Identification of genomic loci regulating platelet plasminogen activator inhibitor-1 in mice

BACKGROUND

Plasminogen activator inhibitor-1 (PAI-1, Serpine1) is an important circulating fibrinolysis inhibitor. PAI-1 exists in 2 pools, packaged within platelet α-granules and freely circulating in plasma. Elevated plasma PAI-1 levels are associated with cardiovascular disease. However, little is known about the regulation of platelet PAI-1 (pPAI-1).

OBJECTIVES

We investigated the genetic control of pPAI-1 levels in mice and humans.

METHODS

We measured pPAI-1 antigen levels via enzyme-linked immunosorbent assay in platelets isolated from 10 inbred mouse strains, including LEWES/EiJ (LEWES) and C57BL/6J (B6). LEWES and B6 were crossed to produce the F1 generation, B6LEWESF1. B6LEWESF1 mice were intercrossed to produce B6LEWESF2 mice. These mice were subjected to genome-wide genetic marker genotyping followed by quantitative trait locus analysis to identify pPAI-1 regulatory loci.

RESULTS

We identified differences in pPAI-1 between several laboratory strains, with LEWES having pPAI-1 levels more than 10-fold higher than those in B6. Quantitative trait locus analysis of B6LEWESF2 offspring identified a major pPAI-1 regulatory locus on chromosome 5 from 136.1 to 137.6 Mb (logarithm of the odds score, 16.2). Significant pPAI-1 modifier loci on chromosomes 6 and 13 were also identified.

CONCLUSION

Identification of pPAI-1 genomic regulatory elements provides insights into platelet/megakaryocyte-specific and cell type-specific gene expression. This information can be used to design more precise therapeutic targets for diseases where PAI-1 plays a role.

Illustrated State-of-the-Art Capsules of the ISTH 2020 Congress

This year's Congress of the International Society of Thrombosis and Haemostasis (ISTH) was hosted virtually from Philadelphia July 17-21, 2021. The conference, now held annually, highlighted cutting-edge advances in basic, population and clinical sciences of relevance to the Society. Despite being held virtually, the 2021 congress was of the same scope and quality as an annual meeting held in person. An added feature of the program is that talks streamed at the designated times will then be available on-line for asynchronous viewing. The program included 77 State of the Art (SOA) talks, thematically grouped in 28 sessions, given by internationally recognized leaders in the field. The SOA speakers were invited to prepare brief illustrated reviews of their talks that were peer reviewed and are included in this article. The topics, across the main scientific themes of the congress, include Arterial Thromboembolism, Coagulation and Natural Anticoagulants, COVID-19 and Coagulation, Diagnostics and Omics, Fibrinogen, Fibrinolysis and Proteolysis, Hemophilia and Rare Bleeding Disorders, Hemostasis in Cancer, Inflammation and Immunity, Pediatrics, Platelet Disorders, von Willebrand Disease and Thrombotic Angiopathies, Platelets and Megakaryocytes, Vascular Biology, Venous Thromboembolism and Women's Health. These illustrated capsules highlight the major scientific advances with potential to impact clinical practice. Readers are invited to take advantage of the excellent educational resource provided by these illustrated capsules. They are also encouraged to use the image in social media to draw attention to the high quality and impact of the science presented at the congress.

Glomerular endothelial cells and podocytes can express CD80 in patients with minimal change disease during relapse

BACKGROUND

Urinary CD80 has emerged as potential biomarker in idiopathic nephrotic syndrome (INS). However, its cellular source remains controversial. The aim of the study was to assess whether CD80 is truly expressed by glomerular cells in INS patients during relapse and in the LPS mouse model of podocyte injury.

METHODS

The presence of CD80 in glomeruli was evaluated by combining immunostaining, immunogold labeling, and in situ hybridization techniques.

RESULTS

CD80 was present along the surface of glomerular endothelial cells (GEC) and rarely in podocytes in six of nine minimal change disease (MCD) patients in relapse, two of eleven patients with focal segmental glomerulosclerosis in relapse, and absent in controls. In mice, CD80 was upregulated at mRNA and protein level in GEC and podocytes, in a similar pattern to that seen in MCD patients.

CONCLUSIONS

Glomerular endothelial cells and podocytes can express CD80 in patients with MCD during relapse. A better understanding of the role of CD80 in glomerular cells may provide further insights into the mechanisms of proteinuria in INS.

Expression of factor V by resident macrophages boosts host defense in the peritoneal cavity

Macrophages resident in different organs express distinct genes, but understanding how this diversity fits into tissue-specific features is limited. Here, we show that selective expression of coagulation factor V (FV) by resident peritoneal macrophages in mice promotes bacterial clearance in the peritoneal cavity and serves to facilitate the well-known but poorly understood "macrophage disappearance reaction." Intravital imaging revealed that resident macrophages were nonadherent in peritoneal fluid during homeostasis. Bacterial entry into the peritoneum acutely induced macrophage adherence and associated bacterial phagocytosis. However, optimal control of bacterial expansion in the peritoneum also required expression of FV by the macrophages to form local clots that effectively brought macrophages and bacteria in proximity and out of the fluid phase. Thus, acute cellular adhesion and resident macrophage-induced coagulation operate independently and cooperatively to meet the challenges of a unique, open tissue environment. These events collectively account for the macrophage disappearance reaction in the peritoneal cavity.

Whole exome sequencing of ENU-induced thrombosis modifier mutations in the mouse

Although the Factor V Leiden (FVL) gene variant is the most prevalent genetic risk factor for venous thrombosis, only 10% of FVL carriers will experience such an event in their lifetime. To identify potential FVL modifier genes contributing to this incomplete penetrance, we took advantage of a perinatal synthetic lethal thrombosis phenotype in mice homozygous for FVL (F5L/L) and haploinsufficient for tissue factor pathway inhibitor (Tfpi+/-) to perform a sensitized dominant ENU mutagenesis screen. Linkage analysis conducted in the 3 largest pedigrees generated from the surviving F5L/L Tfpi+/- mice ('rescues') using ENU-induced coding variants as genetic markers was unsuccessful in identifying major suppressor loci. Whole exome sequencing was applied to DNA from 107 rescue mice to identify candidate genes enriched for ENU mutations. A total of 3,481 potentially deleterious candidate ENU variants were identified in 2,984 genes. After correcting for gene size and multiple testing, Arl6ip5 was identified as the most enriched gene, though not reaching genome-wide significance. Evaluation of CRISPR/Cas9 induced loss of function in the top 6 genes failed to demonstrate a clear rescue phenotype. However, a maternally inherited (not ENU-induced) de novo mutation (Plcb4R335Q) exhibited significant co-segregation with the rescue phenotype (p = 0.003) in the corresponding pedigree. Thrombosis suppression by heterozygous Plcb4 loss of function was confirmed through analysis of an independent, CRISPR/Cas9-induced Plcb4 mutation (p = 0.01).

Abstract 009: Ribosomal Profiling of Vascular Smooth Muscle Cells in Vivo Identifies Cell-type Specific Transcripts and Enrichment of Blood Pressure Associated Genes

Background: Vascular smooth muscle cells (vSMCs) are essential for maintaining blood vessel tone and vascular remodeling. Although they play an important role in cardiovascular pathologies, studying peripheral artery vSMCs in vivo has been complicated given their interspersed anatomic distribution and technical difficulties with isolating vSMCs from arteries and arterioles while preserving transcriptome profiles.

Methods and Results: Combining the murine Rpl22 fl Ribotag model with a vSMC-specific Transgelin-Cre ( Tagln-Cre ) Recombinase knock-in, we performed translating ribosome affinity purification and isolation of mRNA derived specifically from Cre -expressing + cells only. Subsequent high-throughput sequencing of both whole tissue mRNA and the vSMC-selected mRNA of the brain, kidney and liver was followed by differential expression analysis to identify genes enriched in the vSMC compartment. Genes significantly enriched in all three tissues (FDR <5%) included well known vSMC markers such as Smooth muscle actin ( Acta2 ) and Calponin-1 ( Cnn1 ) in addition to Tagln. Furthermore, transcripts involved in biological processes associated with extracellular matrix and structure organization were enriched and significant overrepresentation of these genes was also seen by gene ontology analysis. Genes with roles in blood pressure regulation, such as Regulator of G protein signaling 5 ( Rgs5 ) and Sphingosine-1-phosphate receptor 3 ( S1pr3 ) were also significantly enriched in the vSMC transcriptome, and the expression and vSMC-specific localization of these genes were confirmed by fluorescent single-molecule in situ hybridization assays. Further, we performed gene set enrichment analysis of genes associated with blood pressure and hypertension based on human genome-wide association studies, and a significant number of these genes ( P =0.003) showed vSMC-specific expression patterns in our in vivo data.

Conclusion: Our data demonstrate the feasibility of profiling vSMC gene expression in vivo. Furthermore, we identified enrichment of blood pressure-associated genes in the vSMC transcriptome. This model has the potential to provide new insights into the role of vSMCs in physiology and a variety of cardiovascular pathologies.

Abstract 31: Platelet Plasminogen Activator Inhibitor-1 is Regulated by a Major Chromosome 5 eQTL in Inbred Mice

Decreased fibrinolytic activity is strongly associated with cardiovascular disease. Plasminogen activator inhibitor-1, (PAI-1, Serpine1) is a major circulating fibrinolysis inhibitor, >80% of which is found in platelets. Platelet PAI-1 (pPAI-1) is produced by the megakaryocytes and packaged directly into platelets, thus it is distinct from plasma PAI-1. Plasma PAI-1 levels have been extensively studied and consistently linked with cardiovascular disease. However, variation in pPAI-1, either in the presence or absence of cardiovascular disease, is unknown. To study PAI-1 expression, we surveyed ten mouse strains for pPAI-1 antigen. In particular, the LEWES/EiJ mouse strain had significantly increased pPAI-1 (and Serpine1 mRNA), with an average concentration of 3.1 pg/μg total platelet protein compared to C57BL/6J (B6), which had an average pPAI-1 concentration of 0.4 pg/μg total protein (q=0.0018). Outcrossing LEWES/EiJ x C57BL/6J produced F1 mice with average pPAI-1 levels of 1.6 pg/μg total protein (q=0.0018), suggesting a semidominantly-inherited Serpine1 regulatory effect. To identify pPAI-1 regulatory regions, we produced 48 F2 mice, measured pPAI-1 levels and genotyped 12 (with <0.4 pg/μg total protein) and 12 (with >1.0 pg/μg total protein) using the Mouse Universal Genotyping Array (MegaMUGA). QTL analysis revealed several candidate regions including a major significant 14.4 megabase locus (128.2-142.6 megabases) on Chromosome 5 (LOD score = 4.81). The Serpine1 gene resides within this candidate interval, strongly suggesting that a Serpine1 cis-eQTL is responsible for pPAI-1 expression differences between LEWES/EiJ and C57BL/6J. Identifying pPAI-1 expression control elements offers insights into platelet-specific gene expression and identifies a putative therapeutic target for modulating hemostasis.