Abstract
BackgroundThe Na+/K+-ATPases are transmembrane ion pumps important for maintenance of ion gradients across the plasma membrane that serve to support multiple cellular functions, such as membrane potentials, regulation of cellular volume and pH, and co-transport of signaling transmitters in all animal cells. The α2Na+/K+-ATPase subunit isoform is predominantly expressed in astrocytes, which us the sharp Na+-gradient maintained by the sodium pump necessary for astroglial metabolism. Prolonged ischemia induces an elevation of [Na+]i, decreased ATP levels and intracellular pH owing to anaerobic metabolism and lactate accumulation. During ischemia, Na+/K+-ATPase-related functions will naturally increase the energy demand of the Na+/K+-ATPase ion pump. However, the role of the α2Na+/K+-ATPase in contusion injury to the spinal cord remains unknown. We used mice heterozygous mice for the loss-of-function disease-mutation G301R in the Atp1a2 gene (α2+/G301R) to study the effect of reduced α2Na+/K+-ATPase expression in a moderate contusion spinal cord injury (SCI) model.ResultsWe found that α2+/G301R mice display significantly improved functional recovery and decreased lesion volume compared to littermate controls (α2+/+) 7 days after SCI. The protein level of the α1 isoform was significantly increased, in contrast to the α3 isoform that significantly decreased 3 days after SCI in both α2+/G301R and α2+/+ mice. The level of the α2 isoform was significantly decreased in α2+/G301R mice both under naïve conditions and 3 days after SCI compared to α2+/+ mice. We found no differences in astroglial aquaporin 4 levels and no changes in the expression of chemokines (CCL2, CCL5 and CXCL1) and cytokines (TNF, IL-6, IL-1β, IL-10 and IL-5) between genotypes, just as no apparent differences were observed in location and activation of CD45 and F4/80 positive microglia and infiltrating leukocytes.ConclusionOur proof of concept study demonstrates that reduced expression of the α2 isoform in the spinal cord is protective following SCI. Importantly, the BMS and lesion volume were assessed at 7 days after SCI, and longer time points after SCI were not evaluated. However, the α2 isoform is a potential possible target of therapeutic strategies for the treatment of SCI.
Highlights
The Na+/K+-ATPases are transmembrane ion pumps important for maintenance of ion gradients across the plasma membrane that serve to support multiple cellular functions, such as membrane potentials, regulation of cellular volume and pH, and co-transport of signaling transmitters in all animal cells
Α1 and α3 isoform levels were comparable between α2+/G301R and α+2 /+ mice, whereas α2 isoform levels were reduced approximately 40% in α+2/ G301R mice compared to littermates (Fig. 1a, b; Table 1)
The morphology of the naïve spinal cord tissue was assessed by immunofluorescent detection of the α2 isoform and the neuronal marker Neuronal Nuclei (NeuN) and counterstained with Hoechst, and revealed no gross morphological differences between the α2+/G301R and α+2 /+ mice under naïve conditions (Fig. 1c, shown for a α+2 / G301R mouse only)
Summary
The Na+/K+-ATPases are transmembrane ion pumps important for maintenance of ion gradients across the plasma membrane that serve to support multiple cellular functions, such as membrane potentials, regulation of cellular volume and pH, and co-transport of signaling transmitters in all animal cells. The α2Na+/K+-ATPase subunit isoform is predominantly expressed in astrocytes, which us the sharp N a+-gradient maintained by the sodium pump necessary for astroglial metabolism. The role of the α2Na+/ K+-ATPase in contusion injury to the spinal cord remains unknown. We used mice heterozygous mice for the lossof-function disease-mutation G301R in the Atp1a2 gene (α2+/G301R) to study the effect of reduced α2Na+/K+-ATPase expression in a moderate contusion spinal cord injury (SCI) model. Results: We found that α2+/G301R mice display significantly improved functional recovery and decreased lesion volume compared to littermate controls (α2+/+) 7 days after SCI. The level of the α2 isoform was significantly decreased in α2+/G301R mice both under naïve conditions and 3 days after SCI com‐ pared to α2+/+ mice. Spinal cord injury (SCI) results in massive cell loss at the site of the lesion. In response to injury, inflammatory cytokines cause adult astrocytes to proliferate and give rise to reactive astrocytes [2, 3]
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