UVM Theses and Dissertations
Format:
Print
Author:
Song, Xiaozheng
Dept./Program:
Animal Sciences
Year:
2014
Degree:
Ph. D.
Abstract:
The mammary gland cell growth and differentiation are under the control of both systemic honnones and locally produced growth factors. Among all these important honnones and growth factors, · estrogen plays a central role in mammary gland development. The biological function of estrogen is mediated by estrogen receptor Alpha. (ER[Alpha].) and estrogen receptor Beta (ER[Beta]). Both ER[Alpha] and ER[Beta] are expressed in the mammary gland, but with distinct expression patterns. In the mammary gland, ER[Alpha] has been proved to be the estrogen receptor that mediates the mitogenic function of estrogen. However the function of ER[Beta] in mammary cell proliferation is less understood and there remains some controversy. Accumulating evidence indicates that ER[Beta], unlike ER[Alpha], is a negative regulator of mammary epithelial cell proliferation.
In this dissertation, ER[Alpha] and ER[Beta] were evaluated for their expression patterns in the mammary gland. In the proestrus phase, ER[Alpha] was detected in about 20% of mammary epithelial cells; in the diestrus phase, no ER[Alpha] staining was detected in the mammary gland. ER[Beta] was expressed in more than 50% of mammary epithelial cells and ER[Beta] staining was detected in some stromal cells in the proestrus phase. In the diestrus phase, ER[Beta] staining cells were very limited and the staining intensity was very weak. These data suggest that the expression levels of both ER[Alpha] and ER[Beta] undergo dynamic changes during the estrous cycle. In the ovariectomised (OVX) rats, both ER[Alpha] and ER[Beta] were detected in more than 50% of mammary epithelial cells. Compared with the ovary-intact rats, the mammary gland of the OVX rats showed more cells with ER[Alpha] expression, but the staining intensity was weaker. Taken together, the expression of ER[Alpha] and ER[Beta] is regulated by estrogen in normal mammary gland, while without estrogen stimulation in the OVX rats, more mammary cells showed ERa expression, but at a lower level in these cells.
The effects of ER[Alpha] and ER[Beta] on mammary cell proliferation were studied by two different approaches, activation of endogenous ER[Alpha] and ER[Beta] via selective agonists, and overexpression of ER[Alpha] and ER[Beta] via lentiviral infection. In the first approach, we used ER[Alpha] and ER[Beta] selective agonists, propylpyrazole-triol (PPT) and diarylpropionitrile (DPN) respectively, to activate endogenous ER[Alpha] and ER[Beta] in the OVX rats. We found that ER[Beta] selective agonist DPN counteracts the proliferative effect of ER[Alpha] selective agonist PPT in the mammary gland. In the second approach, ER[Alpha] and ER[Beta] were ectopically overexpressed in the mammary gland of mature virgin rats by lentivirus infection. We found that ER[Beta] overexpression significantly decreased mammary cell proliferation rate in both the proestrus and diestrus phases, indicating that ER[Beta], unlike ER[Alpha], is a negative regulator for mammary cell proliferation. Collectively, these data supports that in contrast to ER[Alpha], ER[Beta] activation or overexpression is able to inhibit mammary cell proliferation.
In this dissertation, ER[Alpha] and ER[Beta] were evaluated for their expression patterns in the mammary gland. In the proestrus phase, ER[Alpha] was detected in about 20% of mammary epithelial cells; in the diestrus phase, no ER[Alpha] staining was detected in the mammary gland. ER[Beta] was expressed in more than 50% of mammary epithelial cells and ER[Beta] staining was detected in some stromal cells in the proestrus phase. In the diestrus phase, ER[Beta] staining cells were very limited and the staining intensity was very weak. These data suggest that the expression levels of both ER[Alpha] and ER[Beta] undergo dynamic changes during the estrous cycle. In the ovariectomised (OVX) rats, both ER[Alpha] and ER[Beta] were detected in more than 50% of mammary epithelial cells. Compared with the ovary-intact rats, the mammary gland of the OVX rats showed more cells with ER[Alpha] expression, but the staining intensity was weaker. Taken together, the expression of ER[Alpha] and ER[Beta] is regulated by estrogen in normal mammary gland, while without estrogen stimulation in the OVX rats, more mammary cells showed ERa expression, but at a lower level in these cells.
The effects of ER[Alpha] and ER[Beta] on mammary cell proliferation were studied by two different approaches, activation of endogenous ER[Alpha] and ER[Beta] via selective agonists, and overexpression of ER[Alpha] and ER[Beta] via lentiviral infection. In the first approach, we used ER[Alpha] and ER[Beta] selective agonists, propylpyrazole-triol (PPT) and diarylpropionitrile (DPN) respectively, to activate endogenous ER[Alpha] and ER[Beta] in the OVX rats. We found that ER[Beta] selective agonist DPN counteracts the proliferative effect of ER[Alpha] selective agonist PPT in the mammary gland. In the second approach, ER[Alpha] and ER[Beta] were ectopically overexpressed in the mammary gland of mature virgin rats by lentivirus infection. We found that ER[Beta] overexpression significantly decreased mammary cell proliferation rate in both the proestrus and diestrus phases, indicating that ER[Beta], unlike ER[Alpha], is a negative regulator for mammary cell proliferation. Collectively, these data supports that in contrast to ER[Alpha], ER[Beta] activation or overexpression is able to inhibit mammary cell proliferation.