Pharmacological and genetic depletion of fibrinogen protects from kidney fibrosis

STAT3 Protein-Protein Interaction Analysis Finds P300 as a Regulator of STAT3 and Histone 3 Lysine 27 Acetylation in Pericytes

BACKGROUND

Signal transducer and activator of transcription 3 (STAT3) is a member of the cytoplasmic inducible transcription factors and plays an important role in mediating signals from cytokines, chemokines, and growth factors. We and others have found that STAT3 directly regulates pro-fibrotic signaling in the kidney. The STAT3 protein-protein interaction plays an important role in activating its transcriptional activity. It is necessary to identify these interactions to investigate their function in kidney disease. Here, we investigated the protein-protein interaction among three species to find crucial interactions that can be targeted to alleviate kidney disease.

METHOD

In this study, we examined common protein-protein interactions leading to the activation or downregulation of STAT3 among three different species: humans (Homo sapiens), mice (Mus musculus), and rabbits (Oryctolagus cuniculus). Further, we chose to investigate the P300 and STAT3 interaction and performed studies of the activation of STAT3 using IL-6 and inhibition of the P300 by its specific inhibitor A-485 in pericytes. Next, we performed immunoprecipitation to confirm whether A-485 inhibits the binding of P300 to STAT3.

RESULTS

Using the STRING application from ExPASy, we found that six proteins, including PIAS3, JAK1, JAK2, EGFR, SRC, and EP300, showed highly confident interactions with STAT3 in humans, mice, and rabbits. We also found that IL-6 treatment increased the acetylation of STAT3 and increased histone 3 lysine acetylation (H3K27ac). Furthermore, we found that the disruption of STAT3 and P300 interaction by the P300 inhibitor A-485 decreased STAT3 acetylation and H3K27ac. Finally, we confirmed that the P300 inhibitor A-485 inhibited the binding of STAT3 with P300, which inhibited its transcriptional activity by reducing the expression of Ccnd1 (Cyclin D1).

CONCLUSIONS

Targeting the P300 protein interaction with STAT3 may alleviate STAT3-mediated fibrotic signaling in humans and other species.

Endothelial POFUT1 controls injury-induced liver fibrosis by repressing fibrinogen synthesis

BACKGROUND & AIMS

NOTCH signaling in liver sinusoidal endothelial cells (LSECs) regulates liver fibrosis, a pathological feature of chronic liver diseases. POFUT1 is an essential regulator of NOTCH signaling. Here, we investigated the role of LSEC-expressed POFUT1 in liver fibrosis.

METHODS

Endothelial-specific Pofut1 knockout mice were generated and experimental liver fibrosis was induced by chronic carbon tetrachloride exposure or common bile duct ligation. Liver samples were assessed by ELISA, histology, electron microscopy, immunostaining and RNA in situ hybridization. LSECs and hepatic stellate cells (HSCs) were isolated for gene expression analysis by RNA sequencing, qPCR, and western blotting. Signaling crosstalk between LSECs and HSCs was investigated by treating HSCs with supernatant from LSEC cultures. Liver single-cell RNA sequencing datasets from patients with cirrhosis and healthy individuals were analyzed to evaluate the clinical relevance of gene expression changes observed in mouse studies.

RESULTS

POFUT1 loss promoted injury-induced LSEC capillarization and HSC activation, leading to aggravated liver fibrosis. RNA sequencing analysis revealed that POFUT1 deficiency upregulated fibrinogen expression in LSECs. Consistently, fibrinogen was elevated in LSECs of patients with cirrhosis. HSCs treated with supernatant from LSECs of Pofut1 null mice showed exacerbated activation compared to those treated with supernatant from control LSECs, and this effect was attenuated by knockdown of fibrinogen or by pharmacological inhibition of fibrinogen receptor signaling, altogether suggesting that LSEC-derived fibrinogen induced the activation of HSCs. Mechanistically, POFUT1 loss augmented fibrinogen expression by enhancing NOTCH/HES1/STAT3 signaling.

CONCLUSIONS

Endothelial POFUT1 prevents injury-induced liver fibrosis by repressing the expression of fibrinogen, which functions as a profibrotic paracrine signal to activate HSCs. Therapies targeting the POFUT1/fibrinogen axis offer a promising strategy for the prevention and treatment of fibrotic liver diseases.

IMPACT AND IMPLICATIONS

Paracrine signals produced by liver vasculature play a major role in the development of liver fibrosis, which is a pathological hallmark of most liver diseases. Identifying those paracrine signals is clinically relevant in that they may serve as therapeutic targets. In this study, we discovered that genetic deletion of Pofut1 aggravated experimental liver fibrosis in mouse models. Moreover, fibrinogen was identified as a downstream target repressed by Pofut1 in liver endothelial cells and functioned as a novel paracrine signal that drove liver fibrosis. In addition, fibrinogen was found to be relevant to cirrhosis and may serve as a potential therapeutic target for this devastating human disease.

Altered fibrin clot properties are associated with the progression of chronic kidney disease in atrial fibrillation

INTRODUCTION

Formation of denser and resistant to lysis fibrin clot networks has been shown in chronic kidney disease (CKD) and atrial fibrillation (AF). We investigated whether such prothrombotic fibrin clot properties are associated with faster progression of CKD in AF patients.

MATERIAL AND METHODS

We recruited 265 AF patients (men 49.1 %, median age of 64.0 years, median estimated glomerular filtration rate [eGFR] of 77.0 ml/min/1.73 m2), including 137 patients on non-vitamin K antagonist oral anticoagulants (NOACs) (51.7 %) and 109 patients (41.1 %) on vitamin K antagonists (VKAs). At baseline while off anticoagulation, we determined fibrin clot permeability (Ks), and clot lysis time (CLT), along with plasminogen activator inhibitor-1 (PAI-1), endogenous thrombin potential (ETP), and von Willebrand factor (vWF). The kidney function was assessed at baseline and after a median follow-up of 50.0 months.

RESULTS

During follow-up, a median eGFR decreased by 8.0 (5.0-11.0) ml/min/1.73 m2, 1.8 ml/min/1.73 m2/year and this change correlated with age (R = 0.19, P = 0.002), Ks (R = 0.46, P < 0.0001), and CLT (R = -0.17, P = 0.005), but not ETP, fibrinogen, PAI-1 or vWF. A decrease in eGFR was lower in patients who used NOACs at baseline but not in those who started NOACs during follow-up (n = 101) as compared to the remaining patients. On multiple linear regression analysis, adjusted for age and fibrinogen, baseline Ks, eGFR, hypertension, and NOACs use independently predicted a decrease in eGFR.

CONCLUSIONS

This study is the first to show that more compact fibrin clot networks may contribute to faster progression of CKD in AF, indicating novel kidney-related harmful effects of prothrombotic clot properties in humans.

DIA proteomics analysis reveals the mechanism of folic acid-induced acute kidney injury and the effects of icariin

The complexities of acute kidney injury (AKI), a multifaceted pathological occurrence, are not fully understood. At present, there is a lack of effective pharmaceutical treatments in clinical practice. Studies have shown that icariin has beneficial effects in models of acute kidney injury (AKI) caused by cisplatin and lipopolysaccharide (LPS). The aim is to explore the mechanisms that cause folic acid (FA)-induced AKI and examine the protective effects of icariin against this condition. To establish a mouse model of AKI, FA was administered via intraperitoneal injection. Icariin was used as the drug intervention. The model and the impact of drug intervention were assessed using measurements of renal function parameters, staining with hematoxylin and eosin, and Q-PCR. The analysis of protein expression changes in the control, model, and icariin treatment groups was conducted using proteomics. KEGG signaling pathway analysis indicates that differential expressed proteins are enriched in the component and coagulation cascades signaling pathway. Through protein-protein interaction network analysis, it was found that compared to the normal group, the expression of Fibrinogen and other proteins was significantly upregulated at the center of the protein interaction network in the model group. After drug treatment, the expression of these proteins was significantly downregulated. The validation experiment supports the above results. In conclusion, this study clarified the molecular mechanism of FA induced acute renal injury from the proteomics level, and provided target selection for AKI; At the same time, the mechanism of icariin in the treatment of AKI was analyzed from the proteomics level.

TLR2 and TLR9 Blockade Using Specific Intrabodies Inhibits Inflammation-Mediated Pancreatic Cancer Cell Growth

Pancreatic cancer (pancreatic ductal adenocarcinoma, PDAC) remains a deadly cancer worldwide with a need for new therapeutic approaches. A dysregulation in the equilibrium between pro- and anti-inflammatory responses with a predominant immunosuppressive inflammatory reaction in advanced stage tumors seem to contribute to tumor growth and metastasis. The current therapies do not include strategies against pro-tumorigenic inflammation in cancer patients. We have shown that the upregulated cell surface expression of Toll-like Receptor (TLR) 2 and of TLR9 inside PDAC cells maintain chronic inflammatory responses, support chemotherapeutic resistance, and mediate tumor progression in human pancreatic cancer. We further demonstrated intracellular TLR2 and TLR9 targeting using specific intrabodies, which resulted in downregulated inflammatory signaling. In this study, we tested, for the first time, an intrabody-mediated TLR blockade in human TLR2- and TLR9-expressing pancreatic cancer cells for its effects on inflammatory signaling-mediated tumor growth. Newly designed anti-TLR2- and anti-TLR9-specific intrabodies inhibited PDAC growth. Co-expression analysis of the intrabodies and corresponding human TLRs showed efficient retention and accumulation of both intrabodies within the endoplasmic reticulum (ER), while co-immunoprecipitation studies indicated both intrabodies interacting with their cognate TLR antigen within the pancreatic cancer cells. Cancer cells with attenuated proliferation expressing accumulated TLR2 and TRL9 intrabodies demonstrated reduced STAT3 phosphorylation signaling, while apoptotic markers Caspases 3 and 8 were upregulated. To conclude, our results demonstrate the TLR2 and TLR9-specific intrabody-mediated signaling pathway inhibition of autoregulatory inflammation inside cancer cells and their proliferation, resulting in the suppression of pancreatic tumor cell growth. These findings underscore the potential of specific intrabody-mediated TLR inhibition in the ER relevant for tumor growth inhibition and open up a new therapeutic intervention strategy for the treatment of pancreatic cancer.

Prognostic Factors in Children with Acute Kidney Injury Requiring Continuous Renal Replacement Therapy

INTRODUCTION

This study aimed to evaluate prognostic factors and outcomes in a single-center PICU cohort that received continuous renal replacement therapy (CRRT).

METHODS

This retrospective study analyzed clinical characteristics, laboratory data, and outcomes. Ninety-day mortality and advanced chronic kidney disease (CKD) (eGFR <60 mL/min/1.73 m2) were defined as primary and secondary outcomes, respectively.

RESULTS

Seventy-five patients were enrolled, all of whom received CRRT for indications including acute kidney injury with complicated refractory metabolic acidosis, electrolyte derangement, and existed or impending fluid overload. The 90-day mortality and advanced CKD were 53% and 29%, respectively. Multivariate Cox regression analysis demonstrated that only underlying bone marrow transplantation (BMT) (HR 4.58; 95% CI: 2.04-10.27) and a high pSOFA score (HR 1.12; 95% CI: 1.01-1.23) were independent risk factors for 90-day mortality. Among survivors, ten developed advanced CKD on the 90th day, and this group had a higher serum fibrinogen level (OR 1.01; 95% CI: 1.01-1.03) at the start of CRRT.

CONCLUSION

In critically ill children with AKI requiring CRRT, post-BMT and high pSOFA scores are independent risk factors for 90-day mortality. Additionally, a high serum fibrinogen level at the initiation of CRRT is associated with the development of advanced CKD.

Proteomic research on new urinary biomarkers of renal disease in canine leishmaniosis: Survival and monitoring response to treatment

The objective of our study was to search for survival biomarkers (SB) and treatment response monitoring biomarkers (TRMB) in the urinary proteome of dogs with renal disease secondary to canine leishmaniosis (CanL), using UHPLC-MS/MS. The proteomic data are available via ProteomeXchange with identifier PXD042578. Initially, a group of 12 dogs was evaluated and divided into survivors (SG; n = 6) and nonsurvivors (NSG; n = 6). A total of 972 proteins were obtained from the evaluated samples. Then, bioinformatic analysis reduced them to 6 proteins like potential SB increased in the NSG, specifically, Haemoglobin subunit Alpha 1, Complement Factor I, Complement C5, Fibrinogen beta chain (fragment), Peptidase S1 domain-containing protein, and Fibrinogen gamma chain. Afterwards, SG was used to search for TRMB, studying their urine at 0, 30, and 90 days, and 9 proteins that decreased after treatment were obtained: Apolipoprotein E, Cathepsin B, Cystatin B, Cystatin-C-like, Lysozyme, Monocyte differentiation CD14, Pancreatitis-associated precursor protein, Profilin, and Protein FAM3C. Finally, enrichment analysis provided information about the biological mechanisms in which these proteins are involved. In conclusion, this study provides 15 new candidate urinary biomarkers and an improved understanding of the pathogenesis of kidney disease in CanL.

Discovery of Fibrinogen γ-chain as a potential urinary biomarker for renal interstitial fibrosis in IgA nephropathy

BACKGROUND

IgA nephropathy (IgAN) is a major cause of chronic kidney disease (CKD). Renal interstitial fibrosis is a hallmark of CKD progression. Non-invasive biomarkers are needed to dynamically evaluate renal fibrosis. Data independent acquisition (DIA)-based liquid chromatography-mass spectrometry (DIA-MS) was used to identify candidate urinary biomarkers in IgAN patients with different renal interstitial fibrosis degrees.

METHODS

Eighteen biopsy-proven IgAN patients and six healthy controls were recruited in a discovery cohort. Interstitial fibrosis changes were evaluated according to Oxford MEST-C scores. Urinary samples were analyzed with DIA-MS to identify hub proteins. Hub proteins were then confirmed by enzyme-linked immunosorbent assay (ELISA) in a validation cohort and the associated gene mRNA expression was analyzed using public gene expression omnibus (GEO) datasets.

RESULTS

Complement and coagulation cascades pathway was the main KEGG pathway related to the over-expressed proteins. Fibrinogen γ-Chain (FGG) was selected as the potential urinary marker for further validation. Urinary FGG to creatinine ratio (uFGG/Cr) levels were higher in both disease controls and IgAN group than in healthy controls, but were not significantly different between IgAN and disease groups. uFGG/Cr was confirmed to be increased with the extent of renal fibrosis and presented moderate correlations with T score (r = 0.614, p < 0.01) and eGFR (r = -0.682, p < 0.01), and a mild correlation with UTP (r = 0.497, p < 0.01) in IgAN group. In disease control group, uFGG/Cr was higher in patients with T1 + 2 compared to those with T0. uFGG/Cr had a good discriminatory power to distinguish different fibrosis stages in IgAN: interstitial fibrosis ≤ 5% (minimal fibrosis) vs. interstitial fibrosis (mild fibrosis) > 5%, AUC 0.743; T0 vs. T1 + 2, AUC 0.839; T0 + 1 vs. T2, AUC 0.854. In disease control group, uFGG/Cr showed better performance of AUC than UTP between minimal and mild fibrosis (p = 0.038 for Delong's test). Moreover, GSE104954 dataset showed that FGG mRNA expression was up-regulated (fold change 1.20, p = 0.009) in tubulointerstitium of IgAN patients when compared to healthy living kidney donors.

CONCLUSION

Urinary FGG is associated with renal interstitial fibrosis and could be used as a noninvasive biomarker for renal fibrosis in IgAN.

Glomerular deposition of fibrinogen predicts good prognosis of IgA nephropathy: a single-center cohort study

PURPOSE

It has been proven that fibrinogen deposition exists in IgA nephropathy (IgAN), but its clinical significance has not been identified. We aim to investigate the clinical implication of fibrinogen deposition in evaluating the activity and prognosis of IgA nephropathy.

METHODS

In this cohort, 935 adult IgAN patients were divided into 3 groups according to the intensity of glomerular fibrinogen deposition. Primary outcome refers to a composite event of either a ≥ 50% reduction in eGFR or ESRD (eGFR < 15 ml/min/1.73m2, dialysis, or renal transplantation). Factors associated with fibrinogen deposition and prognosis were identified.

RESULTS

The results showed that the intensity of fibrinogen deposition was positively correlated with eGFR (P < 0.001), serum albumin (P = 0.041), and hemoglobin levels (P < 0.05), but negatively correlated with age (P = 0.04), serum fibrinogen levels (P < 0.001), serum C4 (P = 0.023), the proportion of patients with hypertension (P = 0.003), and the percentage of glomeruli sclerosis (P < 0.001). The prognostic analyses identified that fibrinogen deposition was an independent predictor for the progression of IgAN (P = 0.033).

CONCLUSION

Our study indicated that the deposition of renal fibrinogen can predict the prognosis of IgAN with high reliability.

Extensive and Persistent Extravascular Dermal Fibrin Deposition Characterizes Systemic Sclerosis

Systemic sclerosis (SSc) is an autoimmune disease characterized by progressive multiorgan fibrosis. While the cause of SSc remains unknown, a perturbed vasculature is considered a critical early step in the pathogenesis. Using fibrinogen as a marker of vascular leakage, we found extensive extravascular fibrinogen deposition in the dermis of both limited and diffuse systemic sclerosis disease, and it was present in both early and late-stage patients. Based on a timed series of excision wounds, retention on the fibrin deposit of the splice variant domain, fibrinogen αEC, indicated a recent event, while fibrin networks lacking the αEC domain were older. Application of this timing tool to SSc revealed considerable heterogeneity in αEC domain distribution providing unique insight into disease activity. Intriguingly, the fibrinogen-αEC domain also accumulated in macrophages. These observations indicate that systemic sclerosis is characterized by ongoing vascular leakage resulting in extensive interstitial fibrin deposition that is either continually replenished and/or there is impaired fibrin clearance. Unresolved fibrin deposition might then incite chronic tissue remodeling.

Role of coagulation in persistent renal ischemia following reperfusion in an animal model

Ischemic acute kidney injury is common, deadly, and accelerates the progression of chronic kidney disease, yet has no specific therapy. After ischemia, reperfusion is patchy with early and persistent impairment in regional renal blood flow and cellular injury. We tested the hypothesis that intrarenal coagulation results in sustained renal ischemia following reperfusion, using a well-characterized model. Markedly decreased, but heterogeneous, microvascular plasma flow with microthrombi was found postischemia by intravital microscopy. Widespread tissue factor expression and fibrin deposition were also apparent. Clotting was accompanied by complement activation and inflammation. Treatment with exosomes derived from renal tubular cells or with the fibrinolytic urokinase, given 24 h postischemia when renal failure was established, significantly improved microvascular flow, coagulation, serum creatinine, and histological evidence of injury. These data support the hypothesis that intrarenal clotting occurs early and the resultant sustained ischemia is a critical determinant of renal failure following ischemia; they demonstrate that the coagulation abnormalities are amenable to therapy and that therapy results in improvement in both function and postischemic inflammation.NEW & NOTEWORTHY Ischemic renal injury carries very high morbidity and mortality, yet has no specific therapy. We found markedly decreased, heterogeneous microvascular plasma flow, tissue factor induction, fibrin deposition, and microthrombi after renal ischemia-reperfusion using a well-characterized model. Renal exosomes or the fibrinolytic urokinase, administered after renal failure was established, improved microvascular flow, coagulation, renal function, and histology. Data demonstrate that intrarenal clotting results in sustained ischemia amenable to therapy that improves both function and postischemic inflammation.

Tubular IKKβ Deletion Alleviates Acute Ischemic Kidney Injury and Facilitates Tissue Regeneration

Acute kidney injury (AKI) is a common renal injury leading to relevant morbidity and mortality worldwide. Most of the clinical cases of AKI are caused by ischemia reperfusion (I/R) injury with renal ischemia injury followed by reperfusion injury and activation of the innate immune response converging to NF-ĸB pathway induction. Despite the clear role of NF-ĸB in inflammation, it has recently been acknowledged that NF-ĸB may impact other cell functions. To identify NF-ĸB function with respect to metabolism, vascular function and oxidative stress after I/R injury and to decipher in detail the underlying mechanism, we generated a transgenic mouse model with targeted deletion of IKKβ along the tubule and applied I/R injury followed by its analysis after 2 and 14 days after I/R injury. Tubular IKKβ deletion ameliorated renal function and reduced tissue damage. RNAseq data together with immunohistochemical, biochemical and morphometric analysis demonstrated an ameliorated vascular organization and mRNA expression profile for increased angiogenesis in mice with tubular IKKβ deletion at 2 days after I/R injury. RNAseq and protein analysis indicate an ameliorated metabolism, oxidative species handling and timely-adapted cell proliferation and apoptosis as well as reduced fibrosis in mice with tubular IKKβ deletion at 14 days after I/R injury. In conclusion, mice with tubular IKKβ deletion upon I/R injury display improved renal function and reduced tissue damage and fibrosis in association with improved vascularization, metabolism, reactive species disposal and fine-tuned cell proliferation.

Deletion of STAT3 from Foxd1 cell population protects mice from kidney fibrosis by inhibiting pericytes trans-differentiation and migration

Signal transduction and activator of transcription 3 (STAT3) is a key transcription factor implicated in the pathogenesis of kidney fibrosis. Although Stat3 deletion in tubular epithelial cells is known to protect mice from fibrosis, vFoxd1 cells remains unclear. Using Foxd1-mediated Stat3 knockout mice, CRISPR, and inhibitors of STAT3, we investigate its function. STAT3 is phosphorylated in tubular epithelial cells in acute kidney injury, whereas it is expanded to interstitial cells in fibrosis in mice and humans. Foxd1-mediated deletion of Stat3 protects mice from folic-acid- and aristolochic-acid-induced kidney fibrosis. Mechanistically, STAT3 upregulates the inflammation and differentiates pericytes into myofibroblasts. STAT3 activation increases migration and profibrotic signaling in genome-edited, pericyte-like cells. Conversely, blocking Stat3 inhibits detachment, migration, and profibrotic signaling. Furthermore, STAT3 binds to the Collagen1a1 promoter in mouse kidneys and cells. Together, our study identifies a previously unknown function of STAT3 that promotes kidney fibrosis and has therapeutic value in fibrosis.

Adipocyte-Specific Ablation of PU.1 Promotes Energy Expenditure and Ameliorates Metabolic Syndrome in Aging Mice

Objective: Although PU.1/Spi1 is known as a master regulator for macrophage development and function, we have reported previously that it is also expressed in adipocytes and is transcriptionally induced in obesity. Here, we investigated the role of adipocyte PU.1 in the development of the age-associated metabolic syndrome.

Methods: We generated mice with adipocyte-specific PU.1 knockout, assessed metabolic changes in young and older adult PU.1^fl/fl (control) and AdipoqCre PU.1^fl/fl (aPU.1KO) mice, including body weight, body composition, energy expenditure, and glucose homeostasis. We also performed transcriptional analyses using RNA-Sequencing of adipocytes from these mice.

Results: aPU.1KO mice have elevated energy expenditure at a young age and decreased adiposity and increased insulin sensitivity in later life. Corroborating these observations, transcriptional network analysis indicated the existence of validated, adipocyte PU.1-modulated regulatory hubs that direct inflammatory and thermogenic gene expression programs.

Conclusion: Our data provide evidence for a previously uncharacterized role of PU.1 in the development of age-associated obesity and insulin resistance.

Folic acid-induced animal model of kidney disease

The kidneys are a vital organ that is vulnerable to both acute kidney injury (AKI) and chronic kidney disease (CKD) which can be caused by numerous risk factors such as ischemia, sepsis, drug toxicity and drug overdose, exposure to heavy metals, and diabetes. In spite of the advances in our understanding of the pathogenesis of AKI and CKD as well AKI transition to CKD, there is still no available therapeutics that can be used to combat kidney disease effectively, highlighting an urgent need to further study the pathological mechanisms underlying AKI, CKD, and AKI progression to CKD. In this regard, animal models of kidney disease are indispensable. This article reviews a widely used animal model of kidney disease, which is induced by folic acid (FA). While a low dose of FA is nutritionally beneficial, a high dose of FA is very toxic to the kidneys. Following a brief description of the procedure for disease induction by FA, major mechanisms of FA-induced kidney injury are then reviewed, including oxidative stress, mitochondrial abnormalities such as impaired bioenergetics and mitophagy, ferroptosis, pyroptosis, and increased expression of fibroblast growth factor 23 (FGF23). Finally, application of this FA-induced kidney disease model as a platform for testing the efficacy of a variety of therapeutic approaches is also discussed. Given that this animal model is simple to create and is reproducible, it should remain useful for both studying the pathological mechanisms of kidney disease and identifying therapeutic targets to fight kidney disease.

A high value of fibrinogen in immunoglobulin A nephropathy patients is associated with a worse renal tubular atrophy/interstitial fibrosis score

Purpose

The purpose of our study was to investigate the relationship between serum fibrinogen value and renal tubular atrophy/interstitial fibrosis in immunoglobulin A nephropathy patients with eGFR ≥90 ml/min/1.73 m².

Patients and Methods

Of 359 patients diagnosed with immunoglobulin A nephropathy after renal biopsy were enrolled in this retrospective study. Demographic, histopathological features, and clinical data were collected. The relationships among these factors were analyzed by using Student's t test, Mann‐Whitney U test, Kruskal‐Wallis test, Chi‐square test, or Fisher's exact test, where appropriate. The logistic regression analysis was performed to examine the independent risk factors.

Results

Of 176 immunoglobulin A nephropathy patients with eGFR ≥90 ml/min/1.73 m² were included in this study, and patients were classified into low fibrinogen (fibrinogen <304.6 mg/dl) and high fibrinogen (fibrinogen ≥304.6 mg/dl) groups, respectively. High fibrinogen groups had advanced age, a higher classification of renal tubular atrophy/interstitial fibrosis, and higher levels of systolic pressure, D‐dimer, 24 h urine protein quantitation, nag enzyme. Multivariate logistic analysis showed that fibrinogen (OR = 1.018) was significantly associated with tubular atrophy/interstitial fibrosis.

Conclusion

Among patients with immunoglobulin A nephropathy, the higher levels of fibrinogen and uric acid may mean a higher score of tubular atrophy/interstitial fibrosis, which suggests the renal biopsy should be performed for these patients as early as possible to defined pathological classification, even though there is no obvious abnormal change in the test of renal function.

Etodolac improves collagen induced rheumatoid arthritis in rats by inhibiting synovial inflammation, fibrosis and hyperplasia

Synovial hyperplasia is the main cause of chronic rheumatoid arthritis (RA), but the mechanism of synovial hyperplasia is still unclear. Etodolac (ETD) is a selective COX-2 inhibitor for relieving pain and stiffness in RA, but the disease modifying effect is still lack of evidence. Proteomics method was used to study the differential proteome of synovial tissue in collagen induced arthritis (CIA) in rats. With the help of STRING analysis, the upregulated proteins enriched in the cluster of complement and coagulation cascades and platelet degranulation were highlighted, these proteins with fibrogenic factors Lum, CIV, CXI and Tgfbi participated in the synovial inflammation, fibrosis and hyperplasia in CIA. Based on KOG function class analysis, the proteins involved in the events of the central dogma was explored. They might be hyperplasia related proteins for most of them are related to the proliferation of cancer. ETD significantly attenuated synovial inflammation, fibrosis and hyperplasia in CIA rats by downregulating these proteins. Several proteins have not been observed in RA so far, such as Tmsb4x, Pura, Nfic, Ruvbl1, Snrpd3, U2af2, Srrm2, Srsf7, Elavl1, Hnrnph1, Wars, Yars, Bzw2, Mcts1, Eif4b, Ctsh, Lamp1, Dpp7, Ptges3, Cdc37 and Septin9, they might be potentials targets for RA. Blood biochemistry tests showed the safety of 7 months use of ETD on rats. In conclusion, present study displayed a comprehensive mechanism of synovial hyperplasia in CIA rats, on this basis, the clinical value of ETD in the treatment of RA was well confirmed.

Coagulation, Protease-Activated Receptors, and Diabetic Kidney Disease: Lessons from eNOS-Deficient Mice

Endothelial nitric oxide synthase (eNOS) dysfunction is known to exacerbate the progression and prognosis of diabetic kidney disease (DKD). One of the mechanisms through which this is achieved is that low eNOS levels are associated with hypercoagulability, which promotes kidney injury. In the extrinsic coagulation cascade, the tissue factor (factor III) and downstream coagulation factors, such as active factor X (FXa), exacerbate inflammation through activation of the protease-activated receptors (PARs). Recently, it has been shown that the lack of or reduced eNOS expression in diabetic mice, as a model of advanced DKD, increases renal tissue factor levels and PAR1 and 2 expression in their kidneys. Furthermore, pharmaceutical inhibition or genetic deletion of coagulation factors or PARs ameliorated inflammation in DKD in mice lacking eNOS. In this review, we summarize the relationship between eNOS, coagulation, and PARs and propose a novel therapeutic option for the management of patients with DKD.

A Novel Urinary Proteomics Classifier for Non-Invasive Evaluation of Interstitial Fibrosis and Tubular Atrophy in Chronic Kidney Disease

Non-invasive urinary peptide biomarkers are able to detect and predict chronic kidney disease (CKD). Moreover, specific urinary peptides enable discrimination of different CKD etiologies and offer an interesting alternative to invasive kidney biopsy, which cannot always be performed. The aim of this study was to define a urinary peptide classifier using mass spectrometry technology to predict the degree of renal interstitial fibrosis and tubular atrophy (IFTA) in CKD patients. The urinary peptide profiles of 435 patients enrolled in this study were analyzed using capillary electrophoresis coupled with mass spectrometry (CE-MS). Urine samples were collected on the day of the diagnostic kidney biopsy. The proteomics data were divided into a training (n = 200) and a test (n = 235) cohort. The fibrosis group was defined as IFTA ≥ 15% and no fibrosis as IFTA < 10%. Statistical comparison of the mass spectrometry data enabled identification of 29 urinary peptides with differential occurrence in samples with and without fibrosis. Several collagen fragments and peptide fragments of fetuin-A and others were combined into a peptidomic classifier. The classifier separated fibrosis from non-fibrosis patients in an independent test set (n = 186) with area under the curve (AUC) of 0.84 (95% CI: 0.779 to 0.889). A significant correlation of IFTA and FPP_BH29 scores could be observed Rho = 0.5, p < 0.0001. We identified a peptidomic classifier for renal fibrosis containing 29 peptide fragments corresponding to 13 different proteins. Urinary proteomics analysis can serve as a non-invasive tool to evaluate the degree of renal fibrosis, in contrast to kidney biopsy, which allows repeated measurements during the disease course.

Delayed administration of suramin attenuates peritoneal fibrosis in rats

BACKGROUND

Peritoneal fibrosis is the most common complication of peritoneal dialysis, but there is currently no effective treatment. We previously reported that suramin pretreatment prevents the development of peritoneal fibrosis in a rat model of peritoneal fibrosis induced by chlorhexidine gluconate (CG). Here, we further examined the effectiveness of delayed administration of suramin on peritoneal fibrosis and the mechanism (s) involved in this process.

METHODS

In the rat model of peritoneal fibrosis induced by CG, suramin or saline was administered at day 21 and 28. All rats were then sacrificed to collect peritoneal tissues for Western blot analysis and histological staining at day 35.

RESULTS

Our results demonstrated that delayed administration of suramin starting at 21 days following CG injection can ameliorate peritoneal damage, with greater efficacy after two injections. Suramin also reduced the expression of α-smooth muscle actin, Collagen 1, and Fibronectin and suppressed phosphorylation of Smad-3, epidermal growth factor receptor (EGFR), signal transducers, activator of transcription 3 (STAT3) as well as extracellular signal-regulated kinases 1/2 (ERK 1/2) in the peritoneum injured with CG. Moreover, delayed administration of suramin inhibited overproduction of transforming growth factor-β1(TGF-β1) and expression of several pro-inflammatory cytokines, including monocyte chemoattractant protein-1, tumor necrosis factor-α, interleukin-1, and interleukin-6.

CONCLUSIONS

Our results indicated that suramin can attenuate progression of peritoneal fibrosis by a mechanism involving inhibition of the TGF-β1/Smad3 and EGFR signaling pathways as well as suppression of multiple proinflammatory cytokines. Thus, suramin may have the potential to offer an effective treatment for peritoneal fibrosis.

Characterization of Matricellular Protein Expression Signatures in Mechanistically Diverse Mouse Models of Kidney Injury

Fibrosis is the most common pathophysiological manifestation of Chronic Kidney Disease (CKD). It is defined as excessive deposition of extracellular matrix (ECM) proteins. Embedded within the ECM are a family of proteins called Matricellular Proteins (MCPs), which are typically expressed during chronic pathologies for ECM processing. As such, identifying potential MCPs in the pathological secretome of a damaged kidney could serve as diagnostic/therapeutic targets of fibrosis. Using published RNA-Seq data from two kidney injury mouse models of different etiologies, Folic Acid (FA) and Unilateral Ureteral Obstruction (UUO), we compared and contrasted the expression profile of various members from well-known MCP families during the Acute and Fibrotic injury phases. As a result, we identified common and distinct MCP expression signatures between both injury models. Bioinformatic analysis of their differentially expressed MCP genes revealed similar top annotation clusters from Molecular Function and Biological Process networks, which are those commonly involved in fibrosis. Using kidney lysates from FA- and UUO-injured mice, we selected MCP genes from our candidate list to confirm mRNA expression by Western Blot, which correlated with injury progression. Understanding the expressions of MCPs will provide important insight into the processes of kidney repair, and may validate MCPs as biomarkers and/or therapeutic targets of CKD.

Found in Translation: Reasons for Optimism in the Pursuit to Prevent Chronic Kidney Disease After Acute Kidney Injury

Purpose of review:

The current review will discuss on the progress of studying the transition phase between acute kidney injury (AKI) and chronic kidney disease (CKD) through improved animal models, common AKI and CKD pathways, and how human studies may inform different translational approaches.

Sources of information:

PubMed and Google Scholar.

Methods:

A narrative review was performed using the main terms “acute kidney injury,” “chronic kidney disease,” “end-stage renal disease,” “animal models,” “review,” “decision-making,” and “translational research.”

Key findings:

The last decade has shown much progress in the study of AKI, including evidence of a pathophysiological link between AKI and CKD. We are now in a phase of redesigning animal models and discovering mechanisms that can replicate the pathological conditions of the AKI-to-CKD continuum. Translating these findings into the clinic is a barrier that must be overcome. To this end, current efforts include prediction of AKI onset and maladaptive repair, detecting patients susceptible to the progression of chronic maladaptive repair, and understanding shared signaling mechanisms between AKI and CKD.

Limitations:

This is a narrative review of the literature that is partially influenced by the knowledge, perspectives, and experiences of the authors and their research background.

Implications:

Overall, this new knowledge from the AKI-to-CKD continuum will help bridge the discontinuity that exists between animal models and patients, resulting in more effective translational biomarkers and therapeutics to test in known AKI pathologies thereby preventing the chronicity of kidney injury progression.

Multi omics analysis of fibrotic kidneys in two mouse models

Kidney fibrosis represents an urgent unmet clinical need due to the lack of effective therapies and an inadequate understanding of the molecular pathogenesis. We have generated a comprehensive and combined multi-omics dataset (proteomics, mRNA and small RNA transcriptomics) of fibrotic kidneys that is searchable through a user-friendly web application: http://hbcreports.med.harvard.edu/fmm/ . Two commonly used mouse models were utilized: a reversible chemical-induced injury model (folic acid (FA) induced nephropathy) and an irreversible surgically-induced fibrosis model (unilateral ureteral obstruction (UUO)). mRNA and small RNA sequencing, as well as 10-plex tandem mass tag (TMT) proteomics were performed with kidney samples from different time points over the course of fibrosis development. The bioinformatics workflow used to process, technically validate, and combine the single omics data will be described. In summary, we present temporal multi-omics data from fibrotic mouse kidneys that are accessible through an interrogation tool (Mouse Kidney Fibromics browser) to provide a searchable transcriptome and proteome for kidney fibrosis researchers.

Identification of fibrinogen as a natural inhibitor of MMP-2

Non-genetic MMP-2 insufficiency is a relatively unexplored condition which could be induced by pathological overexpression of endogenous MMP-2 inhibitors such as TIMPs and/or the acute phase reactant alpha-2-macroglobulin. Here, we investigate the hypothesis that human fibrinogen (FBG) – an acute phase reactant – inhibits human MMP-2. Following an unexpected observation where sera from human donors including arthritis patients with increased levels of serum FBG exhibited reduced binding of serum proMMP-2 to gelatin, we found that human FBG (0 to 3.6 mg/mL i.e., 0 to 10.6 μM) concentration-dependently inhibited human proMMP-2 and MMP2 from binding to gelatin. Moreover, at normal physiological concentrations, FBG (5.29–11.8 μM) concentration-dependently inhibited (40–70% inhibition) the cleavage of fluorescein-conjugated gelatin by MMP-2, but not MMP-9. Indicative of a mixed-type (combination of competitive and non-competitive) inhibition mechanism, FBG reduced the V_max (24.9 ± 0.7 min⁻¹ to 17.7 ± 0.9 min⁻¹, P < 0.05) and increased the Michaelis-Menten constant K_M (204 ± 6 n_M to 478 ± 50 nM, P < 0.05) for the reaction of MMP-2 cleavage of fluorescein-conjugated gelatin. In silico analyses and studies of FBG neutralization with anti-FBG antibodies implicated the domains D and E of FBG in the inhibition of MMP-2. In conclusion, FBG is a natural selective MMP-2 inhibitor, whose pathological elevation could lead to MMP-2 insufficiency in humans.

Significance of glomerular fibrinogen deposition in children with Henoch-Schönlein purpura nephritis

BACKGROUND

Henoch-Schönlein purpura nephritis (HSPN) is the most common pediatric secondary glomerular disease. This study aimed to investigate the significance of glomerular fibrinogen (Fib) deposition in children with HSPN.

METHODS

Eighty-two patients with HSPN were enrolled retrospectively at the Children's Hospital of Soochow University from January 2015 to March 2017. Patients were divided into groups according to the presence or absence and intensity of glomerular Fib deposits, and clinical and pathological features were compared among the groups.

RESULTS

Glomerular Fib deposition was observed in 64 children (78.05%), including 1 Fib± case (1.22%), 23 Fib+ cases (28.05%), 37 Fib++ cases (45.12%), and 3 Fib+++ cases (3.66%). Significantly different levels of high-sensitivity C-reactive protein (hs-CRP), D-dimer (DD), proportions of CD19 + CD23+ cells and urine microalbumin:creatinine ratios (UMA/Cr) were noted among the different Fib deposition groups (no, mild and severe). Pairwise comparison in multiple groups revealed significantly increased hs-CRP, proportion of CD19 + CD23+ cells and UMA/Cr in the severe deposition group compared with the mild and no deposition groups, and remarkably increased DD levels were noted in the severe and mild deposition groups compared with the no deposition group. The degree of glomerular Fib deposition was positively correlated with the degree of glomerular IgA deposition, and the incidence of glomerular IgG deposition in the severe deposition group was increased compared with the no deposition group.

CONCLUSION

HSPN children with glomerular Fib deposition, especially those with severe Fib deposition, exhibit more severely disordered immunologic function, inflammatory reactions and hypercoagulability; glomerular damage in these patients may also be more severe.

Activation of Hepatic Stellate Cells During Liver Carcinogenesis Requires Fibrinogen/Integrin αvβ5 in Zebrafish

Hepatocellular carcinoma (HCC) is one of the most common cancers and it usually develops from a background of liver fibrosis or inflammation. The crosstalk between tumor cells and stromal cells plays an important and stimulating role during tumor progression. Previously we found in a krasV12-induced zebrafish HCC model that oncogenic hepatocytes activate hepatic stellate cells (HSCs) by up-regulation of serotonin and activate neutrophils and macrophages by up-regulation of cortisol. In the present study, we found a novel signaling transduction mechanism between oncogenic hepatocytes and HSCs. After krasV12 induction, fibrinogen was up-regulated in oncogenic hepatocytes. We reasoned that fibrinogen may bind to integrin αvβ5 on HSCs to activate HSCs. Consistent with this notion, pharmaceutical treatment using an antagonist of integrin αvβ5, cilengitide, significantly blocked HSC activation and function, accompanied by attenuated proliferation of oncogenic hepatocytes and progression of liver fibrosis. On the contrary, adenosine 5'-diphosphate, an agonist of αvβ5, activated HSCs significantly that further stimulated the tumor progression and liver fibrosis. Interestingly, in human liver disease samples, we detected an increased level of fibrinogen during tumor progression which indicated the potential role of fibrinogen signaling in HCC progression. Thus, we concluded a novel interaction between oncogenic hepatocytes and HSCs through the fibrinogen related pathway in both the zebrafish HCC model and human liver disease samples.

Urinary Fibrinogen as a Predictor of Progression of CKD

BACKGROUND AND OBJECTIVES

Fibrinogen has been reported to be involved in kidney tubulointerstitial fibrosis and podocyte injury in mouse models. However, the relationship between urinary fibrinogen and kidney outcomes has not been clarified in patients with CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We evaluated 402 patients with CKD and kidney biopsies, including 101 with diabetic nephropathy, 94 with idiopathic membranous nephropathy, 55 with idiopathic FSGS, and 152 with IgA nephropathy. We quantified urinary fibrinogen by ELISA and tested associations with kidney histology and progression to ESRD.

RESULTS

Median (interquartile range) urinary fibrinogen-to-creatinine ratio was 536 (191-1461) ng/mg for patients with CKD, significantly higher than 2 (2-3) ng/mg for healthy controls (P<0.001). Urinary fibrinogen was positively correlated with urine protein (r=0.64; P<0.001) and interstitial fibrosis and tubular atrophy (r=0.10; P=0.04), and it was negatively correlated with eGFR (r=-0.20; P<0.001). Over a median follow-up period of 35 months (interquartile range, 24-78 months), 68 of 402 patients (17%) developed ESRD. Higher urinary fibrinogen level was associated with increased risk of ESRD (hazard ratio, 2.12; 95% confidence interval, 1.31 to 3.26) per log10 higher urinary fibrinogen-to-creatinine ratio (P=0.003) adjusting for age, sex, BP, urine protein, disease type, eGFR, and interstitial fibrosis and tubular atrophy. For prediction of ESRD, the addition of urinary fibrinogen to eGFR, urine protein, and BP increased the area under the receiver operating curve from 0.73 to 0.76, and the Akaike information criterion improved from 333.6 to 327.0.

CONCLUSIONS

Urinary fibrinogen correlated with interstitial fibrosis and tubular atrophy and was an independent risk factor for progression of CKD to ESRD.

Elevated serum fibrinogen level is an independent risk factor for IgA nephropathy

Background

IgA nephropathy is a primary cause of renal failure, and inflammation and renal fibrosis are the main mechanisms leading to kidney damage. The serum fibrinogen level is closely related to inflammatory states, but its relationship to the prognosis of IgA nephropathy (IgAN) is unclear.

Materials and Methods

1053 patients diagnosed with IgAN after renal biopsy were enrolled from two Nephrology Departments. Demographic and clinical data and histopathological features were collected. The patients were divided into four groups (Q1–Q4) according to the serum fibrinogen levels at the time of renal biopsy, and the relationships of serum fibrinogen levels with other risk factors and the prognosis of IgAN were investigated.

Results

672 patients with proven primary IgAN were included in this study, which included a median follow-up of 36 months. Patients with higher serum fibrinogen levels had elevated serum creatinine levels, 24-hour urinary protein, and blood pressure compared with patients with the lowest levels of serum fibrinogen as well as severe renal damage at the time of renal biopsy. Univariate and multivariate Cox regression analyses confirmed that the serum fibrinogen level at the time of renal biopsy was significantly related to the prognosis of patients with IgAN.

Conclusions

In patients with IgAN, an elevated serum fibrinogen level at the time of renal biopsy is associated with poor renal outcomes, which suggests the need for more aggressive early interventions. Greater benefits of aggressive treatments were observed in patients with higher serum fibrinogen levels.

Prediction of Chronic Kidney Disease Stage 3 by CKD273, a Urinary Proteomic Biomarker

Introduction

CKD273 is a urinary biomarker, which in advanced chronic kidney disease predicts further deterioration. We investigated whether CKD273 can also predict a decline of estimated glomerular filtration rate (eGFR) to <60 ml/min per 1.73 m².

Methods

In analyses of 2087 individuals from 6 cohorts (46.4% women; 73.5% with diabetes; mean age, 46.1 years; eGFR ≥ 60 ml/min per 1.73 m², 100%; urinary albumin excretion rate [UAE] ≥20 μg/min, 6.2%), we accounted for cohort, sex, age, mean arterial pressure, diabetes, and eGFR at baseline and expressed associations per 1-SD increment in urinary biomarkers.

Results

Over 5 (median) follow-up visits, eGFR decreased more with higher baseline CKD273 than UAE (1.64 vs. 0.82 ml/min per 1.73 m²; P < 0.0001). Over 4.6 years (median), 390 participants experienced a first renal endpoint (eGFR decrease by ≥10 to <60 ml/min per 1.73 m²), and 172 experienced an endpoint sustained over follow-up. The risk of a first and sustained renal endpoint increased with UAE (hazard ratio ≥ 1.23; P ≤ 0.043) and CKD273 (≥ 1.20; P ≤ 0.031). UAE (≥20 μg/min) and CKD273 (≥0.154) thresholds yielded sensitivities of 30% and 33% and specificities of 82% and 83% (P ≤ 0.0001 for difference between UAE and CKD273 in proportion of correctly classified individuals). As continuous markers, CKD273 (P = 0.039), but not UAE (P = 0.065), increased the integrated discrimination improvement, while both UAE and CKD273 improved the net reclassification index (P ≤ 0.0003), except for UAE per threshold (P = 0.086).

Discussion

In conclusion, while accounting for baseline eGFR, albuminuria, and covariables, CKD273 adds to the prediction of stage 3 chronic kidney disease, at which point intervention remains an achievable therapeutic target.

A Urinary Fragment of Mucin-1 Subunit α Is a Novel Biomarker Associated With Renal Dysfunction in the General Population

INTRODUCTION

Sequencing peptides included in the urinary proteome identifies the parent proteins and may reveal mechanisms underlying the pathophysiology of chronic kidney disease.

METHODS

In 805 randomly recruited Flemish individuals (50.8% women; mean age, 51.1 years), we determined the estimated glomerular filtration rate (eGFR) from serum creatinine using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. We categorized eGFR according to the National Kidney Foundation Kidney Disease Outcomes Quality Initiative guideline. We analyzed 74 sequenced urinary peptides with a detectable signal in more than 95% of participants. Follow-up measurements of eGFR were available in 597 participants.

RESULTS

In multivariable analyses, baseline eGFR decreased (P ≤ 0.022) with urinary fragments of mucin-1 (standardized association size expressed in ml/min/1.73 m², -4.48), collagen III (-2.84), and fibrinogen (-1.70) and was bi-directionally associated (P ≤ 0.0006) with 2 urinary collagen I fragments (+2.28 and -3.20). The eGFR changes over 5 years (follow-up minus baseline) resulted in consistent estimates (P ≤ 0.025) for mucin-1 (-1.85), collagen (-1.37 to 1.43) and fibrinogen (-1.45) fragments. Relative risk of having or progressing to eGFR <60 ml/min/1.73 m² was associated with mucin-1. Partial least-squares analysis confirmed mucin-1 as the strongest urinary marker associated with decreased eGFR, with a score of 2.47 compared with 1.80 for a collagen I fragment as the next contender. Mucin-1 predicted eGFR decline to <60 ml/min/1.73 m² over and above microalbuminuria (P = 0.011) and retained borderline significance (P = 0.05) when baseline eGFR was accounted for.

DISCUSSION

In the general population, mucin-1 subunit α, an extracellular protein that is shed from renal tubular epithelium, is a novel biomarker associated with renal dysfunction.

Silencing SMOC2 ameliorates kidney fibrosis by inhibiting fibroblast to myofibroblast transformation

Secreted modular calcium-binding protein 2 (SMOC2) belongs to the secreted protein acidic and rich in cysteine (SPARC) family of matricellular proteins whose members are known to modulate cell-matrix interactions. We report that SMOC2 is upregulated in the kidney tubular epithelial cells of mice and humans following fibrosis. Using genetically manipulated mice with SMOC2 overexpression or knockdown, we show that SMOC2 is critically involved in the progression of kidney fibrosis. Mechanistically, we found that SMOC2 activates a fibroblast-to-myofibroblast transition (FMT) to stimulate stress fiber formation, proliferation, migration, and extracellular matrix production. Furthermore, we demonstrate that targeting SMOC2 by siRNA results in attenuation of TGFβ1-mediated FMT in vitro and an amelioration of kidney fibrosis in mice. These findings implicate that SMOC2 is a key signaling molecule in the pathological secretome of a damaged kidney and targeting SMOC2 offers a therapeutic strategy for inhibiting FMT-mediated kidney fibrosis - an unmet medical need.

Regardless of etiology, progressive renal disease causes ultrastructural and functional alterations of peritubular capillaries

Progressive renal diseases are associated with rarefaction of peritubular capillaries, but the ultrastructural and functional alterations of the microvasculature are not well described. To study this, we analyzed different time points during progressive kidney damage and fibrosis in 3 murine models of different disease etiologies. These models were unilateral ureteral obstruction, unilateral ischemia-reperfusion injury, and Col4a3-deficient mice, we analyzed ultrastructural alterations in patient biopsy specimens. Compared with kidneys of healthy mice, we found a significant and progressive reduction of peritubular capillaries in all models analyzed. Ultrastructurally, compared with the kidneys of control mice, focal widening of the subendothelial space and higher numbers of endothelial vacuoles and caveolae were found in fibrotic kidneys. Quantitative analysis showed that peritubular capillary endothelial cells in fibrotic kidneys had significantly and progressively reduced numbers of fenestrations and increased thickness of the cell soma and lamina densa of the capillary basement membrane. Similar ultrastructural changes were also observed in patient's kidney biopsy specimens. Compared with healthy murine kidneys, fibrotic kidneys had significantly increased extravasation of Evans blue dye in all 3 models. The extravasation could be visualized using 2-photon microscopy in real time in living animals and was mainly localized to capillary branching points. Finally, fibrotic kidneys in all models exhibited a significantly greater degree of interstitial deposition of fibrinogen. Thus, peritubular capillaries undergo significant ultrastructural and functional alterations during experimental progressive renal diseases, independent of the underlying injury. Analyses of these alterations could provide read-outs for the evaluation of therapeutic approaches targeting the renal microvasculature.

RNA-binding Protein Musashi Homologue 1 Regulates Kidney Fibrosis by Translational Inhibition of p21 and Numb mRNA

RNA-binding proteins (RBPs) are recognized as key posttranscriptional regulators that not only modulate the spatiotemporal expression of genes during organism development but also regulate disease pathogenesis. Very limited information exists on the potential role of RBPs in modulating kidney fibrosis, which is a major hallmark of chronic kidney disease. Here, we report a novel mechanism in kidney fibrosis involving a RBP, Musashi homologue 1 (Msi1), which is expressed in tubular epithelial cells. Using two mechanistically distinct mouse models of kidney fibrosis, we show that Msi1 protein levels are significantly down-regulated in the kidneys following fibrosis. We found that Msi1 functions by negatively regulating the translation of its target mRNAs, p21 and Numb, whose protein levels are markedly increased in kidney fibrosis. Also, Msi1 overexpression and knockdown in kidney epithelial cells cause p21- and Numb-mediated cell cycle arrest. Furthermore, we observed that Numb looses its characteristic membrane localization in fibrotic kidneys and therefore is likely unable to inhibit Notch resulting in tubular cell death. Oleic acid is a known inhibitor of Msi1 and injecting oleic acid followed by unilateral ureteral obstruction surgery in mice resulted in enhanced fibrosis compared with the control group, indicating that inhibiting Msi1 activity renders the mice more susceptible to fibrosis. Given that deregulated fatty acid metabolism plays a key role in kidney fibrosis, these results demonstrate a novel connection between fatty acid and Msi1, an RNA-binding protein, in kidney fibrosis.

Fibrin deposition following bile duct injury limits fibrosis through an αMβ2-dependent mechanism

Coagulation cascade activation and fibrin deposits have been implicated or observed in diverse forms of liver damage. Given that fibrin amplifies pathological inflammation in several diseases through the integrin receptor αMβ2, we tested the hypothesis that disruption of the fibrin(ogen)-αMβ2 interaction in Fibγ(390-396A) mice would reduce hepatic inflammation and fibrosis in an experimental setting of chemical liver injury. Contrary to our hypothesis, α-naphthylisothiocyanate (ANIT)-induced liver fibrosis increased in Fibγ(390-396A) mice, whereas inflammatory cytokine expression and hepatic necrosis were similar to ANIT-challenged wild-type (WT) mice. Increased fibrosis in Fibγ(390-396A) mice appeared to be independent of coagulation factor 13 (FXIII) transglutaminase, as ANIT challenge in FXIII-deficient mice resulted in a distinct pathological phenotype characterized by increased hepatic necrosis. Rather, bile duct proliferation underpinned the increased fibrosis in ANIT-exposed Fibγ(390-396A) mice. The mechanism of fibrin-mediated fibrosis was linked to interferon (IFN)γ induction of inducible nitric oxide synthase (iNOS), a gene linked to bile duct hyperplasia and liver fibrosis. Expression of iNOS messenger RNA was significantly increased in livers of ANIT-exposed Fibγ(390-396A) mice. Fibrin(ogen)-αMβ2 interaction inhibited iNOS induction in macrophages stimulated with IFNγ in vitro and ANIT-challenged IFNγ-deficient mice had reduced iNOS induction, bile duct hyperplasia, and liver fibrosis. Further, ANIT-induced iNOS expression, liver fibrosis, and bile duct hyperplasia were significantly reduced in WT mice administered leukadherin-1, a small molecule that allosterically enhances αMβ2-dependent cell adhesion to fibrin. These studies characterize a novel mechanism whereby the fibrin(ogen)-integrin-αMβ2 interaction reduces biliary fibrosis and suggests a novel putative therapeutic target for this difficult-to-treat fibrotic disease.

Application of small RNA sequencing to identify microRNAs in acute kidney injury and fibrosis

Establishing a microRNA (miRNA) expression profile in affected tissues provides an important foundation for the discovery of miRNAs involved in the development or progression of pathologic conditions. We conducted small RNA sequencing to generate a temporal profile of miRNA expression in the kidneys using a mouse model of folic acid-induced (250mg/kgi.p.) kidney injury and fibrosis. From the 103 miRNAs that were differentially expressed over the time course (>2-fold, p<0.05), we chose to further investigate miR-18a-5p, which is expressed during the acute stage of the injury; miR-132-3p, which is upregulated during transition between acute and fibrotic injury; and miR-146b-5p, which is highly expressed at the peak of fibrosis. Using qRT-PCR, we confirmed the increased expression of these candidate miRNAs in the folic acid model as well as in other established mouse models of acute injury (ischemia/reperfusion injury) and fibrosis (unilateral ureteral obstruction). In situ hybridization confirmed high expression of miR-18a-5p, miR-132-3p and miR-146b-5p throughout the kidney cortex in mice and humans with severe kidney injury or fibrosis. When primary human proximal tubular epithelial cells were treated with model nephrotoxicants such as cadmium chloride (CdCl₂), arsenic trioxide, aristolochic acid (AA), potassium dichromate (K₂Cr₂O₇) and cisplatin, miRNA-132-3p was upregulated 4.3-fold after AA treatment and 1.5-fold after K₂Cr₂O₇ and CdCl₂ treatment. These results demonstrate the application of temporal small RNA sequencing to identify miR-18a, miR-132 and miR-146b as differentially expressed miRNAs during distinct phases of kidney injury and fibrosis progression.

The emerging role of coagulation proteases in kidney disease

A role of coagulation proteases in kidney disease beyond their function in normal haemostasis and thrombosis has long been suspected, and studies performed in the past 15 years have provided novel insights into the mechanisms involved. The expression of protease-activated receptors (PARs) in renal cells provides a molecular link between coagulation proteases and renal cell function and revitalizes research evaluating the role of haemostasis regulators in renal disease. Renal cell-specific expression and activity of coagulation proteases, their regulators and their receptors are dynamically altered during disease processes. Furthermore, renal inflammation and tissue remodelling are not only associated, but are causally linked with altered coagulation activation and protease-dependent signalling. Intriguingly, coagulation proteases signal through more than one receptor or induce formation of receptor complexes in a cell-specific manner, emphasizing context specificity. Understanding these cell-specific signalosomes and their regulation in kidney disease is crucial to unravelling the pathophysiological relevance of coagulation regulators in renal disease. In addition, the clinical availability of small molecule targeted anticoagulants as well as the development of PAR antagonists increases the need for in-depth knowledge of the mechanisms through which coagulation proteases might regulate renal physiology.

RNA Sequencing Identifies Novel Translational Biomarkers of Kidney Fibrosis

CKD is the gradual, asymptomatic loss of kidney function, but current tests only identify CKD when significant loss has already happened. Several potential biomarkers of CKD have been reported, but none have been approved for preclinical or clinical use. Using RNA sequencing in a mouse model of folic acid-induced nephropathy, we identified ten genes that track kidney fibrosis development, the common pathologic finding in patients with CKD. The gene expression of all ten candidates was confirmed to be significantly higher (approximately ten- to 150-fold) in three well established, mechanistically distinct mouse models of kidney fibrosis than in models of nonfibrotic AKI. Protein expression of these genes was also high in the folic acid model and in patients with biopsy-proven kidney fibrosis. mRNA expression of the ten genes increased with increasing severity of kidney fibrosis, decreased in response to therapeutic intervention, and increased only modestly (approximately two- to five-fold) with liver fibrosis in mice and humans, demonstrating specificity for kidney fibrosis. Using targeted selected reaction monitoring mass spectrometry, we detected three of the ten candidates in human urine: cadherin 11 (CDH11), macrophage mannose receptor C1 (MRC1), and phospholipid transfer protein (PLTP). Furthermore, urinary levels of each of these three proteins distinguished patients with CKD (n=53) from healthy individuals (n=53; P<0.05). In summary, we report the identification of urinary CDH11, MRC1, and PLTP as novel noninvasive biomarkers of CKD.