Renal Mass Reduction Research Articles

The effect of inhibition of endoplasmic reticulum stress on lipolysis in white adipose tissue in a rat model of chronic kidney disease

Lipolysis in fat tissue plays an important role in the development of metabolic disturbances, a characteristic feature of chronic kidney disease (CKD). In the present study, we tested the hypothesis that the inhibition of endoplasmic reticulum (ER) stress could alleviate lipolysis in white adipose tissue in a rat model of CKD. A rat model of CKD was established by a method of reduced renal mass (RRM). Lipolysis was measured as the release of glycerol in ex vivo fat pads and cultured primary adipocytes. The activity of lipases and markers of ER stress were measured by Western blotting and immunoprecipitation. Our data showed that lipolysis in visceral white adipose tissue was increased in RRM rats compared with control rats. In addition, increased phosphorylation of hormone-sensitive lipase (HSL) and binding of adipose triglyceride lipase (ATGL) to comparative gene identification-58 (CGI-58) protein were observed in the RRM rats. The phosphorylation of ER stress markers, including IRE1α, PERK, and eukaryotic initiation factor (eIF) 2α, and the expression of ER stress marker 78 kDa glucose-regulated protein (GRP78) were significantly increased in RRM rats. Treatment with an inhibitor of ER stress partially but significantly alleviated lipolysis, and this alleviation was accompanied by reduced binding of ATGL to CGI-58. Our results showed that enhanced lipolysis and ER stress occurred in visceral white adipose tissue in a rat model of CKD. Moreover, inhibition of ER stress significantly alleviated lipolysis. These findings suggest that ER stress is a potential therapeutic target for the metabolic disturbances associated with CKD.

Wnt pathway activation in long term remnant rat model.

Progression of chronic kidney disease (CKD) is characterized by deposition of extracellular matrix. This is an irreversible process that leads to tubulointerstitial fibrosis and finally loss of kidney function. Wnt/β-catenin pathway was reported to be aberrantly activated in the progressive damage associated with chronic organ failure. Extensive renal ablation is an experimental model widely used to gain insight into the mechanisms responsible for the development of CKD, but it was not evaluated for Wnt/β-catenin pathway. This study aimed to elucidate if the rat 5/6 renal mass reduction model (RMR) is a good model for the Wnt/β-catenin activation and possible next modulation. RMR model was evaluated at 12 and 18 weeks after the surgery, when CKD is close to end-stage kidney disease demonstrated by molecular and histological studies. Wnt pathway components were analyzed at mRNA and protein level. Our results demonstrate that Wnt pathway is active by increase of β-catenin at mRNA level and nuclear translocation in tubular epithelium as well as some target genes. These results validate the RMR model for future modulation of Wnt pathway, starting at shorter time after the surgery.

18F]FPYKYNE- Losartan AT1 Receptor Binding Is Reduced in Chronic Kidney Disease Rat Model With Pet Imaging

Significant renal mass reduction induced by 5/6 subtotal nephrectomy is associated with a chain of events that culminates in hypertension and chronic kidney disease (CKD). The leading cause of death in CKD is cardiovascular diseases. Angiotensin type 1 receptor (AT1R) is thought to play a role in progression of the disease and development of complications because of the beneficial effect of AT1R blockade. However, conflicting results were reported on intrarenal AT1R levels in CKD models. Noninvasive imaging will allow for identification of receptor expression abnormalities, understanding the contribution of the AT1R to the progression of disease and will aid to guide medication.

Compensatory renal growth after unilateral or subtotal nephrectomy in the ovine fetus

Clinical and experimental studies show that unilateral (1/2Nx) and subtotal nephrectomy (5/6Nx) in adults result in compensatory renal growth without formation of new nephrons. During nephrogenesis, the response to renal mass reduction has not been fully investigated. Ovine fetuses underwent 1/2Nx, 5/6Nx, or sham surgery (sham) at 70 d of gestation (term: 150 d), when nephrogenesis is active. At 134 d, renal function was determined, fetuses were killed, and kidneys were further analyzed at the cellular and molecular levels. Additional fetuses subjected to 5/6Nx were killed at 80 and 90 d of gestation to investigate the kinetics of the renal compensatory process. At 134 d, in 1/2Nx, a significant increase in kidney weight and estimated glomerular number was observed. In 5/6Nx, the early and marked catch-up in kidney weight and estimated glomerular number was associated with a striking butterfly-like remodeling of the kidney that developed within the first 10 d following nephrectomy. In all groups, in utero glomerular filtration rates were similar. Compensatory renal growth was observed after parenchymal reduction in both models; however, the resulting compensatory growth was strikingly different. After 5/6Nx, the remnant kidney displayed a butterfly-like remodeling, and glomerular number was restored.

Abstract 29: Hydrogen Peroxide Impairs Myogenic Response of Afferent Arterioles from Mice with the Reduce Renal Mass Model of Chronic Kidney Disease

Background: Impaired autoregulation and systemic hypertension underlie progressive kidney injury in chronic kidney disease (CKD). We reported that the myogenic response (MR) was severely impaired in afferent arterioles (Affs) from mice with reduced renal mass (RRM) and oxidative stress, yet superoxide (O 2 .- ) enhanced MRs of normal mice. Therefore, we tested the hypothesis that an increase in perfusion pressure (PP) enhances the generation of H 2 O 2 selectively in Affs from mice with RRM and that H 2 O 2 causes the impaired MR. Methods and Results: Groups of sham and RRM C57BL/6 mice were fed a high salt (6% NaCl) diet for 3 months. Alternative groups were treated with 2 mM of the redox cycling nitroxide tempol in drinking water for 3 months, which reduced the excretion of both 8-isoprostane (marker of O 2 .- ) and H 2 O 2 . MRs were assessed from the % change in luminal diameter of isolated, perfused Affs after increasing PP from 40 to 80 mmHg, O 2 .- from PEG-SOD inhibitable ethidium:dihydroethidium fluorescence and H 2 O 2 from PEG-catalase (CAT) inhibitable H2DCFDA fluorescence. Results: 1. Compared to sham, increasing PP in Affs from RRM mice increased O 2 .- more (21 ± 2% vs 11 ± 2%, P<0.01), but this was prevented by tempol, and increased H 2 O 2 more (29 ± 8% vs 4 ± 1%, P<0.01), which also was prevented by tempol. 2. Compared to sham, Affs from mice with RRM mice had severely impaired MRs (sham, -14 ± 4% vs RRM, -1 ± 4%, P<0.05), yet this defect was corrected in mice drinking tempol (sham + tempol, -9 ± 6% vs RRM + tempol, -11 ± 2%, NS). 3. Bath addition of PEG-SOD (200 units/ml) attenuated MRs from sham mice (sham + vehicle, -14 ± 4%; sham + SOD, -6 ± 1%; P<0.05), but did not affect responses in RRM mice. 4. Bath addition of PEG-CAT (1000 units/ml) selectively enhanced the MRs in RRM mice (RRM + vehicle -1 ± 4%; RRM + CAT -19 ± 2%; P< 0.01) without effect in sham mice (sham + vehicle, -14 ± 4%; sham + PEG-CAT, -14 ± 2% NS). Conclusions: Excessive H 2 O 2 is released by increased PP of the afferent arterioles only from mice with RRM and accounted for the impaired myogenic response. Tempol, or other drugs that metabolize H 2 O 2 , may preserve renal autoregulation and prevent progressive loss of GFR in CKD.

Abstract 500: Reactive Oxygen Species and Insufficiency of Nitric Oxide Mediate Enhanced Microvascular Contractility and Impaired Endothelium Dependent Relaxation in Mice With Renal Failure

Background: Cardiovascular disease (CVD) is common and major cause of death and disability in chronic kidney disease (CKD). Since CVD starts with endothelial dysfunction, we tested the hypothesis that reactive oxygen species (ROS) and insufficient nitric oxide (NO) contributed to microvascular contractility and endothelial dysfunction in C57BL/6 mice with normotensive reduced renal mass (RRM) 5/6 nephrectomy, a model of progressive CKD. Methods and Results: Mesenteric arterioles (MAs) were isolated from mice 3 months after sham-operation (Sham) or RRM (n=6/group) and were mounted on Mulvany-Halperin wire myograph, preconstricted with norepinephrine and relaxed with acetylcholine (ACh) for: endothelium-dependent relaxation (EDR); endothelium-dependent relaxation factor (EDRF; NOS-dependent relaxation); endothelium-dependent hyperpolarizing factor (EDHF; K + -channel dependent relaxation) and endothelium-independent relaxation (EIR; sodium nitroprusside). Contractions were tested to endothelium-dependent contracting factor (EDCF; ACh-induced contraction with blocked relaxation pathways); phenylephrine (PE); U-46,619 (thromboxane-prostanoid receptor agonist) and endothelin-1 (ET-1). NO activity (DAF-FM fluorescence) and ROS generation (tempo-9-AC fluorescence) were measured by fluorescence microscopy. Data are mean ±SEM. The MAs from RRM mice had diminished EDR (54 ±5 vs. 77±3%; P<0.01) and EDRF (13±5 vs. 27±4%; P<0.01) with reduced NO activity (0.18 ± 0.05 vs. 0.36± 0.04 ΔUnits; P<0.05), but unchanged EDHF (30±4 vs. 38±4%; NS). These vessels from RRM mice developed an EDCF (14±1 vs. 8±1%; P<0.05) and ACh-induced increased in ROS (0.17±0.03 vs. 0.06±0.02 ΔUnits; P<0.05). Contractile responses were enhanced to U-46,619 (107±4 vs. 87±6, P<0.05) and ET-1 (108±7 vs. 89±4, P<0.05), but not to PE (87±6 vs. 77±8%, NS). Conclusion: mice with RRM developed defective microvascular EDR, EDRF with reduced NO activity and enhanced new ACh-induced EDCF, contractilities to thromboxane and endothelin with increased ROS generation. These microvascular disturbances may contribute to the later development of thrombosis, vascular remodeling and dysfunction in patients with CKD. *D. Wang and C.Wang: Equal contribution

Abstract 495: GSTM1 Deficiency Exacerbates Hypertension in the Remnant Model of Chronic Kidney Disease

There is a general consensus that oxidative stress is a factor in the progression of chronic kidney disease (CKD). Hence, genetic variants that affect the capacity to handle oxidative stress may influence the outcomes of CKD. One important class of enzymes that has evolved to combat the damaging effects of reactive oxygen species is the glutathione-S-transferases. In particular, the μ class isoform 1 (GSTM1) has emerged as a potential modifier of multiple chronic diseases in humans. Approximately 30%-50% of humans are completely deficient of the GSTM1 enzyme because of homozygous inheritance of the GSTM1 null allele, GSTM1(0). We have identified the GSTM1 gene as a modifier of disease progression in hypertensive nephrosclerosis (HN). In an ancillary study of the African American (AA) Study of Hypertension and Kidney Disease (AASK) Trial, we reported that participants carrying one ( 1/0 ) or two ( 0/0 ) null alleles had 1.7- and 2-fold higher risk of the composite outcome of a 50% decline in the glomerular filtration rate (GFR), dialysis, or death relative to those with two active alleles. Here, the objective of our study was to determine the consequence of deletion of Gstm1 on the course of chronic kidney disease induced by reduction of renal mass (RRM) model in mice. We generated Gstm1-/- (KO) mice on the 129S6 background through conventional gene targeting strategy. By radiotelemetry, Gstm1 KO mice displayed a modest but significantly higher baseline systolic blood pressure (SBP) compared to their wild type (WT, Gtsm1 +/+ ) littermates: KO (n = 5): 138.8 ± 1.3; WT (n = 5): 132.1 ± 1.1, p < 0.01. Baseline urinary isoprostane (ng/100 mg of body weight) was significantly higher in KO mice than WT mice (15.1 ± 2.9; WT: 8.0 ± 0.8, p < 0.04). Four weeks after sub-total nephrectomy, Gstm1 KO mice developed significantly more severe hypertension than WT mice. The average SBP over a 2 week recording by radiotelemetry was 154.0 ± 3.2 mm Hg in KO mice (n = 5), and 142.3 ± 4.2 in WT mice (n = 3), p < 0.01. The effects of deletion of Gstm1 on kidney function and histopathology are under investigation. In conclusion, loss of GSMT1 increases oxidative stress and exaggerates hypertension in the murine model of chronic kidney disease.

5/6th Nephrectomy in Combination with High Salt Diet and Nitric Oxide Synthase Inhibition to Induce Chronic Kidney Disease in the Lewis Rat

Chronic kidney disease (CKD) is a global problem. Slowing CKD progression is a major health priority. Since CKD is characterized by complex derangements of homeostasis, integrative animal models are necessary to study development and progression of CKD. To study development of CKD and novel therapeutic interventions in CKD, we use the 5/6th nephrectomy ablation model, a well known experimental model of progressive renal disease, resembling several aspects of human CKD. The gross reduction in renal mass causes progressive glomerular and tubulo-interstitial injury, loss of remnant nephrons and development of systemic and glomerular hypertension. It is also associated with progressive intrarenal capillary loss, inflammation and glomerulosclerosis. Risk factors for CKD invariably impact on endothelial function. To mimic this, we combine removal of 5/6th of renal mass with nitric oxide (NO) depletion and a high salt diet. After arrival and acclimatization, animals receive a NO synthase inhibitor (NG-nitro-L-Arginine) (L-NNA) supplemented to drinking water (20 mg/L) for a period of 4 weeks, followed by right sided uninephrectomy. One week later, a subtotal nephrectomy (SNX) is performed on the left side. After SNX, animals are allowed to recover for two days followed by LNNA in drinking water (20 mg/L) for a further period of 4 weeks. A high salt diet (6%), supplemented in ground chow (see time line Figure 1), is continued throughout the experiment. Progression of renal failure is followed over time by measuring plasma urea, systolic blood pressure and proteinuria. By six weeks after SNX, renal failure has developed. Renal function is measured using 'gold standard' inulin and para-amino hippuric acid (PAH) clearance technology. This model of CKD is characterized by a reduction in glomerular filtration rate (GFR) and effective renal plasma flow (ERPF), hypertension (systolic blood pressure>150 mmHg), proteinuria (> 50 mg/24 hr) and mild uremia (>10 mM). Histological features include tubulo-interstitial damage reflected by inflammation, tubular atrophy and fibrosis and focal glomerulosclerosis leading to massive reduction of healthy glomeruli within the remnant population (<10%). Follow-up until 12 weeks after SNX shows further progression of CKD.

Dipeptidyl peptidase IV inhibitor attenuates kidney injury in rat remnant kidney

BackgroundThe inhibition of dipeptidyl peptidase (DPP) IV shows protective effects on tissue injury of the heart, lung, and kidney. Forkhead box O (FoxO) transcriptional factors regulate cellular differentiation, growth, survival, the cell cycle, metabolism, and oxidative stress. The aims of this study were to investigate whether the DPP IV inhibitor sitagliptin could attenuate kidney injury and to evaluate the status of FoxO3a signaling in the rat remnant kidney model.MethodsRats were received two-step surgery of 5/6 renal mass reduction and fed on an oral dose of 200 mg/kg/day sitagliptin for 8 weeks. Before and after the administration of sitagliptin, physiologic parameters were measured. After 8 weeks of treatment, the kidneys were harvested.ResultsThe sitagliptin treatment attenuated renal dysfunction. A histological evaluation revealed that glomerulosclerosis and tubulointerstitial injury were significantly decreased by sitagliptin. Sitagliptin decreased DPP IV activity and increased the renal expression of glucagon-like peptide-1 receptor (GLP-1R). The subtotal nephrectomy led to the activation of phosphatidylinositol 3-kinase (PI3K)-Akt and FoxO3a phosphorylation, whereas sitagliptin treatment reversed these changes, resulting in PI3K-Akt pathway inactivation and FoxO3a dephosphorylation. The renal expression of catalase was increased and the phosphorylation of c-Jun N-terminal kinase (JNK) was decreased by sitagliptin. Sitagliptin treatment reduced apoptosis by decreasing cleaved caspase-3 and −9 and Bax levels and decreased macrophage infiltration.ConclusionsIn rat remnant kidneys, DPP IV inhibitor attenuated renal dysfunction and structural damage. A reduction of apoptosis, inflammation and an increase of antioxidant could be suggested as a renoprotective mechanism together with the activation of FoxO3a signaling. Therefore, DPP IV inhibitors might provide a promising approach for treating CKD, but their application in clinical practice remains to be investigated.

Acute podocyte injury enhances the susceptibility to blood pressure‐induced injury in rats with underlying ¾ renal mass reduction

The mechanism by which acute podocyte loss promotes chronic kidney disease (CKD) progression remains poorly understood. We administered a single dose (75 mg/kg i.p.) of puromycin aminonucleoside (PAN, n=14) or saline (sham, n=12) to male Sprague‐Dawley rats 2 weeks after ¾ renal mass reduction via surgical excision. BP was measured continuously every 10 minutes via radiotelemetry (DSI) and 24 hour urine protein excretion was determined weekly for 4 weeks following PAN administration. Two weeks after renal mass reduction and prior to administration of PAN the average systolic BP (125±3 vs. 129±3 mmHg) and 24‐hour proteinuria (8±1 vs. 18±7 mg/day) were similar in the PAN and sham groups, respectively. By contrast, four weeks after PAN administration the average systolic BP (147±4 vs. 135±5 mmHg; p&lt;0.05) and 24 hour proteinuria (255±16 vs 34+8 mg/day; p&lt;0.05) were significantly increased in the PAN vs. sham rats; respectively. Consistent with these findings, glomerulosclerosis (GS, 68±6% vs. 8+3% per 100 glomeruli; p&lt;0.05) and the slope of the relationship between the %GS and average systolic BP (y=1.1x‐87 vs. y=0.4x‐52 %GS/mmHg) was also greater in PAN vs. sham rats; respectively. These data indicate that podocyte loss in the presence of impaired preglomerular autoregulation results in enhanced glomerular susceptibility to hypertensive injury with even modest increases in BP.

Pathophysiology and treatment of focal segmental glomerulosclerosis: the role of animal models

Focal segmental glomerulosclerosis (FSGS) is a kidney disease with progressive glomerular scarring and a clinical presentation of nephrotic syndrome. FSGS is a common primary glomerular disorder that causes renal dysfunction which progresses slowly over time to end-stage renal disease. Most cases of FSGS are idiopathic Although kidney transplantation is a potentially curative treatment, 40% of patients have recurrence of FSGS after transplantation. In this review a brief summary of the pathogenesis causing FSGS in humans is given, and a variety of animal models used to study FSGS is discussed. These animal models include the reduction of renal mass by resecting 5/6 of the kidney, reduction of renal mass due to systemic diseases such as hypertension, hyperlipidemia or SLE, drug-induced FSGS using adriamycin, puromycin or streptozotocin, virus-induced FSGS, genetically-induced FSGS such as via Mpv-17 inactivation and α-actinin 4 and podocin knockouts, and a model for circulating permeability factors. In addition, an animal model that spontaneously develops FSGS is discussed. To date, there is no exact understanding of the pathogenesis of idiopathic FSGS, and there is no definite curative treatment. One requirement facilitating FSGS research is an animal model that resembles human FSGS. Most animal models induce secondary forms of FSGS in an acute manner. The ideal animal model for primary FSGS, however, should mimic the human primary form in that it develops spontaneously and has a slow chronic progression. Such models are currently not available. We conclude that there is a need for a better animal model to investigate the pathogenesis and potential treatment options of FSGS.

L‐arginine or tempol supplementation improves renal and cardiovascular function in rats with reduced renal mass and chronic high salt intake

Early life reduction in nephron number and chronic high salt intake cause development of renal and cardiovascular disease, which has been associated with oxidative stress and nitric oxide (NO) deficiency. We investigated the hypothesis that interventions stimulating NO signalling or reducing oxidative stress may restore renal autoregulation, attenuate hypertension and reduce renal and cardiovascular injuries following reduction in renal mass and chronic high salt intake. Male Sprague-Dawley rats were uninephrectomized (UNX) or sham-operated at 3 weeks of age and given either a normal-salt (NS) or high-salt (HS) diet. Effects on renal and cardiovascular functions were assessed in rats supplemented with substrate for NO synthase (L-Arg) or a superoxide dismutase mimetic (Tempol). Rats with UNX + HS developed hypertension and displayed increased renal NADPH oxidase activity, elevated levels of oxidative stress markers in plasma and urine, and reduced cGMP in plasma. Histological analysis showed signs of cardiac and renal inflammation and fibrosis. These changes were linked with abnormal renal autoregulation, measured as a stronger tubuloglomerular feedback (TGF) response. Simultaneous treatment with L-Arg or Tempol restored cGMP levels in plasma and increased markers of NO signalling in the kidney. This was associated with normalized TGF responses, attenuated hypertension and reduced signs of histopathological changes in the kidney and in the heart. Reduction in nephron number during early life followed by chronic HS intake is associated with oxidative stress, impaired renal autoregulation and development of hypertension. Treatment strategies that increase NO bioavailability, or reduce levels of reactive oxygen species, were proven beneficial in this model of renal and cardiovascular 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.

Exercise Attenuates Renal Dysfunction with Preservation of Myocardial Function in Chronic Kidney Disease

Previous studies have suggested that exercise improves renal and cardiac functions in patients with chronic kidney disease. The aim of this study was to evaluate the effects of long-term aerobic swimming exercise with overload on renal and cardiac function in rats with 5/6 nefrectomy (5/6Nx). Eight Wistar rats were placed into 4 groups: Control (C), Control+Exercise (E), Sedentary 5/6Nx (NxS) and 5/6Nx+Exercise (NxE). The rats were subjected to swimming exercise sessions with overload for 30 min five days per week for five weeks. Exercise reduced the effect of 5/6Nx on creatinine clearance compared to the NxS group. In addition, exercise minimized the increase in mean proteinuria compared to the NxS group (96.9±10.0 vs. 51.4±9.9 mg/24 h; p<0.05). Blood pressure was higher in the NxS and NxE groups compared to the C and E groups (216±4 and 178±3 vs. 123±2 and 124±2 mm Hg, p<0.05). In the 200 glomeruli that were evaluated, the NxS group had a higher sclerosis index than did the NxE group (16% vs. 2%, p<0.05). Echocardiography demonstrated a higher anterior wall of the left ventricle (LV) in diastole in the NxS group compared with the C, E and NxE groups. The NxS group also had a higher LV posterior wall in diastole and systole compared with the E group. The developed isometric tension in Lmax of the heart papillary muscle was lower in the NxS group compared with the C, E and NxE groups. These results suggested that exercise in 5/6Nx animals might reduce the progression of renal disease and lessen the cardiovascular impact of a reduction in renal mass.

Glomerulopathy in the KK.Cg-Ay/J Mouse Reflects the Pathology of Diabetic Nephropathy

The KK.Cg-A y/J (KK-A y) mouse strain is a previously described model of type 2 diabetes with renal impairment. In the present study, female KK-A y mice received an elevated fat content diet (24% of calories), and a cohort was uninephrectomized (Unx) to drive renal disease severity. Compared to KK-a/a controls, 26-week-old KK-A y mice had elevated HbA1c, insulin, leptin, triglycerides, and cholesterol, and Unx further elevated these markers of metabolic dysregulation. Unx KK-A y mice also exhibited elevated serum BUN and reduced glomerular filtration, indicating that reduction in renal mass leads to more severe impairment in renal function. Glomerular hypertrophy and hypercellularity, mesangial matrix expansion, podocyte effacement, and basement membrane thickening were present in both binephric and uninephrectomized cohorts. Glomerular size was increased in both groups, but podocyte density was reduced only in the Unx animals. Consistent with functional and histological evidence of increased injury, fibrotic (fibronectin 1, MMP9, and TGFβ1) and inflammatory (IL-6, CD68) genes were markedly upregulated in Unx KK-A y mice, while podocyte markers (nephrin and podocin) were significantly decreased. These data suggest podocyte injury developing into glomerulopathy in KK-A y mice. The addition of uninephrectomy enhances renal injury in this model, resulting in a disease which more closely resembles human diabetic nephropathy.

Loss of GSTM1, a NRF2 target, is associated with accelerated progression of hypertensive kidney disease in the African American Study of Kidney Disease (AASK).

Oxidative stress is acknowledged to play a role in kidney disease progression. Genetic variants that affect the capacity to handle oxidative stress may therefore influence the outcome of kidney disease. We examined whether genetic variants of the GSTM1 gene, a member of a superfamily of glutathione S-transferases, influence the course of kidney disease progression in participants of the African American Study of Kidney Disease (AASK) trial. Groups with and without the common GSTM1 null allele, GSTM1(0), differed significantly in the time to a glomerular filtration rate (GFR) event or dialysis (P = 0.04) and in the time to GFR event, dialysis, or death (P = 0.02). The hazard ratios (HR) for the time to a GFR event or dialysis in those with two or one null allele relative to those possessing none were 1.88 [95% confidence interval (CI), 1.07 to 3.30, P = 0.03] and 1.68 (95% CI, 1.00 to 2.84, P < 0.05), respectively. For the time to GFR event, dialysis, or death, the HR for two null alleles was 2.06 (95% CI, 1.20 to 3.55, P = 0.01) and for one null allele 1.70 (95% CI, 1.02 to 2.81, P = 0.04). We demonstrated that GSTM1 directly regulates intracellular levels of 4-hydroxynonenal (4-HNE) in vascular smooth muscle cells. Furthermore, we showed that renal 4-HNE levels and GSTM1 are both increased after reduction of renal mass (RRM) in the mouse. We conclude that GSTM1 is normally upregulated in chronic kidney disease (CKD) in a protective response to increased oxidative stress. A genetic variant that results in loss of GSTM1 activity may be deleterious in CKD.

Normal HDL–apo AI turnover and cholesterol enrichment of HDL subclasses in New Zealand rabbits with partial nephrectomy

ObjectiveThe kidney has been proposed to play a central role in apo AI catabolism, suggesting that HDL structure is determined, at least in part, by this organ. Here, we aimed at determining the effects of a renal mass reduction on HDL size distribution, lipid content, and apo AI turnover. MethodsWe characterized HDL subclasses in rabbits with a 75% reduction of functional renal mass (Nptx group), using enzymatic staining of samples separated on polyacrylamide electrophoresis gels, and also performed kinetic studies using radiolabeled HDL–apo AI in this animal model. ResultsCreatinine clearance was reduced to 35% after nephrectomy as compared to the basal values, but without increased proteinuria. A slight, but significant modification of the relative HDL size distribution was observed after nephrectomy, whereas cholesterol plasma concentrations gradually augmented from large HDL2b (+54%) to small HDL3b particles (+150%, P<0.05). Cholesteryl esters were the increased fraction; in contrast, free cholesterol phospholipids and triglycerides of HDL subclasses were not affected by nephrectomy. HDL–apo AI fractional catabolic rates were similar to controls. ConclusionReduction of functional renal mass is associated to enrichment of HDL subclasses with cholesteryl esters. Structural abnormalities were not related to a low apo AI turnover, suggesting renal contribution to HDL remodeling beyond being just a catabolic site for these lipoproteins.

Abstract 493: Impact of Renal Vasoconstriction on the Relationship Between Blood Pressure and Renal Injury in Angiotensin II-induced Hypertensive Rats

Ang II is thought to play a prominent role in the development of hypertension-induced renal disease via BP dependent and independent pathways; however the quantitative relationships between BP and renal injury have not been rigorously examined in Ang II-induced hypertension. The major goals of the present study were to assess: 1) the relationship between BP and renal injury in rats with hypertension induced by Ang II vs. renal mass reduction (RMR) and 2) the pressure-flow relationships in conscious Ang II-infused rats. One group of male Sprague-Dawley rats (Charles River) were implanted with a BP radiotransmitter and 10 days later administered Ang II (n=12; 500 ng/kg/min via osmotic minipump) or subjected to 3/4 RMR via right uninephrectomy + infarction of ∼ 1/2 of the left kidney (RKI, n=5). BP was measured continuously and kidneys were perfused fixed at 6 weeks for the assessment of renal injury. In a separate experiment, MAP and RBF (Transonic) were measured in conscious chronically instrumented rats. After recovery from surgery (∼7 days), baseline MAP and RBF were assessed (∼4 hours @ 200 Hz) on 2 consecutive days. Subsequently, rats were administered Ang II (n=6; 500 ng/kg/min) or saline (n=7; sham) via osmotic minipump and MAP and RBF were again assessed every 2-3 days for 10 days. Despite a higher average systolic BP over 6 weeks in Ang II (174±3 mmHg) vs. RKI (165±6 mmHg) rats, glomerulosclerosis (GS) was higher (p&lt;0.05) in RKI (15±7% out of 100 glomeruli) vs. Ang II (6±1% out of 100 glomeruli) rats. Moreover, the slope of the relationship between BP and %GS (Δ%GS/ΔmmHg) was greater in RKI vs. Ang II rats. Both MAP (98±2 vs. 99±3 mmHg) and RBF (8.1±1vs. 8.2±1 ml/min) were similar at baseline in Ang II and sham rats, respectively. MAP was elevated by day 3 (123±6 mmHg) and further increased to 157±5 mmHg by day 10 in Ang II rats. Conversely, RBF was decreased at day 3 (6.6±0.6 ml/min) and the vasoconstriction persisted over the experimental protocol as RBF further decreased to 5.6±0.7 ml/min at day 10 in Ang II rats. In conclusion, Ang II-induced hypertension is associated with a diminished susceptibility to renal injury as compared to rats with RMR likely due, in part, to the AngII-induced vasoconstriction, which reduces BP transmission to the renal microvasculature.

Acute kidney injury and chronic kidney disease: an integrated clinical syndrome

The previous conventional wisdom that survivors of acute kidney injury (AKI) tend to do well and fully recover renal function appears to be flawed. AKI can cause end-stage renal disease (ESRD) directly, and increase the risk of developing incident chronic kidney disease (CKD) and worsening of underlying CKD. In addition, severity, duration, and frequency of AKI appear to be important predictors of poor patient outcomes. CKD is an important risk factor for the development and ascertainment of AKI. Experimental data support the clinical observations and the bidirectional nature of the relationships between AKI and CKD. Reductions in renal mass and nephron number, vascular insufficiency, cell cycle disruption, and maladaptive repair mechanisms appear to be important modulators of progression in patients with and without coexistent CKD. Distinction between AKI and CKD may be artificial. Consideration should be given to the integrated clinical syndrome of diminished GFR, with acute and chronic stages, where spectrum of disease state and outcome is determined by host factors, including the balance of adaptive and maladaptive repair mechanisms over time. Physicians must provide long-term follow-up to patients with first episodes of AKI, even if they presented with normal renal function.

Vascular insulin resistance related to endoplasmic reticulum stress in aortas from a rat model of chronic kidney disease

Metabolic insulin resistance has been demonstrated in patients with nondiabetic chronic kidney disease (CKD), yet their vascular insulin signaling remains poorly understood. Here we tested the hypothesis that vascular insulin signaling was impaired and related with endoplasmic reticulum (ER) stress in aortas from the reduced renal mass (RRM) model of CKD. The activity of insulin signaling and markers of ER were determined in aortas from rats with RRM and cultured human umbilical vein endothelial cells. Tyrosine phosphorylation of insulin receptor-β and insulin receptor substrate (IRS)-1 and phosphorylation of protein kinase B and endothelial nitric oxide synthase were all decreased in aorta from RRM rats, whereas serine phosphorylation of IRS-1, a marker of insulin resistance, was increased. In addition, nitric oxide generation and insulin-mediated vasorelaxation were decreased in aortas from RRM rats. Insulin signaling in cultured vascular endothelial cells was impaired by induction of ER stress and was restored in aortas of RRM rats by inhibition of ER stress. Taken together, rats with RRM had vascular insulin resistance that was linked to ER stress. This identified vascular insulin resistance and ER stress as a potential therapeutic target for cardiovascular complications in patients with CKD.