Mechanisms Regulating Angiogenesis Underlie Seasonal Control of Pituitary Function

Proc Natl Acad Sci U S A. 2017 Mar 21;114(12):E2514-E2523. doi: 10.1073/pnas.1618917114. Epub 2017 Mar 7.

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.

Keywords: VEGF; angiogenesis; melatonin; pituitary gland; season.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Breeding
  • Female
  • Gonadotrophs / metabolism
  • Male
  • Melatonin / metabolism
  • Neovascularization, Physiologic*
  • Pituitary Gland / blood supply*
  • Pituitary Gland / physiology*
  • Receptors, Vascular Endothelial Growth Factor / metabolism
  • Reproduction
  • Seasons
  • Sheep / physiology*
  • Vascular Endothelial Growth Factor A / metabolism

Substances

  • Vascular Endothelial Growth Factor A
  • Receptors, Vascular Endothelial Growth Factor
  • Melatonin