Biology subjects

McMillan, D.

Publications and source records attributed to McMillan, D..

5 recordsLinked to original sources

bioRxiv2025

Chronic Cervical Midline Contusion in Rats Disrupts Aerobic, Muscular, and Cardiovascular Function

Cardiovascular dysfunction significantly contributes to morbidity and mortality following cervical spinal cord injury (SCI). Unfortunately, only a limited number of preclinical models have been developed for investigating cardiovascular dysfunction following cervical SCI. Furthermore, the broader consequences of cervical SCI on aerobic capacity and muscle endurance during physiological stress testing also remains understudied preclinically. Therefore, in this study we assessed potential deficits across multiple physiological systems in a rat model of cervical SCI using a battery of stress tests. Female Sprague-Dawley rats (n = 20) received either a C8 midline contusion (cSCI) or laminectomy alone as a control (LAM). Exercise stress testing was conducted to evaluate cardiorespiratory fitness and recovery using a metabolic treadmill, or forelimb fitness using the isometric pull task. Orthostatic stress testing and pharmacological stress testing were also performed to more directly challenge the cardiovascular system. Our findings demonstrate a decline in aerobic fitness in cSCI rats, as evidenced by dysregulated excess post-exercise oxygen consumption. cSCI rats also exhibited impaired muscle endurance compared to LAM. During orthostatic stress testing, 70% of cSCI rats experienced an approximately 25 mmHg decrease in systolic blood pressure and 20 mmHg decrease in diastolic blood pressure, in addition to modest but significant decreases in heart rate, myocardial contractility index, stroke volume index, and cardiac output index. During dobutamine infusion, cardiac output index and stroke volume index were significantly reduced following cSCI compared to LAM. Overall, these stress testing results suggest that preclinical cervical SCI in rats can lead to, and therefore model, clinically relevant impairments in cardiopulmonary exercise performance, muscle endurance, and cardiovascular function.

physiology↗

bioRxiv2025

Molecular basis for multidrug efflux by an anaerobic RND transporter

Bacteria can resist antibiotics and toxic substances within demanding ecological settings, such as low oxygen, extreme acid, and during nutrient starvation. MdtEF, a proton motive force-driven efflux pump from the resistance-nodulation-cell division (RND) superfamily, is upregulated in these conditions but its molecular mechanism is unknown. Here, we report cryo-electron microscopy structures of Escherichia coli multidrug transporter MdtF within native-lipid nanodiscs, including a single-point mutant with an altered multidrug phenotype and associated substrate-bound form. We reveal that drug binding domain and channel conformational plasticity likely governs promiscuous substrate specificity, analogous to its closely related, constitutively expressed counterpart, AcrB. Whereas we discover distinct transmembrane state transitions within MdtF, which create a more engaged proton relay network, altered drug transport allostery and an acid-responsive increase in efflux efficiency. Physiologically, this provides means of xenobiotic and metabolite disposal within remodelled cell membranes that presage encounters with acid stresses, as endured in the gastrointestinal tract.

biochemistry↗

bioRxiv2025

The characteristic of epithelial-specific phenotypes and immunosuppressive microenvironment in the context of tumour budding in colorectal cancer

BackgroundTumour budding (TB), defined as a small cluster of up to four cells at the invasive front of the tumour, is a well-established independent and robust prognostic biomarker in colorectal cancer (CRC). This is strongly associated with adverse clinicopathological features and poor survival outcomes. Despite its clinical relevance, the precise underlying mechanism responsible for TB phenomenon remains unclear. MethodsMulti-omic approaches from bulk, regional GeoMx and Spatial Molecular Imager (SMI) RNA were used to identify the underlying mechanism of TB and its possible correlation with tumour microenvironment (TME) in CRC tissue. The results were validated using immunohistochemistry (IHC) and multiplex immunofluorescence (mIF) staining. ResultsPatients with high TB experience worse outcomes and associate with adverse clinical factors across two independent CRC cohorts. Bulk and regional RNA expression analyses reveal that tumours with high TB are significantly enriched for TNF- and TGF-{beta} signatures in both cohorts. Single cell CosMx SMI analysis confirmed TB cells exhibit higher expression of these signatures than adjacent invasive edge tumour cells. Elevated cyclinD1 expression was also observed within TB, and high cyclinD1 levels tend to experience poorer CRC prognosis. Furthermore, regional bulk RNA expression within the non-tumour (PanCK-) invasive edge areas demonstrated that tumours exhibiting high TB revealed the significantly differential expressions of immune-related genes (e.g. CD3, NKG7, IL6, CXCR6, CD47, IFNAR1 and VSIR). Single cell CosMx SMI analysis revealed that cancer-associated fibroblasts (CAFs) were physically the closest cells to TB cells. This spatial proximity was confirmed at the protein level using mIF, where the distance from TB to CD68+ macrophages predicted significantly poorer CRC outcomes. ConclusionThis multi-omic study confirms the prognostic significance of TB in CRC patients across two independent cohorts. Our findings highlight that TNF- and TGF-{beta} signalling play a crucial role in budding cells development by regulating cyclinD1. Furthermore, the transcriptomic analysis reveals an immunosuppressive niche characterised by reduced immune activity and close spatial interactions with CAFs and macrophages Ultimately, this study provides valuable insight into TBs underlying mechanism and its complex interactions within the TME. This could provide a foundation for developing targeted therapeutic strategies in CRC.

cancer biology↗

bioRxiv2024

Extensive longevity and DNA virus-driven adaptation in nearctic Myotis bats

Summary ParagraphThe genus Myotis is one of the largest clades of bats, and exhibits some of the most extreme variation in lifespans among mammals alongside unique adaptations to viral tolerance and immune defense1-3. To study the evolution of these phenotypes we generated cell lines and near-complete genome assemblies for eight closely related Myotis species. Using genome-wide screens of positive selection, analyses of structural variation, and functional experiments in primary cells, we identify patterns of adaptation contributing to longevity, cancer resistance, and viral interactions. We demonstrate distinct modes of adaptation to DNA and RNA viruses compared to all other mammals, with bats exhibiting genome-wide overrepresentation of positive selection for DNA virus-interacting proteins and elevated rates of copy number variation for RNA virus-interacting proteins. Characterization of Myotis-specific duplications of the key immune factor protein kinase R (PKR) reveals multiple ancient segregating trans-species copy number polymorphisms. We show that the recurrent evolution of longevity seen in Myotis is associated with positive selection in cancer pathways, and demonstrate a unique response to DNA damage in primary cells of the long-lived M. lucifugus. Together, our results suggest that bats remarkable longevity and immunity are linked through pleiotropic adaptations to viruses and aging-related disease.

genomics↗

bioRxiv2022

Spatially Resolved Transcriptomics Deconvolutes Histological Prognostic Subgroups in Patients with Colorectal Cancer and Synchronous Liver Metastases

BackgroundPatients demonstrating strong immune responses to primary colorectal cancer (CRC) have a survival benefit following surgery, while those with predominantly stromal microenvironments do poorly. Biomarkers to identify patients with colorectal cancer liver metastases (CRLM) who have good prognosis following surgery for oligometastatic disease remain elusive. The aim of this study was to determine the practical application of a simple histological assessment of immune cell infiltration and stromal content in predicting outcome following synchronous resection of primary CRC and CRLM, and to interrogate the underlying functional biology that drives disease progression. MethodsPatients undergoing synchronous resection of primary CRC and CRLM underwent detailed histological assessment, panel genomic and bulk transcriptomic assessment, immunohistochemistry (IHC) and GeoMx Spatial Transcriptomics (ST) analysis. Integration with genomic features, pathway enrichment analysis and immune deconvolution were performed. ResultsHigh-immune metastases were associated with improved cancer specific survival (HR, 0.36, P=0.01). Bulk transcriptomic analysis was confounded by stromal content but ST demonstrated that the invasive edge of the metastases of long-term survivors was characterized by adaptive immune cell populations enriched for Type II Interferon signalling (NES=-2.05 P.Adj<0.005) and MHC-Class II Antigen Presentation (NES=-2.09 P.Adj<0.005). In contrast, patients with poor prognosis demonstrated increased abundance of regulatory T-cells and neutrophils with enrichment of Notch (NES=2.2 P.Adj=0.022) and TGF-{beta} (NES=2.2 P.Adj=0.02) signalling pathways at the metastatic tumor centre. ConclusionsHistological assessment stratifies outcome in patients undergoing synchronous resection of CRLM. ST analysis reveals significant intra-tumoral and inter-lesional heterogeneity with underlying transcriptomic programmes identified in driving each phenotype. TRANSLATIONAL RELEVANCEThe current study demonstrates that accurate histological assessment of immune cell infiltration and stromal content can define survival in patients following resection of oligometastatic liver disease when presenting synchronously with primary colorectal cancer. A spatial transcriptomic approach has demonstrated heterogeneity between patients, between matched lesions in the same patient and within individual lesions. Patients with high immune infiltrates at the invasive margin demonstrated lymphocytic infiltration and associated upregulated adaptive immune pathways in long term survivors. In specimens with low immune infiltrate at the tumor edge a significant reduction in survival was observed, this was determined by upregulated immunosuppressive pathways and a predominance of innate immune cells surrounding metastases. Spatial transcriptomics can be used to examine drivers of metastatic progression in CRC and identifies patients with reactive and suppressed immune microenvironments. Application across a larger cohort will build the cartography of CRLM, while in future, studies may assess application of this technology to pre and post treatment biopsy samples with the aim of predicting individual therapeutic responses. The current study has highlighted discrepancies between bulk and ST derived data whilst demonstrating accuracy of deconvoluted transcriptome to determine immune profiling. Now that ST strategies are becoming more achievable at scale, this has implications for the interpretation of the bulk transcriptomic signatures both of primary and metastatic CRC.

cancer biology↗