The role of progestogens in regulating matrix metalloproteinase activity in macrophages and microglial cells.

Although the systemic effects of progestogens have been extensively studied, little is known in regards to the cellular effects of these compounds. Using a cellular model for vascular (macrophages) and brain (microglial) cells, we studied the effects of various progestogens, either alone or in combination with 17β-estradiol (E(2)) on the activity of matrix metalloproteinase-9 (MMP-9), a proteolytic enzyme involved in vascular remodeling and plaque destabilization in cardiovascular events, blood-brain barrier breakdown in stroke and brain regeneration and neurovascular remodeling during repair phases of brain injury. In the absence of E(2), medroxyprogesterone acetate (MPA), a synthetic progestogen and progesterone (PG) metabolites tended to increase MMP-9 enzyme activity in macrophages and microglial cells, whereas PG decreased such activity in macrophages; exceptions being that MPA and the PG metabolite, pregnanediol (Pdiol) had no effect on macrophage MMP-9 enzyme activity and PG had no effect on microglial cell MMP-9 enzyme activity. In the presence of E(2), an opposite affect was observed whereby MPA and the PG metabolites tended to decrease MMP-9 enzyme activity from macrophages and microglial cells, whereas PG had no effect; exceptions being that MPA and Pdiol had no effect on macrophage MMP-9 enzyme activity. In conclusion, these results demonstrate that the effects of PG, PG metabolites and MPA on MMP-9 enzyme activity differ across vascular and brain cells when administered alone or in combination with E(2) which could have important mechanistic implications for hormone therapy.