Alternative Complement Pathway Inhibition Abrogates Pneumococcal Opsonophagocytosis in Vaccine-Naïve, but Not in Vaccinated Individuals

To assess the relative contribution of opsonisation by antibodies, classical and alternative complement pathways to pneumococcal phagocytosis, we analyzed killing of pneumococci by human blood leukocytes collected from vaccine-naïve and PCV13-vaccinated subjects. With serotype 4 pneumococci as model, two different physiologic opsonophagocytosis assays based on either hirudin-anticoagulated whole blood or on washed cells from EDTA-anticoagulated blood reconstituted with active serum, were compared. Pneumococcal killing was measured in the presence of inhibitors targeting the complement components C3, C5, MASP-2, factor B or factor D. The two assay formats yielded highly consistent and comparable results. They highlighted the importance of alternative complement pathway activation for efficient opsonophagocytic killing in blood of vaccine-naïve subjects. In contrast, alternative complement pathway inhibition did not affect pneumococcal killing in PCV13-vaccinated individuals. Independent of amplification by the alternative pathway, even low capsule-specific antibody concentrations were sufficient to efficiently trigger classical pathway mediated opsonophagocytosis. In heat-inactivated or C3-inhibited serum, high concentrations of capsule-specific antibodies were required to trigger complement-independent opsonophagocytosis. Our findings suggest that treatment with alternative complement pathway inhibitors will increase susceptibility for invasive pneumococcal infection in non-immune subjects, but it will not impede pneumococcal clearance in vaccinated individuals

In vaccinated individuals serum bactericidal activity against B meningococci is abrogated by C5 inhibition but not by inhibition of the alternative complement pathway

Dysregulation of complement activation causes a number of diseases, which can be treated with inhibitors of the complement components C5 and C3. However, complement is required for serum bactericidal activity (SBA) against encapsulated Gram-negative bacteria. Therefore, C3 and C5 inhibition increases the risk of invasive disease, in particular by Neisseria meningitidis. As inhibitors against complement components other than C3 and C5 may carry a reduced risk of infection, we compared the effect of inhibitors targeting the central complement component C3, the alternative pathway (fB and fD), the lectin pathway (MASP-2) and the terminal pathway (C5) on SBA against serogroup B meningococci. Serum from adults was collected before and after vaccination with the meningococcal serogroup B vaccine 4CMenB and tested for meningococcal killing. Since the B capsular polysaccharide is structurally similar to certain human polysaccharides, 4CMenB was designed to elicit antibodies against meningococcal outer membrane proteins. While only a few pre-vaccination sera showed SBA against the B meningococcal isolates tested, 4CMenB vaccination induced potent complement activating IgG titers against isolates expressing a matching allele of the bacterial cell surface-exposed lipoprotein Factor H binding protein (fHbp). While SBA triggered by these cell surface protein-specific antibodies was blocked by C5 and reduced by C3 inhibition, alternative (factor B and D) and lectin (MASP-2) pathway inhibitors had no effect on SBA of post-4CMenB vaccination sera. Compared to SBA triggered by A,C,W,Y capsule polysaccharide conjugate vaccination, SBA against B meningococci expressing a matching fHbp allele, was thus remarkably resilient against alternative pathway inhibition

Pharmacological BACE1 and BACE2 inhibition induces hair hypopigmentation by inhibiting PMEL17 processing in mice

Melanocytes of the hair follicle produce melanin and are essential in determining the differences in hair color. Pigment cell-specific MELanocyte Protein (PMEL17) plays a crucial role in melanogenesis. One of the critical steps is the amyloid-like functional oligomerization of PMEL17. Beta Site APP Cleaving Enzyme-2 (BACE2) and γ-secretase have been shown to be key players in generating the proteolytic fragments of PMEL17. The β-secretase (BACE1) is responsible for the generation of amyloid-β (Aβ) fragments in the brain and is therefore proposed as a therapeutic target for Alzheimer’s disease (AD). Currently BACE1 inhibitors, most of which lack selectivity over BACE2, have demonstrated efficacious reduction of amyloid-β peptides in animals and the CSF of humans. BACE2 knock-out mice have a deficiency in PMEL17 proteolytic processing leading to impaired melanin storage and hair depigmentation. Here, we confirm BACE2-mediated inhibition of PMEL17 proteolytic processing in vitro in mouse and human melanocytes. Furthermore, we show that wildtype as well as bace2+/− and bace2−/− mice treated with a potent dual BACE1/BACE2 inhibitor NB-360 display dose-dependent appearance of irreversibly depigmented hair. Retinal pigmented epithelium showed no morphological changes. Our data demonstrates that BACE2 as well as additional BACE1 inhibition affects melanosome maturation and induces hair depigmentation in mice

Deficiency in MALT1 paracaspase activity promotes multi-organ inflammation

The paracaspase MALT1 plays an important role in signaling pathways leading to NF-kB activation. To investigate the contribution of its proteolytic activity to overall pathway regulation we generated MALT1 protease-deficient mice (Malt1PD/PD) and compared them to MALT1 KO animals (Malt1-/-). Malt1PD/PD mice displayed defects in multiple cell types including Treg, IL10-producing B cells and mature T and B cells. Immune defects were more pronounced in Malt1-/- animals. Both mouse lines showed abrogated B cell responses upon immunization and were protected in a Th17-dependent EAE model. Surprisingly, Malt1PD/PD animals developed a multi-organ inflammation characterized by Th2-type responses and enhanced IgG1 and IgE levels which was prevented by reconstitution with WT Treg. These data uncover a previously unappreciated key function of MALT1 protease activity in immune homeostasis and its relevance in human health and disease

Identification of Dlk1-Dio3 imprinted gene cluster non-coding RNAs as novel candidate biomarkers for liver tumor promotion

The molecular events during non-genotoxic carcinogenesis and their temporal order are poorly understood but thought to include long-lasting perturbations of gene expression. Here, we have investigated the temporal sequence of molecular and pathological perturbations at early stages of phenobarbital-mediated liver tumor promotion in vivo. Molecular profiling (mRNA, miRNA, DNA methylation & proteins) of mouse liver during 13 weeks of phenobarbital treatment revealed progressive increases in hepatic expression of long non-coding RNAs and microRNAs originating from the Dlk1-Dio3 imprinted gene cluster, a locus that has recently been associated with stem cell pluripotency in mice and various neoplasms in humans. Phenobarbital-induction of the Dlk1-Dio3 cluster non-coding RNA Meg3 was localised to glutamine synthetase positive hypertrophic perivenous hepatocytes suggesting a role for β-catenin signaling in the dysregulation of Dlk1-Dio3 non-coding RNAs. The carcinogenic relevance of Dlk1-Dio3 locus non-coding RNA induction was further supported by in vivo genetic dependence on Constitutive Androstane Receptor (CAR) and β-catenin pathways. Our data identify Dlk1-Dio3 non-coding RNAs as novel candidate early biomarkers for mouse liver tumor promotion and provide new opportunities for assessing the carcinogenic potential of novel compounds

Identification of Dlk1-Dio3 Imprinted Gene Cluster Noncoding RNAs as Novel Candidate Biomarkers for Liver Tumor Promotion

The molecular events during non-genotoxic carcinogenesis and their temporal order are poorly understood but thought to include long-lasting perturbations of gene expression. Here, we have investigated the temporal sequence of molecular and pathological perturbations at early stages of phenobarbital-mediated liver tumor promotion in vivo. Molecular profiling (mRNA, miRNA, DNA methylation & proteins) of mouse liver during 13 weeks of phenobarbital treatment revealed progressive increases in hepatic expression of long non-coding RNAs and microRNAs originating from the Dlk1-Dio3 imprinted gene cluster, a locus that has recently been associated with stem cell pluripotency in mice and various neoplasms in humans. Phenobarbital-induction of the Dlk1-Dio3 cluster non-coding RNA Meg3 was localised to glutamine synthetase positive hypertrophic perivenous hepatocytes suggesting a role for β-catenin signaling in the dysregulation of Dlk1-Dio3 non-coding RNAs. The carcinogenic relevance of Dlk1-Dio3 locus non-coding RNA induction was further supported by in vivo genetic dependence on Constitutive Androstane Receptor (CAR) and β-catenin pathways. Our data identify Dlk1-Dio3 non-coding RNAs as novel candidate early biomarkers for mouse liver tumor promotion and provide new opportunities for assessing the carcinogenic potential of novel compounds