Recent Progress in the Pathogenesis of Nephrotic Proteinuria

Cholinesterase is a Potential Biomarker with High Accuracy for the Nephrotic Syndrome Diagnosis in Minors

Background

Serum Cholinesterase (CHE) levels have been found to be elevated in individuals with nephrotic syndrome (NS); nevertheless, it is unknown whether CHE can serve as a biomarker for NS diagnosis and what its diagnostic relevance is for NS in minors.

Methods

In this study, 138 minors aged 1–17 years with NS were enrolled, including 101 patients with the first episode of NS and 37 patients with relapsing NS. One hundred and four minors suffering from nephritis and 109 healthy minors were included as control groups. The clinical information and laboratory data of all NS patients and the control group were obtained. Logistic regression, correlation analyses and receiver operator characteristic curve were used to examine the value of CHE for NS patients.

Results

Compared to patients diagnosed with nephritis and healthy minors in the control group, the serum CHE levels of total/first episode/relapsing NS patients were substantially higher (P < 0.05). The CHE was an independent risk predictor of total (adjusted odds ratio [OR] = 2.23, 95% confidence interval [CI]: 1.57–3.18)/first episode (adjusted OR = 4.02, 95% CI: 1.47–11.08)/relapsing (adjusted OR = 2.04, 95% CI: 1.42–2.93) NS, and was positively correlated with total cholesterol in total/first episode/relapsing NS patients, respectively. The optimal cutoff for total/first episode/relapsing NS all was 11 KU/L, but the diagnostic accuracy in first episode NS (area under the curve [AUC] = 0.96, 95% CI: 0.94–0.98) was higher than the total NS (AUC = 0.93, 95% CI: 0.91–0.96) and relapsing NS (AUC = 0.85, 95% CI: 0.78–0.92).

Conclusion

CHE is a possible biomarker for NS and has good diagnostic accuracy for NS in minors, particularly for the first episode of NS in minors.

Soluble urokinase plasminogen activator receptor (suPAR) and glomerular disease in children: a narrative review

Background

Focal segmental glomerulosclerosis (FSGS) is a chronic glomerular disease that responds poorly to treatment, with a large proportion of patients progressing to end-stage renal disease in spite of initial aggressive treatment. It is worth emphasizing that the FSGS group has still a high recurrence rate after kidney transplantation. Therefore, understanding the factors involved in the pathogenesis of FSGS will help nephrologists better understand the pathogenesis as well as find out specific targeted therapies. Circulating immune factors have long been implicated in the pathogenesis of FSGS, and recent studies have suggested that soluble urokinase plasminogen activator receptor (suPAR) is one of the good candidates for this hypothesis. The aim of this review study was to analyze the value of suPAR in glomerular disease, especially in clinical studies.

Methods

In this review study, the PubMed database was searched using relevant keywords (suPAR, circulating permeability factors Children, FSGS, and children). Descriptive and cross-sectional studies were reviewed in the current study with the main focuses on the role of suPAR in FSGS, nephrotic syndrome, and the relation to progression of renal failure, especially the research in children.

Results

Overall, 32 studies from different countries were selected. These clinical studies on suPAR have shown the following: (i) the role of suPAR in the diagnosis of FSGS has not yet been confirmed, and (ii) there is strong evidence demonstrating a significant relationship between suPAR and the severity of kidney disease as well as a high value of suPAR in predicting the steroid responsiveness of nephrotic syndrome.

Conclusion

Researching on circulating permeability factors in FSGS is a current trend, which opens new avenues in targeted diagnosis and treatment. suPAR is a promising candidate, and urinary suPAR has also shown advantages over serum suPAR; therefore, more research on this issue is needed in the future.

Nephrotic Syndrome

Nephrotic syndrome is one cause of end-stage kidney disease. Because edema is a common presenting feature and hypertension and dyslipidemia are often present in nephrotic syndrome, it is important for the primary care physician to suspect this entity. Common causes in adults include diabetic nephropathy, focal segmental glomerulosclerosis, and membranous nephropathy. In adults, many primary causes are due to an underlying disease. A cause of the nephrotic syndrome should be established with serologic workup and renal consultation. Renal biopsy is necessary in those with an unknown cause to or classify disease. Treatment focuses on symptoms, complications, and the primary cause.

Fibronectin type III domain-containing 4 promotes the migration and differentiation of bovine skeletal muscle-derived satellite cells via focal adhesion kinase

FNDC4 is an anti-inflammatory factor that alters the activation state of macrophages; it is used to treat colitis in mice. However, its role in muscle formation and mechanism of function remains unknown. We found that FNDC4 promotes the bovine MDSCs migration and differentiation. Furthermore, we reported that it interacts with integrin β1 (ITGβ1). FAK, mediated by ITGβ1, regulates cell migration. Our results found FNDC4 to influence the expression of p-FAK, p-paxillin, and vinculin. Then, overexpressed or added FNDC4 protein could not influence migration and differentiation any more when the activated form of FAK was reduced. Therefore, we concluded that FNDC4 promotes the differentiation and migration of bovine MDSCs via the FAK, mediated by the ITGβ1 receptor.

Clinicopathologic characteristics, pathology, and prognosis of 77 dogs with focal segmental glomerulosclerosis

BACKGROUND

Focal segmental glomerulosclerosis (FSGS) is a common cause of nonimmune complex glomerulopathy and the prognosis and clinicopathologic findings associated with this condition have not been described in dogs.

OBJECTIVE

To characterize the presentation and identify clinical factors associated with the survival of dogs with FSGS.

ANIMALS

Seventy-seven dogs diagnosed with FSGS based on evaluation of renal biopsy samples submitted to the International Veterinary Renal Pathology Service.

METHODS

Retrospective review of medical records of dogs biopsied for evaluation of proteinuria between January 2015 and May 2017.

RESULTS

The incidence of FSGS among all dogs biopsied for proteinuria was 26%. Significantly more females (48; 62.3%) than males (29; 37.7%) were affected (P = .04). At the time of biopsy, median serum creatinine concentration (SCr) was 1.2 mg/dL (range, 0.3-8.7), median serum albumin concentration (Alb) was 2.8 g/dL (range, 1.1-4.6), median systolic blood pressure was 153.5 mm Hg (range, 95-260), and median urine protein : creatinine ratio was 5.9 (range, 1.4-22). Median survival time after biopsy was 258 days (range, 26-1003) for dogs that died from all causes (n = 32). Factors that were associated with a shorter survival time included SCr ≥ 2.1 mg/dL (P < .01) and Alb < 2 g/dL (P < .01).

CONCLUSIONS AND CLINICAL IMPORTANCE

Most dogs with FSGS were female, and although commonly hypertensive, azotemia, severe hypoalbuminemia and ascites or edema were observed infrequently. Variables significantly associated with survival time were SCr and Alb.

Targeting NLRP3 inflammasome as a promising approach for treatment of diabetic nephropathy: Preclinical evidences with therapeutic approaches

Diabetes mellitus is an increasingly prevalent disease around the globe. The epidemic of diabetes mellitus and its complications pretenses the foremost health threat globally. Diabetic nephropathy is the notable complication in diabetes, leading to end-stage renal disease (ESRD) and premature death. Abundant experimental evidence indicates that oxidative stress and inflammation are the important mediators in diabetic kidney diseases and interlinked with various signal transduction molecular mechanisms. Inflammasomes are the critical components of innate immunity and are recognized as a critical mediator of inflammation and autoimmune disorders. NOD-like receptor protein 3 (NLRP3) inflammasome is the well-characterized protein and it exhibits the sterile inflammation through the regulation of pro-inflammatory cytokines interleukin (IL)-1β and IL-18 production in tissues. In recent years, the role of NLRP3 inflammasome in the pathophysiology of diabetic kidney diseases in both clinical and experimental studies has generated great interest. In the current review, we focused on and discussed the role of NLRP3 inflammasome in diabetic nephropathy. A literature review was performed using online databases namely, PubMed, Scopus, Google Scholar and Web of science to explore the possible pharmacological interventions that blunt the NLRP3 inflammasome-caspase-1-IL-1β/IL-18 axis and shown to have a beneficial effect in diabetic kidney diseases. This review describes the inhibition of NLRP3 inflammasome activation as a promising therapeutic target for drug discovery in future.

Pediatric Patients With Steroid-Sensitive Nephrotic Syndrome Have Higher Expression of T Regulatory Lymphocytes in Comparison to Steroid-Resistant Disease

Background and Aim: Idiopathic nephrotic syndrome (INS) is classified according to the response to drug therapy in steroid-sensitive (SS), steroid-dependent (SD), and steroid-resistant (SR) categories. Previous studies showed changes in inflammatory activity of subpopulations of lymphocytes in INS. This study aimed to compare SS and SR patients in regard to subpopulations of leukocytes, profile of regulatory lymphocytes, and migratory activity of lymphocyte subpopulations. Results obtained in INS patients were also compared to age and sex-matched healthy controls. Methods: This is a cross-sectional study including SS patients (n = 30), SR patients (n = 14), and controls (n = 10). Peripheral blood samples were withdrawn for ex-vivo leukocyte flow cytometry analysis. Results: Percentage of B-lymphocytes and natural killer (NK) cells were significantly reduced in SR patients when compared to controls, while the percentage of NKT cells were decreased in SS patients in comparison to controls. Percentages of CD4⁺ expressing FoxP3 and CTLA4 were significantly higher in SS patients in comparison to SR patients and controls. The expression of integrin CD18 on the surface of T lymphocytes (CD3⁺) was reduced in SS patients if compared to controls. Conclusion: This study found that SS INS patients have higher levels of regulatory T-lymphocytes and lower expression of adhesion molecules than SR patients.

The SGK3-triggered ubiquitin-proteasome degradation of podocalyxin (PC) and ezrin in podocytes was associated with the stability of the PC/ezrin complex

Podocyte damage is commonly accompanied by destabilization of the podocalyxin (PC)/ezrin complex. Serum- and glucocorticoid-inducible kinase 3 (SGK3) plays a role in the maintenance of podocyte function, but the details of this role are poorly understood. Herein we demonstrated that SGK3 and its downstream target protein neural precursor cell expressed developmentally downregulated protein 4 subtype 2 (Nedd4-2) triggered PC and ezrin interaction. In adriamycin (ADR)-induced nephritic mice, and after puromycin aminonucleoside (PAN)-induced podocyte damage in vitro, PC and ezrin protein expression levels decreased significantly, while Nedd4-2 activity increased. Moreover, PAN treatment increased PC and ezrin ubiquitination and decreased PC/ezrin interaction in cultured mouse podocytes. The downregulation of SGK3 activity in mouse podocytes resulted in decreased PC and ezrin protein expression and increased the ubiquitin-proteasome degradation of PC and ezrin. Furthermore, upregulation of SGK3 activity mostly reversed the PAN-induced decrease in PC and ezrin protein expression. Overexpression of Nedd4-2 led to decreased ezrin protein expression via the upregulation of ezrin ubiquitination. In contrast, Nedd4-2 knockdown resulted in increased ezrin protein expression but decreased ezrin ubiquitination. In PC-transfected human embryonic kidney (HEK293T) cells, SGK3 activity downregulation and Nedd4-2 overexpression resulted in decreased PC/ezrin interaction. These results suggested that SGK3 triggers the ubiquitin-proteasome degradation of PC and ezrin, while the SGK3/Nedd4-2 signaling pathway regulates ezrin, but not PC, ubiquitination. Thus SGK3 helps to regulate podocyte function by maintaining the stability of the PC/ezrin complex.

Genetic and in vivo determinants of glucocorticoid sensitivity in relation to clinical outcome of childhood nephrotic syndrome

Following initial glucocorticoid treatment, the clinical course in children with nephrotic syndrome is highly variable. Intrinsic sensitivity to glucocorticoids might be a determinant of this variability. Functional polymorphisms of the glucocorticoid receptor gene NR3C1 have been associated with either relatively impaired (GR-9β) or increased (BclI) glucocorticoid sensitivity. Here, in a prospective, well-defined cohort of children with nephrotic syndrome, we evaluated both carriage of GR-9β+TthIII-1 and BclI haplotypes in 113 children and a dexamethasone suppression test in 90 children in relation to their clinical outcome over a median follow-up of 4.4 years. Carriers of GR-9β+TthIII-1 had a significantly higher incidence of steroid dependence 13/25 (52%) compared with noncarriers 19/75 (25%) with a hazard ratio adjusted for gender, age, and descent of 3.04 with 95% confidence interval 1.37-6.74. Both first and frequent relapses happened significantly more often in GR-9β+TthIII-1 carriers than in noncarriers. There were no significant differences in therapeutic outcomes between carriers and noncarriers of the BclI haplotype. Results of the dexamethasone test showed no associations with clinical outcome. Thus, the GR-9β+TthIII-1 haplotype of the glucocorticoid receptor gene offers new insights into the clinical course of children with nephrotic syndrome.

Study of urinary proteomes in Anderson-Fabry disease

BACKGROUND

Anderson-Fabry disease (AFD) is an X-linked genetic disorder with deficient α-galactosidase A activity. The main aim of this work was to investigate possible differences in urine proteins between healthy controls and AFD patients and to identify abnormal proteins as potential biomarkers of disease.

MATERIAL AND METHODS

We studied 2D electrophoresis images of urine samples collected from AFD patients and healthy subjects. The proteins were separated using isoelectric focusing method followed by SDS-PAGE. The proteins were then visualized by silver staining and characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS).

RESULTS

We found out that the urinary spectra of all the Fabry disease samples included identical proteins with molecular weight around 20-40 kDa. The concentration of some proteins was more than three times higher in the AFD samples, compared to the controls. The abundant proteins were identified by MALDI-TOF MS and included the following: alpha-1-antitrypsin, alpha-1-microglobulin, prostaglandin H2 d-isomerase, complement-c1q tumor necrosis factor-related protein, and Ig kappa chain V-III. Possible glycosylation at Asn51 and Asn78 sites of the prostaglandin H2 d-isomerase was detected.

CONCLUSIONS

AFD urinary proteomics revealed increased secretion of several proteins. We postulate that the observed difference in the amount of prostaglandin H2 d-isomerase and its position on two-dimensional gels might be related to different glycosylation in AFD subjects.

Immunohistochemical evaluation of podocalyxin expression in glomerulopathies associated with nephrotic syndrome

It is now well established that morphological change of podocytes is closely correlated to the development of proteinuria. The aim of this study was to investigate the role of podocalyxin, a major podocyte protein, in the pathogenesis of glomerulopathies primarily associated with the nephrotic syndrome. Immunohistochemical expression of podocalyxin has been evaluated in 51 renal samples, including healthy controls, patients with podocytopathies (minimal change disease [MCD], focal segmental glomerulosclerosis [FSGS]) and membranous glomerulopathy (MG). A computerized image analysis program has been used. Statistical analysis was performed using analysis of variance and Bonferroni tests. Immunohistochemical expression of podocalyxin has been observed within the podocytes of healthy controls. In MCD, podocalyxin expression was globally reduced despite the normal appearance of the glomeruli. In FSGS, podocalyxin loss was observed in both the segmental sclerotic and the nonsclerotic areas being significantly more prominent in the former. Reduction of podocalyxin in MG was demonstrated for the first time immunohistochemically. The percentage of the stained area was statistical significantly higher in the controls than in each pathologic group. However, among pathologic groups (FSGS, MCD, MG), there was no statistically significant difference. This is one of the few studies investigating podocalyxin immunohistochemical expression in glomerulopathies associated with nephrotic syndrome. The observed reduction in podocalyxin expression suggests that it constitutes a target molecule in nephrotic syndrome pathogenesis regardless of the underlying cause.

Expression of beta-carotene 15,15'- monooxygenase gene and retinol status in rats with puromycin aminonucleoside-induced nephrosis

Retinol and its metabolite retinoic acid play a critical role in immunity, reproduction, and development. Retinoids are known to influence renal development, and show beneficial effects in experimental models of renal disease. beta-Carotene (provitamin A) is cleaved to retinal by beta-carotene 15,15'- monooxygenase (BCM), which is an essential enzyme for retinoid biosynthesis. However, the metabolism of retinol and beta-carotene in renal diseases such as nephrosis remains unclear. We studied BCM gene expression and retinol status in rats with nephrotic syndrome induced by puromycin aminonucleoside (PAN). BCM gene expression in the liver and intestines of PAN-treated rats was decreased compared with that in controls, while the expression in the kidney of PAN-treated animals was increased. Plasma retinol and retinol-binding protein levels were decreased in PAN-treated rats, but hepatic retinol level did not differ between PAN-treated and control rats. Up-regulation of BCM gene expression in the kidneys of rats with nephrotic syndrome may result in increased conversion of beta-carotene to retinal, so this change might supply more retinoic acid to the damaged glomeruli. Changes in the metabolism of retinol and beta-carotene might have an important role in protection against the development of nephrosis.