Versican accumulation drives Nos2 induction and aortic disease in Marfan syndrome via Akt activation.

Thoracic aortic aneurysm and dissection (TAAD) is a life-threatening condition associated with Marfan syndrome (MFS), a disease caused by fibrillin-1 gene mutations. While various conditions causing TAAD exhibit aortic accumulation of the proteoglycans versican (Vcan) and aggrecan (Acan), it is unclear whether these ECM proteins are involved in aortic disease. Here, we find that Vcan, but not Acan, accumulated in Fbn1C1041G/+ aortas, a mouse model of MFS. Vcan haploinsufficiency protected MFS mice against aortic dilation, and its silencing reverted aortic disease by reducing Nos2 protein expression. Our results suggest that Acan is not an essential contributor to MFS aortopathy. We further demonstrate that Vcan triggers Akt activation and that pharmacological Akt pathway inhibition rapidly regresses aortic dilation and Nos2 expression in MFS mice. Analysis of aortic tissue from MFS human patients revealed accumulation of VCAN and elevated pAKT-S473 staining. Together, these findings reveal that Vcan plays a causative role in MFS aortic disease in vivo by inducing Nos2 via Akt activation and identify Akt signaling pathway components as candidate therapeutic targets.

Three-dimensional co-culturing of stem cell-derived cardiomyocytes and cardiac fibroblasts reveals a role for both cell types in Marfan-related cardiomyopathy.

Pathogenic variants in the FBN1 gene, which encodes the extracellular matrix protein fibrillin-1, cause Marfan syndrome (MFS), which affects multiple organ systems, including the cardiovascular system. Myocardial dysfunction has been observed in a subset of patients with MFS and in several MFS mouse models. However, there is limited understanding of the intrinsic consequences of FBN1 variants on cardiomyocytes (CMs). To elucidate the CM-specific contribution in Marfan's cardiomyopathy, cardiosphere cultures of CMs and cardiac fibroblasts (CFs) are used. CMs and CFs were derived by human induced pluripotent stem cell (iPSC) differentiation from MFS iPSCs with a pathogenic variant in FBN1 (c.3725G>A; p.Cys1242Tyr) and the corresponding CRISPR-corrected iPSC line (Cor). Cardiospheres containing MFS CMs show decreased FBN1, COL1A2 and GJA1 expression. MFS CMs cultured in cardiospheres have fewer binucleated CMs in comparison with Cor CMs. 13% of MFS CMs in cardiospheres are binucleated and 15% and 16% in cardiospheres that contain co-cultures with respectively MFS CFs and Cor CFs, compared to Cor CMs, that revealed up to 23% binucleation when co-cultured with CFs. The sarcomere length of CMs, as a marker of development, is significantly increased in MFS CMs interacting with Cor CF or MFS CF, as compared to monocultured MFS CMs. Nuclear blebbing was significantly more frequent in MFS CFs, which correlated with increased stiffness of the nuclear area compared to Cor CFs. Our cardiosphere model for Marfan-related cardiomyopathy identified a contribution of CFs in Marfan-related cardiomyopathy and suggests that abnormal early development of CMs may play a role in the disease mechanism.

miR-632 Induces DNAJB6 Inhibition Stimulating Endothelial-to-Mesenchymal Transition and Fibrosis in Marfan Syndrome Aortopathy.

Marfan syndrome (MFS) is a connective tissue disorder caused by FBN1 gene mutations leading to TGF-ß signaling hyperactivation, vascular wall weakness, and thoracic aortic aneurysms (TAAs). The pathogenetic mechanisms are not completely understood and patients undergo early vascular surgery to prevent TAA ruptures. We previously reported miR-632 upregulation in MFS TAA tissues compared with non-genetic TAA tissues. DNAJB6 is a gene target of miR-632 in cancer and plays a critical role in blocking epithelial-to-mesenchymal transition by inhibiting the Wnt/ß catenin pathway. TGF-ß signaling also activates Wnt/ß catenin signaling and induces endothelial-to-mesenchymal transition (End-Mt) and fibrosis. We documented that miR-632 upregulation correlated with DNAJB6 expression in both the endothelium and the tunica media of MFS TAA (p < 0.01). Wnt/ß catenin signaling, End-Mt, and fibrosis markers were also upregulated in MFS TAA tissues (p < 0.05, p < 0.01 and p < 0.001). Moreover, miR-632 overexpression inhibited DNAJB6, inducing Wnt/ß catenin signaling, as well as End-Mt and fibrosis exacerbation (p < 0.05 and p < 0.01). TGF-ß1 treatment also determined miR-632 upregulation (p < 0.01 and p < 0.001), with the consequent activation of the aforementioned processes. Our study provides new insights about the pathogenetic mechanisms in MFS aortopathy. Moreover, the high disease specificity of miR-632 and DNAJB6 suggests new potential prognostic factors and/or therapeutic targets in the progression of MFS aortopathy.

Localized Prox1 Regulates Aortic Valve Endothelial Cell Diversity and Extracellular Matrix Stratification in Mice.

BACKGROUND: Specialized valve endothelial cell (VEC) populations are localized oriented to blood flow in developing aortic and mitral valves, but their roles in valve development and disease are unknown. In the aortic valve (AoV), a population of VECs on the fibrosa side expresses the transcription factor Prox1 together with genes found in lymphatic ECs. In this study, we examine Prox1's role in regulating a lymphatic-like gene network and promoting VEC diversity required for the development of the stratified trilaminar extracellular matrix (ECM) of murine AoV leaflets. METHODS: To determine whether disruption of Prox1 localization affects heart valve development, we generated mice (NFATc1enCre Prox1 gain-of-function) in which Prox1 is overexpressed on the ventricularis side of the AoV beginning in embryonic development. To identify potential targets of Prox1, we performed cleavage under targets and release using nuclease on wild-type and NFATc1enCre Prox1 gain-of-function AoVs with validation by colocalization in vivo using RNA in situ hybridization in NFATc1enCre Prox1 gain-of-function AoVs. Natural induction of Prox1 and target gene expression was evaluated in myxomatous AoVs in a mouse model of Marfan syndrome (Fbn1C1039G/+). RESULTS: The overexpression of Prox1 is sufficient to cause enlargement of AoVs by postnatal day (P)0, as well as a decrease in ventricularis-specific gene expression and disorganized interstitial ECM layers at P7. We identified potential targets of Prox1 known to play roles in lymphatic ECs including Flt1, Efnb2, Egfl7, and Cx37. Ectopic Prox1 colocalized with induced Flt1, Efnb2, and Cx37 expression in NFATc1enCre Prox1 gain-of-function AoVs. Moreover, in Marfan syndrome myxomatous AoVs, endogenous Prox1, and its identified targets, were ectopically induced in ventricularis side VECs. CONCLUSIONS: Our results support a role for Prox1 in localized lymphatic-like gene expression on the fibrosa side of the AoV. Furthermore, localized VEC specialization is required for development of the stratified trilaminar ECM critical for AoV function and is dysregulated in congenitally malformed valves.

Redox Dysregulation of Vascular Smooth Muscle Sirtuin-1 in Thoracic Aortic Aneurysm in Marfan Syndrome.

BACKGROUND: Thoracic aortic aneurysms (TAAs) are abnormal aortic dilatations and a major cardiovascular complication of Marfan syndrome. We previously demonstrated a critical role for vascular smooth muscle (VSM) SirT1 (sirtuin-1), a lysine deacetylase, against maladaptive aortic remodeling associated with chronic oxidative stress and aberrant activation of MMPs (matrix metalloproteinases). METHODS: In this study, we investigated whether redox dysregulation of SirT1 contributed to the pathogenesis of TAA using fibrillin-1 hypomorphic mice (Fbn1mgR/mgR), an established model of Marfan syndrome prone to aortic dissection/rupture. RESULTS: Oxidative stress markers 3-nitrotyrosine and 4-hydroxynonenal were significantly elevated in aortas of patients with Marfan syndrome. Moreover, reversible oxidative post-translational modifications (rOPTM) of protein cysteines, particularly S-glutathionylation, were dramatically increased in aortas of Fbn1mgR/mgR mice, before induction of severe oxidative stress markers. Fbn1mgR/mgR aortas and VSM cells exhibited an increase in rOPTM of SirT1, coinciding with the upregulation of acetylated proteins, an index of decreased SirT1 activity, and increased MMP2/9 activity. Mechanistically, we demonstrated that TGFß (transforming growth factor beta), which was increased in Fbn1mgR/mgR aortas, stimulated rOPTM of SirT1, decreasing its deacetylase activity in VSM cells. VSM cell-specific deletion of SirT1 in Fbn1mgR/mgR mice (SMKO-Fbn1mgR/mgR) caused a dramatic increase in aortic MMP2 expression and worsened TAA progression, leading to aortic rupture in 50% of SMKO-Fbn1mgR/mgR mice, compared with 25% of Fbn1mgR/mgR mice. rOPTM of SirT1, rOPTM-mediated inhibition of SirT1 activity, and increased MMP2/9 activity were all exacerbated by the deletion of Glrx (glutaredoxin-1), a specific deglutathionylation enzyme, while being corrected by overexpression of Glrx or of an oxidation-resistant SirT1 mutant in VSM cells. CONCLUSIONS: Our novel findings strongly suggest a causal role of S-glutathionylation of SirT1 in the pathogenesis of TAA. Prevention or reversal of SirT1 rOPTM may be a novel therapeutic strategy to prevent TAA and TAA dissection/ruptures in individuals with Marfan syndrome, for which, thus far, no targeted therapy has been developed.

Smooth Muscle Cell Klf4 Expression Is Not Required for Phenotype Modulation or Aneurysm Formation in Marfan Syndrome Mice-Brief Report.

BACKGROUND: Smooth muscle cell (SMC) phenotypic reprogramming toward a mixed synthetic-proteolytic state is a central feature of aortic root aneurysm in Marfan syndrome (MFS). Previous work identified Klf4 as a potential mediator of SMC plasticity in MFS. METHODS: MFS (Fbn1C1041G/+) mouse strains with an inducible vascular SMC fluorescent reporter (MFSSMC) with or without SMC-specific deletion of Klf4 exons 2 to 3 (MFSSMC-Klf4Δ) were generated. Simultaneous SMC tracing and Klf4 loss-of-function (Klf4Δ mice) was induced at 6 weeks of age. Aneurysm growth was assessed via serial echocardiography (4-24 weeks). Twenty-four-week-old mice were assessed via histology, RNA in situ hybridization, and aortic single-cell RNA sequencing. RESULTS: MFS mice demonstrated progressive aortic root dilatation compared with control (WTSMC) mice regardless of Klf4 genotype (P<0.001), but there was no difference in aneurysm growth in MFSSMC-Klf4Δ versus MFSSMC (P=0.884). Efficient SMC Klf4 deletion was confirmed via lineage-stratified genotyping, RNA in situ hybridization, and immunohistochemistry. Single-cell RNA sequencing of traced SMCs revealed a highly similar pattern of phenotype modulation marked by loss of contractile markers (eg, Myh11, Cnn1) and heightened expression of matrix genes (eg, Col1a1, Fn1) between Klf4 genotypes. Pseudotemporal quantitation of SMC dedifferentiation confirmed that Klf4 deletion did not alter the global extent of phenotype modulation, but reduced expression of 23 genes during this phenotype transition in MFSSMC-Klf4Δmice, including multiple chondrogenic genes expressed by only the most severely dedifferentiated SMCs (eg, Cytl1, Tnfrsf11b). CONCLUSIONS: Klf4 is not required to initiate SMC phenotype modulation in MFS aneurysm but may exert regulatory control over chondrogenic genes expressed in highly dedifferentiated SMCs.

Fibrillin-1 regulates endothelial sprouting during angiogenesis.

Fibrillin-1 is an extracellular matrix protein that assembles into microfibrils which provide critical functions in large blood vessels and other tissues. Mutations in the fibrillin-1 gene are associated with cardiovascular, ocular, and skeletal abnormalities in Marfan syndrome. Here, we reveal that fibrillin-1 is critical for angiogenesis which is compromised by a typical Marfan mutation. In the mouse retina vascularization model, fibrillin-1 is present in the extracellular matrix at the angiogenic front where it colocalizes with microfibril-associated glycoprotein-1, MAGP1. In Fbn1C1041G/+ mice, a model of Marfan syndrome, MAGP1 deposition is reduced, endothelial sprouting is decreased, and tip cell identity is impaired. Cell culture experiments confirmed that fibrillin-1 deficiency alters vascular endothelial growth factor-A/Notch and Smad signaling which regulate the acquisition of endothelial tip cell/stalk cell phenotypes, and we showed that modulation of MAGP1 expression impacts these pathways. Supplying the growing vasculature of Fbn1C1041G/+ mice with a recombinant C-terminal fragment of fibrillin-1 corrects all defects. Mass spectrometry analyses showed that the fibrillin-1 fragment alters the expression of various proteins including ADAMTS1, a tip cell metalloprotease and matrix-modifying enzyme. Our data establish that fibrillin-1 is a dynamic signaling platform in the regulation of cell specification and matrix remodeling at the angiogenic front and that mutant fibrillin-1-induced defects can be rescued pharmacologically using a C-terminal fragment of the protein. These findings, identify fibrillin-1, MAGP1, and ADAMTS1 in the regulation of endothelial sprouting, and contribute to our understanding of how angiogenesis is regulated. This knowledge may have critical implications for people with Marfan syndrome.

Lineage-Specific Induced Pluripotent Stem Cell-Derived Smooth Muscle Cell Modeling Predicts Integrin Alpha-V Antagonism Reduces Aortic Root Aneurysm Formation in Marfan Syndrome Mice.

BACKGROUND: The role of increased smooth muscle cell (SMC) integrin αv signaling in Marfan syndrome (MFS) aortic aneurysm remains unclear. Herein, we examine the mechanism and potential efficacy of integrin αv blockade as a therapeutic strategy to reduce aneurysm progression in MFS. METHODS: Induced pluripotent stem cells (iPSCs) were differentiated into aortic SMCs of the second heart field (SHF) and neural crest (NC) lineages, enabling in vitro modeling of MFS thoracic aortic aneurysms. The pathological role of integrin αv during aneurysm formation was confirmed by blockade of integrin αv with GLPG0187 in Fbn1C1039G/+ MFS mice. RESULTS: iPSC-derived MFS SHF SMCs overexpress integrin αv relative to MFS NC and healthy control SHF cells. Furthermore, integrin αv downstream targets (FAK [focal adhesion kinase]/AktThr308/mTORC1 [mechanistic target of rapamycin complex 1]) were activated, especially in MFS SHF. Treatment of MFS SHF SMCs with GLPG0187 reduced p-FAK/p-AktThr308/mTORC1 activity back to control SHF levels. Functionally, MFS SHF SMCs had increased proliferation and migration compared to MFS NC SMCs and control SMCs, which normalized with GLPG0187 treatment. In the Fbn1C1039G/+ MFS mouse model, integrin αv, p-AktThr308, and downstream targets of mTORC1 proteins were elevated in the aortic root/ascending segment compared to littermate wild-type control. Mice treated with GLPG0187 (age 6-14 weeks) had reduced aneurysm growth, elastin fragmentation, and reduction of the FAK/AktThr308/mTORC1 pathway. GLPG0187 treatment reduced the amount and severity of SMC modulation assessed by single-cell RNA sequencing. CONCLUSIONS: The integrin αv-FAK-AktThr308 signaling pathway is activated in iPSC SMCs from MFS patients, specifically from the SHF lineage. Mechanistically, this signaling pathway promotes SMC proliferation and migration in vitro. As biological proof of concept, GLPG0187 treatment slowed aneurysm growth and p-AktThr308 signaling in Fbn1C1039G/+ mice. Integrin αv blockade via GLPG0187 may be a promising therapeutic approach to inhibit MFS aneurysmal growth.

FN (Fibronectin)-Integrin α5 Signaling Promotes Thoracic Aortic Aneurysm in a Mouse Model of Marfan Syndrome.

BACKGROUND: Marfan syndrome, caused by mutations in the gene for fibrillin-1, leads to thoracic aortic aneurysms (TAAs). Phenotypic modulation of vascular smooth muscle cells (SMCs) and ECM (extracellular matrix) remodeling are characteristic of both nonsyndromic and Marfan aneurysms. The ECM protein FN (fibronectin) is elevated in the tunica media of TAAs and amplifies inflammatory signaling in endothelial and SMCs through its main receptor, integrin α5ß1. We investigated the role of integrin α5-specific signals in Marfan mice in which the cytoplasmic domain of integrin α5 was replaced with that of integrin α2 (denoted α5/2 chimera). METHODS: We crossed α5/2 chimeric mice with Fbn1mgR/mgR mice (mgR model of Marfan syndrome) to evaluate the survival rate and pathogenesis of TAAs among wild-type, α5/2, mgR, and α5/2 mgR mice. Further biochemical and microscopic analysis of porcine and mouse aortic SMCs investigated molecular mechanisms by which FN affects SMCs and subsequent development of TAAs. RESULTS: FN was elevated in the thoracic aortas from Marfan patients, in nonsyndromic aneurysms, and in mgR mice. The α5/2 mutation greatly prolonged survival of Marfan mice, with improved elastic fiber integrity, mechanical properties, SMC density, and SMC contractile gene expression. Furthermore, plating of wild-type SMCs on FN decreased contractile gene expression and activated inflammatory pathways whereas α5/2 SMCs were resistant. These effects correlated with increased NF-kB activation in cultured SMCs and mgR aortas, which was alleviated by the α5/2 mutation or NF-kB inhibition. CONCLUSIONS: FN-integrin α5 signaling is a significant driver of TAA in the mgR mouse model. This pathway thus warrants further investigation as a therapeutic target.

Fibrillin-1 mutation contributes to Marfan syndrome by inhibiting Cav1.2-mediated cell proliferation in vascular smooth muscle cells.

Marfan syndrome (MFS) is an autosomal dominant connective tissue disorder caused by mutation in fibrillin-1 (FBN1). However, the molecular mechanism underlying MFS remains poorly understood. The study aimed to explore how the L-type calcium channel (CaV1.2) modulates disease progression of MFS and to identify a potential effective target for attenuating MFS. KEGG enrichment analysis showed that the calcium signaling pathway gene set was significantly enriched. We demonstrated that FBN1 deficiency exhibited inhibition on both the expression of Cav1.2 and proliferation of vascular smooth muscle cells (VSMCs). Then, we examined whether FBN1 mediates Cav1.2 via regulating TGF-ß1. Higher levels of TGF-ß1 were observed in the serum and aortic tissues from patients with MFS. TGF-ß1 modulated Cav1.2 expression in a concentration-dependent manner. We evaluated the role of Cav1.2 in MFS by small interfering RNA and Cav1.2 agonist Bay K8644. The effect of Cav1.2 on cell proliferation was dependent on c-Fos activity. These results demonstrated FBN1 deficiency decreased the expression levels of Cav1.2 via regulation of TGF-ß1, and downregulation of Cav1.2 inhibited cell proliferation of human aortic smooth muscle cells (HASMCs) in MFS patients. These findings suggest that Cav1.2 may be an appealing therapeutic target for MFS.

Allopurinol blocks aortic aneurysm in a mouse model of Marfan syndrome via reducing aortic oxidative stress.

BACKGROUND: Increasing evidence indicates that redox stress participates in MFS aortopathy, though its mechanistic contribution is little known. We reported elevated reactive oxygen species (ROS) formation and NADPH oxidase NOX4 upregulation in MFS patients and mouse aortae. Here we address the contribution of xanthine oxidoreductase (XOR), which catabolizes purines into uric acid and ROS in MFS aortopathy. METHODS AND RESULTS: In aortic samples from MFS patients, XOR protein expression, revealed by immunohistochemistry, increased in both the tunicae intima and media of the dilated zone. In MFS mice (Fbn1C1041G/+), aortic XOR mRNA transcripts and enzymatic activity of the oxidase form (XO) were augmented in the aorta of 3-month-old mice but not in older animals. The administration of the XOR inhibitor allopurinol (ALO) halted the progression of aortic root aneurysm in MFS mice. ALO administrated before the onset of the aneurysm prevented its subsequent development. ALO also inhibited MFS-associated endothelial dysfunction as well as elastic fiber fragmentation, nuclear translocation of pNRF2 and increased 3'-nitrotyrosine levels, and collagen maturation remodeling, all occurring in the tunica media. ALO reduced the MFS-associated large aortic production of H2O2, and NOX4 and MMP2 transcriptional overexpression. CONCLUSIONS: Allopurinol interferes in aortic aneurysm progression acting as a potent antioxidant. This study strengthens the concept that redox stress is an important determinant of aortic aneurysm formation and progression in MFS and warrants the evaluation of ALO therapy in MFS patients.

Fibrillin-1 Regulates Arteriole Integrity in the Retina.

Fibrillin-1 is an extracellular matrix protein that assembles into microfibrils that provide critical functions in large blood vessels and other tissues. Mutations in the fibrillin-1 gene are associated with cardiovascular, ocular, and skeletal abnormalities in Marfan syndrome. Fibrillin-1 is a component of the wall of large arteries but has been poorly described in other vessels. We examined the microvasculature in the retina using wild type mice and two models of Marfan syndrome, Fbn1C1041G/+ and Fbn1mgR/mgR. In the mouse retina, fibrillin-1 was detected around arterioles, in close contact with the basement membrane, where it colocalized with MAGP1. Both a mutation in fibrillin-1 or fibrillin-1 underexpression characteristically altered the microvasculature. In Fbn1C1041G/+ and Fbn1mgR/mgR mice, arterioles were enlarged with reduced MAGP1 deposition and focal loss of smooth muscle cell coverage. Losartan, which prevents aortic enlargement in Fbn1C1041G/+ mice, prevented smooth muscle cell loss and vessel leakiness when administrated in a preventive mode. Moreover, losartan also partially rescued the defects in a curative mode. Thus, fibrillin-1/MAGP1 performs essential functions in arteriolar integrity and mutant fibrillin-1-induced defects can be prevented or partially rescued pharmacologically. These new findings could have implications for people with Marfan syndrome.

[Naringenin inhibits thoracic aortic aneurysm formation in mice with Marfan syndrome].

OBJECTIVE: To identify whether naringenin plays a protective role during thoracic aneurysm formation in Marfan syndrome. METHODS: To validate the effect of naringenin, Fbn1C1039G/+ mice, the mouse model of Marfan syndrome, were fed with naringenin, and the disease progress was evaluated. The molecular mechanism of naringenin was further investigated via in vitro studies, such as bioluminescence resonance energy transfer (BRET), atomic force microscope and radioligand receptor binding assay. RESULTS: Six-week-old Fbn1C1039G/+ mice were fed with naringenin for 20 weeks. Compared with the control group, naringenin significantly suppressed the aortic expansion [Fbn1C1039G/+ vs. Fbn1C1039G/++naringenin: (2.49±0.47) mm, n=18 vs. (1.87±0.19) mm, n=22, P < 0.05], the degradation of elastin, and the expression and activity of matrix metalloproteinase 2 (MMP2) and MMP9 in the ascending aorta of Fbn1C1039G/+ mice. Besides, treatment with naringenin for 6 weeks also attenuated the disease progress among the 20-week-old Fbn1C1039G/+ mice with established thoracic aortic aneurysms [Fbn1C1039G/+ vs. Fbn1C1039G/++naringenin: (2.24±0.23) mm, n=8 vs. (1.90±0.17) mm, n=8, P < 0.05]. To understand the underlying molecular mechanisms, we examined the effects of naringenin on angiotensin Ⅱ type 1 receptor (AT1) signaling and transforming growth factor-ß (TGF-ß) signaling respectively, which were the dominant signaling pathways contributing to aortopathy in Marfan syndrome as previously reported. The results showed that naringenin decreased angiotensin Ⅱ (Ang Ⅱ)-induced phosphorylation of protein kinase C (PKC) and extracellular regulating kinase 1/2 (ERK1/2) in HEK293A cell overexpressing AT1 receptor. Moreover, naringenin inhibited Ang Ⅱ-induced calcium mobilization and uclear factor of activated T-cells (NFAT) signaling. The internalization of AT1 receptor and its binding to ß-arrestin-2 with Ang Ⅱ induction were also suppressed by naringenin. As evidenced by atomic force microscope and radioligand receptor binding assay, naringenin inhibited Ang Ⅱ binding to AT1 receptor. In terms of TGF-ß signaling, we found that feeding the mice with naringenin decreased the phosphorylation of Smad2 and ERK1/2 as well as the expression of TGF-ß downstream genes. Besides, the serum level of TGF-ß was also decreased by naringenin in the Fbn1C1039G/+ mice. Furthermore, we detected the effect of naringenin on platelet, a rich source of TGF-ß, both in vivo and in vitro. And we found that naringenin markedly decreased the TGF-ß level by inhibiting the activation of platelet. CONCLUSION: Our study showed that naringenin has a protective effect on thoracic aortic aneurysm formation in Marfan syndrome by suppressing both AT1 and TGF-ß signaling.

Effects of Rapamycin on the Expression of Redox Enzymes in Aortic Vascular Smooth Muscle Cells from Marfan Syndrome Mice.

Activation of the mechanistic target of rapamycin (mTOR) pathway has been implicated in an increasing number of diseases, including Marfan syndrome (MFS), an inherited connective tissue disorder. mTOR-dependent reactive oxygen species (ROS) formation has also been suggested to play a role in aortic aneurysm formation in MFS patients. This study aimed to characterize the effects of mTOR inhibition by rapamycin on key redox enzymes and NADPH oxidases (NOX) in cultured vascular smooth muscle cells of a murine MFS model. Therefore, the influence of 5 and 20 nmol/L rapamycin solved in 0.1% (vol/vol) DMSO on glutathione peroxidases 1 (Gpx1) and 4 (Gpx4), superoxide dismutase 2 (Sod2), and catalase (Cat) mRNA and protein expression was investigated in isolated murine aortic smooth muscle cells. Rapamycin inhibited the mRNA expression of all redox enzymes by 30-50%, except Gpx1. In the same cells, the mRNA expression of the transcription factor NFE2-related factor-2 and peroxisome proliferator-activated receptor-γ, key factors against oxidative stress, and controlling redox gene expression were also inhibited to a comparable extent under these conditions. In addition, Nox1 but not Nox4 mRNA expression was significantly inhibited by up to 40%. DMSO alone increased nearly 2-fold the redox enzyme protein expression, which was reduced considerably to basal levels by rapamycin. Proteasomal inhibition by bortezomib could not reverse the observed decrease of GPx protein content. The rapamycin-mediated decrease in GPx protein abundance was reflected in a reduced total GPx enzymatic activity. Higher rapamycin concentrations did not further decrease but led to a renewed increase in enzymatic activity despite low GPx protein concentrations. Baseline ROS formation was slightly inhibited at 13% with 5 nmol/L rapamycin and returned to baseline levels with the higher 20 nmol/L rapamycin concentration. In conclusion, this study further characterized the mechanism of action of rapamycin. It provided an insight into how rapamycin interferes with the regulation of redox homeostasis essential for ROS-dependent signaling that does not incur cellular damage.

Embryologic Origin Influences Smooth Muscle Cell Phenotypic Modulation Signatures in Murine Marfan Syndrome Aortic Aneurysm.

BACKGROUND: Aortic root smooth muscle cells (SMC) develop from both the second heart field (SHF) and neural crest. Disparate responses to disease-causing Fbn1 variants by these lineages are proposed to promote focal aortic root aneurysm formation in Marfan syndrome (MFS), but lineage-stratified SMC analysis in vivo is lacking. METHODS: We generated SHF lineage-traced MFS mice and performed integrated multiomic (single-cell RNA and assay for transposase-accessible chromatin sequencing) analysis stratified by embryological origin. SMC subtypes were spatially identified via RNA in situ hybridization. Response to TWIST1 overexpression was determined via lentiviral transduction in human aortic SMCs. RESULTS: Lineage stratification enabled nuanced characterization of aortic root cells. We identified heightened SHF-derived SMC heterogeneity including a subset of Tnnt2 (cardiac troponin T)-expressing cells distinguished by altered proteoglycan expression. MFS aneurysm-associated SMC phenotypic modulation was identified in both SHF-traced and nontraced (neural crest-derived) SMCs; however, transcriptomic responses were distinct between lineages. SHF-derived modulated SMCs overexpressed collagen synthetic genes and small leucine-rich proteoglycans while nontraced SMCs activated chondrogenic genes. These modulated SMCs clustered focally in the aneurysmal aortic root at the region of SHF/neural crest lineage overlap. Integrated RNA-assay for transposase-accessible chromatin analysis identified enriched Twist1 and Smad2/3/4 complex binding motifs in SHF-derived modulated SMCs. TWIST1 overexpression promoted collagen and SLRP gene expression in vitro, suggesting TWIST1 may drive SHF-enriched collagen synthesis in MFS aneurysm. CONCLUSIONS: SMCs derived from both SHF and neural crest lineages undergo phenotypic modulation in MFS aneurysm but are defined by subtly distinct transcriptional responses. Enhanced TWIST1 transcription factor activity may contribute to enriched collagen synthetic pathways SHF-derived SMCs in MFS.

Male Marfan mice are predisposed to high-fat diet-induced obesity, diabetes, and fatty liver.

Gene mutations in the extracellular matrix protein fibrillin-1 cause connective tissue disorders including Marfan syndrome (MFS) with clinical symptoms in the cardiovascular, skeletal, and ocular systems. Patients with MFS also exhibit alterations in adipose tissues, which in some individuals leads to lipodystrophy, whereas in others to obesity. We have recently demonstrated that fibrillin-1 regulates adipose tissue homeostasis. Here, we examined how fibrillin-1 abnormality affects metabolic adaptation to different diets. We used two MFS mouse models: hypomorph Fbn1mgR/mgR mice and Fbn1C1041G/+ mice with a fibrillin-1 missense mutation. When Fbn1mgR/mgR mice were fed with high-fat diet (HFD) for 12 wk, male mice were heavier than littermate controls (LCs), whereas female mice gained less weight compared with LCs. Female Fbn1C1041G/+ mice on an HFD for 24 wk were similarly protected from weight gain. Male Fbn1C1041G/+ mice on an HFD demonstrated higher insulin levels, insulin intolerance, circulating levels of cholesterol, and high-density lipoproteins. Moreover, male HFD-fed Fbn1C1041G/+ mice showed a higher liver weight and a fatty liver phenotype, which was reduced to LC levels after orchiectomy. Phosphorylation of protein kinase-like endoplasmic reticulum kinase (PERK) and the expression of sterol regulatory element-binding protein 1 (Srebp1) in livers of HFD-fed male Fbn1C1041G/+ mice were elevated. In conclusion, the data demonstrate that male mice of both the MFS models are susceptible to HFD-induced obesity and diabetes. Moreover, male Fbn1C1041G/+ mice develop a fatty liver phenotype, likely mediated by a baseline increased endoplasmic reticulum stress. In contrast, female MFS mice were protected from the consequence of HFD.

Macromolecular crowding enhances fibrillin-1 deposition in the extracellular matrix.

Biochemical and biophysical factors need consideration when modelling in vivo cellular behaviour using in vitro cell culture systems. One underappreciated factor is the high concentration of macromolecules present in vivo, which is typically not simulated under standard cell culture conditions. This disparity is especially relevant when studying biochemical processes that govern extracellular matrix (ECM) deposition, which may be altered due to dilution of secreted macromolecules by the relatively large volumes of culture medium required for cell maintenance in vitro. Macromolecular crowding (MMC) utilises the addition of inert macromolecules to cell culture medium to mimic such high concentration environments found in vivo. The present study induced MMC using the sucrose polymer Ficoll and examined whether fibrillin-1 deposition by human lung fibroblasts could be augmented. Fibrillin-1 forms extracellular microfibrils, which are versatile scaffolds required for elastic fibre formation, deposition of other ECM proteins and growth factor regulation. Pathogenic variants in the fibrillin-1 gene (FBN1) cause Marfan syndrome, where ECM deposition of fibrillin-1 can be compromised. Using immunocytochemistry, significantly enhanced fibrillin-1 deposition was observed when lung fibroblasts were cultured under MMC conditions. MMC also augmented fibrillin-1 deposition in Marfan syndrome patient-derived skin fibroblasts in a cell line- and likely FBN1 variant-specific manner. The ability of MMC to increase fibrillin-1 deposition suggested potential applications for tissue-engineering approaches, e.g. to generate tendon or vascular tissues, where fibrillin-1 microfibrils and elastic fibres are key determinants of their biomechanical properties. Moreover, it suggested the potency of MMC to better mimic in vivo ECM environments in cell culture studies.

Fibroblast-Secreted Phosphoprotein 1 Mediates Extracellular Matrix Deposition and Inhibits Smooth Muscle Cell Contractility in Marfan Syndrome Aortic Aneurysm.

Fibrillin 1 (Fbn1) mutation causes Marfan syndrome (MFS) with thoracic aortic aneurysm (TAA) as the main complication. The mechanisms for extracellular matrix (ECM) homeostasis disruption in MFS TAA are unclear. Here, we found ECM-related gene secreted phosphoprotein 1 (Spp1) increased in Fbn1C1041G/+ mice using transcriptome sequencing and a distinct fibroblast subcluster with Spp1 as the strongest marker was identified with analysis of the MFS mouse aortic single-cell sequencing dataset. Immunostaining confirmed elevated Spp1 in adventitial fibroblasts, and Spp1 might regulate fibroblast and smooth muscle cell (SMC) communication primarily through Itga8/Itgb1. Then, we observed Spp1 reduced contractile genes Acta2 and Tagln expression in SMCs and increased collagen expression in fibroblasts, which might contribute to TAA development. Finally, we also found elevated SPP1 plasma level was associated with an increased risk of TAA in patients. Therefore, SPP1 may serve as a biomarker and therapeutic target for TAA.

Impact of Notch3 Activation on Aortic Aneurysm Development in Marfan Syndrome.

BACKGROUND: The leading cause of mortality in patients with Marfan syndrome (MFS) is thoracic aortic aneurysm and dissection. Notch signaling is essential for vessel morphogenesis and function. However, the role of Notch signaling in aortic pathology and aortic smooth muscle cell (SMC) differentiation in Marfan syndrome (MFS) is not completely understood. METHODS: RNA-sequencing on ascending aortic tissue from a mouse model of MFS, Fbn1mgR/mgR , and wild-type controls was performed. Notch 3 expression and activation in aortic tissue were confirmed with real-time RT-PCR, immunohistochemistry, and Western blot. Fbn1mgR/mgR and wild-type mice were treated with a γ-secretase inhibitor, DAPT, to block Notch activation. Aortic aneurysms and rupture were evaluated with connective tissue staining, ultrasound, and life table analysis. RESULTS: The murine RNA-sequencing data were validated with mouse and human MFS aortic tissue, demonstrating elevated Notch3 activation in MFS. Data further revealed that upregulation and activation of Notch3 were concomitant with increased expression of SMC contractile markers. Inhibiting Notch3 activation with DAPT attenuated aortic enlargement and improved survival of Fbn1mgR/mgR mice. DAPT treatment reduced elastin fiber fragmentation in the aorta and reversed the differentiation of SMCs. CONCLUSIONS: Our data demonstrated that matrix abnormalities in the aorta of MFS are associated with increased Notch3 activation. Enhanced Notch3 activation in MFS contributed to aortic aneurysm formation in MFS. This might be mediated by inducing a contractile phenotypic change of SMC. Our results suggest that inhibiting Notch3 activation may provide a strategy to prevent and treat aortic aneurysms in MFS.

Exome Sequencing Identifies a Novel FBN1 Variant in a Pakistani Family with Marfan Syndrome That Includes Left Ventricle Diastolic Dysfunction.

INTRODUCTION: Cardiomyopathies are diseases of the heart muscle and are important causes of heart failure. Dilated cardiomyopathy (DCM) is a common form of cardiomyopathy that can be acquired, syndromic or non-syndromic. The current study was conducted to explore the genetic defects in a Pakistani family with cardiac disease and features of Marfan's syndrome (MFS). METHODS: A family with left ventricle (LV) diastolic dysfunction and MFS phenotype was assessed in Pakistan. The clinical information and blood samples from the patients were collected after physical, cardiovascular, and ophthalmologic examinations. An affected individual (proband) was subjected to whole-exome sequencing (WES). The findings were further validated through Sanger sequencing in the family. RESULTS: Through WES and sanger validation, we identified a novel variant NM_000138.4; c.1402A>G in the Fibrillin-1 (FBN1) gene that segregates with LV diastolic dysfunction and MFS. Furthermore, bioinformatic evaluation suggested that the novel variant is deleterious and disease-causing. CONCLUSIONS: This study identified for the first time a novel FBN1 variant in a family with LV diastolic dysfunction and MFS in Pakistan.