Restoring the renal microvasculature to treat chronic kidney disease

Single-cell transcriptomics identifies aberrant glomerular angiogenic signalling in the early stages of WT1 kidney disease

WT1 encodes a podocyte transcription factor whose variants can cause an untreatable glomerular disease in early childhood. Although WT1 regulates many podocyte genes, it is poorly understood which of them are initiators in disease and how they subsequently influence other cell-types in the glomerulus. We hypothesised that this could be resolved using single-cell RNA sequencing (scRNA-seq) and ligand-receptor analysis to profile glomerular cell-cell communication during the early stages of disease in mice harbouring an orthologous human mutation in WT1 (Wt1R394W/+). Podocytes were the most dysregulated cell-type in the early stages of Wt1R394W/+ disease, with disrupted angiogenic signalling between podocytes and the endothelium, including the significant downregulation of transcripts for the vascular factors Vegfa and Nrp1. These signalling changes preceded glomerular endothelial cell loss in advancing disease, a feature also observed in biopsy samples from human WT1 glomerulopathies. Addition of conditioned medium from murine Wt1R394W/+ primary podocytes to wild-type glomerular endothelial cells resulted in impaired endothelial looping and reduced vascular complexity. Despite the loss of key angiogenic molecules in Wt1R394W/+ podocytes, the pro-vascular molecule adrenomedullin was upregulated in Wt1R394W/+ podocytes and plasma and its further administration was able to rescue the impaired looping observed when glomerular endothelium was exposed to Wt1R394W/+ podocyte medium. In comparative analyses, adrenomedullin upregulation was part of a common injury signature across multiple murine and human glomerular disease datasets, whilst other gene changes were unique to WT1 disease. Collectively, our study describes a novel role for altered angiogenic signalling in the initiation of WT1 glomerulopathy. We also identify adrenomedullin as a proangiogenic factor, which despite being upregulated in early injury, offers an insufficient protective response due to the wider milieu of dampened vascular signalling that results in endothelial cell loss in later disease. © 2024 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Mapping the blood vasculature in an intact human kidney using hierarchical phase-contrast tomography

The architecture of the kidney vasculature is essential for its function. Although structural profiling of the intact rodent kidney vasculature has been performed, it is challenging to map vascular architecture of larger human organs. We hypothesised that hierarchical phase-contrast tomography (HiP-CT) would enable quantitative analysis of the entire human kidney vasculature. Combining label-free HiP-CT imaging of an intact kidney from a 63-year-old male with topology network analysis, we quantitated vasculature architecture in the human kidney down to the scale of arterioles. Although human and rat kidney vascular topologies are comparable, vascular radius decreases at a significantly faster rate in humans as vessels branch from artery towards the cortex. At branching points of large vessels, radii are theoretically optimised to minimise flow resistance, an observation not found for smaller arterioles. Structural differences in the vasculature were found in different spatial zones of the kidney reflecting their unique functional roles. Overall, this represents the first time the entire arterial vasculature of a human kidney has been mapped providing essential inputs for computational models of kidney vascular flow and synthetic vascular architectures, with implications for understanding how the structure of individual blood vessels collectively scales to facilitate organ function.

The impact of hypoxia preconditioning on mesenchymal stem cells performance in hypertensive kidney disease

BACKGROUND

Autologous mesenchymal stem cells (MSCs) have emerged as a therapeutic option for many diseases. Hypertensive kidney disease (HKD) might impair MSCs' reparative ability by altering the biomolecular properties, but the characteristics of this impairment are unclear. In our previous pre-clinical studies, we found hypoxic preconditioning (HPC) enhanced angiogenesis and suppressed senescence gene expression. Thus, we hypothesize that HPC would improve human MSCs by enhancing their functionality and angiogenesis, creating an anti-inflammatory and anti-senescence environment.

METHODS

MSC samples (n = 12 each) were collected from the abdominal fat of healthy kidney donors (HC), hypertensive patients (HTN), and patients with hypertensive kidney disease (HKD). MSCs were harvested and cultured in Normoxic (20% O2) or Hypoxic (1% O2) conditions. MSC functionality was measured by proliferation assays and cytokine released in conditioned media. Senescence was evaluated by senescence-associated beta-galactosidase (SA-beta-gal) activity. Additionally, transcriptome analysis using RNA-sequencing and quantitative PCR (qPCR) were performed.

RESULTS

At baseline, normoxic HTN-MSCs had higher proliferation capacity compared to HC. However, HPC augmented proliferation in HC. HPC did not affect the release of pro-angiogenic protein VEGF, but increased EGF in HC-MSC, and decreased HGF in HC and HKD MSCs. Under HPC, SA-β-gal activity tended to decrease, particularly in HC group. HPC upregulated mostly the pro-angiogenic and inflammatory genes in HC and HKD and a few senescence genes in HKD.

CONCLUSIONS

HPC has a more favorable functional effect on HC- than on HKD-MSC, reflected in increased proliferation and EGF release, and modest decrease in senescence, whereas it has little effect on HTN or HKD MSCs.

Eplerenone reduces lymphangiogenesis in the contralateral kidneys of UUO rats

Inflammation and fibrosis often occur in the kidney after acute injury, resulting in chronic kidney disease and consequent renal failure. Recent studies have indicated that lymphangiogenesis can drive renal inflammation and fibrosis in injured kidneys. However, whether and how this pathogenesis affects the contralateral kidney remain largely unknown. In our study, we uncovered a mechanism by which the contralateral kidney responded to injury. We found that the activation of mineralocorticoid receptors and the increase in vascular endothelial growth factor C in the contralateral kidney after unilateral ureteral obstruction could promote lymphangiogenesis. Furthermore, mineralocorticoid receptor activation in lymphatic endothelial cells resulted in the secretion of myofibroblast markers, thereby contributing to renal fibrosis. We observed that this process could be attenuated by administering the mineralocorticoid receptor blocker eplerenone, which, prevented the development of fibrotic injury in the contralateral kidneys of rats with unilateral ureteral obstruction. These findings offer valuable insights into the intricate mechanisms underlying kidney injury and may have implications for the development of therapeutic strategies to mitigate renal fibrosis in the context of kidney disease.

Advances in laser speckle imaging: From qualitative to quantitative hemodynamic assessment

Laser speckle imaging (LSI) techniques have emerged as a promising method for visualizing functional blood vessels and tissue perfusion by analyzing the speckle patterns generated by coherent light interacting with living biological tissue. These patterns carry important biophysical tissue information including blood flow dynamics. The noninvasive, label-free, and wide-field attributes along with relatively simple instrumental schematics make it an appealing imaging modality in preclinical and clinical applications. The review outlines the fundamentals of speckle physics and the three categories of LSI techniques based on their degree of quantification: qualitative, semi-quantitative and quantitative. Qualitative LSI produces microvascular maps by capturing speckle contrast variations between blood vessels containing moving red blood cells and the surrounding static tissue. Semi-quantitative techniques provide a more accurate analysis of blood flow dynamics by accounting for the effect of static scattering on spatiotemporal parameters. Quantitative LSI such as optical speckle image velocimetry provides quantitative flow velocity measurements, which is inspired by the particle image velocimetry in fluid mechanics. Additionally, discussions regarding the prospects of future innovations in LSI techniques for optimizing the vascular flow quantification with associated clinical outlook are presented.

The Pathophysiological Role of Thymosin β4 in the Kidney Glomerulus

Diseases affecting the glomerulus, the filtration unit of the kidney, are a major cause of chronic kidney disease. Glomerular disease is characterised by injury of glomerular cells and is often accompanied by an inflammatory response that drives disease progression. New strategies are needed to slow the progression to end-stage kidney disease, which requires dialysis or transplantation. Thymosin β4 (Tβ4), an endogenous peptide that sequesters G-actin, has shown potent anti-inflammatory function in experimental models of heart, kidney, liver, lung, and eye injury. In this review, we discuss the role of endogenous and exogenous Tβ4 in glomerular disease progression and the current understanding of the underlying mechanisms.

The vascular protective effect of matrix Gla protein during kidney injury

Matrix Gla protein (MGP) is a small secreted protein and requires vitamin K dependent γ-carboxylation for its function. MGP has been identified as a local inhibitor of vascular calcification because MGP-deficient mice die due to severe arterial calcification and resulting arterial rupture. Clinical trials revealed that reduction in active MGP predicts poor prognosis in patients due to cardiovascular complications. However, recent studies showed that MGP controls angiogenesis during development. MGP-deficient mice demonstrated abnormal hypervascularization and arteriovenous malformations in kidneys and other organs. This abnormal angiogenesis is largely caused by excessive expression of vascular endothelial growth factor-A (VEGF-A) and VEGF receptor-2 (VEGFR2). However, only a few studies have investigated the roles of MGP in tissue injury. We observed mesangial cell proliferation and mild interstitial fibrosis in addition to increased capillaries in kidneys of MGP-null mice even without injury. We also created a mouse model with kidney injury and found that kidney damage greatly increases MGP expression in peritubular capillary endothelial cells and tubular epithelial cells. Finally, our study showed that impairment of MGP expression aggravates peritubular capillary rarefaction and accumulation of collagen-producing myofibroblasts following kidney injury. Peritubular capillary damage induces capillary loss as well as trans-differentiation of vascular pericytes into myofibroblasts. These results indicate that MGP has the vascular protective effect in the injured kidney. Clinical trials have already started to test the efficacy of MGP activation to repair vascular calcification in patients with chronic kidney diseases. In this "Hypothesis and Theory" article, we discuss possible mechanisms by which MGP protects against vascular damage during tissue injury based on our experimental results and previous results from other research groups.

Experimental Aristolochic Acid Nephropathy: A Relevant Model to Study AKI-to-CKD Transition

Aristolochic acid nephropathy (AAN) is a progressive tubulointerstitial nephritis caused by the intake of aristolochic acids (AA) contained in Chinese herbal remedies or contaminated food. AAN is characterized by tubular atrophy and interstitial fibrosis, characterizing advanced kidney disease. It is established that sustained or recurrent acute kidney injury (AKI) episodes contribute to the progression of CKD. Therefore, the study of underlying mechanisms of AA-induced nephrotoxicity could be useful in understanding the complex AKI-to-CKD transition. We developed a translational approach of AKI-to-CKD transition by reproducing human AAN in rodent models. Indeed, in such models, an early phase of acute tubular necrosis was rapidly followed by a massive interstitial recruitment of activated monocytes/macrophages followed by cytotoxic T lymphocytes, resulting in a transient AKI episode. A later chronic phase was then observed with progressive tubular atrophy related to dedifferentiation and necrosis of tubular epithelial cells. The accumulation of vimentin and αSMA-positive cells expressing TGFβ in interstitial areas suggested an increase in resident fibroblasts and their activation into myofibroblasts resulting in collagen deposition and CKD. In addition, we identified 4 major actors in the AKI-to-CKD transition: (1) the tubular epithelial cells, (2) the endothelial cells of the interstitial capillary network, (3) the inflammatory infiltrate, and (4) the myofibroblasts. This review provides the most comprehensive and informative data we were able to collect and examines the pending questions.

The Density of Renal Lymphatics Correlates With Clinical Outcomes in IgA Nephropathy

Introduction

IgA nephropathy (IgAN) is the most common primary glomerulonephritis (GN) worldwide. The disease course fluctuates, and the most important challenge is the considerable variation in the time lag between diagnosis and the development of a hard clinical end point, such as end-stage kidney disease (ESKD). The reaction of renal tissue to damage resembles the common wound-healing response. One part of this repair in IgAN is the expansion of lymphatic vessels known as lymphangiogenesis. The aim of this work was to establish the prognostic value of the density of lymphatic vessels in the renal biopsy at the time of diagnosis, for predicting the risk of ESKD in a Spanish cohort of patients with IgAN.

Methods

We performed a retrospective multicenter study of 76 patients with IgAN. The end point of the study was progression to ESKD. The morphometric analysis of lymphatic vessels was performed on tissue sections stained with antipodoplanin antibody.

Results

Density of lymphatic vessels was significantly higher in patients with IgAN with mesangial hypercellularity >50%, segmental sclerosis, higher degrees of interstitial fibrosis, and tubular atrophy. Patients with more lymphatic vessels had significantly higher values of proteinuria and lower estimated glomerular filtration rate (eGFR). A density of lymphatic vessels ≥8 per mm2 was associated with a significantly higher rate of progression to ESKD at 3 years from biopsy. After adjustment for the International IgAN prediction score, at the multivariate logistic regression, high density of lymphatic vessels (≥8 per mm2) remained significantly associated with a higher rate of early progression to ESKD.

Conclusion

This study contributes to the understanding of the natural history of the progression to ESKD in patients with IgAN revealing the density of lymphatics vessels may optimize the prognostic value of the International IgA predicting tool to calculate the risk of ESKD, favoring the evaluation of new targeted therapies.

Robust arterial spin labeling MRI measurement of pharmacologically induced perfusion change in rat kidneys

Kidney diseases such as acute kidney injury, diabetic nephropathy and chronic kidney disease (CKD) are related to dysfunctions of the microvasculature in the kidney causing a decrease in renal blood perfusion (RBP). Pharmacological intervention to improve the function of the microvasculature is a viable strategy for the potential treatment of these diseases. The measurement of RBP is a reliable biomarker to evaluate the efficacy of pharmacological agents' actions on the microvasculature, and measurement of RBP responses to different pharmacological agents can also help elucidate the mechanism of hemodynamic regulation in the kidney. Magnetic resonance imaging (MRI) with flow-sensitive alternating inversion recovery (FAIR) arterial spin labeling (ASL) has been used to measure RBP in humans and animals. However, artifacts caused by respiratory and peristaltic motions limit the potential of FAIR ASL in drug discovery and kidney research. In this study, the combined anesthesia protocol of inactin with a low dose of isoflurane was used to fully suppress peristalsis in rats, which were ventilated with an MRI-synchronized ventilator. FAIR ASL data were acquired in eight axial slices using a single-shot, gradient-echo, echo-planar imaging (EPI) sequence. The artifacts in the FAIR ASL RBP measurement due to respiratory and peristaltic motions were substantially eliminated. The RBP responses to fenoldopam and L-NAME were measured, and the increase and decrease in RBP caused by fenoldopam and L-NAME, respectively, were robustly observed. To further validate FAIR ASL, the renal blood flow (RBF) responses to the same agents were measured by an invasive perivascular flow probe method. The pharmacological agent-induced responses in RBP and RBF are similar. This indicates that FAIR ASL has the sensitivity to measure pharmacologically induced changes in RBP. FAIR ASL with multislice EPI can be a valuable tool for supporting drug discovery, and for elucidating the mechanism of hemodynamic regulation in kidneys.

Renal Mononuclear Phagocytes in Lupus Nephritis

Renal mononuclear phagocytes are a highly pleiotropic group of immune cells of myeloid origin that play multiple protective and pathogenic roles in tissue homeostasis, inflammation, repair, and fibrosis. Infiltration of kidneys with these cells is a hallmark of lupus nephritis and is associated with more severe disease and with increased risk of progression to end‐stage renal disease. This review presents current knowledge of the diversity of these cells and their involvement in kidney inflammation and resolution and describes how they contribute to the chronic inflammation of lupus nephritis. A better understanding of the subset heterogeneity and diverse functions of mononuclear phagocytes in the lupus nephritis kidney should provide fertile ground for the development of new therapeutic approaches that promote the differentiation and survival of protective subsets while targeting pathogenic cell subsets that cause inflammation and fibrosis.

Application of Advanced Nanomaterials for Kidney Failure Treatment and Regeneration

The implementation of nanomedicine not only provides enhanced drug solubility and reduced off-target adverse effects, but also offers novel theranostic approaches in clinical practice. The increasing number of studies on the application of nanomaterials in kidney therapies has provided hope in a more efficient strategy for the treatment of renal diseases. The combination of biotechnology, material science and nanotechnology has rapidly gained momentum in the realm of therapeutic medicine. The establishment of the bedrock of this emerging field has been initiated and an exponential progress is observed which might significantly improve the quality of human life. In this context, several approaches based on nanomaterials have been applied in the treatment and regeneration of renal tissue. The presented review article in detail describes novel strategies for renal failure treatment with the use of various nanomaterials (including carbon nanotubes, nanofibrous membranes), mesenchymal stem cells-derived nanovesicles, and nanomaterial-based adsorbents and membranes that are used in wearable blood purification systems and synthetic kidneys.

Imaging the Renal Microcirculation in Cell Therapy

Renal microvascular rarefaction plays a pivotal role in progressive kidney disease. Therefore, modalities to visualize the microcirculation of the kidney will increase our understanding of disease mechanisms and consequently may provide new approaches for evaluating cell-based therapy. At the moment, however, clinical practice is lacking non-invasive, safe, and efficient imaging modalities to monitor renal microvascular changes over time in patients suffering from renal disease. To emphasize the importance, we summarize current knowledge of the renal microcirculation and discussed the involvement in progressive kidney disease. Moreover, an overview of available imaging techniques to uncover renal microvascular morphology, function, and behavior is presented with the associated benefits and limitations. Ultimately, the necessity to assess and investigate renal disease based on in vivo readouts with a resolution up to capillary level may provide a paradigm shift for diagnosis and therapy in the field of nephrology.

Retinal oxygen saturation and vessel diameter in patients with chronic kidney disease

PURPOSE

To investigate changes in retinal oximetry and the diameter of retinal vasculature in patients with chronic kidney disease (CKD) and relationships between retinal vasculature and the estimated glomerular filtration rate (eGFR), provide a scientific basis for the early detection and diagnosis of CKD.

METHODS

Eighty-three patients with CKD and 103 healthy individuals were included after providing informed consent. All participants were examined using a noninvasive technology (Oxymap Inc., Reykjavik, Iceland) for measuring the arterial (SaO₂ ) and venous (SvO₂ ) oxygen saturation and the arteriovenous difference in oxygen saturation (Sa-vO₂ ). The corresponding retinal vessel diameters of these arterioles (D-A) and venules (D-V) were measured. The eGFR of patients with CKD was calculated from the serum creatinine concentration.

RESULTS

In general, patients with CKD had higher mean SaO₂ values than healthy individuals (100.15 ± 4.68% versus 97.14 ± 4.22%; p < 0.001, mean ± SD). The mean SaO₂ in the superior temporal, superior nasal and inferior nasal quadrants significantly increased. There was no significant difference measured in the SvO₂ when patients with CKD (63.66 ± 5.29%) and healthy individuals (62.70 ± 5.27%) were compared. The mean Sa-vO₂ of the CKD group (36.49 ± 4.98%) was increased compared with normal subjects (34.44 ± 4.76%) (p = 0.005). The retinal arteriole diameter was narrower in patients with CKD than in normal individuals (117.53 ± 14.88 μm versus 126.87 ± 14.98 μm; p < 0.001, mean ± SD), and the arteriovenous ratio was smaller than in normal individuals (0.71 ± 0.09 versus 0.77 ± 0.09; p < 0.001, mean ± SD). Pearson's two-tailed correlation showed a significant correlation between the SaO₂ and eGFR (R = -0.363, p = 0.001), and narrower retinal arterial calibre was significantly associated with a lower eGFR (R = 0.415, p < 0.001).

CONCLUSION

Based on our results, there were alterations in retinal oxygen saturation and vascular diameter in patients with CKD. Further studies are needed to determine whether such changes play a role in the development of CKD.

IFN-I Mediates Lupus Nephritis From the Beginning to Renal Fibrosis

Lupus nephritis (LN) is a common complication of systemic lupus erythematosus (SLE) and a major risk factor for morbidity and mortality. The abundant cell-free nucleic (DNA/RNA) in SLE patients, especially dsDNA, is a key substance in the pathogenesis of SLE and LN. The deposition of DNA/RNA-immune complexes (DNA/RNA-ICs) in the glomerulus causes a series of inflammatory reactions that lead to resident renal cell disturbance and eventually renal fibrosis. Cell-free DNA/RNA is the most effective inducer of type I interferons (IFN-I). Resident renal cells (rather than infiltrating immune cells) are the main source of IFN-I in the kidney. IFN-I in turn damages resident renal cells. Not only are resident renal cells victims, but also participants in this immunity war. However, the mechanism for generation of IFN-I in resident renal cells and the pathological mechanism of IFN-I promoting renal fibrosis have not been fully elucidated. This paper reviews the latest epidemiology of LN and its development process, discusses the mechanism for generation of IFN-I in resident renal cells and the role of IFN-I in the pathogenesis of LN, and may open a new perspective for the treatment of LN.

Hypoxic preconditioning induces epigenetic changes and modifies swine mesenchymal stem cell angiogenesis and senescence in experimental atherosclerotic renal artery stenosis

BACKGROUND

Atherosclerotic renal artery stenosis (ARAS) is a risk factor for ischemic and hypertensive kidney disease (HKD) for which autologous mesenchymal stem cell (MSC) appears to be a promising therapy. However, MSCs from ARAS patients exhibit impaired function, senescence, and DNA damage, possibly due to epigenetic mechanisms. Hypoxia preconditioning (HPC) exerts beneficial effects on cellular proliferation, differentiation, and gene and protein expression. We hypothesized that HPC could influence MSC function and senescence in ARAS by epigenetic mechanisms and modulating gene expression of chromatin-modifying enzymes.

METHODS

Adipose-derived MSC harvested from healthy control (N = 8) and ARAS (N = 8) pigs were cultured under normoxia (20%O2) or hypoxia (1%O2) conditions. MSC function was assessed by migration, proliferation, and cytokine release in conditioned media. MSC senescence was evaluated by SA-β-gal activity. Specific pro-angiogenic and senescence genes were assessed by reverse transcription polymerase chain reaction (RT-PCR). Dot blotting was used to measure global genome 5-hydroxymethylcytosine (5hmC) levels on DNA and Western blotting of modified histone 3 (H3) proteins to quantify tri-methylated lysine-4 (H3K4me3), lysine-9 (H3K9me3), and lysine-27 (H3K27me3) residues.

RESULTS

Specific pro-angiogenic genes in ARAS assessed by RT-PCR were lower at baseline but increased under HPC, while pro-senescence genes were higher in ARAS at baseline as compared healthy MSCs. ARAS MSCs under basal conditions, displayed higher H3K4me3, H3K27me3, and 5hmC levels compared to healthy MSCs. During HPC, global 5hmC levels were decreased while no appreciable changes occurred in histone H3 tri-methylation. ARAS MSCs cultured under HPC had higher migratory and proliferative capacity as well as increased vascular endothelial growth factor and epidermal growth factor expression compared to normoxia, and SA-β-gal activity decreased in both animal groups.

CONCLUSIONS

These data demonstrate that swine ARAS MSCs have decreased angiogenesis and increased senescence compared to healthy MSCs and that HPC mitigates MSC dysfunction, senescence, and DNA hydroxymethylation in ARAS MSC. Thus, HPC for MSCs may be considered for their optimization to improve autologous cell therapy in patients with nephropathies.

LRG1 Mitigates Renal Interstitial Fibrosis through Alleviating Capillary Rarefaction and Inhibiting Inflammatory and Pro-Fibrotic Cytokines

INTRODUCTION

Increasing evidence has demonstrated that loss of peritubular capillaries plays a critical role in renal interstitial fibrosis. Leucine-rich α2-glycoprotein-1 (LRG1) has been observed promoting angiogenesis in the ocular disease mouse model and myocardial infarction model. We aimed to explore the role of LRG1 in renal interstitial fibrosis.

METHODS

We analyzed the expression of LRG1 in the plasma and kidney of CKD patients by ELISA and immunohistochemistry. Relationships between the expression of LRG1 in plasma and kidney and renal fibrosis and inflammation were analyzed. Tube formation assay was used to detect the angiogenesis in the human umbilical vein endothelial cell lines (HUVECs). And real-time PCR was used to detect the mRNA expression of LRG1, inflammatory factors, renal tubular injury indicators, pro-fibrotic cytokines, and CD31. We examined the effects of genetic ablation of LRG1 on renal fibrosis induced by unilateral ureteral obstruction (UUO) mice model at day 7.

RESULTS

We demonstrated that the expression of LRG1 in renal tissues and plasma samples was upregulated in CKD patients. And the expression of LRG1 was elevated in human renal tubular epithelial cell line (HK-2) cells in response to the stimulation of TNF-α in vitro, and in kidney after UUO in vivo. The deficiency of the LRG1 gene aggravated renal fibrosis, inflammatory cells infiltration, and capillary rarefaction after UUO. In vitro, LRG1 promoted the tube formation of HUVEC cells. LRG1 inhibits fibronectin secretion induced by TGF-β1 in HK-2 and overexpression of LRG1 in HK-2 cells decreased fibronectin secretion.

CONCLUSION

LRG1 may prevent renal fibrosis by inhibiting the secretion of inflammatory and pro-fibrotic cytokines and promoting angiogenesis.

A combined morphometric approach to feature mouse kidney vasculature

Physiological kidney function is closely related to the state of the vascular network. Disorders, such as capillary rarefaction, predispose to chronic kidney disease (CKD). In this context, deepening of the methodologies for studying the renal vascular network can be of basic importance. To meet this need, numerous animal models and, in parallel, several methods have been developed. In this work we propose a protocol to accurately feature kidney vasculature in mouse, however, the same protocol is suitable to be applied also to other animal models. The approach is multiparametric and mainly based on micro-computed tomography (μCT) technique. Micro-ct allows to study in detail the vascular network of any organ by exploiting the possibility to perfuse the sample with a contrast agent. The proposed protocol provides a fast and reliable method to extract quantitative information from the μCT scan by using only the basic functions of the software supplied by the scanner without any additional analysis. Through iterative cropping of the scanned ROI and calculation of a sample-specific threshold we calculated that the average volume of a female BALB/c kidney of eighth weeks is 147.8 mm³ (5.4%). We also pointed out that the average volume of the vascular network is 4.9% (0.3%). In parallel we performed traditional histological and immunofluorescence techniques to integrate the information gained via μCT and to frame them in the tissue context. Vessel count on histological sections showed a different density in the different regions of the organ parenchyma, in detail, vessel density in the cortex was 19.03 ± 2.51 vessels/ROI while in the medulla it was 10.6 ± 1.7 vessels/ROI and 5.4 ± 1.3 vessels/ROI in the outer and inner medulla, respectively. We then studied vessel distribution in the renal parenchyma which showed that the 55% of vascular component is included in the cortex, the 30% in the outer medulla and the 15% in the inner medulla. Collectively, we propose an integrated approach that can be particularly useful in the preclinical setting to characterize the vasculature of any organ accurately and rapidly.

Progress toward the Clinical Application of Mesenchymal Stromal Cells and Other Disease-Modulating Regenerative Therapies: Examples from the Field of Nephrology

Drawing from basic knowledge of stem-cell biology, embryonic development, wound healing, and aging, regenerative medicine seeks to develop therapeutic strategies that complement or replace conventional treatments by actively repairing diseased tissue or generating new organs and tissues. Among the various clinical-translational strategies within the field of regenerative medicine, several can be broadly described as promoting disease resolution indirectly through local or systemic interactions with a patient's cells, without permanently integrating or directly forming new primary tissue. In this review, we focus on such therapies, which we term disease-modulating regenerative therapies (DMRT), and on the extent to which they have been translated into the clinical arena in four distinct areas of nephrology: renovascular disease (RVD), sepsis-associated AKI (SA-AKI), diabetic kidney disease (DKD), and kidney transplantation (KTx). As we describe, the DMRT that has most consistently progressed to human clinical trials for these indications is mesenchymal stem/stromal cells (MSCs), which potently modulate ischemic, inflammatory, profibrotic, and immune-mediated tissue injury through diverse paracrine mechanisms. In KTx, several early-phase clinical trials have also tested the potential for ex vivo-expanded regulatory immune cell therapies to promote donor-specific tolerance and prevent or resolve allograft injury. Other promising DMRT, including adult stem/progenitor cells, stem cell-derived extracellular vesicles, and implantable hydrogels/biomaterials remain at varying preclinical stages of translation for these renal conditions. To date (2021), no DMRT has gained market approval for use in patients with RVD, SA-AKI, DKD, or KTx, and clinical trials demonstrating definitive, cost-effective patient benefits are needed. Nonetheless, exciting progress in understanding the disease-specific mechanisms of action of MSCs and other DMRT, coupled with increasing knowledge of the pathophysiologic basis for renal-tissue injury and the experience gained from pioneering early-phase clinical trials provide optimism that influential, regenerative treatments for diverse kidney diseases will emerge in the years ahead.

Peritubular Capillary Rarefaction: An Underappreciated Regulator of CKD Progression

Peritubular capillary (PTC) rarefaction is commonly detected in chronic kidney disease (CKD) such as hypertensive nephrosclerosis and diabetic nephropathy. Moreover, PTC rarefaction prominently correlates with impaired kidney function and predicts the future development of end-stage renal disease in patients with CKD. However, it is still underappreciated that PTC rarefaction is a pivotal regulator of CKD progression, primarily because the molecular mechanisms of PTC rarefaction have not been well-elucidated. In addition to the established mechanisms (reduced proangiogenic factors and increased anti-angiogenic factors), recent studies discovered significant contribution of the following elements to PTC loss: (1) prompt susceptibility of PTC to injury, (2) impaired proliferation of PTC, (3) apoptosis/senescence of PTC, and (4) pericyte detachment from PTC. Mainly based on the recent and novel findings in basic research and clinical study, this review describes the roles of the above-mentioned elements in PTC loss and focuses on the major factors regulating PTC angiogenesis, the assessment of PTC rarefaction and its surrogate markers, and an overview of the possible therapeutic agents to mitigate PTC rarefaction during CKD progression. PTC rarefaction is not only a prominent histological characteristic of CKD but also a central driving force of CKD progression.

Calcium dobesilate mediates renal interstitial fibrosis and delay renal peritubular capillary loss through Sirt1/p53 signaling pathway

Calcium dobesilate (Cad), a protective agent, protects against microvascular damage, and diseases such as diabetic retinopathy and diabetic nephropathy. However, these vascular protective effects have not been demonstrated in chronic kidney disease (CKD). In this study, we aimed to determine the ability of Cad to protect against renal interstitial fibrosis induced by unilateral ureteral obstruction (UUO) and identify the underlying therapeutic mechanisms of Cad during hypoxia/serum deprivation (H/SD) in human umbilical vein endothelial cells (HUVECs). A total of 36 male mice were randomly assigned into 3 groups (12 mice in each group): the Sham-operated group (Sham), the saline solution-treated UUO mice group (UUO), and the Cad administration (intragastrically) group (Cad). The mice in Cad group were administered Cad (100 mg/kg) daily by oral gavage and slaughtered on the 7th and 14th days post-surgery. Six mice from each group were sacrificed by sodium pentobarbital injection on the 7th and 14th day after surgery. Tissue hypoxia, cell apoptosis and fibrotic lesions were detected by Immunostaining and Western blot. Peritubular capillaries (PTCs) injury was measured by a novel technique of fluorescent microangiography (FMA). Endothelial cell-to-mesenchymal transition (EndMT) were identified by immunofluorescence and Western blot. HUVECs proliferation was measured via Cell Counting Kit‑8 assays and Edu staining. Sirt1 and its downstream gene in Cad regulation of endothelial were detected. Hematoxylin-eosin (HE), Masson-trichrome stains and Histological findings showed that Cad administration markedly reduced hypoxia and renal interstitial fibrosis at each time point in UUO. Meanwhile, Cad protect against EndMT process of PTCs by increasing CD31 expression and decreasing α-smooth muscle actin and fibronectin expression. in vitro studies showed that there was a proliferative response of the HUVECs incubated with Cad (10 μM) in H/SD. Sirt1 was suppressed after small interfering RNA (siRNA) was transfected in HUVECs. Mechanistically, Cad enhanced Sirt1 signaling, which was accompanied by increased levels of p53 acetylation (ac-p53). Meanwhile, protein expression of Bcl-2, and VE-cadherin were downregulated, Bax, and α-SMA were upregulated. In summary, the therapeutic effect of Cad in obstructive nephropathy were likely through suppressing EndMT progression and promoting anti-apoptotic effects after via activating the Sirt1/p53 signaling pathway.

Human amniotic epithelial cells ameliorate kidney damage in ischemia-reperfusion mouse model of acute kidney injury

BACKGROUND

Acute kidney injury (AKI) is a common clinical disease with complex pathophysiology and limited therapeutic choices. This prompts the need for novel therapy targeting multiple aspects of this disease. Human amnion epithelial cell (hAEC) is an ideal stem cell source. Increasing evidence suggests that exosomes may act as critical cell-cell communicators. Accordingly, we assessed the therapeutic potential of hAECs and their derived exosomes (hAECs-EXO) in ischemia reperfusion mouse model of AKI and explored the underlying mechanisms.

METHODS

The hAECs were primary cultured, and hAECs-EXO were isolated and characterized. An ischemic-reperfusion injury-induced AKI (IRI-AKI) mouse model was established to mimic clinical ischemic kidney injury with different disease severity. Mouse blood creatinine level was used to assess renal function, and kidney specimens were processed to detect cell proliferation, apoptosis, and capillary density. Macrophage infiltration was analyzed by flow cytometry. hAEC-derived exosomes (hAECs-EXO) were used to treat hypoxia-reoxygenation (H/R) injured HK-2 cells and mouse bone marrow-derived macrophages to evaluate their protective effect in vitro. Furthermore, hAECs-EXO were subjected to liquid chromatography-tandem mass spectrometry for proteomic profiling.

RESULTS

We found that systematically administered hAECs could improve mortality and renal function in IRI-AKI mice, decrease the number of apoptotic cells, prevent peritubular capillary loss, and modulate kidney local immune response. However, hAECs showed very low kidney tissue integration. Exosomes isolated from hAECs recapitulated the renal protective effects of their source cells. In vitro, hAECs-EXO protected HK-2 cells from H/R injury-induced apoptosis and promoted bone marrow-derived macrophage polarization toward M2 phenotype. Proteomic analysis on hAECs-EXO revealed proteins involved in extracellular matrix organization, growth factor signaling pathways, cytokine production, and immunomodulation. These findings demonstrated that paracrine of exosomes might be the key mechanism of hAECs in alleviating renal ischemia reperfusion injury.

CONCLUSIONS

We reported hAECs could improve survival and ameliorate renal injury in mice with IRI-AKI. The anti-apoptotic, pro-angiogenetic, and immunomodulatory capabilities of hAECs are at least partially, through paracrine pathways. hAECs-EXO might be a promising clinical therapeutic tool, overcoming the weaknesses and risks associated with the use of native stem cells, for patients with AKI.

Circulating Long Noncoding RNA LNC-EPHA6 Associates with Acute Rejection after Kidney Transplantation

Acute rejection (AR) of a kidney graft in renal transplant recipients is associated with microvascular injury in graft dysfunction and, ultimately, graft failure. Circulating long noncoding RNAs (lncRNAs) may be suitable markers for vascular injury in the context of AR. Here, we first investigated the effect of AR after kidney transplantation on local vascular integrity and demonstrated that the capillary density markedly decreased in AR kidney biopsies compared to pre-transplant biopsies. Subsequently, we assessed the circulating levels of four lncRNAs (LNC-RPS24, LNC-EPHA6, MALAT1, and LIPCAR), that were previously demonstrated to associate with vascular injury in a cohort of kidney recipients with a stable kidney transplant function (n = 32) and recipients with AR (n = 15). The latter were followed longitudinally six and 12 months after rejection. We found higher levels of circulating LNC-EPHA6 during rejection, compared with renal recipients with a stable kidney function (p = 0.017), that normalized one year after AR. In addition, LNC-RPS24, LNC-EPHA6, and LIPCAR levels correlated significantly with the vascular injury marker soluble thrombomodulin. We conclude that AR and microvascular injury are associated with higher levels of circulating LNC-EPHA6, which emphasizes the potential role of lncRNAs as biomarker in the context of AR.

Successful Introduction of Human Renovascular Units into the Mammalian Kidney

BACKGROUND

Cell-based therapies aimed at replenishing renal parenchyma have been proposed as an approach for treating CKD. However, pathogenic mechanisms involved in CKD such as renal hypoxia result in loss of kidney function and limit engraftment and therapeutic effects of renal epithelial progenitors. Jointly administering vessel-forming cells (human mesenchymal stromal cells [MSCs] and endothelial colony-forming cells [ECFCs]) may potentially result in in vivo formation of vascular networks.

METHODS

We administered renal tubule-forming cells derived from human adult and fetal kidneys (previously shown to exert a functional effect in CKD mice) into mice, alongside MSCs and ECFCs. We then assessed whether this would result in generation of "renovascular units" comprising both vessels and tubules with potential interaction.

RESULTS

Directly injecting vessel-forming cells and renal tubule-forming cells into the subcutaneous and subrenal capsular space resulted in self-organization of donor-derived vascular networks that connected to host vasculature, alongside renal tubules comprising tubular epithelia of different nephron segments. Vessels derived from MSCs and ECFCs augmented in vivo tubulogenesis by the renal tubule-forming cells. In vitro coculture experiments showed that MSCs and ECFCs induced self-renewal and genes associated with mesenchymal-epithelial transition in renal tubule-forming cells, indicating paracrine effects. Notably, after renal injury, renal tubule-forming cells and vessel-forming cells infused into the renal artery did not penetrate the renal vascular network to generate vessels; only administering them into the kidney parenchyma resulted in similar generation of human renovascular units in vivo.

CONCLUSIONS

Combined cell therapy of vessel-forming cells and renal tubule-forming cells aimed at alleviating renal hypoxia and enhancing tubulogenesis holds promise as the basis for new renal regenerative therapies.

Cellular Based Strategies for Microvascular Engineering

Vascularization is a major hurdle in complex tissue and organ engineering. Tissues greater than 200 μm in diameter cannot rely on simple diffusion to obtain nutrients and remove waste. Therefore, an integrated vascular network is required for clinical translation of engineered tissues. Microvessels have been described as <150 μm in diameter, but clinically they are defined as <1 mm. With new advances in super microsurgery, vessels less than 1 mm can be anastomosed to the recipient circulation. However, this technical advancement still relies on the creation of a stable engineered microcirculation that is amenable to surgical manipulation and is readily perfusable. Microvascular engineering lays on the crossroads of microfabrication, microfluidics, and tissue engineering strategies that utilize various cellular constituents. Early research focused on vascularization by co-culture and cellular interactions, with the addition of angiogenic growth factors to promote vascular growth. Since then, multiple strategies have been utilized taking advantage of innovations in additive manufacturing, biomaterials, and cell biology. However, the anatomy and dynamics of native blood vessels has not been consistently replicated. Inconsistent results can be partially attributed to cell sourcing which remains an enigma for microvascular engineering. Variations of endothelial cells, endothelial progenitor cells, and stem cells have all been used for microvascular network fabrication along with various mural cells. As each source offers advantages and disadvantages, there continues to be a lack of consensus. Furthermore, discord may be attributed to incomplete understanding about cell isolation and characterization without considering the microvascular architecture of the desired tissue/organ.

Perspectives on high resolution microvascular imaging with contrast ultrasound

Recent developments in contrast enhanced ultrasound have demonstrated a potential to visualize small blood vessels in vivo, unlike anything possible with traditional grayscale ultrasound. This Perspective article introduces microvascular imaging strategies and their underlying technology.

Beyond a Passive Conduit: Implications of Lymphatic Biology for Kidney Diseases

The kidney contains a network of lymphatic vessels that clear fluid, small molecules, and cells from the renal interstitium. Through modulating immune responses and via crosstalk with surrounding renal cells, lymphatic vessels have been implicated in the progression and maintenance of kidney disease. In this Review, we provide an overview of the development, structure, and function of lymphatic vessels in the healthy adult kidney. We then highlight the contributions of lymphatic vessels to multiple forms of renal pathology, emphasizing CKD, transplant rejection, and polycystic kidney disease and discuss strategies to target renal lymphatics using genetic and pharmacologic approaches. Overall, we argue the case for lymphatics playing a fundamental role in renal physiology and pathology and treatments modulating these vessels having therapeutic potential across the spectrum of kidney disease.

Endothelial-epithelial communication in polycystic kidney disease: Role of vascular endothelial growth factor signalling

Whereas targeting the cyst epithelium and its molecular machinery has been the prevailing clinical strategy for polycystic kidney disease, the endothelium, including blood vasculature and lymphatics, is emerging as an important player in this disorder. In this Review, we provide an overview of the structural and functional alterations to blood vasculature and lymphatic vessels in the polycystic kidney. We also discuss evidence for vascular endothelial growth factor signalling, otherwise critical for endothelial cell development and maintenance, as being a fundamental molecular pathway in polycystic kidney disease and a potential therapeutic target for modulating cyst expansion.

Protecting the kidney in systemic lupus erythematosus: from diagnosis to therapy

Lupus nephritis (LN) is a common manifestation of systemic lupus erythematosus that can lead to irreversible renal impairment. Although the prognosis of LN has improved substantially over the past 50 years, outcomes have plateaued in the USA in the past 20 years as immunosuppressive therapies have failed to reverse disease in more than half of treated patients. This failure might reflect disease complexity and heterogeneity, as well as social and economic barriers to health-care access that can delay intervention until after damage has already occurred. LN progression is still poorly understood and involves multiple cell types and both immune and non-immune mechanisms. Single-cell analysis of intrinsic renal cells and infiltrating cells from patients with LN is a new approach that will help to define the pathways of renal injury at a cellular level. Although many new immune-modulating therapies are being tested in the clinic, the development of therapies to improve regeneration of the injured kidney and to prevent fibrosis requires a better understanding of the mechanisms of LN progression. This mechanistic understanding, together with the development of clinical measures to evaluate risk and detect early disease and better access to expert health-care providers, should improve outcomes for patients with LN.

Inhibition of lysyl oxidase ameliorates renal injury by inhibiting CD44-mediated pericyte detachment and loss of peritubular capillaries

Renal fibrosis is a common pathological manifestation of almost all forms of kidney disease irrespective of the etiological cause. Microvascular rarefaction represents itself as an important phenomenon associated with renal fibrosis and shows strong correlation with decline in renal functions. Lysyl oxidase (LOX) catalyzes crosslinking of extracellular matrix (ECM) proteins including collagens, plays an important role in stabilization of degradation resistant matrix. Since, there seems to be a causal link between deposition of excessive ECM and microvascular rarefaction, we investigated the effects of reduction in renal fibrosis on microvascular rarefaction in acute as well as end stage kidney. We used a well-established unilateral ureteral obstruction (UUO)-induced renal fibrosis model to produce renal fibrosis in animals. We treated animals with a LOX inhibitor, β-aminopropionitrile (BAPN, 100 mg/kg, i.p.) and investigated effects on renal fibrosis and microvascular rarefaction. We observed that LOX inhibition was associated with reduction in collagen deposition in UUO-induced renal fibrosis animal model. Further, ECM normalization by LOX inhibition decreased the loss of peritubular capillaries (PTCs) in fibrotic kidney in acute study while the LOX inhibition failed to inhibit PTCs loss in end stage kidney. The results of present study suggested that inhibition of LOX reduces collagen deposition and renal fibrosis. Further, the reduction in fibrosis fails to protect from PTCs loss in chronic study suggesting the absence of strong link between reduction in fibrosis and improvement in PTCs in an end stage kidney.

Inhibition of tyrosine kinase receptor signaling attenuates fibrogenesis in an ex vivo model of human renal fibrosis

Poor translation from animal studies to human clinical trials is one of the main hurdles in the development of new drugs. Here, we used precision-cut kidney slices (PCKS) as a translational model to study renal fibrosis and to investigate whether inhibition of tyrosine kinase receptors, with the selective inhibitor nintedanib, can halt fibrosis in murine and human PCKS. We used renal tissue of murine and human origins to obtain PCKS. Control slices and slices treated with nintedanib were studied to assess viability, activation of tyrosine kinase receptors, cell proliferation, collagen type I accumulation, and gene and protein regulation. During culture, PCKS spontaneously develop a fibrotic response that resembles in vivo fibrogenesis. Nintedanib blocked culture-induced phosphorylation of platelet-derived growth factor receptor and vascular endothelial growth factor receptor. Furthermore, nintedanib inhibited cell proliferation and reduced collagen type I accumulation and expression of fibrosis-related genes in healthy murine and human PCKS. Modulation of extracellular matrix homeostasis was achieved already at 0.1 μM, whereas high concentrations (1 and 5 μM) elicited possible nonselective effects. In PCKS from human diseased renal tissue, nintedanib showed limited capacity to reverse established fibrosis. In conclusion, nintedanib attenuated the onset of fibrosis in both murine and human PCKS by inhibiting the phosphorylation of tyrosine kinase receptors; however, the reversal of established fibrosis was not achieved.

Nicotinamide mononucleotide (NMN) supplementation promotes anti-aging miRNA expression profile in the aorta of aged mice, predicting epigenetic rejuvenation and anti-atherogenic effects

Understanding molecular mechanisms involved in vascular aging is essential to develop novel interventional strategies for treatment and prevention of age-related vascular pathologies. Recent studies provide critical evidence that vascular aging is characterized by NAD+ depletion. Importantly, in aged mice, restoration of cellular NAD+ levels by treatment with the NAD+ booster nicotinamide mononucleotide (NMN) exerts significant vasoprotective effects, improving endothelium-dependent vasodilation, attenuating oxidative stress, and rescuing age-related changes in gene expression. Strong experimental evidence shows that dysregulation of microRNAs (miRNAs) has a role in vascular aging. The present study was designed to test the hypothesis that age-related NAD+ depletion is causally linked to dysregulation of vascular miRNA expression. A corollary hypothesis is that functional vascular rejuvenation in NMN-treated aged mice is also associated with restoration of a youthful vascular miRNA expression profile. To test these hypotheses, aged (24-month-old) mice were treated with NMN for 2 weeks and miRNA signatures in the aortas were compared to those in aortas obtained from untreated young and aged control mice. We found that protective effects of NMN treatment on vascular function are associated with anti-aging changes in the miRNA expression profile in the aged mouse aorta. The predicted regulatory effects of NMN-induced differentially expressed miRNAs in aged vessels include anti-atherogenic effects and epigenetic rejuvenation. Future studies will uncover the mechanistic role of miRNA gene expression regulatory networks in the anti-aging effects of NAD+ booster treatments and determine the links between miRNAs regulated by NMN and sirtuin activators and miRNAs known to act in the conserved pathways of aging and major aging-related vascular diseases.

The Use of Live Cell Imaging and Automated Image Analysis to Assist With Determining Optimal Parameters for Angiogenic Assay in vitro

Testing angiogenic potential and function of cells in culture is important for the understanding of the mechanisms that can modulate angiogenesis, especially when discovering novel anti- or pro-angiogenic therapeutics. Commonly used angiogenic assays include tube formation, proliferation, migration, and wound healing, and although well-characterized, it is important that methodology is standardized and reproducible. Human endothelial progenitor cells (EPCs) are critical for post-natal vascular homeostasis and can be isolated from human peripheral blood. Endothelial colony forming cells (ECFCs) are a subset of EPCs and are of interest as a possible therapeutic target for hypoxic diseases such as kidney disease, as they have a high angiogenic potential. However, once ECFCs are identified in culture, the exact timing of passaging has not been well-described and the optimal conditions to perform angiogenic assays such as seeding density, growth media (GM) concentrations and end-points of these assays is widely varied in the literature. Here, we describe the process of isolating, culturing and passaging ECFCs from patients with end-stage renal disease (ESRD), aided by image analysis. We further describe optimal conditions, for human bladder endothelial cells (hBECs), challenged in angiogenic assays and confirm that cell density is a limiting factor in accurately detecting angiogenic parameters. Furthermore, we show that GM along is enough to alter the angiogenic potential of cells, seeded at the same density. Lastly, we report on the success of human ECFCs in angiogenic assays and describe the benefits of live-cell imaging combined with time-lapse microscopy for this type of investigation.

Beraprost sodium mitigates renal interstitial fibrosis through repairing renal microvessels

Beraprost sodium (BPS), as a prostacyclin analog, plays a significant role in various diseases based on its antiplatelet and vasodilation functions. However, its regulation and role in chronic kidney disease (CKD) still remain elusive. Here, we determined whether BPS could alleviate renal interstitial fibrosis, and improve the renal function and its therapeutic mechanism. In vitro, BPS increased angiogenesis in the HUVECs incubated with BPS detected by tube formation assay and repair damaged endothelial cell-cell junctions induced by hypoxia. In vivo, mice were randomly assigned to a sham-operation group (sham), a unilateral ureteral obstruction group (UUO), and a BPS intragastrical administration group (BPS), and sacrificed at days 3 and 7 post-surgery (six in each group). In UUO model, tissue hypoxia, renal inflammation, oxidative stress, and fibrotic lesions were detected by q-PCR and Western blot techniques and peritubular capillaries (PTCs) injury was detected by a novel technique of fluorescent microangiography (FMA) and analyzed by MATLAB software. Meanwhile, we identified cells undergoing endothelial cell-to-myofibroblast transition by the coexpression of endothelial cell (CD31) and myofibroblast (a-SMA) markers in the obstructed kidney. In contrast, BPS protected against interstitial fibrosis and substantially reduced the number of endothelial cell-to-myofibroblast transition cells. In conclusion, our data indicate the potent therapeutic of BPS in mitigating fibrosis through repairing renal microvessels and suppressing endothelial-mesenchymal transition (EndMT) progression after inhibiting inflammatory and oxidative stress effects. KEY MESSAGES: BPS could improve renal recovery through anti-inflammatory and anti-oxidative pathways. BPS could mitigate fibrosis through repairing renal microvessels and suppressing endothelial-mesenchymal transition (EndMT).

Long Non-coding RNAs Rian and Miat Mediate Myofibroblast Formation in Kidney Fibrosis

There is an increasing prevalence of chronic kidney disease (CKD), which associates with the development of interstitial fibrosis. Pericytes (perivascular fibroblasts) provide a major source of α-SMA-positive myofibroblasts that are responsible for the excessive deposition of extracellular matrix. In order to identify pericyte long non-coding RNAs (lncRNAs) that could serve as a target to decrease myofibroblast formation and counteract the progression of kidney fibrosis we employed two models of experimental kidney injury, one focused on kidney fibrosis (unilateral ureteral obstruction; UUO), and one focused on acute kidney injury that yields kidney fibrosis in the longer term (unilateral ischemia-reperfusion injury; IRI). This was performed in FoxD1-GC;tdTomato stromal cell reporter mice that allowed pericyte fate tracing. Tomato red-positive FoxD1-derivative cells of control and injured kidneys were FACS-sorted and used for lncRNA and mRNA profiling yielding a distinctive transcriptional signature of pericytes and myofibroblasts with 244 and 586 differentially expressed lncRNAs (>twofold, P < 0.05), in the UUO and IRI models, respectively. Next, we selected two differentially expressed and conserved lncRNAs, Rian (RNA imprinted and accumulated in nucleus) and Miat (Myocardial infarction associated transcript), and explored their potential regulatory role in myofibroblast formation through knockdown of their function with gapmers. While Miat was upregulated in myofibroblasts of UUO and IRI in mice, gapmer silencing of Miat attenuated myofibroblast formation as evidenced by decreased expression of α-SMA, col1α1, SMAD2, and SMAD3, as well as decreased α-SMA and pro-collagen-1α1 protein levels. In contrast, silencing Rian, which was found to be downregulated in kidney myofibroblast after IRI and UUO, resulted in increased myofibroblast formation. In addition, we found microRNAs that were previously linked to Miat (miR-150) and Rian (14q32 miRNA cluster), to be dysregulated in the FoxD1-derivative cells, suggesting a possible interaction between miRNAs and these lncRNAs in myofibroblast formation. Taken together, lncRNAs play a regulatory role in myofibroblast formation, possibly through interacting with miRNA regulation, implicating that understanding their biology and their modulation may have the potential to counteract the development of renal fibrosis.

Magnesium lithospermate B improves renal hemodynamics and reduces renal oxygen consumption in 5/6th renal ablation/infarction rats

BACKGROUND

Magnesium lithospermate B (MLB) can promote renal microcirculation. The aim of the current project was to study whether MLB improves renal hemodynamics, oxygen consumption and subsequently attenuates hypoxia in rats induced by 5/6th renal Ablation/Infarction(A/I).

METHODS

Chronic renal failure (CRF) was induced in male SD rats by the 5/6 (A/I) surgery. 30 rats were randomly divided into three groups: sham group, 5/6 (A/I) + vehicle group (CRF group) and 5/6 (A/I) + MLB (CRF + MLB) group. 28 days after the surgery, rats were given with saline or 100 mg/kg MLB by i.p. injection for 8 weeks. The 24-h urinary protein (24hUp), serum creatinine (Scr), blood urine nitrogen (BUN), systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured. The protein expression of Fibronectin (FN), Collagen-I (Col-I), Connective Tissue Growth Factor(CTGF) and Interleukin-6 (IL-6) were measured by Western blot. Renal blood flow (RBF) and renal O₂ consumption (QO₂) indicated as sodium reabsorption (QO₂/TNa) were detected before sacrifice. Renal hypoxia was assessed by measuring the protein expression of nNOS, HIF-1α and VEGF.

RESULTS

MLB significantly reduced 24hUp, Scr, BUN, SBP and DBP levels in rats with CRF. The expression of FN, Col-I, CTGF and IL-6 were down-regulated by MLB treatment in rats with CRF. In comparison to sham operated rats, 5/6 (A/I) rats had significantly lower RBF, and MLB significantly increased RBF in rats with CRF. Moreover, QO₂/TNa was higher in the CRF group as compared to that in the sham group, and it was significantly attenuated in the CRF + MLB group. MLB reversed the expression of nNOS (neuronal nitric oxide synthase), HIF-1α (hypoxia inducible factor-1) and VEGF in rats with CRF.

CONCLUSIONS

MLB improves renal function, fibrosis and inflammation in CRF rats induced by 5/6 (A/I), which is probably related to the increase in RBF, reduction of oxygen consumption and attenuation of renal hypoxia in the remnant kidney with CRF.

In vivo three-dimensional photoacoustic imaging of the renal vasculature in preclinical rodent models

Noninvasive imaging of the kidney vasculature in preclinical murine models is important for the assessment of renal development, studying diseases and evaluating new therapies but is challenging to achieve using existing imaging modalities. Photoacoustic imaging is a promising new technique that is particularly well suited to visualizing the vasculature and could provide an alternative to existing preclinical imaging methods for studying renal vascular anatomy and function. To investigate this, an all-optical Fabry-Perot-based photoacoustic scanner was used to image the abdominal region of mice. High-resolution three-dimensional, noninvasive, label-free photoacoustic images of the mouse kidney and renal vasculature were acquired in vivo. The scanner was also used to visualize and quantify differences in the vascular architecture of the kidney in vivo due to polycystic kidney disease. This study suggests that photoacoustic imaging could be utilized as a novel preclinical imaging tool for studying the biology of renal disease.

Consistency of Multiple Renal Functional MRI Measurements Over 18 Months

BACKGROUND

Identification of patients with progressive chronic kidney disease (CKD) and those likely to respond to candidate therapeutics is urgently needed. Functional MRI measurements have shown promise. However, knowledge about the consistency of the measurements is essential to conduct longitudinal studies.

PURPOSE/HYPOTHESIS

To investigate the consistency of repeated functional MRI measurements in healthy subjects.

STUDY TYPE

Prospective, longitudinal study.

SUBJECTS

Seventeen healthy subjects were examined on two different occasions, 18 months apart.

FIELD STRENGTH/SEQUENCE

Multiple gradient-recalled-echo, 2D navigator-gated flow-sensitive alternating inversion recovery True-FISP and spin-echo planar diffusion-weighted sequences were used on a 3T scanner. Images were acquired on two different scanner configurations.

ASSESSMENT

Blood oxygenation level-dependent (BOLD) R2*, arterial spin labeling (ASL) perfusion-derived blood flow (BF) and apparent diffusion coefficient (ADC) maps were analyzed using a custom image processing toolbox. Regions of interest (ROIs) were placed on renal cortex, medulla, and whole kidney. Multiple researchers were involved in defining the ROIs.

STATISTICAL TESTS

Intra- and intersubject coefficients of variation (CV) and Bland-Altman plots were used to measure consistency and evaluate bias in the measurements. A nonparametric Wilcoxon test was used to compare differences between two timepoints.

RESULTS

The intrasubject CV for R2* and ADC were 6.8% and 5.3% with small (-3.8 and 5.3%) bias, respectively, comparing baseline and 18-month data. Intrasubject CV for renal cortex BF was higher (18.7%) compared to R2* and ADC, but comparable to prior literature values over shorter durations. It also exhibited a larger bias (-15.4%) between two timepoints and significantly lower values (P = 0.022) at 18-month data.

DATA CONCLUSION

All three MRI parameters over 18 months, even with a scanner upgrade and involving multiple observers, showed good consistency. These results are useful for the interpretation of longitudinal data and support the use of these methods to monitor progression in patients with CKD.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2018;48:514-521.

Cannabinoid-1 receptor deletion in podocytes mitigates both glomerular and tubular dysfunction in a mouse model of diabetic nephropathy

AIMS

To determine the specific role of podocyte-expressed cannabinoid-1 receptor (CB₁ R) in the development of diabetic nephropathy (DN), relative to CB₁ R in other renal cell types.

MATERIAL AND METHODS

We developed a mouse model with a podocyte-specific deletion of CB₁ R (pCB1Rko) and challenged this model with streptozotocin (STZ)-induced type-1 DN. We also assessed the podocyte response to high glucose in vitro and its effects on CB₁ R activation.

RESULTS

High glucose exposure for 48 hours led to an increase in CB₁ R gene expression (CNR1) and endocannabinoid production in cultured human podocytes. This was associated with podocyte injury, reflected by decreased podocin and nephrin expression. These changes could be prevented by Cnr1-silencing, thus identifying CB1R as a key player in podocyte injury. After 12 weeks of chronic hyperglycaemia, STZ-treated pCB1Rko mice showed elevated blood glucose similar to that of their wild-type littermates. However, they displayed less albuminuria and less podocyte loss than STZ-treated wild-type mice. Unexpectedly, pCB1Rko mice also have milder tubular dysfunction, fibrosis and reduction of cortical microcirculation compared to wild-type controls, which is mediated, in part, by podocyte-derived endocannabinoids acting via CB₁ R on proximal tubular cells.

CONCLUSIONS

Activation of CB₁ R in podocytes contributes to both glomerular and tubular dysfunction in type-1 DN, which highlights the therapeutic potential of peripheral CB₁ R blockade.

Hypoxia Activates Src and Promotes Endocytosis Which Decreases MMP-2 Activity and Aggravates Renal Interstitial Fibrosis

The aggravation of renal interstitial fibrosis in the advanced-stage of chronic kidney disease is related to decreased matrix metalloproteinase-2 (MMP-2) activity, which is induced by hypoxia in the kidney; however, the specific mechanism remains unclear. We previously demonstrated that inhibition of Caveolin-1, a key gene involved in endocytosis, increased MMP-2 activity in hypoxic HK-2 cells. It has been reported that activated Src (phospho-Src Tyr416) is a key molecule in multiple fibrotic pathways. However, whether Src functions on the regulation of Caveolin-1 and MMP-2 activity in hypoxic HK-2 cells remains poorly understood. To explore the underlying mechanism, a rat model of renal interstitial fibrosis was established, then we observed obvious hypoxia in fibrotic kidney tissue and the protein levels of phospho-Src and Caveolin-1 increased, while MMP-2 activity decreased. Next, we treated HK-2 cells with the phospho-Src inhibitor PP1. Compared with normal cells grown in hypoxia, in cells treated with PP1, the protein levels of phospho-Src and Caveolin-1 decreased, as did the protein levels of the MMP-2-activity-regulated molecules RECK (reversion-inducing-cysteine-rich protein with kazal motifs) and TIMP-2 (tissue inhibitor of metalloproteinase-2), while the protein level of MT1-MMP (membrane type 1-matrix metalloproteinase) increased and MMP-2 activity was enhanced. Therefore, hypoxia promotes the phosphorylation of Src and phospho-Src can enhance the endocytosis of HK-2 cells, which leads to decreased MMP-2 activity and aggravates renal interstitial fibrosis.

Comprehensive miRNA Analysis of Human Umbilical Cord-Derived Mesenchymal Stromal Cells and Extracellular Vesicles

BACKGROUND/AIMS

Mesenchymal stromal cells (MSCs) participate in the tissue-specific repair of many different organs, especially the kidney. Their effects are primarily mediated by the paracrine release of factors including extracellular vesicles (EVs), which are composed of micro-vesicles and exosomes. The corresponding microRNAs (miRNAs) of EVs are considered important for their biological functions.

METHODS

MSCs were cultured from the human umbilical cord, and EVs were isolated from the medium. The expression levels of miRNAs in MSCs and EVs were determined by microarray analysis, and gene ontology (GO) was used to analyze the functions of their target genes.

RESULTS

MSCs and EVs had similar miRNA expression profiles, with the exception of a small number of selectively enriched miRNAs. GO analysis indicated that, unlike MSCs, the target genes of EV-enriched miRNAs were associated with calcium channel regulation and cell junction activities, which may indicate that MSC and EVs have different regulatory properties. Angiogenesis, oxidative stress, and inflammatory signaling pathways related to the repair of renal injury were also analyzed, and EV-enriched miRNAs targeted genes associated with oxidative stress, T cell activation, and Toll-like receptor signaling. The miRNAs enriched in both MSCs and EVs targeted different genes in signaling pathways regulating angiogenesis and chemokine release.

CONCLUSION

MSCs and their EVs shared similar miRNA component, and some selectively enriched miRNAs observed in MSCs and EVs may affect different target genes through some specific signaling pathways.

Glucagon-Like Peptide-1 Mediates the Protective Effect of the Dipeptidyl Peptidase IV Inhibitor on Renal Fibrosis via Reducing the Phenotypic Conversion of Renal Microvascular Cells in Monocrotaline-Treated Rats

Chronic kidney diseases are characterized by renal fibrosis with excessive matrix deposition, leading to a progressive loss of functional renal parenchyma and, eventually, renal failure. Renal microcirculation lesions, including the phenotypic conversion of vascular cells, contribute to renal fibrosis. Here, renal microcirculation lesions were established with monocrotaline (MCT, 60 mg/kg). Sitagliptin (40 mg/kg/d), a classical dipeptidyl peptidase-4 (DPP-4) inhibitor, attenuated the renal microcirculation lesions by inhibiting glomerular tuft hypertrophy, glomerular mesangial expansion, and microvascular thrombosis. These effects of sitagliptin were mediated by glucagon-like peptide-1 receptor (GLP-1R), since they were blocked by the GLP-1R antagonist exendin-3 (Ex-3, 40 ug/kg/d). The GLP-1R agonist liraglutide showed a similar renal protective effect in a dose-independent manner. In addition, sitagliptin, as well as liraglutide, alleviated the MCT-induced apoptosis of renal cells by increasing the expression of survival factor glucose-regulated protein 78 (GRP78), which was abolished by the GLP-1R antagonist Ex-3. Sitagliptin and liraglutide also effectively ameliorated the conversion of vascular smooth muscle cells (SMCs) from a synthetic phenotype to contractile phenotype. Moreover, sitagliptin and liraglutide inhibited endothelial-mesenchymal transition (EndMT) via downregulating transforming growth factor-β1 (TGF-β1). Collectively, these findings suggest that DPP-4 inhibition can reduce microcirculation lesion-induced renal fibrosis in a GLP-1-dependent manner.

Microarray analysis reveals gene and microRNA signatures in diabetic kidney disease

The current study aimed to identify therapeutic gene and microRNA (miRNA) biomarkers for diabetic kidney disease (DKD). The public expression profile GSE30122 was used. Following data preprocessing, the limma package was used to select differentially-expressed genes (DEGs) in DKD glomeruli samples and tubuli samples and they were compared with corresponding controls. Then overlapping DEGs in glomeruli and tubuli were identified and enriched analysis was performed. In addition, protein‑protein interaction (PPI) network analysis as well as sub‑network analysis was conducted. miRNAs of the overlapping DEGs were investigated using WebGestal. A total of 139 upregulated and 28 downregulated overlapping DEGs were selected, which were primarily associated with pathways involved in extracellular matrix (ECM)‑receptor interactions and cytokine‑cytokine receptor interactions. CD44, fibronectin 1, C‑C motif chemokine ligand 5 and C‑X‑C motif chemokine receptor 4 were four primary nodes in the PPI network. miRNA (miR)‑17‑5p, miR‑20a and miR‑106a were important and nuclear receptor subfamily 4 group A member 3 (NR4A3), protein tyrosine phosphatase, receptor type O (PTPRO) and Kruppel like factor 9 (KLF9) were all predicted as target genes of the three miRNAs in the integrated miRNA‑target network. Several genes were identified in DKD, which may be involved in pathways such as ECM‑receptor interaction and cytokine‑cytokine receptor interaction. Three miRNAs may also be used as biomarkers for therapy of DKD, including miR‑17‑5p, miR‑20a and miR‑106a, with the predicted targets of NR4A3, PTPRO and KLF9.

Acute Rejection After Kidney Transplantation Associates With Circulating MicroRNAs and Vascular Injury

Supplemental digital content is available in the text.

Background

Acute rejection (AR) of kidney transplants is associated with the loss of endothelial integrity, microvascular rarefaction and, ultimately, graft dysfunction. Circulating angiogenic microRNAs (miRNAs) may serve as markers for microvascular injury. Here, we investigated the short- and long-term effects of AR after kidney transplantation on systemic vascular injury and the associated circulating miRNA profile.

Methods

Systemic vascular injury was determined by measuring capillary tortuosity and density within the oral mucosa as well as by assessing circulating levels of angiopoietin-2/angiopoietin-1 ratio, vascular endothelial growth factor and soluble thrombomodulin. After a pilot study, we selected 48 miRNAs to assess the AR- and microvascular injury associated circulating miRNAs.

Results

In stable transplant recipients (n = 25) and patients with AR (n = 13), which were also studied longitudinally (1, 6, and 12 months post-AR), we found an AR-associated increase in markers of systemic vascular injury, of which vascular endothelial growth factor and soluble thrombomodulin normalized within 1 year after AR. Of the 48 selected miRNAs, 8 were either decreased (miR-135a, miR-199a-3p, and miR-15a) or increased (miR-17, miR-140-3p, miR-130b, miR-122 and miR-192) in AR. Of these, miR-130b, miR-199a, and miR-192 associated with markers of vascular injury, whereas miR-140-3p, miR-130b, miR-122, and miR-192 normalized within 1 year after AR.

Conclusions

AR after kidney transplantation is characterized by systemic microvascular injury and associates with specific circulating miRNA levels.

Cardiorenal disease connection during post-menopause: The protective role of estrogen in uremic toxins induced microvascular dysfunction

Female gender, post-menopause, chronic kidney disease (CKD) and (CKD linked) microvascular disease are important risk factors for developing heart failure with preserved ejection fraction (HFpEF). Enhancing our understanding of the interrelation between these risk factors could greatly benefit the identification of new drug targets for future therapy. This review discusses the evidence for the protective role of estradiol (E₂) in CKD-associated microvascular disease and related HFpEF. Elevated circulating levels of uremic toxins (UTs) during CKD may act in synergy with hormonal changes during post-menopause and could lead to coronary microvascular endothelial dysfunction in HFpEF. To elucidate the molecular mechanism involved, published transcriptome datasets of indoxyl sulfate (IS), high inorganic phosphate (HP) or E₂ treated human derived endothelial cells from the NCBI Gene Expression Omnibus database were analyzed. In total, 36 genes overlapped in both IS- and HP-activated gene sets, 188 genes were increased by UTs (HP and/or IS) and decreased by E₂, and 572 genes were decreased by UTs and increased by E₂. Based on a comprehensive in silico analysis and literature studies of collected gene sets, we conclude that CKD-accumulated UTs could negatively impact renal and cardiac endothelial homeostasis by triggering extensive inflammatory responses and initiating dysregulation of angiogenesis. E₂ may protect (myo)endothelium by inhibiting UTs-induced inflammation and ameliorating UTs-related uremic bleeding and thrombotic diathesis via restored coagulation capacity and hemostasis in injured vessels.

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.