Thyroid hormone induces glial lineage of primary neurospheres derived from non-pathological and pathological rat brain: implications for remyelination-enhancing therapies

Thyroid hormone exerts a critical role in developmental myelination, acting on the production and maturation of oligodendrocyte, and on the expression of genes encoding for myelin protein. Since remyelination is considered a recapitulation of cellular and molecular events occurring during development, we tested the possibility of stimulating the oligodendroglial lineage and maturation in neurospheres derived from the subventricular zone of adult rats using 3,5,3′-l-triiodothyronine (T3). Both non-pathological and pathological brains derived from rats affected by the inflammatory-demyelinating disease experimental allergic encephalomyelitis (EAE) were included in the study. We investigated the effect of in vitro T3 exposure on: (i) the expression of nuclear thyroid hormone receptors; (ii) proliferation rate; (iii) differentiation into neurons, astrocytes and oligodendrocytes, focusing our attention on oligodendrocyte maturation. T3 reduced the proliferation rate of neurospheres when cultured in the presence of mitogens, shifting towards oligodendroglial lineage as indicated by increased expression of olig-1, and also favoring oligodendrocyte maturation, as indicated by the expression of antigens associated with different maturation stages. Neurospheres derived from EAE rats show a strong limitation in oligodendrocyte generation, which is completely restored by T3 treatment. These results indicate that T3 is a key factor in regulating neurosphere biology, when derived either from non-pathological or pathological adult brains, suggesting that T3 might be an important factor in favoring remyelination in demyelinating disorders.