Preimplantation factor (PIF) predicts subsequent pregnancy loss

Preimplantation Factor (PIF): a peptide with various functions

Preimplantation Factor (PIF) is a novel fifteen amino acid linear peptide (MVRIKPGSANKPSDD), which has different biological functions in mammalian species e.g. its role in neuron restoration, pregnancy and related disorders, and also in autoimmune diseases. Since all clinical studies have shown that PIF has both local and systemic effects, it can be considered as an integrated therapy for the treatment of inflammation conditions, along with the prevention of advanced disease. The synthetic PIF (sPIF) analog is a good representative of native PIF action, and it regulates peripheral immune cells to achieve endurance without immune suppression - an effective agent in nonpregnant autoimmune models. This study provides information, from evidence-based studies so far about PIF’s different functional aspects.

PreImplantation factor (PIF) protects cultured embryos against oxidative stress: relevance for recurrent pregnancy loss (RPL) therapy

Recurrent pregnancy loss (RPL) affects 2-3% of couples. Despite a detailed work-up, the etiology is frequently undefined, leading to non-targeted therapy. Viable embryos and placentae express PreImplantation Factor (PIF). Maternal circulating PIF regulates systemic immunity and reduces circulating natural killer cells cytotoxicity in RPL patients. PIF promotes singly cultured embryos' development while anti-PIF antibody abrogates it. RPL serum induced embryo toxicity is negated by PIF. We report that PIF rescues delayed embryo development caused by <3 kDa RPL serum fraction likely by reducing reactive oxygen species (ROS). We reveal that protein disulfide isomerase/thioredoxin (PDI/TRX) is a prime PIF target in the embryo, rendering it an important ROS scavenger. The 16F16-PDI/TRX inhibitor drastically reduced blastocyst development while exogenous PIF increased >2 fold the number of embryos reaching the blastocyst stage. Mechanistically, PDI-inhibitor preferentially binds covalently to oxidized PDI over its reduced form where PIF avidly binds. PIF by targeting PDI/TRX at a distinct site limits the inhibitor's pro-oxidative effects. The >3kDa RPL serum increased embryo demise by three-fold, an effect negated by PIF. However, embryo toxicity was not associated with the presence of putative anti-PIF antibodies. Collectively, PIF protects cultured embryos both against ROS, and higher molecular weight toxins. Using PIF for optimizing in vitro fertilization embryos development and reducing RPL is warranted.

Insight into PreImplantation Factor (PIF*) mechanism for embryo protection and development: target oxidative stress and protein misfolding (PDI and HSP) through essential RIKP [corrected] binding site

Background

Endogenous PIF, upon which embryo development is dependent, is secreted only by viable mammalian embryos, and absent in non-viable ones. Synthetic PIF (sPIF) administration promotes singly cultured embryos development and protects against their demise caused by embryo-toxic serum. To identify and characterize critical sPIF-embryo protein interactions novel biochemical and bio-analytical methods were specifically devised.

Methods

FITC-PIF uptake/binding by cultured murine and equine embryos was examined and compared with scrambled FITC-PIF (control). Murine embryo (d10) lysates were fractionated by reversed-phase HPLC, fractions printed onto microarray slides and probed with Biotin-PIF, IDE and Kv1.3 antibodies, using fluorescence detection. sPIF-based affinity column was developed to extract and identify PIF-protein interactions from lysates using peptide mass spectrometry (LC/MS/MS). In silico evaluation examined binding of PIF to critical targets, using mutation analysis.

Results

PIF directly targets viable cultured embryos as compared with control peptide, which failed to bind. Multistep Biotin-PIF targets were confirmed by single-step PIF-affinity column based isolation. PIF binds protein disulfide isomerases a prolyl-4-hydroxylase β-subunit, (PDI, PDIA4, PDIA6-like) containing the antioxidant thioredoxin domain. PIF also binds protective heat shock proteins (70&90), co-chaperone, BAG-3. Remarkably, PIF targets a common RIPK site in PDI and HSP proteins. Further, single PIF amino acid mutation significantly reduced peptide-protein target bonding. PIF binds promiscuous tubulins, neuron backbones and ACTA-1,2 visceral proteins. Significant anti-IDE, while limited anti-Kv1.3b antibody-binding to Biotin-PIF positive lysates HPLC fractions were documented.

Conclusion

Collectively, data identifies PIF shared targets on PDI and HSP in the embryo. Such are known to play a critical role in protecting against oxidative stress and protein misfolding. PIF-affinity-column is a novel utilitarian method for small molecule targets direct identification. Data reveals and completes the understanding of mechanisms involved in PIF-induced autotrophic and protective effects on the embryo.

Preimplantation factor (PIF) promoting role in embryo implantation: increases endometrial integrin-α2β3, amphiregulin and epiregulin while reducing betacellulin expression via MAPK in decidua

BACKGROUND

Viable embryos secrete preimplantation factor (PIF), a peptide that has autocrine effects where levels correlate with cultured embryos development. sPIF (PIF synthetic analog) promotes implantation by regulating decidual-cells immunity, adhesion, apoptosis and enhances trophoblastic cell invasion. Herein sPIF priming effects on non-decidualized endometrium and decidualized-stroma are investigated, assessing elements critical for effective embryo-maternal cross-talk, prior to and at implantation.

METHODS

We tested sPIF effect on human non-pregnant endometrial epithelial and non-decidualized stroma α2β3 integrin expression (IHC and flow cytometry), comparing with scrambled PIF (PIFscr-control). We examined sPIF effect on decidualized non-pregnant human endometrial stromal cells (HESC) determining pro-inflammatory mediators expression and secretion (ELISA) and growth factors (GFs) expression (Affymetrix global gene array). We tested sPIF effect on HESC Phospho-kinases (BioPlex) and isolated kinases activity (FastKinase).

RESULTS

sPIF up-regulates α2β3 integrin expression in epithelial cells, (P < 0.05) while PIFscr had no effect. In contrast, in stromal cell cultures sPIF had no effect on the same. In HESC, sPIF up-regulates pro-inflammatory cytokines; IL8, IL1β and IL6 expression. The major increase in GRO-α, ICAM-1 and MCP-3 expression is coupled with same ligands secretion (P < 0.05). sPIF modulates in HESC GFs expression: up-regulates amphiregulin and epiregulin- critical for implantation and enhances several fibroblast growth factors (FGF) relevant for decidual function. In contrast, sPIF down-regulates major pro-proliferative ligands, betacellulin and IGF1 expression. sPIF modulatory effect on GFs is exerted by down-regulating pro-proliferative phospho-activated MAPkinases, p-MEK1 and p-ERK (P < 0.01, P < 0.04, respectively). Stress-induced p-38-MAPK (P = 0.04) and c-Jun kinase signaling involved MAPK8IP2 (-2.1 fold) expression decreased which protects against reactive oxygen species. Although pro-inflammatory p-NFkB (P = 0.06) decrease was mild, its promoter TNFRS11 expression markedly (-25-fold) decreased. In contrast, anti-proliferative phosphatases PTPRZ1 and PPP2R2C expression increased.

CONCLUSIONS

sPIF post-fertilization primes endometrial-epithelium, while during implantation creates a beneficial pro-inflammatory milieu. PIF acts by balancing decidual pro-implantation properties while controlling excessive pro-proliferative and inflammatory signals expression. Overall, PIF influences critical peri-implantation events in a sequential coordinated fashion which facilitates embryo implantation.

A genomic and proteomic investigation of the impact of preimplantation factor on human decidual cells

OBJECTIVE

Preimplantation factor (PIF) is a novel, 15 amino acid peptide, secreted by viable embryos. This study aims to elucidate PIF's effects in human endometrial stromal cells (HESC) decidualized by estrogen and progestin, which mimics the preimplantation milieu, and in first-trimester decidua cultures (FTDC).

STUDY DESIGN

HESC or FTDC were incubated with 100 nmol/L synthetic PIF or vehicle control. Global gene expression was analyzed using microarray and pathway analysis. Proteins were analyzed using quantitative mass spectrometry, and PIF binding by protein array.

RESULTS

Gene and proteomic analysis demonstrate that PIF affects immune, adhesion, and apoptotic pathways. Significant up-regulation in HESC (fold change) include: nuclear factor-k-beta activation via interleukin-1 receptor-associated kinase binding protein 1 (53); Toll-like receptor 5 (9); FK506 binding protein 15, 133kDa protein (2.3); and Down syndrome cell adhesion molecule like 1 (16). B-cell lymphoma protein 2 was down-regulated in HESC (21.1) and FTDC (27.1). Protein array demonstrates PIF interaction with intracellular targets insulin-degrading enzyme and beta-K+ channels.

CONCLUSION

PIF displays essential multitargeted effects, of regulating immunity, promoting embryo-decidual adhesion, and regulating adaptive apoptotic processes.

Endometrial modifications during early pregnancy in bonnet monkeys (Macaca radiata)

The present study was undertaken to investigate endometrial modifications that occur before embryo invasion in bonnet monkeys (Macaca radiata). These changes were analysed in luminal epithelium, glandular epithelium and stroma of endometrial functionalis on Day 6 post ovulation from pregnant and non-pregnant animals (n = 4 each) by transmission electron microscopy. Distinct features (i.e. loss of columnar shape by epithelial cells, changes in mitochondrial size and diffused apicolateral gap junctions) were observed in the luminal and glandular epithelium in pregnant animals. Stromal compaction was also observed in pregnant animals. Further, immunogold localisation studies demonstrated significantly higher expression (P < 0.05) of oestrogen receptor alpha, an oestrogen-regulated gene, in the glandular epithelium and stroma of the endometrium in pregnant animals compared with non-pregnant animals. Expression of two other genes known to be regulated by oestradiol, namely beta-actin and cyclo-oxygenase-1, were also significantly higher (P < 0.05) in the endometria of pregnant animals. These studies demonstrate marked changes in the endometrium before embryo invasion in bonnet monkeys. These studies also indicate altered oestrogenic activity in the uterine milieu before embryo invasion.

Applying Embryo-Derived Immune Tolerance to the Treatment of Immune Disorders

Pregnancy is a unique immune state in which both mother and embryo/fetus tolerate and interact with one another through term, without interfering with the mother's native immunity. When the embryo is viable, it initiates maternal immune tolerance (IT)--ut not immune suppression. The balance is complex: some immune disorders are ameliorated during pregnancy, despite the presence of an "inflammatory" environment. We have identified a pregnancy viability biomarker--preimplantation factor (PIF)--secreted only by viable embryos, which helps to initiate this maternal tolerance and uterine receptivity. Using anti-PIF antibodies, we have detected PIF in the fetus and placenta. Beyond enhancing uterine receptivity locally, PIF has also been detected in maternal circulation, and may promote peripheral tolerance. In the fetus, PIF may help avoid a "graft-versus-host"-type reaction PIF exhibits unique potent immune-modulatory effects and its synthetic analogue has been shown to exert significant protection in diverse immune scenarios. Nontoxic, low-dose, short-term PIF administration has led to long-term effects in preclinical models of multiple sclerosis (MS), juvenile diabetes mellitus (JDM), and graft-versus-host disease (GVHD), in a manner enabling its translation into a clinical setting. Further investigation of this compound is warranted.

Morphological events in the primate endometrium in the presence of a preimplantation embryo, detected by the serum preimplantation factor bioassay

BACKGROUND

Hormonal modulation of the endometrium towards receptivity is well established; however, the role of embryonic stimuli in modulation of the endometrium prior to implantation, especially in primates, is unknown. The aim of the present study was to evaluate the endometrial histology when the embryo was present in its vicinity prior to implantation.

METHODS

Preimplantation factor (PIF) bioassay was used as a tool to detect the presence of an embryo in the uterine lumen of mated bonnet monkeys (Macaca radiata) (n=9). The control group comprised seven non-mated animals. The specificity of the PIF bioassay for the presence of an embryo was tested by studies in pregnant humans and monkeys. The effects of embryonic stimuli on the endometrial morphology were analysed by routine haematoxylin-eosin staining. The expressions of CD34, an endothelial cell marker, alpha-smooth muscle actin (alpha-SMA), a marker for blood vessel maturation, and prolactin, a marker of endometrial decidualization, were studied by immunohistochemistry.

RESULTS

That PIF is embryo specific was established by its presence in sera of pregnant humans, monkeys and also in embryo culture media. Six mated bonnet monkeys were found to be PIF positive. Morphologically, the endometria from these PIF-positive animals showed the presence of the pre-epithelial plaque reaction, increased angiogenesis and stromal compaction. The significantly increased number of CD34- and alpha-SMA-positive blood vessels (P<0.05) in the endometria of PIF-positive animals indicated increased angiogenesis in response to embryonic stimuli. The endometrial expression of immunoreactive prolactin was also significantly increased (P<0.05) in the PIF-positive animals, indicating decidualization.

CONCLUSIONS

Using PIF as a marker to detect early pregnancy in bonnet monkeys, we have shown that the embryo induces a pre-epithelial plaque type of reaction, increased angiogenesis and decidual reaction in the endometrium prior to implantation.

Embryo-maternal interactions at the implantation site: a delicate equilibrium

Blastocyst implantation and successful establishment of pregnancy require delicate interactions between the embryo and the maternal environment. During preimplantation, maternal/embryo communication is mediated by the trophectoderm. In the late luteal phase, physiological changes occur in the endometrium to allow blastocyst implantation. The "window of implantation" represents the period of maximum uterine receptivity for implantation. In response to signals from the embryo, pregnancy-specific proteins are released in maternal serum and a series of morphological, biochemical and immunological changes occur in the uterine environment. These systemic and local modifications can be considered to constitute "the maternal recognition of pregnancy". The human hemochorial placenta arises primarily through proliferation, migration and invasion of the endometrium and its vasculature by the embryonic trophoblast. The complex invasive processes accompanying implantation of the embryo are controlled at the embryo-maternal interface by factors from decidualized endometrium and the trophoblast itself. An inflammatory reaction and a proper maternal immune response allow survival and development of the feto-placental unit. In this review, we focus on interactions between trophoblast and uterine tissues and on cellular mechanisms and molecular signals involved in the closely regulated process of implantation.

Development and validation of an assay for measuring preimplantation factor (PIF) of embryonal origin

PROBLEM

Tests to determine presence of embryos prior to implantation are needed.

METHODS

Sera from women after embryo transfer were tested for preimplantation factor (PIF) using the lymphocyte/platelet binding assay. Autorosettes were counted using blood type O+ donor lymphocytes and platelets incubated with blinded serum in the presence of antiCD2 antibody and rabbit complement. Human chorion gonadotropin (hCG) concentrations were determined 7 days later and compared with results of the lymphocyte/platelet assay. Implantation was confirmed by ultrasonographic evidence of presence of an intrauterine gestational sac. The roles of platelet activating factor (PAF) and chaperonin 10 in the observed phenomena were studied experimentally.

RESULTS

Significantly more lymphocyte/platelet rosette formations were observed when sera from women who successfully implanted were compared to sera from women who failed to implant. Neither PAF nor chaparonin added to the tested sera controls influenced the percentage of lymphocyte/platelets rosettes.

CONCLUSIONS

PIF is a likely candidate to be the next frontier of diagnosing the presence of viable preimplantation embryos in vivo.