Female reproductive functions of the neuropeptide PACAP

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide originally isolated as a hypothalamic peptide. It has a widespread distribution in the body and has a diverse spectrum of actions. Among other processes, PACAP has been shown to be involved in reproduction. In this review we summarize findings related to the entire spectrum of female reproduction. PACAP is a regulatory factor in gonadal hormone production, influences follicular development and plays a role in fertilization and embryonic/placental development. Furthermore, PACAP is involved in hormonal changes during and after birth and affects maternal behavior. Although most data come from cell cultures and animal experiments, increasing number of evidence suggests that similar effects of PACAP can be found in humans. Among other instances, PACAP levels show changes in the serum during pregnancy and birth. PACAP is also present in the human follicular and amniotic fluids and in the milk. Levels of PACAP in follicular fluid correlate with the number of retrieved oocytes in hyperstimulated women. Human milk contains very high levels of PACAP compared to plasma levels, with colostrum showing the highest concentration, remaining steady thereafter for the first 7 months of lactation. All these data imply that PACAP has important functions in reproduction both under physiological and pathological conditions.

Pituitary adenylate cyclase activating polypeptide concentrations in the sheep mammary gland, milk, and in the lamb blood plasma after suckling

Pituitary adenylate cyclase activating polypeptide (PACAP) is involved in development and reproduction. We previously described elevated PACAP levels in the milk compared to the plasma, and the presence of its specific PAC1 receptor in the mammary gland. This study aimed to determine PACAP and vasoactive intestinal peptide (VIP) levels in female suckling lambs compared to ewe plasma and mammary gland, as well as their age-dependent alterations. mRNA expressions of PACAP, VIP, PAC1 receptor and brain-derived neurotrophic factor (BDNF) were quantified in the milk whey and mammary gland. PACAP38-like immunoreactivity (PACAP38-LI) was measured in plasma, milk whey and mammary gland by radioimmunoassay, VIP-LI by enzyme-linked immunoassay. PACAP38-LI was 5, 6 times higher in the milk compared to the plasma of lactating sheep. It significantly increased in the lamb plasma 1 h, but returned to basal level 2 h after suckling. However, VIP mRNA was not present in the mammary gland, we detected the VIP protein in the milk whey. BDNF mRNA significantly decreased with age to approximately 60% and 25% in the 3- and 10-year-old sheep respectively, compared to the 3-month-old lambs. No differences were found between mammary and jugular vein plasma PACAP and VIP concentrations, or during the daily cycle. We propose a rapid absorption of PACAP38 from the milk and/or its release in suckling lambs. PACAP accumulated in the milk might be synthesized in the mammary gland or secreted from the plasma of the mothers. PACAP is suggested to have differentiation/proliferation promoting and immunomodulatory effects in the newborns and/or a local function in the mammary gland.

Investigation of pituitary adenylate cyclase activating polypeptide (PACAP) in human amniotic fluid samples

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide acting as a hormone, a neuromodulator, a neurotransmitter, a trophic factor and is involved in a variety of developmental and regenerative processes. PACAP is present in several human tissues and biological fluids. In many pathological conditions, changes in PACAP levels have been described to reflect disease progression, therefore PACAP has diagnostic value as a potential biomarker. Since PACAP has been shown to play an important role in reproductive physiology and development, it was of interest to examine whether this neuropeptide occurs in the human amniotic fluid. Amniotic fluid samples were collected between the 15-19^th weeks of gestation from volunteering pregnant women undergoing amniocentesis as a prenatal diagnostic tool due to maternal age. Pathological cases were excluded after prenatal karyotype analysis. PACAP-like immunoreactivity was measured by radioimmunoassay and could be detected in all samples. The present study provides evidence for the presence of PACAP in human amniotic fluid, but determination of the exact physiological or pathological significance awaits further investigation.

Current knowledge of pituitary adenylate cyclase activating polypeptide (PACAP) in articular cartilage

Pituitary adenylate cyclase activating polypeptide (PACAP) is an evolutionally well conserved neuropeptide, mainly expressed by neuronal and peripheral cells. It proves to be an interesting object of study both for its trophic functions during the development of several tissues and for its protective effects against oxidative stress, hypoxia, inflammation and apoptosis in different degenerative diseases. This brief review summarises the recent findings concerning the role of PACAP in the articular cartilage. PACAP and its receptors are expressed during chondrogenesis and are shown to activate the pathways involved in regulating cartilage development. Moreover, this neuropeptide proves to be chondroprotective against those stressors that determine cartilage degeneration and contribute to the onset of osteoarthritis (OA), the most common form of degenerative joint disease. Indeed, the degenerated cartilage exhibits low levels of PACAP, suggesting that its endogenous levels in adult cartilage may play an essential role in maintaining physiological properties. Thanks to its peculiar characteristics, exogenous administration of PACAP could be suggested as a potential tool to slow down the progression of OA and for cartilage regeneration approaches.

PACAP and VIP signaling in chondrogenesis and osteogenesis

Skeletal development is a complex process regulated by multifactorial signaling cascades that govern proper tissue specific cell differentiation and matrix production. The influence of certain regulatory peptides on cartilage or bone development can be predicted but are not widely studied. In this review, we aimed to assemble and overview those signaling pathways which are modulated by PACAP and VIP neuropeptides and are involved in cartilage and bone formation. We discuss recent experimental data suggesting broad spectrum functions of these neuropeptides in osteogenic and chondrogenic differentiation, including the canonical downstream targets of PACAP and VIP receptors, PKA or MAPK pathways, which are key regulators of chondro- and osteogenesis. Recent experimental data support the hypothesis that PACAP is a positive regulator of chondrogenesis, while VIP has been reported playing an important role in the inflammatory reactions of surrounding joint tissues. Regulatory function of PACAP and VIP in bone development has also been proved, although the source of the peptides is not obvious. Crosstalk and collateral connections of the discussed signaling mechanisms make the system complicated and may obscure the pure effects of VIP and PACAP. Chondro-protective properties of PACAP during oxidative stress observed in our experiments indicate a possible therapeutic application of this neuropeptide.