Activation of necroptosis pathway in podocyte contributes to the pathogenesis of focal segmental glomerular sclerosis

Cross Talk Between Macrophages and Podocytes in Diabetic Nephropathy: Potential Mechanisms and Novel Therapeutics

Diabetic nephropathy (DN) is a leading cause of chronic kidney disease and end-stage renal failure worldwide. Podocytes, essential components of the glomerular filtration barrier (GFB), are profoundly affected in the diabetic milieu, resulting in structural and functional alterations. Concurrently, macrophages, pivotal innate immune cells, infiltrate the diabetic kidney and exhibit diverse activation states influenced by the local environment, playing a crucial role in kidney physiology and pathology. This review synthesizes current insights into how the dynamic cross talk between these two cell types contributes to the progression of DN, exploring the molecular and cellular mechanisms underlying this interaction, with a particular focus on how macrophages influence podocyte survival through various forms of cell death, including apoptosis, pyroptosis, and autophagy. The review also discusses the potential of targeting macrophages to develop more effective treatments for DN.

The mitochondrial dysfunction regulated by JAK2/STAT3 pathway leads to the necroptosis in the renal cells under patulin exposure

Patulin (PAT) is a common mycotoxin widely found in various agricultural products and fruits, which has obvious toxic effects on animals and humans. Some studies have shown that PAT can cause nephrotoxicity, but the exact mechanism remains to be elucidated. In the present study, we investigated PAT-induced nephrotoxicity and the possible molecular mechanisms involved in its action. In vivo, the results showed that PAT affected the integrity of the glomerular basement membrane and peduncles, leading to necroptosis. We further demonstrated that PAT up-regulated the expression of JAK2, STAT3, RIPK1, RIPK3, and MLKL. This observation was also confirmed in MPC-5 cells. In vitro, pretreatment with Nec-1 (a specific inhibitor of necroptosis) or si-STAT3 resulted in a significant reduction in necroptosis and improved mitochondrial dysfunction. Notably, the pharmacological protection of mitochondrial function by SS-31 significantly attenuated the onset of PAT-induced necroptosis. Taken together, our study suggested that STAT3 activation, and mitochondrial dysfunction played critical roles in PAT-induced necroptosis in the kidney. These findings revealed the mechanisms by which PAT triggered necroptosis, potentially providing a new therapeutic strategy for PAT poisoning.

Damage-Associated Molecular Patterns and Pattern Recognition Receptors in the Podocyte

Podocytes possess immune system components allowing for a variety of innate responses to endogenous and exogenous stimuli. Recently, several groups have linked inappropriate innate immune signaling to podocyte injury, particularly chronic, sustained injury; however, the immune capabilities of podocytes have not been fully elucidated. Damage-associated molecular patterns (DAMPs) are endogenous danger molecules released from damaged cells, including podocytes, and can elicit an inflammatory response and recruit immune cells to areas of injury. This is performed through binding to pattern recognition receptors. Believed largely to be protective and responsive to injury or infection, recent evidence suggests signaling through DAMP pathways can aggravate and promote chronic diseases already associated with inflammation. The purpose of this narrative review was to highlight current knowledge with respect to specific podocyte DAMPs and pattern recognition receptors and to provide insight into ongoing work and possible future research avenues to advance our understanding of podocyte immune mechanisms.

The role of inflammasomes in human diseases and their potential as therapeutic targets

Inflammasomes are large protein complexes that play a major role in sensing inflammatory signals and triggering the innate immune response. Each inflammasome complex has three major components: an upstream sensor molecule that is connected to a downstream effector protein such as caspase-1 through the adapter protein ASC. Inflammasome formation typically occurs in response to infectious agents or cellular damage. The active inflammasome then triggers caspase-1 activation, followed by the secretion of pro-inflammatory cytokines and pyroptotic cell death. Aberrant inflammasome activation and activity contribute to the development of diabetes, cancer, and several cardiovascular and neurodegenerative disorders. As a result, recent research has increasingly focused on investigating the mechanisms that regulate inflammasome assembly and activation, as well as the potential of targeting inflammasomes to treat various diseases. Multiple clinical trials are currently underway to evaluate the therapeutic potential of several distinct inflammasome-targeting therapies. Therefore, understanding how different inflammasomes contribute to disease pathology may have significant implications for developing novel therapeutic strategies. In this article, we provide a summary of the biological and pathological roles of inflammasomes in health and disease. We also highlight key evidence that suggests targeting inflammasomes could be a novel strategy for developing new disease-modifying therapies that may be effective in several conditions.

Early growth response 1 as a podocyte injury marker in human glomerular diseases

Background

In human glomerular diseases, visualizing podocyte injury is desirable since podocytes do not regenerate and podocyte injury leads to podocyte loss. Herein, we investigated the utility of immunostaining for early growth response 1 (EGR1), which is expressed in injured podocytes from the early stages of injury in animal experiments, as a podocyte injury marker in human glomerular diseases.

Methods

This study included 102 patients with biopsy-proven glomerular diseases between 2018 and 2021. The proportion of EGR1 expression in podocytes (%EGR1pod) was analyzed in relation to clinical and histopathological features, including glomerular and urinary podocyte-specific markers.

Results

%EGR1pod correlated significantly with the urinary protein:creatinine ratio, urinary nephrin and podocin mRNA levels, and glomerular podocin staining (rho = 0.361, 0.514, 0.487 and -0.417, respectively; adjusted P = .002, <.001, <.001 and <.001, respectively). Additionally, %EGR1pod correlated with cellular/fibrocellular crescents (rho = 0.479, adjusted P <.001). %EGR1pod was high in patients with glomerulonephritis, such as immunoglobulin A nephropathy (IgAN), lupus nephritis and antineutrophil cytoplasmic antibody-associated glomerulonephritis, and in those with podocytopathies, such as membranous nephropathy and primary focal segmental glomerulosclerosis, while %EGR1pod was low in patients with minimal change disease. In a subgroup analysis of IgAN, %EGR1pod was higher in Oxford C1 patients than in C0 patients. However, unexpectedly, patients with higher %EGR1pod were more prone to attain proteinuria remission, suggesting that EGR1 in the context of IgAN reflects reversible early injury.

Conclusions

Our findings indicate that EGR1 is a promising potential marker for identifying active early podocyte injury in human glomerular diseases.

Inflammasome pathway in kidney transplantation

Kidney transplantation is the best available renal replacement therapy for patients with end-stage kidney disease and is associated with better quality of life and patient survival compared with dialysis. However, despite the significant technical and pharmaceutical advances in this field, kidney transplant recipients are still characterized by reduced long-term graft survival. In fact, almost half of the patients lose their allograft after 15-20 years. Most of the conditions leading to graft loss are triggered by the activation of a large immune-inflammatory machinery. In this context, several inflammatory markers have been identified, and the deregulation of the inflammasome (NLRP3, NLRP1, NLRC4, AIM2), a multiprotein complex activated by either whole pathogens (including fungi, bacteria, and viruses) or host-derived molecules, seems to play a pivotal pathogenetic role. However, the biological mechanisms leading to inflammasome activation in patients developing post-transplant complications (including, ischemia-reperfusion injury, rejections, infections) are still largely unrecognized, and only a few research reports, reviewed in this manuscript, have addressed the association between abnormal activation of this pathway and the onset/development of major clinical effects. Finally, the regulation of the inflammasome machinery could represent in future a valuable therapeutic target in kidney transplantation.

Targeting ferroptosis attenuates podocytes injury and delays tubulointerstitial fibrosis in focal segmental glomerulosclerosis

Ferroptosis is a non-apoptotic form of cell death, involved in chronic kidney diseases (CKD) and acute kidney injury (AKI), so far, the role of ferroptosis in focal segmental glomerulosclerosis (FSGS) remains largely unknown. We aimed to investigate the role of ferroptosis in FSGS, in this study, we found the reduced expression of GPX4 in podocytes, as well as tubular epithelial cells (TECs), from patients with FSGS. Treatment with ferrostatin-1 (Fer-1), a potent and selective ferroptosis inhibitor, significantly reduced proteinuria, prevented glomerulosclerosis, attenuated podocyte injury in ADR-induced FSGS murine model. As expected, ADR treatment caused downregulation of GPX4 in human podocytes, treatment with Fer-1 greatly blocked the downregulation of GPX4, restored the GSH level and attenuated cell death. Furthermore, Fer-1 treatment greatly delayed the development of tubulointerstitial fibrosis in ADR-induced FSGS murine model. Taken together, ferroptosis is involved in the pathogenesis of FSGS, targeting ferroptosis is a promising therapeutic option for patients with FSGS.