Lars Bø

Axonal Transection in the Lesions of Multiple Sclerosis

BACKGROUND Multiple sclerosis is an inflammatory demyelinating disease of the central nervous system and is the most common cause of neurologic disability in young adults. Despite antiinflammatory or immunosuppressive therapy, most patients have progressive neurologic deterioration that may reflect axonal loss. We conducted pathological studies of brain tissues to define the changes in axons in patients with multiple sclerosis. METHODS Brain tissue was obtained at autopsy from 11 patients with multiple sclerosis and 4 subjects without brain disease. Fourteen active multiple-sclerosis lesions, 33 chronic active lesions, and samples of normal-appearing white matter were examined for demyelination, inflammation, and axonal pathologic changes by immunohistochemistry and confocal microscopy. Axonal transection, identified by the presence of terminal axonal ovoids, was detected in all 47 lesions and quantified in 18 lesions. RESULTS Transected axons were a consistent feature of the lesions of multiple sclerosis, and their frequency was related to the degree of inflammation within the lesion. The number of transected axons per cubic millimeter of tissue averaged 11,236 in active lesions, 3138 at the hypocellular edges of chronic active lesions, 875 in the hypocellular centers of chronic active lesions, and less than 1 in normal-appearing white matter from the control brains. CONCLUSIONS Transected axons are common in the lesions of multiple sclerosis, and axonal transection may be the pathologic correlate of the irreversible neurologic impairment in this disease.

Transected neurites, apoptotic neurons, and reduced inflammation in cortical multiple sclerosis lesions

Multiple Sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system that causes motor, sensory, and cognitive deficits. The present study characterized demyelinated lesions in the cerebral cortex of MS patients. One hundred twelve cortical lesions were identified in 110 tissue blocks from 50 MS patients. Three patterns of cortical demyelination were identified: type I lesions were contiguous with subcortical white matter lesions; type II lesions were small, confined to the cortex, and often perivascular; type III lesions extended from the pial surface to cortical layer 3 or 4. Inflammation and neuronal pathology were studied in tissue from eight and seven patients, respectively. Compared to white matter lesions, cortical lesions contained 13 times fewer CD3‐positive lymphocytes (195 vs 2,596/mm3 of tissue) and six times fewer CD68‐positive microglia/macrophages (11,948 vs 67,956/mm3 of tissue). Transected neurites (both axons and dendrites) occurred at a density of 4,119/mm3 in active cortical lesions, 1,107/mm3 in chronic active cortical lesions, 25/mm3 in chronic inactive cortical lesions, 8/mm3 in myelinated MS cortex, and 1/mm3 in control cortex. In active and chronic active cortical lesions, activated microglia closely apposed and ensheathed apical dendrites, neurites, and neuronal perikarya. In addition, apoptotic neurons were increased significantly in demyelinated cortex compared to myelinated cortex. These data support the hypothesis that demyelination, axonal transection, dendritic transection, and apoptotic loss of neurons in the cerebral cortex contribute to neurological dysfunction in MS patients.

Intracortical multiple sclerosis lesions are not associated with increased lymphocyte infiltration

The present study examined the extent and distribution of lymphocyte infiltration in demyelinated lesions in the cerebral cortex of multiple sclerosis (MS) patients. Tissue sections from the brain of 10 MS patients and five patients without neurological disease were double labeled for myelin basic protein and the lymphocyte markers C D3, C D4, C D8, C D45RO, and C D20. The highest density of C D3- positive T cells was found in MS white matter lesions (40.4/10 high power fields (hpf)). Fewer T cells were detected in cortical lesions that extended through both white and gray matter (12.1/10 hpf; P B-0.001). The lowest number of T cells was detected in intracortical demyelinated lesions (1.1/10 hpf). This was equal to the lymphocyte density in nondemyelinated cerebral cortex within the same tissue block (1.1/10 hpf) or cerebral cortex in control brains (1.8/10 hpf). A similar distribution was found using the C D4, C D8, and C D45RO markers. C D20-positive B cells were scarce in all specimens examined. These data indicate that areas of intracortical demyelination in chronic MS are not associated with an increased number of lymphocytes, or an altered distribution of lymphocyte subsets, when compared with control areas in MS and control patients. This finding indicates that the extent of lymphocyte infiltration in MS lesions is dependent on lesion location.

Pathogenesis of tissue injury in MS lesions

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system. The primary pathological target in multiple sclerosis is myelin. Most MS patients follow a relapsing-remitting (RR-MS) course for 10 to 15 years that transforms into a chronic or secondary progressive disease (SP-MS). This review summarizes studies from our laboratory that implicate activated microglia and astrocytes in early stages of myelin destruction in MS brain. In addition, we review evidence that indicates that axonal transection is a major pathological process in multiple sclerosis. Our data support the hypothesis that neurological disability in RR-MS is due to inflammatory demyelination while axonal loss plays a significant role in the irreversible neurological decline in SP-MS. Further elucidation of the pathological targets and pathological mechanisms of tissue destruction in MS brain will help identify new therapeutics.

Homogeneity of active demyelinating lesions in established multiple sclerosis.

Four different patterns of demyelination have been described in active demyelinating lesions of multiple sclerosis (MS) patients that were biopsied shortly after disease onset. These patterns were suggested to represent heterogeneity of the underlying pathogenesis. The aim of this study was to determine whether lesion heterogeneity also exists in an unselected collection of autopsy material from patients with established MS.

Extensive Hippocampal Demyelination in Multiple Sclerosis

Abstract Memory impairment is especially prominent within the spectrum of cognitive deficits in multiple sclerosis (MS), and a crucial role for hippocampal pathology may therefore be expected in this disease. This study is the first to systematically assess hippocampal demyelination in MS. Hippocampal tissue samples of 19 chronic MS cases and 7 controls with non-neurologic disease were stained immunohistochemically for myelin proteolipid protein. Subsequently, number, location, and size of demyelinated lesions were assessed. Furthermore, the specimens were stained for HLA-DR to investigate microglia/macrophage activity. An unexpectedly high number of lesions (n = 37) was found in 15 of the 19 MS cases. Mixed intrahippocampal-perihippocampal lesions, which were more often found in cases with cognitive decline, were large and did not respect anatomical borders. Moderate microglial activation was frequently observed at the edges of these mixed lesions. Isolated intrahippocampal lesions were also frequently found. These were smaller than the mixed lesions and had a specific anatomical predilection: the cornu ammonis 2 subregion and the hilus of the dentate gyrus were consistently spared. Microglial activation was rare in isolated intrahippocampal lesions. Our results indicate that hippocampal demyelination is frequent and extensive in MS and that anatomical localization, size, and inflammatory activity vary for different lesion types.

Regional variations in the extent and pattern of grey matter demyelination in Multiple Sclerosis: a comparison between the cerebral cortex, cerebellar cortex, deep grey matter nuclei and the spinal cord

Background: Substantial grey matter (GM) demyelination occurs in both the cerebral cortex and spinal cord in multiple sclerosis (MS). GM demyelination also occurs in the cerebellar cortex and the deep GM nuclei of the brain. However, no study has made a direct “within subject” comparison of the extent of GM pathology between these regions. Aim: To examine the extent and pattern of GM demyelination in the motor cortex, cingulate gyrus, cerebellum, thalamus and spinal cord in MS. Methods: Postmortem study using material from 14 MS cases and three controls. Sections were taken from the five predetermined areas and stained for proteolipid protein. The extent of GM and white matter (WM) demyelination was assessed in each region. Results and conclusion: Overall, 28.8% of the GM was demyelinated compared with 15.6% of the WM (p<0.001), with demyelination being greater in the GM than in the WM at each of the anatomical sites. There was substantial variation in the extent of demyelination between the different CNS regions. GM demyelination was most extensive in the spinal cord and cerebellum while WM demyelination was most prominent in the spinal cord.

Distribution of immunoglobulin superfamily members ICAM-1, -2, -3, and the β2 integrin LFA-1 in multiple sclerosis lesions

To identify potential molecular substrates for leukocyte trafficking and activation in multiple sclerosis (MS) brain, we determined the immunocytochemical distribution of the beta, integrin lymphocyte-function-associated antigen-1 (LFA-1) and its major ligands, intercellular adhesion molecule (ICAM)-1, ICAM-2, and ICAM-3 in MS tissue. Colocalization of these adhesion molecules with lineage-specific markers was analyzed by dual-labeling immunocytochemistry and confocal microscopy. ICAM-1 and ICAM-2 were detected on endothelial cells, and ICAM-3 immunoreactivity was restricted to infiltrating leukocytes. In control brain, 10% of glucose transporter-1 positive vessels contained ICAM-1 immunoreactivity on their luminal surface and 21% were ICAM-2-positive. A significant increase in ICAM-1-positive vessels was found in MS brains. This increase was greater in MS lesions (81% of vessels) than in nonlesion areas (37% of vessels). A significant increase in ICAM-1-positive vessels was found in encephalitis (55% of vessels) but not in Parkinsons (17% of vessels) brains. The percentage of vessels expressing ICAM-2 was not increased in MS, encephalitis, or Parkinsons brains. Both ICAM-3 and LFA-1 were detected on the vast majority of infiltrating lymphocytes and monocytes in and near MS lesions, and these cells were often closely apposed to each other. In addition, LFA-1 was detected on activated microglia located close to the edge of demyelinating lesions. ICAM-3-positive leukocytes were often closely apposed to LFA-1-positive microglia. These results suggest a role for ICAM-1, -2, and LFA-1 in the transendothelial migration of leukocytes into MS brain and a role for ICAM 3/LFA-1 interactions in the activation of lymphocytes, monocytes, and microglia in MS lesions.

Enhanced number and activity of mitochondria in multiple sclerosis lesions.

Mitochondrial dysfunction has been implicated in the development and progression of multiple sclerosis (MS) lesions. Mitochondrial alterations might occur as a response to demyelination and inflammation, since demyelination leads to an increased energy demand in axons and could thereby affect the number, distribution and activity of mitochondria. We have studied the expression of mitochondrial proteins and mitochondrial enzyme activity in active demyelinating and chronic inactive MS lesions. Mitochondrial protein expression and enzyme activity in active and chronic inactive MS lesions was investigated using (immuno)histochemical and biochemical techniques. The number of mitochondria and their co‐localization with axons and astrocytes within MS lesions and adjacent normal‐appearing white matter (NAWM) was quantitatively assessed. In both active and inactive lesions we observed an increase in mitochondrial protein expression as well as a significant increase in the number of mitochondria. Mitochondrial density in axons and astrocytes was significantly enhanced in active lesions compared to adjacent NAWM, whereas a trend was observed in inactive lesions. Complex IV activity was strikingly up‐regulated in MS lesions compared to control white matter and, to a lesser extent, NAWM. Finally, we demonstrated increased immunoreactivity of the mitochondrial stress protein mtHSP70 in MS lesions, particularly in astrocytes and axons. Our data indicate the occurrence of severe mitochondrial alterations in MS lesions, which coincides with enhanced mitochondrial oxidative stress. Together, these findings support a mechanism whereby enhanced density of mitochondria in MS lesions might contribute to the formation of free radicals and subsequent tissue damage. Copyright

Downregulation of macrophage inhibitory molecules in multiple sclerosis lesions

Inflammatory and demyelinating activity of activated resident macrophages (microglia) and recruited blood‐borne macrophages are considered crucial in multiple sclerosis (MS) lesion development. The membrane glycoproteins CD200 and CD47, highly expressed on neurons, are mediators of macrophage inhibition via their receptors CD200R and signal‐regulatory protein α, respectively, on myeloid cells. We determined the expression pattern of immune inhibitory molecules in relation to genes involved in macrophage activation and MS lesion pathology.