Overexpression of Mafb in podocytes protects against diabetic nephropathy

Astragaloside IV Alleviates Podocyte Injury in Diabetic Nephropathy through Regulating IRE-1α/NF-κ B/NLRP3 Pathway

OBJECTIVE

To investigate the effects of astragaloside IV (AS-IV) on podocyte injury of diabetic nephropathy (DN) and reveal its potential mechanism.

METHODS

In in vitro experiment, podocytes were divided into 4 groups, normal, high glucose (HG), inositol-requiring enzyme 1 (IRE-1) α activator (HG+thapsigargin 1 µmol/L), and IRE-1α inhibitor (HG+STF-083010, 20 µmol/L) groups. Additionally, podocytes were divided into 4 groups, including normal, HG, AS-IV (HG+AS-IV 20 µmol/L), and IRE-1α inhibitor (HG+STF-083010, 20 µmol/L) groups, respectively. After 24 h treatment, the morphology of podocytes and endoplasmic reticulum (ER) was observed by electron microscopy. The expressions of glucose-regulated protein 78 (GRP78) and IRE-1α were detected by cellular immunofluorescence. In in vivo experiment, DN rat model was established via a consecutive 3-day intraperitoneal streptozotocin (STZ) injections. A total of 40 rats were assigned into the normal, DN, AS-IV [AS-IV 40 mg/(kg·d)], and IRE-1α inhibitor [STF-083010, 10 mg/(kg·d)] groups (n=10), respectively. The general condition, 24-h urine volume, random blood glucose, urinary protein excretion rate (UAER), urea nitrogen (BUN), and serum creatinine (SCr) levels of rats were measured after 8 weeks of intervention. Pathological changes in the renal tissue were observed by hematoxylin and eosin (HE) staining. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) and Western blot were used to detect the expressions of GRP78, IRE-1α, nuclear factor kappa Bp65 (NF-κBp65), interleukin (IL)-1β, NLR family pyrin domain containing 3 (NLRP3), caspase-1, gasdermin D-N (GSDMD-N), and nephrin at the mRNA and protein levels in vivo and in vitro, respectively.

RESULTS

Cytoplasmic vacuolation and ER swelling were observed in the HG and IRE-1α activator groups. Podocyte morphology and ER expansion were improved in AS-IV and IRE-1α inhibitor groups compared with HG group. Cellular immunofluorescence showed that compared with the normal group, the fluorescence intensity of GRP78 and IRE-1α in the HG and IRE-1α activator groups were significantly increased whereas decreased in AS-IV and IRE-1α inhibitor groups (P<0.05). Compared with the normal group, the mRNA and protein expressions of GRP78, IRE-1α, NF-κ Bp65, IL-1β, NLRP3, caspase-1 and GSDMD-N in the HG group was increased (P<0.05). Compared with HG group, the expression of above indices was decreased in the AS-IV and IRE-1α inhibitor groups, and the expression in the IRE-1α activator group was increased (P<0.05). The expression of nephrin was decreased in the HG group, and increased in AS-IV and IRE-1α inhibitor groups (P<0.05). The in vivo experiment results revealed that compared to the normal group, the levels of blood glucose, triglyceride, total cholesterol, BUN, blood creatinine and urinary protein in the DN group were higher (P<0.05). Compared with DN group, the above indices in AS-IV and IRE-1α inhibitor groups were decreased (P<0.05). HE staining revealed glomerular hypertrophy, mesangial widening and mesangial cell proliferation in the renal tissue of the DN group. Compared with the DN group, the above pathological changes in renal tissue of AS-IV and IRE-1α inhibitor groups were alleviated. Quantitative RT-PCR and Western blot results of GRP78, IRE-1α, NF-κ Bp65, IL-1β, NLRP3, caspase-1 and GSDMD-N were consistent with immunofluorescence analysis.

CONCLUSION

AS-IV could reduce ERS and inflammation, improve podocyte pyroptosis, thus exerting a podocyte-protective effect in DN, through regulating IRE-1α/NF-κ B/NLRP3 signaling pathway.

MafB regulates NLRP3 inflammasome activation by sustaining p62 expression in macrophages

Activation of the NLRP3 inflammasome is a two-step process: the priming and the activating. The priming step involves the induction of NLRP3 and pro-IL-1β, while the activating step leads to the full inflammasome activation triggered by a NLRP3 activator. Although mechanisms underlying the NLRP3 inflammasome activation have been increasingly clear, the regulation of this process remains incompletely understood. In this study, we find that LPS and Pseudomonas aeruginosa cause a rapid downregulation in MafB transcription in macrophages, which leads to a quick decline in the level of MafB protein because MafB is short-lived and constantly degraded by the ubiquitin/proteasome system. We find that MafB knockdown or knockout markedly enhances the NLRP3, but not the NLRP1, NLRC4, or AIM2, inflammasome activation in macrophages. Conversely, pharmacological induction of MafB diminishes the NLRP3 inflammasome activation. Mechanistically, we find that MafB sustains the expression of p62, a key mediator of autophagy/mitophagy. We find that MafB inhibits mitochondrial damage, and mitochondrial ROS production and DNA cytoplasmic release. Furthermore, we find that myeloid MafB deficient mice demonstrate increased systemic and lung IL-1β production in response to LPS treatment and P. aeruginosa infection and deficient lung P. aeruginosa clearance in vivo. In conclusion, our study demonstrates that MafB is an important negative regulator of the NLRP3 inflammasome. Our findings suggest that strategies elevating MafB may be effective to treat immune disorders due to excessive activation of the NLRP3 inflammasome.

Modification of histidine repeat proteins by inorganic polyphosphate

Inorganic polyphosphate (polyP) is a linear polymer of orthophosphate that is present in nearly all organisms studied to date. A remarkable function of polyP involves its attachment to lysine residues via non-enzymatic post-translational modification (PTM), which is presumed to be covalent. Here, we show that proteins containing tracts of consecutive histidine residues exhibit a similar modification by polyP, which confers an electrophoretic mobility shift on NuPAGE gels. Our screen uncovers 30 human and yeast histidine repeat proteins that undergo histidine polyphosphate modification (HPM). This polyP modification is histidine dependent and non-covalent in nature, although remarkably it withstands harsh denaturing conditions-a hallmark of covalent PTMs. Importantly, we show that HPM disrupts phase separation and the phosphorylation activity of the human protein kinase DYRK1A, and inhibits the activity of the transcription factor MafB, highlighting HPM as a potential protein regulatory mechanism.

Induced pluripotent stem cells-podocytes promote repair in acute kidney injury is dependent on Mafb/CCR5/Nampt axis-mediated M2 macrophage polarization

Induced pluripotent stem cells (iPSCs) have been the focus of cellular therapy studies. The use of iPSCs in regenerative medicine is limited by their tumorigenic potential. This study sought to determine whether iPSCs-derived podocytes attenuate acute kidney injury (AKI) and the molecular mechanism. Inoculation of iPSCs-podocytes significantly promoted the repair of kidney injury in AKI mice, reduced the levels of kidney injury factors Scr, BUN, and urinary NAG, and alleviated the inflammatory response. Histological analysis revealed a significant increase in the number of M2 macrophages and a significant decrease in M1 macrophages in the kidney tissues. Subsequently, the genes and signaling pathways that may be associated with kidney injury repair in mice were analyzed by RNA-seq and bioinformatics prediction. The polarization of M2 macrophages was promoted by MAF bZIP transcription factor B (Mafb)-mediated activation of C-C motif chemokine receptor 5 (Ccr5) and nicotinamide phosphoribosyltransferase (Nampt) signaling pathway. Taken together, these results show that iPSCs-podocytes depend on Mafb to activate the Nampt signaling pathway through transcriptional activation of Ccr5, thereby promoting the repair of AKI caused by ischemia-reperfusion.

Misexpression of LINC01410, FOSL1, and MAFB in peripheral blood mononuclear cells associated with diabetic nephropathy

AIMS

Currently, diabetic nephropathy (DN) is considered the leading cause of the end-stage renal disease (ESRD). However, its specific molecular mechanism is still unclear, and there is still a lack of effective diagnostic and therapeutic methods.

METHOD

A pathway was assumed after bioinformatics analysis of GEO datasets related to individuals with various levels of DN, LINC01410, MAFB, and FOSL1. Then, 46 patients with type 2 diabetes (T2DM) and different levels of albuminuria, and 12 individuals without diabetes, were selected. qPCR was performed to evaluate gene expression. One-way ANOVA followed by Tukey's -and linear trend tests were performed to analyze gene expression in different stages of the disease. Moreover, receiver operating characteristic (ROC) curves and the correlation between LINC01410, FOSL1, and MAFB were analyzed.

RESULTS

LINC01410, MAFB, and FOSL1 were selected based on bioinformatics analyses. The qPCR results showed that the expression of LINC01410 decreased, and FOSL1 and MAFB increased in micro-and macroalbuminuria groups compared to normoalbuminuria groups (P < 0.05). ROC curves demonstrated a significant diagnostic accuracy of LINC01410, MAFB, and FOSL1 between DN and participants with normoalbuminuria (P < 0.05). Pearson's correlation analysis revealed a positive association between the expressions of FOSL1 and MAFB (p = 0.01, r = 0.39). However, there was no correlation between LINC01410 with MAFB and FOSL1 (p = 0.23 and p = 0.21, respectively).

CONCLUSION

Dysregulation of LINC01410, MAFB, and FOSL1 is related to DN. These results may provide new insights into the role of LINC01410, MAFB, and FOSL1 as potential biomarkers in DN.

An in vitro approach to understand contribution of kidney cells to human urinary extracellular vesicles

Extracellular vesicles (EV) are membranous particles secreted by all cells and found in body fluids. Established EV contents include a variety of RNA species, proteins, lipids and metabolites that are considered to reflect the physiological status of their parental cells. However, to date, little is known about cell-type enriched EV cargo in complex EV mixtures, especially in urine. To test whether EV secretion from distinct human kidney cells in culture differ and can recapitulate findings in normal urine, we comprehensively analysed EV components, (particularly miRNAs, long RNAs and protein) from conditionally immortalised human kidney cell lines (podocyte, glomerular endothelial, mesangial and proximal tubular cells) and compared to EV secreted in human urine. EV from cell culture media derived from immortalised kidney cells were isolated by hydrostatic filtration dialysis (HFD) and characterised by electron microscopy (EM), nanoparticle tracking analysis (NTA) and Western blotting (WB). RNA was isolated from EV and subjected to miRNA and RNA sequencing and proteins were profiled by tandem mass tag proteomics. Representative sets of EV miRNAs, RNAs and proteins were detected in each cell type and compared to human urinary EV isolates (uEV), EV cargo database, kidney biopsy bulk RNA sequencing and proteomics, and single-cell transcriptomics. This revealed that a high proportion of the in vitro EV signatures were also found in in vivo datasets. Thus, highlighting the robustness of our in vitro model and showing that this approach enables the dissection of cell type specific EV cargo in biofluids and the potential identification of cell-type specific EV biomarkers of kidney disease.

Podocyte-specific Transcription Factors: Could MafB Become a Therapeutic Target for Kidney Disease?

The increasing number of patients with chronic kidney disease (CKD) is being recognized as an emerging global health problem. Recently, it has become clear that injury and loss of glomerular visceral epithelial cells, known as podocytes, is a common early event in many forms of CKD. Podocytes are highly specialized epithelial cells that cover the outer layer of the glomerular basement membrane. They serve as the final barrier to urinary protein loss through the formation and maintenance of specialized foot-processes and an interposed slit-diaphragm. We previously reported that the transcription factor MafB regulates the podocyte slit diaphragm protein production and transcription factor Tcf21. We showed that the forced expression of MafB was able to prevent CKD. In this review, we discuss recent advances and offer an updated overview of the functions of podocyte-specific transcription factors in kidney biology, aiming to present new perspectives on the progression of CKD and respective therapeutic strategies.

Identification of Potential Diagnostic Biomarkers and Biological Pathways in Hypertrophic Cardiomyopathy Based on Bioinformatics Analysis

Hypertrophic cardiomyopathy (HCM) is a genetic heterogeneous disorder and the main cause of sudden cardiac death in adolescents and young adults. This study was aimed at identifying potential diagnostic biomarkers and biological pathways to help to diagnose and treat HCM through bioinformatics analysis. We selected the GSE36961 dataset from the Gene Expression Omnibus (GEO) database and identified 893 differentially expressed genes (DEGs). Subsequently, 12 modules were generated through weighted gene coexpression network analysis (WGCNA), and the turquoise module showed the highest negative correlation with HCM (cor = −0.9, p-value = 4 × 10−52). With the filtering standard gene significance (GS) < −0.7 and module membership (MM) > 0.9, 19 genes were then selected to establish the least absolute shrinkage and selection operator (LASSO) model, and LYVE1, MAFB, and MT1M were finally identified as key genes. The expression levels of these genes were additionally verified in the GSE130036 dataset. Gene Set Enrichment Analysis (GSEA) showed oxidative phosphorylation, tumor necrosis factor alpha-nuclear factor-κB (TNFα-NFκB), interferon-gamma (IFNγ) response, and inflammatory response were four pathways possibly related to HCM. In conclusion, LYVE1, MAFB, and MT1M were potential biomarkers of HCM, and oxidative stress, immune response as well as inflammatory response were likely to be associated with the pathogenesis of HCM.

Oxidative Stress Genes in Diabetes Mellitus Type 2: Association with Diabetic Kidney Disease

Diabetic type 2 patients compared to nondiabetic patients exhibit an increased risk of developing diabetic kidney disease (DKD), the leading cause of end-stage renal disease. Hyperglycemia, hypertension, oxidative stress (OS), and genetic background are some of the mechanisms and pathways implicated in DKD pathogenesis. However, data on OS pathway susceptibility genes show limited success and conflicting or inconclusive results. Our study is aimed at exploring OS pathway genes and variants which could be associated with DKD. We recruited 121 diabetes mellitus type 2 (DM2) patients with DKD (cases) and 220 DM2, non-DKD patients (control) of Greek origin and performed a case-control association study using genome-wide association data. PLINK and EIGENSOFT were used to analyze the data. Our results indicate 43 single nucleotide polymorphisms with their 21 corresponding genes on the OS pathway possibly contributing or protecting from DKD: SPP1, TPO, TTN, SGO2, NOS3, PDLIM1, CLU, CCS, GPX4, TXNRD2, EPHX2, MTL5, EPX, GPX3, ALOX12, IPCEF1, GSTA, OXR1, GPX6, AOX1, and PRNP. Therefore, a genetic OS background might underlie the complex pathogenesis of DKD in DM2 patients.

Preparation of single-cell suspensions of mouse glomeruli for high-throughput analysis

The kidney glomerulus is essential for proper kidney function. Until recently, technical challenges associated with glomerular isolation and subsequent dissolution into single cells have limited the detailed characterization of cells in the glomerulus. Previous techniques of kidney dissociation result in low glomerular cell yield, which limits high-throughput analysis. The ability to efficiently purify glomeruli and digest the tissue into single cells is especially important for single-cell characterization methods. Here, we present a detailed and comprehensive technique for the extraction and preparation of mouse glomerular cells, with high yield and viability. The method includes direct renal perfusion of Dynabeads via the renal artery followed by kidney dissociation and isolation of glomeruli by magnet; these steps provide a high number and purity of isolated glomeruli, which are further dissociated into single cells. The balanced representation of podocytes, mesangial and endothelial cells in single-cell suspensions of mouse glomeruli, and the high cell viability observed, confirm the efficiency of our method. With some practice, the procedure can be done in <3 h (excluding equipment setup and data analysis). This protocol provides a valuable technique for advancing future single-cell-based studies of the glomerulus in health, injury and disease.

Super-Enhancer-Associated Transcription Factors Maintain Transcriptional Regulation in Mature Podocytes

BACKGROUND

Transcriptional programs control cell fate, and identifying their components is critical for understanding diseases caused by cell lesion, such as podocytopathy. Although many transcription factors (TFs) are necessary for cell-state maintenance in glomeruli, their roles in transcriptional regulation are not well understood.

METHODS

The distribution of H3K27ac histones in human glomerulus cells was analyzed to identify superenhancer-associated TFs, and ChIP-seq and transcriptomics were performed to elucidate the regulatory roles of the TFs. Transgenic animal models of disease were further investigated to confirm the roles of specific TFs in podocyte maintenance.

RESULTS

Superenhancer distribution revealed a group of potential TFs in core regulatory circuits in human glomerulus cells, including FOXC1/2, WT1, and LMX1B. Integration of transcriptome and cistrome data of FOXC1/2 in mice resolved transcriptional regulation in podocyte maintenance. FOXC1/2 regulated differentiation-associated transcription in mature podocytes. In both humans and animal models, mature podocyte injury was accompanied by deregulation of FOXC1/2 expression, and FOXC1/2 overexpression could protect podocytes in zebrafish.

CONCLUSIONS

FOXC1/2 maintain podocyte differentiation through transcriptional stabilization. The genome-wide chromatin resources support further investigation of TFs' regulatory roles in glomeruli transcription programs.

Sleeve Gastrectomy Attenuates Diabetic Nephropathy by Upregulating Nephrin Expressions in Diabetic Obese Rats

PURPOSE

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease, and sleeve gastrectomy (SG) is considered to be an effective strategy to improve pre-existing DN. However, the mechanism remains unknown.

MATERIALS AND METHODS

Animal model of DN was induced by high-fat diet (HFD) and streptozotocin (STZ). SG or sham surgery was performed and rats were sacrificed at 4, 8, and 12 weeks after surgery. The basic parameters (blood glucose, body weight, kidney weight), indicators of renal function including serum creatinine (Scr), blood urea nitrogen (BUN), urine microalbumin, urine creatinine (Ucr), microalbumin creatinine ratio (UACR), ultrastructural changes of glomerulus, and the expression of nephrin gene and protein in glomerular podocytes were compared among groups.

RESULTS

Blood glucose and body weight of SG rats were significantly lower than those of the sham-operated rats, and renal function of SG groups were also significantly improved within the postoperative period of 12 weeks. The results of periodic acid-Schiff staining (PAS) and transmission electron microscopy (TEM) showed that glomerular hypertrophy and accumulation of extracellular matrix proteins were significantly alleviated after SG, and the thickness of basement membrane and the fusion or effacement of foot processes were also significantly improved. The mRNA and protein expression of nephrin in SG groups was significantly higher than that in the sham group.

CONCLUSION

These results suggest that SG attenuates DN by upregulating the expression of nephrin and improving the ultrastructure of glomerular filtration membrane. This study indicates that SG can be used as an available therapeutic intervention for DN.

Diabetic Nephropathy: Novel Molecular Mechanisms and Therapeutic Targets

Diabetic nephropathy (DN) is one of the major microvascular complications of diabetes mellitus and the leading cause of end-stage kidney disease. The standard treatments for diabetic patients are glucose and blood pressure control, lipid lowering, and renin-angiotensin system blockade; however, these therapeutic approaches can provide only partial renoprotection if started late in the course of the disease. One major limitation in developing efficient therapies for DN is the complex pathobiology of the diabetic kidney, which undergoes a set of profound structural, metabolic and functional changes. Despite these difficulties, experimental models of diabetes have revealed promising therapeutic targets by identifying pathways that modulate key functions of podocytes and glomerular endothelial cells. In this review we will describe recent advances in the field, analyze key molecular pathways that contribute to the pathogenesis of the disease, and discuss how they could be modulated to prevent or reverse DN.

Transcription factor 21 expression in injured podocytes of glomerular diseases

Transcription factor 21 (TCF21) is one of the essential transcription factors in kidney development. To elucidate its influence on glomerular disease, we have investigated TCF21 expression in human and rat kidney tissue, and its urinary concentration. Immunohistological analysis suggested the highest TCF21 expression in nephrotic syndrome along with the urinary protein level. Urinary TCF21 concentration in human showed a positive correlation with its podocyte expression level. In nephrotic rat models, TCF21 expression in podocytes increased along with the severity of nephrotic syndrome. Next, in vitro experiments using Tcf21-expressing murine podocyte cell line, we could observe some Tcf21-dependent effects, related with actin cytoskeleton dysregulation and apoptosis. Our study illustrated TCF21 expression changes in vivo and its in vitro-functional significance injured podocytes.

Epigenetic transcriptional reprogramming by WT1 mediates a repair response during podocyte injury

In the context of human disease, the mechanisms whereby transcription factors reprogram gene expression in reparative responses to injury are not well understood. We have studied the mechanisms of transcriptional reprogramming in disease using murine kidney podocytes as a model for tissue injury. Podocytes are a crucial component of glomeruli, the filtration units of each nephron. Podocyte injury is the initial event in many processes that lead to end-stage kidney disease. Wilms tumor-1 (WT1) is a master regulator of gene expression in podocytes, binding nearly all genes known to be crucial for maintenance of the glomerular filtration barrier. Using murine models and human kidney organoids, we investigated WT1-mediated transcriptional reprogramming during the course of podocyte injury. Reprogramming the transcriptome involved highly dynamic changes in the binding of WT1 to target genes during a reparative injury response, affecting chromatin state and expression levels of target genes.

A reciprocal regulation of spermidine and autophagy in podocytes maintains the filtration barrier

Podocyte maintenance and stress resistance are exquisitely based on high basal rates of autophagy making these cells a unique model to unravel mechanisms of autophagy regulation. Polyamines have key cellular functions such as proliferation, nucleic acid biosynthesis and autophagy. Here we test whether endogenous spermidine signaling is a driver of basal and dynamic autophagy in podocytes by using genetic and pharmacologic approaches to interfere with different steps of polyamine metabolism. Translational studies revealed altered spermidine signaling in focal segmental glomerulosclerosis in vivo and in vitro. Exogenous spermidine supplementation emerged as new treatment strategy by successfully activating autophagy in vivo via inhibition of EP300, a protein with an essential role in controlling cell growth, cell division and prompting cells to differentiate to take on specialized functions. Surprisingly, gas chromatography-mass spectroscopy based untargeted metabolomics of wild type and autophagy deficient primary podocytes revealed a positive feedback mechanism whereby autophagy itself maintains polyamine metabolism and spermidine synthesis. The transcription factor MAFB acted as an upstream regulator of polyamine metabolism. Thus, our data highlight a novel positive feedback loop of autophagy and spermidine signaling allowing maintenance of high basal levels of autophagy as a key mechanism to sustain the filtration barrier. Hence, spermidine supplementation may emerge as a new therapeutic to restore autophagy in glomerular disease.

The Antioxidative Role of Cytoglobin in Podocytes: Implications for a Role in Chronic Kidney Disease

Aims: Cytoglobin (CYGB) is a member of the mammalian globin family of respiratory proteins. Despite extensive research efforts, its physiological role remains largely unknown, but potential functions include reactive oxygen species (ROS) detoxification and signaling. Accumulating evidence suggests that ROS play a crucial role in podocyte detachment and apoptosis during diabetic kidney disease. This study aimed to explore the potential antioxidative renal role of CYGB both in vivo and in vitro. Results: Using a Cygb-deficient mouse model, we demonstrate a Cygb-dependent reduction in renal function, coinciding with a reduced number of podocytes. To specifically assess the putative antioxidative function of CYGB in podocytes, we first confirmed high endogenous CYGB expression levels in two human podocyte cell lines and subsequently generated short hairpin RNA-mediated stable CYGB knockdown podocyte models. CYGB-deficient podocytes displayed increased cell death and accumulation of ROS as assessed by 2'7'-dichlorodihydrofluorescein diacetate assays and the redox-sensitive probe roGFP2-Orp1. CYGB-deficient cells also exhibited an impaired cellular bioenergetic status. Consistently, analysis of the CYGB-dependent transcriptome identified dysregulation of multiple genes involved in redox balance, apoptosis, as well as in chronic kidney disease (CKD). Finally, genome-wide association studies and expression studies in nephropathy biopsies indicate an association of CYGB with CKD. Innovation: This study demonstrates a podocyte-related renal role of Cygb, confirms abundant CYGB expression in human podocyte cell lines, and describes for the first time an association between CYGB and CKD. Conclusion: Our results provide evidence for an antioxidative role of CYGB in podocytes.

Phenotypic analysis of mice carrying human-type MAFB p.Leu239Pro mutation

The transcription factor, MafB, plays important role in the differentiation and functional maintenance of various cells and tissues, such as the inner ear, kidney podocyte, parathyroid gland, pancreatic islet, and macrophages. The rare heterozygous substitution (p.Leu239Pro) of the DNA binding domain in MAFB is the cause of Focal Segmental Glomerulosclerosis associated with Duane Retraction Syndrome, which is characterized by impaired horizontal eye movement due to cranial nerve maldevelopment in humans. In this research, we generated mice carrying MafB p.Leu239Pro (Mafb^mt/mt) and retrieved their tissues for analysis. As a result, we found that the phenotype of Mafb^mt/mt mouse was similar to that of the conventional Mafb deficient mouse. This finding suggests that the Leucine residue at 239 in the DNA binding domain plays a key role in MafB function and could contribute to the diagnosis or development of treatment for patients carrying the MafB p.Leu239Pro missense variant.

Effect of fosinopril on the renal cortex protein expression profile of Otsuka Long-Evans Tokushima Fatty rats

Angiotensin-converting enzyme inhibitors (ACEIs) can reduce urinary protein excretion and postpone the deterioration of renal function. However, the mechanisms of renal protection are not yet fully understood. To investigate the mechanisms of ACEIs in the treatment of diabetic nephropathy (DN), the present study determined the effects of the ACEI fosinopril (FP) on the profiling of renal cortex protein expression in Otsuka Long-Evans Tokushima Fatty (OLETF) rats using Long-Evans Tokushima Otsuka (LETO) rats as controls. Urinary protein levels at 24 h were examined using the Broadford method. PAS staining was performed to observe renal histopathological changes. The kidney cortices of OLETF, FP-treated OLETF and LETO rats were examined using soluble and insoluble high-resolution subproteomic analysis methodology at age of 36 and 56 weeks. Differentiated proteins were further confirmed using western blotting analysis. The results demonstrated that FP significantly decreased the glomerulosclerosis index and reduced the 24 h urinary protein excretion of OLETF rats. Additionally, 17 proteins significantly changed following FP-treatment. Amongst these proteins, the abundances of the stress-response protein heat shock protein family A member 9 and the antioxidant glutathione peroxidase 3 were particularly increased. These results indicated that FP ameliorated diabetic renal injuries by inhibiting oxidative stress. In conclusion, the differentially expressed proteins may improve our understanding of the mechanism of ACEIs in the OLETF rats.

MiR-320a induces diabetic nephropathy via inhibiting MafB

Multiple studies indicate that microRNAs (miRNAs) are involved in diabetes. However, the roles of miRNA in the target organ damages in diabetes remain unclear. This study investigated the functions of miR-320a in diabetic nephropathy (DN). In this study, db/db mice were used to observe the changes in podocytes and their function in vivo, as well as in cultured mouse podocyte cells (MPC5) exposed to high glucose in vitro. To further explore the role of miR-320a in DN, recombinant adeno-associated viral particle was administered intravenously to manipulate the expression of miR-320a in db/db mice. Overexpression of miR-320a markedly promoted podocyte loss and dysfunction in DN, including mesangial expansion and increased levels of proteinuria, serum creatinine and urea nitrogen. Furthermore, MafB was identified as a direct target of miR-320a through AGO2 co-immunoprecipitation, luciferase reporter assay, and Western blotting. Moreover, re-expression of MafB rescued miR-320a-induced podocyte loss and dysfunction by upregulating the expressions of Nephrin and glutathione peroxidase 3 (Gpx3). Our data indicated that miR-320a aggravated renal disfunction in DN by targeting MafB and downregulating Nephrin and Gpx3 in podocytes, which suggested that miR-320a could be a potential therapeutic target of diabetic nephropathy.

Neuron-specific Mafb knockout causes growth retardation accompanied by an impaired growth hormone/insulin-like growth factor I axis

Mammalian postnatal growth is regulated primarily by the growth hormone (GH)/insulin-like growth factor I (IGF-I) axis. MafB is a basic leucine zipper (bZip) transcription factor that has pleiotropic functions. Although MafB plays a critical role in fetal brain development, such as in guidance for hindbrain segmentation, its postnatal role in neurons remains to be elucidated. To investigate this, we used neuron-specific Mafb conditional knockout (cKO) mice. In addition to an approximately 50% neonatal viability, the Mafb cKO mice exhibited growth retardation without apparent signs of low energy intake. Notably, serum IGF-I levels of these mice in the postnatal stage were lower than those of control mice. They seemed to have a neuroendocrine dysregulation, as shown by the upregulation of serum GH levels in the resting state and an inconsistent secretory response of GH upon administration of growth hormone-releasing hormone. These findings reveal that neuronal MafB plays an important role in postnatal development regulated by the GH/IGF-I axis.

LncRNA ZEB1-AS1 inhibits renal fibrosis in diabetic nephropathy by regulating the miR-217/MAFB axis

Diabetic nephropathy (DN) is a common chronic microvascular complication of diabetes, characterized by the deposition of extracellular matrix (ECM) proteins.

Mice harboring an MCTO mutation exhibit renal failure resembling nephropathy in human patients

Multicentric carpotarsal osteolysis (MCTO) is a condition involving progressive osteolysis of the carpal and tarsal bones that is associated with glomerular sclerosis and renal failure (MCTO nephropathy). Previous work identified an autosomal dominant missense mutation in the transactivation domain of the transcription factor MAFB as the cause of MCTO. Several methods are currently used for MCTO nephropathy treatment, but these methods are invasive and lead to severe side effects, limiting their use. Therefore, the development of alternative treatments for MCTO nephropathy is required; however, the pathogenesis of MCTO in vivo is unclear without access to a mouse model. Here, we report the generation of an MCTO mouse model using the CRISPR/Cas9 system. These mice exhibit nephropathy symptoms that are similar to those observed in MCTO patients. Mafb^MCTO/MCTO mice show developmental defects in body weight from postnatal day 0, which persist as they age. They also exhibit high urine albumin creatinine levels from a young age, mimicking the nephropathic symptoms of MCTO patients. Characteristics of glomerular sclerosis reported in human patients are also observed, such as histological evidence of focal segmental glomerulosclerosis (FSGS), podocyte foot process microvillus transformation and podocyte foot process effacement. Therefore, this study contributes to the development of an alternative treatment for MCTO nephropathy by providing a viable mouse model.

Erzhi Formula Extracts Reverse Renal Injury in Diabetic Nephropathy Rats by Protecting the Renal Podocytes

Podocytes injury was a crucial factor resulting in diabetic nephropathy (DN). Erzhi formula extract (EZF) was a clinical effective Chinese medicine on DN, but its mechanism was unclear. In this study, the main compounds of EZF and their pharmacokinetics in rat were detected by HPLC-MS/MS. And then, blood glucose, urine protein, renal index, renal microstructural (HE/PAS staining), inflammatory factors (IL-β, TNF-α, IL-6), and protein/mRNA expression related to the function of podocyte (CD2AP and Podocin) in DN rats were investigated after the oral administration of EZF. The concentrations of specnuezhenide and wedelolactone in rat kidney were 7.19 and 0.057 mg/kg, respectively. The T_max of specnuezhenide and wedelolactone were 2.0 and 1.50 h, respectively. Their C_max were, respectively, 30.24 ± 2.68 and 6.39 ± 0.05 μg/L. Their AUC_(0-∞) were 123.30 ± 2.68 and 16.56 ± 0.98 μg/L⁎h, respectively. Compared with the model group, the blood glucose and the 24-hour urinary protein were significantly decreased (P < 0.05) after 16 weeks' treatment of EZF. The expressions of Podocin and CD2AP protein/mRNA were increased (P < 0. 05). The deteriorate of glomerular morphology was alleviated under the treatment of EZF. EZF prominently decreased the levels of inflammatory factors (P < 0.05). MDA was significantly decreased (P < 0.05) with the significant increase of SOD activity (P < 0.05) in EZF groups. All the results proved that EZF repaired glomerular mesangial matrix, protected renal tubule, and improved renal function in DN rats by upregulating the expression of Podocin and CD2AP protein/mRNA in podocytes.

MAFB mediates the therapeutic effect of sleeve gastrectomy for obese diabetes mellitus by activation of FXR expression

Farnesoid X receptor (FXR) and related pathways are involved in the therapeutic effect of sleeve gastrectomy for overweight or obese patients with diabetes mellitus. This study aimed to investigate the mechanism of FXR expression regulation during the surgical treatment of obese diabetes mellitus by sleeve gastrectomy. Diabetic rats were established by combined streptozotocin and high-fat diet induction. Data collection included body weight, chemical indexes of glucose and lipid metabolism, liver function, and the expression levels of musculoaponeurotic fibrosarcoma oncogene family B (MAFB), FXR, and related genes induced by sleeve gastrectomy. Chang liver cells overexpressing MAFB gene were established to confirm the expression of related genes. The binding and activation of FXR gene by MAFB were tested by Chip and luciferase reporter gene assays. Vertical sleeve gastrectomy induced significant weight loss and decreased blood glucose and lipids in diabetic rat livers, as well as decreased lipid deposition and recovered lipid function. The expression of MAFB, FXR, and FXR-regulated genes in diabetic rat livers were also restored by sleeve gastrectomy. Overexpression of MAFB in Chang liver cells led to FXR gene expression activation and the alteration of multiple FXR-regulated genes. Chip assay showed that MAFB could directly bind with FXR promoter, and the activation of FXR expression was confirmed by luciferase reporter gene analysis. The therapeutic effect of sleeve gastrectomy for overweight or obese patients with diabetes mellitus was mediated by activation of FXR expression through the binding of MAFB transcription factor.

Prolonged exposure of mouse and human podocytes to insulin induces insulin resistance through lysosomal and proteasomal degradation of the insulin receptor

AIMS/HYPOTHESIS

Podocytes are insulin-responsive cells of the glomerular filtration barrier and are key in preventing albuminuria, a hallmark feature of diabetic nephropathy. While there is evidence that a loss of insulin signalling to podocytes is detrimental, the molecular mechanisms underpinning the development of podocyte insulin resistance in diabetes remain unclear. Thus, we aimed to further investigate podocyte insulin responses early in the context of diabetic nephropathy.

METHODS

Conditionally immortalised human and mouse podocyte cell lines and glomeruli isolated from db/db DBA/2J mice were studied. Podocyte insulin responses were investigated with western blotting, cellular glucose uptake assays and automated fluorescent imaging of the actin cytoskeleton. Quantitative (q)RT-PCR was employed to investigate changes in mRNA. Human cell lines stably overproducing the insulin receptor (IR) and nephrin were also generated, using lentiviral constructs.

RESULTS

Podocytes exposed to a diabetic environment (high glucose, high insulin and the proinflammatory cytokines TNF-α and IL-6) become insulin resistant with respect to glucose uptake and activation of phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) signalling. These podocytes lose expression of the IR as a direct consequence of prolonged exposure to high insulin concentrations, which causes an increase in IR protein degradation via a proteasome-dependent and bafilomycin-sensitive pathway. Reintroducing the IR into insulin-resistant human podocytes rescues upstream phosphorylation events, but not glucose uptake. Stable expression of nephrin is also required for the insulin-stimulated glucose uptake response in podocytes and for efficient insulin-stimulated remodelling of the actin cytoskeleton.

CONCLUSIONS/INTERPRETATION

Together, these results suggest that IR degradation, caused by high levels of insulin, drives early podocyte insulin resistance, and that both the IR and nephrin are required for full insulin sensitivity of this cell. This could be highly relevant for the development of nephropathy in individuals with type 2 diabetes, who are commonly hyperinsulinaemic in the early phases of their disease.

MAFB Determines Human Macrophage Anti-Inflammatory Polarization: Relevance for the Pathogenic Mechanisms Operating in Multicentric Carpotarsal Osteolysis

Macrophage phenotypic and functional heterogeneity derives from tissue-specific transcriptional signatures shaped by the local microenvironment. Most studies addressing the molecular basis for macrophage heterogeneity have focused on murine cells, whereas the factors controlling the functional specialization of human macrophages are less known. M-CSF drives the generation of human monocyte-derived macrophages with a potent anti-inflammatory activity upon stimulation. We now report that knockdown of MAFB impairs the acquisition of the anti-inflammatory profile of human macrophages, identify the MAFB-dependent gene signature in human macrophages and illustrate the coexpression of MAFB and MAFB-target genes in CD163⁺ tissue-resident and tumor-associated macrophages. The contribution of MAFB to the homeostatic/anti-inflammatory macrophage profile is further supported by the skewed polarization of monocyte-derived macrophages from multicentric carpotarsal osteolysis (Online Mendelian Inheritance in Man #166300), a pathology caused by mutations in the MAFB gene. Our results demonstrate that MAFB critically determines the acquisition of the anti-inflammatory transcriptional and functional profiles of human macrophages.

FK506 reduces albuminuria through improving podocyte nephrin and podocin expression in diabetic rats

Objective and design

Several works in the setting of early experimental diabetic nephropathy using anti-inflammatory drugs, such as the calcineurin inhibitor FK506, have shown prevention of the development or amelioration of renal injury including proteinuria. The exact mechanisms by which anti-inflammatory drugs lower the albuminuria have not been still clarified well.

Materials

The diabetic rats were induced by using streptozotocin.

Treatment

The diabetic rats were subjected to oral FK506 treatment at a dose of 0.5 or 1.0 mg/kg daily for 4 weeks.

Methods

Renal histology for the ultrastructural evaluation was determined by electron microscope, followed by analyses of renal nephrin and podocin and detection of renal iNOS⁺ macrophages and NF-κB-p-p65⁺.

Results

Elevated 24-h urinary albumin excretion rate was markedly attenuated by FK506 treatment. In diabetic model rats, FK506 treatment at a dose of 0.5 or 1.0 mg/kg significantly increased the expression of nephrin and podocin when compared to control. As expected, rats in control diabetic group had an increase in GBM thickening and foot process effacement when compared to normal rats; increased GBM thickening and foot process effacement were ameliorated by FK506 treatment with 0.5 and 1.0 mg/kg. Histologically, there was marked accumulation of ED-1⁺cells (macrophages) in diabetic kidneys, and FK506 treatment failed to inhibit it. In contrast, FK506 treatment at 0.5 and 1.0 mg/kg doses significantly inhibited the elevated ED-1⁺/iNOS⁺ cells in the kidneys of diabetic rats. ED-1⁺/NF-κB-p-p65⁺ cells were significantly increased in positive diabetic kidneys compared to those of normal rats. FK506 treatment at 0.5 and 1.0 mg/kg significantly attenuated the elevated ED-1⁺/NF-κB-p-p65⁺ cells in diabetic kidneys. Additionally, a positive correlation was observed between ED-1⁺/iNOS⁺ cells and albuminuria (r = 0.87, p < 0.05). Likewise, ED-1⁺/iNOS⁺ cells were correlated negatively with both nephrin and podocin protein (r = −0.70, p < 0.05; r = −0.68, p < 0.05, respectively).

Conclusion

Our results show that FK506 not only upregulates expression of nephrin and podocin but also inhibits macrophage activation to protect against podocyte injury.

Genome-Wide Analysis of Wilms' Tumor 1-Controlled Gene Expression in Podocytes Reveals Key Regulatory Mechanisms

The transcription factor Wilms' tumor suppressor 1 (WT1) is key to podocyte development and viability; however, WT1 transcriptional networks in podocytes remain elusive. We provide a comprehensive analysis of the genome-wide WT1 transcriptional network in podocytes in vivo using chromatin immunoprecipitation followed by sequencing (ChIPseq) and RNA sequencing techniques. Our data show a specific role for WT1 in regulating the podocyte-specific transcriptome through binding to both promoters and enhancers of target genes. Furthermore, we inferred a podocyte transcription factor network consisting of WT1, LMX1B, TCF21, Fox-class and TEAD family transcription factors, and MAFB that uses tissue-specific enhancers to control podocyte gene expression. In addition to previously described WT1-dependent target genes, ChIPseq identified novel WT1-dependent signaling systems. These targets included components of the Hippo signaling system, underscoring the power of genome-wide transcriptional-network analyses. Together, our data elucidate a comprehensive gene regulatory network in podocytes suggesting that WT1 gene regulatory function and podocyte cell-type specification can best be understood in the context of transcription factor-regulatory element network interplay.

Glomerular development--shaping the multi-cellular filtration unit

The glomerulus represents a highly structured filtration unit, composed of glomerular endothelial cells, mesangial cells, podocytes and parietal epithelial cells. During glomerulogenesis an intricate network of signaling pathways involving transcription factors, secreted factors and cell-cell communication is required to guarantee accurate evolvement of a functional, complex 3-dimensional glomerular architecture. Here, we want to provide an overview on the critical steps and relevant signaling cascades of glomerular development.