COL4A3 Mutation Induced Podocyte Apoptosis by Dysregulation of NADPH Oxidase 4 and MMP-2.

Introduction: Podocyte apoptosis is a common mechanism driving progression in Alport syndrome (AS). This study aimed to investigate the mechanism of podocyte apoptosis caused by COL4A3 mutations. Methods: We recruited patients with autosomal dominant AS (ADAS). Patients with minimal change disease (MCD) were recruited as controls. Microarray analysis was carried out on isolated glomeruli from the patients and validated. Then, corresponding mutant human podocytes (p.C1616Y) and 129 mice (p.C1615Y, the murine homolog to the human p.C1616Y) were constructed. The highest differentially expressed genes (DEGs) from microarray analysis were validated in transgenic mice and podocytes before and after administration of MMP-2 inhibitor (SB-3CT) and NOX4 inhibitor (GKT137831). We further validated NOX4/MMP-2/apoptosis pathway by real-time polymerase chain reaction (PCR), immunohistochemistry, and western blot in renal tissues from the ADAS patients. Results: Using microarray analysis, we observed that DEGs, including NOX4/H2O2, MMP-2, and podocyte apoptosis-related genes were significantly upregulated. These genes were validated by real-time PCR, histologic analysis, and western blot in corresponding mutant human podocyte (p.C1616Y) and/or mice models (p.C1615Y). Moreover, we found podocyte apoptosis was abrogated and MMP-2 expression was down-regulated both in vivo and in vitro by NOX4 inhibition, urinary albumin-to-creatinine ratio, 24-hour proteinuria; and renal pathologic lesion was attenuated by NOX4 inhibition in vivo. Furthermore, podocyte apoptosis was attenuated whereas NOX4 expression remained the same by inhibition of MMP-2 both in vivo and in vitro. Conclusion: These results indicated that NOX4 might induce podocyte apoptosis through the regulation of MMP-2 in patients with COL4A3 mutations. Our findings provided new insights into the mechanism of ADAS.

Adult-Onset Focal Segmental Glomerulosclerosis With Steroid-Dependent Nephrotic Syndrome Caused by a Novel TBC1D8B Variant: A Case Report and Literature Review.

Focal segmental glomerulosclerosis (FSGS) is a histological lesion with a variety of potential causes, including rare variants of podocyte-related genes. Recently, it has been found that variants in the TBC1D8B gene on the X chromosome can lead to early-onset focal segmental glomerulosclerosis and steroid-resistant nephrotic syndrome by affecting endocytosis and recycling of nephrin. Here, we report a 19-year-old Chinese patient with nephrotic syndrome and normal kidney function. He had a complete remission of nephrotic syndrome after full-dose prednisone and cyclosporine treatment. Unfortunately, a relapse of nephrotic syndrome occurred during prednisone tapering. Focal segmental glomerulosclerosis was proven by a kidney biopsy, and a hemizygous pathogenic variant located in the TBC (Tre-2-Bub2-Cdc16) domain of TBC1D8B was detected by whole-exome sequencing. By comparing our case with reports of other patients with TBC1D8B variants, we suggest possible genotype-phenotype correlations. To our knowledge, this is the first report identifying a pathogenetic variant in the TBC domain of TBC1D8B in an adult-onset focal segmental glomerulosclerosis patient with steroid-dependent NS. With this report, we broaden the clinical and genetic spectrum of X-linked genetic FSGS.

Mutation in XPO5 causes adult-onset autosomal dominant familial focal segmental glomerulosclerosis.

BACKGROUND: Focal and segmental glomerulosclerosis (FSGS) is a histological pathology that characterizes a wide spectrum of diseases. Many genes associated with FSGS have been studied previously, but there are still some FSGS families reported in the literature without the identification of known gene mutations. The aim of this study was to investigate the new genetic cause of adult-onset FSGS. METHODS: This study included 40 FSGS families, 77 sporadic FSGS cases, 157 non-FSGS chronic kidney disease (CKD) families and 195 healthy controls for analyses. Whole-exome sequencing (WES) and Sanger sequencing were performed on probands and family members of all recruited families and sporadic FSGS cases. RESULTS: Using WES, we have identified a novel heterozygous missense variant (c.T1655C:p.V552A) in exportin 5 gene (XPO5) in two families (FS-133 and CKD-05) affected with FSGS and CKD. Sanger sequencing has confirmed the co-segregation of this identified variant in an autosomal dominant pattern within two families, while this variant was absent in healthy controls. Furthermore, the identified mutation was absent in 195 ethnically matched healthy controls by Sanger sequencing. Subsequently, in silico analysis demonstrated that the identified variant was highly conservative in evolution and likely to be pathogenic. CONCLUSIONS: Our study reports an adult-onset autosomal dominant inheritance of the XPO5 variant in familial FSGS for the first time. Our study expanded the understanding of the genotypic, phenotypic and ethnical spectrum of mutation in this gene.

Particulate matter of air pollution may increase risk of kidney failure in IgA nephropathy.

IgA nephropathy (IgAN) is characterized by deposition of galactose-deficient IgA1 (Gd-IgA1) in glomerular mesangium associated with mucosal immune disorders. Since environmental pollution has been associated with the progression of chronic kidney disease in the general population, we specifically investigated the influence of exposure to fine particulate matter less than 2.5 µm in diameter (PM2.5) on IgAN progression. Patients with biopsy-proven primary IgAN were recruited from seven Chinese kidney centers. PM2.5 exposure from 1998 to 2016 was derived from satellite aerosol optical depth data and a total of 1,979 patients with IgAN, including 994 males were enrolled. The PM2.5 exposure levels for patients from different provinces varied but, in general, the PM2.5 exposure levels among patients from the north were higher than those among patients from the south. The severity of PM2.5 exposure in different regions was correlated with regional kidney failure burden. In addition, each 10 µg/m3 increase in annual average concentration of PM2.5 exposure before study entry (Hazard Ratio, 1.14; 95% confidence interval, 1.06-1.22) or time-varying PM2.5 exposure after study entry (1.10; 1.01-1.18) were associated with increased kidney failure risk after adjustment for age, gender, estimated glomerular filtration rate, urine protein, uric acid, hemoglobin, mean arterial pressure, Oxford classification, glucocorticoid and renin-angiotensin system blocker therapy. The associations were robust when the time period, risk factors of cardiovascular diseases or city size were further adjusted on the basis of the above model. Thus, our results suggest that PM2.5 is an independent risk factor for kidney failure in patients with IgAN, but these findings will require validation in more diverse populations and other geographic regions.

Case Report: Adolescent-Onset Isolated Nephronophthisis Caused by a Novel Homozygous Inversin Mutation.

Objective: Nephronophthisis (NPHP) is a rare autosomal recessive inherited kidney disease that can cause cystic enlargement of the kidneys, and lead to end-stage renal disease (ESRD) before the age of 30 years. Herein we describe a case of adolescent-onset NPHP with a novel homozygous mutation in the inversin gene (INVS). Methods: The patient was a 15-year-old Chinese boy who presented with ESRD. Genetic testing was performed via whole exome sequencing and validated via Sanger sequencing. A novel homozygous INVS mutation was identified (c. 1909C > T; p. Gln637Ter). Results: The results of laboratory examinations included urinary protein 1.05 g/24 h, urine erythrocyte count 5/high-power field, serum creatinine 1,026.2 µmol/L, and estimated glomerular filtration rate 5.8 ml/min/1.73 mm2. Extrarenal features included hypertension and moderate anemia, and his parents were consanguineous (first cousins). A homozygous 1-bp substitution resulting in a nonsense mutation (c. 1909C > T; p. Gln637Ter) in exon 15 of INVS was detected via whole exome sequencing, and validated via Sanger sequencing. According to the classification system of the American College of Medical Genetics and Genomics, the mutated gene in INVS is strongly pathogenic (PVS1+PM2+PP3+PP5). His parents and a younger brother were heterozygous carriers. Based on the above results he was diagnosed with juvenile type 2 NPHP. He underwent hemodialysis, and received a kidney transplant after 2 months. He is currently recovering well, with a serum creatinine level of 117 µmol/L and an estimated glomerular filtration rate of 79.6 ml/min/1.73 mm2. Conclusion: Here we have described an extremely rare case of adolescent-onset type 2 NPHP caused by a homozygous INVS mutation. The patient had progressed to ESRD by the age of 15 years. The current report will deepen our understanding of the clinical and genetic basis of this disease.

A Validation Study Comparing Risk Prediction Models of IgA Nephropathy.

We aimed to validate three IgAN risk models proposed by an international collaborative study and another CKD risk model generated by an extended CKD cohort with our multicenter Chinese IgAN cohort. Biopsy-proven IgAN patients with an eGFR ≥15 ml/min/1.73 m2 at baseline and a minimum follow-up of 6 months were enrolled. The primary outcomes were a composite outcome (50% decline in eGFR or ESRD) and ESRD. The performance of those models was assessed using discrimination, calibration, and reclassification. A total of 2,300 eligible cases were enrolled. Of them, 288 (12.5%) patients reached composite outcome and 214 (9.3%) patients reached ESRD during a median follow-up period of 30 months. Using the composite outcome for analysis, the Clinical, Limited, Full, and CKD models had relatively good performance with similar C statistics (0.81, 0.81, 0.82, and 0.82, respectively). While using ESRD as the end point, the four prediction models had better performance (all C statistics > 0.9). Furthermore, subgroup analysis showed that the models containing clinical and pathological variables (Full model and Limited model) had better discriminatory abilities than the models including only clinical indicators (Clinical model and CKD model) in low-risk patients characterized by higher baseline eGFR (≥60 ml/min/1.73 m2). In conclusion, we validated recently reported IgAN and CKD risk models in our Chinese IgAN cohort. Compared to pure clinical models, adding pathological variables will increase performance in predicting ESRD in low-risk IgAN patients with baseline eGFR ≥60 ml/min/1.73 m2.

Hypophosphatemia is an independent risk factor for AKI among hospitalized patients with COVID-19 infection.

BACKGROUND: This study sought to investigate incidence and risk factors for acute kidney injury (AKI) in hospitalized COVID-19. METHODS: In this retrospective study, we enrolled 823 COVID-19 patients with at least two evaluations of renal function during hospitalization from four hospitals in Wuhan, China between February 2020 and April 2020. Clinical and laboratory parameters at the time of admission and follow-up data were recorded. Systemic renal tubular dysfunction was evaluated via 24-h urine collections in a subgroup of 55 patients. RESULTS: In total, 823 patients were enrolled (50.5% male) with a mean age of 60.9 ± 14.9 years. AKI occurred in 38 (40.9%) ICU cases but only 6 (0.8%) non-ICU cases. Using forward stepwise Cox regression analysis, we found eight independent risk factors for AKI including decreased platelet level, lower albumin level, lower phosphorus level, higher level of lactate dehydrogenase (LDH), procalcitonin, C-reactive protein (CRP), urea, and prothrombin time (PT) on admission. For every 0.1 mmol/L decreases in serum phosphorus level, patients had a 1.34-fold (95% CI 1.14-1.58) increased risk of AKI. Patients with hypophosphatemia were likely to be older and with lower lymphocyte count, lower serum albumin level, lower uric acid, higher LDH, and higher CRP. Furthermore, serum phosphorus level was positively correlated with phosphate tubular maximum per volume of filtrate (TmP/GFR) (Pearson r = 0.66, p < .001) in subgroup analysis, indicating renal phosphate loss via proximal renal tubular dysfunction. CONCLUSION: The AKI incidence was very low in non-ICU patients as compared to ICU patients. Hypophosphatemia is an independent risk factor for AKI in patients hospitalized for COVID-19 infection.

A validation study of UCSD-Mayo risk score in predicting hospital-acquired acute kidney injury in COVID-19 patients.

INTRODUCTION: Acute kidney injury (AKI) in coronavirus disease 2019 (COVID-19) patients is associated with poor prognosis. Early prediction and intervention of AKI are vital for improving clinical outcome of COVID-19 patients. As lack of tools for early AKI detection in COVID-19 patients, this study aimed to validate the USCD-Mayo risk score in predicting hospital-acquired AKI in an extended multi-center COVID-19 cohort. METHODS: Five hundred seventy-two COVID-19 patients from Wuhan Tongji Hospital Guanggu Branch, Wuhan Leishenshan Hospital, and Wuhan No. Ninth Hospital was enrolled for this study. Patients who developed AKI or reached an outcome of recovery or death during the study period were included. Predictors were evaluated according to data extracted from medical records. RESULTS: Of all patients, a total of 44 (8%) developed AKI. The UCSD-Mayo risk score achieved excellent discrimination in predicting AKI with the C-statistic of 0.88 (95%CI: 0.84-0.91). Next, we determined the UCSD-Mayo risk score had good overall performance (Nagelkerke R2 = 0.32) and calibration in our cohort. Further analysis showed that the UCSD-Mayo risk score performed well in subgroups defined by gender, age, and several chronic comorbidities. However, the discrimination of the UCSD-Mayo risk score in ICU patients and patients with mechanical ventilation was not good which might be resulted from different risk factors of these patients. CONCLUSIONS: We validated the performance of UCSD-Mayo risk score in predicting hospital-acquired AKI in COVID-19 patients was excellent except for patients from ICU or patients with mechanical ventilation.

Increased Lifetime Risk of ESRD in Familial IgA Nephropathy.

INTRODUCTION: Familial IgA nephropathy (IgAN) has been widely reported. However, its clinicohistologic characteristics and long-term prognosis are not clear. METHODS: A total of 348 familial IgAN cases from 167 independent families were recruited and their clinicohistologic characteristics as well as lifetime risk of end-stage renal disease (ESRD) were compared to 1116 sporadic IgAN patients from the same geographic region. RESULTS: Of all familial IgAN patients, 60 (17%) came from 32 single-generation (SG; all affected individuals are siblings) families, whereas 286 (82%) came from 134 multiple-generation (MG; affected individuals were present in at least 2 consecutive generations) families. The lifetime ESRD risk was significantly higher in familial patients than sporadic ones after adjusting by gender (hazard ratio [HR]=1.40, 95% confidence interval [CI]: 1.12-1.74, P = 0.004), with 5 years younger in median ESRD age (60 years vs. 65 years in familial and sporadic cases separately). Interestingly, among familial patients, we found cases from SG families (vs. MG families: HR = 2.62, 95% CI: 1.59-4.31, P < 0.001) or with early onset (onset age <30 years) (vs. late onset: HR = 4.79, 95% CI: 3.16-7.26, P < 0.001) had higher lifetime ESRD risk. Furthermore, among sporadic patients, men had lower estimated glomerular filtration rate (eGFR), higher urine protein, higher Oxford T score, and higher risk for life span ESRD compared with women (male vs. female, 25% vs. 17%, P = 0.003) whereas these gender differences were not seen in familial patients. CONCLUSION: Familial IgAN cases had poorer renal outcomes and less gender differences compared with sporadic cases. These findings provide evidence that familial disease represent a distinct subtype of more progressive IgAN. Early diagnosis could improve the prognosis of cases with familial IgAN.