Functional consequence of Iron dyshomeostasis and ferroptosis in systemic lupus erythematosus and lupus nephritis.

Systemic lupus erythematosus (SLE) and its renal manifestation Lupus nephritis (LN) are characterized by a dysregulated immune system, autoantibodies, and injury to the renal parenchyma. Iron accumulation and ferroptosis in the immune effectors and renal tubules are recently identified pathological features in SLE and LN. Ferroptosis is an iron dependent non-apoptotic form of regulated cell death and ferroptosis inhibitors have improved disease outcomes in murine models of SLE, identifying it as a novel druggable target. In this review, we discuss novel mechanisms by which iron accumulation and ferroptosis perpetuate immune cell mediated pathology in SLE/LN. We highlight intra-renal dysregulation of iron metabolism and ferroptosis as an underlying pathogenic mechanism of renal tubular injury. The basic concepts of iron biology and ferroptosis are also discussed to expose the links between iron, cell metabolism and ferroptosis, that identify intracellular pro-ferroptotic enzymes and their protein conjugates as potential targets to improve SLE/LN outcomes.

Male kidney-specific BMAL1 knockout mice are protected from K+-deficient, high-salt diet-induced blood pressure increases.

The circadian clock protein basic helix-loop-helix aryl hydrocarbon receptor nuclear translocator-like protein 1 (BMAL1) is a transcription factor that impacts kidney function, including blood pressure (BP) control. Previously, we have shown that male, but not female, kidney-specific cadherin Cre-positive BMAL1 knockout (KS-BMAL1 KO) mice exhibit lower BP compared with littermate controls. The goal of this study was to determine the BP phenotype and immune response in male KS-BMAL1 KO mice in response to a low-K+ high-salt (LKHS) diet. BP, renal inflammatory markers, and immune cells were measured in male mice following an LKHS diet. Male KS-BMAL1 KO mice had lower BP following the LKHS diet compared with control mice, yet their circadian rhythm in pressure remained unchanged. Additionally, KS-BMAL1 KO mice exhibited lower levels of renal proinflammatory cytokines and immune cells following the LKHS diet compared with control mice. KS-BMAL1 KO mice were protected from the salt-sensitive hypertension observed in control mice and displayed an attenuated immune response following the LKHS diet. These data suggest that BMAL1 plays a role in driving the BP increase and proinflammatory environment that occurs in response to an LKHS diet.NEW & NOTEWORTHY We show here, for the first time, that kidney-specific BMAL1 knockout mice are protected from blood pressure (BP) increases and immune responses to a salt-sensitive diet. Other kidney-specific BMAL1 knockout models exhibit lower BP phenotypes under basal conditions. A salt-sensitive diet exacerbates this genotype-specific BP response, leading to fewer proinflammatory cytokines and immune cells in knockout mice. These data demonstrate the importance of distal segment BMAL1 in BP and immune responses to a salt-sensitive environment.

Kidney tubular epithelial cell ferroptosis links glomerular injury to tubulointerstitial pathology in lupus nephritis.

Ferroptosis is a druggable, iron-dependent form of cell death that is characterized by lipid peroxidation but has received little attention in lupus nephritis. Kidneys of lupus nephritis patients and mice showed increased lipid peroxidation mainly in the tubular segments and an increase in Acyl-CoA synthetase long-chain family member 4, a pro-ferroptosis enzyme. Nephritic mice had an attenuated expression of SLC7A11, a cystine importer, an impaired glutathione synthesis pathway, and low expression of glutathione peroxidase 4, a ferroptosis inhibitor. Lipidomics of nephritic kidneys confirmed ferroptosis. Using nephrotoxic serum, we induced immune complex glomerulonephritis in congenic mice and demonstrate that impaired iron sequestration within the proximal tubules exacerbates ferroptosis. Lupus nephritis patient serum rendered human proximal tubular cells susceptibility to ferroptosis which was inhibited by Liproxstatin-2, a novel ferroptosis inhibitor. Collectively, our findings identify intra-renal ferroptosis as a pathological feature and contributor to tubular injury in human and murine lupus nephritis.

COVID-19-associated pulmonary aspergillosis in immunocompetent patients: a virtual patient cohort study.

The opportunistic fungus Aspergillus fumigatus infects the lungs of immunocompromised hosts, including patients undergoing chemotherapy or organ transplantation. More recently however, immunocompetent patients with severe SARS-CoV2 have been reported to be affected by COVID-19 Associated Pulmonary Aspergillosis (CAPA), in the absence of the conventional risk factors for invasive aspergillosis. This paper explores the hypothesis that contributing causes are the destruction of the lung epithelium permitting colonization by opportunistic pathogens. At the same time, the exhaustion of the immune system, characterized by cytokine storms, apoptosis, and depletion of leukocytes may hinder the response to A. fumigatus infection. The combination of these factors may explain the onset of invasive aspergillosis in immunocompetent patients. We used a previously published computational model of the innate immune response to infection with Aspergillus fumigatus. Variation of model parameters was used to create a virtual patient population. A simulation study of this virtual patient population to test potential causes for co-infection in immunocompetent patients. The two most important factors determining the likelihood of CAPA were the inherent virulence of the fungus and the effectiveness of the neutrophil population, as measured by granule half-life and ability to kill fungal cells. Varying these parameters across the virtual patient population generated a realistic distribution of CAPA phenotypes observed in the literature. Computational models are an effective tool for hypothesis generation. Varying model parameters can be used to create a virtual patient population for identifying candidate mechanisms for phenomena observed in actual patient populations.

Aspergillus Utilizes Extracellular Heme as an Iron Source During Invasive Pneumonia, Driving Infection Severity.

BACKGROUND: Depriving microbes of iron is critical to host defense. Hemeproteins, the largest source of iron within vertebrates, are abundant in infected tissues in aspergillosis due to hemorrhage, but Aspergillus species have been thought to lack heme import mechanisms. We hypothesized that heme provides iron to Aspergillus during invasive pneumonia, thereby worsening the outcomes of the infection. METHODS: We assessed the effect of heme on fungal phenotype in various in vitro conditions and in a neutropenic mouse model of invasive pulmonary aspergillosis. RESULTS: In mice with neutropenic invasive aspergillosis, we found a progressive and compartmentalized increase in lung heme iron. Fungal cells cultured under low iron conditions took up heme, resulting in increased fungal iron content, resolution of iron starvation, increased conidiation, and enhanced resistance to oxidative stress. Intrapulmonary administration of heme to mice with neutropenic invasive aspergillosis resulted in markedly increased lung fungal burden, lung injury, and mortality, whereas administration of heme analogs or heme with killed Aspergillus did not. Finally, infection caused by fungal germlings cultured in the presence of heme resulted in a more severe infection. CONCLUSIONS: Invasive aspergillosis induces local hemolysis in infected tissues, thereby supplying heme iron to the fungus, leading to lethal infection.

Neutrophil-Derived Tumor Necrosis Factor Drives Fungal Acute Lung Injury in Chronic Granulomatous Disease.

Chronic granulomatous disease (CGD) results from deficiency of nicotinamide adenine dinucleotide phosphate(NADPH) oxidase and impaired reactive oxygen species (ROS) generation. This leads to impaired killing of Aspergillus and, independently, a pathologic hyperinflammatory response to the organism. We hypothesized that neutrophil-derived ROS inhibit the inflammatory response to Aspergillus and that acute lung injury in CGD is due to failure of this regulation. Mice with gp91phox deficiency, the most common CGD mutation, had more severe lung injury, increased neutrophilinfiltration, and increased lung tumor necrosis factor (TNF) after Aspergillus challenge compared with wild-types. Neutrophils were surprisingly the predominant source of TNF in gp91phox-deficient lungs. TNF neutralization inhibited neutrophil recruitment in gp91phox-deficient mice and protected from lung injury. We propose that, in normal hosts, Aspergillus stimulates TNF-dependent neutrophil recruitment to the lungs and neutrophil-derived ROS limit inflammation. In CGD, in contrast, recruited neutrophils are the dominant source of TNF, promoting further neutrophil recruitment in a pathologic positive-feedback cycle, resulting in progressive lung injury.

The Mechanism of Mitochondrial Injury in Alpha-1 Antitrypsin Deficiency Mediated Liver Disease.

Alpha-1 antitrypsin deficiency (AATD) is caused by a single mutation in the SERPINA1 gene, which culminates in the accumulation of misfolded alpha-1 antitrypsin (ZAAT) within the endoplasmic reticulum (ER) of hepatocytes. AATD is associated with liver disease resulting from hepatocyte injury due to ZAAT-mediated toxic gain-of-function and ER stress. There is evidence of mitochondrial damage in AATD-mediated liver disease; however, the mechanism by which hepatocyte retention of aggregated ZAAT leads to mitochondrial injury is unknown. Previous studies have shown that ER stress is associated with both high concentrations of fatty acids and mitochondrial dysfunction in hepatocytes. Using a human AAT transgenic mouse model and hepatocyte cell lines, we show abnormal mitochondrial morphology and function, and dysregulated lipid metabolism, which are associated with hepatic expression and accumulation of ZAAT. We also describe a novel mechanism of ZAAT-mediated mitochondrial dysfunction. We provide evidence that misfolded ZAAT translocates to the mitochondria for degradation. Furthermore, inhibition of ZAAT expression restores the mitochondrial function in ZAAT-expressing hepatocytes. Altogether, our results show that ZAAT aggregation in hepatocytes leads to mitochondrial dysfunction. Our findings suggest a plausible model for AATD liver injury and the possibility of mechanism-based therapeutic interventions for AATD liver disease.

Protective role of DJ-1 in endotoxin-induced acute kidney injury.

Acute kidney injury (AKI) is a frequent complication of sepsis and an important cause of morbidity and mortality worldwide. A cornerstone of sepsis-associated AKI is dysregulated inflammation, leading to increased tissue oxidative stress and free radical formation, which leads to multiple forms of cell death. DJ-1 is a peroxiredoxin protein with multiple functions, including its ability to control cellular oxidative stress. Although DJ-1 is expressed prominently by renal tubules, its role in AKI has not been investigated. In the present study, we examined the effect of DJ-1 deficiency in a murine model of endotoxin-induced AKI. Endotoxemia induced greater kidney injury in DJ-1-deficient mice. Furthermore, DJ-1 deficiency increased renal oxidative stress associated with increased renal tubular apoptosis and with expression of death domain-associated protein (DAXX). Similar to the in vivo model, in vitro experiments using a medullary collecting duct cell line (mIMCD3) and cytotoxic serum showed that serum obtained from wild-type mice resulted in increased expression of s100A8/s100A9, DAXX, and apoptosis in DJ-1-deficient mIMCD3 cells. Our findings demonstrate a novel renal protective role for renal tubular DJ-1 during endotoxemia through control of oxidative stress, renal inflammation, and DAXX-dependent apoptosis.

Modulation of iron homeostasis with hepcidin ameliorates spontaneous murine lupus nephritis.

Lupus nephritis is the end organ manifestation of systemic lupus erythematosus. Iron metabolism and its master regulator, hepcidin, are known to regulate cell proliferation and inflammation, but their direct role in the pathophysiology of lupus nephritis remains under-investigated. Exogenous hepcidin reduced the severity of lupus nephritis in MRL/lpr mice, a preclinical model of spontaneous systemic lupus erythematosus without worsening anemia of inflammation. Hepcidin treatment reduced renal iron accumulation, systemic and intrarenal cytokines, and renal immune cell infiltration, independent of glomerular immune complex deposits and circulating autoantibodies. Hepcidin increased renal H-ferritin (a ferroxidase), reduced expression of free iron dependent DNA synthesis enzymes, Ribonucleotide Reductase 1 and 2, and intra-renal macrophage proliferation. These findings were recapitulated in vitro upon treatment of macrophages with hepcidin and murine colony stimulation factor-1. Furthermore, hepcidin-treated macrophages secreted less IL-1ß and IL-6 upon stimulation with the TLR3 agonist polyinosine-polycytidylic acid. Of clinical relevance, hepcidin reduced progression and severity of nephritis in old mice with established systemic autoimmunity and overt proteinuria, highlighting its therapeutic potential. Thus, our findings provide a proof-of-concept that targeting cellular iron metabolism with hepcidin represents a promising therapeutic strategy in lupus nephritis.

Circulating fibrocytes traffic to the lung in murine acute lung injury and predict outcomes in human acute respiratory distress syndrome: a pilot study.

BACKGROUND: Fibrosis is an integral component of the pathogenesis of acute lung injury and is associated with poor outcomes in patients with acute respiratory distress syndrome (ARDS). Fibrocytes are bone marrow-derived cells that traffic to injured tissues and contribute to fibrosis; hence their concentration in the peripheral blood has the potential to serve as a biomarker of lung fibrogenesis. We therefore sought to test the hypothesis that the concentration and phenotype of circulating fibrocytes in patients with ARDS predicts clinical outcomes. METHODS: For the animal studies, C57Bl/6 mice were infected with experimental Klebsiella pneumoniae in a model of acute lung injury; one-way ANOVA was used to compare multiple groups and two-way ANOVA was used to compare two groups over time. For the human study, 42 subjects with ARDS and 12 subjects with pneumonia (without ARDS) were compared to healthy controls. Chi-squared or Fisher's exact test were used to compare binary outcomes. Survival data was expressed using a Kaplan-Meier curve and compared by log-rank test. Univariable and multivariable logistic regression were used to predict death. RESULTS: In mice with acute lung injury caused by Klebsiella pneumonia, there was a time-dependent increase in lung soluble collagen that correlated with sequential expansion of fibrocytes in the bone marrow, blood, and then lung compartments. Correspondingly, when compared via cross-sectional analysis, the initial concentration of blood fibrocytes was elevated in human subjects with ARDS or pneumonia as compared to healthy controls. In addition, fibrocytes from subjects with ARDS displayed an activated phenotype and on serial measurements, exhibited intermittent episodes of markedly elevated concentration over a median of 1 week. A peak concentration of circulating fibrocytes above a threshold of > 4.8 × 106 cells/mL cells correlated with mortality that was independent of age, ratio of arterial oxygen concentration to the fraction of inspired oxygen, and vasopressor requirement. CONCLUSIONS: Circulating fibrocytes increase in a murine model of acute lung injury and elevation in the number of these cells above a certain threshold is correlated with mortality in human ARDS. Therefore, these cells may provide a useful and easily measured biomarker to predict outcomes in these patients.

Biocompatibility of ferritin-based nanoparticles as targeted MRI contrast agents.

Ferritin is a naturally occurring iron storage protein, proposed as a clinically relevant nanoparticle with applications as a diagnostic and therapeutic agent. Cationic ferritin is a targeted, injectable contrast agent to measure kidney microstructure with MRI. Here, the toxicity of horse spleen ferritin is assessed as a step to clinical translation. Adult male mice received cationic, native and high dose cationic ferritin (CF, NF, or HDCF) or saline and were monitored for 3weeks. Transient weight loss occurred in the ferritin groups with no difference in renal function parameters. Ferritin-injected mice demonstrated a lower serum iron 3weeks after administration. In ferritin-injected animals pre-treated with hydrocortisone, there were no structural or weight differences in the kidneys, liver, lung, heart, or spleen. This study demonstrates a lack of significant detrimental effects of horse-derived ferritin-based nanoparticles at MRI-detectable doses, allowing further exploration of these agents in basic research and clinical diagnostics.

Hepcidin Mitigates Renal Ischemia-Reperfusion Injury by Modulating Systemic Iron Homeostasis.

Iron-mediated oxidative stress is implicated in the pathogenesis of renal ischemia-reperfusion injury. Hepcidin is an endogenous acute phase hepatic hormone that prevents iron export from cells by inducing degradation of the only known iron export protein, ferroportin. In this study, we used a mouse model to investigate the effect of renal ischemia-reperfusion injury on systemic iron homeostasis and determine if dynamic modulation of iron homeostasis with hepcidin has therapeutic benefit in the treatment of AKI. Renal ischemia-reperfusion injury induced hepatosplenic iron export through increased ferroportin expression, which resulted in hepatosplenic iron depletion and an increase in serum and kidney nonheme iron levels. Exogenous hepcidin treatment prevented renal ischemia-reperfusion-induced changes in iron homeostasis. Hepcidin also decreased kidney ferroportin expression and increased the expression of cytoprotective H-ferritin. Hepcidin-induced restoration of iron homeostasis was accompanied by a significant reduction in ischemia-reperfusion-induced tubular injury, apoptosis, renal oxidative stress, and inflammatory cell infiltration. Hepcidin -: deficient mice demonstrated increased susceptibility to ischemia-reperfusion injury compared with wild-type mice. Reconstituting hepcidin-deficient mice with exogenous hepcidin induced hepatic iron sequestration, attenuated the reduction in renal H-ferritin and reduced renal oxidative stress, apoptosis, inflammation, and tubular injury. Hepcidin-mediated protection was associated with reduced serum IL-6 levels. In summary, renal ischemia-reperfusion injury results in profound alterations in systemic iron homeostasis. Hepcidin treatment restores iron homeostasis and reduces inflammation to mediate protection in renal ischemia-reperfusion injury, suggesting that hepcidin-ferroportin pathway holds promise as a novel therapeutic target in the treatment of AKI.

Animal models of lupus nephritis: the past, present and a future outlook.

Lupus nephritis (LN) is the most severe end-organ pathology in Systemic Lupus Erythematosus (SLE). Research has enhanced our understanding of immune effectors and inflammatory pathways in LN. However, even with the best available therapy, the rate of complete remission for proliferative LN remains below 50%. A deeper understanding of the resistance or susceptibility of renal cells to injury during the progression of SLE is critical for identifying new targets and developing effective long-term therapies. The complex and heterogeneous nature of LN, combined with the limitations of clinical research, make it challenging to investigate the aetiology of this disease directly in patients. Hence, multiple murine models resembling SLE-driven nephritis are utilised to dissect LN's cellular and genetic mechanisms, identify therapeutic targets, and screen novel compounds. This review discusses commonly used spontaneous and inducible mouse models that have provided insights into pathogenic mechanisms and long-term maintenance therapies in LN.

Enrichment of Bioactive Lipids in Urinary Extracellular Vesicles and Evidence of Apoptosis in Kidneys of Hypertensive Diabetic Cathepsin B Knockout Mice after Streptozotocin Treatment.

Cathepsin B (CtsB) is a ubiquitously expressed cysteine protease that plays important roles in health and disease. Urinary extracellular vesicles (uEVs) are released from cells associated with urinary organs. The antibiotic streptozotocin (STZ) is known to induce pancreatic islet beta cell destruction, diabetic nephropathy, and hypertension. We hypothesized that streptozotocin-induced diabetic kidney disease and hypertension result in the release of bioactive lipids from kidney cells that induce oxidative stress and renal cell death. Lipidomics was performed on uEVs isolated from CtsB knockout mice treated with or without STZ, and their kidneys were used to investigate changes in proteins associated with cell death. Lysophosphatidylethanolamine (LPE) (18:1), lysophosphatidylserine (LPS) (22:6), and lysophosphatidylglycerol (LPG) (22:5) were among the bioactive lipids enriched in uEVs from CtsB knockout mice treated with STZ compared to untreated CtsB mice (n = 3 uEV preparations per group). Anti-oxidant programming was activated in the kidneys of the CtsB knockout mice treated with STZ, as indicated by increased expression of glutathione peroxidase 4 (GPX4) and the cystine/glutamate antiporter SLC7A11 (XCT) (n = 4 mice per group), which was supported by a higher reactivity to 4-hydroxy-2-nonenal (4-HNE), a marker for oxidative stress (n = 3 mice per group). Apoptosis but not ferroptosis was the ongoing form of cell death in these kidneys as cleaved caspase-3 levels were significantly elevated in the STZ-treated CtsB knockout mice (n = 4 mice per group). There were no appreciable differences in the pro-ferroptosis enzyme acyl-CoA synthetase long-chain family member 4 (ACSL4) or the inflammatory marker CD93 in the kidneys (n = 3 mice per group), which further supports apoptosis as the prevalent mechanism of pathology. These data suggest that STZ treatment leads to oxidative stress, inducing apoptotic injury in the kidneys during the development of diabetic kidney disease and hypertension.

COVID-19-associated pulmonary aspergillosis in immunocompetent patients: A virtual patient cohort study.

Purpose: The opportunistic fungus Aspergillus fumigatus infects the lungs of immunocompromised hosts, including patients undergoing chemotherapy or organ transplantation. More recently however, immunocompetent patients with severe SARS-CoV2 have been reported to be affected by COVID-19 Associated Pulmonary Aspergillosis (CAPA), in the absence of the conventional risk factors for invasive aspergillosis. This paper explores the hypothesis that contributing causes are the destruction of the lung epithelium permitting colonization by opportunistic pathogens. At the same time, the exhaustion of the immune system, characterized by cytokine storms, apoptosis, and depletion of leukocytes may hinder the response to A. fumigatus infection. The combination of these factors may explain the onset of invasive aspergillosis in immunocompetent patients. Methods: We used a previously published computational model of the innate immune response to infection with Aspergillus fumigatus . Variation of model parameters was used to create a virtual patient population. A simulation study of this virtual patient population to test potential causes for co-infection in immunocompetent patients. Results: The two most important factors determining the likelihood of CAPA were the inherent virulence of the fungus and the effectiveness of the neutrophil population, as measured by granule half-life and ability to kill fungal cells. Varying these parameters across the virtual patient population generated a realistic distribution of CAPA phenotypes observed in the literature. Conclusions: Computational models are an effective tool for hypothesis generation. Varying model parameters can be used to create a virtual patient population for identifying candidate mechanisms for phenomena observed in actual patient populations.

Metformin Alleviates Diabetes-Associated Hypertension by Attenuating the Renal Epithelial Sodium Channel.

Diabetic nephropathy is the primary cause of morbidity in type 2 diabetes mellitus (T2DM) patients. New data indicate that hypertension, a common comorbidity in T2DM, can worsen outcomes of diabetic nephropathy. While metformin is a commonly prescribed drug for treating type 2 diabetes, its blood pressure regulating ability is not well documented. The aim of this study was to investigate the effect of metformin on normalizing blood pressure in salt-loaded hypertensive diabetic db/db mice. Sixteen-week-old male and female diabetic db/db mice were individually placed in metabolic cages and then randomized to a control vehicle (saline) or metformin treatment group. We evaluated the blood pressure reducing ability of metformin in salt-induced hypertension and progression of nephropathy in db/db mice. We observed that metformin- normalized systolic blood pressure in hypertensive diabetic mice. Mechanistically, metformin treatment reduced renal cathepsin B expression. Low cathepsin B expression was associated with reduced expression and activity of the epithelial sodium channel (ENaC), sodium retention, and thus control of hypertension. In addition, we identified that urinary extracellular vesicles (EVs) from the diabetic mice are enriched in cathepsin B. Compared to treatment with urinary EVs of vehicle-treated hypertensive diabetic mice, the amiloride-sensitive transepithelial current was significantly attenuated upon exposure of renal collecting duct cells to urinary EVs isolated from metformin-treated db/db mice or cathepsin B knockout mice. Collectively, our study identifies a novel blood pressure reducing role of metformin in diabetic nephropathy by regulating the cathepsin B-ENaC axis.

Deficiency of a transcriptional regulator, inhibitor of differentiation 3, induces glomerulonephritis in apolipoprotein E-deficient mice: a model linking hyperlipidemia and renal disease.

The clinical association between hyperlipidemia and renal disease is well established, yet hyperlipidemia as a cause for renal disease is rare. Apolipoprotein E-deficient (ApoE(-/-)) mice develop hyperlipidemia and are a model for atherosclerosis. Introducing deficiency of inhibitor of differentiation 3 (Id3) in ApoE(-/-) mice further exacerbates atherosclerosis. ID3 is a transcription regulator expressed in multiple cell types. Id3(-/-) mice develop antibodies to self-antigens and salivary gland autoimmunity. This study was undertaken to investigate a link between hyperlipidemia, autoimmunity, and renal disease. ApoE(-/-), Id3(-/-), and ApoE(-/-)Id3(-/-) double-knockout (DKO) mice were studied at different ages for renal pathological features and function. Serum samples were analyzed for the presence of autoantibodies. At 16 weeks, DKO mice developed mesangioproliferative glomerulonephritis (GN), leading to severe proteinuria. GN was associated with glomerular deposition of lipids and immune complexes and with macrophage infiltration. DKO mice had high levels of circulating autoantibodies. Although ApoE(-/-) mice had glomerular lipid deposits and Id3(-/-) mice had circulating autoantibodies, neither group of age-matched single-knockout mice developed GN. These data provide support for the hypothesis that induction of renal disease in hyperlipidemia is dictated by additional factors. Our study shows that some of these factors are regulated by ID3. Thus, ID3 is a novel risk factor linking cardiovascular and renal disease.

Activated CD4+ T cells target mesangial antigens and initiate glomerulonephritis.

AIMS: The role of kidney infiltrating T cells in the pathology of lupus nephritis is unclear. This study was undertaken to investigate whether CD4+ T cell responses to a surrogate mesangial antigen can initiate glomerulonephritis. METHODS: Ovalbumin (OVA) was deposited in the glomerular mesangium of C57BL/6 (B6) mice using anti-α8-integrin immunoliposomes (α8ILs). This was followed by injection of activated OVA-reactive CD4+ transgenic OT2 T cells. Trafficking of antigen-specific OT2 T cells to kidneys and lymph nodes was studied by flow cytometry. Glomerular pathology and immune cell infiltration was characterized by immunostaining. Role of CCR2 deficiency on T cell-mediated glomerulonephritis was investigated using B6.ccr2(-/-) mice. RESULTS: α8ILs delivered OVA specifically to the renal glomeruli. Adoptively transferred OT2 T cells preferentially accumulated in renal lymph nodes and in the renal cortex. Kidneys showed glomerular inflammation with recruitment of endogenous T cells, dendritic cells and macrophages. T cell-mediated inflammation induced mesangial cell activation and an increase in glomerular MCP1 and fibronectin. The formation of inflammatory foci was driven by Ly6C monocytes and was CCR2 dependent. CONCLUSIONS: The findings from this study show that T cells reactive with antigens in the mesangium are sufficient to initiate glomerular pathology. Antigen-specific CD4 T cells act by inducing glomerular MCP1 production which mediates recruitment of inflammatory monocytes resulting in glomerulonephritis. Thus, down-modulation of T cell responses within the kidneys of lupus patients will be a beneficial therapeutic approach.

Labile iron accumulation augments T follicular helper cell differentiation.

T follicular helper (Tfh) cells are a subset of CD4+ T cells that are essential in the pathogenesis of systemic lupus erythematosus (SLE). Notably, iron is required for activated CD4+ T lymphocytes to sustain high proliferation and metabolism. In this issue of the JCI, Gao et al. showed that CD4+ T cells from patients with SLE accumulated iron, augmenting their differentiation into Tfh cells and correlating with disease activity. Using human cells and murine models, the authors demonstrated that miR-21 was overexpressed in lupus T cells and inhibited 3-hydroxybutyrate dehydrogenase-2 (BDH2). The subsequent loss of BDH2 drove labile iron to accumulate in the cytoplasm and promoted TET enzyme activity, BCL6 gene demethylation, and Tfh cell differentiation. This work identifies a role for iron in CD4+ T cell biology and the development of pathogenic effectors in SLE. We await future investigations that could determine whether modulating iron levels could regulate Tfh cells in human health and disease.