Neuroprotective effect of l-serine against white matter demyelination by harnessing and modulating inflammation in mice.

Demyelination in white matter is the end product of numerous pathological processes. This study was designed to evaluate the neuroprotective effect of l-serine and the underlying mechanisms against the demyelinating injury of white matter. A model of focal demyelinating lesions (FDL) was established using the two-point stereotactic injection of 0.25% lysophosphatidylcholine (LPC, 10 µg per point) into the corpus callosum of mice. Mice were then intraperitoneally injected with one of three doses of l-serine (114, 342, or 1026 mg/kg) 2 h after FDL, and then twice daily for the next five days. Behavior tests and histological analysis were assessed for up to twenty-eight days post-FDL induction. Electron microscopy was used for ultrastructural investigation. In vitro, we applied primary co-cultures of microglia and oligodendrocytes for oxygen glucose deprivation (OGD). After establishing FDL, l-serine treatment: 1) improved spatial learning, memory and cognitive ability in mice, and relieved anxiety for 4 weeks post-FDL induction; 2) reduced abnormally dephosphorylated neurofilament proteins, increased myelin basic protein, and preserved anatomic myelinated axons; 3) inhibited microglia activation and reduced the release of inflammatory factors; 4) promoted recruitment and proliferation of oligodendrocyte progenitor cells, and the efficiency of subsequent remyelination on day twenty-eight post-FDL induction. In vitro experiments, showed that l-serine not only directly protected against oligodendrocytes from OGD damage, but also provided an indirect protective effect by regulating microglia. In our study, l-serine offered long-lasting behavioral and oligodendrocyte protection and promoted remyelination. Therefore, l-serine may be an effective clinical treatment aganist white matter injury.

A stable and easily reproducible model of focal white matter demyelination.

BACKGROUND: Demyelination is the end product of numerous pathological processes, and also is one of the main causes of neurological disability in Multiple sclerosis (MS). Research into the pathogenesis of MS is hampered by the conventional rodent models' inability to produce stable demyelination. NEW METHOD: Focal demyelinating lesions were stereotactically targeted to the corpus callosum with a two-point injection of lysophosphatidylcholine (LPC-2) in mice. Three groups were analyzed (n = 8, each) and water maze, sensorimotor test, and compound action potential were included in functional tests. Electron microscopy was used for morphological analyses while western blot and immunohistochemistry were included for molecular detection. RESULTS: Ten days after the LPC-2 injection, the expression of myelin basic protein (MBP) was reduced, while non-phosphorylated neurofilament (SMI-32) was increased. The amplitude of the N1 segment decreased and less well-defined myelin sheaths was found. Behavioral tests showed increased latency to escape and reduced time spent in target quadrant. Four weeks later, MBP expression still reduced, SMI-32 expression was increased, both spatial learning (D24-D27) and spatial memory (D28) were still significantly impaired in LPC-2 injection mice. COMPARISON WITH EXISTING METHOD(S): Compared with the classic single-point LPC-injection model, our studies showed that the two-point LPC-injection not only could induce demyelination in a short-term manner, but also could cause demyelination in a long-term manner with little remyelination in the mouse corpus callosum. CONCLUSIONS: We established a simple, reliable, and inexpensive model of demyelination in the corpus callosum in mice, with functional and morphological reproducibility, and good validity.

TRPC6 inhibited NMDA current in cultured hippocampal neurons.

N-methyl-D-aspartate (NMDA) receptors play a key role in excitatory synaptic transmission, plasticity and neural development, and they also mediate excitotoxicity that is involved in both acute neuronal damage and chronic neurodegenerative diseases. Regulation of the NMDA channel activity is critical for the pathological processes of these diseases. The canonical transient receptor potential channels (TRPCs) are Ca(2+)-permeable nonselective cation channels with various physiological functions, including promoting neuronal survival. Here, we reported that TRPC6, a member of the TRPC family, inhibited the NMDA-induced current in primary cultured hippocampal neurons. Overexpression of TRPC6 or application of 1-oleoyl-2-acetyl-sn-glycerol, a compound known to activate TRPCs, inhibited the NMDA-induced current in these neurons assayed by the whole-cell patch-clamp recording. Consistently, downregulation of TRPC6 or application of SKF96365, a compound known to inhibit TRPCs, enhanced this current. The peak amplitude of the NMDA current in the neurons isolated from TRPC6 transgenic mice was greatly suppressed than that in the neurons isolated from the wild-type littermates. Furthermore, TRPC6 might activate calcineurin to inhibit the activity of NMDA receptors in cultured hippocampal neurons. Together, these results suggested that TRPC6 might be a novel negative modulator of NMDA receptors.