LRP1 (Low-Density Lipoprotein Receptor-Related Protein 1) Regulates Smooth Muscle Contractility by Modulating Ca2+ Signaling and Expression of Cytoskeleton-Related Proteins

The role of PCSK9 in heart failure and other cardiovascular diseases-mechanisms of action beyond its effect on LDL cholesterol

Proprotein convertase subtilisin/kexin type-9 (PCSK9) is a protein that regulates low-density lipoprotein (LDL) cholesterol metabolism by binding to the hepatic LDL receptor (LDLR), ultimately leading to its lysosomal degradation and an increase in LDL cholesterol (LDLc) levels. Treatment strategies have been developed based on blocking PCSK9 with specific antibodies (alirocumab, evolocumab) and on blocking its production with small regulatory RNA (siRNA) (inclisiran). Clinical trials evaluating these drugs have confirmed their high efficacy in reducing serum LDLc levels and improving the prognosis in patients with atherosclerotic cardiovascular diseases. Most studies have focused on the action of PCSK9 on LDLRs and the subsequent increase in LDLc concentrations. Increasing evidence suggests that the adverse cardiovascular effects of PCSK9, particularly its atherosclerotic effects on the vascular wall, may also result from mechanisms independent of its effects on lipid metabolism. PCSK9 induces the expression of pro-inflammatory cytokines contributing to inflammation within the vascular wall and promotes apoptosis, pyroptosis, and ferroptosis of cardiomyocytes and is thus involved in the development and progression of heart failure. The elimination of PCSK9 may, therefore, not only be a treatment for hypercholesterolaemia but also for atherosclerosis and other cardiovascular diseases. The mechanisms of action of PCSK9 in the cardiovascular system are not yet fully understood. This article reviews the current understanding of the mechanisms of PCSK9 action in the cardiovascular system and its contribution to cardiovascular diseases. Knowledge of these mechanisms may contribute to the wider use of PCSK9 inhibitors in the treatment of cardiovascular diseases.

Plasma proteomics analysis reveals potential biomarkers for intracranial aneurysm formation and rupture

The aim of this study was to investigate the plasma proteome in individuals with intracranial aneurysms (IAs) and identify biomarkers associated with the formation and rupture of IAs. Proteomic profiles (N = 1069 proteins) were assayed in plasma (N = 120) collected from patients with ruptured and unruptured intracranial aneurysms (RIA and UIA), traumatic subarachnoid hemorrhage (tSAH), and healthy controls (HC) using tandem mass tag (TMT) labeling quantitative proteomics analysis. Gene ontology (GO) and pathway analysis revealed that these relevant proteins were involved in immune response and extracellular matrix organization pathways. Seven candidate biomarkers were verified by ELISA in a completely separate cohort for validation (N = 90). Among them, FN1, PON1, and SERPINA1 can be utilized as diagnosis biomarkers of IA, with a combined area under the ROC curve of 0.891. The sensitivity was 93.33%, specificity was 75.86%, and accuracy was 87.64%. PFN1, ApoA-1, and SERPINA1 can serve as independent risk factors for predicting aneurysm rupture. The combined prediction of aneurysm rupture yielded an area under the ROC curve of 0.954 with a sensitivity of 96.15%, specificity of 81.48%, and accuracy of 88.68%. This prediction model was more effective than PHASES score. In conclusion, high-throughput proteomics analysis with population validation was performed to assess blood-based protein expression characteristics. This revealed the potential mechanism of IA formation and rupture, facilitating the discovery of biomarkers. SIGNIFICANCE: Although the annual rupture rate of small unruptured aneurysms is believed to be minimal, studies have indicated that ruptured aneurysms typically have an average size of 6.28 mm, with 71.8% of them being <7 mm in diameter. Hence, evaluating the possibility of rupture in UIA and making a choice between aggressive treatment and conservative observation emerges as a significant challenge in the management of UIA. No biomarker or scoring system has been able to satisfactorily address this issue to date. It would be significant to develop biomarkers that could be used for early diagnosis of IA as well as for prediction of IA rupture. After TMT proteomics analysis and ELISA validation in independent populations, we found that FN1, PON1, and SERPINA1 can be utilized as diagnostic biomarkers for IA, and PFN1, ApoA-1, and SERPINA1 can serve as independent risk factors for predicting aneurysm rupture. Especially, when combined with ApoA-1, SERPINA1, and PFN1 for predicting IA rupture, the area under the curve (AUC) was 0.954 with a sensitivity of 96.15%, specificity of 81.48%, and accuracy of 88.68%. This prediction model was more effective than PHASES score.

Angiotensinogen as a Therapeutic Target for Cardiovascular and Metabolic Diseases

AGT (angiotensinogen) is the unique precursor for the generation of all the peptides of the renin-angiotensin system, but it has received relatively scant attention compared to many other renin-angiotensin system components. Focus on AGT has increased recently, particularly with the evolution of drugs to target the synthesis of the protein. AGT is a noninhibitory serpin that has several conserved domains in addition to the angiotensin II sequences at the N terminus. Increased study is needed on the structure-function relationship to resolve many unknowns regarding AGT metabolism. Constitutive whole-body genetic deletion of Agt in mice leads to multiple developmental defects creating a challenge to use these mice for mechanistic studies. This has been overcome by creating Agt-floxed mice to enable the development of cell-specific deficiencies that have provided considerable insight into a range of cardiovascular and associated diseases. This has been augmented by the recent development of pharmacological approaches targeting hepatocytes in humans to promote protracted inhibition of AGT synthesis. Genetic deletion or pharmacological inhibition of Agt has been demonstrated to be beneficial in a spectrum of diseases experimentally, including hypertension, atherosclerosis, aortic and superior mesenteric artery aneurysms, myocardial dysfunction, and hepatic steatosis. This review summarizes the findings of recent studies utilizing AGT manipulation as a therapeutic approach.

Identification of co-diagnostic effect genes for aortic dissection and metabolic syndrome by multiple machine learning algorithms

Aortic dissection (AD) is a life-threatening condition in which the inner layer of the aorta tears. It has been reported that metabolic syndrome (MS) has a close linkage with aortic dissection. However, the inter-relational mechanisms between them were still unclear. This article explored the hub gene signatures and potential molecular mechanisms in AD and MS. We obtained five bulk RNA-seq datasets of AD, one single cell RNA-seq (scRNA-seq) dataset of ascending thoracic aortic aneurysm (ATAA), and one bulk RNA-seq dataset of MS from the gene expression omnibus (GEO) database. Identification of differentially expressed genes (DEGs) and key modules via weighted gene co-expression network analysis (WGCNA), functional enrichment analysis, and machine learning algorithms (Random Forest and LASSO regression) were used to identify hub genes for diagnosing AD with MS. XGBoost further improved the diagnostic performance of the model. The receiver operating characteristic (ROC) and precision-recall (PR) curves were developed to assess the diagnostic value. Then, immune cell infiltration and metabolism-associated pathways analyses were created to investigate immune cell and metabolism-associated pathway dysregulation in AD and MS. Finally, the scRNA-seq dataset was performed to confirm the expression levels of identified hub genes. 406 common DEGs were identified between the merged AD and MS datasets. Functional enrichment analysis revealed these DEGs were enriched for applicable terms of metabolism, cellular processes, organismal systems, and human diseases. Besides, the positively related key modules of AD and MS were mainly enriched in transcription factor binding and inflammatory response. In contrast, the negatively related modules were significantly associated with adaptive immune response and regulation of nuclease activity. Through machine learning, nine genes with common diagnostic effects were found in AD and MS, including MAD2L2, IMP4, PRPF4, CHSY1, SLC20A1, SLC9A1, TIPRL, DPYD, and MAPKAPK2. In the training set, the AUC of the hub gene on RP and RR curves was 1. In the AD verification set, the AUC of the Hub gene on RP and RR curves were 0.946 and 0.955, respectively. In the MS set, the AUC of the Hub gene on RP and RR curves were 0.978 and 0.98, respectively. scRNA-seq analysis revealed that the SLC20A1 was found to be relevant in fatty acid metabolic pathways and expressed in endothelial cells. Our study revealed the common pathogenesis of AD and MS. These common pathways and hub genes might provide new ideas for further mechanism research.

LRP1 in vascular mural cells modulates cerebrovascular integrity and function in the presence of APOE4

Cerebrovasculature is critical in maintaining brain homeostasis; its dysregulation often leads to vascular cognitive impairment and dementia (VCID) during aging. VCID is the second most prevalent cause of dementia in the elderly, after Alzheimer's disease (AD), with frequent cooccurrence of VCID and AD. While multiple factors are involved in the pathogenesis of AD and VCID, APOE4 increases the risk for both diseases. A major apolipoprotein E (apoE) receptor, the low-density lipoprotein receptor-related protein 1 (LRP1), is abundantly expressed in vascular mural cells (pericytes and smooth muscle cells). Here, we investigated how deficiency of vascular mural cell LRP1 affects the cerebrovascular system and cognitive performance using vascular mural cell-specific Lrp1-KO mice (smLrp1-/-) in a human APOE3 or APOE4 background. We found that spatial memory was impaired in the 13- to 16-month-old APOE4 smLrp1-/- mice but not in the APOE3 smLrp1-/- mice, compared with their respective littermate control mice. These disruptions in the APOE4 smLrp1-/- mice were accompanied with excess paravascular glial activation and reduced cerebrovascular collagen IV. In addition, blood-brain barrier (BBB) integrity was disrupted in the APOE4 smLrp1-/- mice. Together, our results suggest that vascular mural cell LRP1 modulates cerebrovasculature integrity and function in an APOE genotype-dependent manner.

LRP1 protects against excessive superior mesenteric artery remodeling by modulating angiotensin II-mediated signaling

Vascular smooth muscle cells (vSMCs) exert a critical role in sensing and maintaining vascular integrity. These cells abundantly express the low-density lipoprotein receptor-related protein 1 (LRP1), a large endocytic signaling receptor that recognizes numerous ligands, including apolipoprotein E-rich lipoproteins, proteases, and protease-inhibitor complexes. We observed the spontaneous formation of aneurysms in the superior mesenteric artery (SMA) of both male and female mice in which LRP1 was genetically deleted in vSMCs (smLRP1-/- mice). Quantitative proteomics revealed elevated abundance of several proteins in smLRP1-/- mice that are known to be induced by angiotensin II-mediated (AngII-mediated) signaling, suggesting that this pathway was dysregulated. Administration of losartan, an AngII type I receptor antagonist, or an angiotensinogen antisense oligonucleotide to reduce plasma angiotensinogen concentrations restored the normal SMA phenotype in smLRP1-/- mice and prevented aneurysm formation. Additionally, using a vascular injury model, we noted excessive vascular remodeling and neointima formation in smLRP1-/- mice that was restored by losartan administration. Together, these findings reveal that LRP1 regulates vascular integrity and remodeling of the SMA by attenuating excessive AngII-mediated signaling.

A genomic deep field view of hypertension

Blood pressure is regulated by a complex neurohumoral system including the renin-angiotensin-aldosterone system, natriuretic peptides, endothelial pathways, the sympathetic nervous system, and the immune system. This review charts the evolution of our understanding of the genomic basis of hypertension at increasing resolution over the last 5 decades from monogenic causes to polygenic associations, spanning ∼30 monogenic rare variants and >1500 single nucleotide variants. Unexpected early wins from blood pressure genomics include deepening of our understanding of the complex causation of hypertension; refinement of causal estimates bidirectionally between blood pressure, risk factors, and outcomes through Mendelian randomization; risk stratification using polygenic risk scores; and opportunities for precision medicine and drug repurposing.

Fibromuscular Dysplasia and Abdominal Aortic Aneurysms Are Dimorphic Sex-Specific Diseases With Shared Complex Genetic Architecture

BACKGROUND

The risk of arterial diseases may be elevated among family members of individuals having multifocal fibromuscular dysplasia (FMD). We sought to investigate the risk of arterial diseases in families of individuals with FMD.

METHODS

Family histories for 73 probands with FMD were obtained, which included an analysis of 463 total first-degree relatives focusing on FMD and related arterial disorders. A polygenic risk score for FMD (PRSFMD) was constructed from prior genome-wide association findings of 584 FMD cases and 7139 controls and evaluated for association with an abdominal aortic aneurysm (AAA) in a cohort of 9693 AAA cases and 294 049 controls. A previously published PRSAAA was also assessed among the FMD cases and controls.

RESULTS

Of all first degree relatives of probands, 9.3% were diagnosed with FMD, aneurysms, and dissections. Aneurysmal disease occurred in 60.5% of affected relatives and 5.6% of all relatives. Among 227 female first-degree relatives of probands, 4.8% (11) had FMD, representing a relative risk (RR)FMD of 1.5 ([95% CI, 0.75-2.8]; P=0.19) compared with the estimated population prevalence of 3.3%, though not of statistical significance. Of all fathers of FMD probands, 11% had AAAs resulting in a RRAAA of 2.3 ([95% CI, 1.12-4.6]; P=0.014) compared with population estimates. The PRSFMD was found to be associated with an AAA (odds ratio, 1.03 [95% CI, 1.01-1.05]; P=2.6×10-3), and the PRSAAA was found to be associated with FMD (odds ratio, 1.53 [95% CI, 1.2-1.9]; P=9.0×10-5) as well.

CONCLUSIONS

FMD and AAAs seem to be sex-dimorphic manifestations of a heritable arterial disease with a partially shared complex genetic architecture. Excess risk of having an AAA according to a family history of FMD may justify screening in family members of individuals having FMD.

Aortic Cellular Diversity and Quantitative Genome-Wide Association Study Trait Prioritization Through Single-Nuclear RNA Sequencing of the Aneurysmal Human Aorta

BACKGROUND

Mural cells in ascending aortic aneurysms undergo phenotypic changes that promote extracellular matrix destruction and structural weakening. To explore this biology, we analyzed the transcriptional features of thoracic aortic tissue.

METHODS

Single-nuclear RNA sequencing was performed on 13 samples from human donors, 6 with thoracic aortic aneurysm, and 7 without aneurysm. Individual transcriptomes were then clustered based on transcriptional profiles. Clusters were used for between-disease differential gene expression analyses, subcluster analysis, and analyzed for intersection with genetic aortic trait data.

RESULTS

We sequenced 71 689 nuclei from human thoracic aortas and identified 14 clusters, aligning with 11 cell types, predominantly vascular smooth muscle cells (VSMCs) consistent with aortic histology. With unbiased methodology, we found 7 vascular smooth muscle cell and 6 fibroblast subclusters. Differentially expressed genes analysis revealed a vascular smooth muscle cell group accounting for the majority of differential gene expression. Fibroblast populations in aneurysm exhibit distinct behavior with almost complete disappearance of quiescent fibroblasts. Differentially expressed genes were used to prioritize genes at aortic diameter and distensibility genome-wide association study loci highlighting the genes JUN, LTBP4 (latent transforming growth factor beta-binding protein 1), and IL34 (interleukin 34) in fibroblasts, ENTPD1, PDLIM5 (PDZ and LIM domain 5), ACTN4 (alpha-actinin-4), and GLRX in vascular smooth muscle cells, as well as LRP1 in macrophage populations.

CONCLUSIONS

Using nuclear RNA sequencing, we describe the cellular diversity of healthy and aneurysmal human ascending aorta. Sporadic aortic aneurysm is characterized by differential gene expression within known cellular classes rather than by the appearance of novel cellular forms. Single-nuclear RNA sequencing of aortic tissue can be used to prioritize genes at aortic trait loci.

The Genetics and Typical Traits of Thoracic Aortic Aneurysm and Dissection

Genetic predisposition and risk factors such as hypertension and smoking can instigate the development of thoracic aortic aneurysm (TAA), which can lead to highly lethal aortic wall dissection and/or rupture. Monogenic defects in multiple genes involved in the elastin-contractile unit and the TGFβ signaling pathway have been associated with TAA in recent years, along with several genetic modifiers and risk-conferring polymorphisms. Advances in omics technology have also provided significant insights into the processes behind aortic wall degeneration: inflammation, epigenetics, vascular smooth muscle phenotype change and depletion, reactive oxygen species generation, mitochondrial dysfunction, and angiotensin signaling dysregulation. These recent advances and findings might pave the way for a therapy that is capable of stopping and perhaps even reversing aneurysm progression.

The complex genetic basis of fibromuscular dysplasia, a systemic arteriopathy associated with multiple forms of cardiovascular disease

Artery stenosis is a common cause of hypertension and stroke and can be due to atherosclerosis accumulation in the majority of cases and in a small fraction of patients to arterial fibromuscular dysplasia (FMD). Artery stenosis due to atherosclerosis is widely studied with known risk factors (e.g. increasing age, male gender, and dyslipidemia) to influence its etiology, including genetic factors. However, the causes of noninflammatory and nonatherosclerotic stenosis in FMD are less understood. FMD occurs predominantly in early middle-age women, a fraction of the population where cardiovascular risk is different and understudied. FMD arteriopathies are often diagnosed in the context of hypertension and stroke and co-occur mainly with spontaneous coronary artery dissection, an atypical cause of acute myocardial infarction. In this review, we provide a comprehensive overview of the recent advances in the understanding of molecular origins of FMD. Data were obtained from genetic studies using complementary methodological approaches applied to familial, syndromic, and sporadic forms of this intriguing arteriopathy. Rare variation analyses point toward mechanisms related to impaired prostacyclin signaling and defaults in fibrillar collagens. The study of common variation, mainly through a recent genome-wide association study, describes a shared genetic link with blood pressure, in addition to point at potential risk genes involved in actin cytoskeleton and intracellular calcium homeostasis supporting impaired vascular contraction as a key mechanism. We conclude this review with future strategies and approaches needed to fully understand the genetic and molecular mechanisms related to FMD.

The role of vascular smooth muscle cells in the development of aortic aneurysms and dissections

BACKGROUND

Aortic aneurysms (AA) are pathological dilations of the aorta, associated with an overall mortality rate up to 90% in case of rupture. In addition to dilation, the aortic layers can separate by a tear within the layers, defined as aortic dissections (AD). Vascular smooth muscle cells (vSMC) are the predominant cell type within the aortic wall and dysregulation of vSMC functions contributes to AA and AD development and progression. However, since the exact underlying mechanism is poorly understood, finding potential therapeutic targets for AA and AD is challenging and surgery remains the only treatment option.

METHODS

In this review, we summarize current knowledge about vSMC functions within the aortic wall and give an overview of how vSMC functions are altered in AA and AD pathogenesis, organized per anatomical location (abdominal or thoracic aorta).

RESULTS

Important functions of vSMC in healthy or diseased conditions are apoptosis, phenotypic switch, extracellular matrix regeneration and degradation, proliferation and contractility. Stressors within the aortic wall, including inflammatory cell infiltration and (epi)genetic changes, modulate vSMC functions and cause disturbance of processes within vSMC, such as changes in TGF-β signalling and regulatory RNA expression.

CONCLUSION

This review underscores a central role of vSMC dysfunction in abdominal and thoracic AA and AD development and progression. Further research focused on vSMC dysfunction in the aortic wall is necessary to find potential targets for noninvasive AA and AD treatment options.

Genetic Variation in LRP1 Associates with Stanford Type B Aortic Dissection Risk and Clinical Outcome

Genetic variation in LRP1 (low-density lipoprotein receptor-related protein 1) was reported to be associated with thoracic aortic dissections and aneurysms. The aims of this study were to confirm this association in a prospective single-center patient cohort of patients with acute Stanford type B aortic dissections (STBAD) and to assess the impact of LRP1 variation on clinical outcome. The single nucleotide variation (SNV) rs11172113 within the LRP1 gene was genotyped in 113 STBAD patients and 768 healthy control subjects from the same population. The T-allele of rs11172113 was more common in STBAD patients as compared to the reference group (72.6% vs. 59.6%) and confirmed to be an independent risk factor for STBAD (p = 0.002) after sex and age adjustment in a logistic regression model analyzing diabetes, smoking and hypertension as additional risk factors. Analysis of clinical follow-up (median follow-up 2.0 years) revealed that patients with the T-allele were more likely to suffer aorta-related complications (T-allele 75.6% vs. 63.8%; p = 0.022). In this study sample of STBAD patients, variation in LRP1 was an independent risk factor for STBAD and affected clinical outcome.

Genetic investigation of fibromuscular dysplasia identifies risk loci and shared genetics with common cardiovascular diseases

Fibromuscular dysplasia (FMD) is an arteriopathy associated with hypertension, stroke and myocardial infarction, affecting mostly women. We report results from the first genome-wide association meta-analysis of six studies including 1556 FMD cases and 7100 controls. We find an estimate of SNP-based heritability compatible with FMD having a polygenic basis, and report four robustly associated loci (PHACTR1, LRP1, ATP2B1, and LIMA1). Transcriptome-wide association analysis in arteries identifies one additional locus (SLC24A3). We characterize open chromatin in arterial primary cells and find that FMD associated variants are located in arterial-specific regulatory elements. Target genes are broadly involved in mechanisms related to actin cytoskeleton and intracellular calcium homeostasis, central to vascular contraction. We find significant genetic overlap between FMD and more common cardiovascular diseases and traits including blood pressure, migraine, intracranial aneurysm, and coronary artery disease.

LDL receptor-related protein 1 and its interacting partners in tissue homeostasis

PURPOSE OF REVIEW

LDL receptor-related protein 1 (LRP1) is a multifunctional protein with endocytic and signal transduction properties due to its interaction with numerous extracellular ligands and intracellular proteins. This brief review highlights key developments in identifying novel functions of LRP1 in liver, lung, and the central nervous system in disease pathogenesis.

RECENT FINDINGS

In hepatocytes, LRP1 complexes with phosphatidylinositol 4-phosphate 5-kinase-1 and its related protein to maintain intracellular levels of phosphatidylinositol (4,5) bisphosphate and preserve lysosome and mitochondria integrity. In contrast, in smooth muscle cells, macrophages, and endothelial cells, LRP1 interacts with various different extracellular ligands and intracellular proteins in a tissue-dependent and microenvironment-dependent manner to either enhance or suppress inflammation, disease progression or resolution. Similarly, LRP1 expression in astrocytes and oligodendrocyte progenitor cells regulates cell differentiation and maturation in a developmental-dependent manner to modulate neurogenesis, gliogenesis, and white matter repair after injury.

SUMMARY

LRP1 modulates metabolic disease manifestation, inflammation, and differentiation in a cell-dependent, time-dependent, and tissue-dependent manner. Whether LRP1 expression is protective or pathogenic is dependent on its interaction with specific ligands and intracellular proteins, which in turn is dependent on the cell type and the microenvironment where these cells reside.

FMD and SCAD: Sex-Biased Arterial Diseases With Clinical and Genetic Pleiotropy

Multifocal fibromuscular dysplasia (FMD) and spontaneous coronary artery dissection are both sex-biased diseases disproportionately affecting women over men in a 9:1 ratio. Traditionally known in the context of renovascular hypertension, recent advances in knowledge about FMD have demonstrated that FMD is a systemic arteriopathy presenting as arterial stenosis, aneurysm, and dissection in virtually any arterial bed. FMD is also characterized by major cardiovascular presentations including hypertension, stroke, and myocardial infarction. Similar to FMD, spontaneous coronary artery dissection is associated with a high prevalence of extracoronary vascular abnormalities, including FMD, aneurysm, and extracoronary dissection, and recent studies have also found genetic associations between the two diseases. This review will summarize the relationship between FMD and spontaneous coronary artery dissection with a focus on common clinical associations, histopathologic mechanisms, genetic susceptibilities, and the biology of these diseases. The current status of disease models and critical future research directions will also be addressed.

Thymosin β4 protects against aortic aneurysm via endocytic regulation of growth factor signaling

Vascular stability and tone are maintained by contractile smooth muscle cells (VSMCs). However, injury-induced growth factors stimulate a contractile-synthetic phenotypic modulation which increases susceptibility to abdominal aortic aneurysm (AAA). As a regulator of embryonic VSMC differentiation, we hypothesized that Thymosin β4 (Tβ4) may function to maintain healthy vasculature throughout postnatal life. This was supported by the identification of an interaction with low density lipoprotein receptor related protein 1 (LRP1), an endocytic regulator of platelet-derived growth factor BB (PDGF-BB) signaling and VSMC proliferation. LRP1 variants have been implicated by genome-wide association studies with risk of AAA and other arterial diseases. Tβ4-null mice displayed aortic VSMC and elastin defects that phenocopy those of LRP1 mutants, and their compromised vascular integrity predisposed them to Angiotensin II-induced aneurysm formation. Aneurysmal vessels were characterized by enhanced VSMC phenotypic modulation and augmented PDGFR-β signaling. In vitro, enhanced sensitivity to PDGF-BB upon loss of Tβ4 was associated with dysregulated endocytosis, with increased recycling and reduced lysosomal targeting of LRP1-PDGFR-β. Accordingly, the exacerbated aneurysmal phenotype in Tβ4-null mice was rescued upon treatment with the PDGFR-β antagonist Imatinib. Our study identifies Tβ4 as a key regulator of LRP1 for maintaining vascular health, and provides insights into the mechanisms of growth factor-controlled VSMC phenotypic modulation underlying aortic disease progression.

The molecular mechanism of LRP1 in physiological vascular homeostasis and signal transduction pathways

Interactions between vascular smooth muscle cells (VSMCs), endothelial cells (ECs), pericytes (PCs) and macrophages (MФ), the major components of blood vessels, play a crucial role in maintaining vascular structural and functional homeostasis. Low-density lipoprotein (LDL) receptor-related protein-1 (LRP1), a transmembrane receptor protein belonging to the LDL receptor family, plays multifunctional roles in maintaining endocytosis, homeostasis, and signal transduction. Accumulating evidence suggests that LRP1 modulates vascular homeostasis mainly by regulating vasoactive substances and specific intracellular signaling pathways, including the plasminogen activator inhibitor 1 (PAI-1) signaling pathway, platelet-derived growth factor (PDGF) signaling pathway, transforming growth factor-β (TGF-β) signaling pathway and vascular endothelial growth factor (VEGF) signaling pathway. The aim of the present review is to focus on recent advances in the discovery and mechanism of vascular homeostasis regulated by LRP1-dependent signaling pathways. These recent discoveries expand our understanding of the mechanisms controlling LRP1 as a target for studies on vascular complications.

Lrp1 Regulation of Pulmonary Function. Follow-Up of Human GWAS in Mice

Human genome-wide association studies (GWASs) have identified more than 270 loci associated with pulmonary function; however, follow-up studies to determine causal genes at these loci are few. SNPs in low-density lipoprotein receptor-related protein 1 (LRP1) are associated with human pulmonary function in GWASs. Using murine models, we investigated the effect of genetic disruption of the Lrp1 gene in smooth muscle cells on pulmonary function in naive animals and after exposure to bacterial LPS or house dust mite extract. Disruption of Lrp1 in smooth muscle cells leads to an increase in tissue resistance, elastance, and tissue elastance at baseline. Furthermore, disruption of Lrp1 in smooth muscle increases airway responsiveness as measured by increased total lung resistance and airway resistance after methacholine. Immune cell counts in BAL fluid were increased in animals with Lrp1 disruption. The difference in airway responsiveness by genotype observed in naive animals was not observed after LPS or house dust mite extract exposure. To further explore the mechanisms contributing to changes in pulmonary function, we identified several ligands dysregulated with Lrp1 disruption in smooth muscle cells. These data suggest that dysregulation of LRP1 in smooth muscle cells affects baseline pulmonary function and airway responsiveness and helps establish LRP1 as the causal gene at this GWAS locus.

Is there an immunogenomic difference between thoracic and abdominal aortic aneurysms?

BACKGROUND AND AIM

Aortic aneurysms most commonly occur in the infra-renal and proximal thoracic regions. While generally asymptomatic, progressive aneurysmal dilation can become rapidly lethal when dissection or ruptures occurs, highlighting the need for more robust screening. Abdominal aortic aneurysm (AAA) is more prevalent compared to thoracic aortic aneurysm (TAA). The true incidence of TAA is underreported due to the absence of population screening and the silent nature of TAA. To achieve the optimum survival rate in aortic aneurysms, knowledge of natural course, genetic association, and surgical results are needed to be applied with adequate medical treatment and careful selection of patients for operation. The purpose of this paper is to provide a comprehensive review of the literature on natural history, immunology, and genetic differences between thoracic and AAAs.

METHOD

The literature was collected from OVID, SCOPUS, and PubMed.

RESULTS

(1) AAA expands faster than TAA. AAA expands at approximately 0.3-0.45 cm annually, depending on various factors (advancing age, diameter of aorta, smoking etc.). TAA expands up to 0.3 cm annually in a non-bicuspid aortic valve patient. (2) An increase in Matrix metallopeptidase 1, 2, 9, 12, 14 led to degrading extracellular matrix of the aortic vessel wall. This significantly contributed to the pathogenesis in AAA, whereas overactive Transforming growth factor-beta played a major role in the pathogenesis of TAA.

CONCLUSION

In the future, genetic testing may be the gold standard for tackling the geneticheterogeneity of aneurysms, therefore, identifying at-risk individuals developing TAA andAAA earlier.

Macrophage Biology in Cardiovascular Diseases

Macrophages have a key functional role in the pathogenesis of various cardiovascular diseases, such as atherosclerosis and aortic aneurysms. Their accumulation within the vessel wall leads to sustained local inflammatory responses characterized by secretion of chemokines, cytokines, and matrix protein degrading enzymes. Here, we summarize some recent findings on macrophage contribution to cardiovascular disease. We focus on the origin, survival/death, and phenotypic switching of macrophages within vessel walls.

Physiology and role of PCSK9 in vascular disease: Potential impact of localized PCSK9 in vascular wall

Proprotein convertase subtilisin/kexin type-9 (PCSK9), a member of the proprotein convertase family, is an important drug target because of its crucial role in lipid metabolism. Emerging evidence suggests a direct role of localized PCSK9 in the pathogenesis of vascular diseases. With this in our consideration, we reviewed PCSK9 physiology with respect to recent development and major studies (clinical and experimental) on PCSK9 functionality in vascular disease. PCSK9 upregulates low-density lipoprotein (LDL)-cholesterol levels by binding to the LDL-receptor (LDLR) and facilitating its lysosomal degradation. PCSK9 gain-of-function mutations have been confirmed as a novel genetic mechanism for familial hypercholesterolemia. Elevated serum PCSK9 levels in patients with vascular diseases may contribute to coronary artery disease, atherosclerosis, cerebrovascular diseases, vasculitis, aortic diseases, and arterial aging pathogenesis. Experimental models of atherosclerosis, arterial aneurysm, and coronary or carotid artery ligation also support PCSK9 contribution to inflammatory response and disease progression, through LDLR-dependent or -independent mechanisms. More recently, several clinical trials have confirmed that anti-PCSK9 monoclonal antibodies can reduce systemic LDL levels, total nonfatal cardiovascular events, and all-cause mortality. Interaction of PCSK9 with other receptor proteins (LDLR-related proteins, cluster of differentiation family members, epithelial Na⁺ channels, and sortilin) may underlie its roles in vascular disease. Improved understanding of PCSK9 roles and molecular mechanisms in various vascular diseases will facilitate advances in lipid-lowering therapy and disease prevention.

High-Affinity Binding of LDL Receptor-Related Protein 1 to Matrix Metalloprotease 1 Requires Protease:Inhibitor Complex Formation

Matrix metalloprotease (MMP) activation contributes to the degradation of the extracellular matrix (ECM), resulting in a multitude of pathologies. Low-density lipoprotein receptor-related protein 1 (LRP1) is a multifaceted endocytic and signaling receptor that is responsible for internalization and lysosomal degradation of diverse proteases, protease inhibitors, and lipoproteins along with numerous other proteins. In this study, we identified MMP-1 as a novel LRP1 ligand. Binding studies employing surface plasmon resonance revealed that both proMMP-1 and active MMP-1 bind to purified LRP1 with equilibrium dissociation constants (K_D) of 19 and 25 nM, respectively. We observed that human aortic smooth muscle cells readily internalize and degrade ¹²⁵I-labeled proMMP-1 in an LRP1-mediated process. Our binding data also revealed that all tissue inhibitors of metalloproteases (TIMPs) bind to LRP1 with K_D values ranging from 23 to 33 nM. Interestingly, the MMP-1/TIMP-1 complex bound to LRP1 with an affinity (K_D = 0.6 nM) that was 30-fold higher than that of either component alone, revealing that LRP1 prefers the protease:inhibitor complex as a ligand. Of note, modification of lysine residues on either proMMP-1 or TIMP-1 ablated the ability of the MMP-1/TIMP-1 complex to bind to LRP1. LRP1's preferential binding to enzyme:inhibitor complexes was further supported by the higher binding affinity for proMMP-9/TIMP-1 complexes than for either of these two components alone. LRP1 has four clusters of ligand-binding repeats, and MMP-1, TIMP-1, and MMP-1/TIMP-1 complexes bound to cluster III most avidly. Our results reveal an important role for LRP1 in controlling ECM homeostasis by regulating MMP-1 and MMP-9 levels.

Pathophysiology of Aortic Aneurysms: Insights from Animal Studies

Aortic aneurysms are defined as dilations of the aorta greater than 50 percent. Currently, the only effective treatment for aortic aneurysms is surgical repair, which is recommended only to those that meet criteria. There is no available pharmaceutical therapy to slow aneurysm growth and thus prevent lethal rupture. The development of a number of murine models has allowed in depth studies of various cellular and extracellular components of aneurysm pathophysiology. The identification of key therapeutic targets has resulted in several clinical trials evaluating pharmaceutical candidates to treat aneurysm progression. In this review, we focus on providing recent updates on developments in murine models of aortic aneurysm. In addition, we discuss recent studies of the various cellular and extracellular components of the aorta along with the abutting aortic structures that contribute to aneurysm development and progression.

Identification of Susceptibility Loci for Spontaneous Coronary Artery Dissection

Importance

Spontaneous coronary artery dissection (SCAD), an idiopathic disorder that predominantly affects young to middle-aged women, has emerged as an important cause of acute coronary syndrome, myocardial infarction, and sudden cardiac death.

Objective

To identify common single-nucleotide variants (SNVs) associated with SCAD susceptibility.

Design, Setting, and Participants

This single-center genome-wide association study examined approximately 5 million genotyped and imputed SNVs and subsequent SNV-targeted replication analysis results in individuals enrolled in the Mayo Clinic SCAD registry from August 30, 2011, to August 2, 2018. Data analysis was performed from June 21, 2017, to December 30, 2019.

Main Outcomes and Measures

Genetic loci and positional candidate genes associated with SCAD.

Results

This study included 484 white women with SCAD (mean [SD] age, 46.6 [9.2] years) and 1477 white female controls in the discovery cohort (mean [SD] age, 64.0 [14.5] years) and 183 white women with SCAD (mean [SD] age, 47.1 [9.9] years) and 340 white female controls in the replication cohort (mean [SD] age, 51.0 [15.3] years). Associations with SCAD risk reached genome-wide significance at 3 loci (1q21.3 [OR, 1.78; 95% CI, 1.51-2.09; P = 2.63 × 10-12], 6p24.1 [OR, 1.77; 95% CI, 1.51-2.09; P = 7.09 × 10-12], and 12q13.3 [OR, 1.67; 95% CI, 1.42-1.97; P = 3.62 × 10-10]), and 7 loci had evidence suggestive of an association (1q24.2 [OR, 2.10; 95% CI, 1.58-2.79; P = 2.88 × 10-7], 3q22.3 [OR, 1.47; 95% CI, 1.26-1.71; P = 6.65 × 10-7], 4q34.3 [OR, 1.84; 95% CI, 1.44-2.35; P = 9.80 × 10-7], 8q24.3 [OR, 2.57; 95% CI, 1.76-3.75; P = 9.65 × 10-7], 15q21.1 [OR, 1.75; 95% CI, 1.40-2.18; P = 7.23 × 10-7], 16q24.1 [OR, 1.91; 95% CI, 1.49-2.44; P = 2.56 × 10-7], and 21q22.11 [OR, 2.11; 95% CI, 1.59-2.82; P = 3.12 × 10-7]) after adjusting for the top 5 principal components. Associations were validated for 5 of the 10 risk alleles in the replication cohort. In a meta-analysis of the discovery and replication cohorts, associations for the 5 SNVs were significant, with relatively large effect sizes (1q21.3 [OR, 1.77; 95% CI, 1.54-2.03; P = 3.26 × 10-16], 6p24.1 [OR, 1.71; 95% CI, 1.49-1.97; P = 4.59 × 10-14], 12q13.3 [OR, 1.69; 95% CI, 1.47-1.94; P = 1.42 × 10-13], 15q21.1 [OR, 1.79; 95% CI, 1.48-2.17; P = 2.12 × 10-9], and 21q22.11 [OR, 2.18; 95% CI, 1.70-2.81; P = 1.09 × 10-9]). Each index SNV was within or near a gene highly expressed in arterial tissue and previously linked to SCAD (PHACTR1) and/or other vascular disorders (LRP1, LINC00310, and FBN1).

Conclusions and Relevance

This study revealed 5 replicated risk loci and positional candidate genes for SCAD, most of which are associated with extracoronary arteriopathies. Moreover, the alternate alleles of 3 SNVs have been previously associated with atherosclerotic coronary artery disease, further implicating allelic susceptibility to coronary artery atherosclerosis vs dissection.

Aortic Aneurysms and Dissections Series: Part II: Dynamic Signaling Responses in Aortic Aneurysms and Dissections

Aortic structure and function are controlled by the coordinated actions of different aortic cells and the extracellular matrix. Several pathways have been identified that control the aortic wall in a cell-type-specific manner and play diverse roles in various phases of aortic injury, repair, and remodeling. This complexity of signaling in the aortic wall poses challenges to the development of therapeutic strategies for treating aortic aneurysms and dissections. Here, in part II of this Recent Highlights series on aortic aneurysms and dissections, we will summarize recent studies published in Arteriosclerosis, Thrombosis, and Vascular Biology that have contributed to our knowledge of the signaling pathway-related mechanisms of aortic aneurysms and dissections.

Aortic Aneurysms and Dissections Series

The aortic wall is composed of highly dynamic cell populations and extracellular matrix. In response to changes in the biomechanical environment, aortic cells and extracellular matrix modulate their structure and functions to increase aortic wall strength and meet the hemodynamic demand. Compromise in the structural and functional integrity of aortic components leads to aortic degeneration, biomechanical failure, and the development of aortic aneurysms and dissections (AAD). A better understanding of the molecular pathogenesis of AAD will facilitate the development of effective medications to treat these conditions. Here, we summarize recent findings on AAD published in ATVB. In this issue, we focus on the dynamics of aortic cells and extracellular matrix in AAD; in the next issue, we will focus on the role of signaling pathways in AAD.

LRP1 promotes synthetic phenotype of pulmonary artery smooth muscle cells in pulmonary hypertension

Pulmonary hypertension (PH) is characterized by a thickening of the distal pulmonary arteries caused by medial hypertrophy, intimal proliferation and vascular fibrosis. Low density lipoprotein receptor-related protein 1 (LRP1) maintains vascular homeostasis by mediating endocytosis of numerous ligands and by initiating and regulating signaling pathways. Here, we demonstrate the increased levels of LRP1 protein in the lungs of idiopathic pulmonary arterial hypertension (IPAH) patients, hypoxia-exposed mice, and monocrotaline-treated rats. Platelet-derived growth factor (PDGF)-BB upregulated LRP1 expression in pulmonary artery smooth muscle cells (PASMC). This effect was reversed by the PDGF-BB neutralizing antibody or the PDGF receptor antagonist. Depletion of LRP1 decreased proliferation of donor and IPAH PASMC in a β1-integrin-dependent manner. Furthermore, LRP1 silencing attenuated the expression of fibronectin and collagen I and increased the levels of α-smooth muscle actin and myocardin in donor, but not in IPAH, PASMC. In addition, smooth muscle cell (SMC)-specific LRP1 knockout augmented α-SMA expression in pulmonary vessels and reduced SMC proliferation in 3D ex vivo murine lung tissue cultures. In conclusion, our results indicate that LRP1 promotes the dedifferentiation of PASMC from a contractile to a synthetic phenotype thus suggesting its contribution to vascular remodeling in PH.