Thyroid hormone receptor isoform expression in livers of critically ill patients.

OBJECTIVE: The THRA gene encodes two isoforms of the thyroid hormone receptor (TR), TRalpha1 and TRalpha2. The ratio of these splice variants could have a marked influence on T3-regulated gene expression, especially during illness. DESIGN: We studied the expression of the isoforms TRbeta1, TRalpha1, and TRalpha2 and 5'-deiodinase in postmortem liver biopsies of 58 patients who were critically ill and died in the intensive care unit (ICU). All mRNA levels were determined using real-time PCR. MAIN OUTCOME: All ratios of the biopsies were higher than those found in three normal liver biopsies due to an increased TRalpha1 level. The TRalpha1/TRalpha2 ratio increased with age and severity of illness following the equation: TRalpha1/TRalpha2 ratio = - 1.854 + (0.0323 x age) + (0.0431 x Therapeutic Intervention Scoring System score) indicating that 28% of the changed TRalpha1/TRalpha2 ratio can be predicted by these clinical variables. There was no effect of randomization to intensive insulin therapy or glucocorticoid or thyroid hormone treatment on the TRalpha1/TRalpha2 ratio or TRbeta1. Furthermore, no relation was seen between the expression levels of the 5'-deiodinase mRNA and TR isoforms or the triiodothyronine T3 levels. CONCLUSION: It appears that in critically ill patients the ratio of TRalpha1/TRalpha2 expression increases with age and severity of illness, possibly indicating a mechanism to enhance sensitivity to T3 in the oldest and sickest patients.

Memory function and serotonin transporter promoter gene polymorphism in ecstasy (MDMA) users.

Although 3,4-methylenedioxymethamphetamine (MDMA or ecstasy) has been shown to damage brain serotonin (5-HT) neurons in animals and possibly humans, little is known about the long-term consequences of MDMA-induced 5-HT neurotoxic lesions on functions in which 5-HT is involved, such as cognitive function. Because 5-HT transporters play a key element in the regulation of synaptic 5-HT transmission it may be important to control for the potential covariance effect of a polymorphism in the 5-HT transporter promoter gene region (5-HTTLPR) when studying the effects of MDMA as well as cognitive functioning. The aim of the study was to investigate the effects of moderate and heavy MDMA use on cognitive function, as well as the effects of long-term abstention from MDMA, in subjects genotyped for 5-HTTLPR. A second aim of the study was to determine whether these effects differ for females and males. Fifteen moderate MDMA users (<55 lifetime tablets), 22 heavy MDMA+ users (>55 lifetime tablets), 16 ex-MDMA+ users (last tablet > 1 year ago) and 13 controls were compared on a battery of neuropsychological tests. DNA from peripheral nuclear blood cells was genotyped for 5-HTTLPR using standard polymerase chain reaction methods.A significant group effect was observed only on memory function tasks (p = 0.04) but not on reaction times (p = 0.61) or attention/executive functioning (p = 0.59). Heavy and ex-MDMA+ users performed significantly poorer on memory tasks than controls. In contrast, no evidence of memory impairment was observed in moderate MDMA users. No significant effect of 5-HTTLPR or gender was observed. While the use of MDMA in quantities that may be considered "moderate" is not associated with impaired memory functioning, heavy use of MDMA use may lead to long lasting memory impairments. No effect of 5-HTTLPR or gender on memory function or MDMA use was observed.

Thyroid hormone receptor expression in the human hypothalamus and anterior pituitary.

In the present study, we describe for the first time the distribution of thyroid hormone receptor (TR) isoforms in the human postmortem hypothalamus and anterior pituitary using immunocytochemistry. We used a set of polyclonal antisera raised against the specific isoforms of the human TR. The distribution of TR alpha 1, alpha 2, beta 1, and beta 2 was studied in consecutive sections of six hypothalami and pituitaries. Staining intensity showed strong interindividual variation but was consistently present in the infundibular nucleus, paraventricular nucleus, and supraoptic nucleus. In addition, strong TR immunoreactivity was observed in the anterior pituitary. Neuropeptide Y and proopiomelanocortin mRNA-positive cells in the infundibular nucleus, which were studied in three other hypothalami, appeared not to express TRs, and thus, the neurons expressing TRs in the human mediobasal hypothalamus remain to be characterized.

TR(beta)1 protein is preferentially expressed in the pericentral zone of rat liver and exhibits marked diurnal variation.

We investigated the distribution and diurnal variation of TR(beta)1 protein expression in liver with specific antibodies against TR(beta)1. Immunohistochemistry showed a zonal distribution of TR(beta)1 with maximum expression in the pericentral zone matching some known T(3)-responsive enzyme activities in the liver, such as glutamine synthetase, cholesterol 7alpha- hydroxylase, and spot 14. Combining immunohistochemistry and image analysis we found and quantified the same zonal distribution for 5'-deiodinase type 1 as for TR(beta)1. Western blot analysis revealed a profound diurnal variation for TR(beta)1 protein expression, with highest levels at the beginning of the dark period. TR(beta)1 diurnal variation partly overlaps with the T(3)-responsive genes, cholesterol 7alpha-hydroxylase and spot 14. Furthermore, TR(beta)1 distribution along the porto-central axis does not change during the day, indicating that the zonal expression of TR(beta)1 is stable. This is the first time that zonal distribution in liver has been demonstrated for a member of the nuclear receptor family. This finding together with the observed diurnal rhythm has major implications for interpreting and timing experiments concerning the TR and its downstream actions in liver.

Induction of thyroid hormone-degrading deiodinase in cardiac hypertrophy and failure.

The similarities between the changes in cardiac gene expression in pathological ventricular hypertrophy and hypothyroidism suggest a role of impaired cardiac thyroid hormone (TH) action in the development of contractile dysfunction during chronic cardiac pressure overload. Here we studied the possible involvement of altered cardiac TH metabolism using a rat model of right-ventricular (RV) hypertrophy induced by pressure-overload. Pathological RV hypertrophy was indicated by decreased mRNA levels of sarcoplasmic reticulum(SR) Ca2-ATPase type 2a (SERCA2a) and myosin heavy chain a (MHCalpha), and increased levels of MHCbeta mRNA. Enzyme activity of type HI deiodinase (D3), which converts T4 and T3 to the inactive compounds rT3 and 3,3'-T2, respectively, was identified in ventricular tissue. This activity was stimulated up to five fold in hypertrophic RV, but remained unaltered in the non-hypertrophic left ventricle (LV). A low level of type Ideiodinase activity was also detected, which decreased significantly in both RV and LV. Stimulation of RV D3 activity was significantly higher in those animals in which hypertrophy progressed to heart failure, compared to animals that developed compensatory hypertrophy. The induction of a cardiac TR-degrading deiodinase maybe expected to result in reduced cellular levels of T3 and thereby contribute to a local hypothyroid state in the hypertrophic and, particularly, in the failing ventricle.

The COX-2 promoter polymorphism -765 G>C is associated with early-onset, conventional and stump gastric cancers.

COX-2 overexpression is known to be an important mechanism in gastric carcinogenesis. Previously we have found that early-onset gastric cancer has a unique COX-2 low-expressing phenotype that differs significantly from that of the frequent overexpression seen in conventional gastric cancers. To investigate whether the COX-2 -765 G>C promoter polymorphism (known to lead to a reduction of COX-2 promoter activity in the colon) may explain this difference in expression, we carried out single-nucleotide polymorphism (SNP) analysis of 241 gastric cancers, including early-onset gastric cancer, conventional gastric cancers and gastric stump cancers, as well as in 100 control patients, using real-time PCR and sequence analysis, and correlated these findings with COX-2 expression using immunohistochemistry. We found that the C allele was present in 30% of early-onset gastric cancers, 24% of conventional gastric cancer, 23% of stump cancers, in contrast to 41% in the control group. There was a statistically significant difference in the presence of the C allele in patients with gastric cancer compared with the control group (P=0.007), with the C allele being associated with protection against gastric cancer. However, there was no significant difference between the early-onset, conventional and stump gastric cancer groups. Interestingly, there was no correlation between the presence of the C allele and a difference in COX-2 expression. In summary, we show that the COX-2 -765 G allele promoter polymorphism is significantly associated with gastric cancer when compared with the normal control group, but does not appear to be related directly to COX-2 expression pattern in gastric cancer. Although early-onset gastric cancers appear to have a unique COX-2 expression pattern when compared with conventional gastric cancer, the exact mechanism by which this occurs is yet to be elucidated.

Expression of thyroid hormone receptors A and B in developing rat tissues; evidence for extensive posttranscriptional regulation.

The perinatal changes in the pattern of expression of the thyroid hormone receptor (TR) isoforms TRalpha (1) TRalpha (2), TRbeta (1), and TRbeta (2) were investigated using in situ hybridization and immunohistochemistry, and RT-PCR and western blotting as visualization and quantification techniques respectively. In liver, lung, and kidney, TRalpha mRNA was expressed in the stromal and TRbeta mRNA in the parenchymal component of the tissues. When compared with liver, TRalpha mRNA concentrations were tenfold higher in lung, kidney, and intestine, and 100-fold higher in brain, with TRalpha (2) mRNA concentrations exceeding those of TRalpha (1) 5-to 10-fold. Tissue TRbeta (1) mRNA concentrations were similar in liver, lung, and brain, and 3- to 5-fold higher in kidney and intestine. None of the TRbeta (2) mRNA could be detected outside the pituitary. Tissue TRalpha (2) and TRbeta (1) protein levels reached adult levels at 5 days before birth, whereas TRalpha (1) protein peaked after birth. Because of the distinct time-course of thyroid hormone-binding receptors TRalpha (1) and TRbeta (1), we speculate that an initiating, TRbeta (1)-mediated signaling from the parenchyma is followed by a TRalpha (1)-mediated response in the stroma. When compared with organs with a complementary parenchymal-stromal expression pattern, organs with extensive cellular co-expression of TRalpha and TRbeta (brain and intestinal epithelium) were characterized by a very low TRalpha protein: mRNA ratio, implying a low translational efficiency of TR mRNA or a high turnover of TR protein. The data indicate that the TR-dependent regulatory cascades are controlled differently in organs with a complementary tissue expression pattern and in those with cellular co-expression of the TRalpha and TRbeta genes.