title: Mechanisms regulating angiogenesis underlie seasonal control of pituitary function.
abstract: Seasonal changes in mammalian physiology, such as those affecting reproduction, hibernation, and metabolism, are controlled by pituitary hormones released in response to annual environmental changes. In temperate zones, the primary environmental cue driving seasonal reproductive cycles is the change in day length (i.e., photoperiod), encoded by the pattern of melatonin secretion from the pineal gland. However, although reproduction relies on hypothalamic gonadotrophin-releasing hormone output, and most cells producing reproductive hormones are in the pars distalis (PD) of the pituitary, melatonin receptors are localized in the pars tuberalis (PT), a physically and functionally separate part of the gland. How melatonin in the PT controls the PD is not understood. Here we show that melatonin time-dependently acts on its receptors in the PT to alter splicing of vascular endothelial growth factor (VEGF). Outside the breeding season (BS), angiogenic VEGF-A stimulates vessel growth in the infundibulum, aiding vascular communication among the PT, PD, and brain. This also acts on VEGF receptor 2 (VEGFR2) expressed in PD prolactin-producing cells known to impair gonadotrophin secretion. In contrast, in the BS, melatonin releases antiangiogenic VEGF-Axxxb from the PT, inhibiting infundibular angiogenesis and diminishing lactotroph (LT) VEGFR2 expression, lifting reproductive axis repression in response to shorter day lengths. The time-dependent, melatonin-induced differential expression of VEGF-A isoforms culminates in alterations in gonadotroph function opposite to those of LTs, with up-regulation and down-regulation of gonadotrophin gene expression during the breeding and nonbreeding seasons, respectively. These results provide a mechanism by which melatonin can control pituitary function in a seasonal manner.
authors.affiliation: Centre for Comparative and Clinical Anatomy, Faculty of Health Sciences, University of Bristol, Bristol BS2 8EJ, United Kingdom.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Castle-Miller
authors.affiliation: Cancer Biology, Division of Cancer and Stem Cells, School of Medicine, University of Nottingham, Queen's Medical Centre, Nottingham NG7 2UH, United Kingdom david.bates@nottingham.ac.uk d.tortonese@bristol.ac.uk.
authors.forename: David O
authors.initials: DO
authors.lastname: Bates
authors.affiliation: Centre for Comparative and Clinical Anatomy, Faculty of Health Sciences, University of Bristol, Bristol BS2 8EJ, United Kingdom; david.bates@nottingham.ac.uk d.tortonese@bristol.ac.uk.
authors.forename: Domingo J
authors.initials: DJ
authors.lastname: Tortonese
mesh_terms: D000818:Animals; D001947:Breeding; D005260:Female; D052681:Gonadotrophs / Q000378:metabolism; D008297:Male; D008550:Melatonin / Q000378:metabolism; D018919:Neovascularization, Physiologic; D010902:Pituitary Gland / Q000098:blood supply* / Q000502:physiology*; D040262:Receptors, Vascular Endothelial Growth Factor / Q000378:metabolism; D012098:Reproduction; D012621:Seasons; D012756:Sheep / Q000502:physiology*; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
chemical_list: D042461:Vascular Endothelial Growth Factor A; D040262:Receptors, Vascular Endothelial Growth Factor; D008550:Melatonin
keywords: VEGF; angiogenesis; melatonin; pituitary gland; season