Invasion of Mycoplasma bovis into bovine synovial cells utilizing the clathrin-dependent endocytosis pathway.

Mycoplasma bovis causes chronic arthritis in cattle, accompanied by a severe inflammatory reaction of the joints. Recent studies demonstrated that M. bovis can invade bovine non-phagocytic cells, but the mechanism of M. bovis internalization in the cells remains unclear. In this study, we examined the mechanism by which M. bovis invades synovial cells, including the pathway of cell invasion. Using fluorescence and electron microscopy, multiple M. bovis were observed to adhere to and be internalized in cultured bovine synovial cells. The number of M. bovis colocalized with clathrin heavy chain (CLTC) per cell was significantly higher than the number of M. bovis colocalized with caveolin-1 (Cav-1). The internalized ratio of M. bovis in synovial cells treated with clathrin-dependent endocytosis inhibitor and small interfering RNA (siRNA) against CLTC was significantly lower than that in control cells. In contrast, the internalized ratio of M. bovis in synovial cells was unaffected by siRNA against Cav-1. These findings provide the first evidence that clathrin-dependent endocytosis is one of the major pathways by which M. bovis invades into synovial cells.

Impaired intracellular pathogen clearance and inflammatory joint disease: Is Whipple's disease a guiding light?

Whipple's disease can mimic spondyloarthritis (SpA) or rheumatoid arthritis (RA) for many years and, in a few cases, induces the development of antibodies to cyclic citrullinated peptides. The causative agent Tropheryma whipplei can smolder within cells, including macrophages, by suppressing the xenophagic process, a type of selective autophagy that targets pathogens. Other inflammatory joint diseases may also stem from impaired xenophagy with persistence of bacteria or viruses that can eventually migrate from the mucous membranes to the joints and entheses, where they may exert adverse effects on immune responses, even if they fail to replicate. Xenophagy interferes with the loading of peptides (including self-peptides) onto major histocompatibility complex proteins. Another effect of xenophagy is the induction of citrullination, which accelerates pathogen clearance but can also contribute to loss of self-tolerance. Pathogens react to citrullination by becoming dormant. These facts suggest a role in SpA and RA for impaired xenophagy with migration of pathogens to joints and entheses, where they may remain dormant. Studies of fibroblast-like synoviocytes showed alterations in autophagy that correlated with citrullination of vimentin, alpha-enolase, and filaggrin, which are targets of RA-specific autoantibodies. Compared to autoimmune responses (T-cell or B-cell clones, autoantibodies) alone, metastatic spread of pathogens initially located in the mucous membranes as the event inducing inflammatory joint disease would constitute a better explanation to the heterogeneous distribution of the joint involvement, palindromic onset in some cases (as seen in Whipple's disease), occurrence of flares, and possible development of escape phenomenon to immunomodulating drugs in a manner reminiscent of delayed antibiotic resistance.

Majoon ushba, a polyherbal compound, suppresses pro-inflammatory mediators and RANKL expression via modulating NFкB and MAPKs signaling pathways in fibroblast-like synoviocytes from adjuvant-induced arthritic rats.

Fibroblast-like synoviocytes (FLS) are inhabitant mesenchymal cells of synovial joints and have been recognized to play an imperative role in the immunopathogenesis of rheumatoid arthritis (RA). Blocking these pathological roles of FLS provides a potentially important therapeutic strategy for the treatment for RA. A recent study had confirmed that majoon ushba (MU), a polyherbal unani compound, possesses anti-arthritic effects in in vivo. Toward this direction, an effort has been made to understand the effect of MU on FLS derived from adjuvant-induced arthritis (AIA) rats. Here, we observed that MU administration (100-300 µg/ml) significantly inhibited the expression and phosphorylation of NFкB-p65 protein similar to that of the Bay 11-7082 (NFкB inhibitor) in NFкB signaling pathway and suppressed the protein expression of ERK1/2 and JNK1/2 in MAPKs signaling pathway in AIA-FLS. In addition, the protein expression of TNF-α, IL-17, RANKL, and iNOS was also found reduced. MU treatment significantly inhibited the mRNA expression of pro-inflammatory mediators (TNF-α, IL-1ß, IL-6, MCP-1, IL-17, iNOS, and COX-2), transcription factors (NFкB-p65 and AP-1), and RANKL and attenuated the overproduction of TNF-α, IL-1ß, IL-6, and MCP-1 (ELISA) in AIA-FLS. Furthermore, MU treatment significantly inhibited the level of lipid peroxidation, lysosomal enzymes release, and glycoproteins and increased antioxidant status (superoxide dismutase and catalase) in AIA-FLS. In conclusion, the results of this study provide evidence that MU possesses anti-inflammatory effect against AIA-FLS through the decrease in pro-inflammatory mediators expression by suppressing NFкB and MAPKs signaling pathways.