title: Thyroid hormone receptor binding to DNA and T3-dependent transcriptional activation are inhibited by uremic toxins.
abstract: BACKGROUND: There is a substantial clinical overlap between chronic renal failure (CRF) and hypothyroidism, suggesting the presence of hypothyroidism in uremic patients. Although CRF patients have low T3 and T4 levels with normal thyroid-stimulating hormone (TSH), they show a higher prevalence of goiter and evidence for blunted tissue responsiveness to T3 action. However, there are no studies examining whether thyroid hormone receptors (TRs) play a role in thyroid hormone dysfunction in CRF patients. To evaluate the effects of an uremic environment on TR function, we investigated the effect of uremic plasma on TRbeta1 binding to DNA as heterodimers with the retinoid X receptor alpha (RXRalpha) and on T3-dependent transcriptional activity. RESULTS: We demonstrated that uremic plasma collected prior to hemodialysis (Pre-HD) significantly reduced TRbeta1-RXRalpha binding to DNA. Such inhibition was also observed with a vitamin D receptor (VDR) but not with a peroxisome proliferator-activated receptor gamma (PPARgamma). A cell-based assay confirmed this effect where uremic pre-HD ultrafiltrate inhibited the transcriptional activation induced by T3 in U937 cells. In both cases, the inhibitory effects were reversed when the uremic plasma and the uremic ultrafiltrate were collected and used after hemodialysis (Post-HD). CONCLUSION: These results suggest that dialyzable toxins in uremic plasma selectively block the binding of TRbeta1-RXRalpha to DNA and impair T3 transcriptional activity. These findings may explain some features of hypothyroidism and thyroid hormone resistance observed in CRF patients.
authors.affiliation: Molecular Pharmacology Laboratory, Department of Pharmaceutical Sciences, School of Health Sciences, University of Brasilia, Brazil. chico@unb.br.
authors.forename: Guilherme M
authors.initials: GM
authors.lastname: Santos
authors.forename: Carlos J
authors.initials: CJ
authors.lastname: Pantoja
authors.forename: Aluízio
authors.initials: A
authors.lastname: Costa E Silva
authors.forename: Maria C
authors.initials: MC
authors.lastname: Rodrigues
authors.forename: Ralff C
authors.initials: RC
authors.lastname: Ribeiro
authors.forename: Luiz A
authors.initials: LA
authors.lastname: Simeoni
authors.forename: Noureddine
authors.initials: N
authors.lastname: Lomri
authors.forename: Francisco Ar
authors.initials: FA
authors.lastname: Neves