Multiple sclerosis (MS) is a chronic inflammatory demyelinating disorder of the central nervous system wherein, after an initial phase of transient neurological defects, slow neurological ...deterioration due to progressive neuronal loss ensues. Age is a major determinant of MS progression onset and disability. Over the past years, several mechanisms have been proposed to explain the key drivers of neurodegeneration and disability accumulation in MS. However, the effect of commonly encountered age‐related cerebral vessel disease, namely small vessel disease (SVD), has been largely neglected and constitutes the aim of this review. SVD shares some features with MS, that is, white matter demyelination and brain atrophy, and has been shown to contribute to the neuronal damage seen in vascular cognitive impairment. Several lines of evidence suggest that an interaction between MS and SVD may influence MS‐related neurodegeneration. SVD may contribute to hypoperfusion, reduced vascular reactivity and tissue hypoxia, features seen in MS. Venule and endothelium abnormalities have been documented in MS but the role of arterioles and of other neurovascular unit structures, such as the pericyte, has not been explored. Vascular risk factors (VRF) have recently been associated with faster progression in MS, though the mechanisms are unclear since very few studies have addressed the impact of VRF and SVD on MS imaging and pathology outcomes. Therapeutic agents targeting the microvasculature and the neurovascular unit may impact both SVD and MS and may benefit patients with dual pathology.
Objective
Neuronal loss, a key substrate of irreversible disability in multiple sclerosis (MS), is a recognized feature of MS cortical pathology of which the cause remains unknown. Fibrin(ogen) ...deposition is neurotoxic in animal models of MS, but has not been evaluated in human progressive MS cortex. The aim of this study was to investigate the extent and distribution of fibrin(ogen) in progressive MS cortex and elucidate its relationship with neurodegeneration.
Methods
A postmortem cohort of pathologically confirmed MS (n = 47) and control (n = 10) cases was used. The extent and distribution of fibrin(ogen) was assessed and related to measures of demyelination, inflammation, and neuronal density. In a subset of cases (MS, n = 20; control, n = 10), expression of plasminogen activator inhibitor 1 (PAI‐1), a key enzyme in the fibrinolytic cascade, was assessed and related to the extent of fibrin(ogen).
Results
Motor cortical fibrin(ogen) deposition was significantly over‐represented in MS compared to control cases in all compartments studied (ie, extracellular p = 0.001, cell body p = 0.003, and neuritic/glial‐processes p = 0.004). MS cases with high levels of extracellular fibrin(ogen) had significantly upregulated PAI‐1 expression in all cortical layers assessed (p < 0.05) and reduced neuronal density (p = 0.017), including in the functionally‐relevant layer 5 (p = 0.001).
Interpretation
For the first time, we provide unequivocal evidence that fibrin(ogen) is extensively deposited in progressive MS motor cortex, where regulation of fibrinolysis appears perturbed. Progressive MS cases with severe fibrin(ogen) deposition have significantly reduced neuronal density. Future studies are needed to elucidate the provenance and putative neurotoxicity of fibrin(ogen), and its potential impact on clinical disability. Ann Neurol 2017;82:259–270
Recent findings in the animal model for multiple sclerosis (MS), experimental autoimmune encephalomyelitis, implicate a novel CD4+ T-cell subset (TH 17), characterized by the secretion of ...interleukin-17 (IL-17), in disease pathogenesis. To elucidate its role in MS, brain tissues from patients with MS were compared to controls. We detected expression of IL-17 mRNA (by in situ hybridization) and protein (by immunohistochemistry) in perivascular lymphocytes as well as in astrocytes and oligodendrocytes located in the active areas of MS lesions. Further, we found a significant increase in the number of IL-17+ T cells in active rather than inactive areas of MS lesions. Specifically, double immunofluorescence showed that IL-17 immunoreactivity was detected in 79% of T cells in acute lesions, 73% in active areas of chronic active lesions, but in only 17% of those in inactive lesions and 7% in lymph node control tissue. CD8+ , as well as CD4+ , T cells were equally immunostained for IL-17 in MS tissues. Interestingly, and in contrast to lymph node T cells, no perivascular T cells showed FoxP3 expression, a marker of regulatory T cells, at any stage of MS lesions. These observations suggest an enrichment of both IL-17+ CD4+ and CD8+ T cells in active MS lesions as well as an important role for IL-17 in MS pathogenesis, with some remarkable differences from the experimental autoimmune encephalomyelitis model.
Vascular comorbidities have a deleterious impact on multiple sclerosis clinical outcomes but it is unclear whether this is mediated by an excess of extracranial vascular disease (i.e. ...atherosclerosis) and/or of cerebral small vessel disease or worse multiple sclerosis pathology. To address these questions, a study using a unique post-mortem cohort wherein whole body autopsy reports and brain tissue were available for interrogation was established. Whole body autopsy reports were used to develop a global score of systemic vascular disease that included aorta and coronary artery atheroma, cardiac hypertensive disease, myocardial infarction and ischaemic stroke. The score was applied to 85 multiple sclerosis cases (46 females, age range 39 to 84 years, median 62.0 years) and 68 control cases. Post-mortem brain material from a subset of the multiple sclerosis (n = 42; age range 39-84 years, median 61.5 years) and control (n = 39) cases was selected for detailed neuropathological study. For each case, formalin-fixed paraffin-embedded tissue from the frontal and occipital white matter, basal ganglia and pons was used to obtain a global cerebral small vessel disease score that captured the presence and/or severity of arteriolosclerosis, periarteriolar space dilatation, haemosiderin leakage, microinfarcts, and microbleeds. The extent of multiple sclerosis-related pathology (focal demyelination and inflammation) was characterized in the multiple sclerosis cases. Regression models were used to investigate the influence of disease status on systemic vascular disease and cerebral small vessel disease scores and, in the multiple sclerosis group, the relationship between multiple sclerosis-related pathology and both vascular scores. We show that: (i) systemic cardiovascular burden, and specifically atherosclerosis, is lower and cerebral small vessel disease is higher in multiple sclerosis cases that die at younger ages compared with control subjects; (ii) the association between systemic vascular disease and cerebral small vessel disease is stronger in patients with multiple sclerosis compared with control subjects; and (iii) periarteriolar changes, including periarteriolar space dilatation, haemosiderin deposition and inflammation, are key features of multiple sclerosis pathology outside the classic demyelinating lesion. Our data argue against a common primary trigger for atherosclerosis and multiple sclerosis but suggest that an excess burden of cerebral small vessel disease in multiple sclerosis may explain the link between vascular comorbidity and accelerated irreversibility disability.
The pathophysiology of white matter hypoperfusion is poorly understood. Barker et al. quantify ante-mortem hypoperfusion by measuring myelin proteins differentially susceptible to ischaemia, and ...assess the extent to which vasoregulatory factors protect from or contribute to ischaemic white matter injury in Alzheimer’s disease and vascular dementia.
Little is known about the contributors and physiological responses to white matter hypoperfusion in the human brain. We previously showed the ratio of myelin-associated glycoprotein to proteolipid protein 1 in post-mortem human brain tissue correlates with the degree of ante-mortem ischaemia. In age-matched post-mortem cohorts of Alzheimer’s disease (n = 49), vascular dementia (n = 17) and control brains (n = 33) from the South West Dementia Brain Bank (Bristol), we have now examined the relationship between the ratio of myelin-associated glycoprotein to proteolipid protein 1 and several other proteins involved in regulating white matter vascularity and blood flow. Across the three cohorts, white matter perfusion, indicated by the ratio of myelin-associated glycoprotein to proteolipid protein 1, correlated positively with the concentration of the vasoconstrictor, endothelin 1 (P = 0.0005), and negatively with the concentration of the pro-angiogenic protein, vascular endothelial growth factor (P = 0.0015). The activity of angiotensin-converting enzyme, which catalyses production of the vasoconstrictor angiotensin II was not altered. In samples of frontal white matter from an independent (Oxford, UK) cohort of post-mortem brains (n = 74), we confirmed the significant correlations between the ratio of myelin-associated glycoprotein to proteolipid protein 1 and both endothelin 1 and vascular endothelial growth factor. We also assessed microvessel density in the Bristol (UK) samples, by measurement of factor VIII-related antigen, which we showed to correlate with immunohistochemical measurements of vessel density, and found factor VIII-related antigen levels to correlate with the level of vascular endothelial growth factor (P = 0.0487), suggesting that upregulation of vascular endothelial growth factor tends to increase vessel density in the white matter. We propose that downregulation of endothelin 1 and upregulation of vascular endothelial growth factor in the context of reduced ratio of myelin-associated glycoprotein to proteolipid protein 1 are likely to be protective physiological responses to reduced white matter perfusion. Further analysis of the Bristol cohort showed that endothelin 1 was reduced in the white matter in Alzheimer’s disease (P < 0.05) compared with control subjects, but not in vascular dementia, in which endothelin 1 tended to be elevated, perhaps reflecting abnormal regulation of white matter perfusion in vascular dementia. Our findings demonstrate the potential of post-mortem measurement of myelin proteins and mediators of vascular function, to assess physiological and pathological processes involved in the regulation of cerebral perfusion in Alzheimer’s disease and vascular dementia.
White matter ischemia is difficult to quantify histologically. Myelin-associated glycoprotein (MAG) is highly susceptible to ischemia, being expressed only adaxonally, far from the oligodendrocyte ...cell body. Myelin-basic protein (MBP) and proteolipid protein (PLP) are expressed throughout the myelin sheath. We compared MAG, MBP, and PLP levels in parietal white matter homogenates from 17 vascular dementia (VaD), 49 Alzheimer's disease (AD), and 33 control brains, after assessing the post-mortem stability of these proteins. Small vessel disease (SVD) and cerebral amyloid angiopathy (CAA) severity had been assessed in paraffin sections. The concentration of MAG remained stable post-mortem, declined with increasing SVD, and was significantly lower in VaD than controls. The concentration of MBP fell progressively post-mortem, limiting its diagnostic utility in this context. Proteolipid protein was stable post-mortem and increased significantly with SVD severity. The MAG/PLP ratio declined significantly with SVD and CAA severity. The MAG and PLP levels and MAG/PLP did not differ significantly between AD and control brains. We validated the utility of MAG and MAG/PLP measurements on analysis of 74 frontal white matter samples from an Oxford cohort in which SVD had previously been scored. MAG concentration and the MAG/PLP ratio are useful post-mortem measures of ante-mortem white matter ischemia.
Stroke mostly occurs in elderly people and patient outcomes after stroke are highly influenced by age. A better understanding of the causes of stroke in the elderly might have important practical ...implications not only for clinical management, but also for preventive strategies and future health-care policies. In this Review, we explore the evidence from both human and animal studies relating to the effect of old age-in terms of susceptibility, patient outcomes and response to treatment-on ischemic stroke. Several aging-related changes in the brain have been identified that are associated with an increase in vulnerability to ischemic stroke in the elderly. Furthermore, risk factor profiles for stroke and mechanisms of ischemic injury differ between young and elderly patients. Elderly patients with ischemic stroke often receive less-effective treatment and have poorer outcomes than younger individuals who develop this condition. Neuroprotective agents for ischemic stroke have been sought for decades but none has proved effective in humans. One contributing factor for this translational failure is that most preclinical studies have used young animals. Future research on ischemic stroke should consider age as a factor that influences stroke prevention and treatment, and should focus on the management of acute stroke in the elderly to reduce the incidence and improve outcomes in this vulnerable group.
Diffusion imaging of post mortem brains has great potential both as a reference for brain specimens that undergo sectioning, and as a link between in vivo diffusion studies and “gold standard” ...histology/dissection. While there is a relatively mature literature on post mortem diffusion imaging of animals, human brains have proven more challenging due to their incompatibility with high-performance scanners. This study presents a method for post mortem diffusion imaging of whole, human brains using a clinical 3-Tesla scanner with a 3D segmented EPI spin-echo sequence. Results in eleven brains at 0.94×0.94×0.94mm resolution are presented, and in a single brain at 0.73×0.73×0.73mm resolution. Region-of-interest analysis of diffusion tensor parameters indicate that these properties are altered compared to in vivo (reduced diffusivity and anisotropy), with significant dependence on post mortem interval (time from death to fixation). Despite these alterations, diffusion tractography of several major tracts is successfully demonstrated at both resolutions. We also report novel findings of cortical anisotropy and partial volume effects.
► Acquisition and processing protocols for diffusion MRI of post-mortem human brains. ► Effect of post-mortem and scan intervals on diffusion indices. ► Tractography in post-mortem human brains. ► Radial diffusion anisotropy in cortical gray matter.
The anterior optic pathway is one of the preferential sites of involvement in CNS inflammatory demyelinating diseases, such as multiple sclerosis and neuromyelitis optica, with optic neuritis being a ...common presenting symptom. What is more, optic nerve involvement in these diseases is often subclinical, with optical coherence tomography demonstrating progressive neuroretinal thinning in the absence of optic neuritis. The pathological substrate for these findings is poorly understood and requires investigation. We had access to post-mortem tissue samples of optic nerves, chiasms and tracts from 29 multiple sclerosis (mean age 59.5, range 25-84 years; 73 samples), six neuromyelitis optica spectrum disorders (mean age 56, range 18-84 years; 22 samples), six acute disseminated encephalomyelitis (mean age 25, range 10-39 years; 12 samples) cases and five non-neurological controls (mean age 55.2, range 44-64 years; 16 samples). Formalin-fixed paraffin-embedded samples were immunolabelled for myelin, inflammation (microglial/macrophage, T- and B-cells, complement), acute axonal injury and astrocytes. We assessed the extent and distribution of these markers along the anterior optic pathway for each case in all compartments (i.e. parenchymal, perivascular and meningeal), where relevant. Demyelinated plaques were classified as active based on established criteria. In multiple sclerosis, demyelination was present in 82.8% of cases, of which 75% showed activity. Microglia/macrophage and lymphocyte inflammation were frequently found both in the parenchymal and meningeal compartments in non-demyelinated regions. Acute axonal injury affected 41.4% of cases and correlated with extent of inflammatory activity in each compartment, even in cases that died at advanced age with over 20 years of disease duration. An antero-posterior gradient of anterior optic pathway involvement was observed with optic nerves being most severely affected by inflammation and acute axonal injury compared with the optic tract, where a higher proportion of remyelinated plaques were seen. In neuromyelitis optica spectrum disorder, cases with a history of optic neuritis had extensive demyelination and lost aquaporin-4 reactivity. In contrast, those without prior optic neuritis did not have demyelination but rather diffuse microglial/macrophage, T- and B-lymphocyte inflammation in both parenchymal and meningeal compartments, and acute axonal injury was present in 75% of cases. Acute demyelinating encephalomyelitis featured intense inflammation, and perivenular demyelination in 33% of cases. Our findings suggest that chronic inflammation is frequent and leads to neurodegeneration in multiple sclerosis and neuromyelitis optica, regardless of disease stage. The chronic inflammation and subsequent neurodegeneration occurring along the optic pathway broadens the plaque-centred view of these diseases and partly explains the progressive neuroretinal changes observed in optic coherence tomography studies.
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