Browsing by Author "Roden, Laura"

Now showing 1 - 13 of 13
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    ASMT gene polymorphisms are associated with Autism Spectrum Disorder (ASD) symptom severity in a South African population
    (2016) De Waal, Margaretha; O'Ryan, Colleen; Roden, Laura
    Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterised by behavioural and social impairments. ASD shows evidence of a genetic aetiology, with a large body of research linking ASD to polymorphisms in several different genes and gene families, including those involved in circadian rhythm generation and melatonin biosynthesis. Sleep disorders are highly comorbid with ASD in both children and adults, and range from sleep onset delay, phase shift and sleep disruption. These parasomnias can have a significant impact on the quality of life for persons with ASD and their families, and sleep deprivation can feed into the behavioural deficits in ASD. Melatonin supplementation is often prescribed to assist in alleviating the above mentioned sleep dysfunction. Melatonin is a hormone in the circadian clock system, and is a biochemical signal for darkness to synchronise peripheral cells to the master oscillator. Clinical trials reported that melatonin supplementation at night assists in sleep initiation. However both the mode of action of supplemental melatonin, as well as whether melatonin deficiency is common in ASD, remains unclear. Furthermore, any research on ASD is often hamstrung by the heterogeneous nature of the disorder, necessitating clear phenotyping. This study examines single nucleotide polymorphisms (SNPs) in the gene acetylserotonin methyl transferase (ASMT), which encodes an enzyme in melatonin biosynthesis, in a South African ASD cohort (n=28) and controls (n=6). All participants completed and Autism Diagnostic Observation Schedule-2 assessment that allowed partitioning of the ASD individuals into ASD endophenotypes, to reduce phenotyping heterogeneity. This study found SNPs previously associated with ASD in the promoter and intronic region. Additionally, this study found novel SNPs, and a SNP in a putative transcription factor binding site not previously associated with ASD. The associations found between SNPs and ASD endophenotypes, together with the positions of the SNPs, suggest a potential link between ASMT polymorphisms and ASD symptom severity. Further research, using language assessment tools as well as quantitative measures of melatonin and sleep disruption, may establish the role of melatonin in language impairment in ASD.
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    Chronotype in the South African population: the influence of longitudinal location
    (2014) Shawa, Nyambura; Roden, Laura
    Most human beings experience the pull of three different daily timers, the solar clock, their endogenous circadian clock and the societal clock. Solar time is generated by the Earth’s revolution on its axis, resulting in its surface being alternately exposed to and shielded from the sun every 24 hours. The endogenous clock, or circadian oscillator, is driven by a network of transcriptional translational feedback loops, and has a period of close to 24 hours. The circadian oscillator is synchronised to the 24 hour light-dark cycle of the solar clock. The third timer is the standardised societal clock that organises and schedules work, school, transport, appointments and free time in a 24 hour period. The way an individual’s endogenous clock synchronises to the solar clock, through advances or delays relative to sunrise and sunset, results in a phenomenon known as diurnal preference or chronotype. A person may have a morning-chronotype, where they enjoy rising and being active early in the day, an evening-chronotype where they prefer to be active later in the day into the late night, retiring in the early morning hours, or have no strong preference for early or late rising. This renders it easy for some to cope with the demands of the societal clock and others to struggle. Chronotype has both genetic and environmental influences. As society’s schedule is governed by the standardised clock, it was hypothesised that chronotype may be influenced by one’s longitudinal location within a time zone. South Africa presents an interesting case because although it uses just one time zone, in the most Easterly regions of the country, the sun rises and sets up to an hour earlier than in the most Westerly regions throughout the year. Sunrise times have an impact on the way the endogenous clock synchronises to the solar clock. It was hypothesised firstly, that South Africans living in the East of the country may have a greater preference for mornings (more morningchronotypes) than those living in the West; and secondly, that this difference would not be due to genetic differences in the populations, particularly two gene polymorphisms previously shown to influence chronotype. Therefore the aims of this study were to describe and compare the distribution of chronotype in Eastern (n=222) and Western (n=205) sample populations with the use of a validated tool, the Horne–Östberg Morningness, Eveningness Questionnaire. Secondly to describe the genotype and allelic frequency distributions of the PER2 single nucleotide polymorphism (SNP) G3853A (rs934945) in the Eastern (n= 184) and Western (n=186) populations, and the PER3 variable number tandem repeat (VNTR) polymorphism in the Eastern (n=143) and Western (n=176) populations from buccal cell samples. There was a significantly higher proportion of morning-types in the Eastern population (60.6%) than in the Western population (40.5%) (p<0.001). Whereas there were higher proportions of neither-types and evening-types in the Western population (50.8% and 8.7% respectively) than in the Eastern population (35.1% and 4.3% respectively) (p<0.001). There were no significant differences in distribution of the PER2 genotype (p=0.121) and allele frequencies (p=0.051) between the Eastern and Western populations nor in the PER3 genotype (p=0.879) and allele (p=0.075) frequencies. Although previous studies have shown associations between chronotype and PER2 G3853A and PER3 VNTR genotypes, no significant associations were observed in either the Eastern (PER2 p=0.769; PER3 p=0.221) or the Western (PER2 p=0.584; PER3 p=0.733) populations. These findings indicate that, in South African populations, longitude influences chronotype independently of genotype. Factors that may contribute to this may be the difference in the rising times of the sun, which is exacerbated to some extent by the study areas being at dissimilar latitudes and thus experiencing slight differences in climate. The impact of the differences in chronotype but the maintenance of the same societal temporal organisation in the Eastern and Western regions were not assessed. However, they may be revealed by investigating certain general health indicators in such as quality of sleep and prevalence of depressive symptoms which are affected when there is incongruence between societal time and endogenous time.
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    Circadian rhythm, activity level, training habits and sports performance : the molecular and subjective components
    (2013) Stephenson, Kim Jenna; Rae, Dale; Roden, Laura
    Circadian rhythmicity, which is driven by a circadian clock, is a property of a biological process that displays an oscillation of approximately 24-hours even in the absence of external time cues. Individual differences in the preferred times of waking, activity and rest (sleep) are known as chronotype or diurnal preference; which arise due to differences in circadian rhythmicity due to the fact that rhythms are not exactly 24-hours. Various polymorphisms of certain genes involved in circadian rhythm generation have been associated with extreme chronotype. Of interest to this study is the PER3 gene as it has a variable number tandem repeat (VNTR) polymorphism in the coding region, which is repeated either four of five times, encoding proteins of different lengths.
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    Diurnal preference and sports performance : a subjective and genetic view
    (2011) Kunorozva, Lovemore; Roden, Laura; Rae, Dale
    [T]he purpose of this study was to describe the distribution of morning- or evening-preferring individuals (measured using the Horne-Östberg morningness-eveningness personality questionnaire) and PER3 VNTR polymorphism (from genomic DNA products extracted from human buccal cell samples amplified and digested with NcoI) within male Caucasian, trained cyclists (CYC, n=138), Ironman triathletes (IM, n=301) and an active, but non-competitive control population of Caucasian males (CON, n=120). In addition, performance was assessed in trained cyclists strongly preferring mornings or evenings at various times of day.
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    Flowering in protea : a molecular and physiological study.
    (2012) Smart, Mariette; Roden, Laura; Cramer, Michael D
    Proteas have been extensively cultivated and are grown as floricultural crop plants in many parts of the world, including South Africa. However, the factors that influence the initiation of flowering in Protea have not been identified. From data gathered by the Protea Atlas Project it is evident that Protea spp. have greatly varying flowering times. Furthermore, flowering times between Protea spp. and their hybrid cultivars are also very different. Towards a better understanding of the factors involved in floral initiation in this cultivated crop, three aspects of flowering were investigated in this study. The carbon input into Protea inflorescence development was determined by measuring respiration rates and weights of developing structures. By manipulating source-sink ratios in plants, the carbon assimilatory capacities to support inflorescences were investigated in three cultivars and one wild-grown species of Protea which develop different sized flowers. As some Proteas flower in response to seasonal change, an orthologue of the floral inducer FLOWERING LOCUS T (FT), ProteaFT (ProFT), was isolated from ‘Carnival’ (P. compacta x P. neriifolia) and its expression pattern followed diurnally and seasonally. Finally, the functions of paralogous genes of Protea LEAFY (ProLFY) from ‘Carnival’ displaying sequence similarity to the meristem identity gene LEAFY from Arabidopsis thaliana, were investigated through heterologous expression studies in A. thaliana.
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    Histone modifications and the Arabidopsis thaliana circadian clock
    (2010) Motleleng, Liabo Lilian; Roden, Laura
    The circadian system has a regulatory role in almost all aspects of a plant's life. In Arabidopsis thaliana, almost 36% of the genome has been shown to be circadianly regulated and many genes that are circadianly regulated have been shown to be light responsive or involved in light responses. Rhythmic histone acetylation has been demonstrated in the promoter of TIMING OF CAB EXPRESSION1 (TOC1). Here, I used semi-quantitative Reverse Transcriptase Polymerase Chain Reaction (semi-quantitative RT -PCR) to investigate which enzymes are involved in the rhythmic expression of TOC1. I also determined whether loss-of-function histone acetylation and methylation mutants could affect the overall functioning of the circadian oscillator by measuring their circadian leaf movement and delayed fluorescence (DF) rhythms. GCN5/ HAG1 mutant plants (gcn5) exhibited erratic TOC1 expression in both constant dark (DD) and constant light (LL) conditions. Although TOC1 expression appeared to be rhythmic in both DD and LL conditions, the waveform of the rhythm was altered in TATA-binding protein associated factor 1 (taf1) mutants. This suggested that TAF1 and GCN5 might play different roles in the rhythmic histone acetylation affecting TOC1 expression. DF data and leaf movement data indicated that both TAF1 and GCN5 might play a role in the overall functioning of the A. thaliana circadian clock. Arrhythmic TOC1 expression and DF was observed in histone deacetylase 1 (hd1) mutants, suggesting that HD1 is not only involved in the rhythmic histone deacetylation affecting TOC1 expression but in the overall functioning of the circadian clock. Semi-quantitative RTPCR, DF and leaf movement studies demonstrated that CURLY LEAF (CLF), a histone methylase is involved in both the histone methylation affecting TOC1 expression and in the overall functioning of the A. thaliana circadian clock.
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    Investigation of DNA methylation at the promoter region of the aralkylamine N-acetyltransferase (AANAT ) gene in South African children with Autism Spectrum Disorder
    (2017) Van Wyk, Gerrit; O'Ryan, Colleen; Roden, Laura
    Sleep problems and suppressed melatonin production commonly presents with core Autism Spectrum Disorder (ASD) traits. Aralkylamine N-acetyltransferase (AANAT) acts as the penultimate and rate-limiting enzyme in the melatonin biosynthetic pathway, and a study by Hu et al. (2009) reported that AANAT expression was suppressed in an ASD population with severe language impairments. The mechanism responsible for this suppressed expression is unknown. Therefore, the aim of the study was to investigate the genetic and epigenetic features of AANAT in a cohort of South African children with ASD versus children with typical development in combination with a melatonin production study to explore melatonin's contribution to ASD symptomatology. It was expected that meeting this aim would reveal DNA methylation (DNAme) modifications were statistically significant different between case and control participants. Alternatively, that DNAme features would correlate with distinct ASD traits or sleep problems and/or altered melatonin production in case participants. Biological samples and phenotypic data were collected from boys, aged between 6 and 14 years old who were assessed with the Autism Diagnostic Observation Schedule (ADOS-2). The promoter region and gene body of AANAT was sequenced (case n=26, control n=26) and DNAme analysis was performed with the Epityper massARRAY system (case n=19, control n=20). Urinary 6-hydroxymelatonin sulphate (6-OHMS) was quantified with an enzyme-linked immunosorbent assay (case n=4, control n=4). The 6-OHMS investigation was complemented with actigraphy data and a description of sleep behaviour as determined by an abbreviated version of the Children's Sleep Questionnaire. Sequence analysis found no novel single nucleotide polymorphisms and no significant differences between case and control participants. In contrast, a difference (p=0.014) in DNAme at the third CpG site in the promoter region (CpG 3) was identified in case participants assessed with ADOS-2 Module 1 in comparison to case participants assessed with ADOS-2 Modules 2 - and 3. In particular, hypomethylation was more common in participants assessed with Module 1 which is the module used to assess participants with little or no speech abilities. The transcription factor (TF) binding motifs for ZID (zinc finger protein with interaction domain), MEIS1 (Meis homeobox 1) and ZIC1 (zinc finger protein of the cerebellum 1) were identified at or near to CpG 3. These three TFs have known gene ontology terms that relate to neurodevelopment. The age of participants did not correlate with DNAme, and no further statistical significant differences were identified between the DNAme features of case and control participants, nor the correlation analysis of DNAme and ASD traits in case participants. No Module 1 participants volunteered for the 6-OHMS study, and it was therefore not possible to confirm whether DNAme features at CpG 3 correlated with altered melatonin production. The data from the study suggest that hypomethylation at the promoter region of AANAT may be related to speech impairment in ASD, and that epigenetic investigations can uncover molecular underpinnings that correlate to ASD symptomatology. Furthermore, the current study addresses the paucity of molecular information on ASD in Sub-Saharan Africa and thereby contributes to a comprehensive understanding of disease biology. It remains unknown if hypomethylation at AANAT also correlates with suppressed melatonin synthesis in ASD individuals with speech impairments and this need further investigation.
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    Keeping time on the plant-pathogen arms race : a role for the plant circadian clock in immune response
    (2011) Bhardwaj, Vaibhav; Roden, Laura; Ingle, Robert
    In this study, Arabidopsis thaliana (Arabidopsis) in the Columbia-0 (Col-0) background showed time-of-day variation in susceptibility to the plant-pathogen Pseudomonas syringae DC3000 pathovar tomato (P. syringae DC3000) when infected under constant light and temperature conditions. Wild type plants showed least susceptibility at circadian time (CT) 26 and 50, which correspond to "subjective" morning. Plants were most susceptible when infected at CT42 and CT66, "subjective" night.
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    Molecular genetics of the floral response in Xerophta humilis
    (2008) Myers, Marleen; Roden, Laura
    Includes abstract Includes bibliographical references
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    Protocol: Precision engineering of plant gene loci by homologous recombination cloning in Escherichia coli
    (BioMed Central Ltd, 2005) Roden, Laura; Gottgens, Berthold; Mutasa-Gottgens, Effie
    Plant genome sequence data now provide opportunities to conduct molecular genetic studies at the level of the whole gene locus and above. Such studies will be greatly facilitated by adopting and developing further the new generation of genetic engineering tools, based on homologous recombination cloning in Escherichia coli, which are free from the constraints imposed by the availability of suitably positioned restriction sites. Here we describe the basis for homologous recombination cloning in E. coli, the available tools and resources, together with a protocol for long range cloning and manipulation of an Arabidopsis thaliana gene locus, to create constructs co-ordinately driven by locus-specific regulatory elements.
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    The role of chronotype in the participation and performance of South African and Dutch marathon runners
    (2014) Henst, Rob; Rae, Dale; Roden, Laura
    Introduction: Our circadian rhythms are internal biological rhythms of approximately (circa) 24 - hours (dies) allowing us to synchronize our internal biological “clock” with external time cues. Many innate biological functions are dependent on time-of-day, such as secreting adrenaline and cortisol in the mornings and melatonin in the evenings. The time-of-day at which these and other physiological functions are active, change or reach a certain level may influence a person’s diurnal preference, i.e. preference for mornings (morning-types) or evenings (evening-types), and is referred to as ‘chronotype’. Many different factors may affect a person’s chronotype, including age, sex, physical activity, ethnicity and geographical location. Certain clock-related genotypes have also been shown to be associated with chronotype. For example, some studies have found that the 5-repeat allele of the PER3 variable number tandem repeat (VNTR) polymorphism (PER35) is associated with a preference for mornings. Recent research has shown a high prevalence of morning-types and PER35VNTR allele carriers in trained South African runners, cyclists and triathletes. It was proposed that the early morning start-times of these endurance events might select people with a preference for mornings, since morning-types may cope better with rising early and being physically active in the early morning. Alternatively, the habitual early waking for training or endurance events may have conditioned the athletes to adapt to become morning-types. However, the geographical location of South Africa (i.e. climate and day length) and the fact that each group was physically active may also have contributed to this finding. Comparison of South African and Dutch runners would allow us to explore the effects of race start time and geography on this observation, since marathons in The Netherlands on average start at 11:41, and since the two countries differ significantly in latitude and as such have noticeable differences in daylight exposure. Aims: The aims of this study were 1) to compare the PER3VNTR genotype and chronotype distribution of South African and Dutch recreational marathon runners and active but non-competitive controls; 2) to investigate the relationship between the PER3VNTR genotype and chronotype in both the Dutch and South African samples; and 3) to determine whether marathon race time is associated with chronotype and PER3VNTR genotype in Dutch and South African marathon Methods: Ninety-five trained South African male marathon runners, 97 South African male active but non-competitive controls, 90 trained Dutch male marathon runners and 98 Dutch male active but non-competitive controls completed a questionnaire capturing demographics, training and race history, including personal best and most recent full and half-marathon race time (if applicable) and the Horne-Östberg morningness-eveningness personality questionnaire (HÖ-MEQ, a tool to assess a person’s chronotype). Each participant provided a buccal cell swab from with total genomic DNA was extracted to determine his PER3VNTR polymorphism genotype. The official race time from each runner who completed the designated marathons in South Africa or the Netherlands was collected from the event websites. Results: The South African and Dutch runners were more morning-orientated than their respective control groups and the South African runners were more morning-orientated than the Dutch runners. The PER3 VNTR polymorphism distribution was similar between the four groups and was not associated with chronotype. The marathon performance of the morning-type South African runners was better than the evening-types, and a higher HÖ-MEQ score (morningness) correlated with better personal best and most recent half-marathon race time. Similar observations were not found in the Dutch runners. Discussion: Since a higher prevalence of morning-types in South African marathon runners compared to Dutch marathon runners was found, it is proposed that the early marathon start-times in South Africa may favour morning-types, who are able to cope with those early morning start times. Alternatively, one could argue that through repetitive early-morning racing (i.e. participating in competitive running events), the chronotype of South African runners may be conditioned to that of a morning-type over time. It is proposed that this ability to cope with early morning marathon start times may lead to better marathon performances for morning-types than neither-types and evening-types in the South African running group. This effect does not occur in the Netherlands, where marathons start later in the morning and do thus not favour a certain chronotype. The difference in daylight exposure between the two countries as a function of latitude does not seem to affect chronotype, since the active but non-competitive control groups did not differ significantly between South Africa and the Netherlands. Unlike the findings from a previous study, the PER35allele was not more prevalent among the South African runners, but rather the distribution wasi n line with what has been described in most, but not all, other populations. No association between the PER35VNTR xpolymorphism and chronotype was found in any of the four groups. Since the four groups investigated in this study comprised physically active individuals, it is proposed that this lack of association may be due to the habituation effects of physical activity and early morning start times of marathon events(for only the South African runners). Conceivably,this habituation may even shift the diurnal preference of those with the PER34/5 and PER34/4VNTR genotypes towards morningness, disassociating any relationship between chronotype and the PER3VNTR genotype. Conclusion: The early morning start time of South African marathon events may favour morning-types, due to their ability to cope with being physically active in the early morning. We propose that the PER3VNTR genotype cannot solely explain the higher prevalence of morning-types in the South African runners in this study, however, it is very likely that the PER3VNTR genotype does play an important role in the chronotype distributions found in the study of Kunorozva et al.(2012). Since the PER3VNTR genotype was not associated with chronotype in any of the four groups, it is proposed that habituation to early-morning marathon racing may be the causal effect of the high number of morning-types in the South African runners group, and the apparent disassociation between chronotype and the PER3VNTR genotype. We also propose that the habituation effect of physical activity and training time-of-day on chronotype in the other groups may dissociate the PER3VNTR genotype with chronotype in a similar manner to which the early-morning start times of South African endurance events dissociates the two. No effect of geographical location on chronotype was found when comparing the Dutch and the South African groups. The morning-orientated South African runners seem to perform better in marathon running than the more evening-orientated runners do, which may be caused by their ability to cope with these early-morning marathon events. Further studies may explore whether marathon performance in later chronotypes can be improved by training-based habituation.
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    The MYC transcription factors are involved in regulating the time-of-day variations in susceptibility to Botrytis cinerea in Arabidopsis thaliana
    (2021) Joseph, Rageema; Ingle, Robert; Roden, Laura
    Plants are exposed to pathogens at specific, yet predictable times of the day-night cycle. The circadian clock, an endogenous timing mechanism, allows plants to anticipate recurring changes in pathogen abundance. A recent study showed that in Arabidopsis thaliana (hereafter: Arabidopsis), the circadian clock influences temporal differences in susceptibility to the necrotrophic pathogen, B. cinerea. Plants were less susceptible following inoculation at subjective dawn compared to subjective midnight. Based on the time required for B. cinerea spores to germinate and hyphae to penetrate host tissue and infect plants, infection takes place approximately 12 hours after inoculation. The jasmonic acid (JA) pathway regulates immune responses against B. cinerea. The paralogous basic helix-loop-helix transcription factors, MYC2, MYC3 and MYC4 are primary regulators of the JA pathway and have been implicated in immune responses against B. cinerea but it is not known whether any or all of these transcription factors are involved in regulating time-of-day variations in susceptibility. This study aimed to investigate whether MYC2, MYC3, and MYC4 are involved in the timeof-day differences in susceptibility to B. cinerea, and if they serve as molecular links to regulate interactions between the JA pathway and the circadian clock in Arabidopsis. In this work, the wild-type temporal variation in susceptibility was abolished in the myc234 triple mutant coupled with increased susceptibility following inoculation at both times of the day. The presence of MYC2, MYC3 or MYC4 alone was sufficient to maintain the wild-type time-of-day differences in susceptibility. Constitutive expression of MYC2, MYC3 or MYC4 abolished time-of-day differences in susceptibility but had different effects on overall susceptibility; constitutive expression of MYC2 and MYC4 decreased susceptibility while constitutive expression of MYC3 increased susceptibility to B. cinerea. Gene expression analyses performed on leaves revealed that the transcripts of MYC2 and MYC3 but not MYC4 are expressed rhythmically with peak transcript abundance timed to discrete times of the day under both light-dark and constant light conditions. Constitutive expression of circadian clock genes CCA1 and TOC1 abolished rhythmic MYC expression. The circadian clock modulates rhythmic leaf movement and rhythmic leaf movement was abolished in plants with constitutive MYC2 and MYC3 expression but not in plants with constitutive MYC4 expression and/or in the myc234 triple mutant. Altogether, the data suggest that the MYCs are involved in circadian-driven defence responses against B. cinerea. More specifically, MYC2, MYC3 and MYC4 function redundantly in regulating time-of-day differences in defence responses. In addition, the MYCs function as a point of convergence between the JA pathway and the circadian clock. MYC2 and MYC3 (but not MYC4) may be involved in reciprocal interactions between the JA pathway and the circadian clock.
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    Towards an understanding of the relationship between sleep and cardiovascular disease risk in adults of African descent living in a low socioeconomic status community
    (2025) Forshaw, Philippa; Rae, Dale; Roden, Laura; Lambert, Estelle
    Background: Individuals of African descent, specifically African Americans and those from Sub-Saharan Africa, experience a higher burden of cardiovascular disease (CVD) and its associated risk factors (such as obesity, diabetes and hypertension) as well as shorter, poorer sleep quality, compared to Caucasian American individuals. Blood pressure (BP) non-dipping (i.e. the failure of BP to decrease at night during sleep) and nocturnal hypertension are important markers of CVD risk and are substantially more prevalent in African American, compared to Caucasian American, individuals. Two additional layers that need consideration are socioeconomic status (SES) and sex. In contrast to much of the research in the Global North predominantly demonstrating shorter objective and subjective sleep durations (around 6- 7h per night) among African descended individuals living in low SES environments, South Africans of African descent living in low SES communities report much longer sleep durations, around 8-10h per night. Thus, while on one hand, lower SES has been associated with higher risk for CVD possibly through shorter sleep, the nature of the relationship between long sleep duration and CVD risk in the South African context is not well understood. Given the significant sex-specific differences in both CVD risk and sleep, there is a need for research focused on understanding sex-specific associations between CVD and sleep health. Thus, the purpose of this thesis was to investigate sex-specific relationships between CVD risk, nocturnal BP and sleep health in adults of African descent living in a low SES community in South Africa. This purpose was achieved through the following aims: i) to investigate sex-specific relationships between self-reported sleep characteristics and CVD risk among individuals of African descent living in a low SES community, ii) to investigate sex-specific relationships between actigraphy-derived sleep characteristics and CVD risk in these same individuals, iii) to systematically review the literature on sleep and BP dipping in apparently healthy individuals, iv) to explore sex-specific associations between actigraphy-derived sleep characteristics, nocturnal BP and CVD risk among adults of African descent living in a low SES community and v) to conduct qualitative interviews with these same individuals to explore how external (e.g. environmental barriers to and promoters of good sleep) and internal (e.g. individual knowledge, attitudes, beliefs and perceptions around sleep) factors might impact sleep health. This thesis explored the hypothesis that adverse environmental conditions associated with living in low SES communities are not conducive to healthy sleep, driving BP non-dipping, nocturnal hypertension and higher CVD risk. Methods: For Chapters 2 and 3, individuals of African descent (56% women, 29-51y, 40% employed) living in Khayelitsha (an informal settlement in South Africa characterised by high rates of crime, violence and poverty) were recruited and studied. Sleep characteristics were measured subjectively using self-reported questionnaires (Pittsburgh Sleep Quality Index (PSQI), Epworth Sleepiness Scale (ESS), Insomnia Severity Index (ISI); n=412) and objectively with seven days of wrist-worn actigraphy (n=194). CVD risk was assessed using the body mass index (BMI)-modified Framingham 10-year CVD risk score and clinical measures (BMI, waist circumference, resting BP, fasting glucose). We then conducted a systematic review (Chapter 4) exploring associations between BP dipping and sleep in healthy individuals. In Chapter 5 we measured twenty-four hour ambulatory BP in a sub-set of individuals from the original cohort (n=59) to explore associations between BP dipping, nocturnal hypertension, sleep characteristics and CVD risk scores. Finally, we conducted one-on-one qualitative interviews (Chapter 6) in a further sub-set of participants (n=15) to explore possible external (e.g. environmental barriers to and promoters of good sleep) and internal (e.g. individual knowledge, attitudes, beliefs and perceptions around sleep) factors related to sleep health in this population.Results: When we examined associations between subjectively measured sleep and CVD risk (Chapter 2), found that men (n=178) reporting poor sleep quality (PSQI>5, OR: 1.95, 95%CI: 1.07, 3.51, p=0.025) and earlier bedtimes (OR: 0.54, 95%CI: 0.39, 0.74, p<0.001)were more likely to have higher CVD risk scores. Women (n=234) reporting earlier bedtimes (OR: 0.72, 95%CI: 0.55, 0.95, p=0.020) and wake-up times (OR: 0.30, 95%CI: 0.13, 0.73, p=0.007), longer sleep onset latencies (OR: 1.47, 95%CI: 1.43, 1.88, p=0.003), shorter total sleep times (OR: 0.84, 95%CI: 0.72, 0.98, p=0.029), higher PSQI global scores (OR: 1.93, 95%CI: 1.29, 2.90, p=0.001) and more moderate to severe insomnia symptoms (ISI≥15, OR: 3.24, 95%CI: 1.04, 10.04, p=0.042) were more likely to have higher CVD risk scores. We confirm actigraphy derived long (men: 9.4 ± 1.4h, women: 8.9 ± 1.2h) but disturbed sleep (low sleep efficiencies [men: 81.8 (76.8, 85.7)%), women: 79.9 (72.5, 84.6)%], high sleep fragmentation indices [men: 58.3 (52.5, 65.2)%, women: 63.4 (56.3, 68.2)%] and high wake after sleep onset (WASO) times [men: 103.1 (76.1, 127.0)min, women: 84.9 (68.8, 110.4)min]) in this population, for whom obesity (specifically among women: 60.3%) and hypertension (men: 48%, women: 44%) are prevalent. Associations between actigraphy-derived sleep measures and CVD risk (Chapter 3) found that among men (n=94), earlier midsleep time was associated with higher CVD risk scores (b =–0.17, 95%CI:–0.33, –0.02, p=0.030) while shorter sleep duration was associated with obesity (OR: 0.48, 95%CI: 0.25, 0.90, p=0.023). Among women (n=100), earlier wake-up times (b: –0.24, 95%CI: –0.41, –0.07, p=0.007) and midsleep times (b: – 0.18, 95%CI: –0.39, 0.00, p=0.046) were associated with higher CVD risk scores. Women with earlier bedtimes (OR: 0.53, 95%CI: 0.33, 0.85, p=0.009) and midsleep times (OR: 0.47, 95%CI: 0.26, 0.83, p=0.010) were more likely to have elevated BP, and those with earlier wake-up times (OR: 0.54, 95%CI: 0.35, 0.81, p=0.003) and midsleep times (OR: 0.46, 95%CI: 0.27, 0.77, p=0.003) were also more likely to be obese. Interaction effects revealed that among women, CVD risk scores were higher in those who had shorter sleep combined with later bedtimes or in those who had longer sleep combined with earlier bedtimes (β:–2.38, 95%CI: –0.35, –0.12, p<0.001). A weaker interaction effect was found for WASO such that CVD risk score was higher in women with longer sleep and more WASO or shorter sleep with less WASO (β: 0.004, 95%CI: 0.00, 0.00, p=0.014). The systematic review (Chapter 4) showed that BP non dipping in apparently healthy individuals was associated with short sleep duration, more sleep fragmentation, less sleep depth and increased variability in sleep timing. Measuring 24h ambulatory BP (Chapter 5) found a high proportion of SBP non-dipping (men: 50%, women: 61%), with 48% of men and 72% of women also presenting with nocturnal hypertension. Among the women (n=36), shorter total sleep times (rho: 0.42, p=0.020) and worse sleep efficiencies (rho: 0.51, p=0.003) were correlated with smaller SBP dipping percentages. Similarly, shorter sleep durations (rho: 0.39, p=0.029), shorter total sleep times (rho: 0.44, p=0.014) and worse sleep efficiencies (rho: 0.37, p=0.037) were correlated with smaller DBP dipping percentages. Women with worse sleep efficiencies (rho: –0.39, p=0.016) has higher nocturnal SBP. Among the men (n=23), worse sleep efficiencies (SBP rho: –0.47, p=0.024; DBP rho: – 0.50, p=0.015), greater WASO (SBP rho: 0.59, p=0.003; DBP rho: 0.50, p=0.014) and greater sleep fragmentation indices (SBP rho: 0.59, p=0.003; DBP rho: 0.59, p=0.003) were correlated with higher nocturnal SBP and DBP. Worse sleep duration regularity scores were correlated with lower SBP (rho: – 0.48, p=0.025) and DBP (rho: –0.52, p=0.013) dipping percentages. Men with nocturnal hypertension had higher WASO (116.8 (88.8, 163.3)min vs. 88.1 (65.1, 98.3)min, p=0.031) and sleep fragmentation indices (36.4(33.4, 40.8)% vs. 29.6(25.8, 34.7)%, p=0.019) compared to those without nocturnal hypertension. Insights from the qualitative interviews (Chapter 6) revealed that external factors such as high-density living, noise, crime, violence and excessive alcohol use within the community primarily contributed to disturbing the sleep of participants. Conclusions: This thesis provides new insights, from a Global South lens, to relationships between sleep and cardiovascular health as they relate to adults of African descent living in a low SES environment. 4 Two main features of sleep emerge as important risk factors for CVD in these study participants: mistimed sleep and disturbed sleep, despite adequate sleep opportunities. By considering the lived experiences of individuals in this low SES community, we gained an understanding of the major role that the adverse conditions of the neighbourhood has on impairing sleep health in this population. We speculate that this earlier timed sleep observed predominantly in women, but to some extent in men, might be a direct consequence of environment-related fear, prompting residents to seek refuge in bed at a time which may be too early, potentially contributing to circadian misalignment, which in turn may increase CVD risk. We further hypothesise that when faced with these adverse neighbourhood conditions, some residents may be in a state of hypervigilance at night, resulting in insufficient sympathetic nervous system (SNS) withdrawal, which in turn leads to disturbed sleep. Disturbed sleep may contribute to BP non-dipping or nocturnal hypertension, which may subsequently increase CVD risk, potentially through insufficient cardiovascular system recovery at night. Interestingly, we note that some participants appear to demonstrate resilience through attaining healthy sleep despite living in a challenging neighbourhood environment. Perhaps these are the individuals in whom appropriate SNS withdrawal takes place at night, improving their sleep health and reducing their CVD risk. Considering all the evidence generated though these studies, this thesis proposes the term Sleep Health Insecurity - a lack of regular access to healthy sleep (that which is of sufficient duration, regular, appropriately timed, consolidated, satisfying and refreshing), which is essential for optimal mental and physical health, emotional well-being and cognition. Although we propose that residents of Khayelitsha are experiencing Sleep Health Insecurity, which may increase their CVD risk, these residents likely represent not only a large sector of the South African population but also other similar low SES populations around the world, making this concept a fundamental global health issue.