Microenvironment regulation of PRG4 phenotype of chondrocytes.

Articular cartilage is a heterogeneous tissue with superficial (S), middle (M), and deep (D) zones. Chondrocytes in the S zone secrete the lubricating PRG4 protein, while chondrocytes from the M and D zones are more specialized in producing large amounts of the glycosaminoglycan (GAG) component of the extracellular matrix. Soluble and insoluble chemicals and mechanical stimuli regulate cartilage development, growth, and homeostasis; however, the mechanisms of regulation responsible for the distinct PRG4-positive and negative phenotypes of chondrocytes are unknown.

Tailoring secretion of proteoglycan 4 (PRG4) in tissue-engineered cartilage.

Articular cartilage provides a low-friction surface for joint articulation, with boundary lubrication facilitated by proteoglycan 4 (PRG4), which is secreted by chondrocytes of the superficial zone. Chondrocytes from different zones are phenotypically distinct, and their phenotypes in vitro are influenced by the system in which they are cultured. We hypothesized that culturing cells from the superficial (S) zone in two-dimensional monolayer or three-dimensional alginate would affect their synthesis of PRG4, and that subsequently seeding them atop alginate-recovered cells from the middle/ deep (M) zone in various proportions would result in tissue-engineered constructs with varying levels of PRG4 secretion and matrix accumulation.

Dynamic shear stimulation of bovine cartilage biosynthesis of proteoglycan 4.

Objective: The boundary lubrication function of articular cartilage is mediated in part by proteoglycan 4 (PRG4) molecules at the articular surface and in synovial fluid. The objective of this study was to determine the effects of dynamic shear stimulation on PRG4 biosynthesis by bovine cartilage explants.

Methods: Cartilage disks with intact articular surfaces were harvested from immature bovines.

Tracking chondrocytes and assessing their proliferation with PKH26: effects on secretion of proteoglycan 4 (PRG4).

Distinguishing between implanted and host-derived cells, as well as between distinct cell phenotypes, would be useful in assessing the mechanisms of cell-based repair of cartilage. The fluorescent tracker dye, PKH26, was previously applied to several cell types to assess proliferation in vitro and to track cells in vivo. The objectives of this study were to assess the utility of PKH26 for tracking chondrocytes from superficial and middle zones and their proliferation, and determine the effects of PKH26 on chondrocyte functions, in particular, proliferation and secretion of Proteoglycan 4 (PRG4).

Proteoglycan 4 (PRG4) synthesis and immunolocalization in bovine meniscus.

Proteoglycan 4 (PRG4) is synthesized and secreted into the synovial fluid by articular chondrocytes and synovial cells, lining the cavity of joints. A thin layer of PRG4 is also present at the articular surface, where it appears to be involved in boundary lubrication. This study investigated if PRG4 is also synthesized and secreted by the cells within meniscus, and if PRG4 is also present in, and at the surface of, meniscus.

Synthesis of proteoglycan 4 by chondrocyte subpopulations in cartilage explants, monolayer cultures, and resurfaced cartilage cultures.

Objective: To quantify the levels of proteoglycan 4 (PRG4) expression by subpopulations of chondrocytes from superficial, middle, and deep layers of normal bovine calf cartilage in various culture systems.

Methods: Bovine calf articular cartilage discs or isolated cells were used in 1 of 3 systems of chondrocyte culture: explant, monolayer, or transplant, for 1-9 days. PRG4 expression was quantified by enzyme-linked immunosorbent assay of spent medium and localized by immunohistochemistry at the articular surface and within chondrocytes in explants and cultured cells.