Mechanistic analysis of VDR-mediated renin suppression.

BACKGROUND: The vitamin D receptor (VDR) is involved in the regulation of renin expression and vitamin D analogs down-regulated renin mRNA expression in As4.1 cells. METHODS: Microarray analysis was used to assess the VDR-mediated gene expression profile in As4.1 cells treated with paricalcitol, followed by real-time RT-PCR. Mechanistic analyses were done using siRNA, electrophoretic mobility shift assay (EMSA) and Western blotting. RESULTS: Microarray analysis shows that 709 target genes were affected by paricalcitol with 286 up- and 423 downregulated. A number of major pathways were impacted including transcription factors. Real-time RT-PCR confirmed the microarray results. Treatment of the cells with siRNA against nuclear receptor co-repressor (NCOR1) eliminated VDR-mediated renin suppression. Using EMSA, paricalcitol treatment reduced the level of protein complex binding to the cyclic AMP-responsive element (CRE)-like domain in the renin distal enhancer region. VDR, CRE-binding protein (CREB1) and NCOR1 were identified in the complex binding to the CRE-like domain by Western blot in the paricalcitol-treated cells. Paricalcitol treatment resulted in an increase in the VDR level, but no significant change in the CREB1 and NCOR1 levels. CONCLUSION: These results suggest that VDR-mediated renin suppression likely acts through a transcriptional regulatory complex including CREB1, NCOR1 and VDR that binds to the CRE-like domain in the renin enhancer region.

siRNA-mediated off-target gene silencing triggered by a 7 nt complementation.

A growing body of evidence suggests that siRNA could generate off-target effects through different mechanisms. However, the full impact of off-target gene regulation on phenotypic induction and accordingly on data interpretation in the context of large-scale siRNA library screen has not been reported. Here we report on off-target gene silencing effects observed in a large-scale knockdown experiment designed to identify novel regulators of the HIF-1 pathway. All of the three 'top hits' from our screen have been demonstrated to result from off-target gene silencing. Two of the three 'siRNA hits' were found to directly trigger down-regulation of hif-1alpha mRNA through a 7 nt motif, AGGCAGT, that is present in both the hif-1alpha mRNA and the siRNAs. Further analysis revealed that the generation of off-target gene silencing via this 7 nt motif depends on the characteristics of the target mRNA, including the sequence context surrounding the complementary region, the position of the complementary region in the mRNA and the copy number of the complementary region. Interestingly, the off-target siRNA against hif-1alpha was also shown to trigger mRNA degradation with high probability of other genes that possess multiple copies of the AGGCAGT motif in the 3'-untranslated region. Lessons learned from this study will be a valuable asset to aid in designing siRNAs with more stringent target selectivity and improving 'hits-follow-up' strategies for future large-scale knockdown experiments.

Effects of Vitamin D analogs on gene expression profiling in human coronary artery smooth muscle cells.

Vitamin D analogs provide survival benefit for chronic kidney disease patients with cardiovascular complications. Activation of smooth muscle cells plays a role in cardiovascular diseases. It is not known how Vitamin D analogs modulate gene expression in smooth muscle cells. In this study, DNA microarray technology was used to assess the gene expression profile in human coronary artery smooth muscle cells treated with 0.1microM 1alpha,25-dihydroxyvitamin D3 (calcitriol) or paricalcitol (an analog of calcitriol) for 30 h. The effects of calcitriol and paricalcitol were similar. A total of 176 target genes were identified with 115 up-regulated and 61 down-regulated genes in the paricalcitol group. Target genes fall into various categories including cell differentiation/proliferation. Real-time RT-PCR analysis demonstrated that paricalcitol dose- and time-dependently regulated the expression of IGF1, WT1 and TGFbeta3, three genes known to modulate cell proliferation. Paricalcitol also down-regulated the expression of natriuretic peptide precursor B and thrombospondin 1. Both drugs inhibited cell proliferation in a dose-dependent manner. This study identified genes not previously known to be regulated by VDR, providing insight into understanding the role of VDR on regulating smooth muscle cell growth, thrombogenicity, fibrinolysis and endothelial regeneration.

Expression of VDR and CYP24A1 mRNA in human tumors.

1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and its analogues have been shown to inhibit proliferation of human cancer cells mediated by vitamin D receptor (VDR). The over-expression of 25-hydroxyvitamin D-24-hydroxylase (CYP24A1), an enzyme involved in the metabolism of 1,25(OH)2D3 and its analogues, is associated with poor prognosis of some human cancers. In this study, we employed real-time reverse transcription PCR to examine the expression of VDR and CYP24A1 mRNA in a cohort of human breast, lung, colon and ovary tumor samples. We found that CYP24A1 mRNA was significantly up-regulated in colon, ovary and lung tumors, but down-regulated in breast tumor relative to the analogous normal tissues. As a comparison, VDR mRNA was modestly down-regulated in colon, breast and lung tumors, but highly up-regulated in ovarian tumors. Treatment of two breast cancer cell lines, SW-620 and MCF-7, and one colon cancer cell line, HT-29, by 1,25(OH)2D3 for 48 h profoundly stimulated CYP24A1 mRNA expression (EC50=0.6, 0.8 and 29.5 nM in SW-620, HT-29 and MCF-7, respectively), but did not significantly affect VDR mRNA expression. Growth as assessed by DNA synthesis was modestly arrested by 1,25(OH)2D3 after 72 h of incubation, but was not altered after a 5-day incubation period. These data suggest that the VDR signaling pathway may be compromised via the modulation of CYP24A1 and VDR in human tumors.

Evidence for tolerance following repeated dosing in rats with ciproxifan, but not with A-304121.

Blockade of presynaptic histamine H(3) receptors with potent and selective ligands improves cognitive function in rodents and there is significant interest in developing such drugs for long-term symptomatic treatment of CNS disorders such as attention deficit hyperactivity disorder (ADHD). Unfortunately, little is known about the effects of repeated exposure to H(3) receptor antagonists/inverse agonists. We therefore investigated the effects of acute and repeated daily administration of two potent, brain penetrating H(3) receptor antagonists/inverse agonists, ciproxifan and A-304121, on rat body weight, food and water intake, core temperature and locomotor activity, as well as H(3) receptor density and gene expression levels. Methylphenidate, used clinically for the treatment of ADHD, was included as an additional comparator. Ciproxifan, an imidazole-based compound, decreased food intake over the first 10 days and locomotor activity acutely, but these effects were lost after further repeated administration. The ex vivo binding studies revealed increased H(3) receptor density in rats following repeated administration of ciproxifan for 10 or 15 days; however, H(3) receptor gene expression was not changed. In contrast, rats treated with the non-imidazole, A-304121, did not differ from controls on any measure during the observation period, while rats treated with methylphenidate exhibited hyperthermia and hyperactivity. The implications for potential long-term treatment with H(3) receptor antagonists in CNS disorders such as ADHD are discussed.

Cardiovascular disease in chronic kidney failure: is there a role for vitamin D analogs?

Vitamin D3 is modified by vitamin D3-25-hydroxylase in the liver, and 25-hydroxyvitamin D3-1alpha-hydroxylase in the kidney, to form the active metabolite, 1,25-dihydroxyvitamin D3. Chronic kidney disease (CKD) is characterized by reduced synthesis of 1,25-dibydroxyvitamin D3, inadequate renal phosphate clearance and calcium imbalance, secondary hyperparathyroidism (SHPT) and bone disease. CKD patients encounter a much higher risk of cardiovascular disease (CVD) than the general public. The cardiovascular risk factors for CKD patients include conventional factors such as age, gender, hypertension, diabetes, dyslipidemia and smoking, and non-conventional factors, such as anemia, uremia, reduced vascular compliance, inflammation and various hormonal factors. Several vitamin D analogs are currently available for the treatment of SHPT, and recent clinical data show that these analogs provide survival benefit for CKD patients in the order of paricalcitol > calcitriol > no vitamin D analog, independent of parathyroid hormone and calcium. Moreover, the survival benefit seems to be associated with cardiovascular causes. The observations made from these clinical studies raised intriguing questions about the involvement of the vitamin D receptor locus (VDR) in the cardiovascular system. This review discusses recent data regarding the role of vitamin D and its analogs in the CVD associated with CKD.

Protein tyrosine phosphatase 1B negatively regulates leptin signaling in a hypothalamic cell line.

Protein tyrosine phosphatase 1B (PTP1B) has recently been implicated in the regulation of body weight. A surprising phenotype of PTP1B-deficient mice is their resistance to diet-induced obesity. Since leptin is one of the primary hormones involved in the regulation of body weight and energy homeostasis, we investigated whether PTP1B affects leptin receptor (lepR) signaling directly. A mouse hypothalamic cell line, GT1-7, was established as a suitable cell model for the study of leptin signaling. Stimulation of GT1-7 cells by leptin caused tyrosine phosphorylation of endogenous STAT3 and activation of a STAT-dependent luciferase reporter gene. Over-expression of PTP1B in GT1-7 cells resulted in a dose-dependent decrease in endogenous JAK2 and STAT3 tyrosine phosphorylation compared with cells transfected with lepR alone. Consistent with inhibition of JAK-STAT signaling, PTP1B over-expression caused a dose-dependent decrease in leptin-induced, STAT-dependent luciferase reporter gene activation in GT1-7 cells. Furthermore, over-expression of PTP1B led to a decrease in mRNA accumulation of suppressor-of-cytokine-signalling-3 (SOCS3) and c-fos, genes that are acutely induced by leptin. Using gene microarray analysis, we confirmed that PTP1B reduces the level of gene expression of SOCS3 and showed that the expression level of other leptin-regulated genes was affected. Genes up-regulated by leptin were decreased in cells over-expressing PTP1B. Conversely, the expression of genes down-regulated by leptin was enhanced by PTP1B over-expression in GT1-7 cells. Our findings indicate that PTP1B is a negative regulator of leptin signaling and suggest that PTP1B inhibitors might be efficacious in the treatment of obesity by increasing leptin sensitivity.

In vitro and in vivo effects of an alpha3 neuronal nicotinic acetylcholine receptor antisense oligonucleotide.

In the mammalian central nervous system (CNS), a family of alpha and beta subunits (alpha2-7, beta2-4) assemble to form both hetero- and homopentameric neuronal nicotinic acetylcholine receptors (nAChRs). In contrast to alpha4beta2 and alpha7, the predominant brain subtypes, far less is known regarding the functional expression and significance of alpha3-containing nAChRs in the CNS. In trying to better understand the role alpha3 in the CNS, an antisense knockdown strategy was utilized in the present studies. Specifically, Isis 106567 was identified out of 80 antisense oligonucleotides (aONs) designed and screened for their ability to reduce alpha3 mRNA expression in PC-12 cells. In addition to reducing alpha3 mRNA by greater than 75%, Isis 106567 attenuated nicotine-induced calcium influx in alpha3-expressing F11 cells. In vivo studies revealed significant reduction of alpha3 mRNA levels in both thalamus and medial habenula, regions known to express alpha3, following continuous (7 days) intracerebroventricular (i.c.v.) infusion of Isis 106567 in rats. Consistent with functional alpha3 knockdown, epibatidine-induced c-Fos expression in the medial habenula was attenuated in aON-treated rats. Known physiological responses elicited by epibatidine, such as hypothermia and micturition, were not affected by alpha3 aON treatment. However, the incidence of epibatidine-induced seizures was reduced in alpha3-antisense aON-treated rats, suggesting that alpha3 may be involved in mediating seizures produced by the nAChR agonist. Results of our studies suggest that Isis 106567 may be a useful in vivo tool for characterizing the functional significance of alpha3 expression in the CNS.

Differential action potentials and firing patterns in injured and uninjured small dorsal root ganglion neurons after nerve injury.

The profile of tetrodotoxin sensitive (TTX-S) and resistant (TTX-R) Na(+) channels and their contribution to action potentials and firing patterns were studied in isolated small dorsal root ganglion (DRG) neurons after L5/L6 spinal nerve ligation (SNL). Total TTX-R Na(+) currents and Na(v) 1.8 mRNA were reduced in injured L5 DRG neurons 14 days after SNL. In contrast, TTX-R Na(+)currents and Na(v) 1.8 mRNA were upregulated in uninjured L4 DRG neurons after SNL. Voltage-dependent inactivation of TTX-R Na(+) channels in these neurons was shifted to hyperpolarized potentials by 4 mV. Two types of neurons were identified in injured L5 DRG neurons after SNL. Type I neurons (57%) had significantly lower threshold but exhibited normal resting membrane potential (RMP) and action potential amplitude. Type II neurons (43%) had significantly smaller action potential amplitude but retained similar RMP and threshold to those from sham rats. None of the injured neurons could generate repetitive firing. In the presence of TTX, only 26% of injured neurons could generate action potentials that had smaller amplitude, higher threshold, and higher rheobase compared with sham rats. In contrast, action potentials and firing patterns in uninjured L4 DRG neurons after SNL, in the presence or absence of TTX, were not affected. These results suggest that TTX-R Na(+) channels play important roles in regulating action potentials and firing patterns in small DRG neurons and that downregulation in injured neurons and upregulation in uninjured neurons confer differential roles in shaping electrogenesis, and perhaps pain transmission, in these neurons.

Identification of expression signatures predictive of sensitivity to the Bcl-2 family member inhibitor ABT-263 in small cell lung carcinoma and leukemia/lymphoma cell lines.

ABT-263 inhibits the antiapoptotic proteins Bcl-2, Bcl-x(L), and Bcl-w and has single-agent efficacy in numerous small cell lung carcinoma (SCLC) and leukemia/lymphoma cell lines in vitro and in vivo. It is currently in clinical trials for treating patients with SCLC and various leukemia/lymphomas. Identification of predictive markers for response will benefit the clinical development of ABT-263. We identified the expression of Bcl-2 family genes that correlated best with sensitivity to ABT-263 in a panel of 36 SCLC and 31 leukemia/lymphoma cell lines. In cells sensitive to ABT-263, expression of Bcl-2 and Noxa is elevated, whereas expression of Mcl-1 is higher in resistant cells. We also examined global expression differences to identify gene signature sets that correlated with sensitivity to ABT-263 to generate optimal signature sets predictive of sensitivity to ABT-263. Independent cell lines were used to verify the predictive power of the gene sets and to refine the optimal gene signatures. When comparing normal lung tissue and SCLC primary tumors, the expression pattern of these genes in the tumor tissue is most similar to sensitive SCLC lines, whereas normal tissue is most similar to resistant SCLC lines. Most of the genes identified using global expression patterns are related to the apoptotic pathway; however, all but Bcl-rambo are distinct from the Bcl-2 family. This study leverages global expression data to identify key gene expression patterns for sensitivity to ABT-263 in SCLC and leukemia/lymphoma and may provide guidance in the selection of patients in future clinical trials.

Elevated phosphorus modulates vitamin D receptor-mediated gene expression in human vascular smooth muscle cells.

Clinical observations show that an increase in serum inorganic phosphorus (Pi) is linked to higher cardiovascular (CV) mortality, while vitamin D receptor (VDR) agonist therapy is associated with survival benefit in stage 5 chronic kidney disease. Smooth muscle cells (SMCs) play an important role in CV pathophysiology, but the interaction between Pi and the VDR signaling pathway in SMCs is not known. Real-time RT-PCR studies revealed that elevated Pi (2.06 mM) modulated VDR-mediated regulation of a panel of genes including thrombomodulin and osteopontin in SMCs. DNA microarray results demonstrated that increasing Pi from 0.9 to 2.06 mM exerted a widespread modulating effect on VDR-mediated gene expression. A total of 325 target genes were affected by paricalcitol at 0.9 mM Pi, with 195 up- and 130 downregulated. The number of target genes affected by paricalcitol at 2.06 mM Pi decreased to 86, with 55 up- and 31 downregulated. VDR-mediated gene expression in As4.1 cells (a juxtaglomerular cell-like cell line derived from kidney tumors in SV40 T-antigen transgenic mice) and peroxisome proliferator-activated receptor (PPAR)gamma-mediated gene expression in SMCs were also altered by elevated Pi, suggesting that the observation is not unique to VDR in SMCs. Mechanism analysis showed that elevated Pi had no significant effect on VDR or PPARgamma protein level but altered the cytosolic vs. nuclear distribution of NF-kappaB or nuclear receptor corepressor 1 (NCoR1). Our results demonstrate for the first time that elevated Pi affects VDR-mediated gene expression in human coronary artery SMCs and the effect is not limited to VDR in SMCs.

VDR-mediated gene expression patterns in resting human coronary artery smooth muscle cells.

Vitamin D analogs such as paricalcitol and calcitriol that activate the vitamin D receptor (VDR) provide survival benefit for Stage 5 chronic kidney disease (CKD) patients, possibly associated with a decrease in cardiovascular (CV)-related incidents. Phenotypic changes of smooth muscle cells play an important role in CV disease. The role of vitamin D analogs in modulating gene expression in smooth muscle cells is still not well understood. In this study, DNA microarray analysis of approximately 22,000 different human genes was used to characterize the VDR-mediated gene expression profile in human coronary artery smooth muscle cells (CASMC) at rest. Cells in serum free medium were treated with 0.1 microM calcitriol (1alpha,25-dihydroxyvitamin D(3)) or paricalcitol (19-nor-1alpha,25-(OH)(2)D(2)) for 30 h. A total of 181 target genes were identified, with 103 genes upregulated and 78 downregulated (>two fold changes in either drug treatment group with P < 0.01). No significant difference was observed between calcitriol and paricalcitol. Target genes fell into various categories with the top five in cellular process, cell communication, signal transduction, development, and morphogenesis. Twenty-two selected genes linked to the CV system were also impacted. Real-time RT-PCR and/or Western blotting analysis were employed to confirm the expression patterns of selected genes such as 25-hydroxyvitamin D-24-hydroxylase, Wilms' tumor gene 1, transforming growth factorbeta3, plasminogen activator inhibitor-1, thrombospondin-1 (THBS1), and thrombomodulin (TM). This study provides insight into understanding the role of VDR in regulating gene expression in resting smooth muscle cells.

Activated vitamin D attenuates left ventricular abnormalities induced by dietary sodium in Dahl salt-sensitive animals.

Observations in hemodialysis patients suggest a survival advantage associated with activated vitamin D therapy. Left ventricular (LV) structural and functional abnormalities are strongly linked with hemodialysis mortality. Here, we investigated whether paricalcitol (PC, 19-nor-1,25(OH)(2)D(2)), an activated vitamin D compound, attenuates the development of LV abnormalities in the Dahl salt-sensitive (DSS) rat and whether humans demonstrate comparable findings. Compared with DSS rats fed a high-salt (HS) diet (6% NaCl for 6 weeks), HS+PC was associated with lower heart and lung weights, reduced LV mass, posterior wall thickness and end diastolic pressures, and increased fractional shortening. Blood pressures did not significantly differ between the HS groups. Plasma brain natriuretic peptide levels, and cardiac mRNA expression of brain natriuretic peptide, atrial natriuretic factor, and renin were significantly reduced in the HS+PC animals. Microarray analyses revealed 45 specific HS genes modified by PC. In a retrospective pilot study of hemodialysis patients, PC-treated subjects demonstrated improved diastolic function and a reduction in LV septal and posterior wall thickness by echocardiography compared with untreated patients. In summary, PC attenuates the development of LV alterations in DSS rats, and these effects should be examined in human clinical trials.

TRPV1b overexpression negatively regulates TRPV1 responsiveness to capsaicin, heat and low pH in HEK293 cells.

Transient receptor potential channel type V (TRPV) 1 is a non-selective cation channel that can be activated by capsaicin, endogenous vanilloids, heat and protons. The human TRPV1 splice variant, TRPV1b, lacking exon 7, was cloned from human dorsal root ganglia (DRG) RNA. The expression profile and relative abundance of TRPV1b and TRPV1 in 35 different human tissues were determined by quantitative RT-PCR using isoform-specific probes. TRPV1b was most abundant in fetal brain, adult cerebellum and DRG. Functional studies using electrophysiological techniques showed that recombinant TRPV1b was not activated by capsaicin (1 microM), protons (pH 5.0) or heat (50 degrees C). However, recombinant TRPV1b did form multimeric complexes and was detected on the plasma membrane of cells, demonstrating that the lack of channel function was not due to defects in complex formation or cell surface expression. These results demonstrate that exon 7, which encodes the third ankyrin domain and 44 amino acids thereafter, is required for normal channel function of human TRPV1. Moreover, when co-expressed with TRPV1, TRPV1b formed complexes with TRPV1, and inhibited TRPV1 channel function in response to capsaicin, acidic pH, heat and endogenous vanilloids, dose-dependently. Taken together, these data support the hypothesis that TRPV1b is a naturally existing inhibitory modulator of TRPV1.

PTP1B antisense oligonucleotide lowers PTP1B protein, normalizes blood glucose, and improves insulin sensitivity in diabetic mice.

The role of protein-tyrosine phosphatase 1B (PTP1B) in diabetes was investigated using an antisense oligonucleotide in ob/ob and db/db mice. PTP1B antisense oligonucleotide treatment normalized plasma glucose levels, postprandial glucose excursion, and HbA(1C). Hyperinsulinemia was also reduced with improved insulin sensitivity. PTP1B protein and mRNA were reduced in liver and fat with no effect in skeletal muscle. Insulin signaling proteins, insulin receptor substrate 2 and phosphatidylinositol 3 (PI3)-kinase regulatory subunit p50alpha, were increased and PI3-kinase p85alpha expression was decreased in liver and fat. These changes in protein expression correlated with increased insulin-stimulated protein kinase B phosphorylation. The expression of liver gluconeogenic enzymes, phosphoenolpyruvate carboxykinase, and fructose-1,6-bisphosphatase was also down-regulated. These findings suggest that PTP1B modulates insulin signaling in liver and fat, and that therapeutic modalities targeting PTP1B inhibition may have clinical benefit in type 2 diabetes.