Regeneration in the pituitary after cell-ablation injury: time-related aspects and molecular analysis

We recently showed that the mouse pituitary holds regenerative competence. Young-adult GHCre/iDTR mice, expressing diphtheria toxin (DT) receptor in growth hormone (GH)-producing cells, regenerate the GH+ cells, as ablated by 3-day DT treatment (3DT), up to 60% after 5 months. The pituitary's stem cells participate in this restoration process. Here, we characterized this regenerative capacity in relation to ageandrecovery period,andstarted to search for underlying molecular mechanisms. Extending the recovery period (up to 19 months) does not result in higher regeneration levels. In addition, the regenerative competence disappears at older age, coinciding with a reduction in pituitary stem cell number and fitness. Surprisingly, prolonging DT treatment of young-adult mice to 10 days (10DT) completely blocks the regeneration, although the stem cell compartment still reacts by promptly expanding, and retains in vitro stem cell functionality. To obtain a first broad view on molecular grounds underlying reparative capacity and/or failure, the stem cell-clustering side population (SC-SP) was analyzed by whole-genome expression analysis. A number of stemness factors and components of embryonic, epithelial-mesenchymal transition, growth factor and Hippo pathways are higher expressed in the SC-SP of the regenerating pituitary (after 3DT) when compared to the basal gland and to the non-regenerating pituitary (after 10DT). Together, the regenerative capacity of the pituitary is limited both in age-related terms and final efficacy, and appears to rely on stem cell-associated pathway activation. Dissection of the molecular profiles may eventually identify targets to induce or boost regeneration in situations of (injury-related) pituitary deficiency.status: publishe