Mitochondrial protein MPV17 promotes ß-cell apoptosis in diabetogenesis.

MPV17 is a mitochondrial inner membrane protein, and its deficiency can cause mitochondrial DNA (mtDNA) depletion, increase reactive oxygen species (ROS), and promote apoptosis in several cell types, suggesting that MPV17 plays a protective role in cells although the underlying mechanism remains unknown. To test whether MPV17 is also protective in diabetic kidney disease, we treated Mpv17-deficient mice with streptozotocin (STZ) and surprisingly found that they were resistant to diabetes. Mpv17 deficiency was also found to confer resistance to the diabetes induced by an insulin mutation (Ins2Akita), which represents a mouse model of monogenic diabetes characterized by proinsulin misfolding and ß-cell failure. In both STZ and Ins2Akita models, Mpv17 mutants had significantly less severe ß-cell loss and apoptosis compared with the wild-type mice. We next showed that MPV17 is expressed in ß-cells of mice normally, suggesting that MPV17 acts ß-cells autonomously to facilitate apoptosis. Consistently, Mpv17 knockdown improved the viability and ameliorated the apoptosis of cultured MIN6 cells treated with STZ and palmitic acid (PA), respectively, accompanied by prevention of caspase 3 activation. The proapoptotic effect of MPV17 in ß-cells is in contrast with its known anti-apoptotic effect in other cell types. Thus, we have identified a novel regulator of ß-cell death in diabetes development.

Regulon analysis identifies protective FXR and CREB5 in proximal tubules in early diabetic kidney disease.

Diabetic kidney disease (DKD) is the most common complication of diabetes mellitus and a leading cause of kidney failure worldwide. Despite its prevalence, the mechanisms underlying early kidney damage in DKD remain poorly understood. In this study, we used single nucleus RNA-seq to construct gene regulatory networks (GRNs) in the kidney cortex of patients with early DKD. By comparing these networks with those of healthy controls, we identify cell type-specific changes in genetic regulation associated with diabetic status. The regulon activities of FXR (NR1H4) and CREB5 were found to be upregulated in kidney proximal convoluted tubule epithelial cells (PCTs), which were validated using immunofluorescence staining in kidney biopsies from DKD patients. In vitro experiments using cultured HK2 cells showed that FXR and CREB5 protected cells from apoptosis and epithelial-mesenchymal transition. Our findings suggest that FXR and CREB5 may be promising targets for early intervention in patients with DKD.

Urinary miR-196a predicts disease progression in patients with chronic kidney disease.

BACKGROUND: Urinary miRNAs may potentially serve as noninvasive biomarkers in various kidney diseases to reflect disease activity, severity and progression, especially those correlated with the pathogenesis of kidney diseases. This study demonstrates that urinary miR-196a, a kidney-enriched miRNA, can predict progression of chronic kidney disease (CKD). METHODS: Focal segmental glomerulosclerosis (FSGS) cohorts were used as the representative example of CKD. First, correlation of miR-196a with disease activity was analyzed using paired urine and plasma samples from FSGS patients with nephrotic-range proteinuria (FSGS-A), complete remission (FSGS-CR) and normal controls (NCs). Then, the value of urinary miR-196a in predicting disease progression was validated using another cohort of 231 FSGS patients who were followed-up until over 36 months or reaching end-stage renal disease (ESRD). MiR-196a levels were analyzed by quantitative reverse transcription-polymerase chain reaction. RESULTS: The results showed that urinary miR-196a significantly increased in FSGS-A compared with FSGS-CR and NCs, clearly distinguishing FSGS-A from FSGS-CR and NCs, whereas plasma miR-196a showed no difference among these groups. Moreover, urinary miR-196a, which was associated with proteinuria, estimated glomerular filtration rate (eGFR), interstitial fibrosis and tubular atrophy, significantly increased in patients progressed to ESRD compared to those not. Furthermore, patients with higher urinary miR-196a displayed poorer renal survival than those with lower urinary miR-196a. Multivariate Cox analysis confirmed urinary miR-196a as an independent risk factor for FSGS progression after adjusting for age, sex, proteinuria and eGFR. Prediction accuracy of ESRD was significantly improved by combining urinary miR-196a with other indicators including eGFR and proteinuria. CONCLUSION: Urinary miR-196a may serve as a biomarker for predicting CKD progression.

Single-cell RNA-sequence analysis of mouse glomerular mesangial cells uncovers mesangial cell essential genes.

Mesangial cells are essential for the structure and function of glomeruli, but the mechanisms underlying these roles are not well understood. Here, we performed a single-cell RNA-sequence (RNA-seq) analysis of mouse mesangial cells using the Fluidigm C1 platform. We found that gene expression in individual mesangial cells was tremendously heterogeneous, with mean correlation coefficients of 0.20, and most mesangial genes were actually expressed in only a portion of mesangial cells and are therefore presumably dispensable. In contrast, 1,045 genes were expressed in every single mesangial cell and were considered mesangial cell essential genes. A gene ontology analysis revealed a significant enrichment of genes associated with the endothelium, supporting the inference that mesangial cells function as pericytes. Among 58 endothelium-associated genes, 18 encode proteins that are secreted and may be directly involved in endothelial homeostasis. Importantly, 11 (Angpt2, Anxa5, Axl, Ecm1, Eng, Fn1, Mfge8, Msn, Nrp1, Serpine2, and Sparc) were upregulated, while 2 (Apoe and Fgf1) were downregulated in various glomerulopathies. The enrichment of genes associated with other reported functions of mesangial cells was also found. Furthermore, we identified 173 genes specifically expressed in every mesangial cell in glomeruli from the mesangial cell essential gene list. Finally, based on single mesangial cell RNA-seq results, we found that commonly used glomerular cell type markers, including Fhl2, Igfbp5, Wt1, Tek/Tie2, Kdr/Flk1, Flt1/Vegfr1, and Cd34, are actually not specific. Thus, single mesangial cell RNA-seq analysis has provided insights into the functions and underlying mechanisms of mesangial cells.

Genome-wide identification of genes essential for podocyte cytoskeletons based on single-cell RNA sequencing.

Gene expression differs substantially among individual cells of the same type. We speculate that genes that are expressed in all but a portion of cells of a given cell type would be likely essential and required for either the cell survival (housekeeping) or for the cell type's unique structure and function, enabling the organism to survive. Here, we performed RNA-seq of 20 mouse podocytes using the Fluidigm C1 system and identified 335 genes that were expressed in all of them. Among them, 239 genes were also expressed in mesangial and endothelial cells and were involved in energy metabolism, protein synthesis, etc., as housekeeping genes. In contrast, 92 genes were preferentially expressed in podocytes (over five-fold versus expression in mesangial and endothelial cells) and are, therefore, the essential candidate genes specific for podocytes. Assessments by bioinformatics, conserved expression in human podocytes, and association with injury/disease all support the essentiality of these genes for podocytes. Factually, 27 of the 92 genes are already known to be essential for podocyte structure and function. Thirty-seven novel genes were functionally analyzed by siRNA silencing, and we found that a deficiency of 30 genes led to either cytoskeletal injury (FGFR1, AOX1, AIF1L, HAUS8, RAB3B, LPIN2, GOLIM4, CERS6, ARHGEF18, ARPC1A, SRGAP1, ITGB5, ILDR2, MPP5, TSC22D1, DNAJC11, SEPT10, MOCS2, FNBP1L, and TMOD3) or significant downregulation of CD2AP and synaptopodin (IFT80, MYOM2, ANXA4, CYB5R4, GPC1, ZNF277, NSF, ITGAV, CRYAB, and MTSS1). Thus, the list of genes essential for podocyte cytoskeletons is expanded by single-cell RNA sequencing. It appears that podocyte-specific essential genes are mainly associated with podocyte cytoskeletons.

Plasma microRNA-186 and proteinuria in focal segmental glomerulosclerosis.

BACKGROUND: MicroRNAs (miRNAs) are stable in circulation, and their unique expression profiles can serve as fingerprints for various diseases. This study explored whether plasma miRNAs could be used as biomarkers to evaluate disease activity in patients with focal segmental glomerulosclerosis (FSGS). STUDY DESIGN: Retrospective and prospective cohorts. SETTING & PARTICIPANTS: 78 patients with FSGS with nephrotic proteinuria (protein excretion > 3.5g/24 h), 35 patients with FSGS in complete remission, 63 patients with membranous nephropathy, 59 patients with diabetic nephropathy, and 69 apparently healthy controls were recruited. Plasma samples from 51 other patients with FSGS with nephrotic proteinuria were collected prospectively before and after steroid treatment. PREDICTORS: Plasma miRNA concentration. OUTCOMES: Complete remission (protein excretion < 0.4g/24 h), or no response (sustained protein excretion > 3.5g/24 h after 8 weeks of steroid treatment). MEASUREMENTS: Quantitative reverse transcription-polymerase chain reaction analysis of plasma miRNAs. RESULTS: Increases in miR-125b, miR-186, and miR-193a-3p levels were identified in a pooled plasma sample of 9 patients with FSGS compared with that of 9 healthy controls and were confirmed with individual samples from patients with FSGS (n=32) and healthy controls (n=30). Areas under the receiver operating characteristic curves of miR-125b, miR-186, miR-193a-3p, and the 3 miRNAs in combination were 0.882, 0.789, 0.910, and 0.963, respectively. miR-125b and miR-186 concentrations were significantly lower in patients with FSGS in complete remission (n=35) than those with nephrotic proteinuria (n=37). In a prospective study, miR-125b and miR-186 levels declined markedly in patients with FSGS with complete remission (n=29), but not those with no response (n=22), after steroid treatment. Plasma miR-125b and miR-186 levels were not elevated in patients with membranous nephropathy (n=63) and diabetic nephropathy (n=59) regardless of degree of proteinuria. Last, plasma miR-186, but not miR-125b, level was correlated with degree of proteinuria in patients with FSGS (151 samples). LIMITATIONS: Relatively small cohort size. CONCLUSIONS: Plasma miR-186 may be a biomarker for FSGS with nephrotic proteinuria.

Podocyte autophagic activity plays a protective role in renal injury and delays the progression of podocytopathies.

The progression of podocytopathies is quite variable among patients and the underlying reason for this remains unclear. Here, we report that autophagic activity in podocytes plays a critical role in controlling the progression of podocytopathies. Morphological and biochemical studies on renal biopsies from patients with minimal change disease (MCD) or focal segmental glomerulosclerosis (FSGS) showed that glomeruli, and in particular podocytes, from MCD patients had higher levels of Beclin1-mediated autophagic activity than glomeruli from FSGS patients. Repeat renal biopsies of MCD patients enabled tracking of podocyte autophagic activity and confirmed that patients maintaining high podocyte autophagic activity retained MCD status, whereas patients with decreased podocyte autophagic activity progressed to FSGS. Inhibition of autophagic activity, by knocking down Beclin1 or by treating with 3-methyladenine (3-MA) or chloroquine, enhanced puromycin aminonucleoside (PAN)-induced apoptosis of podocytes. In contrast, rapamycin-mediated promotion of autophagic activity decreased this apoptosis. In PAN-treated rats, inhibition of autophagy with 3-MA or chloroquine resulted in earlier onset and greater proteinuria, more extensive foot-process effacement, and reduction in podocyte markers, whereas rapamycin-mediated stimulation of autophagy led to decreased proteinuria and less severe foot-process effacement, but higher expression of podocyte markers. This study demonstrates that podocyte autophagic activity plays a critical protective role in renal injury and that maintaining podocyte autophagic activity represents a potential therapeutic strategy for controlling the progression of podocytopathies.

Mpv17 in mitochondria protects podocytes against mitochondrial dysfunction and apoptosis in vivo and in vitro.

Mitochondrial dysfunction is increasingly recognized as contributing to glomerular diseases, including those secondary to mitochondrial DNA (mtDNA) mutations and deletions. Mitochondria maintain cellular redox and energy homeostasis and are a major source of intracellular reactive oxygen species (ROS) production. Mitochondrial ROS accumulation may contribute to stress-induced mitochondrial dysfunction and apoptosis and thereby to glomerulosclerosis. In mice, deletion of the gene encoding Mpv17 is associated with glomerulosclerosis, but the underlying mechanism remains poorly defined. Here we report that Mpv17 localizes to mitochondria of podocytes and its expression is reduced in several glomerular injury models and in human focal segmental glomerulosclerosis (FSGS) but not in minimal change disease. Using models of mild or severe nephrotoxic serum nephritis (NTSN) in Mpv17(+/+) wild-type (WT) and Mpv17(-/-) knockout mice, we found that Mpv17 deficiency resulted in increased proteinuria (mild NTSN) and renal insufficiency (severe NTSN) compared with WT. These lesions were associated with increased mitochondrial ROS generation and mitochondrial injury such as oxidative DNA damage. In vitro, podocytes with loss of Mpv17 function were characterized by increased susceptibility to apoptosis and ROS injury including decreased mitochondrial function, loss of mtDNA content, and change in mitochondrial configuration. In summary, the inner mitochondrial membrane protein Mpv17 in podocytes is essential for the maintenance of mitochondrial homeostasis and protects podocytes against oxidative stress-induced injury both in vitro and in vivo.

Inhibition of miRNA-21 prevents fibrogenic activation in podocytes and tubular cells in IgA nephropathy.

Podocytopathy and tubular interstitial fibrosis impact on renal outcomes of IgA nephropathy (IgAN). We found that level of miR-21 was up regulated in both glomerular and tubular-interstitial tissues of patients with IgAN. Enhanced expression of miR-21 mainly located in podocytes and tubular cells. Mesangial cell derived cytokines contributed to the increase of miR-21 in podocytes and HK2 cells. IgA-HMC medium prepared with pIgA from IgAN, lead to obvious fibrogenic activation, evidenced by the loss of Podocin and CD2AP in podocytes, loss of E-cadherin and Megalin in HK2 cells and increase of FN and Col I in both cells. miR-21 targeted PTEN in these cells. Expression of PTEN was decreased and phosphorylation of Akt was increased in podocytes and HK2 cells exposed to the medium prepared with pIgA from IgAN. Inhibition of miR-21 preserved the expression of PTEN, prevented the activation of Akt and inhibited the fibrogenic activation in podocytes and HK2 cells exposed to the IgA-HMC medium prepared with pIgA from IgAN. In conclusion, our study suggests that inhibition of miR-21 prevents fibrogenic activation in podocytes and tubular cells by preventing PTEN/Akt pathway activation in IgAN.

Epithelial cell TGFß signaling induces acute tubular injury and interstitial inflammation.

TGFß signaling plays a central role in the development of acute and chronic kidney diseases. Previous in vivo studies involved systemic alteration of TGFß signaling, however, limiting conclusions about the direct role of TGFß in tubular cell injury. Here, we generated a double transgenic mouse that inducibly expresses a ligand-independent constitutively active TGFß receptor type 1 (TßR1) kinase specifically in tubular epithelial cells, with expression restricted by the Pax8 promoter. In this model, activation of TGFß signaling in the tubular epithelium alone was sufficient to cause AKI characterized by marked tubular cell apoptosis and necrosis, oxidative stress, dedifferentiation and regenerative cell proliferation, reduced renal function, and interstitial accumulation of inflammatory cells. This tubular injury was associated with mitochondrial-derived generation of reactive oxygen species (ROS), but cell damage and apoptosis were partially independent of mitochondrial-derived ROS. TßR1 signaling-induced tubular injury also associated with significant leukocyte infiltration consisting of F4/80(+) macrophages, CD11c(+) F4/80(+) dendritic cells, CD11c(+) F4/80(-) Ly6C(high) dendritic cells/monocytes, and T cells. Inhibition of mitochondrial-derived ROS significantly reduced accumulation of CD11c(+) F4/80(+) dendritic cells and T cells, suggesting a role for ROS in the activation and recruitment of the adaptive immune response to tubular injury. Taken together, these results suggest that TGFß signaling in the tubular epithelium alone is sufficient to cause acute tubular injury and inflammation; therefore, TGFß may be a mechanistic link between acute injury and chronic progression of kidney disease.

Dynamic chromatin landscape encodes programs for perinatal transition of cardiomyocytes.

The perinatal period occurring immediately before and after birth is critical for cardiomyocytes because they must change rapidly to accommodate the switch from fetal to neonatal circulation after birth. This transition is a well-orchestrated process, and any perturbation leads to unhealthy cardiomyocytes and heart disease. Despite its importance, little is known about how this transition is regulated and controlled. Here, by mapping the genome-wide chromatin accessibility, transcription-centered long-range chromatin interactions and gene expression in cardiomyocytes undergoing perinatal transition, we discovered two key transcription factors, MEF2 and AP1, that are crucial for driving the phenotypic changes within the perinatal window. Thousands of dynamic regulatory elements were found in perinatal cardiomyocytes and we show these elements mediated the transcriptional reprogramming through an elegant chromatin high-order architecture. We recompiled transcriptional program of induced stem cell-derived cardiomyocytes according to our discovered network, and they showed adult cardiomyocyte-like electrophysiological expression. Our work provides a comprehensive regulatory resource of cardiomyocytes perinatal reprogramming, and aids the gap-filling of cardiac translational research.

Genetic susceptibility to diabetic kidney disease is linked to promoter variants of XOR.

The lifetime risk of kidney disease in people with diabetes is 10-30%, implicating genetic predisposition in the cause of diabetic kidney disease (DKD). Here we identify an expression quantitative trait loci (QTLs) in the cis-acting regulatory region of the xanthine dehydrogenase, or xanthine oxidoreductase (Xor), a binding site for C/EBPß, to be associated with diabetes-induced podocyte loss in DKD in male mice. We examine mouse inbred strains that are susceptible (DBA/2J) and resistant (C57BL/6J) to DKD, as well as a panel of recombinant inbred BXD mice, to map QTLs. We also uncover promoter XOR orthologue variants in humans associated with high risk of DKD. We introduced the risk variant into the 5'-regulatory region of XOR in DKD-resistant mice, which resulted in increased Xor activity associated with podocyte depletion, albuminuria, oxidative stress and damage restricted to the glomerular endothelium, which increase further with type 1 diabetes, high-fat diet and ageing. Therefore, differential regulation of Xor contributes to phenotypic consequences with diabetes and ageing.

A Single-Cell RNA-Seq-Based Approach for Genome-Wide Identification of Cell Essential Genes.

Identification of genes essential for structure, function, and survival of a cell type is critical for understanding of the underlying mechanisms. Unfortunately, there is no efficient way to identify such genes. Studies by single-cell RNA sequencing have shown that gene expressions of single cells of the same type are highly heterogeneous. We therefore speculate that the genes expressed in all individual cells of the same type are essential for the cell type, including the housekeeping genes and cell type-specific essential genes. Based on this rationale, we design a high-throughput approach to identify podocyte essential genes. In this approach, mouse podocytes are subjected to ultra-deep single-cell RNA-seq, and the genes expressed in all single podocytes are sorted out and considered as the candidates of podocyte essential genes. The essentiality of these genes for podocytes is assessed by bioinformatics, cross-species conserved expression, association with injury/disease, inclusion of known essential genes, and experimental validation. By comparison with the essential genes of other cell types, podocyte-specific essential genes can be distinguished. This approach applies to any cell types. In this chapter, we describe the approach and detailed methods.

Mitochondria bridge HIF signaling and ferroptosis blockage in acute kidney injury.

Ferroptosis, a form of regulated cell death, plays an important role in acute kidney injury (AKI). Previous studies have shown that prolyl hydroxylase domain protein (PHD) inhibitors that activate HIF signaling provide strong protection against AKI, which is characterized by marked cell death. However, the relationship between PHD inhibition/HIF signaling and ferroptosis in AKI has not been elucidated. Here, we review recent studies to explore the issue. First, we will review the literature concerning the functions of HIF in promoting mitophagy, suppressing mitochondrial respiration and modulating redox homeostasis. Second, we will describe the current understanding of ferroptosis and its role in AKI, particularly from the perspective of mitochondrial dysfunction. Finally, we will discuss the possibility that mitochondria link PHD inhibition/HIF signaling and ferroptosis in AKI. In conclusion, we propose that HIF may protect renal cells against ferroptosis in AKI by reducing mitochondrial oxidative stress and damage.

Fe2O3 supported Pt single atom catalysts for the selective hydrogenation of cinnamaldehyde.

Atomically dispersed Pt species supported on Fe2O3 (Pt1/Fe2O3) are successfully constructed by a simple ball milling process. In the selective hydrogenation of cinnamaldehyde (CAL), Pt1/Fe2O3 achieves an excellent cinnamyl alcohol (COL) selectivity of 81.7% at a CAL conversion of 91.2% in pure water medium due to the superior dissociation ability of H2 and preferential adsorption of CAL via CO.

Highly Efficient Fabrication of Kilogram-Scale Palladium Single-Atom Catalysts for the Suzuki-Miyaura Cross-Coupling Reaction.

Palladium single-atom catalysts (SACs) have caught great attention owing to their maximal atom utilization and outstanding activity for the Suzuki-Miyaura cross-coupling reaction. However, a facile manufacturing method for kilogram-scale synthesis of noble metal SACs with high productivity is still in demand. This study reports on the synthesis of SACs by direct ball milling of commercial metal oxides and nitrate precursors with a productivity of ∼100%. The as-prepared Pd1/FeOx SACs show high catalytic performance (the TOFs are 7844 h-1), high stability, and general applicability for the Suzuki-Miyaura cross-coupling reaction under mild conditions. More encouragingly, kilogram-scale Pd1/FeOx SACs can be synthesized in one batch by this approach, endowing great potential for industrial applications. Furthermore, the preparation of Pt, Ru, and Rh SACs is also successfully carried out via the ball milling method, demonstrating favorable applicability. Our findings illustrate exciting chances presented by the highly efficient synthesis of SACs for the formation of C-C bonds.

Glucocorticoids Inhibit EGFR Signaling Activation in Podocytes in Anti-GBM Crescentic Glomerulonephritis.

Glucocorticoids are commonly used to treat anti-GBM crescentic glomerulonephritis, however, the mechanism underlying its therapeutic effectiveness is not completely understood. Since podocyte EGFR/STAT3 signaling is known to mediate the development of anti-GBM glomerulonephritis, we investigated the effect of glucocorticoids on EGFR/STAT3 signaling in podocytes. We found that the levels of phosphorylated (activated) EGFR and STAT3 in podocytes were markedly elevated in anti-GBM patients without glucocorticoids treatment, but were normalized in patients with glucocorticoids treatment. In a rat model of anti-GBM glomerulonephritis, glucocorticoids treatment significantly attenuated the proteinuria, crescent formation, parietal epithelial cell (PEC) activation and proliferation, accompanied by elimination of podocyte EGFR/STAT3 signaling activation. In cultured podocytes, glucocorticoids were found to inhibit HB-EGF-induced EGFR and STAT3 activation. The conditioned medium from podocytes treated with HB-EGF in the absence but not presence of glucocorticoids was capable of activating Notch signaling (which is known to be involved in PEC proliferation and crescent formation) and enhancing proliferative activity in primary PECs, suggesting that glucocorticoids prevent podocytes from producing secreted factors that cause PEC proliferation and crescent formation. Furthermore, we found that glucocorticoids can downregulate the expression of EGFR ligands, EGF and HB-EGF, while upregulate the expression of EGFR inhibitor, Gene 33, explaining how glucocorticoids suppress EGFR signaling. Taken together, glucocorticoids exert therapeutic effect on anti-GBM crescentic glomerulonephritis through inhibiting podocyte EGFR/STAT3 signaling and the downstream pathway that leads to PEC proliferation and crescent formation.

Glomerular Exostosin as a Subtype and Activity Marker of Class 5 Lupus Nephritis.

BACKGROUND AND OBJECTIVES: There have been only several studies on the correlation between glomerular exostosin expression and membranous lupus nephritis. In this study, we validate the previous findings in Chinese patients with class 5 lupus nephritis. DESIGN, SETTING, PARTICIPANTS, & MEASURE: One hundred sixty-five patients with class 5 lupus nephritis and varying numbers of control patients were included. Exostosin1/exostosin2 staining was performed by immunohistochemistry, and the staining intensity was quantified using an imaging analysis system. Between-group comparisons were tested for statistical significance using the Pearson chi-squared test, the Fisher exact test, the unpaired t test, the Mann-Whitney U test, or one-way ANOVA. RESULTS: In total, 46% of patients with class 5 lupus nephritis, 9% of patients with class 5 + 3/4 lupus nephritis, and none of the other classes of lupus nephritis were exostosin positive. Only three patients were exostosin positive among the 61 patients with other secondary membranous nephropathy. The exostosin-positive rate in nephrotic patients was significantly higher than that in patients without nephrotic syndrome (P<0.001), and the exostosin staining intensities of the patients with exostosin-positive class 5 were positively correlated with proteinuria (r=0.53; P<0.001). Compared with the patients with exostosin-negative cases, the patients with exostosin-positive cases had higher proteinuria levels (3.9 [interquartile range, 2.0-6.3] g/d versus 2.3 [interquartile range, 1.0-3.6] g/d; P<0.001); lower scores of activity index (1 [interquartile range, 1-2] versus 2 [interquartile range, 1-3]; P=0.001), chronicity index (1 [interquartile range, 0-2] versus 2 [interquartile range, 1-2]; P=0.02), and tubular atrophy score (0 [interquartile range, 0-1] versus 1 [interquartile range, 0-1]; P=0.008); a higher proportion of extensive subepithelial deposition (62% versus 27%; P<0.001); a similar treatment response; and comparable time to kidney end point. Among the 47 patients with class 5 who underwent repeat biopsy, 97% of those with exostosin-negative cases remained negative, whereas 44% of those with exostosin-positive cases were still positive. The rate of histologic transition in the patients with exostosin-negative class 5 was significantly higher than that in the patients with exostosin-positive class 5 (59% versus 22%; P=0.03). CONCLUSIONS: Exostosin positivity occurred frequently in patients with class 5 lupus nephritis, and patients with exostosin-positive cases had more severe proteinuria and a lower rate of histologic transition than the exostosin-negative patients.

Slc35c2 promotes Notch1 fucosylation and is required for optimal Notch signaling in mammalian cells.

Mammalian Notch receptors require modification by fucose on epidermal growth factor-like (EGF) repeats of their extracellular domain to respond optimally to signal induction by canonical Notch ligands. Inactivation of the Golgi GDP-fucose transporter Slc35c1 in mouse or human does not cause marked defects in Notch signaling during development, and shows milder fucosylation defects than those observed in mice unable to synthesize GDP-fucose, indicating the existence of another mechanism for GDP-fucose transport into the secretory pathway. We show here that fibroblasts from mice or humans lacking Slc35c1 exhibit robust Notch signaling in co-culture signaling assays. A potential candidate for a second GDP-fucose transporter is the related gene Slc35c2. Overexpression of Slc35c2 reduces expression of the fucosylated epitopes Lewis X and sialylated Lewis X in CHO cells, indicating competition with Slc35c1. The fucosylation of a Notch1 EGF repeat fragment that occurs in the endoplasmic reticulum was increased in CHO transfectants overexpressing Slc35c2. In CHO cells with low levels of Slc35c2, both Delta1- and Jagged1-induced Notch signaling were reduced, and the fucosylation of a Notch1 fragment was also decreased. Immunofluorescence microscopy of rat intestinal epithelial cells and HeLa cells, and analysis of rat liver membrane fractions showed that Slc35c2 is primarily colocalized with markers of the cis-Golgi network and endoplasmic reticulum-Golgi intermediate compartment (ERGIC). The combined results suggest that Slc35c2 is either a GDP-fucose transporter that competes with Slc35c1 for GDP-fucose, or a factor that otherwise enhances the fucosylation of Notch and is required for optimal Notch signaling in mammalian cells.

Mpv17l protects against mitochondrial oxidative stress and apoptosis by activation of Omi/HtrA2 protease.

Cellular localization determines whether the serine protease HtrA2 exerts pro- or antiapoptotic functions. In contrast to the well-characterized proapoptotic function of cytosolic HtrA2, mechanisms underlying the mitochondrial protective role are poorly understood. Mpv17l is a transmembrane protein previously implicated in peroxisomal reactive oxygen species metabolism and a close homolog of the inner mitochondrial membrane protein Mpv17. Here we demonstrate a previously undescribed direct interaction between Mpv17l and HtrA2 in mitochondria. The interaction is mediated by a PDZ domain and induces protease activation of HtrA2. HtrA2 inhibits mitochondrial superoxide generation, stabilizes mitochondrial membrane potential, and prevents apoptosis at baseline and in response to extracellular inducers of mitochondrial stress. The physiological role of Mpv17l is underscored by the finding that oxidative stress-induced downregulation of Mpv17l is a consistent feature in renal injury models. Our findings identify Mpv17l as a unique interacting protein and regulator of HtrA2 protease mediating antioxidant and antiapoptotic function in mitochondria.