Vascular Medicine Inhibition of Hyaluronan Synthesis Accelerates Murine Atherosclerosis Novel Insights Into the Role of Hyaluronan Synthesis

Background—Hyaluronan is thought to mediate neointimal hyperplasia but also vasoprotection as an integral component of the endothelial glycocalyx. The present study addressed for the first time the effects of long-term pharmacological inhibition of hyaluronan synthesis on vascular function and atherosclerosis. Methods and Results—Four-week-old apolipoprotein E– deficient mice on a Western diet received orally an inhibitor of hyaluronan synthesis, 4-methylumbelliferone (4-MU; 10 mg/g body wt), resulting in 600 nmol/L 4-MU in plasma. As a result, aortic plaque burden was markedly increased at 25 weeks. Furthermore, acetylcholine-dependent relaxation of aortic rings was decreased and mean arterial blood pressure was increased in response to 4-MU. However, hydralazine blunted the hypertensive effect of 4-MU without inhibiting the proatherosclerotic effect. A photothrombosis model revealed a prothrombotic state that was not due to increased platelet activation or increased thrombin activation as monitored by CD62P expression and the endogenous thrombin potential. Importantly, increased recruitment of macrophages to vascular lesions was detected after 2 and 21 weeks of 4-MU treatment by immunohistochemistry, by intravital microscopy, and in a peritonitis model. As a potential underlying mechanism, severe damage of the endothelial glycocalyx after 2 and 21 weeks of treatment with 4-MU was detected by electron microscopy of the innominate artery and myocardial capillaries. Furthermore, 600 nmol/L 4-MU inhibited hyaluronan synthesis in cultured endothelial cells. Conclusions—The data suggest that systemic inhibition of hyaluronan synthesis by 4-MU interferes with the protective function of the endothelial glycocalyx, thereby facilitating leukocyte adhesion, subsequent inflammation, and progression of atherosclerosis. H yaluronan is a ubiquitous constituent of the extracellular matrix. The synthesis is mediated through 3 hyaluronan synthase (HAS) isoforms (HAS1, HAS2, and HAS3) that assemble UDP-glucuronic acid and UDP-N-glucosamine at the plasma membrane, forming a high-molecular-weight glycosaminoglycan chain. 1 Hyaluronan is unbranched and is not further modified, in contrast to sulfated glycosaminogly-cans such as heparan sulfate. 2 Extensive research on the hyaluronan system in tumor biology, 2 reproductive biology, 3 lung injury, 4 and cardiovascular pathology 5,6 has contributed to an understanding of the physiological and pathophysiolog-ical role of hyaluronan in vitro and in vivo. In the healthy arterial vessel wall, hyaluronan is positioned at 2 strategic positions: the endothelial glycocalyx and the adventitia. However, during atherosclerosis, hyaluronan is produced by activated vascular smooth muscle cells (VSMC) in the neointima. Extensive evidence from studies on athero-sclerosis and restenosis shows that hyaluronan promotes VSMC proliferation and migration and that hyaluronan accumulates during neointimal hyperplasia in …