Hypertension and kidneys: unraveling complex molecular mechanisms underlying hypertensive renal damage

Management of Hypertension in CAKUT: Protective Factor for CKD

Patients with congenital kidney and urinary tract abnormalities (CAKUT) will often develop end-stage renal disease at some point and the need for renal replacement therapy is associated with high rates of morbidity and mortality. Hence, efforts to slow the progression of the disease are essential. Hypertension has been proven to be an independent risk factor for faster decline of glomerular filtration rate in renal patients, but studies involving only children with CAKUT are scarce. We performed a literature review to explore the association of hypertension with faster chronic kidney disease progression in children with CAKUT and also treatment options in this condition. A recent study reported an annual decline in GFR of 1.8 ml/min/1.73 m² among hypertensive patients with non-glomerular CKD, compared with 0.8 ml/min/1.73 m² in normotensive children. A multicenter prospective cohort in Brazil showed that a 1-unit increase in systolic blood pressure Z-score was associated with a 1.5-fold higher risk of disease progression. Since renin-angiotensin-aldosterone system activation is the most important mechanism of hypertension in these children, the first-line therapy involves the use of inhibitors of this axis, including angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers type I, which also promote an anti-fibrotic effect. Recent studies have shown a good safety profile for use in patients with chronic kidney disease and also in those with solitary kidneys. Hypertension is an independent risk factor for kidney disease progression and should be promptly managed for renal protection, especially among patients with CAKUT, the primary cause of chronic kidney disease in the pediatric population.

Naringenin Ameliorates Renovascular Hypertensive Renal Damage by Normalizing the Balance of Renin-Angiotensin System Components in Rats

Background: Naringenin, a member of the dihydroflavone family, has been shown to have a protective function in multiple diseases. We previously demonstrated that naringenin played a protective role in hypertensive myocardial hypertrophy by decreasing angiotensin-converting enzyme (ACE) expression. The kidney is a primary target organ of hypertension. The present study tested the effect of naringenin on renovascular hypertensive kidney damage and explored the underlying mechanism. Methods and Results: An animal model of renovascular hypertension was established by performing 2-kidney, 1-clip (2K1C) surgery in Sprague Dawley rats. Naringenin (200 mg/kg/day) or vehicle was administered for 10 weeks. Blood pressure and urinary protein were continuously monitored. Plasma parameters, renal pathology and gene expression of nonclipped kidneys were evaluated by enzyme-linked immunosorbent assay, histology, immunohistochemistry, real-time polymerase chain reaction, and Western blot at the end of the study. Rats that underwent 2K1C surgery exhibited marked elevations of blood pressure and plasma Ang II levels and renal damage, including mesangial expansion, interstitial fibrosis, and arteriolar thickening in the nonclipped kidneys. Naringenin significantly ameliorated hypertensive nephropathy and retarded the rise of Ang II levels in peripheral blood but had no effect on blood pressure. 2K1C rats exhibited increases in the ACE/ACE2 protein ratio and AT1R/AT2R protein ratio in the nonclipped kidney compared with sham rats, and these increases were significantly suppressed by naringenin treatment. Conclusions: Naringenin attenuated renal damage in a rat model of renovascular hypertension by normalizing the imbalance of renin-angiotensin system activation. Our results suggest a potential treatment strategy for hypertensive nephropathy.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Apocynin combined with drugs as coadjuvant could be employed to prevent and/or treat the chronic kidney disease

A worldwide public health problem is chronic kidney disease (CKD) presenting alarming epidemiological data. It currently affects about 10% of the adult population worldwide and has a high mortality rate. It is now known that oxidative stress represents one of the most important mechanisms in its pathophysiology, from the early stages to the terminal phase. Oxidation increases inflammation and reduces the capacity of NO• to relax vascular smooth muscle, in part by decreasing bioavailability of tetrahydrobiopterin (BH4), leading to endothelial dysfunction and high blood pressure, and due to the limited effectiveness of existing treatments, new drugs are needed to prevent and/or treat these mechanisms. The aim of this study was to test apocynin in a 5/6 nephrectomy mouse model of CKD to investigate whether its known antioxidant effect can improve the disease outcome. This effect results from the inhibition of NADPH oxidase and consequently a reduced production of the superoxide anion ([Formula: see text]). Animals were divided into five groups: sham, 5/6 nephrectomy only, and 5/6 nephrectomy followed by treatment with captopril, losartan or apocynin. The parameters evaluated were blood pressure and markers of oxidative stress ([Formula: see text]) and endothelial function (BH4). There were significantly lower levels of [Formula: see text] and a greater availability of serum BH4 in the apocynin-treated animals versus the control group and the two other drug treatments. The present findings suggest that apocynin in conjunction with a coadjuvant for modulating blood pressure may be useful for controlling the progression of CRF.

Epidemiology and Risk Factors for Kidney Cancer

The purpose of this narrative review is to summarize evidence of the epidemiology of and risk factors for kidney cancer with a focus on renal cell carcinoma in adults. The etiology of kidney cancer is largely unknown and the main epidemiologic determinants are large geographic and temporal variations in incidence rates. Established risk factors include tobacco smoking, body size, and history of hypertension and chronic kidney disease. Other suspected risk factors require additional investigation, as do the underlying biologic mechanisms that are responsible for disease occurrence. Opportunities to prevent kidney cancer include targeting modifiable risk factors-for example, smoking abstinence/cessation and body weight control-as well as interventions along the diagnostic pathway to improve early diagnosis. Molecular epidemiology, including, but not limited to, metabolomics and tumor genomics, are new areas of research that promise to play important roles in identifying some of the underlying causes of kidney cancer.

Pancreas grafts for transplantation from donors with hypertension: an analysis of the scientific registry of transplant recipients database

BACKGROUND

With the rising demands for pancreas transplantation, surgeons are trying to extend the donors pool and set up a more appropriate assessment system. We aim to evaluate the effect of donor hypertension on recipient overall and graft survival rates.

METHODS

Twenty-four thousand one hundred ninety-two pancreas transplantation patients from the Scientific Registry of Transplant Recipients database were subdivided into hypertension group (HTN, n = 1531) and non-hypertension group (non-HTN, n = 22,661) according to the hypertension status of donors. Recipient overall and graft survival were analyzed and compared by log rank test, and hazard ratios of predictors were estimated using Cox proportional hazard models.

RESULTS

Patient overall and graft survival of non-HTN group were higher than that of the HTN group (both p < 0.001). The duration of hypertension negatively influenced both overall and graft survival rates (both p < 0.001). Multivariate analyses demonstrated that hypertension was an independent factor for reduced survival (hazard ratio [HR], 1.10; 95% confidence interval [CI], 1.01-1.18; p < 0.001). Other independent factors included recipient body mass index (HR, 1.02; 95% CI, 1.01-1.05; p < 0.001) and transplant type (pancreas after kidney transplants / pancreas transplant alone vs. simultaneous pancreas-kidney transplants; HR, 1.41; 95% CI, 134-1.55; p < 0.001).

CONCLUSIONS

Donor hypertension is an independent factor for recipient survival after pancreas transplantation and could be considered in donor selection as well as post-transplant surveillance in clinical practice.

The association of miR-29a with proteinuria in essential hypertension

Recently, miRNAs have emerged as new indirect markers of inflammation that are associated with adverse outcomes in cardiovascular disease. The aim of the study was to evaluate the relationship between miR29a and proteinuria in hypertension. Fifty patients with normal albuminuria, fifty patients with micro-albuminuria, and fifty patients with macro-albuminuria were enrolled. The highest levels of miR-29a and transforming growth factor-β1 (TGF-β1) were observed in the macro-albuminuria group, followed by the micro-albuminuria and the normal albuminuria groups. The level of miR-29a was negatively correlated with the glomerular filtration rate, but was positively correlated with C-reactive protein, TGF-β1, and the urinary albumin to creatinine ratio (UACR). Circulating miR-29a was found to be significantly and independently associated with proteinuria. Our findings showed that miR-29a reflects the pathogenesis of hypertensive nephropathy and may serve as a potential non-invasive marker for detecting early stages of hypertensive nephropathy.

Anthropometric and Biochemical Determinants of Estimated Glomerular Filtration Rate in a Large Cohort of Obese Children

OBJECTIVE

We aimed to investigate which clinical and metabolic factors could influence the estimated glomerular filtration rate (eGFR) levels, evaluating a large population of obese children without suspect of primary kidney disease.

DESIGN

Retrospective, cross-sectional study.

SETTING

Pediatric university department.

SUBJECTS

We enrolled 2,957 obese children and adolescents consecutively attending our department between January 2000 and 2017. Inclusion criteria were body mass index (BMI) > 95th percentile and eGFR > 90 mL/min/1.73 m². Exclusion criteria were secondary forms of obesity, eGFR < 90 mL/min/1.73 m², proteinuria/hematuria at urine dipstick, or consumption of any medication.

INTERVENTIONS

Weight, waist circumference, height, waist to height ratio (W/Hr), BMI-standard deviation score (SDS), pubertal stage, systolic blood pressure (SBP) and diastolic blood pressure (DBP), duration of obesity, insulin, eGFR, and homeostasis model assessment (HOMA-IR) were obtained. A general linear model was performed for a multiple variable analysis.

MAIN OUTCOME MEASURE

The population was divided in tertiles for BMI-SDS, W/Hr, SBP- and DBP-SDS, HOMA-IR, and duration of obesity. We compared eGFR levels among these tertiles.

RESULTS

The eGFR levels significantly increased across both BMI-SDS and W/Hr tertiles. Conversely the eGFR levels significantly decreased across SBP-SDS, HOMA-IR, and duration of obesity tertiles. No significant differences in eGFR levels across DBP-SDS tertiles were detected. Pubertal patients presented significantly lower eGFR values compared with prepubertal patients. A general linear model for eGFR variance including as covariates W/Hr, HOMA-IR, duration of obesity, pubertal stage, BMI-SDS, and SBP-SDS (model R² 39.7%; model P < .00001) was performed. It confirmed a direct association of eGFR values with BMI-SDS and an indirect association with HOMA-IR, duration of obesity, pubertal stage, and SBP-SDS.

CONCLUSIONS

We showed a positive correlation of eGFR with both BMI-SDS and a negative one with SBP-SDS, HOMA-IR, pubertal stage, and duration of obesity. The duration of obesity was the variable most significantly associated to eGFR levels.

BCL6 attenuates renal inflammation via negative regulation of NLRP3 transcription

Renal inflammation contributes to the pathogeneses of hypertension. This study was designed to determine whether B-cell lymphoma 6 (BCL6) attenuates renal NLRP3 inflammasome activation and inflammation and its underlying mechanism. Male spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) were used in the present study. Angiotensin (Ang) II or lipopolysaccharides (LPS) was used to induce inflammation in HK-2 cells, a human renal tubular epithelial (RTE) cell line. NLRP3 inflammasome was activated and BCL6 was downregulated in the kidneys of SHR. Either Ang II or LPS suppressed BCL6 expression in HK-2 cells. BCL6 overexpression in HK-2 cells attenuated Ang II-induced NLRP3 upregulation, inflammation and cell injury. The inhibitory effects of BCL6 overexpression on NLRP3 expression and inflammation were also observed in LPS-treated HK-2 cells. BCL6 inhibited the NLRP3 transcription via binding to the NLRP3 promoter. BCL6 knockdown with shRNA increased NLRP3 and mature IL-1β expression levels in both PBS- or Ang II-treated HK-2 cells but had no significant effects on ASC, pro-caspase-1 and pro-IL-1β expression levels. BCL6 overexpression caused by recombinant lentivirus expressing BCL6 reduced blood pressure in SHR. BCL6 overexpression prevented the upregulation of NLRP3 and mature IL-1β expression levels in the renal cortex of SHR. The results indicate that BCL6 attenuates Ang II- or LPS-induced inflammation in HK-2 cells via negative regulation of NLRP3 transcription. BCL6 overexpression in SHR reduced blood pressure, NLRP3 expression and inflammation in the renal cortex of SHR.

Oxidative imbalance and kidney damage in spontaneously hypertensive rats: activation of extrinsic apoptotic pathways

In both humans and animals, essential hypertension acts as a risk factor for subclinical kidney damage and precedes renal dysfunction. Several lines of evidence indicate that hypertension and oxidative stress are closely related. The increase in vascular oxidative stress plays a key role in the pathophysiological consequences of hypertension, including kidney disease. Our study examined this issue in spontaneously hypertensive rat (SHR), a reliable model of essential hypertension. We used SHR 20 weeks old when hypertension is stably developed, vascular remodeling started, but kidney function is preserved. We examined plasmatic pro-oxidant and antioxidant status showing a significant alteration in oxidative balance in SHR. As index of oxidative damage, we evaluated lipid peroxidation in kidney, liver, and skeletal muscle, detecting a significant rise in lipid peroxidation levels in all SHR tissues, particularly relevant in kidney. In addition, we analyzed the expression of cytoplasmic antioxidant enzymes, superoxide dismutase 1 (SOD1) and glutatione S-tranferasi P1 (GSTP1). In SHR liver, SOD1 expression slight increased while we have not detected any variation in other tissues. Concerning GSTP1, SHR renal tissues did not display variations in enzyme expression, while in the other tissues, we observed a significant increase in both monomeric and pro-apoptotic dimeric form of the enzyme. By analyzing apoptotic signal, we founded c-Jun N-terminal kinase (JNK) activation in all SHR tissues, but only kidney presented extrinsic apoptotic pathway activation. Our results suggest that, in hypertensive animals with preserved renal function, despite the remarkable oxidative damage of renal tissues, only the extrinsic apoptotic pathway is activated.

Renalase Protects against Renal Fibrosis by Inhibiting the Activation of the ERK Signaling Pathways

Renal interstitial fibrosis is a common pathway for the progression of chronic kidney disease (CKD) to end-stage renal disease. Renalase, acting as a signaling molecule, has been reported to have cardiovascular and renal protective effects. However, its role in renal fibrosis remains unknown. In this study, we evaluated the therapeutic efficacy of renalase in rats with complete unilateral ureteral obstruction (UUO) and examined the inhibitory effects of renalase on transforming growth factor-β1 (TGF-β1)-induced epithelial-mesenchymal transition (EMT) in human proximal renal tubular epithelial (HK-2) cells. We found that in the UUO model, the expression of renalase was markedly downregulated and adenoviral-mediated expression of renalase significantly attenuated renal interstitial fibrosis, as evidenced by the maintenance of E-cadherin expression and suppressed expression of α-smooth muscle actin (α-SMA), fibronectin and collagen-I. In vitro, renalase inhibited TGF-β1-mediated upregulation of α-SMA and downregulation of E-cadherin. Increased levels of Phospho-extracellular regulated protein kinases (p-ERK1/2) in TGF-β1-stimulated cells were reversed by renalase cotreatment. When ERK1 was overexpressed, the inhibition of TGF-β1-induced EMT and fibrosis mediated by renalase was attenuated. Our study provides the first evidence that renalase can ameliorate renal interstitial fibrosis by suppression of tubular EMT through inhibition of the ERK pathway. These results suggest that renalase has potential renoprotective effects in renal interstitial fibrosis and may be an effective agent for slowing CKD progression.

Protective effects of nebivolol from oxidative stress to prevent hypertension-related target organ damage

Hypertension is one of the leading risk factors for morbidity and mortality in patients with cardiovascular and cerebrovascular diseases and renal impairment. It also leads to target organ damage (TOD), which worsens organ function and the patient's clinical status. Reactive oxygen species (ROS)-mediated oxidative stress may contribute significantly to TOD in patients with hypertension. NO (nitric oxide) is a paracrine factor derived from endothelial cells that has been shown to alleviate ROS-mediated oxidative damage. Nebivolol is a third-generation β-blocker with vasodilator activity, both actions contributing to decreased blood pressure in hypertensive patients. Its vasodilatory function is mediated by the endothelial l-arginine NO pathway. Nebivolol increases the bioavailability of NO in the vasculature. Its efficacy and safety profile is comparable to other commonly used antihypertensive agents. In this article, we review the current literature to understand TOD secondary to oxidative stress in patients with hypertension and the role of nebivolol in its prevention. A better understanding of the underlying mechanisms by which nebivolol reduces ROS-mediated TOD will not only help in the development of targeted therapies but may also improve health outcomes in hypertensive patients.

Different regulation of miR-29a-3p in glomeruli and tubules in an experimental model of angiotensin II-dependent hypertension: potential role in renal fibrosis

The aim of this study was to evaluate the role of the angiotensin II (Ang II) induced-differential miRNA expression in renal glomerular and tubulo-interstitial fibrosis in an experimental model of Ang II-dependent hypertension. To clarify this issue, Sprague Dawley rats were treated with Ang II (200 ng/kg per minute, n = 15) or physiological saline (n = 14) for 4 weeks. Systolic blood pressure and albuminuria were measured every 2 weeks. At the end of the experimental period, renal glomerular and tubulo-interstitial fibrosis was evaluated by histomorphometric analysis, after Sirius-Red and Masson's trichrome staining. Ang II increased systolic blood pressure (P < 0.0001), albuminuria (P < 0.01) and both glomerular and tubulo-interstitial fibrosis (P < 0.01). Using laser capture microdissection and miRNA microarray analysis this study showed that miR-29a-3p was down-regulated in renal tubules and up-regulated in glomeruli. Real-time polymerase chain reaction (PCR) experiments confirmed in Ang II-treated rats a down-regulation of miR-29a-3p in tubules (P < 0.01), while no significant changes were observed in glomeruli. Matrix metalloproteinase-2 (MMP-2) was identified as putative miR-29a-3p target (by TargetScan, miRanda, Tarbase software) and functionally confirmed by luciferase activity assay. These data demonstrate that the effects of Ang II on miR-29a-3p expression in renal tubules is different from the one exerted in the glomeruli and that miR-29a-3p targets MMP-2. These results suggest that the development of renal fibrosis at glomerular and tubulo-interstitial level depends on different molecular mechanisms.

The angiotensin-I converting enzyme gene I/D variation contributes to end-stage renal disease risk in Chinese patients with type 2 diabetes receiving hemodialysis

Whether the DD genotype of the angiotensin-I converting enzyme (ACE) I/D variation contributes to end-stage renal disease (ESRD) risk in type 2 diabetes mellitus (T2DM) remains controversial. Differences in study design, case and control definition, sample size and ethnicity may contribute to the discrepancies reported in association studies. We performed a case-control study to evaluate the association of the ACE I/D variation with ESRD risk in Chinese patients with T2DM receiving hemodialysis and analyzed the genotype-phenotype interaction. Unrelated Chinese patients (n = 432) were classified into the non-diabetic nephropathy (DN) control group (n = 222, duration of diabetes >10 years, no signs of renal involvement) and the DN-ESRD group (n = 210; ESRD due to T2DM, receiving hemodialysis). Polymerase chain reaction was used to genotype ACE I/D for all 432 subjects. The frequencies of the ID + DD genotypes were higher in the DN-ESRD group than non-DN control group (65.2 vs. 50.9 %; adjusted OR 1.98 (95 % CI, 1.31-3.00; P = 0.001). In the DN-ESRD group, the DD genotypic subgroup had significantly elevated HbA1c and diastolic blood pressure (DBP) compared to the II subgroup (both P < 0.05). The DD genotype of the ACE I/D variation may be associated with more elevated blood pressure and HbA1c, and therefore may predict the development, progression and severity of DN-ESRD in Chinese patients with T2DM undergoing hemodialysis.

Low potassium excretion but not high sodium excretion is associated with increased risk of developing chronic kidney disease

It is unclear whether sodium and potassium intake is relevant to the development of chronic kidney disease (CKD) in the general population. Our aim was to examine the associations of urinary sodium (UNaV) and potassium excretion (UKV), as estimates of intake, with risk of developing CKD in a population-based cohort. We studied 5315 individuals free of CKD at baseline of the Prevention of Renal and Vascular End-Stage Disease (PREVEND) study, a prospective, population-based cohort of Dutch men and women aged 28 to 75 years. UNaV and UKV were measured in two 24-hour urine specimens at baseline (1997-1998) and midway during follow-up (2001-2003). CKD was defined as de novo development of eGFR under 60 ml/min per 1.73 m(2) or albuminuria over 30 mg/24 hours, or both. Baseline UNaV and UKV were 135 mmol/24 hours (interquartile range: 106-169 mmol/24 hours) and 70 mmol/24 hours (interquartile range, 57-85 mmol/24 hours), respectively. During a median follow-up of 10.3 years, 872 patients developed CKD. After multivariable adjustment for important covariables, no association was observed between UNaV and risk of CKD (hazard ratio per 50 mmol/24 hours [1 SD] increment, 0.97; 95% confidence interval, 0.89-1.06). Each 21 mmol/24 hours (1 SD) decrement in UKV was significantly associated with a 16% higher risk of developing CKD (multivariable-adjusted hazard ratio, 1.16; 95% confidence interval, 1.06-1.28). Thus, low UKV, and not high UNaV, was associated with an increased risk of developing CKD in a population-based cohort with normal kidney function.

CXCL16 Deficiency Attenuates Renal Injury and Fibrosis in Salt-Sensitive Hypertension

Inflammation plays an important role in the pathogenesis of hypertensive kidney disease. However, the molecular mechanisms underlying the induction of inflammation are not completely understood. We have found that CXCL16 is induced in the kidney in deoxycorticosterone acetate (DOCA)-salt hypertension. Here we examined whether CXCL16 is involved in DOCA-salt-induced renal inflammation and fibrosis. Wild-type and CXCL16 knockout mice were subjected to uninephrectomy and DOCA-salt treatment for 3 weeks. There was no difference in blood pressure at baseline between wild-type and CXCL16 knockout mice. DOCA-salt treatment resulted in significant elevation in blood pressure that was comparable between wild-type and CXCL16 knockout mice. CXCL16 knockout mice exhibited less severe renal dysfunction, proteinuria, and fibrosis after DOCA-salt treatment compared with wild-type mice. CXCL16 deficiency attenuated extracellular matrix protein production and suppressed bone marrow–derived fibroblast accumulation and myofibroblast formation in the kidneys following DOCA-salt treatment. Furthermore, CXCL16 deficiency reduced macrophage and T cell infiltration into the kidneys in response to DOCA-salt hypertension. Taken together, our results indicate that CXCL16 plays a key role in the pathogenesis of renal injury and fibrosis in salt-sensitive hypertension through regulation of bone marrow–derived fibroblast accumulation and macrophage and T cell infiltration.

Role of the Renin-Angiotensin-Aldosterone System beyond Blood Pressure Regulation: Molecular and Cellular Mechanisms Involved in End-Organ Damage during Arterial Hypertension

Arterial hypertension is a common condition worldwide and an important predictor of several complicated diseases. Arterial hypertension can be triggered by many factors, including physiological, genetic, and lifestyle causes. Specifically, molecules of the renin-angiotensin-aldosterone system not only play important roles in the control of blood pressure, but they are also associated with the genesis of arterial hypertension, thus constituting a need for pharmacological interventions. Chronic high pressure generates mechanical damage along the vascular system, heart, and kidneys, which are the principal organs affected in this condition. In addition to mechanical stress, hypertension-induced oxidative stress, chronic inflammation, and the activation of reparative mechanisms lead to end-organ damage, mainly due to fibrosis. Clinical trials have demonstrated that renin-angiotensin-aldosterone system intervention in hypertensive patients lowers morbidity/mortality and inflammatory marker levels as compared to placebo patients, evidencing that this system controls more than blood pressure. This review emphasizes the detrimental effects that a renin-angiotensin-aldosterone system (RAAS) imbalance has on health considerations above and beyond high blood pressure, such as fibrotic end-organ damage.

Protective effects of Brassica oleracea sprouts extract toward renal damage in high-salt-fed SHRSP: role of AMPK/PPARα/UCP2 axis

OBJECTIVES

Renal damage precedes occurrence of stroke in high-sodium/low-potassium-fed stroke-prone spontaneously hypertensive rat (SHRSP). We previously reported a marked suppression of uncoupling protein-2 (UCP2) upon high-salt Japanese-style diet in SHRSP kidneys. Vegetable compounds are known to exert protective effects in cardiovascular diseases. We aimed at evaluating the impact of Brassica oleracea sprouts juice toward renal damage in Japanese diet-fed SHRSP and exploring the role of 5'-adenosine monophosphate-activated protein kinase (AMPK)/NAD-dependent deacetylase sirtuin-1 (SIRT1)/peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α)/peroxisome proliferator-activated receptor-α (PPARα)/UCP2 axis.

METHODS

SHRSP received Japanese diet for 4 weeks. A group of SHRSP received Japanese diet and B. oleracea. A third group received Japanese diet, B. oleracea, and PPARα inhibitor (GW6471). A group of SHRSP fed with regular diet served as control.

RESULTS

Japanese diet induced marked increases of oxidative stress, inflammation, and proteinuria, along with glomerular and tubular damage, as compared with regular diet. A significant suppression of AMPK/UCP2 pathway was observed. Despite Japanese diet feeding, concomitant administration of B. oleracea prevented oxidative stress accumulation, inflammation, renal damage, and proteinuria. All components of the UCP2 regulatory pathway were significantly increased by B. oleracea. Superoxide dismutase 2 and phosphoendothelial nitric oxide synthase were also stimulated. Addition of PPARα inhibitor to B. oleracea and Japanese diet significantly reduced the B. oleracea beneficial effects. SBP levels were comparable among the different groups of rats.In vitro, UCP2 inhibition by genipin offset the antioxidant effect of B. oleracea in renal mesangial and proximal tubular cells.

CONCLUSION

B. oleracea administration prevented renal damage in salt-loaded SHRSP, independently from SBP, with parallel stimulation of AMPK/SIRT1/PGC1α/PPARα/UCP2 axis. Stimulation of the latter mechanism may provide relevant renal protective effect and play a therapeutic role in target organ damage progression in hypertension.

Endothelial Gata5 transcription factor regulates blood pressure

Despite its high prevalence and economic burden, the aetiology of human hypertension remains incompletely understood. Here we identify the transcription factor GATA5, as a new regulator of blood pressure (BP). GATA5 is expressed in microvascular endothelial cells and its genetic inactivation in mice (Gata5-null) leads to vascular endothelial dysfunction and hypertension. Endothelial-specific inactivation of Gata5 mimics the hypertensive phenotype of the Gata5-null mice, suggestive of an important role for GATA5 in endothelial homeostasis. Transcriptomic analysis of human microvascular endothelial cells with GATA5 knockdown reveals that GATA5 affects several genes and pathways critical for proper endothelial function, such as PKA and nitric oxide pathways. Consistent with a role in human hypertension, we report genetic association of variants at the GATA5 locus with hypertension traits in two large independent cohorts. Our results unveil an unsuspected link between GATA5 and a prominent human condition, and provide a new animal model for hypertension.

Unravelling the molecular basis of hypertension remains a major challenge. Here, the authors identify the transcription factor GATA5 as a novel regulator of blood pressure and potential genetic determinant of human hypertension and describe a unique mouse model for research of salt-sensitive hypertension.

Renal depletion of myo-inositol is associated with its increased degradation in animal models of metabolic disease

Renal depletion of myo-inositol (MI) is associated with the pathogenesis of diabetic nephropathy in animal models, but the underlying mechanisms involved are unclear. We hypothesized that MI depletion was due to changes in inositol metabolism and therefore examined the expression of genes regulating de novo biosynthesis, reabsorption, and catabolism of MI. We also extended the analyses from diabetes mellitus to animal models of dietary-induced obesity and hypertension. We found that renal MI depletion was pervasive across these three distinct disease states in the relative order: hypertension (−51%) > diabetes mellitus (−35%) > dietary-induced obesity (−19%). In 4-wk diabetic kidneys and in kidneys derived from insulin-resistant and hypertensive rats, MI depletion was correlated with activity of the MI-degrading enzyme myo-inositol oxygenase (MIOX). By contrast, there was decreased MIOX expression in 8-wk diabetic kidneys. Immunohistochemistry localized the MI-degrading pathway comprising MIOX and the glucuronate-xylulose (GX) pathway to the proximal tubules within the renal cortex. These findings indicate that MI depletion could reflect increased catabolism through MIOX and the GX pathway and implicate a common pathological mechanism contributing to renal oxidative stress in metabolic disease.

Podocyte Purinergic P2X4 Channels Are Mechanotransducers That Mediate Cytoskeletal Disorganization

Podocytes are specialized, highly differentiated epithelial cells in the kidney glomerulus that are exposed to glomerular capillary pressure and possible increases in mechanical load. The proteins sensing mechanical forces in podocytes are unconfirmed, but the classic transient receptor potential channel 6 (TRPC6) interacting with the MEC-2 homolog podocin may form a mechanosensitive ion channel complex in podocytes. Here, we observed that podocytes respond to mechanical stimulation with increased intracellular calcium concentrations and increased inward cation currents. However, TRPC6-deficient podocytes responded in a manner similar to that of control podocytes, and mechanically induced currents were unaffected by genetic inactivation of TRPC1/3/6 or administration of the broad-range TRPC blocker SKF-96365. Instead, mechanically induced currents were significantly decreased by the specific P2X purinoceptor 4 (P2X4) blocker 5-BDBD. Moreover, mechanical P2X4 channel activation depended on cholesterol and podocin and was inhibited by stabilization of the actin cytoskeleton. Because P2X4 channels are not intrinsically mechanosensitive, we investigated whether podocytes release ATP upon mechanical stimulation using a fluorometric approach. Indeed, mechanically induced ATP release from podocytes was observed. Furthermore, 5-BDBD attenuated mechanically induced reorganization of the actin cytoskeleton. Altogether, our findings reveal a TRPC channel-independent role of P2X4 channels as mechanotransducers in podocytes.

Pathogenesis of target organ damage in hypertension: role of mitochondrial oxidative stress

Hypertension causes target organ damage (TOD) that involves vasculature, heart, brain and kidneys. Complex biochemical, hormonal and hemodynamic mechanisms are involved in the pathogenesis of TOD. Common to all these processes is an increased bioavailability of reactive oxygen species (ROS). Both in vitro and in vivo studies explored the role of mitochondrial oxidative stress as a mechanism involved in the pathogenesis of TOD in hypertension, especially focusing on atherosclerosis, heart disease, renal failure, cerebrovascular disease. Both dysfunction of mitochondrial proteins, such as uncoupling protein-2 (UCP2), superoxide dismutase (SOD) 2, peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α), calcium channels, and the interaction between mitochondria and other sources of ROS, such as NADPH oxidase, play an important role in the development of endothelial dysfunction, cardiac hypertrophy, renal and cerebral damage in hypertension. Commonly used anti-hypertensive drugs have shown protective effects against mitochondrial-dependent oxidative stress. Notably, few mitochondrial proteins can be considered therapeutic targets on their own. In fact, antioxidant therapies specifically targeted at mitochondria represent promising strategies to reduce mitochondrial dysfunction and related hypertensive TOD. In the present article, we discuss the role of mitochondrial oxidative stress as a contributing factor to hypertensive TOD development. We also provide an overview of mitochondria-based treatment strategies that may reveal useful to prevent TOD and reduce its progression.

The association between underweight and the development of albuminuria is different between sexes in relatively healthy Korean subjects

BACKGROUND

There are limited data on the association between underweight and albuminuria. The aim of this study is to verify the effect of underweight on the development of albuminuria.

METHODS

Participants who underwent two health check-ups with a 2-year interval at a tertiary hospital in Korea between 2002 and 2009 were studied. After exclusion of participants with estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m(2) or dipstick albuminuria ≥1+ at the first check-up, 53 876 participants were enrolled. We measured the incidence of albuminuria at the second check-up and calculated the odds ratio (OR) for the development of albuminuria according to body mass index (BMI).

RESULTS

After 2 years, 746 cases of incident albuminuria were observed among 53 876 participants. The effect of BMI on the development of albuminuria was modified by sex in a multivariate logistic model with adjustment for age, diabetes, hypertension, dyslipidaemia, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, uric acid, eGFR, current smoking status and alcohol intake (P-value for interaction <0.001). Compared with participants in the normal weight range (BMI, 18.5-22.9), the ORs for incident albuminuria were 1.93 [95% confidence interval (CI), 1.35-2.76; P ≤ 0.001], 1.19 (0.84-1.67; P = 0.329) and 0.71 (0.43-1.17; P = 0.177) in underweight (BMI, <18.5), overweight (BMI, 23.0-24.9) and obese (BMI, ≥25) women. However, the ORs were 0.9 (95% CI, 0.39-2.05; P = 0.794), 1.08 (0.84-1.38; P = 0.567) and 1.38 (1.09-1.75; P = 0.007) for each corresponding group of men.

CONCLUSIONS

Underweight was significantly associated with the development of albuminuria after 2 years in relatively healthy Korean females, but this relationship was not significant in males. This study suggests the need for more studies on the role of underweight in renal injury in men and women.