MMP9 and temporal arteritis: On the other hand, PLG, encoding plasminogen, is involved in different processes relevant for GCA, such as angiogenesis, lymphocyte recruitment, and production of inflammatory mediators, including tumor necrosis factor alpha (TNF-α) and IL-6 (78), and P4HA2, encoding an isoform of the alpha subunit of the collagen prolyl 4-hydroxylase, is an important hypoxia response gene whose expression is induced by hypoxia-inducible factor-1 (HIF-1), which also induces the expression of other genes involved in GCA such as IL6, MMP9 (matrix metallopeptidase 9), and VEGF (79).