CD44 mediates hyaluronan to promote the differentiation of human amnionic mesenchymal stem cells into chondrocytes through the activation of Erk1/2 and Smad2 signals

Abstract Background: Hyaluronan (HA), as a major component of the cellular matrix, plays an important role in cartilage formation. Our previous studies showed that HA may induce human amnion mesenchymal stem cells (hAMSCs) to differentiate into chondrocytes. The surface molecule CD44, as the main receptor of hyaluronic acid, is crucial for maintaining cartilage homeostasis. But the effect and molecular mechanism of CD44 on HA-induced hAMSCs differentiation into cartilage is unknown. Results: The expression of aggrecan and type II collagen was down-regulated after using the antibody blocker anti-CD44 antibody (A3D8) in HA-induced group. Meanwhile, the transcriptional levels of chondrocyte‑associated genes SRY‑box transcription factor 9 (SOX9), aggrecan (ACAN) and collagen type II alpha 1 chain (COL2A1) were also decreased. Thus CD44 may mediates HA-induced differentiation of hAMSCs into chondrocytes. Further investigation indicated that expression of phosphorylated (p)‑Erk1/2 and p‑Smad2 was decreased following CD44 inhibition. The changes in the expression levels of p-Erk1/2 and p-Smad2 were consistent after treatment with ERK1/2 inhibitor (U0126) and agonist (EGF), respectively. At the same time, after the use of p-Smad2 inhibitor, the expression levels of p-ERK1/2 and p-Smad2 were both down-regulated, and TGF-β, an agonist of p-Smad2, had no effect on the expression of p-ERK1/2, but decreased the expression of p-Smad2. Results showed that there was a cross-talk between Erk1/2 and Smad2. In addition, inhibition of p-Erk1/2 and p-Smad2 can significantly reduce the accumulation of aggrecan and type II collagen.Conclusion: These data indicated that CD44 mediated HA-induced differentiation of hAMSCs into chondrocytes via regulating Erk1/2 and Smad2 Signals.