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Congenital hypothyroidism (CH) can lead to irreversible central nervous system (CNS) damage. However, the pathogenesis of the developmental brain disorders caused by CH has not been completely elucidated. ARPC5 and CRMP2 are closely associated with neurite outgrowth in brain development. Thus, the aim of the present study was to determine whether CRMP2B and ARPC5 expression is altered in the developing cerebral cortex of rats with CH. Control rats and rats with hypothyroidism were sacrificed at birth and at 15 days postpartum. We performed qRT-PCR to detect differences in the crmp2B and arpc5 mRNA expression in the right half of the frontal cortex of these rats. Western blotting was then used to detect differences in CRMP2B and ARPC5 protein expression. Furthermore, immunohistochemical analysis was performed on the left half of the frontal cortex to detect abnormal localization of CRMP2B and ARPC5. Results showed increased expression of the nuclear short isoform of CRMP2B and decreased expression of full-length CRMP2B and ARPC5 in cortical neurons of rats with hypothyroidism. These findings demonstrate that reduced levels of thyroid hormones can inhibit the expression of full-length CRMP2B and ARPC5 and promote nuclear transformation of the short isoform of CRMP2B. CRMP2B and ARPC5 may participate in CNS injury mediated by hypothyroidism by inducing neurite outgrowth inhibition and cytoskeletal protein disorganization.

Objective: To screen differentially expressed brain proteins with proteomic method in cerebral cortex of neonatal rats with congenital hypothyroidism., Method: From the 13th day of gestation, pregnant Wistar rats from the experimental group were given intragastrically with 2.5 ml of 1% propylthiouracil daily. Cerebral cortex specimens were collected from the control and hypothyroidism neonatal rats. Two-directional electrophoresis (2-DE) was applied to analyze protein expression diversities between the euthyroid and hypothyroidism neonatal rat cerebral cortex. Protein spots with significantly different expression were screened and identified by mass spectrometry. Radioimmunoassay (RIA) was used to analyze serum FT(3), FT(4) levels of each groups., Result: The body weight of hypothyroid neonatal rats were lower than those in the corresponding control group (t = -8.07, P < 0.01). The FT(3) levels of hypothyroid neonatal rats were lower than those in the corresponding control group (t = 5.39, P < 0.01). The FT(4) levels of hypothyroid neonatal rats were lower than those in the corresponding control group (t = 7.62, P < 0.01). Stable 2-DE maps of normal and CH neonatal rat were constantly obtained. The maps were analyzed by software. Seven protein spots with high reproducibility, high resolution and significantly different expression were chosen and identified by mass spectrometry, including collapsing response mediator protein 2, actin related protein 2/3 complex subunit 5, ubiquitin-conjugating enzyme E2-25K, ATP synthase subunit d, Cu-Zn superoxide dismutase, synuclein alpha, and nucleoside diphosphate kinase., Conclusion: The value of this research is demonstrated here by the identification of several proteins known to be associated with nerve synapse structures formation, cell survival, metabolism, cell signal transduction, neural differentiation and nerve growth in the central nervous system. Furthermore this study identified several proteins except for collapsing response mediator protein 2 and Cu-Zn superoxide dismutase that have not previously been described in the literature and which may play an important role as either sensitive biomarkers of brain dysfunction caused by congenital hypothyroidism. In congenital hypothyroidism, brain development retardation may be related with some important processes, including abnormal synaptic formation, excess ROS production and apoptosis. The above-mentioned proteins may play critical roles in the processes, which provide valuable clues to clarify the pathogenesis of brain developmental disorders induced by congenital hypothyroidism.