Alex C. Pettey

Aims: Plasminogen activator inhibitor-1 (PAI-1) regulates plasmin-mediated proteolysis, thereby influencing vascular stability and tissue remodeling. Angiotensin II (AngII) induces an increase in PAI-1 during the development of ascending thoracic aortic aneurysm (ATAA). The initial purpose of this study was to determine whether deletion of PAI-1 influenced development of ATAA. Subsequently, this study aimed to define the early pathological events preceding cardiac fibrosis in PAI-1 deficiency and the structural domain responsible for its protective effect. Methods and results: AngII was infused for 4 weeks in whole-body PAI-1 deficient (PAI-1-/-) mice and their wild-type littermates (PAI-1+/+) to examine the role of PAI-1 in ATAA. PAI-1 deficiency did not alter AngII-induced aortopathy but revealed a striking cardiac phenotype characterized by replacement fibrosis predominantly within the epicardium and posterior septum. Ferric iron, indicative of prior hemorrhage, was coincident with fibrosis. Similar phenotypes were observed in PAI-1-/- mice infused with norepinephrine for 4 weeks. To define the pathological events preceding cardiac fibrosis, either AngII or norepinephrine was infused for 1 week in PAI-1+/+ or -/- mice. Both infusions induced extensive epicardial hemorrhage and posterior septal fibrosis in PAI-1-/- mice. To explore the initiation of cardiac pathology, AngII was infused for approximately 1 day. PAI-1-/- mice developed diffuse hemorrhage and cardiomyocyte injury localized to the posterior septum, pathologic changes that preceded overt fibrosis. Finally, to determine the protective domain of PAI-1, saline or AngII was administered to mice harboring loss-of-function point mutations in the protease inhibitory (PAI-1Ala/Ala) or somatomedin B-binding domains (PAI-1AK/AK). Compared to saline infusion, 1 week of AngII induced hemorrhage and heterogeneous fibrosis in PAI-1Ala/Ala, but not PAI-1AK/AK mice. Conclusions: These findings support that, under hemodynamic stress, PAI-1 deficiency promotes early cardiac hemorrhage and cardiomyocyte injury that lead to fibrosis. Mutational studies implicate dysregulated plasmin generation as an initiator of cardiac injury and fibrosis.

Background: Activation of the renin-angiotensin system (RAS) contributes to aortic diseases caused by fibrillin-1 haploinsufficiency ( Fbn1 ^C1041G/+ ). However, whether RAS activation influences mitral valve disease associated with FBN1 variants remains undefined. This study determined whether inhibition or augmentation of the RAS affects mitral valve pathology in Fbn1 ^C1041G/+ mice. Methods: Angiotensinogen (AGT) antisense oligonucleotides (ASOs) were administered for 12 weeks to inhibit the RAS in male and female Fbn1 ^C1041G/+ mice. To augment the RAS, mice were infused with angiotensin II (AngII; 1,000 ng/kg/min) for 28 days. Mitral valve and heart function were monitored by ultrasound. At termination, hearts were dissected free and tissue sectioned to assess mitral valve leaflet thickness and pathology. Results: Mitral valve leaflet thickness was significantly increased in Fbn1 ^C1041G/+ mice compared to Fbn1 ^+/+ littermates of both sexes. ASO-mediated AGT inhibition did not alter this phenotype despite markedly reduced plasma AGT concentrations. AngII infusion increased mitral valve leaflet thickness in Fbn1 ^C1041G/+ mice with increased proteoglycan and collagen content, while exerting minimal effects in Fbn1 ^+/+ mice. Twenty-five percent of AngII-infused Fbn1 ^C1041G/+ mice died of non-vascular causes. Ultrasound showed mitral valve dysfunction in AngII-infused Fbn1 ^C1041G/+ mice. Grossly expanded left atria were common in AngII-infused Fbn1 ^C1041G/+ mice. These markedly enlarged left atria contained increased fibrosis, macrophage accumulation, and platelet-rich masses. Conclusions: Mitral valves of Fbn1 ^C1041G/+ mice did not respond to AGT inhibition but were markedly more susceptible to AngII infusion, with greater increases in thickness and compositional changes than mitral valves of Fbn1 ^+/+ mice. In addition, AngII promoted mitral valve dysfunction that were associated with pronounced left atrial pathology. What are the Clinical Implications?: Manipulation of fibrillin-1 in mice leads to vascular pathology that is attenuated by sustained inhibition of the renin-angiotensin system and exacerbated by its activation. However, whether modulation of the RAS influences mitral valve disease in mice harboring fibrillin-1 variants remains unknown. This study demonstrated that the presence of a missense variant of fibrillin-1 greatly augments the effects of renin-angiotensin system activation on mitral valve pathology compared with wild-type mice, with increased leaflet thickness and enhanced accumulation of proteoglycan and collagen. These structural changes are accompanied by mitral valve dysfunction and pronounced left atrial pathology, likely attributable to angiotensin II-induced mitral valve prolapse. These findings provide an experimental basis for determining whether inhibition of the renin-angiotensin system attenuates the development or progression of mitral valve dysfunction in humans with fibrillin-1 variants.

Aims: Plasminogen activator inhibitor-1 (PAI-1) regulates plasmin-mediated proteolysis, thereby influencing vascular stability and tissue remodeling. Angiotensin II (AngII) induces an increase in PAI-1 during the development of ascending thoracic aortic aneurysm (ATAA). The initial purpose of this study was to determine whether deletion of PAI-1 influenced development of ATAA. Subsequently, this study aimed to define the early pathological events preceding cardiac fibrosis in PAI-1 deficiency and the structural domain responsible for its protective effect. Methods and results: AngII was infused for 4 weeks in whole-body PAI-1 deficient (PAI-1−/−) mice and their wild-type littermates (PAI-1+/+) to examine the role of PAI-1 in ATAA. PAI-1 deficiency did not alter AngII-induced aortopathy but revealed a striking cardiac phenotype characterized by replacement fibrosis predominantly within the epicardium and posterior septum. Ferric iron, indicative of prior hemorrhage, was coincident with fibrosis. Similar phenotypes were observed in PAI-1−/− mice infused with norepinephrine for 4 weeks. To define the pathological events preceding cardiac fibrosis, either AngII or norepinephrine was infused for 1 week in PAI-1+/+ or −/− mice. Both infusions induced extensive epicardial hemorrhage and posterior septal fibrosis in PAI-1−/− mice. To explore the initiation of cardiac pathology, AngII was infused for approximately 1 day. PAI-1−/− mice developed diffuse hemorrhage and cardiomyocyte injury localized to the posterior septum, pathologic changes that preceded overt fibrosis. Finally, to determine the protective domain of PAI-1, saline or AngII was administered to mice harboring loss-of-function point mutations in the protease inhibitory (PAI-1 ^Ala/Ala ) or somatomedin B-binding domains (PAI-1 ^AK/AK ). Compared to saline infusion, 1 week of AngII induced hemorrhage and heterogeneous fibrosis in PAI-1 ^Ala/Ala , but not PAI-1 ^AK/AK mice. Conclusions: These findings support that, under hemodynamic stress, PAI-1 deficiency promotes early cardiac hemorrhage and cardiomyocyte injury that lead to fibrosis. Mutational studies implicate dysregulated plasmin generation as an initiator of cardiac injury and fibrosis. TRANSLATIONAL PERSPECTIVE: Cardiac fibrosis has been reported in a human population with PAI-1 deficiency and currently lacks targeted therapy. Our findings demonstrate that in animal models, PAI-1 deficiency confers susceptibility to cardiac injury in response to hemodynamic stress, which may accelerate fibrotic remodeling. Mutational disruption of the protease-inhibitory domain of PAI-1 induced similar pathology, supporting a protective role for this function. These observations suggest that interventions aimed at controlling hypertension, promoting endothelial integrity, or regulating plasmin activation could reduce fibrotic remodeling in this population.

Liver steatosis is a common cause of chronic liver disease. To investigate the molecular basis of hepatic steatosis, low-density lipoprotein receptor-deficient (LDLR -/-) mice were fed a Western diet (WD, 42% of calories from fat) for 5, 14, or 42 days and evaluated against mice fed a normal laboratory diet. Histological analyses revealed that steatosis was detected as early as 14 days of WD feeding. Bulk RNA sequencing demonstrated that WD feeding altered liver transcriptomes related to inflammation and cell adhesion consistent with the progression of liver steatosis. Previous studies determined that hepatocyte-specific deficiency of angiotensinogen (AGT), the unique substrate of the renin-angiotensin system (RAS), alleviates WD-induced hepatic steatosis in mice. However, the effects of hepatic AGT deficiency were not mimicked by pharmacological inhibition of the RAS, and the molecular mechanisms by which AGT deficiency protects against WD-induced steatosis is unknown. Therefore, liver transcriptomes were compared between hepatocyte-specific AGT-deficient mice (hepAGT -/-) and their wild-type littermates (hepAGT +/+) after 14 days of WD feeding. Gene ontology analyses showed that upregulated genes in hepAGT -/- mice were enriched for metabolic processes and downregulated genes were enriched for cell division pathways. The integration analysis of the two RNA sequencing data identified 5 key genes, Smpd3, Dtl, Cdc6, Mki67, and Top2a, which were primarily associated with cell division processes in hepAGT +/+ mice and were suppressed in hepAGT -/- mice. In conclusion, hepatic AGT deficiency downregulated genes related to cell division during the progression of liver steatosis.

BACKGROUND: Angiotensinogen (AGT) is an essential component in the renin-angiotensin system. AGT has highly conserved sequences in the loop and β-sheet regions among species; however, their functions have not been studied. METHODS: Adeno-associated viral vector (AAV) serotype 2/8 encoding mouse AGT with mutations of conserved sequences in the loop (AAV.loop-Mut), β-sheet (AAV.βsheet-Mut), or both regions (AAV.loop/βsheet-Mut) was injected into male hepatocyte-specific AGT-deficient (hepAGT ^−/− ) mice in an LDL (low-density lipoprotein) receptor–deficient background. AAV containing mouse wild-type AGT (AAV.mAGT) or a null vector (AAV.null) were used as controls. Two weeks after AAV administration, all mice were fed a western diet for 12 weeks. To determine how AGT secretion is regulated in hepatocytes, AAVs containing the above mutations were transducted into HepG2 cells. RESULTS: In hepAGT ^−/− mice infected with AAV.loop-Mut or βsheet-Mut, plasma AGT concentrations, systolic blood pressure, and atherosclerosis were comparable to those in AAV.mAGT-infected mice. Interestingly, plasma AGT concentrations, systolic blood pressure, and atherosclerotic lesion size in hepAGT ^−/− mice infected with AAV.loop/βsheet-Mut were not different from mice infected with AAV.null. In contrast, hepatic Agt mRNA abundance was elevated to a comparable magnitude as AAV.mAGT-infected mice. Immunostaining showed that AGT protein was accumulated in hepatocytes of mice infected with AAV.loop/βsheet-Mut or HepG2 cells transducted with AAV.loop/βsheet-Mut. Accumulated AGT was not located in the endoplasmic reticulum. CONCLUSIONS: The conserved sequences in either the loop or β-sheet region individually have no effect on AGT regulation, but the conserved sequences in both regions synergistically contribute to the secretion of AGT from hepatocytes.

Background: Angiotensinogen (AGT) is an essential component in the renin-angiotensin system. AGT has highly conserved sequences in the loop and β-sheet regions among species; however, their functions have not been studied. Methods: Adeno-associated viral vector (AAV) serotype 2/8 encoding mouse AGT with mutations of conserved sequences in the loop (AAV.loop-Mut), β-sheet (AAV.βsheet-Mut), or both regions (AAV.loop/βsheet-Mut) were injected into male hepatocyte-specific AGT deficient (hepAGT-/-) mice in an LDL receptor –/– background. AAV containing mouse wild-type AGT (AAV.mAGT) or a null vector (AAV.null) were used as controls. Two weeks after AAV administration, all mice were fed a Western diet for 12 weeks. To determine how AGT secretion is regulated in hepatocytes, AAVs containing the above mutations were transducted into HepG2 cells. Results: In hepAGT-/– mice infected with AAV.loop-Mut or βsheet-Mut, plasma AGT concentrations, systolic blood pressure, and atherosclerosis were comparable to those in AAV.mAGT-infected mice. Surprisingly, plasma AGT concentrations, systolic blood pressure, and atherosclerotic lesion size in hepAGT-/– mice infected with AAV.loop/βsheet-Mut were not different from mice infected with AAV.null. In contrast, hepatic Agt mRNA abundance was elevated to a comparable magnitude as AAV.mAGT-infected mice. Immunostaining showed that AGT protein was accumulated trol and AAV containing wild-type mouse AGT as a positive control. We have demonstra ted consistently in this and previous studies tht located in the endoplasmic reticulum. Conclusions: The conserved sequences in either the loop or β-sheet region individually have no effect on AGT regulation, but the conserved sequences in both regions synergistically contribute to the secretion of AGT from hepatocytes. HIGHLIGHTS: The loop and β-sheet regions in the distal face of angiotensinogen (AGT) have highly conserved sequences across species. Mutations on either the loop or β-sheet regions do not affect plasma AGT concentrations, blood pressure, and atherosclerosis in hypercholesterolemic mice. The conserved sequences in the loop and β-sheet regions regulate the secretion of AGT from hepatocytes synergistically in vivo and in cultured cells.