The Regulation Of Lubricin Expression In The Chondrogenic Differentiation Of Bone-derived Mesenchymal Stem Cells

Osteoarthritis(OA),a common joint degeneration,can cause breakdown of articular cartilage with a mild regeneration potential in the presence of lubricin metabolic abnormalities.Lubricin is a multi-level chondroprotective mucinous glycoprotein encoded by prg4 gene and exists mainly in superficial zone chondrocytes and synovial fluid.Lubricin provides anti-adhesion,chondroprotective feature and bacteriostatic nature in the treatment of joint diseases.Studies have shown that joint infection and defect were elevated and accompanied by accelerated cartilage lesions involving degradation and loss of lubricin.However,a novel,heterocyclic compound called kartogenin(KGN)was discovered to stimulate chondrogenic differentiation of human bone-derived mesenchymal stem cells(BMSCs)that is in agreement with that of the synergistic effect of transforming growth factor-?1(TGF-?1)and bone morphogenetic protein-7(BMP-7).The molecular was further proved to provoke characteristic proteins of chondrocytes(such as lubricin).But the regulation of lubricin expression and the chondrogenic differentiation of BMSCs stimulated with TGF-?1,BMP-7 and/or KGN have not been well established.Hence,we investigated the expression and secretion of intracellular and extracellular lubricin and gross GAGs in BMSCs treated with different combination of TGF-?1,BMP-7 and/or KGN.Using an in vitro BMSCs system,we observed the content of lubricin from BMSCs treated with TGF-?1,BMP-7 and KGN was the highest compared to the other groups at both the transcriptional level and the translational level.At the same time,the degree of chondrogenic differentiation of BMSCs was also provoked to the highest.That is to say,TGF-?1,BMP-7 and KGN coordinately enhanced lubricin accumulation and chondrogenic differentiation of BMSCs.Through the quantitative analysis of several key genes,we also found that the accumulation of lubricin was enhanced sharply which resulted from the increase of synthesis and decrease of degradation coordinately possibly via changing the signaling pathway of c-Myc and adamts5 with the synergy of TGF-?1,BMP-7 and KGN.In addition,hypoxia signaling pathway,Wnt signaling pathway and nuclear-related factors were also potentially associated with expression of lubricin.When treated with TGF-?1,BMP-7,KGN and calcium gluconate in vitro BMSCs system,the secretion of extracellular lubricin increased.Under Ca2+ concentration of 10-1M,accompanied by prolonged culture,lubricin showed the biggest accumulation.Cell proliferation was not suppressed by the addition of calcium gluconate.These results further suggested that improving the accumulation of lubricin in the defect parts of cartilago articularis using the synergy of growth factors and small molecules would be a promising approach to preventing joint deterioration in patients with acquired or genetic deficiency of lubricin in the future of regenerative medicine.This study may provide a preliminary theoretical basis for later clinical trials.