome of EAE-astrocytes more broadly. This idea emerges from published work with the oral MS drug and sphingosine-1-phosphate (S1P) receptor modulator, fingolimod, in which it was shown that astrocyte activation in the presence of fingolimod, yields a secretome that is less pro- inflammatory. Our lab recently showed pathological involvement of Sur1-Trpm4 in MS/ EAE. During the chronic phase of EAE, Sur1-Trpm4 channels are robustly upregulated predominantly by reactive astrocytes (EAE- astrocytes), with global suppression of SUR1 reducing secretion of several pro-inflammatory cytokines/chemokines, and reducing clinical symptoms, demyelination and axonal loss. New experiments have expanded on this work, revealing what may be a critical interaction between Sur1-Trpm4 and S1P signaling in EAE-astrocytes. Preliminary data show that: (i) in EAE, Sur1-Trpm4, S1P1 and S1P3 receptors are highly co- localized in EAE-astrocytes; (ii) in EAE, astrocyte-specific deletion of Abcc8, which encodes Sur1, yields a secretome similar to that with fingolimod; (iii) in cultured astrocytes, Sur1-Trpm4 channels are downstream of, and are required for, S1P signaling; (iv) in cultured astrocytes, Sur1-Trpm4 channels regulate the transcription of numerous pro-inflammatory factors. Our central hypothesis is that Sur1-Trpm4 channels are required for the S1P-mediated signaling that perpetuates the pro-inflammatory astrocytic secretome and contributes to disease maintenance/progression in MS/ EAE. DESCRIPTION: This project has three mechanistic aims, all focused on Sur1-Trpm4 in EAE.
In Aim 1, we will study myelin oligodendrocyte glycoprotein (MOG) 35?55 EAE in male and female mice with genetic deletion of Sur1 in astrocytes, initiated at different times after EAE induction, to establish the role of astrocytic Sur1 at different stages of EAE.
In Aim 2, molecular and patch clamp experiments will be used to demonstrate the role of Sur1-Trpm4 in S1P signaling that regulates the secretome of activated astrocytes.
In Aim 3, molecular experiments will be used to characterize the role of Sur1-Trpm4 in regulating nuclear factor of activated T-cell (NFAT)-mediated transcription of cytokines/chemokines in activated astrocytes. These studies will contribute new mechanistic insights into the molecular interactions between Sur1-Trpm4 and S1P signaling in astrocytes, and thereby reveal new treatment targets for MS.
Multiple sclerosis (MS), the most frequent inflammatory disease of the central nervous system (CNS), afflicts up to 2.5 million people globally. It begins at age 20?50 years, and there is no known cure. Medications used to treat MS are modestly effective, at least in relapsing remitting MS, but all available therapies are immunosuppressive, and thus predispose to opportunistic infections including JC virus leading to progressive multifocal leukoencephalopathy (PML), which may be fatal. To date, no therapy has been advanced that specifically targets astrocytes, which are key players in CNS innate immunity, and which may be targeted without immunosuppression.