Deletion, but not heterozygosity, of eNOS raises blood pressure and aggravates nephropathy in BTBR ob/ob mice

INTRODUCTION

ob/ob mice are a leptin-deficient type 2 diabetes mellitus model, which, on a BTBR background, mimics glomerular pathophysiology of diabetic nephropathy (DN). Since leptin deficiency reduces blood pressure (BP), and endothelial nitric oxide synthase (eNOS) lowers BP and is kidney protective, we attempted to develop a more robust DN model by introducing eNOS deficiency in BTBR ob/ob mice.

METHODS

Six experimental groups included littermate male and female BTBR ob/ob or wild-type for ob (control) as well as wild-type (WT), heterozygote (HET) or knockout (KO) for eNOS. Systolic BP (by automated tail-cuff) and GFR (by FITC sinistrin plasma kinetics) were determined in awake mice at 27-30 weeks of age followed by molecular and histological kidney analyses.

RESULTS

Male and female ob/ob WT presented hyperglycemia and larger body and kidney weight, GFR, glomerular injury, and urine albumin to creatinine ratio (UACR) despite modestly lower BP vs control WT. These effects were associated with higher tubular injury score and renal mRNA expression of NGAL only in males, whereas female ob/ob WT unexpectedly had lower KIM-1 and COL1A1 expression vs control WT, indicating sex differences. HET for eNOS did not consistently alter BP or renal outcome in control or ob/ob. In comparison, eNOS KO increased BP (15-25 mmHg) and worsened renal markers of injury, inflammation and fibrosis, GFR, UACR, and survival rates, as observed in control and, more pronounced, in ob/ob mice and independent of sex.

CONCLUSIONS

Deletion, but not heterozygosity, of eNOS raises blood pressure and aggravates nephropathy in BTBR ob/ob mice.

Tailored Chemical Reactivity Probes for Systemic Imaging of Aldehydes in Fibroproliferative Diseases

During fibroproliferation, protein-associated extracellular aldehydes are formed by the oxidation of lysine residues on extracellular matrix proteins to form the aldehyde allysine. Here we report three Mn(II)-based, small-molecule magnetic resonance probes that contain α-effect nucleophiles to target allysine in vivo and report on tissue fibrogenesis. We used a rational design approach to develop turn-on probes with a 4-fold increase in relaxivity upon targeting. The effects of aldehyde condensation rate and hydrolysis kinetics on the performance of the probes to detect tissue fibrogenesis non-invasively in mouse models were evaluated by a systemic aldehyde tracking approach. We showed that, for highly reversible ligations, off-rate was a stronger predictor of in vivo efficiency, enabling histologically validated, three-dimensional characterization of pulmonary fibrogenesis throughout the entire lung. The exclusive renal elimination of these probes allowed for rapid imaging of liver fibrosis. Reducing the hydrolysis rate by forming an oxime bond with allysine enabled delayed phase imaging of kidney fibrogenesis. The imaging efficacy of these probes, coupled with their rapid and complete elimination from the body, makes them strong candidates for clinical translation.

Tailored chemical reactivity probes for systemic imaging of aldehydes in fibroproliferative diseases

During fibroproliferation, protein-associated extracellular aldehydes are formed by the oxidation of lysine residues on extracellular matrix proteins to form the aldehyde allysine. Here we report three Mn(II)-based, small molecule magnetic resonance (MR) probes that contain α-effect nucleophiles to target allysine in vivo and report on tissue fibrogenesis. We used a rational design approach to develop turn-on probes with a 4-fold increase in relaxivity upon targeting. The effects of aldehyde condensation rate and hydrolysis kinetics on the performance of the probes to detect tissue fibrogenesis noninvasively in mouse models were evaluated by a systemic aldehyde tracking approach. We showed that for highly reversible ligations, off-rate was a stronger predictor of in vivo efficiency, enabling histologically validated, three-dimensional characterization of pulmonary fibrogenesis throughout the entire lung. The exclusive renal elimination of these probes allowed for rapid imaging of liver fibrosis. Reducing the hydrolysis rate by forming an oxime bond with allysine enabled delayed phase imaging of kidney fibrogenesis. The imaging efficacy of these probes, coupled with their rapid and complete elimination from the body, make them strong candidates for clinical translation.

Mitochondrial and NAD+ metabolism predict recovery from acute kidney injury in a diverse mouse population

Acute kidney failure and chronic kidney disease are global health issues steadily rising in incidence and prevalence. Animal models on a single genetic background have so far failed to recapitulate the clinical presentation of human nephropathies. Here, we used a simple model of folic acid-induced kidney injury in 7 highly diverse mouse strains. We measured plasma and urine parameters, as well as renal histopathology and mRNA expression data, at 1, 2, and 6 weeks after injury, covering the early recovery and long-term remission. We observed an extensive strain-specific response ranging from complete resistance of the CAST/EiJ to high sensitivity of the C57BL/6J, DBA/2J, and PWK/PhJ strains. In susceptible strains, the severe early kidney injury was accompanied by the induction of mitochondrial stress response (MSR) genes and the attenuation of NAD+ synthesis pathways. This is associated with delayed healing and a prolonged inflammatory and adaptive immune response 6 weeks after insult, heralding a transition to chronic kidney disease. Through a thorough comparison of the transcriptomic response in mouse and human disease, we show that critical metabolic gene alterations were shared across species, and we highlight the PWK/PhJ strain as an emergent model of transition from acute kidney injury to chronic disease.

Novel roles of the renal angiotensin-converting enzyme

The observation that all components of the renin angiotensin system (RAS) are expressed in the kidney and the fact that intratubular angiotensin (Ang) II levels greatly exceed the plasma concentration suggest that the synthesis of renal Ang II occurs independently of the circulating RAS. One of the main components of this so-called intrarenal RAS is angiotensin-converting enzyme (ACE). Although the role of ACE in renal disease is demonstrated by the therapeutic effectiveness of ACE inhibitors in treating several conditions, the exact contribution of intrarenal versus systemic ACE in renal disease remains unknown. Using genetically modified mouse models, our group demonstrated that renal ACE plays a key role in the development of several forms of hypertension. Specifically, although ACE is expressed in different cell types within the kidney, its expression in renal proximal tubular cells is essential for the development of high blood pressure. Besides hypertension, ACE is involved in several other renal diseases such as diabetic kidney disease, or acute kidney injury even when blood pressure is normal. In addition, studies suggest that ACE might mediate at least part of its effect through mechanisms that are independent of the Ang I conversion into Ang II and involve other substrates such as N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP), Ang-(1-7), and bradykinin, among others. In this review, we summarize the recent advances in understanding the contribution of intrarenal ACE to different pathological conditions and provide insight into the many roles of ACE besides the well-known synthesis of Ang II.

Structure-function relationships of the soluble form of the antiaging protein Klotho have therapeutic implications for managing kidney disease

The fortuitously discovered antiaging membrane protein αKlotho (Klotho) is highly expressed in the kidney, and deletion of the Klotho gene in mice causes a phenotype strikingly similar to that of chronic kidney disease (CKD). Klotho functions as a co-receptor for fibroblast growth factor 23 (FGF23) signaling, whereas its shed extracellular domain, soluble Klotho (sKlotho), carrying glycosidase activity, is a humoral factor that regulates renal health. Low sKlotho in CKD is associated with disease progression, and sKlotho supplementation has emerged as a potential therapeutic strategy for managing CKD. Here, we explored the structure-function relationship and post-translational modifications of sKlotho variants to guide the future design of sKlotho-based therapeutics. Chinese hamster ovary (CHO)- and human embryonic kidney (HEK)-derived WT sKlotho proteins had varied activities in FGF23 co-receptor and β-glucuronidase assays in vitro and distinct properties in vivo Sialidase treatment of heavily sialylated CHO-sKlotho increased its co-receptor activity 3-fold, yet it remained less active than hyposialylated HEK-sKlotho. MS and glycopeptide-mapping analyses revealed that HEK-sKlotho is uniquely modified with an unusual N-glycan structure consisting of N,N'-di-N-acetyllactose diamine at multiple N-linked sites, one of which at Asn-126 was adjacent to a putative GalNAc transfer motif. Site-directed mutagenesis and structural modeling analyses directly implicated N-glycans in Klotho's protein folding and function. Moreover, the introduction of two catalytic glutamate residues conserved across glycosidases into sKlotho enhanced its glucuronidase activity but decreased its FGF23 co-receptor activity, suggesting that these two functions might be structurally divergent. These findings open up opportunities for rational engineering of pharmacologically enhanced sKlotho therapeutics for managing kidney disease.

The Absence of the ACE N-Domain Decreases Renal Inflammation and Facilitates Sodium Excretion during Diabetic Kidney Disease

BACKGROUND

Recent evidence emphasizes the critical role of inflammation in the development of diabetic nephropathy. Angiotensin-converting enzyme (ACE) plays an active role in regulating the renal inflammatory response associated with diabetes. Studies have also shown that ACE has roles in inflammation and the immune response that are independent of angiotensin II. ACE's two catalytically independent domains, the N- and C-domains, can process a variety of substrates other than angiotensin I.

METHODS

To examine the relative contributions of each ACE domain to the sodium retentive state, renal inflammation, and renal injury associated with diabetic kidney disease, we used streptozotocin to induce diabetes in wild-type mice and in genetic mouse models lacking either a functional ACE N-domain (NKO mice) or C-domain (CKO mice).

RESULTS

In response to a saline challenge, diabetic NKO mice excreted 32% more urinary sodium compared with diabetic wild-type or CKO mice. Diabetic NKO mice also exhibited 55% less renal epithelial sodium channel cleavage (a marker of channel activity), 55% less renal IL-1β, 53% less renal TNF-α, and 53% less albuminuria than diabetic wild-type mice. This protective phenotype was not associated with changes in renal angiotensin II levels. Further, we present evidence that the anti-inflammatory tetrapeptide N-acetyl-seryl-asparyl-lysyl-proline (AcSDKP), an ACE N-domain-specific substrate that accumulates in the urine of NKO mice, mediates the beneficial effects observed in the NKO.

CONCLUSIONS

These data indicate that increasing AcSDKP by blocking the ACE N-domain facilitates sodium excretion and ameliorates diabetic kidney disease independent of intrarenal angiotensin II regulation.

Abstract 035: Increasing Renal AcSDKP by Eliminating the ACE N-Domain Blocks Renal Inflammation and Sodium Retention During Diabetic Nephropathy

Angiotensin-converting enzyme (ACE) plays a key role in renal inflammation and sodium retention associated with diabetic nephropathy. Although most effects of ACE have been classically related to angiotensin (Ang) II synthesis, studies highlight an Ang II-independent role of ACE in inflammation. Indeed, ACE has two catalytic domains, the N- and C-domains, that can process a wide diversity of substrates besides Ang I. Here, we study the relative contributions of ACE domains to renal inflammation and sodium retention during diabetic nephropathy. Diabetes was induced with streptozotocin in wild-type (WT) mice and mice lacking either a functional ACE N-domain (NKO) or C-domain (CKO) (n=5-8). After 6 months of diabetes, we evaluated the natriuretic response to volume expansion. For this, mice were injected with 0.9% NaCl equivalent to 10% of their body weight. After 5 hours, diabetic NKO mice excreted 30% more urinary sodium in response to the saline challenge compared to diabetic WT or CKO mice ( P <0.05). This enhanced natriuretic response was associated with a 47% reduction ( P <0.05) of renal epithelial sodium channel (ENaC) cleaved (active) α and γ subunits. Further, diabetic NKO displayed lower levels of renal fibrosis (46% reduction, P <0.05), IL-1β (56% reduction, P <0.05), TNFα (50% reduction, P <0.05) and albuminuria (53% reduction, P <0.01) compared to WT and CKO diabetic mice. This protective phenotype was not associated with changes in renal Ang II levels (WT: 237 ± 73; NKO: 283 ± 53 CKO: 245 ± 39 fmol/g kidney, P =NS). We next evaluated whether the anti-inflammatory tetrapeptide N-acetyl-seryl-asparyl-lysyl-proline (AcSDKP), an ACE N-domain specific substrate, mediates the protective phenotype of NKO. For this, diabetic mice were treated with the prolyl oligopeptidase inhibitor, S17092 (10 mg/kg, IP), that prevents the synthesis of AcSDKP. In diabetic NKO mice receiving S17092, sodium excretion in response to a saline challenge, ENaC α and γ subunit cleavage, renal inflammation and renal injury were indistinguishable from equally treated diabetic WT mice. In summary, these data indicate that increasing AcSDKP by blocking the ACE N-domain improves sodium handling and ameliorates diabetic kidney disease independently of intrarenal Ang II regulation.

Renal tubular ACE-mediated tubular injury is the major contributor to microalbuminuria in early diabetic nephropathy

Diabetic nephropathy is a major cause of end-stage renal disease in developed countries. While angiotensin-converting enzyme (ACE) inhibitors are used to treat diabetic nephropathy, how intrarenal ACE contributes to diabetic renal injury is uncertain. Here, two mouse models with different patterns of renal ACE expression were studied to determine the specific contribution of tubular vs. glomerular ACE to early diabetic nephropathy: it-ACE mice, which make endothelial ACE but lack ACE expression by renal tubular epithelium, and ACE 3/9 mice, which lack endothelial ACE and only express renal ACE in tubular epithelial cells. The absence of endothelial ACE normalized the glomerular filtration rate and endothelial injury in diabetic ACE 3/9 mice. However, these mice developed tubular injury and albuminuria and displayed low renal levels of megalin that were similar to those observed in diabetic wild-type mice. In diabetic it-ACE mice, despite hyperfiltration, the absence of renal tubular ACE greatly reduced tubulointerstitial injury and albuminuria and increased renal megalin expression compared with diabetic wild-type and diabetic ACE 3/9 mice. These findings demonstrate that endothelial ACE is a central regulator of the glomerular filtration rate while tubular ACE is a key player in the development of tubular injury and albuminuria. These data suggest that tubular injury, rather than hyperfiltration, is the main cause of microalbuminuria in early diabetic nephropathy.

Abstract P415: ACE N-domain Regulates High-glucose Mediated Interleukin-1 beta Production by Renal Epithelial Cells Independently From Angiotensin II Generation

Research studies demonstrated that interleukin (IL)-1β contributes to the development of diabetic nephropathy and hypertension. However, the origin and regulation of IL-1β synthesis during diabetic kidney injury are still unknown. Here, we hypothesize that renal epithelial cells produce IL-1β in response to a high glucose stress and that angiotensin converting enzyme (ACE) plays a key role in this process. To study this, we isolated proximal tubular (PT) epithelial cells from wild-type (WT) and mice lacking either the ACE N-domain (NKO) or the C-domain (CKO) catalytic activity. These cells were exposed to normal (5 mM) or high (30 mM) glucose for 24 hours. IL-1β produced by PT cells were assessed by ELISA and RT-PCR. High glucose induced WT PT cells to release significant amounts of IL-1β (from 5±1 to 70±6 pg/ml, p<0.001; n=6). When WT PT cells were exposed to a high glucose media in the presence of an ACE inhibitor (lisinopril, 10 mM), IL-1β levels were significantly reduced (from 70±6 to 38±6 pg/ml, p<0.01). In contrast, AT1 receptor blockade by losartan did not change the amount of IL-1β produced by WT PT cells. To determine which ACE domain is associated with IL-1β production, NKO and CKO PT cells were exposed to high glucose. Strikingly, NKO PT cells released lower amounts of IL-1β when exposed to high glucose compared to WT (NKO: 15±7 vs. WT: 79±9 pg/ml, p<0.01, n=4). No differences were observed between WT and CKO PT cells. Since the ACE N-domain degrades the anti-inflammatory tetrapeptide N-acetyl-Ser-Asp-Lys-Pro (AcSDKP), we tested whether the lower IL-1β production in NKO PT cells was due to an accumulation of AcSDKP. For this, we pre-treated NKO PT cells with a prolyl endopeptidase inhibitor (S17092, 50μM) to prevent the production of AcSDKP. Notably, this treatment increased the IL-1β response to high glucose in NKO PT cells (2.1±0.3-fold increase, p<0.01, n=4). Our data indicate that: 1) PT cells can sense and respond to high glucose by secreting IL-1β and 2) the absence of the ACE N-domain blunts the production of IL-1β through a mechanism that involves AcSDKP accumulation. In conclusion, ACE might contribute to the inflammatory response that underlays diabetic nephropathy independently from angiotensin II generation.

Renal tubular angiotensin converting enzyme is responsible for nitro-L-arginine methyl ester (L-NAME)-induced salt sensitivity

Renal parenchymal injury predisposes to salt-sensitive hypertension, but how this occurs is not known. Here we tested whether renal tubular angiotensin converting enzyme (ACE), the main site of kidney ACE expression, is central to the development of salt sensitivity in this setting. Two mouse models were used: it-ACE mice in which ACE expression is selectively eliminated from renal tubular epithelial cells; and ACE 3/9 mice, a compound heterozygous mouse model that makes ACE only in renal tubular epithelium from the ACE 9 allele, and in liver hepatocytes from the ACE 3 allele. Salt sensitivity was induced using a post L-NAME salt challenge. While both wild-type and ACE 3/9 mice developed arterial hypertension following three weeks of high salt administration, it-ACE mice remained normotensive with low levels of renal angiotensin II. These mice displayed increased sodium excretion, lower sodium accumulation, and an exaggerated reduction in distal sodium transporters. Thus, in mice with renal injury induced by L-NAME pretreatment, renal tubular epithelial ACE, and not ACE expression by renal endothelium, lung, brain, or plasma, is essential for renal angiotensin II accumulation and salt-sensitive hypertension.

Overexpression of angiotensin-converting enzyme in myelomonocytic cells enhances the immune response

Angiotensin-converting enzyme (ACE) converts angiotensin I to the vasoconstrictor angiotensin II and thereby plays an important role in blood pressure control. However, ACE is relatively non-specific in its substrate specificity and cleaves many other peptides. Recent analysis of mice overexpressing ACE in monocytes, macrophages, and other myelomonocytic cells shows that these animals have a marked increase in resistance to experimental melanoma and to infection by Listeria monocytogenes or methicillin-resistant Staphylococcus aureus (MRSA). Several other measures of immune responsiveness, including antibody production, are enhanced in these animals. These studies complement a variety of studies indicating an important role of ACE in the immune response.

Angiotensin-converting enzyme overexpression in myelocytes enhances the immune response

Angiotensin-converting enzyme (ACE) plays an important role in blood pressure control. ACE also has effects on renal function, reproduction, hematopoiesis, and several aspects of the immune response. ACE 10/10 mice overexpress ACE in monocytic cells; macrophages from ACE 10/10 mice demonstrate increased polarization toward a proinflammatory phenotype. As a result, ACE 10/10 mice have a highly effective immune response following challenge with melanoma, bacterial infection, or Alzheimer disease. As shown in ACE 10/10 mice, enhanced monocytic function greatly contributes to the ability of the immune response to defend against a wide variety of antigenic and non-antigenic challenges.

Abstract 019: Specific Knockdown of Renal Tubular Epithelial Ace Prevents Salt Sensitivity

We previously showed that mice lacking renal angiotensin-converting enzyme (ACE) do not accumulate angiotensin (Ang) II in the kidney and are protected against different forms of experimental hypertension, including salt sensitivity. However, these studies did not identify the locus of renal Ang II generation. Since ACE expression is high in the renal epithelium, we hypothesize that tubular epithelial ACE is the main source of renal Ang II and, is responsible for salt sensitivity. To study this, we designed an inducible tubular ACE knockdown mouse (it-ACE) that has three transgenes: one encoding the transcription factor tTA (Tet-off transactivator) that is under the control of the KSP-cadherin promoter only expressed in renal tubular cells. The second and third transgenes are activated by tTA and encode a short-hairpin RNAs (sh-RNA) degrading ACE mRNA in renal tubules. We found a lower basal ACE expression in the kidney of it-ACE compared to WT mice (19 ± 4 vs. 100 ± 26 AU; p<0.01 by Western blot). Selective tubular ACE suppression was confirmed by immunohistochemistry. At baseline, it-ACE mice display normal systolic blood pressure (SBP; 108 ± 4 mmHg), GFR (1288 ± 24 μl/min/100g b.w.) and urine concentration (2516 ± 184 mOsm/Kg after 12h water deprivation) compared to WT mice. To test the response of it-ACE mice to salt-sensitivity, we used a post L-NAME salt sensitivity protocol: L-NAME (0.5 mg/mL; 4 weeks), washout (1 week), high salt diet (HS, NaCl 4%, 3 weeks). In WT mice, L-NAME increased SBP from 109 ± 5 to 139 ± 4 mmHg (p<0.01; n=5). SBP then returned to baseline during the washout and increased again in response to the HS diet (135 ± 3 mmHg; p<0.01). Thus, WT mice, previously salt resistant, became salt sensitive. Remarkably, it-ACE mice, despite being as hypertensive as WT during the L-NAME phase, were still protected against salt sensitivity (110 ± 3 mmHg; p<0.01 vs. WT; n=6). Finally, we treated it-ACE mice with doxycycline (a tTA blocker) to restore tubular ACE specifically during the HS phase. Restoring tubular ACE in the mutant mice induced the development of salt sensitivity (134 ± 6 mmHg; p<0.01 vs. baseline; n=5). In conclusion, our data indicate that tubular epithelial ACE, and not ACE expression in endothelium or other locations, is essential for salt sensitivity.

Salt Sensitivity in Response to Renal Injury Requires Renal Angiotensin-Converting Enzyme

Recent evidence indicates that salt-sensitive hypertension can result from a subclinical injury that impairs the kidneys' capacity to properly respond to a high-salt diet. However, how this occurs is not well understood. Here, we showed that although previously salt-resistant wild-type mice became salt sensitive after the induction of renal injury with the nitric oxide synthase inhibitor Nω-nitro-l-arginine methyl ester hydrochloride; mice lacking renal angiotensin-converting enzyme, exposed to the same insult, did not become hypertensive when faced with a sodium load. This is because the activity of renal angiotensin-converting enzyme plays a critical role in (1) augmenting the local pool of angiotensin II and (2) the establishment of the antinatriuretic state via modulation of glomerular filtration rate and sodium tubular transport. Thus, this study demonstrates that the presence of renal angiotensin-converting enzyme plays a pivotal role in the development of salt sensitivity in response to renal injury.

ACE overexpression in myelomonocytic cells: effect on a mouse model of Alzheimer's disease

While it is well known that angiotensin converting enzyme (ACE) plays an important role in blood pressure control, ACE also has effects on renal function, hematopoiesis, reproduction, and aspects of the immune response. ACE 10/10 mice overexpress ACE in myelomonocytic cells. Macrophages from these mice have an increased polarization towards a pro-inflammatory phenotype that results in a very effective immune response to challenge by tumors or bacterial infection. In a mouse model of Alzheimer's disease (AD), the ACE 10/10 phenotype provides significant protection against AD pathology, including reduced inflammation, reduced burden of the neurotoxic amyloid-β protein and preserved cognitive function. Taken together, these studies show that increased myelomonocytic ACE expression in mice alters the immune response to better defend against many different types of pathologic insult, including the cognitive decline observed in an animal model of AD.

The intrarenal generation of angiotensin II is required for experimental hypertension

Hypertension is a major risk factor for cardiovascular disease. While the cause of hypertension is multifactorial, renal dysregulation of salt and water excretion is a major factor. All components of the renin-angiotensin system are produced locally in the kidney, suggesting that intrarenal generation of angiotensin II plays a key role in blood pressure regulation. Here, we show that two mouse models lacking renal angiotensin converting enzyme (ACE) are protected against angiotensin II and l-NAME induced hypertension. In response to hypertensive stimuli, mice lacking renal ACE do not produce renal angiotensin II. These studies indicate that the intrarenal renin-angiotensin system works as an entity separate from systemic angiotensin II generation. Renal ACE appears necessary for experimental hypertension.

Renal generation of angiotensin II and the pathogenesis of hypertension

The existence of a complete and functional renin-angiotensin system along the nephron is widely recognized. However, its precise role in blood pressure control and, by extension, hypertension is still uncertain. While most investigators agree that overexpressing RAS components along the nephron results in hypertension, two important issues remain: whether the local RAS works as a separate entity or represents an extension of the systemic RAS and whether locally generated angiotensin II has specific renal effects on blood pressure that are distinct from systemic angiotensin II. This review addresses these issues while emphasizing the unique role of local angiotensin II in the response of the kidney to hypertensive stimuli and the induction of hypertension.

Renal angiotensin-converting enzyme is essential for the hypertension induced by nitric oxide synthesis inhibition

The kidney is an important source of angiotensin-converting enzyme (ACE) in many species, including humans. However, the specific effects of local ACE on renal function and, by extension, BP control are not completely understood. We previously showed that mice lacking renal ACE, are resistant to the hypertension induced by angiotensin II infusion. Here, we examined the responses of these mice to the low-systemic angiotensin II hypertensive model of nitric oxide synthesis inhibition with L-NAME. In contrast to wild-type mice, mice without renal ACE did not develop hypertension, had lower renal angiotensin II levels, and enhanced natriuresis in response to L-NAME. During L-NAME treatment, the absence of renal ACE was associated with blunted GFR responses; greater reductions in abundance of proximal tubule Na(+)/H(+) exchanger 3, Na(+)/Pi co-transporter 2, phosphorylated Na(+)/K(+)/Cl(-) cotransporter, and phosphorylated Na(+)/Cl(-) cotransporter; and greater reductions in abundance and processing of the γ isoform of the epithelial Na(+) channel. In summary, the presence of ACE in renal tissue facilitates angiotensin II accumulation, GFR reductions, and changes in the expression levels and post-translational modification of sodium transporters that are obligatory for sodium retention and hypertension in response to nitric oxide synthesis inhibition.

JAK-STAT and the renin-angiotensin system: The role of the JAK-STAT pathway in blood pressure and intrarenal renin-angiotensin system regulation

The renin-angiotensin system (RAS) plays important roles in blood pressure control and tissue disease. An inappropriate local angiotensin II elevation in the kidneys leads to the development of hypertension, tissue damage and chronic injury. Studies have demonstrated that the JAK-STAT pathway mediates angiotensin II-triggered gene transcription. The JAK-STAT pathway in turn, acting as an amplifying system, contributes to further intrarenal RAS activation. These observations prompt the suggestion that the JAK-STAT pathway may be of importance in elucidating the mechanisms RAS-associated tissue injury. Accordingly, this review provides a brief overview of the interactions between the JAK-STAT pathway and the RAS, specifically the RAS expressed in the kidneys.

The NLRP3 inflammasome is required for the development of hypoxemia in LPS/mechanical ventilation acute lung injury

IL-1β is a potent proinflammatory cytokine that is implicated in the pathogenesis of acute respiratory distress syndrome. We hypothesized that LPS and mechanical ventilation (MV) together could lead to IL-1β secretion and the development of acute lung injury (ALI), and that this process would be dependent on caspase-1 and the nucleotide binding domain and leucine-rich repeat (NLR) pyrin domain containing 3 (NLRP3) inflammasome activation. The objectives of this study were to determine the specific role of IL-1β, caspase-1, and the NLRP3 inflammasome in a two-hit model of ALI due to LPS plus MV. We used a two-hit murine model of ALI in which both inhaled LPS and MV were required for the development of hypoxemia, pulmonary neutrophil infiltration, and alveolar leakage. Nlrp3-deficent and Casp1-deficient mice had significantly diminished IL-1β levels in bronchoalveolar lavage fluid, and were specifically protected from hypoxemia, despite similar alveolar neutrophil infiltration and leakage. The IL-1 receptor antagonist, Anakinra, significantly improved the specific development of hypoxemia without significant effects on neutrophil infiltration or alveolar leakage. MV resulted in increased bronchoalveolar lavage extracellular ATP and alveolar macrophage apoptosis as triggers of NLRP3 inflammasome activation. NLRP3 inflammasome activation and IL-1β production play a key role in ALI caused by the combination of LPS and MV, particularly in the hypoxemia associated with acute respiratory distress syndrome. Blocking IL-1 signaling in this model specifically ameliorates hypoxemia, without affecting neutrophil infiltration and alveolar leakage, disassociating these readouts of ALI. MV causes alveolar macrophage apoptosis, a key step in the activation of NLRP3 inflammasome and production of IL-1β.

Renal angiotensin-converting enzyme and blood pressure control

PURPOSE OF REVIEW

This review presents novel findings regarding the renal angiotensin-converting enzyme (ACE) and its role in blood pressure (BP) control.

RECENT FINDINGS

The textbook flow diagram of the renin-angiotensin system (RAS) shows the pulmonary endothelium as the main source of the ACE that converts angiotensin I to angiotensin II. However, ACE is made in large quantities by the kidneys, which raises the important question of what precisely is the function of renal ACE? Recent studies in gene-targeted mice indicates that renal ACE plays a dominant role in regulating the response of the kidney to experimental hypertension. In particular, renal ACE and locally generated angiotensin II affect the activity of several key sodium transporters and the induction of sodium and water retention resulting in the elevation of BP.

SUMMARY

New experimental data link the renal ACE/angiotensin II pathway and the local regulation of sodium transport as key elements in the development of hypertension.

Rediscovering ACE: novel insights into the many roles of the angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is best known for the catalytic conversion of angiotensin I to angiotensin II. However, the use of gene-targeting techniques has led to mouse models highlighting many other biochemical properties and actions of this enzyme. This review discusses recent studies examining the functional significance of ACE tissue-specific expression and the presence in ACE of two independent catalytic sites with distinct substrates and biological effects. It is these features which explain why ACE makes important contributions to many different physiological processes including renal development, blood pressure control, inflammation, and immunity.

Abstract 187: The Absence of Renal ACE Blunts the Renal Response and the Hypertension Induced by Nitric Oxide Synthesis Inhibition

We previously showed that the responses to angiotensin (Ang) II infusion observed in wild type (WT) mice were effectively prevented in mice lacking renal ACE (ACE 3/3 and ACE 10/10 mice) including: hypertension, renal Ang II accumulation, sodium and water retention, and activation of ion transporters in the loop of Henle (NKCC2) and distal nephron (NCC, ENaC, and pendrin). The aim of this study was to test if the absence of renal ACE also protects against hypertension induced by nitric oxide (NO) synthesis inhibition with L-NAME, a low-plasma Ang II hypertension model associated with renal renin-angiotensin system (RAS) activation. In response to L-NAME (0.5 mg/mL in drinking water, 4 wk; n=12-17), systolic blood pressure (SBP) of WT rose from 110±2 to 135±3 mmHg (p<0.01) while SBP in mice lacking renal ACE did not significantly increase: in ACE 10/10, SBP went from 109±3 to 113±2 mmHg (NS), in ACE 3/3 mice from 103±5 to 110±5 mmHg (NS). ACE 10/10 mice exhibited an enhanced natriuretic/diuretic response vs. WT mice: UNaV during the first 24 h of L-NAME was 188±14 μmol in WT and 314±17 μmol in ACE 10/10 (p<0.01). Ang II content [by immunohistochemistry (IHC)] increased from 8±2 to 28±4 % of positive staining/area (p<0.001) in L-NAME-treated WT mice but remained unchanged in ACE 10/10 mice (from 3±1 to 5±1 % of positive staining/area, NS). Consistent with the dissimilar Ang II content, L-NAME increased renal AGT levels by 2.3±0.3 (p<0.01) in WT but not in the ACE 10/10 mice, 0.8±0.1 fold (NS) vs. non-treated animals. The enhanced natriuresis of the L-NAME-treated ACE 10/10 mice was associated with lower NHE3 expression (0.5±0.1 AU) and lower phosphorylation (-P) of NKCC-P (0.48±0.05 AU) and NCC-P (0.5±0.1 AU) vs. equally treated WT (WT defined as 1, p<0.01). In addition, L-NAME-treated WT mice had higher renal macrophage infiltration (82±8 F4/80+ cells/field, by IHC), higher TNF-α content (24±3 pg/mg, by ELISA) and IL-6 (36±2 pg/mg, by ELISA) vs. L-NAME-treated ACE 10/10 (51±3 F4/80+ cells/field, 14±1 pg/mg and 21±1 pg/mg respectively, p<0.01). In conclusion, our results demonstrate that renal ACE plays a fundamental role driving renal responses, hypertension and inflammation induced by NO synthesis inhibition.

The absence of intrarenal ACE protects against hypertension

Activation of the intrarenal renin-angiotensin system (RAS) can elicit hypertension independently from the systemic RAS. However, the precise mechanisms by which intrarenal Ang II increases blood pressure have never been identified. To this end, we studied the responses of mice specifically lacking kidney angiotensin-converting enzyme (ACE) to experimental hypertension. Here, we show that the absence of kidney ACE substantially blunts the hypertension induced by Ang II infusion (a model of high serum Ang II) or by nitric oxide synthesis inhibition (a model of low serum Ang II). Moreover, the renal responses to high serum Ang II observed in wild-type mice, including intrarenal Ang II accumulation, sodium and water retention, and activation of ion transporters in the loop of Henle (NKCC2) and distal nephron (NCC, ENaC, and pendrin) as well as the transporter activating kinases SPAK and OSR1, were effectively prevented in mice that lack kidney ACE. These findings demonstrate that ACE metabolism plays a fundamental role in the responses of the kidney to hypertensive stimuli. In particular, renal ACE activity is required to increase local Ang II, to stimulate sodium transport in loop of Henle and the distal nephron, and to induce hypertension.

A modern understanding of the traditional and nontraditional biological functions of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidase responsible for converting angiotensin I into the vasoconstrictor angiotensin II. However, ACE is a relatively nonspecific peptidase that is capable of cleaving a wide range of substrates. Because of this, ACE and its peptide substrates and products affect many physiologic processes, including blood pressure control, hematopoiesis, reproduction, renal development, renal function, and the immune response. The defining feature of ACE is that it is composed of two homologous and independently catalytic domains, the result of an ancient gene duplication, and ACE-like genes are widely distributed in nature. The two ACE catalytic domains contribute to the wide substrate diversity of ACE and, by extension, the physiologic impact of the enzyme. Several studies suggest that the two catalytic domains have different biologic functions. Recently, the X-ray crystal structure of ACE has elucidated some of the structural differences between the two ACE domains. This is important now that ACE domain-specific inhibitors have been synthesized and characterized. Once widely available, these reagents will undoubtedly be powerful tools for probing the physiologic actions of each ACE domain. In turn, this knowledge should allow clinicians to envision new therapies for diseases not currently treated with ACE inhibitors.

Abstract 227: The Protective Effect of Kidney-Specific ACE Inhibition Against Chronic Angiotensin II Infusions is Associated with Blunted Intrarenal Renin-Angiotensin System Activation

Introduction: The responses to chronic angiotensin (Ang) II infusions of gene-targeted mice lacking kidney angiotensin-converting enzyme (ACE), in terms of intrarenal Ang II accumulation, hypertension, sodium and water retention are all blunted or absent. The objective of this study was to determine if these reduced responses were associated with changes in the intrarenal renin-angiotensin system (RAS).

METHODS: Mice lacking intrarenal ACE (ACE10/10) were generated by targeted homologous recombination placing the expression of ACE only in macrophages. As a result, these mice have normal circulating ACE levels, but no kidney ACE. Wild-type (WT) mice of the same background (C57Bl/J) served as controls. Mice were subjected to sham-operation or subcutaneous infusion of Ang II for two weeks (n=6-10, 400 ng/kg/min via osmotic minipump). Mean arterial pressure (MAP) was followed by telemetry. At the end of the experiment, the kidneys were collected for analysis. Ang II content was measured by RIA. Renal abundance of ACE, angiotensinogen (AGT) and Ang II receptor type 1 (AT1R) were determined by Western Blot in total kidney homogenates.

Results: At baseline, the MAP of WT and ACE 10/10 mice was similar 110 ± 4 mmHg vs. 109 ± 3 mmHg respectively (p>0.05). However, when subjected to chronic Ang II infusions, the hypertensive response was blunted in ACE 10/10 mice (129 ± 6 mmHg) vs. WT (146 ± 5 mmHg; P<0.05). Also, intrarenal Ang II accumulation was lower in ACE10/10 mice (724 ± 81 fmol/g) vs. WT (1130 ± 105 fmol/g, p<0.05). In non-treated mice, intrarenal RAS components analysis revealed that the absence of ACE in ACE10/10 mice was accompanied by a significant reduction in AGT (0.41 ± 0.06) and increased AT1R expression (1.32 ± 0.05) when compared to WT (normalized to 1.00, p<0.05 in both instances). Importantly, after chronic Ang II infusions, AGT, ACE and AT1R expression increased in WT (1.36, 1.26 and 1.17 fold increase respectively compared to non-treated WT, p<0.05) but not in the ACE10/10 mice (1.19, 1.06, 0.89 fold increase respectively compared to non-treated ACE10/10, p>0.05).

Conclusion: The blunted hypertension and Ang II accumulation of mice devoid of kidney ACE in response to Ang II infusions is associated with a failed induction of renal AGT and the AT1R.

Interferon-γ biphasically regulates angiotensinogen expression via a JAK-STAT pathway and suppressor of cytokine signaling 1 (SOCS1) in renal proximal tubular cells

Renal inflammation modulates angiotensinogen (AGT) production in renal proximal tubular cells (RPTCs) via inflammatory cytokines, including interleukin-6, tumor necrosis factor α, and interferon-γ (IFN-γ). Among these, the effects of IFN-γ on AGT regulation in RPTCs are incompletely delineated. This study aimed to elucidate mechanisms by which IFN-γ regulates AGT expression in RPTCs. RPTCs were incubated with or without IFN-γ up to 48 h. AGT expression, STAT1 and STAT3 activities, and SOCS1 expression were evaluated. RNA interference studies against STAT1, SOCS1, and STAT3 were performed to elucidate a signaling cascade. IFN-γ decreased AGT expression at 6 h (0.61±0.05, ratio to control) and 12 h (0.47±0.03). In contrast, longer exposure for 24 and 48 h increased AGT expression (1.76±0.18, EC(50)=3.4 ng/ml, and 1.45±0.08, respectively). IFN-γ treatment for 6 h strongly induced STAT1 phosphorylation and SOCS1 augmentation, and decreased STAT3 activity. However, STAT1 phosphorylation and SOCS1 augmentation waned at 24 h, while STAT3 activity increased. RNA interference studies revealed that activation of STAT1-SOCS1 axis decreased STAT3 activity. Thus, IFN-γ biphasically regulates AGT expression in RPTCs via STAT3 activity modulated by STAT1-SOCS1 axis, suggesting the STAT1-SOCS1 axis is important in IFN-γ-induced activation of the intrarenal renin-angiotensin system.

Increased angiotensin II-induced hypertension and inflammatory cytokines in mice lacking angiotensin-converting enzyme N domain activity

-Angiotensin-converting enzyme (ACE) is composed of the N- and C-terminal catalytic domains. To study the role of the ACE domains in the inflammatory response, N-knockout (KO) and C-KO mice, models lacking 1 of the 2 ACE domains, were analyzed during angiotensin II-induced hypertension. At 2 weeks, N-KO mice have systolic blood pressures that averaged 173±4.6 mm Hg, which is more than 25 mm Hg higher than the blood pressures observed in wild-type or C-KO mice (146±3.2 and 147±4.2 mm Hg). After 3 weeks, blood pressure differences between N-KO, C-KO, and wild-type were even more pronounced. Macrophages from N-KO mice have increased expression of tumor necrosis factor α after stimulation with either lipopolysaccharide (about 4-fold) or angiotensin II (about 2-fold), as compared with C-KO or wild-type mice. Inhibition of the enzyme prolyl oligopeptidase, responsible for the formation of acetyl-SerAspLysPro and other peptides, eliminated the blood pressure difference and the difference in tumor necrosis factor α expression between angiotensin II-treated N-KO and wild-type mice. However, this appears independent of acetyl-SerAspLysPro. These data establish significant differences in the inflammatory response as a function of ACE N- or C-domain catalytic activity. They also indicate a novel role of prolyl oligopeptidase in the cytokine regulation and in the blood pressure response to experimental hypertension.

Angiotensin II induced catabolic effect and muscle atrophy are redox dependent

Angiotensin II (Ang II) causes skeletal muscle wasting via an increase in muscle catabolism. To determine whether the wasting effects of Ang II were related to its ability to increase NADPH oxidase-derived reactive oxygen species (ROS) we infused wild-type C57BL/6J or p47(phox)(-/-) mice with vehicle or Ang II for 7days. Superoxide production was increased 2.4-fold in the skeletal muscle of Ang II infused mice, and this increase was prevented in p47(phox)(-/-) mice. Apocynin treatment prevented Ang II-induced superoxide production in skeletal muscle, consistent with Ang II increasing NADPH oxidase derived ROS. Ang II induced loss of body and skeletal muscle weight in C57BL/6J mice, whereas the reduction was significantly attenuated in p47(phox)(-/-) animals. The reduction of skeletal muscle weight caused by Ang II was associated with an increase of proteasome activity, and this increase was completely prevented in the skeletal muscle of p47(phox)(-/-) mice. In conclusion, Ang II-induced skeletal muscle wasting is in part dependent on NADPH oxidase derived ROS.

Intrarenal angiotensin-converting enzyme induces hypertension in response to angiotensin I infusion

The contribution of the intrarenal renin-angiotensin system to the development of hypertension is incompletely understood. Here, we used targeted homologous recombination to generate mice that express angiotensin-converting enzyme (ACE) in the kidney tubules but not in other tissues. Mice homozygous for this genetic modification (ACE 9/9 mice) had low BP levels, impaired ability to concentrate urine, and variable medullary thinning. In accord with the ACE distribution, these mice also had reduced circulating angiotensin II and high plasma renin concentration but maintained normal kidney angiotensin II levels. In response to chronic angiotensin I infusions, ACE 9/9 mice displayed increased kidney angiotensin II, enhanced rate of urinary angiotensin II excretion, and development of hypertension. These findings suggest that intrarenal ACE-derived angiotensin II formation, even in the absence of systemic ACE, increases kidney angiotensin II levels and promotes the development of hypertension.

Different in vivo functions of the two catalytic domains of angiotensin-converting enzyme (ACE)

Angiotensin-converting enzyme (ACE) can cleave angiotensin I, bradykinin, neurotensin and many other peptide substrates in vitro. In part, this is due to the structure of ACE, a protein composed of two independent catalytic domains. Until very recently, little was known regarding the specific in vivo role of each ACE domain, and they were commonly regarded as equivalent. This is not true, as shown by mouse models with a genetic inactivation of either the ACE N- or C-domain. In vivo, most angiotensin II is produced by the ACE C-domain. Some peptides, such as the anti-fibrotic peptide AcSDKP, are substrates only of the ACE N-domain. Knowing the in vivo role of each ACE domain has great significance for developing ACE domain-specific inhibitors and for understanding the full effects of the anti-ACE pharmaceuticals in widespread clinical use.

IL-6 augments angiotensinogen in primary cultured renal proximal tubular cells

In human kidneys, the mechanisms underlying angiotensinogen (AGT) augmentation by interleukin 6 (IL-6) are poorly understood and the only information available is in HK-2, immortalized human renal proximal tubular epithelial cells. Therefore, the present study was performed to elucidate the effects of IL-6 on AGT expression in primary cultured human renal proximal tubular epithelial cells (RPTEC) after characterization of HK-2 and RPTEC. RPTEC showed low basal AGT mRNA (11+/-1%) and protein (7.0+/-0.9%) expression, high IL-6 receptor (IL-6R) expression (282+/-17%), and low basal NF-kappaB (43+/-7%) and STAT3 (43+/-7%) activities compared to those in HK-2. In RPTEC, AGT mRNA and protein expressions were enhanced by IL-6 (172+/-31% and 378+/-39%, respectively). This AGT augmentation was attenuated by an IL-6R antibody. STAT3 phosphorylation (366+/-55% at 30min) and translocation were enhanced by IL-6. The AGT augmentation was attenuated by a STAT3 inhibitor. These data indicate that IL-6 increases AGT expression via STAT3 pathway in RPTEC.

Intrarenal mouse renin-angiotensin system during ANG II-induced hypertension and ACE inhibition

Angiotensin-converting enzyme (ACE) inhibition (ACEi) ameliorates the development of hypertension and the intrarenal ANG II augmentation in ANG II-infused mice. To determine if these effects are associated with changes in the mouse intrarenal renin-angiotensin system, the expression of angiotensinogen (AGT), renin, ACE, angiotensin type 1 receptor (AT(1)R) mRNA (by quanitative RT-PCR) and protein [by Western blot (WB) and/or immunohistochemistry (IHC)] were analyzed. C57BL/6J male mice (9-12 wk old) were distributed as controls (n = 10), ANG II infused (ANG II = 8, 400 ng x kg(-1) x min(-1) for 12 days), ACEi only (ACEi = 10, lisinopril, 100 mg/l), and ANG II infused + ACEi (ANG II + ACEi = 11). When compared with controls (1.00), AGT protein (by WB) was increased by ANG II (1.29 +/- 0.13, P < 0.05), and this was not prevented by ACEi (ACEi + ANG II, 1.31 +/- 0.14, P < 0.05). ACE protein (by WB) was increased by ANG II (1.21 +/- 0.08, P < 0.05), and it was reduced by ACEi alone (0.88 +/- 0.07, P < 0.05) or in combination with ANG II (0.80 +/- 0.07, P < 0.05). AT(1)R protein (by WB) was increased by ANG II (1.27 +/- 0.06, P < 0.05) and ACEi (1.17 +/- 0.06, P < 0.05) but not ANG II + ACEi [1.15 +/- 0.06, not significant (NS)]. Tubular renin protein (semiquantified by IHC) was increased by ANG II (1.49 +/- 0.23, P < 0.05) and ACEi (1.57 +/- 0.15, P < 0.05), but not ANG II + ACEi (1.10 +/- 0.15, NS). No significant changes were observed in AGT, ACE, or AT(1)R mRNA. In summary, reduced responses of intrarenal tubular renin, ACE, and the AT(1)R protein to the stimulatory effects of chronic ANG II infusions, in the presence of ACEi, are associated with the effects of this treatment to ameliorate augmentations in blood pressure and intrarenal ANG II content during ANG II-induced hypertension.

Angiotensin-converting enzyme-derived angiotensin II formation during angiotensin II-induced hypertension

The extent to which endogenous angiotensin (Ang) II formation is responsible for increasing kidney Ang II content and blood pressure during Ang II-induced hypertension is unknown. To address this, mice were treated with an Ang-converting enzyme (ACE) inhibitor (ACEi) to block endogenous Ang II formation during chronic Ang II infusions. C57BL/6J male mice (8 to 12 weeks) were subjected to Ang II infusions (400 ng/kg per minute) with or without an ACEi (lisinopril, 100 mg/L in the drinking water) for 12 days. Blood pressure was monitored by tail-cuff method and telemetry. Ang II content was determined by radioimmunoanalysis. Ang II infusions increased 24-hour mean arterial pressure significantly (141.0+/-3.7 mm Hg) versus controls (110.0+/-1.0 mm Hg). ACEi prevented the increase in concentration in Ang II-infused mice (Ang II+ACEi; 114.0+/-7.4 mm Hg; P value not significant). Plasma Ang II content was significantly increased by Ang II (367+/-60 fmol/mL) versus controls (128+/-22 fmol/mL; P<0.05); plasma Ang II was not altered by ACEi alone (90+/-31) or in combination with Ang II infusions (76+/-27). Intrarenal Ang II content was significantly increased by Ang II (998+/-143 fmol/g) versus controls (524+/-60 fmol/g; P<0.05), and this was prevented by ACEi (Ang II+ACEi; 484+/-102 fmol/g; P value not significant). Thus, ACEi ameliorates the increases in blood pressure and intrarenal Ang II content caused by Ang II infusions, indicating that endogenous ACE-mediated Ang II formation plays a significant role in the increases of blood pressure and intrarenal Ang II during Ang II-induced hypertension.

Intrarenal angiotensin II and angiotensinogen augmentation in chronic angiotensin II-infused mice

The objectives of this study were to determine the effects of chronic angiotensin II (ANG II) infusions on ANG II content and angiotensinogen expression in the mouse kidney and the role of the angiotensin II type 1 receptor (AT(1)R) in mediating these changes. C57BL/6J male mice were subjected to ANG II infusions at doses of 400 or 1,000 ng.kg(-1).min(-1) either alone or with an AT(1)R blocker (olmesartan; 3 mg.kg(-1).day(-1)) for 12 days. Systolic and mean arterial pressures were determined by tail-cuff plethysmography and radiotelemetry. On day 13, blood and kidneys were collected for ANG II determinations by radioimmunoanalysis and intrarenal angiotensinogen expression studies by quantitative RT-PCR, Western blotting, and immunohistochemistry. ANG II infusions at the low dose elicited progressive increases in systolic blood pressure (135 +/- 2.5 mmHg). In contrast, the high dose induced a rapid increase (152 +/- 2.5, P < 0.05 vs. controls, 109 +/- 2.8). Renal ANG II content was increased by ANG II infusions at the low dose (1,203 +/- 253 fmol/g) and the high dose (1,258 +/- 173) vs. controls (499 +/- 40, P < 0.05). Kidney angiotensinogen mRNA and protein were increased only by the low dose to 1.13 +/- 0.02 and 1.26 +/- 0.10, respectively, over controls (1.00, P < 0.05). These effects were not observed in mice infused at the high dose and those receiving olmesartan. The results indicate that chronic ANG II infusions augment mouse intrarenal ANG II content with AT(1)R-dependent uptake occurring at both doses, but only the low dose of infusion, which elicited a slow progressive response, causes an AT(1)R-dependent increase in intrarenal angiotensinogen expression.

Elevated epidermal growth factor receptor phosphorylation induces resistance artery dysfunction in diabetic db/db mice

OBJECTIVE

We previously showed epidermal growth factor receptor (EGFR) transactivation to be key mechanism in the regulation of resistance artery myogenic tone. Type 2 diabetes is associated with microvascular complications. We hypothesized that elevated EGFR phosphorylation contributes to resistance artery dysfunction in type 2 diabetes.

RESEARCH DESIGN AND METHODS AND RESULTS

Diabetic db/db and nondiabetic (control) mice were treated with EGFR inhibitor (AG1478; 10 mg x kg(-1) x day(-1)) for 2 weeks. Isolated coronary artery and mesenteric resistance artery (MRA) were mounted in an arteriograph. Pressure-induced myogenic tone was increased in MRA and coronary artery from diabetic mice and normalized by AG1478. Phenylephrine-induced contraction and nitric oxide donor-induced relaxation were similar in all groups. Endothelium-dependent relaxation in response to shear stress and acetylcholine of MRA and coronary artery from diabetic mice was altered and associated with reduced endothelial nitric oxide synthase (eNOS) expression and phosphorylation. Treated diabetic mice with AG1478 improved coronary artery and MRA endothelial function and restored eNOS expression. Immunostaining and Western blot analysis showed increased endothelial and smooth muscle cell EGFR phosphorylation of MRA and coronary artery from diabetic mouse, which was reduced by AG1478. Primary cultured endothelial cells from resistance arteries treated with high glucose for 48 h showed an increase of EGFR phosphorylation associated with eNOS expression and phosphorylation decrease in response to calcium ionophore. Pretreatment of endothelial cells with AG1478 prevented the effect of high glucose.

CONCLUSIONS

This study provides evidence of the role of elevated EGFR phosphorylation in coronary artery and MRA dysfunction in diabetic db/db mice. Therefore, EGFR should be a potential target for overcoming diabetic small artery complications.

Role of advanced glycation end products with oxidative stress in resistance artery dysfunction in type 2 diabetic mice

OBJECTIVE

Type 2 diabetes is associated with increased advanced glycation end product (AGE) formation and vasculopathy. We hypothesized that AGEs contribute to resistance artery dysfunction.

METHODS AND RESULTS

Type 2 diabetic db(-)/db(-) (diabetic) and nondiabetic db(-)/db(+) (control) mice were treated with the AGE inhibitor (aminoguanidine: 50 mg/Kg/d) for 3 months. Isolated mesenteric resistance arteries (MRAs) were mounted in an arteriograph. Pressure-induced myogenic tone (MT) was increased in diabetic mice but was unaffected by aminoguanidine treatment. Phenylephrine-induced contraction and nitric oxide donor-induced endothelium-independent relaxation were similar in all groups. In diabetic mice, endothelium-dependent relaxation in response to shear-stress or acetylcholine was altered and was associated with reduced eNOS protein and mRNA expression. Aminoguanidine treatment improved endothelial function and restored eNOS expression. AGE formation and hypoxia markers (plasminogen activator inhibitor 1 and Bnip3) were increased in MRA from diabetic mice and normalized with Aminoguanidine. Primary cultured endothelial cells (ECs) isolated from resistance arteries subjected to high glucose for 48 hours showed decreased eNOS expression and phosphorylation in response to calcium ionophore. High glucose decreased antioxidant protein (MnSOD) and increased prooxidant proteins (gp91phox) expression leading to increased oxidative stress generation, as assessed by DHE staining and endothelial NADH/NADPH oxidase activity. The preincubation of ECs with aminoguanidine restored eNOS-phosphorylation and expression as well as the balance between pro- and antioxidant factors induced by high glucose.

CONCLUSIONS

We provide evidence of a link between AGEs, oxidative stress, and resistance artery EC dysfunction in type 2 diabetic mice. Thus, AGEs and oxidative stress may be a potential target for overcoming diabetic microvessels complications.

Costimulation with angiotensin II and interleukin 6 augments angiotensinogen expression in cultured human renal proximal tubular cells

Augmented intrarenal ANG II stimulates IL-6, which contributes to renal injury. The expression of intrarenal angiotensinogen (AGT) is enhanced by increased intrarenal ANG II in human renin/human AGT double transgenic mice. ANG II also augments AGT expression in hepatocytes and cardiac myocytes. However, the mechanisms underlying AGT augmentation by ANG II and the contribution of IL-6 to this system are poorly understood. This study was performed in human renal proximal tubular epithelial cells (HRPTECs) to test the hypothesis that IL-6 contributes to the upregulation of AGT expression by ANG II. Human kidney-2 (HK-2) cells, immortalized HRPTECs, were incubated with 10(-7) M ANG II and/or 10 ng/ml IL-6 for up to 24 h. AGT mRNA and protein expressions were measured by real-time RT-PCR and ELISA, respectively. The activities of NF-kappaB and STAT3 were evaluated by Western blotting and EMSA. Stimulation with either ANG II or IL-6 did not significantly alter AGT mRNA or protein expression. In contrast, costimulation with ANG II and IL-6 significantly increased AGT mRNA and protein expressions (1.26 +/- 0.10 and 1.16 +/- 0.13 over control, respectively). Olmesartan, an ANG II type 1 receptor blocker, and an IL-6 receptor antibody individually inhibited this synergistic effect. NF-kappaB was also activated by costimulation with ANG II and IL-6. Phosphorylation and activity of STAT3 were increased by stimulation with IL-6 alone and by costimulation. The present study indicates that IL-6 plays an important role in ANG II-mediated augmentation of AGT expression in human renal proximal tubular cells.

Diamagnetic levitation changes growth, cell cycle, and gene expression of Saccharomyces cerevisiae

Inhomogeneous magnetic fields are used in magnetic traps to levitate biological specimens by exploiting the natural diamagnetism of virtually all materials. Using Saccharomyces cerevisiae, this report investigates whether magnetic field (B) induces changes in growth, cell cycle, and gene expression. Comparison to the effects of gravity and temperature allowed determination of whether the responses are general pathways or stimulus specific. Growth and cell cycle analysis were examined in wild-type (WT) yeast and strains with deletions in transcription factors Msn4 or Sfp1. Msn4, Sfp1, and Rap1 have been implicated in responses to physical forces, but only Msn4 and Sfp1 deletions are viable. Gene expression changes were examined in strains bearing GFP-tagged reporters for YIL052C (Sfp1-dependent), YST-2 (Sfp1/Rap1-dependent), or SSA4 (Msn4-dependent). The cell growth and gene expression responses were highly stimulus specific. B increased growth only following Msn4 or Sfp1 deletion, associated with decreased G1 and G2/M and increased S phase of the cell cycle. In addition, B suppressed expression of both YIL052C and YST2. Gravity decreased growth in an Sfp1 but not Msn4-dependent manner, in association with decreased G2/M and increased S phase of the cell cycle. Additionally, gravity decreased expression of SSA4 and YIL052C genes. Temperature increased cell growth in an Msn4- and Sfp1-dependent manner in association with increased G1 and G2/M with decreased S phase of the cell cycle. In addition, temperature increased YIL052C gene expression. This study shows that B has selective effects on cell growth, cell cycle, and gene expression that are stimulus specific.

Metabolic inhibition-induced transient Ca2+ increase depends on mitochondria in a human proximal renal cell line

During ischemia or hypoxia an increase in intracellular cytosolic Ca(2+) induces deleterious events but is also implicated in signaling processes triggered in such conditions. In MDCK cells (distal tubular origin), it was shown that mitochondria confer protection during metabolic inhibition (MI), by buffering the Ca(2+) overload via mitochondrial Na(+)-Ca(2+) exchanger (NCX). To further assess this process in cells of human origin, human cortical renal epithelial cells (proximal tubular origin) were subjected to MI and changes in cytosolic Ca(2+) ([Ca(2+)](i)), Na(+), and ATP concentrations were monitored. MI was accomplished with both antimycin A and 2-deoxyglucose and induced a 3.5-fold increase in [Ca(2+)](i), reaching 136.5 +/- 15.8 nM in the first 3.45 min. Subsequently [Ca(2+)](i) dropped and stabilized to 62.7 +/- 7.3 nM by 30 min. The first phase of the transient increase was La(3+) sensitive, not influenced by diltiazem, and abolished when mitochondria were deenergized with the protonophore carbonylcyanide p-trifluoromethoxyphenylhydrazone. The subsequent recovery phase was impaired in a Na(+)-free medium and weakened when the mitochondrial NCX was blocked with 7-chloro-5-(2-chlorophenyl)-1,5-dihydro-4,1-benzothiazepin-2(3H)-one (CGP-37157). Thus Ca(2+) entry is likely mediated by store-operated Ca(2+) channels and depends on energized mitochondria, whereas [Ca(2+)](i) recovery relied partially on the activity of mitochondrial NCX. These results indicate a possible mitochondrial-mediated signaling process triggered by MI, support the hypothesis that mitochondrial NCX has an important role in the Ca(2+) clearance, and overall suggest that mitochondria play a preponderant role in the regulation of responses to MI in human renal epithelial cells.

Gene expression and survival changes inSaccharomyces cerevisiae during suspension culture

This study explores the connection between changes in gene expression and the genes that determine strain survival during suspension culture, using the model eukaryotic organism, Saccharomyces cerevisiae. The Saccharomyces cerevisiae homozygous diploid deletion pool (HDDP), and the BY4743 parental strain were grown for 18 h in a rotating wall vessel (RWV), a suspension culture device optimized to minimize the delivered shear. In addition to the reduced shear conditions, the RWVs were also placed in a static position or in a shaker in order to change the amount of shear stress on the cells. Using simple linear regression, it was found that there were 140 differentially expressed genes for which >70% of the variation can be explained by shear stress alone. A significant number of these genes are involved in catalytic activity. In the HDDP, shear stress was associated with significant survival changes in 15 deletion strains (R(2>) > 0.7) Interestingly, both analyses uncovered changes in the ribosomal protein machinery. Comparing the changes in gene expression and strain survival under the different shear conditions allows for the insights into the molecular mechanisms behind the cells response to shear stress. This in turn can provide information for the optimization of suspension culture.