Developmental regulation of muscle mitochondrial function

At birth, the newborn faces many new challenges. It must establish breathing, shivering and, in many animals, locomotion for the first time. The heart also has to pump harder to support these new activities. More energy is, therefore, needed immediately after birth to ensure the newborn survives. This energy is provided by small structures within the cells called mitochondria which use oxygen to produce energy rich molecules that then fuel the muscular and other processes essential for life. In many tissues, preparations to ensure neonatal survival begin before birth and are dependent on the normal increase in a hormone, cortisol, in the fetal blood towards delivery. However, at present, little is known about how the mitochondria in muscles and other tissues prepare for the increase in energy demands at birth or whether these maturational changes depend on the increase fetal cortisol before birth.
Previous studies in animals have suggested that the conditions experienced during development before birth may affect the way mitochondria function in the adult. Since a progressive decline in mitochondrial function is part of the normal aging process, changes in mitochondrial function induced before birth may be important in determining the quality of life and health much later in life. However, we know little about how mitochondrial function changes with growth and development from fetal to adult life or whether this trajectory can be altered by events before delivery. Cortisol levels in the fetus not only rise towards term as a normal maturational signal of impending delivery but can also increase earlier in pregnancy in response to poor conditions for development such as maternal stress or a shortage of nutrients or oxygen. These conditions are known to have implications for health after birth and can accelerate aging and the onset of adult degenerative diseases like diabetes and high blood pressure that shorten lifespan. Consequently, changes in mitochondrial function induced by early exposure to cortisol before birth may have an important role in explaining how conditions during fetal life affect life-long health and wellbeing.

The aim of this study is to determine whether functioning of the mitochondria in muscles matures in late pregnancy in preparation for birth as a result of the normal rise in fetal cortisol towards term but is impaired at birth and with aging, if fetal overexposure to cortisol occurs prematurely. The studies will be carried out in sheep because development of their fetuses more closely resembles the human infant than rodent pups. They are also large enough to study experimentally before birth and, because they born mature, the increase in energy requirements for muscular activity is high at birth. Mitochondrial function will be measured in the heart and skeletal muscles of fetal, newborn and adult animals with normal cortisol profiles and in those in which fetal cortisol levels have been altered experimentally during late pregnancy. By providing information about the development and regulation of muscle mitochondrial function, the study will provide potential biomarkers of future health and therapeutic targets to improve life-long well being if compromised by events before birth. In particular, the study has important clinical implications for infants that were growth restricted before birth, delivered prematurely with or without antenatal glucocorticoid treatment or experienced other stressful conditions during pregnancy which raised cortisol concentrations.

Little is known about the developmental regulation or programming of muscle mitochondrial function before birth despite the importance of mitochondria in meeting the increased neonatal energy demands and in the normal aging process. This study is designed to test the hypothesis that mitochondria mature in late gestation in a cortisol dependent manner and are altered adversely with aging postnatally by premature fetal cortisol overexposure. The specific objectives are to establish: 1. What is the normal ontogeny of mitochondrial function before and after birth? 2. To what extent do prenatal maturational changes in mitochondrial function depend on the normal prepartum increment in fetal cortisol? 3. Does prenatal cortisol exposure earlier than normal alter postnatal mitochondrial function?
High resolution respirometry will be used to quantify mitochondrial O2 consumption in right and left ventricles of the heart and two skeletal muscles, the biceps femoris and soleus, with different fibre types in fetal, newborn and adult sheep. These measurements will be related to cortisol concentrations, muscle structure and fibre content, expression of genes and proteins involved in the mitochondrial electron transport chain, and to the level of tissue oxidative stress and senescence markers. These measurements will also be made in fetuses with cortisol levels manipulated by cortisol infusion before the normal prepartum increment and surgical removal of the fetal adrenal glands to prevent this natural surge. The effects of elevating fetal cortisol concentration prematurely on mitochondrial function in newborn and adult muscles will also be examined and related to measures of insulin-glucose dynamics in the adults as an index of metabolic status. The project will provide mechanistic data on mitochondrial programming important in identifying potential biomarkers of future health and targets for therapeutic intervention in infants exposed to excess cortisol in utero

The proposed research will have both academic and wider economic and societal impacts. The primary beneficiaries from the proposed research include (a) academic scientists in a wide range of biological disciplines (b) clinicians caring for pregnant women and their infants, and for those planning pregnancy, (c) other health care professionals and public policy makers involved with maternity and child services (d) pharmaceutical organisations who may translate the research findings into potential therapeutic treatments, (e) students and researchers at all levels receiving general laboratory experience or specific techniques training during the project and (f) the lay public, particularly women planning pregnancies. The academic impacts are three fold. First, there will be impacts on the wider scientific community as the novel data generated by this project is disseminated widely through publications, presentations at national and international meetings. Secondly, there will be increased opportunities for collaboration through providing (i) tissues and blood samples for new projects and (ii) scientific expertise to others for skills training and exploitation of scarce animal resources. Finally, there will be capacity building in this area of research by the training opportunities offered for the postdoctoral researcher and other PhD and undergraduate students involved in the project as well as for researchers attending formal training course delivered by the applicants. Academic impact will be measured by publication citations, invitations to international meetings, new collaborations and partnerships, further grant funding and employment of additional trained researchers in academia or industry. At the economic and societal level, the impacts of the project are twofold. First, through our industrial links, there is potential for exploitation of data from this project by commercial partners and stakeholders with major interests in mitochondrial biology and aging. In particular, the detailed mechanistic information about the interactions between mitochondria, stress and the endocrine environment during pregnancy has applications to government in providing health advice with impacts on public health. Secondly, through public engagement via both the applicants' own activities and the University's Office of External Affairs and Communication, the benefits of scientific research and of this project, in particular, to population health and wellbeing will be promoted widely. The applicants are actively engaged in communicating their research and the understanding of science more generally to the lay public through a wide range of media including Twitter, YouTube and webcasts. They give guest lectures at lay organisations, write opinion pieces in magazines and participate in science festivals and outreach activities for schools, university applicants and adult further learning centres. They are also active in promoting equality and diversity in science and governance. Throughout the project, all applicants and researchers will seek opportunities to shape public opinion, science policy and clinical practice. Impact of these activities will be measured by an increased profile of the research area with funding bodies, the wider scientific community and the lay public with improved lifestyle advice during pregnancy and better early life biomarkers of longer term health risks for the general population.