Internalization of hyaluronan by chondrocytes occurs via receptor-mediated endocytosis

Abstract

Several studies have suggested that chondrocytes must have the capacity to internalize and degrade extracellular hyaluronan. In the present study we show direct evidence that hyaluronan is, in fact, endocytosed by chondrocytes and that the endocytosis is mediated via cell surface CD44/hyaluronan receptors. Cultures of bovine articular chondrocytes as well as rat chondrosarcoma chondrocytes were incubated with either fluorescein- or 3H-labeled hyaluronan. Intense binding and accumulation of labeled hyaluronan was visualized by fluorescence microscopy or bright-field/dark-field microscopy following autoradiography. Cell surface hyaluronan was removed with either trypsin or Streptomyces hyaluronidase in order to distinguish and quantify intracellular endocytosed hyaluronan. Labeled hyaluronan was visualized within small discrete intracellular vesicles distributed throughout the cytoplasm. Binding and endocytosis of fluorescein- or 3H-labeled hyaluronan was totally blocked by the addition of excess unlabeled hyaluronan or hyaluronan hexasaccharides, competitive inhibitors of hyaluronan/hyaluronan receptor interactions. Binding and endocytosis was also blocked by the addition of anti-CD44 monoclonal antibodies. Characterization of endocytosed 3H-labeled hyaluronan demonstrated that a significant portion of the hyaluronan was degraded by both the bovine articular and rat chondrosarcoma chondrocytes. Interestingly, a higher proportion of bound hyaluronan was internalized by the bovine chondrocytes. Therefore, hyaluronan receptor-mediated endocytosis and degradation of hyaluronan may provide a critical link to the maintenance and homeostasis of cartilage tissue.

Evaluating the Efficiency of Hyaluronic Acid for Tumor Targeting via CD44

“…To further investigate internalization solely, all of the cell lines were incubated with HA-RhoB for different times, i.e.,1, 4, and 24 h, and internalization was measured as MFI with FC (Figure C). Prior to FC analysis, cells were trypsinized to remove cell surface-bound HA-RhoB (Figure 2SI), as previously reported . Thus, the fluorescence measured in the trypsinized cells was attributable to internalized HA-RhoB only.…”

Hyaluronic acid modified mesoporous silica nanoparticles for targeted drug delivery to CD44-overexpressing cancer cells

“…Hyaluronic acid (HA) is a biodegradable, biocompatible and non-immunogenic glycosaminoglycan. As a major component of the extracellular matrix, HA is essential for proper cell growth, organ structural stability and tissue organization, 21,22 and has been extensively investigated for biomedical and pharmaceutical applications. In particular, researchers focused on the use of HA as a targeting moiety for cancer therapy, because many types of tumor cells over-express HA receptors like CD44.…”

Pathogenesis of glaucoma: Extracellular matrix dysfunction in the trabecular meshwork‐A review

“…188,199 As HA is degraded into fragments by hyaluronidases, CD44 facilitates the uptake of HA into the cell where it is intracellularly degraded. [200][201][202] If HA fragments are too large, or are bound by other proteoglycans such as versican, then internalisation by CD44 is sterically inhibited. sCD44 may disrupt membrane-bound CD44-HA interactions, or competitively disrupt binding to other ECM components, and affect HA internalisation.…”