Hong Shen Lu

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: Low-density lipoprotein receptor-related protein 1 (LRP1) in smooth muscle cells (SMCs) is essential for maintaining aortic wall integrity. This study investigated whether deletion of LRP1 in SMCs induces region-specific aortic pathology and evaluated a potential therapeutic strategy. Methods: Lrp1 -floxed mice were bred with Sm22-Cre +/0 mice to generate mice with SMC-LRP1 deletion (SMC-LRP1-/-) and wild-type littermates (SMC-LRP1+/+). Micro-computed tomography (micro-CT) was used to visualize the aorta, and aortic tissue sections were characterized histologically. To evaluate a potential therapeutic strategy, antisense oligonucleotides (ASOs) targeting hepatocyte-derived angiotensinogen (AGT) were administered to inhibit AGT synthesis. Results: Immunostaining and Western blotting confirmed LRP1 deletion in aortic SMCs. At 40 weeks of age, micro-CT revealed marked increases in aortic width and volume. Although dilatation occurred throughout the aorta, the infrarenal region exhibited the greatest expansion in both male and female SMC-LRP1-/-mice compared with SMC-LRP1+/+ littermates; subsequent analyses therefore focused on this region. LRP1 deletion in SMCs caused pronounced SMC loss and increased collagen deposition in the infrarenal aorta. Inhibition of hepatocyte-derived AGT with ASO attenuated infrarenal aortic dilatation and preserved aortic wall integrity in both male and female mice. Conclusions: Deletion of LRP1 in SMCs causes progressive aortic dilatation that includes the infrarenal aorta. Pharmacologic inhibition of hepatocyte-derived AGT attenuates infrarenal aortic dilatation. What Are the Clinical Implications?: Deletion of low-density lipoprotein receptor-related protein 1 (LRP1) in smooth muscle cells (SMCs) causes diffuse aortic dilatation, with spontaneous aneurysm formation most prominent in the infrarenal abdominal aorta—the most common site of abdominal aortic aneurysms (AAAs) in humans. Given the strong association between LRP1 variants and human AAAs, these findings identify SMC-derived LRP1 as a critical contributor to aortic wall integrity and provide a valuable tool for investigating disease mechanisms. Importantly, pharmacological inhibition of hepatocyte-derived angiotensinogen with an antisense oligonucleotide significantly attenuated infrarenal aortic dilatation, highlighting a promising therapeutic strategy for AAAs. GRAPHIC

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.

Angiotensinogen (AGT) deletion in hepatocytes reduces Western diet–induced adiposity and hepatic steatosis in mice maintained under conventional room-temperature (RT) housing. Given the high metabolic activity of mice, this temperature imposes adaptive metabolic responses in this species. Whether this metabolic protection persists independent of increased thermogenic demand remains unclear. In this study, we first determined whether thermoneutral housing (TN, 30 °C) alters Western diet–induced metabolic phenotypes compared with RT housing (20 °C) in wild-type mice. Although body weight did not differ significantly between housing conditions, Western diet–fed mice housed at TN exhibited brown adipose tissue whitening and more pronounced hepatic steatosis than mice housed at RT, confirming that thermoneutrality exacerbated diet-induced metabolic dysfunction. We then housed hepatocyte Agt deficient (hepAGT-/-) mice and wild-type (hepAGT+/+) littermates at TN and fed them Western diet for 12 weeks. Despite enhanced metabolic dysfunction under TN, hepatocyte AGT deletion resulted in reductions in diet-induced body weight gain, fat mass, liver weight, and hepatic triglyceride accumulation. Bulk RNA sequencing of liver revealed hepatocyte AGT deficiency–dependent alterations in lipid-metabolic pathways. Cross-temperature analysis of RT and TN housing identified 35 shared differentially expressed genes, including 27 concordantly downregulated genes enriched in lipid metabolism and transport. Extended Western diet feeding for 24 weeks confirmed sustained reductions in body weight gain, liver weight, and hepatic lipid accumulation in hepAGT-/- mice. These findings demonstrate that hepatocyte AGT deletion provides sustained protection against Western diet–induced metabolic dysfunction under thermoneutral housing, a condition that more closely recapitulates human basal metabolism. NEW & NOTEWORTHY: This study investigated hepatocyte angiotensinogen (AGT) biology during Western diet feeding in mice under thermoneutral housing, a condition relevant to human metabolism. By minimizing adaptive thermogenesis induced by standard room temperature housing, thermoneutrality more closely recapitulates human basal metabolic conditions. Under this condition, hepatocyte AGT deletion remains protective against adipo and hepatic lipid accumulation, despite exacerbated Western diet-induced metabolic dysfunction in wild-type mice, demonstrating that this protection persists in a human-relevant thermal environment. GRAPHIC

BACKGROUND: Mice harboring a missense variant (C1041G) of Fbn1 have been used extensively for aortopathy research, but do not mimic all facets of the human disease. The role of increased AngII (angiotensin II) or blood pressure in determining the arterial phenotype of these mice remains incompletely defined. The purpose of this study was to determine whether AngII, either directly or indirectly through increased blood pressure, promotes pathology in the proximal thoracic aorta and beyond. METHODS: Fbn1 ^+/+ and Fbn1 ^C1041G/+ littermates were infused with either AngII or norepinephrine via subcutaneously implanted osmotic pumps. Microcomputed tomography was used to visualize vascular pathologies. Maximal arterial dimensions were measured using in situ or microcomputed tomography images. RESULTS: AngII infusion dramatically augmented aortopathy in Fbn1 ^C1041G/+ mice. Aortic dissection was visible within 3 days of AngII infusion. Over 50% of male Fbn1 ^C1041G/+ mice died during AngII infusion, primarily due to aortic rupture in either the thoracic or abdominal regions. Surviving males had increased ascending and suprarenal aortic diameters and developed pathological lesions at the celiac and superior mesenteric branches of the abdominal aorta. Female mice had a much lower incidence of death but had increased ascending aortic and branch diameters. Although norepinephrine infusion also increased systolic blood pressure, it did not affect mortality or enlarge aortic or branch diameters in Fbn1 ^C1041G/+ mice. While microcomputed tomography identified novel pathological changes during AngII infusion, including the development of aortic branch aneurysms in the celiac and superior mesenteric arteries, the maximal diameters of the adjacent suprarenal aorta showed only modest increases in male Fbn1 ^C1041G/+ mice. CONCLUSIONS: AngII exacerbated aortic pathology in Fbn1 ^C1041G/+ mice. It also promoted the development of pathologies at aortic branch points, including the celiac and superior mesenteric arteries.

Thoracic aortic aneurysms involving the root and ascending aorta progressively enlarge and can lead to life-threatening acute aortic dissections, collectively termed thoracic aortic disease (TAD). Oxidative stress due to an excess of reactive oxygen species (ROS), has been implicated in TAD pathogenesis by promoting vascular inflammation, extracellular matrix (ECM) degradation, and smooth muscle cell (SMC) apoptosis. Cobinamide (Cbi), a potent antioxidant and vitamin B12 analog, has been reported to slow aortic aneurysm growth in TAD mouse models. We evaluated its efficacy in mice administered β-aminopropionitrile (BAPN) to induce TAD, a model in which aneurysms progress to dissections. C57BL/6J mice of both sexes were administered either BAPN alone or BAPN plus Cbi in drinking water from postnatal day 21 (P21). Survival analysis showed that 56% of mice in the BAPN group died from aortic rupture by P49, whereas mortality increased to 91% in the BAPN+Cbi group (P=0.049). Necropsy confirmed thoracic aortic rupture as the cause of death. At P35, proximal aortic analyses showed that Cbi significantly reduced ROS abundance in the ascending aorta, based on decreased dihydroethidium staining and lower oxidative stress markers, including protein carbonylation and DNA oxidation by 8-hydroxy-deoxyguanosine staining. Cbi did not affect aortic diameters by echocardiography, or elastic fiber fragmentation. Cbi was associated with reduced oxidative stress in aortic tissue, it did not prevent aortic dissection and was associated with increased rupture-related mortality in the BAPN model. These findings highlight context-dependent roles of ROS in TAD and the importance of carefully evaluating antioxidant strategies in dissection-prone settings.

Following aortic dissection (AD), there is a sustained risk of vascular complications, progressive false lumen aneurysm formation, and rupture. However, no effective therapy exists to prevent these complications, highlighting the need to elucidate the pathophysiology following AD. Elastic fibers are crucial for maintaining aortic wall integrity but are thought to have limited regenerative capacity once disrupted during AD. This study defined that elastic fibers were newly generated in the false lumen wall following AD in humans and mice. In human ADs, new elastic fibers were observed in the false lumen wall 6 months after onset. In mice with descending AD induced by β-aminopropionitrile (BAPN), elastin mRNA was markedly upregulated in the chronic phase following AD, accompanied by elastic fiber formation. These fibers coincided with smooth muscle cell (SMC) markers within the false lumen wall. Of note, lineage tracing studies demonstrated that these cells were not derived from resident SMCs but adventitial progenitor cells. In vitro experiments further demonstrated that adventitial progenitor cells produced elastic fibers while expressing SMC markers. Collectively, these findings suggest that adventitial progenitor cells differentiate into elastogenic SMC-like cells, contributing to false lumen remodeling through de novo elastic fiber formation following AD.

Cardiac microvascular endothelial cells (CMECs) dysfunction is a well-recognized mediator of heart failure with preserved ejection fraction (HFpEF), but the underlying mechanism remains unclear. Here we find that scavenger receptor class B type I (SR-B1) is predominantly expressed in CMECs and decreased significantly in HFpEF. Endothelial-specific SR-B1 deficiency exacerbates cardiac pathological remodeling and diastolic dysfunction in HFpEF, which can be prevented by endothelial SR-B1 reconstitution through adeno-associated virus serotype 1 (AAV1)-mediated delivery in endothelial-specific SR-B1-deficient mice. Single-cardiac-endothelial-cell transcriptomics and lineage-tracing system reveal that inflammatory CMECs subcluster activation is responsible for the deteriorating HFpEF progression induced by endothelial SR-B1 loss, rather than endothelial-to-mesenchymal transition. Mechanistically, SR-B1 loss drives increased CXCL10 secretion, which orchestrates CMECs activation and CXCR3-positive T-cell cardiotropism to promote diastolic dysfunction—a process associated with endothelial IRF1 activation. Most importantly, the SR-B1-CXCL10-CXCR3 axis is activated in human HFpEF cardiac tissue, and the elevated CXCL10 level in plasma is independently associated with a higher HFpEF prevalence. This study uncovers that activation of the SR-B1–CXCL10-CXCR3 axis in CMECs aggravates HFpEF pathogenesis through the accumulation of CXCR3-positive T-cells in hearts.