Multimodality and molecular imaging of matrix metalloproteinase activation in calcific aortic valve disease

Th1 cells reduce the osteoblast-like phenotype in valvular interstitial cells by inhibiting NLRP3 inflammasome activation in macrophages

BACKGROUND AND AIMS

Inflammation is initiates the propagation phase of aortic valve calcification. The activation of NLRP3 signaling in macrophages plays a crucial role in the progression of calcific aortic valve stenosis (CAVS). IFN-γ regulates NLRP3 activity in macrophages. This study aimed to explore the mechanism of IFN-γ regulation and its impact on CAVS progression and valve interstitial cell transdifferentiation.

METHODS AND RESULTS

The number of Th1 cells and the expression of IFN-γ and STAT1 in the aortic valve, spleen and peripheral blood increased significantly as CAVS progressed. To explore the mechanisms underlying the roles of Th1 cells and IFN-γ, we treated CAVS mice with IFN-γ-AAV9 or an anti-IFN-γ neutralizing antibody. While IFN-γ promoted aortic valve calcification and dysfunction, it significantly decreased NLRP3 signaling in splenic macrophages and Ly6C+ monocytes. In vitro coculture showed that Th1 cells inhibited NLPR3 activation in ox-LDL-treated macrophages through the IFN-γR1/IFN-γR2-STAT1 pathway. Compared with untreated medium, conditioned medium from Th1-treated bone marrow-derived macrophages reduced the osteogenic calcification of valvular interstitial cells.

CONCLUSION

Inhibition of the NLRP3 inflammasome by Th1 cells protects against valvular interstitial cell calcification as a negative feedback mechanism of adaptive immunity toward innate immunity. This study provides a precision medicine strategy for CAVS based on the targeting of anti-inflammatory mechanisms.

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.

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.

Multimodality Imaging of Aortic Valve Calcification and Function in a Murine Model of Calcific Aortic Valve Disease and Bicuspid Aortic Valve

Calcific aortic valve disease (CAVD) is a prevailing disease with increasing occurrence and no known medical therapy. Dcbld2-/- mice have a high prevalence of bicuspid aortic valve (BAV), spontaneous aortic valve calcification, and aortic stenosis (AS). 18F-NaF PET/CT can detect the aortic valve calcification process in humans. However, its feasibility in preclinical models of CAVD remains to be determined. Here, we sought to validate 18F-NaF PET/CT for tracking murine aortic valve calcification and leveraged it to examine the development of calcification with aging and its interdependence with BAV and AS in Dcbld2-/- mice. Methods: Dcbld2-/- mice at 3-4 mo, 10-16 mo, and 18-24 mo underwent echocardiography, 18F-NaF PET/CT (n = 34, or autoradiography (n = 45)), and tissue analysis. A subset of mice underwent both PET/CT and autoradiography (n = 12). The aortic valve signal was quantified as SUVmax on PET/CT and as percentage injected dose per square centimeter on autoradiography. The valve tissue sections were analyzed by microscopy to identify tricuspid and bicuspid aortic valves. Results: The aortic valve 18F-NaF signal on PET/CT was significantly higher at 18-24 mo (P < 0.0001) and 10-16 mo (P < 0.05) than at 3-4 mo. Additionally, at 18-24 mo BAV had a higher 18F-NaF signal than tricuspid aortic valves (P < 0.05). These findings were confirmed by autoradiography, with BAV having significantly higher 18F-NaF uptake in each age group. A significant correlation between PET and autoradiography data (Pearson r = 0.79, P < 0.01) established the accuracy of PET quantification. The rate of calcification with aging was significantly faster for BAV (P < 0.05). Transaortic valve flow velocity was significantly higher in animals with BAV at all ages. Finally, there was a significant correlation between transaortic valve flow velocity and aortic valve calcification by both PET/CT (r = 0.55, P < 0.001) and autoradiography (r = 0.45, P < 0.01). Conclusion: 18F-NaF PET/CT links valvular calcification to BAV and aging in Dcbld2-/- mice and suggests that AS may promote calcification. In addition to addressing the pathobiology of valvular calcification, 18F-NaF PET/CT may be a valuable tool for evaluation of emerging therapeutic interventions in CAVD.

Prognostic role of tissue plasminogen activator in coronary artery disease with or without aortic valve sclerosis

AIMS

We sought to investigate the relationship between circulating tissue plasminogen activator (t-PA) level and long-term outcomes in stable coronary artery disease patients with or without aortic valve sclerosis (AVSc).

METHODS AND RESULTS

Serum levels of t-PA were determined in 347 consecutive stable angina patients with (n = 183) or without (n = 164) AVSc. Outcomes were prospectively recorded as planned clinic evaluations every 6 months up to 7 years. The primary endpoint was a composite of cardiovascular death and rehospitalization due to heart failure. The secondary endpoint included all-cause mortality, cardiovascular death, and rehospitalization due to heart failure. Serum t-PA was significantly higher in AVSc than in non-AVSc patients (2131.22 pg/mL vs. 1495.85 pg/mL, P < 0.001). For patients with AVSc, those with t-PA level above the median (>1840.68 pg/mL) were more likely to meet the primary and secondary endpoints (all P < 0.001). After adjusting for potential confounding factors, serum t-PA level remained significantly predictive for each endpoint in the Cox proportional hazard models. The prognostic value of t-PA was good, with an AUC-ROC of 0.753 (P < 0.001). The combination of t-PA with traditional risk factors improved the risk reclassification of AVSc patients, with a net reclassification index of 0.857 and an integrated discrimination improvement of 0.217 (all P < 0.001). However, for patients without AVSc, both primary and secondary endpoints were similar, irrespective of t-PA levels.

CONCLUSIONS

Elevated circulating t-PA confers an increased risk for poor long-term clinical outcomes in stable coronary artery disease patients with AVSc.

Abnormally elevated EZH2-mediated H3K27me3 enhances osteogenesis in aortic valve interstitial cells by inhibiting SOCS3 expression

BACKGROUND AND AIMS

The osteogenic transition of aortic valve interstitial cells (AVICs) plays a critical role for the progression of calcific aortic valve disease (CAVD). Enhancer of zeste homolog 2 (EZH2) is an important methyltransferase for histone H3 Lys27 (H3K27) that has been found to be involved in osteogenesis. Here, we investigated the effect and mechanism of EZH2 in CAVD progression.

METHODS

High throughout mRNA sequencing, qRT-PCR and immunoblot were performed to screen differentially expressed genes in non-CAVD and CAVD aortic valves. To investigate the role of EZH2 and SOCS3 in osteogenesis, AVICs were treated with siRNA, adenovirus and specific inhibitors, then osteogenic markers and mineralized deposits were examined. In vivo, the morphology and function of aortic valves were investigated by HE stain and echocardiography in ApoE^-/- mice fed a long-term western diet (WD).

RESULTS

We discovered that EZH2 was upregulated and SOCS3 was downregulated in calcified aortic valves. In AVICs, inhibition or silencing of EZH2 attenuated the osteogenic responses. On the other hand, demethylases inhibitor (GSK-J4) enhanced osteogenic transition of AVICs. Moreover, SOCS3 knockdown enhanced the expression of osteogenic markers, while SOCS3 overexpression suppressed osteogenesis and calcification. The chromatin immunoprecipitation and restored experiments indicated that EZH2 directly targeted SOCS3 to promote osteogenic responses of AVICs. In vivo, treatment with EZH2 inhibitor through intraperitoneal injection attenuated aortic valve thickening, calcification and dysfunction induced by WD.

CONCLUSIONS

Collectively, we found that EZH2-mediated H3K27me3 enhanced osteogenesis and microcalcification of AVICs via inhibiting SOCS3 expression, which provides potential targets for future therapeutic interventions of CAVD.

Potential novel imaging targets of inflammation in cardiac sarcoidosis

Cardiac sarcoidosis (CS) is an inflammatory disease with high morbidity and mortality, with a pathognomonic feature of non-caseating granulomatous inflammation. While 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) is a well-established modality to image inflammation and diagnose CS, there are limitations to its specificity and reproducibility. Imaging focused on the molecular processes of inflammation including the receptors and cellular microenvironments present in sarcoid granulomas provides opportunities to improve upon FDG-PET imaging for CS. This review will highlight the current limitations of FDG-PET imaging for CS while discussing emerging new nuclear imaging molecular targets for the imaging of cardiac sarcoidosis.

Radiotracers to Address Unmet Clinical Needs in Cardiovascular Imaging, Part 2: Inflammation, Fibrosis, Thrombosis, Calcification, and Amyloidosis Imaging

Cardiovascular imaging is evolving in response to systemwide trends toward molecular characterization and personalized therapies. The development of new radiotracers for PET and SPECT imaging is central to addressing the numerous unmet diagnostic needs that relate to these changes. In this 2-part review, we discuss select radiotracers that may help address key unmet clinical diagnostic needs in cardiovascular medicine. Part 1 examined key technical considerations pertaining to cardiovascular radiotracer development and reviewed emerging radiotracers for perfusion and neuronal imaging. Part 2 covers radiotracers for imaging cardiovascular inflammation, thrombosis, fibrosis, calcification, and amyloidosis. These radiotracers have the potential to address several unmet needs related to the risk stratification of atheroma, detection of thrombi, and the diagnosis, characterization, and risk stratification of cardiomyopathies. In the first section, we discuss radiotracers targeting various aspects of inflammatory responses in pathologies such as myocardial infarction, myocarditis, sarcoidosis, atherosclerosis, and vasculitis. In a subsequent section, we discuss radiotracers for the detection of systemic and device-related thrombi, such as those targeting fibrin (e.g., ⁶⁴Cu-labeled fibrin-binding probe 8). We also cover emerging radiotracers for the imaging of cardiovascular fibrosis, such as those targeting fibroblast activation protein (e.g., ⁶⁸Ga-fibroblast activation protein inhibitor). Lastly, we briefly review radiotracers for imaging of cardiovascular calcification (¹⁸F-NaF) and amyloidosis (e.g., ^99mTc-pyrophosphate and ¹⁸F-florbetapir).

S2 Heart Sound Detects Aortic Valve Calcification Independent of Hemodynamic Changes in Mice

Background

Calcific aortic valve disease (CAVD) is often undiagnosed in asymptomatic patients, especially in underserved populations. Although artificial intelligence has improved murmur detection in auscultation exams, murmur manifestation depends on hemodynamic factors that can be independent of aortic valve (AoV) calcium load and function. The aim of this study was to determine if the presence of AoV calcification directly influences the S2 heart sound.

Methods

Adult C57BL/6J mice were assigned to the following 12-week-long diets: (1) Control group (n = 11) fed a normal chow, (2) Adenine group (n = 4) fed an adenine-supplemented diet to induce chronic kidney disease (CKD), and (3) Adenine + HP (n = 9) group fed the CKD diet for 6 weeks, then supplemented with high phosphate (HP) for another 6 weeks to induce AoV calcification. Phonocardiograms, echocardiogram-based valvular function, and AoV calcification were assessed at endpoint.

Results

Mice on the Adenine + HP diet had detectable AoV calcification (9.28 ± 0.74% by volume). After segmentation and dimensionality reduction, S2 sounds were labeled based on the presence of disease: Healthy, CKD, or CKD + CAVD. The dataset (2,516 S2 sounds) was split subject-wise, and an ensemble learning-based algorithm was developed to classify S2 sound features. For external validation, the areas under the receiver operating characteristic curve of the algorithm to classify mice were 0.9940 for Healthy, 0.9717 for CKD, and 0.9593 for CKD + CAVD. The algorithm had a low misclassification performance of testing set S2 sounds (1.27% false positive, 1.99% false negative).

Conclusion

Our ensemble learning-based algorithm demonstrated the feasibility of using the S2 sound to detect the presence of AoV calcification. The S2 sound can be used as a marker to identify AoV calcification independent of hemodynamic changes observed in echocardiography.

Novel Biomarkers of Atherosclerotic Vascular Disease-Latest Insights in the Research Field

The atherosclerotic vascular disease is a cardiovascular continuum in which the main role is attributed to atherosclerosis, from its appearance to its associated complications. The increasing prevalence of cardiovascular risk factors, population ageing, and burden on both the economy and the healthcare system have led to the development of new diagnostic and therapeutic strategies in the field. The better understanding or discovery of new pathophysiological mechanisms and molecules modulating various signaling pathways involved in atherosclerosis have led to the development of potential new biomarkers, with key role in early, subclinical diagnosis. The evolution of technological processes in medicine has shifted the attention of researchers from the profiling of classical risk factors to the identification of new biomarkers such as midregional pro-adrenomedullin, midkine, stromelysin-2, pentraxin 3, inflammasomes, or endothelial cell-derived extracellular vesicles. These molecules are seen as future therapeutic targets associated with decreased morbidity and mortality through early diagnosis of atherosclerotic lesions and future research directions.

Differential BMP Signaling Mediates the Interplay Between Genetics and Leaflet Numbers in Aortic Valve Calcification

Expression of a neuropilin-like protein, DCBLD2, is reduced in human calcific aortic valve disease (CAVD). DCBLD2-deficient mice develop bicuspid aortic valve (BAV) and CAVD, which is more severe in BAV mice compared with tricuspid littermates. In vivo and in vitro studies link this observation to up-regulated bone morphogenic protein (BMP)2 expression in the presence of DCBLD2 down-regulation, and enhanced BMP2 signaling in BAV, indicating that a combination of genetics and BAV promotes aortic valve calcification and stenosis. This pathway may be a therapeutic target to prevent CAVD progression in BAV.

Serotonin receptor type 2B activation augments TNF-α-induced matrix mineralization in murine valvular interstitial cells

Calcification, fibrosis, and chronic inflammation are the predominant features of calcific aortic valve disease, a life-threatening condition. Drugs that induce serotonin (5-hydroxytryptamine [5-HT]) are known to damage valves, and activated platelets, which carry peripheral serotonin, are known to promote calcific aortic valve stenosis. However, the role of 5-HT in valve leaflet pathology is not known. We tested whether serotonin mediates inflammation-induced matrix mineralization in valve cells. Real-time reverse transcription-polymerase chain reaction analysis showed that murine aortic valve interstitial cells (VICs) expressed both serotonin receptor types 2A and 2B (Htr2a and Htr2b). Although Htr2a expression was greater at baseline, Htr2b expression was induced several-fold more than Htr2a in response to the pro-calcific tumor necrosis factor-α (TNF-α) treatment. 5-HT also augmented TNF-α-induced osteoblastic differentiation and matrix mineralization of VIC, but 5-HT alone had no effects. Inhibition of serotonin receptor type 2B, using specific inhibitors or lentiviral knockdown in VIC, attenuated 5-HT effects on TNF-α-induced osteoblastic differentiation and mineralization. 5-HT treatment also augmented TNF-α-induced matrix metalloproteinase-3 expression, which was also attenuated by Htr2b knockdown. Htr2b expression in aortic roots and serum levels of peripheral 5-HT were also greater in the hyperlipidemic Apoe^-/- mice than in control normolipemic mice. These findings suggest a new role for serotonin signaling in inflammation-induced calcific valvulopathy.

Role of Interleukin 17A in Aortic Valve Inflammation in Apolipoprotein E-deficient Mice

Interleukin 17A (IL17A) is reported to be involved in many inflammatory processes, but its role in aortic valve diseases remains unknown. We examined the role of IL17A based on an ApoE^-/- mouse model with strategies as fed with high-fat diet or treated with IL17A monoclonal antibody (mAb). 12 weeks of high-fat diet feeding can elevate cytokines secretion, inflammatory cells infiltration and myofibroblastic transition of valvular interstitial cells (VICs) in aortic valve. Moreover, diet-induction accelerated interleukin 17 receptor A (IL17RA) activation in VICs. In an IL17A inhibition model, the treatment group was intra-peritoneally injected with anti-IL17A mAb while controls received irrelevant antibody. Functional blockade of IL17A markedly reduced cellular infiltration and transition in aortic valve. To investigate potential mechanisms, NF-κB was co-stained in IL17RA⁺ VICs and IL17RA⁺ macrophages, and further confirmed by Western blotting in VICs. High-fat diet could activate NF-κB nuclear translocation in IL17RA⁺ VICs and IL17RA⁺ macrophages and this process was depressed after IL17A mAb-treatment. In conclusion, high-fat diet can lead to IL17A upregulation, VICs myofibroblastic transition and inflammatory cells infiltration in the aortic value of ApoE^-/- mice. Blocking IL17A with IL17A mAb can alleviate aortic valve inflammatory states.

A Role for MMP-10 (Matrix Metalloproteinase-10) in Calcific Aortic Valve Stenosis

OBJECTIVE

Aortic valve (AV) calcification plays an important role in the progression of aortic stenosis (AS). MMP-10 (matrix metalloproteinase-10 or stromelysin-2) is involved in vascular calcification in atherosclerosis. We hypothesize that MMP-10 may play a pathophysiological role in calcific AS. Approach and Results: Blood samples (n=112 AS and n=349 controls) and AVs (n=88) from patients undergoing valve replacement were analyzed. Circulating MMP-10 was higher in patients with AS compared with controls (P<0.001) and correlated with TNFα (tumor necrosis factor α; r_S=0.451; P<0.0001). MMP-10 was detected by immunochemistry in AVs from patients with AS colocalized with aortic valve interstitial cells markers α-SMA (α-smooth muscle actin) and vimentin and with calcification markers Runx2 (Runt-related transcription factor 2) and SRY (sex-determining region Y)-box 9. MMP-10 expression in AVs was further confirmed by RT-qPCR and western blot. Ex vivo, MMP-10 was elevated in the conditioned media of AVs from patients with AS and associated with interleukin-1β (r_S=0.5045, P<0.001) and BMP (bone morphogenetic protein)-2 (r_S=0.5003, P<0.01). In vitro, recombinant human MMP-10 induced the overexpression of inflammatory, fibrotic, and osteogenic markers (interleukin-1β, α-SMA, vimentin, collagen, BMP-4, Sox9, OPN [osteopontin], BMP-9, and Smad 1/5/8; P<0.05) and cell mineralization in aortic valve interstitial cells isolated from human AVs, in a mechanism involving Akt (protein kinase B) phosphorylation. These effects were prevented by TIMP-1 (tissue inhibitor of metalloproteinases type 1), a physiological MMP inhibitor, or specifically by an anti-MMP-10 antibody.

CONCLUSIONS

MMP-10, which is overexpressed in aortic valve from patients with AS, seems to play a central role in calcification in AS through Akt phosphorylation. MMP-10 could be a new therapeutic target for delaying the progression of aortic valve calcification in AS.

IL-21 promotes osteoblastic differentiation of human valvular interstitial cells through the JAK3/STAT3 pathway

Objectives: This study amied to whether IL-21 promotes osteoblast transdifferentiation of cultured human Valvular interstitial cells (VICs). Methods: We first confirmed that IL-21 alters gene expression between CAVD aortic valve tissue and normal samples by immunohistochemistry, qPCR, and western blotting. VICs were cultured and treated with IL-21. Gene and protein expression levels of the osteoblastic markers ALP and Runx2, which can be blocked by specific JAK3 inhibitors and/or siRNA of STAT3, were measured. Results: IL-21 expression was upregulated in calcified aortic valves and promotes osteogenic differentiation of human VICs. IL-21 accelerated VIC calcification through the JAK3/STAT3 pathway. Conclusion: Our data suggest that IL-21 is a key factor in valve calcification and a promising candidate for targeted therapeutics for CAVD.

Development of calcific aortic valve disease: Do we know enough for new clinical trials?

Calcific aortic valve disease (CAVD), previously thought to represent a passive degeneration of the valvular extracellular matrix (VECM), is now regarded as an intricate multistage disorder with sequential yet intertangled and interacting underlying processes. Endothelial dysfunction and injury, initiated by disturbed blood flow and metabolic disorders, lead to the deposition of low-density lipoprotein cholesterol in the VECM further provoking macrophage infiltration, oxidative stress, and release of pro-inflammatory cytokines. Such changes in the valvular homeostasis induce differentiation of normally quiescent valvular interstitial cells (VICs) into synthetically active myofibroblasts producing excessive quantities of the VECM and proteins responsible for its remodeling. As a result of constantly ongoing degradation and re-deposition, VECM becomes disorganised and rigid, additionally potentiating myofibroblastic differentiation of VICs and worsening adaptation of the valve to the blood flow. Moreover, disrupted and excessively vascularised VECM is susceptible to the dystrophic calcification caused by calcium and phosphate precipitating on damaged collagen fibers and concurrently accompanied by osteogenic differentiation of VICs. Being combined, passive calcification and biomineralisation synergistically induce ossification of the aortic valve ultimately resulting in its mechanical incompetence requiring surgical replacement. Unfortunately, multiple attempts have failed to find an efficient conservative treatment of CAVD; however, therapeutic regimens and clinical settings have also been far from the optimal. In this review, we focused on interactions and transitions between aforementioned mechanisms demarcating ascending stages of CAVD, suggesting a predisposing condition (bicuspid aortic valve) and drug combination (lipid-lowering drugs combined with angiotensin II antagonists and cytokine inhibitors) for the further testing in both preclinical and clinical trials.

CC chemokine receptor 2 functions in osteoblastic transformation of valvular interstitial cells

AIMS

Calcific aortic valve disease (CAVD) emerges as a challenging clinical issue, which is associated with high cardiovascular mortality. It has been demonstrated that osteoblastic transformation of AVICs is a key mechanism of CAVD and C-C motif chemokine receptors (CCRs) may favor this process. Thus, we aimed to investigate whether CCRs were involved in osteoblastic transformation of AVICs during the development CAVD.

MAIN METHODS

We first analyzed microarray data (GSE51472 and GSE12644) to identify differentially expressed genes between CAVD aortic valve tissue and normal samples, followed by verification of immunohistochemistry, qPCR and western blotting. Primary aortic valvular interstitial cells (AVICs) were incubated with specific inhibitors and/or siRNA of CCR2 and CCL2 under pro-calcifying medium. The levels of CCL2 in the medium were measured by ELISA. In addition, we used recombinant CCL2 to activate CCR2 in calcifying AVICs. Alizarin red S staining and calcium deposition were used to evaluate the degree of calcification. Western blotting was used to determine osteoblastic transformation of AVIC and total Akt and phosphorylated Akt expression.

KEY FINDING

CCR2 levels were remarkably up-regulated in calcified aortic valve and calcifying AVICs. Silencing CCR2 inhibited the osteoblastic transformation and calcification of AVICs. In addition, recombinant CCL2 activated CCR2 and accelerated AVICs calcification through PI3K/Akt pathway.

SIGNIFICANCE

We characterize abnormal activation of CCL2/CCR2 axis as a promoter of AVICs osteoblastic transformation and calcification. Our findings implicate the CCL2/CCR2-PI3K/Akt pathway as a potential target for treatment of CAVD.

Novel Arginine-containing Macrocyclic MMP Inhibitors: Synthesis, 99mTc-labeling, and Evaluation

Matrix metalloproteinases (MMPs) are involved in tissue remodeling. Accordingly, MMP inhibitors and related radiolabeled analogs are important tools for MMP-targeted imaging and therapy in a number of diseases. Herein, we report design, synthesis, and evaluation of a new Arginine-containing macrocyclic hydroxamate analog, RYM, its hydrazinonicotinamide conjugate, RYM1 and 99mTc-labeled analog 99mTc-RYM1 for molecular imaging. RYM exhibited potent inhibition against a panel of recombinant human (rh) MMPs in vitro. RYM1 was efficiently labeled with 99mTcO4- to give 99mTc-RYM1 in a high radiochemical yield and high radiochemical purity. RYM1 and its decayed labeling product displayed similar inhibition potencies against rhMMP-12. Furthermore, 99mTc-RYM1 exhibited specific binding with lung tissue from lung-specific interleukin-13 transgenic mice, in which MMP activity is increased in conjunction with tissue remodeling and inflammation. The results support further development of such new water-soluble Arginine-containing macrocyclic hydroxamate MMP inhibitors for targeted imaging and therapy.

Molecular imaging of calcific aortic valve disease

Calcific aortic valve disease (CAVD) can progress to symptomatic aortic stenosis in a subset of patients. The severity of aortic stenosis and the extent of valvular calcification can be evaluated readily by echocardiography, CT, and MRI using well-established imaging protocols. However, these techniques fail to address optimally other important aspects of CAVD, including the propensity for disease progression, risk of complications in asymptomatic patients, and the effect of therapeutic interventions on valvular biology. These gaps may be addressed by molecular imaging targeted at key biological processes such as inflammation, remodeling, and calcification that mediate the development and progression of CAVD. In this review, recent advances in valvular molecular imaging, including 18F-fluorodeoxyglucose (FDG) and 18F-sodium fluoride (NaF) PET, and matrix metalloproteinase-targeted SPECT imaging in the preclinical and clinical settings are presented and discussed.

Postnatal and Adult Aortic Heart Valves Have Distinctive Transcriptional Profiles Associated With Valve Tissue Growth and Maintenance Respectively

Heart valves are organized connective tissues of high mechanical demand. They open and close over 100,000 times a day to preserve unidirectional blood flow by maintaining structure-function relationships throughout life. In affected individuals, structural failure compromises function and often leads to regurgitant blood flow and progressive heart failure. This is most common in degenerative valve disease due to age-related wear and tear, or congenital malformations. At present, the only effective treatment of valve disease is surgical repair or replacement and this is often impermanent and requires anti-coagulation therapy throughout life. Therefore, there is a critical need to discover new alternatives. A promising therapeutic area is tissue regeneration and in non-valvular tissues this requires a tightly regulated genetic “growth program” involving cell proliferation. To explore this in heart valves, we performed RNA-seq analysis to compare transcriptional profiles of aortic valve tissue isolated from mice during stages of growth (postnatal day (PND) 2) and adult maintenance (4 months). Data analysis reveals distinct mRNA profiles at each time point and pathway ontology identifies associated changes in biological functions. The PND2 aortic valve is characterized by extensive cell proliferation and expression of mRNAs related to the extracellular matrix (ECM). At 4 months, proliferation is not significant and a differential set of ECM-related genes are expressed. Interestingly there is enrichment of the defense response biological process at this later time point. Together, these data highlight the unique transcriptome of the postnatal valve during stages of growth and maturation, as well as biological functions associated with adult homeostatic valves. These studies create a platform for future work exploring the molecular programs altered in the onset of heart valve disease after birth and provide insights for the development of mechanistic-based therapies.

Association of matrix metalloprotease 1, 3, and 12 polymorphisms with rheumatic heart disease in a Chinese Han population

BACKGROUND

Rheumatic heart disease (RHD) is an autoimmune disease triggered by acute rheumatic fever (ARF). Matrix metalloproteinases (MMPs) play an important role in the modulation of immune responses. The purpose of this study was to evaluate the association of MMP1, 3, and 12 promoter polymorphisms with RHD in a Han population in Southern China since the 3 genes are localized on the same chromosome and have a combined effect.

METHODS

DNA samples were obtained from 90 adult patients with RHD and 90 control subjects. Polymorphisms in MMP1 (rs1799750), MMP3 (rs3025058), and MMP12 (rs2276109) were genotyped by direct sequencing. Differences in genotype and allele frequencies of these polymorphisms were compared between the cases and the controls using Unconditional logistic regression models and Chi-squared test.

RESULTS

The 2G/2G genotype of rs1799750 in MMP1 was associated with a significantly higher risk of RHD when compared with the 1G/1G genotype (OR = 3.227; 95% CI:1.118-9.31; p = 0.03). The frequency of allele 2G was higher in patients with RHD compared to the controls (69.4% vs. 58.9%; p = 0.048) No significant differences in genotype and allele frequencies of rs3025058 in MMP3 and rs2276109 in MMP12 were found between the patients with RHD and the controls (p > 0.05).

CONCLUSIONS

Our results suggest that rs1799750 in MMP1 might be a risk factor for RHD in a Han population in Southern China, and individuals carrying the 2G/2G genotype are likely more susceptible to RHD. In contrast, rs3025058 in MMP3 and rs2276109 in MMP12 might not contribute to the risk of developing RHD in this population. Further studies with larger samples and other ethnic populations are required to confirm these findings.

Preclinical Evaluation of RYM1, a Matrix Metalloproteinase-Targeted Tracer for Imaging Aneurysm

Matrix metalloproteinases (MMPs) play a key role in abdominal aortic aneurysm (AAA) development. Accordingly, MMP-targeted imaging provides important information regarding vessel wall biology in the course of aneurysm development. Given the small size of the vessel wall and its proximity with blood, molecular imaging of aneurysm optimally requires highly sensitive tracers with rapid blood clearance. To this end, we developed a novel hydrosoluble zwitterionic MMP inhibitor, RYM, on the basis of which a pan-MMP tracer, RYM1, was designed. Here, we describe the development and preclinical evaluation of RYM1 in comparison with RP805, a commonly used pan-MMP tracer in murine models of aneurysm. Methods: The macrocyclic hydroxamate-based pan-MMP inhibitor coupled with 6-hydrazinonicotinamide, RYM1, was synthesized and labeled with ^99mTc. Radiochemical stability of ^99mTc-RYM1 was evaluated by radio-high-performance liquid chromatography analysis. Tracer blood kinetics and biodistribution were compared with ^99mTc-RP805 in C57BL/6J mice (n = 10). ^99mTc-RYM1 binding to aneurysm and specificity were evaluated by quantitative autoradiography in apolipoprotein E-deficient (apoE^-/-) mice with CaCl₂-induced carotid aneurysm (n = 11). Angiotensin II-infused apoE^-/- (n = 16) mice were used for small-animal SPECT/CT imaging. Aortic tissue MMP activity and macrophage marker CD68 expression were assessed by zymography and reverse-transcription polymerase chain reaction. Results: RYM1 showed nanomolar range inhibition constants for several MMPs. ^99mTc-RYM1 was radiochemically stable in mouse blood for 5 h and demonstrated rapid renal clearance and lower blood levels in vivo compared with ^99mTc-RP805. ^99mTc-RYM1 binding to aneurysm and its specificity were shown by autoradiography in carotid aneurysm. Angiotensin II infusion in apoE^-/- mice for 4 wk resulted in AAA formation in 36% (4/11) of surviving animals. In vivo ^99mTc-RYM1 small-animal SPECT/CT images showed higher uptake of the tracer in AAA than nondilated aortae. Finally, aortic uptake of ^99mTc-RYM1 in vivo correlated with aortic MMP activity and CD68 expression. Conclusion: The newly developed pan-MMP inhibitor-based tracer ^99mTc-RYM1 displays favorable pharmacokinetics for early vascular imaging and enables specific detection of inflammation and MMP activity in aneurysm.

Mechanosensitive microRNA-181b Regulates Aortic Valve Endothelial Matrix Degradation by Targeting TIMP3

Calcific aortic valve disease (CAVD) is a major cause of morbidity in the aging population, but the underlying mechanisms of its progression remain poorly understood. Aortic valve calcification preferentially occurs on the fibrosa, which is subjected to disturbed flow. The side-specific progression of the disease is characterized by inflammation, calcific lesions, and extracellular matrix (ECM) degradation. Here, we explored the role of mechanosensitive microRNA-181b and its downstream targets in human aortic valve endothelial cells (HAVECs). Mechanistically, miR-181b is upregulated in OS and fibrosa, and it targets TIMP3, SIRT1, and GATA6, correlated with increased gelatinase/MMP activity. Overexpression of miR-181b led to decreased TIMP3 and exacerbated MMP activity as shown by gelatinase assay, and miR-181b inhibition decreased gelatinase activity through the repression of TIMP3 levels. Luciferase assay showed specific binding of miR-181b to the TIMP3 gene. Overexpression of miR-181b in HAVECs subjected to either LS or OS increased MMP activity, and miR-181b inhibition abrogated shear-sensitive MMP activity. These studies suggest that targeting this shear-dependent miRNA may provide a novel noninvasive treatment for CAVD.

Deletion of CD73 in mice leads to aortic valve dysfunction

Aortic stenosis is known to involve inflammation and thrombosis. Changes in activity of extracellular enzyme - ecto-5'-nucleotidase (referred also as CD73) can alter inflammatory and thrombotic responses. This study aimed to evaluate the effect of CD73 deletion in mice on development of aortic valve dysfunction and to compare it to the effect of high-fat diet. Four groups of mice (normal-diet Wild Type (WT), high-fat diet WT, normal diet CD73-/-, high-fat diet CD73-/-) were maintained for 15weeks followed by echocardiographic analysis of aortic valve function, measurement of aortic surface activities of nucleotide catabolism enzymes as well as alkaline phosphatase activity, mineral composition and histology of aortic valve leaflets. CD73-/- knock out led to an increase in peak aortic flow (1.06±0.26m/s) compared to WT (0.79±0.26m/s) indicating obstruction. Highest values of peak aortic flow (1.26±0.31m/s) were observed in high-fat diet CD73-/- mice. Histological analysis showed morphological changes in CD73-/- including thickening and accumulation of dark deposits, proved to be melanin. Concentrations of Ca²⁺, Mg²⁺ and PO₄^3- in valve leaflets were elevated in CD73-/- mice. Alkaline phosphatase (ALP) activity was enhanced after ATP treatment and reduced after adenosine treatment in aortas incubated in osteogenic medium. AMP hydrolysis in CD73-/- was below 10% of WT. Activity of ecto-adenosine deaminase (eADA), responsible for adenosine deamination, in the CD73-/- was 40% lower when compared to WT. Deletion of CD73 in mice leads to aortic valve dysfunction similar to that induced by high-fat diet suggesting important role of this surface protein in maintaining heart valve integrity.

Matrix metalloproteinase inhibitor, doxycycline and progression of calcific aortic valve disease in hyperlipidemic mice

Calcific aortic valve disease (CAVD) is the most common cause of aortic stenosis. Currently, there is no non-invasive medical therapy for CAVD. Matrix metalloproteinases (MMPs) are upregulated in CAVD and play a role in its pathogenesis. Here, we evaluated the effect of doxycycline, a nonselective MMP inhibitor on CAVD progression in the mouse. Apolipoprotein (apo)E^−/− mice (n = 20) were fed a Western diet (WD) to induce CAVD. After 3 months, half of the animals was treated with doxycycline, while the others continued WD alone. After 6 months, we evaluated the effect of doxycycline on CAVD progression by echocardiography, MMP-targeted micro single photon emission computed tomography (SPECT)/computed tomography (CT), and tissue analysis. Despite therapeutic blood levels, doxycycline had no significant effect on MMP activation, aortic valve leaflet separation or flow velocity. This lack of effect on in vivo images was confirmed on tissue analysis which showed a similar level of aortic valve gelatinase activity, and inflammation between the two groups of animals. In conclusion, doxycycline (100 mg/kg/day) had no effect on CAVD progression in apoE^−/− mice with early disease. Studies with more potent and specific inhibitors are needed to establish any potential role of MMP inhibition in CAVD development and progression.

Morphology, Clinicopathologic Correlations, and Mechanisms in Heart Valve Health and Disease

The clinical and pathological features of the most frequent intrinsic structural diseases that affect the heart valves are well established, but heart valve disease mechanisms are poorly understood, and effective treatment options are evolving. Major advances in the understanding of the structure, function and biology of native valves and the pathobiology, biomaterials and biomedical engineering, and the clinical management of valvular heart disease have occurred over the past several decades. This communication reviews contemporary considerations relative to the pathology of valvular heart disease, including (1) clinical significance and epidemiology of valvular heart disease; (2) functional and dynamic valvular macro-, micro- and ultrastructure; (3) causes, morphology and mechanisms of human valvular heart disease; and (4) pathologic considerations in valve replacement, repair and, potentially, regeneration of the heart valves.

Matrix Metalloproteinase-Targeted Imaging of Lung Inflammation and Remodeling

Imaging techniques for detection of molecular and cellular processes that precede or accompany lung diseases are needed. Matrix metalloproteinases (MMPs) play key roles in the development of pulmonary pathology. The objective of this study was to investigate the feasibility of in vivo MMP-targeted molecular imaging for detection of lung inflammation and remodeling.

METHODS

Lung-specific IL-13 transgenic (Club cell 10-kDa protein [CC10]-IL-13 Tg) mice and wild-type littermates were used in this study. Lung structure, gene expression, and MMP activity were assessed by histology, real-time reverse transcription polymerase chain reaction, Western blotting, and zymography. MMP activation was imaged by in vivo small-animal SPECT/CT followed by ex vivo planar imaging. Signal specificity was addressed using a control tracer. The correlation between in vivo MMP signal and gene expression was addressed.

RESULTS

CC10-IL-13 Tg mice developed considerable pulmonary tissue remodeling and inflammation. CD68, MMP-12, and MMP-13 were significantly higher in CC10-IL-13 Tg lungs. On in vivo small-animal SPECT/CT and ex vivo planar images, the MMP signal was significantly higher in the lungs of CC10-IL-13 Tg mice than wild-type animals. Furthermore, a nonbinding analog tracer showed significantly lower accumulation in CC10-IL-13 Tg lungs relative to the specific tracer. There was a significant correlation between small-animal SPECT/CT-derived MMP signal and CD68 expression in the lungs (r = 0.70, P < 0.01).

CONCLUSION

Small-animal SPECT/CT-based MMP-targeted imaging of the lungs is feasible and reflects pulmonary inflammation. If validated in humans, molecular imaging of inflammation and remodeling can potentially help early diagnosis and monitoring of the effects of therapeutic interventions in pulmonary diseases.

Molecular Imaging of Angiogenesis and Vascular Remodeling in Cardiovascular Pathology

Angiogenesis and vascular remodeling are involved in a wide array of cardiovascular diseases, from myocardial ischemia and peripheral arterial disease, to atherosclerosis and aortic aneurysm. Molecular imaging techniques to detect and quantify key molecular and cellular players in angiogenesis and vascular remodeling (e.g., vascular endothelial growth factor and its receptors, αvβ3 integrin, and matrix metalloproteinases) can advance vascular biology research and serve as clinical tools for early diagnosis, risk stratification, and selection of patients who would benefit most from therapeutic interventions. To target these key mediators, a number of molecular imaging techniques have been developed and evaluated in animal models of angiogenesis and vascular remodeling. This review of the state of the art molecular imaging of angiogenesis and vascular (and valvular) remodeling, will focus mostly on nuclear imaging techniques (positron emission tomography and single photon emission tomography) that offer high potential for clinical translation.

Heart valve health, disease, replacement, and repair: a 25-year cardiovascular pathology perspective

The past several decades have witnessed major advances in the understanding of the structure, function, and biology of native valves and the pathobiology and clinical management of valvular heart disease. These improvements have enabled earlier and more precise diagnosis, assessment of the proper timing of surgical and interventional procedures, improved prosthetic and biologic valve replacements and repairs, recognition of postoperative complications and their management, and the introduction of minimally invasive approaches that have enabled definitive and durable treatment for patients who were previously considered inoperable. This review summarizes the current state of our understanding of the mechanisms of heart valve health and disease arrived at through innovative research on the cell and molecular biology of valves, clinical and pathological features of the most frequent intrinsic structural diseases that affect the valves, and the status and pathological considerations in the technological advances in valvular surgery and interventions. The contributions of many cardiovascular pathologists and other scientists, engineers, and clinicians are emphasized, and potentially fruitful areas for research are highlighted.