Mixed lineage kinase-3 prevents cardiac dysfunction and structural remodeling with pressure overload

Guidelines for assessing ventricular pressure-volume relationships in rodents

Ventricular catheterization with a pressure-volume (PV) catheter is the gold-standard method for assessing in vivo cardiac function in animal studies, providing valuable "load-independent" indices of systolic and diastolic heart performance. PV studies are commonly performed to elucidate mechanistic insights into cardiovascular disease using surgical and genetically engineered rat and mouse models, but there is considerable heterogeneity in how these studies are performed. Wide variation in protocol design, volume calibration, anesthesia, manipulation of cardiac loading conditions, how load-independent indices of cardiac function are derived, as well as in data analysis and reporting is constraining reliability and reproducibility in the field. The purpose of this manuscript is to combine our collective expertise in performing open- and closed-chest left and right ventricle PV studies in rodents to provide consensus guidelines on how to perform, analyze, and interpret these studies using either conductance or admittance PV catheters. We first review recent methodological reporting in rodent PV studies in this journal and discuss important details required to improve reproducibility within and across PV studies. We then recommend steps to obtain high-quality PV data, from volume calibration to choice of anesthetic agent and acquiring load-independent indices of both systolic and diastolic function. We also consider between- and within-animal variation and recommend how to perform data analysis and visualization. We hope that this consensus paper guides those performing PV studies in rodents and helps align the field with best practices in surgical/analytical methodologies and reporting, facilitating better reliability and reproducibility in the PV field.

The splicing factor hnRNPL demonstrates conserved myocardial regulation across species and is altered in heart failure

Heart failure (HF) is highly prevalent. Mechanisms underlying HF remain incompletely understood. Splicing factors (SF), which control pre-mRNA alternative splicing, regulate cardiac structure and function. This study investigated regulation of the splicing factor heterogeneous nuclear ribonucleoprotein-L (hnRNPL) in the failing heart. hnRNPL protein increased in left ventricular tissue from mice with transaortic constriction-induced HF and from HF patients. In left ventricular tissue, hnRNPL was detected predominantly in nuclei. Knockdown of the hnRNPL homolog Smooth in Drosophila induced cardiomyopathy. Computational analysis of predicted mouse and human hnRNPL binding sites suggested hnRNPL-mediated alternative splicing of tropomyosin, which was confirmed in C2C12 myoblasts. These findings identify hnRNPL as a sensor of cardiac dysfunction and suggest that disturbances of hnRNPL affect alternative splicing in HF.

The role of JNK signaling pathway in organ fibrosis

BACKGROUND

Fibrosis is a tissue damage repair response caused by multiple pathogenic factors which could occur in almost every apparatus and leading to the tissue structure damage, physiological abnormality, and even organ failure until death. Up to now, there is still no specific drugs or strategies can effectively block or changeover tissue fibrosis. JNKs, a subset of mitogen-activated protein kinases (MAPK), have been reported that participates in various biological processes, such as genetic expression, DNA damage, and cell activation/proliferation/death pathways. Increasing studies indicated that abnormal regulation of JNK signal pathway has strongly associated with tissue fibrosis.

AIM OF REVIEW

This review designed to sum up the molecular mechanism progresses in the role of JNK signal pathway in organ fibrosis, hoping to provide a novel therapy strategy to tackle tissue fibrosis.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Recent evidence shows that JNK signaling pathway could modulates inflammation, immunoreaction, oxidative stress and Multiple cell biological functions in organ fibrosis. Therefore, targeting the JNK pathway may be a useful strategy in cure fibrosis.

20(S)-ginsenoside Rh2 inhibits angiotensin-2 mediated cardiac remodeling and inflammation associated with suppression of the JNK/AP-1 pathway

BACKGROUND

Enhanced levels of angiotensin-2 (Ang-II) causes hypertensive heart failure (HHF) through non-hemodynamical and hemodynamical alterations. 20(S)-ginsenoside Rh2 (20(S)-Rh2) is a natural ginseng compound with numerous cardiovascular benefits. This investigation elucidates the influence of 20(S)-Rh2 on Ang-II-induced heart failure and cardiac alterations.

METHODS

Ang-II was administered in C57BL/6 mice for 4 weeks to induce HHF. In the last 2 weeks of treatment, 20(S)-Rh2 was orally administered in mice to assess the potential 20(S)-Rh2 mechanism. Subsequently, RNA sequencing was carried out.

RESULTS

It was indicated that 20(S)-Rh2 suppresses myocardial fibrosis, hypertrophy, and inflammation, thereby inhibiting cardiac disruption in Ang-II-challenged mice without affecting blood pressure. According to the RNA sequencing data, this cardio-protective effect was linked with the (JNK)/AP 1 pathway. 20(S)-Rh2 alleviated heart tissue and cardiomyocytes inflammation by inhibiting the Ang-II-mediated JNK/AP-1 pathway. Within cardiomyocytes, JNK or AP-1 absence abolished the anti-inflammatory effects of 20(S)-Rh2.

CONCLUSION

This study investigation indicated that 20(S)-Rh2 prevents cardiovascular dysfunction induced by Ang-II induced by decreasing JNK-regulated inflammatory responses, providing evidence for its use as an efficient regimen for HHF.

Ginsenoside Rg5 alleviates Ang II-induced cardiac inflammation and remodeling by inhibiting the JNK/AP-1 pathway

Increased level of Angiotensin II (Ang II) contributes to hypertensive heart failure via -hemodynamic and non-hemodynamic actions. Ginsenoside Rg5 (Rg5) occurs naturally in ginseng, which has shown various benefits for cardiovascular diseases. This study evaluated Rg5's effects on Ang II-caused cardiac remodeling and heart failure. C57BL/6 mice developed hypertensive cardiac failure after four weeks of Ang II infusion. The mice were administered Rg5 via oral gavage for the last two weeks to investigate the potential mechanism of Rg5. RNA sequencing of heart tissues was performed for mechanistic studies. It was discovered that Rg5 inhibited cardiac inflammation, myocardial fibrosis, and hypertrophy, and prevented cardiac malfunction in mice challenged with Ang II, without altering blood pressure. RNA sequencing showed that Rg5's cardioprotective effect involves the JNK/AP-1 signaling pathway. Rg5 diminished inflammation in mice hearts and cultured cardiomyocytes by blocking Ang II-activated JNK/AP-1 pathway. In the absence of JNK or AP-1 in cardiomyocytes, the anti-inflammatory effects of Rg5 were nullified. The study found that Rg5 preserved the hearts of Ang II-induced mice by reducing JNK-mediated inflammatory responses, suggesting that Rg5 is an effective therapy for hypertensive heart failure.

hnRNPL expression dynamics in the embryo and placenta

Heterogeneous nuclear ribonucleoprotein L (hnRNPL) is a conserved RNA binding protein (RBP) that plays an important role in the alternative splicing of gene transcripts, and thus in the generation of specific protein isoforms. Global deficiency in hnRNPL in mice results in preimplantation embryonic lethality at embryonic day (E) 3.5. To begin to understand the contribution of hnRNPL-regulated pathways in the normal development of the embryo and placenta, we determined hnRNPL expression profile and subcellular localization throughout development. Proteome and Western blot analyses were employed to determine hnRNPL abundance between E3.5 and E17.5. Histological analyses supported that the embryo and implantation site display distinct hnRNPL localization patterns. In the fully developed mouse placenta, nuclear hnRNPL was observed broadly in trophoblasts, whereas within the implantation site a discrete subset of cells showed hnRNPL outside the nucleus. In the first-trimester human placenta, hnRNPL was detected in the undifferentiated cytotrophoblasts, suggesting a role for this factor in trophoblast progenitors. Parallel in vitro studies utilizing Htr8 and Jeg3 cell lines confirmed expression of hnRNPL in cellular models of human trophoblasts. These studies [support] coordinated regulation of hnRNPL during the normal developmental program in the mammalian embryo and placenta.

A time-series minimally invasive transverse aortic constriction mouse model for pressure overload-induced cardiac remodeling and heart failure

Transverse aortic constriction (TAC) is a widely-used animal model for pressure overload-induced cardiac hypertrophy and heart failure (HF). The severity of TAC-induced adverse cardiac remodeling is correlated to the degree and duration of aorta constriction. Most studies of TAC are performed with a 27-gauge needle, which is easy to cause a tremendous left ventricular overload and leads to a rapid HF, but it is accompanied by higher mortality attributed to tighter aortic arch constriction. However, a few studies are focusing on the phenotypes of TAC applied with a 25-gauge needle, which produces a mild overload to induce cardiac remodeling and has low post-operation mortality. Furthermore, the specific timeline of HF induced by TAC applied with a 25-gauge needle in C57BL/6 J mice remains unclear. In this study, C57BL/6 J mice were randomly subjected to TAC with a 25-gauge needle or sham surgery. Echocardiography, gross morphology, and histopathology were applied to evaluate time-series phenotypes in the heart after 2, 4, 6, 8, and 12 weeks. The survival rate of mice after TAC was more than 98%. All mice subjected to TAC maintained compensated cardiac remodeling during the first two weeks and began to exhibit heart failure characteristics after 4 weeks upon TAC. At 8 weeks post-TAC, the mice showed severe cardiac dysfunction, hypertrophy, and cardiac fibrosis compared to sham mice. Moreover, the mice raised a severe dilated HF at 12 weeks. This study provides an optimized method of the mild overload TAC-induced cardiac remodeling from the compensatory period to decompensatory HF in C57BL/6 J mice.

Mixed lineage kinase 3 requires a functional CRIB domain for regulation of blood pressure, cardiac hypertrophy, and left ventricular function

Mixed lineage kinase 3 (MLK3) modulates blood pressure and left ventricular function, but the mechanisms governing these effects remain unclear. In the current study, we therefore investigated the role of the MLK3 Cdc42/Rac interactive binding (CRIB) domain in cardiovascular physiology. We examined baseline and left ventricular pressure overload responses in a MLK3 CRIB mutant (MLK3C/C) mouse, which harbors point mutations in the CRIB domain to disrupt MLK3 activation by Cdc42. Male and female MLK3C/C mice displayed increased invasively measured blood pressure compared with wild-type (MLK3+/+) littermate controls. MLK3C/C mice of both sexes also developed left and right ventricular hypertrophy but normal baseline LV function by echocardiography and invasive hemodynamics. In LV tissue from MLK3C/C mice, map3k11 mRNA, which encodes MLK3, and MLK3 protein were reduced by 74 ± 6% and 73 ± 7%, respectively. After 1-wk LV pressure overload with 25-gauge transaortic constriction (TAC), male MLK3C/C mice developed no differences in LV hypertrophy but displayed reduction in the LV systolic indices ejection fraction and dP/dt normalized to instantaneous pressure. JNK activation was also reduced in LV tissue of MLK3C/C TAC mice. TAC induced MLK3 translocation from cytosolic fraction to membrane fraction in LV tissue from MLK3+/+ but not MLK3C/C mice. These findings identify a role of the MLK3 CRIB domain in MLK3 regulation of basal blood pressure and cardiac morphology, and in promoting the compensatory LV response to pressure overload.NEW & NOTEWORTHY Here, we identified that the presence of two discrete point mutations within the Cdc42/Rac interaction and binding domain of the protein MLK3 recapitulates the effects of whole body MLK3 deletion on blood pressure, cardiac hypertrophy, and left ventricular compensation after pressure overload. These findings implicate the CRIB domain, and thus MLK3 activation by this domain, as critical for maintenance of cardiovascular homeostasis.

New Progress in the Molecular Regulations and Therapeutic Applications in Cardiac Oxidative Damage Caused by Pressure Overload

Chronic pressure overload is a key risk factor for mortality due to its subsequent development of heart failure, in which the underlying molecular mechanisms remain vastly undetermined. In this review, we updated the latest advancements for investigating the role and relevant mechanisms of oxidative stress involved in the pathogenesis of pressure-overload-induced cardiomyopathy and cardiac dysfunction, focusing on significant biological sources of reactive oxygen species (free radical) production, antioxidant defenses, and their association with the cardiac metabolic remodeling in the stressed heart. We also summarize the newly developed preclinical therapeutic approaches in animal models for pressure-overload-induced myocardial damage. This review aims to enhance the current understanding of the mechanisms of chronic hypertensive heart failure and potentially improve the development of better therapeutic strategies for the associated diseases.

The lncRNA MIAT regulates CPT-1a mediated cardiac hypertrophy through m6A RNA methylation reading protein Ythdf2

Pathological cardiac hypertrophy is a key contributor in heart failure (HF). Long non-coding RNAs (lncRNAs) and N⁶-methyladenosine (m⁶A) modification play a vital role in cardiac hypertrophy respectively. Nevertheless, the interaction between lncRNA and m⁶A methylase in cardiac hypertrophy is scarcely reported. Here, we constructed a cardiac hypertrophy mouse model by transverse aortic constriction (TAC) surgery and H9c2 cell model by stimulating with AngII. We found that lncRNA MIAT mRNA level, and m⁶A RNA methylation reading protein Ythdf2 mRNA and protein levels, were significantly increased in the cardiac hypertrophy model both in vivo and vitro. MIAT or Ythdf2 overexpression aggravated cardiac hypertrophy, and vice versa. Through bioinformatics prediction, western blotting, FISH, RNA pull-down, and RIP, we found that MIAT bound to Ythdf2 and regulated its expression. Furthermore, we discovered that Ythdf2 function was a downstream of MIAT in cardiac hypertrophy. Finally, we found that MIAT was a necessary regulator of cardiac hypertrophy due to its regulation of the Ythdf2/PPARα/CPT-1a axis. This study indicated a new hypertrophic signaling pathway: MIAT/Ythdf2/PPARα/CPT-1a. The results provided a new understanding of the MIAT and m⁶A RNA methylation reading protein, Ythdf2, function and mechanism in cardiac hypertrophy and highlighted the potential therapeutic benefits in the heart.

MLK3 mediates impact of PKG1α on cardiac function and controls blood pressure through separate mechanisms

cGMP-dependent protein kinase 1α (PKG1α) promotes left ventricle (LV) compensation after pressure overload. PKG1-activating drugs improve heart failure (HF) outcomes but are limited by vasodilation-induced hypotension. Signaling molecules that mediate PKG1α cardiac therapeutic effects but do not promote PKG1α-induced hypotension could therefore represent improved therapeutic targets. We investigated roles of mixed lineage kinase 3 (MLK3) in mediating PKG1α effects on LV function after pressure overload and in regulating BP. In a transaortic constriction HF model, PKG activation with sildenafil preserved LV function in MLK3+/+ but not MLK3-/- littermates. MLK3 coimmunoprecipitated with PKG1α. MLK3-PKG1α cointeraction decreased in failing LVs. PKG1α phosphorylated MLK3 on Thr277/Ser281 sites required for kinase activation. MLK3-/- mice displayed hypertension and increased arterial stiffness, though PKG stimulation with sildenafil or the soluble guanylate cyclase (sGC) stimulator BAY41-2272 still reduced BP in MLK3-/- mice. MLK3 kinase inhibition with URMC-099 did not affect BP but induced LV dysfunction in mice. These data reveal MLK3 as a PKG1α substrate mediating PKG1α preservation of LV function but not acute PKG1α BP effects. Mechanistically, MLK3 kinase-dependent effects preserved LV function, whereas MLK3 kinase-independent signaling regulated BP. These findings suggest augmenting MLK3 kinase activity could preserve LV function in HF but avoid hypotension from PKG1α activation.

Xinyang Tablet inhibits MLK3-mediated pyroptosis to attenuate inflammation and cardiac dysfunction in pressure overload

ETHNOPHARMACOLOGICAL RELEVANCE

Xinyang tablet (XYT) has been traditionally used in the treatment of cardiovascular diseases (CVDs). Our previous study indicated that XYT exhibited protective effects in heart failure (HF).

AIM OF THE STUDY

The aim of the present study was to determine the protective effects of XYT in pressure overload induced HF and to elucidate its underlying mechanisms of action.

MATERIALS AND METHODS

We analyzed XYT content using high-performance liquid chromatography (HPLC.). Mice were subjected to transverse aortic constriction (TAC) to generate pressure overload-induced cardiac remodeling and were then orally administered XYT or URMC-099 for 1 week after the operation. HL1 mouse cardiomyoblasts were induced by lipopolysaccharides (LPS) to trigger pyroptosis and were then treated with XYT or URMC-099. We used echocardiography (ECG), hematoxylin and eosin (H&E) staining, Masson's trichrome staining and a terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay to evaluate the effects of XYT. Messenger ribonucleic acid (mRNA) levels of collagen metabolism biomarkers and inflammation-related factors were detected. We determined protein levels of inflammation- and pyroptosis-related signaling pathway members via Western blot (WB). Caspase-1 activity was measured in cell lysate using a Caspase-1 Activity Assay Kit. Subsequently, to define the candidate ingredients in XYT that regulate mixed-lineage kinase-3 (MLK3), we used molecular docking (MD) to predict and evaluate binding affinity with MLK3. Finally, we screened 24 active potential compounds that regulate MLK3 via MD.

RESULTS

ECG, H&E staining, Masson's trichrome staining and TUNEL assay results showed that XYT remarkably improved heart function, amelorated myocardial fibrosis and inhibited apoptosis in vivo. Moreover, it reduced expression of proteins or mRNAs related to collagen metabolism, including collagen type 1 (COL1), fibronectin (FN), alpha smooth-muscle actin (α-SMA), and matrix metalloproteinases-2 and -9 (MMP-2, MMP-9). XYT also inhibited inflammation and the induction of pyroptosis at an early stage, as well as attenuated inflammation and pyroptosis levels in vitro.

CONCLUSION

Our data indicated that XYT exerted protective effects against pressure overload induced myocardial fibrosis (MF), which might be associated with the induction of pyroptosis-mediated MLK3 signaling.

Distinct Phenotypes Induced by Different Degrees of Transverse Aortic Constriction in C57BL/6N Mice

The transverse aortic constriction (TAC) model surgery is a widely used disease model to study pressure overload–induced cardiac hypertrophy and heart failure in mice. The severity of adverse cardiac remodeling of the TAC model is largely dependent on the degree of constriction around the aorta, and the phenotypes of TAC are also different in different mouse strains. Few studies focus on directly comparing phenotypes of the TAC model with different degrees of constriction around the aorta, and no study compares the difference in C57BL/6N mice. In the present study, C57BL/6N mice aged 10 weeks were subjected to sham, 25G TAC, 26G TAC, and 27G TAC surgery for 4 weeks. We then analyzed the different phenotypes induced by 25G TAC, 26G TAC, and 27G TAC in c57BL/6N mice in terms of pressure gradient, cardiac hypertrophy, cardiac function, heart failure situation, survival condition, and cardiac fibrosis. All C57BL/6N mice subjected to TAC surgery developed significantly hypertrophy. Mice subjected to 27G TAC had severe cardiac dysfunction, severe cardiac fibrosis, and exhibited characteristics of heart failure at 4 weeks post-TAC. Compared with 27G TAC mice, 26G TAC mice showed a much milder response in cardiac dysfunction and cardiac fibrosis compared to 27G TAC, and a very small fraction of the 26G TAC group exhibited characteristics of heart failure. There was no obvious cardiac dysfunction, cardiac fibrosis, and characteristics of heart failure observed in 25G TAC mice. Based on our results, we conclude that the 25G TAC, 26G TAC, and 27G TAC induced distinct phenotypes in C57BL/6N mice.

Maternal diet high in linoleic acid alters offspring fatty acids and cardiovascular function in a rat model

Linoleic acid (LA), an essential n-6 fatty acid (FA), is critical for fetal development. We investigated the effects of maternal high LA (HLA) diet on offspring cardiac development and its relationship to circulating FA and cardiovascular function in adolescent offspring, and the ability of the postnatal diet to reverse any adverse effects. Female Wistar Kyoto rats were fed low LA (LLA; 1·44 % energy from LA) or high LA (HLA; 6·21 % energy from LA) diets for 10 weeks before pregnancy and during gestation/lactation. Offspring, weaned at postnatal day 25, were fed LLA or HLA diets and euthanised at postnatal day 40 (n 6-8). Maternal HLA diet decreased circulating total cholesterol and HDL-cholesterol in females and decreased total plasma n-3 FA in males, while maternal and postnatal HLA diets decreased total plasma n-3 FA in females. α-Linolenic acid (ALA) and EPA were decreased by postnatal but not maternal HLA diets in both sexes. Maternal and postnatal HLA diets increased total plasma n-6 and LA, and a maternal HLA diet increased circulating leptin, in both male and female offspring. Maternal HLA decreased slopes of systolic and diastolic pressure-volume relationship (PVR), and increased cardiac Col1a1, Col3a1, Atp2a1 and Notch1 in males. Maternal and postnatal HLA diets left-shifted the diastolic PVR in female offspring. Coronary reactivity was altered in females, with differential effects on flow repayment after occlusion. Thus, maternal HLA diets impact lipids, FA and cardiac function in offspring, with postnatal diet modifying FA and cardiac function in the female offspring.

JNK signaling pathway in metabolic disorders: An emerging therapeutic target

Metabolic Syndrome is a multifactorial disease associated with increased risk of cardiovascular disorders, type 2 diabetes mellitus, fatty liver disease, etc. Various stress stimuli such as reactive oxygen species, endoplasmic reticulum stress, mitochondrial dysfunction, increased cytokines, or free fatty acids are known to aggravate progressive development of hyperglycemia and hyperlipidemia. Although the exact mechanism contributing to altered metabolism is unclear. Evidence suggests stress kinase role to be a crucial one in metabolic syndrome. Stress kinase, c-jun N-terminal kinase activation (JNK) is involved in various metabolic manifestations including obesity, insulin resistance, fatty liver disease as well as cardiometabolic disorders. It emerged as a foremost mediator in regulating metabolism in the liver, skeletal muscle, adipose tissue as well as pancreatic β cells. It has three isoforms each having a unique and tissue-specific role in altered metabolism. Current findings based on genetic manipulation or chemical inhibition studies identified JNK isoforms to play a central role in the regulation of whole-body metabolism, suggesting it to be a novel therapeutic target. Hence, it is imperative to elucidate its role in metabolic syndrome onset and progression. The purpose of this review is to elucidate in vitro and in vivo implications of JNK signaling along with the therapeutic strategy to inhibit specific isoform. Since metabolic syndrome is an array of diseases and complex pathway, carefully examining each tissue will be important for specific treatment strategies.

The regulatory function of mixed lineage kinase 3 in tumor and host immunity

Protein kinases are the second most sought-after G-protein coupled receptors as drug targets because of their overexpression, mutations, and dysregulated catalytic activities in various pathological conditions. Till 2019, 48 protein kinase inhibitors have received FDA approval for the treatment of multiple illnesses, of which the majority of them are indicated for different malignancies. One of the attractive sub-group of protein kinases that has attracted attention for drug development is the family members of MAPKs that are recognized to play significant roles in different cancers. Several inhibitors have been developed against various MAPK members; however, none of them as monotherapy has shown sustainable efficacy. One of the MAPK members, called Mixed Lineage Kinase 3 (MLK3), has attracted considerable attention due to its role in inflammation and neurodegenerative diseases; however, its role in cancer is an emerging area that needs more investigation. Recent advances have shown that MLK3 plays a role in cancer cell survival, migration, drug resistance, cell death, and tumor immunity. This review describes how MLK3 regulates different MAPK pathways, cancer cell growth and survival, apoptosis, and host's immunity. We also discuss how MLK3 inhibitors can potentially be used along with immunotherapy for different malignancies.

cGMP Signaling and Modulation in Heart Failure

Cyclic GMP (cGMP) represents a classic intracellular second messenger molecule. Over the past 2 decades, important discoveries have identified that cGMP signaling becomes deranged in heart failure (HF) and that cGMP and its main kinase effector, protein kinase G, generally oppose the biological abnormalities contributing to HF, in experimental studies. These findings have influenced the design of clinical trials of cGMP-augmenting drugs in HF patients. At present, the trial results of cGMP-augmenting therapies in HF remain mixed. As detailed in this review, strong evidence now exists that protein kinase G opposes pathologic cardiac remodeling through regulation of diverse biological processes and myocardial substrates. Potential reasons for the failures of cGMP-augmenting drugs in HF may be related to biological mechanisms opposing cGMP or because of certain features of clinical trials, all of which are discussed.

Pyroptosis and ferroptosis induced by mixed lineage kinase 3 (MLK3) signaling in cardiomyocytes are essential for myocardial fibrosis in response to pressure overload

Chronic heart failure (CHF) is the final outcome of many cardiovascular diseases, and is a severe health issue faced by the elderly population. Mixed lineage kinase 3 (MLK3), a member of MAP3K family, is associated with aging, inflammation, oxidative stress, and related diseases, such as CHF. MLK3 has also been reported to play an important role in protecting against cardiomyocyte injury; however, its function in myocardial fibrosis is unknown. To investigate the role of MLK3 in myocardial fibrosis, we inhibited the expression of MLK3, and examined cardiac function and remodeling in TAC mice. In addition, we assessed the expression of MLK3 protein in ventricular cells and its downstream associated protein. We found that MLK3 mainly regulates NF-κB/NLRP3 signaling pathway-mediated inflammation and that pyroptosis causes myocardial fibrosis in the early stages of CHF. Similarly, MLK3 mainly regulates the JNK/p53 signaling pathway-mediated oxidative stress and that ferroptosis causes myocardial fibrosis in the advanced stages of CHF. We also found that promoting the expression of miR-351 can inhibit the expression of MLK3, and significantly improve cardiac function in mice subjected to TAC. These results suggest the pyroptosis and ferroptosis induced by MLK3 signaling in cardiomyocytes are essential for adverse myocardial fibrosis, in response to pressure overload. Furthermore, miR-351, which has a protective effect on ventricular remodeling in heart failure caused by pressure overload, may be a key target for the regulation of MLK3.

Hemodynamic assessment of diastolic function for experimental models

Traditionally, the evaluation of cardiac function has focused on systolic function; however, there is a growing appreciation for the contribution of diastolic function to overall cardiac health. Given the emerging interest in evaluating diastolic function in all models of heart failure, there is a need for sensitivity, accuracy, and precision in the hemodynamic assessment of diastolic function. Hemodynamics measure cardiac pressures in vivo, offering a direct assessment of diastolic function. In this review, we summarize the underlying principles of diastolic function, dividing diastole into two phases: 1) relaxation and 2) filling. We identify parameters used to comprehensively evaluate diastolic function by hemodynamics, clarify how each parameter is obtained, and consider the advantages and limitations associated with each measure. We provide a summary of the sensitivity of each diastolic parameter to loading conditions. Furthermore, we discuss differences that can occur in the accuracy of diastolic and systolic indices when generated by automated software compared with custom software analysis and the magnitude each parameter is influenced during inspiration with healthy breathing and a mild breathing load, commonly expected in heart failure. Finally, we identify key variables to control (e.g., body temperature, anesthetic, sampling rate) when collecting hemodynamic data. This review provides fundamental knowledge for users to succeed in troubleshooting and guidelines for evaluating diastolic function by hemodynamics in experimental models of heart failure.

PKCδ Mediates Mineralocorticoid Receptor Activation by Angiotensin II to Modulate Smooth Muscle Cell Function

Angiotensin II (AngII) and the mineralocorticoid receptor (MR) ligand aldosterone both contribute to cardiovascular disorders, including hypertension and adverse vascular remodeling. We previously demonstrated that AngII activates MR-mediated gene transcription in human vascular smooth muscle cells (SMCs), yet the mechanism and the impact on SMC function are unknown. Using an MR-responsive element-driven transcriptional reporter assay, we confirm that AngII induces MR transcriptional activity in vascular SMCs and endothelial cells, but not in Cos1 or human embryonic kidney-293 cells. AngII activation of MR was blocked by the MR antagonist spironolactone or eplerenone and the protein kinase C-δ (PKCδ) inhibitor rottlerin, implicating both in the mechanism. Similarly, small interfering RNA knockdown of PKCδ in SMCs prevented AngII-mediated MR activation, whereas knocking down of MR blocked both aldosterone- and AngII-induced MR function. Coimmunoprecipitation studies reveal that endogenous MR and PKCδ form a complex in SMCs that is enhanced by AngII treatment in association with increased serine phosphorylation of the MR N terminus. AngII increased mRNA expression of the SMC-MR target gene, FKBP51, via an MR-responsive element in intron 5 of the FKBP51 gene. The impact of AngII on FKBP51 reporter activity and gene expression in SMCs was inhibited by spironolactone and rottlerin. Finally, the AngII-induced increase in SMC number was also blocked by the MR antagonist spironolactone and the PKCδ inhibitor rottlerin. These data demonstrate that AngII activates MR transcriptional regulatory activity, target gene regulation, and SMC proliferation in a PKCδ-dependent manner. This new mechanism may contribute to synergy between MR and AngII in driving SMC dysfunction and to the cardiovascular benefits of MR and AngII receptor blockade in humans.

JNK and cardiometabolic dysfunction

Cardiometabolic syndrome (CMS) describes the cluster of metabolic and cardiovascular diseases that are generally characterized by impaired glucose tolerance, intra-abdominal adiposity, dyslipidemia, and hypertension. CMS currently affects more than 25% of the world’s population and the rates of diseases are rapidly rising. These CMS conditions represent critical risk factors for cardiovascular diseases including atherosclerosis, heart failure, myocardial infarction, and peripheral artery disease (PAD). Therefore, it is imperative to elucidate the underlying signaling involved in disease onset and progression. The c-Jun N-terminal Kinases (JNKs) are a family of stress signaling kinases that have been recently indicated in CMS. The purpose of this review is to examine the in vivo implications of JNK as a potential therapeutic target for CMS. As the constellation of diseases associated with CMS are complex and involve multiple tissues and environmental triggers, carefully examining what is known about the JNK pathway will be important for specificity in treatment strategies.

Distinct Phenotypes Induced by Three Degrees of Transverse Aortic Constriction in Mice

Transverse aortic constriction (TAC) is a well-established model of pressure overload-induced cardiac hypertrophy and failure in mice. The degree of constriction “tightness” dictates the TAC severity and is determined by the gauge (G) of needle used. Though many reports use the TAC model, few studies have directly compared the range of resulting phenotypes. In this study adult male mice were randomized to receive TAC surgery with varying degrees of tightness: mild (25G), moderate (26G) or severe (27G) for 4 weeks, alongside sham-operated controls. Weekly echocardiography and terminal haemodynamic measurements determined cardiac remodelling and function. All TAC models induced significant, severity-dependent left ventricular hypertrophy and diastolic dysfunction compared to sham mice. Mice subjected to 26G TAC additionally exhibited mild systolic dysfunction and cardiac fibrosis, whereas mice in the 27G TAC group had more severe systolic and diastolic dysfunction, severe cardiac fibrosis, and were more likely to display features of heart failure, such as elevated plasma BNP. We also observed renal atrophy in 27G TAC mice, in the absence of renal structural, functional or gene expression changes. 25G, 26G and 27G TAC produced different responses in terms of cardiac structure and function. These distinct phenotypes may be useful in different preclinical settings.