Characteristics of Hyaluronan Synthesis Inhibition by 4-Methylumbelliferone in Orbital Fibroblasts

Purpose Hyaluronan (HA) overproduction by orbital fibroblasts (OFs) is a major factor in the pathogenesis of Graves’ orbitopathy (GO). 4-methylumbelliferone (4-MU) is an inhibitor of HA synthesis in different cell types in vitro and has beneficial effects in animal models of autoimmune diseases. Methods HA production and mRNA expression of HA synthases ( HAS1 , HAS2 , and HAS3 ) and hyaluronidases ( HYAL1 and HYAL2 ) were measured in the presence and absence of 4-MU in unstimulated and transforming growth factor–β–stimulated fibroblasts from GO orbital (n = 4), non-GO orbital (n = 4), and dermal origin (n = 4). Results The 4-MU treatment (1 mM) for 24 hours resulted in an average 87% reduction ( P < 0.001) of HA synthesis, decreased the expression of the dominant HAS isoform ( HAS2 ) by 80% ( P < 0.0001), and increased the HYAL2 expression by 2.5-fold ( P < 0.001) in control OFs, GO OFs, and dermal fibroblasts (DFs) regardless of the origin of the cells. The proliferation rate of all studied cell lines was reduced to an average 16% by 4-MU ( P < 0.0001) without any effects on cell viability. HA production stimulated by transforming growth factor–β was decreased by 4-MU via inhibition of stimulated HAS1 expression in addition to the observed effects of 4-MU in unstimulated cases. Characteristics of HA synthesis inhibition by 4-MU did not differ in OFs compared with DFs. Conclusions 4-MU has been found to inhibit the HA synthesis and the proliferation rate in OFs in vitro, adding it to the list of putative therapeutic agents in a disease the cure of which is largely unresolved.