本篇論文主要是在探討黃體激素 (progesterone) 對於老鼠的主動脈平滑肌細胞 (Rat aortic smooth muscl e cells) 生長的抑制情形及其相關的作用機轉。由動脈粥狀硬化等心血管疾病所造成的死亡人數的研 究發現，停經前的婦女要比同年齡的男性得病機會少 (Gordon et al., 1978) ，而停經後的婦女如果同 時服用適量的雌性素 (estrogen) 以及助孕素 (progestin) ，也會比只有單獨服用 estrogen 的人較不易得 心血管疾病。已經發表的文獻中對於 estrogen 的效用探討頗多，但對於 progestin 的單獨作用效果則 較少探究。 Progesterone 已被發現對於老鼠動脈平滑肌細胞的生長具有抑制的效果。利用北方墨點 法 (Northern blotting) 發現和細胞週期相關的細胞週期素 Cyclin A 及 Cyclin E 的 mRNA 在老鼠的動脈 平滑肌細胞內表現有受到 progesterone 的抑制。因此，推測 progesterone 可能是影響細胞在由 G1 pha se 進入到 S phase 的過程。本研究即以西方墨點法（ Western blotting) 的方法來進一步的探討 progest erone 對於老鼠的動脈平滑肌細胞的細胞週期之影響。
由我們的研究結果發現，黃體激素 (progesterone) 存在時 (500 nM) ，會使得老鼠的主動脈平滑肌細胞 (Rat aortic smooth muscle cells) 的生長受到抑制。而進一步去探討其作用機轉時，發現隨著 progestero ne 濃度的增加 (0~500 nM) ，一些和細胞週期調控相關的蛋白質如： Cyclin A 、 Cyclin E 、 Cdk 2 、 Cdk 4 的表現量都有逐漸減少的情形。除此之外，一些已知會抑制細胞週期進行的 cyclin dependent k inase(CDK) inhibitor 如 p21 、 p27 蛋白質的表現量則隨著 progesterone 濃度的增加 (0~500 nM) 而增 加。而由免疫沉澱法的結果顯示，和 Cdk 2 結合的 cyclin dependent kinase inhibitor p21 及 p27 的蛋白 質表現量隨著 progesterone 濃度的增加 (0~500 nM) 而有增加的情形出現。而 kinase assay 的研究結果 發現， Cdk 2 的酵素活性也隨著 progesterone 濃度的增加 (0~500 nM) 而受到抑制，但是 Cdk 4 的酵 素活性卻沒有受到影響。以 p21 的 antisense oligonucleotide 預處理細胞 (5 nM, 10 nM, 20 nM/1 hr) ， 發現可以避免由 progesterone 所造成的細胞週期抑制現象，而單獨加入 p21 antisense oligonucleotide 則對 DNA 合成能力沒有影響，推測 p21 這種 cyclin dependent kinase inhibitor 在 progesterone 對 RAS MCs 所造成的細胞週期抑制現象中扮演了一種關鍵的角色。
本篇論文的研究結果顯示，黃體激素 (progesterone) 的存在會造成老鼠的主動脈平滑肌細胞的生長受 到抑制，而了解其相關的作用機轉之後，相信對於研究這種荷爾蒙在預防心血管疾病發生的保護作 用方面能夠有所助益。
黃體激素對老鼠動脈平滑肌細胞的生長抑制作用
The objective of this thesis research is to investigate the anti-proliferation effect of progesterone on the cell line Rat a ortic smooth muscle cell and its underlying molecular mechanisms. Cardiovascular diseases, the principal cause of de ath in the developed world, affect men far more frequently than premenopausal women of the same age (Gordon et a l., 1978). Estrogens or progestins appear to have a protective effect in premenopausal women. Resent reports show th at the risk of coronary heart disease is lower in women who take estrogens and progestins together rather than estroge ns alone. However, there has been little evidence of an independent effect of progestins in animal studies
Progesterone has been shown to have a direct and inhibitory effect on the proliferation of subcultured arterial smooth muscle cells. The levels of Cyclin A and Cyclin E mRNA decline in the prescene of progesterone in rat aortic smooth muscle cells (RASMCs), suggesting that progesterone interrupts the cell cycle at the G1/S transition. This cell cycle- dependent inhibition of arterial smooth muscle cell proliferation by progesterone may represent a mechanism for the hormone’s protective effect against cardiovascular diseases.
In vitro studies demonstrated that progesterone (500 nM) induced inhibition of Rat aortic smooth muscle cell growth.
Further more, western blot analysis demonstrated that progesterone (5~500 nM) induced a dose-dependent decreased expression of protein which mediated cell cycle progression ： Cyclin A 、 Cyclin E 、 Cdk 2 、 Cdk 4. On the othe r hand, western blot also demonstrated an increased expression of cyclin-dependent kinase(CDK) inhibitor, p21 、 p2 7. Immunoprecipitation demonstrated that progesterone (5~500 nM) induced a dose-dependent increased expression of cyclin dependent kinase inhibitor, p21 and p27 which bind to Cdk 2. Kinase assay demonstrated that progesterone (5~500 nM) induced a dose-dependent decrease of Cdk 2 enzyme activity, but it has no effect on the enzyme activity of Cdk 4. Pretreating cells with p21 antisense oligonucleotide (5 nM, 10 nM, 20 nM/1 hr) prevents the effect of cell c ycle inhibition due to progesterone, p21 antisense oligonucleotide alone in RASMC has no effect on DNA synthesis, we suggest that p21, the cyclin dependent kinase inhibitor plays a key role in RASMC cell cycle inhibition results fro m progesterone.
In conclusion, our data demonstrated that progesterone induced an anti-proliferation effect in rat aortic smooth muscl e cells. Understanding the mechanism of its effect may represent an advance to study the hormone’s protective effect against cardiovascular diseases
The antiproliferation effect of progesterone in rat arterial smooth muscle cells
