A potential defensive role of TIM-3 on T lymphocytes in the inflammatory involvement of diabetic kidney disease.

Objective: The aberrant mobilization and activation of various T lymphocyte subpopulations play a pivotal role in the pathogenesis of diabetic kidney disease (DKD), yet the regulatory mechanisms underlying these processes remain poorly understood. Our study is premised on the hypothesis that the dysregulation of immune checkpoint molecules on T lymphocytes disrupts kidney homeostasis, instigates pathological inflammation, and promotes DKD progression. Methods: A total of 360 adult patients with DKD were recruited for this study. The expression of immune checkpoint molecules on T lymphocytes was assessed by flow cytometry for peripheral blood and immunofluorescence staining for kidney tissue. Single-cell sequencing (scRNA-seq) data from the kidneys of DKD mouse model were analyzed. Results: Patients with DKD exhibited a reduction in the proportion of CD3+TIM-3+ T cells in circulation concurrent with the emergence of significant albuminuria and hematuria (p=0.008 and 0.02, respectively). Conversely, the incidence of infection during DKD progression correlated with an elevation of peripheral CD3+TIM-3+ T cells (p=0.01). Both univariate and multivariate logistic regression analysis revealed a significant inverse relationship between the proportion of peripheral CD3+TIM-3+ T cells and severe interstitial mononuclear infiltration (OR: 0.193, 95%CI: 0.040,0.926, p=0.04). Immunofluorescence assays demonstrated an increase of CD3+, TIM-3+ and CD3+TIM-3+ interstitial mononuclear cells in the kidneys of DKD patients as compared to patients diagnosed with minimal change disease (p=0.03, 0.02 and 0.002, respectively). ScRNA-seq analysis revealed decreased gene expression of TIM3 on T lymphocytes in DKD compared to control. And one of TIM-3's main ligands, Galectin-9 on immune cells showed a decreasing trend in gene expression as kidney damage worsened. Conclusion: Our study underscores the potential protective role of TIM-3 on T lymphocytes in attenuating the progression of DKD and suggests that monitoring circulating CD3+TIM3+ T cells may serve as a viable strategy for identifying DKD patients at heightened risk of disease progression.

Podocyte-derived soluble RARRES1 drives kidney disease progression through direct podocyte and proximal tubular injury.

Retinoic acid receptor responder protein-1 (RARRES1) is a podocyte-enriched transmembrane protein whose increased expression correlates with human glomerular disease progression. RARRES1 promotes podocytopenia and glomerulosclerosis via p53-mediated podocyte apoptosis. Importantly, the cytopathic actions of RARRES1 are entirely dependent on its proteolytic cleavage into a soluble protein (sRARRES1) and subsequent podocyte uptake by endocytosis, as a cleavage mutant RARRES1 exerted no effects in vitro or in vivo. As RARRES1 expression is upregulated in human glomerular diseases, here we investigated the functional consequence of podocyte-specific overexpression of RARRES1 in mice in the experimental focal segmental glomerulosclerosis and diabetic kidney disease. We also examined the effects of long-term RARRES1 overexpression on slowly developing aging-induced kidney injury. As anticipated, the induction of podocyte overexpression of RARRES1 (Pod-RARRES1WT) significantly worsened glomerular injuries and worsened kidney function in all three models, while overexpression of RARRES1 cleavage mutant (Pod-RARRES1MT) did not. Remarkably, direct uptake of sRARRES1 was also seen in proximal tubules of injured Pod-RARRES1WT mice and associated with exacerbated tubular injuries, vacuolation, and lipid accumulation. Single-cell RNA sequence analysis of mouse kidneys demonstrated RARRES1 led to a marked deregulation of lipid metabolism in proximal tubule subsets. We further identified matrix metalloproteinase 23 (MMP23) as a highly podocyte-specific metalloproteinase and responsible for RARRES1 cleavage in disease settings, as adeno-associated virus 9-mediated knockdown of MMP23 abrogated sRARRES1 uptake in tubular cells in vivo. Thus, our study delineates a previously unrecognized mechanism by which a podocyte-derived protein directly facilitates podocyte and tubular injury in glomerular diseases and suggests that podocyte-specific functions of RARRES1 and MMP23 may be targeted to ameliorate glomerular disease progression in vivo.

Causal relationship between gut microbiota and diabetic nephropathy: a two-sample Mendelian randomization study.

Objective: Emerging evidence has provided compelling evidence linking gut microbiota (GM) and diabetic nephropathy (DN) via the "gut-kidney" axis. But the causal relationship between them hasn't been clarified yet. We perform a Two-Sample Mendelian randomization (MR) analysis to reveal the causal connection with GM and the development of DN, type 1 diabetes nephropathy (T1DN), type 2 diabetes nephropathy (T2DN), type 1 diabetes mellitus (T1DM), and type 2 diabetes mellitus (T2DM). Methods: We used summary data from MiBioGen on 211 GM taxa in 18340 participants. Generalized MR analysis methods were conducted to estimate their causality on risk of DN, T1DN, T2DN, T1DM and T2DM from FinnGen. To ensure the reliability of the findings, a comprehensive set of sensitivity analyses were conducted to confirm the resilience and consistency of the results. Results: It was showed that Class Verrucomicrobiae [odds ratio (OR) =1.5651, 95%CI:1.1810-2.0742,PFDR=0.0018], Order Verrucomicrobiales (OR=1.5651, 95%CI: 1.1810-2.0742, PFDR=0.0018) and Family Verrucomicrobiaceae (OR=1.3956, 95%CI:1.0336-1.8844, PFDR=0.0296) had significant risk of DN. Our analysis found significant associations between GM and T2DN, including Class Verrucomimicrobiae (OR=1.8227, 95% CI: 1.2414-2.6763, PFDR=0.0139), Order Verrucomimicrobiae (OR=1.5651, 95% CI: 1.8227-2.6764, PFDR=0.0024), Rhodospirillales (OR=1.8226, 95% CI: 1.2412-2.6763, PFDR=0.0026), and Family Verrucomicroniaceae (OR=1.8226, 95% CI: 1.2412-2.6763, PFDR=0.0083). The Eubacteriumprotogenes (OR=0.4076, 95% CI: 0.2415-0.6882, PFDR=0.0021) exhibited a protection against T1DN. Sensitivity analyses confirmed that there was no significant heterogeneity and pleiotropy. Conclusions: At the gene prediction level, we identified the specific GM that is causally linked to DN in both T1DM and T2DM patients. Moreover, we identified distinct microbial changes in T1DN that differed from those seen in T2DN, offering valuable insights into GM signatures associated with subtype of nephropathy.

Bowman's capsule rupture and the Oxford MEST-C score in adult patients with Immunoglobulin a vasculitis nephritis: a single center experience.

OBJECTIVE: Bowman's capsule rupture (BCR) is a glomerular pathological change, but it is still not well recognized in immunoglobulin A vasculitis nephritis (IgAV-N). The Oxford MEST-C score is a classification for IgA nephropathy; however, its clinical correlation and prognostic value in adult patients with IgAV-N are unclear. METHODS: A retrospective study of 145 adult patients with IgAV-N diagnosed by renal biopsy was conducted. Clinical manifestations, pathological changes and the prognosis of IgAV-N patients were compared depending on the presence or absence of BCR, International Study of Kidney Disease in Children (ISKDC) classification and MEST-C score. The primary endpoint events were end-stage renal disease, renal replacement therapy and all-cause death. RESULTS: In total, 51 of 145 (35.17%) patients with IgAV-N presented with BCR. Patients with BCR had more proteinuria, lower serum albumin, and more crescents. Compared with IgAV-N patients with crescents only, 51/100 patients with crescents combined with BCR had a higher proportion of crescents in all glomeruli (15.79% vs. 9.09%; p = 0.003). Patients with higher ISKDC grades had more severe clinical presentation, but it did not reflect the prognosis. However, the MEST-C score not only reflected clinical manifestations but also predicted prognosis (p < 0.05). BCR contributed to the effectiveness of the MEST-C score in predicting the prognosis of IgAV-N (C-index: 0.845 to 0.855). CONCLUSIONS: BCR is associated with clinical manifestations and pathological changes in patients with IgAV-N. The ISKDC classification and MEST-C score are related to the patient's condition, but only the MEST-C score is correlated with the prognosis of patients with IgAV-N, while BCR can improve its predictive ability.

BCR was associated with clinical manifestations and pathological changes in patients with IgAV-N, particularly crescents.The ISKDC classification was related to clinical manifestations of patients with IgAV-N, but it wasn't associated with prognosis.The Oxford MEST-C score was correlated to clinical presentations and prognosis of patients with IgAV-N, while BCR can improve its predictive ability.

Mendelian randomization study supports the causal association between serum cystatin C and risk of diabetic nephropathy.

Aims: Cystatin C, an inhibitor of cysteine protease, has been used as a biomarker for estimating glomerular filtration rate. However, the causal relation between cystatin C and diabetic nephropathy remains uncertain. Methods: We assessed the causal effect of cystatin C together with other five serum biomarkers including KIM-1, GDF-15, TBIL, uric acid, and Scr on diabetic nephropathy by Mendelian randomization (MR) analysis. 234 genetic variants were selected as instrumental variables to evaluate the causal effect of cystatin C (NGWAS=361194) on diabetic nephropathy (Ncase/Ncontrol up to 3283/210463). Multivariable MR (MVMR) was performed to assess the stability of cystatin C's causal relationship. Two-step MR was used to assess the mediation effect of BMI and SBP. Results: Among the six serum biomarkers, only cystatin C causally associated with diabetic nephropathy (IVW OR: 1.36, 95%CI [1.15, 1.61]). After adjusting for the potential confounders BMI and SBP, cystatin C maintained its causal effect on the DN (OR: 1.17, 95%CI [1.02, 1.33]), which means that the risk of DN increased by 17% with an approximate 1 standard deviation (SD) increment of serum cystatin C level. Two-step MR results indicated that BMI might mediate the causal effect of cystatin C on diabetic nephropathy. Interpretation: Our findings discovered that cystatin C was a risk factor for diabetic nephropathy independent of BMI and SBP in diabetes mellitus patients. Future research is required to illustrate the underlying mechanism and prove targeting circulating cystatin C could be a potential therapy method.

Differences in Phenotypic Plasticity between Invasive and Native Plants Responding to Three Environmental Factors.

The phenotypic plasticity hypothesis suggests that exotic plants may have greater phenotypic plasticity than native plants. However, whether phenotypic changes vary according to different environmental factors has not been well studied. We conducted a multi-species greenhouse experiment to study the responses of six different phenotypic traits, namely height, leaf number, specific leaf area, total biomass, root mass fraction, and leaf mass fraction, of native and invasive species to nutrients, water, and light. Each treatment was divided into two levels: high and low. In the nutrient addition experiment, only the leaf mass fraction and root mass fraction of the plants supported the phenotypic plasticity hypothesis. Then, none of the six traits supported the phenotypic plasticity hypothesis in the water or light treatment experiments. The results show that, for different environmental factors and phenotypes, the phenotypic plasticity hypothesis of plant invasion is inconsistent. When using the phenotypic plasticity hypothesis to explain plant invasion, variations in environmental factors and phenotypes should be considered.

Treating crescentic glomerulonephritis by targeting macrophages.

Macrophage accumulation in the kidney is associated with the progression of crescentic glomerulonephritis (GN) and is mostly derived from circulating monocytes. FROUNT, a C-C motif chemokine receptor 2 (CCR2)-interacted protein, which is strongly expressed in monocytes/macrophages, enhances macrophage infiltration through CCR2-mediated chemotaxis. In this issue of the journal, Toda et al. reported that disulfiram, an inhibitor of FROUNT, attenuates GN by inhibition of the FROUNT-CCR2 interaction and macrophage migration and activation, suggesting a potential therapeutic role for crescentic GN.

Endoplasmic reticulum stress contributes to cisplatin-induced chronic kidney disease via the PERK-PKCδ pathway.

BACKGROUND: Cisplatin is an effective chemotherapeutic drug, but it may induce both acute and chronic kidney problems. The pathogenesis of chronic kidney disease (CKD) associated with cisplatin chemotherapy remains largely unclear. METHODS: Mice and renal tubular cells were subjected to repeated low-dose cisplatin (RLDC) treatment to induce CKD and related pathological changes. The roles of endoplasmic reticulum (ER) stress, PERK, and protein kinase C-δ (PKCδ) were determined using pharmacological inhibitors and genetic manipulation. RESULTS: ER stress was induced by RLDC in kidney tubular cells in both in vivo and in vitro models. ER stress inhibitors given immediately after RLDC attenuated kidney dysfunction, tubular atrophy, kidney fibrosis, and inflammation in mice. In cultured renal proximal tubular cells, inhibitors of ER stress or its signaling kinase PERK also suppressed RLDC-induced fibrotic changes and the expression of inflammatory cytokines. Interestingly, RLDC-induced PKCδ activation, which was blocked by ER stress or PERK inhibitors, suggesting PKCδ may act downstream of PERK. Indeed, suppression of PKCδ with a kinase-dead PKCδ (PKCδ-KD) or Pkcδ-shRNA attenuated RLDC-induced fibrotic and inflammatory changes. Moreover, the expression of active PKCδ-catalytic fragment (PKCδ-CF) diminished the beneficial effects of PERK inhibitor in RLDC-treated cells. Co-immunoprecipitation assay further suggested PERK binding to PKCδ. CONCLUSION: These results indicate that ER stress contributes to chronic kidney pathologies following cisplatin chemotherapy via the PERK-PKCδ pathway.

Inflammation in kidney repair: Mechanism and therapeutic potential.

The kidney has a remarkable ability of repair after acute kidney injury (AKI). However, when injury is severe or persistent, the repair is incomplete or maladaptive and may lead to chronic kidney disease (CKD). Maladaptive kidney repair involves multiple cell types and multifactorial processes, of which inflammation is a key component. In the process of inflammation, there is a bidirectional interplay between kidney parenchymal cells and the immune system. The extensive and complex crosstalk between renal tubular epithelial cells and interstitial cells, including immune cells, fibroblasts, and endothelial cells, governs the repair and recovery of the injured kidney. Further research in this field is imperative for the discovery of biomarkers and promising therapeutic targets for kidney repair. In this review, we summarize the latest progress in the immune response and inflammation during maladaptive kidney repair, analyzing the interaction between immune cells and intrinsic kidney cells, pointing out the potentialities of inflammation-related pathways as therapeutic targets, and discussing the challenges and future research prospects in this field.

Gasdermin D is involved in switching from apoptosis to pyroptosis in TLR4-mediated renal tubular epithelial cells injury in diabetic kidney disease.

BACKGROUND: Toll-like receptor 4 (TLR4) mediated pathway plays a pivotal role in promoting tubulointerstitial inflammation and contributes to the progression in type 2 diabetic kidney disease (T2DKD). As the first identified key pyroptosis executor, gasdermin D (GSDMD) is activated by caspases and might be the key protein to switch apoptosis to pyroptosis. It remains unclear that role of TLR4 on canonical pyroptosis pathway, and whether GSDMD is involved in switching from apoptosis to pyroptosis in the TLR4-related tubular injury in T2DKD. METHODS: Immunohistochemistry staining was used to detect the expression of pyroptosis-related proteins in renal tissues of T2DKD patients. T2DKD models was induced in TLR4 knockout (TLR4-/-) mice through a high-fat diet combined with streptozotocin. Pyroptosis (caspase-1, GSDMD, interleukin 18(IL-18), interleukin 1ß(IL-1ß)) and apoptosis levels (caspase-3, Bax and Bcl-2) were detected by Western blot. HK-2 cells were cultured under high-glucose (HG) conditions as an in vitro model and then challenged with a TLR4-specific antagonist (TAK-242). GSDMD small interfering RNA (siRNA) and overexpression plasmid were transfected into HK-2 cells to down- or up-regulate GSDMD. The pyroptosis and apoptosis rates were determined by flow cytometry. RESULTS: The expression levels of caspase-1, GSDMD, IL-18 and IL-1ß were increased in renal biopsy tissues of T2DKD patients and GSDMD expression was positively correlated with tubular injury. Silencing GSDMD attenuated HG-induced IL-18, IL-1ß, FN and α-SMA, and reduced pyroptotic cells rate in HK-2 cells. Up-regulation of GSDMD inhibited HG-induced expression of Bax and cleaved caspase-3 and reduced apoptosis rate. TLR4 knockout alleviated tubular injury and interstitial macrophages infiltration, improved impaired renal dysfunction, and decreased the expressions of active N-terminal of GSDMD(GSDMD-N), cleaved caspase-1(cl-caspase-1) and cleaved caspase-3(cl-caspase-3) in T2DKD mice. TLR4 inhibition reduced HG-induced pyroptosis and apoptosis level in HK-2 cells, while GSDMD up-regulation increased pyroptosis rate and decreased apoptosis rate. CONCLUSIONS: TLR4 could exacerbate tubular injury and fibrosis via GSDMD-mediated canonical pyroptosis pathway in T2DKD. Activation of GSDMD could inhibit apoptosis and activate pyroptosis, which may involve the potential switch mechanism between TLR4-mediated pyroptosis and apoptosis in T2DKD.

Association of Bowman's capsule rupture with prognosis in patients with lupus nephritis.

BACKGROUND AND OBJECTIVE: Lupus nephritis is one of the most severe manifestations of systemic lupus erythematosus. The clinical and prognostic significance of Bowman's capsule rupture in patients with lupus nephritis is unknown. METHODS: One hundred eighty patients with lupus nephritis were enrolled in the study and the integrity of Bowman's capsule was assessed. Both inflammatory and proliferative cells were detected by immunochemistry staining. The primary events of interest were end-stage renal disease and death. RESULTS: After retrospective analysis of the data, 52 (28.9%) patients were found to have Bowman's capsule rupture, which was accompanied by high levels of serum creatinine, 24 h urine protein, and Activity/Chronicity Index. Bowman's capsule rupture was correlated with the level of crescents, tubular atrophy, and interstitial fibrosis. The number of CD20+ cells was higher in the Bowman's capsule rupture ( +) group compared with the Bowman's capsule rupture (-) group, while no differences in other inflammatory cells were observed. In addition, the end stage renal disease-free survival in the Bowman's capsule rupture ( +) group was lower than in the Bowman's capsule rupture (-) group. Moreover, serum creatinine (HR 39.56, P < 0.001), Activity Index (HR 1.50, P < 0.05) as well as Bowman's capsule rupture (HR 1.09, P < 0.05) predicted end-stage renal disease progression. Notably, for patients with existing crescents, Bowman's capsule rupture increased the cumulative risk of end-stage renal disease. CONCLUSIONS: Bowman's capsule rupture is an important renal pathological lesion, which correlates with severe clinical manifestations, pathological changes, and poor prognosis in patients with lupus nephritis.

Digital Spatial Profiling of Individual Glomeruli From Patients With Anti-Neutrophil Cytoplasmic Autoantibody-Associated Glomerulonephritis.

We previously showed that the rupture of Bowman's capsule (BC) promotes the progression of crescentic glomerulonephritis by enhancing the entry of CD8+ T cells into the glomeruli. In the present study, we utilized digital spatial profiling to simultaneously profile the altered abundances of the messenger RNA (mRNA) transcripts and proteins in the glomerular and periglomerular areas of four biopsy samples of anti-neutrophil cytoplasmic autoantibody-associated glomerulonephritis (ANCA-GN) and two biopsy specimens of minimal change disease (MCD) controls. The paraffin-embedded biopsy samples were stained with collagen IV, CD45, and SYTO 13 to distinguish the glomeruli with periglomerular infiltration but intact BC, with focal BC rupture, and with extensive rupture of BC and glomeruli without crescent formation and leukocytic infiltration in ANCA-GN. By assessing multiple discrete glomerular areas, we found that the transcript expression levels of the secreted phosphoprotein-1 and its receptor CD44 were upregulated significantly in the glomeruli with more severe ruptures of BC, and their expression levels correlated positively with the fibrotic markers. We also found that both alternative and classic complement pathways were activated in the glomeruli from patients with ANCA-GN. Furthermore, M1 macrophages were involved mostly in the early stage of BC rupture, while M2 macrophages were involved in the late stage and may contribute to the fibrosis process of the crescents. Finally, loss of glomerular cells in ANCA-GN was likely mediated by apoptosis. Our results show that digital spatial profiling allows the comparative analysis of the mRNA and protein profiles in individual glomeruli affected differently by the disease process and the identification of potential novel mechanisms in ANCA-GN.

Pentosan polysulfate ameliorates fibrosis and inflammation markers in SV40 MES13 cells by suppressing activation of PI3K/AKT pathway via miR-446a-3p.

BACKGROUND: Renal fibrosis is a common outcome of various renal damage, including diabetic nephropathy (DN), the leading cause of end-stage renal disease. Currently, there are no effective therapies for renal fibrosis. The present study aimed to determine whether pentosan polysulphate sodium (PPS), a FDA approved medication for interstitial cystitis, protects diabetic renal fibrosis. METHODS: Cell viability and apoptosis were evaluated in mouse mesangial cells (SV40-MES13) after incubating with the advanced glycation end products (AGEs), which play important roles in the pathogenesis of DN. Western blot and ELISA were performed to determine the expression of transforming growth factor-beta1 (TGF-ß1) and fibronectin (FN), two biomarkers of renal fibrosis, as well as interleukin-6 (IL-6) and tumor necrosis factor alpha (TNFα), two biomarkers of inflammation. The miRNA-mRNA regulatory network involved in the phosphatidylinositol 3-kinase (PI3K)/Ser and Thr Kinase (AKT) signalling was investigated by miRNA deep sequencing and validated by RT-PCR and miRNA transfection. RESULTS: AGEs significantly inhibited cell proliferation and promoted cell apoptosis, which was associated with the overexpression of TGF-ß1, FN, IL-6, and TNFα. PPS almost completely reversed AGEs-induced biomarkers of fibrosis and inflammation, and significantly altered the miRNA expression profile in AGEs-treated cells. Notably, the PI3K/AKT signalling was one of the most significantly enriched pathways targeted by PPS-related differentially expressed miRNAs. PPS significantly up-regulated miR-466a-3p, which was shown to target PIK3CA, and mediated the inhibitory effect of PPS on AGEs-induced activation of PI3K/AKT pathway. CONCLUSIONS: The treatment of PPS protected against AGEs-induced toxicity in SV40 MES13 cells via miR-466a-3p-mediated inhibition of PI3K/AKT pathway.

Similarities and Differences between COVID-19-Associated Nephropathy and HIV-Associated Nephropathy.

Kidney disease is a major complication of viral infection, which can cause both acute and chronic kidney diseases via different mechanisms such as immune-mediated injury, kidney cell injury from a direct viral infection, systemic effects, and antiviral drug-induced nephrotoxicity. HIV-associated nephropathy (HIVAN), characterized by collapsing focal segmental glomerulosclerosis (cFSGS), has been described 2 decades ago as a major complication of acquired-immunodeficiency syndrome. The pathogenesis of HIVAN has been well studied, including viral entry, host response, and genetic factors. The incidence of this disease has been dramatically dropped with current antiretroviral therapy. In the recent severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) pandemic, acute kidney injury was also found to be a major complication in patients with (coronavirus disease) COVID-19. These patients also developed glomerular disease such as cFSGS in African Americans with apolipoprotein L1 risk alleles, similar to HIVAN. Whether SARS-CoV-2 can infect kidney cells locally remains controversial, but both local infection and systemic effects are likely involved in the pathogenesis of this disease. In this review, we present a comparison of the clinical presentations, pathological findings, disease mechanisms, and potential treatments between HIVAN and COVID-19. Leveraging the knowledge in HIVAN and experimental approaches used to study HIVAN will facilitate the exploration in the pathogenesis of COVID-19-associated kidney disease and improve our management of COVID-19 patients.

Controversies in Podocyte Loss: Death or Detachment?

Glomerular podocytes are characterized by terminally differentiated epithelial cells with limited proliferating ability; thus, podocyte loss could not be fully compensated by podocyte regeneration. A large body of clinical studies collectively demonstrated that podocyte loss correlated with glomerular diseases progression. Both podocyte death and podocyte detachment lead to podocyte loss; however, which one is the main cause remains controversial. Up to date, multiple mechanisms are involved in podocyte death, including programmed apoptotic cell death (apoptosis and anoikis), programmed nonapoptotic cell death (autophagy, entosis, and podoptosis), immune-related cell death (pyroptosis), and other types of cell death (necroptosis and mitotic catastrophe-related cell death). Apoptosis is considered a common mechanism of podocyte loss; however, most of the data were generated in vitro and the evidence of in vivo podocyte apoptosis is limited. The isolation of podocytes in the urine and subsequent culture of urinary podocytes in vitro suggest that detachment of viable podocytes could be another important mechanism for podocyte loss. In this review, we summarize recent advances that address this controversial topic on the specific circumstances of podocyte loss.

Reciprocal regulation between ER stress and autophagy in renal tubular fibrosis and apoptosis.

Both endoplasmic reticulum (ER) stress and autophagy have been implicated in chronic kidney injury and renal fibrosis. However, the relationship and regulatory mechanisms between ER stress and autophagy under this condition remain largely unknown. In this study, we first established a mouse model of ER stress-induced chronic kidney injury by 2 weekly injections of a low dose of tunicamycin (TM), a classical ER stress inducer. This model showed the induction of ER stress, autophagy, fibrosis and apoptosis in kidney tissues. In vitro, TM also induced ER stress, autophagy, fibrosis and apoptosis in HK-2 human kidney proximal tubular cells and BUMPT-306 mouse kidney proximal tubular cells. In these cells, autophagy inhibitor suppressed TM-induced fibrotic changes and apoptosis, suggesting an involvement of autophagy in ER stress-associated chronic kidney injury. PERK inhibitor ameliorated autophagy, fibrotic protein expression and apoptosis in TM-treated cells, indicating a role of the PERK/eIF2α pathway in autophagy activation during ER stress. Similar results were shown in TGF-ß1-treated HK-2 cells. Interestingly, in both TM- or TGF-ß1-treated kidney proximal tubular cells, inhibition of autophagy exaggerated ER stress, suggesting that autophagy induced by ER stress provides a negative feedback mechanism to reduce the stress. Together, these results unveil a reciprocal regulation between ER stress and autophagy in chronic kidney injury and fibrosis.

Clinical implication of the circumferential crescents lesions in immunoglobulin A nephropathy: a single-center study of Han Chinese population.

A crescentic lesion in renal biopsy could be segmental or circumferential, but the distribution and clinical implication of the circumferential crescents in immunoglobulin A nephropathy (IgAN) remains unknown. A total of 384 crescentic IgAN patients between 2011 and 2019 were included. The subjects were classified as the circumferential crescent who have at least one crescent involving ≥50% circumference of Bowman's capsule, otherwise as to the segmental crescent. Clinical, pathological, and prognostic relationships were analyzed. The primary endpoint was a 30% decline in eGFR, and the secondary endpoint was more than 3.5 g/d proteinuria during follow-up. Of the 384 patients, 72 (18.8%) patients had more than one circumferential crescent. 52 (17.6%) Oxford C1 patients have circumferential crescent. During a mean follow-up of 32.3 months, both the primary and secondary endpoints have occurred more in the circumferential crescent patients. Kaplan-Meier analysis showed the patient with the circumferential crescent had significantly lower renal survival than those without. In multivariable Cox analyses, having the circumferential crescents in at least one-fifth of glomeruli was independently associated with primary endpoint (hazard ratio:3.60, 95% CI:1.46-8.83), after adjusting for Oxford-score, eGFR, systolic blood pressure, and proteinuria. Furthermore, those patients who scored C1 in Oxford and presenting with circumferential crescents, had better renal survival if they received the other immunosuppressants therapy. The circumferential crescents lesion was associated with adverse outcomes in IgAN, and more than one-fifth of glomeruli circumferential crescents is an independent predictor of 30% eGFR decline after adjusting for clinical and histological parameters.

Autocrine and paracrine effects of a novel podocyte gene, RARRES1.

Retinoic acid receptor responder protein 1 (RARRES1) has been identified as a novel gene for the regulation of podocyte function, and its expression is increased in glomerular disease and associated with disease progression. Increased expression of RARRES1 in podocytes leads to apoptosis through an autocrine effect. Möller-Hackbarth et al. recently found that RARRES1 expression is increased in the endothelial cells in some diseased kidneys to promote podocyte injury, likely through a paracrine effect.

Disparate roles of retinoid acid signaling molecules in kidney disease.

Retinoid acid (RA) is synthesized mainly in the liver and has multiple functions in development, cell differentiation and proliferation, and regulation of inflammation. RA has been used to treat multiple diseases, such as cancer and skin disorders. The kidney is a major organ for RA metabolism, which is altered in the diseased condition. RA is known to have renal-protective effects in multiple animal models of kidney disease. RA has been shown to ameliorate podocyte injury through induction of expression of differentiation markers and regeneration of podocytes from its progenitor cells in animal models of kidney disease. The effects of RA in podocytes are mediated mainly by activation of the cAMP/PKA pathway via RA receptor-α (RARα) and activation of its downstream transcription factor, Kruppel-like factor 15. Screening of RA signaling molecules in human kidney disease has revealed RAR responder protein 1 (RARRES1) as a risk gene for glomerular disease progression. RARRES1, a podocyte-specific growth arrest gene, is regulated by high doses of both RA and TNF-α. Mechanistically, RARRES1 is cleaved by matrix metalloproteinases to generate soluble RARRES1, which then induces podocyte apoptosis through interaction with intracellular RIO kinase 1. Therefore, a high dose of RA may induce podocyte toxicity through upregulation of RARRES1. Based on the current findings, to avoid potential side effects, we propose three strategies to develop future therapies of RA for glomerular disease: 1) develop RARα- and Kruppel-like factor 15-specific agonists, 2) use the combination of a low dose of RAR-α agonist with phosphodiesterase 4 inhibitors, and 3) use a combination of RARα agonist with RARRES1 inhibitors.NEW & NOTEWORTHY Retinoic acid (RA) exerts pleotropic cellular effects, including induction of cell differentiation while inhibiting proliferation and inflammation. These effects are mediated by both RA responsive element-dependent or -independent pathways. In kidneys, RA confers renoprotection by signaling through podocyte RA receptor (RAR)α and activation of cAMP/PKA/Kruppel-like factor 15 pathway to promote podocyte differentiation. Nevertheless, in kidney disease settings, RA can also promote podocyte apoptosis and loss through downstream expression of RAR responder protein 1, a recently described risk factor for glomerular disease progression. These disparate roles of RA underscore the complexity of its effects in kidney homeostasis and disease, and a need to target specific RA-mediated pathways for effective therapeutic treatments against kidney disease progression.