This project focused on extracellular signal-regulated kinase (ERK) and focal adhesion proteins related to ERK activity, and found a novel signaling pathway contributing to aging-related defects in smooth muscle contractility. Previous members of our lab have used ERK inhibitors to demonstrate the role of ERK in smooth muscle contraction. Dr. Nicholson used the ERK inhibitor FR 18024 and noted that, in the presence of this inhibitor phenylephrine (PE) induced a higher stress increase in young mouse aortas compared to old aortas. Inhibition of the kinase ERK abolished this difference. He also quantitated ERK phosphorylation, a marker of ERK activation in PE-stimulated aortas from both young and aged mice and found a significant lower level of phosphorylated-ERK (p-ERK) in aged mouse aortas. I was interested in determining the substrate of ERK that is affected in aging. Caldesmon (CaD) is one of the known substrates of ERK in smooth muscle. More importantly, CaD, as an actin-binding protein, inhibits cross-bridge formation by blocking the interaction between actin and myosin. Thus, I tested the hypothesis that, caldesmon phosphorylation is inhibited in aged mouse aortas. To determine the mechanism by which regulation of ERK activation changes with age, the role of micro-RNAs (miRs) in the regulation ERK phosphorylation was investigated. Transfection of miR-137 and -34a into A7r5 cells resulted in a significantly lower level of p-ERK in response to the phorbol ester DPBA. Further, together with my collaborators I found that transfection of miR-137 and -34a led to significantly decreased focal adhesion protein levels in A7r5 smooth muscle cells, such as paxillin and src. To confirm whether focal adhesion proteins contribute to the impairment of agonist-induced ERK phosphorylation, paxillin siRNA and src inhibitor were used. The results showed that paxillin is required for the phosphorylation of ERK1 and ERK2 and src is required for ERK2 phosphorylation. In conclusion, age-related increases in miR-137 and -34a decrease ERK phosphorylation via downregulation of paxillin and src. The decrease in ERK phosphorylation leads to a decrease in CaD phosphorylation and inhibits contraction. Thus, the thin filament-coupled pathway in differentiated vascular smooth muscle is inhibited in the aged mouse aorta and this leads to aging-associated defects in smooth muscle contractility. / 2021-06-18T00:00:00Z

Doctor of Philosophy / Department of Food, Nutrition, Dietetics and Health / Tonatiuh Melgarejo / Mark Haub / Human umbilical cord-derived mesenchymal stromal cells (HUC-MSCs) have an enormous therapeutic potential because of their immunomodulatory and anti-inflammatory properties. However, there are limitations for their therapeutic use due to low cell survival after implantation, the risk of culture-borne pathogens, and the risk of embolism and thrombosis after intravenous infusion. Exosomes, on the other hand, constitute an important part of the MSCs secretome and may play a role in their therapeutic effects. Here, it was demonstrated that HUC-MSC-derived exosomes accumulate in human and mouse osteosarcoma cell lines in vitro and reduce their proliferation. The distribution of HUC-MSCs exosomes was shown in osteosarcoma tumor- bearing mice. Exosome distribution in vivo was observed using Magnetic Resonance Imaging (MRI) of gadolinium-labeled exosomes and by fluorescent imaging after infusion of near infrared dye-labeled exosomes. HUC-MSC exosomes accumulated in the tumor throughout the 48 hours ours post-injection period. In contrast, synthetic lipid nanoparticle accumulate in tumor only for the first 3ours post-injection. These results suggest that labeling with gadolinium or near-infrared dye may affect exosome accumulation within the spleen. In summary, this study showed that HUC-MSCs exosomes can accumulate to osteosarcoma cells in vitro and in vivo, and thus they may be useful for detecting cancer metastasis.

The replication of Moloney Murine Leukemia Virus (MoMLV or MLV) is restricted in mouse embryonic stem (ES) and embryonic carcinoma (EC) cells, but not in differentiated cells. The restriction is mediated by the primer binding site (PBS) of proviral DNA of MLV. A restriction complex can bind to the PBS of MLV and block the transcription of viral genes. Two major components of the PBS-mediated silencing complex were identified in our lab, ZFP809 and Trim28. ZFP809 contains two conserved domains, a zinc finger domain responsible for DNA binding and a KRAB box recruiting Trim28, and hence other transcription repressors, such as HP1γ and ESET. A protein called L1td1 was identified during the purification of PBS-mediated restriction complex. L1td1 is a stem cell specific protein but little is known about the function of L1td1. In differentiated cells, the replication of MLV is not restricted. Overexpression of ZFP809 in differentiated cells is sufficient to re-establish the PBS mediated restriction. However, data from various expression libraries shows that the mRNA levels of ZFP809 in stem cells and differentiated cells are approximately the same, which indicating that there is some post-transcriptional mechanism negatively regulating the protein levels of ZFP809 in differentiated cells. To study the post-translational regulation of ZFP809 may help us understand how retroviral restriction is regulated in different cell types. Here we found that the down-regulation of ZFP809 proteins is due to the rapid degradation of protein but not on mRNA. The protein of ZFP809 is degraded rapidly in differentiated cells but not in stem cells. The last 50 amino acids, as well as the lysine residue within the peptide, are important for the turnover of ZFP809 protein in differentiated cells. The drug MG132 can stabilize the ZFP809 protein in differentiated and in vivo ubiquitination assay show that ZFP809 is heavily ubiquinated in differentiated cells, suggesting that ZFP809 is degraded through the ubiquitin-dependent proteasomal pathway. Interestingly, the protein Trim28, which is an essential factor for in the silencing complex, can promote the degradation of ZFP809. Mutations with the lysine residue mutated to alanine or abolished the interaction between Trim28 are less ubiquitinated. A small drug, MLN4924, which is the neddylation inhibitor, stabilizes ZFP809 in differentiated cells. Overall, these observations suggest that, during the differentiation of mouse stem cells, ZFP809 protein is eliminated by the proteasomal system, which leads to the loss of restriction of MLV in differentiated cells. In addition, we studied the role of L1td1 in retroviral silencing. Knockdown or knockout of L1td1 partially relieves the restriction of MLV replication. Immunoprecipitation and pulldown assays show that L1td1 might interact with Trim28 and ZFP809 bridging by Trim28. In summary, L1td1 might interact with the essential factors of silencing complex and help the silencing of MLV in stem cells. Proteins of the nucleosome remodeling deacetylase (NuRD) complex were also identified during purification of the restriction. The NuRD complex is shown to be involved in the transcriptional repression. However, depletion of single subunits of the NuRD complex does not affect the PBS-mediated retroviral restriction in mouse EC cells.

In mammalian development, endoderm formation occurs in two phases and the fate of these populations is different. In the blastocyst, inner cell mass (ICM) cells generate the primitive endoderm (PrE), which will give rise to the extra-embryonic parietal (PE) and visceral endoderm (VE). Hematopoietically expressed homeobox (Hhex) protein is initially expressed throughout the PrE and subsequently becomes restricted to the anterior visceral endoderm (AVE), one of two important early embryonic signalling centres in the mouse. During gastrulation a second wave of endoderm differentiation occurs, the definitive endoderm (DE), generating the foregut. Immediately following the induction of DE, regional identity is initially established in the anterior region with the expression of Hhex. One of the earliest specification events in this lineage is the specification of anterior fate by Hhex, this time in a second signalling centre, the anterior definitive endoderm (ADE). The ADE is both important for embryonic patterning, and as the precursor population for differentiating to the foregut and its derivatives the thyroid, liver and pancreas. The literature surrounding these early embryonic patterning events is covered in depth in chapter 1. Embryonic stem cells (ESCs) are normal cell lines derived from the mammalian blastocyst at the time that it is making PrE. A number of laboratories have generated protocols to make endoderm from ESCs and in my thesis I define approaches to distinguish between PrE and DE. I generated a new ESC reporter line utilising a gene normally expressed in both the PrE and later in hepatic endoderm; this reporter contains a GFP in the first exon of the Hnf4α locus. This was combined with a second fluorescent reporter containing DSRed in the Hhex locus. This cell line is described and characterised in chapter 3. As Hnf4α is initially expressed in PrE prior to Hhex, but in the DE following Hhex, I was able to use the temporal expression of this reporter to distinguish the induction of PrE from DE. As Activin and Wnt are known to induce endoderm from ESCs, I was then able to ask what sort of endoderm the combination of these two signals induced. In chapter 4 I found that normal ESCs would readily differentiate to iPrE in the presence of Activin and Wnt3a. While this has not been described previously, my analysis suggests that ESC protocols applying these cytokines directly to ESCs have produced PrE. Given that ESCs are derived from the blastocyst, the generation of iPrE from Wnt3a/Activin treatment fits with developmental paradigms. However, Act/Wnt3a is used routinely on Human ESCs (hESCs) and so I attempted to reconcile these observations. HESCs, while derived from the blastocyst, appear to progress developmentally in vitro, to a stage closer to the epiblast, immediately prior to gastrulation. I therefore assessed the effect of Activin and Wnt3a on mouse stem cell lines derived from the epiblast (Epiblast Stem Cells, EpiSCs), that are grown under similar conditions to hESCs. When Wnt3a/Act is applied to these cells I found that they made DE rather than PrE, which I describe in chapter 4. Taken together my observations suggest that Act/Wnt3a are general endoderm inducers that induce context specific differentiation in vitro. The cell type derived in response to this treatment depends on the developmental stage of the starting stem cell culture. During the course of this work, I also observed that PrE was growing under Activin/Wnt3a treatment. As a number of cell culture systems have been established that reflect PE, but not truly bipotent PrE, I investigated the conditions under which PrE can be expanded. In chapter 5 I characterize a new PrE culture system, in which bipotent extra-embryonic endoderm can be expanded indefinitely in culture. I also explore a bit more precisely the nature of the starting cells that initially become exposed to Activin/Wnt3a treatment. Previous work has extensively characterized the existence of a primed population of PrE in ESC culture and in chapter 6 I explore the existence of a primed DE population in EpiSC culture. Taken together, my thesis is the first demonstration that Activin/Wnt3a can induce different endoderm populations in different embryonic stem cell populations. It underlies the notion that the evolutionary origin of both cell types is the same and that the pathways evolved for extra-embryonic development in mammals just exploit the ancient modes of germ layer specification that evolved with gastrulation.

Colorectal cancer (CRC) is the third most common cancer globally with around 1.3 million cases diagnosed annually. In cases of inherited CRC where none of the rare, high-risk mutations associated with familial syndromes are observed it has been theorised that the heritable risk is due to common, low-risk variants in the genome. Identifying these variants of modest or small effect size has become possible due to the use of large genome-wide association studies (GWAS). Through a meta-analysis of five previous GWAS, Dunlop et al. identified three novel susceptibility loci at 6p21, 11q13.4 and Xp22.2. The aims of this study were to further characterise the Xp22.2 risk locus and investigate the function of the putative risk gene SHROOM2. The variant originally identified in the Dunlop et al. study as showing an association with CRC risk rs5934683 is located between SHROOM2 and GPR143. Genome–wide expression analysis has shown that the variant is an eQTL (expression quantitative locus), affecting expression of SHROOM2, but not GPR143. An important caveat to this analysis was that the commercial array used to measure gene expression does not detect all predicted GPR143 transcripts. Hence it was important to understand whether GPR143 might be involved at the locus and whether there was altered expression in normal colonic mucosa. I have analysed the expression of GPR143 and shown that it is poorly expressed in normal mucosa and that expression of the alternative transcripts is rare. This provided further evidence for the gene of interest at Xp22.2 being SHROOM2 and thus became the focus for further investigation. In order to understand SHROOM2 function a knockout mouse was generated allowing studies of gene function beyond the previously used in vitro systems. Embryonic stem cells containing a Shroom2 knockout first allele were obtained from the International Knockout Mouse Consortium and a novel mouse line established. This mouse line was found to be an incomplete knockout and a Cre recombination strategy was employed to remove the critical exon and create a true null allele for Shroom2. This model was validated as being a true knockout of Shroom2 at both the RNA and protein level and the model subjected to initial phenotyping focusing on tissues where the gene has previously been identified as expressed. To investigate the role of Shroom2 as a CRC susceptibility gene preliminary data has been gathered from crosses to the ApcMin/+ CRC model, and analysis of the intestines of the Shroom2KO line has been undertaken. Two spontaneously occurring anorectal adenomas have been identified in Shroom2 null mice, and an additional mid-colonic polyp phenotype identified when crossed onto the ApcMin/+ background. Additionally, embryonic fibroblasts have been used in growth and wound healing assays to determine what effect total loss of Shroom2 has at a cellular level. Proteomics analysis to identify significantly altered pathways associated with Shroom2 loss has also been carried out and has highlighted a number of interesting targets for further investigation. In summary, a novel Shroom2 knockout mouse model has been developed to investigate the CRC susceptibility locus identified at Xp22.2. Preliminary data from this mouse model appears to confirm SHROOM2 as having a role in tumour development in the large intestine.

Glucocorticoids - cortisol and corticosterone - are steroid hormones synthesised in the adrenal gland that are important mediators of the stress response. Glucocorticoids are also vital in development to aid in organ maturation. Endogenous glucocorticoid levels rapidly rise before birth in all mammals to promote fetal organ maturation. Because preterm birth occurs before this natural rise in glucocorticoid levels, pregnant women at risk of preterm delivery are administered synthetic glucocorticoids to mature the fetal lung and aid neonatal survival. Mice that globally lack the glucocorticoid receptor (GR) die at birth, attributed to lung immaturity. Effects on tissues other than the lung remain less well characterised. Previous work has shown endogenous glucocorticoid action is also essential to mature the mouse fetal heart. Mice globally lacking GR have small, functionally and structurally immature hearts. Mice with tissue-specific deletion of GR in cardiomyocytes and vascular smooth muscle cells (SMGRKO mice; generated using Sm22α-Cre) also have an increased risk of death around the time of birth, suggesting that glucocorticoid maturation of the cardiovascular system is important for neonatal survival. GR expression within the fetal mouse heart initiates at E10.5 but GR in the myocardium is not activated and localised to the nucleus until E15.5. This suggests that mice can respond to glucocorticoid from E10.5. Here, it was hypothesised that antenatal glucocorticoid exposure, prior to the increase in endogenous glucocorticoid levels, would advance fetal heart maturation and this will depend on cardiovascular GR. To investigate the effects of antenatal glucocorticoid treatment on fetal heart maturation in mid-gestation and identify effects mediated by GR, mice with a conditional deletion of GR in cardiomyocytes and vascular smooth muscle cells were studied (SMGRKO mice). Pregnant mice received dexamethasone (dex) in the drinking water from E12.5-E15.5. Levels of Fkbp5 mRNA (a marker of glucocorticoid action) were unchanged between control and SMGRKO mice at E15.5 or following dex treatment. This suggested a lack of response to dex treatment. However, liquid chromatography mass spectrometry measurement confirmed the presence of dex and its active metabolite 6- hydroxydexamethasone (6OHDex) in livers of E15.5 fetuses from dex treated dams (fetal: Dex 0.46 ± 0.1 ng/g, 6OHDex 13.6 ± 0.35 ng/g; dam: Dex 7.96 ± 3.65 ng/g, 6OHDex 4.75 ± 1.2 ng/g). Livers of fetuses exposed to dex had lower levels of the naturally occurring active glucocorticoid, corticosterone, compared to vehicle treated fetuses. This suggests HPA axis suppression in dex exposed fetuses. Maternal liver showed no significant difference in corticosterone levels between dex and vehicle treated mice, suggesting that whilst dex suppressed the HPA axis in fetuses, it did not in the dams. To determine any persistent effects of early antenatal dex treatment on fetal heart, a later time point in gestation, E17.5, was also assessed. At E17.5, 2-days following cessation of dex treatment, dex and its metabolites were undetectable in the fetal and maternal liver. However, corticosterone levels remained reduced in fetal liver at E17.5 in dex exposed animals (vehicle treated: 4.31 ± 0.47 ng/g, Dex treated: 1.72 ± 0.42 ng/g, p < 0.01), whilst levels in the dam liver did not differ from vehicle treated controls. This suggests prolonged HPA axis suppression following dex treatment, which reduced the natural late-gestation rise in glucocorticoids required for fetal organ maturation. To determine whether early antenatal dex treatment could advance fetal heart function, Doppler imaging with a Vevo 770 high frequency ultrasound imager was used. Isovolumetric contraction time, isovolumetric relaxation time and ejection time of the left ventricle were unaltered by dex treatment. However, at E15.5 the mitral deceleration index (MDI), a measure of diastolic function that takes into account loading conditions, was 1.5 fold lower in vehicle treated SMGRKO mice than control (Cre-) littermates (p < 0.05). This reduction in SMGRKO mice suggests glucocorticoids are required within the fetal cardiomyocytes and/or vascular smooth muscle cells to mature the diastolic function of the fetal heart. Dex exposure had no effect on MDI in SMGRKO fetuses, but reduced the MDI by 1.5 fold in control mice to similar levels as in SMGRKO mice (p < 0.05). RNA analysis revealed a trend (p=0.09) for reduced levels of Nr3c1 mRNA (encoding GR) in hearts of E15.5 control (Cre-) fetuses following dex treatment. Although this requires confirmation at the level of GR protein, this finding together with the lack of induction of the GR target, Fkbp5, suggests dex may cause glucocorticoid resistance through down-regulation of GR. At E17.5, 2-days following cessation of dex there were no changes in systolic parameters and the reduction in MDI found at E15.5, following dex, had normalised. Litter size was reduced (close to a 50% reduction) at E17.5 in dex treated mice. This was similar between SMGRKO and control fetuses. The cause of death was not established, but potentially could be due to the reduction in the natural rise in glucocorticoids at E17.5, previously shown to be important for fetal heart maturation. It is therefore possible that mice with more immature hearts may die before reaching E17.5. RNA analysis was undertaken to determine any mechanistic alterations following dex treatment, which could support fetal heart functional alterations found at E15.5. In contrast to expectation, dex also decreased expression of mRNA encoding the calcium handling proteins SERCA2a, NCX1, and CaV1.2 in E15.5 fetal mouse hearts in both control and SMGRKO mice (p < 0.05), compared with the respective vehicle treated mice. These proteins had previously shown to be induced by glucocorticoid action in cardiomyocytes. However, the similar down-regulation in both genotypes indicates this effect is not dependent on GR in cardiomyocytes. Lowered SERCA2a activity following dex treatment could contribute to the changes in MDI observed in control mice. Similarly, Scnn1a and Kcnj12 mRNA levels, previously found to be induced by glucocorticoids in cardiomyocytes, were down-regulated in the E15.5 fetal heart in vivo following dex. Collectively, these data are consistent with glucocorticoid resistance or down-regulation of glucocorticoid action in E15.5 fetal hearts following dex administration. Mutations in KCNJ12 are associated with long QT syndrome, which is characterised by a delayed repolarisation of the heart following each contraction. An altered relaxation of the fetal heart found in control mice following dex could therefore be due to a prolongation of the cardiac action potential, particularly with a delayed repolarisation, because of lower Kcnj12 expression. At E17.5, there were no significant differences in expression of calcium handling genes or ion channel mRNAs between genotypes or following earlier dex exposure. Thus, effects of dex on mRNA expression level may not persist, which could account for the lack of functional changes observed 2-days following cessation of treatment. Because effects seen in vivo with dex treatment were contrary to those predicted, and to further investigate the effect of dex upon calcium content, an in vitro model of primary fetal E15.5 cardiomyocytes was used. Cardiomyocytes were treated with dex for 24 hours and effects on membrane potential voltage changes and calcium transients measured. Following dex, isolated fetal cardiomyocytes showed an elongated repolarisation phase of the action potential (untreated: 120.45 ± 13.81 ms, Dex: 142.34 ± 12.97 ms, p < 0.01), and duration of calcium transients (untreated: 103.31 ± 13.78 ms, Dex: 120.43 ± 23.36 ms, p < 0.05). This assessment of fetal cardiomyocytes was preliminary work to aid in the understanding of mechanisms of fetal heart functional alterations associated with glucocorticoid regulation. The results suggest glucocorticoids may be important in regulating calcium levels. In summary, dex treatment in mice from E12.5-E15.5 did not advance fetal heart maturation. It reduced litter size at E17.5, irrespective of whether GR was expressed in cardiomyocytes or not. The normal late-gestation increase in endogenous glucocorticoid levels in the fetus was reduced by dex, even after treatment finished. / The suppression of corticosterone levels following antenatal dex may reduce maturation of the heart at E15.5 and could be responsible for the reduction in litter size. Downregulation of GR in the fetal heart, may be a mechanism that results in glucocorticoid resistance following antenatal dex treatment, which could explain the lack of beneficial effects of antenatal dex upon fetal heart maturation in these experiments in mice.

Intellectual disability (ID) is categorised by a significant reduction in cognitive function and adaptive abilities that begin in childhood. ID is part of a heterogeneous group of neurodevelopmental conditions associated with impairment in developmental domains and a cause of particularly adverse socioeconomic impact worldwide. There have been many recent advances in identifying causative genetic mutations in previously unexplained ID cases. With these advances comes an increasing demand for understanding mechanisms underpinning these pathogenic pathways. In this PhD thesis, I have studied rare monogenic novel neurodevelopmental disorders associated with ID. The objective of the thesis was to model a subset of mutations associated with novel neurodevelopmental disorders in mice to demonstrate a causal link between mutation and phenotype and to further understand the mechanisms by which these mutations result in human neurodevelopmental disorders. In order to achieve this, I adopted a multi-phase approach. Firstly, I designed a phenotyping platform, by combining behavioural and cognitive tests with morphometric brain analysis and genome-wide transcriptional analysis. I then used this approach to study KPTN-related syndrome, a novel developmental disorder that to date has not been characterised in mice, successfully recapitulating the main phenotypes described in the patients. Moreover, I gained further insight into the underlying pathogenic mechanisms associated with the disorder, opening the possibility of a therapy that could treat some aspects of cognitive and morphological impairments identified in the patients with KPTN-related syndrome. Lastly, I determined whether such an approach could be scaled-up to study multiple novel neurodevelopmental disorders, each with a mutation associated with a haploinsufficient novel neurodevelopmental disorder. I identified specific phenotypes for each of the four mouse lines under investigation, providing a platform for comparison between several developmental disorders. These refinements contributed to a larger five-year project starting at the Sanger Institute, aimed at characterising a wider diversity of human neurodevelopmental disorders.

The respiratory system forms a major mucosal interface with the external environment. Consequently, the respiratory tract is constantly exposed to inhaled foreign antigens, commensal microorganisms, and potential pathogens. The respiratory system has evolved a complex regulatory network designed to prevent unnecessary inflammation to harmless antigens and to limit immune-mediated damage to the fragile lung epithelium in response to infection. The lung maintains a default anti-inflammatory state that is coordinated by the respiratory epithelium, alveolar macrophages, dendritic cells, and regulatory Foxp3+ CD4 T cells (Tregs). It is likely that all of these cells influence the development of pathogen-specific T cell responses in the lung. Following infection with a respiratory virus, virus-specific CD8 T cells in the lung are inhibited in their ability to produce cytokines. Current studies suggest that this functional inactivation occurs following infection with respiratory viruses within the Paramyxoviridae family. The data presented here demonstrate that suppression of effector functions of virus-specific CD8 T cells in the lungs occurs following infection with several unrelated respiratory viruses. These results indicate that the functional inhibition of virus-specific T cell responses is not restricted to infection with viruses from the Paramyxoviridae family. Furthermore, I show data indicating that the functional inactivation of virus-specific CD8 T cells in the lungs occurs in the absence of infection. I also demonstrate for the first time that the lung environment also regulates the effector functions of virus-specific CD4 T cells. Inhibition of cytokine production by pulmonary T cells is reversible as stimulation with exogenous peptide-pulsed antigen-presenting cells rescues IFN-gamma production. The inhibition of IFN-gamma production by virus-specific T cells occurs in other organs such as the kidney. These data suggest that regulation of T cell cytokine production by peripheral tissues may serve as an important mechanism to prevent immunopathology and preserve normal tissue function. Foxp3+ Tregs have been shown to inhibit conventional effector T cell responses in a large number of chronic infection models. However, their role during acute infections remains unclear. Examination of Foxp3+ Tregs during RSV infection showed that Tregs are rapidly recruited into the lungs and acquire an activated phenotype. Depletion of Foxp3+ Tregs prior to RSV infection revealed that Tregs facilitate the early recruitment of RSV-specific CD8 T cells from the draining lymph nodes to the lung and later limit the overall magnitude of the virus-specific CD8 T cell response. Depletion of Tregs increased TNF-αa production by RSV-specific CD8 T cells and enhanced T-cell-mediated immunopathology. These data demonstrate that Foxp3+ Tregs play a major role in regulating CD8 T cell responses to respiratory virus infections. Collectively, the data presented here demonstrate that CD8 T cell responses to respiratory pathogens are tightly regulated within the lung environment.

Human eyes with exfoliation syndrome (XFS) exhibit a distinctive pattern of iris transillumination defects that are recapitulated in Lyst mutant mice carrying the beige allele. Here I present the identification and characterization of the B6-Lystbg-J mouse model of XFS, modifiers of Lyst mediated ocular phenotypes, mechanisms of intraocular pressure (IOP) pathology related to circadian rhythms, and mechanisms of iris transillumination defects in the B6-Lystbg-J mice. Clinical and histological analysis shows that the B6-Lystbg-J mice have multiple similarities to human XFS including: iris transillumination defects, production of an exfoliative-like material, and pronounced pigment dispersion. Despite these insults, Lyst mutation does not cause increased IOP or optic nerve damage within the context of a C57BL/6J genetic background. However, defects in the circadian rhythm regulation of IOP were identified. Sequence analysis identifies that the beige mutation is predicted to delete a single isoleucine from the WD40 domain of the LYST protein. I identified CSNK2B as a binding partner of LYST and showed that LYSTbg-J completely disrupts the interaction. CSNK2B function in regulating E-cadherin and β-catenin binding is subsequently disrupted. These results lead to a working hypothesis that aspects of the XFS phenotype involve LYST and CSNK2B pathways, likely influencing cell-cell adherens junctions. Epistasis experiments were used to test for genetic modifiers of Lyst, which demonstrated that albino Lyst mutant mice exhibited complete rescue of Lyst-dependent iris phenotypes. In a genetic background-driven approach, a DBA/2J strain of congenic mice was created. The DBA/2J background, which harbors multiple mutations influencing melanosomal-proteins, enhanced Lyst dependent iris phenotypes. Thus, both experimental approaches implicated melanosomes, a potential source of oxidative stress, as mechanistically contributory. Supporting a contributory role of oxidative damage, Lyst mutation resulted in genetic context sensitive changes in iris lipid hydroperoxide levels, being lowest in albino and highest in DBA/2J mice. These results identified an association between oxidative damage to lipid membranes and severity of Lyst-mediated phenotypes, uncovering a new mechanism contributing to pathophysiology involving LYST. In conclusion these results demonstrate that mutation of the Lyst gene can produce ocular features of human XFS and suggests that LYST or LYST-interacting genes may contribute to XFS.

Cyclodextrins (CDs) are naturally occurring cyclic oligosaccharides. Since it is believed that OxC blocks the removal of normal cholesterol from cells in the artery wall, it is possible that selective removal of OxC in the vessel wall in-vivo may prevent or reverse atherosclerosis.As a prelude to major studies, this research project was designed to answer two critical questions; 1/. What is the best route for delivery of CD. 2/. How do animals (apoE-/- mice) tolerate it. Pilot studies were established and results noted. These studies have provided valuable information in the apoE-/- mouse for subsequent studies to prevent or reverse atherosclerosis in this animal model. / Master of Science (Hons)