Biology subjects

Ansell, B.

Publications and source records attributed to Ansell, B..

7 recordsLinked to original sources

bioRxiv2025

Patient induced pluripotent stem cells identify specificities of a reticular pseudodrusen phenotype in age-related macular degeneration

BackgroundAge-related macular degeneration (AMD) is a leading cause of vision loss. Reticular pseudodrusen (RPD), deposits on the apical side of the retinal pigment epithelium (RPE), signify a distinctive and critical AMD phenotype. Yet, their molecular basis and relationship to the conventional drusen seen in AMD remain unclear. ResultsWe generated induced pluripotent stem cell-derived RPE cells from a clinically phenotyped cohort comprising only individuals with conventional drusen (AMD/RPD-) or drusen coexisting with RPD (AMD/RPD+). From these cells, we generated single-cell transcriptomics, proteomics, and functional data to identify differences between the two cohorts. We show that AMD/RPD+ RPE cells exhibit enrichment in extracellular matrix (ECM) remodelling, cytoskeletal, and hypoxia-responsive programs, whereas AMD/RPD- RPE cells display a relatively greater representation of mitochondrial and protein homeostasis pathways. Both subtypes engaged pathways classically linked to ageing, including ECM remodelling and mitochondrial function, but differed in the direction and extent of these changes. Expression and protein quantitative trait loci (QTLs) highlight shared genetic influences on mitochondrial and iron-handling pathways, while disease-interacting eQTLs and transcriptome-wide association study identify regulatory signals that are distinctive of the RPD subtype within AMD, including through regulation of ECM. Functionally, all iPSC-derived RPE formed drusen-like deposits in vitro: AMD/RPD-lines generated more basal deposits, whereas AMD/RPD+ cells exhibited greater structural instability under bisretinoid-induced stress. ConclusionsThese findings indicate that AMD with and without RPD represent mechanistically distinct entities and provide novel insight into the molecular mechanisms underlying disease heterogeneity in AMD.

genetics↗

bioRxiv2023

The Energetics and Ion Coupling of Cholesterol Transport Through Patched1

Patched1 (PTCH1) is the principal tumour suppressor protein of the mammalian Hedgehog (HH) signalling pathway, implicated in embryogenesis and tissue homeostasis. PTCH1 inhibits the Class F G protein-coupled receptor Smoothened (SMO) via a debated mechanism involving modulating accessible cholesterol levels within ciliary membranes. Using extensive molecular dynamics (MD) simulations and free energy calculations to evaluate cholesterol transport through PTCH1, we find an energetic barrier of ~15-20 kJ mol-1 for cholesterol export. In simulations we identify cation binding sites within the PTCH1 transmembrane domain (TMD) which may provide the energetic impetus for cholesterol transport. In silico data are coupled to in vivo biochemical assays of PTCH1 mutants to probe coupling between transmembrane motions and PTCH1 activity. Using complementary simulations of Dispatched1 (DISP1) we find that transition between inward-open and solvent occluded states is accompanied by Na+ induced pinching of intracellular helical segments. Thus, our findings illuminate the energetics and ion-coupling stoichiometries of PTCH1 transport mechanisms, whereby 1-3 Na+ or 2-3 K+ couple to cholesterol export, and provide the first molecular description of transitions between distinct transport states.

biophysics↗

bioRxiv2022

Mouse microglia express unique miRNA-mRNA networks to facilitate age-specific functions in the developing central nervous system

Microglia regulate multiple processes in the central nervous system, exhibiting a significant level of cellular plasticity which is facilitated by an equally dynamic transcriptional environment. While many gene networks that regulate microglial functions have been characterised, the influence of epigenetic regulators such as small non-coding microRNAs (miRNAs) is less well defined. We have sequenced the miRNAome and mRNAome of mouse microglia during brain development and adult homeostasis, identifying unique profiles of known and novel miRNAs. Microglia express both a consistently enriched miRNA signature as well as temporally distinctive subsets of miRNAs. We generated robust miRNA-mRNA networks related to fundamental developmental processes, in addition to networks associated with immune function and dysregulated disease states. There was no apparent influence of sex on miRNA expression. This study reveals a unique developmental trajectory of miRNA expression in microglia during critical stages of CNS development, establishing miRNAs as important modulators of microglial phenotype.

neuroscience↗

bioRxiv2021

PyLipID: A Python package for analysis of protein-lipid interactions from MD simulations

Lipids play important modulatory and structural roles for membrane proteins. Molecular dynamics simulations are frequently used to provide insights into the nature of these proteinlipid interactions. Systematic comparative analysis requires tools that provide algorithms for objective assessment of such interactions. We introduce PyLipID, a python package for the identification and characterization of specific lipid interactions and binding sites on membrane proteins from molecular dynamics simulations. PyLipID uses a community analysis approach for binding site detection, calculating lipid residence times for both the individual protein residues and the detected binding sites. To assist structural analysis, PyLipID produces representative bound lipid poses from simulation data, using a density-based scoring function. To estimate residue contacts robustly, PyLipID uses a dual-cutoff scheme to differentiate between lipid conformational rearrangements whilst bound from full dissociation events. In addition to the characterization of protein-lipid interactions, PyLipID is applicable to analysis of the interactions of membrane proteins with other ligands. By combining automated analysis, efficient algorithms, and open-source distribution, PyLipID facilitates the systematic analysis of lipid interactions from large simulation datasets of multiple species of membrane proteins. ToC Graphic O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=143 SRC="FIGDIR/small/452312v1_ufig1.gif" ALT="Figure 1"> View larger version (53K): org.highwire.dtl.DTLVardef@1f6530corg.highwire.dtl.DTLVardef@c639d5org.highwire.dtl.DTLVardef@1fef967org.highwire.dtl.DTLVardef@a80446_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2020

The Glycosphingolipid GM3 Modulates Conformational Dynamics of the Glucagon Receptor

The extracellular domain (ECD) of Class B1 G-protein coupled receptors (GPCRs) plays a central role in signal transduction and is uniquely positioned to sense both the extracellular and membrane environments. Whilst recent studies suggest a role for membrane lipids in the modulation of Class A and Class F GPCR signalling properties, little is known about the effect of lipids on Class B1 receptors. In this study, we employed multiscale molecular dynamics (MD) simulations to access the dynamics of the glucagon receptor (GCGR) ECD in the presence of native-like membrane bilayers. Simulations showed that the ECD could move about a hinge region formed by residues Q122-E126 to adopt both closed and open conformations relative to the TMD. ECD movements were modulated by binding of the glycosphingolipid GM3. These large-scale fluctuations in ECD conformation that may affect the ligand binding and receptor activation properties. We also identify a unique PIP2 interaction profile near ICL2/TM3 at the G-protein coupling interface, suggesting a mechanism of engaging G-proteins which may have a distinct dependence on PIP2 compared to Class A GPCRs. Given the structural conservation of Class B1 GPCRs, the modulatory effects of GM3 and PIP2 on GCGR may be conserved across these receptors, offering new insights into potential therapeutic targeting. Statement of SignificanceThe role of lipids in regulation of Class B GPCRs remains elusive, despite recent structural advances. In this study, multi-scale molecular dynamics simulations are used to evaluate lipid interactions with the glucagon receptor, a Class B1 GPCR. We find that the glycosphingolipid GM3 binds to the glucagon receptor extracellular domain (ECD), modulating the dynamics of the ECD and promoting movement away from the transmembrane domain. We also identify a unique PIP2 interaction fingerprint in a region known to be important for bridging G-protein coupling in Class A GPCRs. Thus, this study provides molecular insight into the behaviour of the glucagon receptor in a complex lipid bilayer environment which may aid understanding of glucagon receptor signalling properties.

biophysics↗

bioRxiv2020

Genetic Disruption of Serine Biosynthesis is a Key Driver of Macular Telangiectasia Type 2 Etiology and Progression

PurposeMacular telangiectasia type 2 (MacTel) is a rare, heritable and largely untreatable retinal disorder, often comorbid with diabetes. Genetic risk loci subtend retinal vascular calibre, and glycine/serine/threonine metabolism genes. Serine deficiency may contribute to MacTel via neurotoxic deoxysphingolipid production, however, an independent vascular contribution is also suspected. Here we use statistical genetics to dissect the causal mechanisms underpinning this complex disease. O_TBL View this table: org.highwire.dtl.DTLVardef@1c529f3org.highwire.dtl.DTLVardef@1451baforg.highwire.dtl.DTLVardef@1ca0a9org.highwire.dtl.DTLVardef@177efb9org.highwire.dtl.DTLVardef@11b67bf_HPS_FORMAT_FIGEXP M_TBL O_TABLECAPTIONSupplementary Table 8: C_TABLECAPTION C_TBL MethodsWe integrated genetic markers for MacTel, vascular, and metabolic traits, and applied Mendelian randomization, MTAG, and conditional/interaction genome-wide association analysis to discover causal contributors to both disease, and spatial retinal imaging sub-phenotypes. ResultsSerine was a key causal driver of disease occurrence and progression, with a lesser contribution to type 2 diabetes risk. Conversely, glycine, threonine and retinal vascular traits are unlikely to be causal for MacTel. Conditional regression analysis resolved three novel disease loci independent of endogenous serine biosynthetic capacity. By aggregating retinal phenotypes into endophenotypes, we demonstrate that SNPs constituting independent risk loci act via related endophenotypes. DiscussionOur findings will aid in early diagnosis and accurate prognosis of MacTel, and improve prospects for effective therapeutic intervention. Our integrative genetics approach also serves as a useful template for post-GWAS analyses in other disorders.

genetics↗

bioRxiv2017

Integrated transcriptomic, proteomic and epigenomic analysis of Plasmodium vivax salivary-gland sporozoites

Plasmodium vivax is the key obstacle to malaria elimination in Asia and Latin America, largely attributed to its ability to form resilient hypnozoites (sleeper-cells) in the host liver that escape treatment and cause relapsing infections. The decision to form hypnozoites is made early in the liver infection and may already be set in sporozoites prior to invasion. To better understand these early stages of infection, we undertook a comprehensive transcriptomic and histone epigenetic characterization of P. vivax sporozoites. The salivary-gland sporozoite transcriptome is heavily composed of transcripts associated with functions needed for early infection of the vertebrate host and development within hepatocytes. Through comparisons to recently published proteome data for the P. vivax sporozoite, our study finds that although highly transcribed, these transcripts are not detectable as proteins and may be regulated through translational repression; a finding we test for a small subset of transcripts and proteins through immunofluorescent microscopy of sporozoites and liver stages in humanized mice. We identify differential transcription between the sporozoite and published transcriptomes of asexual blood-stages and mixed versus hypnozoite-enriched liver stages. These comparisons point to multiple layers of transcriptional, post-transcriptional and post-translational control that appear active in sporozoites and to a lesser extent hypnozoites, but largely absent in replicating liver schizonts or mixed blood-stages. Common transcripts up-regulated in sporozoites and hypnozoites compared to mixed (i.e., schizont) liver-stages identify genes linked to dormancy/persistence in bacteria, amoebae and plants. We also characterise histone epigenetic modifications in the P. vivax sporozoite and explore their role in regulating transcription. Collectively, these data support the hypothesis that the sporozoite as a tightly programmed stage primed to infect the human host and identifies potential mechanisms for hypnozoite-formation that may be further explored in liver stage models.

microbiology↗