Studies to improve cartilage tissue engineering

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Chondrocytes are enclosed to form the chondron by its embedding in the pericellular matrix (PCM). The matrix also plays its role in the formation of the chondrocytes and the reactions that take place in the chondron. The PCM is made up of several elements, and the Type IV collagen forms the major part of it. In case the Type IV collagen is lacking in the pericellular matrix it is direct notification that the matrix system is not in its optimal condition. This study focuses on how the conditions provided to the cultured cells create changes to the expression of the collagen in the chondron and the individual chondrocytes. The study also involved the co-culturing of mesenchymal cells with chondrons in different proportions, and the influence of this difference is also investigated to evaluate its effect on maintaining the type IV collagen and also the deposition of extracellular matrix. The required chondrocytes and chondrons for the experiment was extracted and used in various proportions with the cell source being bovine knee for the chondrons and rat mesenchymal cells. The culture was studied for 7 days with different passage numbers. Comparative studies were conducted for the production of Glycosaminoglycan by adding mesenchymal cells to the cartilage cell cultures. Increased GAG levels were noticed which directed at the conclusion that the cartilage-specific matrix production was also increased compared to specific chondron or chondrocyte cultures. The production level of GAG was the highest in the culture with half chondron and half mesenchymal cells when compared to other culture ratios. It was observed on immunohistochemical staining of the tissue that only the chondron contained type IV collagen. With an increase in cultures and passage numbers, the level of type IV collagen also decreased significantly. High-temperature requirement serine protease A1(HtrA1) expression in the culture was also investigated to show an opposite relation with type IV collagen in chondron. A control culture was created with optimal type IV collagen expression in the presence of HtrA1. This was compared to the further cultures which had decreased expression of HtrA1 and it was noted that the reduction of typeIV collagen expression was reduced. This led to the speculation that the mesenchymal cells were able to produce HtrA1 inhibitors which stood as a blockage to the degradation of type IV collagen in the matrix. These comparative studies proved that the combined culture of the mesenchymal cells and the chondrons increased the ECM production, chondrogenesis and also showed the property of maintaining the PCM with its high type IV collagen content.

Type IV collagen is a unique kind which is degraded by certain serine proteases. HtrA1 and other serine proteases are capable of impacting this action.

Hyaline cartilage is capable of spreading out the load placed on it and thus reducing the expression of friction on the surface. This is achieved with its intricate tissue structure. Any wear and tear of the articular cartilage can only be partially repaired as there are no neuron or blood vessel systems present in it.

This caused significant damage to the cartilage between the joints and towards the exterior of the joints to be easily damaged due to excess loading. More than 33% of the people of UK above 45 years of age suffer from osteoarthritis.

With cartilage treatment being taken up as a shortcoming of modern medicine, several studies are being conducted to make advancements in this field. Tissue and cell therapy researchers over the last 30 years have shed some light and made available newer treatment techniques to surpass the conventional methods. Autologous Chondrocyte Implantation (ACI) is a method whereby chondrocytes or stem cells are directed into the cartilage that has to be repaired.

One of the primary challenges faced by cartilage tissue engineering is the difficulty in obtaining the cells. Articular chondrocytes have a tendency to expand and dedifferentiate to lose its characteristics and convert to fibroblast-like form in its phenotype.

Several approaches and techniques have been tried to supplement and retain the phenotype of the chondron cells even after expansion. One of the best results were achieved in tests with mesenchymal cells. But the problem noted was due to the reduced quality of the cartilage tissues produced by these when compared to the chondrocytes. This was attributed to the oxidation and enlargement of the cells in culture.

It led to the usage of co-cultures of chondrocytes and mesenchymal cells to be used in cartilage tissue engineering. Studies conducted by co-culturing proved that it could enhance the chondrogenesis and increased the matrix production too.

Chondron consists of the PCM and the chondrocytes. The type IV collagen and aggrecan found in PCM increases the metabolism and signaling property of the matrix. The collagen has a fibrillar structure and forms an interwoven network around the cell. It gives a multiangular protective coating to the cell and thus prevents the mechanical protection to the cartilage. It decreases the stress on the cartilage. The PCM has a direct impact on the matrix producing capacity of the chondrocytes. The PCM covers the chondrocytes and therefore all intercellular activity or elements have to pass through PCM. This implies that matrix enzymes will have its effect on the PCM, and it can lead to issues with type II collagen and aggrecan which will impact the characteristics of the chondron.

After several studies to improve cartilage tissue engineering, it was only recently that the potential of the co-culture was realized. Studies also express doubts over the production of cytokines and growth factors by the MSC's which prevent inflammation.