Peter Duong

Osteoarthritis (OA), currently the most common form of arthritis, is a progressive degenerative disease affecting the joint cartilage and surrounding joint infrastructure^1,2. Treatments for OA are limited to pain relief and functional rehabilitation^1,2. Regeneration of cartilage in the affected joint(s) provide potential solutions to reverse degeneration of joint cartilage altogether^2,3. 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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