Background In mammals, tissue or organ damage often results in fibrotic scar formation, which in turn may impair proper organ function. Many urodele amphibians are capable of regenerating different tissues including lenses, heart, and spinal cord or even entire body parts like limbs or tails without any functional impairment.
We previously established the red-spotted newt Notophthalmus viridescens as a model organism to study endogenous knee joint regeneration in adult vertebrates. After surgical removal of articular cartilage from the femur or after intra-articular collagenase injection, newts displayed osteoarthritis (OA)-like symptoms, including joint instability and luxation. However, after approximately 3 months the joint function was completely restored in the treated animals. To evaluate the underlying molecular mechanisms guiding this regenerative process, a cDNA approach was used in this study.
Methods A cDNA array derived from regenerating newt myocardium containing 100000 normalised expressed sequence tags (ESTs) was carried out after surgically and collagenase-induced knee damage in newts to identify key players involved in knee joint regeneration. Several ESTs were found to be regulated during the regenerative process. By using public databases, several deregulated candidate genes were identified and selected for further analysis on mRNA (Real‑Time PCR) and protein level (immunohistochemistry).
Results In the cDNA array, a number of genes was found to be deregulated during the course of knee joint regeneration, including several matricellular proteins like tenascin-C (TN-C), periostin and osteonectin/SPARC. Among them, TN-C showed the strongest upregulation during the regenerative process and was selected for further studies. On the mRNA level, a strong upregulation of TN-C mRNA was found in both models: While in the collagenase model TN-C was upregulated at 10 days and 40 days after OA induction, TN-C expression ceased in the surgically-induced OA model at day 40. In immunohistochemical analyses, TN-C expression was restricted to the periosteum 10 days after damage. As knee joint regeneration progressed, TN-C was also found in regenerating cartilage (40 days after damage).
Conclusions TN-C is involved in the regenerative process after OA induction in the newt. In vitro siRNA knockdown of TN-C might help to identify the molecular pathways involved. Analysis of the selected candidate genes and identification of underlying pathways guiding regeneration might ease the development of new treatment modalities of OA in humans.