MMP9 and periodontitis: p.g‐LPS also up‐regulated the mRNA and protein expression of RANKL (Figure 3I, J and L), a key factor in osteoclastogenesis and bone resorption in periodontitis.21 Moreover, p.g‐LPS increased the mRNA expression and enzymatic activities of MMP‐9/2 as indicated by qRT‐PCR (Figure 3G and H) and gelatin zymography tests (Figure 3J and K) respectively.