Adding HMWHA to PBMC does not appear to affect the levels of the hyaluronic acid receptor CD44, whereas adding LMWHA decreases CD44 levels. of the effect of hyaluronic acid on fibrocyte Oxethazaine differentiation. The fibrocyte differentiation-inhibiting factor serum amyloid P (SAP) inhibits HMWHA-induced fibrocyte differentiation and potentiates LMWHA-induced inhibition. Conversely, LMWHA inhibits the ability of HMWHA, interleukin-4 (IL-4), or interleukin-13 (IL-13) to promote fibrocyte differentiation. Conclusions We hypothesize that hyaluronic acid signals at least in part through CD44 to regulate fibrocyte differentiation, with a dominance hierarchy of SAP LMWHAHMWHA IL-4 or IL-13. Introduction After tissue injury, local fibroblasts proliferate to repair the wound [1], [2]. Oxethazaine In addition to fibroblasts, bone-marrow-derived progenitor cells infiltrate the injured site and differentiate into fibroblast-like cells called fibrocytes [3]. Fibrocytes can differentiate from purified CD14+ peripheral blood monocytes, but fibrocytes lose expression of CD14 [4]C[8]. Other studies also suggest that fibrocytes differentiate from a population of bone-marrow derived CD45+ CXCR4+ cells found in peripheral blood [9]C[11]. Fibrocytes are spindle-shaped cells that express hematopoietic cell markers such as MHC class II, CD34, CD45RO, 25F9, and S100A8/A9, stromal cell markers such as collagen I, and collagen III, and chemokine receptors such as CCR2, CXCR4, and CCR7 that mediate their entry into the site of injury [3], [9], [12]C[15]. Fibrocytes produce cytokines, collagens, angiogenic and fibrogenic growth factors, and matrix metalloproteinases that help to rebuild tissue after injury [3]C[5], [16]C[20]. Fibrocytes are found as a circulating population of cells Oxethazaine present in the peripheral blood, and there are elevated numbers of fibrocytes in patients with inflammatory and fibrotic diseases [10], [21], [22]. Peripheral blood monocytes generally become macrophages, and much remains to be understood about the factors that determine whether or not a monocyte becomes a fibrocyte [23]. During tissue injury, the extracellular matrix component hyaluronic acid (HA) breaks down into smaller fragments [24]C[26]. HA is a negatively charged linear polymer of repeating units of (,1C4)-D-glucuronic acid-(,1C3)-N-acetyl-D-glucosamine that gives mechanical strength to tissues [27]. High molecular weight hyaluronic acid (HMWHA) has a molecular mass 1106 Da and is Rabbit Polyclonal to Cortactin (phospho-Tyr466) found in normal healthy tissue [28]. The concentration of hyaluronic acid is 15C150 g/g in lung tissue, 200 g/g in the vitreous humor of the eye, 500 g/g in skin, and 1400C3600 g/g in synovial fluid [29]. In injured tissue, HMWHA breaks down to low molecular weight HA (LMWHA) [24]. LMWHA masses range from 0.8 to 8105 Da [24]. However, there are variations in the use of the terms HMWHA or LMWHA. HMWHA often refers to any hyaluronic acid that has not been degraded [30], therefore, in this report, we will use HMWHA for hyaluronic acid that is greater than 1106 Da, LMWHA for 0.8 to 8105 Da Oxethazaine hyaluronic acid, and oligo-HA for 6103 Da hyaluronic acid. Cells appear to be able to Oxethazaine sense the difference between HMWHA, LMWHA, and oligo-HA [25], [31]C[37]. For instance, LMWHA but not HMWHA stimulates alveolar macrophages to secrete inflammatory cytokines such as IL-8 [25], while the maturation and activation of monocyte-derived dendritic cells is promoted by 1.2103 Da HA, but not HMWHA or LMWHA [36]. One of the major receptors that monocytes and lymphocytes express to detect HA is CD44 [24], [28], [38], [39]. During lung injury, CD44 is used to clear degraded HA [25], [28], [40]. HA-CD44 interactions help the movement of migratory cells during development and help the migration of immune cells into injured sites [24], [27], [41]. HA-CD44 interactions also promote the adhesion and motility of fibroblasts, thus facilitating tissue repair and remodeling of the injured sites [42]. Monocytes, dendritic cells, and lymphocytes also bind HA using Toll-like receptors (TLR) such as TLR2 and TLR4 [32], [33]. LMWHA binds to either TLR2 or TLR4 to elicit pro-inflammatory action, while HMWHA dampens inflammation by inhibiting TLR2 or TLR4 signaling [33], [43]. HA can also bind CD168 (receptor for hyaluronan-mediated motility, RHAMM), a cell-surface receptor on fibroblasts and macrophages.