The Role of TGF-β3 on Mesenchymal Stem Cell Chondrogenesis and the Potential for Therapeutic Use in Osteoarthritis
Osteoarthritis (OA), currently the most common form of arthritis, is a progressive degenerative disease affecting the joint cartilage and surrounding joint infrastructure1,2. Treatments for OA are limited to pain relief and functional rehabilitation1,2. Regeneration of cartilage in the affected joint(s) provide potential solutions to reverse degeneration of joint cartilage altogether2,3. Mesenchymal stem cells (MSC) have garnered interest for their differentiative abilities. Transforming growth factor-beta 3 (TGF-B3) is a cytokine capable of inducing MSCs to undergo chondrogenesis. Upon binding of TGF-B3 to TGF-Receptors in MSCs, intracellular Smad2/Smad3 proteins are phosphorylated6. Smad2/3 recruit signaling molecules, forming a complex6. The complex enters the nucleus to upregulate expression of chondrogenic genes6. Studies show TGF-B3 induces differentiation of weight-bearing articular cartilage and interplays with other chondrogenic signaling factors: CCN4, EGF and TGF-B3 Receptor 3 (TBRIII). Understanding how TGF-B3 interplays with signaling molecules allows for clinical applications of induced chondrogenesis to provide the framework for cartilage regenerative therapies. Methods: TGF-B3 only and TGF-B3/BMP4 micromass cultures were developed with 15-day mesoderm cells from human pluripotent stem cells and analyzed for gene expression3. In the signaling molecule studies, CCN4 transfection via virus vector and CCN4 knockout with siRNA was administered to bone marrow stromal cells5. In the EGF study, co-stimulation of EGF with TGF-B3 used chondrogenic progenitor cells from tissue samples of OA and normal patients4. Cultures of 2ng/mL TGF-b3, 10/20/40 ng/mL of hrEGF and costimulatory 2ng/mL TGF-b3 and 10ng/mL of hrEGF was analyzed for gene expression4. To study TBRIII activity, MSCs were isolated and purified from samples of 3 healthy volunteers6. The MSCs were transfected with siRNA specific for TBRIII for knockout, a scrambled sequence for negative control, or without infection and later exposed to TGF-B3 in all groups6. Results: Gene analysis from the TGF-B3 only culture derived from the micromass cultures showed similar gene expressions found in interzone cells, providing evidence of articular cartilage differentiation3. CCN4 transfected cells showed an increase in Sox9 levels and stimulation with TGF-B3 increased the phosphorylation of Smad2/3 compared to knockout group5. The co-stimulatory group TGF-B3 and EGF showed increased Runx2 expression, aggrecan and Col2 mRNA levels4. In the knockout-TBRIII group, increased Smad2/3 signaling was seen, indicative of increased chondrogenic activity6. Discussion: Studies show TGF-B3 play a large role in chondrogenic differentiation of MSCs via TGF-B/Smad pathway. Understanding signaling molecules’ impact on TGF-B3 to enhance chondrogenesis in MSCs open possibilities to study viable cartilage regenerative therapies for treatment of OA.
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