Aim: Tendon is tissue that transmits force from muscle to bone to facilitate joint movement. ‘Tendinopathy’ is a pathology in, and/or pain arising from a tendon, being highly prevalent. APC is a natural anti-coagulant with strong anti-inflammatory and cytoprotective properties, mediating by its receptors, endothelial protein C receptor (EPCR), protease activated receptor (PAR)-1 and PAR-2. The aim of the study was to determine whether APC stimulates the healing ability of tenocytes and the involvement of its receptors, (EPCR, PAR-1 and PAR-2).

Method:  Mouse tail tendons and tenocytes were isolated from from wild type (WT), PAR-1 knockout (KO) and PAR-2 KO mice. The expression of EPCR, PAR-1/2 and the effect of APC (0, 1 and 10 μg/ml) on tendons/tenocytes were detected by PCR, western blot and immunohistochemistry, MTT assay, ELISA, zymography, scratch migration assay as well as biomechanical tensile strength.

Results:  EPCR, PAR-1 and PAR-2 were expressed by tendon and tenocytes and this expression was increased in a dose dependent manner to APC treatment in WT tenocytes, showing a 2, 2.7 and 2.7 fold increase, respectively, when APC was used at 10 ug/ml. At 1 µg/ml, APC increased proliferation by 40%, in vitro healing by 30%, MMP-2 activity by 4.3-fold while having no effect on MMP-9, in WT tenocytes from 3 w/o mice. PAR-1 KO and PAR-2 KO tenocytes displayed elevated levels of PAR-2 and PAR-1 respectively after treatment with APC.  PAR-1 mediated decreased proliferation and MMP-2 activity, increased MMP-9 activity, decreased ERK1/2 and increased p38 signaling. In contrast, PAR-2 mediated increased proliferation, MMP-2 and 9 activity, migration, ERK1/2 and p38 signaling.

Conclusion: APC improves tenocyte healing in vitro however more research is required to harvest its therapuetic potential for the treatment of tendinopathy. PAR-1 and PAR-2 work differentially to mediate APCs benefical effects.