Cyclosporin A inhibits PDGF-BB induced hyaluronan synthesis in orbital fibroblasts

Orbital connective tissue changes are contributors to the pathogenesis in thyroid eye disease (TED). Activated fibroblasts respond to immune stimuli with proliferation and increased hyaluronan (HA) production. Cyclosporin A (CsA) was reported to be beneficial in the treatment of TED. PDGF isoforms are increased in orbital tissue of TED patients and enhance HA production. We aimed to study the effect of CsA on HA production and hyaluronan synthase (HAS1, 2 and 3) and hyaluronidase (HYAL1 and 2) mRNA expressions in orbital fibroblasts (OFs). Measurements were performed in the presence or absence of CsA (10 μM) in unstimulated or PDGF-BB (10 ng/ml) stimulated OFs. The HA production of TED OFs (n=7) and NON-TED OFs (n=6) were measured by ELISA. The levels of mRNA expressions were examined using RT-PCR. The proliferation rate and metabolic activity were measured by BrdU incorporation and MTT assays, respectively. Treatment with CsA resulted in an average 42% decrease in HA production of OFs (p<0.0001). CsA decreased the expression levels of HAS2, HAS3 and HYAL2 (p=0.005, p=0.005 and p=0.002, respectively.) PDGF-BB increased HA production (p<0.001) and HAS2 expression (p=0.004). CsA could reduce the PDGF-BB-stimulated HA production (p<0.001) and HAS2 expression (p=0.005) below the untreated level. In addition, CsA treatment caused a decrease in proliferation potential (p=0.002) and metabolic activity (p<0.0001). These findings point to the fact that CsA affects HA metabolism via HAS2, HAS3 and HYAL2 inhibition in OFs. In addition to its well characterized immunosuppressant properties, CsA's beneficial effect in TED may be related to its direct inhibitory effect on basal and growth factor stimulated HA production.