Role of albumin and its modifications in glomerular injury

Investigation of ferroptosis-associated molecular subtypes and immunological characteristics in lupus nephritis based on artificial neural network learning

BACKGROUND

Lupus nephritis (LN) is a severe complication of systemic lupus erythematosus (SLE) with poor treatment outcomes. The role and underlying mechanisms of ferroptosis in LN remain largely unknown. We aimed to explore ferroptosis-related molecular subtypes and assess their prognostic value in LN patients.

METHODS

Molecular subtypes were classified on the basis of differentially expressed ferroptosis-related genes (FRGs) via the Consensus ClusterPlus package. The enriched functions and pathways, immune infiltrating levels, immune scores, and immune checkpoints were compared between the subgroups. A scoring algorithm based on the subtype-specific feature genes identified by artificial neural network machine learning, referred to as the NeuraLN, was established, and its immunological features, clinical value, and predictive value were evaluated in patients with LN. Finally, immunohistochemical analysis was performed to validate the expression and role of feature genes in glomerular tissues from LN patients and controls.

RESULTS

A total of 10 differentially expressed FRGs were identified, most of which showed significant correlation. Based on the 10 FRGs, LN patients were classified into two ferroptosis subtypes, which exhibited significant differences in immune cell abundances, immune scores, and immune checkpoint expression. A NeuraLN-related protective model was established based on nine subtype-specific genes, and it exhibited a robustly predictive value in LN. The nomogram and calibration curves demonstrated the clinical benefits of the protective model. The high-NeuraLN group was closely associated with immune activation. Clinical specimens demonstrated the alterations of ALB, BHMT, GAMT, GSTA1, and HAO2 were in accordance with bioinformatics analysis results, GSTA1 and BHMT were negatively correlated with the severity of LN.

CONCLUSION

The classification of ferroptosis subtypes and the establishment of a protective model may form a foundation for the personalized treatment of LN patients.

Cardiotrophin-1 therapy reduces disease severity in a murine model of glomerular disease

Cardiotrophin-1 (CT-1), a member of the interleukin (IL)-6 cytokine family, has renoprotective effects in mouse models of acute kidney disease and tubulointerstitial fibrosis, but its role in glomerular disease is unknown. To address this, we used the mouse model of nephrotoxic nephritis to test the hypothesis that CT-1 also has a protective role in immune-mediated glomerular disease. Using immunohistochemistry and analysis of single-cell RNA-sequencing data of isolated glomeruli, we demonstrate that CT-1 is expressed in the glomerulus in male mice, predominantly in parietal epithelial cells and is downregulated in mice with nephrotoxic nephritis. Furthermore, analysis of data from patients revealed that human glomerular disease is also associated with reduced glomerular CT-1 transcript levels. In male mice with nephrotoxic nephritis and established proteinuria, administration of CT-1 resulted in reduced albuminuria, prevented podocyte loss, and sustained plasma creatinine, compared with mice administered saline. CT-1 treatment also reduced fibrosis in the kidney cortex, peri-glomerular macrophage accumulation and the kidney levels of the pro-inflammatory mediator complement component 5a. In conclusion, CT-1 intervention therapy delays the progression of glomerular disease in mice by preserving kidney function and inhibiting renal inflammation and fibrosis.

Profound Changes in Functional Structure and Dynamics of Serum Albumin in Children with Nephrotic Syndrome: An Exploratory Research Study

Patients with nephrotic syndrome (NS) suffer from urinary loss of albumin. As a cause, previous studies focused on the glomerular filter rather than analyzing the molecular properties of albumin itself. Later one was initiated by clinical observations indicating unexplained molecular alterations of human serum albumin (HSA) in an NS pediatric patient. Therefore, we examined serum from eight pediatric patients with steroid-sensitive and -resistant NS and compared it with serum from healthy subjects as well as commercial HSA. We used dynamic and electrophoretic light scattering to characterize the protein size and effective surface charge and electron paramagnetic resonance spectroscopy to measure the local environment and binding dynamics of up to seven fatty acids associated with HSA. Our findings suggest that pronounced differences in binding behavior and surface charge of HSA could enhance their filtration through the GBM, leading to direct toxicity of HSA to podocytes.

Modes of podocyte death in diabetic kidney disease: an update

Diabetic kidney disease (DKD) accounts for a large proportion of end-stage renal diseases that require renal replacement therapies including dialysis and transplantation. Therefore, it is critical to understand the occurrence and development of DKD. Podocytes are mainly injured during the development of DKD, ultimately leading to their extensive death and loss. In turn, the injury and death of glomerular podocytes are also the main culprits of DKD. This review introduces the characteristics of podocytes and summarizes the modes of their death in DKD, including apoptosis, autophagy, mitotic catastrophe (MC), anoikis, necroptosis, and pyroptosis. Apoptosis is characterized by nuclear condensation and the formation of apoptotic bodies, and it exerts a different effect from autophagy in mediating DKD-induced podocyte loss. MC mediates a faulty mitotic process while anoikis separates podocytes from the basement membrane. Moreover, pyroptosis activates inflammatory factors to aggravate podocyte injuries whilst necroptosis drives signaling cascades, such as receptor-interacting protein kinases 1 and 3 and mixed lineage kinase domain-like, ultimately promoting the death of podocytes. In conclusion, a thorough knowledge of the modes of podocyte death in DKD can help us understand the development of DKD and lay the foundation for strategies in DKD disease therapy.

Overexpression of Myo1e promotes albumin endocytosis by mouse glomerular podocytes mediated by Dynamin

Background

As a fundamental process internalizing molecules from the plasma membrane, endocytosis plays a crucial role in podocyte biology. Our previous study has identified that overexpression of Myole may enhance podocyte endocytosis. However, its potential mechanism has been not well understand. Thus, we aimed to analyze whether albumin endocytosis by mouse glomerular podocytes is dependent on Myo1e expression. Also, we aimed to elucidate whether the underlying mechanism is mediated by Dynamin.

Methods

Firstly, mouse podocyte cells (MPC5) were treated with different concentrations of FITC-bovine serum albumin (BSA). The fluorescence intensity and cell viability were detected by flow cytometry and MTT assays, respectively. Afterwards, the optimal concentration of FITC-BSA was determined. Secondly, MPC5 cells were treated with Myole overexpression or knockdown. Cell morphology was observed under microscope. Immunofluorescence assay was used to determine the expression of F-actin. The protein expression of nephrin and podocin was detected by western blot. Flow cytometry was used to detect MPC5 cell apoptosis with annexin V. Finally, MPC5 cells were treated with Myole overexpression and/or Dynasore (a GTPase inhibitor of Dynamin). The fluorescence intensity was detected using flow cytometry assay.

Results

MPC5 endocytosis BSA was elevated with a concentration-dependent manner. MTT results showed that MPC5 cell viability was inhibited with a concentration-dependent manner. Myo1e overexpression promoted podocyte endocytic FITC-BSA, which was contrary to its knockdown. Under microscope, after inhibition of Myo1e, podocyte foot process fusion was observed. Myo1e overexpression promoted the expression of cytoskeleton F-actin and podocyte-specific molecules (nephrin and podocin) in podocyte endocytic FITC-BSA. Furthermore, we found that Myo1e promoted the apoptosis of podocytes. Dynasore attenuated the increase in endocytosis of FITC-BSA induced by Myo1e overexpression, suggesting that podocytes might mediate albumin endocytosis via Myo1e-Dynamin-Albumin.

Conclusion

Our findings revealed that overexpression of Myo1e promotes albumin endocytosis in mouse glomerular podocyte endocytic albumin mediated by Dynamin.

A next generation setup for pre-fractionation of non-denatured proteins reveals diverse albumin proteoforms each carrying several post-translational modifications

Proteomic biomarker search requires the greatest analytical reproducibility and detailed information on altered proteoforms. Our protein pre-fractionation applies orthogonal native chromatography and conserves important features of protein variants such as native molecular weight, charge and major glycans. Moreover, we maximized reproducibility of sample pre-fractionation and preparation before mass spectrometry by parallelization and automation. In blood plasma and cerebrospinal fluid (CSF), most proteins, including candidate biomarkers, distribute into a multitude of chromatographic clusters. Plasma albumin, for example, divides into 15-17 clusters. As an example of our technique, we analyzed these albumin clusters from healthy volunteers and from dogs and identified cluster-typical modification patterns. Renal disease further modifies these patterns. In human CSF, we found only a subset of proteoforms with fewer modifications than in plasma. We infer from this example that our method can be used to identify and characterize distinct proteoforms and, optionally, enrich them, thereby yielding the characteristics of proteoform-selective biomarkers.