Effect of dietary salt on regulation of TGF-β in the kidney

Canagliflozin and irbesartan ameliorate renal fibrosis via the TGF-β1/Smad signaling pathway in Dahl salt-sensitive rats

OBJECTIVES

This study assessed the antifibrotic effects of canagliflozin, with or without irbesartan, on renal injury in Dahl salt-sensitive (SS) rats fed a high-salt (HS) diet.

METHODS

After the preconditioning stage, Dahl SS rats (n = 47) were divided into five experimental groups as follows: low-salt (LS, n = 7), HS (n = 10), HS with canagliflozin (n = 10), HS with irbesartan (n = 10), and HS with canagliflozin and irbesartan (n = 10).

RESULTS

The HS diet increased systolic blood pressure (SBP), renal fibrosis, fibrotic protein expression, and transforming growth factor-β1 (TGF-β1)/Smad2/3 pathway protein expression compared with the findings in the LS group. Irbesartan reduced SBP and slowed the loss of renal function. Canagliflozin significantly reduced body weight and renal fibrosis and suppressed the TGF-β1/Smad2/3 pathway. The combined therapy exerted better renoprotective effects on all outcome parameters.

CONCLUSIONS

These results indicate that canagliflozin and irbesartan exert different effects on renal injury in SS hypertensive rats, and the combined regimen could have stronger effects than either monotherapy.

Hypertension in chronic kidney disease: What lies behind the scene

Hypertension is a frequent condition encountered during kidney disease development and a leading cause in its progression. Hallmark factors contributing to hypertension constitute a complexity of events that progress chronic kidney disease (CKD) into end-stage renal disease (ESRD). Multiple crosstalk mechanisms are involved in sustaining the inevitable high blood pressure (BP) state in CKD, and these play an important role in the pathogenesis of increased cardiovascular (CV) events associated with CKD. The present review discusses relevant contributory mechanisms underpinning the promotion of hypertension and their consequent eventuation to renal damage and CV disease. In particular, salt and volume expansion, sympathetic nervous system (SNS) hyperactivity, upregulated renin–angiotensin–aldosterone system (RAAS), oxidative stress, vascular remodeling, endothelial dysfunction, and a range of mediators and signaling molecules which are thought to play a role in this concert of events are emphasized. As the control of high BP via therapeutic interventions can represent the key strategy to not only reduce BP but also the CV burden in kidney disease, evidence for major strategic pathways that can alleviate the progression of hypertensive kidney disease are highlighted. This review provides a particular focus on the impact of RAAS antagonists, renal nerve denervation, baroreflex stimulation, and other modalities affecting BP in the context of CKD, to provide interesting perspectives on the management of hypertensive nephropathy and associated CV comorbidities.

The ubiquitin ligase NEDD4-2/NEDD4L regulates both sodium homeostasis and fibrotic signaling to prevent end-stage renal disease

Kidney disease progression can be affected by Na⁺ abundance. A key regulator of Na⁺ homeostasis is the ubiquitin ligase NEDD4-2 and its deficiency leads to increased Na⁺ transport activity and salt-sensitive progressive kidney damage. However, the mechanisms responsible for high Na⁺ induced damage remain poorly understood. Here we show that a high Na⁺ diet compromised kidney function in Nedd4-2-deficient mice, indicative of progression toward end-stage renal disease. Injury was characterized by enhanced tubule dilation and extracellular matrix accumulation, together with sustained activation of both Wnt/β-catenin and TGF-β signaling. Nedd4-2 knockout in cortical collecting duct cells also activated these pathways and led to epithelial-mesenchymal transition. Furthermore, low dietary Na⁺ rescued kidney disease in Nedd4-2-deficient mice and silenced Wnt/β-catenin and TGF-β signaling. Our study reveals the important role of NEDD4-2-dependent ubiquitination in Na⁺ homeostasis and protecting against aberrant Wnt/β-catenin/TGF-β signaling in progressive kidney disease.

Identification of Halophilic Microbes in Lung Fibrotic Tissue by Oligotyping

Idiopathic pulmonary fibrosis (IPF) is an incurable disease with poor prognosis and unknown etiology. The poor clinical outcome is associated with enhanced microbial burden in bronchoalveolar lavage fluid from IPF patients. However, whether microbes from the respiratory tract fluid cause the disease remains uncertain. Tissue-associated microbes can influence host physiology in health and disease development. The aim of this study was to evaluate the existence of microbes in lung fibrotic tissues. We evaluated the microbial community in lung tissues from IPF and from human transforming growth factor-β1 (TGF-β1) transgenic mice with lung fibrosis by oligotyping. We also evaluated the microbial population in non-tumor-bearing tissues from surgical specimens of lung cancer patients. The phyla Firmicutes and the genus Clostridium tended to be predominant in the lung tissue from IPF and lung cancer patients. Oligotyping analysis revealed a predominance of bacteria belonging to the genera Halomonas, Shewanella, Christensenella, and Clostridium in lung tissue from IPF and lung cancer. Evaluation of the microbial community in the lung tissue from mice revealed abundance of Proteobacteria in both wild-type (WT) littermates and transgenic mice. However, the genus Halomonas tended to be more abundant in TGF-β1 transgenic mice compared to WT mice. In conclusion, this study describes tissue-associated microbes in lung fibrotic tissues from IPF patients and from aging TGF-β1 transgenic mice.

Regulation of transforming growth factor β-mediated epithelial-mesenchymal transition of lens epithelial cells by c-Src kinase under high glucose conditions

Recent studies have reported that high glucose (HG) conditions may contribute to the acceleration of renal cell apoptosis and renal fibrosis by inducing epithelial-mesenchymal transition (EMT) of tubular epithelial cells, in which c-Src kinase and transforming growth factor (TGF)-β are key modulators. In the present study, the roles of c-Src kinase and TGF-β in EMT of lens epithelial cells (LECs) under HG conditions were investigated. Results indicated human lens epithelial B3 (HLE-B3) cells under HG conditions exhibited significantly increased protein expression levels of phosphorylated c-Src (p-Src⁴¹⁸) (P<0.05) and secreted a significantly increased amount of TGF-β compared with HLE-B3 cells under normal glucose conditions (P<0.05). Notably the c-Src inhibitor PP1 and the activin receptor-like kinase 5 (ALK5) inhibitor SB431542 suppressed EMT of HLE-B3 cells. Results indicated that PP1 significantly inhibited the activities of c-Src and ALK5 and the secretion of TGF-β, whereas SB431542 only significantly downregulated the protein expression levels and secretion of TGF-β (P<0.05). Following c-Src knockdown, the protein expression levels of p-Src⁴¹⁸, ALK5 and TGF-β were significantly decreased, the secretion of TGF-β was significantly suppressed (both P<0.05) and EMT was decreased in HLE-B3 cells. These results suggest that c-Src and TGF-β may promote EMT of LECs under HG conditions, with c-Src as the upstream regulatory molecule. Thus, the signal axis of c-Src/TGF-β in EMT of LECs may be a potential novel therapeutic target for the prevention of diabetic subcapsular cataract.

Management of Hypertension in Patients with Chronic Kidney Disease

Hypertension is the leading factor in the global burden of disease. It is the predominant modifiable risk factor for stroke, heart disease, and kidney failure. Chronic kidney disease (CKD) is both a common cause and sequel of uncontrolled hypertension. The pathophysiology of CKD-associated hypertension is complex and multi-factorial. This paper reviews the key pathogenic mechanisms of CKD-associated hypertension, the importance of standardized blood pressure (BP) measurement in establishing the diagnosis and management plus the significance of ambulatory BP monitoring for assessment of diurnal BP variation commonly seen in CKD. The optimal BP target in CKD remains a matter of discussion despite recent clinical trials. Medical therapy can be difficult and challenging. In addition to lifestyle modification and dietary salt restriction, treatment may need to be individualized based on co-morbidities. Combination of antihypertensive drugs, including appropriate diuretic choice and dose, is of great significance in hypertension management in CKD.

Differential activation of CD95-mediated apoptosis related proteins in proximal and distal tubules during rat renal development

The CD95-mediated apoptotic pathway is the best characterized of the death receptor-mediated apoptotic pathways. The present study characterized localization and expression of proteins involved in CD95-mediated apoptosis during rat renal development. Kidneys were obtained from embryonic (E) 18 and 20-day-old fetuses and postnatal (P) 1-, 3-, 5-, 7-, 14-, and 21-day-old pups. Immunohistochemical characterization revealed that CD95, FasL and cleaved caspase-3 were strongly expressed in proximal tubules and weakly expressed in distal tubules, but that expression of caspase-8 in distal tubules was stronger than that in proximal tubules. Results from terminal deoxynucleotidyl transferase dUTP nick end labeling assays showed that levels of apoptosis in proximal tubules slowly increased after E18, while those of distal tubules slowly decreased after P5. Western blotting demonstrated that expression of CD95, FasL and FADD was very weak during embryonic development, but rapidly increased at P14. Expression of cleaved caspase-3 was maintained at high levels after P1, while caspase-8 expression gradually reached a peak at P7. Results from this study reveal that the CD95-mediated apoptotic pathway is a key driver of apoptosis in proximal tubules during late postnatal kidney development in rats and suggest that apoptosis in distal tubules is mediated by a different apoptotic pathway.

Hypertension in Chronic Kidney Disease

Hypertension, a global public health problem, is currently the leading factor in the global burden of disease. It is the major modifiable risk factor for heart disease, stroke and kidney failure. Chronic kidney disease (CKD) is both a common cause of hypertension and CKD is also a complication of uncontrolled hypertension. The interaction between hypertension and CKD is complex and increases the risk of adverse cardiovascular and cerebrovascular outcomes. This is particularly significant in the setting of resistant hypertension commonly seen in patient with CKD. The pathophysiology of CKD associated hypertension is multi-factorial with different mechanisms contributing to hypertension. These pathogenic mechanisms include sodium dysregulation, increased sympathetic nervous system and alterations in renin angiotensin aldosterone system activity. Standardized blood pressure (BP) measurement is essential in establishing the diagnosis and management of hypertension in CKD. Use of ambulatory blood pressure monitoring provides an additional assessment of diurnal variation in BP commonly seen in CKD patients. The optimal BP target in the treatment of hypertension in general and CKD population remains a matter of debate and controversial despite recent guidelines and clinical trial data. Medical therapy of patients with CKD associated hypertension can be difficult and challenging. Additional evaluation by a hypertension specialist may be required in the setting of treatment resistant hypertension by excluding pseudo-resistance and treatable secondary causes. Treatment with a combination of antihypertensive drugs, including appropriate diuretic choice, based on estimated glomerular filtration rate, is a key component of hypertension management in CKD patients. In addition to drug treatment non-pharmacological approaches including life style modification, most important of which is dietary salt restriction, should be included in the management of hypertension in CKD patients.

Management of hypertension in chronic kidney disease

Hypertension is a common comorbidity in patients with impaired kidney function. The kidney exerts a marked degree of control over blood pressure through various mechanisms, such as by regulating sodium balance and hormone secretion through the activity of the renin-angiotensin system. The kidney is susceptible to injury, and if already damaged can be at risk of further loss of function as a consequence of elevated blood pressure. Once elevated blood pressure is identified, a combination of sensible lifestyle measures, such as sodium restriction and weight loss, with pharmacological intervention to reduce blood pressure will usually achieve blood pressure goals. In this Review, we outline the importance of blood pressure control for patients with chronic kidney disease (CKD), the mechanisms that affect blood pressure control, and the basis for non-drug and drug therapies. We further discuss the rationale for <140 mmHg systolic and <90 mmHg diastolic targets for blood pressure in patients with CKD, with consideration for tighter targets in the setting of proteinuria.

Pathogenesis of drug-resistant hypertension

More is known about the epidemiology of drug-resistant hypertension than particular pathogenic factors and pathways. Several recurring themes, however, seem evident on using insight from epidemiology and general knowledge of the pathophysiology of hypertension. Specifically, 4 main pathways converge on drug resistance including sodium handling, sympathetic nervous system activation, endothelial dysfunction, and arterial stiffness. These factors, and the various pathways and elements contributing to them, are reviewed. In addition to describing how these factors exert their individual influences on resistant hypertension, several examples of how interactions between these factors, particularly in the case of chronic kidney disease, are included. At the conclusion of this review some thoughts are offered on additional mechanisms and areas for potential research.

Salt restriction in chronic kidney disease: a simple need or a must?

Dietary salt restriction is one of the most important non pharmacological intervention in the management of hypertension and cardiovascular complications. In Chronic Kidney Disease (CKD) patients, observational and recent interventional studies investigating the relationship between sodium intake and renal outcomes suggest that low salt diet is warranted in this high risk category of patients. Moreover reducing and maintaining a low salt intake in these patients plays a fundamental role for maximizing the beneficial effect of ACE inhibitors on CKD progression. On the other hand, in hypertensive patients there is experimental evidence indicating that a very low sodium diet (<50 mEq/day) generates a pro-inflammatory phenotype characterized by an increase in Procalcitonin and TNF-alpha and a reduction in an anti-inflammatory cytokine like Adiponectin. In this brief review the main mechanisms whereby salt intake may determine kidney damage and studies showing that salt restriction may have a beneficial effect in CKD patients will be discussed.

Nitric oxide and carbon monoxide antagonize TGF-β through ligand-independent internalization of TβR1/ALK5

Transforming growth factor (TGF)-β plays a central role in vascular homeostasis and in the pathology of vascular disease. There is a growing appreciation for the role of nitric oxide (NO) and carbon monoxide (CO) as highly diffusible, bioactive signaling molecules in the vasculature. We hypothesized that both NO and CO increase endocytosis of TGF-β receptor type 1 (TβR1) in vascular smooth muscle cells (VSMCs) through activation of dynamin-2, shielding cells from the effects of circulating TGF-β. In this study, primary cultures of VSMCs from Sprague-Dawley rats were treated with NO-releasing molecule 3 (a NO chemical donor), CO-releasing molecule 2 (a CO chemical donor), or control. NO and CO stimulated dynamin-2 activation in VSMCs. NO and CO promoted time- and dose-dependent endocytosis of TβR1. By decreasing TβR1 surface expression through this dynamin-2-dependent process, NO and CO diminished the effects of TGF-β on VSMCs. These findings help explain an important mechanism by which NO and CO signal in the vasculature by decreasing surface expression of TβR1 and the cellular response to TGF-β.

Salt Loading Promotes Kidney Injury via Fibrosis in Young Female Ren2 Rats

BACKGROUND/AIMS

It is increasingly recognized that there is sexual dimorphism in kidney disease progression; however, this disparity is lost in the presence of diabetes where women progress at a similar rate to men. The renin-angiotensin-aldosterone system (RAAS) is known to regulate diabetes-induced kidney injury, and recent literature would suggest that gender differences exist in RAAS-dependent responses in the kidney. In this regard, these gender differences may be overcome by excessive salt intake. Thereby, we hypothesized that salt would promote proteinuria in transgenic female rats under conditions of excess tissue angiotensin (Ang) II and circulating aldosterone.

MATERIALS AND METHODS

We utilized young female transgenic (mRen2)27 (Ren2) rats and Sprague-Dawley (SD) littermates and fed a high-salt diet (4%) over 3 weeks.

RESULTS

Compared to SD and Ren2 controls, female Ren2 rats fed a high-salt diet displayed increases in proteinuria, periarterial and interstitial fibrosis as well as ultrastructural evidence of basement membrane thickening, loss of mitochondrial elongation, mitochondrial fragmentation and attenuation of basilar canalicular infoldings. These findings occurred temporally with increases in transforming growth factor-β but not indices of oxidant stress.

CONCLUSIONS

Our current data suggest that a diet high in salt promotes progressive kidney injury as measured by proteinuria and fibrosis associated with transforming growth factor-β under conditions of excess tissue Ang II and circulating aldosterone.

Impaired pressure natriuresis is associated with interstitial inflammation in salt-sensitive hypertension

PURPOSE OF REVIEW

Impairment of the pressure natriuresis relationship is a central event in the pathogenesis of hypertension. Renal tubulointerstitial inflammation results in salt-sensitive hypertension and, until recently, the changes in pressure natriuresis induced by renal inflammation received little attention.

RECENT FINDINGS

Oxidative stress and increased intrarenal angiotensin II activity, in association with rarefaction and loss of peritubular vascular network, may be involved in the inflammation-induced blunting of the natriuresis resulting from increments in renal perfusion pressure.

SUMMARY

Here, we review the mechanisms for the impairment in pressure natriuresis resulting from renal tubulointerstitial inflammation in reference to the normal physiologic mechanisms involved in this response.