VGF changes during the estrous cycle: a novel endocrine role for TLQP peptides?

PLoS One. 2014 Oct 3;9(10):e108456. doi: 10.1371/journal.pone.0108456. eCollection 2014.

Abstract

Although the VGF derived peptide TLQP-21 stimulates gonadotropin-releasing hormone (GnRH) and gonadotropin secretion, available data on VGF peptides and reproduction are limited. We used antibodies specific for the two ends of the VGF precursor, and for two VGF derived peptides namely TLQP and PGH, to be used in immunohistochemistry and enzyme-linked immunosorbent assay complemented with gel chromatography. In cycling female rats, VGF C-/N-terminus and PGH peptide antibodies selectively labelled neurones containing either GnRH, or kisspeptin (VGF N-terminus only), pituitary gonadotrophs and lactotrophs, or oocytes (PGH peptides only). Conversely, TLQP peptides were restricted to somatostatin neurones, gonadotrophs, and ovarian granulosa, interstitial and theca cells. TLQP levels were highest, especially in plasma and ovary, with several molecular forms shown in chromatography including one compatible with TLQP-21. Among the cycle phases, TLQP levels were higher during metestrus-diestrus in median eminence and pituitary, while increased in the ovary and decreased in plasma during proestrus. VGF N- and C-terminus peptides also showed modulations over the estrous cycle, in median eminence, pituitary and plasma, while PGH peptides did not. In ovariectomised rats, plasmatic TLQP peptide levels showed distinct reduction suggestive of a major origin from the ovary, while the estrogen-progesterone treatment modulated VGF C-terminus and TLQP peptides in the hypothalamus-pituitary complex. In in vitro hypothalamus, TLQP-21 stimulated release of growth hormone releasing hormone but not of somatostatin. In conclusion, various VGF peptides may regulate the hypothalamus-pituitary complex via specific neuroendocrine mechanisms while TLQP peptides may act at further, multiple levels via endocrine mechanisms involving the ovary.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Estradiol / pharmacology
  • Estrous Cycle / drug effects
  • Estrous Cycle / metabolism*
  • Female
  • Hypothalamus / metabolism
  • Neuropeptides / chemistry
  • Neuropeptides / metabolism*
  • Ovariectomy
  • Ovary / metabolism
  • Peptide Fragments / metabolism
  • Pituitary Gland / metabolism
  • Progesterone / pharmacology
  • Protein Transport
  • Rats

Substances

  • Neuropeptides
  • Peptide Fragments
  • TLQP-21 peptide
  • Vgf protein, rat
  • Progesterone
  • Estradiol

Grants and funding

This study was sponsored by the ARS (Autonomous Region of Sardinia) through the ‘Sardinia PO FSE 2007-1013’ funds (the L.R. 7/2007 for the ‘Promotion of the Scientific Research and of the Technological Innovation in Sardinia’). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.