Dissertation committee:
Αριάδνη Μαλαμίτση-Πούχνερ, Καθηγήτρια, Ιατρική Σχολή, ΕΚΠΑ
Μαρία Τσολιά, Καθηγήτρια, Ιατρική Σχολή, ΕΚΠΑ
Βασιλική Παπαευαγγέλου, Καθηγήτρια, Ιατρική Σχολή, ΕΚΠΑ
Αργύριος Ντινόπουλος, Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Κωνσταντίνος Πανουλής, Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Δέσποινα Μπριάνα, Αναπληρώτρια Καθηγήτρια, Ιατρική Σχολή, ΕΚΠΑ
Θεοδώρα Μπούτσικου, Αναπληρώτρια Καθηγήτρια, Ιατρική Σχολή, ΕΚΠΑ
Summary:
This thesis consists of two parts, the GENERAL and the SPECIFIC
The General Part consists of Parts A and B and includes the following chapters:
Part A
I. The family of neurotrophic factors
The definition of the neurotrophic factor is referred to the three main families of factors that fall under this definition. Most neurotrophic factors belong to one of the following three families: (i) the family of neurotrophins, (ii) the TGF-β superfamily and (iii) the CNTF family of neurotrophic cytokines.
II. Neurotrophins, their structure and action
In the human body, four structurally related molecules: a) neuron growth factor (NGF), b) brain-derived neurotrophic factor (BDNF), c) neurotrophin-3 ( neurotrophin-3 -NT-3) and d) neurotrophin-4 (neurotrophin-4 - NT-4), form the family of neurotrophins, a group of substances that provide neuroprotection, through their anti-apoptotic action and the promotion of survival, differentiation and development of neurons of the central and peripheral nervous system. They exert their functions through two classes of neurotrophin receptors, the high-affinity tyrosine kinase (Trk) receptors and the p75NTR receptors to which they are associated with low affinity. This chapter makes extensive reference to the structure of neurotrophins and the signaling pathways through which they exert their neurological activities.
III. Non-neurological effects of neurotrophins
In addition to their actions on the central and peripheral nervous systems, neurotrophins, through their pleiotropic potential, have been shown to be involved in angiogenesis mechanisms, carbohydrate and lipid metabolism, and the pathology of metabolic syndrome and atherosclerosis. Decreased plasma levels of NGF and BDNF have been associated with acute coronary and metabolic syndromes. NGF is known to have insulinotropic, angiogenic and antioxidant functions. In addition, they are involved in immune mechanisms, as elevated levels of neurotrophins have been found in inflammatory, autoimmune and allergic diseases. These actions of neurotrophins are listed in this chapter.
IV. Neurotrophins and their involvement in neuropsychiatric disorders
It is well known that neurotrophic factors control many aspects of neuronal development and function, in both the peripheral and central nervous systems. In the developing brain, they play an important role in controlling the number of surviving neurons and in cell differentiation. In addition to these survival effects, neurotrophic factors play an important role in maintaining the function of adult neurons, regulation of their growth, synaptic function, and plasticity, as well as related metabolic functions, such as protein synthesis and neurotransmission. Thus, neurotrophic factors play a key role in maintaining normal behavioral processes and are therapeutic targets for a number of neurodegenerative and psychiatric disorders.
This chapter analyzes the involvement of neurotrophins in common behavioral processes, such as cognitive processes, anxiety disorders, stress adaptation, defensive and aggressive behavior, reward and addiction, as well as their relationship to major neurodegenerative and psychiatric diseases, such as Alzheimer's disease, depression, bipolar disorder, schizophrenia and autism spectrum disorders.
V. Neurotrophins and their relationship to the fetus and the newborn
This chapter makes extensive reference to the data available to date on the role of neurotrophins in the fetal-placental unit and their differential expression depending on gestational age and neonatal birth weight. It also describes the fluctuations recorded in the literature on the levels of circulating neurotrophins in the umbilical cord blood, in cases of fetal growth disorders, ie in IUGR or LGA neonates, as well as in the changes observed in them during the transition to extrauterine life. Reference is also made to the effect of perinatal stress and the consequent hypoxia of the fetus on the expression of neurotrophins.
Part B
I. Diabetes mellitus in pregnancy and its effects
This chapter provides data on the definition of gestational diabetes and epidemiological data on its prevalence in the population. Reference is made to diagnostic criteria and therapeutic approaches in women with pregnancies complicated by gestational diabetes. It also mentions the complications and side effects that may be caused by gestational diabetes in the developing fetus and newborn. Diabetes mellitus during pregnancy has been implicated in the development of congenital anomalies and growth disorders in the offspring of diabetic mothers. It is also responsible for both short-term neonatal complications (such as hypoglycemia, hypocalcaemia, hypermagnesaemia, hyperbilirubinemia, polycythemia), and long-term complications, which include increased rates of childhood and adolescent obesity, decreased glucose tolerance or development of diabetes mellitus, and neuropsychological dysfunction in the offspring.
II. Gestational Diabetes and Schizophrenia
The comorbidity of schizophrenia-diabetes has recently emerged as a major challenge for clinicians and researchers. Epidemiological studies have shown that the offspring of mothers who develop diabetes during pregnancy are 7 times more likely to develop schizophrenia than those who have not been exposed to a diabetic pregnancy. Possible underlying mechanisms by which GDM during pregnancy could predispose to the subsequent onset of neuropsychiatric disorders include hyperglycemia, hypoxia, oxidative stress, and the immune activation that the latter entails. All of these mechanisms are analyzed in this chapter and supporting data from epidemiological research are provided, as well as studies in animal and human models that support this relationship between gestational diabetes and schizophrenia.
The Specific Part includes:
I. The hypothesis and the aim of the study
The study was based on the hypothesis that abnormal expression of neurotrophic factors in the developing fetal brain may mediate the relationship between maternal diabetes and subsequent neurodevelopmental disorders of the offspring. The aim of the present study was to investigate whether the circulating concentrations of neurotrophins in the umbilical cord blood at birth, which reflect the corresponding levels of neurotrophins in the CNS of the fetus, differ in pregnancies complicated by GDM compared to normal pregnancies. In addition, we sought to investigate whether these changes in BDNF, NGF, and NT-4 levels are further modified in cases where GDM during pregnancy leads to fetal growth disorders, i.e., the birth of a LGA or IUGR newborn, relative to pregnancy in which GDM is controlled and not complicated by fetal growth disorders, i.e. leads to the birth of AGA newborn.
II. The study population and the methods of determination of neurotrophins
For the purpose of the study, 80 samples were collected, relating to the following pregnancies: 15 complicated with GDM and LGA newborn, 12 complicated with GDM and IUGR newborn, 33 complicated with GDM and normal fetal growth newborn (AGA), and 20 uncomplicated full-term pregnancies (control group). A blood sample was taken from the doubly clamped umbilical cord from each pregnancy. All mothers provided informed consent before enrolment. Each blood sample taken was centrifuged immediately and the supernatant serum and plasma were stored in a deep freezer (-80 ° C). Umbilical cord BDNF, NGF, and NT-4 concentrations were determined by ELISA (USCN Life Science Inc., Houston, TX 77082, USA). Parametric and non-parametric methods were applied in the statistical analysis, based on the normality of data distribution.
III. The results of the study
BDNF concentrations in umbilical cord blood samples were significantly reduced in neonates with a positive history of GDM. In addition, BDNF concentrations were significantly higher in female neonates.
Umbilical cord NGF concentrations were found to be significantly lower in IUGR than in AGA neonates, whereas in the control group, umbilical cord NGF concentrations were significantly lower in non-primiparous mothers.
The effect of gestational age on NT-4 concentrations was also statistically significant. In particular, NT-4 concentrations were found to be significantly reduced in cases of advanced gestational age.
Umbilical cord BDNF concentrations were found to correlate positively with those of NGF and NT-4, respectively.
Umbilical cord NT-4 concentrations were higher in female infants, whereas in the IUGR group, BDNF concentrations were higher in fetuses born vaginally.
IV. The conclusions of the study
Summarizing our results, we conclude that:
1.The finding that BDNF is down-regulated in fetuses exposed to gestational diabetes mellitus, regardless of the fetal growth pattern, provides a serologically based indication of fetal BDNF signaling disorder in response to maternal diabetes. It is tempting to assume that lower umbilical cord blood BDNF concentrations in gestational diabetes mellitus, possibly reflecting the degree of neural maturity, may be a candidate mechanism for the association between gestational diabetes and later psychopathology in the offspring .
2. The IUGR fetuses of our study born to diabetic mothers show NGF deficiency. This finding is likely to have implications for the long-term neurodevelopmental consequences of IUGR, which include cortical dysfunction, neurodegenerative deficits, and an increased incidence of later psychiatric disorders.
3. Another interesting observation of the study is that vaginal delivery is associated with higher concentrations of BDNF in IUGR fetuses, possibly providing fetal neuroprotection. Given the involvement of BDNF in various aspects of brain function and the increasing incidence of cesareans section, we consider this finding to be very important.
4. BDNF and NT-4 concentrations were significantly higher in female neonates. This gender-dependent difference in umbilical cord blood BDNF reported in the present study may partly explain the known higher prevalence of adverse neurodevelopmental effects following brain injury in males.
5.Another interesting observation of the study is that normal delivery is associated with higher concentrations of BDNF in IUGR fetuses, possibly providing fetal neuroprotection. Given the involvement of BDNF in various aspects of brain function and the increasing frequency of cesarean section, we consider this finding to be very important.
6.BDNF and NT-4 concentrations were significantly higher in female neonates. Given this, we can assume that gender-dependent differences in umbilical cord blood BDNF reported in the present study may partly explain the known higher prevalence of adverse neurodevelopmental effects following brain injury in males.
7.Increased concentrations of NT-4 in umbilical cord blood with reduced gestational age in full-term infants may signal the role of NGF during an early stage of human brain development, as elevated NT-4 concentrations are associated with increased fetal neurogenesis. In addition, higher maternal parity appears to adversely affect fetal NGF expression, possibly due to increased oxidative stress in umbilical cord blood.
8.Finally, the positive correlation between umbilical cord blood BDNF and NGF as well as NT-4 concentrations appears to be consistent with a previously mentioned coordinated gene activation mechanism between these neurotrophins during embryonic development.
Further studies are needed to confirm the above findings as well as to further investigate the relationship between neurotrophin levels in pregnancies complicated by diabetes mellitus and subsequent neurodevelopmental disorders of the offspring.
