Research team

Veterinary physiology and biochemistry

Expertise

Ongoing studies: - Maternal obesity and "fetal programming": the consequences for reproductive physiology of the offspring. - Fundamental understanding and development of preconception care strategies to improve maternal fertility and to protect offspring's health in obese individuals - Development of polymeric nanoparticle carriers for targeted drug delivery to oocytes. - Protective and reparative strategies to improve oocyte developmental capacity under metabolic stress conditions.

The link between mitochondrial dysfunction and epigenetic alterations in metabolically compromised oocytes: a key pathway to subfertility and a target to improve embryo quality and offspring health. 01/11/2020 - 31/10/2022

Abstract

Maternal metabolic disorders, e.g. obesity, affect millions worldwide and are known to cause subfertility. Altered ovarian micro-environment and the direct impact on oocyte quality is a key factor in this pathogenesis. The oocyte undergoes dynamic epigenetic reprogramming during normal follicular development. Timely acquisition of epigenetic modifications is critical for genomic imprinting and regulation of transcription during subsequent development. Dysregulated oocytes carry persistent epigenetic defects that harm offspring health. Recent insights from somatic cells and cancer biology show that mitochondria are the machinery by which metabolic changes can translate into epigenetic (dys)regulation. This is due to altered bioenergetics or changed availability of intermediate products needed for the establishment of epigenetic marks. We learned that mitochondrial dysfunction is a main cause of reduced oocyte quality under metabolic stress. Fundamental understanding of the mitochondrial-nuclear communication in growing oocytes is lacking but crucial for the development of efficient interventions to improve oocyte quality and fertility and for the protection of embryo quality and offspring health. We aim to examine the direct link between mitochondrial dysfunction in growing oocytes and epigenetic alterations, to study if these alterations are preventable or reversible using mitochondrial targeted treatments, and to test the impact of these treatments on the offspring's health.

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Fundamental understanding and development of preconception care strategies to improve maternal fertility and to protect offspring's health in obese individuals 01/01/2019 - 31/12/2022

Abstract

Obesity is becoming a global threat, reducing mother's health and reproductive capacities and affecting the offspring's health. Clear preconception care guidelines for obese future mothers are lacking. Clinical studies are flawed and fundamental studies in basic animal models are scarce. The importance of preconception weight loss on reproduction and baby's health is heavily debated and has never been investigated in detail. This project aims to uncover the role and the importance of clinically relevant preconception care advices to obese women planning for pregnancy. To do so, we propose strategically designed fundamental obese mouse models to assess the impact of preconception weight loss, diet normalization, increased physical activity, omega-3 rich diet or the combination thereof. We will focus on four distinct major research challenges: 1) can we find improvements of mother's metabolic profile before conception in relation to the observed weight loss; 2) does the mother's own fertility success increase; 3) can we improve the postnatal health of the offspring and 4) can we safeguard the offspring's reproductive physiology. Physiological and in depth molecular outcome parameters will be combined to generate a clear and integrated view on the effects of preconception care lifestyle interventions. If successful, these novel insights will be the basis for developing future awareness and education programs aiming at improved human maternal health at the time of conception.

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Maternale obesitas en "fetal programming": de gevolgen voor de voortplantingsfysiologie van de nakomelingen. 01/10/2018 - 30/09/2022

Abstract

A disturbed maternal metabolism like in obesity or type II diabetes has clearly been associated with disappointing fertility. We extensively showed that such metabolic disorders have direct effects on the micro-environment of the growing and maturing oocyte, ultimately leading to reduced oocyte and embryo quality. Obesity is a global health threatening problem and recent studies indicated that maternal obesity may result in significant health issues in the offspring. More in depth mechanistic research clearly pointed out the importance of uterine programming in early pregnancy. It is not known however whether the metabolic status of obesity as such and/or potential direct effects of the typical fat rich western type diet are responsible for these observations. Based on the epidemiological relevance of obesity and hypercholesterolemia we hypothesize that obesity or an obesogenic diet of the mother around conception or during the entire pregnancy will alter the micro-environment of the growing embryo and fetus. This will change uterine programming ultimately leading to compromised offspring's health and reproductive physiology. To systematically investigate this hypothesis, we will feed female LDLR knock-out mice (LDLR-/-) an obesogenic diet A) several weeks before conception resulting in maternal obesity at conception or B) solely around conception or C) throughout the entire pregnancy. The offspring will be cross-fostered upon birth and will be used to study the general health of the offspring, the ovarian follicular reserve and the process of folliculo- and oogenesis, the offspring's pre-implantation embryo physiology and gene expression pattern and the receptivity of the offspring's uterus to support full pregnancy resulting in healthy offspring. By using this strategic experimental model we will be able to find the most sensitive window during pregnancy for uterine programming of reproduction, and it allows us to study the effects on every specific step on reproductive functioning. We believe that this project proposal may significantly contribute to the concept of "Developmental Origin of Health and Fertility" by further spreading the knowledge that epigenetic effects of maternal metabolism and diet may jeopardize health but also fertility in the offspring.

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Development of polymeric nanoparticle carriers for targeted drug delivery to oocytes. 01/04/2019 - 30/03/2020

Abstract

According to WHO reports, over 10% of women in reproductive age (20-44y) are infertile or subfertile. Oocyte quality is one of the major causes of infertility, as evident in several metabolic diseases such as obesity and type II diabetes, as well as aging. During the last 5-7 years a substantial scientific evidence has been built in our research unit focusing on maternal metabolic health in relation to oocyte and embryo quality. We showed evidence that the ovarian follicular microenvironment is significantly altered under the influence of metabolic disorders leading to a direct detrimental lipotoxic impact on the oocyte, manifested by oxidative stress, mitochondrial dysfunction, endoplasmic reticulum (ER) stress and apoptosis. This fundamental knowledge should now form the basis to design a sustainable treatment or prevention strategy. There is a large need for safe drug formulations that can reach the oocyte and particularly influence mitochondrial and ER functions, with high bioavailability and efficiency. Targeting these pathways and organelles usually require the use of hydrophobic compounds. In addition, the oocyte is surrounded by several cumulus cell layers and a glycoprotein layer (zona pellucida) which form biological barriers. At the subcellular level, drug delivery to the mitochondria (such as antioxidants) is another challenge due to the complex inner membrane network structure, unusual phospholipid, Cardiolipin, and a strong negative charge. Information about clathrin- and caveolin-mediated endocytosis in mammalian oocytes, and subsequent formation of endosomes and liposomal degradation are very scarce. Studying these mechanisms and understanding the role gap junctional communication in delivering molecules from cumulus cells (CCs) to the oocyte may facilitate delivery of therapeutics or protective compounds to the ooplasm. This can be combined with strategically designed formulations of e.g. antioxidants to target defective organelles, such as mitochondrial and endoplasmic reticulum, and to reduce oxidative stress at the subcellular level. Our preliminary proteomics data show that proteins related to these endocytosis mechanisms are expressed in oocytes and cumulus cells, and are affected by oocyte quality, cellular metabolic stress and the microenvironment in which an oocyte is matured. The present project proposal aims to take the first steps in understanding the role of these proteins in mediating uptake of nutrients and other compounds in oocytes and CCs. This will be investigated by gene and protein expression analysis at different time points, uptake of trace molecules and using specific inhibitors of each mechanism. The effect of the latter on oocyte developmental competence will be examined. With this approach we aim to provide new fundamental knowledge that may increase treatment efficiency of enhance oocyte quality and fertility.

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Mitochondrial and endoplasmic reticulum stress in oocytes and embryos as treatment targets for infertile patients with metabolic diseases. 01/04/2017 - 31/03/2018

Abstract

Oxidative stress, mitochondrial and endoplasmic reticulum (ER) stress have been recently postulated as main drivers of altered pathways in the oocyte linking maternal metabolic disorders to low fertility outcomes. Upregulated lipolysis, commonly associated with obesity and other metabolic disorders, increases the concentrations of lipotoxic fatty acids in the follicular fluid, which were shown to have a direct detrimental impact on oocyte quality and subsequent embryo development. Oocyte maturation involves complex nuclear, cytoplasmic, and molecular changes that determines its developmental competence. In human IVF clinics, oocytes are usually collected after hormonal stimulation and thus after exposure to metabolic stress during maturation in the follicle in affected mothers. It is not known if the deterioration in developmental competence of these metabolically-compromised oocytes can be rescued by alleviating mitochondrial and endoplasmic stress during or after fertilization, or should the stress be prevented during maturation. This project aims to test sensitive windows for preventative or reparative measures that may improve in vitro embryo production from metabolically-compromised oocytes, and examine the intrinsic quality of the embryos produced after treatment. A well-established bovine in vitro model will be used to generate metabolically-compromised oocytes by exposure to elevated pathophysiological levels of palmitic acid. MitoQ, a highly efficient mitochondria-targeted antioxidant, and Sirolimus, a specific ER-stress inhibitor, will be used to alleviate cellular stress either during fertilization or embryo culture, or during maturation. Embryo development will be recorded and blastocysts quality will be assessed by examining their metabolism, cell proliferation, cell lineage, DNA damage, markers for cellular stress and apoptosis. RNA-seq will be used to detect any persistent alterations in the transcriptomic profile. These studies will help defining windows of sensitivity and efficiency of targeting intracellular stress as a treatment option for infertile patients suffering from metabolic diseases.

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Mitochondria take centre stage: pathways to reduced oocyte quality and opportunities for curative strategies under maternal metabolic stress conditions. 01/10/2016 - 30/09/2019

Abstract

Infertility is a major socio-economic problem affecting millions worldwide and is specifically linked to maternal obesity and other (diet induced) metabolic disorders. Understanding the mechanisms by which altered metabolism affect fertility is crucial for successful interventions. Mitochondria are the power house within the oocyte. Reduced somatic cell mitochondrial function occurs early in the pathogenesis of metabolic diseases. This is mainly due to the lipotoxic effects of elevated free fatty acid concentrations in blood. For the oocyte to be developmentally competent, the number and function of mitochondria should reach a certain threshold. There are several thousands of mitochondria in the mature oocyte derived from about 20 mitochondria in the germ cell. In addition to their bio-energetic roles, mitochondria are also sensors of stress. Oxidative stress and associated cellular damage elicit stress signalling between the mitochondria and the nucleus to start a protective machinery. The effects of metabolic stress on mitochondrial replication and stress responses during oocyte growth and subsequent embryo development are not known. In this project we will use in vitro and in vivo animal models to study mitochondrial functions and stress responses under maternal metabolic stress conditions in growing oocytes. Defect-based protective and rescue interventions will also be tested to investigate opportunities for curative interventions.

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