UCH-L1 expression of podocytes in diseased glomeruli and in vitro

Urinary biomarkers associated with podocyte injury in lupus nephritis

The most prevalent and devastating form of organ damage in systemic lupus erythematosus (SLE) is lupus nephritis (LN). LN is characterized by glomerular injury, inflammation, cell proliferation, and necrosis, leading to podocyte injury and tubular epithelial cell damage. Assays for urine biomarkers have demonstrated significant promise in the early detection of LN, evaluation of disease activity, and tracking of reaction to therapy. This is because they are non-invasive, allow for frequent monitoring and easy self-collection, transport and storage. Podocyte injury is believed to be a essential factor in LN. The extent and type of podocyte injury could be connected to the severity of proteinuria, making podocyte-derived cellular debris and injury-related urinary proteins potential markers for the diagnosis and monitoring of LN. This article focuses on studies examining urinary biomarkers associated with podocyte injury in LN, offering fresh perspectives on the application of biomarkers in the early detection and management of LN.

Preliminary study of anti-CD40 and ubiquitin proteasome antibodies in primary podocytopaties

Background

Minimal change disease and focal segmental glomerulosclerosis are primary podocytopathies that are clinically presented in adults presenting with severe nephrotic syndrome. The pathogenesis of these diseases is not clear and many questions remain to be answered. A new concept about the role of changes in the antigenic determinant of podocytes and the production of anti-podocyte antibodies that cause podocyte damage is being developed. The aim of the study is to evaluate the levels of anti-CD40 and anti-ubiquitin carboxyl-terminal hydrolase L1 (anti-UCH-L1) antibodies in patients with podocytopathies in comparison with other glomerulopathies.

Methods

One hundred and six patients with glomerulopathy and 11 healthy subjects took part in the study. A histological study revealed primary FSGS in 35 patients (genetic cases of FSGS and secondary FSGS in the absence of NS were excluded), 15 had MCD, 21 - MN, 13 - MPGN, 22 patients - IgA nephropathy. The effect of steroid therapy was evaluated in patients with podocytopathies (FSGS and MCD). The serum levels of anti-UCH-L1 and anti-CD40 antibodies were measured by ELISA before steroid treatment.

Results

The levels of anti-UCH-L1 antibodies were significantly higher in MCD patients and anti-CD40 antibodies were higher in MCD and FSGS than in the control group and other groups of glomerulopathies. In addition, the level of anti-UCH-L1 antibodies was higher in patients with steroid-sensitive FSGS and MCD, and anti-CD40 antibodies were lower than in patients with steroid-resistant FSGS. An increase in anti-UCH-L1 antibody levels above 6.44 ng/mL may be a prognostic factor of steroid-sensitivity. The ROC curve (AUC = 0.875 [95% CI 0.718-0.999]) for response to therapy showed a sensitivity of 75% and specificity of 87.5%.

Conclusion

An increase in the level of anti-UCH-L1 antibodies is specific for steroid-sensitive FSGS and MCD, while an increase in anti-CD40 antibodies - for steroid-resistant FSGS, compared with other glomerulopathies. It suggests that these antibodies could be a potential factor for differential diagnosis and treatment prognosis.

Non-functional ubiquitin C-terminal hydrolase L1 drives podocyte injury through impairing proteasomes in autoimmune glomerulonephritis

Little is known about the mechanistic significance of the ubiquitin proteasome system (UPS) in a kidney autoimmune environment. In membranous nephropathy (MN), autoantibodies target podocytes of the glomerular filter resulting in proteinuria. Converging biochemical, structural, mouse pathomechanistic, and clinical information we report that the deubiquitinase Ubiquitin C-terminal hydrolase L1 (UCH-L1) is induced by oxidative stress in podocytes and is directly involved in proteasome substrate accumulation. Mechanistically, this toxic gain-of-function is mediated by non-functional UCH-L1, which interacts with and thereby impairs proteasomes. In experimental MN, UCH-L1 becomes non-functional and MN patients with poor outcome exhibit autoantibodies with preferential reactivity to non-functional UCH-L1. Podocyte-specific deletion of UCH-L1 protects from experimental MN, whereas overexpression of non-functional UCH-L1 impairs podocyte proteostasis and drives injury in mice. In conclusion, the UPS is pathomechanistically linked to podocyte disease by aberrant proteasomal interactions of non-functional UCH-L1.

Podocyte-specific deletion of ubiquitin carboxyl-terminal hydrolase L1 causes podocyte injury by inducing endoplasmic reticulum stress

Ubiquitin carboxyl-terminal hydrolase L1 (UCHL1) is a unique component of the ubiquitin-proteasome system (UPS), which has multiple activities in maintaining intracellular ubiquitin levels. We previously reported the aberrant low expression of UCHL1 in podocytes of non-immune complex-mediated glomerulonephritis, and recent studies indicate that anti-UCHL1 antibody was responsible for the refractory minimal change disease (MCD), but the specific effect of UCHL1 to the podocytopathy has not been determined. Therefore, we generated podocyte-specific UCHL1 gene knockout (UCHL1cre/cre) rats model. Podocyte-specific UCHL1 knockout rats exhibited severe kidney damage, including segmental/global glomerulosclerosis, kidney function damage and severe proteinuria, compared with littermate control. Subsequently, by carrying out mass spectrometry analysis of isolated glomeruli of rats, abnormal protein accumulation of ECM-receptor Interaction was found in UCHL1cre/cre rats. Mechanistic studies in vivo and in vitro revealed that aberrant protein accumulation after UCHL1 deficiency induced endoplasmic reticulum (ER) stress, unfolded protein reaction (UPR) to reduce the protein level of podocyte skeleton proteins, and CHOP mediated apoptosis as well, which related to the dysfunction of the ubiquitin-proteasome system with decreased free monomeric ubiquitin level, thereby affecting protein ubiquitination and degradation. In addition, inhibition of ER stress by 4-PBA could attenuate the degree of ER stress and podocyte dysfunction. Our study indicates that UCHL1 is a potential target for preventing podocytes injury in some non-immune complex-mediated glomerulopathy.

Ubiquitin C‑terminal hydrolase‑L1: A new cancer marker and therapeutic target with dual effects (Review)

Ubiquitin C-terminal hydrolase-L1 (UCH-L1), a member of the lesser-known deubiquitinating enzyme family, has deubiquitinase and ubiquitin (Ub) ligase activity and the role of stabilizing Ub. UCH-L1 was first discovered in the brain and is associated with regulating cell differentiation, proliferation, transcriptional regulation and numerous other biological processes. UCH-L1 is predominantly expressed in the brain and serves a role in tumor promotion or inhibition. There is still controversy about the effect of UCH-L1 dysregulation in cancer and its mechanisms are unknown. Extensive research to investigate the mechanism of UCH-L1 in different types of cancer is key for the future treatment of UCH-L1-associated cancer. The present review details the molecular structure and function of UCH-L1. The role of UCH-L1 in different types of cancer is also summarized and how novel treatment targets provide a theoretical foundation in cancer research is discussed.

Bortezomib: a proteasome inhibitor for the treatment of autoimmune diseases

Autoimmune diseases (ADs) are conditions in which the immune system cannot distinguish self from non-self and, as a result, tissue injury occurs primarily due to the action of various inflammatory mediators. Different immunosuppressive agents are used for the treatment of patients with ADs, but some clinical cases develop resistance to currently available therapies. The proteasome inhibitor bortezomib (BTZ) is an approved agent for first-line therapy of people with multiple myeloma. BTZ has been shown to improve the symptoms of different ADs in animal models and ameliorated symptoms in patients with systemic lupus erythematous, rheumatoid arthritis, myasthenia gravis, neuromyelitis optica spectrum disorder, Chronic inflammatory demyelinating polyneuropathy, and autoimmune hematologic diseases that were nonresponsive to conventional therapies. Proteasome inhibition provides a potent strategy for treating ADs. BTZ represents a proteasome inhibitor that can potentially be used to treat AD patients resistant to conventional therapies.

UCHL1 regulates inflammation via MAPK and NF-κB pathways in LPS-activated macrophages

Inflammation is a common pathophysiological process as well as a clinical threat that occurs in various diseases worldwide. It is well-documented that nuclear factor-κB (NF-κB) and mitogen-activated protein kinase pathways are involved in inflammatory reactions to microbial infections in lipopolysaccharide (LPS)-activated macrophages. The deubiquitinase ubiquitin carboxyl-terminal hydrolase-L1 (UCHL1) has been reported as an oncoprotein to promote the growth and progression of cancer cells. However, the regulatory mechanism of UCHL1 in inflammation is currently unclear. Here, we aimed to assess the effects of UCHL1 on LPS-associated inflammatory response in vitro and in vivo by enzyme-linked immunosorbent assay, quantitative reverse-transcription polymerase chain reaction, and western blot analysis. This study identified that inhibition or knockdown of UCHL1 decreased the amounts of the key pro-inflammatory cytokines, including interleukin-6 and tumor necrosis factor-α in macrophages. Additionally, inhibition of UCHL1 suppressed LPS-induced extracellular signal-regulated protein kinase 1/2 phosphorylation and NF-κB translocation by regulating the inhibitor of NF-κB. Mechanically, UCHL1 interacts with IκBα protein in THP-1. Meanwhile, inhibition of UCHL1 blocked the LPS-induced degradation of IκBα through the ubiquitin-proteasome system. Moreover, in vivo assay showed that suppression of UCHL1 notably reduced the LPS-induced animal death and release of pro-inflammatory cytokines. Overall, the current findings uncover that UCHL1 functions as a crucial regulator for inflammatory response via reversing the degradation of IκBα, representing a potential target for the treatment of inflammatory diseases.

Ubiquitin C-terminal hydrolase L1 (UCHL1) regulates post-myocardial infarction cardiac fibrosis through glucose-regulated protein of 78 kDa (GRP78)

Abnormal cardiac fibrosis indicates cardiac dysfunction and poor prognosis in myocardial infarction (MI) patients. Many studies have demonstrated that the ubiquitin proteasome system (UPS) plays a significant role in the pathogenesis of fibrosis. Ubiquitin C-terminal hydrolase L1 (UCHL1), a member of the UPS, is related to fibrosis in several heart diseases. However, whether UCHL1 regulates cardiac fibrosis following MI has yet to be determined. In the present study, we found that UCHL1 was dramatically increased in infarct hearts and TGF-β1-stimulated cardiac fibroblasts (CFs). Inhibition of UCHL1 with LDN57444 (LDN) reversed the myocardial fibrosis in post-MI heart and improved cardiac function. Treatment of LDN or UCHL1 siRNA abolished the TGF-β1-induced fibrotic response of CFs. We further identified GRP78 as an interactor of UCHL1 through screening using immunoprecipitation-mass spectrometer. We determined that UCHL1 interacted with glucose-regulated protein of 78 kDa (GRP78) and prompted GRP78 degradation via ubiquitination. Furthermore, we found that GRP78 was upregulated after UCHL1 knockdown and that the GRP78 inhibitor HA15 diminished the antifibrotic function exerted by UCHL1 knockdown in CFs stimulated with TGF-β1. This suggests that UCHL1 regulates cardiac fibrosis post MI through interactions with GRP78. This work identifies that the UCHL1-GRP78 axis is involved in cardiac fibrosis after MI.

Plakoglobin is involved in cytoskeletal rearrangement of podocytes under the regulation of UCH-L1

UCH-L1 is a de-ubiquitination enzyme comprehensively distributed in neural cells and podocytes, which is involved in several kinds of nervous system and kidney related diseases. Our previous studies have demonstrated the aberrant up-regulation of UCH-L1 in podocytes of renal diseases, but how dose podocytes are injured by up-regulated UCH-L1 is waiting to be elucidated. Here, we observed the cytoskeleton rearrangement in podocytes with over-expression of UCH-L1, accompanied with a down-regulation of synaptopodin and RhoA, which are closely related to cytoskeletal stabilization. However, we did not see any alteration of RhoA ubiquitination level under the stimulation of UCH-L1 in podocytes. Subsequently, mass spectrum was applied in UCH-L1-flag immunoprecipitation and plakoglobin was screened out, which was among the UCH-L1-combined proteins and most likely related to cytoskeleton rearrangement. Our experiment demonstrates UCH-L1 may not injure podocytes cytoskeleton through a direct regulation on RhoA/Synaptopodin, but through the regulation of plakoglobin, which could be a promising target for treatment of renal disease in the future.

Ubiquitin carboxy-terminal hydrolase L1 - physiology and pathology

Ubiquitin C-terminal hydrolase 1 (UCHL1) is an enzyme unique for its multiple activity - both ligase and hydrolase. UCHL1 was first identified as an abundant protein found in the brain and testes, however its expression is not limited to the neuronal compartment. UCHL1 is also highly expressed in carcinomas of various tissue origins, including those from brain, lung, breast, kidney, colon, prostate, pancreas and mesenchymal tissues. Loss-of-function studies and an inhibitor for UCHL1 confirmed the importance of UCHL1 for cancer therapy. So far biological significance of UCHL1 was described in the following processes: spermatogenesis, oncogenesis, angiogenesis, cell proliferation and differentiation in skeletal muscle, inflammation, tissue injury, neuronal injury and neurodegeneration.

Role of A20/TNFAIP3 deficiency in lupus nephritis in MRL/lpr mice

BACKGROUND

The activation of the nuclear factor-κB (NF-κB) signaling pathway gives rise to inflammation in the pathogenesis of lupus nephritis (LN), with A20 serving as a negative feedback regulator and ubiquitin C‑terminal hydrolase L1 (UCH-L1) acting as a downstream target protein. However, their roles in the mechanism of LN remain undetermined.

METHODS

In the present study, the expression of A20 and UCH-L1, the activity of NF-κB and ubiquitin-proteasome system (UPS) were measured in MRL/lpr mice and A20 gene silenced podocytes. The severity of podocyte injury and immune complex deposits were detected by transmission electron microscopy.

RESULTS

The in vivo experiments revealed that A20 failed to terminate the activation of NF-κB, which was accompanied by UCH-L1 overexpression, ubiquitin accumulation, and glomerular injury in LN mice. Immunosuppression therapy did improve LN progression by attenuating A20 deficiency. In vitro experiments confirmed that tumor necrosis factor-α induced NF-κB activation, which led to UCH-L1 overexpression, UPS impairment, the upregulation of desmin and the downregulation of synaptopodin in A20 gene silenced podocytes.

CONCLUSION

Thus, the results of the present study suggest that A20 regulates UCH-L1 expression via the NF-κB signaling pathway and A20 deficiency might play an important role in LN pathogenesis. Therefore, the A20 protein may serve as a promising therapeutic target for LN.

A20 overexpression exerts protective effects on podocyte injury in lupus nephritis by downregulating UCH-L1

Lupus nephritis (LN), an autoimmune kidney disease caused by systemic lupus erythematosus (SLE), is the inflammation of the kidney. Although the treatment of LN is still a therapeutic challenge for many practitioners, the present study aims to provide a new insight for the treatment and management. The study aims to explore the effect of A20 on LN in relation to the nuclear factor-kappa B (NF-κB) signaling pathway. MRL/lpr mice were used as the LN mouse model. Next, A20, UCH-L1, and NF-κB expression in LN patients and MRL/lpr mice was determined. A20 was upregulated in podocytes to assess biological functions of A20 in LN. Furthermore, to further investigate the pivotal role of the NF-κB pathway in LN, the NF-κB pathway was blocked in podocytes. Next, UCH-L1 was downregulated in MRL/lpr mice to assess biological functions of UCH-L1 in LN. A20 was downregulated, whereas UCH-L1 was upregulated in LN. Overexpressed A20 declined NF-κB, UCH-L1 expression, and the extent of p65 phosphorylation. A20 overexpression or UCH-L1 inhibition increased expression of synaptoporin and nephrin but decreased desmin expression and ubiquitin accumulation level in podocytes. Moreover, A20 overexpression or UCH-L1 inhibition increased the podocyte number but decreased protein level of cleaved caspase-3, podocyte lesion improvement, decreased foot process width, glomerulus basement membrane, and foot process fusion rate. In addition, urine protein, blood urea nitrogen, serum creatinine, and ds-DNA antibody levels decreased with elevated A20 or depleted UCH-L1. Collectively, it could be concluded that A20 protects against podocyte injury in LN via UCH-L1 by inactivating the NF-κB signaling pathway.

Podocyte Injury in Lupus Nephritis

Systemic lupus erythematosus (SLE) is characterized by a broad spectrum of renal lesions. In lupus glomerulonephritis, histological classifications are based on immune-complex (IC) deposits and hypercellularity lesions (mesangial and/or endocapillary) in the glomeruli. However, there is compelling evidence to suggest that glomerular epithelial cells, and podocytes in particular, are also involved in glomerular injury in patients with SLE. Podocytes now appear to be not only subject to collateral damage due to glomerular capillary lesions secondary to IC and inflammatory processes, but they are also a potential direct target in lupus nephritis. Improvements in our understanding of podocyte injury could improve the classification of lupus glomerulonephritis. Indeed, podocyte injury may be prominent in two major presentations: lupus podocytopathy and glomerular crescent formation, in which glomerular parietal epithelial cells play also a key role. We review here the contribution of podocyte impairment to different presentations of lupus nephritis, focusing on the podocyte signaling pathways involved in these lesions.

High glucose-induced apoptosis and necroptosis in podocytes is regulated by UCHL1 via RIPK1/RIPK3 pathway

Diabetic nephrology (DN) is attributed largely to the depletion of podocytes, which is closely associated to apoptosis. However, the complex mechanism of podocyte loss in DN pathogenesis remains unclear. Recently, necroptosis has emerged as an important cell death model in many pathological conditions, which is regulated through RIPK1/RIPK3 pathway. In addition, necroptosis was found to share several upstream signaling pathways with apoptosis. Therefore, it was speculated that both apoptosis and necroptosis may occur in podocytes during the process of podocyte injury in DN. Herein, necroptosis and apoptosis were shown to be involved in podocyte injury induced by high glucose (HG), both in vitro and in vivo, with a high level of positive signaling markers RIPK1 (298.4 ± 17.35), cleaved caspase 3 (497.1 ± 23.09), RIPK3 (108.4 ± 14.92), and MLKL (470.4 ± 15.73) than the control groups. Scaning electron microscopy examination revealed the morphological characteristics of necroptotic and apoptotic cells, which differed remarkably. z-VAD-fmk, a pan-inhibitor of apoptosis, could block apoptosis and enhance necroptosis. Furthermore, UCHL1 was found to play a major role in promoting podocyte necroptosis by regulating the ubiquitination state of the RIPK1/RIPK3 pathway. The half-life of RIPK1 and RIPK3 proteins reduced and the expression of RIPK1, RIPK3, and MLKL decreased significantly after the knockdown of UCHL1. It was shown that UCHL1 exerted a more regulatory response to necroptosis. These data suggested that necroptosis may have more effect on the loss of podocytes than apoptosis in DN with the regulation of UCHL1. Thus, inhibiting UCHL1 to downregulate the RIPK1/RIPK3 pathway may be a novel strategy to protect the podocytes in DN patients.

Autoantibodies against podocytic UCHL1 are associated with idiopathic nephrotic syndrome relapses and induce proteinuria in mice

Idiopathic steroid sensitive nephrotic syndrome (INS), the most frequent childhood nephropathy, is thought to be mediated by a circulating soluble factor that reversibly affects the renal protein sieving. The efficiency of rituximab therapy recently highlighted the involvement of B cells. Here we studied the involvement of a specific immunoglobulin G (IgG) in the disease. After plasma fractionation by size exclusion chromatography, a detachment of cultured podocyte was observed with one IgG-containing fraction from 47% patients in relapse, 9% of patients in remission and 0% of controls. Podocyte protein lysates were immunoprecipitated by IgG from those plasma fractions identifying a list of 41 podocyte proteins after proteomic analysis. Five podocyte targets were selected on statistical and biological criteria. Specific antibodies were tested and only anti-Ubiquitin Carboxyl-Terminal Hydrolase L1 (UCHL1) IgG led to podocyte detachment. UCHL1 was mainly found inside the podocyte but also weakly expressed on podocyte cell surface. Incubation of either anti-UCHL1 IgG or plasma fractions with recombinant UCHL1 prevented podocyte detachment. Plasma levels of anti-UCHL1 IgG were significantly increased in relapsing INS patients compared to patients in remission and controls. Proteinuria correlated with anti-UCHL1 IgG level at various stages of the disease. Purified patient anti-UCHL1 antibodies induced proteinuria and podocyte foot effacement in mice. Altogether, these results identified UCHL1 as a target podocyte protein of autoantibodies in a set of relapsing patients and support a causative role of anti-UCHL1 autoantibodies in the development of INS.

IgLON5 antibody: Neurological accompaniments and outcomes in 20 patients

OBJECTIVE

To describe the phenotypes, treatment response, and outcome of IgLON5 autoimmunity.

METHODS

Archived serum and CSF specimens from 367 patients known to harbor unclassified antibodies which stained neural synapses diffusely (mimicking amphiphysin-IgG) were reevaluated by indirect immunofluorescence assay (IFA) using a composite of mouse tissues and recombinant IgLON5-transfected cell-based assay (CBA, Euroimmun).

RESULTS

Available specimens (serum, 25; CSF, 9) from 26/367 patients (7%) had identical IFA appearance and robust IgLON5 CBA positivity. Clinical information was available for 20/26 patients; 13 were women. Median disease-onset age was 62 years (range, 46-75 years). Most patients had insidious onset and progression of neurological symptoms affecting movement and sleep predominantly. Sleep disorders were sleep-disordered breathing (11) and parasomnias (3). Brainstem disorders were gait instability (14), dysphagia (10), abnormal eye movements (7), respiratory dysfunction (6), ataxia (5), craniocervical dystonia (3), and dysarthria (3). Findings compatible with hyperexcitability included myoclonus (3), cramps (3), fasciculations (2), and exaggerated startle (2). Neuropsychiatric disorders included cognitive dysfunction (6), psychiatric symptoms (5), and seizures (1). Dysautonomia, in 9, affected bladder function (7), gastrointestinal motility (3), thermoregulation (3), and orthostatic tolerance (1). Just 2 patients had coexisting autoimmune disease. Brain MRI findings were nonspecific and CSF was noninflammatory in all tested. Seven of 9 immunotherapy-treated patients improved: 6 of those 7 were stable at last follow-up. Three untreated patients died. Each IgLON5-IgG subclass (1-4) was readily detectable in ≥80% of specimens using CBA.

CONCLUSIONS

IgLON5-IgG is diagnostic of a potentially treatable neurological disorder, where autoimmune clues are otherwise lacking.

USP40 gene knockdown disrupts glomerular permeability in zebrafish

Unbiased transcriptome profiling and functional genomics approaches have identified ubiquitin-specific protease 40 (USP40) as a highly specific glomerular transcript. This gene product remains uncharacterized, and its biological function is completely unknown. Here, we showed that mouse and rat glomeruli exhibit specific expression of the USP40 protein, which migrated at 150 kDa and was exclusively localized in the podocyte cytoplasm of the adult kidney. Double-labeling immunofluorescence staining and confocal microscopy analysis of fetal and neonate kidney samples revealed that USP40 was also expressed in the vasculature, including in glomerular endothelial cells at the premature stage. USP40 in cultured glomerular endothelial cells and podocytes was specifically localized to the intermediate filament protein nestin. In glomerular endothelial cells, immunoprecipitation confirmed actual protein-protein binding of USP40 with nestin, and USP40-small-interfering RNA transfection revealed significant reduction of nestin. In a rat model of minimal-change nephrotic syndrome, USP40 expression was apparently reduced, which was also associated with the reduction of nestin. Zebrafish morphants lacking Usp40 exhibited disorganized glomeruli with the reduction of the cell junction in the endothelium and foot process effacement in the podocytes. Permeability studies in these zebrafish morphants demonstrated a disruption of the selective glomerular permeability filter. These data indicate that USP40/Usp40 is a novel protein that might play a crucial role in glomerulogenesis and the glomerular integrity after birth through the modulation of intermediate filament protein homeostasis.

Hidden targets of ubiquitin proteasome system: To prevent diabetic nephropathy

Diabetic nephropathy (DN) is the major cause of end stage renal failure. Although, several therapeutic targets have emerged to prevent the progression of DN, the number of people with DN still continues to rise worldwide, suggesting an urgent need of novel targets to prevent DN completely. Currently, the role of ubiquitin proteasome system (UPS) has been highlighted in the pathogenesis and progression of various diseases like obesity, insulin resistance, atherosclerosis, cancers, neurodegerative disorders and including secondary complications of diabetes. UPS mainly involves in protein homeostatis through ubiquitination (post translational modification) and proteasomal degradation of various proteins. Ubiquitination, not only involves in proteasomal degradation, but also directs the substrate proteins to participate in multitude of cell signalling pathways. However, very little is known about ubiquitination and UPS in the progression of DN. This review mainly focuses on UPS and its components including E2 conjugating enzymes, E3 ligases and deubiquitinases (DUBs) in the development of DN and thus may help us to find novel therapeutic targets with in UPS to prevent DN completely in future.

Wnt/β-Catenin Signaling Mediated-UCH-L1 Expression in Podocytes of Diabetic Nephropathy

Increasing studies identified podocyte injury as a key early risk factor resulting in diabetic nephropathy (DN). The ubiquitin carboxy-terminal hydrolase 1 (UCH-L1) participates in podocyte differentiation and injury, which is elevated in the podocytes of a variety of nephritis. Whether UCH-L1 expression is positively related to podocyte injury of DN remains unclear. In this study, elevated expression of UCH-L1 and its intrinsic mechanism in high glucose (HG)-stimulated murine podocytes were investigated using western blot and real-time quantitative PCR. Kidney biopsies of DN patients and health individuals were stained by immunofluorescence (IF) method. The morphological and functional changes of podocytes were tested by F-actin staining and cell migration assay. Results demonstrated that HG induced upregulation of UCH-L1 and activation of the Wnt/β-catenin signaling pathway in podocytes. However, blocking of the Wnt pathway by dickkopf related protein 1 (DKK1) eliminated the above changes. Furthermore, IF staining confirmed that, compared with healthy individuals, the expression of UCH-L1 and β-catenin were obviously increased in kidney biopsy of DN patients. Overexpression of UCH-L1 remodeled its actin cytoskeleton, increased its cell migration and impacted its important proteins. All the findings manifested that Wnt/β-catenin/UCH-L1 may be a new potential therapy method in the treatment of DN in future.

Cell cycle re-entry sensitizes podocytes to injury induced death

Podocytes are terminally differentiated renal cells, lacking the ability to regenerate by proliferation. However, during renal injury, podocytes re-enter into the cell cycle but fail to divide. Earlier studies suggested that re-entry into cell cycle results in loss of podocytes, but a direct evidence for this is lacking. Therefore, we established an in vitro model to test the consequences of re-entry into the cell cycle on podocyte survival. A mouse immortalized podocyte cell line was differentiated to non-permissive podocytes and stimulated with e.g. growth factors. Stimulated cells were analyzed for mRNA-expression or stained for cell cycle analysis using flow cytometry and immunocytofluorescence microscopy. After stimulation to re-entry into cell cycle, podocytes were stressed with puromycin aminonucleoside (PAN) and analyzed for survival. During permissive stage more than 40% of immortalized podocytes were in the S-phase. In contrast, S-phase in non-permissive differentiated podocytes was reduced to 5%. Treatment with b-FGF dose dependently induced re-entry into cell cycle increasing the number of podocytes in the S-phase to 10.7% at an optimal bFGF dosage of 10 ng/ml. Forty eight hours after stimulation with bFGF the number of bi-nucleated podocytes significantly increased. A secondary injury stimulus significantly reduced podocyte survival preferentially in bi-nucleated podocytes In conclusion, stimulation of podocytes using bFGF was able to induce re-entry of podocytes into the cell cycle and to sensitize the cells for cell death by secondary injuries. Therefore, this model is appropriate for testing new podocyte protective substances that can be used for therapy.

DC-SIGN expression on podocytes and its role in inflammatory immune response of lupus nephritis

Podocytes, the main target of immune complex, participate actively in the development of glomerular injury as immune cells. Dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) is an innate immune molecular that has an immune recognition function, and is involved in mediation of cell adhesion and immunoregulation. Here we explored the expression of DC-SIGN on podocytes and its role in immune and inflammatory responses in lupus nephritis (LN). Expression of DC-SIGN and immunoglobulin (Ig)G1 was observed in glomeruli of LN patients. DC-SIGN was co-expressed with nephrin on podocytes. Accompanied by increased proteinuria of LN mice, DC-SIGN and IgG1 expressions were observed in the glomeruli from 20 weeks, and the renal function deteriorated up to 24 weeks. Mice with anti-DC-SIGN antibody showed reduced proteinuria and remission of renal function. After the podocytes were stimulated by serum of LN mice in vitro, the expression of DC-SIGN, major histocompatibility complex (MHC) class II and CD80 was up-regulated, stimulation of T cell proliferation was enhanced and the interferon (IFN)-γ/interleukin (IL)-4 ratio increased. However, anti-DC-SIGN antibody treatment reversed these events. These results suggested that podocytes in LN can exert DC-like function through their expression of DC-SIGN, which may be involved in immune and inflammatory responses of renal tissues. However, blockage of DC-SIGN can inhibit immune functions of podocytes, which may have preventive and therapeutic effects.

Alterations in the ubiquitin proteasome system in persistent but not reversible proteinuric diseases

Podocytes are the key cells affected in nephrotic glomerular kidney diseases, and they respond uniformly to injury with cytoskeletal rearrangement. In nephrotic diseases, such as membranous nephropathy and FSGS, persistent injury often leads to irreversible structural damage, whereas in minimal change disease, structural alterations are mostly transient. The factors leading to persistent podocyte injury are currently unknown. Proteolysis is an irreversible process and could trigger persistent podocyte injury through degradation of podocyte-specific proteins. We, therefore, analyzed the expression and functional consequence of the two most prominent proteolytic systems, the ubiquitin proteasome system (UPS) and the autophagosomal/lysosomal system, in persistent and transient podocyte injuries. We show that differential upregulation of both proteolytic systems occurs in persistent human and rodent podocyte injury. The expression of specific UPS proteins in podocytes differentiated children with minimal change disease from children with FSGS and correlated with poor clinical outcome. Degradation of the podocyte-specific protein α-actinin-4 by the UPS depended on oxidative modification in membranous nephropathy. Notably, the UPS was overwhelmed in podocytes during experimental glomerular disease, resulting in abnormal protein accumulation and compensatory upregulation of the autophagosomal/lysosomal system. Accordingly, inhibition of both proteolytic systems enhanced proteinuria in persistent nephrotic disease. This study identifies altered proteolysis as a feature of persistent podocyte injury. In the future, specific UPS proteins may serve as new biomarkers or therapeutic targets in persistent nephrotic syndrome.

The expression and significance of neuronal iconic proteins in podocytes

Growing evidence suggests that there are many common cell biological features shared by neurons and podocytes; however, the mechanism of podocyte foot process formation remains unclear. Comparing the mechanisms of process formation between two cell types should provide useful guidance from the progress of neuron research. Studies have shown that some mature proteins of podocytes, such as podocin, nephrin, and synaptopodin, were also expressed in neurons. In this study, using cell biological experiments and immunohistochemical techniques, we showed that some neuronal iconic molecules, such as Neuron-specific enolase, nestin and Neuron-specific nuclear protein, were also expressed in podocytes. We further inhibited the expression of Neuron-specific enolase, nestin, synaptopodin and Ubiquitin carboxy terminal hydrolase-1 by Small interfering RNA in cultured mouse podocytes and observed the significant morphological changes in treated podocytes. When podocytes were treated with Adriamycin, the protein expression of Neuron-specific enolase, nestin, synaptopodin and Ubiquitin carboxy terminal hydrolase-1 decreased over time. Meanwhile, the morphological changes in the podocytes were consistent with results of the Small interfering RNA treatment of these proteins. The data demonstrated that neuronal iconic proteins play important roles in maintaining and regulating the formation and function of podocyte processes.

Ubiquitin C-terminal hydrolase L1 deletion ameliorates glomerular injury in mice with ACTN4-associated focal segmental glomerulosclerosis

Renal ubiquitin C-terminal hydrolase L1 (UCHL1) is upregulated in a subset of human glomerulopathies, including focal segmental glomerulosclerosis (FSGS), where it may serve to promote ubiquitin pools for degradation of cytotoxic proteins. In the present study, we tested whether UCHL1 is expressed in podocytes of a mouse model of ACTN4-associated FSGS. Podocyte UCHL1 protein was detected in glomeruli of K256E-ACTN4(pod+)/UCHL1+/+ mice. UCHL1+/- mice were intercrossed with K256E-ACTN4(pod+) mice and monitored for features of glomerular disease. 10-week-old K256E-ACTN4(pod+)/UCHL1-/- mice exhibited significantly ameliorated albuminuria, glomerulosclerosis, tubular pathology and blood pressure. Interestingly, while UCHL1 deletion diminished both tubular and glomerular apoptosis, WT1-positive nuclei were unchanged. Finally, UCHL1 levels correlated positively with poly-ubiquitinated proteins but negatively with K256E-α-actinin-4 levels, implying reduced K256E-α-actinin-4 proteolysis in the absence of UCHL1. Our data suggest that UCHL1 upregulation in ACTN4-associated FSGS fuels the proteasome and that UCHL1 deletion may impair proteolysis and thereby preserve K256E/wt-α-actinin-4 heterodimers, maintaining podocyte cytoskeletal integrity and protecting the glomerular filtration barrier.

A Uchl1-Histone2BmCherry:GFP-gpi BAC transgene for imaging neuronal progenitors

Uchl1 encodes the protein gene product 9.5 antigen (PGP9.5) that is a widely used to identify migrating neural progenitors in the PNS, mature neurons of the central and peripheral nervous systems, as well as neuroendocrine cells. To facilitate analysis of developing peripheral neurons, we linked regulatory regions of Uchl1 carried within a 160kb bacterial artificial chromosome (BAC) to the dual fluorescent reporter H2BmCherry:GFP-gpi. The Uchl1-H2BmCherry:GFP-gpi transgene exhibits robust expression and allows clear discrimination of individual cells and cellular processes in cranial ganglia, sympathetic chain, the enteric nervous system (ENS), and autonomic ganglia of the urogenital system. The transgene also labels subsets of cells in endocrine tissues where earlier in situ hybridization (ISH) studies have previously identified expression of this deubiquinating enzyme. The Uchl1-H2BmCherry:GFP-gpi transgene will be a powerful tool for static and live imaging, as well as isolation of viable neural progenitors to investigate processes of autonomic neurogenesis.

The regulation of the UCH-L1 gene by transcription factor NF-κB in podocytes

In kidney, the ubiquitin carboxy-terminal hydrolase 1 (UCH-L1) is involved in podocyte injury and proteinuria but details of the mechanism underlying its regulation are not known. Activation of NF-κB is thought to be the predominant risk factor for kidney disease; therefore, it is postulated that UCH-L1 may be one of the NF-κB target genes. In this study, we investigated the involvement of NF-κB activation in the regulation of UCH-L1 expression and the function of murine podocytes. Stimulation of podocytes with the cytokines TNF-α and IL-1β up-regulated UCH-L1 expression rapidly at the mRNA and protein levels and the NF-κB-specific inhibitor pyrrolidine dithiocarbamate resulted in down-regulation. NF-κB up-regulates UCH-L1 via binding the --300 bp and --109 bp sites of its promoter, which was confirmed by the electrophoretic mobility shift assay of DNA-nuclear protein binding. In the renal biopsy from lupus nephritis patients, the expressions of NF-κB and UCH-L1 increased in immunohistochestry staining and were positively correlated. Activation of NF-κB up-regulates UCH-L1 expression following changing of other podocytes molecules, such as nephrin and snail. These results suggest that activation of the NF-κB signaling pathway could be the major pathogenesis to up-regulate UCH-L1 in podocyte injury, followed by the turnover of other molecules, which might result in morphological changes and dysfunction of podocytes. This work help us to understand the effect of NF-κB on specific target molecules of podocytes, and suggest that targeting the NF-κB-UCH-L1 interaction could be a novel therapeutic strategy for the treatment of podocyte lesions and proteinuria.

Proteomic analysis of podocyte exosome-enriched fraction from normal human urine

Urine results from a coordinated activity of glomerular and tubular compartments of the kidney. As a footprint of these cellular functional processes, urinary exosomes, and 40-80 nm membrane vesicles released after fusion with the plasma membrane into the extracellular environment by renal epithelial cells, are a source for identification of proteins and investigation of their role in the kidney. The aim of the present study was the identification of podocyte exosome proteins based on urine immunoabsorption using podocyte-specific CR1-immunocoated beads followed by proteomic analysis using LC MS/MS techniques. This methodology allowed the identification of 1195 proteins. By using a bioinformatic approach, 27 brain-expressed proteins were identified, in which 14 out of them were newly demonstrated to be expressed in the kidney at a mRNA level, and, one of them, the COMT protein, was demonstrated to be expressed in podocytes at a protein level. These results, attesting the reliability of the methodology to identify podocyte proteins, need now to be completed by further experiments to analyze more precisely their biological function(s) in the podocytes.

De novo membranous nephropathy (MN) in kidney allografts. A peculiar form of alloimmune disease?

De novo membranous nephropathy (MN) is an uncommon complication of kidney transplantation, which shows histological findings similar to those seen in recurrent MN, but with some distinct differences. The clinical presentation may be variable, from asymptomatic to nephrotic proteinuria. The disease may run an indolent course or may have an accelerated course leading to allograft loss. De novo membranous nephropathy (MN) can develop in transplant recipients with viral hepatitis, Alport syndrome, ureteral obstruction, renal infarction, or in conjunction with recurrent IgA nephritis. Histologic signs of allograft rejection are often associated with or can antedate de novo MN. These findings suggest that donor-specific antibodies and antibody-mediated rejection might play a pathogenetic role in some patients with de novo MN. However, signs of rejection were absent in a number of cases, and in some instances the disease developed in recipients of "full house" HLA- matched kidneys. Thus, it seems possible that de novo MN is not because of allograft rejection per se, but is triggered by different injuries that can create an inflammatory environment, activate innate immunity, and expose hidden (cryptic) antigens, probably different from those observed to be involved in idiopathic MN. These events can lead to the production of circulating antibodies and in situ formation of immune complexes (IC) and the morphological lesion of MN.

Expression of USP2-69 in mesangial cells in vivo and in vitro

Ubiquitin-specific protease 2 (USP2) is a member of a family of de-ubiquitinating enzymes. It may play an important role in the regulation of cell growth and differentiation. It is known that expression of the isoform USP2-69 kD is high in kidney tissue, but its role remains unclear. Mesangial cell proliferation is a prominent element of various types of glomerulonephritides. Therefore, whether USP2 plays a role in mesangial cell proliferation during glomerulonephritides is an interesting question to explore. The purpose of the present study was to evaluate USP2-69 expression in needle biopsies of human kidneys and in cultured rat mesangial cells. On immunohistochemistry USP2-69 was upregulated in some mesangial proliferative glomerulonephritides. The proportion of USP2-69 positive area in the glomeruli was 3.90% in normal kidney, 4.96% in minimal change disease, and 4.39% in membranous glomerulonephritides, while it was 14.84% in IgA nephropathy (IgAN) (mesangial proliferative type), 16.18% in lupus nephritis (LN; diffuse proliferative type) and 15.54% in acute proliferative glomerulonephritides (APGN); the difference of the percentages between IgAN, LN (IV subtype) and APGN and normal kidney were statistically significant (P < 0.05). Additionally, the number of proliferating cell nuclear antigen (PCNA)-positive nuclei in the glomeruli was statistically significantly higher in the various glomerulonephritides than in the normal kidney (P < 0.05). Immunohistochemistry showed that the distribution of the USP2(+) area and PCNA(+) nuclei overlapped in the glomeruli. Treatment with interleukin-1beta for 12 h and 24 h, or with anti-thymocyte serum for 6 h and 12 h resulted in elevated USP2-69 mRNA and protein expression in the rat mesangial cells. Also, PCNA expression increased and p27 expression decreased significantly in the treated mesangial cells. These findings suggest that USP2-69 was upregulated in mesangial cells during mesangial proliferative glomerulonephritides in vivo and in vitro, which may relate to the proliferation of mesangial cells.