## 4 Discussion  
Through the MIA-induced OA animal model conducted in this study, we observed that a combination of hUC-MSCs and HA could synergistically mitigate the cartilage degradation process better when compared to each individual administration. Where hUC-MSCs exposed to 0.1% HA increased the secretion of DKK-1, HGF and a higher antioxidation capability by might provide an insight on the mechanism of this event. Moreover, the HA addition to hUC-MSCs did not result in any adverse effect, such as a reduction in cell viability. In addition to serving its role as a vehicle during MSC administration, several studies reported that HA provides beneficial effects by enhancing the MSC chondrogenic differentiation ability [22] and delaying cellular senescence [23], which might lead to better attenuation capability. Here, we showed that 0.1% HA could not only increase DKK-1 and HGF secretion from hUC-MSCs (Figure 2D,E) but also reduce the effect of H2O2 oxidative stress towards human chondrocyte viability (Figure 4). Interestingly, in vitro studies using 0.1% HA also showed beneficial effects toward human articular chondrocyte proliferation and viability [24] due to the binding of HA with CD44, a cell surface receptor expressed in chondrocytes, resulting in the induction of c-myc and TGF-\(\beta\) mRNA expression, as indicated by [PERSON] et al. [25]. hUC-MSCs were also identified to express high levels of CD44 on the cell surface [26], which indicates a possibility of a similar HA-binding mechanism as chondrocytes but needs to be proven with further studies. The binding of HA with the hUC-MSC CD44 surface marker triggers various signaling cascades. One event resulted in an increase of GSK3\(\beta\) expression, which, in turn, induced \(\beta\)-catenin expression and its downstream target. \(\beta\)-catenin was reported to be able to translocate into the cell nucleus and, in concert with the coactivators BCL19, Pygo and CBP/p300, regulated Wnt target genes, such as DKK-1, c-Myc, cyclin D1 and Axin2 but not HGF [27; 28; 29; 30; 31]. In our study, the HGF expression did not follow a dose-dependent manner to increase the HA concentration, which might suggest that only a specific concentration of HA could increase the HGF expression in hUC-MSCs. A KOA patient might have aberrant synovial fluid (SF) biochemical expression due to a loss of normal joint homeostasis [32]. A reduced expression of DKK-1 in the plasma and SF of the KOA patient was inversely correlated with the disease severity [19; 33], while the GDF-15 [34] and ApoA1 [35] expressions were also found to be impaired in the os teoarthritic cartilage and chondrocytes, respectively. DKK-1 is recognized as an inhibitor of canonical Wnt signaling [36], and the addition of DKK-1 to OA SF reduced the degradation of the cartilage oligomeric matrix protein (COMP) by decreasing the ADAMTS-7 expression, a metalloproteinase, through blocking Wnt signaling in the cartilage explant [37]. DKK-1 also elicits protective effects to inhibit H2O2-induced oxidative stress and DNA damage via Wnt/ \(\beta\)-catenin pathway blockage [38]; this observation might provide some explanation for the results observed shown in Figure 4, where MSC-CM could reduce the damage caused by H2O2. ApoA1 is a protein that has an important role in the metabolism of lipoproteins [39]. Osteoarthritis is associated with irregular lipid metabolism, such as the intracellular accumulation of lipid in chondrocytes, and a study done by [PERSON] et al. demonstrated that restoring ApoA1 promotes a chondrocytes cholesterol efflux [35]. Therefore, the therapy targeting restoration of DKK-1 and ApoA1 might be beneficial for the OA patient. On the other hand, a lower-than-normal GDF-15 expression in OA SF suggests it could be used as a biomarker, although more sample studies should be conducted. A critical regulatory system for cartilage maintenance is the \(\beta\)-catenin-mediated canonical Wnt signaling pathway.