Extracellular Matrix Profiling and Disease Modelling in Engineered Vascular Smooth Muscle Cell Tissues

Engineered pulmonary artery tissues for measuring contractility, drug testing and disease modelling

BACKGROUND AND PURPOSE

Vasoreactivity of pulmonary arteries regulates blood flow through the lungs. Excessive constriction of these vessels contributes to pulmonary arterial hypertension (PAH), a progressive and incurable condition, resulting in right heart failure. The search for new and improved drug treatments is hampered by laboratory models that do not reproduce the vasoactive behaviour of healthy and diseased human arteries.

EXPERIMENTAL APPROACH

We have developed an innovative technique for producing miniature, three-dimensional arterial structures that allow proxy evaluation of human pulmonary artery contractility. These "engineered pulmonary artery tissues" or "EPATs" are fabricated by suspending human pulmonary artery vascular smooth muscle cells (VSMCs) in fibrin hydrogels between pairs of silicone posts, located on custom-made racks, in 24-well culture plates.

KEY RESULTS

EPATs exhibit rapid, robust and reproducible contraction responses to vasoconstrictors (KCl, ET-1, U46619) as well as relaxation responses to clinically approved PAH vasodilatory drugs that target several signalling pathways, such as bosentan, epoprostenol, selexipag and imatinib. EPATs composed of pulmonary artery VSMCs from PAH patients exhibit enhanced contraction to vasoconstrictors and relaxation in response to vasodilators. We also demonstrate the incorporation of endothelial cells into EPATs for the measurement of endothelium-dependent dilatory responses.

CONCLUSION AND IMPLICATIONS

We demonstrate the capacity and suitability of EPATs for studying the contractile behaviour of human arterial cells and preclinical drug testing. This novel biomimetic platform has the potential to dramatically improve our understanding and treatment of cardiovascular disease.

Ultrastructural and Molecular Analysis of Vascular Smooth Muscle Cells During the Switch from a Physiological to a Pathological Phenotype

Background/Objectives: Under physiological conditions, vascular smooth muscle cells (VSMCs) are in a quiescent contractile state, but under pathological conditions, such as atherosclerosis, they change their phenotype to synthetic, characterized by increased proliferation, migration, and production of an extracellular matrix. Furthermore, VSMCs can undergo calcification, switching to an osteoblast-like phenotype, contributing to plaque instability. Methods: In this study, we analyzed the phenotypic changes in VSMCs during the transition from a physiological to a pathological state, a key process in the progression of atherosclerosis, using confocal and transmission electron microscopy, real-time PCR, and intracellular calcium quantification. Results: Confocal and transmission electron microscopy revealed a prominent remodeling of the actin cytoskeleton, increasing autophagic vacuoles in synthetic VSMCs and the deposition of calcium microcrystals in calcified cells. Immunofluorescence analysis revealed differential expression of α-SMA (contractile marker) and galectin-3 (synthetic marker), confirming the phenotypic changes. Real-time PCR further validated these changes, showing upregulation of RUNX-2, a marker of osteogenic transition, in calcified VSMCs. Conclusions: This study highlights the dynamic plasticity of VSMCs and their role in atherosclerosis progression. Understanding the characteristics of these phenotypic transitions can help develop targeted therapies to mitigate vascular calcification and plaque instability, potentially countering cardiovascular disease.

Effects of Extracellular Matrix Changes Induced by a High-Fat Diet on Gallbladder Smooth Muscle Dysfunction

BACKGROUND

Gallstone formation is a common digestive ailment, with unclear mechanisms underlying its development. Dysfunction of the gallbladder smooth muscle (GSM) may play a crucial role, particularly with a high-fat diet (HFD). This study aimed to investigate the effects of an HFD on GSM and assess how it alters contractility through changes in the extracellular matrix (ECM).

METHODS

Guinea pigs and C57BL/6 mice were fed either an HFD or normal diet (ND). Primary cultures of their (guinea pigs) gallbladder smooth muscle cells (GSMCs) were used for in vitro experiments. Histological stains, RNA-sequencing, bioinformatics analysis, three-dimensional tissue culture, real-time polymerase chain reaction (PCR), Western blot, atomic force microscopy, and muscle tension measurements were performed.

RESULTS

Histological evidence indicated structural changes in the gallbladder muscle layer and ECM collagen deposition in the HFD group. The HFD group also showed increased expression of collagen, integrin family, and matrix metalloproteinase (MMP) and the phosphoinositide 3-kinase (PI3K)-protein kinase B (PKB/Akt) signaling pathway. Compared with GSMCs cultured on Matrigel containing 1 mg/mL of collagen I, those cultured with 2 mg/mL showed a phenotype change from contractile to synthetic cells. Consistent with these findings, the HFD group also demonstrated increased ECM stiffness and decreased smooth muscle contractility.

CONCLUSIONS

Our findings reveal a mechanism by which an HFD alters the ECM composition of the gallbladder muscle, activating the integrin/PI3K-Akt/MMP signaling pathway, thereby impacting GSMC phenotype and contractility. These insights enhance the understanding of gallstone formation mechanism and provide potential therapeutic targets to treat gallbladder dysfunction.

Understanding genomic medicine for thoracic aortic disease through the lens of induced pluripotent stem cells

Thoracic aortic disease (TAD) is often silent until a life-threatening complication occurs. However, genetic information can inform both identification and treatment at an early stage. Indeed, a diagnosis is important for personalised surveillance and intervention plans, as well as cascade screening of family members. Currently, only 20% of heritable TAD patients have a causative mutation identified and, consequently, further advances in genetic coverage are required to define the remaining molecular landscape. The rapid expansion of next generation sequencing technologies is providing a huge resource of genetic data, but a critical issue remains in functionally validating these findings. Induced pluripotent stem cells (iPSCs) are patient-derived, reprogrammed cell lines which allow mechanistic insights, complex modelling of genetic disease and a platform to study aortic genetic variants. This review will address the need for iPSCs as a frontline diagnostic tool to evaluate variants identified by genomic discovery studies and explore their evolving role in biological insight through to drug discovery.

Insights into elastic fiber fragmentation: Mechanisms and treatment of aortic aneurysm in Marfan syndrome

Marfan syndrome (MFS) is an autosomal dominant connective tissue disorder caused by mutations in fibrillin 1 (FBN1) gene. These mutations result in defects in the skeletal, ocular, and cardiovascular systems. Aortic aneurysm is the leading cause of premature mortality in untreated MFS patients. Elastic fiber fragmentation in the aortic vessel wall is a hallmark of MFS-associated aortic aneurysms. FBN1 mutations result in FBN1 fragments that also contribute to elastic fiber fragmentation. Although recent research has advanced our understanding of MFS, the contribution of elastic fiber fragmentation to the pathogenesis of aneurysm formation remains poorly understood. This review provides a comprehensive overview of the molecular mechanisms of elastic fiber fragmentation and its role in the pathogenesis of aortic aneurysm progression. Increased comprehension of elastic fragmentation has significant clinical implications for developing targeted interventions to block aneurysm progression, which would benefit not only individuals with Marfan syndrome but also other patients with aneurysms. Moreover, this review highlights an overlooked connection between inhibiting aneurysm and the restoration of elastic fibers in the vessel wall with various aneurysm inhibitors, including drugs and chemicals. Investigating the underlying molecular mechanisms could uncover innovative therapeutic strategies to inhibit elastin fragmentation and prevent the progression of aneurysms.

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 α5β1. 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.

Echinatin maintains glutathione homeostasis in vascular smooth muscle cells to protect against matrix remodeling and arterial stiffening

Decreased vascular compliance of the large arteries as indicated by increased pulse wave velocity is shown to be associated with atherosclerosis and the related cardiovascular events. The positive correlation between arterial stiffening and disease progression derives a hypothesis that softening the arterial wall may protect against atherosclerosis, despite that the mechanisms controlling the cellular pathological changes in disease progression remain unknown. Here, we established a mechanical-property-based screening to look for compounds alleviating the arterial wall stiffness through their actions on the interaction between vascular smooth muscle cells (VSMCs) and the wall extracellular matrix (ECM). We found that echinatin, a chalcone preferentially accumulated in roots and rhizomes of licorice (Glycyrrhiza inflata), reduced the stiffness of ECM surrounding cultured VSMCs. We examined the potential beneficial effects of echinatin on mitigating arterial stiffening and atherosclerosis, and explored the mechanistic basis by which the compound exert the effects. Administration of echinatin in mice fed on an adenine diet and in hyperlipidemia mice subjected to 5/6 nephrectomy mitigated arterial stiffening and atherosclerosis. Mechanistic insights were gained from the RNA-sequencing results showing that echinatin upregulated the expression of glutamate cysteine ligases (GCLs), both the catalytic (GCLC) and modulatory (GCLM) subunits. Further study indicated that upregulation of GCLC/GCLM in VSMCs by echinatin maintains the homeostasis of glutathione (GSH) metabolism; adequate availability of GSH is critical for counteracting arterial stiffening. As a consequence of regulating the GSH synthesis, echinatin inhibits ferroptosis and matrix remodeling that being considered two contributors of arterial stiffening and atherosclerosis. These data demonstrate a pivotal role of GSH dysregulation in damaging the proper VSMC-ECM interaction and uncover a beneficial activity of echinatin in preventing vascular diseases.