Disrupted propionate metabolism evokes transcriptional changes in the heart by increasing histone acetylation and propionylation

Propiogenic substrates and gut bacteria produce propionate, a post-translational protein modifier. In this study, we used a mouse model of propionic acidaemia (PA) to study how disturbances to propionate metabolism result in histone modifications and changes to gene expression that affect cardiac function. Plasma propionate surrogates were raised in PA mice, but female hearts manifested more profound changes in acyl-CoAs, histone propionylation and acetylation, and transcription. These resulted in moderate diastolic dysfunction with raised diastolic Ca2+, expanded end-systolic ventricular volume and reduced stroke volume. Propionate was traced to histone H3 propionylation and caused increased acetylation genome-wide, including at promoters of Pde9a and Mme, genes related to contractile dysfunction through downscaled cGMP signaling. The less severe phenotype in male hearts correlated with β-alanine buildup. Raising β-alanine in cultured myocytes treated with propionate reduced propionyl-CoA levels, indicating a mechanistic relationship. Thus, we linked perturbed propionate metabolism to epigenetic changes that impact cardiac function.

A New Era of Morphological Investigations: Reviewing methods for comparative anatomical studies

The increased use of imaging technology in biological research has drastically altered morphological studies in recent decades and allowed for the preservation of important collection specimens alongside detailed visualization of bony and soft-tissue structures. Despite the benefits associated with these newer imaging techniques, there remains a need for more “traditional” methods of morphological examination in many comparative studies. In this paper, we describe the costs and benefits of the various methods of visualizing, examining, and comparing morphological structures. There are significant differences in the costs associated with these different methods (monetary, time, equipment, and software), but also in the degree to which specimens are destroyed. We argue not for any one particular method over another in morphological studies, but instead suggest a combination of methods is useful not only for breadth of visualization, but also for the financial and time constraints often imposed on early-career research scientists.

Elevated propionate signalling drives Pde9a overexpression and contractile dysfunction through increased histone acetylation and propionylation

Funding Acknowledgements

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): British Heart Foundation and Propionic Acidemia Foundation

Background

In the heart, various metabolic pathways produce the three-carbon intermediate, propionate. This metabolite has been postulated to increase histone propionylation and acetylation (via deacetylase inhibition), and therefore affect transcription. Normally, propionate levels are kept low by propionyl-CoA carboxylase (PCC), but build-up has been reported in cardiometabolic diseases. The highest levels are attained in propionic acidaemia (PA; mutations in PCC), which also serves as a model for studying propionate biology [1].

Purpose

To establish the effect of propionate on cardiac gene expression and physiology using a mouse model of elevated propionate/propionyl-CoA signalling.

Methods

Experiments were performed using either wild-type (WT) neonatal ventricular myocytes (NRVMs) treated with propionate in vitro, or the hypomorphic mouse model of PA (Pcca-/- A138T) [2]. IC-MS metabolomics was performed on methanol-extracted metabolites. RNA-sequencing was carried out on an Illumina HiSeq 4000. For chromatin immunoprecipitation (ChIP), chromatin was isolated from PFA-fixed ventricular tissue. cGMP levels were measured by the FRET-based sensor, cGi500. Ca2+ transients were imaged in isolated myocytes using FuraRed. Cine-MRI was performed in a 7 tesla MR scanner.

Results

PA mice had the metabolic signature of propionate accumulation in plasma and cardiac lysates (metabolomics). RNA-seq of ventricular lysates identified differentially expressed genes (DEGs), but the effect was more pronounced in females. Thus, subsequent experiments were performed in females. To determine which DEGs are likely a direct response to propionate, RNA-seq was performed on propionate-treated NRVMs. The most significant DEGs common to both datasets were upregulated Pde9a (cGMP-selective phosphodiesterase) and Mme (degrades natriuretic peptides). ChIP-qPCR for histone acylation in PA and WT hearts demonstrated increases in H3K27ac at Pde9a, and strikingly, increases in propionylation at Pde9a and Mme, indicating a mechanism for this transcriptional induction. Propionate-treated NRVMs show greater sensitivity of cGMP to pharmacological inhibition of PDE9A (measured by FRET), consistent with Pde9a induction. Such changes are expected to result in diastolic dysfunction [3]. Indeed, ventricular myocytes from PA mice had higher diastolic Ca2+. Cine-MRI confirmed contractile dysfunction in vivo, with PA mice manifesting increased end-systolic and end-diastolic volumes.

Conclusions

We demonstrate that cardiac elevations of the metabolic intermediate, propionate, increases histone modifications that drive transcriptional changes in the heart, including those involved in cyclic nucleotide signalling. We also present evidence for histone propionylation, which has not been described previously in the heart. Thus, using a mouse model of a rare metabolic disease, we show how propionate/propionyl-CoA signalling affects cardiac function through epigenetic changes.

Serum potassium variability as a predictor of clinical outcomes in patients with cardiorenal disease or diabetes: a retrospective UK database study

Background

Hyperkalaemia is an electrolyte abnormality associated with adverse clinical outcomes; however, few studies have investigated the relationship with patterns of hyperkalaemia over time. This study explored the impact of time spent in a hyperkalaemic state and variability of serum potassium (sK⁺) on major adverse cardiovascular events (MACE) and all-cause mortality in patients with chronic kidney disease (CKD), resistant hypertension, heart failure and diabetes.

Methods

Cohorts comprised adult patients diagnosed with CKD stage 3+, resistant hypertension, heart failure or diabetes, and/or renin–angiotensin–aldosterone system inhibitor prescription, between 1 January 2003 and 30 June 2018, from the UK Clinical Practice Research Datalink. Associations between percentage of follow-up spent in a hyperkalaemic state (sK⁺ ≥5.0 mmol/L, ≥5.5 mmol/L, ≥6.0 mmol/L) or sK⁺ variability (standard deviation above or below median standard deviation) and all-cause mortality or MACE were investigated.

Results

For sK⁺ ≥5.0 mmol/L, time spent in a hyperkalaemic state was associated with reduced risk of all-cause mortality across all cohorts. For higher sK⁺ thresholds, this trend was attenuated or reversed; for time spent in a hyperkalaemic state at sK⁺ ≥6.0 mmol/L, an increased risk of mortality was seen in the overall cohort and for patients with diabetes, resistant hypertension or prescribed renin–angiotensin–aldosterone system inhibitors, with no consistent association seen for patients with CKD or heart failure. Risk of MACE in the overall cohort and in patients with CKD, diabetes or resistant hypertension increased with time spent in a hyperkalaemic state at all sK⁺ thresholds; however, no correlation was seen in patients with heart failure or those receiving dialysis. High sK⁺ variability was associated with a higher risk of MACE compared with low sK⁺ variability across most sK⁺ categories in the overall population and in all disease cohorts, except patients on dialysis; however, no association between sK⁺ variability and all-cause mortality was observed.

Conclusions

Patterns of hyperkalaemia, including time spent in hyperkalaemia and sK⁺ variability, are associated with adverse clinical outcomes. Regular monitoring of sK⁺ in high-risk populations in broader community, primary care and outpatient settings may enable guideline-recommended management of hyperkalaemia and help avoid adverse events.

MicroRNAs as potential biomarkers in congenital heart surgery

OBJECTIVE

Pediatric congenital heart surgery (CHS) involves intracardiac, valvular, and vascular repairs. Accurate tools to aid short-term outcome prediction in pediatric CHS are lacking. Clinical scores, such as the vasoactive-inotrope score and ventilation index, are used to define outcome in clinical studies. MicroRNA-1-3p (miR-1) is expressed by both cardiomyocytes and vascular cells and is regulated by hypoxia. In adult patients, miR-1 increases in the circulation after open-heart cardiac surgery, suggesting its potential as a clinical biomarker. Thus, we investigated whether perioperative circulating miR-1 measurements can help predict post-CHS short-term outcomes in pediatric patients.

METHODS

Plasma miR-1 was retrospectively measured in a cohort of 199 consecutive pediatric CHS patients (median age 1.2 years). Samples were taken before surgery and at the end of the operation. Plasma miR-1 concentration was measured by reverse transcription-quantitative polymerase chain reaction and expressed as miR-1 copies/μL and as relative expression to spiked-in exogenous cel-miR-39.

RESULTS

Baseline plasma miR-1 did not vary across different diagnoses, increased during surgery (204-fold median relative increase, P < .001), and was associated with aortic crossclamp duration postoperatively (P < .001). Importantly, miR-1 levels at the end of the operation positively correlated with intensive care stay (P < .001), early severe cardiovascular events (P = .01), and with high vasoactive-inotrope score (P = .001) and ventilation index (P < .001), suggesting that miR-1 could accelerate the identification of patients with cardiopulmonary bypass-related ischemic complications, requiring more intensive support.

CONCLUSIONS

Our study suggests miR-1 as a novel potential circulating biomarker to predict early postoperative outcome and inform clinical management in pediatric heart surgery.

Elevated cyclic-AMP represses expression of exchange protein activated by cAMP (EPAC1) by inhibiting YAP-TEAD activity and HDAC-mediated histone deacetylation

Ligand-induced activation of Exchange Protein Activated by cAMP-1 (EPAC1) is implicated in numerous physiological and pathological processes, including cardiac fibrosis where changes in EPAC1 expression have been detected. However, little is known about how EPAC1 expression is regulated. Therefore, we investigated regulation of EPAC1 expression by cAMP in cardiac fibroblasts. Elevation of cAMP using forskolin, cAMP-analogues or adenosine A2B-receptor activation significantly reduced EPAC1 mRNA and protein levels and inhibited formation of F-actin stress fibres. Inhibition of actin polymerisation with cytochalasin-D, latrunculin-B or the ROCK inhibitor, Y-27632, mimicked effects of cAMP on EPAC1 mRNA and protein levels. Elevated cAMP also inhibited activity of an EPAC1 promoter-reporter gene, which contained a consensus binding element for TEAD, which is a target for inhibition by cAMP. Inhibition of TEAD activity using siRNA-silencing of its co-factors YAP and TAZ, expression of dominant-negative TEAD or treatment with YAP-TEAD inhibitors, significantly inhibited EPAC1 expression. However, whereas expression of constitutively-active YAP completely reversed forskolin inhibition of EPAC1-promoter activity it did not rescue EPAC1 mRNA levels. Chromatin-immunoprecipitation detected a significant reduction in histone3-lysine27-acetylation at the EPAC1 proximal promoter in response to forskolin stimulation. HDAC1/3 inhibition partially reversed forskolin inhibition of EPAC1 expression, which was completely rescued by simultaneously expressing constitutively active YAP. Taken together, these data demonstrate that cAMP downregulates EPAC1 gene expression via disrupting the actin cytoskeleton, which inhibits YAP/TAZ-TEAD activity in concert with HDAC-mediated histone deacetylation at the EPAC1 proximal promoter. This represents a novel negative feedback mechanism controlling EPAC1 levels in response to cAMP elevation.

Optimisation of laboratory methods for whole transcriptomic RNA analyses in human left ventricular biopsies and blood samples of clinical relevance

This study aimed to optimise techniques for whole transcriptome and small RNA analyses on clinical tissue samples from patients with cardiovascular disease. Clinical samples often represent a particular challenge to extracting RNA of sufficient quality for robust RNA sequencing analysis, and due to availability, it is rarely possible to optimise techniques on the samples themselves. Therefore, we have used equivalent samples from pigs undergoing cardiopulmonary bypass surgery to test different protocols for optimal RNA extraction, and then validated the protocols in human samples. Here we present an assessment of the quality and quantity of RNA obtained using a variety of commercially-available RNA extraction kits on both left ventricular biopsies and blood plasma. RNA extraction from these samples presents different difficulties; left ventricular biopsies are small and fibrous, while blood plasma has a low RNA content. We have validated our optimised extraction techniques on human clinical samples collected as part of the ARCADIA (Association of non-coding RNAs with Coronary Artery Disease and type 2 Diabetes) cohort study, resulting in successful whole transcriptome and small RNA sequencing of human left ventricular tissue.

Regional acidosis locally inhibits but remotely stimulates Ca2+ waves in ventricular myocytes

Aims

Spontaneous Ca²⁺ waves in cardiomyocytes are potentially arrhythmogenic. A powerful controller of Ca²⁺ waves is the cytoplasmic H⁺ concentration ([H⁺]_i), which fluctuates spatially and temporally in conditions such as myocardial ischaemia/reperfusion. H⁺-control of Ca²⁺ waves is poorly understood. We have therefore investigated how [H⁺]_i co-ordinates their initiation and frequency.

Methods and results

Spontaneous Ca²⁺ waves were imaged (fluo-3) in rat isolated ventricular myocytes, subjected to modest Ca²⁺-overload. Whole-cell intracellular acidosis (induced by acetate-superfusion) stimulated wave frequency. Pharmacologically blocking sarcolemmal Na⁺/H⁺ exchange (NHE1) prevented this stimulation, unveiling inhibition by H⁺. Acidosis also increased Ca²⁺ wave velocity. Restricting acidosis to one end of a myocyte, using a microfluidic device, inhibited Ca²⁺ waves in the acidic zone (consistent with ryanodine receptor inhibition), but stimulated wave emergence elsewhere in the cell. This remote stimulation was absent when NHE1 was selectively inhibited in the acidic zone. Remote stimulation depended on a locally evoked, NHE1-driven rise of [Na⁺]_i that spread rapidly downstream.

Conclusion

Acidosis influences Ca²⁺ waves via inhibitory Hi+ and stimulatory Nai+ signals (the latter facilitating intracellular Ca²⁺-loading through modulation of sarcolemmal Na⁺/Ca²⁺ exchange activity). During spatial [H⁺]_i-heterogeneity, Hi+-inhibition dominates in acidic regions, while rapid Nai+ diffusion stimulates waves in downstream, non-acidic regions. Local acidosis thus simultaneously inhibits and stimulates arrhythmogenic Ca²⁺-signalling in the same myocyte. If the principle of remote H⁺-stimulation of Ca²⁺ waves also applies in multicellular myocardium, it raises the possibility of electrical disturbances being driven remotely by adjacent ischaemic areas, which are known to be intensely acidic.

The Function and Therapeutic Potential of Long Non-coding RNAs in Cardiovascular Development and Disease

The popularization of genome-wide analyses and RNA sequencing led to the discovery that a large part of the human genome, while effectively transcribed, does not encode proteins. Long non-coding RNAs have emerged as critical regulators of gene expression in both normal and disease states. Studies of long non-coding RNAs expressed in the heart, in combination with gene association studies, revealed that these molecules are regulated during cardiovascular development and disease. Some long non-coding RNAs have been functionally implicated in cardiac pathophysiology and constitute potential therapeutic targets. Here, we review the current knowledge of the function of long non-coding RNAs in the cardiovascular system, with an emphasis on cardiovascular development and biology, focusing on hypertension, coronary artery disease, myocardial infarction, ischemia, and heart failure. We discuss potential therapeutic implications and the challenges of long non-coding RNA research, with directions for future research and translational focus.

Intracellular tortuosity underlies slow cAMP diffusion in adult ventricular myocytes

Aims

3′,5′-Cyclic adenosine monophosphate (cAMP) signals in the heart are often confined to concentration microdomains shaped by cAMP diffusion and enzymatic degradation. While the importance of phosphodiesterases (degradative enzymes) in sculpting cAMP microdomains is well established in cardiomyocytes, less is known about cAMP diffusivity (D_cAMP) and factors affecting it. Many earlier studies have reported fast diffusivity, which argues against sharply defined microdomains.

Methods and results

[cAMP] dynamics in the cytoplasm of adult rat ventricular myocytes were imaged using a fourth generation genetically encoded FRET-based sensor. The [cAMP]-response to the addition and removal of isoproterenol (β-adrenoceptor agonist) quantified the rates of cAMP synthesis and degradation. To obtain a read out of D_cAMP, a stable [cAMP] gradient was generated using a microfluidic device which delivered agonist to one half of the myocyte only. After accounting for phosphodiesterase activity, D_cAMP was calculated to be 32 µm²/s; an order of magnitude lower than in water. Diffusivity was independent of the amount of cAMP produced. Saturating cAMP-binding sites with the analogue 6-Bnz-cAMP did not accelerate D_cAMP, arguing against a role of buffering in restricting cAMP mobility. cAMP diffused at a comparable rate to chemically unrelated but similar sized molecules, arguing for a common physical cause of restricted diffusivity. Lower mitochondrial density and order in neonatal cardiac myocytes allowed for faster diffusion, demonstrating the importance of mitochondria as physical barriers to cAMP mobility.

Conclusion

In adult cardiac myocytes, tortuosity due to physical barriers, notably mitochondria, restricts cAMP diffusion to levels that are more compatible with microdomain signalling.

Primary biliary cirrhosis: MR imaging findings and description of MR imaging periportal halo sign

OBJECTIVE

This study reviews the prevalence of MR imaging abnormalities seen in 21 consecutive patients with primary biliary cirrhosis before transplantation and describes a new MR imaging sign in these patients: the MR imaging periportal halo sign.

CONCLUSION

Abdominal adenopathy was present in 62% of the patient population, and none of the patients with adenopathy had a known malignancy. Findings associated with end-stage cirrhosis and portal hypertension were seen and included ascites (62%), splenomegaly (71%), portosystemic collaterals (57%), portal vein thrombosis (5%), and hepatocellular carcinoma (5%). The MR imaging periportal halo sign was seen in 43% of patients with primary biliary cirrhosis, but none of the patients in a sex- and age-matched cohort of 21 patients with cirrhosis not caused by primary biliary cirrhosis had the finding. Statistical analysis of these results produced a t score of 3.97 and a p value of less than 0.001, suggesting that this new MR imaging sign is highly specific for the diagnosis of primary biliary cirrhosis.

Cystic ovarian necrosis complicating tamoxifen therapy for breast cancer in a premenopausal woman. A case report

A premenopausal woman with recurrent stage II ductal breast carcinoma was treated with tamoxifen. After ten months of therapy her ovaries became acutely cystic and necrotic, but vascular torsion was not present. This case illustrates the special complications of tamoxifen therapy in premenopausal women.

Intrauterine fetal surgery: a nursing challenge

Surgical treatment of the fetus in utero offers new options for selected families with fetal anomalies. Nurses caring for these families must be prepared to meet their unique needs. The diagnosis, treatment, support, and follow-up care of the family is discussed.