Implementation of a human podocyte injury model of chronic kidney disease for profiling of renoprotective compounds

Molecular signaling pathways in doxorubicin-induced nephrotoxicity and potential therapeutic agents

Doxorubicin (DOX), an anthracycline chemotherapeutic agent, is extensively utilized in the clinical management of both solid and hematological malignancies. Nevertheless, the clinical application of this treatment is significantly limited by adverse reactions and toxicity that may arise during or after administration. Its cytotoxic effects are multifaceted, with cardiotoxicity being the most prevalent side effect. Furthermore, it has the potential to adversely affect other organs, including the brain, kidneys, liver, and so on. Notably, it has been reported that DOX may cause renal failure in patients and there is currently no effective treatment for DOX-induced kidney damage, which has raised a high concern about DOX-induced nephrotoxicity (DIN). Although the precise molecular mechanisms underlying DIN remain incompletely elucidated, prior research has indicated that reactive oxygen species (ROS) are pivotal in this process, triggering a cascade of detrimental pathways including apoptosis, inflammation, dysregulated autophagic flux, and fibrosis. In light of these mechanisms, decades of research have uncovered several DIN-associated signaling pathways and found multiple potential therapeutic agents targeting them. Thus, this review intends to delineate the DIN associated signaling pathways, including AMPK, JAKs/STATs, TRPC6/RhoA/ROCK1, YAP/TEAD, SIRTs, Wnt/β-catenin, TGF-β/Smad, MAPK, Nrf2/ARE, NF-κB, and PI3K/AKT, and to summarize their potential regulatory agents, which provide a reference for the development of novel medicines against DIN.

PODO/TERT256 - A promising human immortalized podocyte cell line and its potential use for in vitro research at different oxygen levels

Podocytes are of key interest for the prediction of nephrotoxicity as they are especially sensitive to toxic insults due to their central role in the glomerular filtration apparatus. However, currently, prediction of nephrotoxicity in humans remains insufficiently reliable, thus highlighting the need for advanced in vitro model systems using human cells with improved prediction capacity. Recent approaches for refining in vitro model systems focus on closely replicating physiological conditions as observed under the in vivo situation typical of the respective nephron section of interest. PODO/TERT256, a human immortalized podocyte cell line, were employed in a semi-static transwell system to evaluate its potential use as a human podocyte in vitro system for modelling potential human glomerular toxicity. Furthermore, the impact of routinely employed excessive oxygen tension (21 % - AtmOx), when compared to the physiological oxygen tensions (10 % - PhysOx) observed in vivo, was analyzed. Generally, cultured PODO/TERT256 formed a stable, contact-inhibited monolayer with typical podocyte morphology (large cell body, apical microvilli, finger-like cytoplasmic projections (reminiscent of foot processes), and interdigitating cell-cell junctions) and developed a size-selective filtration barrier. PhysOx, however, induced a more pronounced in vivo like phenotype, comprised of significantly larger cell bodies, significantly enhanced filtration barrier size-selectivity, and a remarkable re-localization of nephrin to the cell membrane, thus suggesting an improved in vitro replication of in vivo characteristics. Preliminary toxicity characterization with the known glomerulotoxin doxorubicin (DOX) suggested an increasing change in filtration permeability, already at the lowest DOX concentrations tested (0.01 μM) under PhysOx, whereas obvious changes under AtmOx were observed as of 0.16 μM and higher with a near all or nothing effect. The latter findings suggested that PODO/TERT256 could serve as an in vitro human podocyte model for studying glomerulotoxicity, whereby culturing at PhyOx tension appeared critical for an improved in vivo-like phenotype and functionality. Moreover, PODO/TERT256 could be incorporated into advanced human glomerulus systems in vitro, recapitulating microfluidic conditions and multiple cell types (endothelial and mesenchymal cells) that can even better predict human glomerular toxicity.

Laminaria japonica polysaccharide attenuates podocyte epithelial-mesenchymal transformation via TGF-β1-mediated Smad3 and p38MAPK pathways

In the present work, we explored the interventional effect and potential mechanism of a purified Laminaria japonica polysaccharide (LJP61A) on podocyte epithelial-mesenchymal transition (EMT) in TGF-β1-induced podocytes and adriamycin-treated mice. Results showed that compared to the model groups, LJP61A significantly up-regulated the levels of epithelial markers (Nephrin, WT-1, podocin) and down-regulated the levels of mesenchymal markers (α-SMA, FN1) in vitro and in vivo, thus preventing EMT-like morphological changes of podocytes, proteinuria and kidney injury. Smad3 and p38MAPK are two central pathways mediating podocyte EMT activated by TGF-β1. We found that LJP61A suppressed TGF-β1-induced activation of Smad3, Smad4 and p38MAPK in vitro and in vivo. Moreover, the inhibitory actions of LJP61A on podocyte EMT were synergistically strengthened by Smad3 inhibitor SIS3 and p38MAPK inhibitor SB203580. Taken together, these findings revealed that LJP61A could prevent podocyte EMT, which might be related to the inhibition of TGF-β1-mediated Smad3 and p38MAPK pathways.

Biochemical composition of the glomerular extracellular matrix in patients with diabetic kidney disease

In the glomeruli, mesangial cells produce mesangial matrix while podocytes wrap glomerular capillaries with cellular extensions named foot processes and tether the glomerular basement membrane (GBM). The turnover of the mature GBM and the ability of adult podocytes to repair injured GBM are unclear. The actin cytoskeleton is a major cytoplasmic component of podocyte foot processes and links the cell to the GBM. Predominant components of the normal glomerular extracellular matrix (ECM) include glycosaminoglycans, proteoglycans, laminins, fibronectin-1, and several types of collagen. In patients with diabetes, multiorgan composition of extracellular tissues is anomalous, including the kidney, so that the constitution and arrangement of glomerular ECM is profoundly altered. In patients with diabetic kidney disease (DKD), the global quantity of glomerular ECM is increased. The level of sulfated proteoglycans is reduced while hyaluronic acid is augmented, compared to control subjects. The concentration of mesangial fibronectin-1 varies depending on the stage of DKD. Mesangial type III collagen is abundant in patients with DKD, unlike normal kidneys. The amount of type V and type VI collagens is higher in DKD and increases with the progression of the disease. The GBM contains lower amount of type IV collagen in DKD compared to normal tissue. Further, genetic variants in the α3 chain of type IV collagen may modulate susceptibility to DKD and end-stage kidney disease. Human cellular models of glomerular cells, analyses of human glomerular proteome, and improved microscopy procedures have been developed to investigate the molecular composition and organization of the human glomerular ECM.

How Qualification of 3D Disease Models Cuts the Gordian Knot in Preclinical Drug Development

Preclinical research struggles with its predictive power for drug effects in patients. The clinical success of preclinically approved drug candidates ranges between 3% and 33%. Regardless of the approach, novel disease models and test methods need to prove their relevance and reliability for predicting drug effects in patients, which is usually achieved by method validation. Nevertheless, validating all models appears unrealistic due to the variety of diseases. Thus, novel concepts are needed to increase the quality of preclinical research.Herein, we introduce qualification as a minimal standard to establish the relevance of preclinical models and test methods. Qualification starts with prioritizing and translating scientific requirements into technical parameters by quality function deployment. Qualified models use authenticated cells, which resemble the corresponding cells in humans in morphology and drug target expression. Moreover, disease models differ from normal models in the expression of relevant biomarkers. As a result, qualified test methods can discriminate effects of treatment standards and the effects of weakly effective or ineffective substances. Observer-blind readout, adequate data documentation, dropout inclusion, and a priori power studies are as crucial as realistic dosage regimens for qualified approaches. Here, we showcase the implementation of qualification. Adjusting the level of model complexity and qualification to three defined phases of preclinical research assures the optimal level of certainty at each step.In conclusion, qualification strengthens the researchers' impact by defining basic requirements that novel approaches must fulfill while still allowing for scientific creativity. Qualification helps to improve the predictive power of preclinical research. Applied to human cell-based models, qualification reduces animal testing, since only effective drug candidates are subjected to final animal testing and subsequently to clinical trials.

Further Evidence That the Soluble Urokinase Plasminogen Activator Receptor Does Not Directly Injure Mice or Human Podocytes

BACKGROUND

The role of the soluble urokinase plasminogen activator receptor (suPAR) in focal segmental glomerulosclerosis (FSGS) as the circulating factor or as a predictor of recurrence after transplantation remains controversial. Previously published studies in mice and isolated podocytes produced conflicting results on the effect of suPAR on podocyte injury, effacement of foot processes, and proteinuria. These discordant results were in part due to diverse experimental designs and different strains of mice. The aim of our study was to determine the reasons for the inconsistencies of the previous studies results with suPAR by using uniform methods and studies in different strains of mice.

METHODS

We utilized a primary culture of human podocytes and 2 mouse models, the wild type (WT) and the urokinase plasminogen activator receptor (uPAR) KO (uPAR), in an attempt to resolve the reported conflicting results.

RESULTS

In both WT and uPAR mouse models, injection of recombinant uPAR, even at a high dose (100 μg), did not induce proteinuria, effacement of podocytes, or disruption of the cytoskeleton. Injection of suPAR resulted in its deposition exclusively in the glomerular endothelial cells and not in the podocytes of WT mice and was not detected at the uPAR KO mice. Kidneys from patients with recurrent FSGS had negative immunostaining for uPAR. We also evaluated the effect of recombinant uPAR on primary culture of human podocytes. uPAR did not result in podocytes damage.

CONCLUSIONS

suPAR by itself is not the cause for direct podocyte injury, in vitro or in vivo. These findings suggest a more complex and still poorly understood role of suPAR in FSGS.

Oestrogen inhibits PTPRO to prevent the apoptosis of renal podocytes

Podocytes are a major component of the glomerular filtration membrane, and their apoptosis is involved in a variety of nephrotic syndromes. In the current study, the effects and molecular mechanisms of oestrogen on the proliferation and apoptosis of podocytes were investigated to elucidate the role of oestrogen in the pathogenesis of childhood nephrotic syndrome. The cell proliferation of mouse renal podocytes (MPC-5) and human primary renal podocytes was promoted by 17β-oestradiol (E2) in what appear to be a time-dependent manner. Apoptosis was inhibited by E2 and promoted by the E2 antagonist, tamoxifen. The expression of protein tyrosine phosphatase receptor type O (PTPRO) decreased with the increasing dosage of E2, but increased with the increasing dosage tamoxifen in MPC-5 and human podocytes. The protein, oestrogen receptor (ER)α, was not expressed in MPC-5 and human podocytes. E2 binding to ERβ completely eliminated PTPRO expression in MPC-5. In podocytes, PTPRO was phosphorylated by E2 at the Y1007 and associated with tyrosine-protein kinase JAK2 (JAK2) activation, rather than JAK1 activation. PTPRO was involved in the binding of E2 to signal transducer and activator of transcription (STAT)3 at the Y705 and S727 sites, resulting in the phosphorylation of STAT3 in podocytes. Through PTPRO, E2 also regulated the proliferation and apoptosis of podocytes. In conclusion, oestrogen binding to ERβ, rather than ERα, promoted the proliferation of podocytes and inhibited the apoptosis of podocytes by inhibiting the expression of PTPRO. The mechanism may be associated with the activation of the JAK2/STAT3 signalling pathway. The current study may provide a novel direction for the treatment of childhood nephrotic syndrome.