Hormone Replacement Therapy Influences Matrix Metalloproteinase Expression and Intimal Hyperplasia Development after Vascular Injury: A Follow-Up Study

Postmenopausal women taking hormone replacement therapy (HRT) have increased intimal hyperplasia (IH) following vascular intervention. Matrix metalloproteinases (MMPs) play a major role in IH development, and we have shown that hormone exposure results in unbalanced MMP regulation in vascular smooth muscle cells in vitro. Previously we presented data from a small pilot study suggesting a role for HRT in the development of IH via MMP modulation in vivo, using a postmenopausal rodent model of vascular injury. Here we further investigated the role of HRT as a modulator of MMPs and IH in a larger follow-up study. Female rats were aged to 12 months and ovariectomized (OVX). Four weeks later estrogen (E), progesterone (P), estrogen + progesterone (E/P), or placebo (Plac) were delivered via 90-day slow-release pellets. Following 6 weeks of HRT, each rat underwent balloon angioplasty of the left common carotid artery. At 14 days postinjury, tissue samples were collected and stained with Trichrome elastin for intima:media (I:M) measurement and stained for various MMP isoforms. Following vascular injury I:M was decreased in OVX rats compared to non-OVX controls (Fig 1, n = 5-6, P = NS). In OVX animals, HRT exposure did not significantly increase the I:M ratios. (Fig 1, n = 5-6, P = NS). Injury-induced expression of MMP-2 and −9 was significantly decreased in OVX animals compared to non-OVX controls (Table 1; n = 5-6). MMP-2 and −9 levels were subsequently increased by each type of hormone therapy compared to placebo, with a significant increase in MMP-9 in response to estrogen with and without progesterone (Table; n = 5-6). Conversely, TIMP-2 was significantly decreased by estrogen compared to placebo (Table; n = 5-6). There was no effect on intimal MT1-MMP in any group.Table 1% intima stainedNonOVX COVX - PlacOVX - EOVX - POVX - EPMMP-237.8 ± 10.015.4 ± 3.7⁎P < 0.05 vs. NonOVX C26.5 ± 3.738.8 ± 7.638.5 ± 7.6MMP-94.3 ± 0.12.7 ± 0.4⁎P < 0.05 vs. NonOVX C4.7 ± 0.6#P < 0.05 vs. OVX-Plac6.0 ± 1.37.1 ± 1.0#P < 0.05 vs. OVX-PlacTIMP-250.9 ± 8.922.2 ± 3.4⁎P < 0.05 vs. NonOVX C8.7 ± 1.4#P < 0.05 vs. OVX-Plac24.8 ± 10.128.2 ± 9.4 P < 0.05 vs. NonOVX C# P < 0.05 vs. OVX-Plac Open table in a new tab Here we were not able to demonstrate a statistically significant decrease in IH as a result of ovariectomy. Furthermore, HRT at the doses given did not remarkably increase IH. Here we also demonstrate a significant reduction in MMP-2, −9, and TIMP-2 in response to ovariectomy. Subsequent hormone exposure results in the upregulation of MMP-2 and −9 without a counter-regulatory increase in TIMP. We have previously shown elevation in MT1-MMP to occur during the initial phases of IH development; therefore, examination earlier than 14 days postinjury is needed to determine the effect of HRT on this MMP regulatory isoform. Future studies should investigate in vivo manipulation of this unbalanced MMP regulation for prevention of IH in response to HRT exposure.