Hypoxia inducible factor-1 alpha promotes mesangial cell proliferation in lupus nephritis

Abnormal energy metabolism in the pathogenesis of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a severe autoimmune disease with significant socioeconomic impact worldwide. Orderly energy metabolism is essential for normal immune function, and disordered energy metabolism is increasingly recognized as an important contributor to the pathogenesis of SLE. Disorders of energy metabolism are characterized by increased reactive oxygen species, ATP deficiency, and abnormal metabolic pathways. Oxygen and mitochondria are critical for the production of ATP, and both mitochondrial dysfunction and hypoxia affect the energy production processes. In addition, several signaling pathways, including mammalian target of rapamycin (mTOR)/adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) signaling and the hypoxia-inducible factor (HIF) pathway also play important regulatory roles in energy metabolism. Furthermore, drugs with clear clinical effects on SLE, such as sirolimus, metformin, and tacrolimus, have been proven to improve the disordered energy metabolism of immune cells, suggesting the potential of targeting energy metabolism for the treatment of SLE. Moreover, several metabolic modulators under investigation are expected to have potential therapeutic effects in SLE. This review aimed to gain insights into the role and mechanism of abnormal energy metabolism in the pathogenesis of SLE, and summarizes the progression of metabolic modulator in the treatment of SLE.

LATS2 degradation promoted fibrosis damage and rescued by vitamin K3 in lupus nephritis

BACKGROUND

Lupus nephritis (LN) is the most common complication of systemic lupus erythematosus (SLE). The limited treatment options for LN increase the economic burdens on patients. Because fibrotic progression leads to irreversible renal damage in LN patients and further progresses to chronic kidney disease (CKD) and the end stage of renal disease (ESRD), developing new targets to prevent LN fibrotic progression could lead to a feasible treatment strategy for LN patients.

METHODS

In this study, we examined YAP activation and LATS2 downregulation in LN kidney biopsy samples (LN: n = 8, normal: n = 2) and lupus-prone MRL/lpr mice (n = 8 for each disease stage). The function of LATS2 was further investigated by in situ injection of Ad-LATS2 into mice with LN (n = 6 mice per group). We examined the role of SIAH2-LATS2 regulation by IP-MS and co-IP, and the protective effect of the SIAH2 inhibitor was investigated in mice with LN.

RESULTS

Restoring LATS2 by an adenovirus in vivo alleviated renal fibrotic damage in mice with LN. Moreover, we found that LATS2 was degraded by a K48 ubiquitination-proteasome pathway mediated by SIAH2 and promoted YAP activation to worsen fibrosis progression in LN. The H150 region of the substrate binding domain (SBD) is an important site for SIAH2-LATS2 binding. The SIAH2-specific inhibitor vitamin K3 protected against LN-associated fibrotic damage in vivo.

CONCLUSION

In summary, we identified the SIAH2-LATS2 axis as an attractive intervention target in LN to alter the resistance to fibrosis.

Transcription Factors in the Pathogenesis of Lupus Nephritis and Their Targeted Therapy

Systemic lupus erythematosus (SLE) is a prototype inflammatory autoimmune disease, characterized by breakdown of immunotolerance to self-antigens. Renal involvement, known as lupus nephritis (LN), is one of the leading causes of morbidity and a significant contributor to mortality in SLE. Despite current pathophysiological advances, further studies are needed to fully understand complex mechanisms underlying the development and progression of LN. Transcription factors (TFs) are proteins that regulate the expression of genes and play a crucial role in the development and progression of LN. The mechanisms of TF promoting or inhibiting gene expression are complex, and studies have just begun to reveal the pathological roles of TFs in LN. Understanding TFs in the pathogenesis of LN can provide valuable insights into this disease's mechanisms and potentially lead to the development of targeted therapies for its management. This review will focus on recent findings on TFs in the pathogenesis of LN and newly developed TF-targeted therapy in renal inflammation.

Hypoxia-induced signaling in the cardiovascular system: pathogenesis and therapeutic targets

Hypoxia, characterized by reduced oxygen concentration, is a significant stressor that affects the survival of aerobic species and plays a prominent role in cardiovascular diseases. From the research history and milestone events related to hypoxia in cardiovascular development and diseases, The "hypoxia-inducible factors (HIFs) switch" can be observed from both temporal and spatial perspectives, encompassing the occurrence and progression of hypoxia (gradual decline in oxygen concentration), the acute and chronic manifestations of hypoxia, and the geographical characteristics of hypoxia (natural selection at high altitudes). Furthermore, hypoxia signaling pathways are associated with natural rhythms, such as diurnal and hibernation processes. In addition to innate factors and natural selection, it has been found that epigenetics, as a postnatal factor, profoundly influences the hypoxic response and progression within the cardiovascular system. Within this intricate process, interactions between different tissues and organs within the cardiovascular system and other systems in the context of hypoxia signaling pathways have been established. Thus, it is the time to summarize and to construct a multi-level regulatory framework of hypoxia signaling and mechanisms in cardiovascular diseases for developing more therapeutic targets and make reasonable advancements in clinical research, including FDA-approved drugs and ongoing clinical trials, to guide future clinical practice in the field of hypoxia signaling in cardiovascular diseases.

Systemic lupus erythematosus: From non-coding RNAs to exosomal non-coding RNAs

Systemic lupus erythematosus (SLE), as an immunological illness, frequently impacts young females. Both vulnerabilities to SLE and the course of the illness's clinical symptoms have been demonstrated to be affected by individual differences in non-coding RNA expression. Many non-coding RNAs (ncRNAs) are out of whack in patients with SLE. Because of the dysregulation of several ncRNAs in peripheral blood of patients suffering from SLE, these ncRNAs to be showed valuable as biomarkers for medication response, diagnosis, and activity. NcRNAs have also been demonstrated to influence immune cell activity and apoptosis. Altogether, these facts highlight the need of investigating the roles of both families of ncRNAs in the progress of SLE. Being aware of the significance of these transcripts perhaps elucidates the molecular pathogenesis of SLE and could open up promising avenues to create tailored treatments during this condition. In this review we summarized various non-coding RNAs and Exosomal non-coding RNAs in SLE.

Urinary Extracellular Vesicles in Chronic Kidney Disease: From Bench to Bedside?

Extracellular vesicles are a diverse group of particles that include exosomes, microvesicles, and apoptotic bodies and are defined by size, composition, site of origin, and density. They incorporate various bioactive molecules from their cell of origin during formation, such as soluble proteins, membrane receptors, nucleic acids (mRNAs and miRNAs), and lipids, which can then be transferred to target cells. Extracellular vesicles/exosomes have been extensively studied as a critical factor in pathophysiological processes of human diseases. Urinary extracellular vesicles could be a promising liquid biopsy for determining the pattern and/or severity of kidney histologic injury. The signature of urinary extracellular vesicles may pave the way for noninvasive methods to supplement existing testing methods for diagnosing kidney diseases. We discuss the potential role of urinary extracellular vesicles in various chronic kidney diseases in this review, highlighting open questions and discussing the potential for future research.

Emerging role of hypoxia-inducible factor-1α in inflammatory autoimmune diseases: A comprehensive review

Hypoxia-inducible factor-1α (HIF-1α) is a primary metabolic sensor, and is expressed in different immune cells, such as macrophage, dendritic cell, neutrophil, T cell, and non-immune cells, for instance, synovial fibroblast, and islet β cell. HIF-1α signaling regulates cellular metabolism, triggering the release of inflammatory cytokines and inflammatory cells proliferation. It is known that microenvironment hypoxia, vascular proliferation, and impaired immunological balance are present in autoimmune diseases. To date, HIF-1α is recognized to be overexpressed in several inflammatory autoimmune diseases, such as systemic lupus erythematosus (SLE), rheumatoid arthritis, and function of HIF-1α is dysregulated in these diseases. In this review, we narrate the signaling pathway of HIF-1α and the possible immunopathological roles of HIF-1α in autoimmune diseases. The collected information will provide a theoretical basis for the familiarization and development of new clinical trials and treatment based on HIF-1α and inflammatory autoimmune disorders in the future.

Molecular mechanisms governing the progression of nephritis in lupus prone mice and human lupus patients

Introduction

Pathologic inflammation is a major driver of kidney damage in lupus nephritis (LN), but the immune mechanisms of disease progression and risk factors for end organ damage are poorly understood.

Methods

To characterize molecular profiles through the development of LN, we carried out gene expression analysis of microdissected kidneys from lupus-prone NZM2328 mice. We examined male mice and the congenic NZM2328.R27 strain as a means to define mechanisms associated with resistance to chronic nephritis. Gene expression profiles in lupus mice were compared with those in human LN.

Results

NZM2328 mice exhibited progress from acute to transitional and then to chronic glomerulonephritis (GN). Each stage manifested a unique molecular profile. Neither male mice nor R27 mice progressed past the acute GN stage, with the former exhibiting minimal immune infiltration and the latter enrichment of immunoregulatory gene signatures in conjunction with robust kidney tubule cell profiles indicative of resistance to cellular damage. The gene expression profiles of human LN were similar to those noted in the NZM2328 mouse suggesting comparable stages of LN progression.

Conclusions

Overall, this work provides a comprehensive examination of the immune processes involved in progression of murine LN and thus contributes to our understanding of the risk factors for end-stage renal disease. In addition, this work presents a foundation for improved classification of LN and illustrates the applicability of murine models to identify the stages of human disease.

Association of Circulating Levels of Hypoxia-Inducible Factor-1α and miR-210 with Photosensitivity in Systemic Lupus Erythematosus Patients

BACKGROUND

miR-210, a key hypoxamiR, regulates hypoxia and inflammation-linked hypoxia. Systemic lupus erythematosus (SLE), a chronic autoimmune disease, is responsible for many pathological disorders, including photosensitivity.

OBJECTIVE

This study aimed to find the correlation between circulating miR-210/HIF-1α levels and photosensitivity in SLE patients and other SLE-associated pathological complications in a single-center case-control study.

METHODS

The study population comprised 104 SLE Egyptian patients with photosensitivity, 32 SLE patients without photosensitivity, and 32 healthy subjects. SLE activity was assessed for all patients using the SLE Disease Activity Index (SLEDAI). Clinical complications/manifestations and hematological/serological analyses were recorded. HIF-α concentration was investigated by ELISA, and miR-210 expression was analyzed by qRT-PCR.

RESULTS

The results revealed that circulating miR-210 was significantly increased in the SLE/photosensitivity group versus the SLE and control groups. The additional occurrence of malar rash, oral ulcers, renal disorders, or hypertension resulted in a higher expression of miR-210. SLEDAI activity status showed no effect on miR-210. Erythrocyte sedimentation rate, white blood cells, hemoglobin, platelets, patient age, and disease duration were positively correlated with circulatory miR-210. HIF-α concentration was significantly induced in the SLE/photosensitivity group versus the SLE and control groups. In SLE/photosensitivity, the presence of renal disorders and hypertension resulted in the highest HIF-α concentrations. A strong positive correlation was recorded between HIF-α concentration and circulatory miR-210 in SLE/photosensitivity patients (r = 0.886).

CONCLUSION

The dysregulation of circulating miR-210/HIF-1α levels in SLE/ photosensitivity patients is controlled by the presence of additional pathological complications, and results suggest that the hypoxia pathway might interact positively with the pathogenesis and disease progression of SLE.

Mesangial cell: A hub in lupus nephritis

Lupus nephritis (LN) is a severe renal disease caused by the massive deposition of the immune complexes (ICs) in renal tissue, acting as one of the significant organ manifestations of systemic lupus erythematosus (SLE) and a substantial cause of death in clinical patients. As mesangium is one of the primary sites for IC deposition, mesangial cells (MCs) constantly undergo severe damage, resulting in excessive proliferation and increased extracellular matrix (ECM) production. In addition to playing a role in organizational structure, MCs are closely related to in situ immunomodulation by phagocytosis, antigen-presenting function, and inflammatory effects, aberrantly participating in the tissue-resident immune responses and leading to immune-mediated renal lesions. Notably, such renal-resident immune responses drive a second wave of MC damage, accelerating the development of LN. This review summarized the damage mechanisms and the in situ immune regulation of MCs in LN, facilitating the current drug research for exploring clinical treatment strategies.

Circulating Levels of Hypoxia-regulating MicroRNAs in Systemic Lupus Erythematosus Patients with Hemolytic Anemia

OBJECTIVE

MicroRNAs are fine regulators for gene expression during the post-transcriptional stage in many autoimmune diseases. HypoxamiRs (miR-210 and miR-21) play an important role in hypoxia and in inflammation-associated hypoxia. Systemic lupus erythematosus (SLE) is a chronic systemic autoimmune disease that would potentiate many pathological complications, including hemolytic anemia. This study aimed to investigate the role of hypoxamiRs in SLE/hemolytic anemia patients.

METHODS

This work was designed to analyze the circulating levels of↱ the miR-210 and miR-21 expressions and hypoxia-inducible factor-1α (HIF-α) in SLE/hemolytic anemia patients. SLE activity was evaluated for all patients by SLE Disease Activity Index (SLEDAI). Clinical manifestations/complications and serological/hematological investigations were reported. HIF-α concentration was assayed by ELISA and expression of miR-21 and miR-210 was analyzed by qRT-PCR.

RESULTS

The results indicated that the fold change of the miR-210/miR-21 expressions in plasma was significantly elevated in SLE/hemolytic anemia patients. A strong positive correlation between the miR-210 and miR-21 expression levels was also recorded. Among the associated-disease complications, hypertension, arthritis, oral ulcers, and serositis were associated with a high circulating miR-210 expression, while the occurrence of renal disorders was associated with the increased miR-21 expression. Furthermore, the HIF-α level was remarkably elevated in SLE/hemolytic anemia patients. A high positive correlation was recorded between the HIF-α concentration and miR-210/miR-21 expression levels. The occurrence of oral ulcers, arthritis, and hypertension was associated with the increased HIF-α concentration. On the other hand, SLEDAI and white blood cell count were positively correlated with miR-21/ miR-210. The erythrocyte sedimentation rate was positively correlated with miR-21.

CONCLUSION

The dysregulation of the circulating miR-210/miR-210/HIF-1α levels in SLE/hemolytic anemia patients advocated that the hypoxia pathway might have an essential role in the pathogenesis and complications of these diseases.

New Approaches to Diabetic Nephropathy from Bed to Bench

Diabetic nephropathy (DN) is the main cause of end-stage kidney disease (ESKD). DN-related ESKD has the worst prognosis for survival compared with other causes. Due to the complex mechanisms of DN and the heterogeneous presentations, unmet needs exist for the renal outcome of diabetes mellitus. Clinical evidence for treating DN is rather solid. For example, the first Kidney Disease: Improving Global Outcomes (KDIGO) guideline was published in October 2020: KDIGO Clinical Practice Guideline for Diabetes Management in Chronic Kidney Disease. In December of 2020, the International Society of Nephrology published 60 (+1) breakthrough discoveries in nephrology. Among these breakthroughs, four important ones after 1980 were recognized, including glomerular hyperfiltration theory, renal protection by renin-angiotensin system inhibition, hypoxia-inducible factor, and sodium-glucose cotransporter 2 inhibitors. Here, we present a review on the pivotal and new mechanisms of DN from the implications of clinical studies and medications.

Targets of Tripterygium glycosides in systemic lupus erythematosus treatment: A network-pharmacology study

OBJECTIVE

We aimed to explore the underlying mechanism of Tripterygium glycosides (TGs) in treating systemic lupus erythematosus (SLE) through network-pharmacology approach.

METHODS

The protein targets of TGs' three active ingredients (triptolide, tripterine, and wilforlide) and SLE were identified by database search. Then, the intersection of the two groups was studied. The drug-target network between the active ingredients of TGs and the overlapping genes was constructed, visualized, and analyzed with Cytoscape software. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment were performed to analyze these genes. Finally, we validated our predictions of the potential targets through docking study.

RESULTS

A total of 55 overlapping genes were discovered. Results suggested that the TGs' mechanism in SLE treatment was associated with heat shock protein family A member 5, heat shock protein family A member 8, eukaryotic translation elongation factor 1 alpha 1, and so forth with their related 4042 gene network, which regulated ribosome, spliceosome, viral carcinogenesis, Epstein-Barr virus infection signaling, and so forth. Molecular-docking analysis proved that hydrogen bonding was the main form of interaction.

CONCLUSIONS

Our research provided the protein targets affected by TGs in SLE treatment. The key targets (CASP3, MAPK1, HIF1A, and so forth) involving 4042 proteins became the multitarget mechanism of TGs in SLE treatment.

Kidney tissue hypoxia dictates T cell-mediated injury in murine lupus nephritis

The kidney is a frequent target of autoimmune injury, including in systemic lupus erythematosus; however, how immune cells adapt to kidney's unique environment and contribute to tissue damage is unknown. We found that renal tissue, which normally has low oxygen tension, becomes more hypoxic in lupus nephritis. In the injured mouse tissue, renal-infiltrating CD4⁺ and CD8⁺ T cells express hypoxia-inducible factor-1 (HIF-1), which alters their cellular metabolism and prevents their apoptosis in hypoxia. HIF-1-dependent gene-regulated pathways were also up-regulated in renal-infiltrating T cells in human lupus nephritis. Perturbation of these environmental adaptations by selective HIF-1 blockade inhibited infiltrating T cells and reversed tissue hypoxia and injury in murine models of lupus. The results suggest that targeting HIF-1 might be effective for treating renal injury in autoimmune diseases.

CCL17-producing cDC2s are essential in end-stage lupus nephritis and averted by a parasitic infection

Lupus nephritis is a severe organ manifestation in systemic lupus erythematosus leading to kidney failure in a subset of patients. In lupus-prone mice, controlled infection with Plasmodium parasites protects against the progression of autoimmune pathology including lethal glomerulonephritis. Here, we demonstrate that parasite-induced protection was not due to a systemic effect of infection on autoimmunity as previously assumed, but rather to specific alterations in immune cell infiltrates into kidneys and renal draining lymph nodes. Infection of lupus-prone mice with a Plasmodium parasite did not reduce the levels or specificities of autoreactive antibodies, vasculitis, immune complex-induced innate activation, or hypoxia. Instead, infection uniquely reduced kidney-infiltrating CCL17-producing bone marrow-derived type 2 inflammatory dendritic cells (iDC2s). Bone marrow reconstitution experiments revealed that infection with Plasmodium caused alterations in bone marrow cells that hindered the ability of DC2s to infiltrate the kidneys. The essential role for CCL17 in lupus nephritis was confirmed by in vivo depletion with a blocking antibody, which reduced kidney pathology and immune infiltrates, while bypassing the need for parasitic infection. Therefore, infiltration into the kidneys of iDC2s, with the potential to prime local adaptive responses, is an essential regulated event in the transition from manageable glomerulonephritis to lethal tubular injury.

Tubular Numb promotes renal interstitial fibrosis via modulating HIF-1α protein stability

Tubulointerstitial fibrosis is the ultimate common pathway of all manners of chronic kidney disease. We previously demonstrated that specific deletion of Numb in proximal tubular cells (PTCs) prevented G2/M arrest and attenuated renal fibrosis. However, how Numb modulates cell cycle arrest remains unclear. Here, we showed that Numb overexpression significantly increased the protein level of hypoxia-inducible factor-1α (HIF-1α). Numb overexpression-induced G2/M arrest was blocked by silencing endogenous HIF-1α, subsequently downregulated the expression of cyclin G1 which is an atypical cyclin to promote G2/M arrest of PTCs. Further analysis revealed that Numb-augmented HIF-1α protein was blocked by simultaneously overexpressing MDM2. Moreover, silencing Numb decreased TGF-β1-induceded HIF-1α protein expression. While endogenous MDM2 was knocked down this reduction was reversed, indicating that Numb stabilized HIF-1α protein via interfering MDM2-mediated HIF-1α protein degradation. Interestingly, HIF-1α overexpression significantly upregulated the expression of Numb and silencing endogenous HIF-1α blocked CoCl₂ or TGF-β1-induced Numb expression. Chromatin immunoprecipitation (ChIP) assays demonstrated that HIF-1α binded to the promoter region of Numb. This binding was significantly increased by TGF-β1. Collectively, these data indicate that Numb and HIF-1α cooperates to promote G2/M arrest of PTCs, and thus aggravates tubulointerstitial fibrosis. Numb might be a potential target for the therapy of tubulointerstitial fibrosis.

Quantitative planar array screen of 1000 proteins uncovers novel urinary protein biomarkers of lupus nephritis

OBJECTIVE

The goal of these studies is to discover novel urinary biomarkers of lupus nephritis (LN).

METHODS

Urine from systemic lupus erythematosus (SLE) patients was interrogated for 1000 proteins using a novel, quantitative planar protein microarray. Hits were validated in an independent SLE cohort with inactive, active non-renal (ANR) and active renal (AR) patients, in a cohort with concurrent renal biopsies, and in a longitudinal cohort. Single-cell renal RNA sequencing data from LN kidneys were examined to deduce the cellular origin of each biomarker.

RESULTS

Screening of 1000 proteins revealed 64 proteins to be significantly elevated in SLE urine, of which 17 were ELISA validated in independent cohorts. Urine Angptl4 (area under the curve (AUC)=0.96), L-selectin (AUC=0.86), TPP1 (AUC=0.84), transforming growth factor-β1 (TGFβ1) (AUC=0.78), thrombospondin-1 (AUC=0.73), FOLR2 (AUC=0.72), platelet-derived growth factor receptor-β (AUC=0.67) and PRX2 (AUC=0.65) distinguished AR from ANR SLE, outperforming anti-dsDNA, C3 and C4, in terms of specificity, sensitivity and positive predictive value. In multivariate regression analysis, urine Angptl4, L-selectin, TPP1 and TGFβ1 were highly associated with disease activity, even after correction for demographic variables. In SLE patients with serial follow-up, urine L-selectin (followed by urine Angptl4 and TGFβ1) were best at tracking concurrent or pending disease flares. Importantly, several proteins elevated in LN urine were also expressed within the kidneys in LN, either within resident renal cells or infiltrating immune cells, based on single-cell RNA sequencing analysis.

CONCLUSION

Unbiased planar array screening of 1000 proteins has led to the discovery of urine Angptl4, L-selectin and TGFβ1 as potential biomarker candidates for tracking disease activity in LN.

Mutual Antagonism of Hypoxia-Inducible Factor Isoforms in Cardiac, Vascular, and Renal Disorders

Hypoxia-inducible factor (HIF)-1α and HIF-2α promote cellular adaptation to acute hypoxia, but during prolonged activation, these isoforms exert mutually antagonistic effects on the redox state and on proinflammatory pathways. Sustained HIF-1α signaling can increase oxidative stress, inflammation, and fibrosis, actions that are opposed by HIF-2α. Imbalances in the interplay between HIF-1α and HIF-2α may contribute to the progression of chronic heart failure, atherosclerotic and hypertensive vascular disorders, and chronic kidney disease. These disorders are characterized by activation of HIF-1α and suppression of HIF-2α, which are potentially related to mitochondrial and peroxisomal dysfunction and suppression of the redox sensor, sirtuin-1. Hypoxia mimetics can potentiate HIF-1α and/or HIF-2α; ideally, such agents should act preferentially to promote HIF-2α while exerting little effect on or acting to suppress HIF-1α. Selective activation of HIF-2α can be achieved with drugs that: 1) inhibit isoform-selective prolyl hydroxylases (e.g., cobalt chloride and roxadustat); or 2) promote the actions of the redox sensor, sirtuin-1 (e.g., sodium-glucose cotransporter 2 inhibitors). Selective HIF-2α signaling through sirtuin-1 activation may explain the effect of sodium-glucose cotransporter 2 inhibitors to simultaneously promote erythrocytosis and ameliorate the development of cardiomyopathy and nephropathy.

The Emerging Role of Renal Tubular Epithelial Cells in the Immunological Pathophysiology of Lupus Nephritis

Systemic lupus erythematosus (SLE) is a systemic, autoimmune disease that can involve virtually any organ of the body. Lupus nephritis (LN), the clinical manifestation of this disease in the kidney, is one of the most common and severe outcomes of SLE. Although a key pathological hallmark of LN is glomerular inflammation and damage, tubulointerstitial lesions have been recognized as an important component in the pathology of LN. Renal tubular epithelial cells are resident cells in the tubulointerstitium that have been shown to play crucial roles in various acute and chronic kidney diseases. In this context, recent progress has been made in examining the functional role of tubular epithelial cells in LN pathogenesis. This review summarizes recent advances in our understanding of renal tubular epithelial cells in LN, the potential role of tubular epithelial cells as biomarkers in the diagnosis, prognosis, and treatment of LN, and the future therapeutic potential of targeting the tubulointerstitium for the treatment of patients with LN.

Hypoxia in chronic kidney disease: towards a paradigm shift?

Chronic kidney disease (CKD) is defined as an alteration of kidney structure and/or function lasting for >3 months [1]. CKD affects 10% of the general adult population and is responsible for large healthcare costs [2]. Since the end of the last century, the role of hypoxia in CKD progression has controversially been discussed. To date, there is evidence of the presence of hypoxia in late-stage renal disease, but we lack time-course evidence, stage correlation and also spatial co-localization with fibrotic lesions to ensure its causative role. The classical view of hypoxia in CKD progression is that it is caused by peritubular capillary alterations, renal anaemia and increased oxygen consumption regardless of the primary injury. In this classical view, hypoxia is assumed to further induce pro-fibrotic and pro-inflammatory responses, as well as oxidative stress, leading to CKD worsening as part of a vicious circle. However, recent investigations tend to question this paradigm, and both the presence of hypoxia and its role in CKD progression are still not clearly demonstrated. Hypoxia-inducible factor (HIF) is the main transcriptional regulator of the hypoxia response. Genetic HIF modulation leads to variable effects on CKD progression in different murine models. In contrast, pharmacological modulation of the HIF pathway [i.e. by HIF hydroxylase inhibitors (HIs)] appears to be generally protective against fibrosis progression experimentally. We here review the existing literature on the role of hypoxia, the HIF pathway and HIF HIs in CKD progression and summarize the evidence that supports or rejects the hypoxia hypothesis, respectively.

Metabolic Targets for Treatment of Autoimmune Diseases

There is a considerable unmet demand for safe and efficacious medications in the realm of autoimmune and inflammatory diseases. The fate of the immune cells is precisely governed by control of various metabolic processes such as mitochondrial oxidative phosphorylation, glycolysis, fatty acid synthesis, beta-oxidation, amino acid metabolism, and several others including the pentose phosphate pathway, which is a unique source of metabolites for cell proliferation and maintenance of a reducing environment. These pathways are tightly regulated by the cytokines, growth factors, availability of the nutrients and host-microbe interaction. Exploring the immunometabolic pathways that govern the fate of cells of the innate and adaptive immune system, during various stages of activation, proliferation, differentiation and effector response, is crucial for new development of new treatment targets. Identifying the pathway connections and key enzymes will help us to target the dysregulated inflammation in autoimmune diseases. The mechanistic target of rapamycin (mTOR) pathway is increasingly recognized as one of the key drivers of proinflammatory responses in autoimmune diseases. In this review, we provide an update on the current understanding of the metabolic signatures noted within different immune cells of many different autoimmune diseases with a focus on selecting pathways and specific metabolites as targets for treatment.

The Urinary Exosomal miRNA Expression Profile is Predictive of Clinical Response in Lupus Nephritis

Data on exosomal-derived urinary miRNAs have identified several miRNAs associated with disease activity and fibrosis formation, but studies on prognosis are lacking. We conducted a qPCR array screening on urinary exosomes from 14 patients with biopsy-proven proliferative lupus glomerulonephritis with a renal outcome of clinical response (n = 7) and non-response (n = 7) following therapy. Validation studies were performed by qRT-PCR in a new lupus nephritis (LN) cohort (responders = 22 and non-responders = 21). Responder patients expressed significantly increased levels of miR-31, miR-107, and miR-135b-5p in urine and renal tissue compared to non-responders. MiR-135b exhibited the best predictive value to discriminate responder patients (area under the curve = 0.783). In vitro studies showed exosome-derived miR-31, miR-107, and miR-135b-5p expression to be mainly produced by tubular renal cells stimulated with inflammatory cytokines (e.g IL1, TNFα, IFNα and IL6). Uptake of urinary exosomes from responders by mesangial cells was superior compared to that from non-responders (90% vs. 50%, p < 0.0001). HIF1A was identified as a potential common target, and low protein levels were found in non-responder renal biopsies. HIF1A inhibition reduced mesangial proliferation and IL-8, CCL2, CCL3, and CXCL1 mesangial cell production and IL-6/VCAM-1 in endothelial cells. Urinary exosomal miR-135b-5p, miR-107, and miR-31 are promising novel markers for clinical outcomes, regulating LN renal recovery by HIF1A inhibition.

Cellular Metabolic Regulation in the Differentiation and Function of Regulatory T Cells

Regulatory T cells (Tregs) are essential for maintaining immune tolerance and preventing autoimmune and inflammatory diseases. The activity and function of Tregs are in large part determined by various intracellular metabolic processes. Recent findings have focused on how intracellular metabolism can shape the development, trafficking, and function of Tregs. In this review, we summarize and discuss current research that reveals how distinct metabolic pathways modulate Tregs differentiation, phenotype stabilization, and function. These advances highlight numerous opportunities to alter Tregs frequency and function in physiopathologic conditions via metabolic manipulation and have important translational implications.

RNAi Silencing of HIF-1α Ameliorates Lupus Development in MRL/lpr Mice

Th17 cell and IL-17-mediated autoimmunity and inflammatory responses have been implicated in the development of organ damage in systemic lupus erythematosus (SLE), and new evidence suggests that hypoxia-inducible factor 1α (HIF-1α) enhances Th17 differentiation and promotes IL-17 production. However, the role of HIF-1α in the pathogenesis of lupus has not been examined. In this study, we silenced HIF-1α in vivo in a murine model of SLE to investigate whether lupus progression and the associated inflammatory pathways were affected by downregulating HIF-1α. Treatment with HIF1α-shRNA suppressed serum IL-17 level in MRL/lpr mice. Decreased anti-nucleosome antibody level, reduced urinary protein concentrations, ameliorated pathological damage, and remarkably reduced renal IgG and C3 depositions were observed in HIF1α-shRNA-treated group compared to those in the controls. Our results provide the first evidence for a role of HIF-1α in the pathogenesis of lupus and suggest a potential new therapeutic avenue for the treatment of lupus patients through reducing the HIF-1α level.

Hypoxia and Renal Tubulointerstitial Fibrosis

Hypoxia, one of the most common causes of kidney injury, is a key pathological condition in various kidney diseases. Renal fibrosis is the terminal pathway involved in the continuous progression of chronic kidney disease (CKD), characterized by glomerulosclerosis and tubulointerstitial fibrosis (TIF). Recent studies have shown that hypoxia is a key factor promoting the progression of TIF. Loss of microvasculature, reduced oxygen dispersion, and metabolic abnormality of cells in the kidney are the main causes of the hypoxic state. Hypoxia can, in turn, profoundly affect the tubular epithelial cells, endothelial cells, pericytes, fibroblasts, inflammatory cells, and progenitor cells. In this chapter, we reviewed the critical roles of hypoxia in the pathophysiology of TIF and discussed the potential of anti-hypoxia as its promising therapeutic target.

REDD1/autophagy pathway promotes thromboinflammation and fibrosis in human systemic lupus erythematosus (SLE) through NETs decorated with tissue factor (TF) and interleukin-17A (IL-17A)

OBJECTIVES

The release of neutrophil extracellular traps (NETs) represents a novel neutrophil effector function in systemic lupus erythematosus (SLE) pathogenesis. However, the molecular mechanism underlying NET release and how NETs mediate end-organ injury in SLE remain elusive.

METHODS

NET formation and NET-related proteins were assessed in the peripheral blood and biopsies from discoid lupus and proliferative nephritis, using immunofluorescence, immunoblotting, quantitative PCR and ELISA. Autophagy was assessed by immunofluorescence and immunoblotting. The functional effects of NETs in vitro were assessed in a primary fibroblast culture.

RESULTS

Neutrophils from patients with active SLE exhibited increased basal autophagy levels leading to enhanced NET release, which was inhibited in vitro by hydroxychloroquine. NETosis in SLE neutrophils correlated with increased expression of the stress-response protein REDD1. Endothelin-1 (ET-1) and hypoxia-inducible factor-1α (HIF-1α) were key mediators of REDD1-driven NETs as demonstrated by their inhibition with bosentan and L-ascorbic acid, respectively. SLE NETs were decorated with tissue factor (TF) and interleukin-17A (IL-17A), which promoted thrombin generation and the fibrotic potential of cultured skin fibroblasts. Notably, TF-bearing and IL-17A-bearing NETs were abundant in discoid skin lesions and in the glomerular and tubulointerstitial compartment of proliferative nephritis biopsy specimens.

CONCLUSIONS

Our data suggest the involvement of REDD1/autophagy/NET axis in end-organ injury and fibrosis in SLE, a likely candidate for repositioning of existing drugs for SLE therapy. Autophagy-mediated release of TF-bearing and IL-17A-bearing NETs provides a link between thromboinflammation and fibrosis in SLE and may account for the salutary effects of hydroxychloroquine.

Novel therapeutic strategy for cancer and autoimmune conditions: Modulating cell metabolism and redox capacity

Dysregulation of cell metabolism and redox balance is implicated in the pathogenesis and progression of cancer and autoimmune diseases. Because the cell proliferation and apoptotic regulatory pathways are interconnected with metabolic and redox signalling pathways, the current mono-target treatment is ineffective, and multi-drug resistance remains common. Complex diseases are often implicated in a network-based context of pathology; therefore, a new holistic intervention approach is required to block multi-crosstalk in such complicated circumstances. The use of therapeutic agents isolated from herbs to holistically modulate metabolism and redox state has been shown to relieve carcinoma growth and the inflammatory response in autoimmune disorders. Multiple clinically applied or novel herbal chemicals with metabolic and redox modulatory capacity as well as low toxicity have recently been identified. Moreover, new metabolic targets and mechanisms of drug action have been discovered, leading to the exploration of new pathways for drug repositioning, clinical biomarker spectra, clinical treatment strategies and drug development. Taken together with multiple supporting examples, the modulation of cell metabolism and the redox capacity using herbal chemicals is emerging as a new, alternative strategy for the holistic treatment of cancer and autoimmune disorders. In the future, the development of new diagnostic tools based on the detection of metabolic and redox biomarkers, reformulation of optimized herbal compositions using artificial intelligence, and the combination of herbs with mono-targeting drugs will reveal new potential for clinical application.

Renal hypoxia in kidney disease: Cause or consequence?

Tissue hypoxia has been proposed as an important factor in the pathophysiology of both chronic kidney disease (CKD) and acute kidney injury (AKI), initiating and propagating a vicious cycle of tubular injury, vascular rarefaction, and fibrosis and thus exacerbation of hypoxia. Here, we critically evaluate this proposition by systematically reviewing the literature relevant to the following six questions: (i) Is kidney disease always associated with tissue hypoxia? (ii) Does tissue hypoxia drive signalling cascades that lead to tissue damage and dysfunction? (iii) Does tissue hypoxia per se lead to kidney disease? (iv) Does tissue hypoxia precede pathology? (v) Does tissue hypoxia colocalize with pathology? (vi) Does prevention of tissue hypoxia prevent kidney disease? We conclude that tissue hypoxia is a common feature of both AKI and CKD. Furthermore, at least under in vitro conditions, renal tissue hypoxia drives signalling cascades that lead to tissue damage and dysfunction. Tissue hypoxia itself can lead to renal pathology, independent of other known risk factors for kidney disease. There is also some evidence that tissue hypoxia precedes renal pathology, at least in some forms of kidney disease. However, we have made relatively little progress in determining the spatial relationships between tissue hypoxia and pathological processes (i.e. colocalization) or whether therapies targeted to reduce tissue hypoxia can prevent or delay the progression of renal disease. Thus, the hypothesis that tissue hypoxia is a "common pathway" to both AKI and CKD still remains to be adequately tested.

DNA induction of MDM2 promotes proliferation of human renal mesangial cells and alters peripheral B cells subsets in pediatric systemic lupus erythematosus

The study is aimed to investigate the role of MDM2 in the pathogenesis of lupus nephritis (LN) in pediatric SLE (pSLE). We confirmed that MDM2 expression was increased in peripheral blood mononuclear cells (PBMCs) as well as renal specimen of SLE compared with that of controls by western blot and immunofluorescence staining. Percentage of apoptotic and necrotic CD4⁺T, CD8⁺T and B cells were detected by flow cytometry respectively and levels of plasma cell free DNA (cfDNA) were quantified in SLE and healthy controls (HC). We also proved that elevated apoptotic and necrotic CD4⁺T cells were the main cause for increased plasma levels of cfDNA in pSLE. Additionally, upon DNA transfection MDM2 increased while P53 and P21 decreased in human renal mesangial cells (HRMC), with concomitant increase in proliferation rate and proportion of cells in S phase, as demonstrated by cell proliferation assay and cell cycle analysis. However, MDM2 inhibition reversed the trend. Furthermore, percentage of switched memory B cells decreased and proportion of double negative B cells increased upon blockage of MDM2 in PBMC. In summary, our study provided the first evidence that DNA induction of MDM2 promotes proliferation of HRMC and alters peripheral B cells subsets in pSLE. Thus our study has not only elucidated the pathogenesis of MDM2 in pediatric LN but also provided a novel target for drug development. In conclusion, our data suggested that apoptosis, cfDNA and MDM2 could form a pathological axis in SLE, especially in pSLE.

Local CD34-positive capillaries decrease in mouse models of kidney disease associating with the severity of glomerular and tubulointerstitial lesions

Background

The renal vasculature plays important roles in both homeostasis and pathology. In this study, we examined pathological changes in the renal microvascular in mouse models of kidney diseases.

Methods

Glomerular lesions (GLs) in autoimmune disease-prone male BXSB/MpJ-Yaa (Yaa) mice and tubulointerstitial lesions (TILs) in male C57BL/6 mice subjected to unilateral ureteral obstruction (UUO) for 7 days were studied. Collected kidneys were examined using histopathological techniques. A nonparametric Mann–Whitney U test (P < 0.05) was performed to compare healthy controls and the experimental mice. The Kruskal-Wallis test was used to compare three or more groups, and multiple comparisons were performed using Scheffe’s method when significant differences were observed (P < 0.05).

Results

Yaa mice developed severe autoimmune glomerulonephritis, and the number of CD34⁺ glomerular capillaries decreased significantly in GLs compared to that in control mice. However, UUO-treated mice showed severe TILs only, and CD34⁺ tubulointerstitial capillaries were decreased significantly in TILs with the progression of tubulointerstitial fibrosis compared to those in untreated control kidneys. Infiltrations of B-cells, T-cells, and macrophages increased significantly in the respective lesions of both disease models (P < 0.05). In observations of vascular corrosion casts by scanning electron microscopy and of microfil rubber-perfused thick kidney sections by fluorescence microscopy, segmental absences of capillaries were observed in the GLs and TILs of Yaa and UUO-treated mice, respectively. Further, transmission electron microscopy revealed capillary endothelial injury in the respective lesions of both models. The numbers of CD34⁺ glomerular and tubulointerstitial capillaries were negatively correlated with all examined parameters in GLs (P < 0.05) and TILs (P < 0.01), respectively.

Conclusions

From the analysis of mouse models, we identified inverse pathological correlations between the number of local capillaries in GLs and TILs and the severity of kidney diseases.

Electronic supplementary material

The online version of this article (10.1186/s12882-017-0694-3) contains supplementary material, which is available to authorized users.

Hypoxia-inducible factor-1α: a promising therapeutic target for autoimmune diseases

INTRODUCTION

Hypoxia-inducible factor-1α (HIF-1α) plays a crucial role in both innate and adaptive immunity. Emerging evidence indicates that HIF-1α is associated with the inflammation and pathologic activities of autoimmune diseases. Areas covered: Considering that the types of autoimmune diseases are complicated and various, this review aims to cover the typical kinds of autoimmune diseases, discuss the molecular mechanisms, biological functions and expression of HIF-1α in these diseases, and further explore its therapeutic potential. Expert opinion: Inflammation and hypoxia are interdependent. HIF-1α as a key regulator of hypoxia, exerts a crucial role in the balance between Th17 and Treg, and involves in the inflammation and pathologic activities of autoimmune diseases. Although there are many challenges remaining to be overcome, targeting HIF-1α could be a promising strategy for autoimmune diseases therapies.

HIF1A (rs11549465) and AKNA (rs10817595) Gene Polymorphisms Are Associated with Primary Sjögren's Syndrome

Objective. To evaluate the allele and genotype frequencies of polymorphic sites of HIF1A and ANKA genes in primary Sjögren's syndrome (pSS). Methods. We included 110 patients with pSS and 141 ethnically matched healthy controls. Three HIF1A gene polymorphisms (Pro582Ser, Ala588Thr, and C191T) and two AKNA gene polymorphisms (−1372C>A and Pro624Leu) were genotyped using TaqMan probes in a Real-Time PCR instrument. Associations between pSS and genotypes, alleles, and inheritance models of the SNPs of interest were evaluated by logistic regression adjusted by age and gender. Results. The C/T genotype and the T allele of the HIF1A Pro582Ser polymorphism protected against pSS (OR = 0.22; 95% CI = 0.09–0.52; P < 0.01; OR = 0.26; 95% CI = 0.12–0.58; P < 0.01, resp.), whereas under a recessive model adjusted by age and gender, the AKNA −1372C>A polymorphism A/A genotype was associated with an increased risk of pSS (OR = 2.60; 95% CI = 1.11–6.12; P = 0.03). Conclusions. We identified HIF1A Pro582Ser T allele and C/T genotype as well as AKNA −1372C>A polymorphism A/A genotype as genetic factors associated with pSS. Further studies in other populations are needed to validate our findings and research is warranted in order to shed some light on their functional implications across biological pathways in this disease.

Immunometabolism in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease mediated by pathogenic autoantibodies directed against nucleoprotein complexes. Beyond the activation of autoreactive B cells, this process involves dysregulation in many other types of immune cells, including CD4⁺ T cells, dendritic cells, macrophages and neutrophils. Metabolic substrate utilization and integration of cues from energy sensors are critical checkpoints of effector functions in the immune system, with common as well as cell-specific programmes. Patients with SLE and lupus-prone mice present with activated metabolism of CD4⁺ T cells, and the use of metabolic inhibitors to normalize these features is associated with therapeutic effects. Far less is known about the metabolic requirements of B cells and myeloid cells in SLE. This article reviews current knowledge of the alterations in metabolism of immune cells in patients with SLE and mouse models of lupus in the context of what is known about the metabolic regulation of these cells during normal immune responses. How these alterations might contribute to lupus pathogenesis and how they can be targeted therapeutically are also discussed.

Hypoxia-Inducible Factor-1α and Autoimmune Lupus, Arthritis

Hypoxia elicits an orchestrated response in cells, tissues, and entire organisms to survive a hypoxic challenge. On a molecular level, this response can be controlled by oxygen-dependent stabilization of the transcription factor hypoxia-inducible factor (HIF)-1α. Recently, studies have shown that HIF-1α plays an important role in the development and function of T helper (Th) cells, regulatory T (Treg) cells, and dendritic cells (DCs). Because these cells are critical in the pathogenesis of autoimmune diseases, such as systemic lupus erythematosus and rheumatoid arthritis, the roles of HIF-1α in these autoimmune disorders cannot be neglected. In this review, we discuss recent findings on the important roles of HIF-1α in immune cells and the possible pathologic roles of HIF-1α in autoimmune diseases. The obtained information may lead to deeper insights into the roles of HIF-1α in these disorders.

Hsa‑miR‑371‑5p inhibits human mesangial cell proliferation and promotes apoptosis in lupus nephritis by directly targeting hypoxia‑inducible factor 1α

MicroRNAs (miRNAs/miR) have emerged as a novel class of gene expression modulators in kidney disease. Lupus nephritis (LN) is the predominant cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). Hsa‑miR‑371‑5p has previously been reported to be dysregulated in LN using a miRNA microarray analysis. The present study aimed to determine the function and molecular mechanisms of hsa‑miR‑371‑5p in human mesangial cells of LN. Quantitative polymerase chain reaction (qPCR) was used to detect hsa‑miR‑371‑5p expression in LN tissues. Furthermore, the MTT assay and flow cytometric analyses were performed to analyze the effects of hsa‑miR‑371‑5p on mesangial cell proliferation and apoptosis. Bioinformatics analysis, luciferase reporter assay, qPCR and western blotting were also conducted to predict and confirm the target gene of hsa‑miR‑371‑5p in mesangial cells. The results demonstrated that hsa‑miR‑371‑5p expression was markedly downregulated in LN renal tissues compared with in normal kidney tissues. Restoration of hsa‑miR‑371‑5p expression using synthetic hsa‑miR‑371‑5p mimics was able to significantly inhibit mesangial cell proliferation and induce apoptosis. In addition, mechanistic exploration demonstrated that hypoxia‑inducible factor 1α (HIF‑1α) was a direct target gene of hsa‑miR‑371‑5p in mesangial cells. In conclusion, these results suggested that hsa‑miR‑371‑5p is downregulated in LN, and overexpression of hsa‑miR‑371‑5p may inhibit mesangial cell proliferation and promote apoptosis by directly targeting HIF‑1α.

Hypoxia-inducible factor-1α promotes glomerulosclerosis and regulates COL1A2 expression through interactions with Smad3

The function of hypoxia-inducible factor-1α (HIF-1α) in chronic kidney disease is disputed. Here we report that interactions of HIF-1α with transforming growth factor-β (TGF-β) signaling may promote its fibrotic effects. Knockout of HIF-1α is protective against glomerulosclerosis and glomerular type-I collagen accumulation in a mouse podocyte ablation model. Transcriptional analysis of cultured renal cells showed that α2(I) collagen expression is directly regulated by HIF-1α binding to a functional hypoxia-responsive element in its promoter at -335 relative to the transcription start site. Activation of COL1A2 transcription by HIF-1α occurred in the absence of hypoxia and is strongly enhanced by TGF-β signaling. TGF-β, in addition to increasing HIF-1α levels, increased both HIF-1α binding to the COL1A2 promoter and HIF-1α N-terminal transactivation domain activity. These effects of TGF-β on HIF-1α were inhibited in Smad3-null mouse embryonic fibroblasts, suggesting a requirement for Smad3. Phosphorylated Smad3 also associated with the -335 hypoxia-responsive element of the COL1A2 promoter independent of a Smad DNA binding sequence. Smad3 binding to the -335 hypoxia-responsive element required HIF-1α both in vitro and in kidney lysate from the disease model, suggesting formation of an HIF-1α-Smad3 transcriptional complex. Thus, HIF-1α-Smad3 has a novel interaction in glomerulosclerosis.