Minerva Access

Pro-apoptotic therapies for the treatment of Mycobacterium tuberculosis infection

Sun, 01 Jan 2017 00:00:00 GMT

Pro-apoptotic therapies for the treatment of Mycobacterium tuberculosis infection Ojaimi, Samar One third of the world’s population is infected with Mycobacterium tuberculosis (Mtb). Tuberculosis (TB) has killed more than 1 billion people over the past two hundred years, surpassing mortality caused by all other pandemics and epidemics combined. Despite a concerted global effort to reduce transmission, Mtb infects an estimated 10.4 million people and kills 1.4 million people each year. Managing this condition is becoming increasingly challenging because Mtb is fast becoming resistant to all first line antibiotic therapies. Novel interventions beyond iterations on antibiotics are required. Understanding host-Mtb interactions, with a view to targeting host signalling pathways that the organism is reliant upon, is a tenable approach to combatting this deadly disease. Host cells are intolerant of intracellular organisms and consequently Mtb must prevent a cell from dying so that it has time to propagate and disseminate. Exactly how it does so is controversial and poorly understood. In my work, I sought to understand the role of apoptosis in Mtb disease pathogenesis. I dissected the role of the extrinsic apoptotic pathway and associated key molecular components including inhibitor of apoptosis (IAP) proteins. I also examined the role of the intrinsic apoptotic pathway and associated Bcl-2 family of proteins. I found that Mtb infected mouse and human macrophages showed major aberrations in the protein expression levels of IAP and Bcl-2 family molecules such that the stoichiometry of these proteins strongly favoured cell survival. I infected mice that were deficient in the three major mammalian IAPs (cIAP1, cIAP2 andXIAP) and found that in the absence of cIAP1, and to a lesser extent cIAP2, Mtb infected macrophages died and disease pathogenesis was strikingly altered. I then sought to reprogram the extrinsic apoptotic pathway to promote death of Mtb infected cells by using a clinical stage drug inhibitor of cIAPs. I was able to optimise a dosing regimen of the cIAP antagonist, birinapant, that proved efficacious in killing Mtb infected macrophages and in reducing bacterial loads in various strains of mice and in mice engrafted with a human immune system. An examination of the intrinsic cell death pathway also proved very interesting. Again, I used a combination of gene-targeted mice and clinical stage drugs to antagonise the function of several Bcl-2 family pro-survival proteins. Interfering with Bcl-xL function had no effect on Mtb disease pathogenesis whilst antagonising the function of Bcl-2 made the disease worse. Notably, as little as a 50% reduction in Mcl-1 function, examined using Mcl-1+/- mice, produced an improvement in Mtb infection outcomes. Given the success in defining targetable host cell pathways involved in TB pathogenesis, I next investigated if these insights were applicable to latent Mtb infection. A large proportion of people infected with Mtb may not progress to overt disease but remain latently infected and can reactivate disease under certain circumstances. There are well defined indications for treating some people who are latently infected. Treatment of latent infection suffers from the same shortcomings as treatment of active disease. I found that birinapant could be optimised to also impact on latent infection. The significance of my work includes providing valuable insights into how apoptosis plays a critical role in determining Mtb infection and disease outcomes. I believe that my work, for the first time, has identified the key molecular components that regulate cell survival / apoptosis signalling during Mtb infection. The importance and implications of these findings are underscored by my preclinical studies showing that these host cell molecules and pathways can be targeted using clinical stage drugs to promote clearance of Mtb infection and disease. © 2017 Dr. Samar Ojaimi

Risk and protective factors associated with successful transition to high school in youth with ADHD: a prospective cohort study

Sun, 01 Jan 2017 00:00:00 GMT

Risk and protective factors associated with successful transition to high school in youth with ADHD: a prospective cohort study Zendarski, Nardia Jane Introduction: Limited research has examined the transition to high school in adolescents with ADHD, despite this period being a critical determinant of future schooling. This thesis aims to describe school functioning in adolescents with ADHD at an academic, social-emotional and school engagement level and to identify risk and protective factors that are predictive of differing levels of functioning as well as trajectories of social-emotional functioning over the transition and their impact on early high school functioning. Methods: This is a prospective cohort study of adolescents (n=130) with ADHD in the first and third years of high school. Primary outcomes included: (1) academic achievement (National Assessment Program-Literacy and Numeracy (NAPLAN) five test domains); (2) social-emotional functioning and trajectories of functioning (parent and teacher-reported Strengths and Difficulties Questionnaire (SDQ)) and (3) school engagement (self-rated attitudes toward school and recorded suspensions). A broad range of adolescent, family and school risk and protective factors were examined in relation to key outcomes including: child IQ, working memory, ADHD symptom severity, behavioural problems, peer victimisation, family functioning, parent mental health, family socioeconomic status (SES) as well as school SES, sector and location. Analyses: Mean scores on outcomes were compared to state benchmarks or normative data using t-tests. Multivariable regressions analyses were used to model risk and protective factors associated with each transition outcome. Results: Academic achievement: Adolescents with ADHD performed below the state average across all NAPLAN test domains and 40% achieved scores below the national minimum standard in one or more areas (e.g. writing and spelling). Higher IQ and SES were associated with better scores. Gender differences were not observed with the exception of writing, where girls outperformed boys. Modifiable factors associated with poorer academic outcomes on individual domains included symptoms of inattention, peer victimisation and poor family management. Social-emotional functioning (SEF): Adolescents exhibited poorer SEF across multiple domains (e.g. internalising symptoms, externalising problems and peer problems) in comparison to norms. The strongest modifiable factors on these three domains were middle childhood SEF on the domain being examined and parent-rated ADHD symptoms. Additional factors varied by domain; concurrent sleep problems, age (younger) and gender (girl) were associated with higher internalising problems; parent mental health problems and peer problems were associated externalising problems. Three trajectories (never, intermittent and persistent) of SEF were identified for internalising, externalising and peer problems. Compared to the never trajectory, children with persistent internalising and externalising trajectories had poorer maths achievement and more school suspensions. School engagement: Adolescents with ADHD in the first year of high school were less motivated and less connected to peers in comparison to state data. There were high rates of suspension across the first and third year of high school in comparison to peers (21% vs 6%, p<.01). Modifiable factors associated with poor attitudes toward school included adolescent depression and poor family management. The risk of suspension increased for adolescents who exhibited higher levels of conduct and hyperactivity symptoms and lower intelligence. Higher family SES and attending an independent school decreased this risk. Conclusion: Findings highlight the large achievement gap and increased risk for adolescents with ADHD in this critical period. Most adolescents will require additional support and intervention and difficulties are likely to be multifaceted spanning multiple domains of functioning. A tailored rather than standard approach to improving outcomes is needed for most students with ADHD. Optimising educational outcomes for all students with ADHD will require both health and educational experts to work together to target potentially modifiable variables associated with poor functioning. Findings point toward a review of current evidence-based interventions addressing modifiable variables that could be adapted, piloted and then rigorously trialled in Australian adolescents with ADHD in early high school. © 2017 Dr. Nardia Jane Zendarski

Prediction and shaping of visual cortex activity for retinal prostheses

Sun, 01 Jan 2017 00:00:00 GMT

Prediction and shaping of visual cortex activity for retinal prostheses Halupka, Kerry Retinal prostheses are a promising treatment for blindness caused by photoreceptor degeneration. Electrodes implanted in the retina deliver electrical stimuli in the form of current pulses that activate surviving neurons to restore a sense of vision. Clinical trials for such devices have shown that the visual percepts evoked are informative, and can improve the day-to-day life of recipients. However, the spatial resolution of retinal prostheses is a limiting factor, with those who have the highest reported acuity measures still classified as legally blind. Simultaneous stimulation of multiple electrodes is a possible strategy to improve device resolution without increasing the number of physical electrodes. However, electrode interactions that occur during simultaneous stimulation are not well understood. This thesis investigates the characteristics of cortical responses to simultaneous stimulation of multiple electrodes. We formulated a quantitative model to characterise the responses of visual cortex neurons to multi-electrode stimulation of the retina to understand how simultaneous stimulation can improve resolution. Activity was recorded in the visual cortex of normally sighted, anaesthetised cats in response to temporally sparse, spatially white stimulation with 21 or 42 electrodes in the suprachoroidal space of the retina. These data were used to constrain the parameters of a linear-nonlinear model using a spike-triggered covariance technique. The recovered model accurately predicted cortical responses to arbitrary patterns of stimulation, and demonstrated that interactions between electrodes are predominantly linear. The linear filters of the model, which can be considered as weighting matrices for the effect of the stimulating electrodes on each cortical site, showed that cortical responses were topographically organised. Photoreceptor degeneration results in a number of changes in the surviving cells of the retina that can negatively impact stimulation strategies. Therefore, in the second study, we investigated the effect of multi-electrode stimulation on the degenerate retina. Characteristics of cortical responses to simultaneous stimulation of multiple electrodes were evaluated in unilaterally, chronically blind anaesthetised cats, bilaterally implanted with suprachoroidal retinal prostheses. Significant differences were found between responses to stimulation of the normally sighted and blind eyes, which may help to explain the varied perceptual observations in clinical trials with simultaneous stimulation. The success of the linear-nonlinear model in predicting responses to arbitrary patterns of stimulation indicated that it may provide a basis for optimising stimulation strategies to shape cortical activity. Therefore, we investigated the possibility of inverting the model to generate stimuli aimed at reliably altering the spatial characteristics of cortical responses. An in vivo preparation with a normally sighted, anaesthetised cat showed that the response characteristics derived by the model could be exploited to steer current and evoke predictable cortical activity. Overall, these results demonstrate that cortical responses to simultaneous stimulation of both the normal and degenerate retina are repeatable, and can be predicted by a simple linear-nonlinear model. Furthermore, the interactions between electrodes are predominantly linear, and can be harnessed to shape cortical activity through inversion of the model. The method shows promise for improving the efficacy of retinal prostheses and patient outcomes. © 2017 Dr. Kerry J. Halupka

Directed self-assembly of block copolymers and nanostructures

Sun, 01 Jan 2017 00:00:00 GMT

Directed self-assembly of block copolymers and nanostructures Chen, Chao Self-assembly of block copolymers (BCPs) has attracted considerable attention for decades due to its potential in novel applications. The key to achieve their function critically relies on the control of nanostructure, shape and morphology of the BCP assemblies. The aim of this thesis is to develop a toolbox to manipulate the nanostructure of BCPs in a reliable and predictable manner, and provide mechanistic insights into their self-assembly behaviour. In this work, the strategies used to control the shape and morphology of BCP assemblies lie in three areas: (a) copolymer composition; (b) control of molecular weight distribution; and (c) interfacial properties. In this thesis, a series of BCPs have been synthesised at different compositions and their self-assembled structures have been reported. The influence of the skewed molecular weight distribution and varied dispersity on BCP self-assembly was explored in both solution and thin film systems. The interface between BCP nanoparticles and the surrounding medium was investigated and a morphological evolution from onion-like spheres to axially stacked lamellae has been observed. It is envisaged that the modification of copolymer chemistry and a combination of these addressed strategies will facilitate the synthesis of BCPs assemblies with higher structural complexity. © 2017 Chao Chen