Association between shear stress and platelet-derived transforming growth factor-β1 release and activation in animal models of aortic valve stenosis

Correlation between staging classification of aortic stenosis based on the extent of cardiac damage and platelet indices

BACKGROUND

Platelets play a key role in the natural history of aortic stenosis (AS) and after transcatheter aortic valve implantation (TAVI). An echo-based staging system stratifies patients with severe AS into 5 groups according to the associated cardiac damage phenotype. We aimed to correlate these AS stages with platelet indices in post-TAVI patients.

METHODS

Patients with severe AS who underwent TAVI and were admitted to intensive cardiac care unit (ICCU) were prospectively identified and divided into 5 groups according to extra-valvular cardiac damage [no extravalvular cardiac damage (Stage 0), left ventricular damage (Stage 1), left atrial or mitral valve damage (Stage 2), pulmonary vasculature or tricuspid valve damage (Stage 3), or right ventricular damage (Stage 4)]. Baseline characteristics and complete blood count including mean platelet volume (MPV) and immature platelet fraction (IPF) were collected within 2 h after the procedure and analyzed in relation to aortic stenosis staging.

RESULTS

A total of 220 patients were included. The mean age was 81 years old and 112 (50.9%) were female. Two (1%) patients were classified in stage 0; 34 (15%) in stage 1; 48 (22%) in stage 2; 49 (22%) in stage 3 and 87 (40%) in stage 4. Higher mean MPV values were correlated with higher AS staging (10.8 fL, 11 fL, 11.3 fL and 10.8 fL in stages 1, 2, 3 and 4, respectively, P = 0.02) as well as lower hemoglobin values (12 mg/dl, 11.6 mg/dl, 11 mg/dl and 11.3 mg/dl in stages 1, 2, 3 and 4, respectively P = 0.04). Mean IPF values were 5.3%, 5.58%, 5.57% and 4.83% in stage 1, 2, 3 and 4, respectively (P = 0.4). In a multivariate logistic regression model only MPV (OR = 2.6, P = 0.03) and body mass index (BMI) (OR = 1.17, P = 0.004) were correlated with higher staging (0-3) of AS.

CONCLUSIONS

Although IPF and MPV levels increased in stages 0-3, there was a decrease in indices in stage 4, (probably due to bone marrow dysfunction) in this end-stage population. Higher levels of MPV and lower levels of hemoglobin were independently correlated with higher stages (0-3) of AS.

Association between the Mean Platelet Volume and Prosthesis-patient Mismatch after Transcatheter Aortic Valve Replacement

Objective The mean platelet volume (MPV), a marker of platelet activity, is significantly higher in patients with aortic stenosis (AS) than in those without AS. The association between the platelet function and prosthesis-patient mismatch (PPM) after transcatheter aortic valve replacement (TAVR) remains unknown. Therefore, we investigated this association by measuring the MPV. Methods Of 237 patients who underwent TAVR, 148 with a median age of 84 years old were enrolled in this study. Blood tests and transthoracic echocardiography were performed at baseline and approximately six months after TAVR. PPM was defined as an aortic valve area index ≤0.85 cm2/m2 after TAVR. Variable changes from baseline to six-month follow-up were compared between patients with and without PPM. Results Forty-five patients (30%) developed PPM. The MPV was significantly higher in patients with PPM than in those without PPM. However, regarding the magnitude of change, the MPV was significantly less reduced in patients with PPM, and the percentage of patients with reduced MPV was lower in patients with PPM than in those without PPM. A logistic regression analysis revealed that a higher MPV and lack of MPV reduction at the six-month follow-up were independent predictors of PPM. Conclusion MPV values at the six-month follow-up were associated with PPM after TAVR in patients with AS. MPV values increase when PPM is present after TAVR and may be an indicator during the postoperative follow-up.

Unmet needs and knowledge gaps in aortic stenosis: A position paper from the Heart Valve Council of the French Society of Cardiology

Nowadays, valvular heart disease remains a significant challenge among cardiovascular diseases, affecting millions of people worldwide and exerting substantial pressure on healthcare systems. Within the spectrum of valvular heart disease, aortic stenosis is the most common valvular lesion in developed countries. Despite notable advances in understanding its pathophysiological processes, improved cardiovascular imaging techniques and expanding therapeutic options in recent years, there are still unmet needs and knowledge gaps regarding aortic stenosis pathophysiology, severity assessment, management and decision-making strategy. This review, prepared on behalf of the Heart Valve Council of the French Society of Cardiology, describes these gaps and future research perspectives to improve the outcome of patients with aortic stenosis.

Unraveling the Mechanisms of Valvular Heart Disease to Identify Medical Therapy Targets: A Scientific Statement From the American Heart Association

Valvular heart disease is a common cause of morbidity and mortality worldwide and has no effective medical therapy. Severe disease is managed with valve replacement procedures, which entail high health care-related costs and postprocedural morbidity and mortality. Robust ongoing research programs have elucidated many important molecular pathways contributing to primary valvular heart disease. However, there remain several key challenges inherent in translating research on valvular heart disease to viable molecular targets that can progress through the clinical trials pathway and effectively prevent or modify the course of these common conditions. In this scientific statement, we review the basic cellular structures of the human heart valves and discuss how these structures change in primary valvular heart disease. We focus on the most common primary valvular heart diseases, including calcific aortic stenosis, bicuspid aortic valves, mitral valve prolapse, and rheumatic heart disease, and outline the fundamental molecular discoveries contributing to each. We further outline potential therapeutic molecular targets for primary valvular heart disease and discuss key knowledge gaps that might serve as future research priorities.

Causal association between triglycerides and cholesterol-lowering medication with non-rheumatic valve disease: A 2-sample Mendelian randomization study

Previous studies have found a possible causal relationship between triglycerides and lipid-lowering drugs and valvular disease. The aim of this study was to explore the potential causal relationship between triglycerides and lipid-lowering drugs and valvular disease using Mendelian randomization (MR) analysis. Data sets associated with triglycerides (441,016 participants and 12,321,875 single nucleotide polymorphisms [SNPs]) and cholesterol-lowering drugs (209,638 participants and 9851,867 SNPs) were retrieved from the Genome-Wide Association Study (GWAS) database. A total of 297 and 49 SNPs significantly associated with triglycerides and cholesterol-lowering drugs, respectively (P < 5 × 10-8), were identified. Similarly, data sets for non-rheumatic valve diseases (NVDs) (361,194 participants and 10,080,950 SNPs) were obtained from the GWAS database. Inverse variance weighting was used as the primary method for calculating the odds ratio (OR) and 95% confidence intervals (CI). The MR-Egger, weighted median, and weighted mode analyses were also used to test the robustness of the main results. The MR-Egger intercept test and the MR-PRESSO test were used to evaluate horizontal pleiotropy. Inverse variance weighted (IVW) results showed that both triglyceride and cholesterol-lowering medication were positively associated with NVDs (OR = 1.001, 95% CI 1.000-1.0012, P = 0.006; OR = 1.007, 95% CI 1.003-1.010; P = 0.002). This study suggests that both triglyceride and cholesterol-lowering medications are positively associated with NVDs, suggesting that lowering triglyceride levels or the use of cholesterol-lowering medications may reduce the incidence of NVDs. However, larger samples are required for further validation.

Platelet-derived TGF-β1 induces functional reprogramming of myeloid-derived suppressor cells in immune thrombocytopenia

ABSTRACT

Platelet α-granules are rich in transforming growth factor β1 (TGF-β1), which is associated with myeloid-derived suppressor cell (MDSC) biology. Responders to thrombopoietin receptor agonists (TPO-RAs) revealed a parallel increase in the number of both platelets and MDSCs. Here, anti-CD61 immune-sensitized splenocytes were transferred into severe combined immunodeficient mice to establish an active murine model of immune thrombocytopenia (ITP). Subsequently, we demonstrated that TPO-RAs augmented the inhibitory activities of MDSCs by arresting plasma cells differentiation, reducing Fas ligand expression on cytotoxic T cells, and rebalancing T-cell subsets. Mechanistically, transcriptome analysis confirmed the participation of TGF-β/Smad pathways in TPO-RA-corrected MDSCs, which was offset by Smad2/3 knockdown. In platelet TGF-β1-deficient mice, TPO-RA-induced amplification and enhanced suppressive capacity of MDSCs was waived. Furthermore, our retrospective data revealed that patients with ITP achieving complete platelet response showed superior long-term outcomes compared with those who only reach partial response. In conclusion, we demonstrate that platelet TGF-β1 induces the expansion and functional reprogramming of MDSCs via the TGF-β/Smad pathway. These data indicate that platelet recovery not only serves as an end point of treatment response but also paves the way for immune homeostasis in immune-mediated thrombocytopenia.

Blood flow assessment technology in aortic surgery: a narrative review

Background and Objective

Blood flow assessment is an emerging technique that allows for assessment of hemodynamics in the heart and blood vessels. Recent advances in cardiovascular imaging technologies have made it possible for this technique to be more accessible to clinicians and researchers. Blood flow assessment typically refers to two techniques: measurement-based flow visualization using echocardiography or four-dimensional flow magnetic resonance imaging (4D flow MRI), and computer-based flow simulation based on computational fluid dynamics modeling. Using these methods, blood flow patterns can be visualized and quantitative measurements of mechanical stress on the walls of the ventricles and blood vessels, most notably the aorta, can be made. Thus, blood flow assessment has been enhancing the understanding of cardiac and aortic diseases; however, its introduction to clinical practice has been negligible yet. In this article, we aim to discuss the clinical applications and future directions of blood flow assessment in aortic surgery. We then provide our unique perspective on the technique's translational impact on the surgical management of aortic disease.

Methods

Articles from the PubMed database and Google Scholar regarding blood flow assessment in aortic surgery were reviewed. For the initial search, articles published between 2013 and 2023 were prioritized, including original articles, clinical trials, case reports, and reviews. Following the initial search, additional articles were considered based on manual searches of the references from the retrieved literature.

Key Content and Findings

In aortic root pathology and ascending aortic aneurysms, blood flow assessment can elucidate postoperative hemodynamic changes after surgical reconfiguration of the aortic valve complex or ascending aorta. In cases of aortic dissection, analysis of blood flow can predict future aortic dilatation. For complicated congenital aortic anomalies, surgeons may use preoperative imaging to perform "virtual surgery", in which blood flow assessment can predict postoperative hemodynamics for different surgical reconstructions and assist in procedural planning even before entering the operating room.

Conclusions

Blood flow assessment and computational modeling can evaluate hemodynamics and flow patterns by visualizing blood flow and calculating biomechanical forces in patients with aortic disease. We anticipate that blood flow assessment will become an essential tool in the treatment planning and understanding of the progression of aortic disease.

Large-Scale Proteomics Identifies Novel Biomarkers and Circulating Risk Factors for Aortic Stenosis

BACKGROUND

Limited data exist regarding risk factors for aortic stenosis (AS). The plasma proteome is a promising phenotype for discovery of novel biomarkers and potentially causative mechanisms.

OBJECTIVES

The aim of this study was to discover novel biomarkers with potentially causal associations with AS.

METHODS

We measured 4,877 plasma proteins (SomaScan aptamer-affinity assay) among ARIC (Atherosclerosis Risk In Communities) study participants in mid-life (visit 3 [V3]; n = 11,430; age 60 ± 6 years) and in late-life (V5; n = 4,899; age 76 ± 5 years). We identified proteins cross-sectionally associated with aortic valve (AV) peak velocity (AVmax) and dimensionless index by echocardiography at V5 and with incident AV-related hospitalization after V3 with the use of multivariable linear and Cox proportional hazard regression. We assessed associations of candidate proteins with changes in AVmax over 6 years and with AV calcification with the use of cardiac computed tomography, replicated analysis in an independent sample, performed Mendelian randomization, and evaluated gene expression in explanted human AV tissue.

RESULTS

Fifty-two proteins cross-sectionally were associated with AVmax and dimensionless index at V5 and with risk of incident AV-related hospitalization after V3. Among 3,413 participants in the Cardiovascular Health Study, 6 of those proteins were significantly associated with adjudicated moderate or severe AS, including matrix metalloproteinase 12 (MMP12), complement C1q tumor necrosis factor-related protein 1 (C1QTNF1), and growth differentiation factor-15. MMP12 was also associated with greater increase in AVmax over 6 years, greater degree of AV calcification, and greater expression in calcific compared with normal or fibrotic AV tissue. C1QTNF1 had consistent potential causal effects on both AS and AVmax according to Mendelian randomization analysis.

CONCLUSIONS

These findings identify MMP12 as a potential novel circulating biomarker of AS risk and C1QTNF1 as a new putative target to prevent AS progression.

Left ventricular-aortic angle is associated with platelet reactivity in patients with aortic stenosis

The impact of aortic stenosis on platelet reactivity is unclear. Previous studies reported contradicting results. The reason for this is unknown. It is known that flow alterations enhance platelet reactivity. A steep left ventricular-aortic angle (LV-AO-angle) is associated with turbulent flow in the aorta ascendens. Therefore, in this study, we hypothesized that LV-AO-angle is associated with platelet reactivity in patients with severe aortic stenosis. We included 289 patients with severe aortic stenosis and performed cardiac computertomography to assess the LV-AO-angle. Platelet function was evaluated by light transmission aggregometry. Platelet reactivity was higher in patients with a steep LV-AO-angle (ADP: <160°: 66.99% ± 20.72% vs. ≥160°: 60.66% ± 19.85%, P  = 0.009; collagen: <160°: 78.67% ± 13.19% vs. ≥160°: 73.85% ± 14.44%, P  = 0.003). Using Spearman correlation, ADP and collagen-induced aggregation was associated with LV-AO-angle (ADP: r  = -0.19, P  = 0.0009, R2  = 0.022; collagen: r  = -0.21, P  = 0.0004, R2  = 0.027). Apart from platelet reactivity, body weight, history of myocardial infarction and other factors were associated with steep LV-AO-angle. However, multivariate cox-regression (including body weight, comorbidities, history of MI and cardiac surgery, kidney function and laboratory parameters) revealed that LV-AO angle was a robust predictor of ADP and collagen-induced platelet aggregation. Steep LV-AO-angle is associated with enhanced platelet reactivity in patients with aortic stenosis. This could be the reason of contradicting results regarding platelet function in patients with aortic stenosis in previous studies. In addition, enhanced platelet reactivity in steep LV-AO-angle aortic stenosis patients might be a promising target in pathogenesis of aortic stenosis.

Uncoupling the Vicious Cycle of Mechanical Stress and Inflammation in Calcific Aortic Valve Disease

Calcific aortic valve disease (CAVD) is a common acquired valvulopathy, which carries a high burden of mortality. Chronic inflammation has been postulated as the predominant pathophysiological process underlying CAVD. So far, no effective medical therapies exist to halt the progression of CAVD. This review aims to outline the known pathways of inflammation and calcification in CAVD, focussing on the critical roles of mechanical stress and mechanosensing in the perpetuation of valvular inflammation. Following initiation of valvular inflammation, dysregulation of proinflammatory and osteoregulatory signalling pathways stimulates endothelial-mesenchymal transition of valvular endothelial cells (VECs) and differentiation of valvular interstitial cells (VICs) into active myofibroblastic and osteoblastic phenotypes, which in turn mediate valvular extracellular matrix remodelling and calcification. Mechanosensitive signalling pathways convert mechanical forces experienced by valve leaflets and circulating cells into biochemical signals and may provide the positive feedback loop that promotes acceleration of disease progression in the advanced stages of CAVD. Mechanosensing is implicated in multiple aspects of CAVD pathophysiology. The mechanosensitive RhoA/ROCK and YAP/TAZ systems are implicated in aortic valve leaflet mineralisation in response to increased substrate stiffness. Exposure of aortic valve leaflets, endothelial cells and platelets to high shear stress results in increased expression of mediators of VIC differentiation. Upregulation of the Piezo1 mechanoreceptor has been demonstrated to promote inflammation in CAVD, which normalises following transcatheter valve replacement. Genetic variants and inhibition of Notch signalling accentuate VIC responses to altered mechanical stresses. The study of mechanosensing pathways has revealed promising insights into the mechanisms that perpetuate inflammation and calcification in CAVD. Mechanotransduction of altered mechanical stresses may provide the sought-after coupling link that drives a vicious cycle of chronic inflammation in CAVD. Mechanosensing pathways may yield promising targets for therapeutic interventions and prognostic biomarkers with the potential to improve the management of CAVD.

N-Acetylcysteine Inhibits Aortic Stenosis Progression in a Murine Model by Blocking Shear-Induced Activation of Platelet Latent Transforming Growth Factor Beta 1

Objective: Aortic stenosis (AS) is characterized by narrowing of the aortic valve opening, resulting in peak blood flow velocity that induces high wall shear stress (WSS) across the valve. Severe AS leads to heart failure and death. There is no treatment available for AS other than valve replacement. Platelet-derived transforming growth factor beta 1 (TGF-β1) partially contributes to AS progression in mice, and WSS is a potent activator of latent TGF-β1. N-acetylcysteine (NAC) inhibits WSS-induced TGF-β1 activation in vitro. We hypothesize that NAC will inhibit AS progression by inhibiting WSS-induced TGF-β1 activation. Approach: We treated a cohort of Ldlr(-/-)Apob(100/100) low density lipoprotein receptor (LDLR) mice fed a high-fat diet with NAC (2% in drinking water) at different stages of disease progression and measured its effect on AS progression and TGF-β1 activation. Results: Short-term NAC treatment inhibited AS progression in mice with moderate and severe AS relative to controls, but not in LDLR mice lacking platelet-derived TGF-β1 (TGF-β1platlet-KO-LDLR). NAC treatment reduced TGF-β signaling, p-Smad2 and collagen levels, and mesenchymal transition from isolectin B4 and CD45-positive cells in LDLR mice. Mechanistically, NAC treatment resulted in plasma NAC concentrations ranging from 75.5 to 449.2 ng/mL, which were sufficient to block free thiol labeling of plasma proteins and reduce active TGF-β1 levels without substantially affecting reactive oxygen species-modified products in valvular cells. Conclusions: Short-term treatment with NAC inhibits AS progression by inhibiting WSS-induced TGF-β1 activation in the LDLR mouse model of AS, motivating a clinical trial of NAC and/or other thiol-reactive agent(s) as a potential therapy for AS.

Impact of calcific aortic valve disease on valve mechanics

The aortic valve is a highly dynamic structure characterized by a transvalvular flow that is unsteady, pulsatile, and characterized by episodes of forward and reverse flow patterns. Calcific aortic valve disease (CAVD) resulting in compromised valve function and increased pressure overload on the ventricle potentially leading to heart failure if untreated, is the most predominant valve disease. CAVD is a multi-factorial disease involving molecular, tissue and mechanical interactions. In this review, we aim at recapitulating the biomechanical loads on the aortic valve, summarizing the current and most recent research in the field in vitro, in-silico, and in vivo, and offering a clinical perspective on current strategies adopted to mitigate or approach CAVD.

Self-eating and Heart: The Emerging Roles of Autophagy in Calcific Aortic Valve Disease

Autophagy is a self-degradative pathway by which subcellular elements are broken down intracellularly to maintain cellular homeostasis. Cardiac autophagy commonly decreases with aging and is accompanied by the accumulation of misfolded proteins and dysfunctional organelles, which are undesirable to the cell. Reduction of autophagy over time leads to aging-related cardiac dysfunction and is inversely related to longevity. However, despite the increasing interest in autophagy in cardiac diseases and aging, the process remains an undervalued and disregarded object in calcific valvular disease. Neither the nature through which autophagy is triggered nor the interplay between autophagic machinery and targeted molecules during aortic valve calcification are fully understood. Recently, the upregulation of autophagy has been shown to result in cardioprotective effects against cell death as well as its origin. Here, we review the evidence that shows how autophagy can be both beneficial and detrimental as it pertains to aortic valve calcification in the heart.

Evaluation and Management of Aortic Stenosis in Chronic Kidney Disease: A Scientific Statement From the American Heart Association

Aortic stenosis with concomitant chronic kidney disease (CKD) represents a clinical challenge. Aortic stenosis is more prevalent and progresses more rapidly and unpredictably in CKD, and the presence of CKD is associated with worse short-term and long-term outcomes after aortic valve replacement. Because patients with advanced CKD and end-stage kidney disease have been excluded from randomized trials, clinicians need to make complex management decisions in this population that are based on retrospective and observational evidence. This statement summarizes the epidemiological and pathophysiological characteristics of aortic stenosis in the context of CKD, evaluates the nuances and prognostic information provided by noninvasive cardiovascular imaging with echocardiography and advanced imaging techniques, and outlines the special risks in this population. Furthermore, this statement provides a critical review of the existing literature pertaining to clinical outcomes of surgical versus transcatheter aortic valve replacement in this high-risk population to help guide clinical decision making in the choice of aortic valve replacement and specific prosthesis. Finally, this statement provides an approach to the perioperative management of these patients, with special attention to a multidisciplinary heart-kidney collaborative team-based approach.

Blood Platelets as an Important but Underrated Circulating Source of TGFβ

When treating diseases related primarily to tissue remodeling and fibrosis, it is desirable to regulate TGFβ concentration and modulate its biological effects. The highest cellular concentrations of TGFβ are found in platelets, with about 40% of all TGFβ found in peripheral blood plasma being secreted by them. Therefore, an understanding of the mechanisms of TGFβ secretion from platelets may be of key importance for medicine. Unfortunately, despite the finding that platelets are an important regulator of TGFβ levels, little research has been carried out into the development of platelet-directed therapies that might modulate the TGFβ-dependent processes. Nevertheless, there are some very encouraging reports suggesting that platelet TGFβ may be specifically involved in cardiovascular diseases, liver fibrosis, tumour metastasis, cerebral malaria and in the regulation of inflammatory cell functions. The purpose of this review is to briefly summarize these few, extremely encouraging reports to indicate the state of current knowledge in this topic. It also attempts to better characterize the influence of TGFβ on platelet activation and reactivity, and its shaping of the roles of blood platelets in haemostasis and thrombosis.

Dynamic changes in platelets caused by shear stress in aortic valve stenosis

BACKGROUND AND OBJECTIVE:

Turbulent blood flow in patients with aortic valve stenosis (AS) results in morphological and functional changes in platelets and coagulation factors. The aim of this study is to determine how shear stress affects platelets and coagulation factors.

METHODS:

We retrospectively evaluated data from 78 patients who underwent AVR to treat AS between March 2008 and July 2017 at Kagoshima University Hospital.

RESULTS:

Platelet (PLT) count obviously decreased at three days after AVR, and increased above preoperative levels at the time of discharge. In contrast, platelet distribution width (PDW), mean platelet volume (MPV), and platelet large cell ratio (P-LCR) increased three days after AVR, then decreased to below preoperative levels. No differences were evident between groups with higher (HPPG > 100 mmHg) and lower (LPPG < 100 mmHg) peak pressure gradients (PPG) before AVR, whereas PLT count, PDW, MPV and P-LCR improved more in the HPPG group. Plateletcrit (PCT), which represents the total volume of platelets, increased after AVR due to decreased shear stress. High increasing rate of PCT was associated with lower PLT count, higher PDW and lower fibrinogen.

CONCLUSION:

Shear stress affects PLT count, PDW, and fibrinogen in patients with AS.

Influence of aneurysmal aortic root geometry on mechanical stress to the aortic valve leaflet

AIMS

While mechanical stress caused by blood flow, e.g. wall shear stress (WSS), and related parameters, e.g. oscillatory shear index (OSI), are increasingly being recognized as key moderators of various cardiovascular diseases, studies on valves have been limited because of a lack of appropriate imaging modalities. We investigated the influence of aortic root geometry on WSS and OSI on the aortic valve (AV) leaflet.

METHODS AND RESULTS

We applied our novel approach of intraoperative epi-aortic echocardiogram to measure the haemodynamic parameters of WSS and OSI on the AV leaflet. Thirty-six patients were included, which included those who underwent valve-sparing aortic root replacement (VSARR) with no significant aortic regurgitation (n = 17) and coronary artery bypass graft (CABG) with normal AV (n = 19). At baseline, those who underwent VSARR had a higher systolic WSS (0.52 ± 0.12 vs. 0.32 ± 0.08 Pa, respectively, P < 0.001) and a higher OSI (0.37 ± 0.06 vs. 0.29 ± 0.04, respectively, P < 0.001) on the aortic side of the AV leaflet than those who underwent CABG. Multivariate regression analysis revealed that the size of the sinus of Valsalva had a significant association with WSS and OSI. Following VSARR, WSS and OSI values decreased significantly compared with the baseline values (WSS: 0.29 ± 0.12 Pa, P < 0.001; OSI: 0.26 ± 0.09, P < 0.001), and became comparable to the values in those who underwent CABG (WSS, P = 0.42; OSI, P = 0.15).

CONCLUSIONS

Mechanical stress on the AV gets altered in correlation with the size of the aortic root. An aneurysmal aortic root may expose the leaflet to abnormal fluid dynamics. The VSARR procedure appeared to reduce these abnormalities.

Biology and Biomechanics of the Heart Valve Extracellular Matrix

Heart valves are dynamic structures that, in the average human, open and close over 100,000 times per day, and 3 × 10⁹ times per lifetime to maintain unidirectional blood flow. Efficient, coordinated movement of the valve structures during the cardiac cycle is mediated by the intricate and sophisticated network of extracellular matrix (ECM) components that provide the necessary biomechanical properties to meet these mechanical demands. Organized in layers that accommodate passive functional movements of the valve leaflets, heart valve ECM is synthesized during embryonic development, and remodeled and maintained by resident cells throughout life. The failure of ECM organization compromises biomechanical function, and may lead to obstruction or leaking, which if left untreated can lead to heart failure. At present, effective treatment for heart valve dysfunction is limited and frequently ends with surgical repair or replacement, which comes with insuperable complications for many high-risk patients including aged and pediatric populations. Therefore, there is a critical need to fully appreciate the pathobiology of biomechanical valve failure in order to develop better, alternative therapies. To date, the majority of studies have focused on delineating valve disease mechanisms at the cellular level, namely the interstitial and endothelial lineages. However, less focus has been on the ECM, shown previously in other systems, to be a promising mechanism-inspired therapeutic target. Here, we highlight and review the biology and biomechanical contributions of key components of the heart valve ECM. Furthermore, we discuss how human diseases, including connective tissue disorders lead to aberrations in the abundance, organization and quality of these matrix proteins, resulting in instability of the valve infrastructure and gross functional impairment.

Activated platelets promote an osteogenic programme and the progression of calcific aortic valve stenosis

AIMS

Calcific aortic valve stenosis (CAVS) is characterized by a fibrocalcific process. Studies have shown an association between CAVS and the activation of platelets. It is believed that shear stress associated with CAVS promotes the activation of platelets. However, whether platelets actively participate to the mineralization of the aortic valve (AV) and the progression of CAVS is presently unknown. To identify the role of platelets into the pathobiology of CAVS.

METHODS AND RESULTS

Explanted control non-mineralized and mineralized AVs were examined by scanning electron microscope (SEM) for the presence of activated platelets. In-depth functional assays were carried out with isolated human valve interstitial cells (VICs) and platelets as well as in LDLR-/- apoB100/100 IGFII (IGFII) mice. Scanning electron microscope and immunogold markings for glycoprotein IIb/IIIa (GPIIb/IIIa) revealed the presence of platelet aggregates with fibrin in endothelium-denuded areas of CAVS. In isolated VICs, collagen-activated platelets induced an osteogenic programme. Platelet-derived adenosine diphosphate induced the release of autotaxin (ATX) by VICs. The binding of ATX to GPIIb/IIIa of platelets generated lysophosphatidic acid (LysoPA) with pro-osteogenic properties. In IGFII mice with CAVS, platelet aggregates were found at the surface of AVs. Administration of activated platelets to IGFII mice accelerated the development of CAVS by 2.1-fold, whereas a treatment with Ki16425, an antagonist of LysoPA receptors, prevented platelet-induced mineralization of the AV and the progression of CAVS.

CONCLUSIONS

These findings suggest a novel role for platelets in the progression of CAVS.

Platelet Membrane-Coated Nanoparticles Target Sclerotic Aortic Valves in ApoE-/- Mice by Multiple Binding Mechanisms Under Pathological Shear Stress

Background

Aortic valve disease is the most common valvular heart disease leading to valve replacement. The efficacy of pharmacological therapy for aortic valve disease is limited by the high mechanical stress at the aortic valves impairing the binding rate. We aimed to identify nanoparticle coating with entire platelet membranes to fully mimic their inherent multiple adhesive mechanisms and target the sclerotic aortic valve of apolipoprotein E-deficient (ApoE^−/−) mice based on their multiple sites binding capacity under high shear stress.

Methods

Considering the potent interaction of platelet membrane glycoproteins with components present in sclerotic aortic valves, platelet membrane-coated nanoparticles (PNPs) were synthetized and the binding capacity under high shear stress was evaluated in vitro and in vivo.

Results

PNPs demonstrated effectively adhering to von Willebrand factor, collagen and fibrin under shear stresses in vitro. In an aortic valve disease model established in ApoE^−/− mice, PNPs exhibited good targeting to sclerotic aortic valves by mimicking platelet multiple adhesive mechanisms.

Conclusion

PNPs could provide a promising platform for the molecular diagnosis and targeting treatment of aortic valve disease.

Dkk (Dickkopf) Proteins

Clinical and preclinical studies over the past 3 decades have uncovered a multitude of signaling pathways involved in the initiation and progression of atherosclerosis. From these studies, signaling by proteins of the Wnt family has recently emerged as an important player in the development of atherosclerosis. Wnt signaling is characterized by a large number of ligands, receptors, and coreceptors and can be regulated at many different levels. Among Wnt modulators, the evolutionary conserved Dkk (Dickkopf) proteins, and especially Dkk-1, the founding member of the family, are the best characterized. The role of Dkks in the pathophysiology of the arterial wall is only partially understood, but their involvement in atherosclerosis is becoming increasingly evident. This review introduces recent key findings on Dkk proteins and their functions in atherosclerosis and discusses the potential importance of modulating Dkk signaling as part of a novel, improved strategy for preventing and treating atherosclerosis-related diseases.

Visual Overview—

An online visual overview is available for this article.

Endoscopic resection of the pancreatic tail and subsequent wound healing mechanisms in a porcine model

BACKGROUND

Laparoscopic resection of the pancreatic body and tail is the predominant methodology to remove lesions in these locations; its safety and surgical planning are relatively mature, but it remains a complex and high-precision surgical operation, requiring abundant experience and skills in laparoscopic surgery, with a 10% rate of complications.

AIM

To verify the feasibility and safety, as well as to examine the complications of endoscopic pancreatectomy and healing mechanisms of pancreatic wounds after endoscopic resection.

METHODS

Transgastric endoscopic resections of varying sizes of pancreases were performed in 15 healthy Bama miniature pigs. The technical success rate, the incidence of serious complications, and the survival of the animals were studied. The healing of the wounds was evaluated by sacrificing the animals at various time points. Finally, the expression of transforming growth factor-β1 and Smad3/Smad7 in the surgical site was examined by immunohistochemistry to explore the role of these factors in wound healing of the pancreas.

RESULTS

Partial and total resections were successfully performed in two groups of animals, respectively. The technical success rate and the survival rate of the pigs were both 100%. We obtained 12 pancreatic tissue samples by endoscopic resection. The pancreatic wounds were closed with metal clips in one group and the wounds healed well by forming scars. There was a small amount of pancreatic leakage in the other group, but it can be fully encapsulated. The level of transforming growth factor-β1 (TGF-β1) in the wounds increased during the inflammatory and fibrous hyperplasia phases, and decreased in the scar phase. The expression of Smad3 paralleled that of TGF-β1, while the expression of Smad7 had an inverse relationship with the expression of TGF-β1.

CONCLUSION

Purely transgastric endoscopic resection of the pancreas is a safe, effective, and feasible procedure, but the incidence of pancreatic leakage in total pancreatic tail resection is high. The expression of TGF-β1 and Smad3/Samd7 is related to the progression of pancreatic wound healing.

Inactivation of platelet-derived TGF-β1 attenuates aortic stenosis progression in a robust murine model

Aortic stenosis (AS) is a degenerative heart condition characterized by fibrosis and narrowing of aortic valves (AV), resulting in high wall shear stress (WSS) across valves. AS is associated with high plasma levels of transforming growth factor-β1 (TGF-β1), which can be activated by WSS to induce organ fibrosis, but the cellular source of TGF-β1 is not clear. Here, we show that platelet-derived TGF-β1 plays an important role in AS progression. We first established an aggressive and robust murine model of AS, using the existing Ldlr -/- Apob100/100 (LDLR) breed of mice, and accelerated AS progression by feeding them a high-fat diet (HFD). We then captured very high resolution images of AV movement and thickness and of blood flow velocity across the AV, using a modified ultrasound imaging technique, which revealed early evidence of AS and distinguished different stages of AS progression. More than 90% of LDLR animals developed AS within 6 months of HFD. Scanning electron microscopy and whole-mount immunostaining imaging of AV identified activated platelets physically attached to valvular endothelial cells (VEC) expressing high phosphorylated Smad2 (p-Smad2). To test the contribution of platelet-derived TGF-β1 in AS, we derived LDLR mice lacking platelet TGF-β1 (TGF-β1platelet-KO-LDLR) and showed reduced AS progression and lower p-Smad2 and myofibroblasts in their AV compared with littermate controls fed the HFD for 6 months. Our data suggest that platelet-derived TGF-β1 triggers AS progression by inducing signaling in VEC, and their subsequent transformation into collagen-producing-myofibroblasts. Thus, inhibiting platelet-derived TGF-β1 might attenuate or prevent fibrotic diseases characterized by platelet activation and high WSS, such as AS.

TGF-β Signaling in Control of Cardiovascular Function

Genetic studies in animals and humans indicate that gene mutations that functionally perturb transforming growth factor β (TGF-β) signaling are linked to specific hereditary vascular syndromes, including Osler-Rendu-Weber disease or hereditary hemorrhagic telangiectasia and Marfan syndrome. Disturbed TGF-β signaling can also cause nonhereditary disorders like atherosclerosis and cardiac fibrosis. Accordingly, cell culture studies using endothelial cells or smooth muscle cells (SMCs), cultured alone or together in two- or three-dimensional cell culture assays, on plastic or embedded in matrix, have shown that TGF-β has a pivotal effect on endothelial and SMC proliferation, differentiation, migration, tube formation, and sprouting. Moreover, TGF-β can stimulate endothelial-to-mesenchymal transition, a process shown to be of key importance in heart valve cushion formation and in various pathological vascular processes. Here, we discuss the roles of TGF-β in vasculogenesis, angiogenesis, and lymphangiogenesis and the deregulation of TGF-β signaling in cardiovascular diseases.

New methodologies to accurately assess circulating active transforming growth factor-β1 levels: implications for evaluating heart failure and the impact of left ventricular assist devices

Transforming growth factor-β1 (TGF-β1) has been used as a biomarker in disorders associated with pathologic fibrosis. However, plasma TGF-β1 assessment is confounded by the significant variation in reported normal values, likely reflecting variable release of the large pool of platelet TGF-β1 after blood drawing. Moreover, current assays measure only total TGF-β1, which is dominated by the latent form of TGF-β1 rather than the biologically active form. To address these challenges, we developed methodologies to prevent ex vivo release of TGF-β1 and to quantify active TGF-β1. We then used these techniques to measure TGF-β1 in healthy controls and patients with heart failure (HF) before and after insertion of left ventricular assist devices (LVAD). Total plasma TGF-β1 was 1.0 ± 0.60 ng/mL in controls and 3.76 ± 1.55 ng/mL in subjects with HF (P < 0.001), rising to 5.2 ± 2.3 ng/mL following LVAD placement (P = 0.006). These results were paralleled by the active TGF-β1 values; controls had 3-16 pg/mL active TGF-β1, whereas levels were 2.7-fold higher in patients with HF before, and 4.2-fold higher after, LVAD implantation. Total TGF-β1 correlated with levels of the platelet-derived protein thrombospondin-1 (r = 0.87; P < 0.001), suggesting that plasma TGF-β1 may serve as a surrogate indicator of in vivo platelet activation. von Willebrand factor high molecular weight multimers correlated inversely with TGF-β1 levels (r = -0.63; P = 0.023), suggesting a role for shear forces in loss of these multimers and platelet activation. In conclusion, accurate assessment of circulating TGF-β1 may provide a valuable biomarker for in vivo platelet activation and thrombotic disorders.

Role of Platelet-Derived Transforming Growth Factor-β1 and Reactive Oxygen Species in Radiation-Induced Organ Fibrosis

SIGNIFICANCE

This review evaluates the role of platelet-derived transforming growth factor (TGF)-β1 in oxidative stress-linked pathologic fibrosis, with an emphasis on the heart and kidney, by using ionizing radiation as a clinically relevant stimulus. Current radiation-induced organ fibrosis interventions focus on pan-neutralization of TGF-β or the use of anti-oxidants and anti-proliferative agents, with limited clinical efficacy. Recent Advances: Pathologic fibrosis represents excessive accumulation of collagen and other extracellular matrix (ECM) components after dysregulation of a balance between ECM synthesis and degradation. Targets based on endogenous carbon monoxide (CO) pathways and the use of redox modulators such as N-acetylcysteine present promising alternatives to current therapeutic regimens.

CRITICAL ISSUES

Ionizing radiation leads to direct DNA damage and generation of reactive oxygen species (ROS), with TGF-β1 activation via ROS, thrombin generation, platelet activation, and pro-inflammatory signaling promoting myofibroblast accumulation and ECM production. Feed-forward loops, as TGF-β1 promotes ROS, amplify these profibrotic signals, and persistent low-grade inflammation insures their perpetuation. We highlight differential roles for platelet- versus monocyte-derived TGF-β1, establishing links between canonical and noncanonical TGF-β1 signaling pathways in relationship to macrophage polarization and autophagy, and define points where pharmacologic agents can intervene.

FUTURE DIRECTIONS

Additional studies are needed to understand mechanisms underlying the anti-fibrotic effects of current and proposed therapeutics, based on limiting platelet TGF-β1 activity, promotion of macrophage polarization, and facilitation of collagen autophagy. Models incorporating endogenous CO and selective TGF-β1 pathways that impact the initiation and progression of pathologic fibrosis, including nuclear factor erythroid 2-related factor (Nrf2) and redox, are of particular interest. Antioxid. Redox Signal. 27, 977-988.

Cardiac Fibrosis and Arrhythmogenesis

Myocardial injury, mechanical stress, neurohormonal activation, inflammation, and/or aging all lead to cardiac remodeling, which is responsible for cardiac dysfunction and arrhythmogenesis. Of the key histological components of cardiac remodeling, fibrosis either in the form of interstitial, patchy, or dense scars, constitutes a key histological substrate of arrhythmias. Here we discuss current research findings focusing on the role of fibrosis, in arrhythmogenesis. Numerous studies have convincingly shown that patchy or interstitial fibrosis interferes with myocardial electrophysiology by slowing down action potential propagation, initiating reentry, promoting after-depolarizations, and increasing ectopic automaticity. Meanwhile, there has been increasing appreciation of direct involvement of myofibroblasts, the activated form of fibroblasts, in arrhythmogenesis. Myofibroblasts undergo phenotypic changes with expression of gap-junctions and ion channels thereby forming direct electrical coupling with cardiomyocytes, which potentially results in profound disturbances of electrophysiology. There is strong evidence that systemic and regional inflammatory processes contribute to fibrogenesis (i.e., structural remodeling) and dysfunction of ion channels and Ca2+ homeostasis (i.e., electrical remodeling). Recognizing the pivotal role of fibrosis in the arrhythmogenesis has promoted clinical research on characterizing fibrosis by means of cardiac imaging or fibrosis biomarkers for clinical stratification of patients at higher risk of lethal arrhythmia, as well as preclinical research on the development of antifibrotic therapies. At the end of this review, we discuss remaining key questions in this area and propose new research approaches. © 2017 American Physiological Society. Compr Physiol 7:1009-1049, 2017.

Specific changes in circulating cytokines and growth factors induced by exercise stress testing in asymptomatic aortic valve stenosis

Background

We evaluated exercise-induced changes in the profile of circulating cytokines and growth factors in patients with AS.

Methods

We studied 32 consecutive asymptomatic moderate-to-severe AS patients and 32 age and sex-matched controls. Plasma levels of interleukin (IL)-6, IL-10, hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF), and transforming growth factor (TGF)-β were measured at 4 time points, i.e. at rest, at peak bicycle exercise, one hour and 24 hours after a symptom-limited exercise.

Results

Exercise increased all the 5 markers in both groups (all p<0.0001). The maximum levels of all tested cytokines were higher in the AS group (all p<0.05) compared with controls. In AS patients the highest levels of VEGF, IL-6, and IL-10 were observed one hour after exercise, while in the control group at peak exercise. In both groups maximum TGF- β levels were observed one hour after exercise. HGF levels were higher at peak and one hour after test in the AS group (p = 0.0001), however the maximum value in AS was observed at peak while in controls after test. In both groups TGF-β was the only marker that remained increased 24 hours after exercise compared with the value at rest (p = 0.0001). The cytokines and growth factors showed no association with heart rate and the workload.

Conclusion

In asymptomatic patients with moderate-to-severe AS, exercise produces a different pattern of changes in circulating cytokines and growth factors, and maximum levels of all tested cytokines were significantly higher in AS patients compared with the control group.

Comparative Histopathological Analysis of Mitral Valves in Barlow Disease and Fibroelastic Deficiency

Whether Barlow disease (BD) and fibroelastic deficiency (FED), the main causes of mitral valve prolapse (MVP), should be considered 2 distinct diseases remains unknown. Mitral valves from patients who required surgery for severe mitral regurgitation due to degenerative nonsyndromic MVP were analyzed. Intraoperative diagnosis of BD or FED was based on leaflet redundancy and thickness, number of segments involved, and annular dimension. The removed medial scallop of the posterior leaflet and attached chordae were used for histopathological and immunohistological assessment. Histologically, compared to normal controls (n = 3), BD (n = 14), and FED (n = 9) leaflets demonstrated an altered architecture and increased thickness. Leaflet thickness was greater and chordae thickness lower in BD than FED (P < 0.0001). In BD, increased thickness was owing to spongiosa expansion (proteoglycan accumulation) and intimal thickening on fibrosa and atrialis; in FED, local thickening was predominant on the fibrosa side, with accumulation of proteoglycan-like material around the chordae. Collagen accumulation was observed in FED leaflets and chords and decreased in BD. Fragmented elastin fibers were present in BD and FED; elastin decreased in BD but increased in FED leaflets and around chordae. Activated myofibroblasts accumulate in both diseased leaflets and chords, but more abundantly in FED chordae (P < 0.0001), independently of age, suggesting a role of these cells in chordal rupture. There were more CD34-positive cells in BD leaflets and in FED chordae (P < 0.01). In BD leaflets (but not chordae) proliferative Ki67-positive cells were more abundant (P < 0.01) and matrix metalloproteinase 2 levels were increased (P < 0.01) indicating tissue remodeling. Upregulation of transforming growth factor beta and pERK signaling pathways was evident in both diseases but more prominent in FED leaflets (continued on next page)(P < 0.001), with pERK upregulation in FED chordae (P < 0.0001). Most cellular and signaling markers were negligible in control valves. Quantitative immunohistopathological analyses demonstrated distinct changes between BD and FED valves: predominant matrix degradation in BD and increased profibrotic signaling pathways in FED, indicating that BD and FED are 2 different entities. These results may pave the way for genetic studies of MVP and development of preventive drug therapies.

Transforming growth factor-β1-mediated cardiac fibrosis: potential role in HIV and HIV/antiretroviral therapy-linked cardiovascular disease

HIV infection elevates the incidence of cardiovascular disease (CVD) independent of traditional risk factors. Autopsy series document cardiac inflammation and endomyocardial fibrosis in the HIV+ treatment naïve, and gadolinium enhancement magnetic resonance imaging has identified prominent myocardial fibrosis in the majority of HIV+ individuals despite use of suppressive antiretroviral therapies (ART). The extent of such disease may correlate with specific ART regimens. For example, HIV-infected patients receiving ritonavir (RTV)-boosted protease inhibitors have the highest prevalence of CVD, and RTV-exposed rodents exhibit cardiac dysfunction coupled with cardiac and vascular fibrosis, independent of RTV-mediated lipid alterations. We recently showed that platelet transforming growth factor (TGF)-β1 is a key contributor to cardiac fibrosis in murine models. We hypothesize that in the HIV+/ART naïve, cardiac fibrosis is a consequence of proinflammatory cytokine and/or ART-linked platelet activation with release of TGF-β1. Resultant TGF-β1/Smad signaling would promote collagen synthesis and organ fibrosis. We document these changes in a pilot immunohistochemical evaluation of cardiac tissue from two ART-naive pediatric AIDS patients. In terms of ART, we showed that RTV inhibits immunoproteasome degradation of TRAF6, a nuclear adapter signaling molecule critical to the regulation of proinflammatory cytokine signaling pathways involved in osteoclast differentiation and accelerated osteoporosis. We now present a model illustrating how RTV could similarly amplify TGF-β1 signaling in the promotion of cardiac fibrosis and accelerated CVD. Supportive clinical data correlate RTV use with elevation of NT-proBNP, a biomarker for CVD. We discuss potential interventions involving intrinsic modulators of inflammation and collagen degradation, including carbon monoxide-based therapeutics.

Increased Smad2/3 phosphorylation in circulating leukocytes and platelet-leukocyte aggregates in a mouse model of aortic valve stenosis: Evidence of systemic activation of platelet-derived TGF-β1 and correlation with cardiac dysfunction

BACKGROUND

Transforming growth factor-β1 (TGF-β1) has been implicated in the pathogenesis of aortic valve stenosis (AS). There is, however, little direct evidence for a role of active TGF-β1 in AS due to the sensitivity of current assays. We searched for evidence of plasma TGF-β1 activation by assaying Smad2/3 phosphorylation in circulating leukocytes and platelet-leukocyte aggregates (PLAs) in a mouse model of AS (Reversa).

METHODS

Echocardiography was used to measure AS and cardiac function. Intracellular phospho-flow cytometry in combination with optical fluorescence microscopy was used to detect PLAs and p-Smad2/3 levels.

RESULTS

Reversa mice on a western diet developed AS, had significantly increased numbers of PLAs and more intense staining for p-Smad2/3 in both PLAs and single leukocytes (all p<0.05). p-Smad2/3 staining was more intense in PLAs than in single leukocytes in both diet groups (p<0.05) and correlated with plasma total TGF-β1 levels (r=0.38, p=0.05 for PLAs and r=0.37, p=0.06 for single leukocytes) and reductions in ejection fraction (r=-0.42, p=0.03 for PLAs and r=-0.37, p=0.06 for single leukocytes).

CONCLUSIONS

p-Smad2/3 staining is more intense in leukocytes of hypercholesterolemic mice that developed AS, suggesting increased circulating active TGF-β1 levels. Leukocyte p-Smad2/3 may be a valuable surrogate indicator of circulating active TGF-β1.

Granule cargo release from bone marrow-derived cells sustains cardiac hypertrophy

Bone marrow-derived inflammatory cells, including platelets, may contribute to the progression of pressure overload-induced left ventricular hypertrophy (LVH). However, the underlying mechanisms for this are still unclear. One potential mechanism is through release of granule cargo. Unc13-d(Jinx) (Jinx) mice, which lack Munc13-4, a limiting factor in vesicular priming and fusion, have granule secretion defects in a variety of hematopoietic cells, including platelets. In the current study, we investigated the role of granule secretion in the development of LVH and cardiac remodeling using chimeric mice specifically lacking Munc13-4 in marrow-derived cells. Pressure overload was elicited by transverse aortic constriction (TAC). Chimeric mice were created by bone marrow transplantation. Echocardiography, histology staining, immunohistochemistry, real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and mass spectrometry were used to study LVH progression and inflammatory responses. Wild-type (WT) mice that were transplanted with WT bone marrow (WT→WT) and WT mice that received Jinx bone marrow (Jinx→WT) developed LVH and a classic fetal reprogramming response early (7 days) after TAC. However, at late times (5 wk), mice lacking Munc13-4 in bone marrow-derived cells (Jinx→WT) failed to sustain the cardiac hypertrophy observed in WT chimeric mice. No difference in cardiac fibrosis was observed at early or late time points. Reinjection of WT platelets or platelet releasate partially restored cardiac hypertrophy in Jinx chimeric mice. These results suggest that sustained LVH in the setting of pressure overload depends on one or more factors secreted from bone marrow-derived cells, possibly from platelets. Inhibiting granule cargo release may represent a novel target for preventing sustained LVH.