Role In Salt-sensitive Hypertension Research Articles

Immune reactivity to heat shock protein 70 expressed in the kidney is cause of salt-sensitive hypertension

Hypertension affects one-third of the adult population of the world. The causes of hypertension are incompletely understood, but relative impairment of sodium excretion is central to its pathogenesis. Immune cell infiltration in the kidney is a constant finding in hypertension that in association with local angiotensin and oxidants causes a defect in sodium excretion. However, it is unclear if the T cell influx into the kidney responds to nonspecific chemokine cues or is due to antigen-driven immune attraction. We found that T cells in experimentally induced salt-driven hypertension present a CD4 clonal response to heat shock protein 70 (HSP70) that is overexpressed in the kidney. We used a highly preserved amino acid sequence within the HSP molecule to induce immune tolerance associated with the generation of IL-10 producing regulatory T cells. Immune tolerant rats to HSP70 developed minimal renal inflammation and were protected from the development of salt-sensitive hypertension. Adoptive transfer of T lymphocytes isolated from spleen of tolerized rats also reversed hypertension. HSP70 gene delivery to the renal vein of the kidneys of rats sensitized to HSP70 caused an increment in blood pressure in response to a high-salt diet. The HSP70 peptide used in this work induces a strong proliferative response in peripheral blood lymphocytes of patients with essential hypertension. These studies provide evidence that autoimmunity plays a role in salt-sensitive hypertension and identifies HSP70 expressed in the kidney as one key antigen. These findings raise the possibility of novel approaches to the treatment of this condition.

Reduced Insulin Secretion and Nocturnal Dipping of Blood Pressure Are Associated with a Disturbed Circadian Pattern of Urine Excretion in Metabolic Syndrome

An impaired Na and water excretion rate during daytime is associated with increased cardiovascular risk factors. Recent findings suggest that disturbed circadian rhythms may play an important role in salt-sensitive hypertension and reduced β-cell function. This study investigated clinical implications of the circadian pattern of urine excretion [evaluated as the day to night ratio of urine flow rate (D/N of V)] in 76 patients with metabolic syndrome (MS) not taking diuretics. We analyzed 24-h urinary excretion and blood pressure (BP) during separate day and night periods. In addition nondiabetic patients (n = 46 of 76) underwent an oral glucose tolerance test. The D/N of V varied largely among subjects (tertile 1 = 1.95 ± 0.40, tertile 3 = 0.67 ± 0.14). In the patients with low D/N of V, systolic BP dipped less at night, independently of age and creatinine clearance (P < 0.01). During the first 60 min of the oral glucose tolerance test, the rise in plasma insulin and the insulinogenic index were positively correlated with the D/N of V, even after adjustment for age, waist circumference, 24-h urine volume, and BP (P < 0.001 for both), suggesting inadequate insulin secretion in poor daytime excretors. In patients with MS, a disturbed circadian pattern of urine excretion is associated with a reduced nocturnal dipping of systolic BP and a reduced glucose-induced insulin secretion. These results underline the clinical importance of impaired circadian rhythms in MS and prompt further studies to evaluate the potential of the D/N of V as a prognostic marker in MS patients.

Are Sodium Transporters in Urinary Exosomes Reliable Markers of Tubular Sodium Reabsorption in Hypertensive Patients?

Background: Altered renal sodium handling has a major pathogenic role in salt-sensitive hypertension. Renal sodium transporters are present in urinary exosomes. We hypothesized that sodium transporters would be excreted into the urine in different amounts in response to sodium intake in salt-sensitive versus salt-resistant patients. Methods: Urinary exosomes were isolated by ultracentrifugation, and their content of Na-K-2Cl cotransporter (NKCC2) and Na-Cl cotransporter (NCC) was analyzed by immunoblotting. Animal studies: NKCC2 and NCC excretion was measured in 2 rat models to test whether changes in sodium transporter excretion are indicative of regulated changes in the kidney tissue. Human studies: in hypertensive patients (n = 41), we investigated: (1) a possible correlation between sodium reabsorption and urinary exosomal excretion of sodium transporters, and (2) the profile of sodium transporter excretion related to blood pressure (BP) changes with salt intake. A 24-hour ambulatory BP monitoring and a 24-hour urine collection were performed after 1 week on a low- and 1 week on a high-salt diet. Results: Animal studies: urinary NKCC2 and NCC excretion rates correlated well with their abundance in the kidney. Human studies:6 patients (15%) were classified as salt sensitive. The NKCC2 and NCC abundance did not decrease after the high-salt period, when the urinary sodium reabsorption decreased from 99.7 to 99.0%. In addition, the changes in BP with salt intake were not associated with a specific profile of exosomal excretion. Conclusions: Our results do not support the idea that excretion levels of NKCC2 and NCC via urinary exosomes are markers of tubular sodium reabsorption in hypertensive patients.

Does Malfunction of Arachidonic Acid Epoxygenase Explain Salt-Sensitive Hypertension?: Salt-Sensitive Hypertension Is Associated with Dysfunctional Cyp4a10 Gene and Kidney Epithelial Sodium Channel. J Clin Invest 116: 1696-1702, 2006.

Does Malfunction of Arachidonic Acid Epoxygenase Explain Salt-Sensitive Hypertension?: Salt-Sensitive Hypertension Is Associated with Dysfunctional Cyp4a10 Gene and Kidney Epithelial Sodium Channel. J Clin Invest 116: 1696-1702, 2006.

Mitochondria buffer NCX-mediated Ca 2+-entry and limit its diffusion into vascular smooth muscle cells

The reverse-mode of the Na +/Ca 2+-exchanger (NCX) mediates Ca 2+-entry in agonist-stimulated vascular smooth muscle (VSM) and plays a central role in salt-sensitive hypertension. We investigated buffering of Ca 2+-entry by peripheral mitochondria upon NCX reversal in rat aortic smooth muscle cells (RASMC). [Ca 2+] was measured in mitochondria ([Ca 2+] MT) and the sub-plasmalemmal space ([Ca 2+] subPM) with targeted aequorins and in the bulk cytosol ([Ca 2+] i ) with fura-2. Substitution of extracellular Na + by N-methyl- d-glucamine transiently increased [Ca 2+] MT (∼2 μM) and [Ca 2+] subPM (∼1.3 μM), which then decreased to sustained plateaus. In contrast, Na +-substitution caused a delayed and tonic increase in [Ca 2+] i (<100 nM). Inhibition of Ca 2+-uptake by the sarcoplasmic reticulum (SR) (30 μM cyclopiazonic acid) or mitochondria (2 μM FCCP or 2 μM ruthenium red) enhanced the elevation of [Ca 2+] subPM. These treatments also abolished the delay in the [Ca 2+] i response to 0Na + and increased its amplitude. Extracellular ATP (1 mM) caused a peak and plateau in [Ca 2+] i , and only the plateau was inhibited by KB-R7943 (10 μM), a selective blocker of reverse-mode NCX. Evidence for ATP-mediated NCX-reversal was also found in changes in [Na +] i . Mitochondria normally exhibited a transient elevation of [Ca 2+] in response to ATP, but inhibiting the mitochondrial NCX with CGP-37157 (10 μM) unmasked an agonist-induced increase in mitochondrial Ca 2+-flux. This flux was blocked by KB-R7943. In summary, mitochondria and the sarcoplasmic reticulum co-operate to buffer changes in [Ca 2+] i due to agonist-induced NCX reversal.

Renal Activation of NF κ B and Up‐regulation of TNF α Correlate with Salt‐sensitive Hypertension in Dahl SS Rats

Recent evidence suggests that a renal pro-inflammatory response plays an important role in salt sensitive hypertension. However, the molecular mechanisms of dietary salt-induced hypertension are poorly understood. We seek to determine whether a high salt diet induces renal activation of NFκB and up-regulation of TNFα related to the development of hypertension in Dahl SS rats. Four, 8-wk-old male Dahl SS rats received a high sodium diet (HS, 4%) and 4 Dahl SS rats received a low sodium diet (LS, 0.3 %) for 5 weeks. In the end, mean arterial pressure (MAP) was determined in conscious rats by continuous monitoring through a catheter placed in the carotid artery. MAP was significantly higher in the HS than the LS group (177.9±3.7 vs. 109.4±2.9 mmHg, P<0.001). There was a significant increase in urinary albumin secretion in the HS group, compared to the LS group (22.3±2.6 vs. 6.1±0.7 mg/d; P<0.001). Total tissue protein or nuclear protein was extracted from the whole kidneys. Electrophoretic mobility shift assay (EMSA) demonstrated that the binding activity of NFκB p65 proteins in the kidneys of Dahl SS rats were significantly increased by 45% in the HS group, compared to the LS group (P=0.007). ELISA indicated that renal protein levels of TNFα were significantly higher in the HS than the LS group (2.3±0.8 vs. 0.7±0.2 pg/mg; P=0.036). The results show that a high salt diet induces the activation of NFκB and TNFα protein expression in the kidneys of Dahl SS rats in relation to the development of hypertension and renal injury. These findings support the hypothesis that NFκB and TNFα may be the key renal pro-inflammatory factors in mediating salt sensitive hypertension. (NIH/HL51971 & NIH/AA013821)

Retrotransposons transcribed preferentially in proximal tubules of salt-hypertensive rats

The kidney is considered to play an important etiologic role in salt-sensitive hypertension. The aim of the present study was to isolate genes whose expression differs between the kidneys of salt-hypertensive and control rats using an mRNA differential display method. Dahl salt-sensitive (DS) and control salt-resistant rats (DR) were fed a 0.3% or 8% NaCl diet. Renal RNA was amplified by RNA arbitrarily primed polymerase chain reaction (RAP-PCR) and compared among DR 0.3%, DR 8%, DS 0.3%, and DS 8%. Gene expression and localization were examined by Northern blotting, RNase protection assay, and in situ hybridization. Full-length nucleotide sequence was determined by screening a DS rat kidney cDNA library. We identified one differentially displayed clone, and its expression was greater in DS than DR, which was not affected by salt loading. The sequence was 90% homologous to the 3'-noncoding region of the nicotinic acetylcholine receptor alpha7 subunit gene. Its expression was kidney-specific, and was localized in the proximal tubules. The transcript level was markedly increased precedent to the development of hypertension. Its expression was also high in other salt-sensitive rats, and low in normotensive Sprague-Dawley and Wistar rats. The full-length cDNA contained elements homologous to the retroviral pol gene, a primer binding site sequence for reverse transcriptase, and long-terminal repeats. These results demonstrated that the newly identified transcripts (REPT1) belong to a novel retrotransposon family, which showed unique strain-, age-, tissue-, and cell type-specific expression pattern.