The Next Frontier in ART: Harnessing the Uterine Immune Profile for Improved Performance.

Assisted reproduction techniques have improved considerably in recent decades, but despite these advances, success rates remain relatively low. Endometrial immune profiling involves the analysis of cytokine biomarkers in the endometrium during the mid-luteal phase. This profiling aims to provide insights into the immune environment of the uterus. The aim is to identify immune disturbances and thus guide the development of personalized therapeutic approaches. The first part of the review looks back at the emergence of innovative concepts, highlighting the specificity of the human uterine environment at the time of implantation. Based on this new knowledge, biomarkers have been selected for endometrial immune profiling. The second part details the results of clinical studies conducted over the last ten years. These clinical results suggest that this approach can increase the rate of live births in patients suffering from repeated implantation failures or repeated pregnancy loss. Uterine immune profiling represents a clinical innovation that can significantly improve the performance of medically assisted reproduction treatments through personalized strategies tailored to the local immune profile. Innovation in personalized medicine for assisted reproduction is crucial to improving the success rates of fertility treatments, while reducing the risks and costs associated with ineffective or unnecessary interventions.

Endometrial Immune Profiling: A Method to Design Personalized Care in Assisted Reproductive Medicine.

Objective: To assess the efficiency of the endometrial immune profiling as a method to design personalized care to enhance the pregnancy rate in a large heterogeneous infertile population. We hypothesized that some reproductive failures could be induced by a uterine immune dysregulation which could be identified and corrected with a targeted plan. Design: Prospective cohort study. Setting: Multicentric study. Intervention(s) and Main outcome measure(s): One thousand and seven hundred thirty-eight infertile patients had an immune profiling on a timed endometrial biopsy between 2012 and 2018. This test documented the absence or the presence of an endometrial immune dysregulation and identified its type. In case of dysregulation, a targeted personalized plan was suggested to the treating clinician aiming to supply the anomaly. One year after the test, the clinician was contacted to provide the outcome of the subsequent embryo transfer with the applied suggested plan. Result(s): After testing, 16.5% of the patients showed no endometrial immune dysregulation, 28% had a local immune under-activation, 45% had a local immune over-activation, and 10.5% had a mixed endometrial immune profile. In patients with a history of repeated implantation failures (RIF) or recurrent miscarriages (RM), the pregnancy rate was significantly higher if an endometrial dysregulation was found and the personalized plan applied, compared to the patients with an apparent balanced immune profile (respectively 37.7 and 56% vs. 26.9 and 24%, p < 0.001). In contrast, in good prognosis IVF (in vitro fertilization) subgroup and patients using donor eggs, this difference was not significant between dysregulated and balanced subgroups, but higher pregnancy rates were observed in absence of dysregulation. For patients with immune over-activation, pregnancy rates were significantly higher for patients who had a test of sensitivity, regarding the type of immunotherapy introduced, when compared to the ones who did not (51 vs. 39.9%, p = 0.012). Conclusion(s): Local endometrial immunity appears to be a new and important parameter able to influence the prognosis of pregnancy. Targeted medical care in case of local immune dysregulation resulted in significantly higher pregnancy rates in RIF and RM patients.

Intralipid® may represent a new hope for patients with reproductive failures and simultaneously an over-immune endometrial activation.

PROBLEM: Continuous failures to achieve a pregnancy despite effective embryo transfers is extremely distressing for couples. In consequence, many adjuvant therapies to IVF have been proposed to achieve an "ideal" immune environment. We here focus on Intralipid® therapy (IL) reported to have immunosuppressive properties on NK cells. METHOD OF STUDY: 94 patients exhibited an immune profile of endometrial over-immune activation and an history of repeated implantation failures despite multiple embryos transfers (RIF). They received a slow perfusion of Intralipid®. We here report the live birth rate following the procedure at the next embryo transfer. To get new insight on its mechanism of action, a second immune profiling had been performed under Intralipid® before the embryo transfer. RESULTS: The live birth rate of the RIF cohort treated with Intralipid® reached 54% (51/94) at the next embryo transfer. In patients successfully pregnant under Intralipid® who benefitted of a test of sensibility before the embryo transfer, we observed a significant decrease of the three biomarkers used to diagnose the over-immune endometrial activation (CD56 cells; IL-18/TWEAK, IL-14/FN-14). CONCLUSIONS: Double blind placebo versus Intralipid® studies should be conducted. Intralipid® may be an option to explore in RIF patients who exhibit an over-immune activation of uNK cells.

Impact of prednisone in patients with repeated embryo implantation failures: Beneficial or deleterious?

INTRODUCTION: Corticotherapy is the leading medication worldwide for patients with history of repeated implantation failures (RIF) after IVF/ICSI. Nevertheless, we still do not know its local mechanism of action, hence its precise indication. Our objective is to document the impact of prednisone on the endometrial expression of immune biomarkers (CD56 cells count, IL-18/TWEAK, IL-15/Fn-14 mRNA ratio) at the time of uterine receptivity in a RIF population. MATERIALS AND METHOD: An endometrial biopsy was realized in the mid luteal phase for immune profiling: IL-15/Fn-14 and IL-18/TWEAK mRNA ratios were determined by quantitative RT-PCR and CD56 mobilization per IHC. Fifty-five patients with a RIF history were diagnosed to have local over-immune activation [high IL-18/TWEAK mRNA ratio, and/or high IL-15/Fn-14 mRNA ratio] likely to impair the implantation process. They underwent a second immune profiling with supplementation of prednisone. A paired comparison of the immune profile before and under prednisone was performed in the subset of patients subsequently pregnant under prednisone. FINDING: In 54.5% of the cases, both immune biomarkers were normalized and in 16.5%, only one was normalized under prednisone. In 29% we observed a paradoxical increase of both immune biomarkers. The IL-18/TWEAK mRNA ratio reflecting the Th-1/Th-2 local equilibrium was significantly reduced (0.29 versus 0.10, p = .004), through very significant increase of TWEAK expression, in patients who were subsequently pregnant under prednisone. CONCLUSION: Testing the response to prednisone in a RIF context may be very useful. Less than half of RIF patients with immune deregulation may be prednisone responders and would benefit from its administration.

Uterine immune profiling for increasing live birth rate: A one-to-one matched cohort study.

BACKGROUND: Embryo implantation remains the main limiting factor in IVF/ICSI program. Endometrial immune remodeling events begin before implantation and are a vital process for pregnancy, preparing future maternal immune tolerance and regulating the placentation process. METHODS: Between 2012 and 2014, 193 patients (analyzed group) enrolled in our IVF program benefitted of an endometrial immune profiling to determine if their uterus was immunologically ready to accept an embryo and, if not, the specific immune mechanisms involved. Subsequently, they had an effective embryo transfer (ET) with personalization of their treatments if an immune deregulation has been diagnosed. Each analyzed patient was paired to the closest patient included in the IVF program according to biological criteria (age, number of mature oocytes, stage and number of transferred embryo), which had no endometrial immune profiling (193 patients, non-analyzed group). FINDING: 78% of analyzed patients had a uterine immune dysregulation and therefore care personalization. Their corresponding live birth rate (LBR) was twice higher than observed in the matched control group with conventional cares (30.5% versus 16.6%, OR: 2.2 [1.27-3.83] p=0.004) with a simultaneous drastic reduction of miscarriages per initiated pregnancy (17.9% versus 43.2%, OR: 0.29 [0.12-0.71], p=0.005). 22% of analyzed patients had no dysregulation. They did not differ from their matched controls for LBR and miscarriages. CONCLUSION: Uterine immune profiling enables an integrated approach of infertility that includes endometrial immunity as a key factor in planning personalized IVF/ICSI treatments. Personalization of treatment according to the woman's uterine immune balance produced a very significantly higher LBR.

The Uterine Immune Profile May Help Women With Repeated Unexplained Embryo Implantation Failure After In Vitro Fertilization.

LABELED PROBLEM: Embryo implantation remains the main limiting factor in assisted reproductive medicine (20% success rate). METHODS OF STUDY: An endometrial immune profiling was performed among 394 women with the previous history of repeated embryo implantation failures (RIF). The endometrial immune profile documented the ratio of IL-15/Fn-14 mRNA as a biomarker of uNK cell activation/maturation (together with the uNK cell count) and the IL-18/TWEAK mRNA ratio as a biomarker of both angiogenesis and the Th1/Th2 balance. According to their profile, we recommended personalized care to counteract the documented dysregulation and assessed its effects by the live birth rate (LBR) for the next embryo transfer. RESULTS: Endometrial immune profiles appeared to be dysregulated in 81.7% of the RIF patients compared to control. Overactivation was diagnosed in 56.6% and low activation in 25%. The LBR among these dysregulated/treated patients at the first subsequent embryo transfer was 39.8%. CONCLUSION: Endometrial immune profiling may improve our understanding of RIF and subsequent LBR if treated.

Critical Role and Therapeutic Control of the Lectin Pathway of Complement Activation in an Abortion-Prone Mouse Mating.

The abortion-prone mating combination CBA/J × DBA/2 has been recognized as a model of preeclampsia, and complement activation has been implicated in the high rate of pregnancy loss observed in CBA/J mice. We have analyzed the implantation sites collected from DBA/2-mated CBA/J mice for the deposition of the complement recognition molecules using CBA/J mated with BALB/c mice as a control group. MBL-A was observed in the implantation sites of CBA/J × DBA/2 combination in the absence of MBL-C and was undetectable in BALB/c-mated CBA/J mice. Conversely, C1q was present in both mating combinations. Searching for other complement components localized at the implantation sites of CBA/J × DBA/2, we found C4 and C3, but we failed to reveal C1r. These data suggest that complement is activated through the lectin pathway and proceeds to completion of the activation sequence as revealed by C9 deposition. MBL-A was detected as early as 3.5 d of pregnancy, and MBL-A deficiency prevented pregnancy loss in the abortion-prone mating combination. The contribution of the terminal complex to miscarriage was supported by the finding that pregnancy failure was largely inhibited by the administration of neutralizing Ab to C5. Treatment of DBA/2-mated CBA/J mice with Polyman2 that binds to MBL-A with high affinity proved to be highly effective in controlling the activation of the lectin pathway and in preventing fetal loss.

Colony Stimulating Factors 1, 2, 3 and early pregnancy steps: from bench to bedside.

Reproductive immunology applies general immunology principles to specialised targets, reproduction and development. The involvement of colony-stimulating factors (CSFs) in reproduction illustrates this. The CSF family includes CSF-1 or macrophage CSF (M-CSF), CSF-2 or granulocyte macrophage CSF (GM-CSF), and CSF-3 or granulocyte CSF (G-CSF). Each member has a specific localisation and timed expression in the reproductive tract with specific functions involving them in ovulation, embryo implantation, placentation and further embryonic development. They are used in reproductive medicine, either as biomarkers of oocyte quality and competence (follicular G-CSF), or to supplement embryo culture media with human recombinant GM-CSF, or they are used as an innovative therapy by using human recombinant G-CSF for infertile patients. Given fundamental considerations on CSFs and their strong implication in reproduction, this review aimed to detail the current knowledge for each member of the family to improve our understanding of their implication in the maternal-foetal cytokinic dialogue and in possibly preventing reproductive disorders.

Granulocyte-Colony Stimulating Factor related pathways tested on an endometrial ex-vivo model.

INTRODUCTION: Recombinant human Granulocyte-Colony Stimulating Factor (rhG-CSF) supplementation seems to be a promising innovative therapy in reproductive medicine, used in case of recurrent miscarriage, embryo implantation failure or thin endometrium, although its mechanisms of action remain unknown. Our aim was to identify possible endometrial pathways influenced by rhG-CSF. MATERIALS AND METHODS: Hypothetical molecular interactions regulated by G-CSF were designed through a previous large scale endometrial microarray study. The variation of endometrial expression of selected target genes was confirmed in control and infertile patients. G-CSF supplementation influence on these targets was tested on an endometrial ex-vivo culture. Middle luteal phase endometrial biopsies were cultured on collagen sponge with or without rhG-CSF supplementation during 3 consecutive days. Variations of endometrial mRNA expression for the selected targets were studied by RT-PCR. RESULTS: At the highest dose of rhG-CSF stimulation, the mRNA expression of these selected target genes was significantly increased if compared with their expression without addition of rhG-CSF. The selected targets were G-CSF Receptor (G-CSFR), Integrin alpha-V/beta-3 (ITGB3) implicated in cell migration and embryo implantation, Plasminogen Activator Urokinase Receptor (PLAUR) described as interacting with integrins and implicated in cell migration, Thymidine Phosphorylase (TYMP) implicated in local angiogenesis, CD40 and its ligand CD40L involved in cell proliferation control. CONCLUSION: RhG-CSF seems able to influence endometrial expressions crucial for implantation process involving endometrial vascular remodelling, local immune modulation and cellular adhesion pathways. These variations observed in an ex-vivo model should be tested in-vivo. The strict indications or counter indication of rhG-CSF supplementation in reproductive field are not yet established, while the safety of its administration in early pregnancy on early embryogenesis still needs to be demonstrated. Nevertheless, rhG-CSF appears as a promising therapy in some difficult and unsolved cases of reproductive failure. Indications of pre-conceptual rhG-CSF supplementation may derive from a diagnosed lack of endometrial expression of some target genes.

An insight into normal and pathological pregnancies using large-scale microarrays: lessons from microarrays.

In the introduction, we briefly recall old but classic evidence that there is no tolerance to paternal alloantigens in a first pregnancy. Therefore, we performed small- and large-scale microarrays in CBA × DBA/2 and CBA × BALB/c combinations, recently described as a murine model for preeclampsia. Our results are in line with other data suggesting a very early deregulation of local immune vascular events rather than a break of immune tolerance. Other data presented at the Tioman 2010 Preeclampsia Workshop supporting this hypothesis are briefly summarised, as well as indications and caveats from a recent human microarray on implantation failure and recurrent pregnancy loss.

TWEAK appears as a modulator of endometrial IL-18 related cytotoxic activity of uterine natural killers.

BACKGROUND: TWEAK (Tumor necrosis factor like WEAK inducer of apoptosis) is highly expressed by different immune cells and triggers multiple cellular responses, including control of angiogenesis. Our objective was to investigate its role in the human endometrium during the implantation window, using an ex-vivo endometrial microhistoculture model. Indeed, previous results suggested that basic TWEAK expression influences the IL-18 related uNK recruitment and local cytotoxicity. METHODOLOGY/PRINCIPAL FINDINGS: Endometrial biopsies were performed 7 to 9 days after the ovulation surge of women in monitored natural cycles. Biopsies were cut in micro-pieces and cultured on collagen sponge with appropriate medium. Morphology, functionality and cell death were analysed at different time of the culture. We used this ex vivo model to study mRNA expressions of NKp46 (a uNK cytotoxic receptor) and TGF-beta1 (protein which regulates uNK cytokine production) after adjunction of excess of recombinant IL-18 and either recombinant TWEAK or its antibody. NKp46 protein expression was also detailed by immunohistochemistry in selected patients with high basic mRNA level of IL-18 and either low or high mRNA level of TWEAK. The NKp46 immunostaining was stronger in patients with an IL-18 over-expression and a low TWEAK expression, when compared with patients with both IL-18 and TWEAK high expressions. We did not observe any difference for TWEAK expression when recombinant protein IL-18 or its antibody was added, or conversely, for IL-18 expression when TWEAK or its antibody was added in the culture medium. In a pro-inflammatory environment (obtained by an excess of IL-18), inhibition of TWEAK was able to increase significantly NKp46 and TGF-beta1 mRNA expressions. CONCLUSIONS/SIGNIFICANCE: TWEAK doesn't act on IL-18 expression but seems to control IL-18 related cytotoxicity on uNK cells when IL-18 is over-expressed. Thus, TWEAK appears as a crucial physiological modulator to prevent endometrial uNK cytotoxicity in human.

Levels of follicular G-CSF and interleukin-15 appear as noninvasive biomarkers of subsequent successful birth in modified natural in vitro fertilization/intracytoplasmic sperm injection cycles.

OBJECTIVE: To explore oocyte competence for subsequent birth. The modified natural IVF/intracytoplasmic sperm injection (ICSI) cycle was used as an experimental model by measuring levels of cytokines, chemokines, and growth factors in individual follicular fluids (FF). DESIGN: A retrospective blinded study. SETTING: European network of research, Embryo Implantation Control (EMBIC). PATIENT(S): Single FF from 83 women were analyzed during a modified natural IVF/ICSI cycle, and reproducibility of follicular composition was evaluated over two cycles for 15 patients. INTERVENTION(S): Each FF sample was blindly tested to assess levels of 26 factors by bead-based immunoassays. MAIN OUTCOME MEASURE(S): Each mediator was evaluated as a potential biomarker of subsequent birth by multivariate regression analysis. RESULT(S): A combination of both FF G-CSF and IL-15 was the optimal model to predict birth (AUC(ROC), 0.85). Birth rates per cycle were 48.9% (16/33) if two good-prognosis criteria were present (FF G-CSF>12 pg/mL and IL-15<7 pg/mL) and 8% (3/36) and 0% (0/14) if, respectively, one or none were present. FF G-CSF was significantly correlated over two cycles (r=.71), suggesting a possible prognostic value of its documentation. CONCLUSION(S): Combined follicular G-CSF and IL-15 quantification appears as an efficient and noninvasive method to define oocyte competence for subsequent successful conception in modified natural IVF/ICSI cycles.

Tolerance to the foetal allograft?

In this review, we will detail the concept of tolerance and its history in reproductive immunology. We will then consider whether it applies to the foetal-maternal relationship and discuss the mechanisms involved in non-rejection of the foeto-placental unit.

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK)/fibroblast growth factor inducible-14 might regulate the effects of interleukin 18 and 15 in the human endometrium.

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) could play a role in the regulation of interleukin (IL)-15 and IL-18, cytokines crucial for angiogenesis and uterine natural killer (uNK) cell recruitment during embryo implantation. We therefore confirmed the endometrial presence of TWEAK/fibroblast growth factor inducible-14 (Fn-14) and documented simultaneously the cytotoxic KIR receptor (NKp46) of uNK cells in the human endometrium while TWEAK, Fn-14, IL-15, and IL-18 mRNA were quantified by real-time polymerase chain reaction in relation to the recruitment of CD56+ cells among fertile control women and patients who had failed to implant after assisted reproduction treatment.

Early regulators in abortion and implications for a preeclampsia model.

This paper reports a summary of our comparative analysis of the uterine expression of interleukin-23 (IL-23), IL-27 and TWEAK in the CBA/J femalexDBA/2 male mouse mating combination, a model of immune-mediated early pregnancy loss. Compared with the MHC-identical CBA/JxBALB/c mating combination, which yields successful pregnancies, immunohistochemistry and qPCR in uterine tissue showed an immediate post-mating IL-27 hyper-expression after mating with DBA/2 males. Intra-uterine TWEAK expression was present in females mated with DBA/2 or Balb/c males from days 0.5 to 4.5 post-coitum (pc), peaking on day 0.5 pc together with uterine TNFalpha. In uteri of DBA/2 mated mice, TWEAK declined to almost undetectable levels on days 6.5-9.5 pc, a steeper drop than in BALB/c mated mice where TWEAK remained detectable. In both mating combinations, neutralisation of TWEAK by antibodies increased resorption rates, but surprisingly, so did IL-27 neutralisation. The complement regulator mannan binding lectin-A (MBL-A), but not MBL-C, was present on day 4.5 pc especially after mating with DBA/2 males. High levels of MBL are present in the uterine luminal fluid of sterile women, and possible functions for TWEAK and MBL in human implantation are indicated by their protein and mRNA expression in uterine biopsies from infertile and fertile individuals. Consistent with the results in mice, increased MBL expression is linked with pregnancy failure. Serum and uterine VEGF and VEGF receptor levels are also different between fertile and sterile patients. The implications of these findings for utilising the CBA/JxDBA/2 mating combination as an early onset model of preeclampsia are discussed.

How should data on murine spontaneous abortion rates be expressed and analyzed?

PROBLEM: Spontaneous abortions in the CBA x DBA/2 model are normally reported as number of resorptions/total number of implantations (R/T), pooling data from individual mice. The significance of differences between groups has been determined using non-parametric statistics (e.g. chi-square or Fisher's Exact test) based on a priori predictions. Recently, it has been argued that medians with box plots should replace the accepted standard, but this deprives readers of data needed to verify P-values, and leads to inferences incompatible with biological and statistical reality. METHOD OF STUDY: Raw data on 173 individual CBA x DBA/2 matings were analyzed by median and mean, along with R/T data from 18 independent experiments containing 5-10 mice per group. Raw data from 19 CBA x BALB/c matings were similarly analyzed. RESULTS: Individual CBA x DBA/2 mouse resorption rates showed a non-Gaussian distribution, but the mean and median differed by <0.5%. Resorption data from 6 and 12 independent pools of mice were normally distributed. Only the mean enabled a between-group P-value calculation. CBA x BALB/c matings gave a median of 0 and mean of 5.1%; the data were not normally distributed, but that was because of a bimodal distribution. One group of mice had 0 abortions, and the second a mean of 13.9% abortions, and the data from the latter group were normally distributed. CONCLUSION: Although it is possible to compare individual mice, and even individual implantation sites, in resorption (abortion) studies, as the relevant question is the significance of differences between treatment groups of mice, and reproducibility, the established classical method of reporting R/T should continue to be provided. In CBA x BALB/c matings, where abortion rates are low, using the median is misleading and may obscure the existence of two distinct populations.

Immune regulation at the interface during early steps of murine implantation: involvement of two new cytokines of the IL-12 family (IL-23 and IL-27) and of TWEAK.

PROBLEM: An important subset of implantation defects/early abortion seems to be linked with a deregulation of the interleukin (IL)-12/IL-15/IL-18 system as well as tumor necrosis factor (TNF)- and natural killer (NK)-controlled/mediated networks at the decidual placental interface, both in case of deficient or excess expression. The presence of TNF in high amounts in the pre/peri-implantation uterus and its pivotal role during pregnancy are difficult to reconcile with its abortive effects in ongoing pregnancy. We therefore searched for regulators of the IL-12/IL-18 family of cytokines as well as for antagonist(s) of TNF with potentially selective effects on implantation. METHOD OF STUDY: We first used Swiss mice to verify the presence in the murine reproductive tract of 'new members' of the IL-12 family of cytokines, IL-23 and IL-27, as well as of tumor necrosis factor-like WEAK inducer of apoptosis (TWEAK), described as acting with TNF as Yin and Yang of innate immunity in murine placenta/ decidua at days 0-12.5. We then compared expression by RT-PCR in the CBA x DBA/2, and CBA x BALB/c murine mating combinations. Finally, we performed in vivo neutralization experiments of TWEAK and IL-27. RESULTS: Immunohistochemistry (IHC) studies showed that IL-23, IL-27, and TWEAK were expressed at the interface. For RT-PCR, IL-23 expression peaked at day 9.5 in the non-aborting mating combination, a peak absent in the aborting one, and thus difficult to explain except by invoking a feed back on EB13 (Epstein-Barr virus-induced gene 3 cytokine). Most important, an immediate post-mating IL-27 hyper expression was seen in the CBA x DBA/2 mating compared to CBA x BALB/c one. The difference in expression resurged and was statistically very significant by days 6.5-9.5, compatible with an early activation of inflammation on day 0.5 which would then peak again in the 'resorption window' where takes place the early NK/mph activation described by Baines et al. A significant TWEAK expression was present in both strains from days 0.5 to 4.5 peaking in both cases in the first days when it is known that intra uterine TNF also reaches high levels as a component of post-mating inflammation. However, it was lower from day 1.5 in the abortion-prone CBA x DBA/2 mating combination, and almost absent by days 6.5-9.5 when compared to the non-aborting CBA x BALB/c mating combination. In both mating combinations, neutralization of TWEAK-enhanced resorption rates, but surprisingly so did IL-27 neutralization. CONCLUSION: TWEAK is likely offering protection against the deleterious effects of TNF in implantation explaining embryo survival in a TNF-rich environment, and equal number of implants in both strains. However, there is a clear difference of protection in abortion-prone mating peaking in the abortion/resorption window but starting early, and therefore possible links with the prevention of abortion in CBA x DBA/2 matings by interfering with complement activation as recently described by Girardi et al. are discussed, as well as consequences for our current view of feto-maternal 'seed and soil' interplay. The apparently paradoxical effects of IL-27 neutralization are also discussed.

Epigenetic modifications and chromatin loop organization explain the different expression profiles of the Tbrg4, WAP and Ramp3 genes.

Whey Acidic Protein (WAP) gene expression is specific to the mammary gland and regulated by lactogenic hormones to peak during lactation. It differs markedly from the more constitutive expression of the two flanking genes, Ramp3 and Tbrg4. Our results show that the tight regulation of WAP gene expression parallels variations in the chromatin structure and DNA methylation profile throughout the Ramp3-WAP-Tbrg4 locus. Three Matrix Attachment Regions (MAR) have been predicted in this locus. Two of them are located between regions exhibiting open and closed chromatin structures in the liver. The third, located around the transcription start site of the Tbrg4 gene, interacts with topoisomerase II in HC11 mouse mammary cells, and in these cells anchors the chromatin loop to the nuclear matrix. Furthermore, if lactogenic hormones are present in these cells, the chromatin loop surrounding the WAP gene is more tightly attached to the nuclear structure, as observed after a high salt treatment of the nuclei and the formation of nuclear halos. Taken together, our results point to a combination of several epigenetic events that may explain the differential expression pattern of the WAP locus in relation to tissue and developmental stages.

[Nuclear organization and expression of milk protein genes]. / Organisation nucléaire et expression des gènes des protéines du lait.

Milk protein gene expression varies during the pregnancy/lactation cycle under the influence of lactogenic hormones which induce the activation of several transcription factors. Beyond this activation modifying the binding properties of these factors to their consensus sequences, their interactions with DNA is regulated by variations of the chromatin structure. In the nuclei of the mammary epithelial cell, the three dimensional organisation of the chromatin loops, located between matrix attachment regions, is now being studied. The main milk components are organised in supramolecular structures. Milk fat globules are made of a triglyceride core enwrapped by a tripartite membrane originating from various intracellular compartments. The caseins, the main milk proteins, form aggregates: the casein micelles. Their gradual aggregation in the secretory pathway is initiated as soon as from the endoplasmic reticulum. The mesostructures of the milk fat globule and of the casein micelle remain to be elucidated. Our goal is to make some progress into the understanding of the molecular and cellular mechanisms involved in the formation of these milk products.