Costimulatory blockade-induced allograft survival requires Beclin1

Deficiency in the mitophagy mediator Parkin accelerates murine skin allograft rejection

Alterations in mitochondrial function and associated quality control programs, including mitochondrial-specific autophagy, termed mitophagy, are gaining increasing recognition in the context of disease. However, the role of mitophagy in organ transplant rejection remains poorly understood. Using mice deficient in Parkin, a ubiquitin ligase that tags damaged or dysfunctional mitochondria for autophagic clearance, we assessed the impact of Parkin-dependent mitophagy on skin-graft rejection. We observed accelerated graft loss in Parkin-deficient mice across multiple skin graft models. Immune cell distributions posttransplant were largely unperturbed compared to wild-type; however, the CD8+ T cells of Parkin-deficient mice expressed more T-bet, IFNγ, and Ki67, indicating greater priming toward effector function. This was accompanied by increased circulating levels of IL-12p70 in Parkin-deficient mice. Using a mixed leukocyte reaction, we demonstrated that naïve Parkin-deficient CD4+ and CD8+ T cells exhibit enhanced activation marker expression and proliferative responses to alloantigen, which were attenuated with administration of a pharmacological mitophagy inducer (p62-mediated mitophagy inducer), known to increase mitophagy in the absence of a functional PINK1-Parkin pathway. These findings indicate a role for Parkin-dependent mitophagy in curtailing skin-graft rejection.

Autophagy: A Silent Protagonist in Kidney Transplantation

Autophagy is a lysosome-dependent regulated mechanism that recycles unnecessary cytoplasmic components. It is now known that autophagy dysfunction may have a pathogenic role in several human diseases and conditions, including kidney transplantation. Both defective and excessive autophagy may induce or aggravate several complications of kidney transplantation, such as ischemia-reperfusion injury, alloimmune response, and immunosuppressive treatment and side effects. Although it is still complicated to measure autophagy levels in clinical practice, more attention should be paid to the factors that may influence autophagy. In kidney transplantation, the association of low doses of a mammalian target of rapamycin inhibitor with low doses of a calcineurin inhibitor may be of benefit for autophagy modulation. However, further studies are needed to explore the role of other autophagy regulators.

Enhanced autophagy alleviated corneal allograft rejection via inhibiting NLRP3 inflammasome activity

Autophagy has been reported to be involved in many aspects of innate and adaptive immunity. Manipulating autophagy is recognized as a promising therapeutic approach for treating immunological diseases, including allograft rejection, and graft-versus-host disease. However, whether autophagy was closely associated with the pathogenesis of corneal allograft rejection remains largely unknown. Here, we showed that rapamycin (RAPA)-induced autophagy alleviated corneal allograft rejection. By contrast, blocking autophagic activity using 3-methyladeine (3-MA) aggravated corneal transplantation rejection. Mechanistically, we revealed that the enhanced autophagic turnover by RAPA inhibited NLRP3 inflammasome activity through NLRP3 degradation. While blocking the fusion of autophagosomes with lysosomes by bafilomycin A1(BafA1), the reduced NLRP3 inflammasome activity induced by RAPA was significantly restored, with increased protein levels of NLRP3 and cleaved Casp-1(p10), as well as IL-1β secretion. Moreover, we further revealed that pharmacologically blocking NLRP3 inflammasome signaling prolonged the survival of corneal allografts. Taken together, these findings underscored the critical roles of enhanced autophagy in treating corneal allograft rejection, which provided an alternative intervention strategy to control corneal transplantation rejection.

BET Protein Inhibition Prolongs Cardiac Transplant Survival via Enhanced Myocardial Autophagy

BACKGROUND

Graft rejection continues to be a major barrier to long-term engraftment after transplantation. Autophagy plays an important role in cardiac injury pathogenesis. The bromodomain and extraterminal protein inhibitor (S)-tert-butyl2-(4-(4-chlorophenyl)-2,3,9-trimethyl-6H-thieno[3,2-f][1,2,4]triazolo[4,3-a][1,4]diazepin-6-yl)acetate (JQ1) inhibits inflammatory responses. However, the beneficial effect of JQ1 on transplant and the potential role of autophagy in the protective effect of graft survival are yet to be investigated.

METHODS

Syngeneic or allogeneic heterotopic heart transplantation was performed using C57BL/6 or BALB/c donors for C57BL/6 recipients through different treatments. Some mice were used to observe the survival of the grafts. The other mice were euthanized on the third, fifth, and seventh days after surgery. The graft samples were taken for cytokines and autophagy pathway analyses.

RESULTS

Our study revealed that JQ1 treatment prolonged cardiac allograft survival. JQ1 increased the expression levels of liver kinase beta 1, autophagy-specific gene 5, and microtubule-associated protein light chain3-II (LC3-II) and potentiated the phosphorylation of AMP-activated protein kinase, unc-51-like kinase 1 (ULK1), and autophagy-specific gene 14 in allografts. A conditional autophagy-specific gene 5 deletion donor was utilized to abrogate the effect induced by JQ1. The combined use of JQ1 with bafilomycin A1 partially reversed the effect of JQ1, suggesting that autophagy is involved in the signaling pathway in graft survival. JQ1 downregulated the expression of inflammatory cytokines, such as interleukin-6, interleukin-1β, tumor necrosis factor-α, and interferon-γ, which was abrogated when autophagy was inhibited.

CONCLUSIONS

JQ1 prolonged cardiac allograft survival by potentiating myocardial autophagy through the liver kinase beta 1-AMP-activated protein kinase-ULK1 signaling pathway and inhibiting the subsequent release of inflammatory cytokines. This result might provide novel insights for extending transplant survival.

Urinary Cell Transcriptome Profiling and Identification of ITM2A, SLAMF6, and IKZF3 as Biomarkers of Acute Rejection in Human Kidney Allografts

Identification of a shared gene expression pattern between T cell–mediated rejection (TCMR) and antibody-mediated rejection (AMR) in human kidney allografts may help prioritize targets for the treatment of both types of acute rejection.

Autophagy in Immune-Related Renal Disease

Autophagy is an important biology process, central to the maintenance of biology process in both physiological and pathological situations. It is regarded as a “double-edged sword”—exerting both protective and/or detrimental effects. These two-way effects are observed in immune cells as well as renal resident cells, including podocytes, mesangial cells, tubular epithelial cells, and endothelial cells of the glomerular capillaries. Mounting evidence suggests that autophagy is implicated in the pathological process of various immune-related renal diseases (IRRDs) as well as the kidney that underwent transplantation. Here, we provide an overview of the pathological role of autophagy in IRRDs, including lupus nephritis, IgA nephropathy, membrane nephropathy, ANCA-associated nephritis, and diabetic nephropathy. The understanding of the pathogenesis and regulatory mechanisms of autophagy in these renal diseases may lead to the identification of new diagnostic targets and refined therapeutic modulation.

Inhibition of Autophagy Prolongs Recipient Survival Through Promoting CD8+ T Cell Apoptosis in a Rat Liver Transplantation Model

In liver transplantation (LT), although various immunosuppressants have been used in clinical practice, acute rejection remains a common complication that significantly shortens recipient survival. In recent years, manipulating immune tolerance has been regarded as one of the promising solutions to rejection. Autophagy, an evolutionarily conserved protein degradation system, has been reported to be involved in immune rejection and may be a target to establish immune tolerance. However, the role of autophagy in acute rejection reaction after LT has not been elucidated. Here, we showed that the autophagy of CD8⁺ T cells was strongly enhanced in patients with graft rejection and that the autophagy level was positively correlated with the severity of rejection. Similar findings were observed in a rat acute hepatic rejection model. Furthermore, administration of the autophagy inhibitor 3-methyladenine (3-MA) largely decreased the viability and function of CD8⁺ T cells through inhibiting autophagy, which significantly prolonged graft survival in rats. In addition, inhibiting the autophagy of activated CD8⁺ T cells in vitro considerably suppressed mitochondria mediated survival and downregulated T cell function.

Conclusions: We first showed that the inhibition of autophagy significantly prolongs liver allograft survival by promoting the apoptosis of CD8⁺ T cells, which may provide a novel strategy for immune tolerance induction.

Harnessing Advances in T Regulatory Cell Biology for Cellular Therapy in Transplantation

Cellular therapy with CD4FOXP3 T regulatory (Treg) cells is a promising strategy to induce tolerance after solid-organ transplantation or prevent graft-versus-host disease after transfer of hematopoietic stem cells. Treg cells currently used in clinical trials are either polyclonal, donor- or antigen-specific. Aside from variations in isolation and expansion protocols, however, most therapeutic Treg cell-based products are much alike. Ongoing basic science work has provided considerable new insight into multiple facets of Treg cell biology, including their stability, homing, and functional specialization; integrating these basic science discoveries with clinical efforts will support the development of next-generation therapeutic Treg cells with enhanced efficacy. In this review, we summarize recent advances in knowledge of how Treg cells home to lymphoid and peripheral tissues, and control antibody production and tissue repair. We also discuss newly appreciated pathways that modulate context-specific Treg cell function and stability. Strategies to improve and tailor Treg cells for cell therapy to induce transplantation tolerance are highlighted.

Novel Application of Localized Nanodelivery of Anti-Interleukin-6 Protects Organ Transplant From Ischemia-Reperfusion Injuries

Ischemia-reperfusion injury (IRI) evokes intragraft inflammatory responses, which markedly augment alloimmune responses against the graft. Understanding the mechanisms underlying these responses is fundamental to develop therapeutic regimens to prevent/ameliorate organ IRI. Here, we demonstrate that IRI results in a marked increase in mitochondrial damage and autophagy in dendritic cells (DCs). While autophagy is a survival mechanism for ischemic DCs, it also augments their production of interleukin (IL)-6. Allograft-derived dendritic cells (ADDCs) lacking autophagy-related gene 5 (Atg5) showed higher death rates posttransplantation. Transplanted ischemic hearts from CD11cCre/Atg5 conditional knockout mice showed marked reduction in intragraft expression of IL-6 compared with controls. To antagonize the effect of IL-6 locally in the heart, we synthesized novel anti-IL-6 nanoparticles with capacity for controlled release of anti-IL-6 over time. Compared with systemic delivery of anti-IL-6, localized delivery of anti-IL-6 significantly reduced chronic rejection with a markedly lower amount administered. Despite improved allograft histology, there were no changes to splenic T cell populations, illustrating the importance of local IL-6 in driving chronic rejection after IRI. These data carry potential clinical significance by identifying an innovative, targeted strategy to manipulate organs before transplantation to diminish inflammation, leading to improved long-term outcomes.

A Negative Feedback Loop Between Autophagy and Immune Responses in Mycobacterium leprae Infection

The obligate intracellular bacterium Mycobacterium leprae is the causative agent of leprosy and primarily infects macrophages, leading to irreversible nerve damage and deformities. So far, the underlying reasons allowing M. leprae to persist and propagate in macrophages, despite the presence of cellular immunity, are still a mystery. Here, we investigated the role of autophagy, a cellular process that degrades cytosolic materials and intracellular pathogens, in M. leprae infection. We found that live M. leprae infection of macrophages resulted in significantly elevated autophagy level. However, macrophages with high autophagy levels preferentially expressed lower levels of proinflammatory cytokines, including interleukin (IL)-1β, IL-6, IL-12, and tumor necrosis factor-α, and preferentially primed anti-inflammatory T cells responses, characterized by high IL-10 and low interferon-γ, granzyme B, and perforin responses. These anti-inflammatory T cells could suppress further induction of autophagy, leading to improved survival of intracellular M. leprae in infected macrophages. Therefore, these data demonstrated that although autophagy had a role in eliminating intracellular pathogens, the induction of autophagy resulted in anti-inflammatory immune responses, which suppressed autophagy in a negative feedback loop and allowed the persistence of M. leprae.

Autophagy in allografts rejection: A new direction?

Despite the introduction of new and effective immunosuppressive drugs, acute cellular graft rejection is still a major risk for graft survival. Modulating the dosage of immunosuppressive drugs is not a good choice for all patients, new rejection mechanisms discovery are crucial to limit the inflammatory process and preserve the function of the transplant. Autophagy, a fundamental cellular process, can be detected in all subsets of lymphocytes and freshly isolated naive T lymphocytes. It is required for the homeostasis and function of T lymphocytes, which lead to cell survival or cell death depending on the context. T cell receptor (TCR) stimulation and costimulator signals induce strong autophagy, and autophagy deficient T cells leads to rampant apoptosis upon TCR stimulation. Autophagy has been proved to be activated during ischemia-reperfusion (I/R) injury and associated with grafts dysfunction. Furthermore, Autophagy has also emerged as a key mechanism in orchestrating innate and adaptive immune response to self-antigens, which relates with negative selection and Foxp3(+) Treg induction. Although, the role of autophagy in allograft rejection is unknown, current data suggest that autophagy indeed sweeps across both in the graft organs and recipients lymphocytes after transplantation. This review presents the rationale for the hypothesis that targeting the autophagy pathway could be beneficial in promoting graft survival after transplantation.

Beclin orthologs: integrative hubs of cell signaling, membrane trafficking, and physiology

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Beclin orthologs are crucial regulators of autophagy and related membrane-trafficking pathways.

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Multiple signaling pathways converge on Beclin 1 to regulate cellular stress responses, membrane trafficking, and physiology.

The Beclin family, including yeast Atg6 (autophagy related gene 6), its orthologs in higher eukaryotic species, and the more recently characterized mammalian-specific Beclin 2, are essential molecules in autophagy and other membrane-trafficking events. Extensive studies of Beclin orthologs have provided considerable insights into the regulation of autophagy, the diverse roles of autophagy in physiology and disease, and potential new strategies to modulate autophagy in a variety of clinical diseases. In this review we discuss the functions of Beclin orthologs, the regulation of such functions by diverse cellular signaling pathways, and the effects of such regulation on downstream cellular processes including tumor suppression and metabolism. These findings suggest that Beclin orthologs serve as crucial molecules that integrate diverse environmental signals with membrane trafficking events to ensure optimal responses of the cell to stressful stimuli.

Immunologic manifestations of autophagy

The broad immunologic roles of autophagy span innate and adaptive immunity and are often manifested in inflammatory diseases. The immune effects of autophagy partially overlap with its roles in metabolism and cytoplasmic quality control but typically expand further afield to encompass unique immunologic adaptations. One of the best-appreciated manifestations of autophagy is protection against microbial invasion, but this is by no means limited to direct elimination of intracellular pathogens and includes a stratified array of nearly all principal immunologic processes. This Review summarizes the broad immunologic roles of autophagy. Furthermore, it uses the autophagic control of Mycobacterium tuberculosis as a paradigm to illustrate the breadth and complexity of the immune effects of autophagy.

Mechanisms and biological functions of autophagy in diseased and ageing kidneys

Autophagy degrades pathogens, altered organelles and protein aggregates, and is characterized by the sequestration of cytoplasmic cargos within double-membrane-limited vesicles called autophagosomes. The process is regulated by inputs from the cellular microenvironment, and is activated in response to nutrient scarcity and immune triggers, which signal through a complex molecular network. Activation of autophagy leads to the formation of an isolation membrane, recognition of cytoplasmic cargos, expansion of the autophagosomal membrane, fusion with lysosomes and degradation of the autophagosome and its contents. Autophagy maintains cellular homeostasis during stressful conditions, dampens inflammation and shapes adaptive immunity. A growing body of evidence has implicated autophagy in kidney health, ageing and disease; it modulates tissue responses during acute kidney injuries, regulates podocyte homeostasis and protects against age-related renal disorders. The renoprotective functions of autophagy in epithelial renal cells and podocytes are mostly mediated by the clearance of altered mitochondria, which can activate inflammasomes and apoptosis, and the removal of protein aggregates, which might trigger inflammation and cell death. In translational terms, autophagy is undoubtedly an attractive target for developing new renoprotective treatments and identifying markers of kidney injury.

Autophagy: basic principles and relevance to transplant immunity

Autophagy developed into a rapidly expanding field detailing its molecular mechanism and relevance in health and disease. Autophagy is an evolutionarily conserved process that summarizes a pathway in which intracellular material is degraded within the lysosome and where the macromolecular constituents are recycled. This "self-eating" process was originally described in a cell under starvation but now numerous studies established autophagy as a cellular response to stress. As a consequence, the autophagy machinery interfaces with most cellular stress-response pathways, including those involved in controlling immune response and inflammation. Autophagy also influences adaptive immunity through its effect on antigen presentation, naïve T cell repertoire selection and homeostasis and TH cell polarization. Data are emerging that dysregulated autophagy has an impact on human pathologies including infectious diseases, cancers, aging and neurodegenerative conditions. This review focuses on recent findings elucidating the ability of autophagy to be of significance in the transplant setting.