Targeting K_Vchannels rescues retinal ganglion cells in vivo directly and by reducing inflammation

Abstract

Addendum to: Koeberle PD, Wang Y, Schlichter LC. K V 1.1 and K V 1.3 channels contribute to the degeneration of retinal ganglion cells after optic nerve transection in vivo. Cell Death Differ 2010; 17:134-44; PMID: 19696788; DOI: 10.1038 DOI: 10. / cdd.2009.113.Key words: neurotrauma, axotomy, optic nerve transection, microglial activation, apoptosis, K V 1.1, K V 1.3, siRNA in vivo, agitoxin-2, margatoxin Abbreviations: RGC, retinal ganglion cell; GCL, ganglion cell layer; NFL, nerve fiber layer; IPL, inner plexiform layer; INL, inner nuclear layer; ONL, outer nuclear layer; CNS, central nervous system; BDNF, brain derived neurotrophic factor; CNTF, ciliary neurotrophic factor; GDNF, glial-cell line derived neurotrophic factor; NGF, nerve growth factor; bFGF, basic fibroblast growth factor; IGF, insulin-like growth factor; EGF, epidermal growth factor; NRTN, neurturin; iNOS, inducible nitric oxide synthase; IL-1β, interleukin-1-beta; IL-1ra, interleukin-1 receptor antagonist; TNFα, tumor necrosis factor-alpha; TGFβ, transforming growth factor-beta; CR3, complement receptor 3; MHC Class II, major histocompatibility complex class 2; GFAP, glial fibrillary acidic protein; HPRT-1, hypoxanthine phosphoribosyltransferase 1; AgTx-2, agitoxin-2; MgTx, margatoxin; α-DTX, alpha-dendrotoxin; K V , voltage gated potassium channel subunit; K V 1.1, voltage gated potassium channel family 1 member 1; K V 1.2, voltage gated potassium channel family 1 member 2; K V 1.3, voltage gated potassium channel family 1 member 3; Caspase-3, cysteine-aspartic protease-3; Caspase-9, cysteine-aspartic protease-9; Bad, Bcl-2-associated death promoter; Bclx L , B-cell lymphoma-extra large Numerous experimental studies have focused on identifying drug targets to rescue these neurons. We recently showed that K V 1.1 and K V 1.3 channels are expressed in adult rat RGCs and that siRNA-mediated knockdown of either channel reduces RGC death after optic nerve transection. Earlier we found that K V 1.3 channels also contribute to microglial activation and neurotoxicity; raising the possibility that these channels contribute to neurodegeneration through direct roles in RGCs and through inflammatory mechanisms. Here, RGC survival was increased by combined siRNA-mediated knockdown of K V 1.1 and K V 1.3 in RGCs, but survival was much greater when knockdown of either channel was combined with intraocular injection of a K V 1.3 channel blocker (agitoxin-2 or margatoxin). After axotomy, increased expression of several inflammation-related molecules preceded RGC loss and, consistent with a dual mechanism, their expression was differentially affected when channel knockdown in RGCs was combined with K V 1.3 blocker injection. K V 1.3 blockers reduced activation of retinal microglia and their tight apposition along RGC axon fascicles after axotomy, but did not prevent their migration from the inner plexiform to the damaged ganglion cell layer. Expression of several growth factors increased after axotomy; and again, there were differences following blocker

Swelling activated Cl- channels in microglia

“…Furthermore, after injury, microglia migrate to the site of injury, as shown in our recent studies of K + channels in rat models of optic nerve transection, ischemic stroke and intracerebral hemorrhage. [8][9][10] In addition, glutamate is involved in signaling between neurons, astrocytes and microglia; thus, potential outcomes of activating I Clswell include trans-activating NMDA receptors to evoke excitotoxic neuronal injury; 11 activating microglia through their metabotropic glutamate receptors, leading to production of other neurotoxic mediators; 12,13 and mediating glia-to-neuron signaling under inflammatory conditions. 14 Here, we first show that the biophysical and pharmacological properties of I Clswell in MLS-9 cells are as previously determined for primary rat microglia.…”

A non-canonical di-acidic signal at the C-terminal of Kv1.3 determines anterograde trafficking and surface expression

“…In this context, the Kv1.3 channel participates in the activity of sensory neurons and also controls the activation and proliferation of leukocytes (Vicente et al, 2003;Rivera et al, 2005;Cahalan and Chandy, 2009;Cavallin et al, 2010;Gazula et al, 2010). Therefore, Kv1.3 is considered to be a fundamental pharmacological target for diseases related to the nervous and immune systems (Koeberle and Schlichter, 2010;Villalonga et al, 2010;Conforti, 2012).…”

What can we learn about stroke from retinal ischemia models?

“…Inhibition of Kv1.1 and Kv1.3 by use of siRNAs was able to successfully inhibit their expression, and protect RGCs from apoptosis in optic nerve transection. As well, it was noted that Kv1.1 depletion increased levels of the antiapoptotic gene Bcl-xL, whereas depletion of Kv1.3 reduced expression of caspase-3, caspase-9 and Bad, all of which are pro-apoptotic [211,212] . Kv2.1 expression has also been shown to increase following damage, but before the appearance of apoptosis [208,214] .…”

“…A large family of voltage-gated potassium channels (Kv) have been found in mammalian brains. They are involved in the mediation of K + efflux upon membrane depolarization, and have been shown to play a role in mediating apoptotic cell death; of these, the most prominent appear to be Kv1.1, Kv1.3, and Kv2.1 [211][212][213] . Inhibition of Kv1.1 and Kv1.3 by use of siRNAs was able to successfully inhibit their expression, and protect RGCs from apoptosis in optic nerve transection.…”