Acute hyperglycemia induces rapid, reversible increases in glomerular permeability in nondiabetic rats

Inhibition of p38 MAPK decreases hyperglycemia-induced nephrin endocytosis and attenuates albuminuria

Abstract

Chronic hyperglycemia, as in diabetes mellitus, may cause glomerular damage with microalbuminuria as an early sign. Noteworthy, even acute hyperglycemia can increase glomerular permeability before structural damage of the glomerular filter can be detected. Despite intensive research, specific antiproteinuric therapy is not available so far. Thus, a deeper understanding of the molecular mechanisms of albuminuria is desirable. P38 MAPK signaling is involved in the development of hyperglycemia-induced albuminuria. However, the mechanism of increased p38 MAPK activity leading to increased permeability and albuminuria remained unclear. Recently, we demonstrated that acute hyperglycemia triggers endocytosis of nephrin, the key molecule of the slit diaphragm, and induces albuminuria. Here, we identify p38 MAPK as a pivotal regulator of hyperglycemia-induced nephrin endocytosis. Activated p38 MAPK phosphorylates the nephrin c-terminus at serine 1146, facilitating the interaction of PKCα with nephrin. PKCα phosphorylates nephrin at threonine residues 1120 and 1125, mediating the binding of β-arrestin2 to nephrin. β-arrestin2 triggers endocytosis of nephrin by coupling it to the endocytic machinery, leading to increased glomerular permeability. Pharmacological inhibition of p38 MAPK preserves nephrin surface expression and significantly attenuates albuminuria.

Key messages

Acute hyperglycemia triggers endocytosis of nephrin.

Activated p38 MAPK phosphorylates the nephrin c-terminus at serine 1146, facilitating the interaction of PKCα with nephrin.

PKCα phosphorylates nephrin at threonine residues 1120 and 1125, mediating the binding of β-arrestin2 to nephrin.

β-arrestin2 triggers endocytosis of nephrin by coupling it to the endocytic machinery, leading to a leaky glomerular filter.

Pharmacological inhibition of p38 MAPK preserves nephrin surface expression and significantly attenuates albuminuria under hyperglycemic conditions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00109-022-02184-5.

Activation of mTOR mediates hyperglycemia-induced renal glomerular endothelial hyperpermeability via the RhoA/ROCK/pMLC signaling pathway

OBJECTIVE

Hyperglycemia is associated with albuminuria and renal glomerular endothelial dysfunction in patients with diabetic nephropathy. The mTOR and RhoA/ROCK signaling pathways are involved in glomerular filtration barrier (GFB) regulation, but their role in high glucose (HG)-induced GFB dysfunction in human renal glomerular endothelial cells (HRGECs) has not been investigated. This study aimed to investigate the mechanisms of HG-induced GFB dysfunction in vitro.

MATERIALS AND METHODS

HRGECs were cultured in vitro and exposed to HG. The horseradish peroxidase-albumin leakage and transendothelial electrical resistance of the endothelial monolayer were measured after HG treatment with or without rapamycin preincubation. A fluorescence probe was used to study the distribution of F-actin reorganization. The phosphorylation levels of myosin light chain (MLC) and mTOR were measured via western blotting. RhoA activity was evaluated via GTPase activation assay. The effects of blocking mTOR or the RhoA/ROCK pathway on endothelial permeability and MLC phosphorylation under HG conditions were observed.

RESULTS

HG exposure induced F-actin reorganization and increased MLC phosphorylation, leading to EC barrier disruption. This effect was attenuated by treatment with rapamycin or Y-27632. Phospho-MLC (pMLC) activation in HRGECs was mediated by RhoA/ROCK signaling. mTOR and RhoA/ROCK inhibition or knockdown attenuated pMLC activation, F-actin reorganization and barrier disruption that occurred in response to HG exposure.

CONCLUSIONS

Our results revealed that HG stimulation upregulated RhoA expression and activity through an mTOR-dependent pathway, leading to MLC-mediated endothelial cell cytoskeleton rearrangement and glomerular endothelial barrier dysfunction.

Effect of diabetes mellitus on the recovery of changes in renal functions and glomerular permeability following reversible 24-hour unilateral ureteral obstruction

BACKGROUND

Following reversal of short periods of ureteral obstruction (UO), glomerular and tubular renal dysfunction recovers with time. Diabetes mellitus (DM) affects glomerular function; thus, the ability of diabetic kidneys to recover from UO may be impaired. This study investigated the effects of long-term DM on the recovery of glomerular and tubular function, as well as permeability of the glomerular filtration barrier (GFB), after unilateral UO (UUO) reversal.

METHODS

Diabetes mellitus was induced in Wistar rats by intraperitoneal streptozotocin. All diabetic and age-matched control rats underwent reversible 24-hour left UUO. The renal function of both kidneys was measured using clearance techniques 3 hours and 7 and 30 days after UUO reversal. Glomerular permeability was assessed by measuring the glomerular sieving coefficients for fluorescein isothiocyanate-conjugated Ficoll (molecular radius: 20-90 Å).

RESULTS

Unilateral UO induced transient changes in the size selectivity of GFB small pores. However, the size selectivity function of large pores had not returned to baseline even 30 days after UUO reversal. Diabetes mellitus caused exaggerated early alterations in glomerular hemodynamic and tubular function, as well as size selectivity dysfunction of both small and large pores. At 30 days after UUO reversal, despite glomerular hemodynamic and tubular function and the size selectivity of small pores returning to normal in both diabetic and non-diabetic rats, the residual size selectivity dysfunction of large pores was more severe in diabetic rats.

CONCLUSION

Unilateral UO caused long-term dysfunction in the size selectivity of large pores of the GFB. In addition, DM significantly exaggerated this dysfunction, indicating a more ominous outcome in diabetic kidneys following UUO.

Sustained, delayed, and small increments in glomerular permeability to macromolecules during systemic ET-1 infusion mediated via the ETA receptor

Emerging evidence indicates that endogenous production of endothelin (ET)-1, a 21-amino acid peptide vasoconstrictor, plays an important role in proteinuric kidney disease. Previous studies in rats have shown that chronic administration of ET-1 leads to increased glomerular albumin leakage. The underlying mechanisms are, however, currently not known. Here, we used size-exclusion chromatography to measure glomerular sieving coefficients for neutral FITC-Ficoll (molecular Stokes-Einstein radius: 15-80 Å, molecular weight: 70 kDa/400 kDa) in anesthetized male Sprague-Dawley rats (n = 12) at baseline and at 5, 15, 30, and 60 min after intravenous administration of ET-1. In separate experiments, ET-1 was given together with the selective ET type A (ET_A) or ET type B (ET_B) receptor antagonists JKC-301 and BQ-788, respectively. At both 15 and 30 min postadministration, the glomerular sieving coefficient for macromolecular Ficoll (70 Å) was significantly increased to 4.4 × 10^-5 ± 0.7 × 10^-5 (P = 0.024) and 4.5 × 10^-5 ± 0.8 × 10^-5 (P = 0.007), respectively, compared with baseline (2.2 × 10^-5 ± 0.4 ×10^-5). Decreased urine production after ET-1 prevented the use of higher doses of ET-1. Data analysis using the two-pore model indicated changes in large-pore permeability after ET-1, with no changes in the small-pore pathway. Administration of ET_A blocker abrogated the permeability changes induced by ET-1 at 30 min, whereas blockade of ET_B receptors was ineffective. Mean arterial pressure was only significantly increased at 60 min, being 123 ± 4 mmHg compared with 111 ± 2 mmHg at baseline (P = 0.02). We conclude that ET-1 evoked small, delayed, and sustained increases in glomerular permeability, mediated via the ET_A receptor.

Association of HbA1C Variability and Renal Progression in Patients with Type 2 Diabetes with Chronic Kidney Disease Stages 3⁻4

Little is known about the predictive value of glycosylated hemoglobin (HbA_1C) variability in patients with advanced chronic kidney disease (CKD). The aim of this study was to investigate whether HbA_1C variability is associated with progression to end-stage renal disease in diabetic patients with stages 3–5 CKD, and whether different stages of CKD affect these associations. Three hundred and eighty-eight patients with diabetes and stages 3–5 CKD were enrolled in this longitudinal study. Intra-individual HbA_1C variability was defined as the standard deviation (SD) of HbA_1C, and the renal endpoint was defined as commencing dialysis. The results indicated that, during a median follow-up period of 3.5 years, 108 patients started dialysis. Adjusted Cox analysis showed an association between the highest tertile of HbA_1C SD (tertile 3 vs. tertile 1) and a lower risk of the renal endpoint (hazard ratio = 0.175; 95% confidence interval = 0.059–0.518; p = 0.002) in the patients with an HbA_1C level ≥ 7% and stages 3–4 CKD, but not in stage 5 CKD. Further subgroup analysis showed that the highest two tertiles of HbA_1C SD were associated with a lower risk of the renal endpoint in the group with a decreasing trend of HbA_1C. Our results demonstrated that greater HbA_1C variability and a decreasing trend of HbA_1C, which may be related to intensive diabetes control, was associated with a lower risk of progression to dialysis in the patients with stages 3–4 CKD and poor glycemic control (HbA1c ≥ 7%).

Acute and chronic exposure to high levels of glucose modulates tight junction-associated epithelial barrier function in a renal tubular cell line

AIMS

Type 2 diabetes mellitus (T2DM) is one of the most prevalent diseases worldwide. Diabetic nephropathy (DN) is a complication of diabetes and the mechanisms underlying onset and progression of this disease are not fully understood. It has been shown that hyperglycemia is an independent factor to predict the development of DN in individuals with T2DM, however, a link between high plasma glucose levels and renal tubular injuries in DN remains unknown. In this study, we investigated the effect of high levels of glucose (i.e. 180 or 360mg/dL) for up to 24h (acute) or over 72h (chronic) upon tight junction (TJ)-mediated epithelial barrier integrity of the kidney tubular cell line, MDCK.

METHODS/KEY FINDINGS

High levels of glucose (180 and 360mg/dL) induced a decrease in transepithelial electrical resistance associated with an increase in TJ cation selectivity at 24h or in TJ permeability to a paracellular marker, Lucifer Yellow, at 72h-exposure when compared to control group (exposed to 100mg/dL glucose). Immunofluorescence analyses showed that glucose treatment induced a significant decrease in the tight junctional content of claudins-1 and -3 as well as a significant increase in claudin-2 (particularly at 24h-exposure) and a time-dependent change in occludin/ZO-1 junctional content. The analyses of total cell content of these junctional proteins by Western blot did not reveal significant changes, except in claudin-2 expression.

SIGNIFICANCE

Our data suggest that high levels of glucose induce time-dependence changes in TJ structure in MDCK monolayers, suggesting a possible link between hyperglycemia-induced tubular epithelial barrier disruption and diabetic nephropathy.

Role of Protein Kinase G and Reactive Oxygen Species in the Regulation of Podocyte Function in Health and Disease

Podocytes and their foot processes form an important cellular layer of the glomerular barrier involved in the regulation of glomerular permeability. Disturbing the function of podocytes plays a central role in the development of proteinuria in diabetic nephropathy. Retraction of the podocyte foot processes that form slit diaphragms is a common feature of proteinuria; although, the correlation between these events in not well understood. Notably, it is unclear whether podocyte foot processes are able to regulate slit diaphragm permeability and glomerular ultrafiltration. The occurrence of reactive oxygen species generation, insulin resistance, and hyperglycemia characterizes early stages of type 2 diabetes. Protein kinase G type I alpha (PKGIα) is an intracellular target for vasorelaxant factors. It is activated in both cGMP-dependent and cGMP-independent manners. Recently, we demonstrated a relationship between oxidative stress, PKGIα activation, actin reorganization, and changes in the permeability of the filtration barrier. This review discusses how redox imbalance affects both the activity of PKGIα and PKGI-dependent signaling pathways in podocytes. J. Cell. Physiol. 232: 691-697, 2017. © 2016 Wiley Periodicals, Inc.

Roles of mTOR complexes in the kidney: implications for renal disease and transplantation

The mTOR pathway has a central role in the regulation of cell metabolism, growth and proliferation. Studies involving selective gene targeting of mTOR complexes (mTORC1 and mTORC2) in renal cell populations and/or pharmacologic mTOR inhibition have revealed important roles of mTOR in podocyte homeostasis and tubular transport. Important advances have also been made in understanding the role of mTOR in renal injury, polycystic kidney disease and glomerular diseases, including diabetic nephropathy. Novel insights into the roles of mTORC1 and mTORC2 in the regulation of immune cell homeostasis and function are helping to improve understanding of the complex effects of mTOR targeting on immune responses, including those that impact both de novo renal disease and renal allograft outcomes. Extensive experience in clinical renal transplantation has resulted in successful conversion of patients from calcineurin inhibitors to mTOR inhibitors at various times post-transplantation, with excellent long-term graft function. Widespread use of this practice has, however, been limited owing to mTOR-inhibitor- related toxicities. Unique attributes of mTOR inhibitors include reduced rates of squamous cell carcinoma and cytomegalovirus infection compared to other regimens. As understanding of the mechanisms by which mTORC1 and mTORC2 drive the pathogenesis of renal disease progresses, clinical studies of mTOR pathway targeting will enable testing of evolving hypotheses.

Reduction in glomerular pore size is not restricted to pregnant women. Evidence for a new syndrome: 'Shrunken pore syndrome'

The plasma levels of cystatin C, β₂-microglobulin, beta-trace protein, retinol binding protein (RBP) and creatinine were determined in plasma samples from 111 randomly selected patients with eGFR_{cystatin C} ≤ 60% of eGFR_creatinine and from 55 control patients with 0.9eGFR_creatinine ≤ eGFR_{cystatin C} ≤ 1.1eGFR_creatinine (eGFR_{cystatin C} ≈ eGFR_creatinine). The concentration ratios of cystatin C/creatinine, β₂-microglobulin/creatinine, beta-trace protein/creatinine and RBP/creatinine were significantly higher in patients with eGFR_{cystatin C} ≤ 60% of eGFR_creatinine than in patients with eGFR_{cystatin C} ≈ eGFR_creatinine. When the patients were divided into three groups with different estimated GFR intervals (≤ 40, 40–60 and ≥ 60 mL/min/1.73m²) the concentration ratios of cystatin C/creatinine, β₂-microglobulin/creatinine, and beta-trace protein/creatinine were significantly higher in patients with eGFR_{cystatin C} ≤ 60% of eGFR_creatinine than in patients with eGFR_{cystatin C} ≈ eGFR_creatinine for all GFR intervals. Similar results were obtained when the population without pregnant women was studied as well as the subpopulations of men or of non-pregnant women. Populations of pre-eclamptic women and pregnant women in the third trimester display similar results. Since the production of these four proteins with sizes similar to that of cystatin C is not co-regulated, the most likely explanation for the simultaneous increase of their creatinine-ratios in patients with eGFR_{cystatin C} ≤ 60% of eGFR_creatinine is that their elimination by glomerular filtration is decreased. We suggest that this is due to a reduction in pore diameter of the glomerular membrane and propose the designation ‘Shrunken pore syndrome’ for this pathophysiological state.

Visit-to-Visit Glucose Variability Predicts the Development of End-Stage Renal Disease in Type 2 Diabetes: 10-Year Follow-Up of Taiwan Diabetes Study

The purpose of this study was to examine the association of glucose variability using coefficient of variation of fasting plasma glucose (FPG-CV) and coefficient of variation of glycated hemoglobin (HbA1c-CV) to end-stage renal disease (ESRD) in 31,841 Chinese patients with type 2 diabetes.Patients with type 2 diabetes enrolled in National Diabetes Care Management Program, aged ≧30 years, and free of ESRD (n = 31,841) in January 1, 2002 to December 31, 2004 were included. Extended Cox proportional hazards regression models with competing risk of all-cause mortality were used to evaluate risk factors on ESRD incidence. Patients were followed till 2012.After a median follow-up period of 8.23 years, 1642 patients developed ESRD, giving a crude incidence rate of 6.27/1000 person-years (6.36 for men, 6.19 for women). After the multivariate adjustment, both FPG-CV and HbA1c-CV were independent predictors of ESRD with corresponding hazard ratios of 1.20 (95% confidence interval [CI] 1.01, 1.41), 1.24 (95% CI 1.05, 1.46) in HbA1c-CV from fourth to fifth quintile and 1.23 (95% CI 1.03, 1.47) in FPG-CV from fifth quintile.One-year visit-to-visit glucose variability expressed by FPG-CV and HbA1c-CV predicted development of ESRD in patients with type 2 diabetes, suggesting therapeutic strategies toward a goal to minimize glucose fluctuation.

Acute reactive oxygen species (ROS)-dependent effects of IL-1β, TNF-α, and IL-6 on the glomerular filtration barrier (GFB) in vivo

This study was performed to investigate the immediate actions of the proinflammatory cytokines IL-1β, TNF-α, and IL-6 on the permeability of the glomerular filtration barrier (GFB) in rats and to test whether these actions are dependent upon the release of reactive oxygen species (ROS). In anesthetized rats, blood access was achieved and the left ureter was cannulated for urine collection. Rats were continuously infused intravenously with either IL-1β (0.4 and 2 μg·kg(-1)·h(-1)), TNF-α (0.4 and 2 μg·kg(-1)·h(-1)), or IL-6 (4 and 8 μg·kg(-1)·h(-1)), together with polydisperse FITC-Ficoll-70/400 and inulin for 1 h. Plasma and urine samples were analyzed by high performance size exclusion chromatography (HPSEC) for determination of glomerular sieving coefficients (θ). The glomerular filtration rate (GFR) was also assessed (51Cr-EDTA). In separate experiments, the superoxide scavenger tempol (30 mg·kg(-1)·h(-1)) was given before and during cytokine infusions. IL-1β and TNF-α caused rapid, partly reversible increases in glomerular permeability to large molecules (Ficoll50-80Å), peaking at 5-30 min, while IL-6 caused a more gradual increase in permeability, leveling off at 60 min. Tempol almost completely abrogated the glomerular permeability effects of the cytokines infused. In conclusion IL-1β, TNF-α, and IL-6, when infused systemically, caused immediate and partly reversible increases in glomerular permeability, which could be inhibited by the superoxide scavenger tempol, suggesting an important role of ROS in acute cytokine-induced permeability changes in the GFB.

Plasma pro-inflammatory cytokines, IgM-uria and cardiovascular events in patients with chest pain: A comparative study

BACKGROUND

Risk stratification of patients presenting with acute chest pain is crucial for immediate and long-term management. Traditional predictors are suboptimal; therefore inflammatory biomarkers are studied for clinical assessment of patients at risk. Recently, we reported the association of IgM-uria with worse cardiovascular outcome in patients with acute chest pain. In this study, in the same cohort of patients with chest pain, we compared the value of IgM-uria to pro-inflammatory cytokines in predicting the occurrence of subsequent cardiovascular events.

METHODS

A total of 178 consecutive patients presenting with acute chest pain to the emergency department at the University Hospital of Lund, were recruited. Twenty-seven of 57 patients with acute coronary syndrome (ACS), and 18 of 118 patients with non-specific chest pain at baseline developed a subsequent major cardiovascular event during the 18 months follow-up. Urinary proteins (IgM-uria and Microalbuminuria) and plasma inflammatory markers (IL-6, Il-8, IL-10, IFN-γ and TNF-α) were measured at time of admission.

RESULTS

Using the receiver operating characteristic curves, the area under the curve for predicting cardiovascular events was 0.71 (95%CI 0.61-0.81) for IgM-uria, 0.61 (95%CI 0.51-0.71) for IL-6, 0.63 (95%CI 0.53-0.72) for IL-8, 0.65 (95%CI 0.56-0.74) for IL-10, and 0.64 (95% CI 0.54-0.74) for TNF-α. In multivariate Cox-regression analysis adjusted for age, microalbuminuria, IgM-uria, IL-10, TNF-α, troponin T, hsCRP and ACS at baseline; IgM-uria was the only biomarker that remained an independent predictor of outcome (HR = 4.2, 95%CI 2.2-7.8, p < 0.001).

CONCLUSION

In patients with chest pain with or without acute coronary syndrome, IgM-uria could better predict the occurrence of cardiovascular events than plasma pro-inflammatory cytokines.

Renal tubular damage may contribute more to acute hyperglycemia induced kidney injury in non-diabetic conscious rats

AIMS

Growing evidences suggest that acute hyperglycemia is strongly related to kidney injury. Our study aimed to investigate the effects of acute hyperglycemia on kidney glomerular and tubular impairment in non-diabetic conscious rats.

METHODS

Non-diabetic conscious rats were randomly subjected to 6h of saline (control group) or high glucose (acute hyperglycemia group) infusion. Blood glucose was maintained at 16.0-18.0 mmol/L in acute hyperglycemia group. Renal structure and function alterations, systemic/renal inflammation and oxidative stress markers were assessed, and apoptosis markers of renal inherent cells were evaluated.

RESULTS

Acute hyperglycemia caused significant injury to structure of glomerular filtration barrier, tubular epithelial cells and peritubular vascular endothelial cells. It increased urinary microalbumin (68.01 ± 27.09 μg/24h vs 33.81 ± 13.81 μg/24h , P=0.014), β2-microglobulin, Cystatin C, urinary and serous neutrophil gelatinase-associated lipocalin levels (P < 0.05). Acute hyperglycemia decreased megalin and cubilin expression, activated systemic and renal oxidative stress as well as inflammation and promoted renal inherent cell apoptosis.

CONCLUSIONS

Acute hyperglycemia causes significant injury to kidney function and structure. Compared with damages of glomerular filtration barrier, renal tubular injury may contribute more to acute hyperglycemia induced proteinuria. Activation of inflammation especially renal inflammation, oxidative stress and enhanced apoptosis may be the underlying mechanisms.

Hyperglycemia abolishes the protective effect of ischemic preconditioning in glomerular endothelial cells in vitro

In preclinical investigations, ischemic preconditioning (IPC) protects kidneys from ischemia/reperfusion injury. The direct effects of IPC on glomerular endothelial cells have not been studied in detail. Most investigations of IPC have focused on healthy cells and animals, and it remains unknown whether IPC is renoprotective in the setting of medical comorbidities such as diabetes. In this study, we determined the preventive potential of IPC in healthy glomerular endothelial cell monolayers, and compared these results to monolayers cultured under hyperglycemic conditions. We exposed glomerular endothelial monolayers to 1 h of IPC 24 h prior to oxygen-glucose deprivation (OGD), an in vitro model of ischemia/reperfusion injury. Glomerular endothelial monolayer integrity was assessed by measuring transendothelial electrical resistance, albumin flux, and cell survival. We found that IPC protected healthy but not hyperglycemic glomerular endothelial monolayers from ischemia/reperfusion injury. Furthermore, not only was the protective effect of IPC lost in the setting of hyperglycemia, but IPC was actually deleterious to the integrity of hyperglycemic glomerular endothelial cell monolayers.

mTOR inhibition with temsirolimus causes acute increases in glomerular permeability, but inhibits the dynamic permeability actions of puromycin aminonucleoside

Inhibitors of the mammalian target of rapamycin (mTORi) can produce de novo proteinuria in kidney transplant patients. On the other hand, mTORi has been shown to suppress disease progression in several animal models of kidney disease. In the present study, we investigated whether glomerular permeability can be acutely altered by the mTORi temsirolimus and whether mTORi can affect acute puromycin aminonucleoside (PAN) or angiotensin II (ANG II)-induced glomerular hyperpermeability. In anesthetized Wistar rats, the left ureter was cannulated for urine collection, while simultaneously blood access was achieved. Temsirolimus was administered as a single intravenous dose 30 min before the start of the experiments in animals infused with PAN or ANG II or in nonexposed animals. Polydispersed FITC-Ficoll-70/400 (molecular radius 10-80 Å) and (51)Cr-EDTA infusion was given during the whole experiment. Measurements of Ficoll in plasma and urine were performed sequentially before the temsirolimus injection (baseline) and at 5, 15, 30, 60, and 120 min after the start of the experiments. Urine and plasma samples were analyzed by high-performance size-exclusion chromatography (HPSEC) to assess glomerular sieving coefficients (θ) for Ficoll10-80Å. Temsirolimus per se increased baseline glomerular permeability to Ficoll50-80Å 45 min after its administration, a reactive oxygen species (ROS)-dependent phenomenon. PAN caused a rapid and reversible increase in glomerular permeability, peaking at 5 min, and again at 60-120 min, which could be blocked by the ROS scavenger tempol. mTORi abrogated the second permeability peak induced by PAN. However, it had no effect on the immediate ANG II- or PAN-induced increases in glomerular permeability.

Research progress in signalling pathway in diabetic nephropathy

Diabetic nephropathy, a lethal diabetic complication, is a leading cause of end-stage renal disease, which is pathologically characterized by thickened tubular basal and glomerular membranes, accumulated extracellular matrix, and progressive mesangial hypertrophy. Growing evidence indicates that diabetic nephropathy is induced by multiple conditions, such as glucose metabolism disorder, oxidative stress, numerous inflammatory factors and cytokines, and haemodynamic changes that lead to the occurrence and development of diabetic nephropathy based on genetic susceptibility. A variety of abnormalities in the signalling pathway may interact to produce these pathologic processes. Research has aimed to highlight the signalling pathway mechanisms that lead to diabetic nephropathy so that preventative strategies and effective therapies might be developed. In this review, important pathways that appear to be involved in driving these processes are discussed.

Rho kinase inhibition in diabetic kidney disease

Small GTPases of the Rho family and their down-stream effectors Rho associated kinases (ROCKs) are the molecules that converge a spectrum of pathophysiological signals triggered by the diabetic milieu and represent promising molecular targets for nephroprotective treatment in diabetes. The review discusses recent studies exploring the consequences of diabetes-induced Rho-ROCK activation in the kidney and the effects of ROCK inhibition (ROCKi) in experimental diabetic kidney disease (DKD). Studies in models of type 1 and type 2 diabetes have indicated blood pressure-independent nephroprotective actions of ROCKi in DKD. The underlying mechanisms include attenuation of diabetes-induced increases in renal expression of prosclerotic cytokines and extracellular matrix, anti-oxidant effects and protection of mitochondrial function, resulting in slower development of glomerulosclerosis and interstitial fibrosis. The studies have also shown antiproteinuric effects of ROCKi that could be related to reductions in permeability of the glomerular barrier and beneficial effects on podocytes. Glomerular haemodynamic mechanisms might also be involved. Despite remaining questions in this field, such as the effects in podocytes later in the course of DKD, specificity of currently available ROCKi, or the roles of individual ROCK isoforms, recent evidence in experimental diabetes suggests that ROCKi might in future broaden the spectrum of treatments available for patients with DKD. This is supported by the evidence generated in models of non-diabetic kidney disease and in clinical studies in patients with various cardiovascular disorders.

Extracellular fetal hemoglobin induces increases in glomerular permeability: inhibition with α1-microglobulin and tempol

Extracellular fetal hemoglobin (HbF) and adult hemoglobin (HbA) are proinflammatory and generate ROS. Increased plasma levels of extracellular HbF have recently been reported to occur in early preeclampsia. α1-Microglobulin (A1M) is a physiological heme-binding protein and radical scavenger that has been shown to counteract vascular permeability increases induced by HbA in the perfused placenta. The present study was performed to investigate whether HbF and HbA will increase glomerular permeability in vivo and to test whether A1M and tempol, a ROS scavenger, can prevent their effects. Anesthetized Wistar rats were continuously infused intravenously with either HbA, HbF, or cyano-inactivated HbF together with FITC-Ficoll-70/400, inulin, and (51)Cr-labeled EDTA for 2 h. Plasma samples and urine samples (left ureter) were taken repeatedly and analyzed by high-performance size exclusion chromatography to assess glomerular sieving coefficients for Ficoll of radius 10-80 Å. In separate experiments, A1M or tempol was given before and during Hb infusions. Extracellular HbF caused rapid, transient increases in glomerular permeability to large Ficoll molecules (50-80Å), contrary to the effects of HbA and cyano-inactivated HbF. For HbF, glomerular sieving coefficients for Ficoll of radius 60Å increased from 3.85 ± 0.85 × 10(-5) to 2.60 ± 0.96 × 10(-4) at 15 min, changes that were abrogated by tempol and reduced by A1M. In conclusion, our data demonstrate that extracellular HbF, infused systemically, can acutely increase glomerular permeability through inducing oxidative stress.

Berberine ameliorates experimental diabetes-induced renal inflammation and fibronectin by inhibiting the activation of RhoA/ROCK signaling

The accumulation of glomerular extracellular matrix proteins, especially fibronectin (FN), is a critical pathological characteristic of diabetic renal fibrosis. Inflammation mediated by nuclear factor-κB (NF-κB) plays a critical role in the pathogenesis of diabetic nephropathy (DN). RhoA/ROCK signaling is responsible for FN accumulation and NF-κB activation. Berberine (BBR) treatment significantly inhibited renal inflammation and thus improved renal damage in diabetes. Here, we study whether BBR inhibits FN accumulation and NF-κB activation by inhibiting RhoA/ROCK signaling and the underlying mechanisms involved. Results showed that BBR effectively inhibited RhoA/ROCK signaling activation in diabetic rat kidneys and high glucose-induced glomerular mesangial cells (GMCs) and simultaneously down-regulated NF-κB activity, which was accompanied by reduced intercellular adhesionmolecule-1, transforming growth factor-beta 1 and FN overproduction. Furthermore, we observed that BBR abrogated high glucose-mediated reactive oxygen species generation in GMCs. BBR and N-acetylcysteine inhibited RhoA/ROCK signaling activation in high glucose-exposed GMCs. Collectively, our data suggest that the renoprotective effect of BBR on DN partly depends on RhoA/ROCK inhibition. The anti-oxidative stress effect of BBR is responsible for RhoA/ROCK inhibition in DN.

Increased urinary IgM excretion in patients with chest pain due to coronary artery disease

BACKGROUND

Micro-albuminuria is a recognized predictor of cardiovascular morbidity and mortality in patients with coronary artery disease. We have previously reported, in diabetic and non-diabetic patients, that an increased urinary excretion of IgM is associated with higher cardiovascular mortality. The purpose of this study was to investigate the pattern of urinary IgM excretion in patients with acute coronary syndrome (ACS) and its correlation to cardiovascular outcome.

METHODS

Urine albumin, and IgM to creatinine concentration ratios were determined in 178 consecutive patients presenting with chest pain to the Department of Emergency Medicine (ED) at the University Hospital of Lund. Fifty eight (23 female) patients had ACS, 55 (19 female) patients had stable angina (SA), and 65 (35 female) patients were diagnosed as non-specific chest pain (NS).

RESULTS

Urine albumin and IgM excretions were significantly higher in patients with ACS (p = 0.001, and p = 0.029, respectively) compared to patients with NS-chest pain. During the 2 years follow-up time, 40 (19 female) patients suffered a new major cardiovascular event (ACS, acute heart failure, stroke) and 5 (4 male/1 female) patients died of cardiovascular cause. A high degree of albuminuria and IgM-uria significantly predicted cardiovascular mortality and morbidity (HR = 2.89, 95% CI: 1.48 - 5.66, p = 0.002). Microalbuminuric patients (≥3 mg/mmol) with high IgM-uria (≥0.005 mg/mmol) had a 3-fold higher risk for cardiovascular new events compared to patients with low IgM-uria (RR = 3.3, 95% CI: 1.1 - 9.9, p = 0.001).

CONCLUSION

In patients with chest pain, an increased urine IgM excretion, is associated with coronary artery disease and long-term cardiovascular complications. Measuring urine IgM concentration could have a clinical value in risk stratification of patients with ACS.

Scavengers of reactive oxygen species, paracalcitol, RhoA, and Rac-1 inhibitors and tacrolimus inhibit angiotensin II-induced actions on glomerular permeability

Systemic infusions of ANG II rapidly induce large, dynamic increases in the permeability of the glomerular filtration barrier (GFB) in rats. After binding to its receptor(s), ANG II generates reactive oxygen species (ROS) and produces Ca2+ influx into cells, leading to activation of a plethora of signaling cascades, including, e.g., calcineurin and small GTPases, such as Rac-1 and RhoA. In the present study we sought to interact with some of these cascades to test potential novel antiproteinuric agents. In anesthetized Wistar rats, the left urether was cannulated for urine collection, and blood access was achieved. Rats were infused with ANG II (16 ng·kg−1·min−1) alone, or together with the ROS scavengers tempol or dimethylthiourea (DMTU) or the D-vitamin analog paracalcitol, the RhoA-kinase inhibitor Y-27632, the Rac-1 inhibitor NSC-23766, or the calcineurin inhibitor tacrolimus. FITC-Ficoll-70/400 (mol.radius 10–80 Å) and 51Cr-EDTA were infused throughout the experiment. Plasma and urine samples were taken during baseline and at 5 and 15 min after the start of the infusions and analyzed by high-performance size-exclusion chromatography for determination of glomerular sieving coefficients (θ) for Ficoll10–80Å. ANG II infusion into rats caused marked increases in glomerular permeability to large Ficoll molecules (Ficoll50–80Å), which were abrogated by the ROS scavenger tempol and partly by DMTU. Paracalcitol, RhoA, and Rac-1 inhibition, and, to some extent tacrolimus, but not prostacyclin, could also inhibit the glomerular permeability actions of ANG II. Our data suggest that cellular ROS generation and active Ca2+ signaling are involved in ANG II-induced increases in glomerular permeability.

Activation of RhoA/ROCK regulates NF-κB signaling pathway in experimental diabetic nephropathy

Both RhoA/ROCK and NF-κB signaling pathways play important roles in the pathogenesis of diabetic nephropathy (DN). However, it remains unknown whether and how RhoA/ROCK regulates NF-κB signaling in diabetic kidneys. In cultured glomerular mesangial cells (GMCs), the high glucose-activated NF-κB nuclear translocation and DNA binding activity were attenuated by ROCK inhibitor Y27632 or dominant-negative RhoA mutant, indicating that RhoA/ROCK signaling regulates high glucose-activated NF-κB pathway. Furthermore, NF-κB-regulated inflammatory factors ICAM-1 and TGF-β1 were markedly increased in high glucose-treated GMCs, leading to accumulation of fibronectin (FN), an important component of extracellular matrix (ECM), This effect was also effectively attenuated by Y27632 or dominant-negative RhoA mutant. In STZ-induced diabetic rats, treatment with ROCK inhibitor fasudil suppressed the RhoA/ROCK activation and NF-κB nuclear translocation, and significantly reduced the renal FN, ICAM-1 and TGF-β1 protein levels. Thus, the RhoA/ROCK pathway may regulate NF-κB to upregulate inflammatory genes and mediate the development of DN.

Inhaled aerosolized insulin ameliorates hyperglycemia-induced inflammatory responses in the lungs in an experimental model of acute lung injury

Introduction

Previous studies have shown that patients with diabetes mellitus appear to have a lower prevalence of acute lung injury. We assumed that insulin prescribed to patients with diabetes has an anti-inflammatory property and pulmonary administration of insulin might exert beneficial effects much more than intravenous administration.

Methods

Twenty-eight mechanically ventilated rabbits underwent lung injury by saline lavage, and then the animals were allocated into a normoglycemia group (NG), a hyperglycemia group (HG), an HG treated with intravenous insulin (HG-VI) group or an HG treated with aerosolized insulin (HG-AI) group with continuous infusion of different fluid solutions and treatments: normal saline, 50% glucose, 50% glucose with intravenous insulin, or 50% glucose with inhaled aerosolized insulin, respectively. After four hours of treatment, the lungs and heart were excised en bloc, and then high-mobility group B1 concentration in bronchoalveolar lavage fluid, interleukin-8 and toll-like receptor 4 mRNA expression in bronchoalveolar lavage fluid cells, and lung myeloperoxidase activity were measured.

Results

Treatment with both aerosolized insulin and intravenous insulin attenuated toll-like receptor 4 mRNA expressions in the bronchoalveolar lavage fluid cells. Interleukin-8 and toll-like receptor 4 mRNA expression was significantly lower in the HG-AI group than in the HG-IV group. The lung myeloperoxidase activity in the normal healthy group showed significantly lower levels compared to the NG group but not different compared to those of the HG, HG-VI and HG-AI groups.

Conclusions

The results suggest that insulin attenuates inflammatory responses in the lungs augmented by hyperglycemia in acute lung injury and the insulin's efficacy may be better when administered by aerosol.

Role of ROCK upregulation in endothelial and smooth muscle vascular functions in diabetic rat aorta

Background

The RhoA/ROCK signaling pathway mediates vascular smooth muscle contraction while endogenous NO induces vasodilation through its inhibition. Since myosin light chain phosphatase (MLCP) and eNOS are targeted by RhoA/ROCK upregulation then turn to lead abnormalities in vasculature, we aimed to examine whether less endothelial NO-production and inhibited eNOS together with an upregulation of RhoA/ROCK signaling pathway in thoracic aorta can play an important role in vascular dysfunction under hyperglycemia.

Methods

We used streptozotocin-injected rats, as a model of type 1 diabetes, and their lean controls to investigate the role of ROCK upregulation in the function of toracic aorta by using electrophysiological and biochemical techniques.

Results

The protein level of ROCK isoform ROCK2 was found to be 2.5-fold higher in endothelium-intact aortic rings of the diabetic rats compared to those of the controls while its level in endothelium-denuded rings was similar among these two groups. Phosphorylation level of eNOS in endothelium-intact rings from the diabetics was 50% less compared to that of the control. ROCK inhibitors, either Y27632 or HA1077, induced concentration-dependent relaxation with a marked left-shift in phenylephrine pre-contracted endothelium-intact rings from either diabetics or high glucose incubated controls while pretreatment of these rings with L-NAME abolished this shift, fully. Moreover, phosphorylation levels of both MLCP and MLC in endothelium-denuded rings were markedly higher in the diabetics than the controls.

Conclusion

We demonstrated that diabetes-induced vascular dysfunction can arise due to either inbition of eNOS, thereby less endothelial NO-production, either directly or indirectly, in part, due to an upregulation of ROCK2 by hyperglycemia. Additionally, our data demonstrate that high phosphorylation levels of both MLC and MLCP in endothelium-denuded rings can be due to a less endothelial NO-production dependent ROCK upregulation in the smooth muscle cells under hyperglycemia, as well.

Rapid, dynamic changes in glomerular permeability to macromolecules during systemic angiotensin II (ANG II) infusion in rats

The actions of systemic angiotensin II (ANG II) infusions on glomerular permeability were investigated in vivo. In anesthetized Wistar rats (250-280 g), the left ureter was cannulated for urine collection, while simultaneously blood access was achieved. Rats were continuously infused intravenously with either of four doses of ANG II ranging from 16 ng·kg(-1)·min(-1) (Lo-ANG II) to 1.82 μg·kg(-1)·min(-1) (Hi-ANG II), and in separate experiments with aldosterone (Aldo; 0.22 mg·kg(-1)·min(-1)), or with the calcium channel blocker nimodipine, or with the Aldo antagonist spironolactone together with a high ANG II dose (910 ng·kg(-1)·min(-1); Hi-Int-ANG II), respectively, and with polydisperse FITC-Ficoll-70/400 (molecular radius 10-80 Å) and (51)Cr-EDTA. Plasma and urine samples were taken at 5, 15, 30, 60, and 120 min and analyzed by high performance size-exclusion chromatography for determination of glomerular sieving coefficients (θ) to Ficoll. Mean arterial pressure (MAP) and glomerular filtration rate (GFR) were also assessed. For ANG II, there was a rapid, marked, partly reversible increase in glomerular permeability (θ) for Ficoll molecules >34 Å in radius, peaking at 5-15 min, which was completely abrogated by the ANG II blocker candesartan but not affected by spironolactone at 15 and 30 min. For Aldo, the response was similar to that found for the lowest dose of ANG II infused. For the two highest ANG II doses given (Hi-Int-ANG II and Hi-ANG II), GFR decreased transiently, concomitant with marked, sustained increases in MAP. Nimodipine completely blocked all hemodynamic ANG II actions, whereas the glomerular permeability response remained unchanged. Thus ANG II directly increased glomerular permeability independently of its hemodynamic actions and largely independently of the concomitant Aldo response. The ANG II-induced increases in glomerular permeability were, according to a two-pore and a log-normal distributed pore model, compatible with an increased number of "large pores" in the glomerular filter, and, to some extent, an increase in the dispersity of the small-pore radius.

High-dose fasudil preserves postconditioning against myocardial infarction under hyperglycemia in rats: role of mitochondrial KATP channels

BACKGROUND

The current study was carried out to determine whether fasudil hydrochloride (fasudil), a Rho-kinase inhibitor, has myocardial postconditioning (PostC) activity under hyperglycemia as well as normoglycemia, and if so, whether the effects could be mediated by mitochondrial ATP-sensitive potassium (m-KATP) channels.

METHODS

Male Sprague-Dawley rats were anesthetized with sodium pentobarbital. After opening the chest, all rats underwent 30-min coronary artery occlusion followed by 2-h reperfusion. The rats received low-dose (0.15 mg/kg) or high-dose (0.5 mg/kg) fasudil or diazoxide, an m-KATP channel opener, at 10 mg/kg, just before reperfusion under normoglycemic or hyperglycemic conditions. In another group, rats received 5-hydroxydecanoic acid (5HD), an m-KATP channel blocker, at 10 mg/kg, before high-dose fasudil. Myocardial infarct size was expressed as a percentage of area at risk (AAR).

RESULTS

Under normoglycemia, low-dose and high-dose fasudil and diazoxide reduced myocardial infarct size (23 ± 8%, 21 ± 9% and 21 ± 10% of AAR, respectively) compared with that in the control (42 ± 7%). Under hyperglycemia, low-dose fasudil (40 ± 11%) and diazoxide (44 ± 14%) could not exert this beneficial effect, but high-dose fasudil reduced myocardial infarct size in the same manner as under normoglycemia (21 ± 13%). 5HD prevented fasudil-induced reduction of myocardial infarct size (42 ± 13%).

CONCLUSION

Fasudil induces PostC against myocardial infarction via activation of m-KATP channels in the rat. Although hyperglycemia attenuates the PostC, high-dose fasudil can restore cardioprotection.

Acute and sustained actions of hyperglycaemia on endothelial and glomerular barrier permeability

Microalbuminuria is an established marker of systemic endothelial dysfunction, which for patients with diabetes signals an increased risk of both diabetic nephropathy and cardiovascular complications. A better understanding of the pathogenesis of microalbuminuria is important in the quest of finding new approaches to treat patients with diabetes. Direct acute effects of episodes of hyperglycaemia (HG) could have implications for the microalbuminuria seen in early diabetes before renal structural alterations have started, especially in those patients with poor glycaemic control. This review summarizes the literature evidence that acute or sustained HG may lead to an increased vascular or glomerular permeability. Special focus is on glomerular barrier permeability. There is evidence in the literature that HG increases systemic capillary and glomerular barrier permeability within 20-30 min in vivo in rats and mice. Furthermore, exposure of monolayers of cultured endothelial cells to HG has been shown to increase monolayer permeability rapidly and transiently (during 60-100 min). Instant cellular changes following F-actin cytoskeleton rearrangements, which could be abrogated by Rho-kinase (ROCK) inhibition, are implicated. Data in this review also suggest that activation of protein kinase C, the polyol pathway, and an increased release of reactive oxygen species (ROS) and cytokines could contribute to the increase in barrier permeability induced by HG. Recent in vitro data from cultured podocyte monolayers also designates a role of insulin in acute podocyte F-actin remodelling, underpinning the complexity of the mechanisms leading to glomerular and endothelial barrier alterations in diabetes mellitus.

Rho kinase inhibition in diabetic nephropathy

PURPOSE OF REVIEW

The Rho GTPases and their downstream effectors Rho-associated kinases (ROCKs) appear to be the molecules that converge numerous pathophysiological signals triggered by the diabetic milieu and represent promising molecular targets for nephroprotective treatment in diabetes. The review discusses recent studies exploring the consequences of diabetes-induced Rho-ROCK activation in the kidney and the effects of ROCK inhibition (ROCKi) in experimental diabetic nephropathy.

RECENT FINDINGS

Recent studies in models of type 1 and type 2 diabetes have indicated blood-pressure-independent nephroprotective actions of ROCKi in diabetic nephropathy. The underlying mechanisms include attenuation of diabetes-induced increases in renal expression of prosclerotic cytokines and extracellular matrix, resulting in slower development of glomerulosclerosis and interstitial fibrosis. The studies have also shown antiproteinuric affects of ROCKi that could be related to reductions in permeability of glomerular barrier and beneficial effects on podocytes. Moreover hemodynamic mechanisms might be also involved.

SUMMARY

Despite remaining questions in this field, such as the specificity of currently available ROCKi, or the roles of individual ROCK isoforms, recent evidence in experimental diabetes, together with evidence generated in models of nondiabetic kidney disease and in clinical studies in patients with various cardiovascular disorders, suggest that ROCKi might in future broaden the spectrum of treatments available for patients with diabetic nephropathy.

Permeability of Peritoneal and Glomerular Capillaries: What are the Differences According to Pore Theory?

Pore and fiber-matrix theory can both be used to model the peritoneal and glomerular filtration barriers in an attempt to shed light on their differing structure–function relationships. The glomerular filtration barrier (GFB) is structurally more specialized, morphologically complex, and also highly dynamic; but paradoxically, because of its uniformity, it conforms more closely to the predictions of pore theory than does the peritoneum, and it in fact resembles a more simple synthetic membrane. Compared with the peritoneal capillary wall, the GFB has no transcellular “third” pores (aquaporins), and it is far less leaky and more size-selective to proteins, mainly as a result of having far fewer “large” pores. It does have charge-selective properties, although these are considered much less important in excluding albumin than was once thought, and it is also able to select polymers according to their shape and flexibility. Even this property might reflect the relative uniformity of the GFB, which has a high diffusion area and short diffusion distances, compared with the peritoneal barrier, which behaves more like a gel filtration column. Furthermore, the length of the diffusion path across the peritoneal membrane is much greater for small solutes, given the relatively high ultrafiltration coefficient for that membrane compared with the GFB—a situation that reflects both the tortuosity of the interendothelial clefts and the distribution of peritoneal capillaries within the interstitium. These comparisons reveal the peritoneal barrier as a relatively complex structure to model; and yet this model may be more representative of the general microcirculation, and thus shed light on systemic endothelial function in renal failure.

PKC alpha mediates beta-arrestin2-dependent nephrin endocytosis in hyperglycemia

Nephrin, the key molecule of the glomerular slit diaphragm, is expressed on the surface of podocytes and is critical in preventing albuminuria. In diabetes, hyperglycemia leads to the loss of surface expression of nephrin and causes albuminuria. Here, we report a mechanism that can explain this phenomenon: hyperglycemia directly enhances the rate of nephrin endocytosis via regulation of the β-arrestin2-nephrin interaction by PKCα. We identified PKCα and protein interacting with c kinase-1 (PICK1) as nephrin-binding proteins. Hyperglycemia induced up-regulation of PKCα and led to the formation of a complex of nephrin, PKCα, PICK1, and β-arrestin2 in vitro and in vivo. Binding of β-arrestin2 to the nephrin intracellular domain depended on phosphorylation of nephrin threonine residues 1120 and 1125 by PKCα. Further, cellular knockdown of PKCα and/or PICK1 attenuated the nephrin-β-arrestin2 interaction and abrogated the amplifying effect of high blood glucose on nephrin endocytosis. In C57BL/6 mice, hyperglycemia over 24 h caused a significant increase in urinary albumin excretion, supporting the concept of the rapid impact of hyperglycemia on glomerular permselectivity. In summary, we have provided a molecular model of hyperglycemia-induced nephrin endocytosis and subsequent proteinuria and highlighted PKCα and PICK1 as promising therapeutic targets for diabetic nephropathy.

Transient and sustained increases in glomerular permeability following ANP infusion in rats

The present study was performed to investigate the effects of systemic atrial natriuretic peptide (ANP) infusion on the glomerular permeability to macromolecules in rats. In anesthetized Wistar rats (250–280 g), the left urether was cannulated for urine collection while simultaneously blood access was achieved. Rats were continuously infused intravenously with ANP [30 ng·kg−1·min−1 (Lo-ANP; n = 8) or 800 ng·kg−1·min−1 (Hi-ANP; n = 10)] or 0.9% NaCl (SHAM; n = 16), respectively, and with polydisperse FITC-Ficoll-70/400 (molecular radius 13–90 Å) and 51Cr-EDTA for 2 h. Plasma and urine samples were taken at 5, 15, 30, 60, and 120 min of ANP infusion and analyzed by high-performance size-exclusion chromatography (HPLC) for determination of glomerular sieving coefficients (θ) for Ficoll. GFR was also assessed (51Cr-EDTA). In Hi-ANP, there was a rapid (within 5 min), but bimodal, increase in glomerular permeability. θ to high-molecular-weight Ficoll thus reached a maximum at 15 min, after which θ returned to near control at 30 min, to again increase moderately at 60 and 120 min. In Lo-ANP, there was also a rapid, reversible increase in glomerular θ, returning to near control at 30 min, followed by just a tendency of a sustained increase in permeability, but with a significant increase in “large-pore” radius. In conclusion, in Hi-ANP there was a rapid increase in glomerular permeability, with an early, partly reversible permeability peak, followed by a (moderate) sustained increase in permeability. In Lo-ANP animals, only the initial permeability peak was evident. In both Lo-ANP and Hi-ANP, the glomerular sieving pattern observed was found to mainly reflect an increase in the number and radius of large pores in the glomerular filter.