Author Of 2 Presentations
P0944 - B-cells uptake citrullinated myelin basic protein in MS meningeal tissue: cause or consequence? (ID 1076)
Abstract
Background
Studies from our lab have reported extensive presence of myelin particles in the leptomeninges of multiple sclerosis (MS) cases, hinting at a potential role of this debris in instigating MS-related immunological responses.
Objectives
Here, to gain further insight into this possibility we closely looked at meningeal myelin fragments for the presence of posttranslational modifications (citrullination) which render myelin debris more immunogenic. We also tested whether citrullinated myelin is associated with antigen presenting cells relevant to induction of autoimmunity in MS, i.e B cells.
Methods
We performed immunohistochemistry experiments on post-mortem meningeal material coming from 8 SPMS patients (age: 61.29±4.66, disease duration: 30±4.40 years) and 7 non-neurological controls (age: 55.88±5.32 years). In addition, using confocal colocalization analysis tools, we investigated the presence of citrullinated myelin basic protein (MBP) in CD19+ B lymphocytes in MS meninges.
Results
Compared with tissue from non-neurological controls, meninges of MS patients presented with a larger surface proportion of citrullinated proteins (p=0.03). In MS material, this effect was accompanied by the presence of meningeal CD19+ B-cells. Almost all the analyzed CD19+ B-cells showed high citrulline content (n=144, 99% citrulline positive cells; mean % citrulline inside B-cells= 50.81±3.86 %) and 95.13% of these cells were also positive for myelin basic protein (MBP; median percent MBP which colocalizes with CD19= 42.05%). Interestingly, Mander´s coefficient analysis to colocalize MBP and citrulline inside B-cells underlined that almost half of the lymphocytic cellular surface was occupied by citrullinated MBP (40.06±3.23 %).
Conclusions
Our results are indicative of a B cell-mediated uptake mechanism that operates in MS meninges to clear up highly immunogenic myelin fragments. Although the question remains on whether myelin citrullination happens in the absence of a primary immunological response, studies in cuprizone mouse models of MS have highlighted that MBP citrullination already occurs before demyelination via intramyelinic Ca2+-dependent activation of protein arginine deiminases. This evidence combined with previous studies showing abundant citrulline content in both MS normal appearing white matter and white matter lesion support the concept that a primary cytodegenerative process instigates demyelination, which elicits secondary immune reactions in MS.
P0961 - Excitation-inhibition balance in multiple sclerosis: a quantification of glutamatergic and GABA-ergic synapse loss (ID 903)
Abstract
Background
Synaptic loss is a key feature of the secondary progressive phase of multiple sclerosis (MS) and is related to clinical and cognitive functioning. However, whether the excitatory or inhibitory synapses are more susceptible to MS pathology is insufficiently clarified to date.
Objectives
To quantify GABAergic and glutamatergic synaptic densities in a sample of post-mortem MS brains and, hence, to investigate whether there is reason to suspect an imbalance in excitatory versus inhibitory neurotransmission.
Methods
Brains of 33 neuro-pathologically verified MS cases (21 women, mean age=63±12y) and 9 non-neurological controls (NC, 5 women, mean age=72±6y) were dissected shortly after death (mean post-mortem delay in MS: 5:37±1:29h; in NC: 9:19±2:85h). Sections of the superior frontal cortices were stained for myelin, parvalbumin- and calretinin-expressing interneurons and glutamatergic and GABAergic synapses. Subsequently, synaptic densities were quantified through confocal microscopy in sections of pre-determined regions of interest (ROIs) and image analyses. Data were analyzed using linear mixed-effects models.
Results
Of the 71 defined ROIs in MS tissue, 24% were demyelinated, the remaining were normal-appearing grey matter (NAGM). No differences in densities of calretinin- and parvalbumin-expressing interneurons were observed between groups. For both excitatory and inhibitory synapse densities, there was a significant interaction between tissue type (NC NAGM, MS NAGM and MS demyelinated cortex) and cortical layer (P=.003; P=.001, respectively). Post-hoc testing revealed that the densities of both synapse types were reduced in cortical layer 6 (excitatory: P=.004; inhibitory: P=.002). NAGM in MS cortical layer 6 showed reductions of 12.5% (excitatory) and 14.9% (inhibitory) synaptic density as compared to NC values (P<.05). In demyelinated MS cortex a loss of 18.5% in excitatory synapses and 29.3% in inhibitory synapses was noted respective to NC values (P<.05).
Conclusions
In post-mortem MS tissue, we found a significant loss of excitatory and inhibitory synapses in layer 6 of superior frontal cortex. Interestingly, in NAGM the proportion of synaptic loss was similar for both synapse types, while in demyelinated cortex inhibitory synapses were affected more. The differential effects of fairly subtle differences in excitatory versus inhibitory synapse loss on functional measures may nonetheless have a substantial effect on cellular and network functioning. This effect is now being investigated in a corticothalamic mean-field model (results pending).