A235 ILEAL MICROBIOME ALPHA DIVERSITY REMAINS LOWER IN ENDOSCOPICALLY AND HISTOLOGICALLY INACTIVE CROHN’S DISEASE COMPARED TO ULCERATIVE COLITIS OR HEALTHY CONTROLS

Background

Crohn’s disease (CD) has been associated with a lower alpha diversity when compared to ulcerative colitis (UC) patients and healthy controls (HC), which also depends on disease location and endoscopic activity. However, it is unclear whether the resolution of histologic inflammation may influence mucosal alpha diversity in the ileum.

Aims

To characterize the ileal mucosa-associated microbiome diversity in subjects with ileal predominant CD (iCD) in endoscopic (ER) and endo-histologic (EHR) remission, compared to subjects with colonic predominant CD (cCD), UC and HC, respectively.

Methods

Data from a large cohort of subjects recruited at Mount Sinai Hospital Toronto (2009–2016) was analyzed. ER was defined as a segmental Simple Endoscopic Score for CD of <3 in the ileum. EHR was defined as ER with the absence of active histologic inflammation in ileal biopsies. CD patients were divided according to the Montreal classification into iCD (L1 and L3) and cCD (L2) and compared against UC patients without backwash ileitis and HC. Patients with history of ileocecal resection and/or antibiotic use at baseline were excluded. Microbial 16S rRNA gene was sequenced using the Illumina MiSeq and processed using QIIME2. Alpha diversity was measured using the Shannon index and compared using Kruskal-Wallis test and further pairwise Wilcoxon with Holm correction. An adjusted p-value < 0.05 was considered significant.

Results

We included 35 CD patients with ileal ER, 81 UC patients and 32 HC. Among CD patients, 20/35 (57.1%) and 15/35 (42.9%) had iCD and cCD, respectively. Ileal mucosal alpha diversity was significantly lower in iCD patients in ER compared with that of UC patients (q=0.004) and HC (q=0.001). No differences in ileal mucosal alpha-diversity were seen between iCD than cCD patients (q=0.12). When histology was included to classify CD and UC patients as EHR, the ileal alpha diversity of iCD patients remained reduced compared to UC patients and HC (q=0.008 and q=0.002, respectively). Again, ileal mucosal alpha-diversity was not significantly lower in iCD than cCD patients among those in ileal EHR (q=0.24).

Conclusions

Ileal mucosa of CD patients in ER and EHR have lower alpha diversity than UC and HC. These findings suggest that the ileal mucosa of CD patients remains dysbiotic despite achieving endoscopic and histologic remission.

Funding Agencies

IBD Genetics Consortium

A161 MUCOSAL TRANSCRIPTOMICS IN NON-INFLAMED ILEUM OF CROHN’S DISEASE PATIENTS SHOWS DIFFERENTIALLY EXPRESSED GENE PROFILE COMPARED TO ILEUM OF HEALTHY CONTROLS

Background

The terminal ileum is the most susceptible location to develop Crohn’s disease (CD) and therefore is a valuable tissue to investigate biological mechanisms underlying chronic inflammation. Gene expression is highly affected by the level of inflammation, however, data on ileal transcriptomic profile in the absence of active inflammation is limited.

Aims

To investigate the ileal mucosal transcriptomic profile of CD patients in endoscopic and histologic remission compared to healthy controls (HC).

Methods

Ileal biopsies were collected during colonoscopy from patients with CD and HC. Biopsies were classified as non-inflamed based on endoscopic appearance and histologic criteria. Endo-histologic remission (EHR) was defined as simple endoscopic score < 3 and absence of active histologic inflammation. We included CD patients with EHR and HC for the analysis of this study. CD phenotype was divided into isolated colonic CD (cCD) that included Montreal L2 and ileal predominant CD (iCD) that included Montreal L1 and L3. Total RNA was extracted from samples, sequenced using a HiSeq 2500 instrument (Illumina, San Diego, CA, USA) and differential expression analysis was performed in EdgeR. Genes that were differentially expressed at the average of 2-fold-change (FC) in mean expression and False Discovery Rate (FDR) < 0.05 were considered significant.

Results

Ileal samples from 14 CD patients in EHR and 29 HC were included in the analysis. CD patients were significantly younger (median age 28.5 years, interquartile range (IQR)=24–40) compared with HC (median age 56 years, IQR=51–64). There were no differences in gender distribution (42.9% males in CD and 55.2% males in HC). We found 101 differentially expressed genes in CD patients compared to HC (99 genes were up-regulated and two were down-regulated). Dual oxidase 2 (DUOX2) and complement C6 were respectively the most significant up-regulated (logFC=4.45, FDR=1.3e-8) and down-regulated (logFC=-2.73, FDR=0.0006) genes in non-inflamed ileum CD group when compared with HC. In a subgroup analysis comparing ileal samples of CD patients with cCD (n=8) versus iCD phenotype (n=6), no differentially expressed genes were identified.

Conclusions

The mucosal transcriptomic profile of patients with inactive endoscopic and histologic ileal CD shows significant differentially expressed gene profile compared to ileal mucosa of HC. The clinical relevance of these findings should be further investigated.

Funding Agencies

IBD Genetics Consortium

A156 MUCOSA-ASSOCIATED MICROBIOTA OF ILEOCOLONIC CROHN’S DISEASE PATIENTS IS DISTINCT FROM COLONIC CROHN’S DISEASE AND ULCERATIVE COLITIS PATIENTS INDEPENDENT OF BIOPSY SITE, ENDOSCOPIC INFLAMMATION AND HOST GENETICS

Background

Colonic IBD encompassing ulcerative colitis (UC) and isolated colonic Crohn’s disease (cCD) shows significant clinical, therapeutic response and genetic differences compared to ileocolonic CD (icCD). Elucidating the microbial signatures characterizing these subphenotypes could help to understand the causal factors underlying these clinical dissimilarities

Aims

We compared the mucosal microbial diversity and differential abundance (DA) among disease locations (UC, cCD and icCD) accounting for potential clinical, endoscopic, and genetic confounders

Methods

Healthy control (HC), UC, cCD and icCD patients (including ileal and ileocolonic involvement) underwent colonoscopy. Biopsy samples were obtained from terminal ileum (TI), ascending colon (AC) and sigmoid colon (SC) for 16s rRNA gene profiling. Patients with prior ileocecal resection, IBD-unclassified and antibiotic exposure within 3 months before colonoscopy were excluded. Endoscopic inflammation was defined as a segmental Mayo endoscopic subscore = 0 in UC and a simple endoscopic score ≤ 2 in CD. A blood sample was drawn for genotyping and a weighted genetic risk score (GRS) was built based on 169 IBD risk variants found in our cohort. Alpha diversity (Chao1) and DA between IBD subphenotypes were compared using a linear mixed-effects model with subjects as random effect and adjusted for biopsy site, endoscopic inflammation, age, sex, and GRS. For DA analysis, the MaAsLin2 protocol was applied. All p-values were corrected by false discovery rate (FDR) with < 0.05 considered significant

Results

A total of 199 IBD patients and 44 HC with a mean age of 37.2 ± 14 were recruited. Of these, 113 (46.5%) were female. At colonoscopy, 535 biopsy samples (TI = 178, AC = 123 and SC = 234) were obtained. Considering disease location, 254, 55 and 148 samples were obtained from UC, cCD and icCD patients, respectively. A total of 168 samples (31.4%) showed endoscopic inflammation. Alpha diversity was significantly reduced in icCD when compared to either HC, UC or cCD. MaAsLin2 identified that the genera Agathobacter and Faecalibacterium, as well as the family Ruminococacceae and the order Oscillospirales were significantly reduced in icCD when compared to either HC, UC or cCD. These findings were independent of age, sex, endoscopic inflammation, biopsied site, and GRS. UC and cCD did not show differences in their microbial profile

Conclusions

Mucosal samples from UC and cCD patients showed marked similarities in their microbial profile while icCD is characterized by a significant decrease in diversity and beneficial microbes. These data suggest that disease location is the main driver of the mucosal microbial landscape independent of IBD GRS

Funding Agencies

NoneNIDDK IBD Genetics Consortium

Combined Histo-endoscopic Remission but not Endoscopic Healing Alone in Ulcerative Colitis is Associated with a Mucosal Transcriptional Profile Resembling Healthy Mucosa

BACKGROUND AND AIMS

A composite endpoint of histological and endoscopic remission is proposed to be the most complete measure of mucosal healing in ulcerative colitis [UC]. We aim to establish the prognosis, and transcriptional and microbial features of histo-endoscopic remission and activity.

METHODS

A cross-sectional endoscopic rectosigmoid colon sample collection from UC patients and healthy controls [HC] was performed for histopathology and host genome-wide RNA-sequencing. Histo-endoscopic remission and histo-endoscopic activity were defined as Mayo endoscopic subscore [MES] 0-1 with and without histological activity, respectively. UC relapse, defined as symptomatic and endoscopic worsening, was retrospectively recorded for survival analysis. Unsupervised and differential gene expression analyses were performed, and the interaction between transcriptomics and mucosal gut microbiota was analysed based on the 16S rRNA gene sequencing profile.

RESULTS

UC patients with histo-endoscopic remission showed a significantly lower risk of relapse compared to histo-endoscopic activity. Unsupervised analysis of the transcriptomic profile showed that histo-endoscopic remission and histo-endoscopic activity samples clustered with HC and MES 2-3 samples, respectively. A total of 452 host genes enriched for humoral immune response, antimicrobial defence, chemokine and TH17 signalling pathway were upregulated in histo-endoscopic activity compared to histo-endoscopic remission. A set of host genes with antimicrobial properties showed significant associations with mucosal microbiota.

CONCLUSIONS

The rectosigmoid mucosa transcriptional profile of UC patients in histo-endoscopic remission resembles that of HC mucosa and confers a lower risk of relapse. These data support that the combination of histo-endoscopic remission could be the most appropriate definition of mucosal healing in UC.

A Role for CXCR3 Ligands as Biomarkers of Post-Operative Crohn's Disease Recurrence

BACKGROUND AND AIMS

Crohn's disease [CD] recurrence following ileocolic resection [ICR] is common. We sought to identify blood-based biomarkers associated with CD recurrence.

METHODS

CD patients undergoing ICR were recruited across six centres. Serum samples were obtained at post-operative colonoscopy. A multiplex immunoassay was used to analyse 92 inflammation-related proteins [Olink Proteomics]. Bayesian analysis was used to identify proteins associated with increasing Rutgeerts score. Identified proteins were used in receiver operating characteristic [ROC] analysis to examine the ability to identify CD recurrence [Rutgeerts score ≥i2]. Existing single cell data were interrogated to further elucidate the role of the identified proteins.

RESULTS

Data from 276 colonoscopies in 213 patients were available. Median time from surgery to first and second colonoscopy was 7 (interquartile range [IQR] 6-9) and 19 [IQR 16-23] months, respectively. Disease recurrence was evident at 60 [30%] first and 36 [49%] second colonoscopies. Of 14 proteins significantly associated with Rutgeerts score, the strongest signal was seen for CXCL9 and MMP1. Among patients on anti-tumour necrosis factor drugs, CXCL9 and CXCL11 were most strongly associated with Rutgeerts score. Both are CXCR3 ligands. Incorporation of identified proteins into ROC analysis improved the ability to identify disease recurrence as compared to C-reactive protein alone: area under the curve [AUC] 0.75 (95% confidence interval [CI]: 0.66-0.82] vs 0.64 [95% CI 0.56-0.72], p = 0.012. Single cell transcriptomic data provide evidence that innate immune cells are the primary source of the identified proteins.

CONCLUSIONS

CXCR3 ligands are associated with CD recurrence following ICR. Incorporation of novel blood-based candidate biomarkers may aid in identification of CD recurrence.

Integrative Analysis of Colonic Biopsies from Inflammatory Bowel Disease Patients Identifies an Interaction Between Microbial Bile Acid-inducible Gene Abundance and Human Angiopoietin-like 4 Gene Expression

BACKGROUND AND AIMS

Microbial-derived bile acids can modulate host gene expression, and their faecal abundance is decreased in active inflammatory bowel disease [IBD]. We analysed the impact of endoscopic inflammation on microbial genes involved in bile acid biotransformation, and their interaction with host transcriptome in the intestinal mucosa of IBD patients.

METHODS

Endoscopic mucosal biopsies were collected from non-inflamed and inflamed terminal ileum, ascending and sigmoid colon of IBD patients. Prediction of imputed metagenome functional content from 16S rRNA profile and real-time quantitative polymerase chain reaction [qPCR] were utsed to assess microbial bile acid biotransformation gene abundance, and RNA-seq was used for host transcriptome analysis. Linear regression and partial Spearman correlation accounting for age, sex, and IBD type were used to assess the association between microbial genes, inflammation, and host transcriptomics in each biopsy location. A Bayesian network [BN] analysis was fitted to infer the direction of interactions between IBD traits and microbial and host genes.

RESULTS

The inferred microbial gene pathway involved in secondary bile acid biosynthesis [ko00121 pathway] was depleted in inflamed terminal ileum of IBD patients compared with non-inflamed tissue. In non-inflamed sigmoid colon, the relative abundance of bile acid-inducible [baiCD] microbial genes was positively correlated with the host Angiopoietin-like 4 [Angptl4] gene expression. The BN analysis suggests that the microbial baiCD gene abundance could affect Angptl4 expression, and this interaction appears to be lost in the presence of inflammation.

CONCLUSIONS

Endoscopic inflammation affects the abundance of crucial microbial bile acid-metabolising genes and their interaction with Angptl4 in intestinal mucosa of IBD patients.

Conducting Translational Gastrointestinal Research in the Era of COVID-19

Spread of the novel coronavirus SARS-CoV-2 has resulted in a global pandemic that is affecting the health and economy of all World Health Organization [WHO] regions. Clinical and translational research activities have been affected drastically by this global catastrophe. In this document we provide a suggested roadmap for resuming gastrointestinal translational research activities, emphasising physical distancing and use of personal protective equipment. We discuss modes of virus transmission in enclosed environments [including clinical workplaces and laboratories] and potential risks of exposure in the endoscopy environment for research staff. The proposed guidelines should be considered in conjunction with local institutional and government guidelines so that translational research can be resumed as safely as possible.

Targeted Synthesis of NIR Luminescent Rhenium Diimine cis,trans-[Re( N N )(CO)2 (L)2 ]n+ Complexes Containing N-Donor Axial Ligands: Photophysical, Electrochemical, and Theoretical Studies

The combined action of ultraviolet irradiation and microwave heating onto acetonitrile solution of [Re( N N )(CO)₃ (NCMe)]OTf ( N N =phenantroline and neocuproine) afforded cis,trans-Re( N N )(CO)₂ (NCMe)₂ ]⁺ acetonitrile derivatives. Substitution of relatively labile NCMe with a series of aromatic N-donor ligands (pyridine, pyrazine, 4,4'-bipyridine, N-methyl-4,4'-bipyridine) gave a novel family of the diimine cis,trans-[Re( N N )(CO)₂ (L)₂ ]⁺ complexes. Photophysical studies of the obtained compounds in solution revealed unusually high absorption across the visible region and NIR phosphorescence with emission band maxima ranging from 711 to 805 nm. The nature of emissive excited states was studied using DFT calculations to show dominant contribution of ³ MLCT (dπ(Re)→π*( N N )) character. Electrochemical (CV and DPV) studies of the monocationic diimine complexes revealed one reduction and one oxidation wave assigned to reduction of the diimine moiety and oxidation of the rhenium center, respectively.

Estimation of genetic parameters for mid-infrared-predicted lactoferrin and milk fat globule size in Holstein cattle

Lactoferrin (LF) and milk fat globule (MFG) are 2 biologically active components of milk with great economical and nutritional value in the dairy industry. The objectives of this study were to estimate (1) the heritability of mid-infrared (MIR)-predicted LF and MFG size (MFGS) and (2) the genetic correlations between predicted LF and MFGS with milk, fat, and protein yields, fat and protein percentages, and somatic cell score in first-parity Canadian Holstein cattle. A total of 109,029 test-day records from 22,432 cows and 1,572 farms for MIR-predicted LF and 109,212 test-day records from 22,424 cows and 1,559 farms for MIR-predicted MFGS were used in the analyses. Four separate 5-trait random regression test-day models were used. The models included days in milk, herd test date, and a polynomial regression on DIM nested in age-season of calving classes as fixed effects, random polynomial regressions on DIM nested in herd-year of calving, animal additive genetic and permanent environment classes, and a residual effect. Regression curves were modeled using orthogonal Legendre polynomials of order 4 for the fixed age-season of calving effect and of order 5 for the random effects. Moderate overall heritability estimates of 0.34 and 0.46 were estimated for the MIR-predicted LF and MIR-predicted MFGS, respectively. These heritability estimates were similar to the ones estimated for the direct measure of MFGS in a previous study. The genetic correlations between predicted MFGS and fat percentage (0.53) and between predicted LF and protein percentage (0.41) were both moderate and positive. Predicted LF and somatic cell score showed a weaker correlation (0.06) compared with other studies. The moderate genetic correlation between MIR-predicted MFGS and fat percentage and between MIR-predicted LF and protein percentage suggests that MIR predictions of MFGS and LF are not simply a function of the amount of fat and protein percentage, respectively, in the milk (i.e., the prediction equations are not simply predicting fat or protein percentages). Thus, these MIR-predicted values may provide additional information for selecting for fine milk components in Holstein cattle.

Genome-wide association analysis for β-hydroxybutyrate concentration in Milk in Holstein dairy cattle

BACKGROUND

Ketosis in dairy cattle has been shown to cause a high morbidity in the farm and substantial financial losses to dairy farmers. Ketosis symptoms, however, are difficult to identify, therefore, the amount of ketone bodies (mainly β-hydroxybutyric acid, BHB) is used as an indicator of subclinical ketosis in cows. It has also been shown that milk BHB concentrations have a strong correlation with ketosis in dairy cattle. Mid-infrared spectroscopy (MIR) has recently became a fast, cheap and high-throughput method for analyzing milk components. The aim of this study was to perform a genome-wide association study (GWAS) on the MIR-predicted milk BHB to identify genomic regions, genes and pathways potentially affecting subclinical ketosis in North American Holstein dairy cattle.

RESULTS

Several significant regions were identified associated with MIR-predicted milk BHB concentrations (indicator of subclinical ketosis) in the first lactation (SCK1) and second and later lactations (SCK2) in Holstein dairy cows. The strongest association was located on BTA6 for SCK1 and BTA14 on SCK2. Several SNPs on BTA6 were identified in regions and variants reported previously to be associated with susceptibility to ketosis and clinical mastitis in Jersey and Holstein dairy cattle, respectively. One highly significant SNP on BTA14 was found within the DGAT1 gene with known functions on fat metabolism and inflammatory response in dairy cattle. A region on BTA6 and three SNPs on BTA20 were found to overlap between SCK1 and SCK2. However, a novel region on BTA20 (55-63 Mb) for SCK2 was also identified, which was not reported in previous association studies. Enrichment analysis of the list of candidate genes within the identified regions for MIR-predicted milk BHB concentrations yielded molecular functions and biological processes that may be involved in the inflammatory response and lipid metabolism in dairy cattle.

CONCLUSIONS

The results of this study confirmed several SNPs and genes identified in previous studies as associated with ketosis susceptibility and immune response, and also found a novel region that can be used for further analysis to identify causal variations and key regulatory genes that affect clinical/ subclinical ketosis.

Genome-wide association studies and genomic prediction of breeding values for calving performance and body conformation traits in Holstein cattle

Background

Our aim was to identify genomic regions via genome-wide association studies (GWAS) to improve the predictability of genetic merit in Holsteins for 10 calving and 28 body conformation traits. Animals were genotyped using the Illumina Bovine 50 K BeadChip and imputed to the Illumina BovineHD BeadChip (HD). GWAS were performed on 601,717 real and imputed single nucleotide polymorphism (SNP) genotypes using a single-SNP mixed linear model on 4841 Holstein bulls with breeding value predictions and followed by gene identification and in silico functional analyses. The association results were further validated using five scenarios with different numbers of SNPs.

Results

Seven hundred and eighty-two SNPs were significantly associated with calving performance at a genome-wise false discovery rate (FDR) of 5%. Most of these significant SNPs were on chromosomes 18 (71.9%), 17 (7.4%), 5 (6.8%) and 7 (2.4%) and mapped to 675 genes, among which 142 included at least one significant SNP and 532 were nearby one (100 kbp). For body conformation traits, 607 SNPs were significant at a genome-wise FDR of 5% and most of them were located on chromosomes 5 (30%), 18 (27%), 20 (13%), 6 (6%), 7 (5%), 14 (5%) and 13 (3%). SNP enrichment functional analyses for calving traits at a FDR of 1% suggested potential biological processes including musculoskeletal movement, meiotic cell cycle, oocyte maturation and skeletal muscle contraction. Furthermore, pathway analyses suggested potential pathways associated with calving performance traits including tight junction, oxytocin signaling, and MAPK signaling (P < 0.10). The prediction ability of the 1206 significant SNPs was between 78 and 83% of the prediction ability of the BovineSNP50 SNPs for calving performance traits and between 35 and 79% for body conformation traits.

Conclusions

Various SNPs that are significantly associated with calving performance are located within or nearby genes with potential roles in tight junction, oxytocin signaling, and MAPK signaling. Combining the significant SNPs or SNPs within or nearby gene(s) from the HD panel with the BovineSNP50 panel yielded a marginal increase in the accuracy of prediction of genomic estimated breeding values for all traits compared to the use of the BovineSNP50 panel alone.

Electronic supplementary material

The online version of this article (10.1186/s12711-017-0356-8) contains supplementary material, which is available to authorized users.

Functional conformations of the nuclear 1alpha,25-dihydroxyvitamin D3 receptor

The nuclear hormone 1alpha,25-dihydroxyvitamin D3 (VD) has important cell regulatory functions. Various synthetic VD analogues are under investigation to identify candidates with an improved therapeutic profile against hyperproliferative diseases. VD directly activates the transcription factor VD receptor (VDR), which in turn stimulates the expression of a cascade of primary and secondary VD-responsive genes. The activation of the VDR through binding of its natural and synthetic ligands is linked to a conformational change presenting the interface with co-activator proteins, referred to as the (trans)activation function 2 (AF-2) domain. Multiple conformations of the VDR might be the key to understanding a selective action of VD analogues. The method of limited protease digestion was used here to characterize up to three different functional VDR conformations stabilized individually by VD and its analogues. The relative potency of VDR ligands can be quantified in the interaction with these VDR conformations by determination of a functional dissociation constant, where a two-concentration-point comparison has already provided important information. In this way seven amino acid residues in the AF-2 domain have been analysed as potential ligand contact points. Interestingly, residues Phe-422 and Val-418 seem to interact with all tested VDR ligands, whereas VD analogues such as the anti-psoriatic drug MC903 displayed additional contact points within the AF-2 domain. Taken together, limited protease digestion is a powerful method for studying functional VDR conformations and seems to be very appropriate for screening VD analogues.

Sensitive induction of apoptosis in breast cancer cells by a novel 1,25-dihydroxyvitamin D3 analogue shows relation to promoter selectivity

The biologically active form of vitamin D3, the nuclear hormone 1 alpha,25-dihydroxyvitamin D3 (VD), is an important regulator of cellular growth, differentiation, and death. The hormone mediates its action through the activation of the transcription factor VDR, which is a member of the superfamily of nuclear receptors. In most cases the ligand-activated VDR is found in complex with the retinoid X receptor (RXR) and stimulates gene transcription mainly from VD response elements (VDREs) that are formed by two hexameric core binding motifs and are arranged either as a direct repeat spaced by three nucleotides (DR3) or as an inverted palindrome spaced by nine nucleotides (1P9). The two VD analogues CB1093 and EB1089 are both very potent inhibitors of the proliferation of MCF-7 cultured breast cancer cells displaying approximately 100-fold lower IC50 values (0.1 nM) than the natural hormone. In addition, CB1093 is even more potent in vivo than EB1089 in producing regression of experimental mammary tumors. Moreover, both VD analogues induce apoptosis in MCF-7 cells, but CB1093 is effective at concentrations approximately 10-fold lower than EB1089. In accordance, the reduction of Bcl-2 protein expression showed CB1093 to be more potent than EB1089. This suggests that the antiproliferative effect of CB1093 may be related mainly to its apoptosis inducing effect, whereas EB1089 may preferentially have effects on growth arrest. EB1089 is known to result in a selectivity for the activation of IP9-type VDREs, whereas CB1093 shows a preference for the activation of DR3-type VDREs. This promoter selectivity suggests that the effects of VD and its analogues on growth arrest and the induction of apoptosis may be mediated by different primary VD responding genes. In conclusion, CB1093 was found to be a potent inhibitor of rat mammary tumor growth in vivo. CB1093 also displayed a high potency in vitro in the induction of apoptosis, a process that may be linked to a promoter selectivity for DR3-type VDREs.

The high affinity ligand binding conformation of the nuclear 1,25-dihydroxyvitamin D3 receptor is functionally linked to the transactivation domain 2 (AF-2)

The nuclear receptor for 1,25-dihydroxyvitamin D3 (VD), VDR, is a transcription factor that mediates all genomic actions of the hormone. The activation of VDR by ligand induces a conformational change within its ligand binding domain (LBD). Due to the lack of a crystal structure analysis, biochemical methods have to be applied in order to investigate the details of this receptor-ligand interaction. The limited protease digestion assay can be used as a tool for the determination of a functional dissociation constant (K(df)) of VDR with any potential ligand. This method provided with the natural hormone VD two protease-resistant fragments of the VDR LBD and with the 20-epi conformation of VD, known as MC1288, even an additional fragment of intermediate size. These fragments were interpreted as different receptor conformations and their decreasing size was found to be associated with decreasing ligand binding affinity. A critical amino acid for VDR's high ligand binding conformation has been identified by C-terminal receptor truncations and point mutations as phenylalanine 422. This amino acid appears to directly contact the ligand and belongs to the ligand-inducible activation function-2 (AF-2) domain. Moreover, functional assays supported the observation that high affinity ligand binding is directly linked to transactivation function.

Potent gene regulatory and antiproliferative activities of 20-methyl analogues of 1,25 dihydroxyvitamin D3

The biological active form of vitamin D3, 1,25-dihydroxyvitamin D3 (VD), regulates cellular growth and differentiation. This provides the hormone with an interesting therapeutic potential. However, hypercalcemia is a side effect, which is caused by VD's classical action, the regulation of calcium homeostasis. This made the need for VD analogues with selectively increased cell regulatory properties. Studies with 20-epi analogues pointed out the importance of the carbon-20 position and led to the development of 20-methyl derivatives of VD. In this report the biological properties of the compounds ZK161422 and ZK157202, which are 20-methyl- and 20-methyl-23-eneanalogues, respectively, have been analyzed in comparison with VD. Both compounds show about 2-fold lower affinity to the VD receptor (VDR) than VD. However, compared to VD, their antiproliferative effect is up to 30-fold higher on human peripheral blood mononuclear cells and even up to 300-fold higher on human breast cancer MCF-7 cells. Whereas the hypercalcemic effect for ZK157202 is also increased 10-fold, ZK161422 has the same calcium-mobilizing potency as VD. Moreover, ZK161422, but not ZK157202, showed preference for gene activation from a promoter carrying a VD response element with a palindromic arrangement of two hexameric receptor binding sites spaced by 9 nucleotides (IP9) rather than for activation from a response element formed by a direct repeat spaced by 3 nucleotides (DR3). This observation supports a model, in which promoter selectivity reflects the selectively increased antiproliferative effect of VD analogues.

High-affinity nuclear receptor binding of 20-epi analogues of 1,25-dihydroxyvitamin D3 correlates well with gene activation

The hormone 1,25-dihydroxyvitamin D3 (VD) has the potential for clinical use in several diseases, such as cancer, osteoporosis, and psoriasis. The action of VD is mediated by primary responding genes that contain in their promoter region a binding site for the transcription factor VDR. Most of the known VD response elements are formed by a direct repeat of two hexameric core binding motifs spaced by three nucleotides (DR3) bound by a heterodimer of VDR and the retinoid X receptor (RXR). Various VD analogues have been developed in order to optimize the therapeutic profile of VD. This report presents a novel experimental system that may help in the understanding of the structural basis for the high potency of a VD analogue like KH1060, which is a 20-epi-22-oxa-derivative of VD. In human breast cancer cells, MCF-7, the half-maximal gene activation values for KH1060 and seven of its structural precursors were determined on a DR3-type VD response element. These eight analogues cover conservative structural changes from 20-epi-VD (MC1288) to KH1060. With a modified version of the limited protease digestion assay the functional affinity of the analogues to VDR was measured. The functional receptor affinity of the eight analogues was found to be directly proportional to their potency in VDR-RXR-mediated gene activity.

Thiazolidine diones, specific ligands of the nuclear receptor retinoid Z receptor/retinoid acid receptor-related orphan receptor alpha with potent antiarthritic activity

Rat adjuvant arthritis is a chronic T cell-dependent autoimmune disease with many similarities to rheumatoid arthritis. We have identified a class of thiazolidine diones with high potency in suppressing chronic inflammation and joint destruction in this experimental model. The lead compound CGP 52608 (1-(3-allyl-4-oxothiazolidine-2-ylidene)-4-methylthiosemicarbazone) exhibits antiarthritic activity at daily oral doses between 0.01 and 1 mg/kg and was shown to specifically activate the retinoid Z receptor/retinoid acid receptor-related orphan receptor alpha (RZR/RORalpha) in low nanomolar concentrations. This receptor is a novel member of the superfamily of ligand-inducible transcription factors, and we have recently identified the pineal gland hormone melatonin as a natural ligand. Structure-activity relationship studies with 13 closely related analogues of CGP 52608 revealed a striking correlation between RZR/RORalpha activation and antiarthritic activity. We therefore suggest that nuclear signaling via RZR/RORalpha is a key mechanism in mediating the antiarthritic effects of these thiazolidine diones and may open a novel therapeutic approach for the treatment of rheumatoid arthritis and other autoimmune diseases. The existence of a nuclear melatonin receptor may lead to a better understanding of the immunomodulatory actions of melatonin.

The anti-proliferative effect of vitamin D3 analogues is not mediated by inhibition of the AP-1 pathway, but may be related to promoter selectivity

The hormone 1,25-dihydroxyvitamin D3 (VD) is able to induce cellular differentiation and to inhibit cellular proliferation, which provides it with an interesting therapeutic potential in cancer. However, side effects of VD on homeostasis (eg hypercalcemia) had made the need for the development of VD analogues with low calcemic effect. On the human breast cancer cell line MCF-7 we obtained with the VD analogue EB1089 an about 100-fold higher anti-proliferative effect than with VD. We found that this difference in biological activity is neither related to increased functional affinity to the VD receptor nor to repression of AP-1 activity. The physiologically most prominent complex of the VD receptor is a heterodimer with the retinoid X receptor that binds VD response elements formed two hexameric core binding motifs being arranged either as direct repeats spaced by 3 nucleotides (DR3s) or as inverted palindromes spaced by 9 nucleotides (IP9s). We observed that EB1089 stimulates transcriptional activation from IP9-type elements at clearly lower concentrations than from DR3-type elements. It is possible that IP9-type response elements play an important role in or contribute to the control of cell proliferation, so that promoter-selectivity may explain the high anti-proliferative effect of EB1089.

The nuclear receptor for melatonin represses 5-lipoxygenase gene expression in human B lymphocytes

The two subtypes of retinoid Z receptor (RZR alpha and beta) and the three splicing variants of retinoid orphan receptor (ROR alpha 1, alpha 2, and alpha 3) form a subfamily within the superfamily of nuclear hormone receptors. Very recently we found that the pineal gland hormone melatonin is a natural ligand of RZR alpha and RZR beta. Ligand-induced transcriptional control is therefore proposed to mediate physiological functions of melatonin in the brain where RZR beta is expressed, but also in peripheral tissues, where RZR alpha was found. However, no natural RZR responding genes have been identified yet. Here, we report that a response element in the promoter of 5-lipoxygenase binds specifically RZR alpha and ROR alpha 1, but not ROR alpha 2 and alpha 3. 5-Lipoxygenase is a key enzyme in the biosynthesis of leukotrienes, which are known to be allergic and inflammatory mediators. We could show that the activity of the whole 5-lipoxygenase promoter as well as of the RZR response element fused to the heterologous thymidine kinase promoter could be repressed by melatonin. The hormone down-regulated the expression of 5-lipoxygenase about 5-fold in B lymphocytes, which express RZR alpha. In contrast, 5-lipoxygenase mRNA levels were not affected in differentiated monocytic and granulocytic cell lines, which do not express RZR alpha. This indicates that 5-lipoxygenase is the first natural RZR alpha responding gene. Furthermore, our results open up a new perspective in understanding the involvement of melatonin in inflammatory and immunological reactions.

Natural vitamin D3 response elements formed by inverted palindromes: polarity-directed ligand sensitivity of vitamin D3 receptor-retinoid X receptor heterodimer-mediated transactivation

VDR, the nuclear receptor for 1,25-dihydroxyvitamin D3 (VD), is a member of the superfamily of nuclear hormone receptors and controls multiple aspects of homeostasis, cell growth, and differentiation. VDR can function as a homodimer, but heterodimerization with the retinoid X receptor (RXR), retinoic acid receptor, or thyroid hormone receptor increases its affinity for response elements in the promoter of target genes. All natural VD response elements identified so far consist of direct repeats of a variety of hexameric core binding motifs with a preferential spacing of three nucleotides (DR3s). However, all four VD signalling pathways function also on response elements formed by inverted palindromes, although these sequences were not of natural origin. Here, we report the identification of two VD response elements consisting of inverted palindromes spaced by nine nucleotides (IP9s) in the promoters of the human calbindin D9k gene and the rat osteocalcin gene. Like most DR3-type VD response elements, both IP9s are preferentially bound by VDR-RXR heterodimers with a 5'-RXR-VDR-3' polarity, whose transcriptional activity can be enhanced by costimulation with 9-cis retinoic acid. We demonstrate that changing the response element orientation relatively to the basal promoter decreases the sensitivity of transcriptional activation by VD by about 10-fold. Our findings indicate that inverted palindromes are as functional as direct repeats. Furthermore, we suggest that the orientation of a nuclear receptor complex in relation to the basic transcriptional machinery, which is directed by heterodimer polarity and response element orientation, influences the ligand sensitivity of the respective target gene expression.

Vitamin D3-thyroid hormone receptor heterodimer polarity directs ligand sensitivity of transactivation

The nuclear receptors for 1,25-dihydroxyvitamin D3 (VD) and 3,5,3'-triiodothyronine (T3), that is, VDRs and T3Rs respectively, control aspects of homeostasis, cell growth and differentiation. They activate transcription from response elements consisting of direct repeats, palindromes and inverted palindromes of a variety of hexameric core-binding motifs. VDRs bind preferentially to direct repeats spaced by three nucleotides, whereas T3Rs bind to direct repeats spaced by four nucleotides. VDRs and T3Rs can function as homodimers but heterodimerization with retinoid X or retinoic acid receptors increases their affinity for DNA in vitro and resulting transcriptional activity in vivo. We recently observed the formation of VDR-T3R heterodimers. Here we show that the polarity of the binding of such heterodimers to the VD response element of the rat 9K (relative molecular mass 9,000) calbindin gene promoter was 5'-T3R-VDR-3', whereas on the mouse 28K calbindin VD response element this polarity was reversed to 5'-VDR-T3R-3'. We also show that the ligand for the downstream receptor controls the transcriptional activity of the heterodimeric complex. Thus, polarity seems to be an important regulatory property of heterodimeric nuclear receptor complexes.