Amelioration of human allograft arterial injury by atorvastatin or simvastatin correlates with reduction of interferon-gamma production by infiltrating T cells

The Biological Parallels Between Atherosclerosis and Cardiac Allograft Vasculopathy: Implications for Solid Organ Chronic Rejection

Atherosclerosis and solid organ chronic rejection are pervasive chronic disease states that account for significant morbidity and mortality in developed countries. Recently, a series of shared molecular pathways have emerged, revealing biological parallels from early stages of development up to the advanced forms of pathology. These shared mechanistic processes are inflammatory in nature, reflecting the importance of inflammation in both disorders. Vascular inflammation triggers endothelial dysfunction and disease initiation through aberrant vasomotor control and shared patterns of endothelial activation. Endothelial dysfunction leads to the recruitment of immune cells and the perpetuation of the inflammatory response. This drives lesion formation through the release of key cytokines such as IFN-y, TNF-alpha, and IL-2. Continued interplay between the adaptive and innate immune response (represented by T lymphocytes and macrophages, respectively) promotes lesion instability and thrombotic complications; hallmarks of advanced disease in both atherosclerosis and solid organ chronic rejection. The aim of this study is to identify areas of overlap between atherosclerosis and chronic rejection. We then discuss new approaches to improve current understanding of the pathophysiology of both disorders, and eventually design novel therapeutics.

Proinflammatory protein signatures in cryptogenic and large artery atherosclerosis stroke

Objectives

The cause of ischemic stroke remains unknown, cryptogenic, in 25% of young and middle‐aged patients. We hypothesized that if atherosclerosis is prominent in cryptogenic stroke, it would have a similar proinflammatory protein signature as large artery atherosclerosis (LAA) stroke.

Materials & Methods

Blood was collected in the acute phase and after 3 months from cryptogenic (n = 162) and LAA (n = 73) stroke patients aged 18–69 years and once from age‐matched controls (n = 235). Cryptogenic stroke was divided into Framingham Risk Score (FRS) quartiles to compare low and high risk of atherosclerosis. Plasma concentrations of 25 proteins were analyzed using a Luminex multiplex assay. The discriminating properties were assessed with discriminant analysis and C‐statistics.

Results

We identified proteins that separated cryptogenic and LAA stroke from controls (area under the curves, AUCs ≥ 0.85). For both subtypes, RANTES, IL‐4, and IFN‐γ contributed the most at both time points. These associations were independent of risk factors of atherosclerosis. We also identified proteins that separated cryptogenic strokes in the lowest quartile of FRS from those in the highest, and from LAA stroke (AUCs ≥ 0.76), and here eotaxin and MCP‐1 contributed the most.

Conclusions

The protein signature separating cases from controls was different from the signature separating cryptogenic stroke with low risk of atherosclerosis from those with high risk and from LAA stroke. This suggests that increased RANTES, IL‐4, and IFN‐γ in stroke may not be primarily related to atherosclerosis, whereas increased eotaxin and MCP‐1 in cryptogenic stroke may be markers of occult atherosclerosis as the underlying cause.

Statin intensity and risk for cardiovascular events after heart transplantation

AIMS

Statins improve survival and reduce rejection and cardiac allograft vasculopathy after heart transplantation (HT). The impact of different statin intensities on clinical outcomes has never been assessed. We set out to determine the impact of statin exposure on cardiovascular outcomes after HT.

METHODS AND RESULTS

We performed a retrospective study of 346 adult patients who underwent HT from 2006 to 2018. Statin intensity was determined longitudinally after HT based on American College of Cardiology/American Heart Association (ACC/AHA) guidelines. The primary outcome was the time to the first primary event defined as the composite of heart failure hospitalization, myocardial infarction, revascularization, and all-cause mortality. Secondary outcomes included time to significant rejection and time to moderate-severe cardiac allograft vasculopathy. Adverse events were evaluated for subjects on high-intensity statin therapy. A Cox proportional hazards model was used to evaluate the relationship between clinical variables, statin intensity, and outcomes. Most subjects were treated with low-intensity statin therapy although this declined from 89.9% of the population at 1month after HT to 42.8% at 5years after HT. History of ischaemic cardiomyopathy, significant acute rejection, older donor age, and lesser statin intensity (p ≤ 0.001) were associated with reduced time to the primary outcome in a multivariable Cox model. Greater intensity of statin therapy was most beneficial early after HT. There were no statin-related adverse events for the 14 subjects on high-intensity statin therapy.

CONCLUSIONS

Greater statin intensity was associated with a reduction in adverse cardiovascular outcomes after HT.

Hyperlipidemia and Allograft Rejection

Purpose of review

Advances in the development of immunosuppressive drug regimens have led to impressive survival rates in the year following organ transplantation. However rates of long-term graft dysfunction remain undesirably high. Recently it has been shown that co-morbidities in the patient population may affect graft survival. In mouse models, hyperlipidemia, a co-morbidity present in the majority of cardiac transplant patients, can significantly alter T cell responses to cardiac and skin allografts, and accelerate graft rejection. Here we review recent advances in our understanding of how alterations in lipids affect immune function and graft survival.

Recent Findings

Recent work in humans has highlighted the importance of controlling low density lipoprotein (LDL) levels in transplant recipients to reduce the development of chronic allograft vasculopathy (CAV). High serum levels of cholesterol containing particles leads to extensive immune system changes to T cell proliferation, differentiation and suppression. Changes in B cell subsets, and the ability of antigen presenting cells to stimulate T cells in hyperlipidemic animals may also contribute to increased organ allograft rejection.

Summary

Cholesterol metabolism is a critical cellular pathway for proper control of immune cell homeostasis and activation. Increasing evidence in both human, and in mouse models shows that elevated levels of serum cholesterol can have profound impact on the immune system. Hyperlipidemia has been shown to increase T cell activation, alter the development of T helper subsets, increase the inflammatory capacity of antigen presenting cells (APC) and significantly accelerate graft rejection in several models.

Impact of hyperlipidemia on alloimmunity

PURPOSE OF REVIEW

Hyperlipidemia is a comorbidity affecting a significant number of transplant patients despite treatment with cholesterol lowering drugs. Recently, it has been shown that hyperlipidemia can significantly alter T-cell responses to cardiac allografts in mice, and graft rejection is accelerated in dyslipidemic mice. Here, we review recent advances in our understanding of hyperlipidemia in graft rejection.

RECENT FINDINGS

Hyperlipidemic mice have significant increases in serum levels of proinflammatory cytokines, and neutralization of interleukin 17 (IL-17) slows graft rejection, suggesting that IL-17 production by Th17 cells was necessary but not sufficient for rejection. Hyperlipidemia also causes an increase in alloreactive T-cell responses prior to antigen exposure. Analysis of peripheral tolerance mechanisms indicated that this was at least in part due to alterations in FoxP3 T cells that led to reduced Treg function and the expansion of FoxP3 CD4 T cells expressing low levels of CD25. Functionally, alterations in Treg function prevented the ability to induce operational tolerance to fully allogeneic heart transplants through costimulatory-molecule blockade, a strategy that requires Tregs.

SUMMARY

These findings highlight the importance of considering the contribution of inflammatory comorbidities to cardiac allograft rejection, and point to the potential importance of managing hyperlipidemia in the transplant population.

Impact of environmental factors on alloimmunity and transplant fate

Although gene-environment interactions have been investigated for many years to understand people's susceptibility to autoimmune diseases or cancer, a role for environmental factors in modulating alloimmune responses and transplant outcomes is only now beginning to emerge. New data suggest that diet, hyperlipidemia, pollutants, commensal microbes, and pathogenic infections can all affect T cell activation, differentiation, and the kinetics of graft rejection. These observations reveal opportunities for novel therapeutic interventions to improve graft outcomes as well as for noninvasive biomarker discovery to predict or diagnose graft deterioration before it becomes irreversible. In this Review, we will focus on the impact of these environmental factors on immune function and, when known, on alloimmune function, as well as on transplant fate.

High Mobility Group Box 1 Mediates Interferon-γ-Induced Phenotypic Modulation of Vascular Smooth Muscle Cells

The phenotypic modulation of VSMCs is a key cellular event driving neointimal formation and vascular remodeling. As a multifaceted cytokine of cell-mediated immunity, IFN-γ has been shown to play a critical role in the pathogenesis of vascular proliferative diseases. Although the important function of IFN-γ on regulating VSMC activation is well established, the molecular mechanisms by which elicits VSMC responses are poorly defined. Recent studies have identified HMGB1 as a principal effector to mediate IFN-γ-dependent biological functions in multiple cell types. Moreover, SIRT1 has emerged as a critical regulator of cellular processes through deacetylating multiple substrates, including HMGB1. Thus, we examined the role of IFN-γ on HMGB1 release, SIRT1 expression, and VSMC phenotypic modulation as well as the underlying molecular mechanisms. We show that IFN-γ dose-dependently induces HMGB1 cytoplasmic accumulation and its active release from VSMCs, resulting in enhanced HMGB1 in the medium. Conversely, IFN-γ treatment led to a dramatic decrease in SIRT1 expression. Additionally, pretreatment with resveratrol, a selective SIRT1 activator, abrogated IFN-γ-induced HMGB1 translocation and its release. Moreover, IFN-γ stimulates VSMC phenotypic modulation to an activated synthetic state characterized by the repression of SMC differentiation markers such as SM22α and calponin and the increase in cell motility. In contrast, blocking HMGB1 release or activity by resveratrol and HMGB1-neutralizing antibody prevents IFN-γ-induced phenotypic modulation of VSMCs. Overall, this study provides the first evidence showing that HMGB1 plays a critical role in regulating VSMC phenotypic modulation, suggesting that HMGB1 may be a potential therapeutic target to prevent vascular occlusive diseases. J. Cell. Biochem. 118: 518-529, 2017. © 2016 Wiley Periodicals, Inc.

Interacting mechanisms in the pathogenesis of cardiac allograft vasculopathy

Cardiac allograft vasculopathy is the major cause of late graft loss in heart transplant recipients. Histological studies of characteristic end-stage lesions reveal arterial changes consisting of a diffuse, confluent, and concentric intimal expansion containing graft-derived cells expressing smooth muscle markers, extracellular matrix, penetrating microvessels, and a host mononuclear cell infiltrate concentrated subjacent to an intact graft-derived luminal endothelial cell lining with little evidence of acute injury. This intimal expansion combined with inadequate compensatory outward remodeling produces severe generalized stenosis extending throughout the epicardial and intramyocardial arterial tree that causes ischemic graft failure. Cardiac allograft vasculopathy lesions affect ≥50% of transplant recipients and are both progressive and refractory to treatment, resulting in ≈5% graft loss per year through the first 10 years after transplant. Lesions typically stop at the suture line, implicating alloimmunity as the primary driver, but pathogenesis may be multifactorial. Here, we will discuss 6 potential contributors to lesion formation (1) conventional risk factors of atherosclerosis; (2) pre- or peritransplant injuries; (3) infection; (4) innate immunity; (5) T-cell-mediated immunity; and (6) B-cell-mediated immunity through production of donor-specific antibody. Finally, we will consider how these various mechanisms may interact with each other.

Randomized clinical trial: atorvastatin versus placebo in patients with acute exacerbation of mild to moderate ulcerative colitis

BACKGROUND

Statins are known to possess pleiotropic anti-inflammatory properties which have been evaluated for clinical benefits in a number of disorders. Studies have demonstrated beneficial actions of statins in experimental models of colitis. Clinical evidence in acute exacerbation of ulcerative colitis (UC) is lacking.

AIM

This study aims to assess the efficacy and safety of add-on atorvastatin in mild to moderately severe acute exacerbation of UC.

METHODS

Patients with acute exacerbation of UC were randomized to receive either atorvastatin (20 mg) or matching placebo once daily orally for 8 weeks in addition to the standard therapy. Clinical efficacy was assessed by using partial Mayo score (PMS).

RESULTS

Previously diagnosed 64 cases of UC presenting with mild to moderately severe acute exacerbation were randomized to receive either atorvastatin of 20 mg or placebo. Mean PMS increased by 1.5 points and decreased by 0.31 points in atorvastatin and placebo groups, respectively, at 8 weeks compared to the baseline values (p = 0.04). Eight (25 %) and 13 (40.6 %) patients attained the primary outcome criteria for clinical improvement in the atorvastatin and placebo arms, respectively (p = 0.18). Fifteen (46.8 %) patients in the atorvastatin group and no patient in the placebo group had ≥2 point increase in PMS after 8 weeks (p < 0.001).

CONCLUSION

Atorvastatin therapy in acute exacerbation of UC may not be associated with beneficial effects. Paradoxical increase in disease activity may be seen in some patients. However, these findings need to be substantiated in larger studies.

Histological assessment of the sclerotic graft-versus-host response in the humanized RAG2-/-γc-/- mouse model

Graft-versus-host disease (GVHD) remains a frequently occurring and difficult-to-treat complication in human allogeneic stem cell transplantation. Murine transplantation models are often used to study and understand the complex pathogenesis of GVHD and to explore new treatment strategies. Although GVHD kinetics may differ in murine and human models, adequate models are essential for identification of the crucial factors responsible for the major pathology in GVHD. We present a detailed description of the specific histological features of a graft-versus-host-induced fibrotic response in xenogeneic RAG2(-/-)γc(-/-) mice after total body irradiation and injection with human peripheral blood mononuclear cells. We describe the full morphological features of this reaction, including a detailed analysis of the specific tissue infiltration patterns of the human peripheral blood mononuclear cells. Our data show the development of fibrosis, predominantly near blood vessels, and reveal different cell populations and specific cell migration patterns in the affected organs. The combination of immunohistochemical cell characterization and mRNA expression analysis of both human (donor)- and murine (host)-derived cytokines reveals an interaction between host tissues and donor-derived cells in an entangled cytokine profile, in which both donor- and host-derived cytokines contribute to the formation of fibrosis.

Regulatory T cells as modulators of chronic allograft dysfunction

Chronic allograft dysfunction (CAD) in solid organ transplantation is a principal cause of patient morbidity and late allograft loss. The pathogenesis of CAD is largely secondary to chronic damage by the adaptive immune system and long-term immunosuppression. Manipulating these factors may be possible with the use of regulatory T cells (Treg), which have the ability to suppress specific immune responses and therefore potentially remove the need for immunosuppressive drugs. Studies of CAD in experimental models have demonstrated the capacity for both mouse and human Treg cellular therapy to prevent the development of some manifestations of CAD. Furthermore, a role for Treg has been demonstrated in clinically tolerant transplant patients. Certain immunosuppressive therapies are also proving to be 'Treg friendly' and may be helpful in promoting Treg while maintaining other immunosuppressive activity. With this in mind, monitoring for biomarkers of operational tolerance with tailored immunosuppressive therapy or controlled weaning in conjunction with Treg cellular therapy may be a useful strategy to pursue.

Peroxisome proliferator-activated receptor-γ agonists prevent in vivo remodeling of human artery induced by alloreactive T cells

BACKGROUND

Ligands activating the transcription factor peroxisome proliferator-activated receptor-γ (PPARγ) have antiinflammatory effects. Vascular rejection induced by allogeneic T cells can be responsible for acute and chronic graft loss. Studies in rodents suggest that PPARγ agonists may inhibit graft vascular rejection, but human T-cell responses to allogeneic vascular cells differ from those in rodents, and the effects of PPARγ in human transplantation are unknown.

METHODS AND RESULTS

We tested the effects of PPARγ agonists on human vascular graft rejection using a model in which human artery is interposed into the abdominal aorta of immunodeficient mice, followed by adoptive transfer of allogeneic (to the artery donor) human peripheral blood mononuclear cells. Interferon-γ-dependent rejection ensues within 4 weeks, characterized by intimal thickening, T-cell infiltrates, and vascular cell activation, a response resembling clinical intimal arteritis. The PPARγ agonists 15-deoxy-prostaglandin-J(2), ciglitazone, and pioglitazone reduced intimal expansion, intimal infiltration of CD45RO(+) memory T cells, and plasma levels of inflammatory cytokines. The PPARγ antagonist GW9662 reversed the protective effects of PPARγ agonists, confirming the involvement of PPARγ-mediated pathways. In vitro, pioglitazone inhibited both alloantigen-induced proliferation and superantigen-induced transendothelial migration of memory T cells, indicating the potential mechanisms of PPARγ effects.

CONCLUSION

Our results suggest that PPARγ agonists inhibit allogeneic human memory T cell responses and may be useful for the treatment of vascular graft rejection.

Statin-induced Krüppel-like factor 2 expression in human and mouse T cells reduces inflammatory and pathogenic responses

The transcription factor Krüppel-like factor 2 (KLF2) is required for the quiescent and migratory properties of naive T cells. Statins, a class of HMG-CoA reductase inhibitors, display pleiotropic immunomodulatory effects that are independent of their lipid-lowering capacity and may be beneficial as therapeutic agents for T cell-mediated inflammatory diseases. Statins upregulate KLF2 expression in endothelial cells, and this activity is associated with an antiinflammatory phenotype. We therefore hypothesized that the immunomodulatory effects of statins are due, in part, to their direct effects on T cell KLF2 gene expression. Here we report that lipophilic statin treatment of mouse and human T cells increased expression of KLF2 through a HMG-CoA/prenylation-dependent pathway. Statins also diminished T cell proliferation and IFN-gamma expression. shRNA blockade of KLF2 expression in human T cells increased IFN-gamma expression and prevented statin-induced IFN-gamma reduction. In a mouse model of myocarditis induced by heart antigen-specific CD8+ T cells, both statin treatment of the T cells and retrovirally mediated overexpression of KLF2 in the T cells had similar ameliorating effects on disease induction. We conclude that statins reduce inflammatory functions and pathogenic activity of T cells through KLF2-dependent mechanisms, and this pathway may be a potential therapeutic target for cardiovascular diseases.