Aldosterone induces albuminuria via matrix metalloproteinase-dependent damage of the endothelial glycocalyx

Mineralocorticoid receptor blockage in kidney transplantation: too much of a good thing or not?

Although, kidney transplantation (KT) is the best treatment option for patients with end-stage kidney disease, long-term complications including chronic kidney allograft disease (CKAD) and major adverse cardiovascular events (MACE) are common. To decrease these complications new therapeutic options are necessary. Mineralocorticoid receptor antagonists (MRAs) are one of the promising drugs in this context. In the general population, MRAs had favorable effects on blood pressure regulation, MACE, proteinuria and progression of chronic kidney disease. In the context of KT, there are limited studies showing beneficial effects such as reducing proteinuria and oxidative stress. In this review, we performed a narrative review to assess the use and impact of MRAs in kidney transplant recipients. We found that in KTRs, MRAs are safe and they have favorable or neutral impact on blood pressure, glomerular filtration rate, urinary protein/albumin excretion, and oxidative stress. No data was found regarding major cardiovascular adverse events.

Glomerular Endothelial Cell Receptor Adhesion G-Protein-Coupled Receptor F5 (ADGRF5) and the Integrity of the Glomerular Filtration Barrier

Key Points

Deletion of endothelial receptor adhesion G-protein–coupled receptor F5 in mice led to abnormal structural and functional properties of the glomerular filtration barrier. Adhesion G-protein–coupled receptor F5 regulates gene expression of glomerular basement membrane components and a mechanosensitive transcription factor.

Background

Glomerular endothelial cells are recognized to be important for maintaining the glomerular filtration barrier. Adhesion G-protein–coupled receptor F5 (ADGRF5), an adhesion G protein–coupled receptor, has been suggested to be involved in endothelial cell function. However, the role of ADGRF5 in the glomerular filtration barrier integrity remains elusive.

Methods

Cellular expression of ADGRF5 in mouse glomerulus was determined by histological analyses. The effect of ADGRF5 deletion on the glomerular morphology, kidney function, and glomerular endothelial gene/protein expression was then analyzed using ADGRF5 knockout (Adgrf5 −/−) mice and human primary glomerular endothelial cells.

Results

ADGRF5 was specifically expressed in the capillary endothelial cells within the glomerulus. Adgrf5 −/− mice developed albuminuria and impaired kidney function with morphological defects in the glomeruli, namely glomerular hypertrophy, glomerular basement membrane splitting and thickening, diaphragmed fenestration and detachment of the glomerular endothelial cells, and mesangial interposition. These defects were accompanied by the altered expression of genes responsible for glomerular basement membrane organization (type 4 collagens and laminins) and Krüppel-like factor 2 (Klf2 ) in glomerular endothelial cells. Moreover, ADGRF5 knockdown decreased COL4A3 and COL4A4 expression and increased KLF2 expression in human primary glomerular endothelial cells.

Conclusions

The loss of ADGRF5 resulted in altered gene expression in glomerular endothelial cells and perturbed the structure and permselectivity of the glomerular filtration barrier.

Sparsentan improves glomerular hemodynamics, cell functions, and tissue repair in a mouse model of FSGS

Dual endothelin-1 (ET-1) and angiotensin II (AngII) receptor antagonism with sparsentan has strong antiproteinuric actions via multiple potential mechanisms that are more pronounced, or additive, compared with current standard of care using angiotensin receptor blockers (ARBs). Considering the many actions of ET-1 and AngII on multiple cell types, this study aimed to determine glomeruloprotective mechanisms of sparsentan compared to the ARB losartan by direct visualization of its effects in the intact kidney in focal segmental glomerulosclerosis (FSGS) using intravital multiphoton microscopy. In both healthy and FSGS models, sparsentan treatment increased afferent/efferent arteriole diameters; increased or preserved blood flow and single-nephron glomerular filtration rate; attenuated acute ET-1 and AngII-induced increases in podocyte calcium; reduced proteinuria; preserved podocyte number; increased both endothelial and renin lineage cells and clones in vasculature, glomeruli, and tubules; restored glomerular endothelial glycocalyx; and attenuated mitochondrial stress and immune cell homing. These effects were either not observed or of smaller magnitude with losartan. The pleiotropic nephroprotective effects of sparsentan included improved hemodynamics, podocyte and endothelial cell functions, and tissue repair. Compared with losartan, sparsentan was more effective in the sustained preservation of kidney structure and function, which underscores the importance of the ET-1 component in FSGS pathogenesis and therapy.

The mineralocorticoid receptor in diabetic kidney disease

Diabetes mellitus is one of the leading causes of chronic kidney disease and its progression to end-stage kidney disease (ESKD). Diabetic kidney disease (DKD) is characterized by glomerular hypertrophy, hyperfiltration, inflammation, and the onset of albuminuria, together with a progressive reduction in glomerular filtration rate. This progression is further accompanied by tubulointerstitial inflammation and fibrosis. Factors such as genetic predisposition, epigenetic modifications, metabolic derangements, hemodynamic alterations, inflammation, and inappropriate renin-angiotensin-aldosterone system (RAAS) activity contribute to the onset and progression of DKD. In this context, decades of work have focused on glycemic and blood pressure reduction strategies, especially targeting the RAAS to slow disease progression. Although much of the work has focused on targeting angiotensin II, emerging data support that the mineralocorticoid receptor (MR) is integral in the development and progression of DKD. Molecular mechanisms linked to the underlying pathophysiological changes derived from MR activation include vascular endothelial and epithelial cell responses to oxidative stress and inflammation. These responses lead to alterations in the microcirculatory environment, the abnormal release of extracellular vesicles, gut dysbiosis, epithelial-mesenchymal transition, and kidney fibrosis. Herein, we present recent experimental and clinical evidence on the MR in DKD onset and progress along with new MR-based strategies for the treatment and prevention of DKD.

Matrix Metalloproteinase-2 and CKD Progression: The Chronic Renal Insufficiency Cohort (CRIC) Study

Rationale & Objective

Matrix metalloproteinase 2 (MMP-2) plays an important role in the development of fibrosis, the final common pathway of chronic kidney disease (CKD). This study aimed to assess the relationship between repeated measures of MMP-2 and CKD progression in a large, diverse prospective cohort.

Study Design

In a prospective cohort of Chronic Renal Insufficiency Cohort (CRIC) participants (N = 3,827), MMP-2 was measured at baseline. In a case-cohort design, MMP-2 was additionally measured at year 2 in a randomly selected subcohort and cases of estimated glomerular filtration rate (eGFR) halving or kidney replacement therapy (KRT) (N = 1,439).

Setting & Participants

CRIC is a multicenter prospective cohort of adults with CKD.

Exposure

MMP-2 measured in plasma at baseline and at year 2.

Outcomes

A composite kidney endpoint (KRT/eGFR halving).

Analytical Approach

Weighted Cox proportional hazards models for case-cohort participants.

Results

Participants were followed for a median of 4.6 years from year 2 and 6.9 years from the baseline. Persistently elevated MMP-2 (≥300 ng/mL at both baseline and year 2) increased the hazard of the composite kidney endpoint (HR, 1.61; 95% CI, 1.07-2.42; P = 0.09) after adjusting for covariates. The relationship of persistently elevated MMP-2 was modified by levels of inflammation, with a 2.6 times higher rate of the composite kidney endpoint in those with high-sensitivity C-reactive protein < 2.5 g/dL at study entry. Heterogeneity of effect was found with proteinuria, with a baseline MMP-2 level of ≥300 ng/mL associated with an increased risk of the composite kidney endpoint (HR, 1.30; 95% CI, 1.09-1.54) only with proteinuria ≥ 442 mg/g.

Limitations

The observational study design limits causal interpretation.

Conclusions

Elevated MMP-2 is associated with CKD progression, particularly among those with low inflammation and those with proteinuria. Future investigations are warranted to confirm the reduction in risk of CKD progression among these subgroups of patients with CKD.

High salt intake and HIV infection on endothelial glycocalyx shedding in salt-sensitive hypertension

The endothelial glycocalyx is closely associated with various physiological and pathophysiological events. Significant modification of the endothelial glycocalyx is an early process in the pathogenesis of cardiovascular disease. High dietary salt and HIV infection damages the endothelial glycocalyx causing endothelial dysfunction and increasing the risk for salt-sensitive hypertension and cardiovascular disease. The two factors, HIV infection and dietary salt are critical independent predictors of hypertension and cardiovascular disease and often synergize to exacerbate and accelerate disease pathogenesis. Salt-sensitive hypertension is more common among people living with HIV and is associated with risk for cardiovascular disease, stroke, heart attack and even death. However, the underlying mechanisms linking endothelial glycocalyx damage to dietary salt and HIV infection are lacking. Yet, both HIV infection/treatment and dietary salt are closely linked to endothelial glycocalyx damage and development of salt-sensitive hypertension. Moreover, the majority of individuals globally, consume more salt than is recommended and the burden of HIV especially in sub-Sahara Africa is disproportionately high. In this review, we have discussed the missing link between high salt and endothelial glycocalyx shedding in the pathogenesis of salt-sensitive hypertension. We have further elaborated the role played by HIV infection and treatment in modifying endothelial glycocalyx integrity to contribute to the development of hypertension and cardiovascular disease.

Adiponectin Reduces Glomerular Endothelial Glycocalyx Disruption and Restores Glomerular Barrier Function in a Mouse Model of Type 2 Diabetes

Adiponectin has vascular anti-inflammatory and protective effects. Although adiponectin protects against the development of albuminuria, historically, the focus has been on podocyte protection within the glomerular filtration barrier (GFB). The first barrier to albumin in the GFB is the endothelial glycocalyx (eGlx), a surface gel-like barrier covering glomerular endothelial cells (GEnCs). In diabetes, eGlx dysfunction occurs before podocyte damage; hence, we hypothesized that adiponectin could protect from eGlx damage to prevent early vascular damage in diabetic kidney disease (DKD). Globular adiponectin (gAd) activated AMPK signaling in human GEnCs through AdipoR1. It significantly reduced eGlx shedding and the tumor necrosis factor-α (TNF-α)-mediated increase in syndecan-4 (SDC4) and MMP2 mRNA expression in GEnCs in vitro. It protected against increased TNF-α mRNA expression in glomeruli isolated from db/db mice and against expression of genes associated with glycocalyx shedding (namely, SDC4, MMP2, and MMP9). In addition, gAd protected against increased glomerular albumin permeability (Ps'alb) in glomeruli isolated from db/db mice when administered intraperitoneally and when applied directly to glomeruli (ex vivo). Ps'alb was inversely correlated with eGlx depth in vivo. In summary, adiponectin restored eGlx depth, which was correlated with improved glomerular barrier function, in diabetes.

ARTICLE HIGHLIGHTS

Glomerular and tubular effects of dapagliflozin, eplerenone and their combination in patients with chronic kidney disease: A post-hoc analysis of the ROTATE-3 study

AIM

Sodium-glucose co-transporter 2 inhibitors and mineralocorticoid receptor antagonists reduce albuminuria and the risk of kidney failure. The aim of this study was to investigate the effects of both agents alone and in combination on markers of the glomerular endothelial glycocalyx and tubular function.

METHODS

This post-hoc analysis utilized data of the ROTATE-3 study, a randomized cross-over study in 46 adults with chronic kidney disease and urinary albumin excretion ≥100 mg/24 h, who were treated for 4 weeks with dapagliflozin, eplerenone or its combination. The effects of dapagliflozin, eplerenone and the combination on outcome measures such as heparan sulphate, neuro-hormonal markers and tubular sodium handling were assessed with mixed repeated measures models.

RESULTS

The mean percentage change from baseline in heparan sulphate after 4 weeks treatment with dapagliflozin, eplerenone or dapagliflozin-eplerenone was -34.8% (95% CI -52.2, -10.9), -5.9% (95% CI -32.5, 31.3) and -28.1% (95% CI -48.4, 0.1) respectively. The mean percentage change from baseline in plasma aldosterone was larger with eplerenone [38.9% (95% CI 2.8, 87.7)] and dapagliflozin-eplerenone [32.2% (95% CI -1.5, 77.4)], compared with dapagliflozin [-12.5% (95% CI -35.0, 17.8)], respectively. Mean percentage change from baseline in copeptin with dapagliflozin, eplerenone or dapagliflozin-eplerenone was 28.4% (95% CI 10.7, 49.0), 4.2% (95% CI -10.6, 21.4) and 23.8% (95% CI 6.6, 43.9) respectively. Dapagliflozin decreased proximal absolute sodium reabsorption rate by 455.9 mmol/min (95% CI -879.2, -32.6), while eplerenone decreased distal absolute sodium reabsorption rate by 523.1 mmol/min (95% CI -926.1, -120.0). Dapagliflozin-eplerenone decreased proximal absolute sodium reabsorption [-971.0 mmol/min (95% CI -1411.0, -531.0)], but did not affect distal absolute sodium reabsorption [-9.2 mmol/min (95% CI -402.0, 383.6)].

CONCLUSIONS

Dapagliflozin and eplerenone exert different effects on markers of glomerular and tubular function supporting the hypothesis that different mechanistic pathways may account for their kidney protective effects.

Heparanase inhibition as a systemic approach to protect the endothelial glycocalyx and prevent microvascular complications in diabetes

BACKGROUND

Diabetes mellitus is a chronic disease which is detrimental to cardiovascular health, often leading to secondary microvascular complications, with huge global health implications. Therapeutic interventions that can be applied to multiple vascular beds are urgently needed. Diabetic retinopathy (DR) and diabetic kidney disease (DKD) are characterised by early microvascular permeability changes which, if left untreated, lead to visual impairment and renal failure, respectively. The heparan sulphate cleaving enzyme, heparanase, has previously been shown to contribute to diabetic microvascular complications, but the common underlying mechanism which results in microvascular dysfunction in conditions such as DR and DKD has not been determined.

METHODS

In this study, two mouse models of heparan sulphate depletion (enzymatic removal and genetic ablation by endothelial specific Exotosin-1 knock down) were utilized to investigate the impact of endothelial cell surface (i.e., endothelial glycocalyx) heparan sulphate loss on microvascular barrier function. Endothelial glycocalyx changes were measured using fluorescence microscopy or transmission electron microscopy. To measure the impact on barrier function, we used sodium fluorescein angiography in the eye and a glomerular albumin permeability assay in the kidney. A type 2 diabetic (T2D, db/db) mouse model was used to determine the therapeutic potential of preventing heparan sulphate damage using treatment with a novel heparanase inhibitor, OVZ/HS-1638. Endothelial glycocalyx changes were measured as above, and microvascular barrier function assessed by albumin extravasation in the eye and a glomerular permeability assay in the kidney.

RESULTS

In both models of heparan sulphate depletion, endothelial glycocalyx depth was reduced and retinal solute flux and glomerular albumin permeability was increased. T2D mice treated with OVZ/HS-1638 had improved endothelial glycocalyx measurements compared to vehicle treated T2D mice and were simultaneously protected from microvascular permeability changes associated with DR and DKD.

CONCLUSION

We demonstrate that endothelial glycocalyx heparan sulphate plays a common mechanistic role in microvascular barrier function in the eye and kidney. Protecting the endothelial glycocalyx damage in diabetes, using the novel heparanase inhibitor OVZ/HS-1638, effectively prevents microvascular permeability changes associated with DR and DKD, demonstrating a novel systemic approach to address diabetic microvascular complications.

Endogenous Dysregulation of Thromboinflammatory Biomarkers in End-Stage Renal Disease, and Their Amplification by Heart Failure

In patients with end-stage renal disease (ESRD), heart failure with reduced ejection fraction (HFrEF) is a common comorbidity. Thromboinflammatory processes in both conditions represent complex pathophysiology, demonstrated by dysregulation of thromboinflammatory biomarkers, and commonly resulting in the combined pathology of cardiorenal syndrome. We sought to investigate the effects of HFrEF on these biomarkers in patients with ESRD, and observe the relationship to mortality. Blood samples from 73 patients with ESRD (mean age 67 ± 13 years, 56% male) and 40 healthy controls were analyzed via enzyme-linked immunosorbent assay and other chromogenic methods for angiopoietin-2 (Ang2), endogenous glycosaminoglycans, fatty acid binding protein, interleukin-6, lipopolysaccharide, free fatty acids, NT-pro B-type natriuretic peptide, tumor necrosis factor α, vascular endothelial growth factor, and von Willebrand factor. Patients were stratified into those with or without HFrEF (EF < 50%). Patients had highly prevalent comorbidities including coronary artery disease 46%, diabetes 69%, hypertension 97%, and smoking 49%. Most biomarkers were upregulated in ESRD compared to controls. Patients with HFrEF and ESRD had greater interleukin-6 and NT-pro B-type natriuretic peptide and lesser lipopolysaccharide compared to ESRD only. Spearman correlations between most biomarkers were increased in HFrEF + ESRD over ESRD only. Ang-2 was associated with mortality in this cohort. The dysregulation of thromboinflammation in ESRD is somewhat amplified in comorbid HFrEF. Correlation among biomarkers in this cohort indicates the mechanisms of thromboinflammatory biomarker generation in ESRD and HFrEF share an integrative process. Ang2, interleukin-6, and lipopolysaccharide show promise as biomarkers for risk stratification among patients with both HFrEF and ESRD.

Association of metabolic syndrome and chronic kidney disease

The prevalence of kidney disease is increasing rapidly worldwide, reflecting rising rates of obesity, diabetes, and associated metabolic syndrome (MetS). Chronic kidney disease and related comorbidities such as obesity, diabetes, and hypertension place a significant financial burden on healthcare systems. Despite the widespread use of RAAS inhibitors, intensive blood pressure and glycemic control, and newer therapeutic options consisting of sodium/glucose cotransporter-2 (SGLT-2) inhibitors or glucagon-like peptide-1 (GLP-1) receptor agonists, a significant risk of progression to end-stage renal disease remains in the high-risk obese and diabetic population. The MetS is a cluster of cardiovascular risk factors that adversely affect the development and progression of chronic kidney failure. According to the criteria of the World Health Organization, it is defined by visceral adiposity, impaired glucose tolerance or insulin resistance, atherogenic dyslipidemia, raised blood pressure, and microalbuminuria with a albumin-to-creatinine ratio ≥30 mg/g. At molecular level MetS is marked by a proinflammatory state and increased oxidative stress leading to various pathophysiological changes causing endothelial dysfunction and a hypercoagulable state. Because the kidney is a highly vascularized organ, it is especially susceptible for those microvascular changes. Therefore, the MetS and its individual components are associated with the premature development, acceleration, and progression of chronic kidney disease. Therefore, it is becoming increasingly important to elucidate the underlying mechanisms of MetS-associated chronic kidney disease in order to develop new strategies for preventing and slowing the progression of renal disease. In this review, we will elucidate (i) the renal structural, hemodynamic, and metabolic changes that occur in obesity and obesity-related kidney injury; (ii) the clinicopathological characteristics of obesity-related kidney injury, primarily focusing on obesity-associated glomerulopathy; (iii) the potential additional factors or predisposing factors that may turn patients more susceptible to renal structural or functional compensatory failure and subsequent injury.

The unique structural and functional characteristics of glomerular endothelial cell fenestrations and their potential as a therapeutic target in kidney disease

Glomerular endothelial cell (GEnC) fenestrations are a critical component of the glomerular filtration barrier. Their unique nondiaphragmed structure is key to their function in glomerular hydraulic permeability, and their aberration in disease can contribute to loss of glomerular filtration function. This review provides a comprehensive update of current understanding of the regulation and biogenesis of fenestrae. We consider diseases in which GEnC fenestration loss is recognized or may play a role and discuss methods with potential to facilitate the study of these critical structures. Literature is drawn from GEnCs as well as other fenestrated cell types such as liver sinusoidal endothelial cells that most closely parallel GEnCs.

Removal of the endothelial surface layer via hyaluronidase does not modulate monocyte and neutrophil interactions with the glomerular endothelium

OBJECTIVE

The endothelial surface layer (ESL), a layer of macromolecules on the surface of endothelial cells, can both impede and facilitate leukocyte recruitment. However, its role in monocyte and neutrophil recruitment in glomerular capillaries is unknown.

METHODS

We used multiphoton intravital microscopy to examine monocyte and neutrophil behavior in the glomerulus following ESL disruption with hyaluronidase.

RESULTS

Constitutive retention and migration of monocytes and neutrophils within the glomerular microvasculature was unaltered by hyaluronidase. Consistent with this, inhibition of the hyaluronan-binding molecule CD44 also failed to modulate glomerular trafficking of these immune cells. To investigate the contribution of the ESL during acute inflammation, we induced glomerulonephritis via in situ immune complex deposition. This resulted in increases in glomerular retention of monocytes and neutrophils but did not induce marked reduction in the glomerular ESL. Furthermore, hyaluronidase treatment did not modify the prolonged retention of monocytes and neutrophils in the acutely inflamed glomerular microvasculature.

CONCLUSIONS

These observations indicate that, despite evidence that the ESL has the capacity to inhibit leukocyte-endothelial cell interactions while also containing adhesive ligands for immune cells, neither of these functions modulate trafficking of monocytes and neutrophils in steady-state or acutely-inflamed glomeruli.

Bidirectional airflow in lung airway-on-a-chip with matrix-derived membrane elicits epithelial glycocalyx formation

Organ-on-a-chip systems are rapidly advancing as a viable alternative to existing experimental models in respiratory research. To date, however, epithelial cell cultures within lung airway-on-a-chip devices have yet to demonstrate the presence of an epithelial glycocalyx, a thin layer of proteoglycans, glycoproteins, and glycolipids known to play an important role in regulating epithelial function. Here, we demonstrate that an airway-on-a-chip device that incorporates bidirectional flow mimicking breathing cycles in combination with an ultra-thin matrix-derived membrane (UMM) layer can generate a glycocalyx layer comprised of heparan sulfate. Results with this device and airflow system showed dramatic differences of airway epithelial cell viability and expression of tight junctions, cilia, and mucus over a wide range of flow rates when cultured under oscillatory flow. More importantly, for the first time in a microfluidic organ-on-a-chip setting, we achieved the visualization of an airflow-induced epithelial glycocalyx layer. Our experiments highlight the importance of physiological mimicry in developing in vitro models, as bidirectional airflow showed more representative mucociliary differentiation compared to continuous unidirectional airflow. Thus, the lung airway-on-a-chip platform demonstrated in this study holds great potential as a lung epithelial barrier model for studying the mechanisms of various respiratory diseases and for testing the efficacy of therapeutic candidates in the presence of bidirectional airflow and the glycocalyx.

EXOSOMES AND MICROVESICLES FROM ADIPOSE-DERIVED MESENCHYMAL STEM CELLS PROTECTS THE ENDOTHELIAL GLYCOCALYX FROM LPS INJURY

ABSTRACT

Introduction: Endothelial glycocalyx damage occurs in numerous pathological conditions and results in endotheliopathy. Extracellular vesicles, including exosomes and microvesicles, isolated from adipose-derived mesenchymal stem cells (ASCs) have therapeutic potential in multiple disease states; however, their role in preventing glycocalyx shedding has not been defined. We hypothesized that ASC-derived exosomes and microvesicles would protect the endothelial glycocalyx from damage by LPS injury in cultured endothelial cells. Methods : Exosomes and microvesicles were collected from ASC conditioned media by centrifugation (10,000 g for microvesicles, 100,000 g for exosomes). Human umbilical vein endothelial cells (HUVECs) were exposed to 1 μg/mL lipopolysaccharide (LPS). LPS-injured cells (n = 578) were compared with HUVECS with concomitant LPS injury plus 1.0 μg/mL of exosomes (n = 540) or microvesicles (n = 510) for 24 hours. These two cohorts were compared with control HUVECs that received phosphate-buffered saline only (n = 786) and HUVECs exposed to exosomes (n = 505) or microvesicles (n = 500) alone. Cells were fixed and stained with FITC-labeled wheat germ agglutinin to quantify EGX. Real-time quantitative reverse-transcription polymerase chain reaction was used on HUVECs cell lystate to quantify hyaluron synthase-1 (HAS1) expression. Results: Exosomes alone decreased endothelial glycocalyx staining intensity when compared with control (4.94 vs. 6.41 AU, P < 0.001), while microvesicles did not cause a change glycocalyx staining intensity (6.39 vs. 6.41, P = 0.99). LPS injury resulted in decreased glycocalyx intensity as compared with control (5.60 vs. 6.41, P < 0.001). Exosomes (6.85 vs. 5.60, P < 0.001) and microvesicles (6.35 vs. 5.60, P < 0.001) preserved endothelial glycocalyx staining intensity after LPS injury. HAS1 levels were found to be higher in the exosome (1.14 vs. 3.67 RE, P = 0.02) and microvesicle groups (1.14 vs. 3.59 RE, P = 0.02) when compared with LPS injury. Hyaluron synthase-2 and synthase-3 expressions were not different in the various experimental groups. Conclusions: Exosomes alone can damage the endothelial glycocalyx. However, in the presence of LPS injury, both exosomes and microvesicles protect the glycocalyx layer. This effect seems to be mediated by HAS1. Level of Evidence : Basic science study.

Aldosterone: Essential for Life but Damaging to the Vascular Endothelium

The renin angiotensin aldosterone system is a key regulator of blood pressure. Aldosterone is the final effector of this pathway, acting predominantly via mineralocorticoid receptors. Aldosterone facilitates the conservation of sodium and, with it, water and acts as a powerful stimulus for potassium excretion. However, evidence for the pathological impact of excess mineralocorticoid receptor stimulation is increasing. Here, we discussed how in the heart, hyperaldosteronism is associated with fibrosis, cardiac dysfunction, and maladaptive hypertrophy. In the kidney, aldosterone was shown to cause proteinuria and fibrosis and may contribute to the progression of kidney disease. More recently, studies suggested that aldosterone excess damaged endothelial cells. Here, we reviewed how damage to the endothelial glycocalyx may contribute to this process. The endothelial glycocalyx is a heterogenous, negatively charged layer on the luminal surface of cells. Aldosterone exposure alters this layer. The resulting structural changes reduced endothelial reactivity in response to protective shear stress, altered permeability, and increased immune cell trafficking. Finally, we reviewed current therapeutic strategies for limiting endothelial damage and suggested that preventing glycocalyx remodelling in response to aldosterone exposure may provide a novel strategy, free from the serious adverse effect of hyperkalaemia seen in response to mineralocorticoid blockade.

Mineralocorticoid Receptor Antagonists for Preventing Chronic Kidney Disease Progression: Current Evidence and Future Challenges

Regulation and action of the mineralocorticoid receptor (MR) have been the focus of intensive research over the past 80 years. Genetic and physiological/biochemical analysis revealed how MR and the steroid hormone aldosterone integrate the responses of distinct tubular cells in the face of environmental perturbations and how their dysregulation compromises fluid homeostasis. In addition to these roles, the accumulation of data also provided unequivocal evidence that MR is involved in the pathophysiology of kidney diseases. Experimental studies delineated the diverse pathological consequences of MR overactivity and uncovered the multiple mechanisms that result in enhanced MR signaling. In parallel, clinical studies consistently demonstrated that MR blockade reduces albuminuria in patients with chronic kidney disease. Moreover, recent large-scale clinical studies using finerenone have provided evidence that the non-steroidal MR antagonist can retard the kidney disease progression in diabetic patients. In this article, we review experimental data demonstrating the critical importance of MR in mediating renal injury as well as clinical studies providing evidence on the renoprotective effects of MR blockade. We also discuss areas of future investigation, which include the benefit of non-steroidal MR antagonists in non-diabetic kidney disease patients, the identification of surrogate markers for MR signaling in the kidney, and the search for key downstream mediators whereby MR blockade confers renoprotection. Insights into these questions would help maximize the benefit of MR blockade in subjects with kidney diseases.

Mineralocorticoid receptor antagonism in diabetes reduces albuminuria by preserving the glomerular endothelial glycocalyx

The glomerular endothelial glycocalyx (GEnGlx) forms the first part of the glomerular filtration barrier. Previously, we showed that mineralocorticoid receptor (MR) activation caused GEnGlx damage and albuminuria. In this study, we investigated whether MR antagonism could limit albuminuria in diabetes and studied the site of action. Streptozotocin-induced diabetic Wistar rats developed albuminuria, increased glomerular albumin permeability (Ps'alb), and increased glomerular matrix metalloproteinase (MMP) activity with corresponding GEnGlx loss. MR antagonism prevented albuminuria progression, restored Ps'alb, preserved GEnGlx, and reduced MMP activity. Enzymatic degradation of the GEnGlx negated the benefits of MR antagonism, confirming their dependence on GEnGlx integrity. Exposing human glomerular endothelial cells (GEnC) to diabetic conditions in vitro increased MMPs and caused glycocalyx damage. Amelioration of these effects confirmed a direct effect of MR antagonism on GEnC. To confirm relevance to human disease, we used a potentially novel confocal imaging method to show loss of GEnGlx in renal biopsy specimens from patients with diabetic nephropathy (DN). In addition, patients with DN randomized to receive an MR antagonist had reduced urinary MMP2 activity and albuminuria compared with placebo and baseline levels. Taken together, our work suggests that MR antagonists reduce MMP activity and thereby preserve GEnGlx, resulting in reduced glomerular permeability and albuminuria in diabetes.

Increased urinary albumin leakage is related to injuries of glomerular glycocalyx and podocytes, and associated with tubular dysfunction in preeclampsia

OBJECTIVE

The pathogenesis of preeclampsia (PE) is known to be endothelial cell damage; however, the existence of dysfunction in glomerular endothelial glycocalyx, podocytes and tubules remains unclear. The glomerular endothelial glycocalyx, basement membrane, podocytes, and tubules are permeability barriers against albumin excretion. This study aimed to assess the relationship between urinary albumin leakage and injuries of the glomerular endothelial glycocalyx, podocytes, and tubules in patients with PE.

METHODS

A total of 81 women with uncomplicated pregnancies (control, n = 22), PE (PE, n = 36), or gestational hypertension (GH) (GH, n = 23) were enrolled. We assessed urinary albumin and serum hyaluronan for glycocalyx injuries, podocalyxin for podocytes injuries, and urinary N-acetyl-β-d-glucosaminidase (NAG) and liver-type fatty acid-binding protein (l-FABP) for renal tubular dysfunctions.

RESULTS

The serum hyaluronan and the urinary podocalyxin levels were higher in the PE and GH groups. The urinary NAG and l-FABP levels were higher in the PE group. Urinary NAG and l-FABP levels positively correlated with urinary albumin excretion.

CONCLUSIONS

Our findings suggest that increased urinary albumin leakage is related to injuries of the glycocalyx and podocytes, and associated with tubular dysfunction in pregnant women with PE. The clinical trial described in this paper was registered at the UMIN Clinical Trials Registry under registration number UMIN000047875. URL of registration: https://centre6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000054437.

Albuminuria as a marker of systemic congestion in patients with heart failure

AIMS

Albuminuria is common in patients with heart failure and associated with worse outcomes. The underlying pathophysiological mechanism of albuminuria in heart failure is still incompletely understood. The association of clinical characteristics and biomarker profile with albuminuria in patients with heart failure with both reduced and preserved ejection fractions were evaluated.

METHODS AND RESULTS

Two thousand three hundred and fifteen patients included in the index cohort of BIOSTAT-CHF were evaluated and findings were validated in the independent BIOSTAT-CHF validation cohort (1431 patients). Micro-albuminuria and macro-albuminuria were defined as urinary albumincreatinine ratio (UACR) 30 mg/gCr and 300 mg/gCr in spot urines, respectively. The prevalence of micro- and macro-albuminuria was 35.4 and 10.0, respectively. Patients with albuminuria had more severe heart failure, as indicated by inclusion during admission, higher New York Heart Association functional class, more clinical signs and symptoms of congestion, and higher concentrations of biomarkers related to congestion, such as biologically active adrenomedullin, cancer antigen 125, and N-terminal pro-B-type natriuretic peptide (NT-proBNP) (all P 0.001). The presence of albuminuria was associated with increased risk of mortality and heart failure (re)hospitalization in both cohorts. The strongest independent association with log UACR was found for log NT-proBNP (standardized regression coefficient 0.438, 95 confidence interval 0.350.53, P 0.001). Hierarchical clustering analysis demonstrated that UACR clusters with markers of congestion and less with indices of renal function. The validation cohort yielded similar findings.

CONCLUSION

In patients with new-onset or worsening heart failure, albuminuria is consistently associated with clinical, echocardiographic, and circulating biomarkers of congestion.

Anatomical and functional remodeling of left ventricle in patients with primary aldosteronism and concomitant albuminuria

Background

Primary aldosteronism (PA) is the leading cause of secondary hypertension globally and is associated with adverse cardiovascular outcomes. However, the cardiac impact of concomitant albuminuria remains unknown.

Objective

To compare anatomical and functional remodeling of left ventricle (LV) in PA patients with or without albuminuria.

Design

Prospective cohort study.

Methods

The cohort was separated into two arms according to the presence or absence of albuminuria (>30 mg/g of morning spot urine). Propensity score matching with age, sex, systolic blood pressure, and diabetes mellitus was performed. Multivariate analysis was conducted with adjustments for age, sex, body mass index, systolic blood pressure, duration of hypertension, smoking, diabetes mellitus, number of antihypertensive agents, and aldosterone level. A local-linear model with bandwidth of 2.07 was used to study correlations.

Results

A total of 519 individuals with PA were enrolled in the study, of whom 152 had albuminuria. After matching, the albuminuria group had a higher creatinine level, at baseline. With regard to LV remodeling, albuminuria was independently associated with a significantly higher interventricular septum (1.22 > 1.17 cm, p = 0.030), LV posterior wall thickness (1.16 > 1.10 cm, p = 0.011), LV mass index (125 > 116 g/m², p = 0.023), and medial E/e' ratio (13.61 > 12.30, p = 0.032), and a lower medial early diastolic peak velocity (5.70 < 6.36 cm/s, p = 0.016). Multivariate analysis further revealed that albuminuria was an independent risk factor for elevated LV mass index (p < 0.001) and medial E/e' ratio (p = 0.010). Non-parametric kernel regression also demonstrated that the level of albuminuria was positively correlated with LV mass index. The remodeling of LV mass and diastolic function under the presence of albuminuria distinctly improved after PA treatment.

Conclusion

The presence of concomitant albuminuria in patients with PA was associated with pronounced LV hypertrophy and compromised LV diastolic function. These alterations were reversible after treatment for PA.

Plain language summary

Cardiac Impact of Primary Aldosteronism and Albuminuria Primary aldosteronism and albuminuria has been, respectively, demonstrated to bring about left ventricular remodeling, but the aggregative effect was unknown. We constructed a prospective single-center cohort study in Taiwan. We proposed the presence of concomitant albuminuria was associated with left ventricular hypertrophy and compromised diastolic function. Intriguingly, management of primary aldosteronism was able to restore these alterations. Our study delineated the cardiorenal crosstalk in the setting of secondary hypertension and the role of albuminuria for left ventricular remodeling. Future interrogations toward the underlying pathophysiology as well as therapeutics will facilitate the improvement of holistic care for such population.

Longitudinal Assessment of Plasma Syndecan-1 Predicts 60-Day Mortality in Patients with COVID-19

Background: Endotheliopathy is a common pathologic finding in patients with acute and long COVID-19. It may be associated with disease severity and predispose patients to long-term complications. Plasma levels of a proteoglycan, syndecan-1, are found to be significantly elevated in patients with COVID-19, but its roles in assessing disease severity and predicting long-term outcome are not fully understood. Methods: A total of 124 consecutive hospitalized patients with SARS-CoV-2 infection were prospectively enrolled and blood samples were collected on admission (T1), 3−4 days following treatment (T2), and 1−2 days prior to discharge or death (T3). Plasma levels of syndecan-1 were determined using an immunosorbent assay; various statistical analyses were performed to determine the association between plasma syndecan-1 levels and disease severity or the 60-day mortality rate. Results: Compared with those in the healthy controls, plasma levels of syndecan-1 in patients with critical COVID-19 were significantly higher (p < 0.0001). However, there was no statistically significant difference among patients with different disease severity (p > 0.05), resulting from large individual variability. Longitudinal analysis demonstrated that while the levels fluctuated during hospitalization in all patients, plasma syndecan-1 levels were persistently elevated from baseline in critical COVID-19 patients. Cox proportional hazard regression analyses revealed that elevated plasma levels of syndecan-1 (>260 ng/mL at T1, >1018 ng/mL at T2, and >461 ng/mL at T3) were significantly associated with the 60-day mortality rate. Conclusions: Endotheliopathy, marked by glycocalyx degradation and elevated plasma syndecan-1, occurs in nearly all hospitalized patients with SARS-CoV-2 infection; elevated plasma syndecan-1 is associated with increased mortality in COVID-19 patients.

Effect of Metabolic Adaptation by Voluntary Running Wheel Activity and Aldosterone Inhibition on Renal Function in Female Spontaneously Hypertensive Rats

Metabolic effects of physical activity may be reno-protective in the context of hypertension, although exercise stresses kidneys. Aldosterone participates in renal disease in hypertension, but exercise affects the plasma concentration of aldosterone. This study was designed to evaluate whether physical activity and pharmacological treatment by aldosterone have additive effects on renal protection in hypertensive rats. Female spontaneously hypertensive rats (SHR) or normotensive Wistar rats performed voluntary running wheel activity alone or in combination with aldosterone blockade (spironolactone). The following groups were studied: young and pre-hypertensive SHR (n = 5 sedentary; n = 10 running wheels, mean body weight 129 g), 10-month-old Wistar rats (n = 6 sedentary; n = 6 running wheels, mean body weight 263 g), 10-month-old SHRs (n = 18 sedentary, mean body weight 224 g; n = 6 running wheels, mean body weight 272 g; n = 6 aldosterone, mean body weight 219 g; n = 6 aldosterone and running wheels, mean body weight 265 g). Another group of SHRs had free access to running wheels for 6 months and kept sedentary for the last 3 months (n = 6, mean body weight 240 g). Aldosterone was given for the last 4 months. SHRs from the running groups had free access to running wheels beginning at the age of 6 weeks. Renal function was analyzed by microalbuminuria (Alb/Cre), urinary secretion of kidney injury molecule-1 (uKim-1), and plasma blood urea nitrogen (BUN) concentration. Molecular adaptation of the kidney to hypertension and its modification by spironolactone and/or exercise were analyzed by real-time PCR, immunoblots, and histology. After six months of hypertension, rats had increased Alb/Cre and BUN but normal uKim-1. Voluntary free running activity normalized BUN but not Alb/Cre, whereas spironolactone reduced Alb/Cre but not BUN. Exercise constitutively increased renal expression of proprotein convertase subtilisin/kexin type 9 (PCSK9; mRNA and protein) and arginase-2 (mRNA). Spironolactone reduced these effects. uKim-1 increased in rats performing voluntary running wheel activity exercise irrespectively of blood pressure and aldosterone blockade. We observed independent but no additive effects of aldosterone blockade and physical activity on renal function and on molecules potentially affecting renal lipid metabolism.

Association of Empagliflozin Treatment With Albuminuria Levels in Patients With Heart Failure: A Secondary Analysis of EMPEROR-Pooled

Importance

Albuminuria, routinely assessed as spot urine albumin-to-creatinine ratio (UACR), indicates structural damage of the glomerular filtration barrier and is associated with poor kidney and cardiovascular outcomes. Sodium-glucose cotransporter-2 (SGLT2) inhibitors have been found to reduce UACR in patients with type 2 diabetes, but its use in patients with heart failure (HF) is less well studied.

Objective

To analyze the association of empagliflozin with study outcomes across baseline levels of albuminuria and change in albuminuria in patients with HF across a wide range of ejection fraction levels.

Design, Setting, and Participants

This post hoc analysis included all patients with HF from the EMPEROR-Pooled analysis using combined individual patient data from the international multicenter randomized double-blind parallel-group, placebo-controlled EMPEROR-Reduced and EMPEROR-Preserved trials. Participants in the original trials were excluded from this analysis if they were missing baseline UACR data. EMPEROR-Preserved was conducted from March 27, 2017, to April 26, 2021, and EMPEROR-Reduced was conducted from April 6, 2017, to May 28, 2020. Data were analyzed from January to June 2022.

Interventions

Randomization to empagliflozin or placebo.

Main Outcomes and Measures

New-onset macroalbuminuria and regression to normoalbuminuria and microalbuminuria.

Results

A total of 9673 patients were included (mean [SD] age, 69.9 [10.4] years; 3551 [36.7%] female and 6122 [63.3%] male). Of these, 5552 patients had normoalbuminuria (UACR <30 mg/g) and 1025 had macroalbuminuria (UACR >300 mg/g). Compared with normoalbuminuria, macroalbuminuria was associated with younger age, races other than White, obesity, male sex, site region other than Europe, higher levels of N-terminal pro-hormone brain natriuretic peptide and high-sensitivity troponin T, higher blood pressure, higher New York Heart Association class, greater HF duration, more frequent previous HF hospitalizations, diabetes, hypertension, lower eGFR, and less frequent use of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers and mineralocorticoid receptor antagonists. An increase in events was observed in individuals with higher UACR levels. The association of empagliflozin with cardiovascular mortality or HF hospitalization was consistent across UACR categories (hazard ratio [HR], 0.80; 95% CI, 0.69-0.92 for normoalbuminuria; HR, 0.74; 95% CI, 0.63-0.86 for microalbuminuria; HR, 0.78; 95% CI, 0.63-0.98 for macroalbuminuria; interaction P trend = .71). Treatment with empagliflozin was associated with lower incidence of new macroalbuminuria (HR, 0.81; 95% CI, 0.70-0.94; P = .005) and an increase in rate of remission to sustained normoalbuminuria or microalbuminuria (HR, 1.31; 95% CI, 1.07-1.59; P = .009) but not with a reduction in UACR in the overall population; however, UACR was reduced in patients with diabetes, who had higher UACR levels than patients without diabetes (geometric mean for diabetes at baseline, 0.91; 95% CI, 0.85-0.98 and for no diabetes at baseline, 1.08; 95% CI, 1.01-1.16; interaction P = .008).

Conclusions and Relevance

In this post hoc analysis of a randomized clinical trial, compared with placebo, empagliflozin was associated with reduced HF hospitalizations or cardiovascular death irrespective of albuminuria levels at baseline, reduced progression to macroalbuminuria, and reversion of macroalbuminuria.

Trial Registration

ClinicalTrials.gov Identifiers: NCT03057977 and NCT03057951.

New insights into proteinuria/albuminuria

The fractional clearance of proteins as measured in healthy human subjects increases 10,000–100,000- fold when studied in nephrotic patients. This remarkable increase cannot be accounted for by extracellular biophysical mechanisms centered at the glomerular filtration barrier. Rather, it is the nephron and its combination of filtration and cellular uptake that can provide a plausible explanation of these fractional clearance changes. The nephron has two regions that critically determine the level proteinuria/albuminuria. Glomerular filtration of plasma proteins is primarily a size selective event that is basically unchanged in acquired and genetic kidney disease. The glomerular concepts of ‘charge selectivity’ and of ‘large pores’, previously used to explain proteinuria, are now recognized to be flawed and non-existent. Filtered proteins then encounter downstream two protein receptors of the Park and Maack type associated with the proximal tubular cell. The high capacity receptor is thought to retrieve the majority of filtered proteins and return them to the blood supply. Inhibition/saturation of this pathway in kidney disease may create the nephrotic condition and hypoproteinemia/hypoalbuminemia. Inhibitors of this pathway (possibly podocyte derived) are still to be identified. A relatively small proportion of the filtered protein is directed towards a high affinity, low capacity receptor that guides the protein to undergo lysosomal degradation. Proteinuria in normoproteinemic states is derived by inhibition of this pathway, such as in diabetes. The combination of glomerular sieving, and the degradation and retrieval pathways can quantitatively account for the changes in fractional clearance of proteins in the nephrotic condition. Finally, the general retrieval of filtered protein by the proximal tubular cell focuses on the teleological importance of this cell as this retrieval represents the third pillar of retrieval that this cell participates in (it also retrieves water and salt).

Mineralocorticoid receptor-antagonism prevents COVID-19-dependent glycocalyx damage

Proinflammatory cytokines target vascular endothelial cells during COVID-19 infections. In particular, the endothelial glycocalyx (eGC), a proteoglycan-rich layer on top of endothelial cells, was identified as a vulnerable, vasoprotective structure during infections. Thus, eGC damage can be seen as a hallmark in the development of endothelial dysfunction and inflammatory processes. Using sera derived from patients suffering from COVID-19, we could demonstrate that the eGC became progressively worse in relation to disease severity (mild vs severe course) and in correlation to IL-6 levels. This could be prevented by administering low doses of spironolactone, a well-known and highly specific aldosterone receptor antagonist. Our results confirm that SARS-CoV-2 infections cause eGC damage and endothelial dysfunction and we outline the underlying mechanisms and suggest potential therapeutic options.

The microvascular endothelial glycocalyx: An additional piece of the puzzle in veterinary medicine

The endothelial glycocalyx (eGlx) is a critically important structure lining the luminal surface of endothelial cells. There is increasing evidence, in human patients and animal models, for its crucial role in the maintenance of health. Moreover, its damage is associated with the pathogenesis of multiple disease states. This review provides readers with an overview of the eGlx; summarising its structure, essential functions, and evidence for its role in disease. We highlight the lack of studies regarding the eGlx in cats and dogs, particularly in naturally occurring diseases. Importantly, we discuss techniques to aid its study, which can be applied to veterinary species. Finally, we present targeted therapies aimed at preserving, and in some cases, restoring damaged eGlx.

Immune cell behaviour and dynamics in the kidney - insights from in vivo imaging

The actions of immune cells within the kidney are of fundamental importance in kidney homeostasis and disease. In disease settings such as acute kidney injury, anti-neutrophil cytoplasmic antibody-associated vasculitis, lupus nephritis and renal transplant rejection, immune cells resident within the kidney and those recruited from the circulation propagate inflammatory responses with deleterious effects on the kidney. As in most forms of inflammation, intravital imaging - particularly two-photon microscopy - has been critical to our understanding of immune cell responses in the renal microvasculature and interstitium, enabling visualization of immune cell dynamics over time rather than statically. These studies have demonstrated differences in the recruitment and function of these cells from those in more conventional vascular beds, and provided a wealth of information on the actions of blood-borne immune cells such as neutrophils, monocytes and T cells, as well as kidney-resident mononuclear phagocytes, in a range of diseases affecting different kidney compartments. In particular, in vivo imaging has furthered our understanding of leukocyte function within the glomerulus in acute glomerulonephritis, and in the tubulointerstitium and interstitial microvasculature during acute kidney injury and following transplantation, revealing mechanisms of immune surveillance, antigen presentation and inflammation in the kidney.

The Glomerular Endothelium Restricts Albumin Filtration

Inflammatory activation and/or dysfunction of the glomerular endothelium triggers proteinuria in many systemic and localized vascular disorders. Among them are the thrombotic microangiopathies, many forms of glomerulonephritis, and acute inflammatory episodes like sepsis and COVID-19 illness. Another example is the chronic endothelial dysfunction that develops in cardiovascular disease and in metabolic disorders like diabetes. While the glomerular endothelium is a porous sieve that filters prodigious amounts of water and small solutes, it also bars the bulk of albumin and large plasma proteins from passing into the glomerular filtrate. This endothelial barrier function is ascribed predominantly to the endothelial glycocalyx with its endothelial surface layer, that together form a relatively thick, mucinous coat composed of glycosaminoglycans, proteoglycans, glycolipids, sialomucins and other glycoproteins, as well as secreted and circulating proteins. The glycocalyx/endothelial surface layer not only covers the glomerular endothelium; it extends into the endothelial fenestrae. Some glycocalyx components span or are attached to the apical endothelial cell plasma membrane and form the formal glycocalyx. Other components, including small proteoglycans and circulating proteins like albumin and orosomucoid, form the endothelial surface layer and are bound to the glycocalyx due to weak intermolecular interactions. Indeed, bound plasma albumin is a major constituent of the endothelial surface layer and contributes to its barrier function. A role for glomerular endothelial cells in the barrier of the glomerular capillary wall to protein filtration has been demonstrated by many elegant studies. However, it can only be fully understood in the context of other components, including the glomerular basement membrane, the podocytes and reabsorption of proteins by tubule epithelial cells. Discovery of the precise mechanisms that lead to glycocalyx/endothelial surface layer disruption within glomerular capillaries will hopefully lead to pharmacological interventions that specifically target this important structure.

Matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases in kidney disease

Matrix metalloproteinases (MMPs) are a group of zinc and calcium endopeptidases which cleave extracellular matrix (ECM) proteins. They are also involved in the degradation of cell surface components and regulate multiple cellular processes, cell to cell interactions, cell proliferation, and cell signaling pathways. MMPs function in close interaction with the endogenous tissue inhibitors of matrix metalloproteinases (TIMPs), both of which regulate cell turnover, modulate various growth factors, and participate in the progression of tissue fibrosis and apoptosis. The multiple roles of MMPs and TIMPs are continuously elucidated in kidney development and repair, as well as in a number of kidney diseases. This chapter focuses on the current findings of the significance of MMPs and TIMPs in a wide range of kidney diseases, whether they result from kidney tissue changes, hemodynamic alterations, tubular epithelial cell apoptosis, inflammation, or fibrosis. In addition, the potential use of these endopeptidases as biomarkers of renal dysfunction and as targets for therapeutic interventions to attenuate kidney disease are also explored in this review.

Circadian Control of Sodium and Blood Pressure Regulation

The attention for the control of dietary risk factors involved in the development of hypertension, includes a large effort on dietary salt restrictions. Ample studies show the beneficial role of limiting dietary sodium as a lifestyle modification in the prevention and management of essential hypertension. Not until the past decade or so have studies more specifically investigated diurnal variations in renal electrolyte excretion, which led us to the hypothesis that timing of salt intake may impact cardiovascular health and blood pressure regulation. Cell autonomous molecular clocks as the name implies, function independently to maintain optimum functional rhythmicity in the face of environmental stressors such that cellular homeostasis is maintained at all times. Our understanding of mechanisms influencing diurnal patterns of sodium excretion and blood pressure has expanded with the discovery of the circadian clock genes. In this review, we discuss what is known about circadian regulation of renal sodium handling machinery and its influence on blood pressure regulation, with timing of sodium intake as a potential modulator of the kidney clock.

Intravital imaging reveals glomerular capillary distension and endothelial and immune cell activation early in Alport syndrome

Alport syndrome (AS) is a genetic disorder caused by mutations in type IV collagen that lead to defective glomerular basement membrane, glomerular filtration barrier (GFB) damage, and progressive chronic kidney disease. While the genetic basis of AS is well known, the molecular and cellular mechanistic details of disease pathogenesis have been elusive, hindering the development of mechanism-based therapies. Here, we performed intravital multiphoton imaging of the local kidney tissue microenvironment in a X-linked AS mouse model to directly visualize the major drivers of AS pathology. Severely distended glomerular capillaries and aneurysms were found accompanied by numerous microthrombi, increased glomerular endothelial surface layer (glycocalyx) and immune cell homing, GFB albumin leakage, glomerulosclerosis, and interstitial fibrosis by 5 months of age, with an intermediate phenotype at 2 months. Renal histology in mouse or patient tissues largely failed to detect capillary aberrations. Treatment of AS mice with hyaluronidase or the ACE inhibitor enalapril reduced the excess glomerular endothelial glycocalyx and blocked immune cell homing and GFB albumin leakage. This study identified central roles of glomerular mechanical forces and endothelial and immune cell activation early in AS, which could be therapeutically targeted to reduce mechanical strain and local tissue inflammation and improve kidney function.

New Endothelial Mechanisms in Glomerular (Patho)biology and Proteinuria Development Captured by Intravital Multiphoton Imaging

In the past two decades, intravital imaging using multiphoton microscopy has provided numerous new visual and mechanistic insights into glomerular biology and disease processes including the function of glomerular endothelial cells (GEnC), podocytes, and the development of proteinuria. Although glomerular endothelial injury is known to precede podocyte damage in several renal diseases, the primary role of GEnCs in proteinuria development received much less attention compared to the vast field of podocyte pathobiology. Consequently, our knowledge of GEnC mechanisms in glomerular diseases is still emerging. This review highlights new visual clues on molecular and cellular mechanisms of GEnCs and their crosstalk with podocytes and immune cells that were acquired recently by the application of multiphoton imaging of the intact glomerular microenvironment in various proteinuric disease models. New mechanisms of glomerular tissue remodeling and regeneration are discussed based on results of tracking the fate and function of individual GEnCs using serial intravital multiphoton imaging over several days and weeks. The three main topics of this review include (i) the role of endothelial injury and microthrombi in podocyte detachment and albumin leakage via hemodynamic and mechanical forces, (ii) the alterations of the endothelial surface layer (glycocalyx) and its interactions with circulating immune cells in lupus nephritis, and (iii) the structural and functional remodeling and regeneration of GEnCs in hypertension, diabetes, and other experimental injury conditions. By the comprehensive visual portrayal of GEnCs and the many other contributing glomerular cell types, this review emphasizes the complexity of pathogenic mechanisms that result in proteinuria development.

TRIM27 contributes to glomerular endothelial cell injury in lupus nephritis by mediating the FoxO1 signaling pathway

Tripartite motif-containing 27 (TRIM27) belongs to the triple motif (TRIM) protein family, which plays a role in a variety of biological activities. Our previous study showed that the TRIM27 protein was highly expressed in the glomerular endothelial cells of patients suffering from lupus nephritis (LN). However, whether TRIM27 is involved in the injury of glomerular endothelial cells in lupus nephritis remains to be clarified. Here, we detected the expression of the TRIM27 protein in glomerular endothelial cells in vivo and in vitro. In addition, the influence of TRIM27 knockdown on endothelial cell damage in MRL/lpr mice and cultured human renal glomerular endothelial cells (HRGECs) was explored. The results revealed that the expression of TRIM27 in endothelial cells was significantly enhanced in vivo and in vitro. Downregulating the expression of TRIM27 inhibited the breakdown of the glycocalyx and the injury of endothelial cells via the FoxO1 pathway. Moreover, HRGECs transfected with the WT-FoxO1 plasmid showed a reduction in impairment caused by LN plasma. Furthermore, suppression of the protein kinase B (Akt) pathway could attenuate damage by mediating the expression of TRIM27. Thus, the present study showed that TRIM27 participated in the injury of glomerular endothelial cells and served as a potential therapeutic target for the treatment of lupus nephritis.

Dietary salt exacerbates intestinal fibrosis in chronic TNBS colitis via fibroblasts activation

Intestinal fibrosis is a frequent complication in inflammatory bowel diseases (IBD). It is a challenge to identify environmental factors such as diet that may be driving this risk. Intestinal fibrosis result from accumulation of extracellular matrix (ECM) proteins secreted by myofibroblasts. Factors promoting intestinal fibrosis are unknown, but diet appears to be a critical component in its development. Consumption of salt above nutritional recommendations can exacerbate chronic inflammation. So far, high salt diet (HSD) have not been thoroughly investigated in the context of intestinal fibrosis associated to IBD. In the present study, we analyze the role of dietary salt in TNBS chronic colitis induced in rat, an intestinal fibrosis model, or in human colon fibroblast cells. Here, we have shown that high-salt diet exacerbates undernutrition and promoted ECM-associated proteins in fibroblasts. Taken together, our results suggested that dietary salt can activate intestinal fibroblasts, thereby contributing to exacerbation of intestinal fibrosis. Dietary salt may be considered as a putative environmental factor that drives intestinal fibrosis risk.

Serial intravital imaging captures dynamic and functional endothelial remodeling with single-cell resolution

Endothelial cells are important in the maintenance of healthy blood vessels and in the development of vascular diseases. However, the origin and dynamics of endothelial precursors and remodeling at the single-cell level have been difficult to study in vivo owing to technical limitations. Therefore, we aimed to develop a direct visual approach to track the fate and function of single endothelial cells over several days and weeks in the same vascular bed in vivo using multiphoton microscopy (MPM) of transgenic Cdh5-Confetti mice and the kidney glomerulus as a model. Individual cells of the vascular endothelial lineage were identified and tracked owing to their unique color combination, based on the random expression of cyan/green/yellow/red fluorescent proteins. Experimental hypertension, hyperglycemia, and laser-induced endothelial cell ablation rapidly increased the number of new glomerular endothelial cells that appeared in clusters of the same color, suggesting clonal cell remodeling by local precursors at the vascular pole. Furthermore, intravital MPM allowed the detection of distinct structural and functional alterations of proliferating endothelial cells. No circulating Cdh5-Confetti⁺ cells were found in the renal cortex. Moreover, the heart, lung, and kidneys showed more significant clonal endothelial cell expansion compared with the brain, pancreas, liver, and spleen. In summary, we have demonstrated that serial MPM of Cdh5-Confetti mice in vivo is a powerful technical advance to study endothelial remodeling and repair in the kidney and other organs under physiological and disease conditions.

Studying the Endothelial Glycocalyx in vitro: What Is Missing?

All human cells are coated by a surface layer of proteoglycans, glycosaminoglycans (GAGs) and plasma proteins, called the glycocalyx. The glycocalyx transmits shear stress to the cytoskeleton of endothelial cells, maintains a selective permeability barrier, and modulates adhesion of blood leukocytes and platelets. Major components of the glycocalyx, including syndecans, heparan sulfate, and hyaluronan, are shed from the endothelial surface layer during conditions including ischaemia and hypoxia, sepsis, atherosclerosis, diabetes, renal disease, and some viral infections. Studying mechanisms of glycocalyx damage in vivo can be challenging due to the complexity of immuno-inflammatory responses which are inextricably involved. Previously, both static as well as perfused in vitro models have studied the glycocalyx, and have reported either imaging data, assessment of barrier function, or interactions of blood components with the endothelial monolayer. To date, no model has simultaneously incorporated all these features at once, however such a model would arguably enhance the study of vasculopathic processes. This review compiles a series of current in vitro models described in the literature that have targeted the glycocalyx layer, their limitations, and potential opportunities for further developments in this field.

Endothelial Glycocalyx as a Regulator of Fibrotic Processes

The endothelial glycocalyx, the gel layer covering the endothelium, is composed of glycosaminoglycans, proteoglycans, and adsorbed plasma proteins. This structure modulates vessels’ mechanotransduction, vascular permeability, and leukocyte adhesion. Thus, it regulates several physiological and pathological events. In the present review, we described the mechanisms that disturb glycocalyx stability such as reactive oxygen species, matrix metalloproteinases, and heparanase. We then focused our attention on the role of glycocalyx degradation in the induction of profibrotic events and on the possible pharmacological strategies to preserve this delicate structure.

Lowest nocturnal systolic blood pressure is related to heavy proteinuria and outcomes in elderly patients with chronic kidney disease

Ambulatory blood pressure monitoring (ABPM) can produce many variables, of which the lowest nocturnal systolic blood pressure (LNSBP) currently used in calculating morning surge is occasionally overlooked in recent kidney studies compared with other ABPM parameters. We explored the clinical effects of LNSBP in elderly patients with chronic kidney disease (CKD) in a multicenter, observational cohort study. A total of 356 elderly patients with CKD from 19 clinics were included in this analysis. We used multiple logistic regression and survival analyses to assess the associations between the lowest nocturnal systolic blood pressure and heavy proteinuria and kidney disease outcomes, respectively. The median age was 66 years, and 66.6% were men. The median eGFR was 49.2 ml/min/1.73 m². Multivariate logistic regression analysis demonstrated that LNSBP (OR 1.24; 95% CI 1.10–1.39; P < 0.001; per 10 mmHg) was associated with heavy proteinuria. During the median follow-up of 23 months, 70 patients (19.7%) had a composite outcome; of these, 25 initiated dialysis, 25 had 40% eGFR loss, and 20 died. Cox analysis showed that the renal risk of LNSBP for CKD outcomes remained significant even after adjusting for background factors, including age, sex, medical history of hypertension and diabetes, smoking status, eGFR, 24-h proteinuria, and etiology of CKD (HR 1.18; 95% CI 1.06–1.32; P = 0.002; per 10 mmHg). Concentrating on LNSBP could be valuable in guiding antihypertensive treatment to control heavy proteinuria and improve renal prognosis in elderly CKD patients.

Investigation and assessment of neutrophil dysfunction early after severe burn injury

BACKGROUND

Extensive burn injury results in a complex immune response that is associated with mortality and prognosis. Studies on acquired immune and the development of sepsis in burn patients have been reported. However, one of the main cells in innate immune, neutrophil dysfunction in the burn shock stage has not been thoroughly characterized.

METHODS

Neutrophil chemotaxis, expression of neutrophil surface markers (P2X1 receptor, [P2RX1]), degranulation (myeloperoxidase [MPO], heparin-binding protein [HBP], matrix metalloproteinase-9 [MMP-9] and neutrophil elastase [NE]), oxidative burst capacity, neutrophil extracellular trap (NET) generation, phagocytosis and apoptosis were measured in 18 patients with major burns (≥30% total body surface area [TBSA]) within 48 h after burn injury. In addition, circulating neutrophils and vascular permeability in mice model with 30% TBSA third-degree burns were also observed and investigated.

RESULTS

Neutrophil functions were reduced considerably in burn shock stage, which was characterized by decreased chemotaxis, phagocytosis and abnormal bactericidal function. Increased release of heparin-binding protein (HBP) and the expression of P2RX1 on the neutrophil surface are related to fluid leakage and decreased chemotaxis during burn shock stage, respectively. The combination of HBP concentration in plasma and P2RX1 expression on neutrophils gives a better prediction of neutrophil dysfunction in burn-injured patients.

CONCLUSION

Neutrophil dysfunction plays a key role in the development of burn injury. Targeting the restoration of neutrophil function may be a feasible therapeutic intervention to help reduce fluid loss during shock and the severity of subsequent infection.

Vascular Endothelial Glycocalyx Damage in COVID-19

The new coronavirus disease-2019 (COVID-19), which is spreading around the world and threatening people, is easily infecting a large number of people through airborne droplets; moreover, patients with hypertension, diabetes, obesity, and cardiovascular disease are more likely to experience severe conditions. Vascular endothelial dysfunction has been suggested as a common feature of high-risk patients prone to severe COVID-19, and measurement of vascular endothelial function may be recommended for predicting severe conditions in high-risk patients with COVID-19. However, fragmented vascular endothelial glycocalyx (VEGLX) is elevated in COVID-19 patients, suggesting that it may be useful as a prognostic indicator. Although the relationship between VEGLX and severe acute respiratory syndrome coronavirus 2 infections has not been well studied, some investigations into COVID-19 have clarified the relationship between VEGLX and the mechanism that leads to severe conditions. Clarifying the usefulness of VEGLX assessment as a predictive indicator of the development of severe complications is important as a strategy for confronting pandemics caused by new viruses with a high affinity for the vascular endothelium that may recur in the future.

Essential role and therapeutic targeting of the glomerular endothelial glycocalyx in lupus nephritis

Lupus nephritis (LN) is a major organ complication and cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). There is an unmet medical need for developing more efficient and specific, mechanism-based therapies, which depends on improved understanding of the underlying LN pathogenesis. Here we present direct visual evidence from high-power intravital imaging of the local kidney tissue microenvironment in mouse models showing that activated memory T cells originated in immune organs and the LN-specific robust accumulation of the glomerular endothelial glycocalyx played central roles in LN development. The glomerular homing of T cells was mediated via the direct binding of their CD44 to the hyaluronic acid (HA) component of the endothelial glycocalyx, and glycocalyx-degrading enzymes efficiently disrupted homing. Short-course treatment with either hyaluronidase or heparinase III provided long-term organ protection as evidenced by vastly improved albuminuria and survival rate. This glycocalyx/HA/memory T cell interaction is present in multiple SLE-affected organs and may be therapeutically targeted for SLE complications, including LN.

A combined immunology and renal pathophysiology study of the local kidney tissue microenvironment in lupus identifies a key role of glomerular endothelial glycocalyx in disease development.

The Glycocalyx and Its Role in Vascular Physiology and Vascular Related Diseases

Purpose

In 2007 the two senior authors wrote a review on the structure and function of the endothelial glycocalyx layer (Weinbaum in Annu Rev Biomed Eng 9:121–167, 2007). Since then there has been an explosion of interest in this hydrated gel-like structure that coats the luminal surface of endothelial cells that line our vasculature due to its important functions in (A) basic vascular physiology and (B) vascular related diseases. This review will highlight the major advances that have occurred since our 2007 paper.

Methods

A literature search mainly focusing on the role of the glycocalyx in the two major areas described above was performed using electronic databases.

Results

In part (A) of this review, the new formulation of the century old Starling principle, now referred to as the Michel–Weinbaum glycoclayx model or revised Starling hypothesis, is described including new subtleties and physiological ramifications. New insights into mechanotransduction and release of nitric oxide due to fluid shear stress sensed by the glycocalyx are elaborated. Major advances in understanding the organization and function of glycocalyx components, and new techniques for measuring both its thickness and spatio-chemical organization based on super resolution, stochastic optical reconstruction microscopy (STORM) are presented. As discussed in part (B) of this review, it is now recognized that artery wall stiffness associated with hypertension and aging induces glycocalyx degradation, endothelial dysfunction and vascular disease. In addition to atherosclerosis and cardiovascular diseases, the glycocalyx plays an important role in lifestyle related diseases (e.g., diabetes) and cancer. Infectious diseases including sepsis, Dengue, Zika and Corona viruses, and malaria also involve the glycocalyx. Because of increasing recognition of the role of the glycocalyx in a wide range of diseases, there has been a vigorous search for methods to protect the glycocalyx from degradation or to enhance its synthesis in disease environments.

Conclusion

As we have seen in this review, many important developments in our basic understanding of GCX structure, function and role in diseases have been described since the 2007 paper. The future is wide open for continued GCX research.

Endothelial glycocalyx damage as a systemic inflammatory microvascular endotheliopathy in COVID-19

In atherosclerosis patients, vascular endothelial dysfunction is commonly observed alongside damage of the vascular endothelial glycocalyx, an extracellular matrix bound to and encapsulating the endothelial cells lining the blood vessel wall. Although atherosclerotic risk factors have been reported in severe patients with coronavirus disease 2019 (COVID-19), the exact mechanisms are unclear. The mortality associated with the COVID-19 outbreak is increased by comorbidities, including hypertension, diabetes, obesity, chronic obstructive pulmonary disease (COPD), and cardiovascular disease. Besides, older individuals and smokers have significantly worse outcomes. Interestingly, these comorbidities and risk factors are consistent with the pathophysiology that causes vascular endothelial glycocalyx damage. Moreover, vascular glycocalyx dysfunction causes microvascular leakage, which results in interstitial pulmonary abnormal shadows (multiple patchy shadows with a ground glass inter-pneumonic appearance). This is frequently followed by severe acute respiratory distress syndrome (ARDS), closely related to coagulo-fibrinolytic changes contributing to disseminated intravascular coagulation (DIC) and Kawasaki disease shock syndrome, as well as inducing activation of the coagulation cascade, leading to thromboembolism and multiple organ failure. Notably, SARS-CoV-2, the causative virus of COVID-19, binds to ACE2, which is abundantly present not only in human epithelia of the lung and the small intestine, but also in vascular endothelial cells and arterial smooth muscle cells. Moreover, COVID-19 can induce severe septic shock, and sepsis can easily lead to systemic degradation of the vascular endothelial glycocalyx. In the current review, we propose new concepts and therapeutic goals for COVID-19-related vascular endothelial glycocalyx damage, based on previous vascular endothelial medicine research.

Dysfunctional HDL takes its Toll on the endothelial glycocalyx

Patients with end-stage renal disease have a high risk of dying from cardiovascular disease that cannot be explained solely by traditional cardiovascular disease risk factors. Hesse et al. suggest that dysfunctional high-density lipoprotein cholesterol generated in patients with end-stage renal disease causes endothelial glycocalyx degradation. Glycocalyx degradation may represent one of the earliest insults leading to atheroma formation, and so this work suggests a novel link between renal failure and cardiovascular disease.

Aldosterone Induces DNA Damage and Activation of Nrf2 Mainly in Tubuli of Mouse Kidneys

Hypertensive patients have an increased risk of developing chronic kidney disease (CKD). Many of these patients have increased levels of the blood pressure regulating mineralocorticoid aldosterone. As a protection against aldosterone-induced damage, kidney cells can upregulate key regulators of the antioxidant defense, such as nuclear factor-erythroid-2-related factor 2 (Nrf2). In the present study aldosterone-induced kidney damage and Nrf2 activation in kidney cells of mice treated with three different concentrations of aldosterone for 4 weeks was localized. Increased albumin and neutrophil gelatinase-associated lipocalin (NGAL) in urine revealed an impaired kidney function of the aldosterone-infused mice. Localization of aldosterone-induced oxidative damage (in the form of DNA lesions) in specific kidney cells showed an increase in proximal tubuli and to an even greater extend in distal tubuli. Phosphorylated Nrf2 was increased in distal tubule cells after aldosterone-infusion. Nrf2 activation in proximal tubuli or in glomeruli after aldosterone-treatment could not be observed. Nrf2 target genes and proteins analyzed, paradoxically, showed a downregulation in the whole kidney. Aldosterone-treated mice exhibited an increased kidney injury and DNA damage in distal and proximal tubuli. Nrf2 seemed only to be specifically activated in distal tubule cells, where we also detected the highest amount of oxidative damage.

Blocking matrix metalloproteinase-mediated syndecan-4 shedding restores the endothelial glycocalyx and glomerular filtration barrier function in early diabetic kidney disease

The endothelial glycocalyx is a key component of the glomerular filtration barrier. We have shown that matrix metalloproteinase (MMP)-mediated syndecan 4 shedding is a mechanism of glomerular endothelial glycocalyx damage in vitro, resulting in increased albumin permeability. Here we sought to determine whether this mechanism is important in early diabetic kidney disease, by studying streptozotocin-induced type 1 diabetes in DBA2/J mice. Diabetic mice were albuminuric, had increased glomerular albumin permeability and endothelial glycocalyx damage. Syndecan 4 mRNA expression was found to be upregulated in isolated glomeruli and in flow cytometry-sorted glomerular endothelial cells. In contrast, glomerular endothelial luminal surface syndecan 4 and Marasmium oreades agglutinin lectin labelling measurements were reduced in the diabetic mice. Similarly, syndecan 4 protein expression was significantly decreased in isolated glomeruli but increased in plasma and urine, suggesting syndecan 4 shedding. Mmp-2, 9 and 14 mRNA expression were upregulated in isolated glomeruli, suggesting a possible mechanism of glycocalyx damage and albuminuria. We therefore characterised in detail the activity of MMP-2 and 9 and found significant increases in kidney cortex, plasma and urine. Treatment with MMP-2/9 inhibitor I for 21 days, started six weeks after diabetes induction, restored endothelial glycocalyx depth and coverage and attenuated diabetes-induced albuminuria and reduced glomerular albumin permeability. MMP inhibitor treatment significantly attenuated glomerular endothelial and plasma syndecan 4 shedding and inhibited plasma MMP activity. Thus, our studies confirm the importance of MMPs in endothelial glycocalyx damage and albuminuria in early diabetes and demonstrate that this pathway is amenable to therapeutic intervention. Hence, treatments targeted at glycocalyx protection by MMP inhibition may be of benefit in diabetic kidney disease.