Akt-dependent enhanced migratory capacity of Th17 cells from children with lupus nephritis

Rab4A-directed endosome traffic shapes pro-inflammatory mitochondrial metabolism in T cells via mitophagy, CD98 expression, and kynurenine-sensitive mTOR activation

Activation of the mechanistic target of rapamycin (mTOR) is a key metabolic checkpoint of pro-inflammatory T-cell development that contributes to the pathogenesis of autoimmune diseases, such as systemic lupus erythematosus (SLE), however, the underlying mechanisms remain poorly understood. Here, we identify a functional role for Rab4A-directed endosome traffic in CD98 receptor recycling, mTOR activation, and accumulation of mitochondria that connect metabolic pathways with immune cell lineage development and lupus pathogenesis. Based on integrated analyses of gene expression, receptor traffic, and stable isotope tracing of metabolic pathways, constitutively active Rab4AQ72L exerts cell type-specific control over metabolic networks, dominantly impacting CD98-dependent kynurenine production, mTOR activation, mitochondrial electron transport and flux through the tricarboxylic acid cycle and thus expands CD4+ and CD3+CD4-CD8- double-negative T cells over CD8+ T cells, enhancing B cell activation, plasma cell development, antinuclear and antiphospholipid autoantibody production, and glomerulonephritis in lupus-prone mice. Rab4A deletion in T cells and pharmacological mTOR blockade restrain CD98 expression, mitochondrial metabolism and lineage skewing and attenuate glomerulonephritis. This study identifies Rab4A-directed endosome traffic as a multilevel regulator of T cell lineage specification during lupus pathogenesis.

Th17 cells: A new target in kidney disease research

Type 17 T helper (Th17) cells, which are a subtype of CD4+ T helper cells, secrete pro-inflammatory cytokines such as IL-17A, IL-17F, IL-21, IL-22, and GM-CSF, which play crucial roles in immune defence and protection against fungal and extracellular pathogen invasion. However, dysfunction of Th17 cell immunity mediates inflammatory responses and exacerbates tissue damage. This pathological process initiated by Th17 cells is common in kidney diseases associated with renal injury, such as glomerulonephritis, lupus nephritis, IgA nephropathy, hypertensive nephropathy, diabetic kidney disease and acute kidney injury. Therefore, targeting Th17 cells to treat kidney diseases has been a hot topic in recent years. This article reviews the mechanisms of Th17 cell-mediated inflammation and autoimmune responses in kidney diseases and discusses the related clinical drugs that modulate Th17 cell fate in kidney disease treatment.

Endosome Traffic Modulates Pro-Inflammatory Signal Transduction in CD4+ T Cells-Implications for the Pathogenesis of Systemic Lupus Erythematosus

Endocytic recycling regulates the cell surface receptor composition of the plasma membrane. The surface expression levels of the T cell receptor (TCR), in concert with signal transducing co-receptors, regulate T cell responses, such as proliferation, differentiation, and cytokine production. Altered TCR expression contributes to pro-inflammatory skewing, which is a hallmark of autoimmune diseases, such as systemic lupus erythematosus (SLE), defined by a reduced function of regulatory T cells (Tregs) and the expansion of CD4⁺ helper T (Th) cells. The ensuing secretion of inflammatory cytokines, such as interferon-γ and interleukin (IL)-4, IL-17, IL-21, and IL-23, trigger autoantibody production and tissue infiltration by cells of the adaptive and innate immune system that induce organ damage. Endocytic recycling influences immunological synapse formation by CD4⁺ T lymphocytes, signal transduction from crosslinked surface receptors through recruitment of adaptor molecules, intracellular traffic of organelles, and the generation of metabolites to support growth, cytokine production, and epigenetic control of DNA replication and gene expression in the cell nucleus. This review will delineate checkpoints of endosome traffic that can be targeted for therapeutic interventions in autoimmune and other disease conditions.

A cellular overview of immunometabolism in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease, characterized by a breakdown of immune tolerance and the development of autoantibodies against nucleic self-antigens. Immunometabolism is a rapidly expanding scientific field investigating the metabolic programming of cells of the immune system. During the normal immune response, extensive reprogramming of cellular metabolism occurs, both to generate adenosine triphosphate and facilitate protein synthesis, and also to manage cellular stress. Major pathways upregulated include glycolysis, oxidative phosphorylation, the tricarboxylic acid cycle and the pentose phosphate pathway, among others. Metabolic reprogramming also occurs to aid resolution of inflammation. Immune cells of both patients with SLE and lupus-prone mice are characterized by metabolic abnormalities resulting in an altered functional and inflammatory state. Recent studies have described how metabolic reprogramming occurs in many cell populations in SLE, particularly CD4+ T cells, e.g. favouring a glycolytic profile by overactivation of the mechanistic target of rapamycin pathway. These advances have led to an increased understanding of the metabolic changes affecting the inflammatory profile of T and B cells, monocytes, dendritic cells and neutrophils, and how they contribute to autoimmunity and SLE pathogenesis. In the current review, we aim to summarize recent advances in the field of immunometabolism involved in SLE and how these could potentially lead to new therapeutic strategies in the future.

Role of T cells in the pathogenesis of systemic lupus erythematous: Focus on immunometabolism dysfunctions

Evidence demonstrates that T cells are implicated in developing SLE, and each of them dominantly uses distinct metabolic pathways. Indeed, intracellular enzymes and availability of specific nutrients orchestrate fate of T cells and lead to differentiation of regulatory T cells (Treg), memory T cells, helper T cells, and effector T cells. The function of T cells in inflammatory and autoimmune responses is determined by metabolic processes and activity of their enzymes. Several studies were conducted to determine metabolic abnormalities in SLE patients and clarify how these modifications could control the functions of the involved T cells. Metabolic pathways such as glycolysis, mitochondrial pathways, oxidative stress, mTOR pathway, fatty acid and amino acid metabolisms are dysregulated in SLE T cells. Moreover, immunosuppressive drugs used in treating autoimmune diseases, including SLE, could affect immunometabolism. Developing drugs to regulate autoreactive T cell metabolism could be a promising therapeutic approach for SLE treatment. Accordingly, increased knowledge about metabolic processes paves the way to understanding SLE pathogenesis better and introduces novel therapeutic options for SLE treatment. Although monotherapy with metabolic pathways modulators might not be sufficient to prevent autoimmune disease, they may be an ideal adjuvant to reduce administration doses of immunosuppressive drugs, thus reducing drug-associated adverse effects. This review summarized emerging data about T cells that are involved in SLE pathogenesis, focusing on immunometabolism dysregulation and how these modifications could affect the disease development.

Truncated isoforms of GPSM2 containing the GoLoco motif region promote CD4+ T-cell migration in SLE

OBJECTIVE

SLE is an autoimmune disease with a complex pathogenesis. T-cell infiltration into organs contributes to inflammation and organ damage in SLE. Recently, G-protein signalling modulator 2 (GPSM2) has been shown to be implicated in T-cell migration.

METHODS

We analysed the expression levels of GPSM2 and of a truncated isoform of GPSM2 containing the GoLoco motif region in CD4⁺ T cells from patients with SLE and from healthy individuals by western blot. In a next step, we studied the role of the truncated GPSM2 isoform using a CD4⁺ T-cell migration assay.

RESULTS

Our experiments revealed comparable levels of GPSM2 in CD4⁺ T cells from patients with SLE and healthy controls. In contrast, the truncated 35 kDa isoform of GPSM2 was significantly more highly expressed in CD4⁺ T cells from patients with SLE as compared with healthy subjects. Antibody-mediated blockade of the 35 kDa GPSM2 isoform reduced the in vitro capacity of CD4⁺ T cells to migrate towards the chemokine CCL20.

CONCLUSIONS

A truncated GPSM2 isoform containing the GoLoco motif region is upregulated in CD4⁺ T cells from patients with SLE and promotes CD4⁺ T-cell migration. Targeting this isoform with specific antibodies might be a promising approach to reduce CD4⁺ T-cell infiltration into inflamed tissues and to prevent organ damage in SLE.

A Mechanistic Insight into the Pathogenic Role of Interleukin 17A in Systemic Autoimmune Diseases

Interleukin 17A (IL-17A) has been put forward as a strong ally in our fight against invading pathogens across exposed epithelial surfaces by serving an antimicrobial immunosurveillance role in these tissues to protect the barrier integrity. Amongst other mechanisms that prevent tissue injury mediated by potential microbial threats and promote restoration of epithelial homeostasis, IL-17A attracts effector cells to the site of inflammation and support the host response by driving the development of ectopic lymphoid structures. Accumulating evidence now underscores an integral role of IL-17A in driving the pathophysiology and clinical manifestations in three potentially life-threatening autoimmune diseases, namely, systemic lupus erythematosus, Sjögren’s syndrome, and systemic sclerosis. Available studies provide convincing evidence that the abundance of IL-17A in target tissues and its prime source, which is T helper 17 cells (Th17) and double negative T cells (DNT), is not an innocent bystander but in fact seems to be prerequisite for organ pathology. In this regard, IL-17A has been directly implicated in critical steps of autoimmunity. This review reports on the synergistic interactions of IL-17A with other critical determinants such as B cells, neutrophils, stromal cells, and the vasculature that promote the characteristic immunopathology of these autoimmune diseases. The summary of observations provided by this review may have empowering implications for IL-17A-based strategies to prevent clinical manifestations in a broad spectrum of autoimmune conditions.

DICAM promotes TH17 lymphocyte trafficking across the blood-brain barrier during autoimmune neuroinflammation

[Figure: see text].

The Th17/IL-17 Axis and Kidney Diseases, With Focus on Lupus Nephritis

Systemic lupus erythematosus (SLE) is a disease characterized by dysregulation and hyperreactivity of the immune response at various levels, including hyperactivation of effector cell subtypes, autoantibodies production, immune complex formation, and deposition in tissues. The consequences of hyperreactivity to the self are systemic and local inflammation and tissue damage in multiple organs. Lupus nephritis (LN) is one of the most worrying manifestations of SLE, and most patients have this involvement at some point in the course of the disease. Among the effector cells involved, the Th17, a subtype of T helper cells (CD4+), has shown significant hyperactivation and participates in kidney damage and many other organs. Th17 cells have IL-17A and IL-17F as main cytokines with receptors expressed in most renal cells, being involved in the activation of many proinflammatory and profibrotic pathways. The Th17/IL-17 axis promotes and maintains repetitive tissue damage and maladaptive repair; leading to fibrosis, loss of organ architecture and function. In the podocytes, the Th17/IL-17 axis effects include changes of the cytoskeleton with increased motility, decreased expression of health proteins, increased oxidative stress, and activation of the inflammasome and caspases resulting in podocytes apoptosis. In renal tubular epithelial cells, the Th17/IL-17 axis promotes the activation of profibrotic pathways such as increased TGF-β expression and epithelial-mesenchymal transition (EMT) with consequent increase of extracellular matrix proteins. In addition, the IL-17 promotes a proinflammatory environment by stimulating the synthesis of inflammatory cytokines by intrinsic renal cells and immune cells, and the synthesis of growth factors and chemokines, which together result in granulopoiesis/myelopoiesis, and further recruitment of immune cells to the kidney. The purpose of this work is to present the prognostic and immunopathologic role of the Th17/IL-17 axis in Kidney diseases, with a special focus on LN, including its exploration as a potential immunotherapeutic target in this complication.

Immunometabolism in systemic lupus erythematosus: Relevant pathogenetic mechanisms and potential clinical applications

Systemic lupus erythematosus (SLE) is a complex, heterogeneous, systemic autoimmune disease involving a wide array of aberrant innate and adaptive immune responses. The immune microenvironment of SLE promotes the metabolic reprogramming of immune cells, leading to immune dyshomeostasis and triggering autoimmune inflammation. Different immune subsets switch from a resting state to a highly metabolic active state by alternating the redox-sensitive signaling pathway and the involved metabolic intermediates to amplify the inflammatory response, which is critical in SLE pathogenesis. In this review, we discuss abnormal metabolic changes in glucose metabolism, tricarboxylic acid cycle, and lipid and amino acid metabolism as well as mitochondrial dysfunction in immune cells in SLE. We also review studies focused on the potential targets for key molecules of metabolic pathways in SLE, such as hypoxia-inducible factor-1α, mammalian target of rapamycin, and AMP-activated protein kinase. We highlight the therapeutic rationale for targeting these pathways in treating SLE and summarize their recent clinical applications in SLE.

Immunometabolic Pathways and Its Therapeutic Implication in Autoimmune Diseases

Autoimmune diseases (AIDs) are characterized with aberrant immune responses and their respective signaling pathways controlling cell differentiation, death, and survival. Cell metabolism is also an indispensable biochemical process that provides the very fundamental energy and materials. Accumulating evidences implicate that metabolism pathways have critical roles in determining the function of different immune subsets. Mechanisms of how immunometabolism participate in the pathogenesis of AIDs were also under intensive exploration. Here, in this review, we summarize the metabolic features of immune cells in AIDs and also the individual function of immunometabolism pathways, including glucose metabolism and tricarboxylic acid (TCA) cycle, in the setting of AIDs, mainly focusing on the potential targets for intervention. We also review studies that explore the intervention strategies targeting key molecules of metabolic pathways, such as mammalian target of rapamycin (mTOR), AMP-activated protein kinase (AMPK), and hypoxia-inducible factor 1a (HIF1a), in systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). The highlight of this review is to provide a comprehensive summary of the status quo of immunometabolism studies in AIDs and the potential translatable drug targets.

LRCH1 suppresses migration of CD4+ T cells and refers to disease activity in ulcerative colitis

Background: Ulcerative colitis (UC) is a chronically remittent and progressive inflammatory disorder. LRCH1 is reported to be involved in the immune-regulation of several diseases. However, the exact roles of LRCH1 in UC are still obscure. Materials and Methods: LRCH1 expression was analyzed in the inflamed mucosa and peripheral blood mononuclear cells (PBMCs) from patients with UC by quantitative RT-PCR and immunohistochemistry. Peripheral blood CD4⁺ T cells were transfected with lentivirus-expressing LRCH1 (LV-LRCH1) or LV-sh-LRCH1, and cytokine expression was determined by using flow cytometry, quantitative RT-PCR and ELISA. Transfected CD4⁺ T cells were harvested to examine the capacity of chemotaxis using Transwell plate. Results: LRCH1 expression was highly decreased in colonic mucosa and PBMCs from patients with A-UC, and negatively correlated with disease activity. Up or down regulation of LRCH1 did not affect the differentiation of CD4⁺ T cells, and the related cytokines expression. Moreover, LRCH1 inhibited migratory capacity of CD4⁺ T cells toward CXCL12 by PKCα. Conclusion: LRCH1 plays an important role in the pathogenesis of UC, possibly through modulating the migration of CD4⁺ T cells. Therefore, targeting LRCH1 might serve as a novel therapeutic approach in the management of UC.

Low dose of IL-2 combined with rapamycin restores and maintains the long-term balance of Th17/Treg cells in refractory SLE patients

BACKGROUND

The development of Systemic lupus erythematosus (SLE) has been associated with the balance of Th17 and Treg cells. IL-2 and rapamycin can influence the populations of both Th17 and Treg cells. However, it is unclear whether low dose of IL-2 and rapamycin can relieve the symptoms of SLE patients and what is the mechanisms. In this study, we aim to analyze the effect of low dose of IL-2 plus rapamycin on the number of Tregs, Th17 cells and the ratio of Th17/Treg cells, as well as to evaluate its therapeutic efficacy in refractory SLE patients.

RESULT

Fifty refractory SLE patients and 70 healthy controls were enrolled and followed up for 24 weeks. We found that compared with HC, the refractory SLE patients had a lower number of Tregs, a similar number of Th17 cells, but an increased ratio of Th17/Treg. After the treatment, the number of Tregs of the patients at 12th and 24th week was significantly increased. While the number of Th17 cells was unchanged, the ratio of Th17/Treg was significantly decreased at both 6 weeks and 24 weeks. After 6, 12 and 24 weeks of treatment, the SLEDAI score was significantly reduced. The prednison dosage at 6th,12th and 24th week post treatment was significantly decreased.

CONCLUSION

Our results support that the reduction of Tregs and the imbalance of Th17/Treg cells were correlated with the occurrence and development of refractory SLE. Low dose of IL-2 combined with rapamycin was able to restore the number of Tregs and the balance of Th17/Treg cells. As a result, this approach was able to induce immune tolerance and promote disease remission, allowing for the reduction in prednisone dosage.

TRIAL REGISTRATION

ChiCTR-IPR-16009451 Registration date: 2016/10/16.

Downregulation of miR-633 activated AKT/mTOR pathway by targeting AKT1 in lupus CD4+ T cells

Background

Accumulating evidence suggests that the AKT/mTOR pathway plays an important role in the pathogenesis of systemic lupus erythematosus (SLE) through activating T cells, and there are few studies looking into the role of microRNA (miRNAs) in the mechanism. We first found that miR-633 expression in CD4+T cells of SLE patients was significantly reduced.

Objective

To investigate the role of miR-633 in the AKT/mTOR pathway in lupus CD4+T cells.

Methods

Samples of 17 SLE cases and 16 healthy controls were collected to detect the expression of miR-633, AKT1, mTOR mRNA and proteins by quantitative polymerase chain reaction (qPCR) and Western-blot, respectively. To determine whether AKT1 is a direct target of miR-633, a luciferase assay was performed. In vitro, AKT1 siRNA, miR-633 mimics/inhibitors or negative controls were transfected to Jurkat cells, human primary CD4+T cells and lupus CD4+T cells. RNA and proteins were extracted after 48 h, and levels of AKT/mTOR pathway markers and downstream multiple cytokines were detected by qPCR or Western-blot.

Results

In SLE patients, the miR-633 levels in CD4+T cells were significantly decreased and negatively correlated with SLEDAI. AKT1, mTOR mRNA and proteins were all up-regulated. The degree of downregulation of miR-633 was correlated negatively with AKT1 mRNA. The luciferase assay proved that AKT1 is a direct target of miR-633. In Jurkat and lupus CD4+T cells, overexpression of miR-633 could result in lower levels of AKT1 and mTOR. Inhibition of miR-633 expression in primary CD4+T cells caused reverse effects, and protein levels of p-AKT, p-mTOR, and p-S6RP increased. Moreover, among various cytokines, the expression of IL-4, IL-17, and IFN-γ mRNA was raised.

Conclusion

Our study suggests that miR-633 deletion can activate the AKT/mTOR pathway by targeting AKT1 to participate in the pathogenesis of SLE.

mTOR inhibitor INK128 attenuates systemic lupus erythematosus by regulating inflammation-induced CD11b+Gr1+ cells

Systemic lupus erythematosus (SLE) is an autoimmune disease, characterized by systemic chronic inflammation that can affect multiple major organ systems. Although the etiology of SLE is known to involve a variety of factors such as the environment, random factors and genetic susceptibility, the exact role of CD11b⁺Gr1⁺ myeloid cells in lupus progression is not fully understood. Myeloid-derived CD11b⁺Gr1⁺ cells are thought to be a heterogeneous group of immature myeloid cells with immune function. Some studies have reported that CD11b⁺Gr1⁺ cells and the activation of mTOR pathway are involved in the pathogenesis of systemic lupus erythematosus (SLE). However, it is still not clarified about the mechanism of influence of lupus microenvironment and mTOR signaling on CD11b⁺Gr1⁺ cells. In the present study, we found that the percentage of CD11b⁺Gr1⁺ cells increased prior to the abnormal changes of Th17, Treg, T and B cells during lupus development. TLR7 and IFN-α signaling synergized to promote CD11b⁺Gr1⁺ cell accumulation in an mTOR-dependent manner. Moreover, compared to a traditional mTOR inhibitor, INK128 inhibited more effectively the disease activity via regulating CD11b⁺Gr1⁺ cell expansion and functions. Furthermore, TLR7/IFN-α-modified CD11b⁺Gr1⁺ cells promoted unbalance of Th17/Tregs and were inclined to differentiate into macrophages via the mTOR pathway. In conclusion, CD11b⁺Gr1⁺ cells increased in the early stages of the lupus progression and mTOR pathway was critical for CD11b⁺Gr1⁺ cells in lupus development, suggesting the changes of inflammation-induced CD11b⁺Gr1⁺ cells initate lupus development. We also provide evidence for the first time that INK128, a second generation mTOR inhibitor, has a good therapeutic action on lupus development by regulating CD11b⁺Gr1⁺ cells.

Curcumin down-regulates IL-17A mediated p53-fibrinolytic system in bleomycin induced acute lung injury in vivo

Bleomycin (BLM) induced cellular damage causes inflammation in the alveolar compartment and impairment of fibrinolytic system leads to alveolar epithelial cell apoptosis. Here, we describe novel inflammatory pathway associated with p53-fibrinolytic system and apoptosis of alveolar epithelial cells and pharmacological efficiency of curcumin against this action. In the present study we used C57BL/6 mice. The specific dose and time interval of curcumin were analyzed to assess the intervention. Experiments were designed to investigate the IL-17A mediated modulation in the alveolar epithelial cell apoptosis and injury. Various techniques such as Western blot, RT-PCR, Immunohistochemistry were used for this study. We observed that the BLM-induced lung injury and its progression were successfully regulated by the effective dose and time intervention of curcumin. There was also decreased expression of chemokines, p53, and fibrinolytic components such as PAI-1 and increased uPA, uPAR expression, and decreased alveolar epithelial cell apoptosis, which indicates the IL-17A mediated novel inflammatory pathway. It is confirmed that the IL-17A involved in the modulation of p53-fibrinolytic system and epithelial cell apoptosis in BLM induced mice. The cross-talk between the inflammatory, fibrinolytic, and apoptotic pathways were resolved by curcumin intervention. This pathway and intervention could serve as a modern therapy to resolve the complications to cure the lung injury and its progression.

Aberrant T Cell Signaling and Subsets in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a chronic multi-organ debilitating autoimmune disease, which mainly afflicts women in the reproductive years. A complex interaction of genetics, environmental factors and hormones result in the breakdown of immune tolerance to "self" leading to damage and destruction of multiple organs, such as the skin, joints, kidneys, heart and brain. Both innate and adaptive immune systems are critically involved in the misguided immune response against self-antigens. Dendritic cells, neutrophils, and innate lymphoid cells are important in initiating antigen presentation and propagating inflammation at lymphoid and peripheral tissue sites. Autoantibodies produced by B lymphocytes and immune complex deposition in vital organs contribute to tissue damage. T lymphocytes are increasingly being recognized as key contributors to disease pathogenesis. CD4 T follicular helper cells enable autoantibody production, inflammatory Th17 subsets promote inflammation, while defects in regulatory T cells lead to unchecked immune responses. A better understanding of the molecular defects including signaling events and gene regulation underlying the dysfunctional T cells in SLE is necessary to pave the path for better management, therapy, and perhaps prevention of this complex disease. In this review, we focus on the aberrations in T cell signaling in SLE and highlight therapeutic advances in this field.

Metabolism as a Target for Modulation in Autoimmune Diseases

Metabolic pathways are now well recognized as important regulators of immune differentiation and activation, and thus influence the development of autoimmune diseases such as systemic lupus erythematosus (SLE). The mechanistic target of rapamycin (mTOR) has emerged as a key sensor of metabolic stress and an important mediator of proinflammatory lineage specification. Metabolic pathways control the production of mitochondrial reactive oxygen species (ROS), which promote mTOR activation and also modulate the antigenicity of proteins, lipids, and DNA, thus placing ROS at the heart of metabolic disturbances during pathogenesis of SLE. Therefore, we review here the pathways that control ROS production and mTOR activation and identify targets for safe therapeutic modulation of the signaling network that underlies autoimmune diseases, focusing on SLE.

T cells and autoimmune kidney disease

Glomerulonephritis is traditionally considered to result from the invasion of the kidney by autoantibodies and immune complexes from the circulation or following their formation in situ, and by cells of the innate and the adaptive immune system. The inflammatory response leads to the proliferation and dysfunction of cells of the glomerulus, and invasion of the interstitial space with immune cells, resulting in tubular cell malfunction and fibrosis. T cells are critical drivers of autoimmunity and related organ damage, by supporting B-cell differentiation and antibody production or by directly promoting inflammation and cytotoxicity against kidney resident cells. T cells might become activated by autoantigens in the periphery and become polarized to secrete inflammatory cytokines before entering the kidney where they have the opportunity to expand owing to the presence of costimulatory molecules and activating cytokines. Alternatively, naive T cells could enter the kidney where they become activated after encountering autoantigen and expand locally. As not all individuals with a peripheral autoimmune response to kidney antigens develop glomerulonephritis, the contribution of local kidney factors expressed or produced by kidney cells is probably of crucial importance. Improved understanding of the biochemistry and molecular biology of T cells in patients with glomerulonephritis offers unique opportunities for the recognition of treatment targets for autoimmune kidney disease.

Activation of the Mechanistic Target of Rapamycin in SLE: Explosion of Evidence in the Last Five Years

The mechanistic target of rapamycin (mTOR) is a central regulator in cell growth, activation, proliferation, and survival. Activation of the mTOR pathway underlies the pathogenesis of systemic lupus erythematosus (SLE). While mTOR activation and its therapeutic reversal were originally discovered in T cells, recent investigations have also uncovered roles in other cell subsets including B cells, macrophages, and "non-immune" organs such as the liver and the kidney. Activation of mTOR complex 1 (mTORC1) precedes the onset of SLE and associated co-morbidities, such as anti-phospholipid syndrome (APS), and may act as an early marker of disease pathogenesis. Six case reports have now been published that document the development of SLE in patients with genetic activation of mTORC1. Targeting mTORC1 over-activation with N-acetylcysteine, rapamycin, and rapalogs provides an opportunity to supplant current therapies with severe side effect profiles such as prednisone or cyclophosphamide. In the present review, we will discuss the recent explosion of findings in support for a central role for mTOR activation in SLE.

T cells in Systemic Lupus Erythematosus

Systemic Lupus Erythematosus is an autoimmune disorder caused by a complex combination of genetic, epigenetic and environmental factors. Different polymorphisms and epigenetic modifications lead to altered gene expression and function of several molecules which lead to abnormal T cell responses. Metabolic and functional alterations result in peripheral tolerance failures and biased differentiation of T cells into pro-inflammatory and B cell-helper phenotypes as well as the accumulation of disease-promoting memory T cells. Understanding these T cell alterations and their origins is necessary to develop more accurate patient classification systems and to discover new therapeutic targets.

Antiphospholipid syndrome and kidney disease

The antiphospholipid syndrome is a common autoimmune disease caused by pathogenic antiphospholipid antibodies, leading to recurrent thrombosis and/or obstetrical complications. Importantly for nephrologists, antiphospholipid antibodies are associated with various renal manifestations including large renal vessel thrombosis, renal artery stenosis, and a constellation of intrarenal lesions that has been termed antiphospholipid nephropathy. This last condition associates various degrees of acute thrombotic microangiopathy, proliferative and fibrotic lesions of the intrarenal vessels, and ischemic modifications of the renal parenchyma. The course of the disease can range from indolent nephropathy to devastating acute renal failure. The pejorative impact of antiphospholipid antibody-related renal complication is well established in the context of systemic lupus erythematous or after renal transplantation. In contrast, the exact significance of isolated antiphospholipid nephropathy remains uncertain. The evidence to guide management of the renal complications of antiphospholipid syndrome is limited. However, the recent recognition of the heterogeneous molecular mechanisms underlying the progression of intrarenal vascular lesions in antiphospholipid syndrome have opened promising tracks for patient monitoring and targeted therapeutic intervention.

Activation of mTOR (mechanistic target of rapamycin) in rheumatic diseases

Mechanistic target of rapamycin (mTOR, also known as mammalian target of rapamycin) is a ubiquitous serine/threonine kinase that regulates cell growth, proliferation and survival. These effects are cell-type-specific, and are elicited in response to stimulation by growth factors, hormones and cytokines, as well as to internal and external metabolic cues. Rapamycin was initially developed as an inhibitor of T-cell proliferation and allograft rejection in the organ transplant setting. Subsequently, its molecular target (mTOR) was identified as a component of two interacting complexes, mTORC1 and mTORC2, that regulate T-cell lineage specification and macrophage differentiation. mTORC1 drives the proinflammatory expansion of T helper (TH) type 1, TH17, and CD4(-)CD8(-) (double-negative, DN) T cells. Both mTORC1 and mTORC2 inhibit the development of CD4(+)CD25(+)FoxP3(+) T regulatory (TREG) cells and, indirectly, mTORC2 favours the expansion of T follicular helper (TFH) cells which, similarly to DN T cells, promote B-cell activation and autoantibody production. In contrast to this proinflammatory effect of mTORC2, mTORC1 favours, to some extent, an anti-inflammatory macrophage polarization that is protective against infections and tissue inflammation. Outside the immune system, mTORC1 controls fibroblast proliferation and chondrocyte survival, with implications for tissue fibrosis and osteoarthritis, respectively. Rapamycin (which primarily inhibits mTORC1), ATP-competitive, dual mTORC1/mTORC2 inhibitors and upstream regulators of the mTOR pathway are being developed to treat autoimmune, hyperproliferative and degenerative diseases. In this regard, mTOR blockade promises to increase life expectancy through treatment and prevention of rheumatic diseases.

mTORC1 signaling and IL-17 expression: Defining pathways and possible therapeutic targets

IL-17 mediates immune responses against extracellular pathogens, and it is associated with the development and pathogenesis of various autoimmune diseases. The expression of IL-17 is regulated by various intracellular signaling cascades. Recently, it has been shown that mechanistic target of rapamycin (mTOR) signaling, comprised mainly of mTORC1 signaling, plays a critical role in IL-17 expression. Here, we review the current knowledge regarding mechanisms by which mTORC1 regulates IL-17 expression. mTORC1 positively modulates IL-17 expression through several pathways, i.e. STAT3, -HIF-1α, -S6K1, and -S6K2. Amino acids (AAs) also regulate IL-17 expression by being the energy source for Th17 cells, and by activating mTORC1 signaling. Altogether, the AA-mTORC1-IL-17 axis has broad therapeutic implications for IL-17-associated diseases, such as EAE, allergies, and colitis.

C5a alters blood-brain barrier integrity in a human in vitro model of systemic lupus erythematosus

The blood-brain barrier (BBB) plays a crucial role in brain homeostasis, thereby maintaining the brain environment precise for optimal neuronal function. Its dysfunction is an intriguing complication of systemic lupus erythematosus (SLE). SLE is a systemic autoimmune disorder where neurological complications occur in 5-50% of cases and is associated with impaired BBB integrity. Complement activation occurs in SLE and is an important part of the clinical profile. Our earlier studies demonstrated that C5a generated by complement activation caused the loss of brain endothelial layer integrity in rodents. The goal of the current study was to determine the translational potential of these studies to a human system. To assess this, we used a two dimensional in vitro BBB model constructed using primary human brain microvascular endothelial cells and astroglial cells, which closely emulates the in vivo BBB allowing the assessment of BBB integrity. Increased permeability monitored by changes in transendothelial electrical resistance and cytoskeletal remodelling caused by actin fiber rearrangement were observed when the cells were exposed to lupus serum and C5a, similar to the observations in mice. In addition, our data show that C5a/C5aR1 signalling alters nuclear factor-κB translocation into nucleus and regulates the expression of the tight junction proteins, claudin-5 and zonula occludens 1 in this setting. Our results demonstrate for the first time that C5a regulates BBB integrity in a neuroinflammatory setting where it affects both endothelial and astroglial cells. In addition, we also demonstrate that our previous findings in a mouse model, were emulated in human cells in vitro, bringing the studies one step closer to understanding the translational potential of C5a/C5aR1 blockade as a promising therapeutic strategy in SLE and other neurodegenerative diseases.