Diminished met signaling in podocytes contributes to the development of podocytopenia in transplant glomerulopathy

Recognition of intraglomerular histological features with deep learning in protocol transplant biopsies and their association with kidney function and prognosis

Background

The Banff Classification may not adequately address protocol transplant biopsies categorized as normal in patients experiencing unexplained graft function deterioration. This study seeks to employ convolutional neural networks to automate the segmentation of glomerular cells and capillaries and assess their correlation with transplant function.

Methods

A total of 215 patients were categorized into three groups. In the Training cohort, glomerular cells and capillaries from 37 patients were manually annotated to train the networks. The Test cohort (24 patients) compared manual annotations vs automated predictions, while the Application cohort (154 protocol transplant biopsies) examined predicted factors in relation to kidney function and prognosis.

Results

In the Test cohort, the networks recognized histological structures with Precision, Recall, F-score and Intersection Over Union exceeding 0.92, 0.85, 0.89 and 0.74, respectively. Univariate analysis revealed associations between the estimated glomerular filtration rate (eGFR) at biopsy and relative endothelial area (r = 0.19, P = .027), endothelial cell density (r = 0.20, P = .017), mean parietal epithelial cell area (r = -0.38, P < .001), parietal epithelial cell density (r = 0.29, P < .001) and mesangial cell density (r = 0.22, P = .010). Multivariate analysis retained only endothelial cell density as associated with eGFR (Beta = 0.13, P = .040). Endothelial cell density (r = -0.22, P = .010) and mean podocyte area (r = 0.21, P = .016) were linked to proteinuria at biopsy. Over 44 ± 29 months, 25 patients (16%) reached the primary composite endpoint (dialysis initiation, or 30% eGFR sustained decline), with relative endothelial area, mean endothelial cell area and parietal epithelial cell density below medians linked to this endpoint [hazard ratios, respectively, of 2.63 (P = .048), 2.60 (P = .039) and 3.23 (P = .019)].

Conclusion

This study automated the measurement of intraglomerular cells and capillaries. Our results suggest that the precise segmentation of endothelial and epithelial cells may serve as a potential future marker for the risk of graft loss.

Focal Segmental Glomerulosclerosis Superimposed on Transplant Glomerulopathy: Implications for Graft Survival

INTRODUCTION

Transplant glomerulopathy (TG) is a morphological lesion resulting from chronic glomerular endothelium injury, and it is strongly associated with poor graft survival. TG coexisting with focal segmental glomerulosclerosis (FSGS) can be found in renal allograft biopsies, but few related studies are available.

METHODS

Consecutive kidney transplant recipients with biopsy-proven TG were studied retrospectively. Patients concomitant with FSGS were identified and compared with those without FSGS. The influence of FSGS on allograft outcomes was assessed using univariate and multivariate Cox regression models.

RESULTS

Of the 66 patients with TG, 40 (60.6%) had concomitant FSGS. TG patients with FSGS had higher proteinuria (median, 2.6 vs. 0.8 g/24 h, p < 0.001) and serum creatinine levels (median, 2.5 vs. 2.1 mg/dL, p = 0.04), lower serum albumin levels, higher chronic glomerulopathy (cg) score, larger glomerular tuft area, lower number of podocytes, and higher incidences of podocyte hyperplasia, pseudotubule formation, and diffuse foot process effacement than those without FSGS (all p < 0.05). The kidney allograft loss rate of patients with FSGS was higher than that of patients without FSGS (65.7% vs. 37.5%, p = 0.03). The presence of FSGS was independently associated with allograft loss in TG (hazard ratio (HR) = 3.42, 95% confidence interval (CI): 1.30-8.98, p = 0.01). Other independent predictors were proteinuria (HR = 1.18, 95% CI: 1.02-1.37, p = 0.02), estimated glomerular filtration rate (HR = 0.94, 95% CI: 0.91-0.97, p < 0.001), and panel reactive antibody (HR = 3.99, 95% CI: 1.14-13.99, p = 0.03). Moreover, FSGS (odds ratio (OR) = 4.39, 95% CI: 1.29-14.92, p = 0.02) and cg (OR = 5.36, 95% CI: 1.56-18.40, p = 0.01) were independent risk factors for proteinuria.

CONCLUSION

In this cohort of patients with TG, the presence of FSGS was strongly associated with more severe clinicopathological features and worse allograft survival.

Protective effects of honokiol against oxidative stress-induced apoptotic signaling in mouse podocytes treated with H2O2

Honokiol (HNK), an important bioactive compound purified from Magnolia officinalis Cortex, has been demonstrated to have manifold beneficial anti-oxidative, anti-inflammatory, anti-bacterial and antitumor pharmacological effects. In the present study, the association of HNK in the signaling mechanism associated with hydrogen peroxide (H₂O₂)-induced apoptosis of cultured mouse podocytes was investigated. HNK did not cause significant changes in podocyte viability when its concentration remained below 20 µM. MTS assay and flow cytometry confirmed that H₂O₂ significantly enhanced the rates of apoptosis while produce significant reduction in viability of podocytes. Following 24 h of pre-treatment with different concentrations of HNK, the viability of adherent podocytes increased and apoptosis significantly decreased in a dose-dependent manner below 20 µM. Reverse transcription-polymerase chain reaction and western blot results indicated that HNK significantly decreased the expression of mRNA and cleaved protein of caspase-3 and caspase-9 in podocytes pre-treated with H₂O₂. Furthermore, phosphorylation of the signaling molecules protein kinase B (Akt) and extracellular signal-regulated kinase (Erk) 1/2 appeared to increase following HNK treatment. In conclusion, HNK largely eliminated the role of promoting podocyte apoptosis in an oxidative stress environment, which was a protective factor on podocytes cultured with H₂O₂. The anti-oxidative stress mechanisms of HNK are partly due to suppressing the expression of caspase-3 and caspase-9 and upregulating phosphorylated-Akt and -Erk 1/2.

Autophagy in kidney transplants of sirolimus treated recipients

Background

Mammalian target of rapamycin (mTOR) inhibitors are increasingly used as immunosuppressive agents in kidney transplantation. In the experimental setting it has been shown that mTOR inhibitors promote autophagy, but the concept that this might also occur in transplant patients has not been addressed.

Objectives

This study was designed to investigate the association between mTOR inhibition and autophagy in renal transplants under routine clinical conditions.

Materials and Methods

Protocol transplant biopsies of patients receiving sirolimus were compared to biopsies of patients treated without mTOR inhibitor. Electron microscopy was used for quantitative stereological analysis of autophagosomal volume fractions. Ultrastructural analysis was focused on podocytes to avoid cell type bias. Autophagy-related gene products were profiled by QPCR from laser assisted microdissected glomeruli and by immunohistochemistry for semiquantitative evaluation.

Results

By electron microscopy, we observed a significant > 50% increase in podocytic autophagosomal volume fractions in patients treated with sirolimus. Evaluation of biopsy material from the same patients using transcriptional profiling of laser capture microdissected glomeruli revealed no differences in autophagy-related gene expressions. Immunohistochemical evaluation of autophagic degradation product p62 was also unaltered whereas a significant increase was observed in podocytic LC3 positivity in biopsies of sirolimus treated patients.

Conclusions

These results indicate an association of sirolimus treatment and autophagosome formation in transplant patients. However, they might reflect autophagosomal buildup rather than increased autophagic flux. Further research is needed to investigate the potential functional consequences in short- and long-term outcome of patients treated with mTOR inhibitors.

Significance of the urokinase-type plasminogen activator and its receptor in the progression of focal segmental glomerulosclerosis in clinical and mouse models

Background

suPAR biomarker generally considered a pathogenic factor in FSGS. However, studies have been published that dispute this conclusion. The current study was designed to investigate the roles of uPA and suPAR in FSGS in clinical and mouse models.

Methods

Clinical subjects including those with biopsy-proven FSGS and MCD were enrolled. To verify the role of uPA in FSGS, Adriamycin was used to induce FSGS in uPA knockout (uPA^−/−) and BALB/c (WT) mice. Proteinuria and suPAR, the cleaved/intact forms of the circulating suPAR, and possible proteases involving cleavage of the suPAR were also studied.

Results

FSGS clinical cases presented significantly higher serum levels of suPAR and Cr and lower serum levels of uPA. In the mice model, the uPA^−/− group exhibited faster disease progression and worsening proteinuria than the WT group. In addition, the uPA^−/− group had higher plasma suPAR levels, glomerular cell apoptosis, and dysregulation of the Th1/Th2 balance. In an analysis of suPAR variants in FSGS, both the intact and cleaved forms of the suPAR were higher in clinical subjects and the mouse model. However, the process of suPAR cleavage was not mediated by enzymatic activities of the uPA, elastase, or cathepsin G.

Conclusions

A deficiency of uPA accelerated the progression of Adriamycin-induced mouse FSGS model. Decrease of serum uPA levels may be an indicator of the progression of FSGS in clinical subjects and animal models.

The two kidney to one kidney transition and transplant glomerulopathy: a podocyte perspective

The attrition rate of functioning allografts beyond the first year has not improved despite improved immunosuppression, suggesting that nonimmune mechanisms could be involved. Notably, glomerulopathies may account for about 40% of failed kidney allografts beyond the first year of engraftment, and glomerulosclerosis and progression to ESRD are caused by podocyte depletion. Model systems demonstrate that nephrectomy can precipitate hypertrophic podocyte stress that triggers progressive podocyte depletion leading to ESRD, and that this process is accompanied by accelerated podocyte detachment that can be measured in urine. Here, we show that kidney transplantation "reverse nephrectomy" is also associated with podocyte hypertrophy and increased podocyte detachment. Patients with stable normal allograft function and no proteinuria had levels of podocyte detachment similar to levels in two-kidney controls as measured by urine podocyte assay. By contrast, patients who developed transplant glomerulopathy had 10- to 20-fold increased levels of podocyte detachment. Morphometric studies showed that a subset of these patients developed reduced glomerular podocyte density within 2 years of transplantation due to reduced podocyte number per glomerulus. A second subset developed glomerulopathy by an average of 10 years after transplantation due to reduced glomerular podocyte number and glomerular tuft enlargement. Reduced podocyte density was associated with reduced eGFR, glomerulosclerosis, and proteinuria. These data are compatible with the hypothesis that podocyte depletion contributes to allograft failure and reduced allograft half-life. Mechanisms may include immune-driven processes affecting the podocyte or other cells and/or hypertrophy-induced podocyte stress causing accelerated podocyte detachment, which would be amenable to nonimmune therapeutic targeting.

Glomerular mRNA expression of prothrombotic and antithrombotic factors in renal transplants with thrombotic microangiopathy

BACKGROUND

Thrombotic microangiopathy (TMA) in renal transplants (rTx-TMA) is a serious complication and is usually either recurrent TMA (RecTMA) due to humoral rejection (HR-TMA) or due to calcineurin inhibitor toxicity (CNI-TMA). Although the triggers are known, our knowledge about the thrombogenic transcriptome changes in the microvessels is rudimentary.

METHODS

We examined the expression of several prothrombotic and antithrombotic genes in 25 biopsies with rTx-TMA (6 RecTMA, 9 HR-TMA, and 10 CNI-TMA) and 8 controls. RNA from microdissected glomeruli of paraffin-embedded tissue was isolated and mRNA transcripts were quantified with real-time polymerase chain reaction after preamplification. Results were correlated with clinicopathologic parameters.

RESULTS

Glomerular mRNA expression of KLF2, KLF4, and tPA was lower and that of PAI-1 was higher in rTx-TMA than in the controls. Glomerular mRNA expression of KLF2 and KLF4 correlated with that of tPA and inversely with that of PAI-1 in rTx-TMA. The mRNA expression of complement regulators CD46 and CD59 were higher in rTx-TMA than in the controls. Only in HR-TMA were glomerular ADAMTS13 and CD55 down-regulated.

CONCLUSIONS

The glomerular capillary bed seems to contribute to all subtypes of rTx-TMA by down-regulation of the endothelial transcription factors KLF2 and KLF4, indicating dedifferentiation with subsequent up-regulation of PAI-1 and down-regulation of tPA, resulting in inhibition of local fibrinolysis. Decreased glomerular expression of ADAMTS13 and CD55 could be an additional pathway toward microthrombosis exclusively in HR-TMA.