The role of transforming growth factor beta superfamily in chondrogenic stem cells

Cartilage is present throughout the human body and works as supporting connective tissue. It assists bones in supporting and connecting the body but differs in structural aspects as bones are more organized at the micro-level than cartilage. Bones can be regenerated if broken but cartilage has less tendency to regenerate after trauma or disease such as osteoarthritis which supports the concept of tissue engineering using stem cells to produce artificial cartilage implants to resurface damaged joints. Mesenchymal stem cells (MSCs) and human-induced pluripotent stem cells (hiPSCs) were used in the current study to address this challenge. The chondrogenic capacity of hiPSC cell lines C19 and OC3 in response to members of the transforming growth factor beta superfamily to derive zonal chondrocytes was investigated. The pellet culture system and 3D scaffold based tissue engineering were used to investigate the impact of transforming growth factor beta in combination with bone morphogenic proteins (BMPs) including BMP2, BMP4, and BMP7 on the constructs phenotype. Chondrogenic markers including type II, type I, and type X collagens, lubricin, aggrecan and Sox9 have been used to evaluate the quality of chondrogenic outcome by quantifying gene expression and histological analysis. The results demonstrated the derivation of chondrocytes of different phenotypes. These phenotypes were mapped to zonal chondrocytes (superficial, deep and hypertrophic). The results demonstrated the possibility of obtaining superficial and hypertrophic chondrocytes but not deep zone chondrocytes. Identical experiments were conducted for comparison using bone marrow mesenchymal stem cells (MSCs). Chondrocytes derived from MSCs treated with various combinations of the transforming growth factor beta superfamily members revealed limited mapping to a particular zonal phenotype. An attempt to ameliorate the phenotypes was sought using 3D bioprinting with limited success. Finally, a cellular reprogramming method was utilised to generate chondrocytes with the aim of controlling their fate and phonotype. Mesenchymal stem cells (MSCs) were treated with different cocktails of small molecules guided by a bioinformatics-based method for cell conversion (Mogrify). Several cocktails targeting the predicted transcription factors were used to drive the conversion process. One cocktail appeared to have limited capacity to upregulate some chondrogenic markers in 2D and 3D cultures. In conclusion, the issues of cartilage related struggles are spreading worldwide and needs to get a permanent solution that can be helpful for every patient. For this purpose the study was conducted to get a better understanding of in vitro chondrogenesis. The study concluded the generation of hypertrophic and superficial chondrocytes through pellet culture system by using BMPs. The aid of 3D bioprinting was also limited because of the limitation in zonal phenotypes. The cocktails of predicted transcriptional factors helped in inducing chondrogenesis. These are not the ideal results but can help the future researchers to develop better strategies and applicable results.