Renal denervation attenuates pressure overload-induced cardiac remodelling in rats with biphasic regulation of autophagy

Smilax glabra Roxb. flavonoids protect against pathological cardiac hypertrophy by inhibiting the Raf/MEK/ERK pathway: In vivo and in vitro studies

ETHNOPHARMACOLOGICAL RELEVANCE

Smilax glabra Roxb., the dry rhizome of Sarsaparilla, which is also known as Tu fuling (TFL) in China, is a well-known traditional CHINESE medicine that is widely used for detoxication, relieving dampness and as a diuretic. We have previously shown that the extracted TFL flavonoids (designated TFLF) possess anti-cardiac hypertrophy effects in vitro. However, the anti-cardiac hypertrophy effects of TFLF in vivo and the underlying mechanisms remain to be elucidated.

AIM OF THE STUDY

To reveal the underlying therapeutic mechanism of TFLF on cardiac hypertrophy by using transverse aortic constriction (TAC) model and cellular assays in vitro.

MATERIAL & METHODS

Cardiac hypertrophy was replicated by TAC surgery in rats or by isoprenaline treatment of rat H9C2 myocardial cells in vitro. Cardiac structure and function were evaluated by echocardiographic and hemodynamic examinations in vivo and histological analysis of tissues ex vivo. Biochemical kits and quantitative PCR were used to analyze markers of cardiac hypertrophy. Expression and phosphorylation of key proteins in the Raf/MEK/ERK pathway were quantified by Western blotting. We further confirmed our findings in H9C2 rat cardiomyocytes treated with isoprenaline and the ERK inhibitor in vitro.

RESULTS

TFLF attenuated cardiac hypertrophy and fibrosis and improved cardiac dysfunction in TAC rats. TFLF treatment induced a strong reduction in serum NT-proBNP levels. Cardiac hypertrophy marker gene (ANP, BNP and β-MHC) expression and the phosphorylation levels of c-Raf and ERK1/2 were decreased by TFLF treatment. TFLF also protected H9C2 cells from isoprenaline-induced hypertrophy in vitro via a similar molecular mechanism as that observed in the rat heart. Moreover, pretreatment with TRLF and the ERK inhibitor further inhibited the mRNA overexpression of hypertrophic genes in vitro.

CONCLUSIONS

TFLFs may protect against pathological cardiac hypertrophy via negative regulation of the Raf/MEK/ERK pathway. Thus, TFLFs are implicated as a potential pharmacological agent for treating cardiac hypertrophy in clinical practice.

Renal denervation reduces atrial remodeling in hypertensive rats with metabolic syndrome

Atrial fibrillation (AF) is highly prevalent in hypertensive patients with metabolic syndrome and is related to inflammation and activation of the sympathoadrenergic system. The multi-ligand Receptor-for-Advanced-Glycation-End-products (RAGE) activates inflammation-associated tissue remodeling and is regulated by the sympathetic nervous system. Its counterpart, soluble RAGE (sRAGE), serves as anti-inflammatory decoy receptor with protective properties. We investigated the effect of sympathetic modulation by renal denervation (RDN) on atrial remodeling, RAGE/sRAGE and RAGE ligands in metabolic syndrome. RDN was performed in spontaneously hypertensive obese rats (SHRob) with metabolic syndrome compared with lean spontaneously hypertensive rats (SHR) and with normotensive non-obese control rats. Blood pressure and heart rate were measured by telemetry. The animals were killed 12 weeks after RDN. Left atrial (LA) and right atrial (RA) remodeling was assessed by histological analysis and collagen types. Sympathetic innervation was measured by tyrosine hydroxylase staining of atrial nerve fibers, RAGE/sRAGE, RAGE ligands, cytokine expressions and inflammatory infiltrates were analyzed by Western blot and immunofluorescence staining. LA sympathetic nerve fiber density was higher in SHRob (+44%) versus controls and reduced after RDN (-64% versus SHRob). RAGE was increased (+718%) and sRAGE decreased (- 62%) in SHRob as compared with controls. RDN reduced RAGE expression (- 61% versus SHRob), significantly increased sRAGE levels (+162%) and induced a significant decrease in RAGE ligand levels in SHRob (- 57% CML and - 51% HMGB1) with reduced pro-inflammatory NFkB activation (- 96%), IL-6 production (- 55%) and reduced inflammatory infiltrates. This led to a reduction in atrial fibrosis (- 33%), collagen type I content (- 72%), accompanied by reduced LA myocyte hypertrophy (- 21%). Transfection experiments on H9C2 cardiomyoblasts demonstrated that RAGE is directly involved in fibrosis formation by influencing cellular production of collagen type I. In conclusion, suppression of renal sympathetic nerve activity by RDN prevents atrial remodeling in metabolic syndrome by reducing atrial sympathetic innervation and by modulating RAGE/sRAGE balance and reducing pro-inflammatory and pro-fibrotic RAGE ligands, which provides a potential therapeutic mechanism to reduce the development of AF.

Immediate Renal Denervation After Acute Myocardial Infarction Mitigates the Progression of Heart Failure via the Modulation of IL-33/ST2 Signaling

Objective: Previous studies have demonstrated the protective effects of renal denervation (RDN) in pre-existing heart failure, but the effects of immediate RDN after acute myocardial infarction (AMI) on subsequent cardiac remodeling have not been reported. This study aimed to investigate the cardioprotective effects of immediate RDN after AMI and its underlying mechanism.

Methods: AMI was induced by intracoronary gelatin sponge embolization in 14 Shanghai white pigs that were randomized to undergo either renal angiography (AMI+sham group) or RDN (AMI+RDN group) after 1 h of hemodynamic monitoring. Cardiac function of the two groups was measured at baseline, 1 h post-AMI and at the 1 month follow-up (1M-FU) by transthoracic echocardiography (TTE). Plasma NT-proBNP, soluble ST2 (sST2), norepinephrine (NE), and renin-angiotensin-aldosterone system activity were detected simultaneously. The renal cortex was harvested for NE measurement after the 1M-FU, and the renal arteries were stained with tyrosine hydroxylase for the evaluation of sympathetic activity. Heart tissues in the non-ischemic areas were collected to assess histological and molecular left ventricular (LV) remodeling by pathological staining, RT-PCR, and western blotting.

Results: There was no difference in the hemodynamic stability or cardiac function between the two groups at baseline and 1 h post-AMI. Six pigs from each of the two groups completed the 1M-FU. TTE analysis revealed the improved cardiac function of immediate RDN in the AMI+RDN group and circulating NT-proBNP levels were lower than those in the AMI+sham group. Further analysis showed significantly less interstitial fibrosis in the remote non-ischemic myocardium after immediate RDN, together with decreased cardiomyocyte hypertrophy and inflammatory cell infiltration. sST2 levels in circulating and myocardial tissues of animals in the AMI+RDN group were significantly higher than those in the AMI+sham group, accompanied by corresponding alterations in IL-33/ST2 and downstream signaling.

Conclusions: Immediate RDN can improve cardiac function and myocardial remodeling after AMI via modulation of IL-33/ST2 and downstream signaling.

MicroRNA-17-5p Promotes Cardiac Hypertrophy by Targeting Mfn2 to Inhibit Autophagy

Pathological cardiac hypertrophy is the leading cause of heart failure, and miRNAs have been recognized as key factors in cardiac hypertrophy. This study aimed to elucidate whether miR-17-5p affects cardiac hypertrophy by targeting the mitochondrial fusion protein mitofusin 2 (Mfn2)-mediated phosphatidylinositol-3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway and regulating autophagy. miR-17-5p expression was shown to be upregulated both in vivo and in vitro. In addition, a miR-17-5p inhibitor significantly reversed AngII-induced cell hypertrophy in neonatal rat left ventricle myocytes (NRVMs). In contrast to miR-17-5p expression, Mfn2 expression was inhibited in rat hearts at 4 weeks after transverse aortic constriction (TAC) and in an Ang II-induced cell hypertrophy model. We examined miR-17-5p targeting of Mfn2 by dual luciferase reporter and Western blot assays. In addition, we also verified the relationship between Mfn2 and the PI3K/AKT/mTOR pathway. Mfn2 overexpression attenuated miR-17-5p-induced cell hypertrophy, and in rat myocardial tissue, miR-17-5p induced autophagy inhibition. In summary, the results of the present study demonstrated that miR-17-5p inhibits Mfn2 expression, activates the PI3K/AKT/mTOR pathway and suppresses autophagy to promote cardiac hypertrophy.

Reversible Treatment of Pressure Overload-Induced Left Ventricular Hypertrophy through Drd5 Nucleic Acid Delivery Mediated by Functional Polyaminoglycoside

Left ventricular hypertrophy and fibrosis are major risk factors for heart failure, which require timely and effective treatment. Genetic therapy has been shown to ameliorate hypertrophic cardiac damage. In this study, it is found that in mice, the dopamine D5 receptor (D5R) expression in the left ventricle (LV) progressively decreases with worsening of transverse aortic constriction-induced left ventricular hypertrophy. Then, a reversible treatment of left ventricular hypertrophy with Drd5 nucleic acids delivered by tobramycin-based hyperbranched polyaminoglycoside (SS-HPT) is studied. The heart-specific increase in D5R expression by SS-HPT/Drd5 plasmid in the early stage of left ventricular hypertrophy attenuates cardiac hypertrophy and fibrosis by preventing oxidative and endoplasmic reticulum (ER) stress and ameliorating autophagic dysregulation. By contrast, SS-HPT/Drd5 siRNA promotes the progression of left ventricular hypertrophy and accelerates the deterioration of myocardial function into heart failure. The reduction in cardiac D5R expression and dysregulated autophagy are observed in patients with hypertrophic cardiomyopathy and heart failure. The data show a cardiac-specific beneficial effect of SS-HPT/Drd5 plasmid on myocardial remodeling and dysfunction, which may provide an effective therapy of patients with left ventricular hypertrophy and heart failure.

Renal denervation improves vascular endothelial dysfunction by inducing autophagy via AMPK/mTOR signaling activation in a rat model of type 2 diabetes mellitus with insulin resistance

BACKGROUND

Recent clinical and animal studies have shown that renal denervation (RDN) improves insulin sensitivity and endothelial dysfunction. However, the specific mechanism remains incompletely understood. The purpose of this study is to investigate the effects of RDN on endothelial dysfunction of type 2 diabetes mellitus (T₂DM) rat models with insulin resistance and to explore the underlying molecular mechanisms.

METHODS

Male Sprague-Dawley rats were fed with or without high-fat diet allocated in different groups, combined with low-dose streptozotocin which induces a rat model to develop T₂DM with insulin resistance. RDN was conducted 1 week after the rat models fully developed T₂DM. The animals were sub-divided into four groups randomly: control group (CON, n = 6), diabetic group (T₂DM, n = 6), diabetic with sham surgery group (Sham, n = 6) and diabetic with RDN group (RDN, n = 6). Rats in all groups were studied at baseline, both preoperatively and 4 weeks after RDN, respectively. Western blot was used to detect the expression of angiotensin-converting enzyme 2 (ACE2) protein and the expression of autophagy-related proteins Beclin1, LC3 and p62 and autophagy signaling pathway AMPK/mTOR proteins and apoptosis-related protein caspase-3 in the aorta endothelial cells. In addition, the effects of ACE2 on autophagy of human umbilical vein insulin resistance endothelial cell culture in vitro were also studied.

RESULTS

RDN decreased plasma and renal tissue norepinephrine levels. The Von Willebrand factor level was also decreased, while the plasma level of nitric oxide (NO) was significantly increased after RDN. Compared with the T₂DM group and the Sham group, the endothelium-dependent and endothelium-independent diastolic function of the RDN group was improved significantly, the expression of Beclin1, LC3, ACE2 and eNOS proteins was higher, and the level of p62 protein was decreased. Furthermore, we found that RDN can activate the expression of p-AMPK and inhibit the expression of p-mTOR. In cell culture experiment, ACE2 activated p-AMPK and inhibited p-mTOR, thus promoting autophagy.

CONCLUSIONS

RDN may not only increase the expression of ACE2 in the vascular endothelium, but also can via ACE2 activate p-AMPK and inhibit p-mTOR, thus promoting autophagy and improving endothelial dysfunction.

Inhibiting SLC26A4 reverses cardiac hypertrophy in H9C2 cells and in rats

Background

It has been confirmed that mutations in solute carrier family 26 member 4 (SLC26A4) contribute to pendred syndrome. However, the role of SLC26A4 in cardiac hypertrophy and the signaling pathways remain unclear.

Methods

Cardiomyocytes were treated by 200 µM phenylephrine (PE) to induce cardiac hypertrophy. Also, the expression of SLC26A4, GSK3, cardiac hypertrophy markers including atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) was detected through real-time quantitative polymerase chain reaction (RT-qPCR). Flow cytometry assay was used to test the apoptosis of PE-induced cardiomyocytes transfected by small interfere RNA (siRNA)-SLC26A4. Furthermore, we detected the expression of autophagy-related markers including light chain 3 (LC3) and P62. Finally, we established a rat model of abdominal aortic constriction (AAC)-induced cardiac hypertrophy in vivo.

Results

RT-qPCR results showed that the mRNA expression of SLC26A4 was significantly up-regulated in PE-induced cardiac hypertrophy. After inhibiting SLC26A4, the release of ANP and BNP was significantly decreased and GSK3β was elevated in vivo and in vitro. Furthermore, inhibiting SLC26A4 promoted apoptosis of cardiac hypertrophy cells. In addition, LC3 was down-regulated and P62 was enhanced after transfection of siRNA-SLC26A4.

Conclusion

Our findings revealed that SLC26A4 increases cardiac hypertrophy, and inhibiting SLC26A4 could decrease the release of ANP/BNP and promote the expression of GSK-3β in vitro and in vivo. Moreover, SLC26A4 silencing inhibits autophagy of cardiomyocytes and induces apoptosis of cardiomyocytes. Therefore, SLC26A4 possesses potential value to be a therapeutic target of cardiac hypertrophy, and our study provides new insights into the mechanisms of cardiac hypertrophy.

miR-29a promotes pathological cardiac hypertrophy by targeting the PTEN/AKT/mTOR signalling pathway and suppressing autophagy

AIM

Although miR-29 has emerged as a crucial non-coding RNA in the regulation of pathological cardiac hypertrophy, further exploration of its specific mechanisms is necessary to resolve controversy about its major role in this condition. This study therefore evaluated the role of miR-29a and whether it acts through the PTEN/AKT/mTOR pathway.

METHODS

In this study, a rat model of pressure-induced cardiac hypertrophy was established by transverse aortic constriction and verified by echocardiography, histological analysis and quantitative RT-PCR. At the cellular level, we explored the role of miR-29a in angiotensin II-stimulated hypertrophic H9c2 cardiomyoblasts by transfecting the cells with miR-29a inhibitor and mimic. The relationship between miR-29a and the signalling pathway was investigated with dual luciferase reporter assays, immunofluorescence analysis and Western blotting. We also examined whether autophagy is involved in the regulatory mechanism of miR-29a through transmission electron microscopy and detection of autophagy-associated proteins.

RESULTS

The results showed that miR-29a was upregulated both in rats 4 weeks after surgery and in 10^-6  M angiotensin II-stimulated cells. In contrast, inhibition of miR-29a partially attenuated angiotensin II-induced hypertrophy. Additionally, bioinformatics analysis revealed that PTEN was one of the target genes of miR-29a, which was also verified by luciferase assay. The results of immunofluorescence and Western blotting indicated that overexpression of miR-29a inhibited the expression of PTEN, activated the AKT/mTOR pathway and suppressed autophagy, which ultimately led to cardiac hypertrophy.

CONCLUSION

In pathological cardiac hypertrophy, miR-29a was overexpressed and promoted cardiac hypertrophy by regulating the PTEN/AKT/mTOR pathway and suppressing autophagy.