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.

Serum Myostatin and Follistatin Levels in Patients With Dermatomyositis and Polymyositis.

BACKGROUND: Myostatin is a protein in the TGF-ß family that negatively regulates muscle mass, and follistatin is a myostatin antagonist. OBJECTIVE: The aim of this study was to measure serum levels of myostatin and follistatin in idiopathic inflammatory myopathy patients and correlate these levels with muscle strength, fatigue, functional capacity, damage, and serum levels of muscle enzymes. METHODS: This was a multicenter cross-sectional study including 50 patients (34 dermatomyositis and 16 polymyositis [PM]) and 52 healthy individuals (control group [CG]). The disease status was evaluated according to the International Myositis Assessment & Clinical Studies. Fatigue was rated according to the Fatigue Severity Scale, and body composition was measured using dual-energy x-ray emission densitometry. Myostatin and follistatin were measured using enzyme-linked immunosorbent assays. RESULTS: Mean age was 50.9 ± 14.0 years, and mean disease duration was 89.2 ± 80.9 months. There were no differences in levels of myostatin (14.15 ± 9.65 vs. 10.97 ± 6.77 ng/mL; p = 0.131) or follistatin (0.53 ± 0.71 vs. 0.49 ± 0.60 ng/mL; p = 0.968) between patients and the CG. However, myostatin levels were higher in PM than CG (16.9 ± 12.1 vs. 11.0 ± 6.8 ng/mL; p = 0.036). There was no difference in serum myostatin among patients with and without low lean mass. Patients not treated with corticosteroids had higher serum levels of myostatin than the CG. There was a weak negative correlation between follistatin and Manual Muscle Testing and a Subset of Eight Muscles and a weak positive correlation between follistatin and Healthy Assessment Questionnaire. CONCLUSIONS: Serum levels of myostatin and follistatin did not differ between dermatomyositis and PM patients and control subjects. The assessment of serum levels of myostatin and follistatin in idiopathic inflammatory myopathy patients seems not to be helpful in clinical practice.

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.].

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.

BACKGROUND: Immune hyperactivity is an important contributing factor to the morbidity and mortality of COVID-19 infection. Nasal administration of anti-CD3 monoclonal antibody downregulates hyperactive immune responses in animal models of autoimmunity through its immunomodulatory properties. We performed a randomized pilot study of fully-human nasal anti-CD3 (Foralumab) in patients with mild to moderate COVID-19 to determine if its immunomodulatory properties had ameliorating effects on disease. METHODS: Thirty-nine outpatients with mild to moderate COVID-19 were recruited at Santa Casa de Misericordia de Santos in Sao Paulo State, Brazil. Patients were randomized to three cohorts: 1) Control, no Foralumab (n=16); 2) Nasal Foralumab (100ug/day) given for 10 consecutive days with 6 mg dexamethasone given on days 1-3 (n=11); and 3) Nasal Foralumab alone (100ug/day) given for 10 consecutive days (n=12). Patients continued standard of care medication. RESULTS: We observed reduction of serum IL-6 and C-reactive protein in Foralumab alone vs. untreated or Foralumab/Dexa treated patients. More rapid clearance of lung infiltrates as measured by chest CT was observed in Foralumab and Foralumab/Dexa treated subjects vs. those that did not receive Foralumab. Foralumab treatment was well-tolerated with no severe adverse events. CONCLUSIONS: This pilot study suggests that nasal Foralumab is well tolerated and may be of benefit in treatment of immune hyperactivity and lung involvement in COVID-19 disease and that further studies are warranted.

IMP dehydrogenase rod/ring structures in acral melanomas.

Acral lentiginous melanoma (ALM) is a rare subtype of melanoma with aggressive behavior. IMPDH enzyme, involved in de novo GTP biosynthesis, has been reported to assemble into large filamentary structures called rods/rings (RR) or cytoophidium (cellular snakes). RR assembly induces a hyperactive state in IMPDH, usually to supply a high demand for GTP nucleotides, such as in highly proliferative cells. We investigate whether aggressive melanoma tumor cells present IMPDH-based RR structures. Forty-five ALM paraffin-embedded tissue samples and 59 melanocytic nevi were probed with anti-IMPDH2 antibody. Both the rod- and ring-shaped RR could be observed, with higher frequency in ALM. ROC curve analyzing the proportions of RR-positive cells in ALM versus nevi yielded a 0.88 AUC. Using the cutoff of 5.5% RR-positive cells, there was a sensitivity of 80% and specificity of 85% for ALM diagnosis. In ALM, 36 (80%) showed RR frequency above the cutoff, being classified as RR-positive, compared with only 9 (15%) of the nevi (p < .001). Histopathology showed that 71% of the RR-positive specimens presented Breslow thickness > 4.0mm, compared with only 29% in the RR-low/negative (p = .039). We propose that screening for RR structures in biopsy specimens may be a valuable tool helping differentiate ALM from nevi and accessing tumor malignancy.

Interfilament interaction between IMPDH and CTPS cytoophidia.

Inosine monophosphate dehydrogenase (IMPDH) and cytidine triphosphate synthase (CTPS) are two metabolic enzymes that perform rate-limiting steps in the de novo synthesis of purine and pyrimidine nucleotides, respectively. It has been shown that IMPDH and CTPS can comprise a filamentous macrostructure termed the cytoophidium, which may play a role in regulation of their catalytic activity. Although these two proteins may colocalise in the same cytoophidium, how they associate with one another is still elusive. As reported herein, we established a model HeLa cell line coexpressing OFP-tagged IMPDH2 and GFP-tagged CTPS1 and recorded the assembly, disassembly and movement of the cytoophidium in live cells. Moreover, by using super-resolution confocal imaging, we demonstrate how IMPDH- and CTPS-based filaments are aligned or intertwined in the mixed cytoophidium. Collectively, our findings provide a panorama of cytoophidium dynamics and suggest that IMPDH and CTPS cytoophidia may coordinate by interfilament interaction.

Anti-rods/rings: a human model of drug-induced autoantibody generation.

In recent years, autoantibodies targeting subcellular structures described as the rods and rings pattern in HEp-2 ANA have been presented as a unique case of autoantibody generation. These rod and ring structures (RR) are at least partially composed of inosine monophosphate dehydrogenase type 2 (IMPDH2), and their formation can be induced in vitro by several small-molecule inhibitors, including some IMPDH2 inhibitors. Autoantibodies targeting these relatively unknown structures have been almost exclusively observed in hepatitis C virus (HCV) patients who have undergone treatment with pegylated interferon-α/ribavirin (IFN/RBV) combination therapy. To date, anti-RR antibodies have not been found in treatment-naïve HCV patients or in patients from any other disease groups, with few reported exceptions. Here, we describe recent advances in characterizing the RR structure and the strong association between anti-RR antibody response and HCV patients treated with IFN/RBV, detailing why anti-RR can be considered a human model of drug-induced autoantibody generation.