Novel role of Vav1-Rac1 pathway in actin cytoskeleton regulation in interleukin-13-induced minimal change-like nephropathy

Canonical effects of cytokines on glomerulonephritis: A new outlook in nephrology

Glomerulonephritis (GN) is an important cause of renal inflammation resulting from kidney-targeted adaptive and innate immune responses and consequent glomerular damage. Given the lack of autoantibodies, immune complexes, or the infiltrating immune cells in some forms of GN, for example, focal segmental glomerulosclerosis and minimal change disease, along with paraneoplastic syndrome and a special form of renal involvement in some viral infections, the likeliest causative scenario would be secreted factors, mainly cytokine(s). Since cytokines can modulate the inflammatory mechanisms, severity, and clinical outcomes of GN, it is rational to consider the umbrella term of cytokine GN as a new outlook to reclassify a group of previously known GN. We focus here, particularly, on cytokines that have the central "canonical effect" in the development of GN.

Proteomic Analysis of Prehypertensive and Hypertensive Patients: Exploring the Role of the Actin Cytoskeleton

Hypertension is a pervasive and widespread health condition that poses a significant risk factor for cardiovascular disease, which includes conditions such as heart attack, stroke, and heart failure. Despite its widespread occurrence, the exact cause of hypertension remains unknown, and the mechanisms underlying the progression from prehypertension to hypertension require further investigation. Recent proteomic studies have shown promising results in uncovering potential biomarkers related to disease development. In this study, serum proteomic data collected from Qatar Biobank were analyzed to identify altered protein expression between individuals with normal blood pressure, prehypertension, and hypertension and to elucidate the biological pathways contributing to this disease. The results revealed a cluster of proteins, including the SRC family, CAMK2B, CAMK2D, TEC, GSK3, VAV, and RAC, which were markedly upregulated in patients with hypertension compared to those with prehypertension (fold change ≥ 1.6 or ≤-1.6, area under the curve ≥ 0.8, and q-value < 0.05). Pathway analysis showed that the majority of these proteins play a role in actin cytoskeleton remodeling. Actin cytoskeleton reorganization affects various biological processes that contribute to the maintenance of blood pressure, including vascular tone, endothelial function, cellular signaling, inflammation, fibrosis, and mechanosensing. Therefore, the findings of this study suggest a potential novel role of actin cytoskeleton-related proteins in the progression from prehypertension to hypertension. The present study sheds light on the underlying pathological mechanisms involved in hypertension and could pave the way for new diagnostic and therapeutic approaches for the treatment of this disease.

Swollen Feet: Considering the Paradoxical Roles of Interleukins in Nephrotic Syndrome

Interleukins are a family of 40 bioactive peptides that act through cell surface receptors to induce a variety of intracellular responses. While interleukins are most commonly associated with destructive, pro-inflammatory signaling in cells, some also play a role in promoting cellular resilience and survival. This review will highlight recent evidence of the cytoprotective actions of the interleukin 1 receptor (IL-1R)- and common gamma chain receptor (IL-Rγc)-signaling cytokines in nephrotic syndrome (NS). NS results from the injury or loss of glomerular visceral epithelial cells (i.e., podocytes). Although the causes of podocyte dysfunction vary, it is clear that pro-inflammatory cytokines play a significant role in regulating the propagation, duration and severity of disease. Pro-inflammatory cytokines signaling through IL-1R and IL-Rγc have been shown to exert anti-apoptotic effects in podocytes through the phosphoinositol-3-kinase (PI-3K)/AKT pathway, highlighting the potential utility of IL-1R- and IL-Rγc-signaling interleukins for the treatment of podocytopathy in NS. The paradoxical role of interleukins as drivers and mitigators of podocyte injury is complex and ill-defined. Emerging evidence of the cytoprotective role of some interleukins in NS highlights the urgent need for a nuanced understanding of their pro-survival benefits and reveals their potential as podocyte-sparing therapeutics for NS.

Rho GTPases in kidney physiology and diseases

Rho family GTPases are molecular switches best known for their pivotal role in dynamic regulation of the actin cytoskeleton, but also of cellular morphology, motility, adhesion and proliferation. The prototypic members of this family (RhoA, Rac1 and Cdc42) also contribute to the normal kidney function and play important roles in the structure and function of various kidney cells including tubular epithelial cells, mesangial cells and podocytes. The kidney's vital filtration function depends on the structural integrity of the glomerulus, the proximal portion of the nephron. Within the glomerulus, the architecturally actin-based cytoskeleton podocyte forms the final cellular barrier to filtration. The glomerulus appears as a highly dynamic signalling hub that is capable of integrating intracellular cues from its individual structural components. Dynamic regulation of the podocyte cytoskeleton is required for efficient barrier function of the kidney. As master regulators of actin cytoskeletal dynamics, Rho GTPases are therefore of critical importance for sustained kidney barrier function. Dysregulated activities of the Rho GTPases and of their effectors are implicated in the pathogenesis of both hereditary and idiopathic forms of kidney diseases. Diabetic nephropathy is a progressive kidney disease that is caused by injury to kidney glomeruli. High glucose activates RhoA/Rho-kinase in mesangial cells, leading to excessive extracellular matrix production (glomerulosclerosis). This RhoA/Rho-kinase pathway also seems involved in the post-transplant hypertension frequently observed during treatment with calcineurin inhibitors, whereas Rac1 activation was observed in post-transplant ischaemic acute kidney injury.

Low regulatory T-cells: A distinct immunological subgroup in minimal change nephrotic syndrome with early relapse following rituximab therapy

Rituximab is an important second line therapy in difficult nephrotic syndrome (NS), especially given toxicity of long-term glucocorticoid or calcineurin inhibitor (CNI) use. However, clinical response to rituximab is heterogenous. We hypothesized that this was underpinned by immunological differences amongst patients with NS. We recruited a cohort of 18 subjects with glucocorticoid-dependent or glucocorticoid-resistant childhood-onset minimal change NS who received rituximab either due to CNI nephrotoxicity, or due to persistent glucocorticoid toxicity with inadequate response to cyclophosphamide or CNIs. Immunological subsets, T-cell activation assays and plasma cytokines were measured at baseline and 6-months post-rituximab. Time to relapse was bifurcated: 56% relapsed within one year ("early relapse"), while the other 44% entered remission mainly lasting ≥3 years ("sustained remission"). At baseline, early relapse compared to sustained remission group had lower regulatory T-cells (Tregs) [2.94 (2.25, 3.33)% vs 6.48 (5.08, 7.24)%, P<0.001], PMA-stimulated IL-2 [0.03 (0, 1.85)% vs 4.78 (0.90, 9.18)%, P=0.014] and IFNγ [2.22 (0.18, 6.89)% vs 9.47 (2.72, 17.0)%, P=0.035] levels. Lower baseline Treg strongly predicted early relapse (ROC-AUC 0.99, 95% CI 0.97-1.00, P<0.001). There were no differences in baseline plasma cytokine levels. Following rituximab, there was significant downregulation of Th2 cytokines in sustained remission group (P=0.038). In particular, IL-13 showed a significant decrease in sustained remission group [-0.56 (-0.64, -0.35)pg/ml, P=0.007)], but not in the early relapse group. In conclusion, early relapse following rituximab is associated with baseline reductions in Treg and T-cell hyporesponsiveness, which suggest chronic T-cell activation and may be useful predictive biomarkers. Sustained remission, on the other hand, is associated with downregulation of Th2 cytokines following rituximab.

A review of nephrotic syndrome and atopic diseases in children

Pediatric nephrotic syndrome (NS) is a common and recurrent glomerular disease in childhood. Furthermore, 50–70% of children with NS have increased total IgE in peripheral blood and a variety of clinical manifestations of atopic diseases. Hence, NS has many similarities with atopic diseases. However, no study has revealed a clear link between these two diseases. The present review discusses the correlation between pediatric NS and atopic diseases in children from three aspects: pathogenesis, cytokine change, and treatment. There are similar changes in T cells in terms of pathogenesis, with Th1/Th2 dysfunction and Treg cell function downregulation. Cytokine changes are similar and manifest as an increase in Th2 cytokines, TNF-α and TGF-β1, and a decrease in IL-10. Glucocorticoids, immunosuppressants and biological agents are used for the treatment of these two diseases. Therefore, it was speculated that NS and atopic diseases may be the same kind of disease, have a similar pathogenesis, and only exhibit different clinical manifestations due to different affected parts of the disease.

IL-13-driven alterations in hepatic cholesterol handling contributes to hypercholesterolemia in a rat model of minimal change disease

Circulating factors have been implicated in the pathogenesis of minimal change disease (MCD), and may have direct effects on cholesterol metabolism. This study investigated the pathogenesis of hypercholesterolemia in an IL-13 overexpression rat model of MCD prior to the onset of proteinuria, so as to establish the direct contribution of IL-13, especially with regard to hepatic cholesterol handling. In this model of MCD, the temporal relationship between hypercholesterolemia and proteinuria was first identified. Plasma proprotein convertase subtilisin/kexin type 9 (Pcsk9) and liver ATP-binding cassette sub-family G member 5 (Abcg5) were measured using ELISA. Liver Ldlr and liver X receptor alpha (Lxra) were quantified with Western blot. Abcg5-mediated cholesterol efflux in IL-13-stimulated rat primary hepatocytes was measured using taurocholate as cholesterol acceptor. The role of Lxra was validated using a luciferase assay in Lxre-luciferase-transfected IL-13-stimulated hepatocytes. IL-13-transfected rats developed hypercholesterolemia prior to proteinuria, with 35% of rats hypercholesterolemic but only 11% proteinuric by Day 20 (P = 0.04). These pre-proteinuric hypercholesterolemic rats showed elevations in total and LDL-cholesterol, but not hypertriglyceridemia or hepatic steatosis. The hypercholesterolemia was associated with increased hepatic Pcsk9 synthesis and enhanced circulating Pcsk9 levels, which correlated strongly with plasma total cholesterol (r = 0.73, P&lt;0.001). The hypercholesterolemia was also contributed by decreased Abcg5 expression and activity, due to reduced Lxra expression. Lxra expression correlated with plasma total cholesterol levels (r = −0.52, P = 0.01), and overexpression of pLxra in rat hepatocytes abrogated the IL-13-mediated down-regulation of Lxre-driven gene expression. In conclusion, we have shown that IL-13 induced changes in hepatic cholesterol handling in a cytokine-induced rat model of MCD, resulting in hypercholesterolemia which can precede the onset of proteinuria.

The Role of Trio, a Rho Guanine Nucleotide Exchange Factor, in Glomerular Podocytes

Nephrotic syndrome is a kidney disease featured by heavy proteinuria. It is caused by injury to the specialized epithelial cells called “podocytes” within the filtration unit of the kidney, glomerulus. Previous studies showed that hyperactivation of the RhoGTPase, Rac1, in podocytes causes podocyte injury and glomerulosclerosis (accumulation of extracellular matrix in the glomerulus). However, the mechanism by which Rac1 is activated during podocyte injury is unknown. Trio is a guanine nucleotide exchange factor (GEF) known to activate Rac1. By RNA-sequencing, we found that Trio mRNA is abundantly expressed in cultured human podocytes. Trio mRNA was also significantly upregulated in humans with minimal change disease and focal segmental glomerulosclerosis, two representative causes of nephrotic syndrome. Reduced expression of Trio in cultured human podocytes decreased basal Rac1 activity, cell size, attachment to laminin, and motility. Furthermore, while the pro-fibrotic cytokine, transforming growth factor β1 increased Rac1 activity in control cells, it decreases Rac1 activity in cells with reduced Trio expression. This was likely due to simultaneous activation of the Rac1-GTPase activation protein, CdGAP. Thus, Trio is important in the basal functions of podocytes and may also contribute to glomerular pathology, such as sclerosis, via Rac1 activation.

Synaptopodin is upregulated by IL-13 in eosinophilic esophagitis and regulates esophageal epithelial cell motility and barrier integrity

Eosinophilic esophagitis (EoE) is an allergic inflammatory disease of the esophagus mediated by an IL-13-driven epithelial cell transcriptional program. Herein, we show that the cytoskeletal protein synaptopodin (SYNPO), previously associated with podocytes, is constitutively expressed in esophageal epithelium and induced during allergic inflammation. In addition, we show that the SYNPO gene is transcriptionally and epigenetically regulated by IL-13 in esophageal epithelial cells. SYNPO was expressed in the basal layer of homeostatic esophageal epithelium, colocalized with actin filaments, and expanded into the suprabasal epithelium in EoE patients, where expression was elevated 25-fold compared with control individuals. The expression level of SYNPO in esophageal biopsies correlated with esophageal eosinophil density and was improved following anti-IL-13 treatment in EoE patients. In esophageal epithelial cells, SYNPO gene silencing reduced epithelial motility in a wound healing model, whereas SYNPO overexpression impaired epithelial barrier integrity and reduced esophageal differentiation. Taken together, we demonstrate that SYNPO is induced by IL-13 in vitro and in vivo, is a nonredundant regulator of epithelial cell barrier function and motility, and is likely involved in EoE pathogenesis.