Intravenous Neuromyelitis Optica Autoantibody in Mice Targets Aquaporin-4 in Peripheral Organs and Area Postrema

The pathogenesis of neuromyelitis optica (NMO) involves binding of IgG autoantibodies (NMO-IgG) to aquaporin-4 (AQP4) on astrocytes in the central nervous system (CNS). We studied the in vivo processing in mice of a recombinant monoclonal human NMO-IgG that binds strongly to mouse AQP4. Following intravenous administration, serum [NMO-IgG] decreased with t1/2 ∼18 hours in wildtype mice and ∼41 hours in AQP4 knockout mice. NMO-IgG was localized to AQP4-expressing cell membranes in kidney (collecting duct), skeletal muscle, trachea (epithelial cells) and stomach (parietal cells). NMO-IgG was seen on astrocytes in the area postrema in brain, but not elsewhere in brain, spinal cord, optic nerve or retina. Intravenously administered NMO-IgG was also seen in brain following mechanical disruption of the blood-brain barrier. Selective cellular localization was not found for control (non-NMO) IgG, or for NMO-IgG in AQP4 knockout mice. NMO-IgG injected directly into brain parenchyma diffused over an area of ∼5 mm2 over 24 hours and targeted astrocyte foot-processes. Our data establish NMO-IgG pharmacokinetics and tissue distribution in mice. The rapid access of serum NMO-IgG to AQP4 in peripheral organs but not the CNS indicates that restricted antibody access cannot account for the absence of NMO pathology in peripheral organs

Blood brain barrier leakage is not a consistent feature of white matter lesions in CADASIL

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a genetic paradigm of small vessel disease (SVD) caused by NOTCH3 mutations that stereotypically lead to the vascular accumulation of NOTCH3 around smooth muscle cells and pericytes. White matter (WM) lesions (WMLs) are the earliest and most frequent abnormalities, and can be associated with lacunar infarcts and enlarged perivascular spaces (ePVS). The prevailing view is that blood brain barrier (BBB) leakage, possibly mediated by pericyte deficiency, plays a pivotal role in the formation of WMLs. Herein, we investigated the involvement of BBB leakage and pericyte loss in CADASIL WMLs. Using post-mortem brain tissue from 12 CADASIL patients and 10 age-matched controls, we found that WMLs are heterogeneous, and that BBB leakage reflects the heterogeneity. Specifically, while fibrinogen extravasation was significantly increased in WMLs surrounding ePVS and lacunes, levels of fibrinogen leakage were comparable in WMLs without other pathology ("pure" WMLs) to those seen in the normal appearing WM of patients and controls. In a mouse model of CADASIL, which develops WMLs but no lacunes or ePVS, we detected no extravasation of endogenous fibrinogen, nor of injected small or large tracers in WMLs. Moreover, there was no evidence of pericyte coverage modification in any type of WML in either CADASIL patients or mice. These data together indicate that WMLs in CADASIL encompass distinct classes of WM changes and argue against the prevailing hypothesis that pericyte coverage loss and BBB leakage are the primary drivers of WMLs. Our results also have important implications for the interpretation of studies on the BBB in living patients, which may misinterpret evidence of BBB leakage within WM hyperintensities as suggesting a BBB related mechanism for all WMLs, when in fact this may only apply to a subset of these lesions.Peer reviewe

Reducing Hypermuscularization of the Transitional Segment between Arterioles and Capillaries Protects Against Spontaneous Intracerebral Hemorrhage

International audienceBackground: Spontaneous deep intracerebral hemorrhage (ICH) is a devastating subtype of stroke without specific treatments. It has been thought that smooth muscle cell (SMC) degeneration at the site of arteriolar wall rupture may be sufficient to cause hemorrhage. However, deep ICHs are rare in some aggressive small vessel diseases that are characterized by significant arteriolar SMC degeneration. Here we hypothesized that a second cellular defect may be required for the occurrence of ICH. Methods: We studied a genetic model of spontaneous deep ICH using Col4a1+/G498V and Col4a1+/G1064D mouse lines that are mutated for the alpha1 chain of Collagen type IV. We analyzed cerebroretinal microvessels, performed genetic rescue experiments, vascular reactivity analysis and computational modeling. We examined post-mortem brain tissues from patients with sporadic deep ICH. Results: We identified in the normal cerebroretinal vasculature a novel segment between arterioles and capillaries, herein called the transitional segment (TS), that is covered by mural cells distinct from SMCs and pericytes. In Col4a1 mutant mice, this TS was hypermuscularized, with a hyperplasia of mural cells expressing more contractile proteins, whereas the upstream arteriole exhibited a loss of SMCs. Mechanistically, TS showed a transient increase in proliferation of mural cells during post-natal maturation. Mutant brain microvessels, unlike mutant arteries, displayed a significant upregulation of SM genes and Notch3 target genes, and genetic reduction of Notch3 in Col4a1+/G498V mice protected against ICH. Retina analysis showed that hypermuscularization of the TS was attenuated but arteriolar SMC loss unchanged in Col4a1+/G498V, Notch3+/- mice. Moreover, hypermuscularization of the retinal TS increased its contractility and tone and raised the intravascular pressure in the upstream feeding arteriole. We similarly found hypermuscularization of the TS and focal arteriolar SMC loss in brain tissues from patients with sporadic deep ICH. Conclusions: Our results suggest that hypermuscularization of the TS, via increased Notch3 activity, is involved in the occurrence of ICH in Col4a1 mutant mice, by raising the intravascular pressure in the upstream feeding arteriole and promoting its rupture at the site of SMC loss. Our human data indicate that these 2 mutually reinforcing vascular defects may represent a general mechanism of deep ICH

Neuromyelitis optica: Aquaporin-4 based pathogenesis mechanisms and new therapies

Neuromyelitis optica (NMO) is an autoimmune 'aquaporinopathy' of the central nervous system that causes inflammatory demyelinating lesions primarily in spinal cord and optic nerve, leading to paralysis and blindness. NMO lesions show loss of aquaporin-4 (AQP4), GFAP and myelin, infiltration of granulocytes and macrophages, and perivascular deposition of activated complement. Most patients with NMO are seropositive for immunoglobulin autoantibodies (AQP4-IgG) against AQP4, the principal water channel of astrocytes. There is strong evidence that AQP4-IgG is pathogenic in NMO, probably by a mechanism involving complement-dependent astrocyte cytotoxicity, causing leukocyte infiltration, cytokine release and blood-brain barrier disruption, which leads to oligodendrocyte death, myelin loss and neuron death. Here, we review the evidence for this and alternative proposed NMO pathogenesis mechanisms, such as AQP4-IgG-induced internalization of AQP4 and glutamate transporters, complement-independent cell-mediated cytotoxicity, and AQP4-IgG inhibition of AQP4 water transport function. Based on the initiating pathogenic role of AQP4-IgG binding to astrocyte AQP4 in NMO, selective blocker therapies are under development in which AQP4-targeted monoclonal antibodies or small molecules block binding of AQP4-IgG to astrocytes and consequent downstream pathology

Nouveaux mécanismes molécualires impliqés dans la pathophysiologie du syndrome néphrotique

Chez l'homme, des mutations des gènes podocytaires WT1 et NPHS2 sont à l'origine de syndromes néphrétiques et perturbent ces interactions pour aboutir à des lésions de sclérose glomérulaire. Pour identifier de nouveaux mécanismes moléculaires impliqués dans ces processus pathologiques, plusieurs modèles murins ont été utilisés. Le premier est un modèle d'invalidation constitutive du gène Nphs2, codant la podocine, une protéine majeure du diaphragme de fente. Les animaux développent un syndrome néphrétique dont la progression est modulée par le fonds génétique et par l'environnement maternel. Par la technique de cartographie de QTL, deux régions sur les chomosomes 3 et 7 ont été associées avec la sévérité de la maladie. Nous proposons également le gène Cyr61 comme modificateur de la maladie rénale. Nous avons également réalisé un modèle murin comportant une mutation hétérozygote de Wtl, qui code un facteur de transcription majeur du podocyte. Le gène Scel, codant la scielline, est sous-exprimé dans les souris mutantes, est exprimé dans le podocyte et est une cible directe de WT1. La sous-expression de Sulfl, codant pour une endosulfatase, est susceptible de modifier l'activité de facteurs de croissance dans le glomérule et de favoriser la sclérose glomérulaire. Sulfl est également une cible directe de WT1 au sein des podocytes. Enfin, Cyp26al est surexprimé dans les podocytes et pourrait être impliqué dans un processus de dédifférenciation de ces cellules.In humans, mutations in the podocyte genes WT1 and NPHS2 lead to nephrotic syndrome and to the disruption of this cross-talk which evolves to glomerulosclerosis. To identify novel molecular mechanisms involved in this pathological process, several mouse models were used. The first model is a Nphs2-deficient mouse. This gene encodes podocin, a major component of the slit diaphragm. We demonstrated that Nphs2-/- mice develop nephrotic syndrome, the severity of which depends on genetic modifiers and maternal environment. By QTL mapping, we isolated two loci linked to disease progression on chromosomes 3 and 7. Furthermore we demonstrated in this model that the angiogenic factor Cyr61 produced in podocytes may be involved in the progression of diffuse mesangiosclerosis and mesangiolysis. We also elaborated a mouse model with a heterozygous mutation of Wtl, which encodes a major transcription factor of the podocyte. The first gene Seel, encoding sciellin, is down-regulated in mutant mice and is shown for the first time to be expressed in podocytes. Moreover this gene is a direct target of WT1. The down-regulation of Sulfl, encoding an endosulfatase, may modify growth factors activity in the glomerulus and lead to glomerulosclerosis. Sulfl is also a direct target of WT1 in podocytes. Finally, Cyp26al encoding an enzyme degrading retinoic acid is up-regulated and may be involved in dedifferentiation of podocytes.PARIS5-BU Méd.Cochin (751142101) / SudocSudocFranceF