Hypoxic regulation of secreted proteoglycans in macrophages

Macrophages are prominent in hypoxic areas of atherosclerotic lesions, and their secreted proteoglycans (PG), such as versican, can modulate the retention of lipoproteins and the activity of enzymes, cytokines, and growth factors involved in atherogenesis. In this study, we report the effects of hypoxia on PG secreted by human monocyte-derived macrophages (HMDM) and the potential regulation by the transcription factor hypoxia-inducible factor (HIF-1 alpha and HIF-2 alpha). We found that versican co-localized with HIF-1 alpha in macrophage-rich areas in human advanced atherosclerotic lesions. Versican and perlecan mRNA expression increased after exposure to 0.5% O-2 (hypoxia) compared with 21% O-2 (control cells). Using precursors to GAG biosynthesis combined with immunoabsorption with a versican antibody an increased versican synthesis was detected at hypoxia. Furthermore, siRNA knockdown of HIF-1 alpha and HIF-2 alpha in THP-1 cells showed that the hypoxic induction of versican and perlecan mRNA expression involved HIF signaling. Versican expression was co-regulated by HIF-1 alpha and HIF-2 alpha but expression of perlecan was influenced only by HIF-1 alpha and not by HIF-2 alpha knockdown. The results show that oxygen concentration is an important modulator of PG expression in macrophages. This may be a novel component of the complex role of macrophages in atherosclerosis.