By Baojian Xue, Zhongming Zhang, Terry G Beltz, Ralph F Johnson, Fang Guo, Meredith Hay, and Alan Kim Johnson.
Journal of Hypertension, June 2013.
Estrogen receptors alpha and beta (ERa and ERb, respectively) are expressed in many nuclei involved in the control of the sympathetic nervous system. Interestingly, the action of estrogen on ERb attenuates glutamate-induced increases in blood pressure in the RVLM. Furthermore, estrogen attenuated Aldosterone (Aldo)-induced hypertension in both males and OVX females. However, it has previously been shown that certain brain areas have a predominant expression of a certain subtype. For example, ERa predominates in the NTS and ERb is predominant in the PVN. The purpose of this study was to investigate the role of ER subtypes in the PVN and RVLM and to measure the protective effects estrogen has on the development of Aldo-induced hypertension in those areas.
10-12 week old female rats were used. There were 12 different groups: Intracerebroventricular (icv) infusions of a vehicle, ERb agonist diarylpropionitrile (DPN), or ERa agonist propyl-pyrazole-triol (PPT) in OVX females; icv injections of adeno-associated virus (AAV) carrying siRNA-SCM (small interfering RNA injected to create a “control” group that did not have any receptors silenced), AAV-siRNA-ERa (to silence ERa), and AAV-siRNA-ERb (to silence ERb) into intact females; PVN microinjections of siRNA-ERb, -ERa, or 1SCM into intact females; and RVLM microinjections into intact females using the same siRNA types. All animals received subcutaneous injections of Aldo and 1% NaCl as their drinking water. Reactive oxygen species studies were also completed. Cultured PVN neurons were incubated in either: (1) siRNA-SCM and vehicle (control group); (2) siRNA-SCM and Aldo (the hypertension group); (3) siRNA-ERa and Aldo and; (4) siRNA-ERb and Aldo.
After 21 days of Aldo/NaCl treatment, the female OVX rats had an average of 21.1 mmHg increase in MAP. Upon PPT and DPN icv infusions for 21 days, the rats had a significant attenuation of Aldo-induced hypertension. Furthermore, when given icv injections of either siRNA-ERa or siRNA-ERb, OVX females had further increases in the MAP. Thus, both ER agonists showed protective effects when circulating throughout the entire brain.
Individual areas of the brain involved in sympathetic nervous system control were investigated to further understand the roles of the different ER subtypes. Microinjections of siRNA-SCM into the PVN produced slight increases in MAP. SiRNA-ERb microinjections into the PVN resulted in a significant average increase of 16.1 mmHg. However, siRNA-ERa only resulted in an average increase of 11.2 that was not significantly different from siRNA-SCM injections. Thus, the researchers believe this helps support the notion that ERb is the predominant receptor in the PVN that helps attenuate Aldo-induced hypertension. Similar results were shown with the microinjections into the RVLM—the siRNA-ERb, and not siRNA-ERa, produced significant increases in MAP when compared to siRNA-SCM.
Hexamethonium (hex) was injected after in OVX females after 21 days of Aldo infusion to further examine effects of the region-specific ER subtypes. Hex caused greater reductions in blood pressure in OVX females compared to those who received icv DPN or PPT. Thus, rats with no circulating estrogen had higher blood pressure compared to those who had circulating estrogen and ER agonist. Furthermore, intact rats who were also treated with siRNA-ERb via icv, PVN, or RVLM microinjections resulted in greater drops of blood pressure when given hex. siRNA-ERa and hex showed no difference in blood change for intact females compared to those with siRNA-SCM and hex injections. These results suggested that ERb is the primary ER subtype that attenuates blood pressure in Aldo-induced hypertensive rats.
AAV knockdown occurred in animals to verify that the siRNA injections was indeed silencing the receptors. AAV-siRNA-ERa and -ERb contained green fluorescent protein (GFP) to verify that the receptors were silenced after injections. If the receptors were silenced, they would express GFR and glow. Micropunches were taken of either the RVLM or PVN, depending on the injection site, to collect samples. These samples confirmed that the receptors were silenced and that the siRNA was contained within the selected brain region. The levels of both receptor types were reduced by 44 to 74% when compared to injections with siRNA-SCM.
Lastly, the ROS levels were measured and compared in the siRNA-ERa and siRNA-ERb intact females after the collected PVN neurons were treated with Aldo overnight. When either receptor was silenced, there was an enhanced Aldo-induced increase in ROS production. Thus, the researchers suggest that Aldo increases sympathetic nerve activity and estrogen works to inhibit those effects. By silencing the receptors, the hypertensive effects become attenuated as the neurons become more active.
Overall, the study showed that both ERa and ERb have protective roles against the development of Aldo-induced hypertension in female rats. Without active ERb in the RVLM or PVN, hypertension is augmented, while silenced ERa showed little effect. Thus, the distribution of ER is region-specific to provide protective protective properties against Aldo-induced hypertension. However, this may be true only for Aldo-induced hypertension. Other studies have suggested that ERa is more active depending on the model of hypertension, and ERb is key for all types of hypertension. More studies need to be done in order to better understand the role of the specific receptors in the different brain areas that control sympathetic nerve outflow and thus blood pressure.
-LivInLaVida
No comments:
Post a Comment