Micro-diffusely abnormal white matter: An early multiple sclerosis lesion phase with intensified myelin blistering

OBJECTIVE

Multiple sclerosis (MS) is a chronic central nervous system disease whose white matter lesion origin remains debated. Recently, we reported subtle changes in the MS normal appearing white matter (NAWM), presenting with an increase in myelin blisters and myelin protein citrullination, which may recapitulate some of the prodromal degenerative processes involved in MS pathogenesis. Here, to clarify the relevance of these changes for subsequent MS myelin degeneration we explored their prevalence in WM regions characterized by subtly reduced myelination (dubbed as micro-diffusely abnormal white matter, mDAWM).

METHODS

We used an in-depth (immuno)histochemistry approach in 27 MS donors with histological presence of mDAWM and 5 controls. An antibody panel against degenerative markers was combined and the presence of myelin/axonal aberrations was analyzed and compared with the NAWM from the same cases/slices/regions.

RESULTS

mDAWM-defined areas exhibit ill-defined borders, no signs of Wallerian degeneration, and they associate with visible veins. Remarkably, such areas present with augmented myelin blister frequency, enhanced prevalence of polar myelin phospholipids, citrullination, and degradation of myelin basic protein (MBP) when compared with the NAWM. Furthermore, enhanced reactivity of microglia/macrophages against citrullinated MBP was also observed in this tissue.

INTERPRETATION

We report a new histologically defined early phase in MS lesion formation, namely mDAWM, which lacks signs of Wallerian pathology. These results support the prelesional nature of the mDAWM. We conceptualize that evolution to pathologically evident lesions comprises the previously documented imbalance of axo-myelinic units (myelin blistering) leading to their degeneration and immune system activation by released myelin components.

Inhibitory synaptic loss drives network changes in multiple sclerosis: An ex vivo to in silico translational study

Background:

Synaptic and neuronal loss contribute to network dysfunction and disability in multiple sclerosis (MS). However, it is unknown whether excitatory or inhibitory synapses and neurons are more vulnerable and how their losses impact network functioning.

Objective:

To quantify excitatory and inhibitory synapses and neurons and to investigate how synaptic loss affects network functioning through computational modeling.

Methods:

Using immunofluorescent staining and confocal microscopy, densities of glutamatergic and GABAergic synapses and neurons were compared between post-mortem MS and non-neurological control cases. Then, a corticothalamic biophysical model was employed to study how MS-induced excitatory and inhibitory synaptic loss affect network functioning.

Results:

In layer VI of normal-appearing MS cortex, excitatory and inhibitory synaptic densities were significantly lower than controls (reductions up to 14.9%), but demyelinated cortex showed larger losses of inhibitory synapses (29%). In our computational model, reducing inhibitory synapses impacted the network most, leading to a disinhibitory increase in neuronal activity and connectivity.

Conclusion:

In MS, excitatory and inhibitory synaptic losses were observed, predominantly for inhibitory synapses in demyelinated cortex. Inhibitory synaptic loss affected network functioning most, leading to increased neuronal activity and connectivity. As network disinhibition relates to cognitive impairment, inhibitory synaptic loss seems particularly relevant in MS.

The Forgotten Brother: The Innate-like B1 Cell in Multiple Sclerosis

Multiple sclerosis (MS) is a neurodegenerative disease of the central nervous system (CNS), traditionally considered a chronic autoimmune attack against the insulating myelin sheaths around axons. However, the exact etiology has not been identified and is likely multi-factorial. Recently, evidence has been accumulating that implies that autoimmune processes underlying MS may, in fact, be triggered by pathological processes initiated within the CNS. This review focuses on a relatively unexplored immune cell-the "innate-like" B1 lymphocyte. The B1 cell is a primary-natural-antibody- and anti-inflammatory-cytokine-producing cell present in the healthy brain. It has been recently shown that its frequency and function may differ between MS patients and healthy controls, but its exact involvement in the MS pathogenic process remains obscure. In this review, we propose that this enigmatic cell may play a more prominent role in MS pathology than ever imagined. We aim to shed light on the human B1 cell in health and disease, and how dysregulation in its delicate homeostatic role could impact MS. Furthermore, novel therapeutic avenues to restore B1 cells' beneficial functions will be proposed.

Myelin Quantification in White Matter Pathology of Progressive Multiple Sclerosis Post-Mortem Brain Samples: A New Approach for Quantifying Remyelination

Multiple sclerosis (MS) is a demyelinating and neurodegenerative disease of the central nervous system (CNS). Repair through remyelination can be extensive, but quantification of remyelination remains challenging. To date, no method for standardized digital quantification of remyelination of MS lesions exists. This methodological study aims to present and validate a novel standardized method for myelin quantification in progressive MS brains to study myelin content more precisely. Fifty-five MS lesions in 32 tissue blocks from 14 progressive MS cases and five tissue blocks from 5 non-neurological controls were sampled. MS lesions were selected by macroscopic investigation of WM by standard histopathological methods. Tissue sections were stained for myelin with luxol fast blue (LFB) and histological assessment of de- or remyelination was performed by light microscopy. The myelin quantity was estimated with a novel myelin quantification method (MQM) in ImageJ. Three independent raters applied the MQM and the inter-rater reliability was calculated. We extended the method to diffusely appearing white matter (DAWM) and encephalitis to test potential wider applicability of the method. Inter-rater agreement was excellent (ICC = 0.96) and there was a high reliability with a lower- and upper limit of agreement up to −5.93% to 18.43% variation in myelin quantity. This study builds on the established concepts of histopathological semi-quantitative assessment of myelin and adds a novel, reliable and accurate quantitative measurement tool for the assessment of myelination in human post-mortem samples.

Mechanistic underpinning of an inside-out concept for autoimmunity in multiple sclerosis

The neuroinflammatory disease multiple sclerosis is driven by autoimmune pathology in the central nervous system. However, the trigger of the autoimmune pathogenic process is unknown. MS models in immunologically naïve, specific‐pathogen‐free bred rodents support an exogenous trigger, such as an infection. The validity of this outside–in pathogenic concept for MS has been frequently challenged by the difficulty to translate pathogenic concepts developed in these models into effective therapies for the MS patient. Studies in well‐validated non‐human primate multiple sclerosis models where, just like in humans, the autoimmune pathogenic process develops from an experienced immune system trained by prior infections, rather support an endogenous trigger. Data reviewed here corroborate the validity of this inside–out pathogenic concept for multiple sclerosis. They also provide a plausible sequence of events reminiscent of Wilkin’s primary lesion theory: (i) that autoimmunity is a physiological response of the immune system against excess antigen turnover in diseased tissue (the primary lesion) and (ii) that individuals developing autoimmune disease are (genetically predisposed) high responders against critical antigens. Data obtained in multiple sclerosis brains reveal the presence in normally appearing white matter of myelinated axons where myelin sheaths have locally dissociated from their enwrapped axon (i.e., blistering). The ensuing disintegration of axon–myelin units potentially causes the excess systemic release of post‐translationally modified myelin. Data obtained in a unique primate multiple sclerosis model revealed a core pathogenic role of T cells present in the normal repertoire, which hyper‐react to post‐translationally modified (citrullinated) myelin–oligodendrocyte glycoprotein and evoke clinical and pathological aspects of multiple sclerosis.

Meningeal inflammation in multiple sclerosis induces phenotypic changes in cortical microglia that differentially associate with neurodegeneration

Meningeal inflammation strongly associates with demyelination and neuronal loss in the underlying cortex of progressive MS patients, thereby contributing significantly to clinical disability. However, the pathological mechanisms of meningeal inflammation-induced cortical pathology are still largely elusive. By extensive analysis of cortical microglia in post-mortem progressive MS tissue, we identified cortical areas with two MS-specific microglial populations, termed MS1 and MS2 cortex. The microglial population in MS1 cortex was characterized by a higher density and increased expression of the activation markers HLA class II and CD68, whereas microglia in MS2 cortex showed increased morphological complexity and loss of P2Y12 and TMEM119 expression. Interestingly, both populations associated with inflammation of the overlying meninges and were time-dependently replicated in an in vivo rat model for progressive MS-like chronic meningeal inflammation. In this recently developed animal model, cortical microglia at 1-month post-induction of experimental meningeal inflammation resembled microglia in MS1 cortex, and microglia at 2 months post-induction acquired a MS2-like phenotype. Furthermore, we observed that MS1 microglia in both MS cortex and the animal model were found closely apposing neuronal cell bodies and to mediate pre-synaptic displacement and phagocytosis, which coincided with a relative sparing of neurons. In contrast, microglia in MS2 cortex were not involved in these synaptic alterations, but instead associated with substantial neuronal loss. Taken together, our results show that in response to meningeal inflammation, microglia acquire two distinct phenotypes that differentially associate with neurodegeneration in the progressive MS cortex. Furthermore, our in vivo data suggests that microglia initially protect neurons from meningeal inflammation-induced cell death by removing pre-synapses from the neuronal soma, but eventually lose these protective properties contributing to neuronal loss.

Nile Red fluorescence spectroscopy reports early physicochemical changes in myelin with high sensitivity

The molecular composition of myelin membranes determines their structure and function. Even minute changes to the biochemical balance can have profound consequences for axonal conduction and the synchronicity of neural networks. Hypothesizing that the earliest indication of myelin injury involves changes in the composition and/or polarity of its constituent lipids, we developed a sensitive spectroscopic technique for defining the chemical polarity of myelin lipids in fixed frozen tissue sections from rodent and human. The method uses a simple staining procedure involving the lipophilic dye Nile Red, whose fluorescence spectrum varies according to the chemical polarity of the microenvironment into which the dye embeds. Nile Red spectroscopy identified histologically intact yet biochemically altered myelin in prelesioned tissues, including mouse white matter following subdemyelinating cuprizone intoxication, as well as normal-appearing white matter in multiple sclerosis brain. Nile Red spectroscopy offers a relatively simple yet highly sensitive technique for detecting subtle myelin changes.

Engine Failure in Axo-Myelinic Signaling: A Potential Key Player in the Pathogenesis of Multiple Sclerosis

Multiple Sclerosis (MS) is a complex and chronic disease of the central nervous system (CNS), characterized by both degenerative and inflammatory processes leading to axonal damage, demyelination, and neuronal loss. In the last decade, the traditional outside-in standpoint on MS pathogenesis, which identifies a primary autoimmune inflammatory etiology, has been challenged by a complementary inside-out theory. By focusing on the degenerative processes of MS, the axo-myelinic system may reveal new insights into the disease triggering mechanisms. Oxidative stress (OS) has been widely described as one of the means driving tissue injury in neurodegenerative disorders, including MS. Axonal mitochondria constitute the main energy source for electrically active axons and neurons and are largely vulnerable to oxidative injury. Consequently, axonal mitochondrial dysfunction might impair efficient axo-glial communication, which could, in turn, affect axonal integrity and the maintenance of axonal, neuronal, and synaptic signaling. In this review article, we argue that OS-derived mitochondrial impairment may underline the dysfunctional relationship between axons and their supportive glia cells, specifically oligodendrocytes and that this mechanism is implicated in the development of a primary cytodegeneration and a secondary pro-inflammatory response (inside-out), which in turn, together with a variably primed host’s immune system, may lead to the onset of MS and its different subtypes.

Axon-Myelin Unit Blistering as Early Event in MS Normal Appearing White Matter

Objective

Multiple sclerosis (MS) is a chronic neuroinflammatory and neurodegenerative disease of unknown etiology. Although the prevalent view regards a CD4⁺‐lymphocyte autoimmune reaction against myelin at the root of the disease, recent studies propose autoimmunity as a secondary reaction to idiopathic brain damage. To gain knowledge about this possibility we investigated the presence of axonal and myelinic morphological alterations, which could implicate imbalance of axon‐myelin units as primary event in MS pathogenesis.

Methods

Using high resolution imaging histological brain specimens from patients with MS and non‐neurological/non‐MS controls, we explored molecular changes underpinning imbalanced interaction between axon and myelin in normal appearing white matter (NAWM), a region characterized by normal myelination and absent inflammatory activity.

Results

In MS brains, we detected blister‐like swellings formed by myelin detachment from axons, which were substantially less frequently retrieved in non‐neurological/non‐MS controls. Swellings in MS NAWM presented altered glutamate receptor expression, myelin associated glycoprotein (MAG) distribution, and lipid biochemical composition of myelin sheaths. Changes in tethering protein expression, widening of nodes of Ranvier and altered distribution of sodium channels in nodal regions of otherwise normally myelinated axons were also present in MS NAWM. Finally, we demonstrate a significant increase, compared with controls, in citrullinated proteins in myelin of MS cases, pointing toward biochemical modifications that may amplify the immunogenicity of MS myelin.

Interpretation

Collectively, the impaired interaction of myelin and axons potentially leads to myelin disintegration. Conceptually, the ensuing release of (post‐translationally modified) myelin antigens may elicit a subsequent immune attack in MS. ANN NEUROL 2021;89:711–725

Endoplasmic reticulum stress in the dorsal root ganglia regulates large-conductance potassium channels and contributes to pain in a model of multiple sclerosis

Neuropathic pain is a common symptom of multiple sclerosis (MS) and current treatment options are ineffective. In this study, we investigated whether endoplasmic reticulum (ER) stress in dorsal root ganglia (DRG) contributes to pain hypersensitivity in the experimental autoimmune encephalomyelitis (EAE) mouse model of MS. Inflammatory cells and increased levels of ER stress markers are evident in post-mortem DRGs from MS patients. Similarly, we observed ER stress in the DRG of mice with EAE and relieving ER stress with a chemical chaperone, 4-phenylbutyric acid (4-PBA), reduced pain hypersensitivity. In vitro, 4-PBA and the selective PERK inhibitor, AMG44, normalize cytosolic Ca²⁺ transients in putative DRG nociceptors. We went on to assess disease-mediated changes in the functional properties of Ca²⁺ -sensitive BK-type K⁺ channels in DRG neurons. We found that the conductance-voltage (GV) relationship of BK channels was shifted to a more positive voltage, together with a more depolarized resting membrane potential in EAE cells. Our results suggest that ER stress in sensory neurons of MS patients and mice with EAE is a source of pain and that ER stress modulators can effectively counteract this phenotype.

Enhanced GABAergic Immunoreactivity in Hippocampal Neurons and Astroglia of Multiple Sclerosis Patients

Cognitive dysfunction occurs frequently in multiple sclerosis (MS). Research suggests that hippocampal lesions and GABAergic neurotransmitter changes contribute to cognitive dysfunction. In the present study, we aim to determine the cellular changes in GABAergic expression in MS hippocampus related to inflammation and demyelination. To this end, the presence and inflammatory activity of demyelinating lesions was determined by immunohistochemistry in human postmortem hippocampal tissue of 15 MS patients and 9 control subjects. Subsequently, GABAergic cells were visualized using parvalbumin (PV) and glutamate acid decarboxylase 67 (GAD67) markers. Fluorescent colabeling was performed of GAD67 with neuronal nuclei, PV, astrocytic glial fibrillary acidic protein, or vesicular GABA transporter. We observed increased GAD67-positive (GAD67⁺) neuron and synapse numbers in the CA1 of MS patients with active hippocampal lesions, not due to neurogenesis. The number and size of PV-positive neurons remained unchanged. GAD67⁺ astrocytes were more numerous in hippocampal white matter than grey matter lesions. Additionally, in MS patients with active hippocampal lesions GAD67⁺ astrocyte surface area was increased. Disturbed cognition was most prevalent in MS patients with active hippocampal lesions. Summarizing, increased GAD67 immunoreactivity occurs in neurons and astrocytes and relates to hippocampal inflammation and possibly disturbed cognition in MS.

Axonal degeneration as substrate of fractional anisotropy abnormalities in multiple sclerosis cortex

Cortical microstructural abnormalities are associated with clinical and cognitive deterioration in multiple sclerosis. Using diffusion tensor MRI, a higher fractional anisotropy has been found in cortical lesions versus normal-appearing cortex in multiple sclerosis. The pathological substrates of this finding have yet to be definitively elucidated. By performing a combined post-mortem diffusion tensor MRI and histopathology study, we aimed to define the histopathological substrates of diffusivity abnormalities in multiple sclerosis cortex. Sixteen subjects with multiple sclerosis and 10 age- and sex-matched non-neurological control donors underwent post-mortem in situ at 3 T MRI, followed by brain dissection. One hundred and ten paraffin-embedded tissue blocks (54 from multiple sclerosis patients, 56 from non-neurological controls) were matched to the diffusion tensor sequence to obtain regional diffusivity measures. Using immunohistochemistry and silver staining, cortical density of myelin, microglia, astrocytes and axons, and density and volume of neurons and glial cells were evaluated. Correlates of diffusivity abnormalities with histological markers were assessed through linear mixed-effects models. Cortical lesions (77% subpial) were found in 27/54 (50%) multiple sclerosis cortical regions. Multiple sclerosis normal-appearing cortex had a significantly lower fractional anisotropy compared to cortex from non-neurological controls (P = 0.047), whereas fractional anisotropy in demyelinated cortex was significantly higher than in multiple sclerosis normal-appearing cortex (P = 0.012) but not different from non-neurological control cortex (P = 0.420). Compared to non-neurological control cortex, both multiple sclerosis normal-appearing and demyelinated cortices showed a lower density of axons perpendicular to the cortical surface (P = 0.012 for both) and of total axons (parallel and perpendicular to cortical surface) (P = 0.028 and 0.012). In multiple sclerosis, demyelinated cortex had a lower density of myelin (P = 0.004), parallel (P = 0.018) and total axons (P = 0.029) versus normal-appearing cortex. Regarding the pathological substrate, in non-neurological controls, cortical fractional anisotropy was positively associated with density of perpendicular, parallel, and total axons (P = 0.031 for all). In multiple sclerosis, normal-appearing cortex fractional anisotropy was positively associated with perpendicular and total axon density (P = 0.031 for both), while associations with myelin, glial and total cells and parallel axons did not survive multiple comparison correction. Demyelinated cortex fractional anisotropy was positively associated with density of neurons, and total cells and negatively with microglia density, without surviving multiple comparison correction. Our results suggest that a reduction of perpendicular axons in normal-appearing cortex and of both perpendicular and parallel axons in demyelinated cortex may underlie the substrate influencing cortical microstructural coherence and being responsible for the different patterns of fractional anisotropy changes occurring in multiple sclerosis cortex.

Cortical axonal loss is associated with both gray matter demyelination and white matter tract pathology in progressive multiple sclerosis: Evidence from a combined MRI-histopathology study

Background:

Neuroaxonal degeneration is one of the hallmarks of clinical deterioration in progressive multiple sclerosis (PMS).

Objective:

To elucidate the association between neuroaxonal degeneration and both local cortical and connected white matter (WM) tract pathology in PMS.

Methods:

Post-mortem in situ 3T magnetic resonance imaging (MRI) and cortical tissue blocks were collected from 16 PMS donors and 10 controls. Cortical neuroaxonal, myelin, and microglia densities were quantified histopathologically. From diffusion tensor MRI, fractional anisotropy, axial diffusivity (AD), radial diffusivity (RD), and mean diffusivity (MD) were quantified in normal-appearing white matter (NAWM) and white matter lesions (WML) of WM tracts connected to dissected cortical regions. Between-group differences and within-group associations were investigated through linear mixed models.

Results:

The PMS donors displayed significant axonal loss in both demyelinated and normal-appearing (NA) cortices (p < 0.001 and p = 0.02) compared with controls. In PMS, cortical axonal density was associated with WML MD and AD (p = 0.003; p = 0.02, respectively), and NAWM MD and AD (p = 0.04; p = 0.049, respectively). NAWM AD and WML AD explained 12.6% and 22.6%, respectively, of axonal density variance in NA cortex. Additional axonal loss in demyelinated cortex was associated with cortical demyelination severity (p = 0.002), explaining 34.4% of axonal loss variance.

Conclusion:

Reduced integrity of connected WM tracts and cortical demyelination both contribute to cortical axonal loss in PMS.

Structural network topology relates to tissue properties in multiple sclerosis

OBJECTIVE

Abnormalities in segregative and integrative properties of brain networks have been observed in multiple sclerosis (MS) and are related to clinical functioning. This study aims to investigate the micro-scale correlates of macro-scale network measures of segregation and integration in MS.

METHODS

Eight MS patients underwent post-mortem in situ whole-brain diffusion tensor (DT) imaging and subsequent brain dissection. Macro-scale structural network topology was derived from DT data using graph theory. Clustering coefficient and mean white matter (WM) fiber length were measures of nodal segregation and integration. Thirty-three tissue blocks were collected from five cortical brain regions. Using immunohistochemistry micro-scale tissue properties were evaluated, including, neuronal size, neuronal density, axonal density and total cell density. Nodal network properties and tissue properties were correlated.

RESULTS

A negative correlation between clustering coefficient and WM fiber length was found. Higher clustering coefficient was associated with smaller neuronal size and lower axonal density, and vice versa for fiber length. Higher whole-brain WM lesion load was associated with higher whole-brain clustering, shorter whole-brain fiber length, lower neuronal size and axonal density.

CONCLUSION

Structural network properties on MRI associate with neuronal size and axonal density, suggesting that macro-scale network measures may grasp cortical neuroaxonal degeneration in MS.

Oscillatory brain activity associates with neuroligin-3 expression and predicts progression free survival in patients with diffuse glioma

Introduction

Diffuse gliomas have local and global effects on neurophysiological brain functioning, which are often seen as ‘passive’ consequences of the tumor. However, seminal preclinical work has shown a prominent role for neuronal activity in glioma growth: mediated by neuroligin-3 (NLGN3), increased neuronal activity causes faster glioma growth. It is unclear whether the same holds true in patients. Here, we investigate whether lower levels of oscillatory brain activity relate to lower NLGN3 expression and predict longer progression free survival (PFS) in diffuse glioma patients.

Methods

Twenty-four newly diagnosed patients with diffuse glioma underwent magnetoencephalography and subsequent tumor resection. Oscillatory brain activity was approximated by calculating broadband power (0.5–48 Hz) of the magnetoencephalography. NLGN3 expression in glioma tissue was semi-quantitatively assessed by immunohistochemistry. Peritumor and global oscillatory brain activity was then compared between different levels of NLGN3 expression with Kruskal–Wallis tests. Cox proportional hazards analyses were performed to estimate the predictive value of oscillatory brain activity for PFS.

Results

Patients with low expression of NLGN3 had lower levels of global oscillatory brain activity than patients with higher NLGN3 expression (P < 0.001). Moreover, lower peritumor (hazard ratio 2.17, P = 0.008) and global oscillatory brain activity (hazard ratio 2.10, P = 0.008) predicted longer PFS.

Conclusions

Lower levels of peritumor and global oscillatory brain activity are related to lower NLGN3 expression and longer PFS, corroborating preclinical research. This study highlights the important interplay between macroscopically measured brain activity and glioma progression, and may lead to new therapeutic interventions in diffuse glioma patients.

Electronic supplementary material

The online version of this article (10.1007/s11060-018-2967-5) contains supplementary material, which is available to authorized users.

Insights into the Mechanisms That May Clarify Obesity as a Risk Factor for Multiple Sclerosis

PURPOSE OF REVIEW

The proportion to which genetic and environmental factors contribute to the etiology of multiple sclerosis (MS) is still incompletely understood. An interesting association between MS etiology and obesity has recently been shown although the mechanisms underlying this association are still unknown. We propose deregulated gut microbiota and increased leptin levels as possible mechanisms underlying MS etiology in obese individuals.

RECENT FINDINGS

Alterations in the human gut microbiota and leptin levels have recently been established as immune modulators in both MS patients and obese individuals. A resemblance between pro-inflammatory bacterial profiles in MS and obese individuals was observed. Furthermore, elevated leptin levels push the immune system towards a more pro-inflammatory state and inhibit the regulatory immune response. Deregulated gut microbiota and elevated leptin levels may explain the increased risk of developing MS in obese individuals. Further research to confirm causality is warranted.

Lipid biochemical changes detected in normal appearing white matter of chronic multiple sclerosis by spectral coherent Raman imaging

Multiple sclerosis (MS) exhibits demyelination, inflammatory infiltration, axonal degeneration, and gliosis, affecting widespread regions of the central nervous system (CNS). While white matter MS lesions have been well characterized pathologically, evidence indicates that the MS brain may be globally altered, with subtle abnormalities found in grossly normal appearing white matter (NAWM). These subtle changes are difficult to investigate by common methods such as histochemical stains and conventional magnetic resonance imaging. Thus, the prototypical inflammatory lesion likely represents the most obvious manifestation of a more widespread involvement of the CNS. We describe the application of spectral coherent anti-Stokes Raman Scattering (sCARS) microscopy to study such changes in chronic MS tissue particularly in NAWM. Subtle changes in myelin lipid biochemical signatures and intra-molecular disorder of fatty acid acyl chains of otherwise normal-appearing myelin were detected, supporting the notion that the biochemical involvement of the MS brain is far more extensive than conventional methods would suggest.

Unique spectral signatures of the nucleic acid dye acridine orange can distinguish cell death by apoptosis and necroptosis

Cellular injury and death are ubiquitous features of disease, yet tools to detect them are limited and insensitive to subtle pathological changes. Acridine orange (AO), a nucleic acid dye with unique spectral properties, enables real-time measurement of RNA and DNA as proxies for cell viability during exposure to various noxious stimuli. This tool illuminates spectral signatures unique to various modes of cell death, such as cells undergoing apoptosis versus necrosis/necroptosis. This new approach also shows that cellular RNA decreases during necrotic, necroptotic, and apoptotic cell death caused by demyelinating, ischemic, and traumatic injuries, implying its involvement in a wide spectrum of tissue pathologies. Furthermore, cells with pathologically low levels of cytoplasmic RNA are detected earlier and in higher numbers than with standard markers including TdT-mediated dUTP biotin nick-end labeling and cleaved caspase 3 immunofluorescence. Our technique highlights AO-labeled cytoplasmic RNA as an important early marker of cellular injury and a sensitive indicator of various modes of cell death in a range of experimental models.

Altered blood-brain barrier transport in neuro-inflammatory disorders

During neurodegenerative and neuroinflammatory disorders of the central nervous system (CNS), such as Alzheimer's disease (AD) and multiple sclerosis (MS), the protective function of the blood-brain barrier (BBB) may be severely impaired. The general neuro-inflammatory response, ranging from activation of glial cells to immune cell infiltration that is frequently associated with such brain diseases may underlie the loss of the integrity and function of the BBB. Consequentially, the delivery and disposition of drugs to the brain will be altered and may influence the treatment efficiency of such diseases. Altered BBB transport of drugs into the CNS during diseases may be the result of changes in both specific transport and non-specific transport pathways. Potential alterations in transport routes like adsorptive mediated endocytosis and receptor-mediated endocytosis may affect drug delivery to the brain. As such, drugs that normally are unable to traverse the BBB may reach their target in the diseased brain due to increased permeability. In contrast, the delivery of (targeted) drugs could be hampered during inflammatory conditions due to disturbed transport mechanisms. Therefore, the inventory of the neuro-inflammatory status of the neurovasculature (or recovery thereof) is of utmost importance in choosing and designing an adequate drug targeting strategy under disease conditions. Within this review we will briefly discuss how the function of the BBB can be affected during disease and how this may influence the delivery of drugs into the diseased CNS.

What drives MRI-measured cortical atrophy in multiple sclerosis?

BACKGROUND

Cortical atrophy, assessed with magnetic resonance imaging (MRI), is an important outcome measure in multiple sclerosis (MS) studies. However, the underlying histopathology of cortical volume measures is unknown.

OBJECTIVE

We investigated the histopathological substrate of MRI-measured cortical volume in MS using combined post-mortem imaging and histopathology.

METHODS

MS brain donors underwent post-mortem whole-brain in-situ MRI imaging. After MRI, tissue blocks were systematically sampled from the superior and inferior frontal gyrus, anterior cingulate gyrus, inferior parietal lobule, and superior temporal gyrus. Histopathological markers included neuronal, axonal, synapse, astrocyte, dendrite, myelin, and oligodendrocyte densities. Matched cortical volumes from the aforementioned anatomical regions were measured on the MRI, and used as outcomes in a nested prediction model.

RESULTS

Forty-five tissue blocks were sampled from 11 MS brain donors. Mean age at death was 68±12 years, post-mortem interval 4±1 hours, and disease duration 35±15 years. MRI-measured regional cortical volumes varied depending on anatomical region. Neuronal density, neuronal size, and axonal density were significant predictors of GM volume.

CONCLUSIONS

In patients with long-standing disease, neuronal and axonal pathology are the predominant pathological substrates of MRI-measured cortical volume in chronic MS.

Kainate-induced epileptogenesis alters circular hole board learning strategy but not the performance of C57BL/6J mice

Patients with mesial temporal lobe epilepsy (mTLE) frequently show cognitive deficits. However, the relation between mTLE and cognitive impairment is poorly understood. To gain more insight into epilepsy-associated alterations in cognitive performance, we studied the spatial learning of C57BL/6J mice five weeks after kainate-induced status epilepticus (SE). Typically, structural hippocampal rearrangements take place within five weeks after SE. Mice were monitored by exposing them to four tasks with a focus on spatial memory and anxiety: the circular hole board, modified hole board, novel object-placement task, and elevated plus maze. On the circular hole board, animals showed a higher preference for hippocampus-independent strategies after SE. In contrast, no change in strategy was seen on the modified hole board, but animals with SE were able to finish the task more often. Animals did not have an increased preference for a relocated object in the novel object-placement task but showed an increased locomotion after SE. No indications for altered anxiety were found when tested on the elevated plus maze following SE. These data suggest that the circular hole board is a well-suited paradigm to detect subtle SE-induced hippocampal deficits.

Roles for HB-EGF and CD9 in multiple sclerosis

Early events in multiple sclerosis (MS) lesion formation are loss of blood-brain barrier (BBB) integrity, immune cell trafficking into the central nervous system, and demyelination. To date, the molecular mechanisms underlying these pathogenic events are poorly understood. Heparin-binding epidermal growth factor (HB-EGF) is a trophic factor that is induced by inflammatory stimuli and has previously been shown to interact with tetraspanins (TSPs), a family of transmembrane proteins that are involved in cellular migration and adhesion. Given the known roles of TSPs and HB-EGF, we hypothesized that HB-EGF and TSPs may play a role in the processes that underlie MS lesion formation. We examined the expression of HB-EGF and the TSPs CD9 and CD81 in MS brain and found that HB-EGF was highly induced in reactive astrocytes in active lesions. TSPs were constitutively expressed throughout normal appearing white matter and control white matter. In contrast, CD9 was reduced in demyelinated lesions and increased on blood vessels in lesion areas. In vitro studies revealed that expression of HB-EGF and TSPs is regulated during inflammation. Importantly, blocking either HB-EGF or CD9 significantly reduced the migration of monocytes across brain endothelial cell monolayers. Moreover, blocking CD9 strongly enhanced the barrier function of the BBB in vitro. Together, we demonstrate that these molecules are likely implicated in processes that are highly relevant for MS lesion formation, and therefore, HB-EGF and TSPs are promising therapeutic targets.

Grey matter damage in multiple sclerosis: a pathology perspective

Over the past decade, immunohistochemical studies have provided compelling evidence that gray matter (GM) pathology in multiple sclerosis (MS) is extensive. Until recently, this GM pathology was difficult to visualize using standard magnetic resonance imaging (MRI) techniques. However, with newly developed MRI sequences, it has become clear that GM damage is present from the earliest stages of the disease and accrues with disease progression. GM pathology is clinically relevant, as GM lesions and/or GM atrophy were shown to be associated with MS motor deficits and cognitive impairment. Recent autopsy studies demonstrated significant GM demyelination and microglia activation. However, extensive immune cell influx, complement activation and blood-brain barrier leakage, like in WM pathology, are far less prominent in the GM. Hence, so far, the cause of GM damage in MS remains unknown, although several plausible underlying pathogenic mechanisms have been proposed. This paper provides an overview of GM damage in MS with a focus on its topology and histopathology.

Hippocampal CARP over-expression solidifies consolidation of contextual fear memories

The Doublecortin-Like Kinase (DCLK) gene is involved in neuronal migration during development. Through alternative splicing the DCLK gene also produces a transcript called Ca(2+)/calmodulin dependent protein kinase (CaMK)-related peptide (CARP) that is expressed exclusively during adulthood in response to neuronal activity. The function of CARP, however, is poorly understood. To study CARP function, we have generated transgenic mice with over-expression of the CARP transcript in, amongst other brain areas, the hippocampus. We aimed to characterize possible behavioral adaptations of these mice by using a Pavlovian fear conditioning approach. This type of fear conditioning, in which both the hippocampus and amygdala are critically involved, allows studying the formation and extinction of fear related memories. We here report on the behavioral adaptations of two distinct transgenic lines: one with high levels of CARP in the hippocampus and amygdala, whilst the other has high levels of CARP in the hippocampal formation, but not in the amygdala. We tested both mouse lines separately by comparing them to their wild-type littermate controls. We provide evidence suggesting consolidation of contextual fear memories is strengthened in mice of both transgenic lines.

Over-expression of δC-DCLK-short in mouse brain results in a more anxious behavioral phenotype

Products of the Doublecortin-Like Kinase (DCLK) gene are associated with cortical migration and hippocampal maturation during embryogenesis. However, the functions of those DCLK gene transcripts that encode kinases and are expressed during adulthood are incompletely understood. To elucidate potential functions of these DCLK gene splice variants we have generated and analyzed transgenic mice with neuronal over-expression of a truncated, constitutively active form of DCLK-short, designated δC-DCLK-short. Previously, we have performed an extensive molecular characterization of these transgenic δC-DCLK-short mice and established that a specific subunit of the GABA(A) receptor, which is involved in anxiety-related GABAergic neurotransmission, is down-regulated in the hippocampus. Here we show that δC-DCLK-short mRNA is highly expressed in the hippocampus, cortex and amygdala of transgenic mice. We provide evidence that the δC-DCLK-short protein is expressed and functional. In addition, we examined anxiety-related behavior in δC-DCLK-short mice in the elevated plus maze. Interestingly, δC-DCLK-short mice spend less time, move less in the open arms of the maze and show a reduction in the number of rim dips. These behaviors indicate that δC-DCLK-short mice display a more anxious behavioral phenotype.

Differential receptor-mediated drug targeting to the diseased brain

The brain is not directly accessible for intravenously administered macro- and most small molecular drugs because of the presence of the blood-brain barrier (BBB). In this respect the BBB functions as a physical and metabolic barrier which is presented by the endothelial cells in brain capillaries. In order to overcome the BBB, therapeutic compounds have been targeted to internalizing receptors at the BBB. In this review we summarize the different approaches that have been described in current literature, including the possible difficulties for clinical application. Particularly, we focus on the possible impact of brain diseases on receptor-mediated transport to the BBB/brain and how this may affect various targeting strategies. Moreover, it is our opinion that a differential drug targeting/delivery approach should be applied to treat central nervous system (CNS) diseases that are related to the BBB alone, and for CNS diseases that are related to both the brain and the BBB.

Can subtle changes in gene expression be consistently detected with different microarray platforms?

Background

The comparability of gene expression data generated with different microarray platforms is still a matter of concern. Here we address the performance and the overlap in the detection of differentially expressed genes for five different microarray platforms in a challenging biological context where differences in gene expression are few and subtle.

Results

Gene expression profiles in the hippocampus of five wild-type and five transgenic δC-doublecortin-like kinase mice were evaluated with five microarray platforms: Applied Biosystems, Affymetrix, Agilent, Illumina, LGTC home-spotted arrays. Using a fixed false discovery rate of 10% we detected surprising differences between the number of differentially expressed genes per platform. Four genes were selected by ABI, 130 by Affymetrix, 3,051 by Agilent, 54 by Illumina, and 13 by LGTC. Two genes were found significantly differentially expressed by all platforms and the four genes identified by the ABI platform were found by at least three other platforms. Quantitative RT-PCR analysis confirmed 20 out of 28 of the genes detected by two or more platforms and 8 out of 15 of the genes detected by Agilent only. We observed improved correlations between platforms when ranking the genes based on the significance level than with a fixed statistical cut-off. We demonstrate significant overlap in the affected gene sets identified by the different platforms, although biological processes were represented by only partially overlapping sets of genes. Aberrances in GABA-ergic signalling in the transgenic mice were consistently found by all platforms.

Conclusion

The different microarray platforms give partially complementary views on biological processes affected. Our data indicate that when analyzing samples with only subtle differences in gene expression the use of two different platforms might be more attractive than increasing the number of replicates. Commercial two-color platforms seem to have higher power for finding differentially expressed genes between groups with small differences in expression.