Biology subjects

Maina, M. B.

Publications and source records attributed to Maina, M. B..

9 recordsLinked to original sources

bioRxiv2025

A proteomic analysis of the PHF-forming tau fragment (tau297-391) following uptake into differentiated human neuronal SHSY5Y cells

Tau self-assembly and intracellular deposition is associated with a group of neurodegenerative diseases called tauopathies, which include Alzheimers disease (AD) and Picks disease. Here, we measured the proteome response in human neuronal cells (differentiated SH-SY5Y) following addition of a spontaneously amyloidogenic region of tau known as dGAE (tau297-391) which forms AD-like paired helical filaments in vitro and proteomic analysis showed increased endogenous tau expression. Further interactome analysis uncovered increased association between tau and proteins associated with nuclear chromatin, the nucleolus, and the spliceosome as well as the thiol-peroxidase, PRDX6 alongside an increase in reactive oxygen species (ROS). This work highlights a method to identify proteome pathways that may play an important role in the development of tau pathology.

cell biology↗

bioRxiv2025

Inhibiting disulphide bonding in truncated tau297-391 results in enhanced self-assembly of tau into seed-competent assemblies.

Tau undergoes fibrillogenesis in a group of neurodegenerative diseases termed tauopathies. Each tauopathy is characterized by tau fibrils with disease-specific conformations, highlighting the complexity of tau self-assembly. This has led to debate surrounding the precise mechanisms that govern the self-assembly of tau in disease, especially the involvement of disulphide bonding (DSB) between cysteine residues. In this study, we use a truncated form of tau, dGAE, capable of forming filaments identical to those in disease. We reveal the impact of DSB in dGAE assembly and propagation by resolving the global mechanisms that dominate its assembly. We found evidence for surface-mediated secondary nucleation and fragmentation being active in dGAE assembly. The inhibition of DSB during dGAE assembly leads to an enhanced aggregation rate through a reduced lag phase, but with no effect on the global assembly mechanisms. We suggest this is due to the formation a dominant, seed-competent species in the absence of DSB that facilitates elongation and secondary nucleation resulting in enhanced assembly. In vitro seeding assays reveal the recruitment of endogenous tau in a cell model only when using dGAE species formed under conditions that inhibit DSB. Our results further support the use of the in vitro dGAE tau aggregation model for investigating the mechanism of tau assembly, the effect of varying conditions on tau assembly and how these conditions affect the resultant species. Further studies may utilise dGAE and its aggregates to investigate tau seeding, propagation and to highlight or test potential targets for therapies that reduce the spread of pathologic tau throughout the brain.

biochemistry↗

bioRxiv2023

Generation of an induced pluripotent stem cell line from a healthy adult indigenous Nigerian participant

Genetic backgrounds contribute to cellular phenotypes, drug responsiveness, and health outcomes. However, the majority of human induced pluripotent stem cell (iPSC) lines are derived from individuals of European descent. Thus, there is a major, unmet need in the generation, characterisation, and distribution of iPSCs from diverse ancestries. To begin to address this need, we have generated iPSCs from dermal fibroblasts isolated from a healthy 60-year-old indigenous Nigerian male belonging to the Babur ethnic group. The iPSCs were generated using Sendai virus, and copy number variation (CNV) analysis revealed no new major abnormalities compared to the parental fibroblasts. The iPSCs have been characterised for pluripotency markers and morphology and successfully differentiated into neural progenitor cells and astrocytes. This iPSC line could serve as a healthy control in comparative studies and can be used in disease modelling, toxicity assessments, genetic analyses, and drug discovery processes within an African genetic background. To bolster the inclusion of African models in biomedical research, this iPSC line will be made available to the broader scientific community. Ongoing efforts focus on generating more lines from diverse indigenous populations towards creating a dedicated open-access African iPSC biobank.

cell biology↗

bioRxiv2022

Simple Models For Neuroscience Research Discoveries: How Often Are These Models Used In Africa

Simple animal model systems such as Drosophila, Zebrafish, and C. Elegans have enabled numerous breakthroughs in understanding human health and disease. Their conserved biological processes, ever-expanding established procedures for handling, and amenability for molecular and genetic manipulation, in addition to the minimal ethical concerns, have made these models preferred choices in several life science disciplines globally. Owing to their cheap maintenance cost, adopting these model systems will help bridge the research gap between Africa and the Global North and contribute to advancing scientific knowledge in African universities through practical sessions. However, the extent to which these models are used across Africa is unknown. Here, we analysed the use of Drosophila, Zebrafish, and C. elegans model systems in scientific publications from African laboratories from the year 2000 to 2021. Of 1851 PubMed-indexed publications in which at least one simple animal model was mentioned, 168 used at least one of these models for the actual investigation. With an average of 21 articles per country, South Africa, Nigeria, Kenya, Egypt, Morocco, and Tunisia contributed 75% of these studies. The remaining 25% were contributed by seven other countries at 2-7 articles per country. From here, we extracted and analysed information on funding and international collaboration. This revealed that 24.4 % of the studies were exclusively funded locally, 28.57 % exclusively funded internationally, 15.5% received both local and international funding, and the rest (31.5%) were unfunded, revealing that there is satisfactory access to funds for simple animal model studies, especially from external funders. By analysing the pattern of collaborations, we show that most of these studies had international collaborations, while very few collaborated within Africa. Our work provides data on the current state of research using simple model systems in African laboratories and argues that incorporating these models will advance biomedical science research in Africa.

neuroscience↗

bioRxiv2022

GNNQQNY: Methodology for biophysical and structural understanding of aggregation

GNNQQNY sequence offers crucial information about the formation and structure of an amyloid fibril. In this study, we demonstrate a reproducible solubilisation protocol where the reduction of pH to 2.0 resulted in the generation of GNNQQNY monomers. The subsequent ultracentrifugation step removes the residual insoluble peptide from the homogeneous solution. This procedure ensures and allows the peptides to remain monomers till their aggregation is triggered by adjusting the pH to 7.2. The aggregation kinetics analysis showed a distinct lag-phase that is concentration-dependent, indicating nucleation-dependent aggregation kinetics. Nucleation kinetics analysis suggested a critical nucleus of size [~]7 monomers at physiological conditions. The formed nucleus acts as a template for further self-assembly leading to the formation of highly ordered amyloid fibrils. These findings suggest that the proposed solubilisation protocol provides the basis for understanding the kinetics and thermodynamics of amyloid nucleation and elongation in GNNQQNY sequences. This procedure can also be used for solubilising such small amyloidogenic sequences for their biophysical studies.

biophysics↗

bioRxiv2020

Oxidative stress conditions result in trapping of PHF-core tau (297-391) intermediates.

The self-assembly of tau into paired helical filaments (PHF) in neurofibrillary tangles (NFTs) is a significant event in Alzheimers disease (AD) pathogenesis. Oxidative stress, which accompanies AD, induces multiple post-translational modifications in proteins including the formation of dityrosine (DiY) cross-links, previously observed for A{beta}. Here, metal catalysed- and ultra-violet oxidation were used to study the influence of DiY cross-linking on the self-assembly of the PHF-core tau fragment. We report that DiY cross-linking facilitates tau assembly into tau oligomers and prevents their elongation into filaments. The DiY cross-linked tau oligomers were not toxic to cells. Our findings suggest that DiY cross-linking of pre-assembled tau, promotes the formation of soluble tau oligomers that show no acute toxicity.

biochemistry↗

bioRxiv2020

Nucleation-dependent aggregation kinetics of Yeast Sup35 fragment GNNQQNY

An N-terminal hepta-peptide sequence of yeast prion protein Sup35 with the sequence GNNQQNY serves as an ideal model for structural understanding of amyloid assembly and kinetics. In this study, we used a reproducible solubilisation protocol that allows the generation of homogenous monomeric solution of GNNQQNY to understand the molecular details of its self-assembly mechanism. The aggregation kinetics data show that the GNNQQNY sequences follow nucleation-dependent aggregation kinetics with a critical nucleus of size ~7 monomers and that the size and efficiency of nucleation was found to be inversely related to the reaction temperature. The generated nucleus reduces the thermodynamic energy barrier by acting as a template for further self-assembly and results in highly ordered amyloid fibrils. The fibers grown at different temperatures showed similar Thioflavin T positivity, Congo red binding and {beta}-sheet rich structures displaying a characteristic cross-{beta} diffraction pattern. These aggregates also share morphological and structural identity with those reported earlier. The mature GNNQQNY fibers exerted no significant oxidative stress or cytotoxicity upon incubating with differentiated SHSY5Y cells. To our knowledge, this is the first study to experimentally validate previous predictions based on theoretical and molecular dynamics simulations. These findings will provide the basis for understanding the kinetics and thermodynamics of amyloid nucleation and elongation of amyloidogenic systems associated with many systemic and neurodegenerative diseases.

biophysics↗

bioRxiv2020

20 years of African Neuroscience: Waking a sleeping giant

Understanding the function and dysfunction of the brain remains one of the key challenges of our time. However, an overwhelming majority of brain research is carried out in the Global North, by a minority of well-funded and intimately interconnected labs. In contrast, with an estimated one neuroscientist per million people in Africa, news about neuroscience research from the Global South remains sparse. Clearly, devising new policies to boost Africa’s neuroscience landscape is imperative. However, the policy must be based on accurate data, which is largely lacking. Such data must reflect the extreme heterogeneity of research outputs across the continent’s 54 countries distributed over an area larger than USA, Europe and China combined. Here, we analysed all of Africa’s Neuroscience output over the past 21 years. Uniquely, we individually verified in each of 12,326 publications that the work was indeed performed in Africa and led by African-based researchers. This step is critical: previous estimates grossly inflated figures, because many of Africa’s high-visibility publications are in fact the result of internationally led collaborations, with most work done outside of Africa. The remaining number of African-led Neuroscience publications was 5,219, on average only ~5 per country and year. From here, we extracted metrics such as the journal and citations, as well as detailed information on funding, international collaborations and the techniques and model systems used. We link these metrics to demographic data and indicators of mobility and economy. For reference, we also extracted the same metrics from 220 randomly selected publications each from the UK, USA, Australia, Japan and Brazil. Our unique dataset allows us to gain accurate and in-depth information on the current state of African Neuroscience research, and to put it into a global context. This in turn allows us to make actionable recommendations on how African research might best be supported in the future.Competing Interest StatementThe authors have declared no competing interest.View Full Text

scientific communication and education↗

bioRxiv2020

Dityrosine cross-link trapping of amyloid-β intermediates reveals that self-assembly is required for Aβ-induced cytotoxicity

Multiple chemical reactions, such as the production of reactive oxygen species (ROS) can lead to dityrosine (DiY) formation via the cross-linking of closely spaced tyrosine residues and this can serve as a marker for aging. Amyloid-{beta} (A{beta}) has been found to be DiY cross-linked in the brains of AD patients. In vitro, A{beta} forms DiY cross-links via metal-catalysed oxidation (Cu2+ and H202) (MCO) leading to the formation of fibrils that are resistant to formic acid denaturation. However, copper is well known to influence and enhance self-assembly. Here, to investigate the interplay between self-assembly and DiY cross-linking we have utilised a non-assembly competent variant of A{beta} (vA{beta}). MCO and UV oxidation experiments using vA{beta} and wild-type A{beta}, revealed that DiY cross-linking stabilises, but does not induce or promote A{beta} assembly. Cu2+ alone, without H202, facilitates the formation and DiY cross-linking of wild-type A{beta} into long-lived oligomers. Our work reveals DiY formation halts further A{beta} self-assembly. DiY cross-linked A{beta} is non-toxic to neuroblastoma cells at all stages of self-assembly in contrast to oligomeric non-cross-linked A{beta}. These findings point to a mechanism of toxicity that necessitates continuing self-assembly of the A{beta} peptide, whereby trapped DiY A{beta} assemblies and assembly incompetent variant A{beta} are unable to result in cell death.

biochemistry↗