MMP13 and osteoarthritis: In addition, the mRNA levels of typical aging markers (e.g., P16 and P21) and inflammation factors (e.g., IL6 and matrix metalloproteinase 13 (MMP13)) that are often upregulated in osteoarthritis were diminished in the articular cavities of the mice with DR8-WT or DR8-mtDRBD (Fig. 8a).