Proteoglycan 4 (Prg4) has a high structural similarity with the established atherosclerosis-modulating proteoglycan versican, but its role in atherogenesis is still unknown. Therefore, the impact... Show moreProteoglycan 4 (Prg4) has a high structural similarity with the established atherosclerosis-modulating proteoglycan versican, but its role in atherogenesis is still unknown. Therefore, the impact of Prg4 deficiency on macrophage function in vitro and atherosclerosis susceptibility in vivo was investigated.The presence and localization of Prg4 was studied in atherosclerotic lesions. Furthermore, the effect of Prg4 deficiency on macrophage foam cell formation, cholesterol efflux and lipopolysaccharide (LPS) response was determined. Finally, susceptibility for atherosclerotic lesion formation was investigated in bone marrow-specific Prg4 knockout (KO) mice.Prg4 mRNA expression was induced 91-fold (p<0.001) in murine initial atherosclerotic lesions and Prg4 protein co-localized with human lesional macrophages. Murine Prg4 KO macrophages showed increased foam cell formation (+2.1-fold, p<0.01). In parallel, the expression of the cholesterol efflux genes ATP-binding cassette transporter A1 and scavenger receptor type B1 was lower (-35%, p<0.05;-40%, p<0.05) in Prg4 KO macrophages. This translated into an impaired cholesterol efflux to high-density lipoprotein (-13%, p<0.001) and apolipoprotein A1 (-8%, p<0.05). Furthermore, Prg4 KO macrophages showed an impaired LPS-induced rise in TNFα secretion as compared to wild-type controls (-31%, p<0.001), indicating a reduced inflammatory response. Combined, these pro- and anti-atherogenic effects did not translate into a significant difference in atherosclerotic lesion formation upon bone marrow-specific deletion of Prg4 in low-density lipoprotein receptor KO mice.Prg4 is present in macrophages in both murine and human atherosclerotic lesions and critically influences macrophage function, but deletion of Prg4 in bone marrow-derived cells does not affect atherosclerotic lesion development. Show less
Chondrocytes interact with their neighbours through their cartilaginous extracellular matrix (ECM). Chondrocyte__matrix interactions compensate the lack of cell__cell contact and are modulated by... Show moreChondrocytes interact with their neighbours through their cartilaginous extracellular matrix (ECM). Chondrocyte__matrix interactions compensate the lack of cell__cell contact and are modulated by proteoglycans and other molecules. The epiphyseal growth plate is a highly organized tissue responsible for long bone elongation. The growth plate is regulated by gradients of morphogens that are established by proteoglycans. Morphogens diffuse across the ECM, creating short- and long-range signalling that lead to the formation of a polarized tissue. Mutations affecting genes that modulate cell__matrix interactions are linked to several human disorders. Homozygous mutations of EXT1/EXT2 result in reduced synthesis and shortened heparan sulphate chains on both cell surface and matrix proteoglycans. This disrupts the diffusion gradients of morphogens and signal transduction in the epiphyseal growth plate, contributing to loss of cell polarity and osteochondroma formation. Osteochondromas are cartilage-capped bony projections arising from the metaphyses of endochondral bones adjacent to the growth plate. The osteochondroma cap is formed by cells with homozygous mutation of EXT1/EXT2 and committed stem cells/wild type chondrocytes. Osteochondroma serves as a niche (a permissive environment), which facilitates the committed stem cells/wild-type chondrocytes to acquire secondary genetic changes to form a secondary peripheral chondrosarcoma. In such a scenario, the microenvironment is the site of the initiating processes that ultimately lead to cancer. Show less
