Mechanisms involving Ang II and MAPK/ERK1/2 signaling pathways underlie cardiac and renal alterations during chronic undernutrition.

BACKGROUND: Several studies have correlated protein restriction associated with other nutritional deficiencies with the development of cardiovascular and renal diseases. The driving hypothesis for this study was that Ang II signaling pathways in the heart and kidney are affected by chronic protein, mineral and vitamin restriction. METHODOLOGY/PRINCIPAL FINDINGS: Wistar rats aged 90 days were fed from weaning with either a control or a deficient diet that mimics those used in impoverished regions worldwide. Such restriction simultaneously increased ouabain-insensitive Na+-ATPase and decreased (Na++K+)ATPase activity in the same proportion in cardiomyocytes and proximal tubule cells. Type 1 angiotensin II receptor (AT1R) was downregulated by that restriction in both organs, whereas AT2R decreased only in the kidney. The PKC/PKA ratio increased in both tissues and returned to normal values in rats receiving Losartan daily from weaning. Inhibition of the MAPK pathway restored Na+-ATPase activity in both organs. The undernourished rats presented expanded plasma volume, increased heart rate, cardiac hypertrophy, and elevated systolic pressure, which also returned to control levels with Losartan. Such restriction led to electrical cardiac remodeling represented by prolonged ventricular repolarization parameters, induced triggered activity, early after-depolarization and delayed after-depolarization, which were also prevented by Losartan. CONCLUSION/SIGNIFICANCE: The mechanisms responsible for these alterations are underpinned by an imbalance in the PKC- and PKA-mediated pathways, with participation of angiotensin receptors and by activation of the MAPK/ERK1/2 pathway. These cellular and molecular alterations culminate in cardiac electric remodeling and in the onset of hypertension in adulthood.

Perinatal Na+ overload programs raised renal proximal Na+ transport and enalapril-sensitive alterations of Ang II signaling pathways during adulthood.

BACKGROUND: High Na(+) intake is a reality in nowadays and is frequently accompanied by renal and cardiovascular alterations. In this study, renal mechanisms underlying perinatal Na(+) overload-programmed alterations in Na(+) transporters and the renin/angiotensin system (RAS) were investigated, together with effects of short-term treatment with enalapril in terms of reprogramming molecular alterations in kidney. METHODOLOGY/PRINCIPAL FINDINGS: Male adult Wistar rats were obtained from dams maintained throughout pregnancy and lactation on a standard diet and drinking water (control) or 0.17 M NaCl (saline group). Enalapril (100 mg/l), an angiotensin converting enzyme inhibitor, was administered for three weeks after weaning. Ninety day old offspring from dams that drank saline presented with proximal tubules exhibiting increased (Na(+)+K(+))ATPase expression and activity. Ouabain-insensitive Na(+)-ATPase activity remained unchanged but its response to angiotensin II (Ang II) was lost. PKC, PKA, renal thiobarbituric acid reactive substances (TBARS), macrophage infiltration and collagen deposition markedly increased, and AT(2) receptor expression decreased while AT(1) expression was unaltered. Early treatment with enalapril reduced expression and activity of (Na(+)+K(+))ATPase, partially recovered the response of Na(+)-ATPase to Ang II, and reduced PKC and PKA activities independently of whether offspring were exposed to high perinatal Na(+) or not. In addition, treatment with enalapril per se reduced AT(2) receptor expression, and increased TBARS, macrophage infiltration and collagen deposition. The perinatally Na(+)-overloaded offspring presented high numbers of Ang II-positive cortical cells, and significantly lower circulating Ang I, indicating that programming/reprogramming impacted systemic and local RAS. CONCLUSIONS/SIGNIFICANCE: Maternal Na(+) overload programmed alterations in renal Na(+) transporters and in its regulation, as well as severe structural lesions in adult offspring. Enalapril was beneficial predominantly through its influence on Na(+) pumping activities in adult offspring. However, side effects including down-regulation of PKA, PKC and AT(2) receptors and increased TBARS could impair renal function in later life.

Metabolic programming during lactation stimulates renal Na+ transport in the adult offspring due to an early impact on local angiotensin II pathways.

BACKGROUND: Several studies have correlated perinatal malnutrition with diseases in adulthood, giving support to the programming hypothesis. In this study, the effects of maternal undernutrition during lactation on renal Na(+)-transporters and on the local angiotensin II (Ang II) signaling cascade in rats were investigated. METHODOLOGY/PRINCIPAL FINDINGS: Female rats received a hypoproteic diet (8% protein) throughout lactation. Control and programmed offspring consumed a diet containing 20% protein after weaning. Programming caused a decrease in the number of nephrons (35%), in the area of the Bowman's capsule (30%) and the capillary tuft (30%), and increased collagen deposition in the cortex and medulla (by 175% and 700%, respectively). In programmed rats the expression of (Na(+)+K(+))ATPase in proximal tubules increased by 40%, but its activity was doubled owing to a threefold increase in affinity for K(+). Programming doubled the ouabain-insensitive Na(+)-ATPase activity with loss of its physiological response to Ang II, increased the expression of AT(1) and decreased the expression of AT(2) receptors), and caused a pronounced inhibition (90%) of protein kinase C activity with decrease in the expression of the α (24%) and ε (13%) isoforms. Activity and expression of cyclic AMP-dependent protein kinase decreased in the same proportion as the AT(2) receptors (30%). In vivo studies at 60 days revealed an increased glomerular filtration rate (GFR) (70%), increased Na(+) excretion (80%) and intense proteinuria (increase of 400% in protein excretion). Programmed rats, which had normal arterial pressure at 60 days, became hypertensive by 150 days. CONCLUSIONS/SIGNIFICANCE: Maternal protein restriction during lactation results in alterations in GFR, renal Na(+) handling and in components of the Ang II-linked regulatory pathway of renal Na(+) reabsorption. At the molecular level, they provide a framework for understanding how metabolic programming of renal mechanisms contributes to the onset of hypertension in adulthood.

Placental malnutrition changes the regulatory network of renal Na-ATPase in adult rat progeny: Reprogramming by maternal α-tocopherol during lactation.

Prenatal malnutrition is responsible for the onset of alterations in renal Na(+) transport in the adult offspring. Here we investigated the molecular mechanisms by which increased formation of reactive oxygen species during prenatal malnutrition affects the pathways that couple angiotensin II (Ang II) receptors (AT(1)R and AT(2)R) to kidney Na(+)-ATPase in adulthood, and how maternal treatment with α-tocopherol can prevent alterations in the main regulatory cascade of the pump. The experiments were carried out on the adult progeny of control and malnourished dams during pregnancy that did or did not receive α-tocopherol during lactation. Malnutrition during pregnancy increased maternal hepatic and adult offspring renal malondialdehyde levels, which returned to control after supplementation with α-tocopherol. In the adult offspring, placental malnutrition programmed: decrease in Na(+)-ATPase activity, loss of the physiological stimulation of this pump by Ang II, up-regulation of AT(1)R and AT(2)R, decrease in membrane PKC activity, selective decrease of the PKCε isoform expression, and increase in PKA activity with no change in PKA α-catalytic subunit expression. These alterations were reprogrammed to normal levels by α-tocopherol during lactation. The influence of α-tocopherol on the signaling machinery in adult offspring indicates selective non-antioxidant effects at the gene transcription and protein synthesis levels.

Placental oxidative stress in malnourished rats and changes in kidney proximal tubule sodium ATPases in offspring.

1. Intrauterine malnutrition has been linked to the development of adult cardiovascular and renal diseases, which are related to altered Na(+) balance. Here we investigated whether maternal malnutrition increases placental oxidative stress with subsequent impact on renal ATP-dependent Na(+) transporters in the offspring. 2. Maternal malnutrition was induced in rats during pregnancy by using a basic regional diet available in north-eastern Brazil. Placental oxidative stress was evaluated by measuring thiobarbituric acid-reactive substances, which were 35-40% higher in malnourished dams (MalN). Na(+) pumps were evaluated in control and prenatally malnourished rats (at 25 and 90 days of age). 3. Identical Na(+)/K(+)-ATPase activity was found in both groups at 25 days (approximately 150 nmol P(i)/mg per min). However, although Na(+)/K(+)-ATPase increased by 40% with growth in control rats, it remained constant in pups from MalN. 4. In juvenile rats, the activity of the ouabain-insensitive Na(+)-ATPase was higher in MalN than in controls (70 vs 25 nmol P(i)/mg per min). Nevertheless, activity did not increase with kidney and body growth: at 90 days, it was 50% lower in MalN than in controls. The maximal stimulation of the Na(+)-ATPase by angiotensin (Ang) II was 35% lower in MalN than in control rats and was attained only with a much higher concentration of the peptide (10(-10) mol/L) than in controls (10(-14) mol/L). 5. Protein kinase C activity, which mediates the effects of AngII on Na(+)-ATPase was only one-third of normal values in the MalN group. 6. These results indicate that placental oxidative stress may contribute to fetal undernutrition, which leads to later disturbances in Na(+) pumps from proximal tubule cells.

Chronic undernutrition alters renal active Na+ transport in young rats: potential hidden basis for pathophysiological alterations in adulthood?

BACKGROUND: Epidemiological studies in the northeastern region of Brazil show an association between hypertension and malnutrition, especially in areas where protein-deficient diets are combined with high salt intake. AIMS OF STUDY: We studied the consequences of a widely consumed deficient diet (basic regional diet, BRD), combined with high NaCl, on growth, renal Na+ and water handling and activities of ATP-dependent Na+ transporters in kidney proximal tubules. METHODS: Young rats were fed after weaning with a low-protein and high-salt diet, which mimics that used in a vast region of Brazil. Body mass was evaluated from weaning up to the 19th week of age. Glomerular filtration rate, proximal Na+ reabsorption, distal Na+ delivery, urinary excretion of Na+ and water, and urine concentration capacity were evaluated from serum and urine concentrations of creatinine, Na+ and Li+, and by measurement of urinary volume and density. The (Na+ + K+)ATPase and the ouabain-insensitive Na+-ATPase were studied in vitro by measuring ATP hydrolysis. Expression of (Na+ + K+)ATPase was evaluated by immunodetection with the use of a specific antibody anti alpha1-catalytic subunit isoform. RESULTS: Undernourished rats reached early adulthood (14 weeks) with body and renal masses that were 2.3 times lower than controls. These rats became hypertensive (mean arterial pressure 18.7 +/- 0.6 kPa vs 15.5 +/- 0.9 kPa in control group) and showed augmented fractional proximal Na+ reabsorption (61.0 +/- 0.3% vs 81.8 +/- 2.2%) with a concomitant decrease in distal Na+ delivery (9.5 +/- 0.5 micromol/min vs 14.0 +/- 0.2 micromol/min per 100 g body weight). Urinary Na+ excretion was higher in BRD rats, (juvenile and adult) being however twice the increase in Na+ intake. The ATP-dependent Na+ transporters were affected in opposite ways. The (Na+ + K+)ATPase activity from undernourished rats fell by 30%, in parallel with a 20% decrease in its immunodetection, whereas the ouabain-insensitive Na+-ATPase, which is responsible for the fine-tune control of Na+ reabsorption, increased threefold. CONCLUSIONS: We conclude that early alterations in proximal tubule Na+ pumps, together with an abnormally augmented urinary Na+ excretion, might be the link between undernutrition and late renal dysfunction.