Effect of culture duration on chondrogenic preconditioning of equine bone marrow mesenchymal stem cells in self-assembling peptide hydrogel.

The research investigated the impact of culture duration on inducing cartilage formation in horse bone marrow stem cells, which were encapsulated in a self-assembling peptide hydrogel, and found that three days of preconditioning led to a significant increase in cartilage formation. However, continued exposure to a specific protein might be necessary to prevent unwanted growth, and there may be an immune response concern for certain applications.

Research Context

• The foundation of this research lies in the field of cartilage tissue engineering, with the goal to enhance the use of bone marrow mesenchymal stem cells (MSCs) for this purpose. MSCs have the ability to differentiate into various cell types, including those that form cartilage (chondrocytes).
• The researchers used a material known as a self-assembling peptide hydrogel to encapsulate the MSCs. This peptide hydrogel is designed to mimic the natural extracellular environment of the cells, providing a suitable platform for their growth and differentiation.

Research Methodology

• The bone marrow mesenchymal stem cells were cultured in a chondrogenic medium, a type of medium that is designed to induce chondrogenesis (the formation of cartilage).
• The potential to induce chondrogenesis was assessed by releasing isolated cells from the hydrogel and cultivating them in the absence of the chondrogenic cytokine TGFβ (Transforming Growth Factor Beta), which is known to promote cartilage formation.
• Controls for the experiment were undifferentiated MSCs seeded in agarose, a gel-like substance, and cultured in medium containing TGFβ.

Research Findings

• Three days of preconditioning was sufficient to generate MSCs with a chondrogenic phenotype, that is, cells specialized in cartilage formation. These cells accumulated around 75% more cartilaginous extracellular matrix (a network of macromolecules that provide structural and biochemical support to cells) than the positive controls by day 17.
• However, the expression of a gene involved in the formation of type X collagen (a molecule associated with the maturation and calcification of cartilage and bone tissue) in these cells was around 65-fold higher than the positive controls. This overexpression was attributed to the absence of TGFβ during the culture period, suggesting that continued exposure to TGFβ might be necessary to prevent this undesired overexpression.
• Furthermore, MSCs showed an indication of possible immunogenicity, that is, the ability to provoke an immune response in the host organism. This was suggested by the expression of major histocompatibility complex class II (MHC II), a group of genes that code for proteins playing a vital role in the immune response. While undifferentiated MSCs showed practically no expression of MHCII, around 7% of the preconditioned cells did, implying a potential issue for allogeneic applications where cells or tissues are transferred from one individual to another.

Conclusions

• This study demonstrated the feasibility of generating cartilage-forming MSCs in just a few days using a self-assembling peptide hydrogel. It also suggested that the hydrogel allows for the isolation of an individual cell suspension, which is suitable for therapies involving injection.
• However, the researchers warn of possible complications, such as the unintended overexpression of the type X collagen gene and potential immunogenicity, which could pose challenges for certain applications of this methodology.