Signature of Alzheimer’s Disease in Intestinal Microbiome: Results From the AlzBiom Study

Background: Changes in intestinal microbiome composition have been described in animal models of Alzheimer’s disease (AD) and AD patients. Here we investigated how well taxonomic and functional intestinal microbiome data and their combination with clinical data can be used to discriminate between amyloid-positive AD patients and cognitively healthy elderly controls. Methods: In the present study we investigated intestinal microbiome in 75 amyloid-positive AD patients and 100 cognitively healthy controls participating in the AlzBiom study. We randomly split the data into a training and a validation set. Intestinal microbiome was measured using shotgun metagenomics. Receiver operating characteristic (ROC) curve analysis was performed to examine the discriminatory ability of intestinal microbiome among diagnostic groups. Results: The best model for discrimination of amyloid-positive AD patients from healthy controls with taxonomic data was obtained analyzing 18 genera features, and yielded an area under the receiver operating characteristic curve (AUROC) of 0.76 in the training set and 0.61 in the validation set. The best models with functional data were obtained analyzing 17 GO (Gene Ontology) features with an AUROC of 0.81 in the training set and 0.75 in the validation set and 26 KO [Kyoto Encyclopedia of Genes and Genomes (KEGG) ortholog] features with an AUROC of 0.83 and 0.77, respectively. Using ensemble learning for these three models including a clinical model with the 4 parameters age, gender, BMI and ApoE yielded an AUROC of 0.92 in the training set and 0.80 in the validation set. Discussion: In conclusion, we identified a specific Alzheimer signature in intestinal microbiome that can be used to discriminate amyloid-positive AD patients from healthy controls. The diagnostic accuracy increases from taxonomic to functional data and is even better when combining taxonomic, functional and clinical models. Intestinal microbiome represents an innovative diagnostic supplement and a promising area for developing novel interventions against AD

The function of autoantibodies targeting aquaporin-4 in the pathogenesis of neuromyelitis optica

Neuromyelitis optica (NMO) ist eine schwerwiegende Autoimmunerkrankung des zentralen Nervensystems, deren pathogene Ursache in Zusammenhang mit Autoantikörpern gegen Aquaporin 4 (AQP4) steht. In einem intrathekalen Passiv-Transfermodell der Ratte wurden die Auswirkungen von NMO-Immunglobulin (IgG) aus Plasmapheresematerial und rekombinanten Antikörpern gegen AQP4 sowie der Effekt von additiver Applikation von humanem Komplement untersucht. NMO-IgG, rekombinante Antikörper und modifizierte Antikörper ohne Fähigkeit zur Aktivierung der Komplementkaskade waren bei repetitiver Applikation in der Lage, auch ohne additives humanes Komplement NMO-ähnliche progrediente motorische Symptome zu induzieren. Durch Ko-Injektion von humanem Komplement konnte keine signifikante Exazerbation der Pathologie bewirkt werden. MRT-Studien zeigten lokale Schrankenstörungen am Ort der höchsten Antikörperkonzentration. In histologischen Aufarbeitungen von Rückenmarksschnitten zeigten sich lokale Deposition an humanem IgG, ein dazu korrelierender Verlust an AQP4 sowie eine darüber hinausgehende Reduktion des Glutamattransporters EAAT2, während GFAP-reaktive Astrozyten tendenziell hypertroph und vermehrt waren. Auch bei additiver Applikation von humanem Komplement wiesen die Läsionsareale im Gegensatz zu histopathologischen Befunden bei NMO-Patienten und anderen Tiermodellen nur eine geringe Ablagerung von aktivem Komplement und wenig Infiltration durch ED1-positive Makrophagen auf. Da in einem Kontrollexperiment mit intrazerebraler intraparenchymaler Applikation von NMO-IgG die beschriebene additive Zytotoxizität von humanem Komplement reproduziert werden konnte, erscheint die Verwendbarkeit des intrathkalen Modells zur Evaluation der Wirkung von humanem Komplement bei Autoimmunerkrankungen mit intraspinalen Zielepitopen nicht geeignet. Die Ergebnisse lassen sich als Komplement-unabhängige intrinsische Wirkungen von Antikörpern gegen AQP4 deuten, die in einer Reduktion der Oberflächenexpresseion von AQP4 und EAAT2 resultieren und zu einer progredienten Myelopathie führen. Neben der bekannten Antikörper-induzierten Komplement-abhängigen Zytotoxizität könnten diese Effekte einen bislang nicht beschriebenen zusätzlichen Pathomechanismus bei der NMO darstellen.Neuromyelitis optica (NMO) is a severe autoimmune disorder of the central nervous system that is causally linked to autoantibodies against aquaporin-4 (AQP4). In a intrathecal passive transfer rat model the effects of purified patient NMO-immunoglobuline (IgG) and recombinant anti-AQP4-antibodies were studied as well as those of additional application of human complement. Repetitive application of NMO-IgG, recombinant antibodies and modified antibodies without the ability of activation of the complement cascade caused NMO-like progressive symptoms. Additional application of human complement did not exacerbate the pathologic symptoms. MRI-studies revealed local spinal cord lesions at the site of the highest antibody concentration. Histopathological analysis of the spinal cord showed local deposition of human IgG, a corresponding loss of AQP4 and - even more pronounced - of the excitatory amino acid transporter 2 (EAAT2), whereas immunoreactivity to the astrocytic marker glial fibrillary acid protein (GFAP) was increased. Even by additional application of human complement, only little deposition of activated complement und poor infiltration by ED1-positive macrophages was observed. However, direct intracerebral application of NMO-IgG revealed complement dependent cytotoxicity as described previously; therefore the intrathecal passive transfer model is not suited to evaluate the effects of human complement in autoimmune disorders with intraspinal targets. The results can be interpreted as intrinsic effects of anti-AQP4-antibodies that are independent of complement activation and that reduce expressivity of AQP4 und EAAT2 and cause a progressive myelopathy. Additionally to the previously described antibody and complement dependent cytotoxicity, these effects might be a new pathogenic pathway in neuromyelitis optica

Next Generation Sequencing of Cerebrospinal Fluid B Cell Repertoires in Multiple Sclerosis and Other Neuro-Inflammatory Diseases-A Comprehensive Review

During the last few decades, the role of B cells has been well established and redefined in neuro-inflammatory diseases, including multiple sclerosis and autoantibody-associated diseases. In particular, B cell maturation and trafficking across the blood–brain barrier (BBB) has recently been deciphered with the development of next-generation sequencing (NGS) approaches, which allow the assessment of representative cerebrospinal fluid (CSF) and peripheral blood B cell repertoires. In this review, we perform literature research focusing on NGS studies that allow further insights into B cell pathophysiology during neuro-inflammation. Besides the analysis of CSF B cells, the paralleled assessment of peripheral blood B cell repertoire provides deep insights into not only the CSF compartment, but also in B cell trafficking patterns across the BBB. In multiple sclerosis, CSF-specific B cell maturation, in combination with a bidirectional exchange of B cells across the BBB, is consistently detectable. These data suggest that B cells most likely encounter antigen(s) within the CSF and migrate across the BBB, with further maturation also taking place in the periphery. Autoantibody-mediated diseases, such as neuromyelitis optica spectrum disorder and LGI1 / NMDAR encephalitis, also show features of a CSF-specific B cell maturation and clonal connectivity with peripheral blood. In conclusion, these data suggest an intense exchange of B cells across the BBB, possibly feeding autoimmune circuits. Further developments in sequencing technologies will help to dissect the exact pathophysiologic mechanisms of B cells during neuro-inflammation