Thesis (doctoral)--Lund University, 1997. / Added t.p. with thesis statement inserted.

Thesis (doctoral)--Lund University, 1997. / Added t.p. with thesis statement inserted.

GPR50, an X-linked orphan G protein-coupled receptor (GPCR), is a risk factor for bipolar disorder (BD) in female subjects. It has been shown that GPR50 plays a part in neurite outgrowth, glucocorticoid receptor signalling and leptin signalling by interacting with major factors involved in these events. Yeast two-hybrid screens have identified multiple putative GPR50 interactors involved in neurodevelopment, stress response and apoptosis, lipid and glucose metabolism, as well as regulation of NMDA receptors and GABA transmission. Among these interactors, RTN3, RTN4, SREBP2 and SNX6 are known regulators of β-secretase (BACE1), a key enzyme in Aβ generation, myelination of the central/peripheral nerve, and neurite outgrowth/synapse formation. Preliminary data indicated that GPR50 expression significantly increased endogenous BACE1 activity in HEK293 cells, so I hypothesised that there is a functional interaction between the two. In this thesis, I investigated the relationship between GPR50 and BACE1 by identifying the effects of GPR50 on BACE1 expression and function, which may provide an explanation of GPR50’s potential association with psychiatric disorders and Alzheimer’s disease. Firstly, studies on expression levels revealed that when GPR50 was over-expressed, BACE1 protein expression was up-regulated in SH-SY5Y cells, but down-regulated in HEK293 cells, suggesting a differentiated regulative system between cell lines. Then I confirmed the physical association between endogenous GPR50 and BACE1 in HEK293 cells by co-localisation and co-immunoprecipitation studies. Their putative interaction sites were located at the plasma membrane and the filopodia/lamellipodia-like structures in HEK293 cells, and at the neurites in mouse primary neuronal cells. Subcellular fractionation of adult mouse brain revealed that endogenous Gpr50 and Bace1 were co-fractionated in the presynaptic vesicles. Secondly, I showed that, in contrast to HEK293 cells, GPR50 overexpression had no effects on β-secretase activity in mouse primary cortical neurons. However, the BD-associated variant GPR50del significantly decreased β-secretase activity compared to the more common variant GPR50, and showed a trend of diminishing β-secretase activity compared to the control condition. Subcellular fractionation experiments showed that in HEK293 cells, there was an increased ratio of mature BACE1 against immature BACE1 localised in the plasma membrane fractions, indicating a role in regulation of BACE1 trafficking to one of its putative activity sites; whereas in mouse primary cortical neurons, GPR50del increased co-fractionation of immature Bace1 with endoplasmic reticulum (ER) marker calreticulin, thus potentially retarding the maturation of Bace1. Importantly, the regulative trend of GPR50/GPR50del on β-secretase activity is cell line-specific and is highly correlated to their effects on β-secretase intracellular distribution. Thirdly, I found that the mRNA levels of human GPR50 and BACE1 were negatively correlated in the dorsolateral prefrontal cortex of female subjects sampled after birth. Mouse Gpr50 and Bace1 mRNA levels were negatively correlated across the telencephalon regions, and had a trend of negative correlation across the hypothalamic regions. Co-localisation of the two proteins was detected in multiple mouse brain regions, with the strongest co-localised signals occurring in CA2 pyramidal neurons, arcuate hypothalamic nucleus and dorsomedial nucleus of the hypothalamus. Finally, preliminary experiments in Alzheimer’s disease model TgSwDI mice, suggested that the expression level of Gpr50 in layer V of the entorhinal cortex was positively correlated with Aβ deposition. Decreased Gpr50 expression was identified in the hippocampus of 9 months transgenic animals compared with age-matched controls. This indicates that Gpr50 expression might be altered in this mouse model co-ordinately with Aβ deposition. The findings in this thesis provide further evidence of GPR50’s correlation to psychiatric illnesses and its interaction with enzyme BACE1 highlights a potential link to neurodegenerative disease.

The purpose of this study was to determine the prevalence of known etiological factors in mildly mentally handicapped students across minority and nonminority groups and to examine the similarities of these patterns. A comparison of early diagnoses was also made. The total population of all children labeled Educable Mentally Handicapped (EMH) and attending regular elementary schools within one of the largest districts in the southwest served as the sample for the present study. There were 128 children, 64 minorities and 64 nonminorities. The student records were reviewed for data regarding etiological factors, previous diagnoses and early medical factors. A pilot study which involved administering a questionnaire to a sample to twenty-eight social workers was conducted to ascertain the validity of obtained data. Eight specific hypotheses were addressed. A Chi-Square analysis yielded information about the patterns of category similarities (congenital, prenatal, perinatal, postnatal and familial), between two groups as well as the presence of professional diagnosis. A set of five factorial analysis of variance were performed to examine the impact of age, number of symptoms, presence of professional diagnosis and length of hospital stay on IQ scores of children in both groups. A discriminant function analysis was performed to determine the discriminatory power of four variables (IQ, length of hospital stay, number of symptoms and presence of professional diagnosis). The prevalence of perinatal and postnatal symptoms and diagnoses occurred with high frequency for both groups. Congenital factors occurred significantly more for the nonminority group. The findings indicated that there were no significant differences across minority and nonminority groups in terms of intellectual functioning due to the impact of the four previously mentioned variables. Consistent with the ANOVA results, the information obtained from the discriminant function analysis suggests similarity of the two groups in terms of the four variables. The results were discussed in relation to the utility of early etiological information and the importance of such research. The implications of such findings for placement of children in general in these classes or for the children from minority groups in particular, were emphasized.

P/Q-type voltage-gated calcium channels (CaV2.1) are expressed in both central and peripheral nervous systems, where they play a critical role in neurotransmitter release. Mutations in the pore-forming α1 subunit of CaV2.1 can cause neurological disorders such as episodic ataxia type 2, familial hemiplegic migraine type 1 and spinocerebellar ataxia type 6. Interestingly, a 190-kDa fragment of CaV2.1 was found in mouse brain tissue and cultured mouse cortical neurons, but not in heterologous systems expressing full-length CaV2.1. In the brain, the 190-kDa species is the predominant form of CaV2.1, while in cultured cortical neurons the amount of the 190-kDa species is comparable to that of the full-length channel. The 190-kDa fragment contains part of the II-III loop, repeat III, repeat IV and the C-terminal tail. A putative complementary fragment of 80-90 kDa was found along with the 190-kDa form. Moreover, preliminary data show that the abundance of the 190-kDa species and the 80-90-kDa species relative to the full-length channel is upregulated by increased intracellular Ca²⁺ concentration. Truncation mutations in the P/Q-type calcium channel have been found to cause the neurological disease episodic ataxia type 2. Some of the disease-causing truncations resemble the 190-kDa truncated channel that we found. Three pairs of truncated versions of CaV2.1 were engineered to resemble putative products of proteolytic cleavage in the three intracellular loops. Electrophysiological properties of these truncated channels were studied. The truncated channel corresponding to the N-terminal fragment produced by cleavage in the II-III loop has a suppressive effect on full-length P/Q channel currents, resembling the effects of several truncation mutants that cause episodic ataxia type 2. The complementary pair of truncated channels created by a truncation site in the I-II loop forms a functional channel when coexpressed. These results shed light on the functional effects of proteolytic cleavage in the intracellular loops of the P/Q channel.

No description available.

Thesis--Copenhagen. / Summary in Danish. Bibliography: p. [215]-219.

Thesis (M.S.)--University of Michigan, 1987.

Thesis (M.S.)--University of Michigan, 1987.

Thesis--Copenhagen. / Summary in Danish. Bibliography: p. [215]-219.