Wnt activation promotes neuronal differentiation of glioblastoma

One of the biggest challenges in tumour research is the possibility to reprogram cancer cells towards less aggressive phenotypes. In this study, we reprogrammed primary Glioblastoma multiforme (GBM)-derived cells towards a more differentiated and less oncogenic phenotype by activating the Wnt pathway in a hypoxic microenvironment. Hypoxia usually correlates with malignant behaviours in cancer cells, but it has been recently involved, together with Wnt signalling, in the differentiation of embryonic and neural stem cells. Here, we demonstrate that treatment with Wnt ligands, or overexpression of β-catenin, mediate neuronal differentiation and halt proliferation in primary GBM cells. An hypoxic environment cooperates with Wnt-induced differentiation, in line with our finding that hypoxia inducible factor-1α (HIF-1α) is instrumental and required to sustain the expression of β-catenin transcriptional partners TCF-1 and LEF-1. In addition, we also found that Wnt-induced GBM cell differentiation inhibits Notch signalling, and thus gain of Wnt and loss of Notch cooperate in the activation of a pro-neuronal differentiation program. Intriguingly, the GBM sub-population enriched of cancer stem cells (CD133⁺ fraction) is the primary target of the pro-differentiating effects mediated by the crosstalk between HIF-1α, Wnt, and Notch signalling. By using zebrafish transgenics and mutants as model systems to visualize and manipulate in vivo the Wnt pathway, we confirm that Wnt pathway activation is able to promote neuronal differentiation and inhibit Notch signalling of primary human GBM cells also in this in vivo set-up. In conclusion, these findings shed light on an unsuspected crosstalk between hypoxia, Wnt and Notch signalling in GBM, and suggest the potential to manipulate these microenvironmental signals to blunt GBM malignancy.

Absence of primary hypothyroidism and goiter in Slc26a4 (-/-) mice fed on a low iodine diet

BACKGROUND

Mutations in the SLC26A4 gene, coding for the anion transporter pendrin, are responsible for Pendred syndrome, characterized by congenital sensorineural deafness and dyshormonogenic goiter. The physiological role of pendrin in the thyroid is still unclear and the lack of a thyroid phenotype in some patients with SLC26A4 mutations and in Slc26a4 (-/-) mice indicate the existence of environmental or individual modifiers able to compensate for pendrin inactivation in the thyroid. Since pendrin can transport iodide in vitro, variations in iodide supply have been claimed to account for the thyroid phenotype associated with pendrin defects.

AIM

The Slc26a4 (-/-) mouse model was used to test the hypothesis that iodide supply may influence the penetrance and expressivity of SLC26A4 mutations.

MATERIALS AND METHODS

Slc26a4 (-/-) and (+/+) mice were fed up to 6 months on a standard or low iodine diet and were evaluated for thyroid structural abnormalities or biochemical hypothyroidism.

RESULTS

A 27-fold iodide restriction induced similar modifications in thyroid histology, but no differences in thyroid size, T4 or TSH levels were observed between between Slc26a4 (-/-) and (+/+) mice, either in standard conditions and during iodine restriction.

CONCLUSIONS

Iodide restriction is not able to induce a thyroid phenotype in Slc26a4 (-/-) mice. These experimental data, together with those coming from a review of familial Pendred cases leaving in regions either with low or sufficient iodide supply, support the idea that the expression of thyroid phenotype in Pendred syndrome is more powerfully influenced by individual factors than by dietary iodide.

Increased risk for non-autoimmune hypothyroidism in young patients with congenital heart defects

CONTEXT

Newborns with congenital hypothyroidism (CH) have an increased risk for congenital heart defects (CHD) due to a common embryonic developmental program between thyroid gland and heart and great vessels.

OBJECTIVE

Our objective was to investigate the prevalence and origin of thyroid disorders in young patients with CHD.

DESIGN AND SETTING

We conducted a prospective observational study between January 2007 and January 2009 in academic Pediatric Cardiosurgery and Endocrinology.

PATIENTS

Patients included 324 children (164 males, 160 females, aged 0.2-15.4 yrs) with CHD.

INTERVENTION

Subjects underwent hormonal and genetic screening.

MAIN OUTCOME MEASURES

Serum TSH and thyroid hormone levels were assessed.

RESULTS

Two CHD patients were diagnosed with CH at the neonatal screening (1:162). Mild hypothyroidism (serum TSH > 4.0 μU/ml) was diagnosed and confirmed 6 months later [TSH = 5.4 ± 1.5 μU/ml; free T(4) = 1.3 ± 0.2 ng/dl (normal values 0.8-1.9)] in 37 children (11.5%) who were negative at neonatal screening. Hypothyroidism was not related to type of CHD, whereas TSH levels positively correlated with serum N-terminal pro-type B natriuretic peptide levels. Biochemical and ultrasound findings consistent with thyroid autoimmunity were present in three of 37 hypothyroid children (8.1%). One patient had hemiagenesis (2.7%). Variations in candidate genes were screened in CHD patients. NKX2.5 coding sequence was normal in all samples. A 3-Mb microdeletion in 22q11.2 was detected in three patients (8.3%), whereas only known polymorphisms were identified in TBX1 coding sequence.

CONCLUSIONS

CHD patients have an increased risk for both CH (10-fold higher) and acquired mild hypothyroidism (3-fold higher). Unrecognized mild hypothyroidism may negatively affect the outcome of CHD children, suggesting that thyroid function should be repeatedly checked. Thyroid autoimmunity and 22q11.2 microdeletions account for small percentages of these cases, and still unknown mechanisms underline such a strong association.

Thyroid gland development and function in the zebrafish model

Thyroid development has been intensively studied in the mouse, where it closely recapitulates the human situation. Despite the lack of a compact thyroid gland, the zebrafish thyroid tissue originates from the pharyngeal endoderm and the main genes involved in its patterning and early development are conserved between zebrafish and mammals. In recent years, the zebrafish has become a powerful model not only for the developmental biology studies, but also for large-scale genetic analyses and drug screenings, mostly thanks to the ease with which its embryos can be manipulated and to its translucent body, which allows in vivo imaging. In this review we will provide an overview of the current knowledge of thyroid gland origin and differentiation in the zebrafish. Moreover, we will consider the action of thyroid hormones and some aspects related to endocrine disruptors.