Autoimmune Valvular Carditis Requires Endothelial Cell TNFR1 Expression

BACKGROUND

Inflammation is a key driver of cardiovascular pathology, and many systemic autoimmune/rheumatic diseases are accompanied by increased cardiac risk. In the K/B.g7 mouse model of coexisting systemic autoantibody-mediated arthritis and valvular carditis, valve inflammation depends on macrophage production of TNF (tumor necrosis factor) and IL-6 (interleukin-6). Here, we sought to determine if other canonical inflammatory pathways participate and to determine whether TNF signaling through TNFR1 (tumor necrosis factor receptor 1) on endothelial cells is required for valvular carditis.

METHODS

We first asked if type 1, 2, or 3 inflammatory cytokine systems (typified by IFNγ, IL-4, and IL-17, respectively) were critical for valvular carditis in K/B.g7 mice, using a combination of in vivo monoclonal antibody blockade and targeted genetic ablation studies. To define the key cellular targets of TNF, we conditionally deleted its main proinflammatory receptor, TNFR1, in endothelial cells. We analyzed how the absence of endothelial cell TNFR1 affected valve inflammation, lymphangiogenesis, and the expression of proinflammatory genes and molecules.

RESULTS

We found that typical type 1, 2, and 3 inflammatory cytokine systems were not required for valvular carditis, apart from a known initial requirement of IL-4 for autoantibody production. Despite expression of TNFR1 on a wide variety of cell types in the cardiac valve, deleting TNFR1 specifically on endothelial cells protected K/B.g7 mice from valvular carditis. This protection was accompanied by reduced expression of VCAM-1 (vascular cell adhesion molecule), fewer valve-infiltrating macrophages, reduced pathogenic lymphangiogenesis, and diminished proinflammatory gene expression.

CONCLUSIONS

TNF and IL-6 are the main cytokines driving valvular carditis in K/B.g7 mice. The interaction of TNF with TNFR1 specifically on endothelial cells promotes cardiovascular pathology in the setting of systemic autoimmune/rheumatic disease, suggesting that therapeutic targeting of the TNF:TNFR1 interaction could be beneficial in this clinical context.

CD47 Promotes Autoimmune Valvular Carditis by Impairing Macrophage Efferocytosis and Enhancing Cytokine Production

Systemic autoantibody-mediated diseases accelerate chronic cardiovascular disease in humans. In the K/B.g7 mouse model of spontaneous autoantibody-mediated inflammatory arthritis, valvular carditis arises in part because of Fc receptor-mediated activation of macrophages, leading to production of pathogenic TNF and IL-6. In this study, we explored whether impaired efferocytosis mediated by the interaction of CD47-expressing apoptotic cells with signal regulatory protein α (SIRPα) on macrophages contributes to disease progression in this model. CD47-expressing apoptotic cells and SIRPα⁺ macrophages were abundant in inflamed/rheumatic cardiac valves from both mice and humans. In vivo anti-CD47 blockade both prevented and treated valvular carditis in K/B.g7 mice. Blocking CD47 enhanced macrophage efferocytosis and reduced macrophage production of TNF and IL-6. These studies highlight the CD47:SIRPα interaction as a key driver of chronic cardiac valve inflammation and suggest these molecules as potential therapeutic targets to reduce cardiovascular disease risk in autoantibody-driven inflammatory diseases.

Long-term results after semiconstrained distal radioulnar joint arthroplasty: A focus on complications

Arthroplasty of the distal radioulnar joint (DRUJ) using a semiconstrained DRUJ implant yields good outcomes according to the literature. The aim of this study was to investigate the subjective, clinical and radiographic outcomes with a special focus on complications in nine patients with a mean follow-up of 6years and to compare them with our previously published 3-year follow-up results. No subjective or objective changes were seen between the 3-year and the 6-year follow-up. In the previous study, one implant loosening and two irritations of the superficial branch of the radial nerve occurred. We saw three complications that needed surgery in addition to the three complications already found 3years after surgery. One patient with a large ulna had loosening of the cemented ulnar stem and therefore the prosthesis was explanted. One patient had an allergic reaction to the metal alloy of the prosthesis, which also led to removal. One patient had an ulnar impaction syndrome caused by too-distal placement of the implant that needed revision. Prior studies reported low complication rates. In our study, six complications occurred in four out of nine patients, requiring reoperation including two revisions and two implant removals. A precise surgical technique is mandatory to avoid the otherwise frequent complications and potential implant failures. LEVEL OF EVIDENCE: IV.

The Contribution of Autoantibodies to Inflammatory Cardiovascular Pathology

Chronic inflammation and resulting tissue damage underlie the vast majority of acquired cardiovascular disease (CVD), a general term encompassing a widely diverse array of conditions. Both innate and adaptive immune mechanisms contribute to chronic inflammation in CVD. Although maladies, such as atherosclerosis and cardiac fibrosis, are commonly conceptualized as disorders of inflammation, the cellular and molecular mechanisms that promote inflammation during the natural history of these diseases in human patients are not fully defined. Autoantibodies (AAbs) with specificity to self-derived epitopes accompany many forms of CVD in humans. Both adaptive/induced iAAbs (generated following cognate antigen encounter) and also autoantigen-reactive natural antibodies (produced independently of infection and in the absence of T cell help) have been demonstrated to modulate the natural history of multiple forms of CVD including atherosclerosis (atherosclerotic cardiovascular disease), dilated cardiomyopathy, and valvular heart disease. Despite the breadth of experimental evidence for the role of AAbs in CVD, there is a lack of consensus regarding their specific functions, primarily due to disparate conclusions reached, even when similar approaches and experimental models are used. In this review, we seek to summarize the current understanding of AAb function in CVD through critical assessment of the clinical and experimental evidence in this field. We additionally highlight the difficulty in translating observations made in animal models to human physiology and disease and provide a summary of unresolved questions that are critical to address in future studies.

CD301b/MGL2+ Mononuclear Phagocytes Orchestrate Autoimmune Cardiac Valve Inflammation and Fibrosis

BACKGROUND

Valvular heart disease is common and affects the mitral valve (MV) most frequently. Despite the prevalence of MV disease (MVD), the cellular and molecular pathways that initiate and perpetuate it are not well understood.

METHODS

K/B.g7 T-cell receptor transgenic mice spontaneously develop systemic autoantibody-associated autoimmunity, leading to fully penetrant fibroinflammatory MVD and arthritis. We used multiparameter flow cytometry, intracellular cytokine staining, and immunofluorescent staining to characterize the cells in inflamed K/B.g7 MVs. We used genetic approaches to study the contribution of mononuclear phagocytes (MNPs) to MVD in this model. Specifically, we generated K/B.g7 mice in which either CX3CR1 or CD301b/macrophage galactose N-acetylgalactosamine-specific lectin 2 (MGL2)-expressing MNPs were ablated. Using K/B.g7 mice expressing Cx3Cr1-Cre, we conditionally deleted critical inflammatory molecules from MNPs, including the Fc-receptor signal-transducing tyrosine kinase Syk and the cell adhesion molecule very late antigen-4. We performed complementary studies using monoclonal antibodies to block key inflammatory molecules. We generated bone marrow chimeric mice to define the origin of the inflammatory cells present in the MV and to determine which valve cells respond to the proinflammatory cytokine tumor necrosis factor (TNF). Finally, we examined specimens from patients with rheumatic heart disease to correlate our findings to human pathology.

RESULTS

MNPs comprised the vast majority of MV-infiltrating cells; these MNPs expressed CX3CR1 and CD301b/MGL2. Analogous cells were present in human rheumatic heart disease valves. K/B.g7 mice lacking CX3CR1 or in which CD301b/MGL2-expressing MNPs were ablated were protected from MVD. The valve-infiltrating CD301b/MGL2⁺ MNPs expressed tissue-reparative molecules including arginase-1 and resistin-like molecule α. These MNPs also expressed the proinflammatory cytokines TNF and interleukin-6, and antibody blockade of these cytokines prevented MVD. Deleting Syk from CX3CR1-expressing MNPs reduced their TNF and interleukin-6 production and also prevented MVD. TNF acted through TNF receptor-1 expressed on valve-resident cells to increase the expression of vascular cell adhesion molecule-1. Conditionally deleting the vascular cell adhesion molecule-1 ligand very late antigen-4 from CX3CR1-expressing MNPs prevented MVD.

CONCLUSIONS

CD301b/MGL2⁺ MNPs are key drivers of autoimmune MVD in K/B.g7 mice and are also present in human rheumatic heart disease. We define key inflammatory molecules that drive MVD in this model, including Syk, TNF, interleukin-6, very late antigen-4, and vascular cell adhesion molecule-1.

Implantation of completely biological engineered grafts following decellularization into the sheep femoral artery

The performance of completely biological, decellularized engineered allografts in a sheep model was evaluated to establish clinical potential of these unique arterial allografts. The 4-mm-diameter, 2-3-cm-long grafts were fabricated from fibrin gel remodeled into an aligned tissue tube in vitro by ovine dermal fibroblasts. Decellularization and subsequent storage had little effect on graft properties, with burst pressure exceeding 4000 mmHg and the same compliance as the ovine femoral artery. Grafts were implanted interpositionally in the femoral artery of six sheep (n=9), with contralateral sham controls (n=3). At 8 weeks (n=5) and 24 weeks (n=4), all grafts were patent and showed no evidence of dilatation or mineralization. Mid-graft lumen diameter was unchanged. Extensive recellularization occurred, with most cells expressing αSMA. Endothelialization was complete by 24 weeks with elastin deposition evident. These completely biological grafts possessed circumferential alignment/mechanical anisotropy characteristic of native arteries and were cultured only 5 weeks prior to decellularization and storage as "off-the-shelf" grafts.

Hypoxic culture and insulin yield improvements to fibrin-based engineered tissue

We examined the effect of insulin supplementation and hypoxic culture (2% vs. 20% oxygen tension) on collagen deposition and mechanical properties of fibrin-based tubular tissue constructs seeded with neonatal human dermal fibroblasts. The results presented here demonstrate that constructs cultured under hypoxic conditions with insulin supplementation increased in collagen density by approximately five-fold and both the ultimate tensile strength (UTS) and modulus by more than three-fold compared with normoxic (20% oxygen tension), noninsulin supplemented controls. In addition, collagen deposited on a per-cell basis increased by approximately four-fold. Interaction was demonstrated for hypoxia and insulin in combination in terms of UTS and collagen production on a per-cell basis. This interaction resulted from two distinct processes involved in collagen fibril formation. Western blot analysis showed that insulin supplementation alone increased Akt phosphorylation and the combined treatment increased collagen prolyl-4-hydroxylase. These molecules are distinct regulators of collagen deposition, having an impact at both the transcriptional and posttranslational modification stages of collagen fibril formation that, in turn, increase collagen density in the tissue constructs. These findings highlight the potential of utilizing insulin supplementation and hypoxic culture in combination to increase the mechanical strength and stiffness of fibrin-based engineered tissues.

Implantable arterial grafts from human fibroblasts and fibrin using a multi-graft pulsed flow-stretch bioreactor with noninvasive strength monitoring

Tissue-engineered arteries based on entrapment of human dermal fibroblasts in fibrin gel yield completely biological vascular grafts that possess circumferential alignment characteristic of native arteries and essential to their mechanical properties. A bioreactor was developed to condition six grafts in the same culture medium while being subjected to similar cyclic distension and transmural flow resulting from pulsed flow distributed among the graft lumens via a manifold. The lumenal pressure and circumferential stretch were noninvasively monitored and used to calculate stiffness in the range of 80-120 mmHg and then to successfully predict graft burst strength. The length of the graft was incrementally shortened during bioreactor culture to maintain circumferential alignment and achieve mechanical anisotropy comparable to native arteries. After 7-9 weeks of bioreactor culture, the fibrin-based grafts were extensively remodeled by the fibroblasts into circumferentially-aligned tubes of collagen and other extracellular matrix with burst pressures in the range of 1400-1600 mmHg and compliance comparable to native arteries. The tissue suture retention force was also suitable for implantation in the rat model and, with poly(lactic acid) sewing rings entrapped at both ends of the graft, also in the ovine model. The strength achieved with a biological scaffold in such a short duration is unprecedented for an engineered artery.