Single-Cell Transcriptomic Profiling of Vascular Smooth Muscle Cell Phenotype Modulation in Marfan Syndrome Aortic Aneurysm.

OBJECTIVE: To delineate temporal and spatial dynamics of vascular smooth muscle cell (SMC) transcriptomic changes during aortic aneurysm development in Marfan syndrome (MFS). Approach and Results: We performed single-cell RNA sequencing to study aortic root/ascending aneurysm tissue from Fbn1C1041G/+ (MFS) mice and healthy controls, identifying all aortic cell types. A distinct cluster of transcriptomically modulated SMCs (modSMCs) was identified in adult Fbn1C1041G/+ mouse aortic aneurysm tissue only. Comparison with atherosclerotic aortic data (ApoE-/- mice) revealed similar patterns of SMC modulation but identified an MFS-specific gene signature, including plasminogen activator inhibitor-1 (Serpine1) and Kruppel-like factor 4 (Klf4). We identified 481 differentially expressed genes between modSMC and SMC subsets; functional annotation highlighted extracellular matrix modulation, collagen synthesis, adhesion, and proliferation. Pseudotime trajectory analysis of Fbn1C1041G/+ SMC/modSMC transcriptomes identified genes activated differentially throughout the course of phenotype modulation. While modSMCs were not present in young Fbn1C1041G/+ mouse aortas despite small aortic aneurysm, multiple early modSMCs marker genes were enriched, suggesting activation of phenotype modulation. modSMCs were not found in nondilated adult Fbn1C1041G/+ descending thoracic aortas. Single-cell RNA sequencing from human MFS aortic root aneurysm tissue confirmed analogous SMC modulation in clinical disease. Enhanced expression of TGF-ß (transforming growth factor beta)-responsive genes correlated with SMC modulation in mouse and human data sets. CONCLUSIONS: Dynamic SMC phenotype modulation promotes extracellular matrix substrate modulation and aortic aneurysm progression in MFS. We characterize the disease-specific signature of modSMCs and provide temporal, transcriptomic context to the current understanding of the role TGF-ß plays in MFS aortopathy. Collectively, single-cell RNA sequencing implicates TGF-ß signaling and Klf4 overexpression as potential upstream drivers of SMC modulation.

Divergent effects of canonical and non-canonical TGF-ß signalling on mixed contractile-synthetic smooth muscle cell phenotype in human Marfan syndrome aortic root aneurysms.

Aortic root aneurysm formation is a cardinal feature of Marfan syndrome (MFS) and likely TGF-ß driven via Smad (canonical) and ERK (non-canonical) signalling. The current study assesses human MFS vascular smooth muscle cell (SMC) phenotype, focusing on individual contributions by Smad and ERK, with Notch3 signalling identified as a novel compensatory mechanism against TGF-ß-driven pathology. Although significant ERK activation and mixed contractile gene expression patterns were observed by traditional analysis, this did not directly correlate with the anatomic site of the aneurysm. Smooth muscle cell phenotypic changes were TGF-ß-dependent and opposed by ERK in vitro, implicating the canonical Smad pathway. Bulk SMC RNA sequencing after ERK inhibition showed that ERK modulates cell proliferation, apoptosis, inflammation, and Notch signalling via Notch3 in MFS. Reversing Notch3 overexpression with siRNA demonstrated that Notch3 promotes several protective remodelling pathways, including increased SMC proliferation, decreased apoptosis and reduced matrix metalloproteinase activity, in vitro. In conclusion, in human MFS aortic SMCs: (a) ERK activation is enhanced but not specific to the site of aneurysm formation; (b) ERK opposes TGF-ß-dependent negative effects on SMC phenotype; (c) multiple distinct SMC subtypes contribute to a 'mixed' contractile-synthetic phenotype in MFS aortic aneurysm; and (d) ERK drives Notch3 overexpression, a potential pathway for tissue remodelling in response to aneurysm formation.

Quantification of aortic and cutaneous elastin and collagen morphology in Marfan syndrome by multiphoton microscopy.

In a mouse model of Marfan syndrome, conventional Verhoeff-Van Gieson staining displays severe fragmentation, disorganization and loss of the aortic elastic fiber integrity. However, this method involves chemical fixatives and staining, which may alter the native morphology of elastin and collagen. Thus far, quantitative analysis of fiber damage in aorta and skin in Marfan syndrome has not yet been explored. In this study, we have used an advanced noninvasive and label-free imaging technique, multiphoton microscopy to quantify fiber fragmentation, disorganization, and total volumetric density of aortic and cutaneous elastin and collagen in a mouse model of Marfan syndrome. Aorta and skin samples were harvested from Marfan and control mice aged 3-, 6- and 9-month. Elastin and collagen were identified based on two-photon excitation fluorescence and second-harmonic-generation signals, respectively, without exogenous label. Measurement of fiber length indicated significant fragmentation in Marfan vs. control. Fast Fourier transform algorithm analysis demonstrated markedly lower fiber organization in Marfan mice. Significantly reduced volumetric density of elastin and collagen and thinner skin dermis were observed in Marfan mice. Cutaneous content of elastic fibers and thickness of dermis in 3-month Marfan resembled those in the oldest control mice. Our findings of early signs of fiber degradation and thinning of skin dermis support the potential development of a novel non-invasive approach for early diagnosis of Marfan syndrome.

Nicotine pharmacokinetics in rats is altered as a function of age, impacting the interpretation of animal model data.

Several behavioral studies report that adolescent rats display a preference for nicotine compared with adults. However, age-related pharmacokinetic differences may confound the interpretation of these findings. Thus, differences in pharmacokinetic analyses of nicotine were investigated. Nicotine was administered via acute s.c. (1.0 mg base/kg) or i.v. (0.2 mg base/kg) injection to early adolescent (EA; postnatal day 25) and adult (AD; postnatal day 71) male Wistar rats. Nicotine and its primary metabolite, cotinine, and additional metabolites nornicotine, nicotine-1'-N-oxide, trans-3'-hydroxycotinine, and norcotinine were sampled from 10 minutes to 8 hours (plasma) and 2 to 8 hours (brain) post nicotine and analyzed by liquid chromatography-tandem mass spectrometry. Following s.c. nicotine, the EA cohort had lower levels of plasma nicotine, cotinine, and nicotine-1'-N-oxide at multiple time points, resulting in a lower area under the plasma concentration-time curve (AUC) for nicotine (P < 0.001), cotinine (P < 0.01), and nicotine-1'-N-oxide (P < 0.001). Brain levels were also lower for these compounds. In contrast, the EA cohort had higher plasma and brain AUCs (P < 0.001) for the minor metabolite nornicotine. Brain-to-plasma ratios varied for nicotine and its metabolites, and by age. Following i.v. nicotine administration, similar age-related differences were observed, and this route allowed detection of a 1.6-fold-larger volume of distribution and 2-fold higher plasma clearance in the EA cohort compared with the AD cohort. Thus, unlike in humans, there are substantial age differences in nicotine pharmacokinetics such that for a given nicotine dose, adolescent rats will have lower plasma and brain nicotine compared with adults, suggesting that this should be considered when interpreting animal model data.

Aortic Dimensions, Biophysical Properties, and Plasma Biomarkers in Children and Adults with Marfan or Loeys-Dietz Syndrome.

BACKGROUND: Aortic dilation, stiffening, and dissection are common and potentially lethal complications of Marfan syndrome (MFS) and Loeys-Dietz syndrome (LDS), which involve abnormal transforming growth factor beta (TGF-ß) signalling. The relation of aortic dimensions, stiffness, and biomarker levels is unknown. The objective of this study was to measure aortic dimensions, stiffness, TGF-ß and matrix metalloproteinase (MMP) levels, and endothelial function in patients with MFS, and to compare TGF-ß levels in patients with MFS receiving different therapeutic regimens. METHODS: This was a cohort study of 40 MFS and 4 LDS patients and 87 control participants. Aortic dimension and stiffness indexes, including pulse wave velocity (PWV), were measured using echocardiography and Doppler. Total and free TGF-ß and MMP blood levels were measured using Quantikine (R&D Systems, Inc, Minneapolis, MN) and Quanterix (Billerica, MA) kits. Endothelial function was measured using brachial artery flow-mediated dilation. RESULTS: PWV was increased in patients with MFS. There were increased MMP-2 levels in those with MFS but no increase in free or total TGF-ß or MMP-9 levels compared with control participants. There was no difference in TGF-ß levels between MFS patients receiving no medications, angiotensin receptor blockers, and ß-blockers. PWV correlated most strongly with age. Endothelial function showed premature gradual decline in patients with MFS. CONCLUSIONS: Despite the increased PWV, monitoring aortic stiffness or TGF-ß levels would not be helpful in patients with MFS. TGF-ß levels were not increased and the increased MMP-2 levels suggest consideration of a different therapeutic target.

CONTEXTE: La dilatation, la rigidification et la dissection de l'aorte sont des complications fréquentes et parfois mortelles du syndrome de Marfan (SM) et du syndrome de Loeys-Dietz (SLD), qui sont tous deux dûs à une anomalie de la voie de signalisation du facteur de croissance transformant bêta (TGF-ß). On ne connaît pas la relation entre les dimensions et la rigidité de l'aorte et la présence de biomarqueurs. Notre étude visait à mesurer les dimensions et la rigidité de l'aorte, les taux de TGF-ß et de métalloprotéases matricielles (MMP) et la fonction endothéliale chez des patients atteints du SM, et à les comparer aux taux de TGF-ß observés chez des patients également atteints de SM, mais recevant un autre traitement. MÉTHODOLOGIE: Il s'agissait d'une étude de cohorte menée auprès de 40 patients atteints du SM et de quatre patients atteints du SLD, ainsi que de 87 témoins. Les indices des dimensions et de la rigidité aortiques, y compris la vitesse d'onde de pouls (VOP), ont été mesurés par échocardiographie et par échographie Doppler. Les taux sanguins de TGF-ß et de MMP totaux et libres ont été mesurés à l'aide de trousses Quantikine (R&D Systems, Inc, Minneapolis, MN) et Quanterix (Billerica, MA). La fonction endothéliale a été mesurée par dilatation liée au flux dans l'artère brachiale. RÉSULTATS: La VOP était plus élevée chez les patients atteints du SM. On a aussi observé une hausse des taux de MMP-2 chez les patients atteints de SM, mais aucune augmentation des taux de TGF-ß ou de MMP-9 libres ou totaux comparativement aux témoins. Il n'y avait pas de différence entre les taux de TGF-ß chez les patients atteints de SM ne recevant aucun traitement, ceux qui prenaient un antagoniste des récepteurs de l'angiotensine et ceux qui prenaient un bêtabloquant. La VOP été plus fortement corrélée avec l'âge. La fonction endothéliale a affiché un déclin progressif prématuré chez les patients atteints du SM. CONCLUSIONS: Malgré l'augmentation de la VOP, il ne semble pas utile de surveiller la rigidité aortique ni les taux de TGF-ß en cas de SM. Les taux de TGF-ß n'étaient pas plus élevés chez les patients atteints du SM, et la hausse des taux de MMP-2 indique qu'il conviendrait de choisir une autre cible thérapeutique.

Characterization of doxycycline-mediated inhibition of Marfan syndrome-associated aortic dilation by multiphoton microscopy.

Marfan syndrome (MFS) is a connective tissue disorder that results in aortic root widening and aneurysm if unmanaged. We have previously reported doxycycline, a nonselective matrix metalloproteinases (MMPs) inhibitor, to attenuate aortic root widening and improve aortic contractility and elasticity in MFS mice. We were also first to use multiphoton microscopy, a non-invasive and label-free imaging technique, to quantify and link the aortic ultrastructure to possible changes in the skin dermis. Here, we aimed to assess the effects of long-term doxycycline treatment on the aortic ultrastructure and skin dermis of MFS mice through immunohistochemical evaluation and quantification of elastic and collagen content and morphology using multiphoton microscopy. Our results demonstrate a rescue of aortic elastic fiber fragmentation and disorganization accompanied by a decrease in MMP-2 and MMP-9 expression within the aortic wall in doxycycline-treated MFS mice. At 12 months of age, reduced skin dermal thickness was observed in both MFS and control mice, but only dermal thinning in MFS mice was rescued by doxycycline treatment. MMP-2 and MMP-9 expression was reduced in the skin of doxycycline-treated MFS mice. A decrease in dermal thickness was found to be positively associated with increased aortic root elastin disorganization and wall thickness. Our findings confirm the beneficial effects of doxycycline on ultrastructural properties of aortic root as well as on skin elasticity and structural integrity in MFS mice.

Androgens Accentuate TGF-ß Dependent Erk/Smad Activation During Thoracic Aortic Aneurysm Formation in Marfan Syndrome Male Mice.

Background Male patients with Marfan syndrome have a higher risk of aortic events and root dilatation compared with females. The role androgens play during Marfan syndrome aneurysm development in males remains unknown. We hypothesized that androgens potentiate transforming growth factor beta induced Erk (extracellular-signal-regulated kinase)/Smad activation, contributing to aneurysm progression in males. Methods and Results Aortic diameters in Fbn1C1039G/+ and littermate wild-type controls were measured at ages 6, 8, 12, and 16 weeks. Fbn1C1039G/+ males were treated with (1) flutamide (androgen receptor blocker) or (2) vehicle control from age 6 to 16 weeks and then euthanized. p-Erk1/2, p-Smad2, and matrix metalloproteinase (MMP) activity were measured in ascending/aortic root and descending aorta specimens. Fbn1C1039G/+ male and female ascending/aortic root-derived smooth muscle cells were utilized in vitro to measure Erk/Smad activation and MMP-2 activity following dihydrotestosterone, flutamide or transforming growth factor beta 1 treatment. Fbn1C1039G/+ males have increased aneurysm growth. p-Erk1/2 and p-Smad2 were elevated in ascending/aortic root specimens at age 16 weeks. Corresponding with enhanced Erk/Smad signaling, MMP-2 activity was higher in Fbn1C1039G/+ males. In vitro smooth muscle cell studies revealed that dihydrotestosterone potentiates transforming growth factor beta-induced Erk/Smad activation and MMP-2 activity, which is reversed by flutamide treatment. Finally, in vivo flutamide treatment reduced aneurysm growth via p-Erk1/2 and p-Smad2 reduction in Fbn1C1039G/+ males. Conclusions Fbn1C1039G/+ males have enhanced aneurysm growth compared with females associated with enhanced p-Erk1/2 and p-Smad2 activation. Mechanistically, in vitro smooth muscle cell studies suggested that dihydrotestosterone potentiates transforming growth factor beta induced Erk/Smad activation. As biological proof of concept, flutamide treatment attenuated aneurysm growth and p-Erk1/2 and p-Smad2 signaling in Fbn1C1039G/+ males.

Quantitative proteomics reveal lineage-specific protein profiles in iPSC-derived Marfan syndrome smooth muscle cells.

Marfan syndrome (MFS) is a connective tissue disorder caused by mutations in the FBN1 gene that produces wide disease phenotypic variability. The lack of ample genotype-phenotype correlation hinders translational study development aimed at improving disease prognosis. In response to this need, an induced pluripotent stem cell (iPSC) disease model has been used to test patient-specific cells by a proteomic approach. This model has the potential to risk stratify patients to make clinical decisions, including timing for surgical treatment. The regional propensity for aneurysm formation in MFS may be related to distinct smooth muscle cell (SMC) embryologic lineages. Thus, peripheral blood mononuclear cell (PBMC)-derived induced pluripotent stem cells (iPSC) were differentiated into lateral mesoderm (LM, aortic root) and neural crest (NC, ascending aorta/transverse arch) SMC lineages to model MFS aortic pathology. Isobaric Tags for Relative and Absolute Quantitation (iTRAQ) proteomic analysis by tandem mass spectrometry was applied to profile LM and NC iPSC SMCs from four MFS patients and two healthy controls. Analysis revealed 45 proteins with lineage-dependent expression in MFS patients, many of which were specific to diseased samples. Single protein-level data from both iPSC SMCs and primary MFS aortic root aneurysm tissue confirmed elevated integrin αV and reduced MRC2 in clinical disease specimens, validating the iPSC iTRAQ findings. Functionally, iPSC SMCs exhibited defective adhesion to a variety of extracellular matrix proteins, especially laminin-1 and fibronectin, suggesting altered cytoskeleton dynamics. This study defines the aortic embryologic origin-specific proteome in a validated iPSC SMC model to identify novel protein markers associated with MFS aneurysm phenotype. Translating iPSC findings into clinical aortic aneurysm tissue samples highlights the potential for iPSC-based methods to model MFS disease for mechanistic studies and therapeutic discovery in vitro.

In vivo characterization of doxycycline-mediated protection of aortic function and structure in a mouse model of Marfan syndrome-associated aortic aneurysm.

Aortic aneurysm is the most life-threatening complication in Marfan syndrome (MFS) patients. Doxycycline, a nonselective matrix metalloproteinases inhibitor, was reported to improve the contractile function and elastic fiber structure and organization in a Marfan mouse aorta using ex vivo small chamber myography. In this study, we assessed the hypothesis that a long-term treatment with doxycycline would reduce aortic root growth, improve aortic wall elasticity as measured by pulse wave velocity, and improve the ultrastructure of elastic fiber in the mouse model of MFS. In our study, longitudinal measurements of aortic root diameters using high-resolution ultrasound imaging display significantly decreased aortic root diameters and lower pulse wave velocity in doxycycline-treated Marfan mice starting at 6 months as compared to their non-treated MFS counterparts. In addition, at the ultrastructural level, our data show that long-term doxycycline treatment corrects the irregularities of elastic fibers within the aortic wall of Marfan mice to the levels similar to those observed in control subjects. Our findings underscore the key role of matrix metalloproteinases during the progression of aortic aneurysm, and provide new insights into the potential therapeutic value of doxycycline in blocking MFS-associated aortic aneurysm.

Mild aerobic exercise blocks elastin fiber fragmentation and aortic dilatation in a mouse model of Marfan syndrome associated aortic aneurysm.

Regular low-impact physical activity is generally allowed in patients with Marfan syndrome, a connective tissue disorder caused by heterozygous mutations in the fibrillin-1 gene. However, being above average in height encourages young adults with this syndrome to engage in high-intensity contact sports, which unfortunately increases the risk for aortic aneurysm and rupture, the leading cause of death in Marfan syndrome. In this study, we investigated the effects of voluntary (cage-wheel) or forced (treadmill) aerobic exercise at different intensities on aortic function and structure in a mouse model of Marfan syndrome. Four-week-old Marfan and wild-type mice were subjected to voluntary and forced exercise regimens or sedentary lifestyle for 5 mo. Thoracic aortic tissue was isolated and subjected to structural and functional studies. Our data showed that exercise improved aortic wall structure and function in Marfan mice and that the beneficial effect was biphasic, with an optimum at low intensity exercise (55-65% V̇o2max) and tapering off at a higher intensity of exercise (85% V̇o2max). The mechanism underlying the reduced elastin fragmentation in Marfan mice involved reduction of the expression of matrix metalloproteinases 2 and 9 within the aortic wall. These findings present the first evidence of potential beneficial effects of mild exercise on the structural integrity of the aortic wall in Marfan syndrome associated aneurysm. Our finding that moderate, but not strenuous, exercise protects aortic structure and function in a mouse model of Marfan syndrome could have important implications for the medical care of young Marfan patients.NEW & NOTEWORTHY The present study provides conclusive scientific evidence that daily exercise can improve aortic health in a mouse model of Marfan syndrome associated aortic aneurysm, and it establishes the threshold for the exercise intensity beyond which exercise may not be as protective. These findings establish a platform for a new focus on promoting regular exercise in Marfan patients at an optimum intensity and create a paradigm shift in clinical care of Marfan patients suffering from aortic aneurysm complications.

Aortic and Cardiac Structure and Function Using High-Resolution Echocardiography and Optical Coherence Tomography in a Mouse Model of Marfan Syndrome.

Marfan syndrome (MFS) is an autosomal-dominant disorder of connective tissue caused by mutations in the fibrillin-1 (FBN1) gene. Mortality is often due to aortic dissection and rupture. We investigated the structural and functional properties of the heart and aorta in a [Fbn1C1039G/+] MFS mouse using high-resolution ultrasound (echo) and optical coherence tomography (OCT). Echo was performed on 6- and 12-month old wild type (WT) and MFS mice (n = 8). In vivo pulse wave velocity (PWV), aortic root diameter, ejection fraction, stroke volume, left ventricular (LV) wall thickness, LV mass and mitral valve early and atrial velocities (E/A) ratio were measured by high resolution echocardiography. OCT was performed on 12-month old WT and MFS fixed mouse hearts to measure ventricular volume and mass. The PWV was significantly increased in 6-mo MFS vs. WT (366.6 ± 19.9 vs. 205.2 ± 18.1 cm/s; p = 0.003) and 12-mo MFS vs. WT (459.5 ± 42.3 vs. 205.3 ± 30.3 cm/s; p< 0.0001). PWV increased with age in MFS mice only. We also found a significantly enlarged aortic root and decreased E/A ratio in MFS mice compared with WT for both age groups. The [Fbn1C1039G/+] mouse model of MFS replicates many of the anomalies of Marfan patients including significant aortic dilation, central aortic stiffness, LV systolic and diastolic dysfunction. This is the first demonstration of the direct measurement in vivo of pulse wave velocity non-invasively in the aortic arch of MFS mice, a robust measure of aortic stiffness and a critical clinical parameter for the assessment of pathology in the Marfan syndrome.