Lipopolysaccharide stimulation of human aortic valve interstitial cells activates inflammation and osteogenesis

Hilaire C. Non-Canonical TERT Activity Initiates Osteogenesis in Calcific Aortic Valve Disease

BACKGROUND

Calcific aortic valve disease is the pathological remodeling of valve leaflets. The initial steps in valve leaflet osteogenic reprogramming are not fully understood. As TERT (telomerase reverse transcriptase) overexpression primes mesenchymal stem cells to differentiate into osteoblasts, we investigated whether TERT contributes to the osteogenic reprogramming of valve interstitial cells.

METHODS

Human control and calcific aortic valve disease aortic valve leaflets and patient-specific human aortic valve interstitial cells were used in in vivo and in vitro calcification assays. Loss of function experiments in human aortic valve interstitial cells and cells isolated from Tert-/- and Terc-/- mice were used for mechanistic studies. Calcification was assessed in Tert+/+ and Tert-/- mice ex vivo and in vivo. In silico modeling, proximity ligation, and coimmunoprecipitation assays defined novel TERT interacting partners. Chromatin immunoprecipitation and cleavage under targets and tagmentation sequencing defined protein-DNA interactions.

RESULTS

TERT protein was highly expressed in calcified valve leaflets without changes in telomere length, DNA damage, or senescence markers, and these features were retained in isolated primary human aortic valve interstitial cells. TERT expression increased with osteogenic or inflammatory stimuli, and knockdown or genetic deletion of TERT prevented calcification in vitro and in vivo. Mechanistically, TERT was upregulated via NF-κB (nuclear factor-kappa B) and required to initiate osteogenic reprogramming, independent of its canonical reverse transcriptase activity and the long noncoding RNA TERC. TERT exerts non-canonical osteogenic functions via binding with STAT5 (signal transducer and activator of transcription 5). Depletion or inhibition of STAT5 prevented calcification. STAT5 was found to bind the promoter region of RUNX2 (runt-related transcription factor 2), the master regulator of osteogenic reprogramming. Finally, we demonstrate that TERT and STAT5 are upregulated and colocalized in calcific aortic valve disease tissue compared with control tissue.

CONCLUSIONS

TERT's non-canonical activity is required to initiate calcification. TERT is upregulated via inflammatory signaling pathways and partners with STAT5 to bind the RUNX2 gene promoter. These data identify a novel mechanism and potential therapeutic target to decrease vascular calcification.

Models for calcific aortic valve disease in vivo and in vitro

Calcific Aortic Valve Disease (CAVD) is prevalent among the elderly as the most common valvular heart disease. Currently, no pharmaceutical interventions can effectively reverse or prevent CAVD, making valve replacement the primary therapeutic recourse. Extensive research spanning decades has contributed to the establishment of animal and in vitro cell models, which facilitates a deeper understanding of the pathophysiological progression and underlying mechanisms of CAVD. In this review, we provide a comprehensive summary and analysis of the strengths and limitations associated with commonly employed models for the study of valve calcification. We specifically emphasize the advancements in three-dimensional culture technologies, which replicate the structural complexity of the valve. Furthermore, we delve into prospective recommendations for advancing in vivo and in vitro model studies of CAVD.

Strategies for Development of Synthetic Heart Valve Tissue Engineering Scaffolds

The current clinical solutions, including mechanical and bioprosthetic valves for valvular heart diseases, are plagued by coagulation, calcification, nondurability, and the inability to grow with patients. The tissue engineering approach attempts to resolve these shortcomings by producing heart valve scaffolds that may deliver patients a life-long solution. Heart valve scaffolds serve as a three-dimensional support structure made of biocompatible materials that provide adequate porosity for cell infiltration, and nutrient and waste transport, sponsor cell adhesion, proliferation, and differentiation, and allow for extracellular matrix production that together contributes to the generation of functional neotissue. The foundation of successful heart valve tissue engineering is replicating native heart valve architecture, mechanics, and cellular attributes through appropriate biomaterials and scaffold designs. This article reviews biomaterials, the fabrication of heart valve scaffolds, and their in-vitro and in-vivo evaluations applied for heart valve tissue engineering.

Models and Techniques to Study Aortic Valve Calcification in Vitro, ex Vivo and in Vivo. An Overview

Aortic valve stenosis secondary to aortic valve calcification is the most common valve disease in the Western world. Calcification is a result of pathological proliferation and osteogenic differentiation of resident valve interstitial cells. To develop non-surgical treatments, the molecular and cellular mechanisms of pathological calcification must be revealed. In the current overview, we present methods for evaluation of calcification in different ex vivo, in vitro and in vivo situations including imaging in patients. The latter include echocardiography, scanning with computed tomography and magnetic resonance imaging. Particular emphasis is on translational studies of calcific aortic valve stenosis with a special focus on cell culture using human primary cell cultures. Such models are widely used and suitable for screening of drugs against calcification. Animal models are presented, but there is no animal model that faithfully mimics human calcific aortic valve disease. A model of experimentally induced calcification in whole porcine aortic valve leaflets ex vivo is also included. Finally, miscellaneous methods and aspects of aortic valve calcification, such as, for instance, biomarkers are presented.

Organ Culture Model of Aortic Valve Calcification

A significant amount of knowledge has been gained with the use of cell-based assays to elucidate the mechanisms that mediate heart valve calcification. However, cells used in these studies lack their association with the extra-cellular matrix or the influence of other cellular components of valve leaflets. We have developed a model of calcification using intact porcine valve leaflets, that relies upon a biological stimulus to drive the formation of calcified nodules within the valve leaflets. Alizarin Red positive regions were formed in response to lipopolysaccharide and inorganic phosphate, which could be quantified when viewed under polarized light. Point analysis and elemental mapping analysis of electron microscope images confirmed the presence of nodules containing calcium and phosphorus. Immunohistochemical staining showed that the development of these calcified regions corresponded with the expression of RUNX2, osteocalcin, NF-kB and the apoptosis marker caspase 3. The formation of calcified nodules and the expression of bone markers were both inhibited by adenosine in a concentration-dependent manner, illustrating that the model is amenable to pharmacological manipulation. This organ culture model offers an increased level of tissue complexity in which to study the mechanisms that are involved in heart valve calcification.

Complement Upregulates Runx-2 to Induce Profibrogenic Change in Aortic Valve Interstitial Cells

BACKGROUND

Calcium accumulation and fibrotic activities are principal mechanisms for calcific aortic valve disease (CAVD). Active complement products are observed in human stenotic aortic valves. Runt-related transcription factor 2 (Runx-2) is involved in tissue calcification. We hypothesized that complement upregulates Runx-2 to induce profibrogenic change in human aortic valve interstitial cells (AVICs).

METHODS

AVICs were isolated from 6 normal and 6 CAVD donor valves. Cells were treated with complement cocktails. Profibrogenic activities and associated signaling molecules were analyzed by Western blot assay and collagen staining.

RESULTS

Complement time and dose dependently enhanced profibrogenic activities in AVICs, and complement exposure also induced total collagen deposition in AVICs. Complement-induced profibrogenic responses were associated with increased Runx-2 expression and phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2). Genetic silencing of Runx-2 decreased both matrix metalloproteinase 9 (MMP-9) and collagen I levels. Pharmacological inhibition of ERK1/2 decreased complement-mediated MMP-9, collagen I, and Runx-2 expression as well as total collagen deposition in human AVICs. Further, treating AVICs with heat-deactivated complement resulted in reduced MMP-9, collagen I, and Runx-2 levels compared with active complement treatment.

CONCLUSIONS

Complement induced profibrogenic activities in AVICs by activation of ERK1/2-mediated Runx-2 signaling pathways. This study demonstrates a potential role for complement-mediated CAVD pathogenesis, establishing a possible therapeutic target to limit CAVD progression.

Wnt Signaling Mediates Pro-Fibrogenic Activity in Human Aortic Valve Interstitial Cells

BACKGROUND

Proinflammatory activation of toll-like receptor-4 (TLR4) drives phenotypic changes in aortic valve interstitial cells (AVICs) and produces a fibrogenic phenotype that mediates valvular fibrosis and contributes to aortic stenosis. Prior work identified upregulated Wnt signaling in AVICs taken from valves affected by aortic stenosis. Our purpose was to determine the contribution of Wnt signaling to TLR4-dependent fibrogenic activity in isolated human AVICs.

METHODS

Human AVICs were isolated from hearts explanted for cardiac transplantation (N = 4). To test whether Wnt signaling contributed to TLR4-dependent fibrogenic activity, AVICs were treated with Wnt inhibitor (Dkk1) prior to TLR4 activation (LPS) and fibrogenic markers assessed. To determine the mediator of TLR4-to-Wnt signaling, expression of the key Wnt ligand, Wnt3a, was assessed after TLR4 activation and neutralizing antibodies confirmed the identity of the mediator. Fibrogenic activity was assessed after AVICs were treated with recombinant Wnt3a. Statistics were by analysis of variance (P < .05).

RESULTS

TLR4 activation upregulated in vitro collagen deposition, type IV collagen and MMP2 expression, and Dkk1 inhibited these responses (P < .05). Expression of Wnt3a was upregulated after TLR4 activation (P < .05). Anti-Wnt3a neutralizing antibodies abrogated TLR4-dependent type IV collagen and MMP2 expression (P < .05). Wnt3a upregulated type IV collagen and MMP2 expression independent of TLR4 activation (P < .05).

CONCLUSIONS

This study found that TLR4-dependent fibrogenic activity was mediated through Wnt signaling. The mediator of profibrogenic TLR4-to-Wnt signaling was a key Wnt ligand, Wnt3a. The abrogation of TLR4-induced fibrogenic activity in human AVICs by Wnt blockade illustrates a potential therapeutic role for Wnt inhibition in treatment and/or prevention of aortic stenosis.

TLR4 Stimulation Promotes Human AVIC Fibrogenic Activity through Upregulation of Neurotrophin 3 Production

BACKGROUND

Calcific aortic valve disease (CAVD) is a chronic inflammatory disease that manifests as progressive valvular fibrosis and calcification. An inflammatory milieu in valvular tissue promotes fibrosis and calcification. Aortic valve interstitial cell (AVIC) proliferation and the over-production of the extracellular matrix (ECM) proteins contribute to valvular thickening. However, the mechanism underlying elevated AVIC fibrogenic activity remains unclear. Recently, we observed that AVICs from diseased aortic valves express higher levels of neurotrophin 3 (NT3) and that NT3 exerts pro-osteogenic and pro-fibrogenic effects on human AVICs.

HYPOTHESIS

Pro-inflammatory stimuli upregulate NT3 production in AVICs to promote fibrogenic activity in human aortic valves.

METHODS AND RESULTS

AVICs were isolated from normal human aortic valves and were treated with lipopolysaccharide (LPS, 0.20 µg/mL). LPS induced TLR4-dependent NT3 production. This effect of LPS was abolished by inhibition of the Akt and extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) pathways. The stimulation of TLR4 in human AVICs with LPS resulted in a greater proliferation rate and an upregulated production of matrix metallopeptidases-9 (MMP-9) and collagen III, as well as augmented collagen deposition. Recombinant NT3 promoted AVIC proliferation in a tropomyosin receptor kinase (Trk)-dependent fashion. The neutralization of NT3 or the inhibition of Trk suppressed LPS-induced AVIC fibrogenic activity.

CONCLUSIONS

The stimulation of TLR4 in human AVICs upregulates NT3 expression and promotes cell proliferation and collagen deposition. The NT3-Trk cascade plays a critical role in the TLR4-mediated elevation of fibrogenic activity in human AVICs. Upregulated NT3 production by endogenous TLR4 activators may contribute to aortic valve fibrosis associated with CAVD progression.

Mechanistic Roles of Matrilin-2 and Klotho in Modulating the Inflammatory Activity of Human Aortic Valve Cells

BACKGROUND

Calcific aortic valve disease (CAVD) is a chronic inflammatory disease. Soluble extracellular matrix (ECM) proteins can act as damage-associated molecular patterns and may induce valvular inflammation. Matrilin-2 is an ECM protein and has been found to elevate the pro-osteogenic activity in human aortic valve interstitial cells (AVICs). Klotho, an anti-aging protein, appears to have anti-inflammatory properties. The effect of matrilin-2 and Klotho on AVIC inflammatory responses remains unclear.

METHODS AND RESULTS

Isolated human AVICs were exposed to matrilin-2. Soluble matrilin-2 induced the production of ICAM-1, MCP-1, and IL-6. It also induced protein kinase R (PKR) activation via Toll-like receptor (TLR) 2 and 4. Pretreatment with PKR inhibitors inhibited NF-κB activation and inflammatory mediator production induced by matrilin-2. Further, recombinant Klotho suppressed PKR and NF-κB activation and markedly reduced the production of inflammatory mediators in human AVICs exposed to matrilin-2.

CONCLUSIONS

This study revealed that soluble matrilin-2 upregulates AVIC inflammatory activity via activation of the TLR-PKR-NF-κB pathway and that Klotho is potent to suppress AVIC inflammatory responses to a soluble ECM protein through inhibiting PKR. These novel findings indicate that soluble matrilin-2 may accelerate the progression of CAVD by inducing valvular inflammation and that Klotho has the potential to suppress valvular inflammation.

Comparative pathology of human and canine myxomatous mitral valve degeneration: 5HT and TGF-β mechanisms

Myxomatous mitral valve degeneration (MMVD) is a leading cause of valve repair or replacement secondary to the production of mitral regurgitation, cardiac enlargement, systolic dysfunction, and heart failure. The pathophysiology of myxomatous mitral valve degeneration is complex and incompletely understood, but key features include activation and transformation of mitral valve (MV) valvular interstitial cells (VICs) into an active phenotype leading to remodeling of the extracellular matrix and compromise of the structural components of the mitral valve leaflets. Uncovering the mechanisms behind these events offers the potential for therapies to prevent, delay, or reverse myxomatous mitral valve degeneration. One such mechanism involves the neurotransmitter serotonin (5HT), which has been linked to development of valvulopathy in a variety of settings, including valvulopathy induced by serotonergic drugs, Serotonin-producing carcinoid tumors, and development of valvulopathy in laboratory animals exposed to high levels of serotonin. Similar to humans, the domestic dog also experiences naturally occurring myxomatous mitral valve degeneration, and in some breeds of dogs, the lifetime prevalence of myxomatous mitral valve degeneration reaches 100%. In dogs, myxomatous mitral valve degeneration has been associated with high serum serotonin, increased expression of serotonin-receptors, autocrine production of serotonin within the mitral valve leaflets, and downregulation of serotonin clearance mechanisms. One pathway closely associated with serotonin involves transforming growth factor beta (TGF-β) and the two pathways share a common ability to activate mitral valve valvular interstitial cells in both humans and dogs. Understanding the role of serotonin and transforming growth factor beta in myxomatous mitral valve degeneration gives rise to potential therapies, such as 5HT receptor (5HT-R) antagonists. The main purposes of this review are to highlight the commonalities between myxomatous mitral valve degeneration in humans and dogs, with specific regards to serotonin and transforming growth factor beta, and to champion the dog as a relevant and particularly valuable model of human disease that can accelerate development of novel therapies.

Interstitial cells in calcified aortic valves have reduced differentiation potential and stem cell-like properties

Valve interstitial cells (VICs) are crucial in the development of calcific aortic valve disease. The purpose of the present investigation was to compare the phenotype, differentiation potential and stem cell-like properties of cells from calcified and healthy aortic valves. VICs were isolated from human healthy and calcified aortic valves. Calcification was induced with osteogenic medium. Unlike VICs from healthy valves, VICs from calcified valves cultured without osteogenic medium stained positively for calcium deposits with Alizarin Red confirming their calcific phenotype. Stimulation of VICs from calcified valves with osteogenic medium increased calcification (p = 0.02), but not significantly different from healthy VICs. When stimulated with myofibroblastic medium, VICs from calcified valves had lower expression of myofibroblastic markers, measured by flow cytometry and RT-qPCR, compared to healthy VICs. Contraction of collagen gel (a measure of myofibroblastic activity) was attenuated in cells from calcified valves (p = 0.04). Moreover, VICs from calcified valves, unlike cells from healthy valves had lower potential to differentiate into adipogenic pathway and lower expression of stem cell-associated markers CD106 (p = 0.04) and aldehyde dehydrogenase (p = 0.04). In conclusion, VICs from calcified aortic have reduced multipotency compared to cells from healthy valves, which should be considered when investigating possible medical treatments of aortic valve calcification.

Short-term LPS induces aortic valve thickening in ApoE*3Leiden mice

BACKGROUND

Recently, it was shown that 12 weeks of lipopolysaccharide (LPS) administration to nonatherosclerotic mice induced thickening of the aortic heart valve (AV). Whether such effects may also occur even earlier is unknown. As most patients with AV stenosis also have atherosclerosis, we studied the short-term effect of LPS on the AVs in an atherosclerotic mouse model.

METHODS

ApoE*3Leiden mice, on an atherogenic diet, were injected intraperitoneally with either LPS or phosphate buffered saline (PBS), and sacrificed 2 or 15 days later. AVs were assessed for size, fibrosis, glycosaminoglycans (GAGs), lipids, calcium deposits, iron deposits and inflammatory cells.

RESULTS

LPS injection caused an increase in maximal leaflet thickness at 2 days (128.4 µm) compared to PBS-injected mice (67.8 µm; P = 0.007), whereas at 15 days this was not significantly different. LPS injection did not significantly affect average AV thickness on day 2 (37.8 µm), but did significantly increase average AV thickness at day 15 (41.6 µm; P = 0.038) compared to PBS-injected mice (31.7 and 32.3 µm respectively). LPS injection did not affect AV fibrosis, GAGs and lipid content. Furthermore, no calcium deposits were found. Iron deposits, indicative for valve haemorrhage, were observed in one AV of the PBS-injected group (a day 2 mouse; 9.1%) and in five AVs of the LPS-injected group (both day 2- and 15 mice; 29.4%). No significant differences in inflammatory cell infiltration were observed upon LPS injection.

CONCLUSION

Short-term LPS apparently has the potential to increase AV thickening and haemorrhage. These results suggest that systemic inflammation can acutely compromise AV structure.

Adaptive immune cells in calcific aortic valve disease

Calcific aortic valve disease (CAVD) is highly prevalent and has no pharmaceutical treatment. Surgical replacement of the aortic valve has proved effective in advanced disease but is costly, time limited, and in many cases not optimal for elderly patients. This has driven an increasing interest in noninvasive therapies for patients with CAVD. Adaptive immune cell signaling in the aortic valve has shown potential as a target for such a therapy. Up to 15% of cells in the healthy aortic valve are hematopoietic in origin, and these cells, which include macrophages, T lymphocytes, and B lymphocytes, are increased further in calcified specimens. Additionally, cytokine signaling has been shown to play a causative role in aortic valve calcification both in vitro and in vivo. This review summarizes the physiological presence of hematopoietic cells in the valve, innate and adaptive immune cell infiltration in disease states, and the cytokine signaling pathways that play a significant role in CAVD pathophysiology and may prove to be pharmaceutical targets for this disease in the near future.

Ectopic mineralization in heart valves: new insights from in vivo and in vitro procalcific models and promising perspectives on noncalcifiable bioengineered valves

Ectopic calcification of native and bioprosthetic heart valves represents a major public health problem causing severe morbidity and mortality worldwide. Valve procalcific degeneration is known to be caused mainly by calcium salt precipitation onto membranes of suffering non-scavenged cells and dead-cell-derived products acting as major hydroxyapatite nucleators. Although etiopathogenesis of calcification in native valves is still far from being exhaustively elucidated, it is well known that bioprosthesis mineralization may be primed by glutaraldehyde-mediated toxicity for xenografts, cryopreservation-related damage for allografts and graft immune rejection for both. Instead, mechanical valves, which are free from calcification, are extremely thrombogenic, requiring chronic anticoagulation therapies for transplanted patients. Since surgical substitution of failed valves is still the leading therapeutic option, progressive improvements in tissue engineering techniques are crucial to attain readily available valve implants with good biocompatibility, proper functionality and long-term durability in order to meet the considerable clinical demand for valve substitutes. Bioengineered valves obtained from acellular non-valvular scaffolds or decellularized native valves are proving to be a compelling alternative to mechanical and bioprosthetic valve implants, as they appear to permit repopulation by the host's own cells with associated tissue remodelling, growth and repair, besides showing less propensity to calcification and adequate hemodynamic performances. In this review, insights into valve calcification onset as revealed by in vivo and in vitro procalcific models are updated as well as advances in the field of valve bioengineering.

Inflammation and Mechanical Stress Stimulate Osteogenic Differentiation of Human Aortic Valve Interstitial Cells

Background: Aortic valve calcification is an active proliferative process, where interstitial cells of the valve transform into either myofibroblasts or osteoblast-like cells causing valve deformation, thickening of cusps and finally stenosis. This process may be triggered by several factors including inflammation, mechanical stress or interaction of cells with certain components of extracellular matrix. The matrix is different on the two sides of the valve leaflets. We hypothesize that inflammation and mechanical stress stimulate osteogenic differentiation of human aortic valve interstitial cells (VICs) and this may depend on the side of the leaflet. Methods: Interstitial cells isolated from healthy and calcified human aortic valves were cultured on collagen or elastin coated plates with flexible bottoms, simulating the matrix on the aortic and ventricular side of the valve leaflets, respectively. The cells were subjected to 10% stretch at 1 Hz (FlexCell bioreactor) or treated with 0.1 μg/ml lipopolysaccharide, or both during 24 h. Gene expression of myofibroblast- and osteoblast-specific genes was analyzed by qPCR. VICs cultured in presence of osteogenic medium together with lipopolysaccharide, 10% stretch or both for 14 days were stained for calcification using Alizarin Red. Results: Treatment with lipopolysaccharide increased expression of osteogenic gene bone morphogenetic protein 2 (BMP2) (5-fold increase from control; p = 0.02) and decreased expression of mRNA of myofibroblastic markers: α-smooth muscle actin (ACTA2) (50% reduction from control; p = 0.0006) and calponin (CNN1) (80% reduction from control; p = 0.0001) when cells from calcified valves were cultured on collagen, but not on elastin. Mechanical stretch of VICs cultured on collagen augmented the effect of lipopolysaccharide. Expression of periostin (POSTN) was inhibited in cells from calcified donors after treatment with lipopolysaccharide on collagen (70% reduction from control, p = 0.001), but not on elastin. Lipopolysaccharide and stretch both enhanced the pro-calcific effect of osteogenic medium, further increasing the effect when combined for cells cultured on collagen, but not on elastin. Conclusion: Inflammation and mechanical stress trigger expression of osteogenic genes in VICs in a side-specific manner, while inhibiting the myofibroblastic pathway. Stretch and lipopolysaccharide synergistically increase calcification.

Simvastatin reduces the TLR4-induced inflammatory response in human aortic valve interstitial cells

BACKGROUND

Calcific aortic stenosis is a chronic inflammatory disease. Proinflammatory stimulation via toll-like receptor 4 (TLR4) causes the aortic valve interstitial cell (AVIC) to undergo phenotypic change. The AVIC first assumes an inflammatory phenotype characterized by the production of inflammatory mediators such as intercellular adhesion molecule-1 (ICAM-1), interleukin-8 (IL-8), and monocyte chemoattractant protein-1 (MCP-1). This change has been linked with an osteogenic phenotypic response. Statins have recently been shown to have anti-inflammatory properties. We therefore hypothesized that statins may have an anti-inflammatory effect on human AVICs by downregulation of TLR4-stimulated inflammatory responses. Our purposes were (1) to determine the effect of simvastatin on TLR4-induced expression of inflammatory mediators in human AVICs and (2) to determine the mechanism(s) through which simvastatin exert this effect.

MATERIALS AND METHODS

Human AVICs were isolated from the explanted hearts of four patients undergoing cardiac transplantation. Cells were treated with simvastatin (50 μM) for 1 h before stimulation with TLR4 agonist lipopolysaccharide (LPS, 0.2 μg/mL). Immunoblotting (IB) was used to analyze cell lysates for ICAM-1 expression, and enzyme-linked immunosorbent assay was used to detect IL-8 and MCP-1 in cell culture media. Likewise, lysates were analyzed for TLR4 and nuclear factor-kappa B activation (IB). After simvastatin treatment, lysates were analyzed for TLR4 levels (IB). Statistics were by analysis of variance (P < 0.05).

RESULTS

Simvastatin reduced TLR4-induced ICAM-1, IL-8, and MCP-1 expression in AVICs. Simvastatin down-regulated TLR4 levels and suppressed TLR4-induced phosphorylation of nuclear factor-kappa B.

CONCLUSIONS

These data demonstrate the potential of a medical therapy (simvastatin) to impact the pathogenesis of aortic stenosis.

Influence of Cryopreservation on Structural, Chemical, and Immunoenzymatic Properties of Aortic Valve Allografts

OBJECTIVES

The problems in preparing (including cryopreservation) and implanting aortic valve allografts (AVAs) is widely elaborated, but some issues need explanation.

MATERIAL AND METHODS

Twenty AVAs cryopreserved in dimethylsulphoxide/RPMI solution under -160°C for 1-15 years and 3 controls stored at +4°C up to 2 weeks, from 19 male and 4 female donors, aged 20-51, ±30.8 years, were examined using light (LM), digital (DM), and scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy (EDS), and enzyme-linked immunosorbent assay immunoenzymatic tests (PECAM1, CD34).

RESULTS

All AVAs were macroscopically correct. LM revealed normal structure of leaflets but massive endothelial decellularization (±59 cells remained on the surface of 5 mm scraps). DM and SEM demonstrated generally normal collagen structures, but local alterations, probably influenced by freezing-thawing (gaps, separated plates) or being initial phase of native degeneration (grains). EDS detected a little elevated calcium amount in 1 specimen only. The mean PECAM1 and CD34 concentrations were at similar low level in all probes.

CONCLUSIONS

Fresh and cryopreservation technologies did not significantly influence the basic properties of AVA leaflets; however, massive endothelial decellularization was present in both groups. Therefore, no endocardial cell activity nor signs of inflammation were observed. These results were independent of donors' age and sex, processing technology, and time of storage of cryopreserved AVAs.

Toll-Like Receptors, Inflammation, and Calcific Aortic Valve Disease

Inflammation, the primary response of innate immunity, is essential to initiate the calcification process underlying calcific aortic valve disease (CAVD), the most prevalent valvulopathy in Western countries. The pathogenesis of CAVD is multifactorial and includes inflammation, hemodynamic factors, fibrosis, and active calcification. In the development of CAVD, both innate and adaptive immune responses are activated, and accumulating evidences show the central role of inflammation in the initiation and propagation phases of the disease, being the function of Toll-like receptors (TLR) particularly relevant. These receptors act as sentinels of the innate immune system by recognizing pattern molecules from both pathogens and host-derived molecules released after tissue damage. TLR mediate inflammation via NF-κB routes within and beyond the immune system, and play a crucial role in the control of infection and the maintenance of tissue homeostasis. This review outlines the current notions about the association between TLR signaling and the ensuing development of inflammation and fibrocalcific remodeling in the pathogenesis of CAVD. Recent data provide new insights into the inflammatory and osteogenic responses underlying the disease and further support the hypothesis that inflammation plays a mechanistic role in the initiation and progression of CAVD. These findings make TLR signaling a potential target for therapeutic intervention in CAVD.

The Role of Toll-Like Receptors and Vitamin D in Cardiovascular Diseases-A Review

Cardiovascular diseases are the leading cause of mortality worldwide. Therefore, a better understanding of their pathomechanisms and the subsequent implementation of optimal prophylactic and therapeutic strategies are of utmost importance. A growing body of evidence states that low-grade inflammation is a common feature for most of the cardiovascular diseases in which the contributing factors are the activation of toll-like receptors (TLRs) and vitamin D deficiency. In this article, available data concerning the association of cardiovascular diseases with TLRs and vitamin D status are reviewed, followed by a discussion of new possible approaches to cardiovascular disease management.

Survival-Related Autophagic Activity Versus Procalcific Death in Cultured Aortic Valve Interstitial Cells Treated With Critical Normophosphatemic-Like Phosphate Concentrations

Valve dystrophic calcification is a common disorder affecting normophosphatemic subjects. Here, cultured aortic valve interstitial cells (AVICs) were treated 3 to 28 days with phosphate (Pi) concentrations spanning the normal range in humans (0.8, 1.3, and 2.0 mM) alone or supplemented with proinflammatory stimuli to assess possible priming of dystrophic-like calcification. Compared with controls, spectrophotometric analyses revealed marked increases in calcium amounts and alkaline phosphatase activity for 2.0-mM-Pi-containing cultures, with enhancing by proinflammatory mediators. Ultrastructurally, AVICs treated with low/middle Pi concentrations showed an enormous endoplasmic reticulum (ER) enclosing organelle debris, so apparently executing a survival-related atypical macroautophagocytosis, consistently with ultracytochemical demonstration of ER-associated acid phosphatase activity and decreases in autophagosomes and immunodetectable MAP1LC3. In contrast, AVICs cultured at 2.0-mM Pi underwent mineralization due to intracellular release and peripheral layering of phospholipid-rich material acting as hydroxyapatite nucleator, as revealed by Cuprolinic Blue and von Kossa ultracytochemical reactions. Lack of immunoblotted caspase-3 cleaved form indicated apoptosis absence for all cultures. In conclusion, fates of cultured AVICs were crucially driven by Pi concentration, suggesting that serum Pi levels just below the upper limit of normophosphatemia in humans may represent a critical watershed between macroautophagy-associated cell restoring and procalcific cell death.

iTRAQ proteomic analysis of extracellular matrix remodeling in aortic valve disease

Degenerative aortic stenosis (AS) is the most common worldwide cause of valve replacement. The aortic valve is a thin, complex, layered connective tissue with compartmentalized extracellular matrix (ECM) produced by specialized cell types, which directs blood flow in one direction through the heart. There is evidence suggesting remodeling of such ECM during aortic stenosis development. Thus, a better characterization of the role of ECM proteins in this disease would increase our understanding of the underlying molecular mechanisms. Aortic valve samples were collected from 18 patients which underwent aortic valve replacement (50% males, mean age of 74 years) and 18 normal control valves were obtained from necropsies (40% males, mean age of 69 years). The proteome of the samples was analyzed by 2D-LC MS/MS iTRAQ methodology. The results showed an altered expression of 13 ECM proteins of which 3 (biglycan, periostin, prolargin) were validated by Western blotting and/or SRM analyses. These findings are substantiated by our previous results demonstrating differential ECM protein expression. The present study has demonstrated a differential ECM protein pattern in individuals with AS, therefore supporting previous evidence of a dynamic ECM remodeling in human aortic valves during AS development.

Lazaroid U-74389G inhibits the osteoblastic differentiation of IL-1β-indcued aortic valve interstitial cells through glucocorticoid receptor and inhibition of NF-κB pathway

BACKGROUND

Aortic valve calcification is characterized as the active process of aortic valve interstitial cells (AVICs), and considered as an inflammatory disease. As an antioxidant, the anti-inflammatory activity of Lazaroid has been exhibited in various models. We hypothesized that Lazaroid U-74389G would inhibit the osteoblastic differentiation of AVICs induced by IL-1β.

METHODS

Normal tricuspid aortic valve leaflets were collected from patients with acute aortic dissection (Type A) undergoing the Bentall procedure. AVICs were isolated and stimulated with IL-1β in presence or absence of U-74389G in culture. Cell lysates were analyzed for osteogenic markers and nuclear factor-κB using real-time PCR and Immunoblotting. Culture media was analyzed for IL-6 and IL-8 with enzyme-linked immunosorbent assay. Alizarin Red Staining was adopted to demonstrate the calcium deposition.

RESULTS

The expression of alkaline phosphatase and bone morphogenetic protein, accompanied by the production of IL-6 and IL-8, was up-regulated in response to IL-1β and was inhibited by the addition of U-74389G. The NF-κB pathway was activated by IL-1β and involved in the suppression of U-74389G on osteoblastic differentiation in AVICs. The negative effects of U-74389G on ostengenic gene expression and mineralization of AVICs were blocked by glucocorticoid receptor antagonist mifepristone and the NF-κB inhibitor Bay 11-7082.

CONCLUSIONS

U-74389G inhibits the pro-osteogenic response to IL-1β stimulation in AVICs. The osteoblastic differentiation and mineralization of AVICs were inhabited by U-74389G though the modulation of NF-κB activation, and this pathway could be potential therapeutic targets for medical treatment of calcified aortic valve disease.

Activated human valvular interstitial cells sustain interleukin-17 production to recruit neutrophils in infective endocarditis

The mechanisms that underlie valvular inflammation in streptococcus-induced infective endocarditis (IE) remain unclear. We previously demonstrated that streptococcal glucosyltransferases (GTFs) can activate human heart valvular interstitial cells (VIC) to secrete interleukin-6 (IL-6), a cytokine involved in T helper 17 (Th17) cell differentiation. Here, we tested the hypothesis that activated VIC can enhance neutrophil infiltration through sustained IL-17 production, leading to valvular damage. To monitor cytokine and chemokine production, leukocyte recruitment, and the induction or expansion of CD4(+) CD45RA(-) CD25(-) CCR6(+) Th17 cells, primary human VIC were cultured in vitro and activated by GTFs. Serum cytokine levels were measured using an enzyme-linked immunosorbent assay (ELISA), and neutrophils and Th17 cells were detected by immunohistochemistry in infected valves from patients with IE. The expression of IL-21, IL-23, IL-17, and retinoic acid receptor-related orphan receptor C (Rorc) was upregulated in GTF-activated VIC, which may enhance the proliferation of memory Th17 cells in an IL-6-dependent manner. Many chemokines, including chemokine (C-X-C motif) ligand 1 (CXCL1), were upregulated in GTF-activated VIC, which might recruit neutrophils and CD4(+) T cells. Moreover, CXCL1 production in VIC was induced in a dose-dependent manner by IL-17 to enhance neutrophil chemotaxis. CXCL1-expressing VIC and infiltrating neutrophils could be detected in infected valves, and serum concentrations of IL-17, IL-21, and IL-23 were increased in patients with IE compared to healthy donors. Furthermore, elevated serum IL-21 levels have been significantly associated with severe valvular damage, including rupture of chordae tendineae, in IE patients. Our findings suggest that VIC are activated by bacterial modulins to recruit neutrophils and that such activities might be further enhanced by the production of Th17-associated cytokines. Together, these factors can amplify the release of neutrophilic contents in situ, which might lead to severe valvular damage.

Lipopolysaccharide stimulation improves the odontoblastic differentiation of human dental pulp cells

Lipopolysaccharide (LPS) is one of the causative agents of pulpitis and previous studies have demonstrated that the LPS stimulation of human aortic valve interstitial cells induces inflammatory mediators and the gene expression of osteogenic factors. Therefore, in the present study, it was hypothesized that LPS affects the odontoblastic differentiation of human dental pulp cells (hDPCs). In order to investigate this, an in vitro study using hDPCs was performed. Increased alkaline phosphatase (ALP) activity was observed in the hDPCs treated with LPS, which was more marked when the cells were costimulated with odontogenic induction medium (OM). LPS also appeared to increase the gene expression levels of dentin sialophosphoprotein and dentin matrix protein‑1 and the protein expression level of dental sialoprotein in the hDPCs, particularly in combination with OM. In addition, the size and the number of nodules formed in the hDPCs exposed to OM and LPS were increased compared to those stimulated by OM alone. To determine the role of nuclear factor κB (NF‑κB) during the LPS‑induced odontoblastic differentiation of hDPCs, immunofluorescence was performed. The nuclear translocation of NF‑κB, induced by LPS was confirmed, suggesting its involvement in the LPS‑induced increase in odontoblastic differentiation of hDPCs. In conclusion, there may be an association between LPS stimulation, with or without OM, and odontoblastic differentiation.

Ectopic visceral fat: a clinical and molecular perspective on the cardiometabolic risk

Worldwide, cardiovascular diseases (CVDs) are a leading cause of mortality. While in many westernized societies there has been a decrease prevalence of smoking and that a special emphasis has been put on the urgency to control the, so called, classical risk factors, it is more and more recognized that there remains a residual risk, which contributes to the development of CVDs. Imaging studies conducted over two decades have highlighted that the accumulation of ectopic visceral fat is associated with a plethora of metabolic dysfunctions, which have complex and intertwined interactions and participate to the development/progression/events of many cardiovascular disorders. The contribution of visceral ectopic fat to the development of coronary artery disease (CAD) is now well established, while in the last several years emerging evidence has pointed out that accumulation of harmful ectopic fat is associated with other cardiovascular disorders such as calcific aortic valve disease (CAVD), atrial fibrillation and left ventricular dysfunction. We review herein the key molecular processes linking the accumulation of ectopic fat to the development of CVDs. We have attempted, whenever possible, to use a translational approach whereby the pathobiology processes are linked to clinical observations.

Adult aortic valve interstitial cells have greater responses to toll-like receptor 4 stimulation

BACKGROUND

Aortic valve interstitial cells (AVICs) have been implicated in the pathogenesis of calcific aortic valve disease. Signal transducer and activator of transcription 3 (Stat3) possesses antiinflammatory effects. Given that calcification occurs in adult valves, we hypothesized that AVICs from adult valves more likely undergo a proosteogenic phenotypic change than those from pediatric valves and that may be related to different Stat3 activation in the response of those two age groups to toll-like receptor 4 (TLR4).

METHODS

AVICs from healthy human aortic valve tissues were treated with TLR4 agonist lipopolysaccharide. Cellular levels of TLR4, intercellular adhesion molecule 1, bone morphogenetic protein 2, and alkaline phosphatase, as well as phosphorylation of p-38 mitogen-activated protein kinase (MAPK), nuclear factor-κβ (NF-κβ), and Stat3, were analyzed.

RESULTS

Toll-like receptor 4 protein levels were comparable between adult and pediatric AVICs. Adult cells produce markedly higher levels of the above markers after TLR4 stimulation, which is negatively associated with phosphorylation of Stat3. Inhibition of Stat3 enhanced p-38 MAPK and NF-κβ phosphorylation and exaggerated the expression of the above markers in pediatric AVICs after TLR4 stimulation.

CONCLUSIONS

Adult AVICs exhibit greater inflammatory and osteogenic responses to TLR4 stimulation. The enhanced responses in adult AVICs are at least partly due to lower levels of Stat3 activation in response to TLR4 stimulation relative to pediatric cells. Stat3 functions as a negative regulator of the TLR4 responses in human AVICs. The results suggest that Stat3 activation (tyrosine phosphorylation) may be protective and that TLR4 inhibition could be targeted pharmacologically to treat calcific aortic valve disease.

Serum phosphate is associated with aortic valve calcification in the Multi-ethnic Study of Atherosclerosis (MESA)

OBJECTIVES

This study sought to investigate associations of phosphate metabolism biomarkers with aortic valve calcification (AVC).

BACKGROUND

Calcific aortic valve disease (CAVD) is a common progressive condition that involves inflammatory and calcification mediators. Currently there are no effective medical treatments, but mineral metabolism pathways may be important in the development and progression of disease.

METHODS

We examined associations of phosphate metabolism biomarkers, including serum phosphate, urine phosphate, parathyroid hormone (PTH) and serum fibroblast growth factor (FGF)-23, with CT-assessed AVC at study baseline and in short-term follow-up in 6814 participants of the Multi-Ethnic Study of Atherosclerosis (MESA).

RESULTS

At baseline, AVC prevalence was 13.2%. Higher serum phosphate levels were associated with significantly greater AVC prevalence (relative risk 1.3 per 1 mg/dL increment, 95% confidence incidence: 1.1 to 1.5, p<0.001). Serum FGF-23, serum PTH, and urine phosphate were not associated with prevalent AVC. Average follow-up CT evaluation was 2.4 years (range 0.9-4.9 years) with an AVC incidence of 4.1%. Overall, phosphate metabolism biomarkers were not associated with incident AVC except in the top FGF-23 quartile.

CONCLUSIONS

Serum phosphate levels are significantly associated with AVC prevalence. Further study of phosphate metabolism as a modifiable risk factor for AVC is warranted.

Interleukin-1 Beta induces an inflammatory phenotype in human aortic valve interstitial cells through nuclear factor kappa Beta

BACKGROUND

Mechanisms of inflammation have been implicated in the pathogenesis of aortic stenosis. When stimulated, human aortic valve interstitial cells (AVICs) have been shown to become inflammatory cells. Increased levels of interleukin (IL)-1β have been found in the leaflets of stenotic aortic valves. The purpose of this study was to determine the effects of IL-1β on isolated human AVICs and to determine the intracellular signaling pathway by which the effects are mediated. The results of this study demonstrated that IL-1β induces an inflammatory phenotype in human AVICs.

METHODS

Human AVICs were isolated from normal aortic valves from explanted hearts of patients undergoing cardiac transplantation (n = 4) and grown in culture. When grown to confluence, the cells were treated with IL-1β (10 ng/mL). Cell culture media was analyzed for IL-6, IL-8, and monocyte chemoattractant protein-1 (enzyme-linked immunosorbent assay). Cell lysates were analyzed for intercellular adhesion molecule-1 (immunoblot). Inhibition of nuclear factor-κβ was by Bay 11-7085 (5 μM). Inhibition of extracellular signal regulated kinase-1/2 was by PD098059 (20 nM). Statistics were by analysis of variance, with p less than 0.05 significant.

RESULTS

Interluekin-1β induced an inflammatory phenotype in human AVICs. The IL-1β stimulation resulted in significantly increased production of the inflammatory cytokines, IL-6 and IL-8, the chemokine monocyte chemoattractant protein-1, and intercellular adhesion molecule-1. Inhibition of nuclear factor-κβ prevented these changes, whereas inhibition of extracellular signal regulated kinase-1/2 had no effect.

CONCLUSIONS

Interleukin-1β induced an inflammatory phenotype in human AVICs, which was prevented by inhibition of nuclear factor-κβ. These data implicate IL-1β in the pathogenesis of aortic stenosis.

ox-LDL induces PiT-1 expression in human aortic valve interstitial cells

BACKGROUND

The aortic valve interstitial cell (AVIC) has been implicated in the pathogenesis of calcific aortic stenosis. When appropriately stimulated, AVICs undergo a phenotypic change from that of a myofibroblast to that of a bone-forming-like cell. An elevated blood level of low-density lipoprotein (LDL) cholesterol is a clinical risk factor for aortic stenosis, and oxidized LDL (ox-LDL) cholesterol has been consistently found in calcified aortic valve leaflets. However, whether it plays a role in the pathogenesis of aortic stenosis is unknown. The process of aortic valve leaflet calcification has been associated with the deposition of calcium phosphate, mediated in part by the phosphate inorganic transporter 1 (PiT-1), a sodium-phosphate ion cotransporter. Therefore, we hypothesized that ox-LDL induces an osteogenic change in human AVICs marked by the induction of PiT-1. Using isolated human AVICs, the purpose of the present study was to examine the effect of ox-LDL on the expression of PiT-1 and the osteogenic factor bone morphogenetic protein 2 (BMP-2), which is a protein necessary for bone formation.

METHODS

Human AVICs were isolated from nonstenotic aortic valves obtained from the explanted hearts of patients undergoing cardiac transplantation (n = 4) and grown in culture. The cells were treated with serum-free media, serum-free media with dimethyl sulfoxide (vehicle control), 40 μg/mL of ox-LDL, or 40 μg/mL of ox-LDL plus 2.5 mM phosphonoformate hexahydrate acid. Phosphonoformate hexahydrate acid is a competitive inhibitor of PiT-1 by mimicking inorganic phosphate. Cell lysis was performed at 24 h after treatment. Cell lysates were analyzed using immunoblot and densitometry for PiT-1 and BMP-2. Statistical analysis was performed using analysis of variance. P < 0.05 was significant.

RESULTS

ox-LDL stimulation of AVICs induced an increase in PiT-1 and BMP-2. ox-LDL induced increased production of the phosphate transporter, PiT-1, and the osteogenic factor, BMP-2. Inhibition of PiT-1 with phosphonoformate hexahydrate acid prevented ox-LDL-induced BMP-2 expression.

CONCLUSIONS

These data offer mechanistic insight into the pathogenesis of calcific aortic stenosis.

Notch1 promotes the pro-osteogenic response of human aortic valve interstitial cells via modulation of ERK1/2 and nuclear factor-κB activation

OBJECTIVE

Calcific aortic valve disease is a leading cardiovascular disease in the elderly, and progressive calcification results in the failure of valvular function. Aortic valve interstitial cells (AVICs) from stenotic valves express higher levels of bone morphogenetic protein-2 in response to Toll-like receptor 4 stimulation. We recently found that Toll-like receptor 4 interacts with Notch1 in human AVICs. This study tests the hypothesis that Notch1 promotes the pro-osteogenic response of human AVICs.

APPROACH AND RESULTS

AVICs isolated from diseased human valves expressed higher levels of bone morphogenetic protein-2 and alkaline phosphatase after lipopolysaccharide stimulation. The augmented pro-osteogenic response is associated with elevated cellular levels of Notch1 and enhanced Notch1 cleavage in response to lipopolysaccharide stimulation. Inhibition or silencing of Notch1 suppressed the pro-osteogenic response in diseased cells, and the Notch 1 ligand, Jagged1, enhanced the response in AVICs isolated from normal human valves. Interestingly, extracellular signal-regulated protein kinases 1/2 (ERK1/2) and nuclear factor-κB phosphorylation induced by lipopolysaccharide was markedly reduced by inhibition or silencing of Notch1 and enhanced by Jagged1. Inhibition of ERK1/2 or nuclear factor-κB also reduced bone morphogenetic protein-2 and alkaline phosphatase expression induced by lipopolysaccharide.

CONCLUSIONS

Notch1 mediates the pro-osteogenic response to Toll-like receptor 4 stimulation in human AVICs. Elevated Notch1 levels and enhanced Notch1 activation play a major role in augmentation of the pro-osteogenic response of AVICs of stenotic valves through modulation of ERK1/2 and nuclear factor-κB activation. These pathways could be potential therapeutic targets for prevention of the progression of calcific aortic valve disease.

Cross-talk between the Toll-like receptor 4 and Notch1 pathways augments the inflammatory response in the interstitial cells of stenotic human aortic valves

BACKGROUND AND PURPOSE

Calcific aortic stenosis is a chronic inflammatory disease, and aortic valve interstitial cells (AVIC) play an important role in valvular inflammation. Whereas AVIC from stenotic aortic valves exhibit an augmented response to Toll-like receptor 4 (TLR4) stimulation, the underlying mechanism is unclear. This study tested the hypothesis that an excessive cross-talk between the TLR4 and Notch1 pathways is responsible for augmentation of the inflammatory response to lipopolysaccharide (LPS) in AVIC of stenotic valves.

METHODS AND RESULTS

Human AVIC were isolated from normal and stenotic leaflets. Nuclear factor kappa-B (NF-κB) activation and production of interleukin-8, monocyte chemoattactrant protein-1, and intercellular adhesion molecule-1 were analyzed after treatment with LPS. The role of Notch1 in the inflammatory response was determined using inhibitor, siRNA, and specific ligand. Cells from diseased valves produced greater levels of chemokines and intercellular adhesion molecule-1 that are associated with enhanced NF-κB activation. Interestingly, diseased cells exhibited augmented Jagged1 release and Notch1 activation after TLR4 stimulation. Inhibition and silencing of Notch1 each resulted in greater suppression of the TLR4-induced inflammatory response in diseased cells. Conversely, activation of Notch1 with a specific ligand, Jagged1, enhanced the LPS-induced inflammatory response in normal AVIC. Further, Notch1 intracellular domain was coimmunoprecipited with the inhibitor of NF-κB kinase after LPS stimulation, and inhibition of Notch1 abrogated the difference in the level of NF-κB activation between diseased and normal cells.

CONCLUSION

Notch1 enhances the inflammatory response to TLR4 stimulation in human AVIC through modulating NF-κB activation. Excessive cross-talk between the TLR4 and Notch1 pathways is responsible for augmentation of the TLR4 response in AVIC of stenotic valves.

Genomics in cardiovascular diseases: analysis of the importance of the toll-like receptor signaling pathway

The development of techniques for genomics study makes it possible for us to further our knowledge about the physiopathology of various immunological or infectious diseases. These techniques improve our understanding of the development and evolution of such diseases, including those of cardiovascular origin, whilst they help to bring about the design of new therapeutic strategies. We are reviewing the genetic alterations of immunity in said field, and focusing on the signaling pathway of toll-like receptors because not only does this play a decisive role in response to microorganisms, it is also heavily involved in modulating the inflammatory response to tissue damage, a side effect of numerous cardiovascular diseases. These alterations in tissue homeostasis are present under a wide range of circumstances, such as reperfusion ischemia (myocardial infarction) phenomena, arteriosclerosis, or valvulopathy.

Ultrastructural and spectrophotometric study on the effects of putative triggers on aortic valve interstitial cells in in vitro models simulating metastatic calcification

Metastatic calcification of cardiac valves is a common complication in patients affected by chronic renal failure. In this study, primary bovine aortic valve interstitial cells (AVICs) were subjected to pro-calcific treatments consisting in cell stimulation with (i) elevated inorganic phosphate (Pi = 3 mM), to simulate hyperphosphatemic conditions; (ii) bacterial endotoxin lipopolysaccharide (LPS), simulating direct effects by microbial agents; and (iii) conditioned media (CM) derived from cultures of either LPS-stimulated heterogenic macrophages (commercial murine RAW264.7 cells) or LPS-stimulated fresh allogenic monocytes/macrophages (bCM), simulating consequent inflammatory responses, alone or combined. Compared to control cultures, spectrophotometric assays revealed shared treatment-dependent higher values of both calcium amounts and alkaline phosphatase activity for cultures involving the presence of elevated Pi. Ultrastructurally, shared peculiar pro-calcific degeneration patterns were exhibited by AVICs from these latter cultures irrespectively of the additional treatments. Disappearance of all cytomembranes and concurrent formation of material showing positivity to Cuprolinic Blue and co-localizing with silver precipitation were followed by the outcropping of such a material, which transformed in layers outlining the dead cells. Subsequent budding of these layers resulted in the formation of bubbling bodies and concentrically laminated calcospherulae mirroring those in actual soft tissue calcification. In conclusion, the in vitro models employed appear to be reliable tools for simulating metastatic calcification and indicate that hyperphosphatemic-like conditions could trigger valve calcification per se, with LPS and allogenic macrophage-derived secretory products acting as possible calcific enhancers via inflammatory responses.

Advanced polymeric matrix for valvular complications

Poly(L-lactic acid) (PLLA) matrix systems incorporated with poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) containing nitric oxide (NO) donors (DETA NONOate) were developed for prevention of heart valve complications through sustained and controlled release of NO. PLLA matrices were prepared using the salt leaching method and the properties and drug release profiles were characterized. For assessment of the effects of PLLA systems on the pharmacological responses and cytotoxicity, various factors, such as calcium content, alkaline phosphatase (ALP) activity, cyclic guanosine monophosphate (cGMP) expression, intercellular adhesion molecule (ICAM-1) expression and cell viability of porcine aortic valve interstitial cells (PAVICs), were evaluated. PLLA matrices embedded with PLGA- NPs demonstrated its usefulness in alleviating the calcification rate of the VICs. The cGMP levels under osteoblastic conditions significantly increased, supporting that anticalcification activity of NO is mediated through NO-cGMP signaling pathway. The level of ICAM-1 expression in cells exposed to NO was lowered, suggesting that NO has an inhibitory activity against tissue inflammation. NO releases from PLLA matrix embedded with PLGA NPs prevented valvular calcification and inflammation without causing any cytotoxic activities. PLLA matrix system loaded with NPs containing NO donors could provide a new platform for sustained and controlled delivery of NO, significantly reducing valvular complications.

Inflammatory regulation of valvular remodeling: the good(?), the bad, and the ugly

Heart valve disease is unique in that it affects both the very young and very old, and does not discriminate by financial affluence, social stratus, or global location. Research over the past decade has transformed our understanding of heart valve cell biology, yet still more remains unclear regarding how these cells respond and adapt to their local microenvironment. Recent studies have identified inflammatory signaling at nearly every point in the life cycle of heart valves, yet its role at each stage is unclear. While the vast majority of evidence points to inflammation as mediating pathological valve remodeling and eventual destruction, some studies suggest inflammation may provide key signals guiding transient adaptive remodeling. Though the mechanisms are far from clear, inflammatory signaling may be a previously unrecognized ally in the quest for controlled rapid tissue remodeling, a key requirement for regenerative medicine approaches for heart valve disease. This paper summarizes the current state of knowledge regarding inflammatory mediation of heart valve remodeling and suggests key questions moving forward.

Aortic valve disease and treatment: the need for naturally engineered solutions

The aortic valve regulates unidirectional flow of oxygenated blood to the myocardium and arterial system. The natural anatomical geometry and microstructural complexity ensures biomechanically and hemodynamically efficient function. The compliant cusps are populated with unique cell phenotypes that continually remodel tissue for long-term durability within an extremely demanding mechanical environment. Alteration from normal valve homeostasis arises from genetic and microenvironmental (mechanical) sources, which lead to congenital and/or premature structural degeneration. Aortic valve stenosis pathobiology shares some features of atherosclerosis, but its final calcification endpoint is distinct. Despite its broad and significant clinical significance, very little is known about the mechanisms of normal valve mechanobiology and mechanisms of disease. This is reflected in the paucity of predictive diagnostic tools, early stage interventional strategies, and stagnation in regenerative medicine innovation. Tissue engineering has unique potential for aortic valve disease therapy, but overcoming current design pitfalls will require even more multidisciplinary effort. This review summarizes the latest advancements in aortic valve research and highlights important future directions.

Differential expression of cartilage and bone-related proteins in pediatric and adult diseased aortic valves

Approximately 5 million people are affected with aortic valve disease (AoVD) in the United States. The most common treatment is aortic valve (AoV) replacement surgery, however, replacement valves are susceptible to failure, necessitating additional surgeries. The molecular mechanisms underlying disease progression and late AoV calcification are not well understood. Recent studies suggest that genes involved in bone and cartilage development play an active role in osteogenic-like calcification in human calcific AoVD (CAVD). In an effort to define the molecular pathways involved in AoVD progression and calcification, expression of markers of valve mesenchymal progenitors, chondrogenic precursors, and osteogenic differentiation was compared in pediatric non-calcified and adult calcified AoV specimens. Valvular interstitial cell (VIC) activation, extracellular matrix (ECM) disorganization, and markers of valve mesenchymal and skeletal chondrogenic progenitor cells were observed in both pediatric and adult AoVD. However, activated BMP signaling, increased expression of cartilage and bone-type collagens, and increased expression of the osteogenic marker Runx2 are observed in adult diseased AoVs. They are not observed in the majority of pediatric diseased valves, representing a marked distinction in the molecular profile between pediatric and adult diseased AoVs. The combined evidence suggests that an actively regulated osteochondrogenic disease process underlies the pathological changes affecting AoVD progression, ultimately resulting in stenotic AoVD. Both pediatric and adult diseased AoVs express protein markers of valve mesenchymal and chondrogenic progenitor cells while adult diseased AoVs also express proteins involved in osteogenic calcification. These findings provide specific molecular indicators of AoVD progression, which may lead to identification of early disease markers and the development of potential therapeutics.

Viral and bacterial patterns induce TLR-mediated sustained inflammation and calcification in aortic valve interstitial cells

BACKGROUND

Aortic stenosis shares some ethiopathological features with atherosclerosis and increasing evidence links Toll-like receptors (TLRs) to atherogenesis.

METHODS

TLR-mediated inflammation and osteogenesis were investigated in human interstitial cells isolated from stenotic and non-stenotic aortic valves. TLR expression and signalling were evaluated by quantitative RT-PCR, flow cytometry, Western blot analysis, ELISA, and cytokine arrays. Osteogenesis was evaluated by measuring alkaline phosphatase activity.

RESULTS

Interstitial cells from control valves express most TLRs, being TLR4 the most abundant, whereas cells from stenotic valves express higher TLR4 and TLR2 and lower TLR5 and TLR9 transcript levels. When pro-inflammatory pathways were analyzed, we observed that TLR4, TLR2 and TLR3 ligands induced an early activation of NF-κB and p38 MAPK activation in cells from control and stenotic valves. Strikingly, when TLRs sensing viral patterns were studied, a sustained TLR3-mediated activation of NF-κB, a κB-independent induction of catalytically active cyclooxigenase (COX)-2 and ICAM-1 expression, and induction of expression of several chemokines were observed. TLR4, but not TLR2, engagement produced a similar but NF-κB-dependent effect. Moreover, TLR3 and TLR4 agonists induced alkaline phosphatase expression and activity.

CONCLUSIONS

Exposure of aortic valve interstitial cells to viral and Gram-negative bacteria molecular patterns induces distinct and long-term TLR-mediated pro-inflammatory and pro-osteogenic responses that might be relevant to the pathogenesis of degenerative aortic stenosis.

Molecular genetic studies of gene identification for osteoporosis: the 2009 update

Osteoporosis is a complex human disease that results in increased susceptibility to fragility fractures. It can be phenotypically characterized using several traits, including bone mineral density, bone size, bone strength, and bone turnover markers. The identification of gene variants that contribute to osteoporosis phenotypes, or responses to therapy, can eventually help individualize the prognosis, treatment, and prevention of fractures and their adverse outcomes. Our previously published reviews have comprehensively summarized the progress of molecular genetic studies of gene identification for osteoporosis and have covered the data available to the end of September 2007. This review represents our continuing efforts to summarize the important and representative findings published between October 2007 and November 2009. The topics covered include genetic association and linkage studies in humans, transgenic and knockout mouse models, as well as gene-expression microarray and proteomics studies. Major results are tabulated for comparison and ease of reference. Comments are made on the notable findings and representative studies for their potential influence and implications on our present understanding of the genetics of osteoporosis.

Increased biglycan in aortic valve stenosis leads to the overexpression of phospholipid transfer protein via Toll-like receptor 2

Aortic stenosis (AS) is the most common valvular heart disease, and it is suspected that atherosclerotic mechanisms are involved in the development of this disorder. Therefore, the retention of lipids within the aortic valve may play a role in the pathobiology of AS. In this study, a gene expression microarray experiment was conducted on human aortic valves with and without AS. The expression levels of transcripts encoding proteoglycans and enzymes involved in lipid retention were compared between the two groups. The microarray results were subsequently replicated in a cohort of 87 AS valves and 36 control valves. In addition, the interaction between proteoglycan and lipid-modifying enzyme was documented in isolated valve interstitial cells (VICs). The microarray results indicated that only biglycan (BGN) and phospholipid transfer protein (PLTP) were overexpressed in the AS valves. These results were then confirmed by quantitative PCR. The immunohistochemical analysis revealed a colocalization of BGN, PLTP, and Toll-like receptor-2 (TLR 2) in AS valves. In vitro, we showed that BGN induces the production of PLTP in VICs via the stimulation of TLR 2. Thus, increased accumulation of BGN in AS valves contributes to the production of PLTP via TLR 2. These results suggest that intricate links between valve matrix proteins, inflammation, and lipid retention are involved in the pathobiology of AS.

Innate immunity and toll-like receptor antagonists: a potential role in the treatment of cardiovascular diseases

Toll-like receptors (TLRs) are germline-encoded receptors that recognize various pathogen-associated molecular patterns (PAMPs). They are key components of the innate immunity which are activated in response to pathogens as well as non-pathogenic components of damaged tissues. TLR agonists have been developed to treat allergies, cancers, and chronic infections by upregulating the innate immune system. TLR antagonists may be used to treat a number of inflammatory conditions, such as rheumatoid arthritis and systemic lupus erythematosus. Recent research also has shown that TLRs are involved in the pathogenesis of atherosclerosis, thrombosis, myocardial remodeling, ischemic/reperfusion injury, and valvular disease. This article reviews the current experimental and clinical evidence for the role of TLRs in the cardiovascular system, and examines the mechanisms by which TLR antagonists could potentially be used in targeted therapy.