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The Journal of Neuroscience, January 3, 2007, 27(1):234-244; doi:10.1523/JNEUROSCI.3593-06.2007

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Neurobiology of Disease
The Ca²⁺-Activated K⁺ Channel KCNN4/KCa3.1 Contributes to Microglia Activation and Nitric Oxide-Dependent Neurodegeneration

Vikas Kaushal,^1,2 Paulo D. Koeberle,¹ Yimin Wang,¹ and Lyanne C. Schlichter^1,2

¹Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada M5T 2S8, and ²Department of Physiology, University of Toronto, Toronto, Ontario, Canada M5S 1A1

Correspondence should be addressed to Lyanne C. Schlichter, Toronto Western Hospital, MC9-417, 399 Bathurst Street, Toronto, Ontario, Canada M5T 2S8. Email: schlicht{at}uhnres.utoronto.ca

Brain damage and disease involve activation of microglia and production of potentially neurotoxic molecules, but there are no treatments that effectively target their harmful properties. We present evidence that the small-conductance Ca²⁺/calmodulin-activated K⁺ channel KCNN4/ KCa3.1/SK4/IK1 is highly expressed in rat microglia and is a potential therapeutic target for acute brain damage. Using a Transwell cell-culture system that allows separate treatment of the microglia or neurons, we show that activated microglia killed neurons, and this was markedly reduced by treating only the microglia with a selective inhibitor of KCa3.1 channels, triarylmethane-34 (TRAM-34). To assess the role of KCa3.1 channels in microglia activation and key signaling pathways involved, we exploited several fluorescence plate-reader-based assays. KCa3.1 channels contributed to microglia activation, inducible nitric oxide synthase upregulation, production of nitric oxide and peroxynitrite, and to consequent neurotoxicity, protein tyrosine nitration, and caspase 3 activation in the target neurons. Microglia activation involved the signaling pathways p38 mitogen-activated protein kinase (MAPK) and nuclear factor B (NF-B), which are important for upregulation of numerous proinflammatory molecules, and the KCa3.1 channels were functionally linked to activation of p38 MAPK but not NF-B. These in vitro findings translated into in vivo neuroprotection, because we found that degeneration of retinal ganglion cells after optic nerve transection was reduced by intraocular injection of TRAM-34. This study provides evidence that KCa3.1 channels constitute a therapeutic target in the CNS and that inhibiting this K⁺ channel might benefit acute and chronic neurodegenerative disorders that are caused by or exacerbated by inflammation.

Key words: microglia activation; neurodegeneration; neuroinflammation; Ca²⁺-activated K⁺ channel; KCNN4/KCa3.1/IK1/SK4; optic nerve; retinal ganglion cell

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Received Aug. 18, 2006; revised Nov. 29, 2006; accepted Nov. 30, 2006.

Correspondence should be addressed to Lyanne C. Schlichter, Toronto Western Hospital, MC9-417, 399 Bathurst Street, Toronto, Ontario, Canada M5T 2S8. Email: schlicht{at}uhnres.utoronto.ca

This article has been cited by other articles:

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