Capillary rarefaction, hypoxia, VEGF and angiogenesis in chronic renal disease

Relationship between angiogenic growth factors and atherosclerosis in renal transplantation recipients: a cross-sectional study

BACKGROUND

Accelerated development of atherosclerosis has been observed in renal transplant recipients (RTRs). Angiopoietin-2 (Ang-2) and vascular endothelial growth factor (VEGF) are vascular enzymes that play important roles in vascular development and angiogenesis.

OBJECTIVE

This study aimed to investigate the relationship between Ang-2 and VEGF and atherosclerosis in RTRs.

DESIGN AND SETTING

This study was conducted at Ankara City Hospital, Turkey.

METHODS

This cross-sectional study included 36 (37.5%) female and 60 (62.5%) male RTRs. All findings were compared with those of 70 healthy controls. Ultrasonographic measurements of the carotid artery intima-media thickness (CA-IMT) and renal resistive index (RRI) were used as indicators of atherosclerosis.

RESULTS

Log10 Ang-2, log10 VEGF, CA-IMT, and RRI levels were significantly higher in patients than in healthy controls. No significant differences were detected in CA-IMT and RRI between those with log10 Ang-2 ≥ 3.53 pg/mL and those with < 3.53 pg/mL. No significant differences were detected in CA-IMT and RRI between those with log10 VEGF ≥ 1.98 pg/mL and those with < 1.98 pg/mL. No correlation was detected between log10 Ang-2 and log10 VEGF, CA-IMT, or RRI.

CONCLUSIONS

Increased serum angiogenic growth factor levels and increased atherosclerosis development were detected in RTRs compared to healthy individuals. No relationship was observed between angiogenic growth factors and atherosclerosis. This may be due to the decreased synthesis and effect of angiogenic growth factor receptors synthesized from atherosclerotic plaques due to atherosclerosis, which improves after renal transplantation.

Nuclear receptor 4A1 ameliorates UUO-induced renal fibrosis by inhibiting the PI3K/AKT pathway

As an ultra-early response gene, Nuclear receptor 4A1 (NR4A1) has been reported to be involved in the development of various diseases through various pathological pathways, but its specific mechanism in chronic kidney disease (CKD) is unknown currently. Our study showed that the expression of NR4A1 was reduced in unilateral ureteral obstruction (UUO) mice and it could exacerbate UUO-induced renal pathological injury when knocked down NR4A1 in UUO mice. We found that the knockdown of NR4A1 could promote angiogenesis, renal inflammation, and cell apoptosis to aggravate renal fibrosis induced by UUO. As an agonist of NR4A1, Cytosporone B (Csn-B) could inhibit the renal fibrosis by attenuating angiogenesis, renal inflammation and cell apoptosis. In addition, the PI3K/AKT pathway was activated with NR4A1 knockdown in vivo and in vitro experiments. In conclusion, our study demonstrates that NR4A1 can ameliorate renal fibrosis. Furthermore, we speculate that its underlying mechanism may be related to the activation of PI3K/AKT pathway according to our present results.

Nuclear receptor 4A1 ameliorates renal fibrosis by inhibiting vascular endothelial growth factor A induced angiogenesis in UUO rats

INTRODUCTION

Angiogenesis is closely related to renal fibrosis; however, its basic mechanism remains unclear. In our study, we found that nuclear receptor 4A1 (NR4A1) inhibits vascular endothelial growth factor A (VEGFA)-induced angiogenesis, ameliorating renal fibrosis.

METHODS

We prepared a renal fibrosis animal model with unilateral ureteral obstruction (UUO) and NR4A1 knockdown UUO mice model, Using Human umbilical vein endothelial cells (HUVECs) to conduct all in vitro experiments. We then detected and analyzed the expression levels of NR4A1 and other genes related to angiogenesis and fibrosis.

RESULTS

The angiogenesis related genes, such as VEGFA, vascular endothelial growth factor receptor-2 (VEGFR-2), endoglin (CD105), as well as the expression of fibrosis related genes that included, α-smooth muscle actin (α-SMA), Vimentin, and Collagen I are all significantly increased in the UUO rat model. In addition, the expression of NR4A1 of the kidney tissue of UUO rats was significantly reduced. Therefore, according to the above results, we speculated that angiogenesis may exacerbate renal fibrosis and NR4A1 may repress renal fibrosis by inhibiting angiogenesis. To further verify the above results, we used VEGFA to stimulate HUVECs with (or without) overexpression or knockdown of NR4A1. The results showed that with prolonged stimulation using VEGFA, the expression of NR4A1 decreases. Overexpression of NR4A1 significantly inhibits the expression of related indicators of angiogenesis and renal fibrosis. Furthermore, knockdown of NR4A1 induces endothelial cell proliferation and migration; therefore, exacerbating angiogenesis and fibrosis. Finally, the results of NR4A1 knockdown UUO mice showed that knockdown of NR4A1 can aggravating kidney damage and induce the expression of angiogenesis and renal fibrosis related indicators, while UUO can significantly induce kidney damage, angiogenesis and renal fibrosis. When knockdown of NR4A1, renal kidney damage, angiogenesis and fibrosis becomes more severe than UUO. Thus, all of these results indicate that NR4A1 can ameliorate renal fibrosis by inhibiting angiogenesis.

CONCLUSIONS

NR4A1 can inhibit angiogenesis to ameliorate renal fibrosis.

Microbubble detection on ultrasound imaging by utilizing phase patterned waves

Objective.Super-resolution ultrasonography offers the advantage of visualization of intricate microvasculature, which is crucial for disease diagnosis. Mapping of microvessels is possible by localizing microbubbles (MBs) that act as contrast agents and tracking their location. However, there are limitations such as the low detectability of MBs and the utilization of a diluted concentration of MBs, leading to the extension of the acquisition time. We aim to enhance the detectability of MBs to reduce the acquisition time of acoustic data necessary for mapping the microvessels.Approach.We propose utilizing phase patterned waves (PPWs) characterized by spatially patterned phase distributions in the incident beam to achieve this. In contrast to conventional ultrasound irradiation methods, this irradiation method alters bubble interactions, enhancing the oscillation response of MBs and generating more significant scattered waves from specific MBs. This enhances the detectability of MBs, thereby enabling the detection of MBs that were undetectable by the conventional method. The objective is to maximize the overall detection of bubbles by utilizing ultrasound imaging with additional PPWs, including the conventional method. In this paper, we apply PPWs to ultrasound imaging simulations considering bubble-bubble interactions to elucidate the characteristics of PPWs and demonstrate their efficacy by employing PPWs on MBs fixed in a phantom by the experiment.Main results.By utilizing two types of PPWs in addition to the conventional ultrasound irradiation method, we confirmed the detection of up to 93.3% more MBs compared to those detected using the conventional method alone.Significance.Ultrasound imaging using additional PPWs made it possible to increase the number of detected MBs, which is expected to improve the efficiency of bubble detection.

Reduction of renal interstitial fibrosis by targeting Tie2 in vascular endothelial cells

BACKGROUND

Tie2, a functional angiopoietin receptor, is expressed in vascular endothelial cells and plays an important role in angiogenesis and vascular stability. This study aimed to evaluate the effects of an agonistic Tie2 signal on renal interstitial fibrosis (RIF) and elucidate the underlying mechanisms.

METHODS

We established an in vivo mouse model of folic acid-induced nephropathy (FAN) and an in vitro model of lipopolysaccharide-stimulated endothelial cell injury, then an agonistic Tie2 monoclonal antibody (Tie2 mAb) was used to intervent these processes. The degree of tubulointerstitial lesions and related molecular mechanisms were determined by histological assessment, immunohistochemistry, western blotting, and qPCR.

RESULTS

Tie2 mAb attenuated RIF and reduced the level of fibroblast-specific protein 1 (FSP1). Further, it suppressed vascular cell adhesion molecule-1 (VCAM-1) and increased CD31 density in FAN. In the in vitro model, Tie2 mAb was found to decrease the expression of VCAM-1, Bax, and α-smooth muscle actin (α-SMA).

CONCLUSIONS

The present findings indicate that the agonistic Tie2 mAb exerted vascular protective effects and ameliorated RIF via inhibition of vascular inflammation, apoptosis, and fibrosis. Therefore, Tie2 may be a potential target for the treatment of this disease.

IMPACT

This is the first report to confirm that an agonistic Tie2 monoclonal antibody can reduce renal interstitial fibrosis in folic acid-induced nephropathy in mice. This mechanism possibly involves vascular protective effects brought about by inhibition of vascular inflammation, apoptosis and fibrosis. Our data show that Tie2 signal may be a novel, endothelium-specific target for the treatment of tubulointerstitial fibrosis.

tRNA-Derived Small RNAs: A Novel Regulatory Small Noncoding RNA in Renal Diseases

Background

tRNA-derived small RNAs (tsRNAs) are an emerging class of small noncoding RNAs derived from tRNA cleavage.

Summary

With the development of high-throughput sequencing, various biological roles of tsRNAs have been gradually revealed, including regulation of mRNA stability, transcription, translation, direct interaction with proteins and as epigenetic factors, etc. Recent studies have shown that tsRNAs are also closely related to renal disease. In clinical acute kidney injury (AKI) patients and preclinical AKI models, the production and differential expression of tsRNAs in renal tissue and plasma were observed. Decreased expression of tsRNAs was also found in urine exosomes from chronic kidney disease patients. Dysregulation of tsRNAs also appears in models of nephrotic syndrome and patients with lupus nephritis. And specific tsRNAs were found in high glucose model in vitro and in serum of diabetic nephropathy patients. In addition, tsRNAs were also differentially expressed in patients with kidney cancer and transplantation.

Key Messages

In the present review, we have summarized up-to-date works and reviewed the relationship and possible mechanisms between tsRNAs and kidney diseases.

Pericyte detachment and renal congestion involve interstitial injury and fibrosis in Dahl salt-sensitive rats and humans with heart failure

Congestive heart failure produces fluid volume overload, central and renal venous pressure elevation, and consequently renal congestion, which results in worsening renal function. Pericyte detachment and pericyte-myofibroblast transition (PMT) were linked to renal interstitial fibrosis. Dahl salt-sensitive hypertensive (DahlS) rats are a non-surgical renal congestion model. The relation, however, between renal interstitial damage, pericyte morphology, and PMT in the renal congestion of DahlS rats has not been reported. DahlS rats (8-week-old) were fed normal salt (NS, 0.4% NaCl) or high salt (HS, 4% NaCl), and the left kidney was decapsulated to reduce renal interstitial hydrostatic pressure (RIHP) at 9 weeks old. One week after capsulotomy, both kidneys were analyzed by molecular and histological techniques. Renal pericyte structure was assessed in the body donors with/without venous stasis. Markers of tubulointerstitial damage, interstitial fibrosis, and PMT were upregulated in the right non-decapsulated kidney of DahlS rats fed HS. Renal tubular injury and fibrosis were detected in the HS diet groups in histological analysis. Pericyte detachment was observed in the right non-decapsulated kidney of DahlS rats fed HS by low vacuum-scanning electron microscopy. Decapsulation in DahlS rats fed HS attenuated these findings. Also, renal pericytes detached from the vascular wall in patients with heart failure. These results suggest that pericyte detachment and PMT induced by increased RIHP are responsible for tubulointerstitial injury and fibrosis in DahlS rats and humans with renal congestion. Renal venous congestion and subsequent physiological changes could be therapeutic targets for renal damage in cardiorenal syndrome.

Cellular Trafficking of Nanotechnology-Mediated mRNA Delivery

Messenger RNA (mRNA)-based therapy has emerged as a powerful, safe, and rapidly scalable therapeutic approach that involves technologies for both mRNA itself and the delivery vehicle. Although there are some unique challenges for different applications of mRNA therapy, a common challenge for all mRNA therapeutics is the transport of mRNA into the target cell cytoplasm for sufficient protein expression. This review is focused on the behaviors at the cellular level of nanotechnology-mediated mRNA delivery systems, which have not been comprehensively reviewed yet. First, the four main therapeutic applications of mRNA are introduced, including immunotherapy, protein replacement therapy, genome editing, and cellular reprogramming. Second, common types of mRNA cargos and mRNA delivery systems are summarized. Third, strategies to enhance mRNA delivery efficiency during the cellular trafficking process are highlighted, including accumulation to the cell, internalization into the cell, endosomal escape, release of mRNA from the nanocarrier, and translation of mRNA into protein. Finally, the challenges and opportunities for the development of nanotechnology-mediated mRNA delivery systems are presented. This review can provide new insights into the future fabrication of mRNA nanocarriers with desirable cellular trafficking performance.

The impact of hypoxia-inducible factors in the pathogenesis of kidney diseases: a link through cell metabolism

Kidneys are sensitive to disturbances in oxygen homeostasis. Hypoxia and activation of the hypoxia-inducible factor (HIF) pathway alter the expression of genes involved in the metabolism of renal and immune cells, interfering with their functioning. Whether the transcriptional activity of HIF protects the kidneys or participates in the pathogenesis of renal diseases is unclear. Several studies have indicated that HIF signaling promotes fibrosis in experimental models of kidney disease. Other reports showed a protective effect of HIF activation on kidney inflammation and injury. In addition to the direct effect of HIF on the kidneys, experimental evidence indicates that HIF-mediated metabolic shift activates inflammatory cells, supporting the HIF cascade as a link between lung or gut damage and worsening of renal disease. Although hypoxia and HIF activation are present in several scenarios of renal diseases, further investigations are needed to clarify whether interfering with the HIF pathway is beneficial in different pathological contexts.

Independent Prognostic and Predictive Role of Interstitial Macrophages in Kidney Biopsies of IgA Nephropathy Patients

A relevant percentage of IgAN patients experience a progressive decline in kidney function. According to the KDIGO guidelines, proteinuria and eGFR are the only validated prognostic markers. The role of interstitial macrophages in kidney biopsies of IgAN patients and the outcome of patients treated with renin-angiotensin system inhibitors (RASBs) alone or combined with glucocorticoids were evaluated. Clinical and laboratory records (age, gender, hypertension, hematuria, proteinuria, eGFR, serum creatinine, and therapy), MEST-C parameters of the Oxford classification, C4d deposition, peritubular capillaries, and glomerular and interstitial macrophages in 47 IgAN patients undergoing kidney biopsy consecutively between 2003 and 2016 were examined. A high number of interstitial macrophages significantly correlated with peritubular capillary rarefaction and impairment of kidney function. Cox's multivariable regression analysis revealed that a value > 19.5 macrophages/HPF behaved as an independent marker of an unfavorable outcome. Patients exhibiting > 19.5 macrophages/HPF treated at the time of diagnosis with RASBs combined with methylprednisolone had an estimated probability of a favorable outcome higher than patients treated with RASBs alone. Thus, a value > 19.5 macrophages/HPF in IgAN biopsies can predict an unfavorable outcome and endorse a well-timed administration of glucocorticoids. Studies evaluating urine biomarkers associated with peritubular capillary rarefaction in patients with marked macrophage infiltration may help personalized treatment decisions.

An Efficacy and Mechanism Driven Study on the Impact of Hypoxia on Lipid Nanoparticle Mediated mRNA Delivery

Hypoxia is a common hallmark of human disease that is characterized by abnormally low oxygen levels in the body. While the effects of hypoxia on many small molecule-based drugs are known, its effects on several classes of next-generation medications including messenger RNA therapies warrant further study. Here, we provide an efficacy- and mechanism-driven study that details how hypoxia impacts the cellular response to mRNA therapies delivered using 4 different chemistries of lipid nanoparticles (LNPs, the frontrunner class of drug delivery vehicles for translational mRNA therapy utilized in the Moderna and Pfizer/BioNTech COVID-19 vaccines). Specifically, our work provides a comparative analysis as to how various states of oxygenation impact LNP-delivered mRNA expression, cellular association, endosomal escape, and intracellular ATP concentrations following treatment with 4 different LNPs across 3 different cell lines. In brief, we first identify that hypoxic cells express less LNP-delivered mRNA into protein than normoxic cells. Next, we identify generalizable cellular reoxygenation protocols that can reverse the negative effects that hypoxia imparts on LNP-delivered mRNA expression. Finally, mechanistic studies that utilize fluorescence-activated cell sorting, confocal microscopy, and enzyme inhibition reveal that decreases in mRNA expression correlate with decreases in intracellular ATP (rather than with differences in mRNA LNP uptake pathways). In presenting this data, we hope that our work provides a comprehensive efficacy and mechanism-driven study that explores the impact of differential oxygenation on LNP-delivered mRNA expression while simultaneously establishing fundamental criteria that may one day be useful for the development of mRNA drugs to treat hypoxia-associated disease.

The Role of Eosinophil-Derived Neurotoxin and Vascular Endothelial Growth Factor in the Pathogenesis of Eosinophilic Asthma

Asthma is a chronic complex pulmonary disease characterized by airway inflammation, remodeling, and hyperresponsiveness. Vascular endothelial growth factor (VEGF) and eosinophil-derived neurotoxin (EDN) are two significant mediators involved in the pathophysiology of asthma. In asthma, VEGF and EDN levels are elevated and correlate with disease severity and airway hyperresponsiveness. Diversity in VEGF polymorphisms results in the variability of responses to glucocorticosteroids and leukotriene antagonist treatment. Targeting VEGF and eosinophils is a promising therapeutic approach for asthma. We identified lichochalcone A, bevacizumab, azithromycin (AZT), vitamin D, diosmetin, epigallocatechin gallate, IGFBP-3, Neovastat (AE-941), endostatin, PEDF, and melatonin as putative add-on drugs in asthma with anti-VEGF properties. Further studies and clinical trials are needed to evaluate the efficacy of those drugs. AZT reduces the exacerbation rate and may be considered in adults with persistent symptomatic asthma. However, the long-term effects of AZT on community microbial resistance require further investigation. Vitamin D supplementation may enhance corticosteroid responsiveness. Herein, anti-eosinophil drugs are reviewed. Among them are, e.g., anti-IL-5 (mepolizumab, reslizumab, and benralizumab), anti-IL-13 (lebrikizumab and tralokinumab), anti-IL-4 and anti-IL-13 (dupilumab), and anti-IgE (omalizumab) drugs. EDN over peripheral blood eosinophil count is recommended to monitor the asthma control status and to assess the efficacy of anti-IL-5 therapy in asthma.

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.

Paracrine Effects of Renal Proximal Tubular Epithelial Cells on Podocyte Injury under Hypoxic Conditions Are Mediated by Arginase-II and TGF-β1

Hypoxia is an important risk for renal disease. The mitochondrial enzyme arginase-II (Arg-II) is expressed and/or induced by hypoxia in proximal tubular epithelial cells (PTECs) and in podocytes, leading to cellular damage. Because PTECs are vulnerable to hypoxia and located in proximity to podocytes, we examined the role of Arg-II in the crosstalk of PTECs under hypoxic conditions with podocytes. A human PTEC cell line (HK2) and a human podocyte cell line (AB8/13) were cultured. Arg-ii gene was ablated by CRISPR/Case9 in both cell types. HK2 cells were exposed to normoxia (21% O₂) or hypoxia (1% O₂) for 48 h. Conditioned medium (CM) was collected and transferred to the podocytes. Podocyte injuries were then analyzed. Hypoxic (not normoxic) HK2-CM caused cytoskeletal derangement, cell apoptosis, and increased Arg-II levels in differentiated podocytes. These effects were absent when arg-ii in HK2 was ablated. The detrimental effects of the hypoxic HK2-CM were prevented by TGF-β1 type-I receptor blocker SB431542. Indeed, TGF-β1 levels in hypoxic HK2-CM (but not arg-ii^-/--HK2-CM) were increased. Furthermore, the detrimental effects of TGF-β1 on podocytes were prevented in arg-ii^-/--podocytes. This study demonstrates crosstalk between PTECs and podocytes through the Arg-II-TGF-β1 cascade, which may contribute to hypoxia-induced podocyte damage.

New mechanisms involved in the development of cardiovascular disease in chronic kidney disease

Chronic kidney disease (CKD) is a pathology with a high worldwide incidence and an upward trend affecting the elderly. When CKD is very advanced, the use of renal replacement therapies is required to prolong its life (dialysis or kidney transplantation). Although dialysis improves many complications of CKD, the disease does not reverse completely. These patients present an increase in oxidative stress, chronic inflammation and the release of extracellular vesicles (EVs), which cause endothelial damage and the development of different cardiovascular diseases (CVD). CKD patients develop premature diseases associated with advanced age, such as CVD. EVs play an essential role in developing CVD in patients with CKD since their number increases in plasma and their content is modified. The EVs of patients with CKD cause endothelial dysfunction, senescence and vascular calcification. In addition, miRNAs free or transported in EVs together with other components carried in these EVs promote endothelial dysfunction, thrombotic and vascular calcification in CKD, among other effects. This review describes the classic factors and focuses on the role of new mechanisms involved in the development of CVD associated with CKD, emphasizing the role of EVs in the development of cardiovascular pathologies in the context of CKD. Moreover, the review summarized the EVs' role as diagnostic and therapeutic tools, acting on EV release or content to avoid the development of CVD in CKD patients.

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.

Exogenous pericyte delivery protects the mouse kidney from chronic ischemic injury

Pericytes are considered reparative mesenchymal stem cell-like cells, but their ability to ameliorate chronic ischemic kidney injury is unknown. We hypothesized that pericytes would exhibit renoprotective effects in murine renal artery stenosis (RAS). Porcine kidney-derived pericytes (5 × 105) or vehicle were injected into the carotid artery 2 wk after the induction of unilateral RAS in mice. The stenotic kidney glomerular filtration rate and tissue oxygenation were measured 2 wk later using magnetic resonance imaging. We subsequently compared kidney oxidative stress, inflammation, apoptosis, fibrosis, and systemic levels of oxidative and inflammatory cytokines. Treatment of xenogeneic pericytes ameliorated the RAS-induced loss of perfusion, glomerular filtration rate, and atrophy in stenotic kidneys and restored cortical and medullary oxygenation but did not blunt hypertension. Ex vivo, pericytes injection partially mitigated RAS-induced renal inflammation, fibrosis, oxidative stress, apoptosis, and senescence. Furthermore, coculture with pericytes in vitro protected pig kidney-1 tubular cells from injury. In conclusion, exogenous delivery of renal pericytes protects the poststenotic mouse kidney from ischemic injury, underscoring the therapeutic potential role of pericytes in subjects with ischemic kidney disease.NEW & NOTEWORTHY Our study demonstrates a novel pericyte-based therapy for the injured kidney. The beneficial effect of pericyte delivery appears to be mediated by ameliorating oxidative stress, inflammation, cellular apoptosis, and senescence in the stenotic kidney and improved tissue hypoxia, vascular loss, fibrosis, and tubular atrophy. Our data may form the basis for pericyte-based therapy, and additional research studies are needed to gain further insight into their role in improving renal function.

Up-Date on Diabetic Nephropathy

Diabetes is one of the leading causes of kidney disease. Diabetic kidney disease (DKD) is a major cause of end-stage kidney disease (ESKD) worldwide, and it is linked to an increase in cardiovascular (CV) risk. Diabetic nephropathy (DN) increases morbidity and mortality among people living with diabetes. Risk factors for DN are chronic hyperglycemia and high blood pressure; the renin-angiotensin-aldosterone system blockade improves glomerular function and CV risk in these patients. Recently, new antidiabetic drugs, including sodium-glucose transport protein 2 inhibitors and glucagon-like peptide-1 agonists, have demonstrated additional contribution in delaying the progression of kidney disease and enhancing CV outcomes. The therapeutic goal is regression of albuminuria, but an atypical form of non-proteinuric diabetic nephropathy (NP-DN) is also described. In this review, we provide a state-of-the-art evaluation of current treatment strategies and promising emerging treatments.

Hypoxia: molecular pathophysiological mechanisms in human diseases

Hypoxia, a low O2 tension, is a fundamental feature that occurs in physiological events as well as pathophysiological conditions, especially mentioned for its role in the mechanism of angiogenesis, glucose metabolism, and cell proliferation/survival. The hypoxic state through the activation of specific mechanisms is an aggravating circumstance commonly noticed in multiple sclerosis, cancer, heart disease, kidney disease, liver disease, lung disease, and in inflammatory bowel disease. On the other hand, hypoxia could play a key role in tissue regeneration and repair of damaged tissues, especially by acting on specific tissue stem cells, but their features may result as a disadvantage when it is concerned for neoplastic stem cells. Furthermore, hypoxia could also have a potential role in tissue engineering and regenerative medicine due to its capacity to improve the performance of biomaterials. The current review aims to highlight the hypoxic molecular mechanisms reported in different pathological conditions to provide an overview of hypoxia as a therapeutic agent in regenerative and molecular therapy.

Graphical abstract

Pro- and anti-fibrotic effects of vascular endothelial growth factor in chronic kidney diseases

Renal fibrosis is the inevitable common end-point of all progressive chronic kidney diseases. The underlying mechanisms of renal fibrosis are complex, and currently there is no effective therapy against renal fibrosis. Renal microvascular rarefaction contributes to the progression of renal fibrosis; however, an imbalance between proangiogenic and antiangiogenic factors leads to the loss of renal microvasculature. Vascular endothelial growth factor (VEGF) is the most important pro-angiogenic factor. Recent studies have unraveled the involvement of VEGF in the regulation of renal microvascular rarefaction and fibrosis via various mechanisms; however, it is not clear whether it has anti-fibrotic or pro-fibrotic effect. This paper reviews the available evidence pertaining to the function of VEGF in the fibrotic process and explores the associated underlying mechanisms. Our synthesis will help identify the future research priorities for developing specialized treatments for alleviating or preventing renal fibrosis. Abbreviation: VEGF: vascular endothelial growth factor; CKD: chronic kidney disease; ESKD: end-stage kidney disease; ER: endoplasmic reticulum; VEGFR: vascular endothelial growth factor receptor; AKI: acute kidney injury; EMT: epithelial-to-mesenchymal transition; HIF: hypoxia-inducible factor; α-SMA: α smooth muscle actin; UUO: unilateral ureteral obstruction; TGF-β: transforming growth factor-β; PMT: pericyte-myofibroblast transition; NO: nitric oxide; NOS: nitric oxide synthase; nNOS: neuronal nitric oxide synthase; iNOS: inducible nitric oxide synthase; eNOS: endothelial nitric oxide synthase; sGC: soluble guanylate cyclase; PKG: soluble guanylate cyclase dependent protein kinases; UP R: unfolded protein response

Acoustic Angiography: Superharmonic Contrast-Enhanced Ultrasound Imaging for Noninvasive Visualization of Microvasculature

Acoustic angiography is a contrast-enhanced ultrasound technique that relies on superharmonic imaging to form high-resolution, three-dimensional maps of the microvasculature. In order to obtain signal separation between tissue and contrast, acoustic angiography has been performed with dual-frequency transducers with nonoverlapping bandwidths. This enables a high contrast-to-tissue ratio, and the choice of a high frequency receiving element provides high resolution. In this chapter, we describe the technology behind acoustic angiography as well as the step-by-step implementation of this contrast enhanced microvascular imaging technique.

Tibetan Medicine for Diabetes Mellitus: Overview of Pharmacological Perspectives

Diabetes mellitus (DM) and its complications pose a major public health threat which is approaching epidemic proportions globally. Current drug options may not provide good efficacy and even cause serious adverse effects. Seeking safe and effective agents for DM treatment has been an area of intensive interest. As a healing system originating in Tibet, Traditional Tibetan Medicine (TTM) has been widely used by Tibetan people for the prevention and treatment of DM and its complications for hundreds of years. Tibetan Materia Medica (TMM) including the flower of Edgeworthia gardneri (Wall.) Meisn., Phyllanthi Fructus, Chebulae Fructus, Huidouba, and Berberidis Cortex are most frequently used and studied. These TMMs possess hypoglycemic, anti-insulin resistant, anti-glycation, lipid lowering, anti-inflammatory, and anti-oxidative effects. The underlying mechanisms of these actions may be related to their α-glucosidase inhibitory, insulin signaling promoting, PPARs-activating, gut microbiota modulation, islet β cell-preserving, and TNF-α signaling suppressive properties. This review presents a comprehensive overview of the mode and mechanisms of action of various active constituents, extracts, preparations, and formulas from TMM. The dynamic beneficial effects of the products prepared from TMM for the management of DM and its complications are summarized. These TMMs are valuable materia medica which have the potential to be developed as safe and effective anti-DM agents.

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.

Hypoxia and chronic kidney disease: Possible mechanisms, therapeutic targets, and relevance to cats

There is mounting evidence that kidney ischaemia/hypoxia plays an important role in feline chronic kidney disease (CKD) development and progression, as well as in human disease and laboratory animal models. Ischaemic acute kidney injury is widely accepted as a cause of CKD in people and data from laboratory species has identified some of the pathways underlying this continuum. Experimental kidney ischaemia in cats results in morphological changes, namely chronic tubulointerstitial inflammation, tubulointerstitial fibrosis, and tubular atrophy, akin to those observed in naturally-occurring CKD. Multiple situations are envisaged that could result in acute or chronic episodes of kidney hypoxia in cats, while risk factors identified in epidemiological studies provide further support that kidney hypoxia contributes to spontaneously occurring feline CKD. This review evaluates the evidence for the role of kidney ischaemia/hypoxia in feline CKD and the proposed mechanisms and consequences of kidney hypoxia. As no effective treatments exist that substantially slow or prevent feline CKD progression, there is a need for novel therapeutic strategies. Targeting kidney hypoxia is one such promising approach, with therapies including those that attenuate the hypoxia-inducible factor (HIF) pathway already being utilised in human CKD.

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.

Microvascular dysfunction and kidney disease: Challenges and opportunities?

Kidneys are highly vascular organs that despite their relatively small size receive 20% of the cardiac output. The highly intricate, delicately organized structure of renal microcirculation is essential to enable renal function and glomerular filtration rate through the local modulation of renal blood flow and intraglomerular pressure. Not surprisingly, the dysregulation of blood flow within the microvessels (abnormal vasoreactivity), fibrosis driven by disordered vascular-renal cross talk, or the loss of renal microvasculature (rarefaction) is associated with kidney disease. In addition, kidney disease can cause microcirculatory dysfunction in distant organs such as the heart and brain, mediated by mechanisms that remain to be elucidated. The objective of this review is to highlight the role of renal microvasculature in kidney disease. The overview will outline the impetus to study renal microvasculature, the bidirectional relationship between kidney disease and microvascular dysfunction, the key pathways driving microvascular diseases such as vasoreactivity, the cell dynamics coordinating fibrosis, and vessel rarefaction. Finally, we will also briefly highlight new therapies targeting the renal microvasculature to improve renal function.

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.

Implication of cellular senescence in the progression of chronic kidney disease and the treatment potencies

Chronic kidney disease (CKD) is an increasing major public health problem worldwide. And CKD shares numerous phenotypic similarities with kidney as well as systemic ageing. Cellular senescence is mainly characterized by a stable cell cycle arrest, senescence-associated secretory phenotype (SASP) and senescent cell anti-apoptotic pathways (SCAPs). Herein, the regulations and the internal mechanisms of cellular senescence will be discussed. Meanwhile, efforts are made to give a comprehensive overview of the recent advances of the implication of cellular senescence in CKD. To date, numerous studies have focused on the effects of ageing risk factors in kidney and thereby trying to interrupt the kidney ageing processes with senolytics. Interestingly, some of them showed enormous clinical application potentials. Therefore, senotherapeutics can be applied as novel potential strategies for the treatment of CKD.

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.

Deciphering the Pharmacological Mechanisms of Taohe-Chengqi Decoction Extract Against Renal Fibrosis Through Integrating Network Pharmacology and Experimental Validation In Vitro and In Vivo

Taohe-Chengqi decoction (THCQ), a classical traditional Chinese medicinal (TCM) formula, has been extensively used for treating chronic kidney disease (CKD). However, the biological activity and mechanisms of action of its constituents against renal fibrosis have not yet been investigated thoroughly. This study was aimed at devising an integrated strategy for investigating the bioactivity constituents and possible pharmacological mechanisms of the n-butanol extract of THCQ (NE-THCQ) against renal fibrosis. The n-butanol extract of THCQ was prepared by the solvent extraction method. The components of NE-THCQ were analyzed using UPLC-Q/TOF-MS/MS techniques and applied for screening the active components of NE-THCQ according to their oral bioavailability and drug-likeness index. Then, we speculated the potential molecular mechanisms of NE-THCQ against renal fibrosis through pharmacological network analysis. Based on data mining techniques and topological parameters, gene ontology, and pathway enrichment, we established compound-target (C-T), protein-protein interaction (PPI) and compound-target-pathway (C-T-P) networks by Cytoscape to identify the hub targets and pathways. Finally, the potential molecular mechanisms of NE-THCQ against renal fibrosis, as predicted by the network pharmacology analyses, were validated experimentally in renal tubular epithelial cells (HK-2) in vitro and against unilateral ureteral obstruction models in the rat in vivo. We identified 26 components in NE-THCQ and screened seven bioactive ingredients. A total of 118 consensus potential targets associated with renal fibrosis were identified by the network pharmacology approach. The experimental validation results demonstrated that NE-THCQ might inhibit the inflammatory processes, reduce ECM deposition and reverse EMT via PI3K/AKT/mTOR and HIF-1α/VEGF signaling pathways to exert its effect against renal fibrosis. This study identified the potential ingredients of the NE-THCQ by UPLC-Q/TOF-MS/MS and explained the possible mechanisms of NE-THCQ against renal fibrosis by integrating network pharmacology and experimental validation.

Microvascular Disease Increases Amputation in Patients With Peripheral Artery Disease

It is estimated that >2 million patients are living with an amputation in the United States. Peripheral artery disease (PAD) and diabetes mellitus account for the majority of nontraumatic amputations. The standard measurement to diagnose PAD is the ankle-brachial index, which integrates all occlusive disease in the limb to create a summary value of limb artery occlusive disease. Despite its accuracy, ankle-brachial index fails to well predict limb outcomes. There is an emerging body of literature that implicates microvascular disease (MVD; ie, retinopathy, nephropathy, neuropathy) as a systemic phenomenon where diagnosis of MVD in one capillary bed implicates microvascular dysfunction systemically. MVD independently associates with lower limb outcomes, regardless of diabetic or PAD status. The presence of PAD and concomitant MVD phenotype reveal a synergistic, rather than simply additive, effect. The higher risk of amputation in patients with MVD, PAD, and concomitant MVD and PAD should prompt aggressive foot surveillance and diagnosis of both conditions to maintain ambulation and prevent amputation in older patients.

Animal Models and Renal Biomarkers of Diabetic Nephropathy

Diabetes mellitus (DM) is the first cause of end stage chronic kidney disease (CKD). Animal models of the disease can shed light on the pathogenesis of the diabetic nephropathy (DN) and novel and earlier biomarkers of the condition may help to improve diagnosis and prognosis. This review summarizes the most important features of animal models used in the study of DN and updates the most recent progress in biomarker research.

Attenuation of mTOR Signaling Is the Major Response Element in the Rescue Pathway of Chronic Kidney Disease in Rats

BACKGROUND

Modern lifestyle changes and the interlinking of non-communicable diseases result in the development of chronic kidney disease (CKD). While research has focused on attenuating the CKD, the role of mTOR in the progression of CKD is still unclear.

OBJECTIVES

The current investigation was undertaken to study the role of mTOR-mediated signaling in CKD using Wistar male rats and adenine-induced CKD as an experimental model.

METHOD

The animals were divided into 3 groups, representing control, CKD, and rapamycin-pretreated rats. At the end of the experimental period, blood biochemical indexes on kidney function and expression levels of fibrotic markers, including TGF-β, PAI-1, α-smooth muscle action, fibronectin, CTGF, and collagen-1, were analyzed. In addition, kidney injury markers such as kim-1, cystatin-C, NAG, and NGAL, indicating a progressive fibrotic response, were also studied.

RESULTS

The results suggest that mTOR inhibition significantly attenuated the induction of fibrosis, with restored serum creatinine and blood urea nitrogen levels. Intriguingly, the microRNA (miRNA) analysis revealed an increased expression of miR-193-5p, miR-221, miR-212, and miR-183-5p in CKD, while an increased mRNA expression of anti-inflammatory cytokines and reduced level of pS6K with attenuated miRNA was found in rapamycin-treated rats compared to the CKD animals.

CONCLUSION

Activation of mTOR is the major responsive element with activation of miRNAs as an elementary role in the progression of kidney disease. Hence, targeting mTOR would be a possible strategy of treatment for CKD.

Identification of dicarbonyl and L-xylulose reductase as a therapeutic target in human chronic kidney disease

An imbalance of nephroprotective factors and renal damaging molecules contributes to development and progression of chronic kidney disease (CKD). We investigated associations of renoprotective factor gene expression patterns with CKD severity and outcome. Gene expression profiles of 197 previously reported renoprotective factors were analyzed in a discovery cohort in renal biopsies of 63 CKD patients. Downregulation of dicarbonyl and L-xylulose reductase (DCXR) showed the strongest association with disease progression. This significant association was validated in an independent set of 225 patients with nephrotic syndrome from the multicenter NEPTUNE cohort. Reduced expression of DCXR was significantly associated with degree of histological damage as well as with lower estimated glomerular filtration rate and increased urinary protein levels. DCXR downregulation in CKD was confirmed in 3 publicly available transcriptomics data sets in the context of CKD. Expression of DCXR showed positive correlations to enzymes that are involved in dicarbonyl stress detoxification based on transcriptomics profiles. The sodium glucose cotransporter-2 (SGLT2) inhibitors canagliflozin and empagliflozin showed a beneficial effect on renal proximal tubular cells under diabetic stimuli-enhanced DCXR gene expression. In summary, lower expression of the renoprotective factor DCXR in renal tissue is associated with more severe disease and worse outcome in human CKD.

Circulating microRNAs as potential biomarkers of chronic kidney disease

Chronic kidney disease (CKD) is a supra - nosological term that reflects the progressive nature of chronic kidney diseases, which are based on the mechanisms of nephrosclerosis. Diagnosis of CKD at the earliest stages is of great importance, because it allows, by using therapeutic agents, to slow the progression of renal dysfunction and the development of cardiovascular complications. However, the currently available methods for diagnosing renal function impairment, including the determination of endogenous creatinine clearance, can detect renal dysfunction too late, when around 40-50% of the renal parenchyma is already reversibly or irreversibly damaged. In this regard, there is an active search for new, more sensitive and specific biomarkers for early diagnosis of CKD. Recent studies in cellular and animal models of CKD have demonstrated the important role of microRNA, a new class of posttranscriptional regulators of gene expression, in physiology and pathophysiology of kidneys. In particular, it has been shown that their expression profile in blood or urine can reflect changes in cells involved in a particular pathological process, since these cells can secrete a specific population of microRNAs, for example, through secretion of microRNA-containing exosomes. This gave grounds for considering increased or decreased expression of individual microRNAs in renal tissue or biological fluids (including urine) as new biomarkers for the diagnosis and monitoring of CKD. This review presents the results of recent experimental and clinical studies on these issues.

Loss of Renal Peritubular Capillaries in Hypertensive Patients Is Detectable by Urinary Endothelial Microparticle Levels

Hypertension, an important cause of chronic kidney disease, is characterized by peritubular capillary (PTC) loss. Circulating levels of endothelial microparticles (EMPs) reflect systemic endothelial injury. We hypothesized that systemic and urinary PTC-EMPs levels would reflect renal microvascular injury in hypertensive patients. We prospectively measured by flow cytometry renal vein, inferior vena cava, and urinary levels of EMPs in essential (n=14) and renovascular (RVH; n=24) hypertensive patients and compared them with peripheral blood and urinary levels in healthy volunteers (n=14). PTC-EMPs were identified as urinary exosomes positive for the PTC marker plasmalemmal-vesicle-associated protein. In 7 RVH patients, PTC and fibrosis were also quantified in renal biopsy, and in 18 RVH patients, PTC-EMPs were measured again 3 months after continued medical therapy with or without stenting (n=9 each). Renal vein and systemic PTC-EMPs levels were not different among the groups, whereas their urinary levels were elevated in both RVH and essential hypertension versus healthy volunteers (56.8%±12.7% and 62.8%±10.7% versus 34.0%±17.8%; both P≤0.001). Urinary PTC-EMPs levels correlated directly with blood pressure and inversely with estimated glomerular filtration rate. Furthermore, in RVH, urinary PTC-EMPs levels correlated directly with stenotic kidney hypoxia, histological PTC count, and fibrosis and inversely with cortical perfusion. Three months after treatment, the change in urinary PTC-EMPs levels correlated inversely with a change in renal function ( r=-0.582; P=0.011). Therefore, urinary PTC-EMPs levels are increased in hypertensive patients and may reflect renal microcirculation injury, whereas systemic PTC-EMPs levels are unchanged. Urinary PTC-EMPs may be useful as novel biomarkers of intrarenal capillary loss.

Danggui Shaoyao San Ameliorates Renal Fibrosis via Regulation of Hypoxia and Autophagy

Danggui Shaoyao San (DSS), a traditional Chinese medicinal prescription, was widely used to reinforce earth to activate collaterals in ancient times. Recently, many clinical studies found that DSS had a renoprotection. In this study, we evaluated the effect of DSS on unilateral ureteral obstruction- (UUO-) induced renal fibrosis in rats and investigated the mechanisms underlying the effect. Sprague Dawley (SD) rats were randomized to UUO or Sham operation. After 1 day, the rats that underwent UUO were randomized to treatment for four experimental groups (n=10 each group): Sham, UUO only, UUO+ benazepril (Bena), and UUO+DSS. After 4 weeks, we demonstrated that DSS significantly suppressed UUO-induced renal hypertrophy by gravimetric. In addition, DSS obviously prevented UUO-induced disorder in renal structure and renal function by HE and biochemistry test. We also found that DSS abrogated UUO-induced renal fibrosis by Masson's staining and collagen volume fraction (CVF) analysis; this is consistent with the western blot analysis that showed DSS abrogated the UUO-induced enhanced TGF-β1 and weakened BMP-7. Compared with the UUO only group, rats treated with DSS exhibited significant increase in vascular density, followed by decrease in hypoxia and HIF-1α protein level through western blot and immunofluorescence analysis. Furthermore, we also determined proteins of autophagy and DSS enhanced autophagy to prevent the damage-induced by UUO. Taken together, our findings demonstrated that DSS had a renoprotection effect in ameliorating renal fibrosis possibly via attenuating tissue hypoxia and regulating autophagy.

Astaxanthin ameliorates renal interstitial fibrosis and peritubular capillary rarefaction in unilateral ureteral obstruction

Loss of peritubular capillaries is a notable feature of progressive renal interstitial fibrosis. Astaxanthin (ASX) is a natural carotenoid with various biological activities. The present study aimed to evaluate the effect of ASX on unilateral ureteral obstruction (UUO)‑induced renal fibrosis in mice. For that purpose, mice were randomly divided into five treatment groups: Sham, ASX 100 mg/kg, UUO, UUO + ASX 50 mg/kg and UUO + ASX 100 mg/kg. ASX was administered to the mice for 7 or 14 days following UUO. The results demonstrated that UUO‑induced histopathological changes in the kidney tissue were prevented by ASX. Renal function was improved by ASX treatment, as evidenced by decreased blood urea nitrogen and serum creatinine levels. Furthermore, the extent of renal fibrosis and collagen deposition induced by UUO was suppressed by ASX. The levels of collagen I, fibronectin and α‑smooth muscle actin were increased by UUO in mice or by transforming growth factor (TGF)‑β1 treatment in NRK‑52E cells, and were reduced by ASX administration. In addition, ASX inhibited the UUO‑induced decrease in peritubular capillary density by upregulating vascular endothelial growth factor and downregulating thrombospondin 1 levels. Inactivation of the TGF‑β1/Smad signaling pathway was involved in the anti‑fibrotic mechanism of ASX in UUO mice and TGF‑β1‑treated NRK‑52E cells. In conclusion, ASX attenuated renal interstitial fibrosis and peritubular capillary rarefaction via inactivation of the TGF‑β1/Smad signaling pathway.

Hypoalbuminemia: Pathogenesis and Clinical Significance

Hypoalbuminemia is associated with inflammation. Despite being addressed repeatedly in the literature, there is still confusion regarding its pathogenesis and clinical significance. Inflammation increases capillary permeability and escape of serum albumin, leading to expansion of interstitial space and increasing the distribution volume of albumin. The half‐life of albumin has been shown to shorten, decreasing total albumin mass. These 2 factors lead to hypoalbuminemia despite increased fractional synthesis rates in plasma. Hypoalbuminemia, therefore, results from and reflects the inflammatory state, which interferes with adequate responses to events like surgery or chemotherapy, and is associated with poor quality of life and reduced longevity. Increasing or decreasing serum albumin levels are adequate indicators, respectively, of improvement or deterioration of the clinical state. In the interstitium, albumin acts as the main extracellular scavenger, antioxidative agent, and as supplier of amino acids for cell and matrix synthesis. Albumin infusion has not been shown to diminish fluid requirements, infection rates, and mortality in the intensive care unit, which may imply that there is no body deficit or that the quality of albumin “from the shelf” is unsuitable to play scavenging and antioxidative roles. Management of hypoalbuminaemia should be based on correcting the causes of ongoing inflammation rather than infusion of albumin. After the age of 30 years, muscle mass and function slowly decrease, but this loss is accelerated by comorbidity and associated with decreasing serum albumin levels. Nutrition support cannot fully prevent, but slows down, this chain of events, especially when combined with physical exercise.

Cellular and molecular mechanisms of kidney fibrosis

Renal fibrosis is the final pathological process common to any ongoing, chronic kidney injury or maladaptive repair. It is considered as the underlying pathological process of chronic kidney disease (CKD), which affects more than 10% of world population and for which treatment options are limited. Renal fibrosis is defined by excessive deposition of extracellular matrix, which disrupts and replaces the functional parenchyma that leads to organ failure. Kidney's histological structure can be divided into three main compartments, all of which can be affected by fibrosis, specifically termed glomerulosclerosis in glomeruli, interstitial fibrosis in tubulointerstitium and arteriosclerosis and perivascular fibrosis in vasculature. In this review, we summarized the different appearance, cellular origin and major emerging processes and mediators of fibrosis in each compartment. We also depicted and discussed the challenges in translation of anti-fibrotic treatment to clinical practice and discuss possible solutions and future directions.

Protective effect of retinoic acid receptor α on hypoxia-induced epithelial to mesenchymal transition of renal tubular epithelial cells associated with TGF-β/MMP-9 pathway

Retinoic acid receptor α (RARα), a member of family of the nuclear retinoic acid receptors (RARs), plays an essential role in various chronic kidney diseases (CKD). Renal tubular epithelial to mesenchymal transition (EMT) is a common mechanism of progression of renal interstitial fibrosis (RIF). Hypoxia has been extensively considered as one of major inducers of renal tubular EMT. However, the effects of RARα on hypoxia-induced EMT have not yet been described so far. The aim of the present study was to explore the roles and potential mechanisms of RARα in hypoxia-induced EMT of renal tubular epithelial cells (RTECs). Our results showed that expression of RARα in RTECs subjected to hypoxia significantly was reduced, accompanied by decreased expression level of the epithelial marker E-cadherin, and increased expression levels of the mesenchymal markers α-smooth muscle actin (α-SMA) and vimentin, in accord with EMT. Meanwhile, hypoxia could cause RTECs to obviously express TGF-β and matrix metalloproteinase-9 (MMP-9). Furthermore, using lentivirus-based delivery vectors to overexpress RARα in RTECs, we demonstrated that RARα alleviated hypoxia-induced EMT of RTECs and downregulated the expression levels of TGF-β and MMP-9. In a word, RARα protects RTECs against EMT induced by hypoxia associated with TGF-β/MMP-9 pathway.

The association of serum angiogenic growth factors with renal structure and function in patients with adult autosomal dominant polycystic kidney disease

PURPOSE

Autosomal dominant polycystic kidney disease (ADPKD) is a common congenital chronic kidney disease (CKD). We report here the relationship of serum angiopoietin-1 (Ang-1), Ang-2, and vascular endothelial growth factor (VEGF) with total kidney volume (TKV), total cyst volume (TCV), and renal failure in adult ADPKD patients at various stages of CKD.

METHODS

This cross-sectional study was conducted with 50 patients diagnosed with ADPKD and a control group of 45 age-matched healthy volunteers. In patient group, TKV and TCV were determined with upper abdominal magnetic resonance imaging, whereas in controls, TKV was determined with ultrasonography according to ellipsoid formula. Renal function was assessed with serum creatinine, estimated glomerular filtration rate (eGFR), and spot urinary protein/creatinine ratio (UPCR). Ang-1, Ang-2, and VEGF were measured using enzyme-linked immunosorbent assay.

RESULTS

Patients with ADPKD had significantly higher TKV (p < 0.001) and UPCR (p < 0.001), and lower eGFR (p ≤ 0.001) compared to the controls. Log₁₀Ang-2 was found to be higher in ADPKD patients at all CKD stages. Multiple linear regression analysis showed that there was no association between log₁₀Ang-1, log₁₀Ang-2, or log₁₀VEGF and creatinine, eGFR, UPCR, log₁₀TKV (p > 0.05).

CONCLUSION

There was no association of serum angiogenic growth factors with TKV or renal failure in ADPKD patients. Increased serum Ang-2 observed in stages 1-2 CKD suggests that angiogenesis plays a role in the progression of early stage ADPKD, but not at later stages of the disease. This may be explained by possible cessation of angiogenesis in advanced stages of CKD due to the increased number of sclerotic glomeruli.

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.

Effects of erythropoietin receptor activity on angiogenesis, tubular injury, and fibrosis in acute kidney injury: a "U-shaped" relationship

The erythropoietin receptor (EpoR) is widely expressed but its renoprotective action is unexplored. To examine the role of EpoR in vivo in the kidney, we induced acute kidney injury (AKI) by ischemia-reperfusion in mice with different EpoR bioactivities in the kidney. EpoR bioactivity was reduced by knockin of wild-type human EpoR, which is hypofunctional relative to murine EpoR, and a renal tubule-specific EpoR knockout. These mice had lower EPO/EpoR activity and lower autophagy flux in renal tubules. Upon AKI induction, they exhibited worse renal function and structural damage, more apoptosis at the acute stage (<7 days), and slower recovery with more tubulointerstitial fibrosis at the subacute stage (14 days). In contrast, mice with hyperactive EpoR signaling from knockin of a constitutively active human EpoR had higher autophagic flux, milder kidney damage, and better renal function at the acute stage but, surprisingly, worse tubulointerstitial fibrosis and renal function at the subacute stage. Either excess or deficient EpoR activity in the kidney was associated with abnormal peritubular capillaries and tubular hypoxia, creating a "U-shaped" relationship. The direct effects of EpoR on tubular cells were confirmed in vitro by a hydrogen peroxide model using primary cultured proximal tubule cells with different EpoR activities. In summary, normal erythropoietin (EPO)/EpoR signaling in renal tubules provides defense against renal tubular injury maintains the autophagy-apoptosis balance and peritubular capillary integrity. High and low EPO/EpoR bioactivities both lead to vascular defect, and high EpoR activity overides the tubular protective effects in AKI recovery.

In Situ Hybridization and Double Immunohistochemistry for the Detection of VEGF-A mRNA and CD34/Collagen IV Proteins in Renal Transplant Biopsies

Quantitative metrics on the tissue distribution of different cell phenotypes, extracellular matrix components, and signaling/cell cycle markers hold the promise for the advent of new-generation tissue-based predictive/prognostic biomarkers in clinical diagnostics. The workflow of this approach is composed of three major phases: (1) detection of multiple molecular targets on a single histologic section, (2) image acquisition, and (3) digital image processing and analysis. Here, we present the most prevalent current alternatives for step (1) and describe a three-plex staining and image acquisition platform that captures the spatial distribution of macromolecules from two different species.

Chronic Hypobaric Hypoxia Modulates Primary Cilia Differently in Adult and Fetal Ovine Kidneys

Hypoxic environments at high altitude have significant effects on kidney injury. Following injury, renal primary cilia display length alterations. Primary cilia are mechanosensory organelles that regulate tubular architecture. The effect of hypoxia on cilia length is still controversial in cultured cells, and no corresponding in vivo study exists. Using fetal and adult sheep, we here study the effect of chronic hypobaric hypoxia on the renal injury, intracellular calcium signaling and the relationship between cilia length and cilia function. Our results show that although long-term hypoxia induces renal fibrosis in both fetal and adult kidneys, fetal kidneys are more susceptible to hypoxia-induced renal injury. Unlike hypoxic adult kidneys, hypoxic fetal kidneys are characterized by interstitial edema, tubular disparition and atrophy. We also noted that there is an increase in the cilia length as well as an increase in the cilia function in the hypoxic fetal proximal and distal collecting epithelia. Hypoxia, however, has no significant effect on primary cilia in the adult kidneys. Increased cilia length is also associated with greater flow-induced intracellular calcium signaling in renal epithelial cells from hypoxic fetuses. Our studies suggest that while hypoxia causes renal fibrosis in both adult and fetal kidneys, hypoxia-induced alteration in cilia length and function are specific to more severe renal injuries in fetal hypoxic kidneys.