Potential involvement of semaphorin 3A in maintaining intervertebral disc tissue homeostasis

Intervertebral discs (IVDs) are avascular; however, ingrowth of blood vessels into their outer regions has been noted during the progression of degeneration. The mechanisms underlying vascularization in IVD degeneration are not completely understood. Semaphorin 3A (Sema3A), originally characterized as a chemorepulsive factor for growing axons in the developing nervous system, inhibits angiogenesis. This study aimed to elucidate the potential involvement of Sema3A in maintaining tissue homeostasis within the avascular IVD. We demonstrated that the mRNA expression of Sema3A was higher in rat annulus fibrosus (AF) than in nucleus pulposus (NP) and that its expression level decreased with age. Both mRNA and protein expression level of Sema3A was also markedly suppressed in AF tissues of a rat IVD degeneration model. Both real-time RT-PCR and Western blot clearly indicated that Sema3A expression significantly reduced by treating inflammatory cytokines in rat AF cells. In a gain- and loss-of-function study, we observed that Sema3A reduced the catabolic shift in rat AF cells. In addition, our results indicated that Sema3A potentially inhibited the IL-6/JAK/STAT pathway. Finally, BrdU assay and tube formation assay revealed that treatment of recombinant Sema3A significantly blocks both proliferation and tube formation of HUVEC. Our results indicate that Sema3A may help maintain IVD tissue homeostasis. Thus, although further studies are needed, Sema3A may be a potential molecular target for suppressing IVD degeneration. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.