Biology subjects

Shearer, J.

Publications and source records attributed to Shearer, J..

5 recordsLinked to original sources

bioRxiv2026

Birth by Cesarean Section Remodels Neonatal Brain Barriers and Associated Immune and Metabolic Pathways in Mice

Delivery mode shapes early-life physiology through multiple pathways, including stress and hormonal signalling, neonatal oxygenation, and exposure to maternal microbes. Cesarean section (CS) bypasses several of these processes and has been associated with altered immune maturation and neurodevelopmental outcomes in humans and animal models. Given that CS is known to disrupt gut barrier integrity and that gut and brain barriers operate as a coordinated network, we investigated whether CS affects early postnatal brain barriers. Using a mouse model, we compared CS-delivered pups to vaginally born (VB) controls at postnatal days 8-9. Brain barrier permeability and structure were assessed using tracer extravasation and vascular and tight junction analyses, choroid plexus immune populations were profiled, and metabolomics was performed in cortex and plasma. The blood-brain barrier in the medial prefrontal cortex was mostly preserved. In contrast, the blood-cerebrospinal fluid barrier (BCSFB) exhibited structural alterations in vascular and epithelial tight junction compartments. These changes were accompanied by immune remodelling, including expansion of antigen-presenting border-associated macrophages and reduced parenchymal microglia density. CS delivery increased brain tracer accumulation, consistent with altered barrier function during this developmental window. Metabolomic analyses revealed lower levels of key brain metabolites, including N-acetylaspartate, a marker of neuronal metabolic state. Together, these findings demonstrate that CS delivery induces early alterations in brain barrier function, BCSFB structure, the immune landscape, and metabolic profiles in mice. This identifies delivery mode as a key perinatal variable shaping neonatal brain physiology and establishes a framework for dissecting how birth context may influence long-term neurodevelopmental trajectories. HIGHLIGHTSO_LICesarean section (CS) reveals the neonatal BCSFB as a vulnerable interface shaped by birth mode C_LIO_LICS increases brain tracer accumulation despite largely preserved BBB structural markers at the mPFC C_LIO_LICS induces region-specific vascular, epithelial, and immune remodeling in the choroid plexus C_LIO_LICesarean birth increases the proportion of antigen-presenting choroid plexus macrophages C_LIO_LICS shifts mPFC metabolic profiles, including reduced N-acetylaspartate and malate C_LI

neuroscience↗

bioRxiv2020

A novel synthetic peptide provides neuroprotection and rescues rat cortical neurons from anesthetic-induced cell death and modulation of growth and synaptic assembly

Anesthetics, although necessary for many modern procedures, exert neurotoxic effects in various experimental models; the underlying mechanisms, however, remain unknown. In the absence of this information, any in vivo mitigation strategy would be challenging. To help address these gaps, we sought to determine whether preserving mitochondrial network integrity with a non-toxic, short-life synthetic peptide, P110, could protect cortical neurons against both inhalational and intravenous anesthetic-induced neurotoxicity. This study provides the first direct comparative account of three key general anesthetics (desflurane, propofol, and ketamine) under identical conditions and demonstrates their impact on cellular viability, neurite outgrowth, and synaptic network assembly on neonatal rat cortical neurons. Further, we discovered that the inhibition of Fis1 receptor-mediated fission reverses anesthetic-induced aberrations in an agent-specific manner. Our data thus underscore the importance of a reductionist approach, offering unique opportunities to explore non-toxic, mitochondria-based therapeutic tools for mitigating anesthetic-induced harm to the developing brain.

neuroscience↗

bioRxiv2020

Structure-based modelling and dynamics of MurM, a Streptococcus pneumoniae penicillin resistance determinant that functions at the cytoplasmic membrane interface

MurM is an aminoacyl-tRNA dependant ligase that aminoacylates the Lipid II peptidoglycan precursor, in the human pathogen Streptococcus pneumoniae. MurM is required for the generation of branched peptidoglycan precursors enabling indirect cross-links in the peptidoglycan and is found to be essential for penicillin resistance. In this study we have solved the X-ray crystal structure of Staphylococcus aureus FemX, an isofunctional homologue of MurM, and used this as a template to generate a homology model of MurM. Using this model, we perform molecular docking and molecular dynamics to examine the interaction of the protein with the phospholipid bilayer and the membrane embedded Lipid II substrate of MurM. Our model suggests that MurM is associated with the major membrane phospholipid cardiolipin, and we confirm this with experimental evidence that the activity of MurM is enhanced by this phospholipid and inhibited by its direct precursor phosphatidylglycerol. This suggests that the spatial association of pneumococcal membrane phospholipids and their impact on MurM activity may be a critical to the final architecture of the peptidoglycan and the expression of clinically relevant penicillin resistance in this pathogen.

biochemistry↗

bioRxiv2020

Molecular Dynamics Simulations of Bacterial Outer Membrane Lipid Extraction: Adequate Sampling?

The outer membrane of Gram-negative bacteria is almost exclusively composed of lipopolysaccharide in its outer leaflet, whereas the inner leaflet contains a mixture of phospholipids. Lipopolysaccharide diffuses at least an order of magnitude slower than phospholipids, which can cause issues for molecular dynamics simulations in terms of adequate sampling. Here we test a number of simulation protocols for their ability to achieve convergence with reasonable computational effort using the MARTINI coarse-grained force-field. This is tested in the context both of potential of mean force (PMF) calculations for lipid extraction from membranes, and of lateral mixing within the membrane phase. We find that decoupling the cations that cross-link the lipopolysaccharide headgroups from the extracted lipid during PMF calculations is the best approach to achieve convergence comparable to that for phospholipid extraction. We also show that lateral lipopolysaccharide mixing/sorting is very slow and not readily addressable even with Hamiltonian replica exchange. We discuss why more sorting may be unrealistic for the short (microseconds) timescales we simulate and provide an outlook for future studies of lipopolysaccharide-containing membranes.

biophysics↗

bioRxiv2018

The outer membrane proteins OmpA, FhuA, OmpF, EstA, BtuB and OmpX have unique lipopolysaccharide fingerprints.

The outer membrane of Gram-negative bacteria has a highly complex asymmetrical architecture, containing a mixture of phospholipids in the inner leaflet and in the outer leaflet they contain almost exclusively lipopolysaccharide (LPS) molecules. In E. coli, the outer membrane contains a wide range proteins with a beta barrel architecture, that vary in size from the smallest having eight strands to larger barrels composed of twenty-two strands. Here we report coarse-grain molecular dynamics simulations of six proteins from the E. coli outer membrane OmpA, OmpX, BtuB, FhuA, OmpF and EstA in a range of membrane environments, which are representative of the in vivo for different strains of E. coli. We show that each protein has a unique pattern of interaction with the surrounding membrane, which is influenced by the composition of the protein, the level of LPS in the outer leaflet and the differing mobilities of the lipids in the two leaflets of the membrane. Overall we present analyses from over 200 microseconds of simulation for each protein.\n\nAuthor summaryWe present data from over 200 microseconds of coarse-grain simulations that show the complexities of protein-lipid interactions within the outer membranes of Gram-negative bacteria. We show that the slow movement of lipolysaccharide molecules necessitate simulations of over 30 microsecond duration to achieve converged properties such as protein tilt angle. Each of the six proteins studied here shows a unique pattern of interactions with the outer membrane and thus constitute a fingerprint or signature.

biophysics↗