TGFβ signaling reinforces pericyte properties of the non-endocrine mouse pituitary cell line TtT/GF

The non-endocrine TtT/GF mouse pituitary cell line was derived from radiothyroidectomy-induced pituitary adenoma. In addition to morphological characteristics, because the cells are S100β-positive, they have been accepted as a model of folliculostellate cells. However, our recent microarray analysis indicated that, in contrast to folliculostellate cells, TtT/GF cells might not be terminally differentiated, as they share some properties with stem/progenitor cells, vascular endothelial cells and pericytes. The present study investigates whether transforming growth factor beta (TGFβ) can elicit further differentiation of these cells. The results showed that canonical (Tgfbr1 and Tgfbr2) and non-canonical TGFβ receptors (Tgfbr3) as well as all TGFβ ligands (Tgfb1–3) were present in TtT/GF cells, based on reverse transcription PCR. SMAD2, an intercellular signaling molecule of the TGFβ pathway, was localized in the nucleus upon TGFβ signaling. Furthermore, TGFβ induced cell colony formation, which was completely blocked by a TGFβ receptor I inhibitor (SB431542). Real-time PCR analysis indicated that TGFβ downregulated stem cell markers (Sox2 and Cd34) and upregulated pericyte markers (Nestin and Ng2). Double immunohistochemistry using mouse pituitary tissue confirmed the presence of NESTIN/NG2 double-positive cells in perivascular areas where pericytes are localized. Our results suggest that TtT/GF cells are responsive to TGFβ signaling, which is associated with cell colony formation and pericyte differentiation. As pericytes have been shown to regulate angiogenesis, tumorigenesis and stem/progenitor cells in other tissues, TtT/GF cells could be a useful model to study the role of pituitary pericytes in physiological and pathological processes.