Adducin Regulates Sarcomere Disassembly During Cardiomyocyte Mitosis.

BACKGROUND: Recent interest in understanding cardiomyocyte cell cycle has been driven by potential therapeutic applications in cardiomyopathy. However, despite recent advances, cardiomyocyte mitosis remains a poorly understood process. For example, it is unclear how sarcomeres are disassembled during mitosis to allow the abscission of daughter cardiomyocytes. METHODS: Here, we use a proteomics screen to identify adducin, an actin capping protein previously not studied in cardiomyocytes, as a regulator of sarcomere disassembly. We generated many adeno-associated viruses and cardiomyocyte-specific genetic gain-of-function models to examine the role of adducin in neonatal and adult cardiomyocytes in vitro and in vivo. RESULTS: We identify adducin as a regulator of sarcomere disassembly during mammalian cardiomyocyte mitosis. α/γ-adducins are selectively expressed in neonatal mitotic cardiomyocytes, and their levels decline precipitously thereafter. Cardiomyocyte-specific overexpression of various splice isoforms and phospho-isoforms of α-adducin in identified Thr445/Thr480 phosphorylation of a short isoform of α-adducin as a potent inducer of neonatal cardiomyocyte sarcomere disassembly. Concomitant overexpression of this α-adducin variant along with γ-adducin resulted in stabilization of the adducin complex and persistent sarcomere disassembly in adult mice, which is mediated by interaction with α-actinin. CONCLUSIONS: These results highlight an important mechanism for coordinating cytoskeletal morphological changes during cardiomyocyte mitosis.

Cell-Cycle-Specific Autoencoding Improves Cluster Analysis of Cycling Cardiomyocytes.

BACKGROUND: Our previous analyses of cardiomyocyte single-nucleus RNA sequencing (snRNAseq) data from the hearts of fetal pigs and pigs that underwent apical resection surgery on postnatal day (P) 1 (ARP1), myocardial infarction (MI) surgery on P28 (MIP28), both ARP1 and MIP28 (ARP1MIP28), or controls (no surgical procedure or CTL) identified 10 cardiomyocyte subpopulations (clusters), one of which appeared to be primed to proliferate in response to MI. However, the clusters composed of primarily proliferating cardiomyocytes still contained noncycling cells, and we were unable to distinguish between cardiomyocytes in different phases of the cell cycle. Here, we improved the precision of our assessments by conducting similar analyses with snRNAseq data for only the 1646 genes included under the Gene Ontology term "cell cycle." METHODS: Two cardiac snRNAseq datasets, one from mice (GEO dataset number GSE130699) and one from pigs (GEO dataset number GSE185289), were evaluated via our cell-cycle-specific analytical pipeline. Cycling cells were identified via the co-expression of 5 proliferation markers (AURKB, MKI67, INCENP, CDCA8, and BIRC5). RESULTS: The cell-cycle-specific autoencoder (CSA) algorithm identified 7 cardiomyocyte clusters in mouse hearts (mCM1 and mCM3-mCM8), including one prominent cluster of cycling cardiomyocytes in animals that underwent MI or Sham surgery on P1. Five cardiomyocyte clusters (pCM1, pCM3-pCM6) were identified in pig hearts, 2 of which (pCM1 and pCM4) displayed evidence of cell cycle activity; pCM4 was found primarily in hearts from fetal pigs, while pCM1 comprised a small proportion of cardiomyocytes in both fetal hearts and hearts from ARP1MIP28 pigs during the 2 weeks after MI induction, but was nearly undetectable in all other experimental groups and at all other time points. Furthermore, pseudotime trajectory analysis of snRNAseq data from fetal pig cardiomyocytes identified a pathway that began at pCM3, passed through pCM2, and ended at pCM1, whereas pCM3 was enriched for the expression of a cell cycle activator that regulates the G1/S phase transition (cyclin D2), pCM2 was enriched for an S-phase regulator (CCNE2), and pCM1 was enriched for the expression of a gene that regulates the G2M phase transition and mitosis (cyclin B2). We also identified 4 transcription factors (E2F8, FOXM1, GLI3, and RAD51) that were more abundantly expressed in cardiomyocytes from regenerative mouse hearts than from nonregenerative mouse hearts, from the hearts of fetal pigs than from CTL pig hearts, and from ARP1MIP28 pig hearts than from MIP28 pig hearts during the 2 weeks after MI induction. CONCLUSIONS: The CSA algorithm improved the precision of our assessments of cell cycle activity in cardiomyocyte subpopulations and enabled us to identify a trajectory across 3 clusters that appeared to track the onset and progression of cell cycle activity in cardiomyocytes from fetal pigs.

Hypoxia-induced stabilization of HIF2A promotes cardiomyocyte proliferation by attenuating DNA damage.

Introduction: Gradual exposure to a chronic hypoxic environment leads to cardiomyocyte proliferation and improved cardiac function in mouse models through a reduction in oxidative DNA damage. However, the upstream transcriptional events that link chronic hypoxia to DNA damage have remained obscure. Aim: We sought to determine whether hypoxia signaling mediated by the hypoxia-inducible factor 1 or 2 (HIF1A or HIF2A) underlies the proliferation phenotype that is induced by chronic hypoxia. Methods and Results: We used genetic loss-of-function models using cardiomyocyte-specific HIF1A and HIF2A gene deletions in chronic hypoxia. We additionally characterized a cardiomyocyte-specific HIF2A overexpression mouse model in normoxia during aging and upon injury. We performed transcriptional profiling with RNA-sequencing on cardiac tissue, from which we verified candidates at the protein level. We find that HIF2A - rather than HIF1A - mediates hypoxia-induced cardiomyocyte proliferation. Ectopic, oxygen-insensitive HIF2A expression in cardiomyocytes reveals the cell-autonomous role of HIF2A in cardiomyocyte proliferation. HIF2A overexpression in cardiomyocytes elicits cardiac regeneration and improvement in systolic function after myocardial infarction in adult mice. RNA-sequencing reveals that ectopic HIF2A expression attenuates DNA damage pathways, which was confirmed with immunoblot and immunofluorescence. Conclusion: Our study provides mechanistic insights about a new approach to induce cardiomyocyte renewal and mitigate cardiac injury in the adult mammalian heart. In light of evidence that DNA damage accrues in cardiomyocytes with aging, these findings may help to usher in a new therapeutic approach to overcome such age-related changes and achieve regeneration.

Promoting cardiomyocyte proliferation for myocardial regeneration in large mammals.

From molecular and cellular perspectives, heart failure is caused by the loss of cardiomyocytes-the fundamental contractile units of the heart. Because mammalian cardiomyocytes exit the cell cycle shortly after birth, the cardiomyocyte damage induced by myocardial infarction (MI) typically leads to dilatation of the left ventricle (LV) and often progresses to heart failure. However, recent findings indicate that the hearts of neonatal pigs completely regenerated the cardiomyocytes that were lost to MI when the injury occurred on postnatal day 1 (P1). This recovery was accompanied by increases in the expression of markers for cell-cycle activity in cardiomyocytes. These results suggest that the repair process was driven by cardiomyocyte proliferation. This review summarizes findings from recent studies that found evidence of cardiomyocyte proliferation in 1) the uninjured hearts of newborn pigs on P1, 2) neonatal pig hearts after myocardial injury on P1, and 3) the hearts of pigs that underwent apical resection surgery (AR) on P1 followed by MI on postnatal day 28 (P28). Analyses of cardiomyocyte single-nucleus RNA sequencing data collected from the hearts of animals in these three experimental groups, their corresponding control groups, and fetal pigs suggested that although the check-point regulators and other molecules that direct cardiomyocyte cell-cycle progression and proliferation in fetal, newborn, and postnatal pigs were identical, the mechanisms that activated cardiomyocyte proliferation in response to injury may differ from those that regulate cardiomyocyte proliferation during development.

Networks that Govern Cardiomyocyte Proliferation to Facilitate Repair of the Injured Mammalian Heart.

Cardiovascular diseases are the number one cause of death worldwide and in the United States (US). Cardiovascular diseases frequently progress to end-stage heart failure, and curative therapies are extremely limited. Intense interest has focused on deciphering the cascades and networks that govern cardiomyocyte proliferation and regeneration of the injured heart. For example, studies have shown that lower organisms such as the adult newt and adult zebrafish have the capacity to completely regenerate their injured heart with restoration of function. Similarly, the neonatal mouse and pig are also able to completely regenerate injured myocardium due to cardiomyocyte proliferation from preexisting cardiomyocytes. Using these animal models and transcriptome analyses, efforts have focused on the definition of factors and signaling pathways that can reactivate and induce cardiomyocyte proliferation in the adult mammalian injured heart. These studies and discoveries have the potential to define novel therapies to promote cardiomyocyte proliferation and repair of the injured, mammalian heart.

Metabolic Control of Cardiomyocyte Cell Cycle.

Current therapies for heart failure aim to prevent the deleterious remodeling that occurs after MI injury, but currently no therapies are available to replace lost cardiomyocytes. Several organisms now being studied are capable of regenerating their myocardium by the proliferation of existing cardiomyocytes. In this review, we summarize the main metabolic pathways of the mammalian heart and how modulation of these metabolic pathways through genetic and pharmacological approaches influences cardiomyocyte proliferation and heart regeneration.

A latent cardiomyocyte regeneration potential in human heart disease.

Cardiomyocytes in the adult human heart show a regenerative capacity, with an annual renewal rate around 0.5%. Whether this regenerative capacity of human cardiomyocytes is employed in heart failure has been controversial. Using retrospective 14C birth dating we analyzed cardiomyocyte renewal in patients with end-stage heart failure. We show that cardiomyocyte generation is minimal in end-stage heart failure patients at rates 18-50 times lower compared to the healthy heart. However, patients receiving left ventricle support device therapy, who showed significant functional and structural cardiac improvement, had a >6-fold increase in cardiomyocyte renewal relative to the healthy heart. Our findings reveal a substantial cardiomyocyte regeneration potential in human heart disease, which could be exploited therapeutically.

FDA approved drugs with antiviral activity against SARS-CoV-2: From structure-based repurposing to host-specific mechanisms.

The continuing heavy toll of the COVID-19 pandemic necessitates development of therapeutic options. We adopted structure-based drug repurposing to screen FDA-approved drugs for inhibitory effects against main protease enzyme (Mpro) substrate-binding pocket of SARS-CoV-2 for non-covalent and covalent binding. Top candidates were screened against infectious SARS-CoV-2 in a cell-based viral replication assay. Promising candidates included atovaquone, mebendazole, ouabain, dronedarone, and entacapone, although atovaquone and mebendazole were the only two candidates with IC50s that fall within their therapeutic plasma concentration. Additionally, we performed Mpro assays on the top hits, which demonstrated inhibition of Mpro by dronedarone (IC50 18 µM), mebendazole (IC50 19 µM) and entacapone (IC50 9 µM). Atovaquone showed only modest Mpro inhibition, and thus we explored other potential mechanisms. Although atovaquone is Dihydroorotate dehydrogenase (DHODH) inhibitor, we did not observe inhibition of DHODH at the respective SARS-CoV-2 IC50. Metabolomic profiling of atovaquone treated cells showed dysregulation of purine metabolism pathway metabolite, where ecto-5'-nucleotidase (NT5E) was downregulated by atovaquone at concentrations equivalent to its antiviral IC50. Atovaquone and mebendazole are promising candidates with SARS-CoV-2 antiviral activity. While mebendazole does appear to target Mpro, atovaquone may inhibit SARS-CoV-2 viral replication by targeting host purine metabolism.

Case Report: Muscle Wasting during Severe Sustained Hypoxia in Two Professional Mountaineers.

PURPOSE: Chronic exposure to hypoxia can induce muscle wasting in unaccustomed individuals. Detailed assessment of the effects of hypoxia on muscle tissue adaptation in elite mountaineers has not been performed. This study aims to assess muscle volume after exposure to normobaric hypoxia. METHODS: Two professional mountaineers (A and B) participated in a 35-d intervention of graded normobaric hypoxia with the aim of 14 d exposure to 8% oxygen corresponding to 7112-m altitude. Volume of the shank, thigh, and hip muscles was assessed by magnetic resonance imaging pre- and postintervention. Dietary intake and physical activity were monitored throughout the study from food images and accelerometry analysis, together with blood analysis and anthropometric measurements. RESULTS: Hypoxia reduced total leg muscle volume by 3.3% ± 6.0% in A and by 9.4% ± 7.3% in B. A lost 288 g and B 642 g of muscle mass, whereas dietary intake only declined by ~23% in the last intervention week. Arterial oxygen saturation declined from 95% and 86% to 77% and 72% in A and B, respectively. In hypoxia, participants could not maintain their physical activity levels. Notably, muscle loss varied substantially across muscle groups amounting to 5.4% ± 3.0%, 8.3% ± 5.2%, and 4.1% ± 8.6% for hip, thigh, and shank muscles, respectively. CONCLUSIONS: Our results indicate that hypoxia and resultant reductions in physical activity and caloric intake lead to substantial loss of muscle mass that was accentuated in proximal muscle as opposed to distal muscles. Surprisingly, thigh muscle wasting during this intervention is comparable with that observed during strict 56-d bed rest.

The Use of Mebendazole in COVID-19 Patients: An Observational Retrospective Single Center Study.

Background: An in-silico screen identified mebendazole with potential antiviral activity that could be a repurposed drug against SARS-CoV-2. Mebendazole is a well-tolerated and cheap antihelminthic agent that is readily available worldwide and thus could be a therapeutic tool in the fight against COVID-19. Methods: This is an observational retrospective study of PCR-confirmed COVID-19 patients who received mebendazole with the intention-to-treat. The study included an inpatient cohort (157 inpatients) and an outpatient cohort (185 outpatients). Of the 157 inpatients and 185 outpatients, 68 (43.3%) and 94 (50.8%) received mebendazole, respectively. Patients who presented within the same timeframe but did not receive mebendazole were used as controls. Patients received standard-of-care treatment including remdesivir, dexamethasone, and anticoagulants as deemed necessary by the treating physician. The following clinical outcomes were evaluated: for the inpatient cohort, length of stay (LOS) at the hospital, need for ventilation (combined invasive and noninvasive), and mortality; for the outpatient cohort, time to symptom resolution, need for hospitalization, and mortality. Results: For the inpatient cohort, the median age did not differ between the treatment and control groups; 62 (56, 67) vs. 62 (56, 68), P, and there was a comparable proportion of males in both groups; 43 (63%) vs. 55 (62%), P=0.85. The hospital LOS was 3.5 days shorter in the treatment group compared to the control group (P < 0.001). There were fewer patients who required invasive or noninvasive ventilation in the treatment group, 2 (2.9%) vs. 7 (7.9%), and the mortality rate is lower in the treatment group, 3 (4.4%) vs. 8 (9.0%), though the differences did not reach statistical significance. For the outpatient cohort, the median age was lower in the treatment group compared with the control group; 40 (34, 48) vs. 48 (41, 54), P < 0.001. There was a comparable proportion of males between both groups; 50 (53%) vs. 52 (57%), P=0.59. Patients in the treatment group were 3.3 days closer to symptom resolution (P < 0.001). There were numerically fewer patients requiring hospitalization in the treatment group compared with the control group, 3 (3.2%) vs. 6 (6.6%), though this did not reach statistical significance (P=0.33). Conclusion: In this retrospective observational study, the use of mebendazole in COVID-19 patients was associated with shorter hospitalizations in the inpatient cohort and shorter durations of symptom resolution in the outpatient cohort. The findings from this small observational study are hypothesis-generating and preclude drawing conclusions about clinical efficacy. Further studies are needed to examine the role of mebendazole in the treatment of COVID-19 patients.

Atovaquone for treatment of COVID-19: A prospective randomized, double-blind, placebo-controlled clinical trial.

Background: An in silico screen was performed to identify FDA approved drugs that inhibit SARS-CoV-2 main protease (Mpro), followed by in vitro viral replication assays, and in vivo pharmacokinetic studies in mice. These studies identified atovaquone as a promising candidate for inhibiting viral replication. Methods: A 2-center, randomized, double-blind, placebo-controlled trial was performed among patients hospitalized with COVID-19 infection. Enrolled patients were randomized 2:1 to atovaquone 1500 mg BID versus matched placebo. Patients received standard of care treatment including remdesivir, dexamethasone, or convalescent plasma as deemed necessary by the treating team. Saliva was collected at baseline and twice per day for up to 10 days for RNA extraction for SARS-CoV-2 viral load measurement by quantitative reverse-transcriptase PCR. The primary outcome was the between group difference in log-transformed viral load (copies/mL) using a generalized linear mixed-effect models of repeated measures from all samples. Results: Of the 61 patients enrolled; 41 received atovaquone and 19 received placebo. Overall, the population was predominately male (63%) and Hispanic (70%), with a mean age of 51 years, enrolled a mean of 5 days from symptom onset. The log10 viral load was 5.25 copies/mL vs. 4.79 copies/mL at baseline in the atovaquone vs. placebo group. Change in viral load did not differ over time between the atovaquone plus standard of care arm versus the placebo plus standard of care arm. Pharmacokinetic (PK) studies of atovaquone plasma concentration demonstrated a wide variation in atovaquone levels, with an inverse correlation between BMI and atovaquone levels, (Rho -0.45, p = 0.02). In post hoc analysis, an inverse correlation was observed between atovaquone levels and viral load (Rho -0.54, p = 0.005). Conclusion: In this prospective, randomized, placebo-controlled trial, atovaquone did not demonstrate evidence of enhanced SARS-CoV-2 viral clearance compared with placebo. However, based on the observed inverse correlation between atovaquone levels and viral load, additional PK-guided studies may be warranted to examine the antiviral effect of atovaquone in COVID-19 patients.

Parasitological, Molecular, and Epidemiological Investigation of Cryptosporidium Infection Among Cattle and Buffalo Calves From Assiut Governorate, Upper Egypt: Current Status and Zoonotic Implications.

Details about the epidemiological patterns and real contributions of different reservoir animals in maintaining the transmission cycle of Cryptosporidium spp. in Upper Egypt remain lacking. This study was designed to investigate the occurrence of Cryptosporidium spp. in cattle and buffalo (n = 608) from Upper Egypt. The parasite for the resulting positive samples by fecal examination was molecularly identified using nested PCR targeting the small subunit rRNA. Moreover, several explanatory variables, including animals' age, sex, condition, seasonal variations, were examined to describe the epidemiological pattern of the disease. Interestingly, the fecal examination revealed that 33.55% (204/608) of the animals under study were infected with Cryptosporidium, including 38.27% among cattle and 28.16% among buffalo. The parasite was molecularly identified using nested PCR, and their amplicons were identified in almost all fecal samples using microscopy (202/204). According to age as an individual variable factor, the infection rates of Cryptosporidium spp. in cattle calves with ages of <1, 1-3, and >3 months were 39.13, 34.04, and 54.54%, respectively. Meanwhile, in buffalo calves, the occurrence rates were 28.57, 27.27, and 29.41%, respectively. Regarding sex, female cattle calves were more susceptible to Cryptosporidium infection (51.28%) than males (26.19%) (p < 0.05), whereas male buffalo calves had a higher infection rate (32.25%) than females (25%). According to seasonal variations, the infection rates of Cryptosporidium spp. in cattle calves during spring, summer, autumn, and winter were 42.11, 30.43, 30, and 52.63%, respectively. In contrast, lower infection rates of 30, 21.42, 23.52, and 35% were reported in buffalo calves during spring, summer, autumn, and winter, respectively. The rate of infection was 45.16% in diarrheic cattle calves and 15.78% in non-diarrheic ones (p < 0.05). Meanwhile, the infection rate was 33.96% in diarrheic buffalo calves and 11.11% in non-diarrheic ones (p < 0.05). This study reported a higher occurrence of Cryptosporidium infection among the animals under study and revealed that buffalos and cattle can contribute to maintaining the transmission cycle of this zoonotic parasite in Upper Egypt.

Serum vitamin D level in healthy individuals versus patients with symptomatic and asymptomatic oral lichen planus.

The aetiology of oral lichen planus (OLP) is multifactorial, having variable triggers. A role for vitamin D related to the immune system has been established. Vitamin D modulating effect is on the adaptive and innate immune responses. Our study aimed to compare serum levels of vitamin D in patients having different clinical symptoms of OLP (symptomatic or asymptomatic) with healthy individuals. Also, in this study, for further evaluation, the expression level of interleukin-17A and interleukin-6 (IL-17A and IL-6) was evaluated because the presence of active vitamin D reduces the expression of these pro-inflammatory factors. This study was included three groups with 30 volunteers in each. The first group included asymptomatic oral lichen planus patients (reticular or plaque-like lesions). The second group consisted of symptomatic oral lichen planus patients (atrophic or bullous-erosive lesions). In contrast, the third group consisted of healthy control subjects. The serum 25-hydroxyvitamin D was measured between the three groups and then correlated with clinical manifestation of oral lichen planus, either symptomatic or non-symptomatic. The Real-Time PCR technique was used to evaluate the expression of IL-17A and IL-6. Patients with symptomatic OLP (second group) had statistically significantly lower Vitamin D levels than asymptomatic OLP patients (first group). Healthy Controls (third group) exhibited statistically significantly higher vitamin D levels than OLP groups. The results of IL-17A and IL-6 genes expression showed that the presence of vitamin D had a statistically significant effect on reducing the expression of these two pro-inflammatory cytokines among symptomatic and asymptomatic OLP patients. Also, the results showed that there was a statistically significant difference between OLP patients (group I and II) and the control group (group III). In general, the current study results showed that lack of vitamin D had an important role in initiating or increasing the OLP's severity.

Turning back the clock: A concise viewpoint of cardiomyocyte cell cycle activation for myocardial regeneration and repair.

Patients with acute myocardial infarction (MI) could progress to end-stage congestive heart failure, which is one of the most significant problems in public health. From the molecular and cellular perspective, heart failure often results from the loss of cardiomyocytes-the fundamental contractile unit of the heart-and the damage caused by myocardial injury in adult mammals cannot be repaired, in part because mammalian cardiomyocytes undergo cell-cycle arrest during the early perinatal period. However, recent studies in the hearts of neonatal small and large mammals suggest that the onset of cardiomyocyte cell-cycle arrest can be reversed, which may lead to the development of entirely new strategies for the treatment of heart failure. In this Viewpoint, we summarize these and other provocative findings about the cellular and molecular mechanisms that regulate cardiomyocyte proliferation and how they may be targeted to turn back the clock of cardiomyocyte cell-cycle arrest and improve recovery from cardiac injury and disease.

Compartmentalized metabolism supports midgestation mammalian development.

Mammalian embryogenesis requires rapid growth and proper metabolic regulation1. Midgestation features increasing oxygen and nutrient availability concomitant with fetal organ development2,3. Understanding how metabolism supports development requires approaches to observe metabolism directly in model organisms in utero. Here we used isotope tracing and metabolomics to identify evolving metabolic programmes in the placenta and embryo during midgestation in mice. These tissues differ metabolically throughout midgestation, but we pinpointed gestational days (GD) 10.5-11.5 as a transition period for both placenta and embryo. Isotope tracing revealed differences in carbohydrate metabolism between the tissues and rapid glucose-dependent purine synthesis, especially in the embryo. Glucose's contribution to the tricarboxylic acid (TCA) cycle rises throughout midgestation in the embryo but not in the placenta. By GD12.5, compartmentalized metabolic programmes are apparent within the embryo, including different nutrient contributions to the TCA cycle in different organs. To contextualize developmental anomalies associated with Mendelian metabolic defects, we analysed mice deficient in LIPT1, the enzyme that activates 2-ketoacid dehydrogenases related to the TCA cycle4,5. LIPT1 deficiency suppresses TCA cycle metabolism during the GD10.5-GD11.5 transition, perturbs brain, heart and erythrocyte development and leads to embryonic demise by GD11.5. These data document individualized metabolic programmes in developing organs in utero.

First report of rare persistence granulomatous extra respiratory Rhinoscleroma of oral pathology.

Rhinoscleroma (RS) is a rare chronic specific progressive granulomatous disease of the upper airway and affect the nasal cavity, larynx, nasopharynx and may spread to the lower respiratory tract. Extra-respiratory involvement has rarely been described. A case report of extra-respiratory RS with oral manifestation in Egyptian female patient has been presented as a tumour extruded from mucosal lining of upper lip. She was living in crowded conditions with malnutrition and poor hygiene. On the first look, the lesion appeared to be carcinoma without any indication of infectious disease, and then patient was prepared for incisional biopsy. Upon clinicopathological evaluation, the diagnosis was made as RS in the granulomatous stage based on the presence of dense plasma cell infiltration with Mikulicz cells and Russell bodies. Long term oral ciprofloxacin 500 mg twice/day was started as a single treatment. By the end of six weeks antibiotic therapy, the large granulomatous mass reached the cicatricial stage, became very stiff fibrotic mass with sclerotic scar, markedly indurated & significantly decreased in size. This case shows the significant of through clinical examination and lab investigations to achieve correct diagnosis.

NBS1-CtIP-mediated DNA end resection suppresses cGAS binding to micronuclei.

Cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) is activated in cells with defective DNA damage repair and signaling (DDR) factors, but a direct role for DDR factors in regulating cGAS activation in response to micronuclear DNA is still poorly understood. Here, we provide novel evidence that Nijmegen breakage syndrome 1 (NBS1) protein, a well-studied DNA double-strand break (DSB) sensor-in coordination with Ataxia Telangiectasia Mutated (ATM), a protein kinase, and Carboxy-terminal binding protein 1 interacting protein (CtIP), a DNA end resection factor-functions as an upstream regulator that prevents cGAS from binding micronuclear DNA. When NBS1 binds to micronuclear DNA via its fork-head-associated domain, it recruits CtIP and ATM via its N- and C-terminal domains, respectively. Subsequently, ATM stabilizes NBS1's interaction with micronuclear DNA, and CtIP converts DSB ends into single-strand DNA ends; these two key events prevent cGAS from binding micronuclear DNA. Additionally, by using a cGAS tripartite system, we show that cells lacking NBS1 not only recruit cGAS to a major fraction of micronuclear DNA but also activate cGAS in response to these micronuclear DNA. Collectively, our results underscore how NBS1 and its binding partners prevent cGAS from binding micronuclear DNA, in addition to their classical functions in DDR signaling.