The biology of renal hypertrophy

Renal Glutathione: Dual roles as antioxidant protector and bioactivation promoter

The tripeptide glutathione (GSH) possesses two key structural features, namely the nucleophilic sulfur and the γ-glutamyl isopeptide bond. The former allows GSH to serve as a critical antioxidant and anti-electrophile. The latter allows GSH to translocate throughout the systemic circulation without being degraded. The kidneys exhibit several unique processes for handling GSH. This includes the extraction of 80% of plasma GSH, in part by glomerular filtration but mostly by transport across the basolateral plasma membrane. Studies on the protective effect of exogenous GSH are summarized, showing the different inherent susceptibility of proximal tubular and distal tubular cells and the impact on pathological or disease states, including hypoxia, diabetic nephropathy, and compensatory renal growth associated with uninephrectomy. Studies on mitochondrial GSH transport show the coordination between the citric acid cycle and oxidative phosphorylation in generating driving forces for both plasma membrane and mitochondrial carriers. The strong protective effects of increasing expression and activity of these carriers against oxidants and mitochondrial toxicants are summarized. Although GSH plays a cytoprotective role in most situations, two distinct exceptions to this are presented. In contrast to expectations, overexpression of the mitochondrial 2-oxoglutarate carrier markedly increased cell death from exposure to the nephrotoxic chemotherapeutic drug cisplatin (CDDP). Another key example of GSH serving a bioactivation role in the kidneys, rather than a detoxification role, is the metabolism of halogenated alkenes such as trichloroethylene (TCE). Although considerable research has gone into this topic, unanswered questions and emerging topics remain and are discussed.

Renal regenerative capacity related to stem cell reserve in nephrectomized rats

PURPOSE

On the new era of stem cell therapy, the present experimental study was conducted to investigate renal regenerative capacity related to kidney stem cell reserve in different nephrectomy (Nx) models.

METHODS

Three- and eight-week-old rats (n = 168) were randomly divided into four groups to include control and three Nx subgroups (1/6 Nx, 1/2 Nx, and 5/6 Nx) (Fig. 1). On post-Nx days 15, 30 and 60, kidney specimens were obtained to determine renal regenerative capacity. The specimens were examined with immunofluorescence. CD90/CD105 and Ki-67 expressions were determined as stem cell and cellular proliferation markers, respectively. Fig. 1 Intraoperative photographs showing three different types of nephrectomies (unilateral total Nx has not been shown in 5/6 Nx group) RESULTS: CD90 and CD105 expressions were stronger in glomeruli, but Ki-67 expressions were present only in tubuli. When all Nx types and post-Nx days were considered, both 3- and 8-week-old rats undergone 5/6 Nx had the highest glomerular CD90 and CD105 double expressions. While the expressions gradually increased toward the day 60 in 3-weeks old rats, 8-week-old rats had almost stable double expressions. The strongest tubular Ki-67 expressions were seen in 5/6 Nx groups of both in 3- and 8-week-old rats. The expressions were strongest on day 15 and then gradually decreased. Ipsilateral 1/6 Nx groups had stronger Ki-67 expression than contralateral ones in both age groups.

CONCLUSIONS

Kidneys may pose a regenerative response to tissue/volume loss through its own CD90- and CD105-related stem cell reserve which mainly takes place in glomeruli and seems to have some interactions with Ki-67-related tubular proliferative process. This response supports that kidney stem cells may have a potential to overcome tissue/volume loss-related damage.

Targeting Glomerular Hemodynamics for Kidney Protection

The kidney microcirculation is a unique structure as it is composed to 2 capillary beds in series: the glomerular and peritubular capillaries. The glomerular capillary bed is a high-pressure capillary bed, having a 60 mm Hg to 40 mm Hg pressure gradient, capable of producing an ultrafiltrate of plasma quantified as the glomerular filtration rate (GFR), thereby allowing for waste products to be removed and establishing sodium/volume homeostasis. Entering the glomerulus is the afferent arteriole, and the exiting one is the efferent arteriole. The concerted resistance of each of these arterioles is what is known as glomerular hemodynamics and is responsible for increasing or decreasing GFR and renal blood flow. Glomerular hemodynamics play an important role in how homeostasis is achieved. Minute-to-minute fluctuations in the GFR are achieved by constant sensing of distal delivery of sodium and chloride in the specialized cells called macula densa leading to upstream alternation in afferent arteriole resistance altering the pressure gradient for filtration. Specifically, 2 classes of medications (sodium glucose cotransporter-2 inhibitors and renin-angiotensin system blockers) have shown to be effective in long-term kidney health by altering glomerular hemodynamics. This review will discuss how tubuloglomerular feedback is achieved, and how different disease states and pharmacologic agents alter glomerular hemodynamics.

Low nephron endowment increases susceptibility to renal stress and chronic kidney disease

Preterm birth results in low nephron endowment and increased risk of acute kidney injury (AKI) and chronic kidney disease (CKD). To understand the pathogenesis of AKI and CKD in preterm humans, we generated potentially novel mouse models with a 30%-70% reduction in nephron number by inhibiting or deleting Ret tyrosine kinase in the developing ureteric bud. These mice developed glomerular and tubular hypertrophy, followed by the transition to CKD, recapitulating the renal pathological changes seen in humans born preterm. We injected neonatal mice with gentamicin, a ubiquitous nephrotoxic exposure in preterm infants, and detected more severe proximal tubular injury in mice with low nephron number compared with controls with normal nephron number. Mice with low nephron number had reduced proliferative repair with more rapid development of CKD. Furthermore, mice had more profound inflammation with highly elevated levels of MCP-1 and CXCL10, produced in part by damaged proximal tubules. Our study directly links low nephron endowment with postnatal renal hypertrophy, which in this model is maladaptive and results in CKD. Underdeveloped kidneys are more susceptible to gentamicin-induced AKI, suggesting that AKI in the setting of low nephron number is more severe and further increases the risk of CKD in this vulnerable population.

In Vivo Evaluation of the Oral Toxicity of the Chlorobutanol

Chlorobutanol (CB) is used as a preservative in cosmetics and has antibacterial activity. This study investigated the single- and repeated-dose 28-day oral toxicity of a CB solvent in Sprague Dawley (SD) rats. For the single-dose oral toxicity study, a dose of 62.5, 125, or 250 mg per kg of body weight (mg/kg b.w.) of CB was given once orally via gavage. For the repeated-dose 28-day toxicity study, the high dose was set as 100 mg/kg b.w./day, and the middle, middle-low, and low doses were set to 50, 25, and 12.5 mg/kg b.w./day, respectively. Body weight was not significantly changed in the repeated-dose toxicity study. Relative liver and kidney weights were significantly increased in both sexes of the 100 mg/kg b.w./day treatment group. However, there were histopathological changes in liver and kidney for females and males, respectively. These data suggested that the approximate lethal dose (ALD) of CB was over 250 mg/kg b.w./day in the single-dose study, and the no adverse effect level (NOAEL) for CB was over 50 and 12.5 mg/kg b.w./day for female and male rats in the repeated-dose toxicity study.

Diverse Roles of Mitochondria in Renal Injury from Environmental Toxicants and Therapeutic Drugs

Mitochondria are well-known to function as the primary sites of ATP synthesis in most mammalian cells, including the renal proximal tubule. Other functions have also been associated with different mitochondrial activities, including the regulation of redox status and the initiation of mitophagy and apoptosis. Mechanisms for the membrane transport of glutathione (GSH) and various GSH-derived metabolites across the mitochondrial inner membrane of renal proximal tubular cells are critical determinants of these functions and may serve as pharmacological targets for potential therapeutic approaches. Specific interactions of reactive intermediates, derived from drug metabolism, with molecular components in mitochondria have been identified as early steps in diverse forms of chemically-induced nephrotoxicity. Applying this key observation, we developed a novel hypothesis regarding the identification of early, sensitive, and specific biomarkers of exposure to nephrotoxicants. The underlying concept is that upon exposure to a diverse array of environmental contaminants, as well as therapeutic drugs whose efficacy is limited by nephrotoxicity, renal mitochondria will release both high- and low-molecular-weight components into the urine or the extracellular medium in an in vitro model. The detection of these components may then serve as indicators of exposure before irreversible renal injury has occurred.

CDCP1 promotes compensatory renal growth by integrating Src and Met signaling

CDCP1 promotes HGF-induced compensatory renal growth by focally and temporally integrating Src and Met-STAT3 signaling in lipid rafts.

Compensatory growth of organs after loss of their mass and/or function is controlled by hepatocyte growth factor (HGF), but the underlying regulatory mechanisms remain elusive. Here, we show that CUB domain-containing protein 1 (CDCP1) promotes HGF-induced compensatory renal growth. Using canine kidney cells as a model of renal tubules, we found that HGF-induced temporal up-regulation of Src activity and its scaffold protein, CDCP1, and that the ablation of CDCP1 robustly abrogated HGF-induced phenotypic changes, such as morphological changes and cell growth/proliferation. Mechanistic analyses revealed that up-regulated CDCP1 recruits Src into lipid rafts to activate STAT3 associated with the HGF receptor Met, and activated STAT3 induces the expression of matrix metalloproteinases and mitogenic factors. After unilateral nephrectomy in mice, the Met-STAT3 signaling is transiently up-regulated in the renal tubules of the remaining kidney, whereas CDCP1 ablation attenuates regenerative signaling and significantly suppresses compensatory growth. These findings demonstrate that CDCP1 plays a crucial role in controlling compensatory renal growth by focally and temporally integrating Src and Met signaling.

Cre/loxP approach-mediated downregulation of Pik3c3 inhibits the hypertrophic growth of renal proximal tubule cells

Nephron loss stimulates residual functioning nephrons to undergo compensatory growth. Excessive nephron growth may be a maladaptive response that sets the stage for progressive nephron damage, leading to kidney failure. To date, however, the mechanism of nephron growth remains incompletely understood. Our previous study revealed that class III phosphatidylinositol-3-kinase (Pik3c3) is activated in the remaining kidney after unilateral nephrectomy (UNX)-induced nephron loss, but previous studies failed to generate a Pik3c3 gene knockout animal model. Global Pik3c3 deletion results in embryonic lethality. Given that renal proximal tubule cells make up the bulk of the kidney and undergo the most prominent hypertrophic growth after UNX, in this study we used Cre-loxP-based approaches to demonstrate for the first time that tamoxifen-inducible SLC34a1 promoter-driven CreER^T2 recombinase-mediated downregulation of Pik3c3 expression in renal proximal tubule cells alone is sufficient to inhibit UNX- or amino acid-induced hypertrophic nephron growth. Furthermore, our mechanistic studies unveiled that the SLC34a1-CreER^T2 recombinase-mediated Pik3c3 downregulation inhibited UNX- or amino acid-stimulated lysosomal localization and signaling activation of mechanistic target of rapamycin complex 1 (mTORC1) in the renal proximal tubules. Moreover, our additional cell culture experiments using RNAi confirmed that knocking down Pik3c3 expression inhibited amino acid-stimulated mTORC1 signaling and blunted cellular growth in primary cultures of renal proximal tubule cells. Together, both our in vivo and in vitro experimental results indicate that Pik3c3 is a major mechanistic mediator responsible for sensing amino acid availability and initiating hypertrophic growth of renal proximal tubule cells by activation of the mTORC1-S6K1-rpS6 signaling pathway.

Olinciguat, an Oral sGC Stimulator, Exhibits Diverse Pharmacology Across Preclinical Models of Cardiovascular, Metabolic, Renal, and Inflammatory Disease

Nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic 3',5' GMP (cGMP) signaling plays a central role in regulation of diverse processes including smooth muscle relaxation, inflammation, and fibrosis. sGC is activated by the short-lived physiologic mediator NO. sGC stimulators are small-molecule compounds that directly bind to sGC to enhance NO-mediated cGMP signaling. Olinciguat, (R)-3,3,3-trifluoro-2-(((5-fluoro-2-(1-(2-fluorobenzyl)-5-(isoxazol-3-yl)-1H-pyrazol-3-yl)pyrimidin-4-yl)amino)methyl)-2-hydroxypropanamide, is a new sGC stimulator currently in Phase 2 clinical development. To understand the potential clinical utility of olinciguat, we studied its pharmacokinetics, tissue distribution, and pharmacologic effects in preclinical models. Olinciguat relaxed human vascular smooth muscle and was a potent inhibitor of vascular smooth muscle proliferation in vitro. These antiproliferative effects were potentiated by the phosphodiesterase 5 inhibitor tadalafil, which did not inhibit vascular smooth muscle proliferation on its own. Olinciguat was orally bioavailable and predominantly cleared by the liver in rats. In a rat whole body autoradiography study, olinciguat-derived radioactivity in most tissues was comparable to plasma levels, indicating a balanced distribution between vascular and extravascular compartments. Olinciguat was explored in rodent models to study its effects on the vasculature, the heart, the kidneys, metabolism, and inflammation. Olinciguat reduced blood pressure in normotensive and hypertensive rats. Olinciguat was cardioprotective in the Dahl rat salt-sensitive hypertensive heart failure model. In the rat ZSF1 model of diabetic nephropathy and metabolic syndrome, olinciguat was renoprotective and associated with lower circulating glucose, cholesterol, and triglycerides. In a mouse TNFα-induced inflammation model, olinciguat treatment was associated with lower levels of endothelial and leukocyte-derived soluble adhesion molecules. The pharmacological features of olinciguat suggest that it may have broad therapeutic potential and that it may be suited for diseases that have both vascular and extravascular pathologies.

Pathophysiology of unilateral ischemia-reperfusion injury: importance of renal counterbalance and implications for the AKI-CKD transition

Unilateral ischemia-reperfusion (UIR) injury leads to progressive renal atrophy and tubulointerstitial fibrosis (TIF) and is commonly used to investigate the pathogenesis of the acute kidney injury-chronic kidney disease transition. Although it is well known that contralateral nephrectomy (CNX), even 2 wk post-UIR injury, can improve recovery, the physiological mechanisms and tubular signaling pathways mediating such improved recovery remain poorly defined. Here, we examined the renal hemodynamic and tubular signaling pathways associated with UIR injury and its reversal by CNX. Male Sprague-Dawley rats underwent left UIR or sham UIR and 2 wk later CNX or sham CNX. Blood pressure, left renal blood flow (RBF), and total glomerular filtration rate were assessed in conscious rats for 3 days before and over 2 wk after CNX or sham CNX. In the presence of a contralateral uninjured kidney, left RBF was lower (P < 0.05) from 2 to 4 wk following UIR (3.6 ± 0.3 mL/min) versus sham UIR (9.6 ± 0.3 mL/min). Without CNX, extensive renal atrophy, TIF, and tubule dedifferentiation, but minimal pimonidazole and hypoxia-inducible factor-1α positivity in tubules, were present at 4 wk post-UIR injury. Conversely, CNX led (P < 0.05) to sustained increases in left RBF (6.2 ± 0.6 mL/min) that preceded the increases in glomerular filtration rate. The CNX-induced improvement in renal function was associated with renal hypertrophy, more redifferentiated tubules, less TIF, and robust pimonidazole and hypoxia-inducible factor-1α staining in UIR injured kidneys. Thus, contrary to expectations, indexes of hypoxia are not observed with the extensive TIF at 4 wk post-UIR injury in the absence of CNX but are rather associated with the improved recovery of renal function and structure following CNX.

The expression level of class III phosphatidylinositol-3 kinase controls the degree of compensatory nephron hypertrophy

Excessive compensatory nephron hypertrophy (CNH) has been implicated in setting the stage for progressive nephron damage. Lack of a class III phosphatidylinositol 3-kinase (Pik3c3) inhibitor suitable for using in animals and lack of a Pik3c3-deficient animal model preclude the possibility of conclusively defining a role for Pik3c3 in CNH in previous studies. Here, we report that insertion of an Frt-flanked PGK-Neo cassette into intron 19 of the mouse Pik3c3 gene resulted in a hypomorphic allele. This allowed us to create a unique mouse model and provide the first definitive genetic evidence demonstrating whether Pik3c3 is essential for the regulation of CNH. Our results indicate that homozygous Pik3c3 hypomorphic (Pik3c3^Hypo/Hypo) mice express significantly low levels of Pik3c3 than heterozygous Pik3c3 hypomorphic (Pik3c3^Hypo/WT) littermates, which already express a lower level of Pik3c3 than wild-type (Pik3c3^WT/WT) littermates. Interestingly, after unilateral nephrectomy (UNX), Pik3c3^Hypo/Hypo mice develop a significantly lower degree of CNH than Pik3c3^WT/WT mice and Pik3c3^Hypo/WT mice, as revealed by measurement of kidney weight, kidney-to-body weight ratio, renal protein-to-DNA ratio, and morphometric analysis of proximal tubular and glomerular size. Mechanistically, UNX-induced mammalian target of rapamycin complex 1 (mTORC1) signaling to phosphorylation of ribosomal protein S6 (rpS6) in the remaining kidney was markedly inhibited in Pik3c3 hypomorphic mice. In conclusion, the present study reports a Pik3c3 hypomorphic mouse model and provides the first definitive evidence that Pik3c3 controls the degree of compensatory nephron hypertrophy. In addition, our signaling data provide the first definitive in vivo proof that Pik3c3 functions upstream of the mTORC1-S6 kinase 1-rpS6 pathway in the regulation of compensatory nephron hypertrophy.

Podocyte hypertrophic stress and detachment precedes hyperglycemia or albuminuria in a rat model of obesity and type2 diabetes-associated nephropathy

Type2 diabetes-associated nephropathy is the commonest cause of renal failure. Mechanisms responsible are controversial. Leptin-deficient hyperphagic Zucker (fa/fa) rats were modeled to test the hypothesis that glomerular enlargement drives podocyte hypertrophic stress leading to accelerated podocyte detachment, podocyte depletion, albuminuria and progression. By 6weeks, prior to development of either hyperglycemia or albuminuria, fa/fa rats were hyperinsulinemic with high urinary IGF1/2 excretion, gaining weight rapidly, and had 1.6-fold greater glomerular volume than controls (P < 0.01). At this time the podocyte number per glomerulus was not yet reduced although podocytes were already hypertrophically stressed as shown by high podocyte phosphor-ribosomal S6 (a marker of mTORC1 activation), high urinary pellet podocin:nephrin mRNA ratio and accelerated podocyte detachment (high urinary pellet podocin:aquaporin2 mRNA ratio). Subsequently, fa/fa rats became both hyperglycemic and albuminuric. 24 hr urine albumin excretion correlated highly with decreasing podocyte density (R2 = 0.86), as a consequence of both increasing glomerular volume (R2 = 0.70) and decreasing podocyte number (R2 = 0.63). Glomerular podocyte loss rate was quantitatively related to podocyte detachment rate measured by urine pellet mRNAs. Glomerulosclerosis occurred when podocyte density reached <50/106um3. Reducing food intake by 40% to slow growth reduced podocyte hypertrophic stress and "froze" all elements of the progression process in place, but had small effect on hyperglycemia. Glomerular enlargement caused by high growth factor milieu starting in pre-diabetic kidneys appears to be a primary driver of albuminuria in fa/fa rats and thereby an under-recognized target for progression prevention. Progression risk could be identified prior to onset of hyperglycemia or albuminuria, and monitored non-invasively by urinary pellet podocyte mRNA markers.

Regenerative medicine in kidney disease: where we stand and where to go

The kidney is a complex organ with more than 20 types of specialized cells that play an important role in maintaining the body's homeostasis. The epithelial tubular cell is formed during embryonic development and has little proliferative capacity under physiological conditions, but after acute injury the kidney does have regenerative capacity. However, after repetitive or severe lesions, it may undergo a maladaptation process that predisposes it to chronic kidney injury. Regenerative medicine includes various repair and regeneration techniques, and these have gained increasing attention in the scientific literature. In the future, not only will these techniques contribute to the repair and regeneration of the human kidney, but probably also to the construction of an entire organ. New mechanisms studied for kidney regeneration and repair include circulating stem cells as mesenchymal stromal/stem cells and their paracrine mechanisms of action; renal progenitor stem cells; the leading role of tubular epithelial cells in the tubular repair process; the study of zebrafish larvae to understand the process of nephron development, kidney scaffold and its repopulation; and, finally, the development of organoids. This review elucidates where we are in terms of current scientific knowledge regarding these mechanisms and the promises of future scientific perspectives.

Vascular complications of sickle cell disease

Sickle cell disease (SCD) is a monogenetic disorder caused by a mutation in the β-globin gene HBB leading to polymerization of red blood cells causing damage to cell membranes, increasing its rigidity and intravascular hemolysis. Multiple lines of evidence suggest that SCD can be viewed as pan-vasculopathy associated with multiple mechanisms but driven by hemoglobin S polymerization. Here we review the pathophysiology, clinical manifestations and management strategies for cerebrovascular disease, pulmonary hypertension and renal disease associated with SCD. These "vascular phenotypes" reflect the systemic nature of the complications of SCD and are a major threat to the well-being of patients with the disorder.

Glomerular Hyperfiltration in Diabetes: Mechanisms, Clinical Significance, and Treatment

An absolute, supraphysiologic elevation in GFR is observed early in the natural history in 10%-67% and 6%-73% of patients with type 1 and type 2 diabetes, respectively. Moreover, at the single-nephron level, diabetes-related renal hemodynamic alterations-as an adaptation to reduction in functional nephron mass and/or in response to prevailing metabolic and (neuro)hormonal stimuli-increase glomerular hydraulic pressure and transcapillary convective flux of ultrafiltrate and macromolecules. This phenomenon, known as glomerular hyperfiltration, classically has been hypothesized to predispose to irreversible nephron damage, thereby contributing to initiation and progression of kidney disease in diabetes. However, dedicated studies with appropriate diagnostic measures and clinically relevant end points are warranted to confirm this assumption. In this review, we summarize the hitherto proposed mechanisms involved in diabetic hyperfiltration, focusing on ultrastructural, vascular, and tubular factors. Furthermore, we review available evidence on the clinical significance of hyperfiltration in diabetes and discuss currently available and emerging interventions that may attenuate this renal hemodynamic abnormality. The revived interest in glomerular hyperfiltration as a prognostic and pathophysiologic factor in diabetes may lead to improved and timely detection of (progressive) kidney disease, and could provide new therapeutic opportunities in alleviating the renal burden in this population.

CT Evaluation of Compensatory Renal Growth in Relation to Postnephrectomy Time

In 27 patients nephrectoraized for renal carcinoma, the compensatory hypertrophy of the remaining kidney was assessed by 72 CT examinations performed one month before and during 32 months after nephrectomy. Kidney size was estimated on CT by multiple measurements of the renal parenchymal thickness. Kidney growth was evaluated by comparing the amount of renal parenchyma before and after contralateral nephrectomy. Renal compensatory hypertrophy varied with postnephrectomy time. Kidney enlargement was 15% in the first 3 months, reached maximum 30% about a year later, and was reduced to 5%, 2 1/2 years postoperatively.

Urinary excretion of polyols and sugars in children with chronic kidney disease

BACKGROUND

The urinary concentrations of monosaccharides and polyols are used for diagnosing inborn errors of metabolism and renal tubular disorders. Reference values are age-related and depend on the method of detection. However, the influence of the renal function is often still neglected. In this study we examined the urinary excretion of monosaccharides and polyols in children with various degrees of chronic kidney disease (CKD), but with no known metabolic or renal tubular disorders.

CASE DIAGNOSIS/TREATMENT

In 25 patients with CKD stage 1-5, urinary concentrations of 18 monosaccharides and polyols were measured by gas chromatography-mass spectrometry (GC-MS) in random urinary samples and were compared with age-related reference values. Serum creatinine was measured at the time of the urine sample, and the height-independent estimated glomerular filtration rate (eGFR-Pottel) was calculated. Urinary excretions of monosaccharides and polyols were above the reference values in 8-88% of all patients. A significant difference between CKD stage 1-2 compared with CKD stage 3-5 was found for allose, arabitol and sorbitol (p < 0.05) and for arabinose, fucose, myoinositol, ribitol, xylitol, and xylose (p < 0.01).

CONCLUSIONS

We show that the excretion of polyols and sugars depends on eGFR, which warrants a cautious interpretation of the results in patients with CKD.

Blocking rpS6 Phosphorylation Exacerbates Tsc1 Deletion-Induced Kidney Growth

The molecular mechanisms underlying renal growth and renal growth-induced nephron damage remain poorly understood. Here, we report that in murine models, deletion of the tuberous sclerosis complex protein 1 (Tsc1) in renal proximal tubules induced strikingly enlarged kidneys, with minimal cystogenesis and occasional microscopic tumorigenesis. Signaling studies revealed hyperphosphorylation of eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) and increased phosphorylation of ribosomal protein S6 (rpS6) in activated renal tubules. Notably, knockin of a nonphosphorylatable rpS6 in these Tsc1-mutant mice exacerbated cystogenesis and caused drastic nephron damage and renal fibrosis, leading to kidney failure and a premature death rate of 67% by 9 weeks of age. In contrast, Tsc1 single-mutant mice were all alive and had far fewer renal cysts at this age. Mechanistic studies revealed persistent activation of mammalian target of rapamycin complex 1 (mTORC1) signaling causing hyperphosphorylation and consequent accumulation of 4E-BP1, along with greater cell proliferation, in the renal tubules of Tsc1 and rpS6 double-mutant mice. Furthermore, pharmacologic treatment of Tsc1 single-mutant mice with rapamycin reduced hyperphosphorylation and accumulation of 4E-BP1 but also inhibited phosphorylation of rpS6. Rapamycin also exacerbated cystic and fibrotic lesions and impaired kidney function in these mice, consequently leading to a premature death rate of 40% within 2 weeks of treatment, despite destroying tumors and decreasing kidney size. These findings indicate that Tsc1 prevents aberrant renal growth and tumorigenesis by inhibiting mTORC1 signaling, whereas phosphorylated rpS6 suppresses cystogenesis and fibrosis in Tsc1-deleted kidneys.

Iron-hepcidin dysmetabolism, anemia and renal hypoxia, inflammation and fibrosis in the remnant kidney rat model

Anemia is a common complication of chronic kidney disease (CKD) that develops early and its severity increases as renal function declines. It is mainly due to a reduced production of erythropoietin (EPO) by the kidneys; however, there are evidences that iron metabolism disturbances increase as CKD progresses. Our aim was to study the mechanisms underlying the development of anemia of CKD, as well as renal damage, in the remnant kidney rat model of CKD induced by 5/6 nephrectomy. This model of CKD presented a sustained degree of renal dysfunction, with mild and advanced glomerular and tubulointerstitial lesions. Anemia developed 3 weeks after nephrectomy and persisted throughout the protocol. The remnant kidney was still able to produce EPO and the liver showed an increased EPO gene expression. In spite of the increased EPO blood levels, anemia persisted and was linked to low serum iron and transferrin levels, while serum interleukin (IL)-6 and high sensitivity C-reactive protein (hs-CRP) levels showed the absence of systemic inflammation. The increased expression of duodenal ferroportin favours iron absorption; however, serum iron is reduced which might be due to iron leakage through advanced kidney lesions, as showed by tubular iron accumulation. Our data suggest that the persistence of anemia may result from disturbances in iron metabolism and by an altered activity/function of EPO as a result of kidney cell damage and a local inflammatory milieu, as showed by the increased gene expression of different inflammatory proteins in the remnant kidney. In addition, this anemia and the associated kidney hypoxia favour the development of fibrosis, angiogenesis and inflammation that may underlie a resistance to EPO stimuli and reduced iron availability. These findings might contribute to open new windows to identify putative therapeutic targets for this condition, as well as for recombinant human EPO (rHuEPO) resistance, which occurs in a considerable percentage of CKD patients.

Sickle cell disease: renal manifestations and mechanisms

Sickle cell disease (SCD) substantially alters renal structure and function, and causes various renal syndromes and diseases. Such diverse renal outcomes reflect the uniquely complex vascular pathobiology of SCD and the propensity of red blood cells to sickle in the renal medulla because of its hypoxic, acidotic, and hyperosmolar conditions. Renal complications and involvement in sickle cell nephropathy (SCN) include altered haemodynamics, hypertrophy, assorted glomerulopathies, chronic kidney disease, acute kidney injury, impaired urinary concentrating ability, distal nephron dysfunction, haematuria, and increased risks of urinary tract infections and renal medullary carcinoma. SCN largely reflects an underlying vasculopathy characterized by cortical hyperperfusion, medullary hypoperfusion, and an increased, stress-induced vasoconstrictive response. Renal involvement is usually more severe in homozygous disease (sickle cell anaemia, HbSS) than in compound heterozygous types of SCD (for example HbSC and HbSβ(+)-thalassaemia), and is typically mild, albeit prevalent, in the heterozygous state (sickle cell trait, HbAS). Renal involvement contributes substantially to the diminished life expectancy of patients with SCD, accounting for 16-18% of mortality. As improved clinical care promotes survival into adulthood, SCN imposes a growing burden on both individual health and health system costs. This Review addresses the renal manifestations of SCD and focuses on their underlying mechanisms.

Candidate genes in quantitative trait loci associated with absolute and relative kidney weight in rats with Inherited Stress Induced Arterial Hypertension

BACKGROUND

The kidney mass is significantly increased in hypertensive ISIAH rats with Inherited Stress Induced Arterial Hypertension as compared with normotensive WAG rats. The QTL/microarray approach was carried out to determine the positional candidate genes in the QTL for absolute and relative kidney weight.

RESULTS

Several known and predicted genes differentially expressed in ISIAH and WAG kidney were mapped to genetic loci associated with the absolute and relative kidney weight in 6-month old F2 hybrid (ISIAHxWAG) males. The knowledge-driven filtering of the list of candidates helped to suggest several positional candidate genes, which may be related to the structural and mass changes in hypertensive ISIAH kidney.

CONCLUSIONS

The further experimental validation of causative genes and detection of polymorphisms will provide opportunities to advance our understanding of the underlying nature of structural and mass changes in hypertensive ISIAH kidney.

Role of the kidney in the fetal programming of adult cardiovascular disease: an update

It is well established that an adverse in utero environment can impinge upon fetal development and place the offspring on a track leading to future cardiovascular disease. Significantly, this may occur in the absence of any outward manifestations at birth. In this brief review, we focus on potential renal mechanisms that lead to adaptations in glomerular and tubular function that initiate hypertension of developmental origin and examine potential therapeutic interventions. This report updates recent data in this field.

Approaches to uremia

The development of dialysis was a dramatic step forward in medicine, allowing people who would soon have died because of lack of kidney function to remain alive for years. We have since found, however, that the "artificial kidney" does not live up fully to its name. Dialysis keeps patients alive but not well. Part of the residual illness that dialysis patients experience is caused by retained waste solutes that dialysis does not remove as well as native kidney function does. New means are available to identify these toxic solutes, about which we currently know remarkably little, and knowledge of these solutes would help us to improve therapy. This review summarizes our current knowledge of toxic solutes and highlights methods being explored to identify additional toxic solutes and to enhance the clearance of these solutes to improve patient outcomes.

Is microalbuminuria a risk factor for hypertension in children with solitary kidney?

BACKGROUND

The correlations between ambulatory blood pressure measurements (ABPM) and serum cystatin C (Cys C), serum creatinine (Cr), microalbumin (MA), and β2-microglobulin (β2-MG) levels in 24 h (24-h) urine were analyzed in children with solitary kidney (SK) and compared to healthy children.

METHODS

Fifty children with normal functioning SK and 25 controls were studied. The ABPM, serum Cys C, serum Cr, MA, and β2-MG levels in 24-h urine were measured in all children. Clinical symptoms and signs, laboratory results, urinary ultrasonography, voiding cystourethrography, and Dimercaptosuccinic acid (DMSA) scintigraphy results were recorded in the SK group. Four patients with Wilms' tumor and two with renal scarring were excluded from the study.

RESULTS

The mean ages of the SK group and controls were 9.6 ± 3.6 and 9.3 ± 3.3 years, respectively. The serum Cys C and Cr levels, 24-h urinary β2-MG and MA levels were similar in both groups (p > 0.05). However, 24-h urinary MA excretion was higher in patients living with SK more than 5 years (p = 0.01). Standard deviation scores of ABPM parameters showed no significant correlation with serum Cr, serum Cys C, MA, and β2-MG in 24-h urine of both groups.

CONCLUSIONS

Children with SK have increased 24-h urinary MA excretion in the long term, and need prolonged follow-up to detect early deterioration of renal function and to prevent end-organ damage later in life.

Antenatal betamethasone exposure alters renal responses to angiotensin-(1-7) in uninephrectomized adult male sheep

Antenatal corticosteroid exposure reduces renal function and alters the intrarenal renin-angiotensin system to favor angiotensin activation of angiotensin type 1 receptor (AT1R) mediated responses in ovine offspring. This study aimed to assess whether antenatal steroid exposure would affect renal responses to the direct intrarenal infusion of angiotensin-(1-7) in rams and the angiotensin receptors involved in mediating responses to the peptide. Adult, uninephrectomized rams exposed to either betamethasone or vehicle before birth received intrarenal angiotensin-(1-7) infusions (1 ng/kg/min) alone or in combination with antagonists to angiotensin receptors for 3 h. Basal sodium excretion (UNa) was significantly lower and mean arterial pressure was significantly higher in betamethasone- compared to the vehicle-treated sheep. Angiotensin-(1-7) decreased UNa more in betamethasone- than in vehicle-treated sheep. Candesartan reversed the response to angiotensin-(1-7) but D-Ala(7)-angiotensin-(1-7) did not. Angiotensin-(1-7) infusion decreased effective renal plasma flow in both groups to a similar extent and the response was reversed by candesartan, but was not blocked by D-Ala(7)-angiotensin-(1-7). Glomerular filtration rate increased significantly in both groups after 3 h infusion of angiotensin-(1-7) plus candesartan. These results suggest that antenatal exposure to a clinically relevant dose of betamethasone impairs renal function in rams. Moreover, angiotensin-(1-7) appears capable of activating the AT1R in uninephrectomized rams.

Mitochondrial impairment in the five-sixth nephrectomy model of chronic renal failure: proteomic approach

BACKGROUND

Kidney injuries provoke considerable adjustment of renal physiology, metabolism, and architecture to nephron loss. Despite remarkable regenerative capacity of the renal tissue, these adaptations often lead to tubular atrophy, interstial and glomerular scaring, and development of chronic kidney disease. The therapeutic strategies for prevention of the transition from acute kidney damage to a chronic condition are limited. The purpose of this study was to elucidate large-scale alterations of the renal cortex proteome in partially nephrecromized rats at an early stage of chronic kidney disease.

METHODS

Sprague-Dawley 5/6 nephrectomized rats and sham-operated controls were sacrificed at day 28 post-surgery. To identify proteins with notable alteration of expression we applied a 2D-proteomics approach followed by mass-spectrometry. Altered expression of identified and related proteins was validated by Western blotting and immunohistochemistry.

RESULTS

Proteins with increased levels of expression after partial nephrectomy were albumin and vimentin. Proteins with decreased expression were metabolic or mitochondrial. Western blotting analysis showed that the renal cortex of nephrectomized rats expressed decreased amount (by ~50%) of proteins from the inner mitochondrial compartment - the beta-oxidation enzyme MCAD, the structural protein GRP-75, and the oxidative phosphorylation protein COXIV. Mitochondrial DNA copy number was decreased by 30% in the cortex of PNx rats. In contrast, the levels of an outer mitochondrial membrane protein, VDAC1, remained unchanged in remnant kidneys. Mitochondrial biogenesis was not altered after renal mass ablation as was indicated by unchanged levels of PPARγ and PGC1α proteins. Autophagy related protein Beclin 1 was up-regulated in remnant kidneys, however the level of LC3-II protein was unchanged. BNIP3 protein, which can initiate both mitochondrial autophagy and cell death, was up-regulated considerably in kidneys of nephrecomized rats.

CONCLUSIONS

The results of the study demonstrated that notable alterations in the renal cortex of 5/6 nephrectomized rats were associated with mitochondrial damage, however mitochondrial biogenesis and autophagy for replacement of damaged mitochondria were not stimulated. Accumulation of dysfunctional mitochondria after 5/6 nephrectomy may cause multiple adjustments in biosynthetic pathways, energy production, ROS signaling, and activation of pro-cell death regulatory pathways thus contributing to the development of chronic kidney disease.

Modulation of mitochondrial glutathione status and cellular energetics in primary cultures of proximal tubular cells from remnant kidney of uninephrectomized rats

Compensatory renal hypertrophy following reduction in renal mass leads to a hypermetabolic state and increases in basal mitochondrial oxidative stress and susceptibility to several nephrotoxicants. Previous studies provide conflicting data on whether renal mitochondria after reduction in renal mass undergo proliferation or hypertrophy or both. In the present study, our goal was to determine whether mitochondria of hypertrophied kidney undergo hypertrophy or proliferation after uninephrectomy using the uninephrectomized (NPX) rat model. Renal proximal tubular (PT) cells from NPX rats exhibited increased mitochondrial density, membrane potential and protein but no significant difference in mitochondrial DNA, as compared to PT cells from control rats. Our previous studies showed that overexpression of two mitochondrial anion transporters, the dicarboxylate (DIC, Slc25a10) and oxoglutarate (OGC, Slc25a11) carriers, in NRK-52E cells resulted in increased mitochondrial uptake of glutathione (GSH) and protection from chemically induced apoptosis. In the present study, we overexpressed DIC- and OGC-cDNA plasmids to assess their function in renal PT cells after compensatory renal hypertrophy. PT cells from NPX rats that were first preincubated with GSH were protected from cytotoxicity due to the mitochondrial inhibitor antimycin A by overexpression of either of the two mitochondrial GSH transporters. Our present results provide further evidence that compensatory renal hypertrophy is associated primarily with mitochondrial hypertrophy and hyperpolarization and that manipulation of mitochondrial GSH transporters in PT cells of hypertrophied kidney can alter susceptibility to chemically induced injury under appropriate conditions and may be a suitable therapeutic approach.

BAMBI regulates angiogenesis and endothelial homeostasis through modulation of alternative TGFβ signaling

BACKGROUND

BAMBI is a type I TGFβ receptor antagonist, whose in vivo function remains unclear, as BAMBI(-/-) mice lack an obvious phenotype.

METHODOLOGY/PRINCIPAL FINDINGS

Identifying BAMBI's functions requires identification of cell-specific expression of BAMBI. By immunohistology we found BAMBI expression restricted to endothelial cells and by electron microscopy BAMBI(-/-) mice showed prominent and swollen endothelial cells in myocardial and glomerular capillaries. In endothelial cells over-expression of BAMBI reduced, whereas knock-down enhanced capillary growth and migration in response to TGFβ. In vivo angiogenesis was enhanced in matrigel implants and in glomerular hypertrophy after unilateral nephrectomy in BAMBI(-/-) compared to BAMBI(+/+) mice consistent with an endothelial phenotype for BAMBI(-/-) mice. BAMBI's mechanism of action in endothelial cells was examined by canonical and alternative TGFβ signaling in HUVEC with over-expression or knock-down of BAMBI. BAMBI knockdown enhanced basal and TGFβ stimulated SMAD1/5 and ERK1/2 phosphorylation, while over-expression prevented both.

CONCLUSIONS/SIGNIFICANCE

Thus we provide a first description of a vascular phenotype for BAMBI(-/-) mice, and provide in vitro and in vivo evidence that BAMBI contributes to endothelial and vascular homeostasis. Further, we demonstrate that in endothelial cells BAMBI interferes with alternative TGFβ signaling, most likely through the ALK 1 receptor, which may explain the phenotype observed in BAMBI(-/-) mice. This newly described role for BAMBI in regulating endothelial function has potential implications for understanding and treating vascular disease and tumor neo-angiogenesis.

Mitochondrial glutathione in toxicology and disease of the kidneys

The tripeptide glutathione (GSH), comprised of the amino acids l-cysteine, glycine, and l-glutamate, is found in all cells of aerobic organisms and plays numerous, critical roles as an antioxidant and nucleophile in regulating cellular homeostasis and drug metabolism. GSH is synthesized exclusively in the cytoplasm of most cells by two ATP-dependent reactions. Despite this compartmentation, GSH is found in other subcellular compartments, including mitochondria. As the GSH molecule has a net negative charge at physiological pH, it cannot cross cellular membranes by diffusion. Rather, GSH is a substrate for a variety of anion and amino acid transporters. Two organic anion carriers in the inner membrane of renal mitochondria, the dicarboxylate carrier (DIC; Slc25a10) and the 2-oxoglutarate carrier (OGC; Slc25a11), are responsible for most of the transport of GSH from cytoplasm into mitochondrial matrix. Genetic manipulation of DIC and/or OGC expression in renal cell lines demonstrated the ability to produce sustained increases in mitochondrial GSH content, which then protected these cells from cytotoxicity due to several oxidants and mitochondrial toxicants. Several diseases and pathological states are associated with mitochondrial dysfunction and oxidative stress, suggesting that the mitochondrial GSH pool may be a therapeutic target. One such disease that is of particular concern for public health is diabetic nephropathy. Another chronic, pathological state that is associated with bioenergetic and redox changes is compensatory renal hypertrophy that results from reductions in functional renal mass. This review summarizes pathways of mitochondrial GSH transport and discusses studies on its manipulation in toxicological and pathological states.

Endothelial dysfunction promotes the transition from compensatory renal hypertrophy to kidney injury after unilateral nephrectomy in mice

Loss of functional nephrons associated with chronic kidney disease induces glomerular hyperfiltration and compensatory renal hypertrophy. We hypothesized that the endothelial nitric oxide synthase (eNOS) [soluble guanylate cyclase (sGC)] protein kinase G (PKG) pathway plays an important role in compensatory renal hypertrophy after unilateral nephrectomy. Analysis of mice subjected to unilateral nephrectomy showed increases in kidney weight-to-body weight and total protein-to-DNA ratios in wild-type but not eNOS knockout (eNOSKO) mice. Serum creatinine and blood urea nitrogen increased after nephrectomy in eNOSKO but not in wild-type mice. Furthermore, Bay 41-2272, an sGC stimulator, induced compensatory renal hypertrophy in eNOSKO mice and rescued renal function. The NO donor S-nitrosoglutathione (GSNO) and Bay 41-2272 stimulated PKG activity and induced phosphorylation of Akt protein in human proximal tubular cells. GSNO also induced phosphorylation of eukaryotic initiation factor 4E-binding protein and ribosomal protein S6. Our results highlight the importance of the eNOS-NO-PKG pathway in compensatory renal hypertrophy and suggest that reduced eNOS-NO bioavailability due to endothelial dysfunction is the underlying mechanism of failure of compensatory hypertrophy and acceleration of progressive renal dysfunction.

Influence of renal compensatory hypertrophy on mitochondrial energetics and redox status

A reduction in functional renal mass is common in numerous renal diseases and aging. The remaining functional renal tissue undergoes compensatory growth primarily due to hypertrophy. This is associated with a series of physiological, morphological and biochemical changes similar to those observed after uninephrectomy. Previous work showed that compensatory renal cellular hypertrophy resulted in an increase in susceptibility to several drugs and environmental chemicals and appeared to be associated with oxidative stress. Compensatory renal cellular hypertrophy was also associated with increases in mitochondrial metabolic activity, uptake of glutathione (GSH) across renal plasma and mitochondrial inner membranes, and intracellular GSH concentrations. Based on these observations, we hypothesize that the morphological, physiological and biochemical changes in the hypertrophied kidney are associated with marked alterations in renal cellular energetics, redox status and renal function in vivo. In this study, we used a uninephrectomized (NPX) rat model to induce compensatory renal growth. Our results show alterations in renal physiological parameters consistent with modest renal injury, altered renal cellular energetics, upregulation of certain renal plasma membrane transporters, including some that have been observed to transport GSH, and evidence of increased oxidative stress in mitochondria from the remnant kidney of NPX rats. These studies provide additional insight into the molecular changes that occur in compensatory renal hypertrophy and should help in the development of novel therapeutic approaches for patients with reduced renal mass.

Effects of low protein intake on the development of the remaining kidney in subtotally nephrectomized immature rats: expression of inducible and endothelial NO synthase

We examined the effects of low protein intake on the development of the remaining kidney in subtotally (5/6) nephrectomized immature rats. Three-week-old rats were kept on a diet containing either 12% protein (Lp rats) or 18% protein (Np rats) for 4 or 8 weeks after subtotal nephrectomy (SUNx). In Western blot analysis, the endothelial NO synthase (eNOS) protein expression of the Lp rats was significantly higher than that of the Np rats at 4 weeks after SUNx. Immunohistochemically, more inducible NO synthase (iNOS)-positive cells were observed in the Np rats than in the Lp rats 4 weeks after SUNx in the distal tubules. In semiquantitative RT-PCR, the expression of renin mRNA was significantly lower in the Lp rats than in the Np rats at 4 and 8 weeks after SUNx. These findings reveal that protein restriction is effective in preventing renal failure of immature rats and that the changes in the expression levels of renin, eNOS, and iNOS is involved in the process of this prevention.

Characterization of a rat model of moderate chronic renal failure--focus on hematological, biochemical, and cardio-renal profiles

The pathophysiological modifications underlying chronic renal failure seems to be dependent on the insufficiency degree, which will determine the moment to start therapy. As there is yet limited information about animal models of moderate chronic renal failure, we intended to perform a complete characterization of the hematological and cardio-renal alterations induced by partial nephrectomy. Blood samples from control and chronic renal failure rats were collected at 0, 3, 9, and 15 weeks in order to evaluate renal function, hematological parameters, iron metabolism, blood lipids, peripheral sympathetic nervous system, and inflammatory and redox status markers. BP, tissues trophy indexes, and kidney histomorphology were also assessed. Our data are consistent with a sustained moderate degree of chronic renal failure with a quickly compensated modest anaemia, though presenting iron metabolism disturbances. Despite the reasonable degree of functionality of the remnant kidney, as suggested by the anaemia correction and by the kidney hypertrophy and moderate lesions, several important cardiovascular modifications were developed. Our model presented hypertension, dyslipidemia, erythropoietic disturbances, sympathetic activation, and oxidative stress. This model might be a good tool to study the cellular/molecular mechanisms underlying moderate stages of chronic renal failure and to evaluate the therapeutic efficacy for prevention and treatment/correction of cardio-renal anaemia syndromes and complications in early stages.

Compensatory renal growth in uninephrectomized immature rats: proliferative activity and epidermal growth factor

Compensatory response to uninephrectomy in immature animals is stronger compared with that in adult ones and the response is due mainly to renal cell proliferation. The present study explored to show the growth pattern of the remaining kidney immediately after uninephrectomy in immature rats with special reference to proliferating activity and epidermal growth factor (EGF). Immunolocalizations of proliferating cell nuclear antigen (PCNA) and EGF in immature rat kidney were examined during the first three days after uninephrectomy. Semi-quantitative analysis of the expression of preproEGF mRNA was performed. One day after the operation, the PCNA positive cell ratios in the glomeruli and the proximal tubules were significantly higher in unilaterally nephrectomized (UNx) rats than in sham-operated (Sham) rats. In UNx and Sham rats, the proximal and distal tubular cells showed positive reactions to EGF antibody. The positive reaction of proximal tubules to EGF antibody was weaker in UNx than in Sham rats 1 day after the operation, while the degree of reactivity was not different between UNx and Sham rats 3 days after the operation. The level of expression of preproEGF mRNA in the kidney was significantly lower in UNx than in Sham rats 1 day after the operation. These results indicate that unilateral nephrectomy in immature rats causes increased proliferative activity and decreased expression of EGF in the remaining kidney during the early period of compensatory renal growth.

Evaluation of Two Protocols of Uremic Rat Model: Partial Nephrectomy and Infarction

Animal models of chronic renal failure have been mostly achieved by partial ablation of renal parenchyma, the two most common techniques employed being surgical resection or infarction. Evaluation of the uremic model using these two techniques was carried out in Wistar rats. Two weeks after operative procedure, measured serum urea levels in the resection and infarction models were 59.1 and 64.3 mg/dL (normal range 15.6-24.4 mg/dL) respectively. However, the standard deviation in the former was significantly lower, 6.3 vs. 97.1 mg/dL from infarction model, p = 0.007. A consistent degree of glomerular filtration rate reduction was obtained in the resection model, resulting in 20-30% of normal creatinine clearance. This compared favorably with the creatinine clearance range (0.3-74% of normal) from the infarction model, in which two animals died of uremia and seven had higher than 50% of normal creatinine clearance. It is reasonable to attribute reproducibility and homogeneity demonstrated in the resection model to (i) more precise control of renal ablation extent with surgical techniques and (ii) less interplay of confounding injury mechanism to remnant kidney. These data support superiority of the resection model as an experimental tool for pathophysiological and/or interventional investigations of chronic renal failure.

Compensatory renal growth and mitochondrial function: the influence of warm ischemia and reperfusion

PURPOSE: To evaluate the influence of ischemia/reperfusion injury on renal compensatory growth (CGR) and mitochondrial function. METHODS: Forty five Wistar rats were divided in 3 groups: Control Group (GC) - 21 rats were submitted to a sham laparotomy and sacrificed at 1st (6 rats) and 7th (15 rats) postoperative days to evaluate the dry weight of both kidneys and their growth during 1 week (6 rats) and to quantify mitochondrial respiration (9 rats); Group 1 (G1) - 12 rats underwent right nephrectomy and were sacrificed 7 days later for analysis of renal mitochondrial function (6 rats) and dry weight (6 rats). Group 2 (G2) - renal warm ischemia for 60 minutes followed by right nephrectomy was performed in 12 rats; they were sacrificed 7 days later to evaluate renal mitochondrial function (6 rats) and dry weight (6 rats). RESULTS: Dry weight (mg) of left kidneys at 7th day: GC - 219±18, G1 - 281±23 and G2 - 338±39 (GCxG1 p<0.01; GCxG2 p<0.001; G1xG2 p<0.01). State 4 mitochondrial respiration rate and respiratory control ratio (RCR) were similar in all groups (p>0.05). State 3 respirations (mM/min/mg) in GC, G1 and G2 was respectively: 99±23, 132±22 and 82±44 (p<0.02; the only statistical difference noted was between groups G1xG2 - p<0.05). CONCLUSIONS: Following unilateral nephrectomy CRG is associated with an increase in state 3 of mitochondrial respiration. Renal ischemia/reperfusion injury enhances the CRG provoked by unilateral nephrectomy but such enhancement seems independent on mitochondrial respiration.

Rosiglitazone treatment attenuates expression of inflammatory hallmarks in the remaining kidney following contralateral nephrectomy

BACKGROUND/AIMS

Following kidney donation, living kidney donors have been reported to develop anemia and pronounced inflammation. Therapeutic strategies for ameliorating unilateral nephrectomy-induced inflammation would be beneficiary for the living donors. We applied rosiglitazone to attenuate inflammatory processes ongoing within the remaining kidney following contralateral nephrectomy.

METHODS

20 Sprague-Dawley rats were subjected to left unilateral nephrectomy and 20 others to sham operation. Half of each group was treated for 2 weeks with rosiglitazone (5 mg/kg body weight). After sacrifice, intrarenal transforming growth factor (TGF)-beta, angiotensin-II (A-II), interleukin (IL)-6, IL-10, IL-4 and nitric oxide (NO) were assessed, and histologic sections stained to assess the inflammatory cell infiltration. Renal function was evaluated by creatinine, urea, cystatin C measurements.

RESULTS

Intrarenal IL-6, A-II and TGF-beta were significantly augmented, while NO was significantly decreased in kidneys remaining after contralateral nephrectomy. Rosiglitazone treatment abrogated augmented IL-6, A-II and TGF-beta synthesis and restored intrarenal NO availability in the remaining kidneys. Rosiglitazone also augmented anti-inflammatory IL-4 cytokine synthesis, while IL-10 production, leukocyte infiltration and renal function parameters remained unchanged.

CONCLUSIONS

Rosiglitazone treatment attenuates the proinflammatory responses, represented by augmented IL-6, A-II and TGF-beta production, developing in the remaining kidney following contralateral nephrectomy. In addition, by stimulating IL-4 synthesis and restoring NO availability, rosiglitazone treatment initiates counteractive anti-inflammatory responses in the remaining kidney.

Evaluation of clinical status, renal function, and hematopoietic variables after unilateral nephrectomy in canine kidney donors

OBJECTIVE

To determine clinical status and renal and hematopoietic function after kidney donation and identify risks associated with kidney donation in dogs.

DESIGN

Prospective study.

ANIMALS

14 dogs that underwent unilateral nephrectomy for kidney donation.

PROCEDURES

Records were reviewed retrospectively to collect data regarding prenephrectomy clinicopathologic variables. Dogs were reexamined prospectively at various times after nephrectomy, and pre- and postnephrectomy CBC, serum biochemical analyses, urinalysis, and urine protein-to-urine creatinine ratio were compared. Six dogs had postnephrectomy renal volume determined ultrasonographically, and 4 of those dogs also underwent scintigraphic determination of glomerular filtration rate and renal biopsy.

RESULTS

All dogs were clinically normal at the time of reevaluation. There were no significant differences between prenephrectomy and postnephrectomy values for BUN concentration or urine specific gravity. Mean postnephrectomy serum creatinine concentration was significantly greater than prenephrectomy concentration. Mean serum phosphorus concentration was significantly decreased after nephrectomy, and mean Hct, corpuscular volume, and corpuscular hemoglobin concentration were significantly increased after nephrectomy. Postnephrectomy renal volume was greatest in dogs < 12 months old at the time of surgery. Mean postnephrectomy glomerular filtration rate was 2.82 +/- 1.12 mL/kg/ min (1.28 +/- 0.51 mL/lb/min). Renal biopsy specimens obtained during and after nephrectomy were histologically normal.

CONCLUSIONS AND CLINICAL RELEVANCE

Renal and hematopoietic variables were within reference ranges in dogs examined up to 2.5 years after unilateral nephrectomy. Compensatory renal hypertrophy was greatest in dogs < 1 year of age at donation. Donor age, along with histocompatability, may be an important factor in selecting dogs for kidney donation.

Distinct quantitative trait loci for kidney, cardiac, and aortic mass dissociated from and associated with blood pressure in Dahl congenic rats

Blood pressure (BP) is largely determined by quantitative trait loci (QTLs) in Dahl salt-sensitive (DSS) rats. Little is known about QTLs controlling kidney (K), cardiac (C), and aortic (A) mass (i.e. Km, Cm, and Am, respectively) of DSS rats independent of BP. Their identification can facilitate our understanding of end organ damage. In this work, 36 congenic strains were employed to define QTLs for Km, Cm, and Am either independent of or associated with BP. Five new QTLs, i.e., KmQTLs, that influence Km independent of Cm, Am, and BP were defined. Four new CakmQTLs were defined for Cm, Am, and Km independent of BP. Among them, the CakmC10QTL1 interval contained 13 genes and undefined loci, and none was known to influence the phenotypes in question, paving the way for a novel gene discovery. Among 17 individual QTLs for BP, 14 also affected Cm, Km, and Am, i.e., they are BpcakmQTLs. In contrast, one BpQTL had no effect on Cm, Am, and Kam. Therefore, BP and Cm, Am, and Km have distinct and shared genetic determinants. The discovery of individual Km and Cakm QTLs will likely facilitate the identification of mechanisms underlying renal, cardiac, and/or aortic hypertrophy independent of hypertension.

Persistent renal hypertrophy and faster decline of glomerular filtration rate precede the development of microalbuminuria in type 1 diabetes

Soon after the onset of type 1 diabetes, renal hypertrophy and hyperfiltration become manifest, particularly among patients who will subsequently develop diabetic nephropathy. Whether these early renal dysfunctions are involved in the pathogenesis of diabetic nephropathy is currently unclear. We evaluated, during the same day, kidney volume and glomerular filtration rate (GFR) in 146 patients with type 1 diabetes and normal renal function. All the individuals were then monitored for a mean of 9.5 +/- 4.4 years for the development of microalbuminuria. Kidney volume and GFR were reevaluated in a subset of 68 patients 4 years after baseline. During follow-up, microalbuminuria developed in 27 of 146 diabetic patients. At baseline, kidney volume (312.8 +/- 52.6 vs. 281.4 +/- 46.1 vs. 236.8 +/- 41.6 ml/1.73 m(2), P < 0.05) but not GFR was increased in patients predisposed to microalbuminuria. Risk of progression was higher in patients with increased kidney volume (P = 0.0058). Patients predisposed to microalbuminuria showed a stable increase in kidney volume (P = 0.003), along with a faster decline of GFR (P = 0.01). Persistent renal hypertrophy and faster decline of GFR precede the development of microalbuminuria in type 1 diabetes. These findings support the hypothesis that renal hypertrophy precedes hyperfiltration during the development of diabetic nephropathy.

Compensatory renal growth protects mice against Shiga toxin 2-induced toxicity

Uninephrectomy (Unx) is followed by the compensatory renal growth (CRG) of the remaining kidney. Previous evidence has shown that during CRG, renal tissue is resistant to a variety of pathologies. We tested the hypothesis that the functional changes that take place during CRG could attenuate Shiga toxin (Stx) toxicity in a mouse model of Stx2-induced hemolytic uremic syndrome (HUS). The participation of nitric oxide (NO) was analyzed. After CRG induction with Unx, mice were exposed to a lethal dose of Stx2, and the degree of renal damage and mortality was measured. Stx2 effects on the growth, renal blood flow (RBF) and NO synthase (NOS) intrarenal expression in the remaining kidney were then studied. The induction of CRG strongly prevented Stx2-mediated mortality and renal damage. Administration of the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME) during CRG partially impaired the protection. Both Stx2 and L-NAME interfered with the hypertrophic and hyperplastic responses to Unx, as well as with the increase in RBF. In intact mice, Stx2 decreased renal perfusion, inhibited endothelial NOS basal expression and enhanced inducible NOS expression; all of these effects were attenuated by prior Unx. It is concluded that during CRG mice are highly protected against Stx2 toxicity and lethality. The protective capacity of CRG could be related to the enhancement of renal perfusion and preservation of eNOS renal expression, counterbalancing two major pathogenic mechanisms of Stx2.

Mesangial cells initiate compensatory renal tubular hypertrophy via IL-10-induced TGF-β secretion: effect of the immunomodulator AS101 on this process

The present study investigated the role of IL-10 produced by the mesangial cells in postnephrectomy compensatory renal growth and the effect of the immunomodulator AS101 on this process. One hundred forty unilateral nephrectomized and sham-operated male Sprague-Dawley rats were treated by AS101 or PBS before and after surgery. The results show that secretion of IL-10 and TGF-β by mesangial cells isolated from the remaining kidneys was increased significantly, compared with those of control and sham animals. Moreover, TGF-β secretion by mesangial cells was increased after the addition of exogenous recombinant IL-10 and inhibited in the presence of neutralizing anti-IL-10 antibodies. In vivo, compensatory growth of the remaining kidneys was associated with significant increase in IL-10 content in renal tissues and plasma. Immunohistochemical studies show that IL-10 was produced by mesangial cells. Elevated IL-10 levels were followed by the rise in TGF-β content in plasma and renal tissue. AS101 treatment decreased IL-10 and TGF-β expression in plasma and kidney tissues and results in 25% reduction in the fresh and fractional kidney weight and decreased hypertrophy of tubular cells (protein/DNA ratio, morphometric analysis). Taken together, these data demonstrate that TGF-β production by mesangial cells is IL-10 dependent. Mesangial cells are the major source of IL-10 in kidneys. AS101, by inhibiting the activity of IL-10, decreases TGF-β production by mesangial cells, thus limiting compensatory tubular cell hypertrophy.

Role of EGF Receptor Activation in Angiotensin II–Induced Renal Epithelial Cell Hypertrophy

For determination of the molecular mechanisms underlying the induction of epithelial cell hypertrophy by angiotensin II (Ang II), a well-characterized porcine renal proximal tubular cell line LLCPKcl4, which does not express endogenous Ang II receptor subtypes, was transfected with cDNA encoding Ang II subtype 1 receptor (AT1R/Cl4). Ang II transactivated the EGF receptor (EGFR) in these AT1R/Cl4 cells, which was blocked by the selective AT1R antagonist losartan but not by the selective AT2R antagonist PD123319. Ang II did not transactivate EGFR in empty vector-transfected LLCPKcl4 cells (Vector/Cl4). Ang II elicited release of soluble heparin-binding EGF-like growth factor (HB-EGF) from AT1R/Cl4 cells, and Ang II-induced EGFR activation was prevented by pretreatment with the specific HB-EGF inhibitor CRM197 or the metalloproteinase inhibitors batimastat or phenanthroline, none of which had any effect on EGFR activation by exogenously administered EGF. Ang II stimulated protein synthesis and cell hypertrophy in AT1R/Cl4 cells without increasing cell number, and signaling studies revealed that Ang II stimulated phosphorylation of the 40S ribosomal protein S6 and the eukaryotic translation initiation factor 4E-binding protein 1, the two downstream target proteins of the mammalian target of rapamycin, which is a central regulator of protein synthesis and cell size. Ang II-induced mammalian target of rapamycin activation, [3H]leucine incorporation, and cellular hypertrophy were inhibited by pretreatment with either batimastat or CRM197 or by pretreatment with rapamycin or the EGFR tyrosine kinase inhibitor AG1478. Ang II also stimulated Smad 2/3 phosphorylation, which was blocked by a selective TGF-beta receptor I kinase inhibitor but not by CRM197. With blockade of TGF-beta receptor, Ang II-mediated hypertrophy was converted into cell proliferation, which was blocked by CRM197. In summary, this is the first demonstration that HB-EGF shedding-dependent EGFR transactivation, along with activation of TGF-beta signaling pathways, mediates Ang II-induced renal tubular epithelial cell hypertrophy.