7420 A Role for Glycoprotein Hormone Subunit Alpha 2 in Pituitary Development

Abstract Disclosure: L.T. Raetzman: None. X. Ge: None. K. Weis: None. Hypopituitarism results when the pituitary gland is not able to make one or more of its hormones. It is estimated that up to 80% of hypopituitarism detected at or near birth has no identifiable cause. We have created a mouse model of congenital hypopituitarism by conditionally deleting the gene Notch2 in the developing pituitary. NOTCH2 is expressed in pituitary stem cells and is necessary for stem cell maintenance, proliferation, and differentiation. However, the pathways NOTCH2 engages to affect pituitary development remain unclear. It is important to determine the mechanism of NOTCH2 action in the pituitary because it might help to reveal novel causes of hypopituitarism. In this study, we hypothesized that glycoprotein hormone subunit A2 (GPHA2), a corneal stem cell factor, is downstream of NOTCH2 signaling in the mouse pituitary. We found Gpha2 is expressed in a subset of quiescent Sox2-expressing pituitary stem cells by RNAscope in situ hybridization and scRNA seq analysis. A scRNA seq study in rats has also localized Gpha2 to Sox2-expressing folliculostellate cells. In Notch2 conditional knockout pituitaries, Gpha2 mRNA is reduced over 75% compared with control littermates. We then investigated the possible functions of GPHA2, hypothesizing it might have a role in stem cell maintenance and quiescence. However, pituitaries treated with a GPHA2 peptide do not have a change in proliferation or stem cell-related gene expression. Another role of GPHA2 may be as a paracrine signal to control lineage restricted cell fate. GPHA2 has been demonstrated to be a ligand for the thyroid stimulating hormone receptor (TSHR) and part of the hormone thyrostimulin. We demonstrated that, in dissociated adult pituitary cells, GPHA2 increased pCREB expression and this induction was reversed by co-treatment with a TSHR inhibitor. Our data show that TSHR is expressed in the rostral tip thyrotropes of the pars tuberalis and in isolated cells in the anterior lobe. These data suggest GPHA2 is a NOTCH2 related stem cell factor that activates TSHR signaling, potentially impacting pituitary development and maintenance as a paracrine signaling molecule. Presentation: 6/3/2024