Chronic activation of the low affinity site of β1-adrenoceptors stimulates haemodynamics but exacerbates pressure-overload cardiac remodelling

Crosstalk between cytotoxic CD8+ T cells and stressed cardiomyocytes triggers development of interstitial cardiac fibrosis in hypertensive mouse hearts

Aims

Cardiac fibrosis is central to heart failure (HF), especially HF with preserved ejection fraction (HFpEF), often caused by hypertension. Despite fibrosis causing diastolic dysfunction and impaired electrical conduction, responsible for arrhythmia-induced sudden cardiac death, the mechanisms are poorly defined and effective therapies are lacking. Here we show that crosstalk between cardiac cytotoxic memory CD8+ T cells and overly stressed cardiomyocytes is essential for development of non-ischemic hypertensive cardiac fibrosis.

Methods and results

CD8 T cell depletion in hypertensive mice, strongly attenuated CF, reduced cardiac apoptosis and improved ventricular relaxation. Interaction between cytotoxic memory CD8+ T cells and overly stressed cardiomyocytes is highly dependent on the CD8+ T cells expressing the innate stress-sensing receptor NKG2D and stressed cardiomyocytes expressing the NKG2D activating ligand RAE-1. The interaction between NKG2D and RAE-1 results in CD8+ T cell activation, release of perforin, cardiomyocyte apoptosis, increased numbers of TGF-β1 expressing macrophages and fibrosis. Deleting NKG2D or perforin from CD8+ T cells greatly attenuates these effects. Activation of the cytoplasmic DNA-STING-TBK1-IRF3 signaling pathway in overly stressed cardiomyocytes is responsible for elevating RAE-1 and MCP-1, a macrophage attracting chemokine. Inhibiting STING activation greatly attenuates cardiomyocyte RAE-1 expression, the cardiomyocyte apoptosis, TGF-β1 and fibrosis.

Conclusion

Our data highlight a novel pathway by which CD8 T cells contribute to an early triggering mechanism in CF development; preventing CD8+ T cell activation by inhibiting the cardiomyocyte RAE-1-CD8+ T cell-NKG2D axis holds promise for novel therapeutic strategies to limit hypertensive cardiac fibrosis.

Endothelial-specific overexpression of cationic amino acid transporter-1 prevents loss of kidney function in heart failure

Heart failure (HF) is associated with impaired L-arginine transport. In the present study, we tested the hypothesis that augmented L-arginine transport prevents the loss of kidney function in HF. Renal function was assessed in wildtype mice (WT), transgenic mice with HF (dilated cardiomyopathy, DCM) and double transgenic mice (double transgenic mice with DCM and CAT-1 overexpression, HFCAT-1) with HF and endothelial-specific overexpression of the predominant L-arginine transporter, cationic amino acid transporter-1 (CAT-1) (n=4-8/group). Cardiac function was assessed via echocardiography and left ventricular catheterisation. Renal function was assessed via quantification of albuminuria and creatinine clearance. Plasma nitrate and nitrite levels together with renal fibrosis and inflammatory markers were also quantified at study end. Albumin/creatinine ratio was two-fold greater in DCM mice than in WT mice (P=0.002), and tubulointerstitial and glomerular fibrosis were approximately eight- and three-fold greater, respectively, in DCM mice than in WT mice (P≤0.02). Critically, urinary albumin/creatinine ratio and tubulointerstitial and glomerular fibrosis were less in HFCAT-1 mice than in DCM mice (P<0.05). Renal CAT-1 expression and plasma nitrate and nitrite levels were less in DCM mice compared with WT (P≤0.03) but was greater in HFCAT-1 mice than in DCM mice (P≤0.009). Renal expression of IL-10 was less in DCM mice compared with WT (P<0.001) but was greater in HFCAT-1 mice compared with DCM mice (P=0.02). Our data provide direct evidence that augmented L-arginine transport prevents renal fibrosis, inflammation and loss of kidney function in HF.

Optimal Medical Therapy Following Transcatheter Aortic Valve Implantation

Limited data exist on optimal medical therapy post-transcatheter aortic valve implantation (TAVI) for late cardiovascular events prevention. We aimed to evaluate the benefits of beta-blocker (BB), renin-angiotensin system inhibitor (RASi), and their combination on outcomes following successful TAVI. In a consecutive cohort of 1,684 patients with severe aortic stenosis undergoing TAVI, the status of BB and RASi treatment at discharge was collected, and patients were classified into 4 groups: no-treatment, BB alone, RASi alone, and combination groups. The primary outcome was a composite of all-cause mortality and rehospitalization for heart failure (HHF) at 2-year. There were 415 (25%), 462 (27%), 349 (21%), and 458 (27%) patients in no-treatment, BB alone, RASi alone, and combination groups, respectively. The primary outcome was lower in RASi alone (21%; adjusted hazard ratio [HR]_adj: 0.58; 95% confidence interval [CI]: 0.42 to 0.81) and combination (22%; HR_adj: 0.53; 95% CI: 0.39 to 0.72) groups than in no-treatment group (34%) but no significant difference between RASi alone and combination groups (HR_adj: 1.14; 95% CI: 0.80 to 1.62). The primary outcome results were maintained in a sensitivity analysis of patients with reduced left ventricular systolic function. Furthermore, RASi treatment was an independent predictor of 2-year all-cause mortality (HR_adj: 0.68; 95% CI: 0.51 to 0.90), while that was not observed in BB therapy (HR_adj: 0.94; 95% CI: 0.71 to 1.25). In conclusion, post-TAVI treatment with RASi, but not with BB, was associated with lower all-cause mortality and HHF at 2-year. The combination of RASi and BB did not add an incremental reduction in the primary outcome over RASi alone.

Intrauterine Programming of Diabetes Induced Cardiac Embryopathy

BACKGROUND

Maternal hyperglycemia is a well-recognized risk factor for fetal congenital heart disease. However, the underlying cellular and molecular mechanisms are not well characterized. We hypothesize that maternal hyperglycemia leading to congenital heart are linked to abnormal DNA methylation and mRNA expression at cardiac specific loci.

METHODS

Hyperglycemia was induced in normal 8-week old CD-1 female mice with a one-time intraperitoneal injection of 150 mg/kg of streptozotocin (STZ) 2 weeks prior to mating. Histological analysis of fetal cardiac morphology was evaluated for malformations on embryonic day (E) 16.5 of control pups and pups exposed to maternal hyperglycemia. We used a massively-parallel sequencing-based methylation sensitive restriction based assay to examine genome-wide cytosine methylation levels at >1.65 million loci in neonatal hearts on post-natal (P) day 0. Functional validation was performed with real time quantitative polymerase chain reaction (RT-qPCR).

RESULTS

Cardiac structural defects occurred in 28% of the pups (n=12/45) of hyperglycemic dams versus 7% (n=4/61) of controls. Notable phenotypes were hypoplastic left or right ventricle, double outlet right ventricle, ventricular septal defect, and left ventricular outflow tract obstruction. A 10-fold increase in DNA methylation of gene promoter regions was seen in many cardiac important genes in the experimental versus control P0 neonates and have corresponding decreases in gene expression in 21/32 genes functionally validated.

CONCLUSION

Maternal hyperglycemia alters DNA methylation and mRNA expression of some cardiac genes during heart development. Quantitative, genome-wide assessment of cytosine methylation can be used as a discovery platform to gain insight into the mechanisms of hyperglycemia-induced cardiac anomalies.