TSP1 is the essential domain of SEMA5A involved in pannus formation in rheumatoid arthritis

OBJECTIVE

In this study, we explored the effect of semaphorin5A (SEMA5A) on RA pathogenesis and its specific TSP1 domain on pannus formation.

METHODS

The expression of SEMA5A was detected in the synovium, the fibroblast-like synoviocytes (FLSs) and the SF of RA patients and healthy controls (HCs) by real-time quantitative PCR (q-PCR), immunohistochemistry staining, western blot and ELISA. SEMA5A-mAb intervention was performed to appraise the severity of joints in the CIA model. Transcriptome sequencing and bioinformatics analysis in SEMA5A-transfected FLSs from HCs were performed to screen differentially expressed genes after SEMA5A overexpression. An MTT assay in RA-FLSs, a chicken embryo allantoic membrane experiment and a tube formation experiment were used to clarify the influence of SEMA5A on cell proliferation and angiogenesis. Furthermore, a rescue experiment verified the function of the TSP1 domain of SEMA5A in the progress of RA with Sema5a-/- CIA mice.

RESULTS

The expression of SEMA5A increased in RA compared with that in HCs. Simultaneously, SEMA5A-mAbs significantly attenuated joint injury and the inflammatory response in CIA models. In addition, transcriptome sequencing and angiogenesis-related experiments verified the ability of SEMA5A to promote FLS proliferation and angiogenesis. Moreover, TSP1 was proved to be an essential domain in SEMA5A-induced angiogenesis in vitro. Additionally, rescue of TSP1-deleted SEMA5A failed to reduce the severity of arthritis in a CIA model constructed with Sema5a -/- mice.

CONCLUSION

In summary, upregulation of SEMA5A was first confirmed in pathological lesions of RA patients. Furthermore, treatment with SEMA5A-mAbs attenuated the progress of RA in the CIA model. Moreover, TSP1 was indicated as the key domain of SEMA5A in the promotion of pannus formation in RA.

The thrombospondin module 1 domain of the matricellular protein CCN3 shows an atypical disulfide pattern and incomplete CWR layers

The members of the CCN (Cyr61/CTGF/Nov) family are a group of matricellular regulatory proteins that are essential to a wide range of functional pathways in cell signalling. Through interacting with extracellular matrix components and growth factors via one of their four domains, the CCN proteins are involved in critical biological processes such as angiogenesis, cell proliferation, bone development, fibrogenesis and tumorigenesis. Here, the crystal structure of the thrombospondin module 1 (TSP1) domain of CCN3 (previously known as Nov) is presented, which shares a similar three-stranded fold with the thrombospondin type 1 repeats of thrombospondin-1 and spondin-1, but with variations in the disulfide connectivity. Moreover, the CCN3 TSP1 domain lacks the typical π-stacked ladder of charged and aromatic residues on one side of the domain that is seen in other TSP1 domains. Using conservation analysis among orthologous domains, it is shown that a charged cluster in the centre of the domain is the most conserved site and this cluster is predicted to be a potential functional epitope for heparan sulfate binding. This variant TSP1 domain has also been used to revise the sequence determinants of TSP1 domains and to derive improved Pfam sequence profiles for the identification of novel TSP1 domains in more than 10 000 proteins across diverse phyla.