No abstract

Tissue damage by ischemia/reperfusion (I/R) results from a temporary cessation of blood flow followed by the restoration of circulation. The injury depresses mitochondrial respiration, increases the production of reactive oxygen species (ROS), decreases the mitochondrial transmembrane potential, and stimulates invasion by inflammatory cells. The primary objective of this work was to address the potential use of bone marrow stem cells (BMSCs) to preserve and restore mitochondrial function in the kidney after I/R. Mitochondria from renal proximal tubule cells were isolated by differential centrifugation from rat kidneys subjected to I/R (clamping of renal arteries followed by release of circulation after 30 min), without or with subcapsular administration of BMSCs. Respiration starting from mitochondrial complex II was strongly affected following I/R. However, when BMSCs were injected before ischemia or together with reperfusion, normal electron fluxes, electrochemical gradient for protons, and ATP synthesis were almost completely preserved, and mitochondrial ROS formation occurred at a low rate. In homogenates from cultured renal cells transiently treated with antimycin A, the coculture with BMSCs induced a remarkable increase in protein S-nitrosylation that was similar to that found in mitochondria isolated from I/R rats, evidence that BMSCs protected against both superoxide anion and peroxynitrite. Labeled BMSCs migrated to damaged tubules, suggesting that the injury functions as a signal to attract and host the injected BMSCs. Structural correlates of BMSC injection in kidney tissue included stimulus of tubule cell proliferation, inhibition of apoptosis, and decreased inflammatory response. Histopathological analysis demonstrated a score of complete preservation of tubular structures by BMSCs, associated with normal plasma creatinine and urinary osmolality. These key findings shed light on the mechanisms that explain, at the mitochondrial level, how stem cells prevent damage by I/R. The action of BMSCs on mitochondrial functions raises the possibility that autologous BMSCs may help prevent I/R injuries associated with transplantation and acute renal diseases.

Renal ischemia-reperfusion injury (IRI) is a major cause of acute renal failure. Doxycycline (Dc) belongs to the tetracycline-class of antibiotics with demonstrated beneficial molecular effects in the brain and heart, mainly through matrix metalloproteinases inhibition (MMP). However, Dc protection of renal function has not been demonstrated. We determined whether low doses of Dc would prevent decreases in glomerular filtration rate (GFR) and maintain tubular Na handling in Wistar rats subjected to kidney I/R. Male Wistar rats underwent bilateral kidney ischemia for 30min followed by 24h reperfusion (I/R). Doxycycline (1, 3, and 10mg/kg, i.p.) was administered 2h before surgery. Untreated I/R rats showed a 250% increase in urine volume and proteinuria, a 60% reduction in GFR, accumulation of urea-nitrogen in the blood, and a 60% decrease in the fractional Na excretion due to unbalanced Na transporter activity. Treatment with Dc 3mg/kg maintained control levels of urine volume, proteinuria, GFR, blood urea-nitrogen, fractional Na excretion, and equilibrated Na transporter activities. The Dc protection effects on renal function were associated with kidney structure preservation and prevention of TGFβ and fibronectin deposition. In vitro, total MMP activity was augmented in I/R and inhibited by 25 and 50μM Dc. In vivo, I/R augmented MMP-2 and -9 protein content without changing their activities. Doxycycline treatment downregulated total MMP activity and MMP-2 and -9 protein content. Our results suggest that treatment with low dose Dc protects from IRI, thereby preserving kidney function.

Atividade inadequada do sistema renina-angiotensina-aldosterona local durante período de alta ingestão de sal: impacto sobre o eixo cardiorrenal Apesar de haver uma concordância geral sobre a necessidade de redução na ingestão de sal como questão de saúde publica, o mecanismo pelo qual a alta ingesta de sal deflagra efeitos patológicos sobre o eixo cardiorrenal não está ainda completamente elucidado. Cada vez mais evidencias indicam que o sistema renina-angiotensinaaldosterona (S-RAA) seja o principal alvo da alta ingesta de Na + . Uma ativação inadequada do S-RAA tecidual pode causar hipertensão e dano ao órgão. Nós revisamos o impacto da dieta com alto teor de sódio sobre o eixo cardiorrenal, destacando as vias moleculares que causam a lesão. Também fizemos uma avaliação de recentes estudos observacionais relacionados às consequên-cias do acúmulo de Na + não osmoticamente ativo, quebrando assim o paradigma de que a alta ingestão de sódio necessariamente aumenta a concentração sérica de Na + , assim promovendo a retenção de água. ResumoPalavras-chave: Renina; Angiotensina II; Sódio na Dieta; Rim; Coração.Although there is a general agreement on the recommendation for reduced salt intake as a public health issue, the mechanism by which high salt intake triggers pathological effects on the cardio--renal axis is not completely understood. Emerging evidence indicates that the renin-angiotensin-aldosterone system (RAAS) is the main target of high Na + intake. An inappropriate activation of tissue RAAS may lead to hypertension and organ damage. We reviewed the impact of high salt intake on the RAAS on the cardio-renal axis highlighting the molecular pathways that leads to injury effects. We also provide an assessment of recent observational studies related to the consequences of non-osmotically active Na + accumulation, breaking the paradigm that high salt intake necessarily increases plasma Na + concentration promoting water retention AbstRAct

Aim of the Study: During type 2 diabetes (T2D) and hypertension there is stimulation of renal proximal tubule angiotensinogen (AGT), but whether urinary excretion of AGT (uAGT) is an indicator of glomerular damage or intrarenal RAS activation is unclear. We tested the hypothesis that elevations in uAGT can be detected in the absence of albuminuria in a mouse model of T2D.Methods: Male C57BL/6 mice (N=10) were fed a high fat (HFD; 45% Kcal from fat) for 28 weeks, and the metabolic phenotype including body weight, blood pressures, glucose, insulin, ippGTT, HOMA-IR, and cholesterol was examined. In addition, kidney Ang II content and reactive oxygen species (ROS) was measured along with urinary albumin, creatinine, Ang II, and AGT.Results: All parameters consistent with T2D were present in mice after 12-14 weeks on the HFD. Systolic BP increased after 18 weeks in HFD but not NFD mice. Intrarenal ROS and Ang II concentrations were also increased in HFD mice. Remarkably, these changes paralleled the augmentation uAGT excretion (3.66 ± 0.50 vs. 0.92 ± 0.13 ng/mg by week 29; P<0.01), which occurred in the absence of overt albuminuria. Conclusions:In HFD-induced T2D mice, increases in uAGT occur in the absence of overt renal injury, indicating that this biomarker accurately detects early intrarenal RAS activation.

No abstract

In the kidney, the stimulation of renin production by the collecting duct (CD-renin) contributes to the development of hypertension. The CD is a major nephron segment for the synthesis of nitric oxide (NO), and low NO bioavailability in the renal medulla is associated with hypertension. However, it is unknown whether NO regulates renin production in the CD. To test the hypothesis that low intrarenal NO levels stimulate the production of CD-renin, we first examined renin expression in the distal nephron segments of CD-eNOS deficient mice. In these mice, specific CD-renin immunoreactivity was increased compared to wild-type littermates; however, juxtaglomerular (JG) renin was not altered. To further assess the intracellular mechanisms involved, we then treated M-1 cells with either 1 mM L-NAME (L-arginine analog), an inhibitor of NO synthase activity, or 1 mM NONOate, a NO donor. Both treatments increased intracellular renin protein levels in M-1 cells. However, only the inhibition of NOS with L-NAME stimulated renin synthesis and secretion as reflected by the increase in Ren1C transcript and renin protein levels in the extracellular media, respectively. In addition, NONOate induced a fast mobilization of cGMP and intracellular renin accumulation. These response was partially prevented by guanylyl cyclase inhibition with ODQ (1H-[1,2,4] oxadiazolo[4,3-a]quinoxalin-1]. Accumulation of intracellular renin was blocked by protein kinase G (PKG) and protein kinase C (PKC) inhibitors. Our data indicate that low NO bioavailability increases CD-renin synthesis and secretion, which may contribute to the activation of intrarenal renin angiotensin system.

The Na+-activated Na+ channel (Nax) and salt-inducible kinase (SIK) are stimulated by increases in local Na+ concentration, affecting (Na+ + K+)-ATPase activity. To test the hypothesis that the triad Nax/SIK/(Na+ + K+)-ATPase contributes to kidney injury and salt-sensitive hypertension (HTN), uninephrectomized male Wistar rats (200 g; n = 20) were randomly divided into 4 groups based on a salt diet (normal salt diet; NSD—0.5% NaCl—or high-salt diet; HSD—4% NaCl) and subcutaneous administration of saline (0.9% NaCl) or deoxycorticosterone acetate (DOCA, 8 mg/kg), as follows: Control (CTRL), CTRL-Salt, DOCA, and DOCA-Salt, respectively. After 28 days, the following were measured: kidney function, blood pressure, (Na+ + K+)-ATPase and SIK1 kidney activities, and Nax and SIK1 renal expression levels. SIK isoforms in kidneys of CTRL rats were present in the glomerulus and tubular epithelia; they were not altered by HSD and/or HTN. CTRL-Salt rats remained normotensive but presented slight kidney function decay. HSD rats displayed augmentation of the Nax/SIK/(Na+ + K+)-ATPase pathway. HTN, kidney injury, and kidney function decay were present in all DOCA rats; these were aggravated by HSD. DOCA rats presented unaltered (Na+ + K+)-ATPase activity, diminished total SIK activity, and augmented SIK1 and Nax content in the kidney cortex. DOCA-Salt rats expressed SIK1 activity and downregulation in (Na+ + K+)-ATPase activity in the kidney cortex despite augmented Nax content. The data of this study indicate that the (Na+ + K+)-ATPase activity response to SIK is attenuated in rats under HSD, independent of HTN, as a mechanism contributing to kidney injury and salt-sensitive HTN.