Transthyretin-thyroid hormone internalization by trophoblasts.

Normal fetal neurological development depends on a regulated supply of maternal thyroid hormone (TH). We have previously demonstrated that transthyretin (TTR) a TH binding protein, is synthesized, secreted and internalized by trophoblast cells and may provide a route for the transfer of TH from mother to fetus. Our objective was to determine if a member of the low-density lipoprotein receptor family mediates TTR or TTR-TH internalization. TTR-TH internalization by JEG-3 cells is reduced in the presence of receptor associated protein (RAP) or albumin suggesting that TTR-TH is internalized through an LDL-receptor dependent endocytic process.

Transthyretin and the human placenta.

Since its discovery, transthyretin (TTR) has been regarded as an important hepatically derived protein carrier of thyroid hormones and retinol in blood. However, in more recent years it has been shown that TTR has other important functions. TTR is abundant in cerebrospinal fluid, where it may be involved in transport of thyroid hormones into the brain. TTR derived amyloid is associated with diseases such as senile systemic amyloidosis, familial amyloid polyneuropathy and familial amyloid cardiomyopathy. Recently, synthesis, secretion and uptake of TTR by human placenta have been reported. TTR appears to play an important role in the delivery of maternal thyroid hormone to the developing fetus. This review explores the various proposed roles of TTR and more recent findings on TTR synthesis and expression in the placenta.

Secretion and transfer of the thyroid hormone binding protein transthyretin by human placenta.

CONTEXT: The thyroid hormone and retinol binding protein transthyretin (TTR) is synthesised by human trophoblasts. Polarised JEG-3 choriocarcinoma cells grown in bicameral chambers secrete TTR predominantly apically but also basally and these cells and human trophoblasts also take up TTR suggesting that there may be a placental TTR shuttle that participates in materno-fetal transfer of thyroid hormones and retinol. OBJECTIVES AND METHODS: Our objective was to investigate TTR secretion into the maternal and fetal circuits of the ex vivo dually perfused placental lobule to confirm that placenta secretes TTR into the fetal circulation. We also investigated translocation of Alexa Fluor-594 labelled TTR from incubation medium into the fetal placental capillaries in early (14-15 weeks) and term placental villus explants. RESULTS: The perfused placental lobule secretes TTR into the maternal and fetal circuits. Secretion in both circuits is linear with time and is predominantly into the maternal circuit (mean maternal/fetal ratio 99.4 ± 25.6). The mean data fitted well to a three compartment mathematical model (maternal circuit, placenta and fetal circuit, constant secretion of TTR and return of maternal circuit TTR to the placental compartment). Explants from early (14-15 weeks) and late (38-40 weeks) placentas translocated fluorescently labelled TTR from medium to villus (fetal) capillaries. CONCLUSIONS: Our results confirm that human placenta secretes TTR into maternal and fetal circulations and supports the hypothesis that placental TTR secreted into the maternal placental circulation can be taken up by trophoblasts and translocated to the fetal circulation, forming a TTR shuttle system. This may have important implications for materno-fetal transfer of thyroid hormones, retinol/retinol binding protein and xenobiotics (such as polychlorinated biphenyls) all of which bind to TTR.

Expression and uptake of the thyroxine-binding protein transthyretin is regulated by oxygen in primary trophoblast placental cells.

Transplacental delivery of maternal thyroid hormones to the fetus, in particular thyroxine (T4), is critical in ensuring normal fetal neurological development. The fetus relies on maternal T4 till around 16 weeks gestation, but mechanisms of placental T4 transport are not yet fully elucidated. Placenta produces, secretes and takes up the thyroid hormone-binding protein transthyretin (TTR). Many placental genes are regulated by oxygen levels, which are relatively low (1%) in the early first trimester, rising to 3% in the mid first trimester and 8% in the early second trimester and thereafter. We examined the expression and uptake of TTR in isolated primary human placental cytotrophoblast cells cultured under different oxygen concentrations (1, 3, 8, 21% O2 and 200 µM desferrioxamine (DFO)) for 24 h. We observed sevenfold higher expression of TTR mRNA and protein levels at 1% O2 than at 8 and 21% O2. Significant increases were observed after culture at 3% O2 and following DFO treatment. We observed significantly higher uptake of ¹²5I-TTR and Alexa-594-TTR when cells were cultured at 1 and 3% O2 and in the presence of 200 µM DFO than at 8 and 21% O2. When JEG-3 choriocarcinoma cells were transfected with TTR promoter reporter constructs, increased luciferase activity was measured in cells cultured at 1 and 3% O2 in comparison to 8 and 21% O2. We conclude that placental TTR expression and uptake is increased by the relative hypoxia observed in the first trimester of pregnancy, a time when materno-fetal T4 transfer is the sole source of fetal T4.

Ontogenic changes in placental transthyretin.

OBJECTIVES: Before secretion of fetal thyroid hormone at around 16 weeks gestation normal fetal development depends on a constant supply of maternal thyroid hormone (TH), particularly thyroxine (T(4)). The detailed mechanisms of transplacental delivery of TH are still uncertain. The TH binding protein, transthyretin (TTR), is produced and secreted by placenta and may play a role in this process. The ontogeny of placental TTR is unknown. Our aim was to study changes in placental TTR in early and late pregnancy. STUDY DESIGN: We collected placentas from surgically terminated pregnancies between 6 and 17 weeks gestation (n = 44) and from normal term (38-39 weeks) pregnancies following caesarean section (n = 5). Real time-PCR, western blotting and immunohistochemistry were used to determine TTR mRNA and protein levels. RESULTS: There were highly significant correlations between gestational age and TTR mRNA (r = 0.974; p < 0.0001) and between gestational age and TTR protein (r = 0.901; p < 0.001) levels between weeks 6 and 13 of gestation. TTR expression did not increase between 13 and 17 weeks and was not different at term. Good correlation was observed between TTR mRNA and TTR protein between individual placental samples (r = 0.916; p < 0.0001). A similar trend was observed using immunohistochemical staining of placental paraffin sections. CONCLUSIONS: Our results demonstrate that TTR is expressed in the human placenta from at least 6 weeks gestation. Levels rise during the first trimester at a time when placental oxygen tensions are also rising. We hypothesise that TTR production and secretion by the placenta may facilitate transplacental delivery of TH to the fetus.

Identification of claudin-4 as a marker highly overexpressed in both primary and metastatic prostate cancer.

In the quest for markers of expression and progression for prostate cancer (PCa), the majority of studies have focussed on molecular data exclusively from primary tumours. Although expression in metastases is inferred, a lack of correlation with secondary tumours potentially limits their applicability diagnostically and therapeutically. Molecular targets were identified by examining expression profiles of prostate cell lines using cDNA microarrays. Those genes identified were verified on PCa cell lines and tumour samples from both primary and secondary tumours using real-time RT-PCR, western blotting and immunohistochemistry. Claudin-4, coding for an integral membrane cell-junction protein, was the most significantly (P<0.00001) upregulated marker in both primary and metastatic tumour specimens compared with benign prostatic hyperplasia at both RNA and protein levels. In primary tumours, claudin-4 was more highly expressed in lower grade (Gleason 6) lesions than in higher grade (Gleason >or=7) cancers. Expression was prominent throughout metastases from a variety of secondary sites in fresh-frozen and formalin-fixed specimens from both androgen-intact and androgen-suppressed patients. As a result of its prominent expression in both primary and secondary PCas, together with its established role as a receptor for Clostridium perfringens enterotoxin, claudin-4 may be useful as a potential marker and therapeutic target for PCa metastases.

High-resistance versus variable-resistance training in older adults.

PURPOSE: The purpose of this study was to compare the effects of high-resistance (HR) training, 3 times.wk(-1) at 80% maximum strength (1RM) with 3 times.wk(-1) variable-resistance (VR) training (once-weekly training at 80%, 65%, and 50% 1RM) in older adults. METHODS: The study was a 6-month resistance training intervention conducted in the Birmingham Alabama metropolitan area, and included healthy volunteer men and women over the age of 60. Twenty-eight subjects were assigned randomly to two training groups. Eight volunteers served as controls. Before and after 25 wk of training, body composition was measured by densitometry; strength by isometric tests; and difficulty in performing daily activity tasks (DAT) by measuring heart rate, oxygen uptake, electromyography, and perceived exertion. In addition, 1RM strength was measured every 25 d throughout the 6 months of training. Repeated measures ANOVA and paired t-tests with Bonferroni corrections for additive alpha were used to analyze the data. RESULTS: The control group did not significantly change in any study parameter. No significant change in body weight occurred for any group. However, the HR and VR groups increased fat free mass (FFM) similarly (1.8 kg and 1.9 kg, respectively). Both training groups increased strength significantly, without significant differences in change. No significant change in oxygen uptake occurred during DAT. However, there was a significant time effect for heart rate and perceived exertion. Greater decrease in normalized integrated electromyography during the carry task was found in the VR group over the HR and control groups. CONCLUSION: Despite similar increases in strength and fat free mass, the VR group decreased difficulty of performing the carry task more than the HR group. These data suggest that larger improvements in DAT may be achieved if frequency of high-resistance training is less than 3 times.wk(-1).

The interrelationship among muscle mass, strength, and the ability to perform physical tasks of daily living in younger and older women.

The purpose of this study was to objectively compare the difficulty and determine the contribution of strength and muscle mass to the performance of physical tasks of daily living in a group of younger and older women. A cross-sectional design was used. Volunteer participants were from the community of Birmingham, AL; there were 21 older (aged 60-75 years) and 20 younger (23-34 years) healthy women in the study. Subjects were matched for height and weight. Their testing included total and regional body composition evaluation by use of dual-energy x-ray absorptiometry, isometric strength tests of elbow flexors and knee extensors, and integrated electromyography (IEMG) evaluation while the subjects were standing from and sitting into a chair, and while they were carrying a small load (weight relative to strength). A two-way analysis of variance and a two-way analysis of covariance with repeated measures, Pearson product correlation, and first-order partial correlations were used to analyze the data. A significant inverse correlation was observed between age and isometric strength of both the knee extensors and elbow flexors. Adjusting for upper leg lean tissue did not change the significant inverse correlation between age and knee extensor strength. However, after an adjustment for arm lean tissue, there was no significant correlation between elbow flexor strength and age. Older women experienced significantly greater difficulty in standing than younger women as measured by quadriceps normalized IEMG (i.e., IEMG during task/IEMG during maximum isometric strength test). This difference persisted even after the covariate upper leg lean tissue was added to the model. No significant difference was observed between younger and older women for difficulty (biceps normalized IEMG) during the carry task after the covariate arm lean tissue was added to the model. The older women in this study had less strength in the knee extensors and experienced greater difficulty standing from a chair than the younger women, even after the covariate upper leg lean tissue was added to the model. This suggests that other factors, in addition to loss of lean tissue, contribute to the age-related decline of muscular strength and the ability to perform tasks with the legs. In contrast, although elbow flexor strength declined, this appeared to be largely due to decreased arm lean tissue mass.