The loss-of-function disease-mutation G301R in the Na+/K+-ATPase α2 isoform decreases lesion volume and improves functional outcome after acute spinal cord injury in mice.

BACKGROUND: 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 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 (α 2+/G301R ) to study the effect of reduced α2Na+/K+-ATPase expression in a moderate contusion spinal cord injury (SCI) model. RESULTS: We found that α 2+/G301R mice display significantly improved functional recovery and decreased lesion volume compared to littermate controls (α 2+/+ ) 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 α 2+/G301R and α 2+/+ mice. The level of the α2 isoform was significantly decreased in α 2+/G301R mice both under naïve conditions and 3 days after SCI compared to α 2+/+ 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-1ß, 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. CONCLUSION: Our 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.

Neuronal Ablation of IKK2 Decreases Lesion Size and Improves Functional Outcome after Spinal Cord Injury in Mice.

Nuclear factor-kappa B (NF-κB) is a key modulator of inflammation and secondary injury responses in neurodegenerative disease, including spinal cord injury (SCI). Inhibition of astroglial NF-κB reduces inflammation, enhances oligodendrogenesis and improves functional recovery after SCI, however the contribution of neuronal NF-κB to secondary inflammatory responses following SCI has yet to be investigated. We demonstrate that conditional ablation of IKK2 in Synapsin 1-expressing neurons in mice (Syn1creIKK2fl/fl) reduces activation of the classical NF-κB signaling pathway, resulting in impaired motor function and altered memory retention under naïve conditions. Following induction of a moderate SCI phosphorylated NF-κB levels decreased in the spinal cord of Syn1creIKK2fl/fl mice compared to controls, resulting in improvement in functional recovery. Histologically, Syn1creIKK2fl/fl mice exhibited reduced lesion volume but comparable microglial/leukocyte responses after SCI. In parallel, interleukin (IL)-1ß expression was significantly decreased within the lesioned spinal cord, whereas IL-5, IL-6, IL-10, tumor necrosis factor (TNF) and chemokine (C-X-C motif) ligand 1 were unchanged compared to control mice. We conclude that conditional ablation of IKK2 in neurons, resulting in reduced neuronal NF-B signaling, and lead to protective effects after SCI and propose the neuronal classical NF-κB pathway as a potential target for the development of new therapeutic, neuroprotective strategies for SCI.