Association of late gadolinium enhancement in cardiac magnetic resonance with heart failure outcomes in patients with non-ischemic cardiomyopathy

Background

Late-gadolinium enhancement (LGE) in cardiac magnetic resonance (CMR) has been found to be associated with increased mortality in patients with non-ischemic cardiomyopathy (NICM). The correlation between LGE and heart failure (HF) hospitalization, referral for heart transplant, and ejection fraction (EF) improvement have not been well established.

Purpose

This meta-analysis assessed the relationship between LGE in CMR with HF hospitalization, referral for heart transplant and EF improvement in patients with NICM.

Methods

We searched the databases for studies reporting the association between LGE in CMR for NICM and HF outcomes including Ovid MEDLINE, EMBASE, Web of Science, and Google Scholar for all studies. The search was not restricted to time or publication status. The minimal follow up duration is one year.

Results

A total of 216 studies resulted from the literature search. A total of 25 studies and 3,039 patients (1,265 with LGE vs 1,774 without LGE) were included; mean follow up is around 33 months (ranging between 13 to 71 months). Our analysis demonstrated that LGE in NICM was associated with increased risk of HF hospitalization (odds ratio 3.38, 95% confidence interval 2.27–5.04; P<0.01), referral for transplant (odds ratio 5.08, 95% confidence interval 2.49–10.35; P<0.01), and lower chance for EF improvement (odds ratio 0.16, 95% confidence interval 0.03–0.85; P 0.03). Heterogeneity is moderate: χ2=49.5, df=21 (P=0.001), I2=57%. (Figures 1 and 2)

Conclusions

Our results suggest that LGE is associated with increased risk of HF hospitalization and referral for heart transplant and lower chance for EF improvement in long-term follow up.

Funding Acknowledgement

Type of funding sources: None.

Outcomes of additional substrate modification in de novo atrial fibrillation ablation

Background

Pulmonary vein isolation (PVI) is the cornerstone of atrial fibrillation (AF) ablation. Data regarding additional substrate modification has been conflicting, both in paroxysmal and persistent atrial fibrillation.

Purpose

To assess the effect of additional linear substrate modification during de novo AF ablation on AF recurrence.

Methods

We reviewed 1575 AF ablations in 1254 patients from January 2013 to June 2021 at a single academic medical center. There were 1096 de novo ablations. We defined substrate modification as linear ablations including cavotricuspid isthmus (CTI), superior vena cava isolation, intercaval line, mitral isthmus, and left atrial roof and floor lines. We evaluated clinical and procedural characteristics to identify risk factors for AF recurrence and complications. Patients were followed for a minimum of 6 months.

Results

The 1096 de novo ablations included 65.5% males with mean age 61.1 years, mean BMI 31.3, 81.8% paroxysmal AF and 18.2% persistent AF. There were four AF ablation subgroups: PVI alone (41.6%), PVI and CTI ablation (37.1%), PVI with CTI and additional substrate modification (15.6%), and PVI with substrate modification without CTI ablation (5.7%). Overall, AF recurred in 36.9% cases. AF recurrence with PVI only ablation was 41% compared to 32.7% in patients with PVI and CTI ablation (p=0.02). When looking at patients with paroxysmal and persistent AF, results were similar, with decreased AF recurrence with the addition of CTI ablation in both paroxysmal (37.3% v. 29.2%, p=0.03) and persistent AF (58.1% v. 40.0%, p=0.02). Additional substrate modification did not result in significant difference in outcome in either paroxysmal or persistent AF (Figure 1).

Conclusions

In de novo AF ablations, addition of CTI ablation to de novo PVI ablation is associated with lower AF recurrence in both paroxysmal and persistent AF. Additional linear substrate modification did not impact outcomes.

Funding Acknowledgement

Type of funding sources: None.

Safety of same day discharge after atrial fibrillation ablation

Background

Atrial fibrillation (AF) ablation is an outpatient procedure with traditionally an overnight hospital observation (OHO). Recently, there has been a trend towards same day discharge (SDD).

Purpose

Compare AF ablation procedure safety outcomes with SDD vs. OHO.

Methods

We reviewed consecutive AF procedures performed from January 2013 to June 2021 at a single academic center. Patients underwent OHO until June 2020, after which patients had SDD whenever feasible. Adverse events were assessed at three months, which included pericardial effusion, pericarditis, post-procedure hypotension, embolic events, and vascular complications. We also assessed emergency department (ED) visits and procedure-related hospital admissions.

Results

There were 1254 patients who underwent 1575 AF ablations. 1440 patients underwent OHO and 135 had SDD. Mean age was 62.2 years, BMI 33 kg/m2, 65% were male, and 27.6% had persistent AF, without significant differences in baseline characteristics between OHO and SDD. We found that SDD was not associated with increased complications (OHO 0.20% v. SDD 0.49%; p>0.05), ED visits, or hospital admissions (2% v. 5%; p>0.05) (Figure 1, 2). There were no gender or age-related disparities in all outcomes (p>0.05).

Conclusion

SDD protocol after AF ablation is feasible and not associated with higher incidence of complications, ED visits, and procedure-related hospitalizations.

Funding Acknowledgement

Type of funding sources: None.

Race disparities in atrial fibrillation detection using implantable loop recorder for cryptogenic stroke

Background

Cryptogenic stroke represents about 25–30% of all ischemic strokes. Continuous electrocardiographic monitoring using implantable loop recorder (ILR) can detect asymptomatic and undiagnosed atrial fibrillation (AF).

Purpose

To assess patient-specific factors in ILR implantation and AF detection in patients with cryptogenic strokes.

Methods

We retrospectively reviewed 379 patients with cryptogenic stroke indicated for ILR implantation, from January 2017 to June 2021 at our university hospital. We evaluated patient demographic and clinical characteristics to assess the risk factors associated with higher incidence of AF detection, using logistic regression models.

Results

Of the 379 ILRs implanted, 60.4% were males with 71.2% Caucasian, mean age 67.6 years, and mean BMI 28.5. The mean CHADSVASC score of 3.9 at the time of ischemic stroke. These patients had prior diagnosis of diabetes mellitus (27.4%), hypertension (65.7%), chronic kidney disease (19.5%), coronary artery disease (20%) and congestive heart failure (2%). Of the entire cohort, AF was diagnosed in 16% of patients with 14 months mean follow up. There were more females diagnosed with AF on ILR (20% v. 18.7%, p>0.05). Caucasians were more likely to have AF detected compared to non-Caucasians (OR 2.3, 95% CI, p<0.02). There were 52 patients with mobile cardiac outpatient telemetry (MCOT) before having ILR implantation. AF was not detected on MCOT, but 15% were diagnosed with AF with ILR monitoring. In univariate analysis, increasing age is strongly associated with the detection of AF (p=0.03).

Conclusions

There continues to exist race disparities in ILR implantation and eventual AF detection, leading to further socioeconomic health disparities. ILR should be considered especially in elderly with cryptogenic stroke given the higher incidence of AF detection.

Funding Acknowledgement

Type of funding sources: None.

Effect of defibrillator on long term all-cause mortality in patients with chronic kidney disease: an updated meta-analysis

Background

The beneficial role of implantable defibrillator (ICD) in patients with chronic kidney disease (CKD) is less understood as this population is often not well represented in clinical trials.

Purpose

Evaluate the effect of ICD use in patients with CKD on long term outcomes.

Methods

Literature search was conducted for studies reporting the effect of ICD on all-cause mortality in patients with CKD, which is defined as glomerular filtration rate (GFR) <60 mL/min. The search was not restricted to time or publication status. The search included the following databases: Ovid MEDLINE, EMBASE, Scopus, Web of Science, Google Scholar, and EBSCO CINAHL. The minimum duration of follow-up required for inclusion was one year.

Results

The literature search identified 834 studies, of which 14 studies with 70,661 patients were included. Mean follow up was 39 months (12–81 months). For all patients with CKD, ICD was associated with lower all-cause mortality (log HR −0.247, SE 0.101, p=0.015); Heterogeneity: df=13 (P<0.01), I2=97.057; Test for overall effect: Z=−2.431 (Figure 1). When further stratified based on dialysis, CKD patients without the need for dialysis had favorable outcome (log HR −0.211, SE 0.095, p=0.026); Heterogeneity: df=6 (P<0.01), I2=70.146; Test for overall effect: Z=−2.225, whereas ICD implantation in CKD patients requiring dialysis was not associated with mortality benefit (log HR −0.262, SE 0.134, p=0.051) (Figure 2A, B).

Conclusion

ICD implantation is associated with mortality benefit in patients with CKD, but this association is not present for patients requiring dialysis.

Funding Acknowledgement

Type of funding sources: None.

Association of late-gadolinium enhancement in cardiac magnetic resonance with ventricular arrhythmias and mortality in patients with non-ischemic cardiomyopathy

Background

Late-gadolinium enhancement (LGE) in cardiac magnetic resonance (CMR) is a predictor of adverse events such as cardiovascular mortality, cardiovascular related hospitalization and defibrillation shocks in patients with non-ischemic cardiomyopathy (NICM). The correlation between LGE and ventricular arrhythmia and mortality has not been completely established.

Purpose

This meta-analysis assessed the relationship between LGE in CMR with ventricular arrhythmias: sustained, non-sustained and ICD therapy; and mortality in patients with NICM.

Methods

Databases were queried for studies reporting the association between LGE in CMR in NICM and ventricular arrhythmias and mortality, including Ovid MEDLINE, EMBASE, Web of Science, and Google Scholar. The search was not restricted to time or publication status. The minimal follow up duration was one year.

Results

A total of 46 studies and 10,548 patients (4,610 with LGE vs 5,938 without LGE) were included; mean follow up was 3 years (ranging between 13 to 71 months) and mean left ventricular ejection fraction 33%. LGE in NICM was associated with increased risk of ventricular arrhythmias and sudden cardiac death (odds ratio 4.595, 95% confidence interval 3.54–5.97; P<0.01) and mortality (odds ratio 2.949, 95% confidence interval 2.285–3.806; P<0.01). Heterogeneity is low to moderate: χ2=82.2, df =45 (P=0.001), I2=45% (Figures 1, 2).

Conclusions

Our results suggest that LGE is associated with increased risk of ventricular arrhythmias, sudden cardiac death and mortality in long-term follow up. These results further substantiate the need for larger prospective randomized trials using LGE to decide ICD indication regardless of EF. There are two ongoing trials testing this indication: CMR-ICD and CMR-GUIDE.

Funding Acknowledgement

Type of funding sources: None.

Does body mass index affect atrial fibrillation ablation outcomes

Background

There are conflicting reports in the literature regarding whether body-mass index (BMI) influences the success and procedural complication rates of atrial fibrillation (AF) ablation.

Purpose

To determine if differences in BMI affect AF ablation outcomes

Methods

At a single academic center, AF ablation procedures were reviewed from 2013 to 2021. Primary outcomes were AF recurrence (after a 90 day blanking period), procedure-related complications, emergency department visits or hospital admission (ED/HOSP). Patients had a minimum of 6 months follow-up

Results

We analyzed 1569 AF ablation consecutive procedures (1093 de novo, 476 repeat ablation) using either radiofrequency or cryoablation. The study population was 65% male with a mean age 62 years, with 28% persistent AF. BMI was separated into three cohorts: <25 kg/m2 (N=218), 25–30 kg/m2 (N=547), and >30 kg/m2 (N=804). There were no significant differences in the type of AF, left atrial diameter, or left ventricular ejection fraction in the BMI subgroups. There was a direct relationship between the prevalence of co-morbid conditions and increasing BMI: hypertension (49.1%, 59.9%, 60.2%; p 0.04), diabetes (6.4%, 13.5%, 21.3%; p 0.01), and obstructive sleep apnea (5.5%, 10.8%, 26.7%; p<0.01). There were no significant differences in AF recurrence, procedural complications or ED/HOSP among the BMI cohorts (p>0.05) (Figure 1). No gender related disparities were noted in outcomes (p>0.05).

Conclusion

Higher BMI was not associated with AF recurrence, complications, or ED/HOSP after AF ablation despite a higher prevalence of comorbid medical conditions

Funding Acknowledgement

Type of funding sources: None.

Building evidence for improving vaccine adoption and uptake of childhood vaccinations in low- and middle-income countries: a systematic review

Vaccine coverage for children is an important indicator of the performance of national health and immunization systems. Most of the existing literature has targeted mothers’ low educational level, living in underserved districts and/or remote rural areas and economic poverty that are correlated with low immunization coverage but the supply- and demand-side constraints to immunization in low- and middle- income countries (LMICs) are not well understood. The reliability of claimed administrative immunization coverage in these contexts is questionable. To address these barriers within the present Expanded Programme on Immunization (EPI), the difficulties related to inadequate vaccination uptake must be addressed in more depth. Building on already produced literature, this study aims to determine the extent of immunization coverage among children in LMICs, as well as to fill in the gaps in awareness about system-level obstacles that currently hinder the effective delivery and uptake of immunization services through EPI. By two reviewers, a literature search using PubMed and Google Scholar along with targeted grey literature was conducted on the 2nd of June 2021 by following PRISMA guidelines. The search techniques for electronic databases used both Medical Subject Headings (Mesh) and free-text words were tailored to each database's specific needs using a controlled vocabulary that was limited to the English language from 2000 and 2020. Of the 689 records, eleven articles were included in this review meeting the inclusion criteria. In total, five articles related to vaccination coverage, four studies on components of the routine immunization system, one article on the implementation of new and under-utilized vaccines and one were on vaccines financing. We evaluated the quality of the included studies and extracted into tables created by one investigator and double-checked by another. Review findings suggest that specific strategies to reduce inequality may be required. Vaccine procurement and pricing strategies, as well as vaccine customization to meet the needs of LMICs, are all critical components in strengthening immunization systems. Our findings could be used to establish practical strategies for countries and development partners to address coverage gaps and improve vaccination system effectiveness.

POS0602 ROLE OF INTRAARTICULAR BIOLOGICS AND METHOTREXATE IN THE MANAGEMENT OF ACTIVE INFLAMMATORY MONOARTHRITIS

Background:

Expansion of immunosuppressive medications has greatly improved disease activity control in rheumatoid arthritis (RA) patients. However, persistent symptomatic monoarthritis can be a problem in some patients who otherwise have satisfactory disease control. Intra-articular (IA) corticosteroid (CS) injections have remained a treatment cornerstone for these patients, but the need for other therapies is clear. Patients can fail such therapy, may develop adverse effects or have comorbidities that are exacerbated by IA CS. 50% of patients relapse after IA CS therapy. Several studies have looked at other agents such as methotrexate (MTX) or tumor necrosis factor inhibitors (TNF-i) as IA treatment options.

Objectives:

To systematically review the evidence regarding utility of IA methotrexate and biologics in managing inflammatory monoarthritis in patients with RA.

Methods:

A systematic literature review, in accordance with PRISMA guidelines, was conducted looking at trials investigating the use of IA MTX and/or TNF-i, against IA CS, in managing inflammatory monoarthritis in patients with RA. A trained librarian conducted search of Ovid MEDLINE, Ovid EMBASE, Scopus, and Web of Science databases. Included studies were assessed for risk of bias as per the Cochrane tool.

Results:

A total of 1013 citations were retrieved from the medical database searches. 12 studies were included in the final review. 6 studies investigated IA MTX while 5 studied IA etanercept. One study investigated different biologic agents: infliximab, etanercept, or adalimumab. Multitude of dosing regimens and administration protocols were used in various studies. 5 of the 6 MTX studies only included knees. IA MTX was compared against saline, CS and as combined MTX/CS vs CS alone. There was no evidence to support the use of IA MTX as a superior or equivalent agent to the comparator groups. Unlike MTX, etanercept was investigated in multiple joint types e.g. elbows, knees and wrists. IA etanercept was found to have utility as a successful IA alternative to CS. The only study investigating infliximab and adalimumab found them to be superior to IA CS across multiple joint types. All therapies were generally well tolerated. Etanercept studies had low risk of bias while the MTX studies mostly suffered from higher risk of bias.

Conclusion:

Etanercept may be used as an IA agent in select patients with inflammatory arthritis when systemic treatment is not an option and IA corticosteroids cannot be used. Limited data also supports the utility of IA adalimumab and infliximab as better IA agents compared to CS. IA MTX, however, did not have such supporting data.

References:

[1]Fisher BA, Keat A. (2006) Should we be using intraarticular tumor necrosis factor blockade in inflammatory monoarthritis? J Rheumatol. 33(10), 1934-5.

[2]Weitoft T, Uddenfeldt P. (2000) Importance of synovial fluid aspiration when injecting intra-articular corticosteroids. Ann Rheum Dis. 59(3), 233-5.

Disclosure of Interests:

None declared

Attitudes and practices of postgraduate medical trainees towards research--a snapshot from Faisalabad

OBJECTIVE

To assess the attitudes and practices of postgraduate medical trainees towards research.

METHODS

It was a self-administered questionnaire based cross-sectional survey conducted on 55 conveniently selected trainees in Allied Hospital, Faisalabad.

RESULTS

Only 11 trainees read journals monthly, seven had written an article for a journal, 51 regarded reading literature important, 39 intended to engage in future research and 37 said they received inappropriate research training. The major reasons cited for poor research activity in Pakistan were poor research training and awareness.

CONCLUSION

Though the attitudes towards research were positive, they were deficient practically in terms of reading and writing literature. There is an immediate need to improve research training in our educational institutes to facilitate the development of the local literature both in terms of research utilization and production

Cardiovascular health--behaviour of medical students in Karachi

OBJECTIVE

To assess the health behaviour and perceptions of medical students towards cardiovascular disease.

METHODS

This descriptive cross-sectional survey was conducted on 203 Pakistani medical students enrolled in a private medical college in Karachi, Pakistan using systematic random sampling. It was based on a self-administered questionnaire.

RESULTS

Eight percent smoked, 9% were overweight, 33% had a family history of coronary artery disease, 32% regulated dietary fat intake, 28% exercised regularly, 62.1% knew personal blood pressure and 5.4% personal cholesterol levels. Regarding developing cardiovascular disease in the future, 62% showed concern but only 54% of these adopted preventive practices. About 46% believed medical college life had a harmful effect on their health. Gender, family history and personal health status perception were behavior modifying influences (p<0.05). Reasons reported for their behavior were: no need of prevention at their age (38.3%) and never thinking about these issues (37.0%).

CONCLUSIONS

The study shows a high prevalence of coronary artery disease family history, inappropriate dietary intake, physical inactivity; poor screening practices and lack of awareness. The results underscore the urgent need to promote preventive knowledge and practices among medical students, if they are to become prevention oriented physicians and counsel patients on preventive strategies to counter the rapidly increasing burden of cardiovascular diseases effectively.

Down-regulation of beta-catenin TCF signaling is linked to colonic epithelial cell differentiation

The beta-catenin TCF pathway is implicated in the regulation of colonic epithelial cell proliferation, but its role in the regulation of cell differentiation is unknown. The colon carcinoma cell line, Caco-2, spontaneously undergoes G(0)/G(1) cell cycle arrest and differentiates along the absorptive cell lineage over 21 days in culture. In parallel, we show that beta-catenin-TCF activity and complex formation are significantly down-regulated. The down-regulation of beta-catenin-TCF signaling was independent of APC, which we characterized as having a nonsense mutation in codon 1367 in Caco-2 cells, but was associated with a decrease in TCF-4 protein levels. Total beta-catenin levels increased during Caco-2 cell differentiation, although this was attributable to an increase in the membrane, E-cadherin-associated, fraction of beta-catenin. Importantly, down-regulation of beta-catenin-TCF signaling in undifferentiated Caco-2 cells by three different mechanisms, ectopic expression of E-cadherin, wild-type APC, or dominant negative TCF-4, resulted in an increase in the promoter activities of two genes that are well-established markers of cell differentiation, alkaline phosphatase and intestinal fatty acid binding protein. These studies demonstrate, therefore, that in addition to its established role in the regulation of cell proliferation, down-regulation of the beta-catenin-TCF pathway is associated with the promotion of a more-differentiated phenotype in colonic epithelial cells.

The Sp family of transcription factors in the regulation of the human and mouse MUC2 gene promoters

Modulation of mucin gene expression is an important component both in the early steps of colon cancer development and in later tumor progression. Previous work from our laboratory and others has suggested that the Sp family of transcription factors may play an important role in the regulation of the human MUC2 gene. To determine whether this was an essential element, we extended our work to the cloning and analysis of 3.5 kb of the 5'-flanking region of the mouse Muc2 (mMuc2) gene. Comparative analysis between the mouse and human MUC2 promoter regions has identified a strong sequence homology between the mouse and human genes, including the presence of GC-rich boxes, the location and composition of which are maintained in the mouse and human genes. We show that these GC boxes are binding sites for Sp-family transcription factors and are functionally important since mithramycin, an inhibitor of Sp1/Sp3 binding, blocks MUC2 gene expression in HT29 cells. Furthermore, by a combination of gel shift analysis and site-directed mutagenesis, we have identified the relative contribution of individual GC boxes, and of the factors they bind, to the regulation of the mouse Muc2 promoter, which appears to be different in the mouse and human genes. Finally, we demonstrate by overexpressing Sp1 and Sp3 that the functional difference between the proximal promoter region of the MUC2 gene in the two species is not attributable to differential ability of this region to bind members of the Sp family of transcription factors, but rather to the different anatomy of the individual GC boxes in the mouse and human proximal promoters.

Butyrate-induced apoptotic cascade in colonic carcinoma cells: modulation of the beta-catenin-Tcf pathway and concordance with effects of sulindac and trichostatin A but not curcumin

Short-chain fatty acids play a critical role in colonic homeostasis because they stimulate pathways of growth arrest, differentiation, and apoptosis. These effects have been well characterized in colonic cell lines in vitro. We investigated the role of beta-catenin-Tcf signaling in these responses to butyrate and other well-characterized inducers of apoptosis of colonic epithelial cells. Unlike wild-type APC, which down-regulates Tcf activity, butyrate, as well as sulindac and trichostatin A, all inducers of G0-G1 cell cycle arrest and apoptosis in the SW620 colonic carcinoma cell line, up-regulate Tcf activity. In contrast, structural analogues of butyrate that do not induce cell cycle arrest or apoptosis and curcumin, which stimulates G2-M arrest without inducing apoptosis, do not alter Tcf activity. Similar to the cell cycle arrest and apoptotic cascade induced by butyrate, the up-regulation of Tcf activity is dependent upon the presence of a mitochondrial membrane potential, unlike the APC-induced down-regulation, which is insensitive to collapse of the mitochondrial membrane potential. Moreover, the butyrate-induced increase in Tcf activity, which is reflected in an increase in beta-catenin-Tcf complex formation, is independent of the down-regulation caused by expression of wild-type APC. Thus, butyrate and wild-type APC have different and independent effects on beta-catenin-Tcf signaling. These data are consistent with other reports that suggest that the absence of wild-type APC, associated with the up-regulation of this signaling pathway, is linked to the probability of a colonic epithelial cell entering an apoptotic cascade.

The cell cycle regulator p27kip1 contributes to growth and differentiation of osteoblasts

The cyclin-dependent kinase (cdk) inhibitors are key regulators of cell cycle progression. p27 and p21 are members of the Cip/Kip family of cdk inhibitors and regulate cell growth by inactivating cell cycle stage-specific CDK-cyclin complexes. Because down-regulation of osteoprogenitor proliferation is a critical step for osteoblast differentiation, we investigated expression of p27 and p21 during development of the osteoblast phenotype in rat calvarial osteoblasts and in proliferating and growth-inhibited osteosarcoma ROS 17/2.8 cells. Expression of these proteins indicates that p21, which predominates in the growth period, is related to proliferation control. p27 levels are maximal postproliferatively, suggesting a role in the transition from cell proliferation to osteoblast differentiation. We directly examined the role of p27 during differentiation of osteoprogenitor cells derived from the bone marrow (BM) of p27-/- mice. BM cells from p27 null mice exhibited increased proliferative activity compared with BM cells from wild-type mice and formed an increased number and larger size of osteoblastic colonies, which further differentiated to the mineralization stage. Although p27-/- adherent marrow cells proliferate faster, they retain competency for differentiation, which may result, in part, from observed higher p21 levels compared with wild type. Histological studies of p27-/- bones also showed an increased cellularity in the marrow cavity compared with the p27+/+. The increased proliferation in bone does not lead to tumorigenesis, in contrast to observed adenomas in the null mice. Taken together, these findings indicate that p27 plays a key role in regulating osteoblast differentiation by controlling proliferation-related events in bone cells.

AP-1 and vitamin D receptor (VDR) signaling pathways converge at the rat osteocalcin VDR element: requirement for the internal activating protein-1 site for vitamin D-mediated trans-activation

Responsiveness of genes to steroid hormones is a complex process involving synergistic and/or antagonistic interactions between specific receptors and other nonreceptor transcription factors. Thus, DNA recognition elements for steroid hormone receptors are often located among binding sites for other trans-acting factors. The hormonal form of vitamin D, 1,25-dihydroxyvitamin D3, stimulates transcription of the tissue-specific osteocalcin (OC) gene in osteoblastic cells. The rat OC vitamin D response element contains an internal acitvating protein-1 (AP-1) site. Here, we report for the first time that this AP-1 site is critical for the transcriptional enhancement of rat osteocalcin gene expression mediated by vitamin D. Precise mutations were introduced either in the steroid half-elements or in the internal AP-1 sequences. One mutation within the internal AP-1 site retained vitamin D receptor/retinoid X receptor binding equivalent to that of the wild-type sequence, but resulted in complete loss of vitamin D inducibility of the OC promoter. These results suggest a functional interaction between the hormone receptor and nuclear oncoproteins at the rat OC vitamin D response element. This cooperation of activities may have important consequences in physiological regulation of osteocalcin transcription during osteoblast differentiation and bone tissue development in vivo.

Developmental association of the beta-galactoside-binding protein galectin-1 with the nuclear matrix of rat calvarial osteoblasts

The protein composition of the nuclear matrix changes significantly as the osteoblast matures from a proliferating pre-osteoblast to an osteocyte embedded in a mineralized matrix. These matrix protein are the result of developmental stage-specific gene expression during osteoblast differentiation. To isolate nuclear matrix proteins unique to the bone phenotype we analyzed nuclear matrix preparations from cultures of rat calvarial osteoblasts by high resolution two-dimensional gel electrophoresis at two different stages: proliferation (day 3) and differentiation (day 18, mineralized). We characterized one protein (14 kDa; pI 5.0), that was detectable only in the nuclear matrix of differentiated osteoblasts. By mass spectrometry and microsequencing, this protein was identified as the beta -galactoside-binding protein galectin-1. Both immunofluorescence staining of nuclear matrix preparations with the galectin-1 antibody and western blot analysis of subcellular fractions confirmed that galectin-1 is only associated with the nuclear matrix in differentiated osteoblasts as the result of differential retention. Galectin-1 protein and mRNA are present throughout osteoblast differentiation. Galectin-1 is present in the cytoplasmic and nuclear fractions in both proliferating and differentiated osteoblasts. However, its only stable binding is to the nuclear matrix of the differentiated osteoblast; but, in proliferating osteoblasts, galectin-1 is not retained in the nuclear matrix. Taken together, our results suggest that developmental association of galectin-1 with the nuclear matrix reflects differential subnuclear binding of galectin-1 during osteoblast differentiation.

Multiple levels of steroid hormone-dependent control of osteocalcin during osteoblast differentiation: glucocorticoid regulation of basal and vitamin D stimulated gene expression

We have examined the contribution of transcriptional mechanisms to the pleiotropic effects of glucocorticoids on basal and vitamin D stimulated expression of the developmentally regulated bone-specific osteocalcin (OC) gene. OC expression was systematically investigated at the level of protein, mRNA, and newly synthesized transcripts during maturation of the bone cell phenotype in cultures of fetal rat calvarial-derived osteoblasts. Our results indicate that transcriptional control of basal and hormone-regulated OC expression predominates in immature osteoblasts prior to matrix mineralization. However, in mature osteoblasts OC expression is controlled primarily by posttranscriptional mechanisms reflected by elevated mRNA levels with a decline in transcription. Vitamin D, alone or in combination with Dex, is a significant factor contributing to mRNA stabilization in mature osteoblasts with a mineralized extracellular matrix. Transcriptional modifications in response to Dex are reflected by quantitative differences between proliferating and mature osteoblasts in the formation of glucocorticoid receptor binding complexes at the proximal OC glucocorticoid response element. Vitamin D and glucocorticoid receptor mRNA levels are significantly higher in mature osteoblasts than in early stage bone cells. However, receptor complexes do not appear to be rate limiting in proliferating osteoblasts when the OC gene is not transcribed. Our results indicate (1) developmental stage-specific effects of steroid hormone on transcriptional regulation of bone expressed genes, and (2) inverse relationships between levels of transcription and cellular representation of mRNA with OC message stabilized in mature osteoblasts.

Species-specific glucocorticoid and 1,25-dihydroxyvitamin D responsiveness in mouse MC3T3-E1 osteoblasts: dexamethasone inhibits osteoblast differentiation and vitamin D down-regulates osteocalcin gene expression

The mouse MC3T3-E1 cell line is nontumorigenic and undergoes a typical program of osteoblast differentiation in vitro, producing a bone-like mineralized extracellular matrix. We report responses of these cells to dexamethasone (Dex) and 1,25-(OH)2D3 that are in contrast to findings from other osteoblast culture systems. First, chronic exposure of both early- and late-passaged MC3T3-E1 cells to 10(-7) M Dex, initiated during the proliferation period, blocked osteoblast differentiation, in contrast to the enhanced differentiation observed in cultures of fetal rat calvarial-derived cells. Secondly, 1,25-(OH)2D3 did not up-regulate expression (messenger RNA or protein synthesis) of the endogenous mouse osteocalcin (OC) gene. Several lines of evidence are presented that suggest this response is caused by sequence specific properties of the mouse OC vitamin D response element. We also observed both qualitative and quantitative differences in expression of cell growth (histone H2B) and phenotype-related genes (collagen, OC, osteopontin, glucocorticoid receptor, and 1, 25-(OH)2D3 receptor), between pre- and postmineralization stage osteoblasts, in response to 24 h steroid hormone treatment. Our findings in MC3T3-E1 cells are consistent with current concepts of selective influences of 1,25-(OH)2D3 and glucocorticoids as a function of osteoblast maturation. However, the inhibition of osteoblast differentiation by chronic Dex at 10(-7) M and the down-regulation of OC by 1,25-(OH)2D3 are novel observations relevant to species-specific responsiveness of mouse bone-expressed genes to steroid hormones during osteoblast differentiation.

YY1 regulates vitamin D receptor/retinoid X receptor mediated transactivation of the vitamin D responsive osteocalcin gene

The responsiveness of genes to steroid hormones is principally mediated by functional interactions between DNA-bound hormone receptors and components of the transcriptional initiation machinery, including TATA-binding protein, TFIIB, or other RNA polymerase II associated factors. This interaction can be physiologically modulated by promoter context-specific transcription factors to facilitate optimal responsiveness of gene expression to hormone stimulation. One postulated regulatory mechanism involves the functional antagonism between hormone receptors and nonreceptor transcription factors interacting at the same hormone response element. Here we demonstrate that the multifunctional regulator YY1 represses 1,25-dihydroxyvitamin D3 (vitamin D)-induced transactivation of the bone tissue-specific osteocalcin gene. We identify YY1 recognition sequences within the vitamin D response element (VDRE) of the osteocalcin gene that are critical for YY1-dependent repression of vitamin D-enhanced promoter activity. We show that YY1 and vitamin D receptor (VDR)/retinoid X receptor heterodimers compete for binding at the osteocalcin VDRE. In addition, we find that YY1 interacts directly with TFIIB, and that one of the two tandemly repeated polypeptide regions of TFIIB spanning the basic domain is responsible for this interaction. TFIIB and VDR can also interact directly, and these factors synergize to mediate transactivation. Our results suggest that YY1 regulates vitamin D enhancement of osteocalcin gene transcription in vivo by interfering with the interactions of the VDR with both the VDRE and TFIIB.

Bone tissue-specific transcription of the osteocalcin gene: role of an activator osteoblast-specific complex and suppressor hox proteins that bind the OC box

Bone-specific expression of the osteocalcin gene is transcriptionally controlled. Deletion analysis of osteocalcin promoter sequences by transient transfection of osseous (ROS 17/2.8) and nonosseous (R2 fibroblast) cells revealed that the most proximal 108 nucleotides are sufficient to confer tissue-specific expression. By gel mobility shift assays with wild-type and mutated oligonucleotides and nuclear extracts from several different cell lines we identified a novel transcription factor complex which exhibits sequence-specific interactions with the primary transcriptional element, the OC box (nt -99 to -76). This OC box binding protein (OCBP) is present only in osteoblast-like cells. Methylation interference demonstrated association of the factor with OC box sequences overlapping the Msx homeodomain consensus binding site. By assaying several mutations of the OC box, both in gel shift and transient transfection studies using ROS 17/2.8, we show the following. First, binding of OCBP correlates with osteocalcin promoter activity in ROS 17/2.8 cells. Increased binding leads to a 2-3-fold increase in transcription, while decreased binding results in transcription 30-40% of control. Second, homeodomain protein binding suppresses transcription. However, Msx expression is critical for full development of the bone phenotype as determined by antisense studies. Last, we show that one of the mutations of the OC box permits expression of osteocalcin in non-osseous cell lines. In summary, we demonstrate association of at least two classes of tissue-restricted transcription factors with the OC box element, the OCBP and Msx proteins, supporting the concept that these sequences contribute to defining tissue specificity.

Basal and vitamin D-responsive activity of the rat osteocalcin promoter in stably transfected osteosarcoma cells: requirement of upstream sequences for control by the proximal regulatory domain

Osteocalcin (OC) is a bone-specific vitamin D- responsive protein that is developmentally expressed during osteoblast differentiation. In transient transfection assays, as little as approximately 0.1 kilobase (kb) of the OC proximal promoter is sufficient for basal expression. Because eukaryotic genes are packaged as nucleosomes that contribute to both chromatin organization and transcriptional control, we functionally examined the activity of OC promoter constructs within a chromatin context. ROS 17/2.8 osteosarcoma cells were stably transfected with a series of rat OC promoter-reporter constructs, containing progressive 5'-deletions. The results demonstrate that in contrast to transient transfection assays, the proximal 0.11-kb promoter is no longer active when integrated in the genome. Progressive gain of basal expression with 0.35-, 0.53-, and 0.72-kb promoters suggests that upstream sequences facilitate the formation of an appropriate higher order nuclear structure, thereby potentiating the activity of the chromosomally integrated proximal promoter elements. This is consistent with location of both deoxyribonuclease I (DNase I)-hypersensitive sites and nuclear matrix protein-DNA interaction sites in the osteocalcin promoter. Vitamin D responsiveness in the stably transfected cells is obtained with the inclusion of 0.53 kb or additional upstream promoter sequences. Therefore, these sequences satisfy the requirements for binding of basal and enhancer transcription factors as well as interactions between them within a chromatin context. Both maximal basal expression and maximal vitamin D responsiveness are obtained with cells carrying either the 0.72-kb or the 1.1-kb promoter fragment. Cells carrying the 1.1-kb promoter show DNase I hypersensitivity at both the basal promoter and the vitamin D response element-containing domains, locations that also exhibit DNase I hypersensitivity in the endogenous OC promoter. In addition, we have documented changes in the basal activity and vitamin D responsiveness of the stably integrated 1.1 kb promoter as a function of cell density-mediated growth inhibition, which is accompanied by up-regulation of bone phenotypic genes. Thus, important aspects of OC gene transcriptional regulation that cannot be investigated in transient transfection assays can be addressed using ROS 17/2.8 cells stably transfected with OC promoter-reporter constructs.

Contributions of distal and proximal promoter elements to glucocorticoid regulation of osteocalcin gene transcription

Previous studies identified several glucocorticoid response elements (GREs) in the 5'-promoter region of the rat osteocalcin (OC) gene by purified receptor binding. The present study addresses functionality of the GRE sequences in the proximal promoter at nucleotide (nt) -16 to -1 downstream of the TATA element together with the GRE half-element in the OC box at nt -86 to -81. This was done by assaying glucocorticoid responsiveness [at 10(-6) M dexamethasone (DEX)], and in combination with 10(-8) M 1,25-dihydroxyvitamin D3, of a series of deleted and mutated OC promoter reporter constructs (OCCAT) in osteoblast-like cells, the ROS 17/2.8 rat osteosarcoma line. Promoter deletion analysis revealed an additional GRE in the distal promoter at nt -697 to -683 that functions to suppress OC transcription. In the absence of this upstream negative GRE (nGRE), the -531 OCCAT construct exhibited enhanced promoter activity in response to DEX (1.8-fold DEX/Control), but further deletion (-348 and -108 OCCAT constructs) restored DEX suppression to OC promoter activity (0.6- and 0.8-fold DEX/Control, respectively). Mutations introduced in both the proximal GRE (nt -16 to -1) and the half-GRE in the OC box, or in the proximal GRE alone, nearly abrogated DEX responsiveness of OC promoter activity. Both distal and proximal GREs specifically bound glucocorticoid receptor present in ROS 17/2.8 nuclear extracts as shown by competition with wild type and mutated oligonucleotides and antibody inhibition of binding. Furthermore, both GREs, independently, conferred DEX-responsive transcriptional repression to the heterologous thymidine kinase basal promoter. We also report that glucocorticoid suppression of 1,25-dihydroxyvitamin D3-stimulated transcription occurs independently of distal or proximal GREs. Taken together, these results demonstrate that in vivo responsiveness of OC to DEX involves the integrative activities of several functional promoter elements.