The brain serotonin transporter binding in young adults; methodological considerations and association with Bulimia Nervosa and acquired obesity

The neurotransmitter serotonin (5-HT) modulates many functions important for life, e.g., appetite and body temperature, and controls development of the neural system. Disturbed 5-HT function has been implicated in mood, anxiety and eating disorders. The serotonin transporter (SERT) controls the amount of effective 5-HT by removing it from the extracellular space. Radionuclide imaging methods single photon emission tomography (SPET) and positron emission tomography (PET) enable studies on the brain SERTs. This thesis concentrated on both methodological and clinical aspects of the brain SERT imaging using SPET. The first study compared the repeatability of automated and manual methods for definition of volumes of interest (VOIs) in SERT images. The second study investigated within-subject seasonal variation of SERT binding in healthy young adults in two brain regions, the midbrain and thalamus. The third study investigated the association of the midbrain and thalamic SERT binding with Bulimia Nervosa (BN) in female twins. The fourth study investigated the association of the midbrain and hypothalamic/thalamic SERT binding and body mass index (BMI) in monozygotic (MZ) twin pairs. Two radioligands for SERT imaging were used: [123I]ADAM (studies I-III) and [123I]nor-beta-CIT (study IV). Study subjects included young adult MZ and dizygotic (DZ) twins screened from the FinnTwin16 twin cohort (studies I-IV) and healthy young adult men recruited for study II. The first study validated the use of an automated brain template in the analyses of [123I]ADAM images and proved automated VOI definition more reproducible than manual VOI definition. The second study found no systematic within-subject variation in SERT binding between scans done in summer and winter in either of the investigated brain regions. The third study found similar SERT binding between BN women (including purging and non-purging probands), their unaffected female co-twins and other healthy women in both brain regions; in post hoc analyses, a subgroup of purging BN women had significantly higher SERT binding in the midbrain as compared to all healthy women. In the fourth study, MZ twin pairs were divided into twins with higher BMI and co-twins with lower BMI; twins with higher BMI were found to have higher SERT binding in the hypothalamus/thalamus than their leaner co-twins. Our results allow the following conclusions: 1) No systematic seasonal variation exists in the midbrain and thalamus between SERT binding in summer and winter. 2) In a population-based sample, BN does not associate with altered SERT status, but alterations are possible in purging BN women. 3) The higher SERT binding in MZ twins with higher BMIs as compared to their leaner co-twins suggests non-genetic association between acquired obesity and the brain 5-HT system, which may have implications on feeding behavior and satiety.

Preterm delivery and selected biomarkers : phosphorylated insulin-like growth factor-binding protein-1 and matrix metalloproteinase-8 – in cervical fluid

Premature delivery is a major cause of neonatal morbidity and mortality. The incidence of premature deliveries has increased around the world. In Finland 5.3%, or about 3,000 children per year are born prematurely, before 37 weeks of gestation. The corresponding figure in the United States is about 13%. The morbidity and mortality are highest among infants delivered before 32 weeks of gestation - about 600 children each year in Finland. Approximately 70% of premature deliveries are unexplained. Preterm delivery can be caused by an asympto-matic infection between uterus and the fetal membranes, such can begin already in early pregnancy. It is difficult to predict preterm delivery, and many patients are therefore unnecessarily admitted to hospital for observation and exposed to medical treatments. On the other hand, the high risk women should be identified early for the best treatment of the mother and preterm infant. --- In the prospective study conducted at the Department of Obstetric and Gynecology, Helsinki University Central Hospital two biochemical inflammation related markers were measured in the lower genital tract fluids of asymp-tomatic women in early and mid pregnancy in an order to see whether these markers could identify women with an increased risk of preterm delivery. These biomarkers were phosphorylated insulin-like growth factor binding protein-1 (phIGFBP-1) and matrix metalloproteinase-8 (MMP-8). The study involved 5180 asymptomatic pregnant women, examined during the first and second ultrasound screening visits. The study samples were taken from the vagina and cervicix. In addition, 246 symptomatic women were studied (pregnancy weeks 22 – 34). The study showed that increased phIGFBP-1 concentration in cervical canal fluid in early pregnancy increased the risk for preterm delivery. The risk for very premature birth (before 32 weeks of gestation) was nearly four-fold. Low MMP-8 concentration in mid pregnancy increased the risk of subsequent premature preterm rupture of fetal membranes (PPROM). Significantly high MMP-8 concentrations in the cervical fluid increased the risk for prema-ture delivery initiated by preterm labour with intact membranes. Among women with preterm contractions the shortened cervical length measured by ultrasound and elevated cervical fluid phIGFBP-1 both predicted premature delivery. In summary, because of the relatively low sensitivity of cervical fluid phIGFBP-1 this biomarker is not suitable for routine screening, but provides an additional tool in assessing the risk of preterm delivery. Cervical fluid MMP-8 is not useful in early or mid pregnancy in predicting premature delivery because of its dual role. Further studies on the role of MMP-8 are therefore needed. Our study confirms that phIGFBP-1 testing is useful in predicting pre-term delivery.

Sterol-binding proteins in late endosomes : Regulation of endosome motility and lipid metabolism

Despite its bad reputation in the mass media, cholesterol is an indispensable constituent of cellular membranes and vertebrate life. It is, however, also potentially lethal as it may accumulate in the arterial intima causing atherosclerosis or elsewhere in the body due to inherited conditions. Studying cholesterol in cells, and research on how the cell biology of cholesterol affects on system level is essential for a better understanding of the disease states associated with cholesterol and for the development of new therapies for these conditions. On its way to the cell, exogenous cholesterol traverses through endosomes, transport vesicles involved in internalizing material to cells, and needs to be transported out of this compartment. This endosomal pool of cholesterol is important for understanding both the common disorders of metabolism and the more rare hereditary disorders of cholesterol metabolism. The study of cholesterol in cells has been hampered by the lack of bright fluorescent sterol analogs that would resemble cholesterol enough to be used in cellular studies. In the first study of my thesis, we present a new sterol analog, Boron-Dipyrromethene (BODIPY)-cholesterol for visualizing sterols in living cells and organism. This fluorescent cholesterol derivative is shown to behave similarly to cholesterol both by atomic scale computer simulations and biochemical experiments. We characterize its localization inside different types of living cells and show that it can be used to study sterol trafficking in living organisms. Two sterol binding proteins associated with the endosomal membrane; the Niemann-Pick type C disease protein 1 (NPC1) and the Oxysterol Binding Protein Related Protein 1 (ORP1) are the subjects of the rest of this study. Sensing cholesterol on endosomes, transporting lipids away from this compartment and the effects these lipids play on cellular metabolism are considered. In the second study we characterize how the NPC1 protein affects lipid metabolism. We show that this cholesterol binding protein affects synthesis of triglycerides and that genetic polymorphisms or a genetic defect in the NPC1 gene affect triglyceride on the whole body level. These effects take place via regulation of carbon fluxes to different lipid classes in cells. In the third part we characterize the effects of another endosomal sterol binding protein, ORP1L on the function and motility of endosomes. Specifically we elucidate how a mutation in the ability of ORP1L to bind sterols affects its behavior in cells, and how a change in ORP1L levels in cells affects the localization, degradative capacity and motility of endosomes. In addition we show that ORP1L manipulations affect cholesterol balance also in macrophages, a cell type important for the development of atherosclerosis.

mRNA-binding protein HuR in breast carcinogenesis

Breast cancer is the most common cancer among women. Although its prognosis has improved nowadays, methods to predict the progression of the disease or to treat it are not comprehensive. This thesis work was initiated to elucidate in breast carcinogenesis the role of HuR, a ubiquitously expressed mRNA-binding protein that regulates gene expression posttranscriptionally. HuR is predominantly nuclear, but it shuttles between the nucleus and the cytoplasm, and this nucleocytoplasmic translocation is important for its function as a RNA-stabilizing and translational regulator. HuR has been associated with diverse cellular processes, for example carcinogenesis. The specific aims of my thesis work were to study the prognostic value of HuR in breast cancer and to clarify the mechanisms by which HuR contributes to breast carcinogenesis. My ultimate goal is, by better understanding the role of HuR in breast carcinogenesis, to aid in the discovery of novel targets for cancer therapies. HuR expression and localization was studied in paraffin-embedded preinvasive (atypical ductal hyperplasia, ADH, and ductal carcinoma in situ, DCIS) specimens as well in sporadic and familial breast cancer specimens. Our results show that cytoplasmic HuR expression was already elevated in ADH and remained elevated in DCIS as well as in cancer specimens. Clinicopathological analysis showed that cytoplasmic HuR expression associated with the more aggressive form of the disease in DCIS, and in cancer specimens it proved an independent marker for poor prognosis. Importantly, cytoplasmic HuR expression was significantly associated with poor outcome in the subgroups of small (2 cm) and axillary lymph node-negative breast cancers. HuR proved to be the first mRNA stability protein the expression of which is associated in breast cancer with poor outcome. To explore the mechanisms of HuR in breast carcinogenesis, lentiviral constructs were developed to inhibit and to overexpress the HuR expression in a breast epithelial cell line (184B5Me). Our results suggest that HuR mediates breast carcinogenesis by participating in processes important in cell transformation, in programmed cell death, and in cell invasion. Global gene expression analysis shows that HuR regulates genes participating in diverse cellular processes, and affects several pathways important in cancer development. In addition, we identified two novel target transcripts (connective tissue growth factor, CTGF, and Ras oncogene family member 31, RAB31) for HuR. In conclusion, because cytoplasmic HuR expression in breast cancer can predict the outcome of the disease it could serve in clinics as a prognostic marker. HuR accumulates in the cytoplasm even at its non-invasive stage (ADH and DCIS) of the carcinogenic process and supports functions essential in cell alteration. These data suggest that HuR contributes to carcinogenesis of the breast epithelium.