HTRA1 and osteoarthritis: Furthermore, when exposed to TNF-a to mimic inflammatory conditions in osteoarthritis, the genes involved in inflammation (PTGS2, CCL2, CXCL14), ECM components (Col2A1, CILP, THBS3), growth factors (IGFBP3, IGFBP6) and matrix remodeling enzymes (MMP1, MMP3, PDK4, HTRA1) were upregulated similar to our study.