Delayed development of specific thyroid hormone-regulated events in transthyretin null mice

Abstract

Thyroid hormones (THs) are vital for normal postnatal development. Extracellular TH distributor proteins create an intravascular reservoir of THs. Transthyretin (TTR) is a TH distributor protein in the circulatory system and is the only TH distributor protein synthesized in the central nervous system. We investigated the phenotype of TTR null mice during development. Total and free 3',5',3,5-tetraiodo-L-thyronine (T(4)) and free 3',3,5-triiodo-L-thyronine (T(3)) in plasma were significantly reduced in 14-day-old (P14) TTR null mice. TTR null mice also displayed a delayed suckling-to-weaning transition, decreased muscle mass, delayed growth, and retarded longitudinal bone growth. In addition, ileums from postnatal day 0 (P0) TTR null mice displayed disordered architecture and contained fewer goblet cells than wild type. Protein concentrations in cerebrospinal fluid from P0 and P14 TTR null mice were higher than in age-matched wild-type mice. In contrast to the current literature based on analyses of adult TTR null mice, our results demonstrate that TTR has an important and nonredundant role in influencing the development of several organs.

Fig. 1.

Femur growth in developing and adult wild-type and transthyretin (TTR) null mice. A transient modification in bone growth was detected in TTR null mice; this was most obvious at 4 wk of age (representative Alizarin Red-stained femurs shown in A). Scale bar is 2.5 mm. Femoral length (B) and width (C) were significantly altered during growth in TTR null mice. Total growth plate width and proliferative (Prol) and hypertrophic (Hyp) zone widths were measured at 2 and 10 wk (D-F). Data are means ± SE; *P < 0.05, **P < 0.01, and ***P < 0.005 (by ANOVA with Fisher's post hoc test); n = 6, except 4-wk-old TTR null mice where n = 5 and 10-wk-old mice where n = 12.

Fig. 2.

The small intestine from postnatal day (P) 0 wild-type (WT) and TTR null mice. A: longitudinal small intestinal ileum sections from P0 wild-type and TTR null mice were stained with Periodic acid-Schiff (PAS) reagent to highlight mucin (red) in goblet cells (G) indicated by arrow. Low-power fields (×10 magnification; scale bar = 100 μm) were captured and printed from slides representing four animals of each genotype, and these were used to count (as coded slides) Pas-positive cells. B: the number of PAS-positive cells/field expressed as means ± SE (n = 4) for each genotype is shown.

Fig. 3.

Protein concentration in cerebrospinal fluid (CSF) from P0, P14, and adult wild-type and TTR null mice. CSF was collected from the cisterna magna of mice and processed as described in materials and methods. P14 and adult CSF samples were pooled according to genotype (n = 2–6). Protein concentrations were determined. Values are means ± SE. P0 wild type, n = 11; P0 TTR null, n = 5; P14 wild type, n = 8; P14 TTR null, n = 4; adult wild type, n = 8; adult TTR null, n = 9. Statistical significance between means (one-way ANOVA with Bonferroni post hoc test) are indicated by ***P < 0.005 and **P < 0.01.