A mouse model of reverse cardiac remodelling following banding-debanding of the ascending aorta

Left ventricular remodeling following aortic root and ascending aneurysm repair

Objective

Adverse left ventricular remodeling due to a mismatch between stiffness of native aortic tissue and current polyester grafts may be under-recognized. This study was conducted to evaluate the impact of proximal aortic replacement on adverse remodeling of the left ventricle.

Materials and methods

All aortic root and ascending aortic aneurysm patients were identified (n = 2,001, 2006-2019). The study cohort consisted of a subset of patients (n = 98) with two or more electrocardiogram (ECG)-gated CT angiograms, but without concomitant aortic valve disease or bicuspid aortic valve, connective tissue disease, acute aortic syndrome or prior history of aortic repair or mitral valve surgery. LV myocardial mass was measured from CT data and indexed to body surface area (LVMI). The study cohort was divided into a surgery group (n = 47) and a control group; optimal medical therapy group (OMT, n = 51).

Results

The mean age was 60 ± 11 years (80% male). Beta-blocker use was significantly more frequent in the surgery group (89 vs. 57%, p < 0.001), whereas, all other antihypertensive drugs were more frequent in the OMT group. The average follow-up was 9.1 ± 4.0 months for the surgery group and 13.7 ± 6.3 months for the OMT group. Average LVMI at baseline was similar in both groups (p = 0.934). LVMI increased significantly in the surgery group compared to the OMT group (3.7 ± 4.1 vs. 0.6 ± 4.4 g/m2, p = 0.001). Surgery, baseline LVMI, age, and sex were found to be independent predictors of LVMI increased on multivariable analysis.

Conclusion

Proximal aortic repair with stiff polyester grafts was associated with increased LV mass in the first-year post-operative and may promote long-term adverse cardiac remodeling. Further studies should be considered to evaluate the competing effects of aortic aneurysm related mortality against risks of long-term graft induced aortic stiffening and the potential implications on current size thresholds for intervention.

Calcineurin-NFAT dynamics correspond to cardiac remodeling during aortic banding and debanding, mimicking aortic valve replacement

Aortic valve stenosis (AS) is a major health problem. Extensive myocardial remodeling increases operative risk and might lead to incomplete reverse remodeling with persistent symptoms after aortic valve replacement (AVR); this makes the optimal timing of AVR a clinical challenge. The pathogenesis behind incomplete reverse remodeling is unclear. Central among signaling pathways in the remodeling heart is the pro-hypertrophic Ca2+-activated calcineurin and its downstream nuclear factor of activated T-cell (NFATc1-c4) transcription factors. We investigated calcineurin-NFATc dynamics in patient and mouse hearts during remodeling and reverse remodeling. Myocardial biopsies were obtained from AS patients during AVR and left ventricles harvested from mice subjected to aortic banding (AB) and debanding (DB). The transcript and protein of the NFATc-responsive gene regulator of calcineurin 1-4 (RCAN1-4) and luciferase activity in NFAT-luciferase mice were used as read-outs for calcineurin-NFATc activity. Calcineurin-NFATc activation was sustained through AB 24 h to 18 weeks and elevated in AS patients. All four NFATc isoforms were elevated in AS, while NFATc4 was persistently elevated during chronic remodeling after AB in mice. NFAT activation remained reversible when 1 week's AB was followed by 1 week's DB and accompanied functional improvement. However, when DB for 1 week followed AB for 4 weeks, NFAT activation was not reversed. In conclusion, calcineurin-NFAT dynamics correspond with cardiac remodeling and reverse remodeling during experimental AB and DB. Our data suggest that calcineurin-NFATc attenuation is important for reverse remodeling and outcomes after AVR for AS.

Large and Small Animal Models of Heart Failure With Reduced Ejection Fraction

Heart failure (HF) describes a heterogenous complex spectrum of pathological conditions that results in structural and functional remodeling leading to subsequent impairment of cardiac function, including either systolic dysfunction, diastolic dysfunction, or both. Several factors chronically lead to HF, including cardiac volume and pressure overload that may result from hypertension, valvular lesions, acute, or chronic ischemic injuries. Major forms of HF include hypertrophic, dilated, and restrictive cardiomyopathy. The severity of cardiomyopathy can be impacted by other comorbidities such as diabetes or obesity and external stress factors. Age is another major contributor, and the number of patients with HF is rising worldwide in part due to an increase in the aged population. HF can occur with reduced ejection fraction (HF with reduced ejection fraction), that is, the overall cardiac function is compromised, and typically the left ventricular ejection fraction is lower than 40%. In some cases of HF, the ejection fraction is preserved (HF with preserved ejection fraction). Animal models play a critical role in facilitating the understanding of molecular mechanisms of how hearts fail. This review aims to summarize and describe the strengths, limitations, and outcomes of both small and large animal models of HF with reduced ejection fraction that are currently used in basic and translational research. The driving defect is a failure of the heart to adequately supply the tissues with blood due to impaired filling or pumping. An accurate model of HF with reduced ejection fraction would encompass the symptoms (fatigue, dyspnea, exercise intolerance, and edema) along with the pathology (collagen fibrosis, ventricular hypertrophy) and ultimately exhibit a decrease in cardiac output. Although countless experimental studies have been published, no model completely recapitulates the full human disease. Therefore, it is critical to evaluate the strength and weakness of each animal model to allow better selection of what animal models to use to address the scientific question proposed.

O-ring-induced transverse aortic constriction (OTAC) is a new simple method to develop cardiac hypertrophy and heart failure in mice

Suture-based transverse aortic constriction (TAC) in mice is one of the most frequently used experimental models for cardiac pressure overload-induced heart failure. However, the incidence of heart failure in the conventional TAC depends on the operator's skill. To optimize and simplify this method, we proposed O-ring-induced transverse aortic constriction (OTAC) in mice. C57BL/6J mice were subjected to OTAC, in which an o-ring was applied to the transverse aorta (between the brachiocephalic artery and the left common carotid artery) and tied with a triple knot. We used different inner diameters of o-rings were 0.50 and 0.45 mm. Pressure overload by OTAC promoted left ventricular (LV) hypertrophy. OTAC also increased lung weight, indicating severe pulmonary congestion. Echocardiographic findings revealed that both OTAC groups developed LV hypertrophy within one week after the procedure and gradually reduced LV fractional shortening. In addition, significant elevations in gene expression related to heart failure, LV hypertrophy, and LV fibrosis were observed in the LV of OTAC mice. We demonstrated the OTAC method, which is a simple and effective cardiac pressure overload method in mice. This method will efficiently help us understand heart failure (HF) mechanisms with reduced LV ejection fraction (HFrEF) and cardiac hypertrophy.

Reverse remodelling in diabetic cardiomyopathy: the role of extracellular matrix

Diabetic patients are prone to suffer from cardiovascular disease, specifically from ischemic heart disease and diabetic cardiomyopathy, which have a huge impact on morbidity and mortality worldwide. Cardiac fibrosis due to alteration of the extracellular matrix (ECM) remodelling is often observed in diabetes and myocardial fibrosis is an important part of cardiac remodeling that leads to heart failure and death. At single-cell level, the ECM govern, metabolism, motility, orientation and proliferation. However, in pathological condition such as diabetes, changes in ECM lead to fibrosis and subsequently cardiac stiffness and cardiomyocytes dysfunction. Anti-diabetic drugs, particularly sodium-glucose cotransporter-2 (SGLT2) inhibitors have anti-fibrotic effects, and may promote ECM reverse remodelling. In this mini-review, the mechanisms and the role of ECM remodelling and reverse remodelling as a potential therapeutic targets for diabetic cardiomyopathy are discussed.

The relationship between miRNA-26b and connective tissue growth factor in rat models of aortic banding and debanding

BACKGROUND/AIMS

Connective tissue growth factor (CTGF) is a profibrotic factor implicated in pressure overload-mediated myocardial fibrosis. In this study, we determined the role of predicted CTGF-targeting microRNAs (miRNAs) in rat models of aortic stenosis and reverse cardiac remodeling.

METHODS

Minimally invasive ascending aortic banding was performed in 24 7-week-old male Sprague-Dawley rats, which were divided into three groups. The banding group consisted of eight rats that were sacrificed immediately after 6 weeks of aortic constriction. The debanding group underwent aortic constriction for 4 weeks and was sacrificed 2 weeks after band removal. The third group underwent sham surgery. We investigated the expression of CTGF, transforming growth factor-β1 (TGFβ1), and matrix metalloproteinase-2 using ELISA and examined miRNA-26b, miRNA-133a, and miRNA-19b as predicted CTGF-targeting miRNAs based on miRNA databases in 24-hour TGFβ-stimulated and TGFβ- washed fibroblasts and myocardial tissues from all subjects.

RESULTS

CTGF was elevated in 24-hour TGFβ-stimulated fibroblasts and decreased in 24-hour TGFβ-washed fibroblasts. miRNA-26b was significantly increased in TGFβ-washed fibroblasts compared with control and TGFβ-stimulated fibroblasts (p < 0.05). CTGF expression was significantly higher in the banding group than that in the sham and debanding groups. The relative expression levels of miRNA-26b were higher in the debanding group than in the banding group.

CONCLUSION

The results of our study using models of aortic banding and debanding suggested that miRNA-26b was significantly increased after aortic debanding. The in vitro model yielded the same results: miRNA-26b was upregulated after removal of TGFβ from fibroblasts.

The Role of Tenascin C in Cardiac Reverse Remodeling Following Banding-Debanding of the Ascending Aorta

Background: Tenascin-C (TN-C) plays a maladaptive role in left ventricular (LV) hypertrophy following pressure overload. However, the role of TN-C in LV regression following mechanical unloading is unknown. Methods: LV hypertrophy was induced by transverse aortic constriction for 10 weeks followed by debanding for 2 weeks in wild type (Wt) and TN-C knockout (TN-C KO) mice. Cardiac function was assessed by serial magnetic resonance imaging. The expression of fibrotic markers and drivers (angiotensin-converting enzyme-1, ACE-1) was determined in LV tissue as well as human cardiac fibroblasts (HCFs) after TN-C treatment. Results: Chronic pressure overload resulted in a significant decline in cardiac function associated with LV dilation as well as upregulation of TN-C, collagen 1 (Col 1), and ACE-1 in Wt as compared to TN-C KO mice. Reverse remodeling in Wt mice partially improved cardiac function and fibrotic marker expression; however, TN-C protein expression remained unchanged. In HCF, TN-C strongly induced the upregulation of ACE 1 and Col 1. Conclusions: Pressure overload, when lasting long enough to induce HF, has less potential for reverse remodeling in mice. This may be due to significant upregulation of TN-C expression, which stimulates ACE 1, Col 1, and alpha-smooth muscle actin (α-SMA) upregulation in fibroblasts. Consequently, addressing TN-C in LV hypertrophy might open a new window for future therapeutics.

The Degree of Cardiac Remodelling before Overload Relief Triggers Different Transcriptome and miRome Signatures during Reverse Remodelling (RR)-Molecular Signature Differ with the Extent of RR

This study aims to provide new insights into transcriptome and miRome modifications occurring in cardiac reverse remodelling (RR) upon left ventricle pressure-overload relief in mice. Pressure-overload was established in seven-week-old C57BL/6J-mice by ascending aortic constriction. A debanding (DEB) surgery was performed seven weeks later in half of the banding group (BA). Two weeks later, cardiac function was evaluated through hemodynamics and echocardiography, and the hearts were collected for histology and small/bulk-RNA-sequencing. Pressure-overload relief was confirmed by the normalization of left-ventricle-end-systolic-pressure. DEB animals were separated into two subgroups according to the extent of cardiac remodelling at seven weeks and RR: DEB1 showed an incomplete RR phenotype confirmed by diastolic dysfunction persistence (E/e' ≥ 16 ms) and increased myocardial fibrosis. At the same time, DEB2 exhibited normal diastolic function and fibrosis, presenting a phenotype closer to myocardial recovery. Nevertheless, both subgroups showed the persistence of cardiomyocytes hypertrophy. Notably, the DEB1 subgroup presented a more severe diastolic dysfunction at the moment of debanding than the DEB2, suggesting a different degree of cardiac remodelling. Transcriptomic and miRomic data, as well as their integrated analysis, revealed significant downregulation in metabolic and hypertrophic related pathways in DEB1 when compared to DEB2 group, including fatty acid β-oxidation, mitochondria L-carnitine shuttle, and nuclear factor of activated T-cells pathways. Moreover, extracellular matrix remodelling, glycan metabolism and inflammation-related pathways were up-regulated in DEB1. The presence of a more severe diastolic dysfunction at the moment of pressure overload-relief on top of cardiac hypertrophy was associated with an incomplete RR. Our transcriptomic approach suggests that a cardiac inflammation, fibrosis, and metabolic-related gene expression dysregulation underlies diastolic dysfunction persistence after pressure-overload relief, despite left ventricular mass regression, as echocardiographically confirmed.

Mitochondrial Reversible Changes Determine Diastolic Function Adaptations During Myocardial (Reverse) Remodeling

BACKGROUND

Often, pressure overload-induced myocardial remodeling does not undergo complete reverse remodeling after decreasing afterload. Recently, mitochondrial abnormalities and oxidative stress have been successively implicated in the pathogenesis of several chronic pressure overload cardiac diseases. Therefore, we aim to clarify the myocardial energetic dysregulation in (reverse) remodeling, mainly focusing on the mitochondria.

METHODS

Thirty-five Wistar Han male rats randomly underwent sham or ascending (supravalvular) aortic banding procedure. Echocardiography revealed that banding induced concentric hypertrophy and diastolic dysfunction (early diastolic transmitral flow velocity to peak early-diastolic annular velocity ratio, E/E': sham, 13.6±2.1, banding, 18.5±4.1, P=0.014) accompanied by increased oxidative stress (dihydroethidium fluorescence: sham, 1.6×10⁸±6.1×10⁷, banding, 2.6×10⁸±4.5×10⁷, P<0.001) and augmented mitochondrial function. After 8 to 9 weeks, half of the banding animals underwent overload relief by an aortic debanding surgery (n=10).

RESULTS

Two weeks later, hypertrophy decreased with the decline of oxidative stress (dihydroethidium fluorescence: banding, 2.6×10⁸±4.5×10⁷, debanding, 1.96×10⁸±6.8×10⁷, P<0.001) and diastolic dysfunction improved simultaneously (E/E': banding, 18.5±4.1, debanding, 15.1±1.8, P=0.029). The reduction of energetic demands imposed by overload relief allowed the mitochondria to reduce its activity and myocardial levels of phosphocreatine, phosphocreatine/ATP, and ATP/ADP to normalize in debanding towards sham values (phosphocreatine: sham, 38.4±7.4, debanding, 35.6±8.7, P=0.71; phosphocreatine/ATP: sham, 1.22±0.23 debanding, 1.11±0.24, P=0.59; ATP/ADP: sham, 6.2±0.9, debanding, 5.6±1.6, P=0.66). Despite the decreased mitochondrial area, complex III and V expression increased in debanding compared with sham or banding. Autophagy and mitophagy-related markers increased in banding and remained higher in debanding rats.

CONCLUSIONS

During compensatory and maladaptive hypertrophy, mitochondria become more active. However, as the disease progresses, the myocardial energetic demands increase and the myocardium becomes energy deficient. During reverse remodeling, the concomitant attenuation of cardiac hypertrophy and oxidative stress allowed myocardial energetics, left ventricle hypertrophy, and diastolic dysfunction to recover. Autophagy and mitophagy are probably involved in the myocardial adaptation to overload and to unload. We conclude that these mitochondrial reversible changes underlie diastolic function adaptations during myocardial (reverse) remodeling.

Progression and regression of left ventricular hypertrophy and myocardial fibrosis in a mouse model of hypertension and concomitant cardiomyopathy

BACKGROUND

Myocardial fibrosis is observed in multiple cardiac conditions including hypertension and aortic stenosis. Excessive fibrosis is associated with adverse clinical outcomes, but longitudinal human data regarding changes in left ventricular remodelling and fibrosis over time are sparse because of the slow progression, thereby making longitudinal studies challenging. The purpose of this study was to establish and characterize a mouse model to study the development and regression of left ventricular hypertrophy and myocardial fibrosis in response to increased blood pressure and to understand how these processes reverse remodel following normalisation of blood pressure.

METHODS

We performed a longitudinal study with serial cardiovascular magnetic resonance (CMR) imaging every 2 weeks in mice (n = 31) subjected to angiotensin II-induced hypertension for 6 weeks and investigated reverse remodelling following normalisation of afterload beyond 6 weeks (n = 9). Left ventricular (LV) volumes, mass, and function as well as myocardial fibrosis were measured using cine CMR and the extracellular volume fraction (ECV) s.

RESULTS

Increased blood pressure (65 ± 12 vs 85 ± 9 mmHg; p < 0.001) resulted in higher indices of LV hypertrophy (0.09 [0.08, 0.10] vs 0.12 [0.11, 0.14] g; p < 0.001) and myocardial fibrosis (ECV: 0.24 ± 0.03 vs 0.30 ± 0.02; p < 0.001) whilst LV ejection fraction fell (LVEF, 59.3 [57.6, 59.9] vs 46.9 [38.5, 49.6] %; p < 0.001). We found a strong correlation between ECV and histological myocardial fibrosis (r = 0.89, p < 0.001). Following cessation of angiotensin II and normalisation of blood pressure (69 ± 5 vs baseline 65 ± 12 mmHg; p = 0.42), LV mass (0.11 [0.10, 0.12] vs 0.09 [0.08, 0.11] g), ECV (0.30 ± 0.02 vs 0.27 ± 0.02) and LVEF (51.1 [42.9, 52.8] vs 59.3 [57.6, 59.9] %) improved but remained impaired compared to baseline (p < 0.05 for all). There was a strong inverse correlation between LVEF and %ECV during both systemic hypertension (r = - 0.88, p < 0.001) and the increases in ECV observed in the first two weeks of increased blood pressure predicted the reduction in LVEF after 6 weeks (r = - 0.77, p < 0.001).

CONCLUSIONS

We have established and characterized angiotensin II infusion and repeated CMR imaging as a model of LV hypertrophy and reverse remodelling in response to systemic hypertension. Changes in myocardial fibrosis and alterations in cardiac function are only partially reversible following relief of hypertension.

Incomplete structural reverse remodeling from late-stage left ventricular hypertrophy impedes the recovery of diastolic but not systolic dysfunction in rats

OBJECTIVE

Pressure overload-induced left ventricular myocardial hypertrophy (LVH) regresses after pressure unloading. However, distinct structural alterations become less reversible during the progression of LVH, which might influence the restoration of cardiac function. Here, we investigated how a reverse remodeling process from early versus late-stage LVH affects different aspects of left ventricular function.

METHODS

Pressure overload was induced in rats for 6, 12 and 18 weeks. Sham-operated animals were used as controls. Pressure unloading was evoked by removing the aortic constriction at week 6 (early-debanded) and week 12 (late-debanded). Echocardiography and histological analyses were carried out to detect structural alterations. Pressure-volume analysis was performed to assess left ventricular function. Molecular alterations were analyzed by quantitative real-time-PCR, and western blot.

RESULTS

Myocardial hypertrophy regressed to a similar degree in early and late-debanded groups. Accordingly, no differences were detected in the extent of regression regarding left ventricular mass, cardiomyocyte diameter, heart weight-to-tibial length ratio and beta-to-alpha myosin heavy chain expression. In contrast, resorption of interstitial and perivascular myocardial fibrosis was only detected in the early-debanded group, whereas it persisted in the late-debanded group. Removing the aortic constriction normalized ventriculo-arterial coupling and increased systolic performance in both debanded groups. However, the residual dysfunction in active relaxation and passive stiffness was more severe in the late-debanded compared to the early-debanded group.

CONCLUSION

Early debanding led to complete structural reverse remodeling (reduced hypertrophy and fibrosis) and full restoration of left ventricular function. In contrast, myocardial fibrosis persisted after late debanding, which impeded the normalization of diastolic but not systolic function.

The extracellular matrix proteoglycan lumican improves survival and counteracts cardiac dilatation and failure in mice subjected to pressure overload

Left ventricular (LV) dilatation is a key step in transition to heart failure (HF) in response to pressure overload. Cardiac extracellular matrix (ECM) contains fibrillar collagens and proteoglycans, important for maintaining tissue integrity. Alterations in collagen production and cross-linking are associated with cardiac LV dilatation and HF. Lumican (LUM) is a collagen binding proteoglycan with increased expression in hearts of patients and mice with HF, however, its role in cardiac function remains poorly understood. To examine the role of LUM in pressure overload induced cardiac remodeling, we subjected LUM knock-out (LUMKO) mice to aortic banding (AB) and treated cultured cardiac fibroblasts (CFB) with LUM. LUMKO mice exhibited increased mortality 1-14 days post-AB. Echocardiography revealed increased LV dilatation, altered hypertrophic remodeling and exacerbated contractile dysfunction in surviving LUMKO 1-10w post-AB. LUMKO hearts showed reduced collagen expression and cross-linking post-AB. Transcriptional profiling of LUMKO hearts by RNA sequencing revealed 714 differentially expressed transcripts, with enrichment of cardiotoxicity, ECM and inflammatory pathways. CFB treated with LUM showed increased mRNAs for markers of myofibroblast differentiation, proliferation and expression of ECM molecules important for fibrosis, including collagens and collagen cross-linking enzyme lysyl oxidase. In conclusion, we report the novel finding that lack of LUM attenuates collagen cross-linking in the pressure-overloaded heart, leading to increased mortality, dilatation and contractile dysfunction in mice.

Characterization of biventricular alterations in myocardial (reverse) remodelling in aortic banding-induced chronic pressure overload

Aortic Stenosis (AS) is the most frequent valvulopathy in the western world. Traditionally aortic valve replacement (AVR) has been recommended immediately after the onset of heart failure (HF) symptoms. However, recent evidence suggests that AVR outcome can be improved if performed earlier. After AVR, the process of left ventricle (LV) reverse remodelling (RR) is variable and frequently incomplete. In this study, we aimed at detecting mechanism underlying the process of LV RR regarding myocardial structural, functional and molecular changes before the onset of HF symptoms. Wistar-Han rats were subjected to 7-weeks of ascending aortic-banding followed by a 2-week period of debanding to resemble AS-induced LV remodelling and the early events of AVR-induced RR, respectively. This resulted in 3 groups: Sham (n = 10), Banding (Ba, n = 15) and Debanding (Deb, n = 10). Concentric hypertrophy and diastolic dysfunction (DD) were patent in the Ba group. Aortic-debanding induced RR, which promoted LV functional recovery, while cardiac structure did not normalise. Cardiac parameters of RV dysfunction, assessed by echocardiography and at the cardiomyocyte level prevailed altered after debanding. After debanding, these alterations were accompanied by persistent changes in pathways associated to myocardial hypertrophy, fibrosis and LV inflammation. Aortic banding induced pulmonary arterial wall thickness to increase and correlates negatively with effort intolerance and positively with E/e′ and left atrial area. We described dysregulated pathways in LV and RV remodelling and RR after AVR. Importantly we showed important RV-side effects of aortic constriction, highlighting the impact that LV-reverse remodelling has on both ventricles.

Experimental modelling of cardiac pressure overload hypertrophy: Modified technique for precise, reproducible, safe and easy aortic arch banding-debanding in mice

Pressure overload left ventricular hypertrophy is a known precursor of heart failure with ominous prognosis. The development of experimental models that reproduce this phenomenon is instrumental for the advancement in our understanding of its pathophysiology. The gold standard of these models is the controlled constriction of the mid aortic arch in mice according to Rockman's technique (RT). We developed a modified technique that allows individualized and fully controlled constriction of the aorta, improves efficiency and generates a reproducible stenosis that is technically easy to perform and release. An algorithm calculates, based on the echocardiographic arch diameter, the intended perimeter at the constriction, and a suture is prepared with two knots separated accordingly. The aorta is encircled twice with the suture and the loop is closed with a microclip under both knots. We performed controlled aortic constriction with Rockman's and the double loop-clip (DLC) techniques in mice. DLC proved superiority in efficiency (mortality and invalid experiments) and more homogeneity of the results (transcoarctational gradients, LV mass, cardiomyocyte hypertrophy, gene expression) than RT. DLC technique optimizes animal use and generates a consistent and customized aortic constriction with homogeneous LV pressure overload morphofunctional, structural, and molecular features.

Calcific Aortic Valve Disease: Part 2-Morphomechanical Abnormalities, Gene Reexpression, and Gender Effects on Ventricular Hypertrophy and Its Reversibility

In part 1, we considered cytomolecular mechanisms underlying calcific aortic valve disease (CAVD), hemodynamics, and adaptive feedbacks controlling pathological left ventricular hypertrophy provoked by ensuing aortic valvular stenosis (AVS). In part 2, we survey diverse signal transduction pathways that precede cellular/molecular mechanisms controlling hypertrophic gene expression by activation of specific transcription factors that induce sarcomere replication in-parallel. Such signaling pathways represent potential targets for therapeutic intervention and prevention of decompensation/failure. Hypertrophy provoking signals, in the form of dynamic stresses and ligand/effector molecules that bind to specific receptors to initiate the hypertrophy, are transcribed across the sarcolemma by several second messengers. They comprise intricate feedback mechanisms involving gene network cascades, specific signaling molecules encompassing G protein-coupled receptors and mechanotransducers, and myocardial stresses. Future multidisciplinary studies will characterize the adaptive/maladaptive nature of the AVS-induced hypertrophy, its gender- and individual patient-dependent peculiarities, and its response to surgical/medical interventions. They will herald more effective, precision medicine treatments.

Myocardial reverse remodeling after pressure unloading is associated with maintained cardiac mechanoenergetics in a rat model of left ventricular hypertrophy

Pressure unloading represents the only effective therapy in increased afterload-induced left ventricular hypertrophy (LVH) as it leads to myocardial reverse remodeling (reduction of increased left ventricular mass, attenuated myocardial fibrosis) and preserved cardiac function. However, the effect of myocardial reverse remodeling on cardiac mechanoenergetics has not been elucidated. Therefore, we aimed to provide a detailed hemodynamic characterization in a rat model of LVH undergoing pressure unloading. Pressure overload was induced in Sprague-Dawley rats by abdominal aortic banding for 6 (AB 6th wk) or 12 wk (AB 12th wk). Sham-operated animals served as controls. Aortic debanding procedure was performed after the 6th experimental week (debanded 12th wk) to investigate the regression of LVH. Pressure unloading resulted in significant reduction of LVH (heart weight-to-tibial length ratio: 0.38 ± 0.01 vs. 0.58 ± 0.02 g/mm, cardiomyocyte diameter: 18.3 ± 0.1 vs. 24.1 ± 0.8 μm debanded 12th wk vs. AB 12th wk, P < 0.05), attenuated the extracellular matrix remodeling (Masson's score: 1.37 ± 0.13 vs. 1.73 ± 0.10, debanded 12th wk vs. AB 12th wk, P < 0.05), provided protection against the diastolic dysfunction, and reversed the maladaptive contractility augmentation (slope of end-systolic pressure-volume relationship: 1.39 ± 0.24 vs. 2.04 ± 0.09 mmHg/μl, P < 0.05 debanded 12th wk vs. AB 6th wk, P < 0.05). In addition, myocardial reverse remodeling was also associated with preserved ventriculoarterial coupling and increased mechanical efficiency (50.6 ± 2.8 vs. 38.9 ± 2.5%, debanded 12th wk vs. AB 12th wk, P < 0.05), indicating a complete functional and mechanoenergetic recovery. According to our best knowledge, this is the first study demonstrating that the regression of LVH is accompanied by maintained cardiac mechanoenergetics.

Cellular, structural and functional cardiac remodelling following pressure overload and unloading

BACKGROUND

The cardiac remodelling process in advanced heart failure due to pressure overload has not been clearly defined but likely involves mechanisms of cardiac fibrosis and cardiomyocyte hypertrophy. The aim of this study was to examine pressure overload (PO)-induced cardiac remodelling processes and their reversibility after unloading in both humans with heart failure and a mouse model of PO induced by aortic constriction.

METHODS & RESULTS

Speckle tracking echocardiography showed PO-induced cardiac dysfunction in mice was reversible after removal of aortic constriction to unload. Masson's Trichrome staining suggested that PO-induced myocardial fibrosis was reversible, however detailed analysis of 3-dimensional collagen architecture by scanning electron microscopy demonstrated that matrix remodelling was not completely normalised as a disorganised network of thin collagen fibres was evident. Analysis of human left ventricular biopsy samples from HF patients revealed increased presence of large collagen fibres which were greatly reduced in paired samples from the same individuals after unloading by left ventricular assist device implantation. Again, an extensive network of small collagen fibres was still clearly seen to closely surround cardiomyocytes after unloading. Other features of PO-induced remodelling including increased myofibroblast content, cardiomyocyte disarray and hypertrophy were largely reversed upon unloading in both humans and mouse model. Previous work in humans demonstrated that receptors for adiponectin, an important mediator of cardiac fibrosis and hypertrophy, decreased in heart failure patients and returned to normal after unloading. Here we provide novel data showing a similar trend for adiponectin receptor adaptor protein APPL1, but not APPL2 isoform.

CONCLUSIONS

LV unloading diminishes PO-induced cardiac remodelling and improves function. These findings add new insights into the cardiac remodelling process, and provide novel targets for future pharmacologic therapies.

Myocardial reverse remodeling: how far can we rewind?

Heart failure (HF) is a systemic disease that can be divided into HF with reduced ejection fraction (HFrEF) and with preserved ejection fraction (HFpEF). HFpEF accounts for over 50% of all HF patients and is typically associated with high prevalence of several comorbidities, including hypertension, diabetes mellitus, pulmonary hypertension, obesity, and atrial fibrillation. Myocardial remodeling occurs both in HFrEF and HFpEF and it involves changes in cardiac structure, myocardial composition, and myocyte deformation and multiple biochemical and molecular alterations that impact heart function and its reserve capacity. Understanding the features of myocardial remodeling has become a major objective for limiting or reversing its progression, the latter known as reverse remodeling (RR). Research on HFrEF RR process is broader and has delivered effective therapeutic strategies, which have been employed for some decades. However, the RR process in HFpEF is less clear partly due to the lack of information on HFpEF pathophysiology and to the long list of failed standard HF therapeutics strategies in these patient's outcomes. Nevertheless, new proteins, protein-protein interactions, and signaling pathways are being explored as potential new targets for HFpEF remodeling and RR. Here, we review recent translational and clinical research in HFpEF myocardial remodeling to provide an overview on the most important features of RR, comparing HFpEF with HFrEF conditions.

Normalization of cardiac substrate utilization and left ventricular hypertrophy precede functional recovery in heart failure regression

AIMS

Impaired cardiac substrate metabolism plays an important role in heart failure (HF) pathogenesis. Since many of these metabolic changes occur at the transcriptional level of metabolic enzymes, it is possible that this loss of metabolic flexibility is permanent and thus contributes to worsening cardiac function and/or prevents the full regression of HF upon treatment. However, despite the importance of cardiac energetics in HF, it remains unclear whether these metabolic changes can be normalized. In the current study, we investigated whether a reversal of an elevated aortic afterload in mice with severe HF would result in the recovery of cardiac function, substrate metabolism, and transcriptional reprogramming as well as determined the temporal relationship of these changes.

METHODS AND RESULTS

Male C57Bl/6 mice were subjected to either Sham or transverse aortic constriction (TAC) surgery to induce HF. After HF development, mice with severe HF (% ejection fraction < 30) underwent a second surgery to remove the aortic constriction (debanding, DB). Three weeks following DB, there was a near complete recovery of systolic and diastolic function, and gene expression of several markers for hypertrophy/HF were returned to values observed in healthy controls. Interestingly, pressure-overload-induced left ventricular hypertrophy (LVH) and cardiac substrate metabolism were restored at 1-week post-DB, which preceded functional recovery.

CONCLUSIONS

The regression of severe HF is associated with early and dramatic improvements in cardiac energy metabolism and LVH normalization that precede restored cardiac function, suggesting that metabolic and structural improvements may be critical determinants for functional recovery.

Lack of collagen VIII reduces fibrosis and promotes early mortality and cardiac dilatation in pressure overload in mice

AIMS

In pressure overload, left ventricular (LV) dilatation is a key step in transition to heart failure (HF). We recently found that collagen VIII (colVIII), a non-fibrillar collagen and extracellular matrix constituent, was reduced in hearts of mice with HF and correlated to degree of dilatation. A reduction in colVIII might be involved in LV dilatation, and we here examined the role of reduced colVIII in pressure overload-induced remodelling using colVIII knock-out (col8KO) mice.

METHODS AND RESULTS

Col8KO mice exhibited increased mortality 3-9 days after aortic banding (AB) and increased LV dilatation from day one after AB, compared with wild type (WT). LV dilatation remained increased over 56 days. Forty-eight hours after AB, LV expression of main structural collagens (I and III) was three-fold increased in WT mice, but these collagens were unaltered in the LV of col8KO mice together with reduced expression of the pro-fibrotic cytokine TGF-β, SMAD2 signalling, and the myofibroblast markers Pxn, α-SMA, and SM22. Six weeks after AB, LV collagen mRNA expression and protein were increased in col8KO mice, although less pronounced than in WT. In vitro, neonatal cardiac fibroblasts from col8KO mice showed lower expression of TGF-β, Pxn, α-SMA, and SM22 and reduced migratory ability possibly due to increased RhoA activity and reduced MMP2 expression. Stimulation with recombinant colVIIIα1 increased TGF-β expression and fibroblast migration.

CONCLUSION

Lack of colVIII reduces myofibroblast differentiation and fibrosis and promotes early mortality and LV dilatation in response to pressure overload in mice.

Myocardial mechanics in a rat model with banding and debanding of the ascending aorta

BACKGROUND

Aortic banding and debanding models have provided useful information on the development and regression of left ventricular hypertrophy (LVH). In this animal study, we aimed to evaluate left ventricular (LV) deformation related to the development and regression of LVH.

METHODS

Minimally invasive ascending aorta banding was performed in rats (10 Sprague Dawley rats, 7 weeks). Ten rats underwent a sham operation. Thirty-five days later, the band was removed. Echocardiographic and histopathologic analysis was assessed at pre-banding, 35 days of banding and 14 days of debanding.

RESULTS

Banding of the ascending aorta created an expected increase in the aortic velocity and gradient, which normalized with the debanding procedure. Pressure overload resulted in a robust hypertrophic response as assessed by gross and microscopic histology, transthoracic echocardiography [heart weight/tibia length (g/m); 21.0 ± 0.8 vs. 33.2 ± 2.0 vs. 26.6 ± 2.8, p < 0.001]. The circumferential (CS) and radial strains were not different between the groups. However, there were significant differences in the degree of fibrosis according to the banding status (fibrosis; 0.10 ± 0.20% vs. 5.26 ± 3.12% vs. 4.03 ± 3.93%, p = 0.003), and global CS showed a significant correlation with the degree of myocardial fibrosis in this animal model (r = 0.688, p = 0.028).

CONCLUSION

In this animal study, simulating a severe LV pressure overload state, a significant increase in the LV mass index did not result in a significant reduction in the LV mechanical parameters. The degree of LV fibrosis, which developed with pressure overload, was significantly related to the magnitude of left ventricular mechanics.

Decorin, lumican, and their GAG chain-synthesizing enzymes are regulated in myocardial remodeling and reverse remodeling in the mouse

On the basis of the role of small, leucine-rich proteoglycans (SLRPs) in fibrogenesis and inflammation, we hypothesized that they could be involved in cardiac remodeling and reverse remodeling as occurs during aortic stenosis and after aortic valve replacement. Thus, in a well-characterized aortic banding-debanding mouse model, we examined the SLRPs decorin and lumican and enzymes responsible for synthesis of their glycosaminoglycan (GAG) chains. Four weeks after banding of the ascending aorta, mice were subjected to a debanding operation (DB) and were subsequently followed for 3 or 14 days. Sham-operated mice served as controls. Western blotting revealed a 2.5-fold increase in the protein levels of glycosylated decorin in mice with left ventricular pressure overload after aortic banding (AB) with a gradual decrease after DB. Interestingly, protein levels of three key enzymes responsible for decorin GAG chain synthesis were also increased after AB, two of them gradually declining after DB. The inflammatory chemokine (C-X-C motif) ligand 16 (CXCL16) was increased after AB but was not significantly altered following DB. In cardiac fibroblasts CXCL16 increased the expression of the GAG-synthesizing enzyme chondroitin polymerizing factor (CHPF). The protein levels of lumican core protein with N-linked oligosaccharides increased by sevenfold after AB and decreased again 14 days after DB. Lumican with keratan sulfate chains was not regulated. In conclusion, this study shows alterations in glycosylated decorin and lumican core protein that might be implicated in myocardial remodeling and reverse remodeling, with a potential important role for CS/DS GAG chain-synthesizing enzymes.

Lumican is increased in experimental and clinical heart failure, and its production by cardiac fibroblasts is induced by mechanical and proinflammatory stimuli

During progression to heart failure (HF), myocardial extracellular matrix (ECM) alterations and tissue inflammation are central. Lumican is an ECM-localized proteoglycan associated with inflammatory conditions and known to bind collagens. We hypothesized that lumican plays a role in the dynamic alterations in cardiac ECM during development of HF. Thus, we examined left ventricular cardiac lumican in a mouse model of pressure overload and in HF patients, and investigated expression, regulation and effects of increased lumican in cardiac fibroblasts. After 4 weeks of aortic banding, mice were divided into groups of hypertrophy (AB) and HF (ABHF) based on lung weight and left atrial diameter. Sham-operated mice were used as controls. Accordingly, cardiac lumican mRNA and protein levels were increased in mice with ABHF. Similarly, cardiac biopsies from patients with end-stage HF revealed increased lumican mRNA and protein levels compared with control hearts. In vitro, mechanical stretch and the proinflammatory cytokine interleukin-1β increased lumican mRNA as well as secreted lumican protein from cardiac fibroblasts. Stimulation with recombinant glycosylated lumican increased collagen type I alpha 2, lysyl oxidase and transforming growth factor-β1 mRNA, which was attenuated by costimulation with an inhibitor of the proinflammatory transcription factor NFκB. Furthermore, lumican increased the levels of the dimeric form of collagen type I, decreased the activity of the collagen-degrading enzyme matrix metalloproteinase-9 and increased the phosphorylation of fibrosis-inducing SMAD3. In conclusion, cardiac lumican is increased in experimental and clinical HF. Inflammation and mechanical stimuli induce lumican production by cardiac fibroblasts and increased lumican altered molecules important for cardiac remodeling and fibrosis in cardiac fibroblasts, indicating a role in HF development.