A central part of the complement system, the anaphylatoxin C5a was investigated in this study to
learn its effects on tenocytes in respect to understanding the potential expression of other
crucial complement factors and pro-inflammatory mediators involved in tendinopathy. Human
hamstring tendon-derived tenocytes were treated with recombinant C5a protein in concentrations
of 25 ng/mL and 100 ng/mL for 0.5 h (early phase), 4 h (intermediate phase), and 24 h (late
phase). Tenocytes survival was assessed after 24 h stimulation by live-dead assay. The gene
expression of complement-related factors C5aR, the complement regulatory proteins (CRPs) CD46,
CD55, CD59, and of the pro-inflammatory cytokines tumor necrosis factor (TNF)-α and interleukin
(IL)-6 was monitored using qPCR. Tenocytes were immunolabeled for C5aR and CD55 proteins. TNFα
production was monitored by ELISA. Tenocyte survival was not impaired through C5a stimulation.
Interestingly, the gene expression of C5aR and that of the CRPs CD46 and CD59 was significantly
reduced in the intermediate and late phase, and that of TNFα only in an early phase, compared to
the control group. ELISA analysis indicated a concomitant not significant trend of impaired TNFα
protein synthesis at 4 h. However, there was also an early significant induction of CD55 and
CD59 mediated by 25 ng/mL anaphylatoxin C5a. Hence, exposure of tenocytes to C5a obviously
evokes a time and concentration-dependent response in their expression of complement and
pro-inflammatory factors. C5a, released in damaged tendons, might directly contribute to
tenocyte activation and thereby be involved in tendon healing and tendinopathy.
Keywords: C5a; anaphylatoxin; complement regulation; complement system; tendinopathy; tenocytes.
Reference
Silawal, S., Kohl, B., Shi, J., & Schulze-Tanzil, G. (2021). Complement Regulation in Human Tenocytes under the Influence of Anaphylatoxin C5a. International Journal of Molecular Sciences, 22(6), 3105.