Thyroid hormone receptor isoform content in cultured type 1 and type 2 astrocytes

Immunohistochemical studies previously reported from this laboratory showed that astrocytes in adult rat brain appear devoid of all thyroid hormone receptor (TR) isoforms. These findings, however, contrast with reports of measurable nuclear T3 binding in astrocytes in cell culture. To address this discrepancy, TR protein and messenger RNA (mRNA) content of type 1 and type 2 astrocytes in culture were assayed. Type 1 cells represent astrocytes present in brain in vivo. Type 2 astrocytes differentiate in culture from bipotential progenitor O-2A cells in the presence of serum. Under serum-free conditions, these progenitor cells differentiate into oligodendroglia. Total nuclear T3 binding capacity in both type 1 and type 2 astrocytes was approximately 3000 sites/cell. Northern blots showed the presence of mRNA for TRbeta1, TRalpha1, and TRalpha2 in type 2 cells but failed to reveal the presence of these mRNAs in type 1 astrocytes. Moreover, Northern blots also failed to reveal TRbeta2 mRNA in both type 1 and ...