The IMPDH cytoophidium couples metabolism and fetal development in mice

The cytoophidium is an evolutionarily conserved subcellular structure formed by filamentous polymers of metabolic enzymes. In vertebrates, inosine monophosphate dehydrogenase (IMPDH), which catalyses the rate-limiting step in guanosine triphosphate (GTP) biosynthesis, is one of the best-known cytoophidium-forming enzymes. Formation of the cytoophidium has been proposed to alleviate the inhibition of IMPDH, thereby facilitating GTP production to support the rapid proliferation of certain cell types such as lymphocytes, cancer cells and pluripotent stem cells (PSCs). However, past studies lacked appropriate models to elucidate the significance of IMPDH cytoophidium under normal physiological conditions. In this study, we demonstrate that the presence of IMPDH cytoophidium in mouse PSCs correlates with their metabolic status rather than pluripotency. By introducing IMPDH2 Y12C point mutation through genome editing, we established mouse embryonic stem cell (ESC) lines incapable of forming IMPDH polymers and the cytoophidium. Our data indicate an important role of IMPDH cytoophidium in sustaining a positive feedback loop that couples nucleotide biosynthesis with upstream metabolic pathways. Additionally, we find that IMPDH2 Y12C mutation leads to decreased cell proliferation and increased DNA damage in teratomas, as well as impaired embryo development following blastocoel injection. Further analysis shows that IMPDH cytoophidium assembly in mouse embryonic development begins after implantation and gradually increases throughout fetal development. These findings provide insights into the regulation of IMPDH polymerisation in embryogenesis and its significance in coordinating cell metabolism and development.

Detection of Autoantibodies Against the Acetylcholine Receptor, Evaluation of Commercially Available Methodologies: Fixed Cell-Based Assay, Radioimmunoprecipitation Assay and Enzyme-Linked Immunosorbent Assay1

BACKGROUND/OBJECTIVE

Myasthenia Gravis (MG) is an autoimmune disorder characterized by pathogenic autoantibodies (AAbs) targeting nicotinic acetylcholine receptors (AChR), disrupting neuromuscular communication. RadioImmunoPrecipitation Assay (RIPA) is recommended to detect AChR AAbs, but its complexity and radioactive requirements limit widespread use. We compare non-RIPA anti-AChR immunoassays, including Cell-Based Assay (CBA) and two ELISA kits, against the gold standard RIPA.

METHODS/RESULTS

145 samples were included with medical indication for anti-AChR testing. By the RIPA method, 63 were negative (RIPA-Neg < 0.02 nmol/L), 18 were classified as Borderline (≥0.02 -1 nmol/L), and 64 were positive (RIPA-Pos > 1 nmol/L). The competitive ELISA showed poor agreement with RIPA (Kappa = 0.216). The indirect ELISA demonstrated substantial agreement with RIPA (Kappa = 0.652), with ∼76% sensitivity and ∼94% specificity for MG diagnostic. The CBA, where fixed cells expressing clustered AChR were used as substrate, exhibited almost perfect agreement with RIPA (Kappa = 0.984), yielding ∼98% sensitivity and 96% specificity for MG. In addition, a semiquantitative analysis showed a strong correlation between CBA titration, indirect ELISA, and RIPA levels (r = 0.793 and r = 0.789, respectively).

CONCLUSIONS

The CBA displayed excellent analytical performance for MG diagnostic when compared to RIPA, making it a potential replacement for RIPA in clinical laboratories. Some solid-phase assays (such as the indirect ELISA applied here), as well as CBA titration, offer reliable options to estimate anti-AChR AAb levels after confirming positivity by the CBA.∥.

Corrigendum: Nasal Administration of Anti-CD3 Monoclonal Antibody (Foralumab) Reduces Lung Inflammation and Blood Inflammatory Biomarkers in Mild to Moderate COVID-19 Patients: A Pilot Study

[This corrects the article DOI: 10.3389/fimmu.2021.709861.].

Y12C mutation disrupts IMPDH cytoophidia and alters cancer metabolism

Guanosine triphosphate (GTP) is a building block for DNA and RNA, and plays a pivotal role in various cellular functions, serving as an energy source, enzyme cofactor and a key component of signal transduction. The activity of the rate-limiting enzyme in de novo GTP synthesis, inosine monophosphate dehydrogenase (IMPDH), is regulated by nucleotide binding. Recent studies have illuminated that IMPDH octamers can assemble into linear polymers, adding another dimension to its enzymatic regulation. This polymerisation reduces IMPDH's sensitivity to the inhibitory effects of GTP binding, thereby augmenting its activity under conditions with elevated GTP levels. Within cells, IMPDH polymers may cluster to form the distinctive structure known as the cytoophidium, which is postulated to reflect the cellular demand for increased GTP concentrations. Nevertheless, the functional significance of IMPDH polymerisation in in vivo metabolic regulation remains unclear. In this study, we report the widespread presence of IMPDH cytoophidia in various human cancer tissues. Utilising the ABEmax base editor, we introduced a Y12C point mutation into IMPDH2 across multiple cancer cell lines. This mutation disrupts the polymerisation interface of IMPDH and prevents cytoophidium assembly. In some cancer xenografts, the absence of IMPDH polymers led to a downregulation of IMPDH, as well as the glycolytic and pentose phosphate pathways. Furthermore, mutant HeLa-cell-derived xenografts were notably smaller than their wild-type counterparts. Our data suggest that IMPDH polymerisation and cytoophidium assembly could be instrumental in modulating metabolic homeostasis in certain cancers, offering insights into the clinical relevance of IMPDH cytoophidium.