Biology subjects

Campbell, S. G.

Publications and source records attributed to Campbell, S. G..

7 recordsLinked to original sources

bioRxiv2026

STMN2 protein depletion via translation deficits and stress granules and its compensation in ALS

STMN2 is an abundant neurospecific protein dysregulated in neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS). We previously reported that cellular stress can lead to STMN2 loss due to TDP-43 nuclear condensation. Here, using human and murine neuronal cell models, multiple pharmacological tools, single-molecule in situ analysis of mRNA localisation and translation, and longitudinal analysis of neuronal fitness/survival, we establish TDP-43-independent mechanisms of STMN2 depletion linked to stress response. We find that human STMN2 protein is extremely labile under acute high-magnitude stress. Early in stress, STMN2 is suppressed via activated proteasomal degradation, phosphorylation and translational repression by stress granules, independently of TDP-43 loss of function in splicing. We further show that STMN2 protein level is highly sensitive to chronic translation deficits, such as those elicited by prolonged low-grade stress. Finally, we demonstrate that STMN2 mRNA is upregulated in non-TDP ALS such as ALS-FUS, which may compensate for translation/stress granule defects in these disease subtypes. Consistent with the compensation hypothesis, STMN2 mRNA is also upregulated in the relatively spared (cortex), but not severely affected (spinal cord), CNS regions in ALS-TDP. In conclusion, our study implicates two common hallmarks of neurodegeneration, translation impairment and abnormal stress granules, in STMN2 depletion and reports an RNA-level compensation that fails in neurons with TDP-43 pathology. Our study supports the development of stress response targeting therapies in ALS with and without TDP-43 pathology.

cell biology↗

bioRxiv2025

eIF2Bα subcellular localisation - a potential link between translation initiation and stress granule formation?

The eukaryotic initiation factor 2B (eIF2B) complex is a guanine nucleotide exchange factor (GEF) that regulates translation initiation and is central to the integrated stress response (ISR). eIF2B exists as a decamer composed of catalytic ({gamma}, {varepsilon}) and regulatory (, {beta}, {delta}) subunits, which localise to cytoplasmic foci termed eIF2B bodies. While eIF2B bodies exhibit dynamic changes during stress, the role of individual subunits in the formation of bodies and localisation of subunits to additional cytoplasmic foci remains unclear. Here, we investigate the contribution of eIF2B to eIF2B body integrity and investigate alterations in eIF2B localisation during cellular stress. Using immunocytochemistry in neural cell lines, we demonstrate that all endogenous eIF2B subunits form cytoplasmic foci. Whilst eIF2B co-localises with the eIF2B{gamma} catalytic subunit in large bodies (>1 m{superscript 2}) it also forms smaller foci independently. We find cell type differences in the formation of foci containing eIF2B and eIF2B{varepsilon} subunits, in the absence of changes in protein expression. Stress induction significantly increased eIF2B and eIF2B{varepsilon} foci without altering protein expression, suggesting cell-type specific and ISR-driven reorganisation. siRNA-mediated knockdown of eIF2B disrupted large eIF2B body formation, an effect reversed by ISRIB, which stabilizes eIF2B tetramers, highlighting eIF2Bs essential role in decamer assembly. Furthermore, we reveal that eIF2B, and to a lesser extent eIF2B{varepsilon}, localize to SGs under ER and oxidative stress, with colocalisation dependent on eIF2 phosphorylation. Cells harbouring an EIF2B1 p.Leu99Pro mutation, which impairs ISR sensing, exhibited reduced SG formation and abolished eIF2B-SG colocalization. These findings suggest that eIF2B not only stabilizes eIF2B bodies but also mediates ISR signalling and SG dynamics via a mechanism reliant on phosphorylated eIF2. Collectively, our study uncovers a dual role for eIF2B in maintaining eIF2B complex integrity and regulating stress-responsive mRNA triage, providing new insights into translational control and disease mechanisms linked to eIF2B dysfunction.

cell biology↗

bioRxiv2025

Desmoplakin loss leads to PKC-dependent insertion of series sarcomeres and contractile dysfunction in cardiomyocytes

BackgroundMutations in DSP, which encodes the protein desmoplakin, lead to cardiomyopathy with unusually high penetrance. Clinical features include ventricular tachyarrhythmias, fibro-fatty infiltration of both ventricles, and ultimately dilated cardiomyopathy. While some data have been gathered to explain the electrophysiological and contractile consequences of desmoplakin cardiomyopathy, a comprehensive mechanism linking DSP mutations to ventricular dilation and heart failure remains elusive. MethodsWe use iPSC-derived engineered heart tissue (EHT) bearing a functional desmoplakin haploinsufficiency to model the heart failure phenotype that occurs in desmoplakin cardiomyopathy. Functional haploinsufficiency is secondary to a missense mutation, R451G, that results in proteolytic degradation of desmoplakin with no detectable protein. We complement functional data obtained in tissue-engineered constructs with cell biology assays in 2D cardiomyocytes to glean insights into the mechanism and mechanobiology of desmoplakin cardiomyopathy. ResultsEngineered heart tissues harboring a desmoplakin insufficiency recapitulate a patient phenotype notable for hypocontractility and ventricular dilation. Surprisingly, DSP-mutant tissues exhibited a shortened resting sarcomere length that was dependent on protein kinase C activity. Concurrently, mechanical load on -catenin was increased, suggesting a mechanism by which desmosomal insufficiency redistributes force to adherens junctions. Excessive loading on adherens junctions may act as a stimulus for avid insertion of series sarcomeres, shortening the length per sarcomere, and resulting in a contractile deficit. PKC inhibition rescues shortened sarcomere length in DSP- mutant tissues, suggesting that it could be a target for future molecular therapies. ConclusionsOur study uncovers a novel mechanism underlying systolic dysfunction in desmoplakin cardiomyopathy. We not only recapitulate the disease phenotype, but we identify sarcomere length regulation through altered force transmission at the intercalated disc as a previously-unrecognized mechanism.

physiology↗

bioRxiv2024

GRASPS: a simple-to-operate translatome technology reveals omics-hidden disease-associated pathways in TDP-43-related amyotrophic lateral sclerosis

Transcriptomes and translatomes measure genome-wide levels of total and ribosome-associated RNAs. A few hundred translatomes were reported over >250,000 transcriptomes highlighting the challenges of identifying translating RNAs. Here, we used a human isogenic inducible model of TDP-43-linked amyotrophic lateral sclerosis, which exhibits altered expression of thousands of transcripts, as a paradigm for the direct comparison of whole-cell, cytoplasmic and translating RNAs, showing broad uncoupling and poor correlation between disease-altered transcripts. Moreover, based on precipitation of endogenous ribosomes, we developed GRASPS (Genome-wide RNA Analysis of Stalled Protein Synthesis), a simple-to-operate translatome technology. Remarkably, GRASPS identified three times more differentially-expressed transcripts with higher fold changes and statistical significance, providing unprecedented opportunities for data modeling at stringent filtering and discovery of previously omics-missed disease-relevant pathways, which functionally map on dense gene regulatory networks of protein-protein interactions. Based on its simplicity and robustness, GRASPS is widely applicable across disciplines in the biotechnologies and biomedical sciences.

molecular biology↗

bioRxiv2022

Optimisation of immunocytochemistry methodology for the detection of endogenous eIF2B localised foci

The multisubunit eukaryotic initiation factor 2B (eIF2B), a guanine nucleotide exchange factor (GEF) for eIF2, is an essential regulator of translation initiation. Activation of the cellular integrated stress response (ISR) by factors such as endoplasmic reticulum stress leads to phosphorylation of eIF2 and inhibition of eIF2B GEF activity. Cytoplasmic bodies containing eIF2B subunits, termed eIF2B bodies, have been shown to alter in subunit composition and fluorescence recovery after photobleaching activity in response to the ISR. Analysis of the subunit composition of endogenous eIF2B bodies is dependent on accurate detection of each protein in a cellular context via immunocytochemistry (ICC). We describe bioinformatic techniques to optimize the ICC detection of eIF2B foci in U373 cells. The screening of commercially available primary antibodies against predicted epitopes enhanced measurements of the number, size and fluorescence intensity of eIF2B bodies. A consistent and reproducible ICC analysis of endogenous eIF2B bodies will aid characterisation of eIF2B bodies during the ISR or under disease conditions. SummaryeIF2B is a housekeeping protein and localised eIF2B foci, named eIF2B bodies, can be detected through immunocytochemistry. Here, we discuss the use of immunoinformatics to optimise eIF2B localisation detection.

cell biology↗

bioRxiv2022

In vitro engineering of the lung alveolus

Therapeutic lung regeneration is predicated upon successful reconstitution of lung alveoli, the functional units of gas exchange. Here, we identify requisite multimodal cues that are critical to reconstructing the alveolar epithelium and alveoli in lung scaffolds. Alveolar reconstruction in vitro is divided into several distinct phases. In the first phase, endothelial cells coordinate with fibroblasts and select exogenous factors to promote alveolar scaffold population with surfactant-secreting alveolar epithelial type 2 cells (AEC2s). After formation of organized epithelial alveolar-like structures, subsequent withdrawal of Wnt and FGF agonism synergizes with tidal-level mechanical strain to induce differentiation of AEC2s to squamous type 1 AECs (AEC1s) in cultured alveoli, in situ. These results outline a rational strategy to engineer an alveolus of AEC2s and AEC1s contained within epithelial-mesenchymal-endothelial units, and reveal the critical interplay amongst biochemical, cellular, and mechanical niche cues within the reconstituting alveolus.

bioengineering↗

bioRxiv2022

Dysregulation of stress-induced translational control by Porphyromonas gingivalis in host cells

Periodontitis, a chronic inflammatory gum disease, is caused in part by the periodontopathogen Porphyromonas gingivalis. Infection triggers activation of host inflammatory responses which induce stresses such as oxidative stress. Under such conditions, cells can activate the Integrated Stress Response (ISR), a signalling cascade which functions to determine cellular fate, by either downregulating protein synthesis and initiating a stress-response gene expression program, or if stress cannot be overcome, initiating programmed cell death. Recent studies have implicated the ISR signalling in both host antimicrobial defences and within the pathomechanism of certain microbes. In this study, we investigated how P. gingivalis infection alters translation attenuation during oxidative stress-induced activation of the ISR pathway in oral epithelial cells. P. gingivalis infection alone did not result in ISR activation. In contrast, infection coupled with stress led to differential stress granule formation and composition, along with dysregulation of the microtubule network. Infection also heightened stress-induced translational repression, a response which could not be rescued by ISRIB, a potent ISR inhibitor. Heightened translational repression during stress was observed with both P. gingivalis conditioned media and outer membrane vesicles, implicating the role of a secretory factor, probably proteases known as gingipains, in this exacerbated translational repression. The effects of gingipain inhibitors and gingipains-deficient P. gingivalis mutants further confirmed these pathogen-specific proteases as the effector. Gingipains are known to degrade the mammalian target of rapamycin (mTOR) and these studies implicate the gingipain-mTOR axis as the effector of host translational dysregulation during stress.

microbiology↗