Roles of mitogen-activated protein kinases and angiotensin II in renal development

Effect of S-allylcysteine against diabetic nephropathy via inhibition of MEK1/2-ERK1/2-RSK2 signalling pathway in streptozotocin-nicotinamide-induced diabetic rats

OBJECTIVE

In the current study, we evaluated the ameliorative effect of S-allylcysteine (SAC) against streptozotocin (STZ)-nicotinamide (NAD)-induced diabetic nephropathy (DN) in rats and also an attempt was made to establish the molecular mechanism of SAC.

METHODS

DN rats were orally supplemented with SAC (150 mg/kg body weight) for a period of 45 days and the effect of SAC on urinary albumin excretion, metabolic parameters, and tubular injury biomarkers by ELISA, total levels and phosphorylation of MEK1/2, ERK1/2, and RSK2 by western blotting analysis in control and experimental rats were assessed.

RESULTS

From this study, we observed that SAC considerably decreased polydipsia, poly urea, polyphagia, albuminuria and the levels of urinary N-acetyl-beta-D-glucosaminidase, neutrophil gelatinase-associated lipocalin, transforming growth factor-β1 and SAC effectively altered the pathological changes in DN rats. SAC also reserved renal cortical phosphorylation of MEK1/2, ERK1/2 and RSK2.

CONCLUSION

Hence this study recommended that SAC can successfully protect the DN through regulation of MEK1/2-ERK1/2-RSK2 signalling.

Angiotensin (1-7) Inhibits Ang II-mediated ERK1/2 Activation by Stimulating MKP-1 Activation in Vascular Smooth Muscle Cells

The renin–angiotensin system (RAS) exerts profound physiological effects on blood pressure regulation and fluid homeostasis, mainly by modulating renal, cardiovascular, and central nervous systems. Angiotensin (Ang)-(1-7), an end-product of RAS, is recognized by its cardiovascular protective properties through stimulation of the Mas receptor, including vasodilation, anti-inflammatory, and antihypertensive actions, and consequently, counter-regulating the well-known Ang II-elicited actions. The overall hypothesis of this study is that Ang-(1-7) inhibits Ang II-induced ERK1/2 activation in vascular smooth muscle cells (VSMCs), via regulation of mitogen-activated protein phosphatase-1 (MKP-1) activity. Aortas from male Wistar rats were incubated with Ang-(1-7) or vehicle. Concentration-response curves to Ang II were performed in endothelium-denuded aortas, in the presence or absence of ERK1/2 (PD98059) inhibitor or Mas receptor (A-779) antagonist. Expression of proteins was assessed by western blot, and immunohistochemistry was conducted in VSMCs. Ang-(1-7) incubation decreased Ang II-induced contractile response in aortas, and this effect was not observed in the presence of PD98059 or A-779. Stimulation of VSMCs with Ang-(1-7) prevented Ang II-induced ERK1/2 phosphorylation, but not C-Raf-activation. Furthermore, Ang II decreased MKP-1 phosphorylation in VSMCs. Interestingly, simultaneous incubation of Ang-(1-7) with Ang II favored MKP-1 phosphorylation, negatively modulating ERK1/2 activation in VSMCs. The results suggest that Ang-(1-7) counter-regulates actions evoked by Ang II overproduction, as observed in cardiovascular diseases, mainly by modulating MKP-1 activity. This evidence suggests that the role of Ang-(1-7) in MKP-1-regulation represents a target for new therapeutic development.

Vitamin D3 potentiates the renoprotective effects of vildagliptin in a rat model of fructose/salt-induced insulin resistance

Insulin resistance (IR) seemingly plays a role in chronic kidney disease (CKD). The present study has elucidated the crucial interplay of oxidative stress, inflammatory, apoptotic and profibrotic signaling pathways, linking IR to CKD. The study aimed at investigating the pleiotropic nephroprotective effects of either vildagliptin or vitamin D3 in a fructose/salt-induced IR rat model, highlighting the potential molecular mechanisms underlying their action. Another interesting target was to evaluate the potential capacity of vitamin D3 to potentiate the nephroprotective effects of vildagliptin. Indeed, a state of impaired fasting glucose, IR and compensatory hyperinsulinemia, constellating with significant weight gain, atherogenic dyslipidemia and hyperuricemia was established 6 weeks after fructose/salt consumption. IR rats were then treated orally with vildagliptin (10 mg/kg/day), vitamin D3 (10 µg/kg/day) or their combination for a further 6 weeks. By the end of the 12^th week, untreated IR rats displayed significantly declined renal function with parallel interwined renal oxidative stress, inflammatory, apoptotic and profibrotic changes, renal histopathological damages and markedly enhanced collagen fiber deposition. Vildagliptin and vitamin D3 reversed hyperuricemia and exerted a plethora of renal anti-oxidant, anti-inflammatory, anti-apoptotic and anti-fibrotic effects. Our study has introduced a new insight into the role of dipeptidyl peptidase-4 inhibition and silent information regulator 1/5'adenosine monophosphate-activated protein kinase activation in the nephroprotective effects of either agent, elucidating their possible crosstalk with renin angiotensin aldosterone system downregulation. Considering the superadditive renoprotective effects evoked by the combination, vitamin D3 is worth being further investigated as an additional therapeutic agent for preventing IR-induced nephropathy.

Oxymatrine attenuates amyloid beta 42 (Aβ1–42)-induced neurotoxicity in primary neuronal cells and memory impairment in rats

Amyloid beta 42 (Aβ1–42)-induced oxidative stress causes the death of neuronal cells and is involved in the development of Alzheimer’s disease. Oxymatrine (OMT) inhibits oxidative stress. In this study, we investigated the effect of OMT on Aβ1–42-induced neurotoxicity in vivo and in vitro. In the Morris water maze test, OMT significantly decreased escape latency and increased the number of platform crossings. In vitro, OMT markedly increased cell viability and superoxide dismutase activity. Moreover, OMT decreased lactate dehydrogenase leakage, malondialdehyde content, and reactive oxygen species in a dose-dependent manner. OMT upregulated the ratio of Bcl-2/Bax and downregulated the level of caspase-3. Furthermore, OMT inhibited the activation of MAP kinase (ERK 1/2, JNK) and nuclear factor κB. In summary, OMT may potentially be used in the treatment of Alzheimer’s disease.

Astragaloside IV ameliorates early diabetic nephropathy by inhibition of MEK1/2-ERK1/2-RSK2 signaling in streptozotocin-induced diabetic mice

Objective The aim of this study was to investigate the renoprotective effects and molecular mechanisms of astragaloside IV (AS-IV) in streptozotocin (STZ)-induced diabetic mice. Methods Male C57BL/6 mice were injected intraperitoneally with STZ at 200 mg/kg body weight. AS-IV was administered for 8 consecutive weeks, beginning 1 week after STZ injection. Body weight, 24-hour urinary albumin excretion, and fasting blood glucose were measured. Kidney tissues were examined by histopathological analyses. Total levels and phosphorylation of mitogen-activated protein kinase 1/2 (MEK1/2), extracellular signal-regulated kinases 1 and 2 (ERK1/2), and ribosomal S6 kinase 2 (RSK2) were determined by Western blotting analysis. Results AS-IV treatment significantly reduced albuminuria and serum creatinine levels, ameliorated mesangial matrix expansion and greater foot process width, and decreased the levels of urinary N-acetyl-beta-D-glucosaminidase, neutrophil gelatinase-associated lipocalin, and transforming growth factor-beta 1 in STZ-induced diabetic mice. AS-IV also inhibited renal cortical phosphorylation of MEK1/2, ERK1/2 and RSK2. Conclusion Our results suggest that AS-IV attenuates renal injury in STZ-induced diabetic mice. This effect might be partially associated with inhibition of the activation of the MEK1/2-ERK1/2-RSK2 signaling pathway.

The concept of crosstalk-directed embryological target mining and its application to essential hypertension treatment failures

This review aims to introduce the novel concept of embryological target mining applied to interorgan crosstalk network genesis, and applies embryological target mining to multidrug-resistant essential hypertension (a prototype, complex, undertreated, multiorgan systemic syndrome) to uncover new treatment targets and critique why existing strategies fail. Briefly, interorgan crosstalk pathways represent the next frontier for target mining in molecular medicine. This is because stereotyped stepwise organogenesis presents a unique opportunity to infer interorgan crosstalk pathways that may be crucial to discovering novel treatment targets. Insights gained from this review will be applied to patient management in a clinician-directed fashion.

Characterization and phosphoproteomic analysis of a human immortalized podocyte model of Fabry disease generated using CRISPR/Cas9 technology

Fabry nephropathy is a major cause of morbidity and premature death in patients with Fabry disease (FD), a rare X-linked lysosomal storage disorder. Gb3, the main substrate of α-galactosidase A (α-Gal A), progressively accumulates within cells in a variety of tissues. Establishment of cell models has been useful as a tool for testing hypotheses of disease pathogenesis. We applied CRISPR/Cas9 genome editing technology to the GLA gene to develop human kidney cell models of FD in human immortalized podocytes, which are the main affected renal cell type. Our podocytes lack detectable α-Gal A activity and have increased levels of Gb3. To explore different pathways that could have distinct patterns of activation under conditions of α-gal A deficiency, we used a high-throughput antibody array to perform phosphorylation profiling of CRISPR/Cas9-edited and control podocytes. Changes in both total protein levels and in phosphorylation status per site were observed. Analysis of our candidate proteins suggests that multiple signaling pathways are impaired in FD.

Effects of Xin-Ji-Er-Kang formula on 2K1C-induced hypertension and cardiovascular remodeling in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Xin-Ji-Er-Kang (XJEK), a Chinese herbal formula, is effective against hypertension induced coronary heart disease, viral myocarditis and toxic myocarditis. In this study, the effect of XJEK on cardiovascular system was investigated. To test the hypothesis that Xin-Ji-Er-Kang (XJEK) has an anti-hypertensive effect mediated through attenuation of cardiac remodeling, and amelioration of vascular endothelial dysfunction and oxidative stress.

MATERIALS AND METHODS

Hypertension was induced in Wistar rats by 2 kidney 1 clip (2K1C) treatment. The hypertensive rats were then randomly assigned into four groups and treated as follows: group 1 (Sham-operated [Sh-Op] group received only drinking water), group 2 (induced hypertensive model+no treatment), and group 3 (induced hypertensive+a single daily oral dose of 24 g kg(-1) XJEK treatment) and group 4 (induced hypertensive+a single oral dose of 15 mg kg(-1) Fosinopril treatment). The rats in all the defined groups were respectively treated for a period of 4 weeks. Cardiovascular parameter such as systolic blood pressure (SBP) was measured weekly by using tail-cuff apparatus; left ventricular systolic pressure (LVSP), left ventricular end-diastolic pressure (LVEDP) and the rate of the rise in left ventricular pressure (±dp/dt max) were measured by using a PowerLab 8/30 apparatus (AD Instruments, Australia) at the end of the 8th week; heart weight/body weight (HW/BW) was determined as an index of myocardial hypertrophy (MH). Hematoxylin and eosin (H&E) and Van Gieson (VG) stain were used to assess the cardio-histological changes. Colorimetric analysis was used to assay serum superoxide dismutase (SOD) activity, malondialdehyde (MDA), nitric oxide (NO), and hydroxyproline (Hyp) contents in cardiac tissue. Angiotensin II (Ang II) content in serum was assessed by radioimmunoassay; tetrahydrobiopterin (BH4) content in cardiac tissue, BNP and endothelial NOS (eNOS) in serum were determined by using ELISA, and the protein expressions of c-Jun NH2-terminal kinase (JNK), P-JNK, p38, P-p38, and NADPH oxidases-2 (Nox-2) were measured by western blot.

RESULTS

XJEK therapy could impair the heart systolic and diastolic function, potently improve the heart weight index, inhibit the elevation of HW/BW ratio, and markedly ameliorate hemodynamic indices and vascular remodeling index. It has blunted the decrease of SOD, NO and the increase in MDA and Ang II serum contents, myocardial cross-section area (CSA), collagen volume fraction (CVF) and perivascular circumferential collagen area (PVCA) compared to the hypertensive model group. It also reduced the serum content of Hyp while increased BH4 levels in cardiac tissue. In addition, the expressions of Nox-2, P-JNK and P-p38MAPK were all suppressed compared to the hypertensive model group. Moreover, treatment with XJEK improved endothelial dysfunction (ED) manifested by promoting eNOS activities and enhancing the NO activity in serum.

CONCLUSION

The results of the present study show that XJEK attenuates 2K1C-induced hypertension in rats, which confirms our hypothesis that XJEK has an anti-hypertensive and cardiovascular remodeling effect via attenuation of cardiac remodeling and improvement of endothelial dysfunction and oxidative stress.

Renal tubular dysgenesis with hypocalvaria and ileocecal valve agenesis: an autopsy report

Renal tubular dysgenesis (RTD) is a rare, lethal, autosomal recessive disorder characterized by non-differentiation of the renal proximal convoluted tubules, resulting in oligohydramnios. It is usually diagnosed in the second trimester of pregnancy, following the oligohydramnios sequence, pulmonary hypoplasia and hypocalvaria. The prognosis is poor, and death usually occurs in utero or within the first few days of life. The pathogenesis of RTD is associated with the perinatal use of drugs, such as angiotensin- converting enzyme inhibitors, angiotensin II receptor antagonists, and anti- inflammatory drugs, as well as with fetal transfusion syndrome, genetic mutations in the pathway of the renin-angiotensin system pathway, cocaine snorting, or other pathological mechanisms that reduce renal blood flow. Here, we report the autopsy of a neonate born to consanguineous parents at 38 weeks of gestation, with RTD, decreased amniotic fluid, oligohydramnios sequence, hypocalvaria, pulmonary hypoplasia, and ileocecal valve agenesis. To our knowledge, the latter has never been reported associated with RTD.

Long-term exercise attenuates blood pressure responsiveness and modulates kidney angiotensin II signalling and urinary sodium excretion in SHR

Observations have been made regarding the effects of long-term exercise training on blood pressure, renal sodium handling and renal renin-angiotensin-aldosterone (RAS) intracellular pathways in conscious, trained Okamoto-Aoki spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKy) normotensive rats, compared with appropriate age-matched sedentary SHR and WKy. To evaluate the influence of exercise training on renal function and RAS, receptors and intracellular angiotensin II (AngII) pathway compounds were used respectively, and lithium clearance and western blot methods were utilised. The current study demonstrated that increased blood pressure in SHR was blunted and significantly reduced by long-term swim training between the ages of 6 and 16 weeks. Additionally, the investigators observed an increased fractional urinary sodium excretion in trained SHR (SHR(T)) rats, compared with sedentary SHR (SHR(S)), despite a significantly decreased creatinine clearance (C(Cr)). Furthermore, immunoblotting analysis demonstrated a decreased expression of AT1(R) in the entire kidney of T(SHR) rats, compared with S(SHR). Conversely, the expression of the AT2(R), in both sedentary and trained SHR, was unchanged. The present study may indicate that, in the kidney, long-term exercise exerts a modulating effect on AngII receptor expression. In fact, the present study indicates an association of increasing natriuresis, reciprocal changes in renal AngII receptors and intracellular pathway proteins with the fall in blood pressure levels observed in T(SHR) rats compared with age-matched S(SHR) rats.

Maternal undernutrition and the offspring kidney: from fetal to adult life

Maternal dietary protein restriction during pregnancy is associated with low fetal birth weight and leads to renal morphological and physiological changes. Different mechanisms can contribute to this phenotype: exposure to fetal glucocorticoid, alterations in the components of the renin-angiotensin system, apoptosis, and DNA methylation. A low-protein diet during gestation decreases the activity of placental 11ß-hydroxysteroid dehydrogenase, exposing the fetus to glucocorticoids and resetting the hypothalamic-pituitary-adrenal axis in the offspring. The abnormal function/expression of type 1 (AT1(R)) or type 2 (AT2(R)) AngII receptors during any period of life may be the consequence or cause of renal adaptation. AT1(R) is up-regulated, compared with control, on the first day after birth of offspring born to low-protein diet mothers, but this protein appears to be down-regulated by 12 days of age and thereafter. In these offspring, AT2(R) expression differs from control at 1 day of age, but is also down-regulated thereafter, with low nephron numbers at all ages: from the fetal period, at the end of nephron formation, and during adulthood. However, during adulthood, the glomerular filtration rate is not altered, due to glomerulus and podocyte hypertrophy. Kidney tubule transporters are regulated by physiological mechanisms; Na(+)/K(+)-ATPase is inhibited by AngII and, in this model, the down-regulated AngII receptors fail to inhibit Na(+)/K(+)-ATPase, leading to increased Na(+) reabsorption, contributing to the hypertensive status. We also considered the modulation of pro-apoptotic and anti-apoptotic factors during nephrogenesis, since organogenesis depends upon a tight balance between proliferation, differentiation and cell death.

AT1 receptor induced alterations in histone H2A reveal novel insights into GPCR control of chromatin remodeling

Chronic activation of angiotensin II (AngII) type 1 receptor (AT(1)R), a prototypical G protein-coupled receptor (GPCR) induces gene regulatory stress which is responsible for phenotypic modulation of target cells. The AT(1)R-selective drugs reverse the gene regulatory stress in various cardiovascular diseases. However, the molecular mechanisms are not clear. We speculate that activation states of AT(1)R modify the composition of histone isoforms and post-translational modifications (PTM), thereby alter the structure-function dynamics of chromatin. We combined total histone isolation, FPLC separation, and mass spectrometry techniques to analyze histone H2A in HEK293 cells with and without AT(1)R activation. We have identified eight isoforms: H2AA, H2AG, H2AM, H2AO, H2AQ, Q96QV6, H2AC and H2AL. The isoforms, H2AA, H2AC and H2AQ were methylated and H2AC was phosphorylated. The relative abundance of specific H2A isoforms and PTMs were further analyzed in relationship to the activation states of AT(1)R by immunochemical studies. Within 2 hr, the isoforms, H2AA/O exchanged with H2AM. The monomethylated H2AC increased rapidly and the phosphorylated H2AC decreased, thus suggesting that enhanced H2AC methylation is coupled to Ser1p dephosphorylation. We show that H2A125Kme1 promotes interaction with the heterochromatin associated protein, HP1α. These specific changes in H2A are reversed by treatment with the AT(1)R specific inhibitor losartan. Our analysis provides a first step towards an awareness of histone code regulation by GPCRs.

Chronic treatment with lisinopril decreases proliferative and apoptotic pathways in autosomal recessive polycystic kidney disease

Angiotensin converting enzyme (ACE) inhibition is a common therapeutic modality in the treatment of autosomal recessive polycystic kidney disease (ARPKD). This study was designed to investigate whether chronic inhibition of ACE would have a therapeutic effect in attenuating the progression of renal cystogenesis in an orthologous rat model of ARPKD, the polycystic kidney (PCK) rat. Lisinopril (3 mg/kg per day) was administered orally for a period of 12 weeks, beginning at post-natal week 4. Lisinopril treatment resulted in an approximately 30% improvement in the collecting duct cystic indices (CT CI) of PCK animals. Activation of extracellular signal-regulated kinase 1 (ERK1) and 2 (ERK2), proliferative signaling markers, and proliferating cell nuclear antigen (PCNA), an end-point marker for proliferation, was reduced following chronic treatment with lisinopril compared to that in vehicle-treated PCK rats. To assess whether apoptotic pathways were altered due to chronic ACE inhibition, we examined p38 mitogen activated protein kinase (MAPK) and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), which are markers of apoptotic signaling cascades. p38 MAPK was significantly reduced (P < 0.0001) following chronic treatment with lisinopril, but no change in the activation of SAPK/JNK could be detected by immunoblot analysis. Lisinopril treatment resulted in a significant reduction (P < 0.01) in cleaved caspase-7 levels, but not caspase-3 activity, in PCK rat kidneys compared to the vehicle-treated PCK rat kidneys. Proteinuria was completely ameliorated in the presence of chronic ACE inhibition in the lisinopril-treated rats compared with the vehicle-treated PCK rats. In all, these findings demonstrated that chronic ACE inhibition can beneficially alter proliferative and apoptotic pathways to promote therapeutic reductions in renal cyst development in ARPKD.