Hypoxia and Dysregulated Angiogenesis in Kidney Disease

RAS protein activator-like 2 (RASAL2) initiates peritubular capillary rarefaction in hypoxic renal interstitial fibrosis

The progression of chronic kidney disease (CKD) often involves renal interstitial fibrosis (RIF) and subsequent loss of peritubular capillaries (PTCs), which enhances disease severity. Despite advancements in our understanding of fibrosis, effective interventions for reversing capillary loss remain elusive. Notably, RIF exhibits reduced capillary density, whereas renal cell carcinoma (RCC) shows robust angiogenesis under hypoxic conditions. Using RNA sequencing and bioinformatics, we identified differentially expressed genes (DEGs) in hypoxic human renal tubular epithelial cells (HK-2) and renal cancer cells (786-0). Analysis of altered Ras and PI3K/Akt pathways coupled with hub gene investigation revealed RAS protein activator-like 2 (RASAL2) as a key candidate. Subsequent in vitro and in vivo studies confirmed RASAL2's early-stage response in RIF, which reduced with fibrosis progression. RASAL2 suppression in HK-2 cells enhanced angiogenesis, as evidenced by increased proliferation, migration, and branching of human umbilical vein endothelial cells (HUVECs) co-cultured with HK-2 cells. In mice, RASAL2 knockdown improved Vascular endothelial growth factor A (VEGFA) and Proliferating cell nuclear antigen (PCNA) levels in unilateral ureteral occlusion (UUO)-induced fibrosis (compared to wild type). Hypoxia-inducible factor 1 alpha (HIF-1α) emerged as a pivotal mediator, substantiated by chromatin immunoprecipitation (ChIP) sequencing, with its induction linked to activation. Hypoxia increased the production of RASAL2-enriched extracellular vesicles (EVs) derived from tubular cells, which were internalized by endothelial cells, contributing to the exacerbation of PTC loss. These findings underscore RASAL2's role in mediating reduced angiogenesis in RIF and reveal a novel EV-mediated communication between hypoxic tubular- and endothelial cells, demonstrating a complex interplay between angiogenesis and fibrosis in CKD pathogenesis.

ELABELA-derived peptide ELA13 attenuates kidney fibrosis by inhibiting the Smad and ERK signaling pathways

Kidney fibrosis is an inevitable result of various chronic kidney diseases (CKDs) and significantly contributes to end-stage renal failure. Currently, there is no specific treatment available for renal fibrosis. ELA13 (amino acid sequence: RRCMPLHSRVPFP) is a conserved region of ELABELA in all vertebrates; however, its biological activity has been very little studied. In the present study, we evaluated the therapeutic effect of ELA13 on transforming growth factor-β1 (TGF-β1)-treated NRK-52E cells and unilateral ureteral occlusion (UUO) mice. Our results demonstrated that ELA13 could improve renal function by reducing creatinine and urea nitrogen content in serum, and reduce the expression of fibrosis biomarkers confirmed by Masson staining, immunohistochemistry, real-time polymerase chain reaction (RT-PCR), and western blot. Inflammation biomarkers were increased after UUO and decreased by administration of ELA13. Furthermore, we found that the levels of essential molecules in the mothers against decapentaplegic (Smad) and extracellular signal-regulated kinase (ERK) pathways were reduced by ELA13 treatment in vivo and in vitro. In conclusion, ELA13 protected against kidney fibrosis through inhibiting the Smad and ERK signaling pathways and could thus be a promising candidate for anti-renal fibrosis treatment.

Advances in imaging techniques to assess kidney fibrosis

As a sign of chronic kidney disease (CKD) progression, renal fibrosis is an irreversible and alarming pathological change. The accurate diagnosis of renal fibrosis depends on the widely used renal biopsy, but this diagnostic modality is invasive and can easily lead to sampling error. With the development of imaging techniques, an increasing number of noninvasive imaging techniques, such as multipara meter magnetic resonance imaging (MRI) and ultrasound elastography, have gained attention in assessing kidney fibrosis. Depending on their ability to detect changes in tissue stiffness and diffusion of water molecules, ultrasound elastography and some MRI techniques can indirectly assess the degree of fibrosis. The worsening of renal tissue oxygenation and perfusion measured by blood oxygenation level-dependent MRI and arterial spin labeling MRI separately is also an indirect reflection of renal fibrosis. Objective and quantitative indices of fibrosis may be available in the future by using novel techniques, such as photoacoustic imaging and fluorescence microscopy. However, these imaging techniques are susceptible to interference or may not be convenient. Due to the lack of sufficient specificity and sensitivity, these imaging techniques are neither widely accepted nor proposed by clinicians. These obstructions must be overcome by conducting technology research and more prospective studies. In this review, we emphasize the recent advancement of these noninvasive imaging techniques and provide clinicians a continuously updated perspective on the assessment of kidney fibrosis.

Identifying key genes related to the peritubular capillary rarefaction in renal interstitial fibrosis by bioinformatics

Renal interstitial fibrosis (RIF) is a key feature of progressive chronic kidney disease (CKD), characterized by tubular epithelial cell (TEC) hypoxia and peritubular capillary (PTC) rarefaction. However, the mechanisms underlying these processes remain poorly understood. To address this knowledge gap, we conducted a comparative transcriptome analysis of hypoxic and normoxic HK-2 cells, identifying 572 differentially expressed genes (DEGs). Subsequent Gene Ontology (GO), protein‒protein interaction (PPI) network, and hub gene analyses revealed significant enrichment of DEGs in the HIF-1 signaling pathway based on KEGG enrichment analysis. To further explore TEC modulation under hypoxic conditions, we performed chromatin immunoprecipitation (ChIP) sequencing targeting HIF-1α, identifying 2915 genes potentially regulated by HIF-1α. By comparing RNA sequencing and ChIP sequencing data, we identified 43 overlapping DEGs. By performing GO analysis and peak annotation with IGV, we identified two candidate molecules, VEGFA and BTG1, that are associated with angiogenesis and whose gene sequences were reliably bound by HIF-1α. Our study elucidates the molecular mechanisms underlying RIF, providing valuable insights for potential therapeutic interventions.

Analysis of microRNA expression in rat kidneys after VEGF inhibitor treatment under different degrees of hypoxia

Previously, we found that the incidence of kidney injury in patients with chronic hypoxia was related to the partial pressure of arterial oxygen. However, at oxygen concentrations that contribute to kidney injury, the changes in the relationship between microRNAs (miRNAs) and the hypoxia-inducible factor-1α (HIF-1α)-vascular endothelial growth factor (VEGF) axis and the key miRNAs involved in this process have not been elucidated. Therefore, we elucidated the relationship between VEGF and kidney injury at different oxygen concentrations and the mechanisms mediated by miRNAs. Sprague-Dawley rats were exposed to normobaric hypoxia and categorized into six groups based on the concentration of the oxygen inhaled and injection of the angiogenesis inhibitor bevacizumab, a humanized anti-VEGF monoclonal antibody. Renal tissue samples were processed to determine pathological and morphological changes and HIF-1α, VEGF, and miRNA expression. We performed a clustering analysis of high-risk pathways and key hub genes. The results were validated using two Gene Expression Omnibus datasets (GSE94717 and GSE30718). As inhaled oxygen concentration decreased, destructive changes in the kidney tissues became more severe. Although the kidney possesses a self-protective mechanism under an intermediate degree of hypoxia (10% O2), bevacizumab injections disrupted this mechanism, and VEGF expression was associated with the ability of the kidney to repair itself. rno-miR-124-3p was identified as a crucial miRNA; a key gene target, Mapk14, was identified during this process. VEGF plays an important role in kidney protection from injury under different hypoxia levels. Specific miRNAs and their target genes may serve as biomarkers that provide new insights into kidney injury treatment.NEW & NOTEWORTHY Renal tolerance to hypoxic environments is limited, and the degree of hypoxia does not show a linear relationship with angiogenesis. VEGF plays an important role in the kidney's self-protective mechanism under different levels of hypoxia. miR-124-3p may be particularly important in kidney repair, and it may modulate VEGF expression through the miR-124-3p/Mapk14 signaling pathway. These microRNAs may serve as biomarkers that provide new insights into kidney injury treatment.

Tubulovascular protection from protease-activated receptor-1 depletion during AKI-to-CKD transition

BACKGROUND

Thromboembolic events are prevalent in chronic kidney disease (CKD) patients due to increased thrombin generation leading to a hypercoagulable state. We previously demonstrated that inhibition of protease-activated receptor-1 (PAR-1) by vorapaxar reduces kidney fibrosis.

METHODS

We used an animal model of unilateral ischemia-reperfusion injury-induced CKD to explore the tubulovascular crosstalk mechanisms of PAR-1 in acute kidney injury (AKI)-to-CKD transition.

RESULTS

During the early phase of AKI, PAR-1-deficient mice exhibited reduced kidney inflammation, vascular injury, and preserved endothelial integrity and capillary permeability. During the transition phase to CKD, PAR-1 deficiency preserved kidney function and diminished tubulointerstitial fibrosis via downregulated transforming growth factor-β/Smad signaling. Maladaptive repair in the microvasculature after AKI further exacerbated focal hypoxia with capillary rarefaction, which was rescued by stabilization of hypoxia-inducible factor and increased tubular vascular endothelial growth factor A in PAR-1-deficient mice. Chronic inflammation was also prevented with reduced kidney infiltration by both M1- and M2-polarized macrophages. In thrombin-induced human dermal microvascular endothelial cells (HDMECs), PAR-1 mediated vascular injury through activation of NF-κB and ERK MAPK pathways. Gene silencing of PAR-1 exerted microvascular protection via a tubulovascular crosstalk mechanism during hypoxia in HDMECs. Finally, pharmacologic blockade of PAR-1 with vorapaxar improved kidney morphology, promoted vascular regenerative capacity, and reduced inflammation and fibrosis depending on the time of initiation.

CONCLUSIONS

Our findings elucidate a detrimental role of PAR-1 in vascular dysfunction and profibrotic responses upon tissue injury during AKI-to-CKD transition and provide an attractive therapeutic strategy for post-injury repair in AKI.

CKD Urine Metabolomics: Modern Concepts and Approaches

One of the primary challenges regarding chronic kidney disease (CKD) diagnosis is the absence of reliable methods to detect early-stage kidney damage. A metabolomic approach is expected to broaden the current diagnostic modalities by enabling timely detection and making the prognosis more accurate. Analysis performed on urine has several advantages, such as the ease of collection using noninvasive methods and its lower protein and lipid content compared with other bodily fluids. This review highlights current trends in applied analytical methods, major discoveries concerning pathways, and investigated populations in the context of urine metabolomic research for CKD over the past five years. Also, we are presenting approaches, instrument upgrades, and sample preparation modifications that have improved the analytical parameters of methods. The onset of CKD leads to alterations in metabolism that are apparent in the molecular composition of urine. Recent works highlight the prevalence of alterations in the metabolic pathways related to the tricarboxylic acid cycle and amino acids. Including diverse patient cohorts, using numerous analytical techniques with modifications and the appropriate annotation and explanation of the discovered biomarkers will help develop effective diagnostic models for different subtypes of renal injury with clinical applications.

Targeted VEGFA therapy in regulating early acute kidney injury and late fibrosis

Damage to peritubular capillaries is a key process that contributes to acute kidney injury (AKI) progression. Vascular endothelial growth factor A (VEGFA) plays a critical role in maintaining the renal microvasculature. However, the physiological role of VEGFA in various AKI durations remains unclear. A severe unilateral ischemia‒reperfusion injury model was established to provide an overview of VEGFA expression and the peritubular microvascular density from acute to chronic injury in mouse kidneys. Therapeutic strategies involving early VEGFA supplementation protecting against acute injury and late anti-VEGFA treatment for fibrosis alleviation were analyzed. A proteomic analysis was conducted to determine the potential mechanism of renal fibrosis alleviation by anti-VEGFA. The results showed that two peaks of extraglomerular VEGFA expression were observed during AKI progression: one occurred at the early phase of AKI, and the other occurred during the transition to chronic kidney disease (CKD). Capillary rarefaction progressed despite the high expression of VEGFA at the CKD stage, and VEGFA was associated with interstitial fibrosis. Early VEGFA supplementation protected against renal injury by preserving microvessel structures and counteracting secondary tubular hypoxic insults, whereas late anti-VEGFA treatment attenuated renal fibrosis progression. The proteomic analysis highlighted an array of biological processes related to fibrosis alleviation by anti-VEGFA, which included regulation of supramolecular fiber organization, cell-matrix adhesion, fibroblast migration, and vasculogenesis. These findings establish the landscape of VEGFA expression and its dual roles during AKI progression, which provides the possibility for the orderly regulation of VEGFA to alleviate early acute injury and late fibrosis.

LTBP4 Protects Against Renal Fibrosis via Mitochondrial and Vascular Impacts

BACKGROUND

As a part of natural disease progression, acute kidney injury (AKI) can develop into chronic kidney disease via renal fibrosis and inflammation. LTBP4 (latent transforming growth factor beta binding protein 4) regulates transforming growth factor beta, which plays a role in renal fibrosis pathogenesis. We previously investigated the role of LTBP4 in chronic kidney disease. Here, we examined the role of LTBP4 in AKI.

METHODS

LTBP4 expression was evaluated in human renal tissues, obtained from healthy individuals and patients with AKI, using immunohistochemistry. LTBP4 was knocked down in both C57BL/6 mice and human renal proximal tubular cell line HK-2. AKI was induced in mice and HK-2 cells using ischemia-reperfusion injury and hypoxia, respectively. Mitochondrial division inhibitor 1, an inhibitor of DRP1 (dynamin-related protein 1), was used to reduce mitochondrial fragmentation. Gene and protein expression were then examined to assess inflammation and fibrosis. The results of bioenergetic studies for mitochondrial function, oxidative stress, and angiogenesis were assessed.

RESULTS

LTBP4 expression was upregulated in the renal tissues of patients with AKI. Ltbp4-knockdown mice showed increased renal tissue injury and mitochondrial fragmentation after ischemia-reperfusion injury, as well as increased inflammation, oxidative stress, and fibrosis, and decreased angiogenesis. in vitro studies using HK-2 cells revealed similar results. The energy profiles of Ltbp4-deficient mice and LTBP4-deficient HK-2 cells indicated decreased ATP production. LTBP4-deficient HK-2 cells exhibited decreased mitochondrial respiration and glycolysis. Human aortic endothelial cells and human umbilical vein endothelial cells exhibited decreased angiogenesis when treated with LTBP4-knockdown conditioned media. Mitochondrial division inhibitor 1 treatment ameliorated inflammation, oxidative stress, and fibrosis in mice and decreased inflammation and oxidative stress in HK-2 cells.

CONCLUSIONS

Our study is the first to demonstrate that LTBP4 deficiency increases AKI severity, consequently leading to chronic kidney disease. Potential therapies focusing on LTBP4-associated angiogenesis and LTBP4-regulated DRP1-dependent mitochondrial division are relevant to renal injury.

The Inflammatory Profile Orchestrated by Inducible Nitric Oxide Synthase in Systemic Lupus Erythematosus

(1) Background: The pathogenesis of systemic lupus erythematosus (SLE) involves complicated and multifactorial interactions. Inducible nitric oxide synthase overactivation (iNOS or NOS2) could be involved in SLE pathogenesis and progression. This study explored the relationship between NOS2-associated inflammation profiles and SLE phenotypes. (2) Methods: We developed a prospective, case control study that included a group of 86 SLE subjects, a group of 73 subjects with lupus nephritis, and a control group of 60 people. Laboratory determinations included serum C reactive protein (CRP-mg/L), enzymatic activity of NOS2 (U/L), serum levels of inducible factors of hypoxia 1 and 2 (HIF1a-ng/mL, HIF2a-ng/mL), vascular endothelial growth factor VEGF (pg/mL), matrix metalloproteinases 2 and 9 (MMP-2, MMP-9-ng/mL), thrombospondin 1 (TSP-1-ng/mL), and soluble receptor of VEGF (sVEGFR-ng/mL). (3) Results: CRP, NOS2, HIF-1a, HIF-2a, VEGF, MMP-2, and MMP-9 were significantly increased, while TSP-1 and sVEGFR were decreased in the SLE and lupus nephritis groups compared with the control group. The variations in these biomarkers were strongly associated with the decrease in eGFR and increase in albuminuria. (4) Conclusions: The inflammatory phenotype of SLE patients, with or without LN, is defined by NOS2 and hypoxia over-expression, angiogenesis stimulation, and inactivation of factors that induce resolution of inflammation in relation with eGFR decline.

Polycythemia with elevated erythropoietin production in a patient with a urinary stone and unilateral hydronephrosis: a case report

BACKGROUND

Absolute polycythemia can be primary or secondary. Erythropoietin-producing diseases (for example, hypoxia) are the major cause of secondary polycythemia. There are reports of polycythemia secondary to hydronephrosis. However, to our knowledge, there is no report on polycythemia secondary to hydronephrosis due to a urinary stone. Herein, we present a case of polycythemia with an elevated erythropoietin level in a patient with a urinary stone and unilateral hydronephrosis.

CASE PRESENTATION

A 57-year-old Japanese man presented with polycythemia and an elevated erythropoietin level. Erythropoietin accumulation was not due to erythropoietin secretion by a tumor as no obvious lesions were detected on contrast-enhanced computed tomography. Abdominal ultrasonography revealed a stone in the left urinary tract and renal hydronephrosis, and 2 weeks later, the patient underwent transurethral ureterolithotripsy without complications. Blood tests 2 weeks after transurethral ureterolithotripsy showed that the erythropoietin level had declined. Hemoglobin concentration decreased from 20.8 mg/dL before and immediately after transurethral ureterolithotripsy to 15.8 mg/dL 3 months after transurethral ureterolithotripsy. This case was diagnosed as erythropoietin elevation due to unilateral hydronephrosis with a urinary stone, resulting in polycythemia.

CONCLUSIONS

Hydronephrosis is a common disease but is not often associated with polycythemia. Further studies are required to elucidate the mechanism and implications of elevated erythropoietin production in hydronephrosis.

Effects of long-term tubular HIF-2α overexpression on progressive renal fibrosis in a chronic kidney disease model

Renal fibrosis is the final manifestation of chronic kidney disease (CKD) regardless of etiology. Hypoxia-inducible factor-2 alpha (HIF-2α) is an important regulator of chronic hypoxia, and the late-stage renal tubular HIF-2α activation exerts protective effects against renal fibrosis. However, its specific role in progressive renal fibrosis remains unclear. Here, we investigated the effects of the long-term tubular activation of HIF-2α on renal function and fibrosis, using in vivo and in vitro models of renal fibrosis. Progressive renal fibrosis was induced in renal tubular epithelial cells (TECs) of tetracycline-controlled HIF-2α transgenic (Tg) mice and wild-type (WT) controls through a 6-week adenine diet. Tg mice were maintained on doxycycline (DOX) for the diet period to induce Tg HIF-2α expression. Primary TECs isolated from Tg mice were treated with DOX (5 μg/ml), transforming growth factor-β1 (TGF-β1) (10 ng/ml), and a combination of both for 24, 48, and 72 hr. Blood was collected to analyze creatinine (Cr) and blood urea nitrogen (BUN) levels. Pathological changes in the kidney tissues were observed using hematoxylin and eosin, Masson's trichrome, and Sirius Red staining. Meanwhile, the expression of fibronectin, E-cadherin and α-smooth muscle actin (α-SMA) and the phosphorylation of p38 mitogenactivated protein kinase (MAPK) was observed using western blotting. Our data showed that serum Cr and BUN levels were significantly lower in Tg mice than in WT mice following the adenine diet. Moreover, the protein levels of fibronectin and E-cadherin and the phosphorylation of p38 MAPK were markedly reduced in the kidneys of adenine-fed Tg mice. These results were accompanied by attenuated fibrosis in Tg mice following adenine administration. Consistent with these findings, HIF-2α overexpression significantly decreased the expression of fibronectin in TECs, whereas an increase in α-SMA protein levels was observed after TGF-β1 stimulation for 72 hr. Taken together, these results indicate that long-term HIF-2α activation in CKD may inhibit the progression of renal fibrosis and improve renal function, suggesting that long-term renal HIF-2α activation may be used as a novel therapeutic strategy for the treatment of CKD. [BMB Reports 2023; 56(3): 196-201].

Assessment of peritubular capillary rarefaction in kidneys of cats with chronic kidney disease

BACKGROUND

Hypoxia is a key driver of fibrosis and is associated with capillary rarefaction in humans.

OBJECTIVES

Characterize capillary rarefaction in cats with chronic kidney disease (CKD).

ANIMALS

Archival kidney tissue from 58 cats with CKD, 20 unaffected cats.

METHODS

Cross-sectional study of paraffin-embedded kidney tissue utilizing CD31 immunohistochemistry to highlight vascular structures. Consecutive high-power fields from the cortex (10) and corticomedullary junction (5) were digitally photographed. An observer counted and colored the capillary area. Image analysis was used to determine the capillary number, average capillary size, and average percent capillary area in the cortex and corticomedullary junction. Histologic scoring was performed by a pathologist masked to clinical data.

RESULTS

Percent capillary area (cortex) was significantly lower in CKD (median 3.2, range, 0.8-5.6) compared to unaffected cats (4.4, 1.8-7.0; P = <.001) and was negatively correlated with serum creatinine concentrations (r = -.36, P = .0013), glomerulosclerosis (r = -0.39, P = <.001), inflammation (r = -.30, P = .009), and fibrosis (r = -.30, P = .007). Capillary size (cortex) was significantly lower in CKD cats (2591 pixels, 1184-7289) compared to unaffected cats (4523 pixels, 1801-7618; P = <.001) and was negatively correlated with serum creatinine concentrations (r = -.40, P = <.001), glomerulosclerosis (r = -.44, P < .001), inflammation (r = -.42, P = <.001), and fibrosis (r = -.38, P = <.001).

CONCLUSIONS AND CLINICAL IMPORTANCE

Capillary rarefaction (decrease in capillary size and percent capillary area) is present in kidneys of cats with CKD and is positively correlated with renal dysfunction and histopathologic lesions.

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.

Pharmacological targeting of cGAS/STING-YAP axis suppresses pathological angiogenesis and ameliorates organ fibrosis

Organ fibrosis is accompanied by pathological angiogenesis. Discovering new ways to ameliorate pathological angiogenesis may bypass organ fibrosis. The cyclic guanosine monophosphate (GMP)-adenosine monophosphate (AMP) synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has been implicated in organ injuries and its activation inhibits endothelial proliferation. Currently, a controversy exists as to whether cGAS/STING activation exacerbates inflammation and tissue injury or mitigates damage, and whether one of these effects predominates under specific context. This study unveiled a new antifibrotic cGAS/STING signaling pathway that suppresses pathological angiogenesis in liver and kidney fibrosis. We showed that cGAS expression was induced in fibrotic liver and kidney, but suppressed in endothelial cells. cGAS genetic deletion promoted liver and kidney fibrosis and pathological angiogenesis, including occurrence of endothelial-to-mesenchymal transition. Meanwhile, cGAS deletion upregulated profibrotic Yes-associated protein (YAP) signaling in endothelial cells, which was evidenced by the attenuation of organ fibrosis in mice specifically lacking endothelial YAP. Pharmacological targeting of cGAS/STING-YAP signaling by both a small-molecule STING agonist, SR-717, and a G protein-coupled receptor (GPCR)-based antagonist that blocks the profibrotic activity of endothelial YAP, attenuated liver and kidney fibrosis. Together, our data support that activation of cGAS/STING signaling mitigates organ fibrosis and suppresses pathological angiogenesis. Further, pharmacological targeting of cGAS/STING-YAP axis exhibits the potential to alleviate liver and kidney fibrosis.

Urinary Thioredoxin as a Biomarker of Renal Redox Dysregulation and a Companion Diagnostic to Identify Responders to Redox-Modulating Therapeutics

Significance: The development and progression of renal diseases, including acute kidney injury (AKI) and chronic kidney disease (CKD), are the result of heterogeneous pathophysiology that reflects a range of environmental factors and, in a lesser extent, genetic mutations. The pathophysiology specific to most kidney diseases is not currently identified; therefore, these diseases are diagnosed based on non-pathological factors. For that reason, pathophysiology-based companion diagnostics for selection of pathophysiology-targeted treatments have not been available, which impedes personalized medicine in kidney disease. Recent Advances: Pathophysiology-targeted therapeutic agents are now being developed for the treatment of redox dysregulation. Redox modulation therapeutics, including bardoxolone methyl, suppresses the onset and progression of AKI and CKD. On the other hand, pathophysiology-targeted diagnostics for renal redox dysregulation are also being developed. Urinary thioredoxin (TXN) is a biomarker that can be used to diagnose tubular redox dysregulation. AKI causes oxidation and urinary excretion of TXN, which depletes TXN from the tubules, resulting in tubular redox dysregulation. Urinary TXN is selectively elevated at the onset of AKI and correlates with the progression of CKD in diabetic nephropathy. Critical Issues: Diagnostic methods should provide information about molecular mechanisms that aid in the selection of appropriate therapies to improve the prognosis of kidney disease. Future Directions: A specific diagnostic method enabling detection of redox dysregulation based on pathological molecular mechanisms is much needed and could provide the first step toward personalized medicine in kidney disease. Urinary TXN is a candidate for a companion diagnostic method to identify responders to redox-modulating therapeutics. Antioxid. Redox Signal. 36, 1051-1065.

Elevated reactivity of Apelin inhibited renal fibrosis induced by chronic intermittent hypoxia

BACKGROUND

Apelin and its receptor angiotensin receptor - like 1 (APJ) are closely related to renal fibrosis, but their specific roles in renal fibrosis are still controversial. In this article, we discussed the role of Apelin/APJ system in renal fibrosis and its mechanism.

METHODS

Chronic intermittent hypoxia (CIH) rat model was established to induce the environment of renal fibrosis and a competitive antagonist of the APJ receptor ML221 was administered to CIH rats. The rats were divided into Control, CIH and ML221 groups. HE staining was used to detect the inflammatory injury and fibrosis of renal tissue. The expressions of renal fibrosis-related indicators transforming growth factor-β (TGF-β), α-smooth muscle actin (α-SMA) and Human type I collagen (Col-Ⅰ) were detected by immunohistochemistry. The levels of oxidative stress indexes reactive oxygen species (ROS), Malondialdehyde (MDA), Superoxide Dismutase (SOD) and inflammation-related indexes Interleukin (IL) -6, tumor necrosis factor-α (TNF-α) and IL-1β were detected by ELISA. At the same time, the levels of Apelin-13 and AngiotensinII (AngⅡ) were also measured by ELISA. Finally, western blot was used to detect the expression of Apelin pathway and renal fibrosis-related proteins. In addition, at the cellular level, we divided the cells into Control, CIH, Apelin-13 and Apelin-13+ML-221 groups to further verify the specific mechanisms at the cellular level.

RESULTS

The expression of Apeline-13 and its related pathways was significantly increased after the induction of CIH in rats. However, the degree of renal fibrosis in ML221 group was further significantly increased after inhibiting the expression of Apelin. At the cellular level, CIH model cells treated with Apelin-13 significantly reduced cell proliferation, oxidative stress and inflammatory response, and decreased the expression of fibrosis-related proteins, which can be reversed by ML221 administration.

CONCLUSION

The increased reactivity of Apelin may be one of the protective mechanisms against renal fibrosis induced by CIH.

Evolving Medical Imaging Techniques for the Assessment of Delayed Graft Function: A Narrative Review

Purpose of review

Delayed graft function (DGF) is a significant complication that contributes to poorer graft function and shortened graft survival. In this review, we sought to evaluate the current and emerging role of medical imaging modalities in the assessment of DGF and how it may guide clinical management.

Sources of information

PubMed, Google Scholar, and ClinicalTrial.gov up until February 2021.

Methods

This narrative review first examined the pathophysiology of DGF and current clinical management. We then summarized relevant studies that utilized medical imaging to assess posttransplant renal complications, namely, DGF. We focused our attention on noninvasive, evolving imaging modalities with the greatest potential for clinical translation, including contrast-enhanced ultrasound (CEUS) and multiparametric magnetic resonance imaging (MRI).

Key findings

A kidney biopsy in the setting of DGF can be used to assess the degree of ischemic renal injury and to rule out acute rejection. Biopsies are accompanied by complications and may be limited by sampling bias. Early studies on CEUS and MRI have shown their potential to distinguish between the 2 most common causes of DGF (acute tubular necrosis and acute rejection), but they have generally included only small numbers of patients and have not kept pace with more recent technical advances of these imaging modalities. There remains unharnessed potential with CEUS and MRI, and more robust clinical studies are needed to better evaluate their role in the current era.

Limitations

The adaptation of emerging approaches for imaging DGF will depend on additional clinical trials to study the feasibility and diagnostic test characteristics of a given modality. This is limited by access to devices, technical competence, and the need for interdisciplinary collaborations to ensure that such studies are well designed to appropriately inform clinical decision-making.

Hypoxic tubular epithelial cells regulate the angiogenesis of HMEC-1 cells via mediation of Rab7/MMP-2 axis

Renal hypoxia is associated with persisting peritubular capillary rarefaction in progression of chronic kidney disease (CKD), and this phenomenon mainly resulted from the dysregulated angiogenesis. Rab7 is known to be involved in renal hypoxia. However, the mechanism by which Rab7 regulates the renal hypoxia remains unclear. Protein expression was detected by western blot. Cell proliferation was detected by EdU staining. Cell migration was tested by transwell assay. Rab7 was upregulated in HK-2 cells under hypoxia conditions. Hypoxia significantly inhibited the viability and proliferation of human microvascular endothelial cells (HMEC-1 cells), while this phenomenon was obviously reversed by Rab7 silencing. Consistently, Hypoxia significantly decreased the migration and tube length of HMECs, which was partially reversed by knockdown of Rab7. Moreover, hypoxia-induced inhibition of MMP2 activity was significantly rescued by knockdown of Rab7. Moreover, ARP100 (MMP-2 inhibitor) significantly reversed the effect of Rab7 shRNA on cell viability, migration and angiogenesis. Furthermore, knockdown of Rab7 significantly alleviated the fibrosis in tissues of mice. Knockdown of Rab7 significantly alleviated the renal hypoxia in chronic kidney disease through regulation of MMP-2. Thus, our study might shed new light on exploring the new strategies against CKD.

Features of skin wound healing in rats with experimental chronic kidney disease

Chronic kidney disease negatively affects the morphofunctional state of all organs due to hemodynamic and metabolic disorders. Changes in the content of cytokines observed in kidney diseases, which regulate the processes of inflammation and tissue repair, can complicate the course of the wound process. This research aimed to study disorders in the process of skin wound repair due to changes in the dynamics of production of interleukins IL-1β, IL-6, IL-10, IL-4, growth factors bFGF and VEGF in animals with experimental chronic kidney disease. The levels of interleukins and growth factors were determined on the 7th, 14th and 28th days after surgical modeling of wounds in the blood of rats with experimental chronic kidney disease and animals of the control group. To assess the dynamics and quality of wound healing, a semi-quantitative histological analysis was performed. The study showed an increase in the content of pro-inflammatory interleukins in the group of sick rats: on the 7th day the level of IL-1β was 1.19 times higher, and IL-6 – 1.55 times, on the 14th day the level of IL-1β was 1.37 times in comparison with the control group. The maximum increase in the concentration of anti-inflammatory interleukins was noted on the 28th day: IL-4 was 2.10 times higher, IL-10 – 1.39 times higher than in the control group. The content of bFGF and VEGF in animals of the control group reached its maximum on the 7th day, and in animals with chronic kidney disease – on the 15th day after surgery. Semi-quantitative histological analysis showed a decrease in indicators in the group of sick animals: the number of fibroblasts and collagen deposition – on the 7th day, reepithelialization – on the 28th day. A persistent increase in the number of polymorphonuclear leukocytes was also noted at all periods of the experiment: by 1.38, 1.99, and 9.82 times – on the 7th, 14th, and 28th days, respectively. The study showed that the dynamics of the production of interleukins and growth factors were impaired in rats with chronic kidney disease. In the process of damage regeneration in sick animals, pro-inflammatory mechanisms prevailed with the involvement of a large number of immunocompetent cells, as a result, skin wounds took longer to heal.

Low-dose rapamycin does not impair vascular integrity and tubular regeneration after kidney transplantation in rats

mTOR inhibitors offer advantages after kidney transplantation including antiviral and antitumor activity besides facilitating low calcineurin inhibitor exposure to reduce nephrotoxicity. Concerns about adverse effects due to antiproliferative and antiangiogenic properties have limited their clinical use particularly early after transplantation. Interference with vascular endothelial growth factor (VEGF)-A, important for physiologic functioning of renal endothelial cells and tubular epithelium, has been implicated in detrimental renal effects of mTOR inhibitors. Low doses of Rapamycin (loading dose 3 mg/kg bodyweight, daily doses 1.5 mg/kg bodyweight) were administered in an allogenic rat kidney transplantation model resulting in a mean through concentration of 4.30 ng/mL. Glomerular and peritubular capillaries, tubular cell proliferation, or functional recovery from preservation/reperfusion injury were not compromised in comparison to vehicle treated animals. VEGF-A, VEGF receptor 2, and the co-receptor Neuropilin-1 were upregulated by Rapamycin within 7 days. Rat proximal tubular cells (RPTC) responded in vitro to hypoxia with increased VEGF-A and VEGF-R1 expression that was not suppressed by Rapamycin at therapeutic concentrations. Rapamycin did not impair proliferation of RPTC under hypoxic conditions. Low-dose Rapamycin early posttransplant does not negatively influence the VEGF network crucial for recovery from preservation/reperfusion injury. Enhancement of VEGF signaling peritransplant holds potential to further improve outcomes.

Mesenchymal stem cells ameliorate renal fibrosis by galectin-3/Akt/GSK3β/Snail signaling pathway in adenine-induced nephropathy rat

BACKGROUND

Tubulointerstitial fibrosis (TIF) is one of the main pathological features of various progressive renal damages and chronic kidney diseases. Mesenchymal stromal cells (MSCs) have been verified with significant improvement in the therapy of fibrosis diseases, but the mechanism is still unclear. We attempted to explore the new mechanism and therapeutic target of MSCs against renal fibrosis based on renal proteomics.

METHODS

TIF model was induced by adenine gavage. Bone marrow-derived MSCs was injected by tail vein after modeling. Renal function and fibrosis related parameters were assessed by Masson, Sirius red, immunohistochemistry, and western blot. Renal proteomics was analyzed using iTRAQ-based mass spectrometry. Further possible mechanism was explored by transfected galectin-3 gene for knockdown (Gal-3 KD) and overexpression (Gal-3 OE) in HK-2 cells with lentiviral vector.

RESULTS

MSCs treatment clearly decreased the expression of α-SMA, collagen type I, II, III, TGF-β1, Kim-1, p-Smad2/3, IL-6, IL-1β, and TNFα compared with model rats, while p38 MAPK increased. Proteomics showed that only 40 proteins exhibited significant differences (30 upregulated, 10 downregulated) compared MSCs group with the model group. Galectin-3 was downregulated significantly in renal tissues and TGF-β1-induced rat tubular epithelial cells and interstitial fibroblasts, consistent with the iTRAQ results. Gal-3 KD notably inhibited the expression of p-Akt, p-GSK3β and snail in TGF-β1-induced HK-2 cells fibrosis. On the contrary, Gal-3 OE obviously increased the expression of p-Akt, p-GSK3β and snail.

CONCLUSION

The mechanism of MSCs anti-renal fibrosis was probably mediated by galectin-3/Akt/GSK3β/Snail signaling pathway. Galectin-3 may be a valuable target for treating renal fibrosis.

Mild Hypoxia Enhances the Expression of HIF and VEGF and Triggers the Response to Injury in Rat Kidneys

Background

Hypoxia contributes to a cascade of inflammatory response mechanisms in kidneys that result in the development of renal interstitial fibrosis and subsequent chronic renal failure. Nonetheless, the kidney possesses a self-protection mechanism under a certain degree of hypoxia and this mechanism its adaptation to hypoxia. As the hypoxia-inducible factor (HIF)–vascular endothelial growth factor (VEGF) axis is a key pathway for neovascularization, the activation of this axis is a target for renal hypoxia therapies.

Methods

Sprague–Dawley rats were exposed to normobaric hypoxia and subdivided into three groups, namely group A (21% O₂), group B (10% O₂), and group C (7% O₂). Renal tissue samples were processed and analyzed to determine pathological morphological changes, the expression of HIF, VEGF, inflammation factor and vascular density.

Results

We found that as the duration of hypoxia increased, destructive changes in the kidney tissues became more severe in group C (7% O₂). In contrast, the increased duration of hypoxia did not exacerbate kidney damage in group B (10% O₂). As the hypoxia was prolonged and the degree of hypoxia increased, the expression of HIF-1α increased gradually. As hypoxia time increased, the expression of VEGF increased gradually, but VEGF expression in group B (10% O₂) was the highest. Group C (7% O₂) had higher levels of IL-6, IL-10, and TNF-alpha. Additionally, the highest vascular density was observed in group B.

Conclusion

These findings suggest that activating the HIF–VEGF signaling pathway to regulate angiogenesis after infliction of hypoxic kidney injury may provide clues for the development of novel CKD treatments.

The renal microcirculation in chronic kidney disease: novel diagnostic methods and therapeutic perspectives

Chronic kidney disease (CKD) affects 8–16% of the population worldwide and is characterized by fibrotic processes. Understanding the cellular and molecular mechanisms underpinning renal fibrosis is critical to the development of new therapeutics. Microvascular injury is considered an important contributor to renal progressive diseases. Vascular endothelium plays a significant role in responding to physical and chemical signals by generating factors that help maintain normal vascular tone, inhibit leukocyte adhesion and platelet aggregation, and suppress smooth muscle cell proliferation. Loss of the rich capillary network results in endothelial dysfunction, hypoxia, and inflammatory and oxidative effects and further leads to the imbalance of pro- and antiangiogenic factors, endothelial cell apoptosis and endothelial-mesenchymal transition. New techniques, including both invasive and noninvasive techniques, offer multiple methods to observe and monitor renal microcirculation and guide targeted therapeutic strategies. A better understanding of the role of endothelium in CKD will help in the development of effective interventions for renal microcirculation improvement. This review focuses on the role of microvascular injury in CKD, the methods to detect microvessels and the novel treatments to ameliorate renal fibrosis.

Enhanced renoprotective effect of GDNF-modified adipose-derived mesenchymal stem cells on renal interstitial fibrosis

Background

The therapeutic effect of mesenchymal stem cells (MSCs) from human adipose tissue on renal interstitial fibrosis has been demonstrated by several groups. However, the way to enhance the renoprotective effect of adipose-derived mesenchymal stem cells (AMSCs) and the possible mechanisms are still unclear. The present study aimed to determine whether glial cell line-derived neurotrophic factor (GDNF)-modified AMSCs hold an enhanced protective effect on renal fibrosis.

Methods

AMSCs were isolated and purified for culture. The gene GDNF has been constructed to transfect into AMSCs. The ability of GFP-AMSCs and GDNF-AMSCs supernatants to promote tube formation of endothelial cells, repair damaged endothelial cell junctions, and improve endothelial cell function was compared by using tube formation assay, immunofluorescence techniques, and vascular ring assay, respectively. Furthermore, HE and Masson staining were used to observe the histological morphology of the kidney in vivo. Peritubular capillary changes were detected and analyzed by fluorescence microangiography (FMA). Meanwhile, the hypoxia, oxidative stress, fibrotic markers, and PI3K/Akt pathway proteins were measured by western blot or qRT-PCR technics.

Results

Compared with GFP-AMSCs only, GDNF-AMSCs could enhance the repair of injured endothelial cells and promote angiogenesis through secreting more growth factors in the supernatant of GDNF-AMSC culture media demonstrated in vitro studies. Studies in vivo, unilateral ureteral obstruction (UUO)-induced mice were injected with transfected AMSCs through their tail veins. We showed that enhanced homing of AMSCs was observed in the GDNF-AMSC group compared with the GFP-AMSC group. The animals treated with GDNF-AMSCs exhibited an improvement of capillary rarefaction and fibrosis induced by obstructed kidney compared with the GFP-AMSC group. Furthermore, we reported that GDNF-AMSCs protect renal tissues against microvascular injuries via activation of the PI3K/Akt signaling pathway. Therefore, GDNF-AMSCs further ameliorated the tissue hypoxia, suppressed oxidative stress, and finally inhibited endothelial to mesenchymal transition noting by decreased coexpression of endothelial cell (CD31) and myofibroblast (a-SMA) markers.

Conclusion

Collectively, our data indicated that the GDNF gene enhances the ability of AMSCs in improving renal microcirculation through PI3K/Akt/eNOS signaling pathway and afterward inhibit the EndMT process and kidney fibrogenesis, which should have a vast of implications in designing future remedies for chronic kidney disease (CKD) treatment.

Indoxyl sulfate impairs angiogenesis via chronic aryl hydrocarbon receptor activation

Chronic kidney disease (CKD) is associated with a substantial increased risk of cardiovascular disease. There is growing evidence that uremic metabolites, which accumulate in the blood with CKD, have detrimental impacts on endothelial cell health and function. However, the molecular mechanisms by which uremic metabolites negatively impact endothelial cell biology are not fully understood. In this study, activation of the aryl hydrocarbon receptor (AHR) via indoxyl sulfate, a known uremic metabolite, was found to impair endothelial cell tube formation and proliferation but not migratory function. Moreover, aortic ring cultures treated with indoxyl sulfate also exhibited decreased sprouting and high AHR activation. Next, genetic knockdown of the AHR using shRNA was found to rescue endothelial cell tube formation, proliferation, and aortic ring sprouting. Similarly, pharmacological AHR antagonism using resveratrol and CH223191 were also found to rescue angiogenesis in cell and aortic ring cultures. Finally, a constitutively active AHR (CAAHR) vector was generated and used to confirm AHR-specific effects. Expression of the CAAHR recapitulated the impaired tube formation and proliferation in cultured endothelial cells and decreased sprouting in aortic ring cultures. Taken together, these data define the impact of AHR activation on angiogenesis and highlight the potential for therapeutic AHR antagonists, which may improve angiogenesis in the context of CKD and cardiovascular disease.

"Adenosine an old player with new possibilities in kidney diseases": Preclinical evidences and clinical perspectives

Renal injury might originate from multiple factors like ischemia reperfusion (I/R), drug toxicity, cystic fibrosis, radio contrast agent etc. The four adenosine receptor subtypes have been identified and found to show diverse physiological and pathological roles in kidney diseases. The activation of A₁ adenosine receptor (A₁) protects against acute kidney injury by improving renal hemodynamic alterations, decreasing tubular necrosis and its inhibition might facilitate removal of toxin or drug metabolite in chronic kidney disease models. Furthermore, recent findings revealed that A_2A receptor subtype activation regulates macrophage phenotype in experimental models of nephritis. Interestingly the emerging role of adenosine kinase inhibitors in kidney diseases has been discussed which act by increasing adenosine availability at target sites and thereby promote A_2A receptor stimulation. In addition, the least explored adenosine receptor subtype A₃ inhibition was observed to exert anti- oxidant, immunosuppressive and anti-fibrotic effects, but more studies are required to confirm its benefits in other renal injury models. The clinical studies targeting A₁ receptor in patients with pre-existing kidney disease have yielded disappointing results, perhaps owing to the origin of unexpected neurological complications during the course of trial. Importantly, conducting well designed clinical trials and testing adenosine modulators with lesser brain penetrability could clear the way for clinical approval of these agents for patients with renal functional impairments.

The endoplasmic reticulum stress and the unfolded protein response in kidney disease: Implications for vascular growth factors

Acute kidney injury (AKI) and chronic kidney disease (CKD) represent an important challenge for healthcare providers. The identification of new biomarkers/pharmacological targets for kidney disease is required for the development of more effective therapies. Several studies have shown the importance of the endoplasmic reticulum (ER) stress in the pathophysiology of AKI and CKD. ER is a cellular organelle devolved to protein biosynthesis and maturation, and cellular detoxification processes which are activated in response to an insult. This review aimed to dissect the cellular response to ER stress which manifests with activation of the unfolded protein response (UPR) with its major branches, namely PERK, IRE1α, ATF6 and the interplay between ER and mitochondria in the pathophysiology of kidney disease. Further, we will discuss the relationship between mediators of renal injury (with specific focus on vascular growth factors) and ER stress and UPR in the pathophysiology of both AKI and CKD with the aim to propose potential new targets for treatment for kidney disease.

Chromolaena odorata flavonoids attenuate experimental nephropathy: Involvement of pro-inflammatory genes downregulation

Nephropathy is a serious complication comorbid with a number of life-threatening diseases such as diabetes. Flavonoids are well known cytoprotective phytochemicals. Here, nephropathy associated with streptozotocin (STZ) treatment in experimental animals was challenged by flavonoids (CoF) isolated from Chromolaena odorata. Experimental animals were divided into control (n = 5), STZ (40 mg/kg b.w. i.p. n = 5) and STZ-CoF (CoF = 30 mg/kg b.w. oral, 60 days, n = 7) groups. Blood urea nitrogen (BUN) and serum creatinine (SC) levels were quantified using ELISA. Kidney function, inflammatory marker, and antioxidant gene expression levels were also evaluated using reverse-transcription and polymerase chain reaction protocols. Histological assessment was also performed using Haematoxylin and Eosin (H&E) staining protocols. CoF improved kidney function by restoring BUN/SC levels to pre-STZ treatment states. KIM-1, TNF-α, and MCP-1 but not TNF-R and IL-10 genes were significantly downregulated in STZ-CoF treated group in comparison with STZ-treated group (p < 0.05). Anti-oxidant genes (GPx-1, CAT) significantly (p < 0.05 vs. control) upregulated in STZ-treatment did not respond to CoF treatment. STZ treatment associated Bowman's space enlargement, thickened basement membrane, and glomerulosclerosis were completely reversed in STZ-CoF group. Finally, CoF has demonstrable anti-nephropathic via downregulation of proinflammatory genes and may represent new management option in clinical nephropathy.

Microvascular disease in chronic kidney disease: the base of the iceberg in cardiovascular comorbidity

Chronic kidney disease (CKD) is a relentlessly progressive disease with a very high mortality mainly due to cardiovascular complications. Endothelial dysfunction is well documented in CKD and permanent loss of endothelial homeostasis leads to progressive organ damage. Most of the vast endothelial surface area is part of the microcirculation, but most research in CKD-related cardiovascular disease (CVD) has been devoted to macrovascular complications. We have reviewed all publications evaluating structure and function of the microcirculation in humans with CKD and animals with experimental CKD. Microvascular rarefaction, defined as a loss of perfused microvessels resulting in a significant decrease in microvascular density, is a quintessential finding in these studies. The median microvascular density was reduced by 29% in skeletal muscle and 24% in the heart in animal models of CKD and by 32% in human biopsy, autopsy and imaging studies. CKD induces rarefaction due to the loss of coherent vessel systems distal to the level of smaller arterioles, generating a typical heterogeneous pattern with avascular patches, resulting in a dysfunctional endothelium with diminished perfusion, shunting and tissue hypoxia. Endothelial cell apoptosis, hypertension, multiple metabolic, endocrine and immune disturbances of the uremic milieu and specifically, a dysregulated angiogenesis, all contribute to the multifactorial pathogenesis. By setting the stage for the development of tissue fibrosis and end organ failure, microvascular rarefaction is a principal pathogenic factor in the development of severe organ dysfunction in CKD patients, especially CVD, cerebrovascular dysfunction, muscular atrophy, cachexia, and progression of kidney disease. Treatment strategies for microvascular disease are urgently needed.

Hirudin reduces nephropathy microangiopathy in STZ-induced diabetes rats by inhibiting endothelial cell migration and angiogenesis

OBJECTIVE

Kidney is the most common location of microangiopathy in diabetic patients, and we designed this study to investigate the effects of hirudin on renal microangiopathy in STZ-induced diabetes rats and in vitro.

METHODS

We established a diabetes model by intraperitoneal injection of STZ and administered hirudin daily by subcutaneous injection. HE staining was used to assess kidney pathological changes. Western blot and immunochemistry was used to detect the protein expression. Glomerular endothelial cells (GEC) in normal rats were assessed by cell scratch test for migration ability and tubule formation experiment for angiogenesis ability.

RESULTS

Compared with DN rats without any treatment, the serum creatinine, serum Cys C, 24-hour urine protein of DN rats with hirudin treatment were significantly decrease, the kidney/body weight and glomerular area of DN rats with hirudin treatment were all significantly decrease, and also significant improvement in renal pathology revealed by HE staining in DN rats after treating with hirudin. Moreover, we also found that hirudin coun not only significantly increase the prothrombin time and aivated partial thromboplastin time in DN rats, but also significantly decrease the expression of VEGF and TM-1 protein in kidney tissues of DN rats. In vitro, we found that high glucose could promote the migration and angiogensis of GEC, and significantly increased the expression of VEGF and Ang protein, but significantly decreased the expression of THBS1 and Arg1 protein. More importantly was that hirudin could inhibit the migration and angiogensis of GEC, and reversed HG-induced the expression of VEGF, Ang, THBS1 and Arg1 protein in GEC. In addition, we also found that hirudin could not only decrease HG-enhanced the activity of RhoA in GEC, but also decrease HG-enhanced the expression of p-MYPT1/MYPT1, p-p38/p38 protein in GEC.

CONCLUSION

Hirudin reduces nephropathy microangiopathy in STZ-induced diabetes, and might be related to hirudin inhibiting glomerular endothelial cell migration and angiogenesis through Rho-kinase and subsequent p38MAPK/NF-kB signaling pathway.

Ultrasound super-resolution imaging provides a noninvasive assessment of renal microvasculature changes during mouse acute kidney injury

Acute kidney injury (AKI) is a risk factor for the development of chronic kidney disease (CKD). One mechanism for this phenomenon is renal microvascular rarefaction and subsequent chronic impairment in perfusion. However, diagnostic tools to monitor the renal microvasculature in a noninvasive and quantitative manner are still lacking. Ultrasound super-resolution imaging is an emerging technology that can identify microvessels with unprecedented resolution. Here, we applied this imaging technique to identify microvessels in the unilateral ischemia-reperfusion injury mouse model of AKI-to-CKD progression in vivo. Kidneys from 21 and 42 day post- ischemia-reperfusion injury, the contralateral uninjured kidneys, and kidneys from sham-operated mice were examined by ultrasound super-resolution and histology. Renal microvessels were successfully identified by this imaging modality with a resolution down to 32 μm. Renal fibrosis was observed in all kidneys with ischemia-reperfusion injury and was associated with a significant reduction in kidney size, cortical thickness, relative blood volume, and microvascular density as assessed by this imaging. Tortuosity of the cortical microvasculature was also significantly increased at 42 days compared to sham. These vessel density measurements correlated significantly with CD31 immunohistochemistry (R²=0.77). Thus, ultrasound super-resolution imaging provides unprecedented resolution and is capable of noninvasive quantification of renal vasculature changes associated with AKI-to-CKD progression in mice. Hence, this technique could be a promising diagnostic tool for monitoring progressive kidney disease.

Losartan protects against intermittent hypoxia-induced peritubular capillary loss by modulating the renal renin-angiotensin system and angiogenesis factors

Obstructive sleep apnea is characterized by chronic intermittent hypoxia (CIH), which is a risk factor for renal peritubular capillary (PTC) loss, and angiotensin II receptor blockers can alleviate PTC loss. However, the mechanism by which losartan (an angiotensin II receptor blocker) reduces CIH-induced PTC loss and attenuates kidney damage is still unknown. Thus, in this study, we examined the protective effects of losartan against CIH-induced PTC loss and explored the underlying mechanisms in rat CIH model. The immunohistochemical staining of CD34 and morphological examination showed that CIH reduced PTC density and damaged tubular epithelial cells. Immunohistochemistry, enzyme-linked immunosorbent assay (ELISA), real-time quantitative PCR, and western blot analysis results revealed that CIH increased the expression of hypoxia inducible factor-1α (HIF-1α), angiotensin II (Ang II), angiotensin II type 1 receptor (AT1R), pro-angiogenesis factor vascular endothelial growth factor (VEGF), and anti-angiogenesis factor thrombospondin-1 (TSP-1) in the renal cortex of rats. CIH may up-regulate VEGF expression and simultaneously increase TSP-1 production. By histopathological, immunohistochemistry, ELISA, RT-qPCR, and western blot analysis, we found that the expressions of renal renin-angiotensin system (RAS), HIF-1α, VEGF, and TSP-1 were decreased, and PTC loss and tubular epithelial cell injury were attenuated with losartan treatment. Losartan ameliorated CIH-induced PTC loss by modulating renal RAS to improve the crosstalk between endothelial cells and tubular epithelial cells and subsequently regulate the balance of angiogenesis factors. Our study provided novel insights into the mechanisms of CIH-induced kidney damage and indicated that losartan could be a potential therapeutic agent for renal protection by alleviating CIH-induced PTC loss.

Resilience to acute kidney injury in offspring of maternal protein restriction

Protein restriction (PR) during pregnancy induces morphofunctional alterations related to deficient nephrogenesis. We studied the renal functional and morphological significance of PR during pregnancy and/or lactation in adult male rat offspring and the repercussions on acute kidney injury (AKI) severity. Female rats were randomly assigned to the following groups: control diet during pregnancy and lactation (CC), control diet during pregnancy and PR diet during lactation (CR), PR during pregnancy and control diet during lactation (RC), and PR during pregnancy and lactation (RR). Three months after birth, at least 12 male offspring of each group randomly underwent either bilateral renal ischemia for 45 min [ischemia-reperfusion (IR)] or sham surgery. Thus, eight groups were studied 24 h after reperfusion: CC, CC + IR, CR, CR + IR, RC, RC + IR, RR, and RR + IR. Under basal conditions, the CR, RC, and RR groups exhibited a significant reduction in nephron number that was associated with a reduction in renal blood flow. Glomerular hyperfiltration was present as a compensatory mechanism to maintain normal renal function. mRNA levels of several vasoactive, antioxidant, and anti-inflammatory molecules were decreased. After IR, renal function was similarly reduced in all of the studied groups. Although all of the offspring from maternal PR exhibited renal injury, the magnitude was lower in the RC and RR groups, which were associated with faster renal blood flow recovery, differential vasoactive factors, and hypoxia-inducible factor-1α signaling. Our results show that the offspring from maternal PR are resilient to AKI induced by IR that was associated with reduced tubular injury and a differential hemodynamic response.

Indoxyl Sulfate Stimulates Angiogenesis by Regulating Reactive Oxygen Species Production via CYP1B1

Indoxyl sulfate (IS) is an accumulative protein-bound uremic toxin found in patients with kidney disease. It is reported that IS impairs the vascular endothelium, but a comprehensive overview of all mechanisms active in IS-injury currently remains lacking. Here we performed RNA sequencing in human umbilical vein endothelial cells (HUVECs) after IS or control medium treatment and identified 1293 genes that were affected in a IS-induced response. Gene enrichment analysis highlighted pathways involved in altered vascular formation and cell metabolism. We confirmed these transcriptome profiles at the functional level by demonstrating decreased viability and increased cell senescence in response to IS treatment. In line with the additional pathways highlighted by the transcriptome analysis, we further could demonstrate that IS exposure of HUVECs promoted tubule formation as shown by the increase in total tubule length in a 3D HUVECs/pericytes co-culture assay. Notably, the pro-angiogenic response of IS and increased ROS production were abolished when CYP1B1, one of the main target genes that was highly upregulated by IS, was silenced. This observation indicates IS-induced ROS in endothelial cells is CYP1B1-dependent. Taken together, our findings demonstrate that IS promotes angiogenesis and CYP1B1 is an important factor in IS-activated angiogenic response.

Circadian Clock Genes in Diabetic Kidney Disease (DKD)

PURPOSE OF REVIEW

The purpose of this review is to provide a brief summary about the current state of knowledge regarding the circadian rhythm in the regulation of normal renal function.

RECENT FINDINGS

There is a lack of information regarding how the circadian clock mechanisms may contribute to the development of diabetic kidney disease. We discuss recent findings regarding mechanisms that are established in diabetic kidney disease and are known to be linked to the circadian clock as possible connections between these two areas. Here, we hypothesize various mechanisms that may provide a link between the clock mechanism and kidney disease in diabetes based on available data from humans and rodent models.

Plasma endostatin predicts kidney outcomes in patients with type 2 diabetes

Novel biomarkers are needed to predict kidney function decline in patients with type 2 diabetes, especially those with preserved glomerular filtration rate (GFR). There are limited data on the association of markers of endothelial dysfunction with longitudinal GFR decline. We used banked specimens from a nested case-control study in the Action to Control Cardiovascular Disease (ACCORD) trial (n=187 cases: 187 controls) and from a diverse contemporary cohort of type 2 diabetic patients from the Mount Sinai BioMe Biobank (n=871) to assess the association of plasma endostatin and kidney outcomes. We measured plasma endostatin at enrollment and examined its association with a composite kidney outcome of sustained 40% decline in estimated GFR or end-stage renal disease. Baseline plasma endostatin levels were higher in participants with the composite outcome. Each log2 increment in plasma endostatin was associated with approximately 2.5-fold higher risk of the kidney outcome (adjusted odds ratio [OR] 2.5; 95% confidence interval [CI] 1.5-4.3 in ACCORD and adjusted hazard ratio [HR] 2.6; 95% CI 1.8-3.8 in BioMe). Participants in the highest vs. lowest quartile of plasma endostatin had approximately four-fold higher risk for the kidney outcome (adjusted OR 3.6; 95% CI 1.8-7.3 in ACCORD and adjusted HR 4.4; 95% CI 2.3-8.5 in BioMe). The AUC for the kidney outcome improved from 0.74 to 0.77 in BioMe with the addition of endostatin to a base clinical model. Plasma endostatin was strongly associated with kidney outcomes in type 2 diabetics with preserved eGFR and improved risk discrimination over traditional predictors.

Proteomic analysis of heart failure hospitalization among patients with chronic kidney disease: The Heart and Soul Study

Background

Patients with chronic kidney disease (CKD) are at increased risk for heart failure (HF). We aimed to investigate differences in proteins associated with HF hospitalizations among patients with and without CKD in the Heart and Soul Study.

Methods and results

We measured 1068 unique plasma proteins from baseline samples of 974 participants in The Heart and Soul Study who were followed for HF hospitalization over a median of 7 years. We sequentially applied forest regression and Cox survival analyses to select prognostic proteins. Among participants with CKD, four proteins were associated with HF at Bonferroni-level significance (p<2.5x10^-4): Angiopoietin-2 (HR[95%CI] 1.45[1.33, 1.59]), Spondin-1 (HR[95%CI] 1.13 [1.06, 1.20]), tartrate-resistant acid phosphatase type 5 (HR[95%CI] 0.65[0.53, 0.78]) and neurogenis locus notch homolog protein 1 (NOTCH1) (HR[95%CI] 0.67[0.55, 0.80]). These associations persisted at p<0.01 after adjustment for age, estimated glomerular filtration and history of HF. CKD was a significant interaction term in the associations of NOTCH1 and Spondin-1 with HF. Pathway analysis showed a trend for higher representation of the Cardiac Hypertrophy and Complement/Coagulation pathways among proteins prognostic of HF in the CKD sub-group.

Conclusions

These results suggest that markers of heart failure differ between patients with and without CKD. Further research is needed to validate novel markers in cohorts of patients with CKD and adjudicated HF events.

Prospective for cytochrome P450 epoxygenase cardiovascular and renal therapeutics

Therapeutics for arachidonic acid pathways began with the development of non-steroidal anti-inflammatory drugs that inhibit cyclooxygenase (COX). The enzymatic pathways and arachidonic acid metabolites and respective receptors have been successfully targeted and therapeutics developed for pain, inflammation, pulmonary and cardiovascular diseases. These drugs target the COX and lipoxygenase pathways but not the third branch for arachidonic acid metabolism, the cytochrome P450 (CYP) pathway. Small molecule compounds targeting enzymes and CYP epoxy-fatty acid metabolites have evolved rapidly over the last two decades. These therapeutics have primarily focused on inhibiting soluble epoxide hydrolase (sEH) or agonist mimetics for epoxyeicosatrienoic acids (EET). Based on preclinical animal model studies and human studies, major therapeutic indications for these sEH inhibitors and EET mimics/analogs are renal and cardiovascular diseases. Novel small molecules that inhibit sEH have advanced to human clinical trials and demonstrate promise for cardiovascular diseases. Challenges remain for sEH inhibitor and EET analog drug development; however, there is a high likelihood that a drug that acts on this third branch of arachidonic acid metabolism will be utilized to treat a cardiovascular or kidney disease in the next decade.

Correlation of Point Shear Wave Velocity and Kidney Function in Chronic Kidney Disease

OBJECTIVES

Point shear wave elastography is a quantitative ultrasound-based imaging method used in the assessment of renal disease. Among point shear wave elastographic options, 2 techniques have been studied considerably: Virtual Touch quantification (VTQ; Siemens AG, Erlangen, Germany) and ElastPQ (EPQ; Philips Healthcare, Bothell, WA). Both rely on the tissue response to an acoustic beam generated by the ultrasound transducer. The data on renal VTQ are more extensive, whereas EPQ has been used less thus far in the assessment of the kidneys. This study aimed to evaluate the performance of EPQ in the kidney and compare it with VTQ.

METHODS

We studied 124 participants using EPQ: 22 with no renal disease and 102 with chronic kidney disease (CKD). Ninety-one were studied with both the EPQ and VTQ methods. We obtained 5 valid measurements in each kidney, expressed in meters per second.

RESULTS

The mean kidney stiffness measurements ± SD obtained with EPQ in the healthy control group were as follows: right kidney, 1.23 ± 0.33 m/s; and left kidney, 1.26 ± 0.32 m/s (P = .6). In the patients with CKD (all stages), the mean kidney stiffness measurements obtained were significantly lower: right kidney, 1.09 ± 0.39 m/s; and left kidney, 1.04 ± 0.38 m/s (P = .4). We observed that, similar to VTQ, EPQ values decreased with CKD progression, based on analysis of variance results using different CKD stages. From a receiver operating characteristic curve analysis, the cutoff value for an estimated glomerular filtration rate of less than 45 mL/min was 1.24 m/s, and the value for an estimated glomerular filtration rate of less than 30 mL/min was 1.07 m/s.

CONCLUSIONS

When using EPQ, the kidney shear wave velocity is decreased in patients with CKD, an observation similar to that obtained by using the VTQ method.

The determinants, biomarkers, and consequences of microvascular injury in kidney transplant recipients

Independent of the initial cause of kidney disease, microvascular injury to the peritubular capillary network appears to play a central role in the development of interstitial fibrosis in both native and transplanted kidney disease. This association is explained by mechanisms such as the upregulation of profibrotic genes and epigenetic changes induced by hypoxia, capillary leakage, endothelial and pericyte transition to interstitial fibroblasts, as well as modifications in the secretome of endothelial cells. Alloimmune injury due to antibody-mediated rejection and ischemia-reperfusion injury are the two main etiologies of microvascular damage in kidney transplant recipients. The presence of circulating donor-specific anti-human leukocyte antigen (HLA) antibodies, histological findings, such as diffuse C4d staining in peritubular capillaries, and the extent and severity of peritubular capillaritis, are commonly used clinically to provide both diagnostic and prognostic information. Complement-dependent assays, circulating non-HLA antibodies, or evaluation of the microvasculature with novel imaging techniques are the subject of ongoing studies.

Immunopathogenesis of Acute Kidney Injury

Pathophysiologically, the classification of acute kidney injury (AKI) can be divided into three categories: (1) prerenal, (2) intrinsic, and (3) postrenal. Emerging evidence supports the involvement of renal tubular epithelial cells and the innate and adaptive arms of the immune system in the pathogenesis of intrinsic AKI. Pro-inflammatory damage-associated molecular patterns, pathogen-associated molecular patterns, hypoxia inducible factors, toll-like receptors, complement system, oxidative stress, adhesion molecules, cell death, resident renal dendritic cells, neutrophils, T and B lymphocytes, macrophages, natural killer T cells, cytokines, and secreted chemokines contribute to the immunopathogenesis of AKI. However, other immune cells and pathways such as M2 macrophages, regulatory T cells, progranulin, and autophagy exhibit anti-inflammatory properties and facilitate kidney tissue repair after AKI. Thus, therapies for AKI include agents such as anti-inflammatory (e.g., recombinant alkaline phosphatase), antioxidants (iron chelators), and apoptosis inhibitors. In preclinical toxicity studies, drug-induced kidney injury can be seen after exposure to a nephrotoxicant test article due to immune mechanisms and dysregulation of innate, and/or adaptive cellular immunity. The focus of this review will be on intrinsic AKI, as it relates to the immune and renal systems cross talks focusing on the cellular and pathophysiologic mechanisms of AKI.

Is decreased lung function associated with chronic kidney disease? A retrospective cohort study in Korea

OBJECTIVE

There is some evidence that lung function and chronic kidney disease (CKD) may be related. We evaluated the impact of lung function on the development of CKD in a large-scale longitudinal study.

METHOD

Retrospective longitudinal analyses were conducted among subjects who participated in comprehensive health check-ups at least four times during 7 years (between 2006 and 2012). We investigated the development of CKD during the follow-up period according to lung function status.

RESULTS

Ten thousand one hundred and twenty-eight individuals (mean age =51.2 years) without CKD at baseline were enrolled. During the mean follow-up of 5 years (58.5±14.4 months), 167 of the 10 128 subjects (1.6%) developed CKD. Multivariable Cox proportional hazards analyses adjusting for age, sex, body mass index, systolic blood pressure, fasting glucose, estimated glomerular filtration rate, uric acid, triglycerides, serum albumin, and the presence of diabetes and hypertension revealed that a decrease of 10% in the forced expiratory volume in 1s (FEV₁)/forced vital capacity (FVC) ratio was associated with a 35% increase in the development of CKD during the follow-up. The incidence of CKD was higher in those with an FEV₁/FVC ratio <0.8 compared with those with FEV₁/FVC ratio ≥0.8 (HR=1.454; 95% CI 1.042 to 2.028, p=0.028).

CONCLUSIONS

Limited airflow as measured by the FEV₁/FVC ratio was associated with an increased risk of CKD.

Chronic kidney disease induces a systemic microangiopathy, tissue hypoxia and dysfunctional angiogenesis

Chronic kidney disease (CKD) is associated with excessive mortality from cardiovascular disease (CVD). Endothelial dysfunction, an early manifestation of CVD, is consistently observed in CKD patients and might be linked to structural defects of the microcirculation including microvascular rarefaction. However, patterns of microvascular rarefaction in CKD and their relation to functional deficits in perfusion and oxygen delivery are currently unknown. In this in-vivo microscopy study of the cremaster muscle microcirculation in BALB/c mice with moderate to severe uremia, we show in two experimental models (adenine feeding or subtotal nephrectomy), that serum urea levels associate incrementally with a distinct microangiopathy. Structural changes were characterized by a heterogeneous pattern of focal microvascular rarefaction with loss of coherent microvascular networks resulting in large avascular areas. Corresponding microvascular dysfunction was evident by significantly diminished blood flow velocity, vascular tone, and oxygen uptake. Microvascular rarefaction in the cremaster muscle paralleled rarefaction in the myocardium, which was accompanied by a decrease in transcription levels not only of the transcriptional regulator HIF-1α, but also of its target genes Angpt-2, TIE-1 and TIE-2, Flkt-1 and MMP-9, indicating an impaired hypoxia-driven angiogenesis. Thus, experimental uremia in mice associates with systemic microvascular disease with rarefaction, tissue hypoxia and dysfunctional angiogenesis.

Diabetic nephropathy: Is there a role for oxidative stress?

Oxidative stress has been implicated in the pathophysiology of diabetic nephropathy. Studies in experimental animal models of diabetes strongly implicate oxidant species as a major determinant in the pathophysiology of diabetic kidney disease. The translation, in the clinical setting, of these concepts have been quite disappointing, and new theories have challenged the concepts that oxidative stress per se plays a role in the pathophysiology of diabetic kidney disease. The concept of mitochondrial hormesis has been introduced to explain this apparent disconnect. Hormesis is intended as any cellular process that exhibits a biphasic response to exposure to increasing amounts of a substance or condition: specifically, in diabetic kidney disease, oxidant species may represent, at determined concentration, an essential and potentially protective factor. It could be postulated that excessive production or inhibition of oxidant species formation might result in an adverse phenotype. This review discusses the evidence underlying these two apparent contradicting concepts, with the aim to propose and speculate on potential mechanisms underlying the role of oxidant species in the pathophysiology of diabetic nephropathy and possibly open future more efficient therapies to be tested in the clinical settings.

Endothelial cell functions impaired by interferon in vitro: Insights into the molecular mechanism of thrombotic microangiopathy associated with interferon therapy

INTRODUCTION

Interferon (IFN)-α and IFN-β approved for treatment of chronic hepatitis C viral infection and multiple sclerosis respectively have been linked to thrombotic microangiopathy (TMA) affecting renal function. Since the molecular mechanisms underlying this severe complication remain largely unclear, we aimed to investigate whether IFN affects directly in vitro endothelial cell functions associated with angiogenesis and blood haemostasis, as well as endothelial cell-derived vasodilators of nitric oxide (NO) and prostacyclin.

METHODS

Proliferation and survival of human umbilical vein endothelial cells (HUVECs) were measured by BrdU incorporation and alamarBlue assays. Angiogenesis was evaluated in co-cultures of HUVECs and human dermal fibroblasts. Fibrinolysis molecules were measured with ELISA. NO and prostacyclin were measured using a fluorescent NO-specific probe and a competitive enzyme immunoassay, respectively.

RESULTS

HUVEC proliferation was dose-dependently inhibited by IFN-β1a and IFN-β1b, but not by IFN-α2a and IFN-α2b. Consistently, IFN-β1a and IFN-β1b also reduced survival of HUVECs, but this again was not observed with IFN-α. However, both IFN subtypes inhibited VEGF-induced development of capillary-like structures, but the effect of IFN-α was less potent than IFN-β. In addition, both IFN subtypes upregulated interferon inducible protein 10 production from treated co-cultures while suppressing angiogenesis. Furthermore, intracellular NO generation was reduced by IFN-α2a and IFN-β1a, whereas prostacyclin release from HUVECs was not affected by IFN. Importantly, both IFN-β1a- and IFN-β1b-treated HUVECs showed a marked reduction in urokinase-type plasminogen activator release and a much greater secretion of plasminogen activator inhibitor-1 than tissue-type plasminogen activator compared with untreated cells, suggesting decreased fibrinolytic activity. IFN-α, however was less effective in modulating the fibrinolysis system.

CONCLUSIONS

We demonstrate the detrimental effects of IFN on endothelial cell functions mediated with angiogenesis and fibrinolysis, which could potentially cause the loss of physiological endothelium thromboresistance and facilitate the development of vascular complications in a clinical setting. Mechanistically, our findings have implications for understanding how IFN therapy can foster the development of TMA.