Complement is activated in progressive multiple sclerosis cortical grey matter lesions

Abstract

BackgroundThe symptoms of multiple sclerosis (MS) are caused by damage to myelin and nerve cells in the brain and spinal cord. Inflammation is tightly linked with neurodegeneration, and it is the accumulation of neurodegeneration that underlies increasing neurological disability in progressive MS. Determining pathological mechanisms at play in MS grey matter is therefore a key to our understanding of disease progression.MethodsWe analysed complement expression and activation by immunocytochemistry and in situ hybridisation in frozen or formalin-fixed paraffin-embedded post-mortem tissue blocks from 22 progressive MS cases and made comparisons to inflammatory central nervous system disease and non-neurological disease controls.ResultsExpression of the transcript for C1qA was noted in neurons and the activation fragment and opsonin C3b-labelled neurons and glia in the MS cortical and deep grey matter. The density of immunostained cells positive for the classical complement pathway protein C1q and the alternative complement pathway activation fragment Bb was significantly increased in cortical grey matter lesions in comparison to control grey matter. The number of cells immunostained for the membrane attack complex was elevated in cortical lesions, indicating complement activation to completion. The numbers of classical (C1-inhibitor) and alternative (factor H) pathway regulator-positive cells were unchanged between MS and controls, whilst complement anaphylatoxin receptor-bearing microglia in the MS cortex were found closely apposed to cortical neurons. Complement immunopositive neurons displayed an altered nuclear morphology, indicative of cell stress/damage, supporting our finding of significant neurodegeneration in cortical grey matter lesions.ConclusionsComplement is activated in the MS cortical grey matter lesions in areas of elevated numbers of complement receptor-positive microglia and suggests that complement over-activation may contribute to the worsening pathology that underlies the irreversible progression of MS.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-016-0611-x) contains supplementary material, which is available to authorized users.

Meningeal inflammation and cortical demyelination in acute multiple sclerosis

“…We have previously shown that complement is activated in progressive MS GM neurons and complement activation correlated with severity of GM pathology, whereas others have shown that complement C1q and C3b expression is associated with degenerating synapses in the progressive MS hippocampus . We performed ISH for complement transcripts that encode the recognition fragment C1q and the central complement component C3.…”

“…Probe design consisted of antisense C1QA (NM_015991) FAM‐TggTccTugAugTuuCcuG and sense FAM‐CagGaaAcaTcaAggAccA; antisense C3 (NM_000064) FAM‐TagAaaGugAugGagAcuA and sense FAM‐AgaAauGauUggUggAuuA; antisense CXCL13 (NM_006419) FAM‐AuuGacTugTucTucTucC and sense FAM‐GgaAgaAgaAcaAguCaaT (where capitals indicate LNA and lower case 2′‐O‐Methyl RNA in all instances; Eurogentec, Southampton, UK). ISH was performed as previously described, and hybridization and wash conditions were optimized so that all sense probes yielded essentially no signal. Appropriate sense probes and no probe controls were included in every experimental run.…”

Fibrin(ogen) and neurodegeneration in the progressive multiple sclerosis cortex

“…Fibrin(ogen), as a potent activator of microglial/ macrophage inflammation, might be a novel therapeutic target that could limit ongoing maladaptive innate immune responses in advanced progressive MS. 6 Activation of cortical microglia/macrophages by fibrin(ogen) might be an early interaction setting the stage for diffuse neuroaxonal loss characteristic of progressive disease through several potential mechanisms, including the generation of reactive oxygen species, 32 glutamate excitotoxicity, 33 and deposition of complement as recently described. 34 In summary, we introduce cortical fibrin(ogen) deposition as a novel component of cortical pathology in progressive MS. We show that fibrin(ogen) is extensively deposited in the progressive MS motor cortex where regulation of fibrinolysis appears perturbed. The inverse relationship between neuronal density and fibrin(ogen) deposition in the MS motor cortex highlights the functional relevance of this protein in disease progression.…”

Targeted complement inhibition at synapses prevents microglial synaptic engulfment and synapse loss in demyelinating disease

“…Interestingly, this classical complement cascade-mediated phagocytic signaling has now been identified to be aberrantly upregulated in mouse models of Alzheimer’s disease, frontotemporal dementia, and West Nile Virus infection, leading to synapse loss (Hong et al, 2016, Vasek et al, 2016, Lui et al, 2016). In MS patients, complement proteins are elevated systemically and in the CNS (Aeinehband et al, 2015, Ingram et al, 2012, Ingram et al, 2009, Watkins et al, 2016), and recent work has suggested that C1q and C3 colocalize with synaptic proteins in postmortem MS brains (Michailidou et al, 2015). However, it remains elusive if complement and/or microglia are necessary for synaptic changes in MS.…”