Several studies support the existence of multipotent stem/progenitor cells in the adult pituitary, whereas the presence of stem cell in pituitary tumors and their role in pituitary tumorigenesis are still on debate. Aim of this study was to identify and characterize stem-like cells in non-functioning pituitary adenomas (NFPAs). To this purpose primary cell cultures from 25 NFPAs were grown in culture conditions that favored stem cell growth (EGF, bFGF and B27 containing medium). The expression of stem cell markers and genes involved in pituitary development was evaluated after 3 weeks of culture by FACS analysis, RT-PCR and immunofluorescence.
We successfully isolated sphere-forming cells from 64% of NFPAs tested (16/25). These cells expressed stem cells associated markers CD90 and CD34, with a proportion of CD90+ and CD34+ cell populations variable between different tumour samples, ranging from 2.7% to 13.5% for CD90+ and from 1.1% to 10.4% for CD34+. Moreover, RT-PCR analysis revealed the expression of stem cell markers Sox2, Oct4, Nanog, Dkk1 and Egr1, transcription factors involved in gonadotroph differentiation (DAX1, SF1) and the glycoprotein hormone alpha subunit (alphaGSU), consistent with gonadotroph lineage derivation of most NFPAs.
By immunofluorescence analysis, we showed that these sphere-forming cells are Nestin+ and coexpress Sox2 with E-cadherin and the pituitary embrionic factor Prop1.
Since some of these spheres expressed also somatostatin (SS) receptor 2 (SST2), we test a possible effects of SS analog octreotide on spheres growth. We found that octreotide treatment reduced the number of sphere-forming cells after 30 days of cell culture in stem cell-permissive medium (about -50% vs untreated cells).
In conclusion, our data demonstrate the existence in a good proportion of NFPAs of stem-like cells, that expressed stem cell-associated markers and pituitary embryonic factors. Further experiment are needed to test long-term self-renewal and multipotency of these cells.