Delayed ischemic preconditioning effectively protects kidneys from ischemia-reperfusion injury but the mechanism underlying renal protection remains poorly understood. Here we examined the in vivo role of microRNA miR-21 in the renal protection conferred by delayed ischemic preconditioning in mice. A 15 minute renal ischemic preconditioning significantly increased the expression of miR-21 by 4 hours and substantially attenuated ischemia-reperfusion injury induced 4 days later. A locked nucleic acid-modified anti-miR-21 given at the time of ischemic preconditioning knocked down miR-21 and significantly exacerbated subsequent ischemia-reperfusion injury in the mouse kidney. Knockdown of miR-21 resulted in significant upregulation of programmed cell death protein 4, a pro-apoptotic target gene of miR-21, and substantially increased tubular cell apoptosis. Hypoxia inducible factor-1α in the kidney was activated after ischemic preconditioning and blockade of its activity with a decoy abolished the up-regulation of miR-21 in cultured human renal epithelial cells treated with the inducer cobalt chloride. In the absence of ischemic preconditioning, knockdown of miR-21 alone did not significantly affect ischemia-reperfusion injury in the mouse kidney. Thus, upregulation of miR-21 contributes to the protective effect of delayed ischemic preconditioning against subsequent renal ischemia-reperfusion injury.

Abstract-MicroRNAs are endogenous repressors of gene expression. We examined microRNAs in the renal medulla of Dahl salt-sensitive rats and consomic SS-13 BN rats. Salt-induced hypertension and renal injury in Dahl salt-sensitive rats, particularly medullary interstitial fibrosis, have been shown previously to be substantially attenuated in SS-13 BN rats. Of 377 microRNAs examined, 5 were found to be differentially expressed between Dahl salt-sensitive rats and consomic SS-13 BN rats receiving a high-salt diet. Real-time PCR analysis demonstrated that high-salt diets induced substantial upregulation of miR-29b in the renal medulla of SS-13 BN rats but not in SS rats. miR-29b was predicted to regulate 20 collagen genes, matrix metalloproteinase 2 (Mmp2), integrin ␤1 (Itgb1), and other genes related to the extracellular matrix. Expression of 9 collagen genes and Mmp2 was upregulated by a high-salt diet in the renal medulla of SS rats, but not in SS-13 BN rats, an expression pattern opposite to miR-29b. Knockdown of miR-29b in the kidneys of SS-13 BN rats resulted in upregulation of several collagen genes. miR-29b reduced expression levels of several collagen genes and Itgb1 in cultured rat renal medullary epithelial cells. Moreover, miR-29b suppressed the activity of luciferase when the reporter gene was linked to a 3Ј-untranslated segment of collagen genes Col1a1, Col3a1, Col4a1, Col5a1, Col5a2, Col5a3, Col7a1, Col8a1, Mmp2, or Itgb1 but not Col12a1. The result demonstrated broad effects of miR-29b on a large number of collagens and genes related to the extracellular matrix and suggested involvement of miR-29b in the protection from renal medullary injury in SS-13 BN rats. (Hypertension. 2010;55:974-982.)

Abstract-In a previous proteomic study, we found dramatic differences in fumarase in the kidney between Dahl salt-sensitive rats and salt-insensitive consomic SS-13 BN rats. Fumarase catalyzes the conversion between fumarate and L-malate in the tricarboxylic acid cycle. Little is known about the pathophysiological significance of fumarate metabolism in cardiovascular and renal functions, including salt-induced hypertension. The fumarase gene is located on the chromosome substituted in the SS-13 BN rat. Sequencing of fumarase cDNA indicated the presence of lysine at amino acid position 481 in Dahl salt-sensitive rats and glutamic acid in Brown Norway and SS-13 BN rats. Total fumarase activity was significantly lower in the kidneys of Dahl salt-sensitive rats compared with SS-13 BN rats, despite an apparent compensatory increase in fumarase abundance in Dahl salt-sensitive rats. Intravenous infusion of a fumarate precursor in SS-13 BN rats resulted in a fumarate excess in the renal medulla comparable to that seen in Dahl salt-sensitive rats. The infusion significantly exacerbated salt-induced hypertension in SS-13 BN rats (140Ϯ3 vs125Ϯ2 mm Hg in vehicle control at day 5 on a 4% NaCl diet; PϽ0.05). In addition, the fumarate infusion increased renal medullary tissue levels of H 2 O 2 . Treatment of cultured human renal epithelial cells with the fumarate precursor also increased cellular levels of H 2 O 2 . These data suggest a novel role for fumarate metabolism in salt-induced hypertension and renal medullary oxidative stress. BN rat has the same genomic makeup as the SS rat except for chromosome 13, which is introgressed from the Brown Norway (BN) rat and substantially attenuates salt-sensitive hypertension and renal injury. 3 A tree-like network of molecular, biochemical, and physiological mechanisms is likely involved in the development of Dahl salt-sensitive hypertension and renal injury. 4 Comparative analysis of SS and SS-13 BN rats has revealed several new components of this regulatory network. Examples include increased levels of superoxide and H 2 O 2 , 5,6 dysregulation of 11␤-hydroxysteroid dehydrogenase, and alterations of glucocorticoid metabolism 4 in the renal medulla of SS rats compared with SS-13 BN rats. Additional mechanisms and particularly sequence variations of specific genes involved in the SS phenotypes remain to be discovered or validated. 4,[7][8][9] Fumarase was one of the proteins exhibiting dramatic differences between SS and SS-13 BN rats according to a recent proteomic study. 10 The analysis indicated a consistent and substantial difference in the isoelectric point of fumarase in SS and SS-13 BN rats, as reflected by a significant shift of the protein spot on 2D gels. Fumarase catalyzes the reversible conversion between fumarate and L-malate in the tricarboxylic acid cycle in mitochondria. Rare loss-of-function mutations of fumarase in humans cause accumulation of fumarate and are associated with the development of hereditary leiomyomatosis, renal cell cancer, or encephalopathy. [11][1...

Antithrombin III, encoded by SerpinC1, is a major anti-coagulation molecule in vivo and has anti-inflammatory effects. We found that patients with low antithrombin III activities presented a higher risk of developing acute kidney injury after cardiac surgery. To study this further, we generated SerpinC1 heterozygous knockout rats and followed the development of acute kidney injury in a model of modest renal ischemia/reperfusion injury. Renal injury, assessed by serum creatinine and renal tubular injury scores after 24 h of reperfusion, was significantly exacerbated in SerpinC1+/− rats compared to wild-type littermates. Concomitantly, renal oxidative stress, tubular apoptosis, and macrophage infiltration following this injury were significantly aggravated in SerpinC1+/− rats. However, significant thrombosis was not found in the kidneys of any group of rats. Antithrombin III is reported to stimulate the production of prostaglandin I2, a known regulator of renal cortical blood flow, in addition to having anti-inflammatory effects and to protect against renal failure. Prostaglandin F1α, an assayable metabolite of prostaglandin I2, was increased in the kidneys of the wild-type rats at 3 h after reperfusion. The increase of prostaglandin F1α was significantly blunted in SerpinC1+/− rats, which preceded increased tubular injury and oxidative stress. Thus, our study found a novel role of SerpinC1 insufficiency in increasing the severity of renal ischemia/reperfusion injury.

We identified the first GRE in the eNOS promoter region and demonstrated that endogenous 11 beta-HSD1 and 11 beta-HSD2 play significant and distinct roles in modulating the effect of glucocorticoids on eNOS expression.

Abstract-We performed an extensive proteomic analysis of the Dahl model of salt-sensitive hypertension. The consomic SS-13 BN rat, genetically similar to the Dahl salt-sensitive rat, while exhibiting a significant amelioration of salt-induced hypertension, was used as a control. Proteomic analysis, using differential in-gel electrophoresis and mass spectrometry techniques, was performed in the renal cortex and the renal medulla of 6-week-old SS and SS-13 BN rats before significant differences in blood pressure were developed between the 2 strains of rat. Several dozen proteins were identified as differentially expressed between SS and SS-13 BN rats fed the 0.4% NaCl diet or switched to the 4% NaCl diet for 3 days (nϭ4). The identified proteins were involved in cellular functions or structures including signal transduction, energy metabolism, and the cytoskeleton. The proteomic analysis and subsequent Western blotting indicated that heterogeneous nuclear ribonucleoprotein K in the renal medulla was upregulated by the 4% NaCl diet in SS-13 BN rats but downregulated in SS rats. The level of angiotensinogen mRNA in the renal medulla was regulated in an opposite manner. Silencing of heterogeneous nuclear ribonucleoprotein K resulted in an upregulation of angiotensinogen in cultured human kidney cells. In summary, we identified significant differences in kidney regional proteomic profiles between SS and SS-13 BN rats and demonstrated a potential role of heterogeneous nuclear ribonucleoprotein K in the regulation of angiotensinogen expression in the renal medulla. (Hypertension. 2008;51:899-904.)

We investigated the role of microRNAs (miRNA) in endothelial dysfunction in the setting of cardiometabolic disorders represented by type 2 diabetes mellitus (T2DM). miR‐29 was dysregulated in resistance arterioles obtained by biopsy in T2DM patients. Intraluminal delivery of miR‐29a‐3p or miR‐29b‐3p mimics restored normal endothelium‐dependent vasodilation (EDVD) in T2DM arterioles that otherwise exhibited impaired EDVD. Intraluminal delivery of anti‐miR‐29b‐3p in arterioles from non‐DM human subjects or rats or targeted mutation of Mir29b‐1/a gene in rats led to impaired EDVD and exacerbation of hypertension in the rats. miR‐29b‐3p mimic increased, while anti‐miR‐29b‐3p or Mir29b‐1/a gene mutation decreased, nitric oxide levels in arterioles. The mutation of Mir29b‐1/a gene led to preferential differential expression of genes related to nitric oxide including Lypla1. Lypla1 was a direct target of miR‐29 and could abrogate the effect of miR‐29 in promoting nitric oxide production. Treatment with Lypla1 siRNA improved EDVD in arterioles obtained from T2DM patients or Mir29b‐1/a mutant rats or treated with anti‐miR‐29b‐3p. These findings indicate miR‐29 is required for normal endothelial function in humans and animal models and has therapeutic potential for cardiometabolic disorders.

Liu Y, Singh RJ, Usa K, Netzel BC, Liang M. Renal medullary 11␤-hydroxysteroid dehydrogenase type 1 in Dahl salt-sensitive hypertension. Physiol Genomics 36: 52-58, 2008. First published September 30, 2008 doi:10.1152/physiolgenomics.90283.2008.-The Dahl salt-sensitive rat is a widely used model of human salt-sensitive forms of hypertension. The kidney plays an important role in the pathogenesis of Dahl salt-sensitive hypertension, but the molecular mechanisms involved remain a subject of intensive investigation. Gene expression profiling studies suggested that 11␤-hydroxysteroid dehydrogenase type 1 might be dysregulated in the renal medulla of Dahl salt-sensitive rats. Additional analysis confirmed that renal medullary expression of 11␤-hydroxysteroid dehydrogenase type 1 was downregulated by a high-salt diet in SS-13 BN rats, a consomic rat strain with reduced blood pressure salt sensitivity, but not in Dahl salt-sensitive rats. 11␤-Hydroxysteroid dehydrogenase type 1 is known to convert inactive 11-dehydrocorticosterone to active corticosterone. The urinary corticosterone/11-dehydrocorticosterone ratio as well as urinary excretion of corticosterone was higher in Dahl salt-sensitive rats than in SS-13 BN rats. Knockdown of renal medullary 11␤-hydroxysteroid dehydrogenase type 1 with small-interfering RNA attenuated the early phase of salt-induced hypertension in Dahl salt-sensitive rats and reduced urinary excretion of corticosterone. Knockdown of 11␤-hydroxysteroid dehydrogenase type 1 did not affect blood pressure in SS-13 BN rats. Long-term attenuation of salt-induced hypertension was achieved with small hairpin RNA targeting renal medullary 11␤-hydroxysteroid dehydrogenase type 1. In summary, we have demonstrated that suppression of 11␤-hydroxysteroid dehydrogenase type 1 expression in the renal medulla attenuates salt-induced hypertension in Dahl salt-sensitive rats.