Systemic stem cell treatment rescues injured motoneurons by reducing L-selectin expression on leukocytes.

BACKGROUND: Avulsion injury results in motoneuron death due to the increased cytotoxicity developing after the injury. We have earlier shown that intraspinally grafted immortalized NE-4C neuroectodermal stem cells derived from 9-day old mouse forebrain vesicles produced a secretome, which induced decreased microglia/macrophage reaction, and promoted the neuroprotection and regeneration following avulsion injury. Here we intended to prove the motoneuron rescuing effect of intravenously grafted NE-4C stem cells and reveal the mechanism of action used by the grafted cells. METHODS: In our experimental model the left lumbar 4 (L4) ventral root of the spinal cord was avulsed and then reimplanted into the L4 spinal segment. Treated animals received various doses of NE-4C stem cells intravenously and the survival and regeneration of the affected motoneurons was checked by morphological and functional analysis. The molecular changes within the treated cord were followed by the ELISA Proteome Profiler rat cytokine array and qPCR analysis. To mimic the effect of stem cells fucoidan treatment (a specific selectin inhibitor, 50 and 100 mg/kg bw) was applied for two weeks intraperitoneally. RESULTS: High doses of intravenous stem cell treatment (4 × 10(5) and 1 × 10(6) cells) induced the reinnervation of the reimplanted ventral root by surviving injured motoneurons (up to 38% of the total L4 pool). Proteome Profiler analysis showed that systemic stem cell treatment downregulated the level of L-selectin, that promotes leukocyte rolling on vascular endothelium. Both systemic stem cell and fucoidan treatment reduced macrophage and microglial densities in the affected spinal segment and administration of fucoidan downregulated inflammatory cytokine and inflammasome levels along with improved morphological and functional reinnervation. CONCLUSIONS: Blocking L-selectin, similarly to systemic NE-4C stem cell treatment decreases the neuroinflammation in the injured spinal cord segment after ventral root avulsion and induces significant motoneuron survival and functional reinnervation of the denervated hind limb muscles.