Presence Of Prolactin Receptor Research Articles

Possible involvement of somatotrophic hormones in the postpartum regulation of ovarian activity in mares

In horses, resumption of ovarian function after parturition occurs early and the majority of mares ovulate within two weeks after parturition. Previous research suggests that early postpartum increases in the peripheral concentration of prolactin and somatotrophic hormones are the major stimulus for resumption of ovarian activity and ovulation. In the present study, we investigated if placental tissue may be a source of somatotrophic hormones and thus influence ovarian activity. Ovarian follicular development and concentrations of prolactin, insulin like growth factor-1 (IGF1) and LH were determined in 14 healthy Haflinger mares (9.2±3.8 years). From D15 before until D15 after parturition (pp), transrectal ultrasonography of ovarian activity was performed and blood samples were collected for determination of hormone concentrations (prolactin, IGF1 by ELISA; LH by RIA). All foals were healthy, mature and stayed with their dams. Samples from the allantochorion and amnion were obtained immediately after delivery. The relative abundance of mRNA for IGF1 and the prolactin receptor (PRLR) was analyzed by qPCR. Formalin fixed samples were analyzed for protein expression of IGF1 and PRLR by immunohistochemistry. Statistical analysis (IBM SPSS 27.0) was done by analysis of variance (for repeated measures) comparing data from mares that ovulated(group ov; n=5) and did not ovulate until D15 pp (group non-ov, n=9). Values are mean ± SD. Mares from group ov foaled later in the year than non-ov mares (day of year 84±29 vs. 50±20, p<0.05), but no differences in gestation length, placental weight or size were detected. Already on D15 before parturition, ovarian follicles <2 cm diameter were present in all mares, but growth to preovulatory size occurred only pp with a higher growth rate in ov mares (day x group p<0.05). Prolactin and IGF1 concentrations increased from D5 before parturition, peaked at D1 pp (ov vs. non-ov: prolactin 13.0±6.3 vs. 7.9±4.4 ng/ml, p<0.05; IGF1 409±71 vs. 350±65 ng/ml, p<0.05) and declined thereafter. The LH concentration increased from D1 pp in group ov (D12 pp: 23.82±15.96 ng/ml) but not in non-ov (D12 pp: 10.82±5.26 ng/ml; day x group p<0.001). There was a high abundance of mRNA and protein for IGF1 and PRLR in placental tissue irrespective of group. In conclusion, ovarian follicles are detectable before foaling, but develop to preovulatory size only pp when prolactin and LH concentrations increase. In agreement with the situation in cattle, IGF1 stimulates ovarian activity in lactating mares. Placental tissue produces IGF1 that may be under the influence of prolactin as suggested by the presence of PRLR in both amnion and allantochorion.

Rankl Impairs Lactogenic Differentiation Through Inhibition of the Prolactin/Stat5 Pathway at Midgestation

Prolactin and progesterone both orchestrate the proliferation and differentiation of the mammary gland during gestation. Differentiation of milk secreting alveoli depends on the presence of prolactin receptor, the downstream Jak2-Stat5 pathway and the transcription factor Elf5. A strict regulation of Rank signaling is essential for the differentiation of the mammary gland and in particular for alveolar commitment. Impaired alveologenesis and lactation failure are observed in both, knockout and Rank overexpressing mice; however, the underlying molecular mechanism responsible for these phenotypes remains largely unknown. Using genome-wide expression analyses and functional studies, we show here that Rankl (RL) exposure leads to impaired secretory differentiation of alveolar cells not only in MMTV-RANK but also in wild-type (WT) mammary acini. Conversely, pharmacological blockage of Rank signaling at midgestation in WT mice leads to precocious and exacerbated lactogenesis. Mechanistically, RL negatively regulates Stat5 phosphorylation and Elf5 expression at the onset of lactogenesis. Continuous RL exposure leads to the expansion of basal and bipotent cells in WT and MMTV-RANK acini. Overall, we demonstrate that enhanced Rank signaling impairs secretory differentiation during pregnancy by inhibition of the prolactin/p-Stat5 pathway.

Evidence for direct effects of prolactin on human osteoblasts: Inhibition of cell growth and mineralization

Hyperprolactinemia is one of the risk factor of decrease in bone mass which has been believed to be mediated by hypogonadism. However, the presence of prolactin receptor in human osteosarcoma cell line and primary bone cell culture from mouse calvariae supported the hypothesis of a direct prolactin (PRL) action on bone cells. Therefore, the aim of this study was to investigate the role of PRL and its signal transduction pathway in the regulation of bone metabolism via osteoblast differentiation. Human pre-osteoblasts (SV-HFO) that differentiate in a 3-week period from proliferating pre-osteoblasts (days 2-7) to extracellular matrix producing cells (days 7-14) which is eventually mineralized (days 14-21) were used. Concentration of PRL mimicked a lactating period (100 ng/ml) was used to incubate SV-HFO for 21 days in osteogenic medium. Human prolactin receptor mRNA and protein are expressed in SV-HFO. PRL significantly decreased osteoblast number (DNA content) which was due to a decrease in proliferation. PRL increased osteogenic markers, RUNX2 and ALP in early stage of osteoblast differentiation while decreasing it later suggesting a bi-directional effect. Calcium measurement and Alizarin red staining showed a reduction of mineralization by PRL while having neither an effect on osteoblast activity nor RANKL/OPG mRNA ratio. We also demonstrated that PRL action on mineralization was not via PI-3 kinase pathway. The present study provides evidence of a direct effect of prolactin on osteoblast differentiation and in vitro mineralization.

Prolactin receptors in rat cholangiocytes: Regulation of level and isoform ratio is sex independent

The presence of prolactin receptor and peculiarities of its isoform expression in bile duct cells (cholangiocytes) differentially isolated from rat liver under different conditions were investigated in the present study. Normal cholangiocytes express prolactin receptor at relatively low level comparable to those of some prolactin-dependent tissues. Long receptor isoform is predominant in cholangiocytes but not in hepatocytes. The prolactin receptor level increases significantly under obstructive cholestasis due to evaluation of long and appearance of short isoforms. In rat cholangiocytes, unlike other tissues, the main positive regulators of prolactin receptor expression are cholestasis-induced factors instead of sex hormone and prolactin levels. Long isoform is predominant and induced primarily by cholestasis-induced factors.

Molecular characterization of the prolactin receptor in two fish species, tilapia &lt;i&gt;Oreochromis niloticus&lt;/i&gt; and rainbow trout, &lt;i&gt;Oncorhynchus mykiss&lt;/i&gt;: A comparative approach

We present recent information on the molecular characterization of the prolactin receptor (PRL-R) in two teleost species, tilapia (Oreochromis niloticus) and rainbow trout (Oncorhynchus mykiss), in the perspective of improved understanding of the physiological differences in the control of osmoregulatory function between these two fish species. Although our interest will mainly focus on osmoregulatory organs, we will also discuss evidence of the presence of PRL-R in other tissues such as gonads and hematopoietic organs. The first fish PRL-R was characterized in tilapia. This receptor is similar to that of the long form of mammalian PRL-R, but the most conserved region (extracellular domain) has only 53% identity with mammalian PRL-R. A rainbow trout PRL-R cDNA has been also isolated and appeared very similar in structure to tilapia PRL-R. Expression of the PRL-R gene was studied by Northern blotting for various tissues from tilapia and trout, and a unique transcript size of 3.2-3.4 kb was observed in all tissues studied (including male and female gonads, skin, brain, spleen, head, kidney, and circulating lymphocytes). Osmoregulatory organs (gills, kidney, intestine) were the richest tissues. Using in situ hybridization, PRL-R transcripts were localized in gill chloride cells, both in trout and tilapia. Analysis of PRL-R transcript levels in gills, kidney, and intestine indicated the maintenance of a high level of expression during adaptation to a hyperosmotic environment. These results support PRL being a pleiotropic hormone in fish and suggest the presence of a unique PRL-R form in tilapia and in trout. Finally, characterization of hormone receptor binding has been carried out in both species using a radioreceptor assay (in tilapia) or surface plasmon resonance (SPR) technology (in trout). These studies indicated the presence of a stable hormone-receptor complex in tilapia, while PRL binds to its receptor through an unstable homodimeric complex in trout. Thus, the characteristics of PRL binding on its receptor appear to be significantly different in tilapia and trout. Whether such differences may lead to different signal transduction mechanisms and osmoregulatory actions of PRL in these two euryhaline species merits further investigation.