Multiple Sclerosis: Neurofilament Pathology in Spinal Motor Neurons

Abstract

Objective: While traditionally a disorder of myelin, in multiple sclerosis (MS) neuronal and axonal damage has in recent years become an important topic of clinical relevance. To address this, alterations in neurofilament phosphorylation, known markers of neuronal health, were investigated in anterior horn cells in MS spinal cord tissue for signs of motor neuron damage. Methods:Spinal cord tissue was examined from 13 MS and 6 control patients. Fresh frozen sections were labelled with antibodies against phosphorylated and non-phosphorylated epitopes of neurofilament H (NF-H) and analyzed by light microscopy. Results:In MS, increased expression of phosphorylated NF-H in spinal motor neuron perikarya (abnormal for neurons) occurred in 61.5% of cases, mostly in chronic active lesions, with the strongest immunoreactivity at the lumbar level. Inflammatory activity was common in chronic active but rare in chronic silent lesions. In one case with an acute lesion, we saw swollen axons positive for non-phosphorylated NF-H, a pathologic marker in axons, but no signs of perikaryal damage. Expression of non-phosphorylated NF-H in spinal motor neuron perikarya was similar in both MS and controls. Conclusion:In line with previous studies, our findings implicate anterior horn cell damage as a common feature in MS. We propose that underlying mechanisms may involve reduced synaptic input and/or retrograde degeneration, subjects which remain to be investigated. For the neuron count of a subgroup of MS cases, 5 serial sections of each patient stained with Nissl stain (0.075 % cresyl violet) were examined with stereological methods using StereoInvestigator software (MicroBrightField Inc., Williston, VT, USA). In the anterior horn as the region of interest, all neuronal perikarya were counted, measured and grouped according to their size into motor neurons (diameter ≥ 24 μm) and interneurons (diameter (≥ 10-24 μm) [21]. For evaluation, total numbers of motor neurons per patient were compared. Further details of the procedure can be found in an earlier publication [11].Images were captured with a digital camera (Axiocam and software by Carl Zeiss); GraphPadPrism software was used for graph production. ResultsEstablished, gliotic lesions devoid of myelin and displaying variable degrees of axonal degeneration were common in all cases with chronic lesions but inflammatory changes (reflecting ongoing demyelination), were only seen in chronic active lesions. Such changes comprised perivascular cuffs and scattered lipid-laden macrophages in the white matter (mainly anterior or lateral columns) and occasional collections of small lymphocytes within the meninges.By immunocytochemistry, clear differences were seen between MS and control cases in the expression of phosphorylated NF-H in anterior horn cell perikarya. Specifically, eight of thirteen MS patients showed widespread phosphorylated (abnormal) NF-H positivity compared to none of the controls (3 healthy, 2 OND: olivopontocerebellar degeneration and polyglucosan inclusion disease...

Neurofilament Proteins as Biomarkers to Monitor Neurological Diseases and the Efficacy of Therapies

“…Abnormal NfP accumulations are also a hallmark pathologic feature of ALS (Cleveland and Rothstein, 2001). In MS, increased expression of phosphorylated NfH (pNfH) is observed in spinal motor neuron perikarya (Muller-Wielsch et al, 2017) and Nfs accumulate excessively in axons in GAN (Bomont et al, 2000).…”

“…(D) Masses of Nf swelling in ALS spinal cord are stained with Silver (adapted from Cleveland and Rothstein, 2001). (E) Anterior horn cell perikarya in MS spinal cord are prominently stained with antibody to pNfH (SMI31) whereas healthy controls remain almost non-reactive (F) (adapted from Muller-Wielsch et al, 2017). Ischemia-affected areas in mouse brain 24 h after experimental stroke induction are demarcated by an increase of NfL degradation fragments immunoreactivity (G), while the immunosignals for NfH (H), alpha-internexin (INA) (I), and NfM (J) are decreased (adapted from Mages et al, 2018).…”