Zoledronate alters natural progression of tissue-engineered vascular grafts.

Macrophages are a critical driver of neovessel formation in tissue-engineered vascular grafts (TEVGs), but also contribute to graft stenosis, a leading clinical trial complication. Macrophage depletion via liposomal delivery of clodronate, a first-generation bisphosphonate, mitigates stenosis, but simultaneously leads to a complete lack of tissue development in TEVGs. This result and the associated difficulty of utilizing liposomal delivery means that clodronate may not be an ideal means of preventing graft stenosis. Newer generation bisphosphonates, such as zoledronate, may have differential effects on graft development with more facile drug delivery. We sought to examine the effect of zoledronate on TEVG neotissue formation and its potential application for mitigating TEVG stenosis. Thus, mice implanted with TEVGs received zoledronate or no treatment and were monitored by serial ultrasound for graft dilation and stenosis. After two weeks, TEVGs were explanted for histological examination. The overall graft area and remaining graft material (polyglycolic-acid) were higher in the zoledronate treatment group. These effects were associated with a corresponding decrease in macrophage infiltration. In addition, zoledronate affected the deposition of collagen in TEVGs, specifically, total and mature collagen. These differences may be, in part, explained by a depletion of leukocytes within the bone marrow that subsequently led to a decrease in the number of tissue-infiltrating macrophages. TEVGs from zoledronate-treated mice demonstrated a significantly greater degree of smooth muscle cell presence. There was no statistical difference in graft patency between treatment and control groups. While zoledronate led to a decrease in the number of macrophages in the TEVGs, the severity of stenosis appears to have increased significantly. Zoledronate treatment demonstrates that the process of smooth muscle cell-mediated neointimal hyperplasia may occur separately from a macrophage-mediated mechanism.

Implantation of VEGF-functionalized cell-free vascular grafts: regenerative and immunological response.

Recently, our group demonstrated that immobilized VEGF can capture flowing endothelial cells (ECs) from the blood in vitro and promote endothelialization and patency of acellular tissue-engineered vessels (A-TEVs) into the arterial system of an ovine animal model. Here, we demonstrate implantability of submillimeter diameter heparin and VEGF-decorated A-TEVs in a mouse model and discuss the cellular and immunologic response. At 1 mo postimplantation, the graft lumen was fully endothelialized, as shown by expression of EC markers such as CD144, eNOS, CD31, and VEGFR2. Interestingly, the same cells coexpressed leukocyte/macrophage (Mϕ) markers CD14, CD16, VEGFR1, CD38, and EGR2. Notably, there was a stark difference in the cellular makeup between grafts containing VEGF and those containing heparin alone. In VEGF-containing grafts, infiltrating monocytes (MCs) converted into anti-inflammatory M2-Mϕs, and the grafts developed well-demarcated luminal and medial layers resembling those of native arteries. In contrast, in grafts containing only heparin, MCs converted primarily into M1-Mϕs, and the endothelial and smooth muscle layers were not well defined. Our results indicate that VEGF may play an important role in regulating A-TEV patency and regeneration, possibly by regulating the inflammatory response to the implants.-Smith, R. J., Jr., Yi, T., Nasiri, B., Breuer, C. K., Andreadis, S. T. Implantation of VEGF-functionalized cell-free vascular grafts: regenerative and immunological response.

Discovery of a novel fluorescent chemical probe suitable for evaluation of neuropilin-1 binding of small molecules.

Neuropilin-1 (NRP1) is emerging as an important molecule in immune signaling where it has been shown to modulate the actions of TGF-ß1 in macrophages and regulatory T cells. The development of cost-effective and reliable assays for NRP1 binding is therefore important. We synthesized three new NRP1 small molecule fluorophores and examined their performance as fluorescent polarization probes. One molecule DS108 exhibited favorable binding and fluorescent characteristics and allowed us to establish a simple assay suitable for medium to high throughput screening of small molecules.

Intratumoral Delivery of Interferonγ-Secreting Mesenchymal Stromal Cells Repolarizes Tumor-Associated Macrophages and Suppresses Neuroblastoma Proliferation In Vivo.

Neuroblastoma, the most common extracranial solid tumor in childhood, remains a therapeutic challenge. However, one promising patient treatment strategy is the delivery of anti-tumor therapeutic agents via mesenchymal stromal cell (MSC) therapy. MSCs have been safely used to treat genetic bone diseases such as osteogenesis imperfecta, cardiovascular diseases, autoimmune diseases, and cancer. The pro-inflammatory cytokine interferon-gamma (IFNγ) has been shown to decrease tumor proliferation by altering the tumor microenvironment (TME). Despite this, clinical trials of systemic IFNγ therapy have failed due to the high blood concentration required and associated systemic toxicities. Here, we developed an intra-adrenal model of neuroblastoma, characterized by liver and lung metastases. We then engineered MSCs to deliver IFNγ directly to the TME. In vitro, these MSCs polarized murine macrophages to the M1 phenotype. In vivo, we attained a therapeutically active TME concentration of IFNγ without increased systemic concentration or toxicity. The TME-specific IFNγ reduced tumor growth rate and increased survival in two models of T cell deficient athymic nude mice. Absence of this benefit in NOD SCID gamma (NSG) immunodeficient mouse model indicates a mechanism dependent on the innate immune system. IL-17 and IL-23p19, both uniquely M1 polarization markers, transiently increased in the tumor interstitial fluid. Finally, the MSC vehicle did not promote tumor growth. These findings reveal that MSCs can deliver effective cytokine therapy directly to the tumor while avoiding systemic toxicity. This method transiently induces inflammatory M1 macrophage polarization, which reduces tumor burden in our novel neuroblastoma murine model. Stem Cells 2018;36:915-924.

Angiotensin II receptor I blockade prevents stenosis of tissue engineered vascular grafts.

We previously developed a tissue-engineered vascular graft (TEVG) made by seeding autologous cells onto a biodegradable tubular scaffold, in an attempt to create a living vascular graft with growth potential for use in children undergoing congenital heart surgery. Results of our clinical trial showed that the TEVG possesses growth capacity but that its widespread clinical use is not yet advisable due to the high incidence of TEVG stenosis. In animal models, TEVG stenosis is caused by increased monocytic cell recruitment and its classic ("M1") activation. Here, we report on the source and regulation of these monocytes. TEVGs were implanted in wild-type, CCR2 knockout ( Ccr2-/-), splenectomized, and spleen graft recipient mice. We found that bone marrow-derived Ly6C+hi monocytes released from sequestration by the spleen are the source of mononuclear cells infiltrating the TEVG during the acute phase of neovessel formation. Furthermore, short-term administration of losartan (0.6 g/L, 2 wk), an angiotensin II type 1 receptor antagonist, significantly reduced the macrophage populations (Ly6C+/-/F480+) in the scaffolds and improved long-term patency in TEVGs. Notably, the combined effect of bone marrow-derived mononuclear cell seeding with short-term losartan treatment completely prevented the development of TEVG stenosis. Our results provide support for pharmacologic treatment with losartan as a strategy to modulate monocyte infiltration into the grafts and thus prevent TEVG stenosis.-Ruiz-Rosado, J. D. D., Lee, Y.-U., Mahler, N., Yi, T., Robledo-Avila, F., Martinez-Saucedo, D., Lee, A. Y., Shoji, T., Heuer, E., Yates, A. R., Pober, J. S., Shinoka, T., Partida-Sanchez, S., Breuer, C. K. Angiotensin II receptor I blockade prevents stenosis of tissue engineered vascular grafts.

Identification of danthron as an isoform-specific inhibitor of HEME OXYGENASE-1/cytochrome P450 reductase interaction with anti-tumor activity.

BACKGROUND: Heme oxygenase (HO) catalyzes NADPH-dependent degradation of heme to liberate iron, carbon monoxide and biliverdin. The interaction between HO and cytochrome P450 reductase (CPR), an electron donor, is essential for HO activity. HO-1 is a stress-inducible isoform whereas HO-2 is constitutively expressed. HO-1 induction is commonly seen in cancers and impacts disease progression, supporting the possibility of targeting HO-1 for cancer therapy. METHODS: We employed a cell-based bioluminescence resonance energy transfer assay to screen compounds with ability to inhibit HO-1/CPR interaction. The effect of the identified compound on HO-1/CPR interaction was confirmed by pull down assay. Moreover, the anti-tumorigenic activity of the identified compound on HO-1-enhanced tumor growth and migration was assessed by trypan blue exclusion method and wound healing assay. RESULTS: Danthron was identified as an effective small molecule able to interfere with the interaction between HO-1 and CPR but not HO-2 and CPR. Additional experiments with structural analogues of danthron revealed that the positions of hydroxyl moieties significantly affected the potency of inhibition on HO-1/CPR interaction. Pull-down assay confirmed that danthron inhibited the interaction of CPR with HO-1 but not HO-2. Danthron suppressed growth and migration of HeLa cells with stable HO-1 overexpression but not mock cells. In contrast, anthrarufin, a structural analog with no ability to interfere HO-1/CPR interaction, exhibited no significant effect on HO-1-overexpressing HeLa cells. CONCLUSIONS: These findings demonstrate that danthron is an isoform-specific inhibitor for HO-1/CPR interaction and may serve as a lead compound for novel anticancer drug.

Fast-degrading bioresorbable arterial vascular graft with high cellular infiltration inhibits calcification of the graft.

OBJECTIVE: Bioresorbable vascular grafts are biologically active grafts that are entirely reconstituted by host-derived cells through an inflammation-mediated degradation process. Calcification is a detrimental condition that can severely affect graft performance. Therefore, prevention of calcification is of great importance to the success of bioresorbable arterial vascular grafts. The objective of this study was to test whether fast-degrading (FD) bioresorbable arterial grafts with high cellular infiltration will inhibit calcification of grafts. METHODS: We created two versions of bioresorbable arterial vascular grafts, slow-degrading (SD) grafts and FD grafts. Both grafts had the same inner layer composed of a 50:50 poly(l-lactic-co-ε-caprolactone) copolymer scaffold. However, the outer layer of SD grafts was composed of poly(l-lactic acid) nanofiber, whereas the outer layer of FD grafts was composed of a combination of poly(l-lactic acid) and polyglycolic acid nanofiber. Both grafts were implanted in 8- to 10-week-old female mice (n = 15 in the SD group, n = 10 in the FD group) as infrarenal aortic interposition conduits. Animals were observed for 8 weeks. RESULTS: von Kossa staining showed calcification in 7 of 12 grafts in the SD group but zero in the FD group (P < .01, χ2 test). The cell number in the outer layer of FD grafts was significantly higher than in the SD grafts (SD, 0.87 ± 0.65 × 103/mm2; FD, 2.65 ± 1.91 × 103/mm2; P = .02). CONCLUSIONS: The FD bioresorbable arterial vascular graft with high cellular infiltration into the scaffold inhibited calcification of grafts.

TGF-ß receptor 1 inhibition prevents stenosis of tissue-engineered vascular grafts by reducing host mononuclear phagocyte activation.

Stenosis is a critical problem in the long-term efficacy of tissue-engineered vascular grafts (TEVGs). We previously showed that host monocyte infiltration and activation within the graft drives stenosis and that TGF-ß receptor 1 (TGF-ßR1) inhibition can prevent it, but the latter effect was attributed primarily to inhibition of mesenchymal cell expansion. In this study, we assessed the effects of TGF-ßR1 inhibition on the host monocytes. Biodegradable TEVGs were implanted as inferior vena cava interposition conduits in 2 groups of C57BL/6 mice (n = 25/group): unseeded grafts and unseeded grafts with TGF-ßR1 inhibitor systemic treatment for the first 2 wk. The TGF-ßR1 inhibitor treatment effectively improved TEVG patency at 6 mo compared to the untreated control group (91.7 vs. 48%, P < 0.001), which is associated with a reduction in classic activation of mononuclear phagocytes. Consistent with these findings, the addition of rTGF-ß to LPS/IFN-γ-stimulated monocytes enhanced secretion of inflammatory cytokines TNF-α, IL-12, and IL-6; this effect was blocked by TGF-ßR1 inhibition (P < 0.0001). These findings suggest that the TGF-ß signaling pathway contributes to TEVG stenosis by inducing classic activation of host monocytes. Furthermore, blocking monocyte activation by TGF-ßR1 inhibition provides a viable strategy for preventing TEVG stenosis while maintaining neotissue formation.-Lee, Y.-U., de Dios Ruiz-Rosado, J., Mahler, N., Best, C. A., Tara, S., Yi, T., Shoji, T., Sugiura, T., Lee, A. Y., Robledo-Avila, F., Hibino, N., Pober, J. S., Shinoka, T., Partida-Sanchez, S., Breuer, C. K. TGF-ß receptor 1 inhibition prevents stenosis of tissue-engineered vascular grafts by reducing host mononuclear phagocyte activation.

Interferon-γ-mediated allograft rejection exacerbates cardiovascular disease of hyperlipidemic murine transplant recipients.

RATIONALE: Transplantation, the most effective therapy for end-stage organ failure, is markedly limited by early-onset cardiovascular disease (CVD) and premature death of the host. The mechanistic basis of this increased CVD is not fully explained by known risk factors. OBJECTIVE: To investigate the role of alloimmune responses in promoting CVD of organ transplant recipients. METHODS AND RESULTS: We established an animal model of graft-exacerbated host CVD by combining murine models of atherosclerosis (apolipoprotein E-deficient recipients on standard diet) and of intra-abdominal graft rejection (heterotopic cardiac transplantation without immunosuppression). CVD was absent in normolipidemic hosts receiving allogeneic grafts and varied in severity among hyperlipidemic grafted hosts according to recipient-donor genetic disparities, most strikingly across an isolated major histocompatibility complex class II antigen barrier. Host disease manifested as increased atherosclerosis of the aorta that also involved the native coronary arteries and new findings of decreased cardiac contractility, ventricular dilatation, and diminished aortic compliance. Exacerbated CVD was accompanied by greater levels of circulating cytokines, especially interferon-γ and other Th1-type cytokines, and showed both systemic and intralesional activation of leukocytes, particularly T-helper cells. Serological neutralization of interferon-γ after allotransplantation prevented graft-related atherosclerosis, cardiomyopathy, and aortic stiffening in the host. CONCLUSIONS: Our study reveals that sustained activation of the immune system because of chronic allorecognition exacerbates the atherogenic diathesis of hyperlipidemia and results in de novo cardiovascular dysfunction in organ transplant recipients.

The innate immune system contributes to tissue-engineered vascular graft performance.

The first clinical trial of tissue-engineered vascular grafts (TEVGs) identified stenosis as the primary cause of graft failure. In this study, we aimed to elucidate the role of the host immune response in the development of stenosis using a murine model of TEVG implantation. We found that the C.B-17 wild-type (WT) mouse (control) undergoes a dramatic stenotic response, which is nearly completely abolished in the immunodeficient SCID/beige (bg) variant. SCID mice, which lack an adaptive immune system due to the absence of T and B lymphocytes, experienced rates of stenosis comparable to WT controls (average luminal diameter, WT: 0.071 ± 0.035 mm, SCID: 0.137 ± 0.032 mm, SCID/bg: 0.804 ± 0.039 mm; P < 0.001). The bg mutation is characterized by NK cell and platelet dysfunction, and systemic treatment of WT mice with either NK cell-neutralizing (anti-NK 1.1 antibody) or antiplatelet (aspirin/Plavix [clopidogrel bisulfate]; Asp/Pla) therapy achieved nearly half the patency observed in the SCID/bg mouse (NK Ab: 0.356 ± 0.151 mm, Asp/Pla: 0.452 ± 0.130 mm). Scaffold implantation elicited a blunted immune response in SCID/bg mice, as demonstrated by macrophage number and mRNA expression of proinflammatory cytokines in TEVG explants. Implicating the initial innate immune response as a critical factor in graft stenosis may provide a strategy for prognosis and therapy of second-generation TEVGs.

Comparison of inducible versus constitutive expression of plectasin on yields and antimicrobial activities in Pichia pastoris.

BACKGROUND: Plectasin might serve as a substitute for traditional antibiotics, but its yields and antimicrobial activities warrant further investigation. OBJECTIVE: To identify the influence of inducible versus constitutive expression of plectasin on yields and antimicrobial activities. METHODS: Through SOE-PCR, a recombinant plectasin gene was generated and inserted into inducible (pPICZαA) and constitutive (pGAPZαA) vectors in order to create Pichia pastoris GS115 strains. After 120 h of fermentation, supernatants were purified by an AKTA purifier using nickel columns. Minimal inhibitory concentration (MIC) and inhibition zone assays were performed after Tricine-SDS-PAGE. RESULTS: After 120 h of fermentation, the yield of constitutive plectasin (370 µg/ml) was much lower than that from inducible vector (880 µg/ml) (P < 0.05). However, constitutive strain reached its plateau phase faster and keep more consistent yield (P < 0.05). The MICs of inducible plectasin against Methicillin-resistant Staphylococcus aureus (MRSA) 15471118, vancomycin-resistant Enterococcus feces (VREF), and penicillin-resistant Streptococcus pneumonia (PRSP) 31355 were 64, 32, and 64 µg/ml, respectively, while those of constitutive plectasin were 4, 4, and 16 µg/ml. No significant differences were observed in antimicrobial activities between inducible and constitutive plectasin for MRSA 15471118, VREF and PRSP 31355 (all P ï¼ž 0.05). However, constitutive plectasin had a larger inhibition zone than inducible plectasin with the same mass. CONCLUSIONS: Although P. pastoris GS115 (pGAPZαA-Plectasin-GS115) had lower expression than P. pastoris GS115 (pPICZαA-plectasin-GS115), it reached the plateau phase faster, had steadier yields and showed superiority in antimicrobial activities. Therefore, pGAPZαA might be more suitable for expression of plectasin in GS115 compared with pPICZαA.

Cilostazol, Not Aspirin, Prevents Stenosis of Bioresorbable Vascular Grafts in a Venous Model.

OBJECTIVE: Despite successful translation of bioresorbable vascular grafts for the repair of congenital heart disease, stenosis remains the primary cause of graft failure. In this study, we investigated the efficacy of long-term treatment with the antiplatelet drugs, aspirin and cilostazol, in preventing stenosis and evaluated the effect of these drugs on the acute phase of inflammation and tissue remodeling. APPROACH AND RESULTS: C57BL/6 mice were fed a drug-mixed diet of aspirin, cilostazol, or normal chow during the course of follow-up. Bioresorbable vascular grafts, composed of poly(glycolic acid) mesh sealed with poly(l-lactide-co-ε-caprolactone), were implanted as inferior vena cava interposition conduits and followed up for 2 weeks (n=10 per group) or 24 weeks (n=15 per group). Both aspirin and cilostazol suppressed platelet activation and attachment onto the grafts. On explant at 24 weeks, well-organized neotissue had developed, and cilostazol treatment resulted in 100% graft patency followed by the aspirin (67%) and no-treatment (60%) groups (P<0.05). Wall thickness and smooth muscle cell proliferation in the neotissue of the cilostazol group were decreased when compared with that of the no-treatment group at 24 weeks. In addition, cilostazol was shown to have an anti-inflammatory effect on neotissue at 2 weeks by regulating the recruitment and activation of monocytes. CONCLUSIONS: Cilostazol prevents stenosis of bioresorbable vascular graft in a mouse inferior vena cava implantation model up to 24 weeks and is accompanied by reduction of smooth muscle cell proliferation and acute inflammation.

Phytoremediation potential of transplanted bare-root seedlings of trees for lead/zinc and copper mine tailings.

Selecting plant species that can overcome unfavorable conditions and increase the recovery of degraded mined lands remains a challenge. A pot experiment was conducted to evaluate the feasibility of using transplanted tree seedlings for the phytoremediation of lead/zinc and copper mine tailings. One-year-old bare-root of woody species (Rhus chinensis Mill, Quercus acutissima Carruth, Liquidambar formosana Hance, Vitex trifolia Linn. var. simplicifolia Cham, Lespedeza cuneata and Amorpha fruticosa Linn) were transplanted into pots with mine tailings and tested as potential metal-tolerant plants. Seedling survival, plant growth, root trait, nutrient uptake, and metal accumulation and translocation were assessed. The six species grew in both tailings and showed different tolerance level. A. fruticosa was highly tolerant of Zn, Pb and Cu, and grew normally in both tailings. Metal concentrations were higher in the roots than in the shoots of the six species. All of the species had low bioconcentration and translocation factor values. However, R. chinensis and L. formosana had significantly higher translocation factor values for Pb (0.88) and Zn (1.78) than the other species. The nitrogen-fixing species, A. fruticosa, had the highest tolerance and biomass production, implying that it has great potential in the phytoremediation of tailing areas in southern China.

Evaluation of remodeling process in small-diameter cell-free tissue-engineered arterial graft.

OBJECTIVE: Autologous grafts are used to repair atherosclerotic cardiovascular diseases; however, many patients lack suitable donor graft tissue. Recently, tissue engineering techniques have emerged to make biologically active blood vessels. We applied this technique to produce arterial grafts using established biodegradable materials without cell seeding. The grafts were evaluated in vivo for vessel remodeling during 12 months. METHODS: Poly(L-lactide-co-ε-caprolactone) scaffolds reinforced by poly(lactic acid) (PLA) fiber were prepared as arterial grafts. Twenty-eight cell-free grafts were implanted as infrarenal aortic interposition grafts in 8-week-old female SCID/Bg mice. Serial ultrasound and micro computed tomography angiography were used to monitor grafts after implantation. Five grafts were harvested for histologic assessments and reverse transcription-quantitative polymerase chain reaction analysis at time points ranging from 4 months to 1 year after implantation. RESULTS: Micro computed tomography indicated that most implanted mice displayed aneurysmal changes (three of five mice at 4 months, four of five mice at 8 months, and two of five mice at 12 months). Histologic assessments demonstrated extensive tissue remodeling leading to the development of well-circumscribed neovessels with an endothelial inner lining, a neointima containing smooth muscle cells and elastin, and a collagen-rich extracellular matrix. There were a few observed calcified deposits, located around residual PLA fibers at 12 months after implantation. Macrophage infiltration into the scaffold, as evaluated by F4/80 immunohistochemical staining, remained after 12 months and was focused mostly around residual PLA fibers. Reverse transcription-quantitative polymerase chain reaction analysis revealed that gene expression of Itgam, a marker for macrophages, and of matrix metalloproteinase 9 was higher than in native aorta during the course of 12 months, indicating prolonged inflammation (Itgam at 8 months: 11.75 ± 0.99 vs native aorta, P < .01; matrix metalloproteinase 9 at 4 months: 4.35 ± 3.05 vs native aorta, P < .05). CONCLUSIONS: In this study, we demonstrated well-organized neotissue of cell-free biodegradable arterial grafts. Although most grafts experienced aneurysmal change, such findings provide insight into the process of tissue-engineered vascular graft remodeling and should allow informed rational design of the next generation of arterial grafts.

Protective effects of metformin on reproductive function in obese male rats induced by high-fat diet.

PURPOSE: The study aims to elucidate the changes in testicular spermatogenic function in high-fat diet (HFD)-induced obese rats and to evaluate the protective effects of metformin intervention. METHODS: Male Sprague-Dawley rats (n = 18) were randomly divided into a control group (standard diet), an HFD group, and a metformin group (HFD + metformin at 100 mg/kg, once daily by oral gavage). After 8 weeks, rats were euthanized, and the weights of body and testes were measured. Testis and epididymis were dissected and hematoxylin-eosin-stained for histopathological examination and semen parameter analysis. Blood samples were collected for assessment of sex hormones and metabolic parameters (serum glucose, insulin, and leptin). Spermatogenic cell apoptosis was accessed by TUNEL. RESULTS: Compared with the control group, the final body weight and weight gain were significantly higher in HFD rats, while the testicle weight and coefficients were lower. In HFD rats, metformin treatment induced weight loss and increased testicle weight (P < 0.05). In HFD rats, obvious pathological changes in the testicular tissue were characterized by small, atrophic, and distorted seminiferous tubules and destroyed basement membrane. Metformin treatment protected against the HFD-induced decrease in the number of spermatogonia, Sertoli cells, and Leydig cells (P < 0.05); ameliorated the HFD-induced increases in serum glucose, insulin, leptin, and estrogen; and decreased serum testosterone (P < 0.05) and reduced the rate of testicular cell apoptosis in obese male rats. Finally, metformin significantly improved semen parameters (including concentration, viability, motility, and normal morphology) in HFD rats (P < 0.05). CONCLUSIONS: HFD-induced obesity in rats results in detrimental effects on spermatogenesis, semen quality, endogenous hormones, and testicular cell apoptosis. Metformin intervention improved the semen parameters, possibly due to its effects on weight loss, increased testicular weight, reduced testicular cell apoptosis, and resulted in restoration of hormonal homeostasis and correction of metabolic disorder.

Alloantibody and complement promote T cell-mediated cardiac allograft vasculopathy through noncanonical nuclear factor-κB signaling in endothelial cells.

BACKGROUND: Cardiac allograft vasculopathy is the major cause of late allograft loss after heart transplantation. Cardiac allograft vasculopathy lesions contain alloreactive T cells that secrete interferon-γ, a vasculopathic cytokine, and occur more frequently in patients with donor-specific antibody. Pathological interactions between these immune effectors, representing cellular and humoral immunity, respectively, remain largely unexplored. METHODS AND RESULTS: We used human panel reactive antibody to form membrane attack complexes on allogeneic endothelial cells in vitro and in vivo. Rather than inducing cytolysis, membrane attack complexes upregulated inflammatory genes, enhancing the capacity of endothelial cells to recruit and activate allogeneic interferon-γ--producing CD4(+) T cells in a manner dependent on the activation of noncanonical nuclear factor-κB signaling. Noncanonical nuclear factor-κB signaling was detected in situ within endothelial cells both in renal biopsies from transplantation patients with chronic antibody-mediated rejection and in panel-reactive antibody--treated human coronary artery xenografts in immunodeficient mice. On retransplantation into immunodeficient hosts engrafted with human T cells, panel-reactive antibody--treated grafts recruited more interferon-γ--producing T cells and enhanced cardiac allograft vasculopathy lesion formation. CONCLUSIONS: Alloantibody and complement deposition on graft endothelial cells activates noncanonical nuclear factor-κB signaling, initiating a proinflammatory gene program that enhances alloreactive T cell activation and development of cardiac allograft vasculopathy. Noncanonical nuclear factor-κB signaling in endothelial cells, observed in human allograft specimens and implicated in lesion pathogenesis, may represent a target for new pharmacotherapies to halt the progression of cardiac allograft vasculopathy.

Regional Differences in Vascular Graft Degradation and Regeneration Contribute to Dilation.

Severe coronary artery disease is often treated with a coronary artery bypass graft using an autologous blood vessel. When this is not available, a commercially available synthetic graft can be used as an alternative but is associated with high failure rates and complications. Therefore, the research focus has shifted toward the development of biodegradable, regenerative vascular grafts that can convert into neoarteries. We previously developed an electrospun tropoelastin (TE)-polyglycerol sebacate (PGS) vascular graft that rapidly regenerated into a neoartery, with a cellular composition and extracellular matrix approximating the native aorta. We noted, however, that the TE-PGS graft underwent dilation until sufficient neotissue had been regenerated. This study investigated the mechanisms behind the observed dilation following TE-PGS vascular graft implantation in mice. We saw more pronounced dilation at the graft middle compared with the graft proximal and graft distal regions at 8 weeks postimplantation. Histological analysis revealed less degradation at the graft middle, although the remaining graft material appeared pitted, suggesting compromised structural and mechanical integrity. We also observed delayed cellular infiltration and extracellular matrix (ECM) deposition at the graft middle, corresponding with the area's reduced ability to resist dilation. In contrast, the graft proximal region exhibited greater degradation and significantly enhanced cellular infiltration and ECM regeneration. The nonuniform dilation was attributed to the combined effect of the regional differences in graft degradation and arterial regeneration. Consideration of these findings is crucial for graft optimization prior to its use in clinical applications.

Transmural macrophage migration into an arterial bioresorbable vascular graft promotes inflammatory-mediated response and collagen deposition for vascular remodeling.

Macrophages are the primary cell type orchestrating bioresorbable vascular graft (BVG) remodeling and infiltrate from three sources: the adjacent native vessel, circulating blood, and transmural migration from outer surface of the graft. To elucidate the kinetics of macrophage infiltration into the BVG, we fabricated two different bilayer arterial BVGs consisting of a macroporous sponge layer and a microporous electrospun (ES) layer. The Outer ES graft was designed to reduce transmural cell infiltration from the outer surface and the Inner ES graft was designed to reduce cell infiltration from the circulation. These BVGs were implanted in mice as infrarenal abdominal aorta grafts and extracted at 1, 4, and 8 weeks (n = 5, 10, and 10 per group, respectively) for evaluation. Cell migration into BVGs was higher in the Inner ES graft than in the Outer ES graft. For Inner ES grafts, the majority of macrophage largely expressed a pro-inflammatory M1 phenotype but gradually changed to tissue-remodeling M2 macrophages. In contrast, in Outer ES grafts macrophages primarily maintained an M1 phenotype. The luminal surface endothelialized faster in the Inner ES graft; however, the smooth muscle cell layer was thicker in the Outer ES graft. Collagen fibers were more abundant and matured faster in the Inner ES graft than that in the Outer ES graft. In conclusion, compared to macrophages infiltrating from the circulating blood, transmural macrophages from outside promote the acute inflammatory-mediated response for vascular remodeling and subsequent collagen deposition within BVGs. STATEMENT OF SIGNIFICANCE: To elucidate the kinetics of macrophage infiltration into the bioresorbable vascular graft (BVG), two different bilayer arterial BVGs were implanted in mice as infrarenal abdominal aorta grafts. Cell migration into BVGs was higher in the inner electrospun graft which cells mainly infiltrate from outer surface than in the outer electrospun graft which cells mainly infiltrate from the circulating blood. In the inner electrospun grafts, the majority of macrophages changed from the M1 phenotype to the M2 phenotype, however, outer electrospun grafts maintained the M1 phenotype. Collagen fibers matured faster in the Inner electrospun graft. Compared to macrophages infiltrating from the circulating blood, transmural macrophages from outside promote the acute inflammatory-mediated response for vascular remodeling and subsequent collagen deposition within BVGs.

Reperfusion injury intensifies the adaptive human T cell alloresponse in a human-mouse chimeric artery model.

OBJECTIVE: Perioperative nonimmune injuries to an allograft can decrease graft survival. We have developed a model for studying this process using human materials. METHODS AND RESULTS: Human artery segments were transplanted as infrarenal aortic interposition grafts into an immunodeficient mouse host, allowed to "heal in" for 30 days, and then retransplanted into a second mouse host. To induce a reperfusion injury, the healed-in artery segments were incubated for 3 hours under hypoxic conditions ex vivo before retransplantation. To induce immunologic rejection, the animals receiving the retransplanted artery segment were adoptively transferred with human peripheral blood mononuclear cells or purified T cells from a donor allogeneic to the artery 1 week before surgery. To compare rejection of injured versus healthy tissues, these manipulations were combined. Results were analyzed ex vivo by histology, morphometry, immunohistochemistry, and mRNA quantitation or in vivo by ultrasound. Our results showed that reperfusion injury, which otherwise heals with minimal sequelae, intensifies the degree of allogeneic T cell-mediated injury to human artery segments. CONCLUSIONS: We developed a new human-mouse chimeric model demonstrating interactions of reperfusion injury and alloimmunity using human cells and tissues that may be adapted to study other forms of nonimmune injury and other types of adaptive immune responses.

Neutralizing IL-6 reduces human arterial allograft rejection by allowing emergence of CD161+ CD4+ regulatory T cells.

Perioperative injuries to an allograft exacerbate graft rejection, which in humans is primarily mediated by effector memory T cells. IL-6 transcripts in human coronary artery segments rapidly increase posttransplantation into immunodeficient mouse hosts compared with those of pretransplant specimens and fall dramatically by 30 d. Adoptive transfer of human PBMCs allogeneic to the artery 2 d postoperatively results in T cell infiltrates and intimal expansion 4 wk later. Ab neutralization of human IL-6 reduces the magnitude of intimal expansion and total T cell infiltration but increases the relative expression of CD161 while decreasing other Th17 markers. Coculture of MHC class II-expressing human endothelial cells (ECs) with allogeneic CD4(+) memory T cells results in T cell activation and EC secretion of IL-6. Neutralizing IL-6 in primary allogeneic T cell-EC cocultures results in enhanced T cell proliferation of CD161(+) CD4(+) T cells, reduces total T cell proliferation upon restimulation in secondary cultures (an effect dependent on CD161(+) T cells), increases expression of FOXP3 in CD161(+) T cells, and generates T cells that suppress proliferation of freshly isolated T cells. These data suggest that IL-6 released from injured allograft vessels enhances allogeneic T cell infiltration and intimal expansion in a model of human allograft rejection by inhibiting an increase in CD161(+) regulatory T cells.