Functional role of endogenous Kv1.4 in experimental demyelination
Graphical abstract
Introduction
Multiple sclerosis (MS) is the most common inflammatory demyelinating disease of the human central nervous system (CNS) and the number one cause of neurological disability in young adults. Despite several available immune therapies, treatment of MS is insufficient and a possible cure remains elusive. To some degree, MS lesions show repair, although with a high inter- and intraindividual variability (Goldschmidt et al., 2009; Patrikios et al., 2006). Such repair may be due to remyelination, which refers to the production of a new myelin layer around naked axons. The proliferation, migration and maturation of oligodendrocyte precursor cells (OPCs) is a prerequisite for remyelination (Zawadzka et al., 2010). Remyelination mechanisms are to some degree shared with developmental myelination. However, the level of similarity between both processes remains unknown.
Previous research has shown that developmentally regulated molecules may be re-expressed during remyelinating processes (Duncan et al., 2017; Gareth et al., 2002). These data imply that factors physiologically involved in oligodendroglial and myelin development may play a role during remyelination. One of such factors are potassium channels, which show a differential expression during oligodendrocyte (Ol) development and have been found to be re-expressed after a demyelinating event (Edwards et al., 2002; Herrero-Herranz et al., 2007; Kettenmann and Blankenfled, 1991).
Different subunits of the potassium family shaker type Kv1 have been implicated in controlling OPC proliferation in vitro (Vautier et al., 2004; Chittajallu et al., 2002). Kv1.4 has been identified as one of them. However, its effects in vivo are less well described. Previously, it has been shown that the developmentally restricted potassium channel Kv1.4 is re-expressed in pre-myelinating Ols at the peak of experimental autoimmune encephalomyelitis (EAE), a model mimicking many aspects of MS, suggesting an implication of Kv1.4 in Ol proliferation in vivo (Edwards et al., 2002; Herrero-Herranz et al., 2007).
Here we investigate a mouse line lacking the expression of endogenous Kv1.4 in an autoimmune (EAE) and a toxic (cuprizone) animal model of MS, as well as in primary Ol cell culture. These Kv1.4 knockout mice are fertile and do not show any obvious neurological phenotype (London et al., 1998). Our data suggest a critical role for endogenous Kv1.4 in Ol proliferation in vitro. However, the absence of endogenous Kv1.4 in vivo does not directly affect processes of remyelination.
Section snippets
Animal experimentation
C57BL/6J mice were initially purchased from Charles River breeding laboratories (Sulzfeld, Germany) and mice harboring a knockout of the Kv1.4 gene (Kv 1.4 ko mice) were obtained from Barry London, University of Iowa (London et al., 1998). All mice were housed at the Franz-Penzoldt-Zentrum (FPZ), the animal care facility of the University Erlangen-Nuremberg (Germany) under a 12 h day-night-cycle and standardized environmental conditions receiving normal chow (SNIFF V1534-300, Soest, Germany) or
Kv1.4 deficiency decreases oligodendrocyte proliferation in vitro
First, we cultivated O4+ sorted cells from Kv1.4−/− and wild type control mice under proliferating conditions. The absence of the potassium channel Kv1.4 had a significant effect on the number of proliferating Ol in culture. Lack of Kv1.4 led to a marked reduction in the percentage of Olig2 positive cells expressing the proliferation marker Ki67 after two days in culture (Fig. 1A-B). A similar effect was observed after seven days in culture (Fig. 1A-B). This reduction in proliferation was not
Discussion
After a demyelinating event, OPC proliferation is a fundamental step for remyelination. Here we analyzed primary Ol culture of Kv1.4 knockout mice and found reduced proliferation levels when compared to wild-type Ols. Due to this proliferation defect, it would be anticipated that remyelination processes may also be affected in vivo. Therefore, we investigated the influence of endogenous Kv1.4 during remyelination in the CPZ model. Yet, a lack of Kv1.4 had no effect on remyelination levels and
Funding
The GRK2162 is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - 270949263/ GRK2162. RL is part of the GRK 2162.
Declaration of Competing Interest
None.
Acknowledgments
We wish to thank Silvia Seubert for expert technical assistance. MNGA is a graduate student of the research training group 2162: Neurodevelopment and vulnerability of the central nervous system.
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