Genes overexpressed in cerebral arteries following salt-induced hypertensive disease are regulated by angiotensin II, JunB, and CREB

Molecular mechanisms underlying hypertensive effect of fructose and the preventive properties of inulin - Global transcriptomic analysis in rat aorta

BACKGROUND AND AIMS

Excessive intake of fructose is a significant contributor in the development of hypertension and pathogenesis of cardiometabolic diseases. We previously showed that dietary inulin can prevent fructose-induced hypertension in rats. Nevertheless, molecular mechanisms of both fructose and inulin in aorta remain unknown. The aim of this study was to identify global transcriptomic changes in aorta in rats on fructose-based diet or partial substitution of dietary fructose with inulin.

METHODS AND RESULTS

At the end of study periods, aortas were isolated, RNA extracted, and transcriptomics performed using microarrays followed by in-dept bioinformatic analyses. We observed that fructose-based diet affected the expression of over 1700 genes involved in the regulation of vascular functions, cell signaling, and cellular metabolism. Partial substitution of dietary fructose with inulin affected the expression of over 1300 genes regulating endothelial and vascular functions, including relaxin signaling pathway, immune/inflammatory response, or cellular metabolism. Bioinformatic analyses revealed transcription factors, such as Junb or Nr4a2, and miRNAs, such as miR-206, miR-137 or miR-375, as potential transcriptional and post-transcriptional regulators of identified differentially expressed genes. Genes identified following both diets are associated with development of cardiovascular diseases, hypertension, immune system diseases and metabolic diseases. Moreover, a negative correlation between the expression profiles obtained by fructose-based diet and that by partial substitution of dietary fructose with inulin was observed.

CONCLUSION

Our study showed that fructose can significantly impact global transcriptomic profile in aorta, changes that can be counteracted by inulin and which present relevant molecular mechanisms underlying its anti-hypertensive property.

Activation of Nrf2 contributes to the protective effect of Exendin-4 against angiotensin II-induced vascular smooth muscle cell senescence

Oxidative stress and impaired antioxidant defense are believed to be contributors to the cardiovascular aging process. The transcription factor nuclear factor-E2-related factor 2 (Nrf2) plays a key role in orchestrating cellular antioxidant defenses and maintaining redox homeostasis. Our previous study showed that Exendin-4, a glucagon-like peptide-1 analog, alleviates angiotensin II (ANG II)-induced vascular smooth muscle cell (VSMC) senescence by inhibiting Rac1 activation via cAMP/PKA (Zhao L, Li AQ, Zhou TF, Zhang MQ, Qin XM. Am J Physiol Cell Physiol 307: C1130-C1141, 2014). The objective of this study is to investigate if Nrf2 mediates the antisenescent effect of Exendin-4 in ANG II-induced VSMCs. Here we report that Exendin-4 triggered Nrf2 nuclear translocation, a downstream target of cAMP-responsive element-binding protein (CREB) and expressions of antioxidant genes heme oxygenase-1 (HO-1) and NAD(P)H quinone oxidoreductase-1 (NQO-1) in a dose- and time-dependent manner. In addition, knock-down of Nrf2 attenuated the inhibitory effects of Exendin-4 on ANG II-induced superoxidant generation and VSMC senescence. PKA/CREB pathway participated in the upregulations of HO-1 and NQO-1 induced by Exendin-4. Notably, our study revealed that Exendin-4 dose-dependently increased the acetylation of Nrf2 and the recruitment of transcriptional coactivator CREB binding protein (CBP) to Nrf2. The Exendin-4-induced Nrf2 transactivation was diminished in the presence of CBP small interfering RNA. Microscope imaging of Nrf2, as well as immunoblotting for Nrf2, showed that the Exendin-4-evoked Nrf2 acetylation favored its nuclear retention. Importantly, CBP silencing attenuated the suppressing effects of Exendin-4 on ANG II-induced VSMC senescence and superoxidant production. In conclusion, these results provide a mechanistic insight into how Nrf2 signaling mediates the antisenescent and antioxidative effects induced by Exendin-4 in VSMCs.

Differential gene expression in multiple neurological, inflammatory and connective tissue pathways in a spontaneous model of human small vessel stroke

AIMS

Cerebral small vessel disease (SVD) causes a fifth of all strokes plus diffuse brain damage leading to cognitive decline, physical disabilities and dementia. The aetiology and pathogenesis of SVD are unknown, but largely attributed to hypertension or microatheroma.

METHODS

We used the spontaneously hypertensive stroke-prone rat (SHRSP), the closest spontaneous experimental model of human SVD, and age-matched control rats kept under identical, non-salt-loaded conditions, to perform a blinded analysis of mRNA microarray, qRT-PCR and pathway analysis in two brain regions (frontal and mid-coronal) commonly affected by SVD in the SHRSP at age five, 16 and 21 weeks.

RESULTS

We found gene expression abnormalities, with fold changes ranging from 2.5 to 59 for the 10 most differentially expressed genes, related to endothelial tight junctions (reduced), nitric oxide bioavailability (reduced), myelination (impaired), glial and microglial activity (increased), matrix proteins (impaired), vascular reactivity (impaired) and albumin (reduced), consistent with protein expression defects in the same rats. All were present at age 5 weeks thus predating blood pressure elevation. 'Neurological' and 'inflammatory' pathways were more affected than 'vascular' functional pathways.

CONCLUSIONS

This set of defects, although individually modest, when acting in combination could explain the SHRSP's susceptibility to microvascular and brain injury, compared with control rats. Similar combined, individually modest, but multiple neurovascular unit defects, could explain susceptibility to spontaneous human SVD.

High-salt diet and hypertension: focus on the renin-angiotensin system

A high-salt diet is one of the major risk factors in the development and maintenance of hypertension. Numerous experimental and observational studies have confirmed the association of sodium intake with blood pressure levels. The effects of a high-salt diet are related to the function of the renin-angiotensin system, which is normally suppressed by a high-salt diet. Endothelial dysfunction probably plays an important role in the influence of high sodium intake on blood pressure, although the exact mechanisms remain elusive. Genetic factors are known to be very important, and various consomic and congenic rat strains as animal models have proven to be very useful in bringing us a step closer to understanding the interaction between salt intake and hypertension. In this article, experimental data obtained in studies on animals and humans, as well as epidemiological data are reviewed.

Defining a rat blood pressure quantitative trait locus to a <81.8 kb congenic segment: comprehensive sequencing and renal transcriptome analysis

Evidence from multiple linkage and genome-wide association studies suggest that human chromosome 2 (HSA2) contains alleles that influence blood pressure (BP). Homologous to a large segment of HSA2 is rat chromosome 9 (RNO9), to which a BP quantitative trait locus (QTL) was previously mapped. The objective of the current study was to further resolve this BP QTL. Eleven congenic strains with introgressed segments spanning <81.8 kb to <1.33 Mb were developed by introgressing genomic segments of RNO9 from the Dahl salt-resistant (R) rat onto the genome of the Dahl salt-sensitive (S) rat and tested for BP. The congenic strain with the shortest introgressed segment spanning <81.8 kb significantly lowered BP of the hypertensive S rat by 25 mmHg and significantly increased its mean survival by 45 days. In contrast, two other congenic strains had increased BP compared with the S. We focused on the <81.8 kb congenic strain, which represents the shortest genomic segment to which a BP QTL has been mapped to date in any species. Sequencing of this entire region in both S and R rats detected 563 variants. The region did not contain any known or predicted rat protein coding genes. Furthermore, a whole genome renal transcriptome analysis between S and the <81.8 kb S.R congenic strain revealed alterations in several critical genes implicated in renal homeostasis. Taken together, our results provide the basis for future studies to examine the relationship between the candidate variants within the QTL region and the renal differentially expressed genes as potential causal mechanisms for BP regulation.

Placenta growth factor (PlGF), a novel inducer of plasminogen activator inhibitor-1 (PAI-1) in sickle cell disease (SCD)

Sickle cell disease (SCD) is characterized by a prothrombotic state. Plasminogen activator inhibitor-1 (PAI-1) is known to modulate fibrinolysis, lung injury/fibrosis, and angiogenesis. However, its role in SCD is less understood, and the molecular mechanisms underlying increased PAI-1 are unknown. Herein, we show a novel link between PAI-1 and sickle erythropoiesis. Plasma PAI-1 levels were high in SCD patients at steady state and in two humanized sickle mouse models, with increased PAI-1 immunolabeling in sickle mouse lung, bronchial epithelial cells, alveolar macrophages, and pulmonary microvascular endothelial cells. Placenta growth factor (PlGF), released at high levels by sickle erythroblasts, induced PAI-1 expression in primary human pulmonary microvascular endothelial cells and monocytes through activation of c-Jun N-terminal kinase (JNK), NADPH oxidase, and hypoxia-inducible factor-1alpha (HIF-1alpha). Analysis of the human PAI-1 promoter revealed this induction was mediated by hypoxia-response element (HRE)-1, HRE-2, and distal activator protein (AP-1) sites. We also identify the involvement of c-Jun, c-Jun/c-Fos, and JunD, but not JunB, in binding with AP-1 sites of the PAI-1 promoter upon PlGF induction. Consistent with these findings, levels of PAI-1 were low in PlGF knock-out mice and sickle-PlGF knock-out mice; overexpression of PlGF in normal mice increased circulating PAI-1. In conclusion, we identify a novel mechanism of PAI-1 elevation in SCD.

Regulation of aldosterone synthase by activator transcription factor/cAMP response element-binding protein family members

Aldosterone synthesis is regulated by angiotensin II (Ang II) and K(+) acting in the adrenal zona glomerulosa, in part through the regulation of aldosterone synthase (CYP11B2). Here, we analyzed the role of cAMP response element (CRE)-binding proteins (CREBs) in the regulation of CYP11B2. Expression analysis of activator transcription factor (ATF)/CREB family members, namely the ATF1 and ATF2, the CREB, and the CRE modulator, in H295R cells and normal human adrenal tissue was performed using quantitative real-time PCR. Ang II-induced phosphorylation of ATF/CREB members was analyzed by Western blot analysis, and their subsequent binding to the CYP11B2 promoter using chromatin immunoprecipitation assay. Aldosterone production and CYP11B2 expression were measured in small interfering RNA-transfected cells to knockdown the expression of ATF/CREB members. CYP11B2 promoter activity was measured in H295R cells cotransfected with NURR1 (NR4A2) alone or with constitutively active vectors for ATF/CREB members. Ang II induced phosphorylation of ATF1, ATF2, and CRE modulator in a time-dependent manner. Based on chromatin immunoprecipitation analysis, there was an increased association of these proteins with the CYP11B2 promoter after Ang II and K(+) treatment. Phosphorylated ATF/CREB members also bound the CYP11B2 promoter. Knockdown of ATF/CREB members reduced Ang II and K(+) induction of adrenal cell CYP11B2 mRNA expression and aldosterone production. The constitutively active ATF/CREB vectors increased the promoter activity of CYP11B2 and had a synergistic effect with NURR1. In summary, these results suggest that ATF/CREB and NGFI-B family members play a crucial role in the transcriptional regulation of CYP11B2 and adrenal cell capacity to produce aldosterone.

Essential hypertension: is there a role for inflammatory mechanisms?

Inflammation is a key feature in the initiation, progression, and clinical implications of cardiovascular disorders, including essential hypertension. Increasing evidence shows that activation of renin-angiotensin-aldosterone system and enhanced local production of angiotensin II have been implicated in the pathophysiology of inflammation. Besides being a potent vasoactive peptide, angiotensin II regulates the inflammatory process. Specifically, it increases vascular permeability, participates in the recruitment of inflammatory cells and their adhesion to the activated endothelium, and regulates cell growth and fibrosis. Reactive oxygen species are implicated at every stage in inflammation and activate multiple intracellular signaling molecules and transcription factors associated with inflammatory responses, such as nuclear factor-kappa B and activator protein-1. Other components of the renin-angiotensin-aldosterone system, including aldosterone and/or mineralocorticoid receptor, induce the production of reactive oxygen species and participate in vascular inflammation. Several studies suggest a role of endothelin-1 as an important mediator of chronic inflammation and there is an increasing interest in the relationship between endothelin-1 and reactive oxygen species. These data may have great impact on future therapeutic strategies.

The AP-1 site is essential for the promoter activity of NOX1/NADPH oxidase, a vascular superoxide-producing enzyme: Possible involvement of the ERK1/2-JunB pathway

NADPH oxidase is a major source of the superoxide produced in cardiovascular tissues. The expression of NOX1, a catalytic subunit of NADPH oxidase, is induced by various vasoactive factors, including angiotensin II, prostaglandin (PG) F(2alpha), and platelet-derived growth factor (PDGF). It was reported previously that the inducible expression of NOX1 is governed by the activating transcription factor-1 (ATF-1)-myocyte enhancer factor 2B (MEF2B) cascade downstream of phosphoinositide 3 (PI3) kinase. It was also reported that extracellular signal-regulated kinase (ERK) 1/2 is involved in the expression of NOX1. To further clarify the factors involved in NOX1 induction downstream of ERK1/2, the promoter region of the NOX1 gene was analyzed. A consensus activator protein-1 (AP-1) site was found at -98/-92 in the 5'-flanking region of the rat NOX1 gene. The introduction of mutations at this site abolished PGF(2alpha)-induced transcriptional activation in a luciferase assay. Electrophoresis mobility shift assays demonstrated that PGF(2alpha) and PDGF augmented the binding of JunB to this sequence. PD98059, an inhibitor of MAPK/ERK kinase, suppressed the expression of JunB induced by PGF(2alpha) or PDGF. These results suggest that the ERK1/2-JunB pathway is a key regulator of the inducible expression of the NOX1 gene in vascular smooth muscle cells.

Role of the renin-angiotensin system in vascular inflammation

Angiotensin (Ang) II, the main effector of the renin-angiotensin system (RAS), is one of the major mediators of vascular remodeling in hypertension. Besides being a potent vasoactive peptide, Ang II exerts proinflammatory effects on the vasculature by inducing integrins, adhesion molecules, cytokines and growth and profibrotic mediators through activation of redox-sensitive pathways and transcription factors. Clinical findings suggest that inflammation participates in the mechanisms involved in the pathophysiology of hypertension and its complications. Antagonists of the RAS have been shown to exert cardiovascular protection, in part through their vascular anti-inflammatory effects. However, further studies are needed to better understand whether inflammatory biomarkers might be clinically useful for cardiovascular risk stratification and whether targeting inflammation pharmacologically will improve cardiovascular outcomes beyond blood pressure reduction. The present review addresses recent findings regarding the pathophysiology of vascular inflammation in hypertension, focusing specifically on the role of Ang II.