Effects of Estrogen on the Vascular Injury Response in Estrogen Receptor α,β (Double) Knockout Mice

Abstract

Abstract-The two known estrogen receptors, ER␣ and ER␤, mediate the effects of estrogen in all target tissues, including blood vessels. We have shown previously that estrogen inhibits vascular injury response to the same extent in female wild-type (WT), ER␣ knockout (ER␣KO CH ), and ER␤ knockout (ER␤KO CH ) mice. We generated mice harboring disruptions of both ER␣ and ER␤ genes (ER␣,␤KO CH ) by breeding and studied the effect of 17␤-estradiol ( Using wild-type (WT) and estrogen receptor knockout (KO) mice, we have previously studied the role of ER␣ and ER␤ in mediating the vascular protective effects of estrogen in a mouse carotid artery injury model. 10,17,18 Previous studies used mice developed at the University of North Carolina, Chapel Hill, which harbor gene deletions of either ER␣ (ER␣KO CH ) 19 or ER␤ (ER␤KO CH ). 20 These studies show that treatment of ovariectomized female mice with nanomolar concentrations of 17␤-estradiol (E2) inhibits the response to vascular injury to equivalent levels in wild-type, 17 ER␣KO CH , 10 and ER␤KO CH mice. 18,21 These findings suggest that ER␣ and ER␤ are able to complement one another such that each receptor alone is sufficient to mediate the vascular protective effects of estrogen, or that the vascular protective effects of estrogen are mediated by an ER␣/ER␤-independent pathway. To distinguish between these two hypotheses, we undertook the present study examining the effect of estrogen on the response to vascular injury in ER␣,␤KO CH (double) estrogen receptor knockout mice. Materials and Methods AnimalsA total of over 820 animals were required to ultimately generate the ER␣,␤KO CH mice used in this study. These mice, which have been extensively studied, do not express ER proteins in any tissue. 19,20,[22][23][24] However, ER␣KO CH mice have been shown previously to express mRNA for 2 partial ER␣ transcripts, one of which retains the hormone-and DNA-binding domains of full-length ER␣, and can Original

The AF-1 activation-function of ERα may be dispensable to mediate the effect of estradiol on endothelial NO production in mice

“…It seems that the full-length ER␣66 (which harbors the transactivation function AF-1) mediates fertility in both males and females (39), some vascular effects of E 2 , such as the angiogenic effect (40), as well as inhibition of the constitution of fatty streak in apolipoprotein E-deficient mice (41). Conversely, AF-1 of ER␣ (absent and altered in ER␣46 and ER␣55, respectively) could be at least in part dispensable to mediate the effect of E 2 on the uterine response (present study), the inhibition of smooth muscle hyperplasia in response to endoluminal carotid injury (13,42), and the endothelial production of NO (present study). Thus, the former hypotheses (30, 42) of a reciprocal functional redundancy between ER␣ and ER␤, or of the existence of a putative third isoform ''ER␥,'' seem to be ruled out.…”

Methoxyestradiols Mediate the Antimitogenic Effects of 17β-Estradiol

“…4 Whether the inhibitory effects of estradiol on SMC growth are ER-mediated remains unclear. Estradiol inhibits proliferation of SMCs in injury-induced vascular lesions in mice lacking ER␣, 1 ER␤, 2 and both ER␣ and ER␤, 3 suggesting that the inhibitory effects are ER-independent. An ER-independent mechanism is also supported by the observations that estradiol inhibits injury-induced neointima formation in gonadectomized but not intact male rats, although vascular cells from both express ERs.…”

“…[1][2][3] Because methoxyestradiols (major endogenous metabolites of estradiol with no affinity for ERs) inhibit growth of cancer cells, 4 it is feasible that the vascular antimitogenic effects of estradiol are mediated by methoxyestradiols. Using pharmacological agents, previous studies demonstrate that metabolism of estradiol to hydroxyestradiols by CYP450 followed by methylation of hydroxyestradiols by catechol-O-methyltransferase (COMT) to form methoxyestradiols is critical for estradiol-induced inhibition of SMC growth.…”

Estrogen replacement therapy and cardioprotection: mechanisms and controversies

“…However, the significance of these two receptors in the manifestation of the cardioprotective effect of estrogen is still open to question since mice lacking both of these receptors continue to demonstrate inhibition of intimal proliferation after vascular injury (51). The distribution of these receptors in vascular and other tissues and their interactions with estrogens and antiestrogens are beyond the scope of this article and have been covered in some excellent recent reviews (52).…”