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Chronic estrogen exposure affects gene expression in the rostral ventrolateral medulla of young and aging rats: Possible role in hypertension.

ABSTRACT: Chronic exposure to estradiol-17? (E2) in adult female rats increases mean arterial pressure by stimulating superoxide production in the rostral ventrolateral medulla (RVLM). However the mechanisms behind this phenomenon are unknown. We hypothesized that E2 exposure induces the gene expression of cytokines, chemokines and NADPH oxidase (Nox) in the RVLM that promotes superoxide production and aging would exacerbate this effect.Young adult (3-4 month old) and middle-aged (6-8 month old) female Sprague Dawley rats were sham-implanted (YS and MS respectively) or implanted s.c. with slow-release E2 pellets (20 ng of E2/day for 90 days; YE and ME respectively). Blood pressure (BP) was measured during the last 3 weeks of exposure in a separate set of rats. At the end of treatment, the animals were sacrificed and RVLM was isolated from the brainstem. PCR array and Quantitative RT-PCR were performed with the tissue to quantify genes associated with hypertension and superoxide production. Superoxide dismutase (SOD) activity was also measured in the RVLM from a different set of animals.E2 exposure increased mean arterial pressure in both YE and ME animals. Inflammatory genes such as interleukin-1?, interleukin-6 and monocyte chemoattractant protein-1 were significantly up-regulated in the RVLM of ME treated female rats compared to YS rats, but not in YE rats. Endothelin-1 (ET-1) gene was up-regulated in the RVLM of both YE and ME rats that were exposed to E2. Furthermore, chronic E2 treatment increased the mRNA levels of Nox1 and Nox2 genes in the RVLM of YE but not ME animals. SOD activity was reduced in MA animals, compared to young animals. E2 treatment had no significant effect on SOD activity.Chronic E2 exposure stimulates the expression of inflammatory genes in older animals and increases the expression of Nox subunits in the RVLM of younger animals. SOD activity was reduced in older animals. This suggests increased superoxide production in younger animals, but reduced superoxide elimination in older animals. On the other hand, E2 exposure stimulates ET-1 expression in both young and aging animals. These findings suggest that hypertension caused by chronic E2 exposure may involve different molecular mediators in young and aging animals, however ET-1 and superoxide could be common mediators for both age groups.

SUBMITTER: Subramanian M

PROVIDER: S-EPMC4714716 | biostudies-literature | 2015 Nov

REPOSITORIES: biostudies-literature

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Chronic estrogen exposure affects gene expression in the rostral ventrolateral medulla of young and aging rats: Possible role in hypertension.

Subramanian Madhan M Hahn-Townsend Coral C Clark Kimberly A KA MohanKumar Sheba M J SM MohanKumar P S PS

Brain research 20150912

<h4>Background</h4>Chronic exposure to estradiol-17β (E2) in adult female rats increases mean arterial pressure by stimulating superoxide production in the rostral ventrolateral medulla (RVLM). However the mechanisms behind this phenomenon are unknown. We hypothesized that E2 exposure induces the gene expression of cytokines, chemokines and NADPH oxidase (Nox) in the RVLM that promotes superoxide production and aging would exacerbate this effect.<h4>Methods</h4>Young adult (3-4 month old) and mi ...[more]

PMID: 26375620

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Project description:Neuroinflammation plays hypertensive roles in the uninjured autonomic nuclei of the central nervous system, while its mechanisms remain unclear. The present study is to investigate the effect of neuroinflammation on autophagy in the neurons of the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons for the maintenance of vasomotor tone reside.Stress-induced hypertension (SIH) was induced by electric foot-shock stressors with noise interventions in rats. Systolic blood pressure (SBP) and the power density of the low frequency (LF) component of the SAP spectrum were measured to reflect sympathetic vasomotor activity. Microglia activation and pro-inflammatory cytokines (PICs (IL-1?, TNF-?)) expression in the RVLM were measured by immunoblotting and immunostaining. Autophagy and autophagic vacuoles (AVs) were examined by autophagic marker (LC3 and p62) expression and transmission electron microscopy (TEM) image, respectively. Autophagy flux was evaluated by RFP-GFP-tandem fluorescent LC3 (tf-LC3) vectors transfected into the RVLM. Tissue levels of glutamate, gamma aminobutyric acid (GABA), and plasma levels of norepinephrine (NE) were measured by using high-performance liquid chromatography (HPLC) with electrochemical detection. The effects of the cisterna magna infused minocycline, a microglia activation inhibitor, on the abovementioned parameters were analyzed.SIH rats showed increased SBP, plasma NE accompanied by an increase in LF component of the SBP spectrum. Microglia activation and PICs expression was increased in SIH rats. TEM demonstrated that stress led to the accumulation of AVs in the RVLM of SIH rats. In addition to the Tf-LC3 assay, the concurrent increased level of LC3-II and p62 suggested the impairment of autophagic flux in SIH rats. To the contrary, minocycline facilitated autophagic flux and induced a hypotensive effect with attenuated microglia activation and decreased PICs in the RVLM of SIH rats. Furthermore, SIH rats showed higher levels of glutamate and lower level of GABA in the RVLM, while minocycline attenuated the decrease in GABA and the increase in glutamate of SIH rats.Collectively, we concluded that the neuroinflammation might impair autophagic flux and induced neural excitotoxicity in the RVLM neurons following SIH, which is involved in the development of SIH.

Project description:This study aims to investigate whether tissue oxidative stress in the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons reside, plays an active role in age-dependent susceptibility to hypertension in response to nitric oxide (NO) deficiency induced by systemic l-NAME treatment, and to decipher the underlying molecular mechanisms. Systolic blood pressure (SBP) and heart rate (HR) in conscious rats were recorded, along with measurements of plasma and RVLM level of NO and reactive oxygen species (ROS), and expression of mRNA and protein involved in ROS production and clearance, in both young and adult rats subjected to intraperitoneal (i.p.) infusion of l-NAME. Pharmacological treatments were administered by oral gavage or intracisternal infusion. Gene silencing of target mRNA was made by bilateral microinjection into RVLM of lentivirus that encodes a short hairpin RNA (shRNA) to knock down gene expression of NADPH oxidase activator 1 (Noxa1). We found that i.p. infusion of l-NAME resulted in increases in SBP, sympathetic neurogenic vasomotor activity, and plasma norepinephrine levels in an age-dependent manner. Systemic l-NAME also evoked oxidative stress in RVLM of adult, but not young rats, accompanied by augmented enzyme activity of NADPH oxidase and reduced mitochondrial electron transport enzyme activities. Treatment with L-arginine via oral gavage or infusion into the cistern magna (i.c.), but not i.c. tempol or mitoQ10, significantly offset the l-NAME-induced hypertension in young rats. On the other hand, all treatments appreciably reduced l-NAME-induced hypertension in adult rats. The mRNA microarray analysis revealed that four genes involved in ROS production and clearance were differentially expressed in RVLM in an age-related manner. Of them, Noxa1, and GPx2 were upregulated and Duox2 and Ucp3 were downregulated. Systemic l-NAME treatment caused greater upregulation of Noxa1, but not Ucp3, mRNA expression in RVLM of adult rats. Gene silencing of Noxa1 in RVLM effectively alleviated oxidative stress and protected adult rats against l-NAME-induced hypertension. These data together suggest that hypertension induced by systemic l-NAME treatment in young rats is mediated primarily by NO deficiency that occurs both in vascular smooth muscle cells and RVLM. On the other hand, enhanced augmentation of oxidative stress in RVLM may contribute to the heightened susceptibility of adult rats to hypertension induced by systemic l-NAME treatment.

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Chronic estrogen exposure affects gene expression in the rostral ventrolateral medulla of young and aging rats: Possible role in hypertension.

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Chronic estrogen exposure affects gene expression in the rostral ventrolateral medulla of young and aging rats: Possible role in hypertension.

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