Junior medical researchers: A neglected community with great academic potential

Medical research capacity development is a national priority to improve healthcare in South Africa (SA). The 2011 National Health Research Summit set a target of training 1 000 doctoral candidates in health sciences over the next 10 years. We advocate revitalised research training opportunities for junior clinicians to help achieve this target and to contribute to the creation of a thriving medical research network across SA

Structural basis of TIR-domain-assembly formation in MAL- and MyD88-dependent TLR4 signaling

Toll-like receptor (TLR) signaling is a key innate immunity response to pathogens. Recruitment of signaling adapters such as MAL (TIRAP) and MyD88 to the TLRs requires Toll/interleukin-1 receptor (TIR)-domain interactions, which remain structurally elusive. Here we show that MAL TIR domains spontaneously and reversibly form filaments in vitro. They also form cofilaments with TLR4 TIR domains and induce formation of MyD88 assemblies. A 7-Å-resolution cryo-EM structure reveals a stable MAL protofilament consisting of two parallel strands of TIR-domain subunits in a BB-loop-mediated head-to-tail arrangement. Interface residues that are important for the interaction are conserved among different TIR domains. Although large filaments of TLR4, MAL or MyD88 are unlikely to form during cellular signaling, structure-guided mutagenesis, combined with in vivo interaction assays, demonstrated that the MAL interactions defined within the filament represent a template for a conserved mode of TIR-domain interaction involved in both TLR and interleukin-1 receptor signaling

Host species adaptation of TLR5 signalling and flagellin recognition

Toll-like receptor 5 (TLR5) recognition of flagellin instigates inflammatory signalling. Significant sequence variation in TLR5 exists between animal species but its impact on activity is less well understood. Building on our previous research that bovine TLR5 (bTLR5) is functional, we compared human and bovine TLR5 activity and signalling in cognate cell lines. bTLR5 induced higher levels of CXCL8 when expressed in bovine cells and reciprocal results were found for human TLR5 (hTLR5) in human cells, indicative of host cell specificity in this response. Analysis of Toll/interleukin-1 receptor (TIR) sequences indicated that these differential responses involve cognate MyD88 recognition. siRNA knockdowns and inhibitor experiments demonstrated that there are some host differences in signalling. Although, PI3K activation is required for bTLR5 signalling, mutating bTLR5 F798 to hTLR5 Y798 within a putative PI3K motif resulted in a significantly reduced response. All ruminants have F798 in contrast to most other species, suggesting that TLR5 signalling has evolved differently in ruminants. Evolutionary divergence between bovine and human TLR5 was also apparent in relation to responses measured to diverse bacterial flagellins. Our results underscore the importance of species specific studies and how differences may alter efficacy of TLR-based vaccine adjuvants

The use of human genetics in drug target identification and validation

The process of developing novel medicines is complex, expensive, time-consuming and fraught with failure. A major contributor to the high failure rate of drug development is the poor ability of existing preclinical models to predict drug efficacy and safety in humans. Human genetics enables an emerging set of investigations with utility in drug target identification and validation, akin to a “natural randomised trial”. In this thesis, I applied these methods to examine the efficacy and safety of several drug targets. Using variants in the gene encoding angiotensinogen, I found that inhibition of this novel anti-hypertensive drug target is likely to safely reduce the risk of cardiovascular outcomes, with vascular effects that are comparable to those arising from other targets in the renin-angiotensin pathway, and blood pressure lowering more broadly. Next, I applied human genetics to examine several therapeutic questions relating to coronavirus disease 2019 (COVID-19). I found that genetic proxies for renin-angiotensin system modulating therapies show no strong evidence of association with COVID-19, suggesting that these therapies are unlikely to produce substantial benefit or harm in the context of COVID-19. I then investigated the use of human genetic data for potential repurposing of immunomodulatory therapies for the treatment of COVID-19. This work was the first to show that genetic proxies for interleukin-6 receptor (IL-6R) inhibition associate with a lower risk of severe COVID-19. Meta-analysis of IL-6R inhibitor clinical trial data showed these medicines reduced the risk of COVID-19 progression and mortality, therefore recapitulating the findings from the genetic analysis, and illustrating the value of applying human genetics to guide drug repurposing in the context of an emerging pandemic disease. I perform a further set of analysis to show that COVID-19 GWAS data can be leveraged to prioritise a further set of immunomodulatory drug targets. I next analysed clinical trial data of a sclerostin inhibitor (romosozumab) approved for the treatment of osteoporosis, and found evidence suggesting that this drug may increase cardiovascular risk. Genetic variants in the gene encoding sclerosting (SOST) were also associated with a higher risk of cardiovascular events, suggesting that this adverse effect is likely real and target-mediated. Finally, I performed a genome-wide association meta-analysis of erectile dysfunction, which led to the discovery of the first robust risk locus, and a potential drug target, for this common condition. The work presented in this thesis showcases the utility of human genetics in guiding drug target identification and validation, and its potential for ameliorating the high failure rate of drug development.</p

Identifying predictors of mitral valve (MV) tears resulting from percutaneous balloon mitral valvuloplasty (PBMV): a descriptive study

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Colocalization analysis of polycystic ovary syndrome to identify potential disease-mediating genes and proteins

Polycystic ovary syndrome (PCOS) is a common complex disease in women with a strong genetic component and downstream consequences for reproductive, metabolic and psychological health. There are currently 19 known PCOS risk loci, primarily identified in women of Han Chinese or European ancestry, and 14 of these risk loci were identified or replicated in a genome-wide association study of PCOS performed in up to 10,074 cases and 103,164 controls of European descent. However, for most of these loci the gene responsible for the association is unknown. We therefore use a Bayesian colocalization approach (Coloc) to highlight genes in PCOS-associated regions that may have a role in mediating the disease risk. We evaluated the posterior probabilities of evidence consistent with shared causal variants between 14 PCOS genetic risk loci and intermediate cellular phenotypes in one protein (N = 3301) and two expression quantitative trait locus datasets (N = 31,684 and N = 80–491). Through these analyses, we identified seven proteins or genes with evidence of a possibly shared causal variant for almost 30% of known PCOS signals, including follicle stimulating hormone and ERBB3, IKZF4, RPS26, SUOX, ZFP36L2, and C8orf49. Several of these potential effector proteins and genes have been implicated in the hypothalamic–pituitary–gonadal signalling pathway and provide an avenue for functional follow-up in order to demonstrate a causal role in PCOS pathophysiology