Visualizing Wallerian degeneration in the corticospinal tract after sensorimotor cortex ischemia in mice

Enhancing m6A modification in the motor cortex facilitates corticospinal tract remodeling after spinal cord injury

JOURNAL/nrgr/04.03/01300535-202506000-00026/figure1/v/2024-08-05T133530Z/r/image-tiff Spinal cord injury typically causes corticospinal tract disruption. Although the disrupted corticospinal tract can self-regenerate to a certain degree, the underlying mechanism of this process is still unclear. N6-methyladenosine (m6A) modifications are the most common form of epigenetic regulation at the RNA level and play an essential role in biological processes. However, whether m6A modifications participate in corticospinal tract regeneration after spinal cord injury remains unknown. We found that expression of methyltransferase 14 protein (METTL14) in the locomotor cortex was high after spinal cord injury and accompanied by elevated m6A levels. Knockdown of Mettl14 in the locomotor cortex was not favorable for corticospinal tract regeneration and neurological recovery after spinal cord injury. Through bioinformatics analysis and methylated RNA immunoprecipitation-quantitative polymerase chain reaction, we found that METTL14 regulated Trib2 expression in an m6A-regulated manner, thereby activating the mitogen-activated protein kinase pathway and promoting corticospinal tract regeneration. Finally, we administered syringin, a stabilizer of METTL14, using molecular docking. Results confirmed that syringin can promote corticospinal tract regeneration and facilitate neurological recovery by stabilizing METTL14. Findings from this study reveal that m6A modification is involved in the regulation of corticospinal tract regeneration after spinal cord injury.

NODDI Identifies Cognitive Associations with In Vivo Microstructural Changes in Remote Cortical Regions and Thalamocortical Pathways in Thalamic Stroke

The roles of cerebral structures distal to isolated thalamic infarcts in cognitive deficits remain unclear. We aimed to identify the in vivo microstructural characteristics of remote gray matter (GM) and thalamic pathways and elucidate their roles across cognitive domains. Patients with isolated ischemic thalamic stroke and healthy controls underwent neuropsychological assessment and magnetic resonance imaging. Neurite orientation dispersion and density imaging (NODDI) was modeled to derive the intracellular volume fraction (VFic) and orientation dispersion index. Fiber density (FD) was determined by constrained spherical deconvolution, and tensor-derived fractional anisotropy (FA) was calculated. Voxel-wise GM analysis and thalamic pathway tractography were performed. Twenty-six patients and 26 healthy controls were included. Patients exhibited reduced VFic in remote GM regions, including ipsilesional insular and temporal subregions. The microstructural metrics VFic, FD, and FA within ipsilesional thalamic pathways decreased (false discovery rate [FDR]-p < 0.05). Noteworthy associations emerged as VFic within insular cortices (ρ = -0.791 to -0.630; FDR-p < 0.05) and FD in tracts connecting the thalamus and insula (ρ = 0.830 to 0.971; FDR-p < 0.001) were closely associated with executive function. The VFic in Brodmann area 52 (ρ = -0.839; FDR-p = 0.005) and FA within its thalamic pathway (ρ = -0.799; FDR-p = 0.003) correlated with total auditory memory scores. In conclusion, NODDI revealed neurite loss in remote normal-appearing GM regions and ipsilesional thalamic pathways in thalamic stroke. Reduced cortical dendritic density and axonal density of thalamocortical tracts in specific subregions were associated with improved cognitive functions. Subacute microstructural alterations beyond focal thalamic infarcts might reflect beneficial remodeling indicating post-stroke plasticity.

bFGF-Chitosan "brain glue" promotes functional recovery after cortical ischemic stroke

The mammalian brain has an extremely limited ability to regenerate lost neurons and to recover function following ischemic stroke. A biomaterial strategy of slowly-releasing various regeneration-promoting factors to activate endogenous neurogenesis represents a safe and practical neuronal replacement therapy. In this study, basic fibroblast growth factor (bFGF)-Chitosan gel is injected into the stroke cavity. This approach promotes the proliferation of vascular endothelial cell, the formation of functional vascular network, and the final restoration of cerebral blood flow. Additionally, bFGF-Chitosan gel activates neural progenitor cells (NPCs) in the subventricular zone (SVZ), promotes the NPCs' migration toward the stroke cavity and differentiation into mature neurons with diverse cell types (inhibitory gamma-aminobutyric acid neurons and excitatory glutamatergic neuron) and layer architecture (superficial cortex and deep cortex). These new-born neurons form functional synaptic connections with the host brain and reconstruct nascent neural networks. Furthermore, synaptogenesis in the stroke cavity and Nestin lineage cells respectively contribute to the improvement of sensorimotor function induced by bFGF-Chitosan gel after ischemic stroke. Lastly, bFGF-Chitosan gel inhibits microglia activation in the peri-infarct cortex. Our findings indicate that filling the stroke cavity with bFGF-Chitosan "brain glue" promotes angiogenesis, endogenous neurogenesis and synaptogenesis to restore function, offering innovative ideas and methods for the clinical treatment of ischemic stroke.

Immunohistochemical labeling of ongoing axonal degeneration 10 days following cervical contusion spinal cord injury in the rat

STUDY DESIGN

Experimental Animal Study.

OBJECTIVE

To continue validating an antibody which targets an epitope of neurofilament light chain (NF-L) only available during neurodegeneration and to utilize the antibody to describe the pattern of axonal degeneration 10 days post-unilateral C4 contusion in the rat.

SETTING

University of Florida laboratory in Gainesville, USA.

METHODS

Sprague Dawley rats received either a unilateral 150kdyne C4 contusion (n = 4 females, n = 5 males) or a laminectomy control surgery (n = 2 females, n = 3 males). Ten days following SCI or laminectomy, spinal cords and brainstems were processed for immunohistochemistry. Serial spinal cord and brainstem cross-sections were stained with the degeneration-specific NF-L antibody (MCA-6H63) and dual labeled with either an antibody against the C-terminus portion of NF-L (NF-L-Ct), to label healthy axons, or an antibody against amyloid precursor protein (APP), considered the current "gold standard" for identifying axonal injury. The pattern of ongoing axonal degeneration was assessed.

RESULTS

Spinal cord and brainstem cross-sections from injured rats had punctate MCA-6H63 positive fibers with a pathological appearance, loss of anti-NF-L-Ct colabeling, and frequent colocalization with APP. Immunopositive fibers were abundant rostral and caudal to the lesion in white matter tracts that would be disrupted by the unilateral C4 contusion. This pattern of staining was not observed in control tissue.

CONCLUSIONS

The MCA-6H63 antibody labels degenerating axons following SCI and offers a tool to quantify axonal degeneration.