Renin Enhancer Is Critical for Control of Renin Gene Expression and Cardiovascular Function

Thymoquinone Produces Cardioprotective Effect in β-Receptor Stimulated Myocardial Infarcted Rats via Subsiding Oxidative Stress and Inflammation

Earlier studies reported that long-term treatment with thymoquinone (TQ) at a high dose (20 mg/kg) exerts a cardioprotective effect against isoproterenol (ISO)-triggered myocardial infarction (MI) in rats. In the present study, we tested the hypothesis that TQ, as a potent molecule, can exhibit cardioprotective effects at the lower dose for a short-term regimen. The rats were administered with TQ (5 mg/kg, intraperitoneal) at the 4 h interval for 2 days. ISO (100 mg/kg/day, subcutaneous) was given for 2 days to produce MI. ISO challenge results in deformation in ECG wave front, elevated left ventricular (LV) end-diastolic pressure, and reduced LVdP/dtmax and LVdP/dtmin. The levels of the cardiac biomarker in serum, such as creatine kinase MB, alanine aminotransferase, and aspartate aminotransferase, were increased. In the myocardium, a rise in malonaldehyde and decreased superoxide dismutase, glutathione, and catalase contents were observed. Furthermore, increased levels of tumor necrotic factor-α, interleukin-6, and interleukin-1β were observed in the myocardium. TQ pretreatment significantly normalized alterations in hemodynamic parameters, strengthened the antioxidant defense system, and decreased the contents of pro-inflammatory cytokines and hepatic enzymes as compared to the ISO group. Based on the results, TQ appears to be cardioprotective at low doses, and effective even administered for a shorter duration.

Vitamin D decreases silencer methylation to downregulate renin gene expression

Renin, encoded by REN, is an essential enzyme in the renin-angiotensin aldosterone system (RAAS) which is responsible for the maintenance of blood pressure homeostasis. Transcriptional regulation of REN has been linked to enhancer-promoter crosstalk, cAMP response element-binding protein (CREB), the active metabolite of vitamin D, 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), and a less well-characterized intronic silencer element. We hypothesized that in addition to these, differential DNA methylation is linked to REN expression and influenced by 1,25(OH)₂D₃. REN expressing cells (HEK293) were used to elucidate the effect of 1,25(OH)₂D₃ on REN methylation and expression as quantified by methylation-sensitive qPCR and RT-qPCR, respectively. In vitro 1,25(OH)₂D₃ supplementation (10 nM) induced significant hypomethylation of the REN silencer (P < 0.050), which was linked to a significant reduction in REN expression (P < 0.010) but had no effect on enhancer methylation. In addition, 1,25(OH)₂D₃ increased VDR (P < 0.05), as well as TET1 (P < 0.05) expression, suggesting an association between 1,25(OH)₂D₃ and DNA methylation. Thus, it appears that the silencer element, which is controlled by DNA methylation and influenced by 1,25(OH)₂D₃, plays an essential role in regulating REN expression.

Renin-angiotensin and sympathetic nervous system contribution to high blood pressure in Schlager mice

OBJECTIVE

Schlager hypertensive (BPH/2J) mice have been suggested to have high blood pressure (BP) due to an overactive sympathetic nervous system (SNS), but the contribution of the renin-angiotensin system (RAS) is unclear. In the present study, we examined the cardiovascular effects of chronically blocking the RAS in BPH/2J mice.

METHODS

Schlager normotensive (BPN/3J, n = 6) and BPH/2J mice (n = 8) received the angiotensin AT 1A-receptor antagonist losartan (150 mg/kg per day) in drinking water for 2 weeks. Pre-implanted telemetry devices were used to record mean arterial pressure (MAP), heart rate (HR) and locomotor activity.

RESULTS

MAP was reduced by losartan treatment in BPN/3J (-23 mmHg, P < 0.01) and in BPH/2J mice (-25 mmHg, P < 0.001), whereas HR was increased. Losartan had little effect on initial pressor responses to feeding or to stress, but did attenuate the sustained pressor response to cage-switch stress. During the active period, the hypotension to sympathetic blockade with pentolinium was greater in BPH/2J than BPN/3J (suggesting neurogenic hypertension), but was not affected by losartan. During the inactive period, a greater depressor response to pentolinium was observed in losartan-treated animals.

CONCLUSION

The hypotensive actions of losartan suggest that although the RAS provides an important contribution to BP, it contributes little, if at all, to the hypertension-induced or the greater stress-induced pressor responses in Schlager mice. The effects of pentolinium suggest that the SNS is mainly responsible for hypertension in BPH/2J mice. However, the RAS inhibits sympathetic vasomotor tone during inactivity and prolongs sympathetic activation during periods of adverse stress, indicating an important sympatho-modulatory role.

1,25-dihydroxyvitamin D3 suppresses renin gene transcription by blocking the activity of the cyclic AMP response element in the renin gene promoter

We have shown that 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) down-regulates renin expression. To explore the molecular mechanism, we analyzed the mouse Ren-1c gene promoter by luciferase reporter assays. Deletion analysis revealed two DNA fragments from -2,725 to -2,647 (distal fragment) and from -117 to +6 (proximal fragment) that are sufficient to mediate the repression. Mutation of the cAMP response element (CRE) in the distal fragment blunted forskolin stimulation as well as 1,25(OH)(2)D(3) inhibition of the transcriptional activity, suggesting the involvement of CRE in 1,25(OH)(2)D(3)-induced suppression. EMSA revealed that 1,25(OH)(2)D(3) markedly inhibited nuclear protein binding to the CRE in the promoter. ChIP and GST pull-down assays demonstrated that liganded VDR blocked the binding of CREB to the CRE by directly interacting with CREB with the ligand-binding domain, and the VDR-mediated repression can be rescued by CREB, CBP, or p300 overexpression. These data indicate that 1,25(OH)(2)D(3) suppresses renin gene expression at least in part by blocking the formation of CRE-CREB-CBP complex.

The human renin kidney enhancer is required to maintain base-line renin expression but is dispensable for tissue-specific, cell-specific, and regulated expression

Renin is the rate-limiting enzyme in the renin-angiotensin system and thus dictates the level of the pressor hormone angiotensin-II. The classical site of renin expression and secretion is the renal juxtaglomerular cell, where its expression is tightly regulated by physiological cues. An evolutionarily conserved transcriptional enhancer located 11 kb upstream of the human RENIN gene has been reported to markedly enhance transcription in renin expressing cells in vitro. However, its importance in vivo remains unclear. We tested whether this enhancer is required for appropriate tissue- and cell-specific expression, or for physiological regulation of the human RENIN gene. To accomplish this, we used a retrofitting technique employing homologous recombination in bacteria to delete the enhancer from a 160-kb P1-artificial chromosome containing human RENIN, two upstream genes and one downstream gene, and then generated two lines of transgenic mice. We previously showed that human renin expression in transgenic mice containing the wild type construct is tightly regulated as is expression of the linked genes. Deletion of the enhancer had no effect on tissue-specific expression of human RENIN, but using the downstream gene as an internal control, found that human RENIN mRNA levels were 3-10-fold decreased compared with constructs containing the enhancer. Despite this decrease in expression, renin protein remained localized to renal juxtaglomerular cells and was appropriately regulated by cues that either increase or decrease expression of renin. Our results suggest that sequences other than the enhancer may be necessary for tissue-specific, cell-specific, and regulated expression of human RENIN.