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Dr Sumeet Mahajan
Tau, amyloid and neuronal biology

Professor in Molecular Biophotonics & Imaging
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Current theme Projects:
Deep tissue theranostic imaging
Funded by a recent Transformative Healthcare 2050 award from the EPSRC an interdisciplinary team of Southampton based scientists and researchers are developing new fibre lasers and novel methodologies that will allow early detection, imaging and …
Recent publications:
Human Tau aggregates are permissive to Protein Synthesis Dependent Memory in Drosophila Tauopathy models
Human Tau aggregates are permissive to Protein Synthesis Dependent Memory in Drosophila Tauopathy models
Tauopathies including Alzheimer's disease, are characterized by progressive cognitive decline, neurodegeneration and intraneuronal aggregates comprised largely of the axonal protein Tau. It has been unclear whether cognitive deficits are consequent of aggregate accumulation which compromise neuronal health and eventually lead to neurodegeneration. We use the Drosophila Tauopathy model and mixed sex populations to reveal an adult onset pan-neuronal Tau accumulation-dependent decline in learning efficacy and a specific defect in Protein Synthesis Dependent Memory (PSD-M), but not in its Protein Synthesis Independent variant. We demonstrate that these neuroplasticity defects are reversible upon suppression of new transgenic human Tau expression, but surprisingly correlate with an increase in Tau aggregates. Inhibition of aggregate formation via acute oral administration of Methylene Blue results in re-emergence of deficient memory in animals with suppressed hTau expression. Significantly, aggregate inhibition results in PSD-M deficits in hTau-expressing animals, which present elevated aggregates and normal memory if untreated with Methylene Blue. Moreover, Methylene Blue-dependent hTau aggregate suppression within adult mushroom body neurons, also resulted in emergence of memory deficits. Therefore, deficient PSD-M upon human Tau expression in the Drosophila CNS is not consequent of toxicity and neuronal loss because it is reversible. Furthermore, PSD-M deficits do not result from aggregate accumulation, which appears permissive, if not protective of processes underlying this memory variant.Intraneuronal Tau aggregate accumulation has been proposed to underlie the cognitive decline and eventual neurotoxicity that characterizes the neurodegenerative dementias known as Tauopathies. However, we show in three experimental settings that Tau aggregates in the Drosophila CNS do not impair, but rather appear to facilitate processes underlying Protein Synthesis Dependent memory within affected neurons.
Persistent homology analysis distinguishes pathological bone microstructure in non-linear microscopy images
Persistent homology analysis distinguishes pathological bone microstructure in non-linear microscopy images
We present a topological method for the detection and quantification of bone microstructure from non-linear microscopy images. Specifically, we analyse second harmonic generation (SHG) and two photon excited autofluorescence (TPaF) images of bone tissue which capture the distribution of matrix (fibrillar collagen) structure and autofluorescent molecules, respectively. Using persistent homology statistics with a signed Euclidean distance transform filtration on binary patches of images, we are able to quantify the number, size, distribution, and crowding of holes within and across samples imaged at the microscale. We apply our methodology to a previously characterized murine model of skeletal pathology whereby vascular endothelial growth factor expression was deleted in osteocalcin-expressing cells (OcnVEGFKO) presenting increased cortical porosity, compared to wild type (WT) littermate controls. We show significant differences in topological statistics between the OcnVEGFKO and WT groups and, when classifying the males, or females respectively, into OcnVEGFKO or WT groups, we obtain high prediction accuracies of 98.7% (74.2%) and 77.8% (65.8%) respectively for SHG (TPaF) images. The persistence statistics that we use are fully interpretable, can highlight regions of abnormality within an image and identify features at different spatial scales.
Multi-Excitation Raman Spectroscopy for Label-Free, Strain-Level Characterization of Bacterial Pathogens in Artificial Sputum Media
Multi-Excitation Raman Spectroscopy for Label-Free, Strain-Level Characterization of Bacterial Pathogens in Artificial Sputum Media
The current methods for diagnosis of acute and chronic infections are complex and skill-intensive. For complex clinical biofilm infections, it can take days from collecting and processing a patient's sample to achieving a result. These aspects place a significant burden on healthcare providers, delay treatment, and can lead to adverse patient outcomes. We report the development and application of a novel multi-excitation Raman spectroscopy-based methodology for the label-free and non-invasive detection of microbial pathogens that can be used with unprocessed clinical samples directly and provide rapid data to inform diagnosis by a medical professional. The method relies on the differential excitation of non-resonant and resonant molecular components in bacterial cells to enhance the molecular finger-printing capability to obtain strain-level distinction in bacterial species. Here, we use this strategy to detect and characterize the respiratory pathogens and as typical infectious agents associated with cystic fibrosis. Planktonic specimens were analyzed both in isolation and in artificial sputum media. The resonance Raman components, excited at different wavelengths, were characterized as carotenoids and porphyrins. By combining the more informative multi-excitation Raman spectra with multivariate analysis (support vector machine) the accuracy was found to be 99.75% for both species (across all strains), including 100% accuracy for drug-sensitive and drug-resistant . The results demonstrate that our methodology based on multi-excitation Raman spectroscopy can underpin the development of a powerful platform for the rapid and reagentless detection of clinical pathogens to support diagnosis by a medical expert, in this case relevant to cystic fibrosis. Such a platform could provide translatable diagnostic solutions in a variety of disease areas and also be utilized for the rapid detection of anti-microbial resistance.
Antibiotic-Loaded Polymersomes for Clearance of Intracellular
Antibiotic-Loaded Polymersomes for Clearance of Intracellular
Melioidosis caused by the facultative intracellular pathogen is difficult to treat due to poor intracellular bioavailability of antibiotics and antibiotic resistance. In the absence of novel compounds, polymersome (PM) encapsulation may increase the efficacy of existing antibiotics and reduce antibiotic resistance by promoting targeted, infection-specific intracellular uptake. In this study, we developed PMs composed of widely available poly(ethylene oxide)-polycaprolactone block copolymers and demonstrated their delivery to intracellular infection using multispectral imaging flow cytometry (IFC) and coherent anti-Stokes Raman scattering microscopy. Antibiotics were tightly sequestered in PMs and did not inhibit the growth of free-living . However, on uptake of antibiotic-loaded PMs by infected macrophages, IFC demonstrated PM colocalization with intracellular and a significant inhibition of their growth. We conclude that PMs are a viable approach for the targeted antibiotic treatment of persistent intracellular infection.
Conformational fingerprinting of tau variants and strains by Raman spectroscopy
Conformational fingerprinting of tau variants and strains by Raman spectroscopy
Tauopathies are a group of disorders in which the deposition of abnormally folded tau protein accompanies neurodegeneration. The development of methods for detection and classification of pathological changes in protein conformation are desirable for understanding the factors that influence the structural polymorphism of aggregates in tauopathies. We have previously demonstrated the utility of Raman spectroscopy for the characterization and discrimination of different protein aggregates, including tau, based on their unique conformational signatures. Building on this, in the present study, we assess the utility of Raman spectroscopy for characterizing and distinguishing different conformers of the same protein which in the case of tau are unique tau strains generated . We now investigate the impact of aggregation environment, cofactors, post-translational modification and primary sequence on the Raman fingerprint of tau fibrils. Using quantitative conformational fingerprinting and multivariate statistical analysis, we found that the aggregation of tau in different buffer conditions resulted in the formation of distinct fibril strains. Unique spectral markers were identified for tau fibrils generated using heparin or RNA cofactors, as well as for phosphorylated tau. We also determined that the primary sequence of the tau monomer influenced the conformational signature of the resulting tau fibril, including 2N4R, 0N3R, K18 and P301S tau variants. These results highlight the conformational polymorphism of tau fibrils, which is reflected in the wide range of associated neurological disorders. Furthermore, the analyses presented in this study provide a benchmark for the Raman spectroscopic characterization of tau strains, which may shed light on how the aggregation environment, cofactors and post-translational modifications influence tau conformation in future studies.
Contact:
Institute of Life Sciences
University of Southampton
Highfield Campus
Southampton
SO17 1BJ