Biology subjects

McCullagh, J.

Publications and source records attributed to McCullagh, J..

3 recordsLinked to original sources

bioRxiv2023

Dopamine D2 receptor upregulation in dorsal striatum in the LRRK2-R1441C rat model of early Parkinson's disease revealed by in vivo PET imaging

LRRK2 mutations are the most common cause of dominantly inherited Parkinsons disease (PD). Here, we conducted PET imaging in aged transgenic rats carrying human pathogenic LRRK2 R1441C or G2019S mutations with [18F]FDOPA and dopamine D2/3 receptor ligand [18F]fallypride. We interrogate presynaptic integrity and postsynaptic dopamine receptor availability, and compared these to non-transgenic rats. LRRK2 mutant rats displayed similar [18F]FDOPA uptake to non-transgenic animals, consistent with intact dopamine synthesis in striatal axons. However, LRRK2-R1441C rats demonstrated greater binding of [18F]fallypride than LRRK2-G2019S or non-transgenic controls, exhibiting regionally selective binding increase in the dorsal striatum. Immunocytochemical labelling post-mortem confirmed a greater density of D2 receptors in LRRK2-R1441C than other genotypes restricted to the dorsal striatum, consistent with upregulation of D2-receptors as a compensatory response to the greater dopamine release deficit observed in this genotype. These results show that [18F]fallypride PET imaging is sensitive to dysregulation of dopamine signalling in the LRRK2-R1441C rat, detecting upregulation of D2 receptors that parallels observations in early human sporadic PD. Future studies of candidate therapies could exploit this non-invasive approach to assess treatment efficacy.

neuroscience↗

bioRxiv2023

Analysis of the influence of peptidoglycan turnover and recycling on host-pathogen interaction in the Gram-positive pathogen Staphylococcus aureus

During peptidoglycan recycling (PR) bacteria can recover extracellular fragments of peptidoglycan (PGN) liberated by peptidoglycan turnover (PT) during cell growth and division, and reuse them in cell wall biosynthesis or central carbon metabolism. In Gram-negative bacteria, PR has been well studied, and functions in the induction of resistance to certain classes of antibiotics, and in host-pathogen interaction. However, while Gram-negative cell envelope architecture allows for highly efficient PR, Gram-positive bacteria, which lack an outer cell membrane and are instead enclosed by a glycopolymer layer, can shed large quantities of PGN-derived material to the external environment during growth. Nonetheless, the occurrence of PR was recently demonstrated in several Gram-positive bacteria, including the Gram-positive bacterial pathogen Staphylococcus aureus, and its potential adaptive functions are largely unexplored. Given the known roles of PR in Gram-negative bacteria, and that Gram-positive bacteria include several important human pathogens, we asked what role PR may play during Gram-positive pathogen-host interaction. Usingthe model insect host Drosophila melanogaster, we demonstrate that S. aureus mutants impaired in extracellular PGN hydrolysis ({Delta}atl) and PGN fragment uptake ({Delta}murP) show differential virulence compared to their wild-type counterpart. This was linked to increased activation of the D. melanogaster Toll-cascade by spent supernatant from the {Delta}atl mutant. Thus, we propose that S. aureus, and potentially other Gram-positive bacteria, may use extracellular PGN degradation during PT to simultaneously process PGN fragments for recycling and for immune evasion, while recovery and/or metabolism of peptidoglycan fragments during PR may play more subtle roles in determining virulence. Author summaryPGN is a key component of the bacterial cell wall, forming a stress-bearing sacculus surrounding the cell and providing cell shape. During growth and division, the sacculus is dynamically degraded and remodelled to ensure daughter cell separation, resulting in PT. PGN fragments released during PT can be recovered and reutilised by the cell during PR. In Gram-negative pathogens, PR is linked to antibiotic resistance, virulence and modulation of host immune recognition. In Gram-positive bacteria, PR was only recently observed. Here, we explore the roles of PT and PR in host-pathogen interaction in S. aureus, a Gram-positive pathogen of significant clinical relevance. Disruption of PT in S. aureus affected host-pathogen interaction through altering host recognition of shed PGN fragments and PR through modulation of PGN fragment recovery. This improves our understanding of the biology of this important pathogen and may aid development of novel therapeutic approaches to treat S. aureus infections.

microbiology↗

bioRxiv2022

LARP1 regulates metabolism and mTORC1 activity in cancer

The protein mammalian target of rapamycin (mTOR) is a master regulator of cell homeostasis. Although mTOR is aberrantly overactivated in 70% ovarian cancers, mTOR cascade inhibitors (such as those blocking the kinase activity of mTOR itself or upstream kinases PI3K/AKT) have demonstrated disappointing activity in ovarian cancer clinical trials. These findings indicate that, despite its pivotal role in normal cells, hyperactivated mTOR does not act as a master regulator of metabolism in this cancer context. Surprisingly, we have identified that the RNA binding protein LARP1, a known phospho-target of mTORC1 and activator of ribosomal biogenesis, is responsible for metabolic reprogramming in mTOR-dysregulated cancers. LARP1 post-transcriptionally regulates the expression of several hundred rate-limiting enzymes involved in multiple aspects of metabolism, including glycolysis and oxidative phosphorylation. Through this mechanism LARP1 sustains ATP production and mTORC1 localisation on the lysosome, thereby activating cell proliferation despite the scarcity of extracellular nutrients. Our findings show that, by sustaining global cellular metabolism in response to growth factor signalling, LARP1 has a central post-transcriptional role in controlling mTORC1 localisation and driving cancer progression, a key cancer hallmark.

cancer biology↗