Klotho is a recently discovered antiaging gene. The objective of this study was to test the hypothesis that klotho gene delivery attenuates the progression of spontaneous hypertension and renal damage in spontaneous hypertensive rats (SHRs). An adeno-associated virus (AAV) carrying mouse klotho full-length cDNA (AAV.mKL) was constructed for in vivo expression of klotho. Four groups of male SHRs and 1 group of sex- and age-matched Wistar-Kyoto rats (5 rats per group) were used. Blood pressure was measured twice in all of the animals before gene delivery. Four groups of SHRs received an IV injection of AAV.mKL, AAV.LacZ, AAV.GFP, and PBS, respectively. The Wistar-Kyoto group received PBS and served as a control. AAV.mKL stopped the further increase in blood pressure in SHRs, whereas blood pressures continued to increase in other SHR groups. One single dose of AAV.mKL prevented the progression of spontaneous hypertension for at least 12 weeks (length of the study). Klotho expression and production were suppressed in SHRs, which were reverted by AAV.mKL. AAV.mKL increased plasma interleukin 10 levels but decreased Nox2 expression, NADPH oxidase activity, and superoxide production in kidneys and aortas in SHRs. AAV.mKL abolished renal tubular atrophy and dilation, tubular deposition of proteinaceous material, glomerular collapse, and collagen deposition seen in SHRs, indicating that klotho gene delivery attenuated renal damage. Therefore, the suppressed klotho expression may play a role in the progression of spontaneous hypertension and renal damage in SHRs. AAV delivery of klotho may offer a new approach for the long-term control of hypertension and for renoprotection.
klotho; Nox2; blood pressure; adeno-associated virus; renoprotection
Background and Hypothesis
Klotho is a recently discovered anti-aging gene. The purpose of this study was to investigate if klotho gene transfer attenuates superoxide production and oxidative stress in rat aorta smooth muscle (RASM) cells.
Methods and Results
RASM cells were transfected with AAV plasmids carrying mouse klotho full-length cDNA (mKL) or LacZ as a control. Klotho gene transfer increased klotho expression in RASM cells. Notably, klotho gene expression decreased Nox2 NADPH oxidase protein expression but did not affect Nox2 mRNA expression, suggesting that the inhibition may occur at the post-transcriptional level. Klotho gene transfer decreased intracellular superoxide production and oxidative stress in RASM cells. Klotho gene expression also significantly attenuated the angiotensin II (AngII)-induced superoxide production, oxidative damage, and apoptosis. Interestingly, klotho gene delivery dose-dependently increased the intracellular cAMP level and PKA activity in RASM cells. Rp-cAMP, a competitive inhibitor of cAMP, abolished the klotho-induced increase in PKA activity, indicating that klotho activated PKA via cAMP. Notably, inhibition of cAMP-dependent PKA activity by RP-cAMP abolished klotho-induced inhibition of Nox2 protein expression, suggesting an important role of the cAMP-dependent PKA in this process.
The present finding revealed a previously unidentified role of klotho in regulating Nox2 protein expression in RASM cells. Klotho not only downregulated Nox2 protein expression and intracellular superoxide production but also attenuated AngII-induced superoxide production, oxidative damage, and apoptosis. The klotho-induced suppression of Nox2 protein expression may be mediated by the cAMP PKA pathway.
klotho; Nox2; NADPH oxidase; superoxide; cAMP; PKA; smooth muscle cell
Klotho is an antiaging substance with pleiotropic actions including regulation of mineral metabolism. It is highly expressed in the kidney and is present in the circulation and urine but its role in acute kidney injury (AKI) is unknown. We found that ischemia–reperfusion injury (IRI) in rodents reduced Klotho in the kidneys, urine, and blood, all of which were restored upon recovery. Reduction in kidney and plasma Klotho levels were earlier than that of neutrophil gelatinase-associated lipocalin (NGAL), a known biomarker of kidney injury. Patients with AKI were found to have drastic reductions in urinary Klotho. To examine whether Klotho has a pathogenic role, we induced IRI in mice with different endogenous Klotho levels ranging from heterozygous Klotho haploinsufficient, to wild-type (WT), to transgenic mice overexpressing Klotho. Klotho levels in AKI were lower in haploinsufficient and higher in transgenic compared with WT mice. The haploinsufficient mice had more extensive functional and histological alterations compared with WT mice, whereas these changes were milder in overexpressing transgenic mice, implying that Klotho is renoprotective. Rats with AKI given recombinant Klotho had higher Klotho protein, less kidney damage, and lower NGAL than rats with AKI given vehicle. Hence, AKI is a state of acute reversible Klotho deficiency, low Klotho exacerbates kidney injury and its restoration attenuates renal damage and promotes recovery from AKI. Thus, endogenous Klotho not only serves as an early biomarker for AKI but also functions as a renoprotective factor with therapeutic potential.
acute kidney injury; biomarker; ischemia–reperfusion injury; Klotho; neutrophil gelatinase-associated lipocalin; therapy
Fibroblast growth factor 23 (FGF23) is a phosphaturic hormone mainly produced by bone that acts in the kidney through FGF receptors and Klotho. Here we investigated whether the kidney was an additional source of FGF23 during renal disease using a model of type 2 diabetic nephropathy. Renal expression of FGF23 and Klotho was assessed in Zucker diabetic fatty (ZDF) and control lean rats at 2, 4, 6, 8 months of age. To evaluate whether the renoprotective effect of angiotensin converting enzyme (ACE) inhibitor in this model was associated with changes in FGF23 and Klotho, ZDF rats received ramipril from 4, when proteinuric, to 8 months of age. FGF23 mRNA was not detectable in the kidney of lean rats, nor of ZDF rats at 2 months of age. FGF23 became measurable in the kidney of diabetic rats at 4 months and significantly increased thereafter. FGF23 protein localized in proximal and distal tubules. Renal Klotho mRNA and protein decreased during time in ZDF rats. As renal disease progressed, serum phosphate levels increased in parallel with decline of fractional phosphorus excretion. Ramipril limited proteinuria and renal injury, attenuated renal FGF23 upregulation and ameliorated Klotho expression. Ramipril normalized serum phosphate levels and tended to increase fractional phosphorus excretion. These data indicate that during progressive renal disease the kidney is a site of FGF23 production which is limited by ACE inhibition. Interfering pharmacologically with the delicate balance of FGF23 and phosphorus in diabetes may have implications in clinics.
We have previously shown that myelin abnormalities and loss characterize the normal aging process of the brain and that an age-associated reduction in Klotho is conserved across species. Predominantly generated in brain and kidney, Klotho overexpression extends life span, whereas loss of Klotho accelerates the development of aging-like phenotypes. While the function of Klotho in brain is unknown, loss of Klotho expression leads to cognitive deficits. In the present study, we found significant effects of Klotho on oligodendrocyte functions including induced maturation of rat primary oligodendrocytic progenitor cells (OPCs) in vitro and myelination. Phosphoprotein Western analysis indicated Klotho's downstream effects involve Akt and ERK signal pathways. Klotho increased OPCs maturation, and inhibition of Akt or ERK function blocked this effect on OPCs. In vivo studies of Klotho knockout mice and their control littermates revealed that knockout mice have a significant reduction in major myelin protein and gene expression. By immunohistochemistry, the number of total and mature oligodendrocytes was significantly lower in Klotho knockout mice. Strikingly, at the ultrastructural level, Klotho knockout mice exhibited significantly impaired myelination of the optic nerve and corpus callosum. These mice also displayed severe abnormalities at the nodes of Ranvier. In order to decipher the mechanisms by which Klotho affects oligodendrocytes, we used luciferase pathway reporters to identify the transcription factors involved. Taken together, these studies provide novel evidence for Klotho as a key player in myelin biology, which may thus be a useful therapeutic target in efforts to protect brain myelin against age-dependent changes.
Despite a significant improvement in the management of chronic kidney disease (CKD), its incidence and prevalence has been increasing over the years. Progressive renal fibrosis is present in CKD and involves the participation of several cytokines, including Transforming growth factor-β1 (TGF-β1). Besides cardiovascular diseases and infections, several studies show that Vitamin D status has been considered as a non-traditional risk factor for the progression of CKD. Given the importance of vitamin D in the maintenance of essential physiological functions, we studied the events involved in the chronic kidney disease progression in rats submitted to ischemia/reperfusion injury under vitamin D deficiency (VDD).
Rats were randomized into four groups: Control; VDD; ischemia/reperfusion injury (IRI); and VDD+IRI. At the 62 day after sham or IRI surgery, we measured inulin clearance, biochemical variables and hemodynamic parameters. In kidney tissue, we performed immunoblotting to quantify expression of Klotho, TGF-β, and vitamin D receptor (VDR); gene expression to evaluate renin, angiotensinogen, and angiotensin-converting enzyme; and immunohistochemical staining for ED1 (macrophages), type IV collagen, fibronectin, vimentin, and α-smooth mucle actin. Histomorphometric studies were performed to evaluate fractional interstitial area.
IRI animals presented renal hypertrophy, increased levels of mean blood pressure and plasma PTH. Furthermore, expansion of the interstitial area, increased infiltration of ED1 cells, increased expression of collagen IV, fibronectin, vimentin and α-actin, and reduced expression of Klotho protein were observed. VDD deficiency contributed to increased levels of plasma PTH as well as for important chronic tubulointerstitial changes (fibrosis, inflammatory infiltration, tubular dilation and atrophy), increased expression of TGF-β1 and decreased expression of VDR and Klotho protein observed in VDD+IRI animals.
Through inflammatory pathways and involvement of TGF-β1 growth factor, VDD could be considered as an aggravating factor for tubulointerstitial damage and fibrosis progression following acute kidney injury induced by ischemia/reperfusion.
Diabetes is associated with a high incidence of macrovascular disease (MVD), including peripheral and coronary artery disease. Circulating soluble-Klotho (sKlotho) is produced in the kidney and is a putative anti-aging and vasculoprotective hormone. Reduced Klotho levels may therefore increase cardiovascular risk in diabetes. We investigated if sKlotho levels are decreased in type 2 diabetes and associate with MVD in the absence of diabetic nephropathy, and whether hyperglycemia affects renal Klotho production in vitro and in vivo.
sKlotho levels were determined with ELISA in diabetic and non-diabetic patients with and without MVD, and healthy control subjects. Human renal tubular epithelial cells (TECs) were isolated and exposed to high glucose levels (15 and 30 mM) in vitro and Klotho levels were measured with qPCR and quantitative immunofluorescence. Klotho mRNA expression was quantified in kidneys obtained from long term (3 and 8 months) diabetic Ins2Akita mice and normoglycemic control mice.
No significant differences in sKlotho levels were observed between diabetic patients with and without MVD (527 (433–704) pg/mL, n = 35), non-diabetic MVD patients (517 (349–571) pg/mL, n = 27), and healthy control subjects (435 (346–663) pg/mL, n = 15). High glucose (15 and 30 mM) did not alter Klotho expression in TECs. Long-term hyperglycemia in diabetic Ins2Akita mice (characterized by increased HbA1c levels [12.9 ± 0.3% (3 months) and 11.3 ± 2.0% (8 months)], p < 0.05 vs. non-diabetic mice) did not affect renal Klotho mRNA expression.
These data indicate that sKlotho levels are not affected in type 2 diabetes patients with and without MVD. Furthermore, hyperglycemia per se does not affect renal Klotho production. As type 2 diabetes does not alter sKlotho levels, sKlotho does not seem to play a major role in the pathogenesis of MVD in type 2 diabetes.
Atherosclerosis; Coronary artery disease; Klotho; Macrovascular disease; Peripheral artery disease; Type 2 diabetes
It has been recognized that a defect in klotho gene expression accelerates the degeneration of multiple age-sensitive traits. Accumulating evidence indicates that aging is associated with declines in cognitive function and the activity of growth hormone (GH)/insulin-like growth factor-1 (IGF-1).
In this study, we examined whether a GH-releaser diet could be effective in protecting against cognitive impairment in klotho mutant mice.
The GH-releaser diet significantly induced the expression of IGF-1 and IGF-1 receptors in the hippocampus of klotho mutant mice. Klotho mutant mice showed significant memory impairments as compared with wild-type mice. In addition, the klotho mutation significantly decreased the expression of cell survival/antiapoptotic factors, including phospho-Akt (p-Akt)/phospho-glycogen synthase kinase3β (p-GSK3β), phospho-extracellular signal-related kinase (p-ERK), and Bcl-2, but significantly increased those of cell death/proapoptotic factors, such as phospho-c-jun N-terminal kinase (p-JNK), Bax, and cleaved caspase-3 in the hippocampus. Treatment with GH-releaser diet significantly attenuated both decreases in the expression of cell survival/antiapoptotic factors and increases in the expression of cell death/proapoptotic factors in the hippocampus of klotho mutant mice. In addition, klotho mutation-induced oxidative stress was significantly attenuated by the GH-releaser diet. Consequently, a GH-releaser diet significantly improved memory function in the klotho mutant mice. GH-releaser diet-mediated actions were significantly reversed by JB-1, an IGF-1 receptor antagonist.
The results suggest that a GH-releaser diet attenuates oxidative stress, proapoptotic changes and consequent dysfunction in klotho mutant mice by promoting IGF-1 expression and IGF-1 receptor activation.
klotho gene; Cognitive dysfunction; GH-releaser diet; Receptor, IGF type 1
The aim of this study was to investigate whether the effects of aging on oxidative stress markers and expression of major oxidant and antioxidant enzymes associate with impairment of renal function and increases in blood pressure. To explore this, we determined age-associated changes in lipid peroxidation (urinary malondialdehyde), plasma and urinary hydrogen peroxide (H2O2) levels, as well as renal H2O2 production, and the expression of oxidant and antioxidant enzymes in young (13 weeks) and old (52 weeks) male Wistar Kyoto (WKY) rats. Urinary lipid peroxidation levels and H2O2 production by the renal cortex and medulla of old rats were higher than their young counterparts. This was accompanied by overexpression of NADPH oxidase components Nox4 and p22phox in the renal cortex of old rats. Similarly, expression of superoxide dismutase (SOD) isoforms 2 and 3 and catalase were increased in the renal cortex from old rats. Renal function parameters (creatinine clearance and fractional excretion of sodium), diastolic blood pressure and heart rate were not affected by aging, although slight increases in systolic blood pressure were observed during this 52-week period. It is concluded that overexpression of renal Nox4 and p22phox and the increases in renal H2O2 levels in aged WKY does not associate with renal functional impairment or marked increases in blood pressure. It is hypothesized that lack of oxidative stress-associated effects in aged WKY rats may result from increases in antioxidant defenses that counteract the damaging effects of H2O2.
aging; oxidative stress; kidney; hydrogen peroxide; NADPH oxidase; antioxidant enzymes; Wistar Kyoto rat
Aging is characterized by a gradual functional decrease of all systems including the kidneys. Growing evidence links altered lipid protein redox-homeostasis with renal dysfunction. The effect of sexual dimorphism on the lipid protein redox-homeostasis mechanisms in the aging kidney is obscure. In the current study, we aimed to investigate redox homeostasis as it related to sexual dimorphism on protein oxidation and lipid peroxidation parameters, as protein carbonyl (PCO), total thiol (T-SH), advanced oxidation protein products (AOPP), malondialdehyde, glutathione (GSH), and superoxide dismutase (SOD) activity, as potential aging biomarkers, which may contribute to an analysis of the free radical theory of aging.
Materials and methods
The study was carried out with 16 naturally aged rats (24 months old; eight males and eight females) and their corresponding young rat groups as controls (6 months old; eight males and eight females). All of the aforementioned parameters (PCO, T-SH, AOPP, MDA, GSH, SOD) were measured manually instead of automated devices or ELISA kits.
PCO, AOPP, and malondialdehyde levels in aged rats were significantly higher in the older rat group than in the younger rat group, whereas SOD activities were significantly lower in old rats. T-SH levels were not significantly different in male groups; however, T-SH levels were lower in the aged female group than in the young female control group. In addition, GSH levels were significantly different between the aged rat group and the corresponding young control group for both genders.
With respect to PCO and AOPP, impaired redox homeostasis is substantially more prominent in males than females. The decrease of G-SH levels in male groups could be attributed to stabilizing the redox status of protein thiol groups by the depletion of the GSH groups. Considering the results, the renal tissue proteins and lipids in different genders may have different susceptibilities to oxidative damage.
lipid peroxidation; protein oxidation; radicals; renal aging
NADPH oxidases are the major sources of reactive oxygen species in cardiovascular, neural, and kidney cells. The NADPH oxidase 5 (NOX5) gene is present in humans but not rodents. Because Nox isoforms in renal proximal tubules (RPTs) are involved in the pathogenesis of hypertension, we tested the hypothesis that NOX5 is differentially expressed in RPT cells from normotensive (NT) and hypertensive subjects (HT). We found that NOX5 mRNA, total NOX5 protein, and apical membrane NOX5 protein were 4.2±0.7-fold, 5.2±0.7-fold, and 2.8±0.5-fold greater in HT than NT. Basal total NADPH oxidase activity was 4.5±0.2-fold and basal NOX5 activity in NOX5 immunoprecipitates was 6.2±0.2-fold greater in HT than NT (P=<0.001, n=6–14/group). Ionomycin increased total NOX and NOX5 activities in RPT cells from HT (P<0.01, n=4, ANOVA), effects that were abrogated by pre-treatment of the RPT cells with diphenylene-iodonium or superoxide dismutase. Silencing NOX5 using NOX5-siRNA decreased NADPH oxidase activity (−45.1±3.2% vs. mock-siRNA, n=6–8) in HT. D1-like receptor stimulation decreased NADPH oxidase activity to a greater extent in NT (−32.5±1.8%) than HT (−14.8±1.8). In contrast to the marked increase in expression and activity of NOX5 in HT, NOX1 mRNA and protein were minimally increased in HT, relative to NT; total NOX2 and NOX4 proteins were not different between HT and NT, while the increase in apical RPT cell membrane NOX1, NOX2, and NOX4 proteins in HT, relative to NT, was much less than those observed with NOX5. Thus, we demonstrate, for the first time, that NOX5 is expressed in human RPT cells and to greater extent than the other Nox isoforms in HT than NT. We suggest that the increased expression of NOX5, which may be responsible for the increased oxidative stress in RPT cells in human essential hypertension, is caused, in part, by a defective renal dopaminergic system.
The schematic diagram shows that total cellular and apical membrane NOX5 proteins are greater than the other NOX proteins (NOX1, NOX2, and NOX4) in human renal proximal tubule (RPT) cells from hypertensive subjects. The increase in NOX5 expression is associated with increased reactive oxygen species production in these RPT cells. We suggest that the increased expression of NOX5, which is, in part, due to increased transcription, may be responsible for the increased oxidative stress in RPT cells in human essential hypertension.
•Basal levels of NOX5 mRNA and NOX5 protein in RPT cells were greater in HT than NT.•Basal level of NOX5 protein in apical membrane of RPT cells was greater in HT than NT.•NOX5-dependent oxidase activity, intra and extracellular ROS, and total membrane NADPH oxidase activity in RPT cells were greater in HT than NT.•D1-like receptor inhibition of NADPH oxidase activity is impaired in RPT cells from HT.
NOX5; ROS; Oxidative stress; Dopamine receptor
The klotho gene is expressed in a limited number of tissues, most notably in distal convoluted tubules in the kidney and choroid plexus in the brain. A previous study suggested that Klotho increases resistance to oxidative stress. However, changes of Klotho expression in high glucose-induced oxidative stress remain unclear. In the present study, we used streptozotocin-induced diabetic rats (STZ rats) to examine the effects of insulin, phloridzin or antioxidant, tiron on diabetic nephropathy. Both insulin and phloridzin reversed the lower Klotho expression levels in kidneys of STZ rats by the correction of hyperglycemia. Also, renal functions were improved by these treatments. In addition to the improvement of renal functions, the decrease of Klotho expression in kidney of STZ rats was also reversed by tiron without changing blood glucose levels. The reduction of oxidative stress induced by high glucose can be considered for this action of tiron. This view was further confirmed in vitro using high glucose-exposed Madin-Darby canine kidney (MDCK) epithelial cells. Thus, we suggest that decrease of oxidative stress is not only responsible for the improvement of renal function but also for the recovery of Klotho expression in kidney of STZ rats.
The aging kidney exhibits slowly developing injury and females are usually protected compared to males, in association with maintained renal nitric oxide (NO). Here, we compared renal injury in Fischer 344 (F344) rats in intact, ovariectomized, and ovariectomized + estrogen replaced young (6 month) and old (24 month) female rats with young and old intact male rats and measured renal protein abundance of NO synthase isoforms and oxidative stress. There was no difference in age-dependent glomerular damage between young or old intact male and female F344, and neither ovariectomy nor estrogen replacement affected renal injury; however, tubulointerstitial injury was greater in old males than old females. These data suggest that ovarian hormones do not influence these aspects of kidney aging in F344 rats and that the greater tubulointerstitial injury is caused by male sex. Old males had greater kidney cortex NOS3 abundance than females, and NOS1 abundance (alpha and beta isoforms) was increased in old males compared to both young males and old females. NOS abundance was preserved with age in intact females, ovariectomy did not reduce NOS1 or 3 protein abundance, and estrogen replacement did not uniformly elevate NOS proteins, suggesting that estrogens are not primary regulators of renal NOS abundance in this strain. NADPH oxidase-dependent superoxide production and nitrotyrosine immunoreactivity were increased in the aging male rat kidney compared to the female which could compromise renal NO production and/or bioavailability. In conclusion, the kidney damage expressed in the aging F344 is fairly mild and is not related to loss of renal cortex NOS3 or NOS1 alpha. This is in contrast to the aging male Sprague Dawley rat  where kidney damage is exacerbated and NOS3 and NOS1 alpha are lost compared to the old female.
Nitric oxide; oxidative stress; tubulointerstitial injury; estrogen; ovariectomy
Dietary administration of 0.30% indole-3-carbinol (I3C) to Cyp1a1-Ren2 transgenic rats (TGRs) generates angiotensin II (ANG II)–dependent malignant hypertension (HTN) and increased renal vascular resistance. However, TGRs with HTN maintain a normal or slightly reduced glomerular filtration rate. We tested the hypothesis that maintenance of renal function in hypertensive Cyp1a1-Ren2 TGRs is due to preservation of the intrarenal nitric oxide (NO) and antioxidant systems.
Kidney cortex, kidney medulla, aortic endothelial (e) and neuronal (n) nitric oxide synthase (NOS), superoxide dismutases (SODs), and p22phox (nicotinamide adenine dinucleotide phosphate-oxidase subunit) protein abundances were measured along with kidney cortex total antioxidant capacity (TAC) and NOx. TGRs were fed a normal diet that contained 0.3% I3C or 0.3% I3C + candesartan (AT1 receptor antagonist; 25mg/L in drinking water) (n = 5–6 per group) for 10 days.
Blood pressure increased and body weight decreased in I3C-induced TGRs, while candesartan blunted these responses. Abundances of NOS, SOD, and p22phox as well as TAC were maintained in the kidney cortex of I3C-induced TGRs with and without candesartan, while kidney cortex NOx production increased in both groups. Kidney medulla eNOS and extracellular (EC) SOD decreased and nNOS were unchanged in both groups of I3C-induced TGRs. In addition, a compensatory increase occurred in kidney medulla Mn SOD in I3C-induced TGRs + candesartan. Aortic eNOS and nNOS∝ fell and p22phox and Mn SOD increased in hypertensive I3C-induced TGRs; all changes were reversed with candesartan.
The preservation of renal cortical NO and antioxidant capacity is associated with preserved renal function in Cyp1a1-Ren2 TGRs with ANG II-dependent malignant HTN.
angiotensin receptor blocker; aorta; blood pressure; candesartan; hypertension; kidney; superoxide dismutase; total antioxidant capacity.
Klotho is a single-pass transmembrane protein highly expressed in the kidney. Membrane Klotho protein acts as co-receptor for fibroblast growth factor-23. Its extracellular domain is shed from cell surface and functions as an endocrine substance that exerts multiple renal and extra-renal functions. An exhaustive review is beyond the scope and length of this manuscript; thus only effects with pertinence to mineral metabolism and renoprotection will be highlighted here. Klotho participates in mineral homeostasis via interplay with other “calciophosphoregulatory” hormones (PTH, FGF23, and 1,25-(OH)2 vitamin D3) in kidney, bone, intestine, and parathyroid gland. Klotho may also be involved in acute and chronic kidney diseases development and progression. Acute kidney injury is a temporary and reversible state of Klotho deficiency and chronic kidney disease is a sustained state of systemic Klotho deficiency. Klotho deficiency renders the kidney more susceptible to acute insults, delays kidney regeneration, and promotes renal fibrosis. In addition to direct renal effects, Klotho deficiency also triggers and aggravates deranged mineral metabolism, secondary hyperparathyroidism, vascular calcification, and cardiac hypertrophy and fibrosis. Although studies examining the therapeutic effect of Klotho replacement were performed in animal models, it is quite conceivable that supplementation of exogenous Klotho and/or up-regulation of endogenous Klotho production may be a viable therapeutic strategy for patients with acute or chronic kidney diseases.
Acute kidney injury; Cardiac hypertrophy; Chronic kidney disease; Hyperparathyroidism; Klotho
Klotho is a single-pass transmembrane protein that exerts its biological functions through multiple modes. Membrane-bound Klotho acts as coreceptor for the major phosphatonin fibroblast growth factor-23 (FGF23), while soluble Klotho functions as an endocrine substance. In addition to in the distal nephron where it is abundantly expressed, Klotho is present in the proximal tubule lumen where it inhibits renal Pi excretion by modulating Na-coupled Pi transporters via enzymatic glycan modification of the transporter proteins – an effect completely independent of its role as the FGF23 coreceptor. Acute kidney injury (AKI) and chronic kidney disease (CKD) are states of systemic Klotho deficiency, making Klotho a very sensitive biomarker of impaired renal function. In addition to its role as a marker, Klotho also plays pathogenic roles in renal disease. Klotho deficiency exacerbates decreases in, while Klotho repletion or excess preserves, glomerular filtration rate in both AKI and CKD. Soft tissue calcification, and especially vascular calcification, is a dire complication in CKD, associated with high mortality. Klotho protects against soft tissue calcification via at least 3 mechanisms: phosphaturia, preservation of renal function and a direct effect on vascular smooth muscle cells by inhibiting phosphate uptake and dedifferentiation. In summary, Klotho is a critical molecule in a wide variety of renal diseases and bears great potential as a diagnostic and prognostic biomarker as well as for therapeutic replacement therapy.
Acute kidney injury; Chronic kidney disease; Klotho; Phosphaturia; Vascular calcification
Klotho acts as a co-receptor for and dictates tissue specificity of circulating FGF23. FGF23 inhibits PTH secretion, and reduced Klotho abundance is considered a pathogenic factor in renal secondary hyperparathyroidism. To dissect the role of parathyroid gland resident Klotho in health and disease, we generated mice with a parathyroid-specific Klotho deletion (PTH-KL−/−). PTH-KL−/− mice had a normal gross phenotype and survival; normal serum PTH and calcium; unaltered expression of the PTH gene in parathyroid tissue; and preserved PTH response and sensitivity to acute changes in serum calcium. Their PTH response to intravenous FGF23 delivery or renal failure did not differ compared to their wild-type littermates despite disrupted FGF23-induced activation of the MAPK/ERK pathway. Importantly, calcineurin-NFAT signaling, defined by increased MCIP1 level and nuclear localization of NFATC2, was constitutively activated in PTH-KL−/− mice. Treatment with the calcineurin-inhibitor cyclosporine A abolished FGF23-mediated PTH suppression in PTH-KL−/− mice whereas wild-type mice remained responsive. Similar results were observed in thyro-parathyroid explants ex vivo. Collectively, we present genetic and functional evidence for a novel, Klotho-independent, calcineurin-mediated FGF23 signaling pathway in parathyroid glands that mediates suppression of PTH. The presence of Klotho-independent FGF23 effects in a Klotho-expressing target organ represents a paradigm shift in the conceptualization of FGF23 endocrine action.
Inorganic calcium is a critical element for a diverse range of cellular processes ranging from cell signaling to energy metabolism, and its extracellular concentration is controlled by parathyroid hormone (PTH). Klotho is expressed in parathyroid chief cells and reported to facilitate PTH secretion during hypocalcemia and mediate FGF23 suppression of PTH synthesis and secretion. To dissect the role of parathyroid Klotho in health and disease, we generated parathyroid-specific Klotho knockout mice. The mutant mice had normal serum levels of PTH and calcium. Further, their parathyroid sensitivity to acute fluctuations in serum calcium and response to FGF23 treatment were preserved, and mutant mice developed secondary hyperparathyroidism of similar magnitude as wild-type mice when challenged with renal failure. A previously unknown parathyroid FGF23 signaling pathway involving calcineurin was constitutively activated in the mutant mice, and blocking this pathway abolished FGF23-induced suppression of PTH secretion. Our data challenges the concepts of Klotho as a mandatory factor for the acute hypocalcemic PTH response and decreased Klotho abundance as a pathogenic factor in secondary hyperparathyroidism. Finally, the presence of Klotho-independent FGF23 effects in a Klotho-expressing target organ represents a paradigm shift in the conceptualization of FGF23 endocrine action.
Klotho knockout mice (klotho-/-) have increased renal expression of sodium/phosphate co-transporters (NaPi2a), associated with severe hyperphosphatemia. Such serum biochemical changes in klotho-/-mice lead to extensive soft tissue anomalies and vascular calcification. To determine the significance of increased renal expression of the NaPi2a protein and concomitant hyperphosphatemia and vascular calcification in klotho-/-mice, we generated klotho and NaPi2a double knockout (klotho-/-/NaPi2a-/-) mice.
Methods and Results
Genetic inactivation of NaPi2a activity from klotho-/-mice reversed the severe hyperphosphatemia to mild hypophosphatemia or normophosphatemia. Importantly, despite significantly higher serum calcium and 1,25-dihydroxyvitamin D levels in klotho-/-/NaPi2a-/- mice, the vascular and soft tissue calcifications were reduced,. Extensive soft tissue anomalies and cardiovascular calcification were consistently noted in klotho-/-mice by 6 weeks of age; however, these vascular and soft tissue abnormalities were absent even in 12-week-old double knockout mice. Klotho-/-/NaPi2a-/- mice also regained body weight and did not develop the generalized tissue atrophy often noted in klotho-/-single knockout mice.
Our in vivo genetic manipulation studies have provided compelling evidence for a pathologic role of increased NaPi2a activities in regulating abnormal mineral ion metabolism and soft tissue anomalies in klotho-/- mice. Notably, our results suggest that serum phosphate levels are the important in vivo determinant of calcification, and that lowering serum phosphate levels can reduce or eliminate soft tissue and vascular calcification, even in presence of extremely high serum calcium and 1,25-dihydroxyvitamin D levels. These in vivo observations have significant clinical importance and therapeutic implications for chronic kidney disease patients with cardiovascular calcification.
Klotho; Vitamin-D; NaPi2a; Calcification
Intrauterine growth restriction (IUGR) is associated with impaired vascular function, which contributes to the increased incidence of chronic disease. The aim of this study was to investigate whether aerobic training improves AngII-induced vasoconstriction in IUGR rats. Moreover, we assess the role of superoxide dismutase (SOD) isoforms and NADPH oxidase-derived superoxide anions in this improvement. Female Wistar rats were randomly divided into two groups on day 1 of pregnancy. A control group was fed standard chow ad libitum, and a restricted group was fed 50% of the ad libitum intake throughout gestation. At 8 weeks of age, male offspring from both groups were randomly assigned to 4 experimental groups: sedentary control (SC), trained control (TC), sedentary restricted (SRT), and trained restricted (TRT). The training protocol was performed on a treadmill and consisted of a continuous 60-min session 5 days/week for 10 weeks. Following aerobic training, concentration–response curves to AngII were obtained in endothelium-intact aortic rings. Protein expression of SOD isoforms, AngII receptors and the NADPH oxidase component p47phox was assessed by Western blot analysis. The dihydroethidium was used to evaluate the in situ superoxide levels under basal conditions or in the presence of apocynin, losartan or PD 123,319. Our results indicate that aerobic training can prevent IUGR-associated increases in AngII-dependent vasoconstriction and can restore basal superoxide levels in the aortic rings of TRT rats. Moreover, we observed that aerobic training normalized the increased p47phox protein expression and increased MnSOD and AT2 receptor protein expression in thoracic aortas of SRT rats. In summary, aerobic training can result in an upregulation of antioxidant defense by improved of MnSOD expression and attenuation of NADPH oxidase component p47phox. These effects are accompanied by increased expression of AT2 receptor, which provide positive effects against Ang II–induced superoxide generation, resulting in attenuation of AngII-induced vasoconstriction.
Klotho is an antiaging hormone present in the kidney that extends the lifespan, regulates kidney function, and modulates cellular responses to oxidative stress. We investigated whether Klotho levels and signaling modulate inflammation in diabetic kidneys.
RESEARCH DESIGN AND METHODS
Renal Klotho expression was determined by quantitative real-time PCR and immunoblot analysis. Primary mouse tubular epithelial cells were treated with methylglyoxalated albumin, and Klotho expression and inflammatory cytokines were measured. Nuclear factor (NF)-κB activation was assessed by treating human embryonic kidney (HEK) 293 and HK-2 cells with tumor necrosis factor (TNF)-α in the presence or absence of Klotho, followed by immunoblot analysis to evaluate inhibitor of κB (IκB)α degradation, IκB kinase (IKK) and p38 activation, RelA nuclear translocation, and phosphorylation. A chromatin immunoprecipitation assay was performed to analyze the effects of Klotho signaling on interleukin-8 and monocyte chemoattractant protein-1 promoter recruitment of RelA and RelA serine (Ser)536.
Renal Klotho mRNA and protein were significantly decreased in db/db mice, and a similar decline was observed in the primary cultures of mouse tubule epithelial cells treated with methylglyoxal-modified albumin. The exogenous addition of soluble Klotho or overexpression of membranous Klotho in tissue culture suppressed NF-κB activation and subsequent production of inflammatory cytokines in response to TNF-α stimulation. Klotho specifically inhibited RelA Ser536 phosphorylation as well as promoter DNA binding of this phosphorylated form of RelA without affecting IKK-mediated IκBα degradation, total RelA nuclear translocation, and total RelA DNA binding.
These findings suggest that Klotho serves as an anti-inflammatory modulator, negatively regulating the production of NF-κB–linked inflammatory proteins via a mechanism that involves phosphorylation of Ser536 in the transactivation domain of RelA.
Previous studies have suggested that cerebrospinal fluid from patients with subarachnoid hemorrhage (SAH) leads to pronounced vasoconstriction in isolated arteries. We hypothesized that only cerebrospinal fluid from SAH patients with vasospasm would produce an enhanced contractile response to endothelin-1 in rat cerebral arteries, involving both endothelin ETA and ETB receptors.
Intact rat basilar arteries were incubated for 24 hours with cerebrospinal fluid from 1) SAH patients with vasospasm, 2) SAH patients without vasospasm, and 3) control patients. Arterial segments with and without endothelium were mounted in myographs and concentration-response curves for endothelin-1 were constructed in the absence and presence of selective and combined ETA and ETB receptor antagonists. Endothelin concentrations in culture medium and receptor expression were measured.
Compared to the other groups, the following was observed in arteries exposed to cerebrospinal fluid from patients with vasospasm: 1) larger contractions at lower endothelin concentrations (p<0.05); 2) the increased endothelin contraction was absent in arteries without endothelium; 3) higher levels of endothelin secretion in the culture medium (p<0.05); 4) there was expression of ETA receptors and new expression of ETB receptors was apparent; 5) reduction in the enhanced response to endothelin after ETB blockade in the low range and after ETA blockade in the high range of endothelin concentrations; 6) after combined ETA and ETB blockade a complete inhibition of endothelin contraction was observed.
Our experimental findings showed that in intact rat basilar arteries exposed to cerebrospinal fluid from patients with vasospasm endothelin contraction was enhanced in an endothelium-dependent manner and was blocked by combined ETA and ETB receptor antagonism. Therefore we suggest that combined blockade of both receptors may play a role in counteracting vasospasm in patients with SAH.
Ferulate (4-hydroxy-3-methoxycinnamic acid) is a well-known phenolic compound that scavenges free radicals and exerts anti-inflammatory effects. Forkhead box O3a (FOXO3a), a transcription factor that plays important roles in aging processes, decreases with age and is negatively regulated through phosphorylation by phosphatidylinositol 3-kinase (PI3K)/Akt signaling. The present study investigated the efficacy of short-term ferulate feeding on age-related changes in PI3K/Akt/FOXO3a and upstream insulin signaling pathways in aged rats. In addition, changes in manganese superoxide dismutase (MnSOD) and catalase expression were examined because of their dependence on PI3K/Akt/FOXO3a activity. Short-term feeding experiments were done with a diet containing ferulate that was given to aged rats at doses of 3 or 6 mg kg−1 day−1 for 10 days. Results showed that FOXO3a activity was increased in the ferulate-fed old group compared with the control old group. Also, ferulate suppressed the PI3K/Akt signaling pathway that is responsible for FOXO3a inhibition in aged rats. Plasma insulin levels and the upstream insulin signaling pathway were also modulated by ferulate correspondingly with PI3K/Akt/FOXO3a activity. The age-related decrease in two major antioxidant enzymes, MnSOD and catalase, was blunted by ferulate, which was accompanied by FOXO3a transcriptional activity. The significance of the present study is the finding that short-term feeding of ferulate effectively modulates age-related renal FOXO3a, PI3K/Akt and insulin signaling pathways, and MnSOD and catalase expression, all of which may be beneficial for attenuating the aging process.
Ferulate; FOXO3a; Aging; PI3K/Akt; MnSOD; Catalase
The risk for cardiovascular disease increases with advancing age; however, the chronological development of heart disease differs in males and females. The purpose of this study was to determine whether age-induced alterations in responses of coronary arterioles to the endogenous vasoconstrictor, endothelin, are sex-specific. Coronary arterioles were isolated from young and old male and female rats to assess vasoconstrictor responses to endothelin (ET), and ETa and ETb receptor inhibitors were used to assess receptor-specific signaling. In intact arterioles from males, ET-induced vasoconstriction was reduced with age, whereas age increased vasoconstrictor responses to ET in intact arterioles from female rats. In intact arterioles from both sexes, blockade of either ETa or ETb eliminated age-related differences in responses to ET; however, denudation of arterioles from both sexes revealed age-related differences in ETa-mediated vasoconstriction. In arterioles from male rats, ETa receptor protein decreased, whereas ETb receptor protein increased with age. In coronary arterioles from females, neither ETa nor ETb receptor protein changed with age, suggesting age-related changes in ET signaling occur downstream of ET receptors. Thus, aging-induced alterations in responsiveness of the coronary resistance vasculature to endothelin are sex-specific, possibly contributing to sexual dimorphism in the risk of cardiovascular disease with advancing age.
rat; vasodilation; BQ123; BQ788
Klotho is a renal protein with anti-aging properties that is downregulated in conditions related to kidney injury. Hyperlipidemia accelerates the progression of renal damage, but the mechanisms of the deleterious effects of hyperlipidemia remain unclear.
We evaluated whether hyperlipidemia modulates Klotho expression in kidneys from C57BL/6 and hyperlipidemic apolipoprotein E knockout (ApoE KO) mice fed with a normal chow diet (ND) or a Western-type high cholesterol-fat diet (HC) for 5 to 10 weeks, respectively.
In ApoE KO mice, the HC diet increased serum and renal cholesterol levels, kidney injury severity, kidney macrophage infiltration and inflammatory chemokine expression. A significant reduction in Klotho mRNA and protein expression was observed in kidneys from hypercholesteromic ApoE KO mice fed a HC diet as compared with controls, both at 5 and 10 weeks. In order to study the mechanism involved in Klotho down-regulation, murine tubular epithelial cells were treated with ox-LDL. Oxidized-LDL were effectively uptaken by tubular cells and decreased both Klotho mRNA and protein expression in a time- and dose-dependent manner in these cells. Finally, NF-κB and ERK inhibitors prevented ox-LDL-induced Klotho downregulation.
Our results suggest that hyperlipidemia-associated kidney injury decreases renal expression of Klotho. Therefore, Klotho could be a key element explaining the relationship between hyperlipidemia and aging with renal disease.
Increased oxidative stress and decrease in antioxidant enzymes have been suggested to be involved in the pathophysiology of myocardial infarction (MI). In this study, treadmill exercise training and losartan treatment began 1 week post-MI and lasted 8 weeks. We evaluated the changes in the mRNA and protein expressions for the enzymatic antioxidants-superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase after exercise and losartan treatment in post-MI rats. Our results demonstrated that GPx and catalase mRNA levels were comparable among all the groups, while the mRNA level for manganese SOD (MnSOD) was significantly increased in exercise training with/without losartan treatment as compared to the sedentary MI group. Moreover, the mRNA level for gp91phox was dramatically decreased by a combination of exercise and losartan treatment. The protein levels for MnSOD were significantly elevated by exercise training in combination with losartan treatment. The protein levels for catalase were significantly increased in response to exercise, and it was further augmented by exercise together with losartan treatment. Thiobarbituric acid-reactive substances in plasma were significantly increased in the MI rats, but were decreased by exercise or losartan treatment, indicating that both exercise and losartan may reduce lipid oxidative damage. In addition, catalase and SOD enzymatic activities were significantly enhanced by exercise combined with losartan treatment. Our results suggest that exercise training improves catalase and MnSOD expression and attenuates oxidative stress. These effects are potentiated when combining exercise with angiotensin II receptor blockade.
oxidative stress; losartan; myocardial infarction; free radicals; exercise