Deconstructing the Lectin Pathway in the Pathogenesis of Experimental Inflammatory Arthritis: Essential Role of the Lectin Ficolin B and Mannose-Binding Protein–Associated Serine Protease 2

Abstract

Complement plays an important role in the pathogenesis of rheumatoid arthritis (RA). While the alternative pathway (AP) is known to play a key pathogenic role in models of RA, the importance of the lectin pathway (LP) pattern recognition molecules such as ficolin A (FCN A), ficolin B (FCN B) and collectin-11 (CL-11) as well as the activating enzyme MBL (mannose binding lectin)-associated serine protease-2 (MASP-2) are less well understood. We show here that FCN A−/− and CL-11−/− mice are fully susceptible to collagen antibody-induced arthritis (CAIA). In contrast, FCN B−/− and MASP-2−/−/sMAp−/− mice are substantially protected, with clinical disease activity decreased significantly (p < 0.05) by 47% and 70%, respectively. Histopathology scores, C3, fD, FCN B deposition and infiltration of synovial macrophages and neutrophils were similarly decreased in FCN B−/− and MASP-2−/−/sMAp−/− mice. Our data support that FCN B plays an important role in the development of CAIA, likely through ligand recognition in the joint and MASP activation, and that MASP-2 also contributes to the development of CAIA, likely in a C4-independent manner. Decreased AP activity in the sera from FCN B−/− and MASP-2−/−/sMAp−/− mice with arthritis on adherent anti-collagen antibodies also support the hypothesis that pathogenic antibodies as well as additional inflammation-related ligands are recognized by the LP and operate in vivo to activate complement. Finally, we also speculate that the residual disease seen in our studies is driven by the AP and/or the C2/C4 bypass pathway via the direct cleavage of C3 through a LP-dependent mechanism.

Key Components of the Complement Lectin Pathway Are Not Only Required for the Development of Inflammatory Arthritis but Also Regulate the Transcription of Factor D

“…Here, we found that nearly complete silencing of MASP-2 expression by RNAi in the liver using GalNAc-MASP-2-siRNA leads to a partial but significant decrease in the CDA (Figure 3A). These results were consistent with our previous study in which mice lacking MASP-2/sMAp were also partially protected from CAIA (62). Interestingly, we have generated the same phenotype in WT mice as seen in MASP-2/sMAp −/− mice by injecting GalNAc-MASP-2-siRNA duplex, i.e., nearly complete elimination of MASP-2/sMAp proteins in the circulation (Figure 5B).…”

“…The total duration of the CAIA experiment was day 20 post the first siRNA injection. The clinical disease activity (CDA) in all groups of WT mice was determined every day by two trained laboratory personnel acting independently and blinded as to treatment according to our previously published methods (36,40,61,62).…”

Loss of α2-6 sialylation promotes the transformation of synovial fibroblasts into a pro-inflammatory phenotype in Rheumatoid Arthritis

“…Interestingly, the anti-inflammatory Siglec-2 has predilection for α2-6 sialic acid, but the pro-inflammatory Siglec-1 binds preferentially to α2-3 50 , thereby supporting our conclusion that pro-inflammatory SFs diminish α2-6 sialylation but not α2-3. Thus, homeostatic α2- 53,54 . These glycan-dependent networks and associated signaling for each sialic acid binding protein could explain the SF-mediated actions to establish chronic inflammation and interactions with immune cells in the arthritic synovium.…”

Molecular Characteristics, Functions, and Related Pathogenicity of MERS-CoV Proteins

“…The MERS-CoV N protein is thought to interact with mannoseassociated serine protease 2 (MASP2) [32] and translation elongation factor 1 (EF-1A) [33] in the host. Once the mannose-binding lectin recognizes the mannan on the surface of the virus-infected cell, it recruits MASP2 and then activates its enzymatic activity, eventually causing a local or systemic inflammatory response.…”