1,25-dihydroxyvitamin D3 suppresses renin gene transcription by blocking the activity of the cyclic AMP response element in the renin gene promoter

Podocytopathy in diabetes: a metabolic and endocrine disorder

Diabetic nephropathy (DN) represents a major public health cost. Tight glycemic and blood pressure control can dramatically slow, but not stop, the progression of the disease, and a large number of patients progress toward end-stage renal disease despite currently available interventions. An early and key event in the development of DN is loss of podocyte function (or glomerular visceral epithelial cells) from the kidney glomerulus, where they contribute to the integrity of the glomerular filtration barrier. Recent evidence suggests that podocytes can be the direct target of circulating hormones, lipids, and adipokines that are affected in diabetes. We review the clinical and experimental evidence implicating novel endocrine and metabolic pathways in the pathogenesis of podocyte dysfunction and the development of DN.

[Vitamin D and hypertension]

Low levels of vitamin D, defined as levels of 25-hydroxyvitamin D < 20-30 ng/ml, is a prevalent problem in the general population. Besides the classic relation with musculoskeletal disease, vitamin D has been also related to autoimmune diseases, cancer, metabolic diseases or cardiovascular diseases. High blood pressure, as the main cardiovascular risk factor, also has been related to vitamin D deficiency, constituting two prevalent worldwide health problems. Therefore, this article reviews the most important studies that combine both pathologies, the biological mechanism that relate them and the current evidence about the effect of vitamin D supplementation on hypertension.

The influence of body mass index and renin-angiotensin-aldosterone system activity on the relationship between 25-hydroxyvitamin D and adiponectin in Caucasian men

OBJECTIVE

Previous studies have suggested that circulating adiponectin concentrations are associated positively with vitamin D and negatively with body mass index (BMI) but have not accounted for the influence of the renin-angiotensin-aldosterone system (RAAS) in this relationship. This is particularly relevant because increased RAAS activity is associated with obesity and is known to lower adiponectin levels. We evaluated the association between adiponectin and 25-hydroxyvitamin D (25(OH)D) after controlling RAAS activity with dietary sodium equilibration and also evaluated whether this relationship was influenced by BMI.

DESIGN

Cross-sectional study of 115 hypertensive Caucasian men from the Hypertensive Pathotype Consortium.

METHODS

To manipulate RAAS activity, all subjects underwent 1 week of high dietary sodium (HS) diet to suppress RAAS and 1 week of low dietary sodium (LS) diet to stimulate RAAS. Linear regression was used to evaluate the association between adiponectin and 25(OH)D, and the effect of BMI on this relationship, in each dietary condition.

RESULTS

Adiponectin was higher on HS, where circulating RAAS activity was low, when compared with LS (HS=2.9 versus LS=2.4 μg/ml, P<0.0001). 25(OH)D levels were positively associated with adiponectin, and BMI was a statistically significant effect modifier of the relationship between 25(OH)D and adiponectin on both diets (P interaction <0.01 between BMI and 25(OH)D).

CONCLUSIONS

Higher 25(OH)D concentrations were independently associated with higher adiponectin levels, particularly when BMI was high. Dietary sodium balance and circulating RAAS activity did not appear to affect this relationship. Future studies should explore whether vitamin D supplementation increases adiponectin levels in obesity.

The Fok1 vitamin D receptor gene polymorphism is associated with plasma renin activity in Caucasians

OBJECTIVES

25-Hydroxyvitamin D (25(OH)D) deficiency and excess activity of the renin-angiotensin system (RAS) are both associated with cardiovascular disease. Vitamin D interacts with the vitamin D receptor (VDR) to negatively regulate renin expression in mice; however, human studies linking genetic variation in the VDR with renin are lacking. We evaluated (i) whether genetic variation in the VDR at the Fok1 polymorphism was associated with plasma renin activity (PRA) in a population of hypertensives and a separate population of normotensives and (ii) whether the association between Fok1 genotype and PRA was independent of 25(OH)D levels.

DESIGN/PATIENTS/MEASUREMENTS

Genetic association study, assuming an additive model of inheritance, of 375 hypertensive and 146 normotensive individuals from the HyperPATH cohort, who had PRA assessments after 1 week of high dietary sodium balance (HS) and l week of low dietary sodium balance (LS).

RESULTS

The minor allele (T) at the Fok1 polymorphism was significantly associated with lower PRA in hypertensives (LS: β = -0·22, P < 0·01; HS: β = -0·19, P < 0·01); when repeated in normotensives, a similar relationship was observed (LS: β = -0·17, P < 0·05; HS: β = -0·18, P = 0·14). In multivariable analyses, both higher 25(OH)D levels and the T allele at Fok1 were independently associated with lower PRA in hypertensives; however, 25(OH)D was not associated with PRA in normotensives.

CONCLUSIONS

Genetic variation at the Fok1 polymorphism of the VDR gene, in combination with 25(OH)D levels, was associated with PRA in hypertension. These findings support the vitamin D-VDR complex as a potential regulator of renin activity in humans.

cAMP target sequences enhCRE and CNRE sense low-salt intake to increase human renin gene expression in vivo

This study aimed to assess the role of cAMP target sequences enhancer cAMP response element (enhCRE) and cAMP and overlapping negative response element (CNRE) in the control of human renin gene (REN) in vivo. enhCRE and CNRE were silenced by mutations in a 12.2-kb human renin promoter fused to LacZ reporter gene. This construct was used to generate transgenic mice (RENMut-LacZ). The expression of the transgene was correctly targeted to the juxtaglomerular portions of renal afferent arterioles which express endogenous mouse renin. Therefore, enhCRE and CNRE do not seem to be relevant for the control of the cell-specific expression of the human renin gene. The β-adrenoreceptor agonist isoproterenol (10 mg/kg/day, for 2 days) stimulated the endogenous renin, but not the LacZ mRNA expression. Treatment of RENMut-LacZ mice with the angiotensin converting enzyme inhibitor (enalapril 10 mg/kg/day, for 7 days) or their crossing to angiotensin receptor type 1a knockout mice led to increased renin and LacZ mRNA levels. Renin expression was upregulated by low-salt diet (0.03% NaCl, for 10 days) and downregulated by high-salt diet (4% NaCl, for 10 days). In contrast, low-salt diet did not influence, while high-salt diet inhibited the expression of LacZ. In summary, enhCRE and CNRE appear to be necessary for the transactivation of the human renin gene through β-adrenoreceptors and by low-salt diet. Our data also suggest that different intracellular mechanisms mediate the effect of low- and high-salt intake on renin expression in vivo.

1,25-Dihydroxyvitamin D₃ suppresses inflammation-induced expression of plasminogen activator inhibitor-1 by blocking nuclear factor-κB activation

Plasminogen activator inhibitor (PAI)-1 is a major fibrinolytic inhibitor. High PAI-1 is associated with increased renal and cardiovascular disease risk. Previous studies demonstrated PAI-1 down-regulation by 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), but the molecular mechanism remains unknown. Here we show that exposure of mouse embryonic fibroblasts to TNFα or LPS led to a marked induction of PAI-1, which was blunted by 1,25(OH)₂D₃, NF-κB inhibitor or p65 siRNA, suggesting the involvement of NF-κB in 1,25(OH)₂D₃-induced repression. In mouse Pai-1 promoter a putative cis-κB element was identified at -299. EMSA and ChIP assays showed that TNF-α increased p50/p65 binding to this κB site, which was disrupted by 1,25(OH)₂D₃. Luciferase reporter assays showed that PAI-1 promoter activity was induced by TNFα or LPS, and the induction was blocked by 1,25(OH)₂D₃. Mutation of the κB site blunted TNFα, LPS or 1,25(OH)₂D₃ effects. 1,25(OH)₂D₃ blocked IκBα degradation and arrested p50/p65 nuclear translocation. In mice LPS stimulated PAI-1 expression in the heart and macrophages, and the stimulation was blunted by pre-treatment with a vitamin D analog. Together these data demonstrate that 1,25(OH)₂D₃ down-regulates PAI-1 by blocking NF-κB activation. Inhibition of PAI-1 production may contribute to the reno- and cardio-protective effects of vitamin D.

Role of vitamin D in arterial hypertension

Vitamin D deficiency is highly prevalent and may contribute to arterial hypertension. The antihypertensive effects of vitamin D include suppression of renin and parathyroid hormone levels and renoprotective, anti-inflammatory and vasculoprotective properties. Low 25-hydroxyvitamin D levels, which are used to classify the vitamin D status, are an independent risk factor for incident arterial hypertension. Meta-analyses of randomized controlled trials showed that vitamin D supplementation reduces systolic blood pressure by 2-6 mmHg. However, further studies are needed before drawing a final conclusion on the effect of vitamin D therapy on blood pressure and cardiovascular risk. In our current clinical practice we should take into account the high prevalence of vitamin D deficiency, the easy, cheap and safe way by which it can be supplemented and the promising clinical data suggesting that vitamin D might be useful for the treatment of arterial hypertension as well as other chronic diseases. Therefore, we recommend that testing for and treating vitamin D deficiency in patients with arterial hypertension should be seriously considered.

Vitamin D receptor activator reduces oxidative stress in hemodialysis patients with secondary hyperparathyroidism

Treatment with a vitamin D receptor activator (VDRA) has survival benefits probably related to its effects beyond the traditional role in mineral metabolism. We hypothesized that VDRA reduces oxidative stress in hemodialysis (HD) patients. To test this hypothesis, we investigated the effect of VDRA on the oxidative status of albumin in HD patients with secondary hyperparathyroidism. Eleven HD patients with secondary hyperparathyroidism were treated with calcitriol at an intravenous dose of 1.5 µg/week for four weeks. Serum intact parathyroid hormone, calcium and phosphorus were monitored and we measured the amount of oxidized albumin and albumin hydroperoxides form before and after calcitriol treatment. The ratio of oxidized to un-oxidized albumin was determined as a representative marker of oxidative stress. The radical scavenging activity of albumin was also evaluated. After four weeks of calcitriol therapy, there were no significant changes in serum intact parathyroid hormone, calcium, or phosphorus levels; however, the ratio of oxidized to un-oxidized albumin was markedly decreased and serum thiol content was significantly increased after calcitriol treatment. Furthermore, the radical scavenging activity of albumin was greater after calcitriol treatment compared with that of untreated albumin. Our data suggest that intravenous calcitriol treatment reduces oxidative stress and strengthens antioxidant defenses by inhibiting albumin oxidation in HD patients with secondary hyperparathyroidism.

Vitamin D receptor agonist doxercalciferol modulates dietary fat-induced renal disease and renal lipid metabolism

Diet-induced obesity (DIO) and insulin resistance in mice are associated with proteinuria, renal mesangial expansion, accumulation of extracellular matrix proteins, and activation of oxidative stress, proinflammatory cytokines, profibrotic growth factors, and the sterol regulatory element binding proteins, SREBP-1 and SREBP-2, that mediate increases in fatty acid and cholesterol synthesis. The purpose of the present study was to determine whether treatment of DIO mice with the vitamin D receptor (VDR) agonist doxercalciferol (1α-hydroxyvitamin D2) prevents renal disease. Our results indicate that treatment of DIO mice with the VDR agonist decreases proteinuria, podocyte injury, mesangial expansion, and extracellular matrix protein accumulation. The VDR agonist also decreases macrophage infiltration, oxidative stress, proinflammatory cytokines, and profibrotic growth factors. Furthermore, the VDR agonist also prevents the activation of the renin-angiotensin-aldosterone system including the angiotensin II type 1 receptor and the mineralocorticoid receptor. An additional novel finding of our study is that activation of VDR results in decreased accumulation of neutral lipids (triglycerides and cholesterol) and expression of adipophilin in the kidney by decreasing SREBP-1 and SREBP-2 expression and target enzymes that mediate fatty acid and cholesterol synthesis and increasing expression of the farnesoid X receptor. This study therefore demonstrates multiple novel effects of VDR activation in the kidney which prevent renal manifestations of DIO in the kidney.

Vitamin D and cardiometabolic health: a review of the evidence

The cardiometabolic syndrome (MetS) is a clustering of related metabolic abnormalities including abdominal adiposity, insulin resistance, hypertension, dyslipidaemia and increased inflammatory and thrombotic markers, which is linked to increased risk of type 2 diabetes, CVD and overall mortality. Several cross-sectional and prospective studies have shown an association between low vitamin D status, as indicated by concentrations of serum 25-hydroxyvitamin D (s25(OH)D), and increased prevalence of the MetS and individual CVD risk factors. These epidemiological observations are supported by mechanistic studies but experimental data are limited. The available data from intervention studies are largely confounded as most vitamin D supplementation trials were mainly carried out to explore the role of Ca in CVD and include Ca in the treatment arms. Inadequate consideration of seasonal effects on s25(OH)D concentrations is also a common design flaw in most studies. Further complications arise from shared risk factors such as adiposity and ageing, which predispose individuals to exhibit both a more pronounced risk profile and relatively lower s25(OH)D concentrations. In conclusion, while epidemiological associations are promising and a rationale for low vitamin D status as a potentially modifiable risk factor for CVD is supported by mechanistic data, suitable experimental data from appropriately designed trials are just beginning to emerge. As yet, this body of literature is too immature to draw firm conclusions on the role of vitamin D in CVD prevention. Carefully controlled vitamin D trials in well-described population groups using intervention doses that are titrated against target s25(OH)D concentrations could yield potentially valuable outcomes that may have a positive impact on CVD risk modification.

Vitamin D deficiency and myocardial diseases

Vitamin D deficiency is common among patients with myocardial diseases because sun-induced vitamin D production in the skin and dietary intake of vitamin D is often insufficient. Knockout mice for the vitamin D receptor develop myocardial hypertrophy and dysfunction. It has also been shown that children with rickets who suffered from severe heart failure could be successfully treated with supplementation of vitamin D plus calcium. In adults, almost all patients with heart failure exhibit reduced 25-hydroxyvitamin D levels, which are used to classify the vitamin D status. In prospective studies, vitamin D deficiency was an independent risk factor for mortality, deaths due to heart failure and sudden cardiac death. Several vitamin D effects on the electrophysiology, contractility, and structure of the heart suggest that vitamin D deficiency might be a causal factor for myocardial diseases. Data from interventional trials, however, are rare and urgently needed to elucidate whether vitamin D supplementation is useful for the treatment of myocardial diseases. In our opinion, the current knowledge of the beneficial effects of vitamin D on myocardial and overall health strongly argue for vitamin D supplementation in all vitamin D-deficient patients with or at high risk for myocardial diseases.

Vitamin D and cardiovascular disease risk: emerging evidence

PURPOSE OF REVIEW

Vitamin D deficiency is common throughout the world, with a particularly high prevalence in northern latitudes and colder climates. Although the best known sequelae of vitamin D deficiency involve the musculoskeletal system, a growing body of evidence suggests that vitamin D status may influence cardiovascular health as well. This review focuses on recent studies linking vitamin D and cardiovascular disease risk, emphasizing the potential relevance to primary prevention.

RECENT FINDINGS

There is strong experimental evidence that vitamin D status may influence cardiovascular structure and function. The number of clinical studies has steadily grown in recent years, with the largest number comprising observational studies showing associations between low vitamin D status, the presence of various cardiovascular risk factors, and adverse cardiovascular outcomes. A few small, randomized, controlled studies have been published, but these have been largely inconclusive.

SUMMARY

Despite substantial clinical evidence linking vitamin D deficiency with increased cardiovascular risk, it remains to be established whether this represents a causal association. Further study is needed with prospective, randomized controlled trials before vitamin D supplementation can be routinely recommended for the primary or secondary prevention of cardiovascular disease.

The effect of nutrition on blood pressure

The incidence and severity of hypertension are affected by nutritional status and intake of many nutrients. Excessive energy intake and obesity are major causes of hypertension. Obesity is associated with increased activity of the renin-angiotensin-aldosterone and sympathetic nervous systems, possibly other mineralcorticoid activity, insulin resistance, salt-sensitive hypertension and excess salt intake, and reduced kidney function. High sodium chloride intake strongly predisposes to hypertension. Increased alcohol consumption may acutely elevate blood pressure. High intakes of potassium, polyunsaturated fatty acids, and protein, along with exercise and possibly vitamin D, may reduce blood pressure. Less-conclusive studies suggest that amino acids, tea, green coffee bean extract, dark chocolate, and foods high in nitrates may reduce blood pressure. Short-term studies indicate that specialized diets may prevent or ameliorate mild hypertension; most notable are the Dietary Approaches to Stop Hypertension (DASH) diet, which is high in fruits, vegetables, and low-fat dairy products, and the DASH low-sodium diet. Long-term compliance to these diets remains a major concern.

Therapeutic effects of vitamin D analogs on cardiac hypertrophy in spontaneously hypertensive rats

Vitamin D inhibits renin expression and blocks the compensatory induction of renin associated with the use of renin-angiotensin system inhibitors. Here we test the therapeutic effects of two commonly used vitamin D analogs and their combination with losartan on the development of left ventricular hypertrophy. One-month-old male spontaneously hypertensive rats were treated with vehicle, losartan, paricalcitol, doxercalciferol, a combination of losartan and paricalcitol, or a combination of losartan and doxercalciferol for 2 months. Blood pressure was markedly reduced by losartan, but not by paricalcitol or doxercalciferol alone. Echocardiograpy demonstrated a 65 to 80% reduction in left ventricular wall thickness with losartan, paricalcitol, or doxercalciferol monotherapy and almost complete prevention of left ventricular hypertrophy with the combination therapies. Attenuation of cardiac and cardiomyocyte hypertrophy, and suppression of atrial and brain natriuretic peptides, were most marked in the combination therapy groups. These changes were well correlated with left ventricular gene and microRNA expression profiles in the different treatment groups. Renal and cardiac renin expression was markedly increased in losartan-treated animals, but nearly normalized with combination therapy. The same vitamin D analogs suppressed plasma renin activity in patients receiving chronic hemodialysis. These data demonstrate that vitamin D analogs have potent antihypertrophic activity in part via suppression of renin in the kidney and heart, and combination of these analogs with losartan achieves much better therapeutic effects because of the blockade of the compensatory renin increase.

Myocardial effects of VDR activators in renal failure

Cardiovascular complications are the leading cause of death in patients with chronic kidney disease (CKD). Traditional causes such as diabetes, smoking, aging and hypertension do not fully explain the high rate of morbidity from cardiovascular disease seen in these patients. The renin-angiotensin-aldosterone system (RAAS) regulates extracellular volume homeostasis, which contributes to blood pressure stability. Overactivity of this system is involved in the pathophysiology of cardio-renal disease. New evidence suggests that vitamin D receptor activators (VDRAs) have a suppressive effect on the RAAS; however, VDRAs also have anti-inflammatory and anti-fibrotic effects. We have demonstrated that paricalcitol, a VDRA, ameliorates left ventricular hypertrophy (LVH) in uremic rats by up-regulating the VDR, decreasing myocardial PCNA and also decreasing myocardial oxidative stress. Thus, paricalcitol can suppress the progression of LVH, myocardial and perivascular fibrosis and myocardial arterial vessel thickness presumably by up-regulating the VDR. Paricalcitol may prove to have a substantial beneficial effect on cardiac disease and its outcome in patients with CKD. Prospective randomized studies in CKD patients are necessary to confirm these results.

Vitamin D receptor attenuates renal fibrosis by suppressing the renin-angiotensin system

Analogs of vitamin D attenuate renal injury in several models of kidney disease, but the mechanism underlying this renoprotective effect is unknown. To address the role of the vitamin D receptor (VDR) in renal fibrogenesis, we subjected VDR-null mice to unilateral ureteral obstruction for 7 days. Compared with wild-type mice, VDR-null mice developed more severe renal damage in the obstructed kidney, with marked tubular atrophy and interstitial fibrosis. Significant induction of extracellular matrix proteins (fibronectin and collagen I), profibrogenic and proinflammatory factors (TGF-beta, connective tissue growth factor, and monocyte chemoattractant protein 1), and epithelial-to-mesenchymal transition accompanied this histologic damage. Because VDR ablation activates the renin-angiotensin system and leads to accumulation of angiotensin II (AngII) in the kidney, we assessed whether elevated AngII in the VDR-null kidney promotes injury. Treatment with the angiotensin type 1 antagonist losartan eliminated the difference in obstruction-induced interstitial fibrosis between wild-type and VDR-null mice, suggesting that AngII contributes to the enhanced renal fibrosis observed in obstructed VDR-null kidneys. Taken together, these results suggest that the VDR attenuates obstructive renal injury at least in part by suppressing the renin-angiotensin system.

Physiology of Kidney Renin

The protease renin is the key enzyme of the renin-angiotensin-aldosterone cascade, which is relevant under both physiological and pathophysiological settings. The kidney is the only organ capable of releasing enzymatically active renin. Although the characteristic juxtaglomerular position is the best known site of renin generation, renin-producing cells in the kidney can vary in number and localization. (Pro)renin gene transcription in these cells is controlled by a number of transcription factors, among which CREB is the best characterized. Pro-renin is stored in vesicles, activated to renin, and then released upon demand. The release of renin is under the control of the cAMP (stimulatory) and Ca2+(inhibitory) signaling pathways. Meanwhile, a great number of intrarenally generated or systemically acting factors have been identified that control the renin secretion directly at the level of renin-producing cells, by activating either of the signaling pathways mentioned above. The broad spectrum of biological actions of (pro)renin is mediated by receptors for (pro)renin, angiotensin II and angiotensin-( 1 – 7 ).

Vitamin D and cardiovascular disease

Vitamin D insufficiency/deficiency has been observed worldwide at all stages of life. It has been characterized as a public health problem, since low concentrations of this vitamin have been linked to the pathogenesis of several chronic diseases. Several studies have suggested that vitamin D is involved in cardiovascular diseases and have provided evidence that it has a role in reducing cardiovascular disease risk. It may be involved in regulation of gene expression through the presence of vitamin D receptors in various cells, regulation of blood pressure (through renin-angiotensin system), and modulation of cell growth and proliferation including vascular smooth muscle cells and cardiomyocytes. Identifying correct mechanisms and relationships between vitamin D and such diseases could be important in relation to patient care and healthcare policies.

Low levels of 25-hydroxyvitamin D in the pediatric populations: prevalence and clinical outcomes

Vitamin D deficiency is becoming increasingly common in the USA. In this review we provide estimates of the prevalence of deficiency, and review the risk factors and the evidence of clinical consequences of vitamin D deficiency. Vitamin D deficiency causes the pediatric disease rickets. In addition, there is some evidence that vitamin D deficiency may lead to other diseases including diabetes mellitus, hypertension, infections, asthma and dyslipidemia.

Effect of vitamin D on blood pressure: a systematic review and meta-analysis

OBJECTIVES

Vitamin D insufficiency has been linked to hypertension and cardiovascular events in observational studies. It is unclear whether vitamin D supplementation can reduce blood pressure, and, if so, by how much.

METHODS

We performed a systematic review and meta-analysis to examine whether vitamin D reduces blood pressure. Databases including MEDLINE, EMBASE, the Cumulative Index to Nursing and Allied Health Literature and the Cochrane library were searched, supplemented by searches of grey literature, unpublished trials and references from included studies. Studies were assessed by two reviewers independently according to a prespecified protocol. Interventions included activated vitamin D, unactivated vitamin D2 and D3 and ultraviolet B radiation.

RESULTS

Eleven randomized, controlled trials fulfilled the inclusion criteria. Studies were small and of variable methodological quality. Mean baseline blood pressure was more than 140/90 mmHg in eight studies. Meta-analysis of these eight studies showed a nonsignificant reduction in systolic blood pressure in the vitamin D group compared with placebo [-3.6 mmHg, 95% confidence interval (CI) -8.0 to 0.7]. A small, statistically significant reduction was seen in diastolic blood pressure (-3.1 mmHg, 95% CI -5.5 to -0.6). Subgroup analysis suggested that unactivated vitamin D produced a greater fall in systolic blood pressure than activated vitamin D (-6.2 mmHg, 95% CI -12.32 to -0.04, vs. +0.7 mmHg, 95% CI -4.8 to 6.2). No reduction in blood pressure was seen in studies examining patients who were normotensive at baseline.

CONCLUSION

We found weak evidence to support a small effect of vitamin D on blood pressure in studies of hypertensive patients.

Vitamin D and cardiovascular risk

Vitamin D deficiency results in abnormal mineralization of bones and has resulted in prevention programs for children with supplementation when they are breast fed. Further activities of vitamin D relate to defence of microbial infections, e.g. tuberculosis, prevention of cancer, contractility of muscle cells and counteraction of congestive heart failure. Given early reports in the 1960s on deleterious effects of vitamin D supplementation in rodents, that is ectopic media ossification of arterial vessels, a pro-atherogenic function had been anticipated for humans as well. However, cross-sectional studies reveal that vitamin D deficiency in humans is associated with elevated blood pressure and propagation of atherogenesis. These contradictory findings on the progression of atherosclerosis may be reconciled by dissecting the activation mechanism(s) of vitamin D in rodents versus humans. Notably, novel findings convincingly indicate that vitamin D exerts anti-inflammatory effects. In conclusion, vitamin D supplementation in adults may be regarded as simple means with few potential side effects to prevent atherogenesis or halt its progression and combat arterial hypertension. Adjustment of vitamin D dosing regimens is required in patients with chronic kidney disease; however, prospective clinical trials are urgently needed to guide these recommendations with evidence.

Genome-wide analysis of histone H3 lysine9 modifications in human mesenchymal stem cell osteogenic differentiation

Mesenchymal stem cells (MSCs) possess self-renewal and multi-lineage differentiation potentials. It has been established that epigenetic mechanisms such as histone modifications could be critical for determining the fate of stem cells. In this study, full human genome promoter microarrays and expression microarrays were used to explore the roles of histone modifications (H3K9Ac and H3K9Me2) upon the induction of MSC osteogenic differentiation. Our results revealed that the enrichment of H3K9Ac was decreased globally at the gene promoters, whereas the number of promoters enriched with H3K9Me2 was increased evidently upon osteogenic induction. By a combined analysis of data from both ChIP-on-chip and expression microarrays, a number of differentially expressed genes regulated by H3K9Ac and/or H3K9Me2 were identified, implicating their roles in several biological events, such as cell cycle withdraw and cytoskeleton reconstruction that were essential to differentiation process. In addition, our results showed that the vitamin D receptor played a trans-repression role via alternations of H3K9Ac and H3K9Me2 upon MSC osteogenic differentiation. Data from this study suggested that gene activation and silencing controlled by changes of H3K9Ac and H3K9Me2, respectively, were crucial to MSC osteogenic differentiation.

Vitamin D and the cardiovascular system

Several epidemiologic and clinical studies have suggested that there is a strong association between hypovitaminosis D and cardiovascular disease (CVD). Hypovitaminosis D was reported as a risk factor for increased cardiovascular events among 1739 adult participants in the Framingham Offspring Study. Analysis of more than 13,000 adults in the Third National Health and Nutrition Examination Survey (NHANES III) showed that even though hypovitaminosis D is associated with an increased prevalence of CVD risk factors, its association with all-cause mortality is independent of these risk factors. Importantly, epidemiologic studies suggested that patients who had chronic kidney disease and were treated with activated vitamin D had a survival advantage when compared with those who did not receive treatment with these agents. Mechanistically, emerging data have linked vitamin D administration with improved cardiac function and reduced proteinuria, and hypovitaminosis D is associated with obesity, insulin resistance, and systemic inflammation. Preliminary studies suggested that activated vitamin D inhibits the proliferation of cardiomyoblasts by promoting cell-cycle arrest and enhances the formation of cardiomyotubes without inducing apoptosis. Activated vitamin D has also been shown to attenuate left ventricular dysfunction in animal models and humans. In summary, emerging studies suggest that hypovitaminosis D has emerged as an independent risk factor for all-cause and cardiovascular mortality, reinforcing its importance as a public health problem. There is a need to advance our understanding of the biologic pathways through which vitamin D affects cardiovascular health and to conduct prospective clinical interventions to define precisely the cardioprotective effects of nutritional vitamin D repletion.

Vitamin D status and arterial hypertension: a systematic review

Vitamin D deficiency is common and is primarily caused by a lack of ultraviolet-B (UVB) radiation from reduced sun exposure, and the consequent limiting of vitamin D production in the skin. The vitamin D endocrine system regulates about 3% of the human genome. Observational data support the concept that vitamin D is involved in the pathogenesis of cardiovascular diseases and arterial hypertension. The antihypertensive properties of vitamin D include renoprotective effects, suppression of the renin-angiotensin-aldosterone system, direct effects on vascular cells, and effects on calcium metabolism, including prevention of secondary hyperparathyroidism. The results of clinical studies largely, but not consistently, favor the hypothesis that vitamin D sufficiency promotes lowering of arterial blood pressure. Randomized, placebo-controlled trials are greatly needed to clarify and definitively prove the effect of vitamin D on blood pressure. In general, the antihypertensive effects of vitamin D seem to be particularly prominent in vitamin-D-deficient patients with elevated blood pressure. Thus, in view of the relatively safe and inexpensive way in which vitamin D can be supplemented, we believe that vitamin D supplementation should be prescribed to patients with hypertension and 25-hydroxyvitamin D levels below target values.

A new role for vitamin D receptor activation in chronic kidney disease

Vitamin D has proven to be much more than a simple "calcium hormone." The fact that the vitamin D receptor has been found in cells not related to mineral metabolism supports that statement. The interest of nephrologists in vitamin D and its effects beyond mineral metabolism has increased over the last few years, evidencing the importance of this so-called "sunshine hormone." In the present review, we highlight the most recent developments in the traditional use of vitamin D in chronic kidney disease (CKD) patients, namely, the control of secondary hyperparathyroidism (sHPT). Furthermore, we also explore the data available regarding the new possible therapeutic uses of vitamin D for the treatment of other complications present in CKD patients, such as vascular calcification, left ventricular hypertrophy, or proteinuria. Finally, some still scarce but very promising data regarding a possible role of vitamin D in kidney transplant patients also are reviewed. The available data point to a potential beneficial effect of vitamin D in CKD patients beyond the control of mineral metabolism.

Vitamin D deficiency and risk for cardiovascular disease

Vitamin D is an important prohormone for optimal intestinal calcium absorption for mineralization of bone. Because the vitamin D receptor is present in multiple tissues, there has been interest in evaluating other potential functions of vitamin D, particularly, in cardiovascular diseases (CVD). Cross-sectional studies have reported that vitamin D deficiency is associated with increased risk of CVD, including hypertension, heart failure, and ischemic heart disease. Initial prospective studies have also demonstrated that vitamin D deficiency increases the risk of developing incident hypertension or sudden cardiac death in individuals with preexisting CVD. Very few prospective clinical studies have been conducted to examine the effect of vitamin D supplementation on cardiovascular outcomes. The mechanism for how vitamin D may improve CVD outcomes remains obscure; however, potential hypotheses include the downregulation of the renin-angiotensin-aldosterone system, direct effects on the heart, and vasculature or improvement of glycemic control. This review will examine the epidemiologic and clinical evidence for vitamin D deficiency as a cardiovascular risk factor and explore potential mechanisms for the cardioprotective effect of vitamin D.

Hypovitaminosis D and valvular calcification in patients with dilated cardiomyopathy

BACKGROUND

In patients with dilated (idiopathic) cardiomyopathy (DCM), little is known about the presence of valvular calcification and its association with hypovitaminosis D, which may predispose affected tissues to calcification. Our objectives were 2-fold: to conduct a retrospective assessment of echocardiographic evidence of valvular calcification in patients with DCM who were known to have hypovitaminosis D (25(OH)D <30 ng/mL) and to conduct a prospective assessment of serum 25(OH)D in patients with DCM, who had demonstrated echocardiographic evidence of valvular calcification.

METHODS

The retrospective study consisted of 48 African American patients (34 men, 14 women; 52.3 +/- 1.5 years) having DCM and ejection fraction <35% with serum creatinine <2.0 mg/dL and 25(OH)D <30 ng/mL; and 20 white patients in the prospective study (20 men; 71.0 +/- 3.0 years) having DCM and ejection fraction <35% with serum creatinine <2.0 mg/dL and echocardiographic evidence of valvular calcification. In the retrospective study, a transthoracic echocardiogram was obtained to address mitral valvular and annular calcification, aortic valvular calcification, and sinotubular calcification; whereas in the prospective study, serum 25(OH)D level was monitored in patients with known valvular calcification. Serum parathyroid hormone (PTH) was monitored in both studies.

RESULTS

In the retrospective study, hypovitaminosis D was found in 19 patients (31%) with valvular calcification and in whom serum PTH was increased (83 +/- 8 pg/mL). In the prospective study, 15 of 20 elderly patients (80%) with known DCM and valvular calcification were found to have hypovitaminosis D (25(OH)D <30 ng/mL), whereas serum PTH was normal (43 +/- 4 pg/mL).

CONCLUSIONS

In patients with DCM without marked renal dysfunction, valvular calcification was seen more frequently and associated with hypovitaminosis D, whereas in elderly patients with valvular calcification, hypovitaminosis D is common, suggesting that the duration of vitamin D deficiency may determine the extent of valvular calcification. The role of hypovitaminosis D in the appearance of valvular calcification deserves further study.

Long-term therapeutic effect of vitamin D analog doxercalciferol on diabetic nephropathy: strong synergism with AT1 receptor antagonist

The intrarenal renin-angiotensin system (RAS) plays a key role in the development of diabetic nephropathy. Recently, we showed that combination therapy with an AT(1) receptor blocker (ARB) and an activated vitamin D analog produced excellent synergistic effects against diabetic nephropathy, as a result of blockade of the ARB-induced compensatory renin increase. Given the diversity of vitamin D analogs, here we used a pro-drug vitamin D analog, doxercalciferol (1alpha-hydroxyvitamin D(2)), to further test the efficacy of the combination strategy in long-term treatment. Streptozotocin-induced diabetic DBA/2J mice were treated with vehicle, losartan, doxercalciferol (0.4 and 0.6 microg/kg), or losartan and doxercalciferol combinations for 20 wk. Vehicle-treated diabetic mice developed progressive albuminuria and glomerulosclerosis. Losartan alone moderately ameliorated kidney injury, with renin being drastically upregulated. A similar therapeutic effect was seen with doxercalciferol alone, which markedly suppressed renin and angiotensinogen expression. The losartan and doxercalciferol combination most effectively prevented albuminuria, restored glomerular filtration barrier structure, and dramatically reduced glomerulosclerosis in a dose-dependent manner. These effects were accompanied by blockade of intrarenal renin upregulation and ANG II accumulation. These data demonstrate an excellent therapeutic potential for doxercalciferol in diabetic renal disease and confirm the concept that blockade of the compensatory renin increase enhances the efficacy of RAS inhibition and produces synergistic therapeutic effects in combination therapy.

Regulation of renin gene expression by oxidative stress

Increased arterial pressure, angiotensin II, and cytokines each result in feedback inhibition of renin gene expression. Because angiotensin II and cytokines can stimulate reactive oxygen species production, we tested the hypothesis that oxidative stress may be a mediator of this inhibition. Treatment of renin-expressing As4.1 cells with the potent cytokine tumor necrosis factor-alpha caused an increase in the steady-state levels of cellular reactive oxygen species, which was reversed by the antioxidant N-acetylcysteine. Exogenous H(2)O(2) caused a dose- and time-dependent decrease in the level of endogenous renin mRNA and decreased the transcriptional activity of a 4.1-kb renin promoter fused to luciferase, which was maximal when the renin enhancer was present. The effect of H(2)O(2) appeared to be specific to renin, because there was no change in the expression of beta-actin or cyclophilin mRNA or transcriptional activity of the SV40 promoter. The tumor necrosis factor-alpha-induced decrease in renin mRNA was partially reversed by either N-acetylcysteine or panepoxydone, a nuclear factor kappaB (NFkappaB) inhibitor. Interestingly, H(2)O(2) did not induce NFkappaB in As4.1 cells, and panepoxydone had no effect on the downregulation of renin mRNA by H(2)O(2). The transcriptional activity of a cAMP response element-luciferase construct was decreased by both tumor necrosis factor-alpha and H(2)O(2). These data suggest that cellular reactive oxygen species can negatively regulate renin gene expression via an NFkappaB-independent mechanism involving the renin enhancer and inhibiting cAMP response element-mediated transcription. Our data further suggest that tumor necrosis factor-alpha decreases renin expression through both NFkappaB-dependent and NFkappaB-independent mechanisms, the latter involving the production of reactive oxygen species.

Renoprotective effects of vitamin D analogs

Recent decades have witnessed the revelation of expanding roles of the vitamin D endocrine system beyond calcium and phosphorus metabolism. Along with these non-calcemic or non-classic actions of vitamin D are newly discovered therapeutic actions of vitamin D analogs in a number of pathological conditions, including kidney disease. The kidney is the major organ involved in the synthesis of the hormonal metabolite of vitamin D, and vitamin D deficiency is a common feature of chronic kidney disease even in its early stages. Experimental data suggest that vitamin D deficiency may in turn accelerate the progression of kidney disease. Low-calcemic vitamin D analogs have exhibited impressive therapeutic effects in various kidney disease models, with targets ranging from the NF-kappaB pathway to the renin-angiotensin system. These recent studies demonstrate that vitamin D analogs have potent renoprotective effects. The emerging experimental and clinical evidence has provided a solid foundation for the continuing exploration of vitamin D analogs in prevention and intervention in kidney disease.

Potential for vitamin D receptor agonists in the treatment of cardiovascular disease

Vitamin D(3) is made in the skin and modified in the liver and kidney to form the active metabolite, 1,25-dihydroxyvitamin D(3) (calcitriol). Calcitriol binds to a nuclear receptor, the vitamin D receptor (VDR), and activates VDR to recruit cofactors to form a transcriptional complex that binds to vitamin D response elements in the promoter region of target genes. During the past three decades the field has focused mainly on the role of VDR in the regulation of parathyroid hormone, intestinal calcium/phosphate absorption and bone metabolism; several VDR agonists (VDRAs) have been developed for the treatment of osteoporosis, psoriasis and hyperparathyroidism secondary to chronic kidney disease (CKD). Emerging evidence suggests that VDR plays important roles in modulating cardiovascular, immunological, metabolic and other functions. For example, data from epidemiological, preclinical and clinical studies have shown that vitamin D and/or 25(OH)D deficiency is associated with increased risk for cardiovascular disease (CVD). However, VDRA therapy seems more effective than native vitamin D supplementation in modulating CVD risk factors. In CKD, where decreasing VDR activation persists over the course of the disease and a majority of the patients die of CVD, VDRA therapy was found to provide a survival benefit in both pre-dialysis and dialysis CKD patients. Although VDR plays an important role in regulating cardiovascular function and VDRAs may be potentially useful for treating CVD, at present no VDRA is approved for CVD, and also no serum markers, beside parathyroid hormone in CKD, exist to indicate the efficacy of VDRA in CVD.

1,25-Dihydroxyvitamin D3 suppresses high glucose-induced angiotensinogen expression in kidney cells by blocking the NF-{kappa}B pathway

The renin-angiotensin system (RAS) is a major mediator of renal injury in diabetic nephropathy. Our previous studies demonstrated that 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] plays a renoprotective role by suppressing the RAS, with renin and angiotensinogen (AGT) as the main targets. The mechanism whereby 1,25(OH)(2)D(3) transcriptionally suppresses renin gene expression has been elucidated; however, how vitamin D regulates AGT remains unknown. Exposure of mesangial cells or podocytes to high glucose (HG; 30 mM) markedly stimulated AGT expression. In mesangial cells, the stimulation was inhibited by 1,25(OH)(2)D(3) (20 nM) or NF-kappaB inhibitor BAY 11-7082, suggesting the involvement of NF- kappaB in HG-induced AGT expression and the interaction between 1,25(OH)(2)D(3) and NF-kappaB in the regulation. Plasmid pNF-kappaB-Luc luciferase reporter assays showed that 1,25(OH)(2)D(3) blocked HG-induced NF-kappaB activity. EMSA and ChIP assays demonstrated increased p65/p50 binding to a NF-kappaB binding site at -1734 in the AGT gene promoter upon high glucose stimulation, and the binding was disrupted by 1,25(OH)(2)D(3) treatment. Overexpression of p65/p50 overcame 1,25(OH)(2)D(3) suppression, and mutation of this NF-kappaB binding site blunted 1,25(OH)(2)D(3) suppression of the promoter activity. In mice lacking the vitamin D receptor, AGT mRNA expression in the kidney was markedly increased compared with wild-type mice, and AGT induction in diabetic mice was suppressed by treatment with a vitamin D analog. These data indicate that 1,25(OH)(2)D(3) suppresses hyperglycemia-induced AGT expression by blocking NF-kappaB-mediated pathway.

Vitamin D and diabetic nephropathy

Diabetic nephropathy (DN) is the most common renal complication of diabetes mellitus and a leading cause of end-stage renal disease. The renin-angiotensin system (RAS) is a major mediator of progressive renal injury in DN, and RAS inhibitors have been used as the mainstay treatment for DN. One major problem limiting the efficacy of the RAS inhibitors is the compensatory renin increase caused by disruption of renin feedback inhibition. Vitamin D negatively regulates the RAS by suppressing renin expression and thus plays a renoprotective role in DN. Diabetic vitamin D receptor-null mutant mice develop more severe renal injuries because of more robust RAS activation. Combination therapy with an RAS inhibitor and a vitamin D analogue markedly ameliorates renal injuries due to blockade of the compensatory renin increase by the analogue. These most recent data demonstrate that vitamin D and its analogues have renoprotective and therapeutic potentials in DN through targeting the RAS.

Combination therapy with AT1 blocker and vitamin D analog markedly ameliorates diabetic nephropathy: blockade of compensatory renin increase

The renin-angiotensin system (RAS) plays a critical role in the development of diabetic nephropathy, and blockade of the RAS is currently used for treatment of diabetic nephropathy. One major problem for the current RAS inhibitors is the compensatory renin increase, which reduces the efficacy of RAS inhibition. We have shown that vitamin D exerts renoprotective actions by transcriptionally suppressing renin. Here we demonstrated that combination therapy with an AT1 receptor blocker and a vitamin D analog markedly ameliorated renal injury in the streptozotocin (STZ)-induced diabetes model due to the blockade of the compensatory renin rise by the vitamin D analog, leading to more effective RAS inhibition. STZ-treated diabetic DBA/2J mice developed progressive albuminuria and glomerulosclerosis within 13 weeks, accompanied by increased intrarenal production of angiotensin (Ang) II, fibronection, TGF-beta, and MCP-1 and decreased expression of slit diaphragm proteins. Treatment of the diabetic mice with losartan or paricalcitol (19-nor-1,25-dihydroxyvitamin D(2), an activated vitamin D analog) alone moderately ameliorated kidney injury; however, combined treatment with losartan and paricalcitol completely prevented albuminuria, restored glomerular filtration barrier structure, and markedly reduced glomerulosclerosis. The combined treatment suppressed the induction of fibronection, TGF-beta, and MCP-1 and reversed the decline of slit diaphragm proteins nephrin, Neph-1, ZO-1, and alpha-actinin-4. These were accompanied by blockade of intrarenal renin and Ang II accumulation induced by hyperglycemia and losartan. These data demonstrate that inhibition of the RAS with combination of vitamin D analogs and RAS inhibitors effectively prevents renal injury in diabetic nephropathy.

Loss of vitamin D receptor produces polyuria by increasing thirst

Vitamin D receptor (VDR)-null mice develop polyuria, but the underlying mechanism remains unknown. In this study, we investigated the relationship between vitamin D and homeostasis of water and electrolytes. VDR-null mice had polyuria, but the urine osmolarity was normal as a result of high salt excretion. The urinary responses to water restriction and to vasopressin were similar between wild-type and VDR-null mice, suggesting intact fluid-handling capacity in VDR-null mice. Compared with wild-type mice, however, renin and angiotensin II were dramatically upregulated in the kidney and brain of VDR-null mice, leading to a marked increase in water intake and salt appetite. Angiotensin II-mediated upregulation of intestinal NHE3 expression partially explained the increased salt absorption and excretion in VDR-null mice. In the brain of VDR-null mice, expression of c-Fos, which is known to associate with increased water intake, was increased in the hypothalamic paraventricular nucleus and the subfornical organ. Treatment with an angiotensin II type 1 receptor antagonist normalized water intake, urinary volume, and c-Fos expression in VDR-null mice. Furthermore, despite a salt-deficient diet to reduce intestinal salt absorption, VDR-null mice still maintained the increased water intake and urinary output. Together, these data indicate that the polyuria observed in VDR-null mice is not caused by impaired renal fluid handling or increased intestinal salt absorption but rather is the result of increased water intake induced by the increase in systemic and brain angiotensin II.

Targeted vitamin D receptor expression in juxtaglomerular cells suppresses renin expression independent of parathyroid hormone and calcium

Previously, we showed that vitamin D receptor gene knockout leads to hyperreninemia independent of calcium metabolism; however, the contribution of parathyroid hormone to renin upregulation remained unclear. Here we separated the role of vitamin D and parathyroid hormone in the regulation of renin expression in vivo by generating transgenic mice that overexpressed the human vitamin D receptor in renin-producing cells using the 4.1 kb Ren-1c gene promoter. Targeting of human vitamin D receptor to the juxtaglomerular cells of the mice was confirmed by immunohistochemistry. Renal renin mRNA levels and plasma renin activity were decreased in these transgenic mice by about 50% and 30%, respectively, with no significant change in blood pressure, calcium, or parathyroid hormone levels. Moreover using vitamin D receptor knockout mice, we found that expression of the human receptor in their juxtaglomerular cells reduced renin expression in these mice without affecting calcium or parathyroid hormone status. Our study shows that suppression of renin expression by 1,25-dihydroxyvitamin D in vivo is independent of parathyroid hormone and calcium.

In vivo analysis of key elements within the renin regulatory region

Renin is responsible for initiating the enzymatic cascade that results in the production of angiotensin II, the major effector molecule of the renin-angiotensin system (RAS). Extensive information on the regulatory region of the renin gene has been derived by transient transfection studies in vitro, particularly using the As4.1 cell line. To verify key factors within the regulatory region of renin in vivo, homologous recombination was used to introduce a green fluorescent protein (GFP) cassette into exon one of the renin gene contained within a 240 kb bacterial artificial chromosome (BAC) to create a construct that has GFP expression controlled by the renin regulatory region (RenGFP BAC). Within the regulatory region of the RenGFP BAC construct we independently deleted the enhancer, as well as mutated the HOX-PBX site within the proximal promoter element. Transgenic lines were generated for each of these BAC constructs and GFP expression was analyzed throughout a spectrum of tissues positive for renin expression including the kidney, adrenal gland, gonadal artery, and submandibular gland. The results described within this manuscript support the interpretation that the renin enhancer is critical for regulating baseline expression where as the Hox/Pbx site is important for the tissue specificity of renin expression.

The Pal3 promoter sequence is critical for the regulation of human renin gene transcription by peroxisome proliferator-activated receptor-gamma

We recently reported that human renin gene transcription is stimulated by the nuclear receptor peroxisome proliferator-activated receptor (PPAR)-gamma in the renin-producing cell line Calu-6. The effect of PPARgamma was mapped to two sequences in the renin promoter: a direct repeat hormone response element (HRE), which is related to the classical PPAR response element (PPRE) and a nonconsensus palindromic element with a 3-bp spacer (Pal3). We now find that PPARgamma binds to the renin HRE. Neither the human renin HRE nor the consensus PPRE was sufficient to attain the maximal stimulation of renin promoter activity by the PPARgamma agonist rosiglitazone. In contrast, the human renin Pal3 element mediates both the full PPARgamma-dependent activation of transcription and the PPARgamma-driven basal renin gene transcription. The human renin Pal3 sequence was found to selectively bind PPARgamma and the retinoid X receptor-alpha from Calu-6 nuclear extracts. This is in contrast to the consensus PPRE, which can bind other nuclear proteins. PPARgamma knockdown paradoxically did not attenuate the stimulation of the endogenous renin gene expression by rosiglitazone. Similarly, a deficiency of PPARgamma did not attenuate the activation of the minimal human renin promoter, which contains the endogenous Pal3 motif. However, when the human renin Pal3 site was replaced by the consensus PPRE sequence, PPARgamma knockdown abrogated the effect of rosiglitazone on renin promoter activity. Thus, the human renin Pal3 site appears to be critical for the PPARgamma-dependent regulation of gene expression by mediating maximal transcription activation, particularly at the low cellular level of PPARgamma.