Gene Knockout Research Articles

Complete inhibition of liver acetyl-CoA carboxylase activity is required to exacerbate liver tumorigenesis in mice treated with diethylnitrosamine

Abstract Background The metabolic pathway of de novo lipogenesis (DNL) is upregulated in fatty liver disease and liver cancer. Inhibitors of DNL are in development for the treatment of these disorders; however, our previous study showed that blocking DNL unexpectedly exacerbated liver tumorigenesis when liver acetyl-CoA carboxylase (ACC) 1 and 2 enzymes were deleted in mice treated with diethylnitrosamine (DEN) and fed high fat diet. Herein, we used 3 new approaches including ACC1 vs. ACC2 isotype-selective inhibition, delaying ACC inhibition until after carcinogen treatment, and feeding mice normal chow diet to better understand the impact of ACC inhibition on liver tumorigenesis. Methods Six genotypes of female C57BL/6J mice with floxed ACC1 and/or ACC2 alleles were injected with DEN at 2 weeks of age followed by liver-specific knockout of ACC genes at 9 weeks. Mice were fed a normal chow diet and evaluated at 52 weeks for liver tumours. Results Compared to the wildtype control group, no genotype decreased tumour multiplicity or burden; however, mice completely lacking liver ACC1 and ACC2 had > 5-fold increases in liver tumour multiplicity and burden. Conclusion ACC inhibition exacerbated DEN-induced liver tumorigenesis only when both ACC isotypes were completely inhibited. The pro-tumour phenotype of ACC inhibition was strongly reproducible irrespective of chow or high fat feeding, and irrespective of ACC inhibition prior to or after DEN treatment. Retaining partial ACC activity at either isotype prevented tumour exacerbation in mice at risk for developing liver tumours.

A single upstream mutation of whiB7 underlies amikacin and clarithromycin resistance in Mycobacterium abscessus

Abstract Aims We aimed to investigate the molecular mechanisms underlying the survival of Mycobacterium abscessus when faced with antibiotic combination therapy. By conducting evolution experiments and whole genome sequencing (WGS), we sought to identify genetic variants associated with stress response mechanisms, with a particular focus on drug survival and resistance. Methods and results We conducted evolution experiments on M. abscessus, exposing the bacteria to a combination therapy of amikacin and rifabutin. Genetic mutations associated with increased antibiotic survival and altered susceptibility were subsequently identified by WGS. We focused on mutations that contribute to stress response mechanisms and tolerance. Of particular interest was a novel frameshift mutation in MAB_3509c, a gene of unknown function within the upstream open reading frame of whiB7. A MAB_3509c knockout mutant was constructed, and expression of downstream drug resistance genes was assessed by RT-qPCR. Mutation of MAB_3509c results in increased RNA levels of whiB7 and downstream stress response genes such as eis2, which is responsible for aminoglycoside resistance. Conclusion Our findings demonstrate the importance of whiB7 in the adaptive stress response in M. abscessus. Moreover, our results highlight the complexity of M. abscessus adapting to drug stress and underscore the need for further research.

Construction, molecular characterization, and safety assessment of purB mutant of Salmonella Gallinarum

This study involves the development and molecular characterization of the isogenic markerless knockout mutant SG ΔpurB, a genetically engineered live attenuated strain aimed at controlling Salmonella Gallinarum (SG) infection in poultry. The mutant was generated by deleting the purB gene using λ-Red recombination technology, impairing adenylosuccinate lyase, necessary for purine biosynthesis. An 1,180 bp deletion was engineered within the purB gene, leaving a residual 298 bp genomic scar resulting in a purine auxotrophic mutant. Phenotypically, SG ΔpurB showed a 66.5% reduction in growth in LB broth compared to the wild-type strain and failed to grow in minimal media without adenosine. Growth was restored to near wild-type levels with 0.3 mM adenosine supplementation, demonstrating the strain’s conditional attenuation. In vivo pathogenicity assessments revealed that oral inoculation of SG ΔpurB into 3-day-old chickens at a dose of 2 × 108 CFU resulted in zero mortality, compared to an 80% mortality rate in chickens challenged with the wild-type strain. The SG ΔpurB strain exhibited significantly reduced clinical signs and lesion scores, with clinical sign scores dropping from 2.5/3 with the wild-type to 0.4/3 with the ΔpurB mutant, and lesion scores decreasing from 2.9/3 to 0.3/3. Additionally, the mutant was efficiently cleared from liver and spleen tissues by 14 days post-inoculation, unlike the wild-type strain, which persisted until the experiment’s end on day 21. The SG ΔpurB mutant shows potential as a safe alternative for preventing fowl typhoid, highlighting the promise of targeted genetic attenuation in developing effective vaccines for poultry diseases.

FgGET3, an ATPase of the GET Pathway, Is Important for the Development and Virulence of Fusarium graminearum

GET3 is an ATPase protein that plays a pivotal role in the guided entry of the tail-anchored (GET) pathway. The protein facilitates the targeting and inserting of tail-anchored (TA) proteins into the endoplasmic reticulum (ER) by interacting with a receptor protein complex on the ER. The role of GET3 in various biological processes has been established in yeast, plants, and mammals but not in filamentous fungi. Fusarium graminearum is the major causal agent of Fusarium head blight (FHB), posing a threat to the yield and quality of wheat. In this study, we found that FgGET3 exhibits a high degree of sequence and structural conservation with its homologs across a wide range of organisms. Ectopic expression of FgGET3 in yeast restored the growth defects of the Saccharomyces cerevisiae ScGET3 knock-out mutant. Furthermore, FgGET3 was found to dimerize and localize to the cytoplasm, similar to its homologs in other species. Deletion of FgGET3 in F. graminearum results in decreased fungal growth, fragmented vacuoles, altered abiotic stress responses, reduced conidia production, delayed conidial germination, weakened virulence on wheat spikes and reduced DON production. Collectively, these findings underscore the critical role of FgGET3 in regulating diverse cellular and biological functions essential for the growth and virulence of F. graminearum.

Strain-Specific Infection of Phage AP1 to Rice Bacterial Brown Stripe Pathogen Acidovorax oryzae

Bacteriophage (phage) AP1 has been reported to effectively lyse Acidovorax oryzae, the causative agent of bacterial brown stripe in rice. However, phage AP1 exhibits strain-specific lysis patterns. In order to enhance the potential of phages for biological control of rice bacterial brown stripe, this study investigated the possible mechanism of strain-specific infection by characterizing phage AP1 and its susceptible (RS-2) and resistant (RS-1) strains. Based on the current classification standards and available database information, phage AP1 was classified into the class Caudoviricetes, and it is a kind of podophage. Comparative analysis of the susceptible and resistant strains showed no significant differences in growth kinetics, motility, biofilm formation, or effector Hcp production. Interestingly, the resistant strain demonstrated enhanced virulence compared to the susceptible strain. Prokaryotic expression studies indicated that six putative structural proteins of phage AP1 exhibited varying degrees of binding affinity (1.90–9.15%) to lipopolysaccharide (LPS). However, pull-down assays and bacterial two-hybrid analyses revealed that only gp66 can interact with four host proteins, which were identified as glycosyltransferase, RcnB, ClpB, and ImpB through immunoprecipitation and mass spectrometry analyses. The role of LPS in the specific infection mechanism of phage AP1 was further elucidated through the construction of knockout mutant strains and complementary strains targeting a unique gene cluster (wbzB, wbzC, wbzE, and wbzF) involved in LPS precursor biosynthesis. These findings provide novel insights into the mechanisms of phage-host specificity, which are crucial for the effective application of phage AP1 in controlling rice bacterial brown stripe.

Inositol pyrophosphate catabolism by three families of phosphatases regulates plant growth and development

Inositol pyrophosphates (PP-InsPs) are nutrient messengers whose cellular levels are precisely regulated. Diphosphoinositol pentakisphosphate kinases (PPIP5Ks) generate the active signaling molecule 1,5-InsP8. PPIP5Ks harbor phosphatase domains that hydrolyze PP-InsPs. Plant and Fungi Atypical Dual Specificity Phosphatases (PFA-DSPs) and NUDIX phosphatases (NUDTs) are also involved in PP-InsP degradation. Here, we analyze the relative contributions of the three different phosphatase families to plant PP-InsP catabolism. We report the biochemical characterization of inositol pyrophosphate phosphatases from Arabidopsis and Marchantia polymorpha. Overexpression of different PFA-DSP and NUDT enzymes affects PP-InsP levels and leads to stunted growth phenotypes in Arabidopsis. nudt17/18/21 knock-out mutants have altered PP-InsP pools and gene expression patterns, but no apparent growth defects. In contrast, Marchantia polymorpha Mppfa-dsp1ge, Mpnudt1ge and Mpvip1ge mutants display severe growth and developmental phenotypes and associated changes in cellular PP-InsP levels. Analysis of Mppfa-dsp1geand Mpvip1ge mutants supports a role for PP-InsPs in Marchantia phosphate signaling, and additional functions in nitrate homeostasis and cell wall biogenesis. Simultaneous elimination of two phosphatase activities enhanced the observed growth phenotypes. Taken together, PPIP5K, PFA-DSP and NUDT inositol pyrophosphate phosphatases regulate growth and development by collectively shaping plant PP-InsP pools.

Abstract 4137713: Epsin-Mediated PCSK9-LDLR Interaction: A New Therapeutic Target for Atherosclerosis

Introduction: Atherosclerosis, a leading cause of cardiovascular diseases, causes about 17.9 million deaths annually. It is driven by high levels of LDL cholesterol (LDL-C). The liver's LDL receptor (LDLR) removes LDL-C from the bloodstream, but its degradation by PCSK9 exacerbates the condition. Epsin, an endocytic adaptor protein crucial for clathrin-mediated endocytosis, plays a significant role in atherosclerosis, particularly lipid metabolism. Hypothesis: We propose that hepatic epsins significantly contribute to atherosclerosis by facilitating the PCSK9-induced degradation of LDLR, thus impeding LDL-C clearance. Objectives: This study aims to investigate hepatic epsins' role in PCSK9-mediated LDLR degradation and its effects on LDL-C levels and atherosclerosis development. Using bioinformatics, we will analyze enriched pathways and networks to study epsins modulation, which will be validated through biochemical assays and in vivo experiments. Methods: Liver-specific double knockout (DKO) mice lacking epsin1 and epsin2 were created on an ApoE -/- background. Atherosclerosis was induced using a Western diet (WD), and blood cholesterol and triglyceride levels were monitored. We employed high-resolution single-cell RNA sequencing (scRNA-seq) to analyze cellular transitions, intercellular interactions, and Gene Ontology pathway enrichment within hepatocyte-derived data. Results: RNA velocity reveals the transition from lipogenic Alb hi Hepatocytes to glucogenic Hnf4a hi Hepatocytes in Liver-DKO mice on an ApoE -/- background on a WD. Liver-DKO mice on an ApoE -/- background on a WD exhibited significantly reduced atherogenesis and lower blood cholesterol and triglyceride levels compared with wild-type on an ApoE -/- background on a WD. Gene Ontology enrichment analysis showed elevated pathways for LDL particle clearance and enhanced LDLR-cholesterol communication scores in Liver-DKO mice, suggesting improved LDL-C clearance. Nanoparticle-encapsulated siRNAs targeting liver epsins effectively inhibited atherosclerosis. Conclusion: Epsin depletion in the liver upregulated LDLR protein levels, and PCSK9-triggered LDLR degradation was abolished, preventing atheroma progression. Targeting liver epsins presents a novel therapeutic strategy for atherosclerosis, supported by network analysis and predictive modeling for effective interventions.

Abstract 4134975: ROS-Traf6-Yap Promotes the Development of Cardiac Hypertrophy

Introduction: Heart failure (HF) is caused by structural and functional abnormalities of the heart and is associated with high morbidity and mortality. Pathological myocardial hypertrophy accounts for a significant portion heart failure. The Yap protein was found to be responsive to mechanotransduction signals and can limit organ size by inducing cell cycle arrest during development. In the heart, pathological activation of Yap has been shown to drive cardiac hypertrophy, but regenerative activation of Yap can promote myocardial cell-cycle re-entry. However, how Yap is pathologically activated in the beating cardiomyocyte remains elusive. Hypothesis: ROS-Traf6 promotes the development of cardiac hypertrophy by activating Yap in a non-canonical fashion. Methods: Traf6 protein levels in heart failure patients biopsies as well as in various murine failing hearts were examined by immunofluorescence. Molecular interrogation of ROS-Traf6-Yap signaling axis was performed in primary neonatal rat cardiomyocytes (NRCM) and human induced pluripotent stem cell derived cardiomyocytes. Yap protein stability and activation by Traf6 was examined by immunoprecipitation, CHX induction, and point mutation. Myocardial specific Traf6 knockout and Yap mutant animals were used to evaluate Traf6-Yap signaling in vivo . Results: We found that Traf6 expression was significantly elevated in multiple heart failure models. Using the transverse aortic constriction (TAC)-induced cardiac hypertrophy model, pressure overload increased ROS levels which activated Traf6. Traf6 overexpression induced myocardial hypertrophy while knockdown blocked myocardial hypertrophy in Ang II treated NRCMs. Mechanistically, Traf6 binds to and ubiquitinates Yap-K234 – this promotes Yap protein stability and nuclear translocation evidenced by increase in phosphorylated Yap. Myocardial Traf6 deficiency prevents TAC-induced cardiac hypertrophy. Moreover, overexpression of Yap-K237 mutant did not restore TAC-induced cardiac hypertrophy in myocardial Yap deficient mice. Conclusions: Our results demonstrate that non-canonical Yap activation is responsible for pressure overload induced cardiac hypertrophy. Targeting of the newly identified ROS-Traf6-Yap signaling axis may provide a new approach to prevent pathogenic cardiac hypertrophy.

CD59 double knockout mice express a CD59ba hybrid fusion protein that mediates insulin secretion

AbstractCD59 is a cell‐surface inhibitor of the terminal step in the complement cascade. However, in addition to its complement inhibitory function, a non‐canonical role of CD59 in pancreatic beta cells has been identified. Two recently discovered intracellular alternative splice forms of CD59, IRIS‐1 and IRIS‐2, are involved in insulin exocytosis through interactions with SNARE‐complex components. In mice, the CD59 gene has undergone duplication and to further explore the role of CD59 in insulin secretion, blood glucose homeostasis was studied in a CD59 double knockout (CD59abKO) mouse model. However, no phenotypic deviation related to insulin secretion or blood glucose homeostasis was observed for the CD59abKO mice. Instead, a CD59ba hybrid transcript formed as a consequence of the mutation induced to generate the model was identified. This hybrid transcript is expressed in pancreatic islets of the CD59abKO mice and is comprised of the remaining exons of the two CD59 genes spliced together. Similar to canonical CD59, the CD59ba hybrid was found to be glycosylated and present on the cell surface when exogenously expressed in INS‐1 832/13 cells. Furthermore, INS‐1 832/13 cells over‐expressing the mouse CD59ba hybrid retained normal insulin secretion following siRNA‐mediated knockdown of canonical CD59. Hence, although the CD59ba hybrid has lost the complement inhibitory function, the intracellular insulin secretory function remains. These results provide further information concerning the structural requirements of CD59 in its intracellular role relative to its role as a complement inhibitor. It also highlights the importance of carefully assessing plausible consequences of induced mutations in research models.

Abstract 4113300: Targeting Liver Epsins Ameliorates Dyslipidemia in Atherosclerosis

Rationale: Low density cholesterol receptor (LDLR) in the liver is critical for the clearance of low-density lipoprotein cholesterol (LDL-C) in the blood. In atherogenic conditions, proprotein convertase subtilisin/kexin 9 (PCSK9) binds to LDLR on the surface of hepatocytes, preventing its recycling and enhancing its degradation in lysosomes, resulting in reduced LDL-C clearance. Our recent studies demonstrate that epsins, a family of ubiquitin-binding endocytic adaptors, are critical regulators of atherogenicity. Given the fundamental contribution of circulating LDL-C to atherosclerosis, we hypothesize that liver epsins promote atherosclerosis by controlling PCSK9-triggered LDLR endocytosis and degradation. Objective: We will determine the role of liver epsins in promoting PCSK9-mediated LDLR degradation and hindering LDL-C clearance to propel atherosclerosis. Methods and Results: We generated double knockout mice using albumin Cre in which both genes of epsin, namely, epsin 1 and epsin 2, are specifically deleted in the liver (Liver-DKO) on an ApoE -/- background. We discovered that western diet (WD)-induced atherogenesis was greatly inhibited, along with diminished blood cholesterol and triglyceride levels. Mechanistically, using scRNA-seq analysis on hepatocyte-derived data revealed elevated pathway involved in LDL particle clearance under WD treatment in ApoE -/- /Liver-DKO, which was coupled with diminished plasma LDL-C levels. Further analysis using the MEBOCOST algorithm revealed enhanced communication score between LDLR and cholesterol, suggesting elevated LDL-C clearance in the ApoE -/- Liver-DKO mice. In addition, we showed that loss of epsins in the liver upregulates of LDLR protein level. We further showed that epsins bind LDLR via the ubiquitin-interacting motif (UIM), and PCSK9-triggered LDLR degradation was abolished by depletion of epsins, preventing atheroma progression. Finally, our therapeutic strategy, which involved targeting liver epsins with nanoparticle-encapsulated siRNAs, was highly efficacious at inhibiting dyslipidemia and impeding atherosclerosis. Conclusions: Liver epsins promote atherogenesis by mediating PCSK9-triggered degradation of LDLR, thus raising the circulating LDL-C levels. Targeting epsins in the liver may serve as a novel therapeutic strategy to treat atherosclerosis by suppression of PCSK9-mediated LDLR degradation.

The Gene Cluster Cj0423–Cj0425 Negatively Regulates Biofilm Formation in Campylobacter jejuni

Abstract: Campylobacter jejuni (C. jejuni) is a zoonotic foodborne pathogen that is widely distributed worldwide. Its optimal growth environment is microaerophilic conditions (5% O2, 10% CO2), but it can spread widely in the atmospheric environment. Biofilms are thought to play an important role in this process. However, there are currently relatively few research works on the regulatory mechanisms of C. jejuni biofilm formation. In this study, a pan-genome analysis, combined with the analysis of biofilm phenotypic information, revealed that the gene cluster Cj0423–Cj0425 is associated with the negative regulation of biofilm formation in C. jejuni. Through gene knockout experiments, it was observed that the Cj0423–Cj0425 mutant strain significantly increased biofilm formation and enhanced flagella formation. Furthermore, pull-down assay revealed that Cj0424 interacts with 93 proteins involved in pathways such as fatty acid synthesis and amino acid metabolism, and it also contains the quorum sensing-related gene luxS. This suggests that Cj0423–Cj0425 affects fatty acid synthesis and amino acid metabolism, influencing quorum sensing and strain motility, ultimately inhibiting biofilm formation.

Aquaporin‐4 activation facilitates glymphatic system function and hematoma clearance post‐intracerebral hemorrhage

AbstractEfficient clearance of hematomas is crucial for improving clinical outcomes in patients with intracerebral hemorrhage (ICH). The glymphatic system, facilitated by aquaporin‐4 (AQP4), plays a crucial role in cerebrospinal fluid (CSF) entry and metabolic waste clearance. This study examined the role of the glymphatic system in ICH pathology, with a focus on AQP4. Collagenase‐induced ICH models were established, with AQP4 expression regulated through mifepristone as an agonist, TGN‐020 as an inhibitor, and Aqp4 gene knockout. Fluorescence tracing and multimodal magnetic resonance imaging (MRI) were employed to observe glymphatic system functionality, hematoma, and edema volumes. Neurological deficit scoring was performed using the modified Garcia Scale. AQP4 expression was quantified using RT‐qPCR and Western blotting, and cellular localization was explored using immunofluorescence. The brain tissue sections were examined for neuronal morphology, degenerative changes, and iron deposition. Three days post‐ICH, the AQP4 agonist group showed increased AQP4 protein expression and perivascular polarization, decreased hemoglobin levels, and reduced iron deposition. Conversely, the inhibition group exhibited contrasting trends. AQP4 activation improved glymphatic system function, leading to a wider distribution, improved neurological function, and reduced hematoma. Pharmacological inhibition and genetic knockout of AQP4 have opposing effects. The glymphatic system, facilitated by AQP4, plays a crucial role in hematoma clearance following cerebral hemorrhage. Upregulation of AQP4 improves glymphatic system function, facilitates hematoma clearance, and promotes brain tissue recovery.

EXTH-22. TARGETING MITOCHONDRIAL PROTEASE IN DIFFUSE GLIOMAS

Abstract BACKGROUND Targeting mitochondrial function has emerged as a promising therapeutic strategy in cancer treatment. TR107 is characterized as a specific activator of caseinolytic protease proteolytic subunit (ClpP) in the mitochondria, potentially affecting oncogenic pathways. Here, we investigated the effects of TR107 on adult malignant gliomas, IDH-wildtype and IDH-mutant METHODS We utilized patient-derived glioma cells to determine the efficacy of TR107 with cell viability, proliferation, cell cycle, and apoptosis assays. Immunofluorescent staining and electron microscopy (EM) were employed to uncover organelle morphological changes upon treatment. Mitochondrial function and ATP production were assessed in live cells utilizing Seahorse analysis. Global proteomics and RNA sequencing were performed to identify treatment-induced dysregulated pathways in glioma cells RESULTS Both IDH-wildtype and IDH-mutant glioma cell lines were highly sensitive to TR107, showing at least 100 times lower IC50 compared to the related compound ONC201. Genetic knock out of ClpP revealed that the growth inhibitory effects of TR107 are ClpP-dependent. Interestingly, IDH-mutant cell lines showed a more profound disintegration of mitochondrial morphology and dysregulation of mitochondrial function evidenced by an enhanced suppression of oxidative phosphorylation, mitochondrial complexes expression, mtDNA copy number, complex I activity, and ATP production, compared to IDH-wildtype cells. Six days of treatment with TR107 led to a complete inhibition of cell growth and up to 97% of cell death in IDH-mutant cells, while 50% of IDH-wildtype cells remained viable. Western blot, EM, and RNAsequencing analyses uncovered autophagy as a potential pro-survival mechanism in IDH-wildtype cells. Importantly, multiple metabolic and DNA repair-related pathways were affected by the treatment, suggested by global proteomics and RNA sequencing. Finally, TR107 was not affected by ABC transporters, supporting its potential use in brain tumor patients CONCLUSION TR107 demonstrated potent cytotoxic effects in patient-derived glioma cells by disrupting mitochondrial structural and functional integrity. TR107 efficacy in vivo is under investigation.

GADD45β‐MTK1 signaling axis mediates oncogenic stress‐induced activation of the p38 and JNK pathways

AbstractThe ERK pathway governs essential biological processes such as cell proliferation and survival, and its hyperactivation by various oncogenes ultimately drives carcinogenesis. However, normal mammalian cells typically recognize aberrant ERK signaling as oncogenic stress and respond by inducing cell cycle arrest or apoptosis through activation of the p38 and JNK pathways. Despite the critical role of this response in preventing carcinogenesis, the precise molecular mechanisms underlying oncogene‐induced, ERK‐dependent activation of p38/JNK and its tumor‐suppressive effects remain unclear. Here, we demonstrate that MAP three kinase 1 (MTK1), a stress‐responsive MAPKKK, serves as a key mediator of p38/JNK activation induced by oncogenic ERK signaling. Mechanistically, aberrant ERK signaling induces sustained expression of the transcription factor early growth response protein 1 (EGR1), which promotes the production of the MTK1 activator GADD45β, leading to persistent activation of MTK1‐p38/JNK signaling. Gene knockout and transcriptome analyses revealed that this GADD45β/MTK1‐mediated cross‐talk between the ERK and p38/JNK pathways preferentially upregulates a specific set of genes involved in apoptosis and the immune response. Notably, the expression of EGR1, GADD45β, and MTK1 is frequently downregulated in many cancers with high ERK activity, resulting in the disruption of the tumor‐suppressive ERK‐p38/JNK cross‐talk. Restoring GADD45β expression in cancer cells reactivates p38/JNK signaling and suppresses tumorigenesis. Our findings delineate a molecular mechanism by which normal cells sense and respond to oncogenic stress to prevent abnormal growth, and highlight the significance of its dysregulation in cancer.

TMIC-75. ICAM-1 PROMOTES AN IMMUNOSUPPRESSIVE LANDSCAPE IN GLIOBLASTOMAS BY REGULATING THE PHENOTYPIC POLARIZATION STATE OF TUMOR ASSOCIATED MACROPHAGES

Abstract Glioblastoma (GBM) is a fatal adult CNS tumor, with a median overall survival of 12-15 months. Intercellular adhesion molecule 1 (ICAM-1) is a cell adhesion molecule whose expression is significantly greater in the mesenchymal transcriptional subtype of GBMs, whereby it is prognostic. We have previously shown that when ICAM-1 is knocked out in the tumor microenvironment (TME) of immune-competent GBM-bearing mice, these mice showed prolonged overall survival and reduced tumor volume. It is yet to be determined how ICAM-1 expression affects infiltration and functional polarization of tumor-associated macrophages (TAMs) and other immune cells in GBM, and if we can suppress the infiltration of M2-like TAMs into the TME by inhibiting ICAM-1. We used a mouse glioma model with and without knockout (KO) of the ICAM-1 gene and intracranially injected GL261 cells. ICAM-1 KO mice survived longer and had reduced tumor volume relative to wildtype, with survival and volume differences being rescued upon ICAM-1 bone marrow reconstitution. Upon endpoint, we performed cytometry by time-of-flight, and found that ICAM-1 KO tumors harbored a reduction in helper T cells, Tregs, and cytotoxic T cells, but an increased proportion in double-negative T cells relative to ICAM-1 WT tumors. ICAM-1 KO tumors also demonstrated an increased proportion of M1-like TAMs relative to M2-like. These results were validated upon administration of ISIS-3082 to tumor models, an antisense oligonucleotide for which a human-specific form has been fast-track approved for other diseases, that targets ICAM-1 transiently in peripheral immune cells prior to TME infiltration. These findings suggest that ICAM-1 expression influences immune cell infiltration, potentially modulates the functional state of TAMs towards a M1-like state, and that ICAM-1 may be targeted in TAMs to ‘reeducate’ them before entering the TME. This may be translated into clinical practice and combined with standards-of-care to render GBMs more sensitive to treatment.

CNSC-36. REGULATION OF CELL FATE IN PAEDIATRIC HIGH-GRADE GLIOMA BY THE HOMEOBOX TRANSCRIPTION FACTOR DLX2

Abstract Paediatric high-grade gliomas (pHGG) are nearly uniformly fatal cancers that arise predominantly in children and adolescents and encompass Diffuse Midline Glioma (DMG) and Diffuse Hemispheric Glioma (DHG). Most patients harbour mutations in histone variants H3.1 or H3.3, resulting in global epigenetic dysregulation and a stalled oligodendroglial progenitor (OPC) or GABAergic interneuron progenitor (IP) fate for DMG and DHG, respectively. DLX2, a homeobox transcription factor, represses OPC fate and promotes IP cell fate and migration during early neurogenesis. Our lab has shown that Dlx2 binds to and regulates the promoters of Gad1/Gad2, as well as early (Olig2, Nkx2.2) and late (Myt1, Plp1) genes required for OPC differentiation in vivo. Co-expression of Dlx2 with these target sequences reduces reporter gene expression in vitro and Dlx1/2 double knockout mice exhibit increased expression of these OPC markers in vivo. Transient overexpression of a Dlx2-GFP construct in murine DMG cells led to significant IP marker increase (Gad1/2), decrease of OPC markers (Olig2, Nkx2.2) and global restoration of H3K27me3. Additionally, decreased proliferation, colony growth, invasion and migration were observed in vitro. To translate these findings in human pHGG, analysis of a bulk RNA-seq database of 62 patient-derived pHGG cell lines revealed an inverse relationship between DLX2 and OLIG2. DLX2 was knocked out of DLX2high/OLIG2low DHG cell lines using CRISPR-Cas9, and overexpressed in DLX2low/OLIG2high DMG cell lines using a DLX2-mCherry overexpression construct. Evaluation of cell fate markers and epigenetic marks will be presented. Changes in migration, invasion, and proliferation in vitro will also be presented, in addition to changes in tumour growth using a neonatal xenograft murine model in vivo. Manipulation of DLX2 in pHGG provides a model for investigating the link between the factors that control cell fate decisions in the developing brain and the aberrant differentiation state in pHGG.

IMMU-58. BCAT1 TARGETED METABOLIC REPROGRAMMING PLAYS CRITICAL ROLES IN MODULATING MYELOID DERIVED SUPPRESSOR CELL FUNCTION IN GLIOBLASTOMA

Abstract A key component that has limited the efficacy of immunotherapy in glioblastoma (GBM) is the significant infiltration of immunosuppressive myeloid cells. Our previous work characterized myeloid derived suppressor cells (MDSCs) unique to GBM that drive tumor growth and immune suppression. Transcriptomic and flow cytometric analyses demonstrated that the most induced programs in these MDSCs are dominated by metabolic and mTOR pathways. Therefore, we aimed to understand the role of metabolic reprogramming in MDSC differentiation and immunosuppressive function. Using single cell RNA sequencing, we identified overexpression of enzymes and transporters involved in branched-chain amino acid (BCAA) metabolism, notably branched chain aminotransferase 1 (BCAT1), the first enzyme in the metabolic pathway. Intriguingly, this was only found in specific populations of early and monocytic MDSCs (E-MDSCs, M-MDSCs), and not polymorphonuclear MDSCs (PMN-MDSCs). Using established MDSC modeling systems, we found that M-MDSC differentiation and T cell suppressive function are dependent on BCAAs and can be hindered by pharmacological inhibition of BCAT1 activity or genetic knockout of BCAT1. We also establish that the influence of BCAA on M-MDSC function is specifically reliant on the BCAT1-mediated step of BCAA metabolism. To determine the underlying mechanism driving BCAT1’s impact on M-MDSC function, we evaluated the activity of signaling pathways known to be critical to M-MDSCs including the mTORC1 pathway. We found that the impact of BCAA and BCAT1 activity on M-MDSC function is abrogated by inhibition of mTORC1 pathway with reduction in M-MDSC differentiation and activity. Consistent with our single cell RNA sequencing analysis, modulation of BCAA levels and BCAT1 activity had no impact on PMN-MDSCs. Our results underscore the critical role of BCAT1 in preferentially modulating M-MDSC activity through mTORC1 signaling. Our finding paves the way for discovery of a targetable therapeutic approach to harness immunometabolism in myeloid cells to develop novel immune therapies.

EXTH-02. MODIFYING CAR T CELL EPIGENETIC PROGRAMS TO IMPROVE THEIR PERSISTENCE AGAINST GROUP 3 MEDULLOBLASTOMAS

Abstract BACKGROUND Safe, effective therapies are desperately needed to improve outcomes for patients with medulloblastoma (MB), a malignant pediatric brain cancer. Chimeric antigen receptor (CAR)-T cells are a promising therapeutic option as they target T-cell cytotoxicity exclusively to tumor associated antigens. B7 homolog 3 (B7-H3) is an ideal target for CAR-T cell therapy as all MB subtypes express B7-H3 but healthy tissues do not. However, a major roadblock to tumor clearance and control is the inability of CAR-T cells to persist, suggesting that improving persistence will improve therapeutic efficacy. The goal of this study was to compare head-to-head the impact of knocking out TET2 and DNMT3A negative epigenetic regulators of CAR-T cell persistence against group 3 MB (G3MB), the most malignant MB subtype. METHODS We generated B7-H3 CAR-T cells with CD28ζ signaling domain and performed CRISPR/Cas9 knockout (KO) of TET2, DNMT3A, and AAVS1 as a control. We compared resulting CAR-T cell persistence via repeat stimulation assays in vitro against G3MB cell lines with varying B7-H3 antigen density (D341low, HDMB03mid, and D425high). We further compared KO CAR-T cells in vivo against D341low, HDMB03mid, and D425high orthotopic xenografts. RESULTS Our data shows that DNMT3A KO, but not TET2 KO, consistently improves the persistence and expansion of CAR-T cells against G3MB in vitro. In vivo, KO of epigenetic regulators, improves CAR-T cell therapy against highly aggressive D341low, HDMB03mid, and D425high but is insufficient to elicit curative responses. CONCLUSIONS Our study demonstrates that genetic KO of negative epigenetic regulators of CAR-T cell persistence can improve anti-tumor function against G3MB. We conclude that for the B7-H3.CD28ζ CAR, DNMT3A KO is superior for improving persistence over TET2 KO, but that DNMT3A KO is insufficient in vivo.

Automatic construction of Petri net models for computational simulations of molecular interaction network

Petri nets are commonly applied in modeling biological systems. However, construction of a Petri net model for complex biological systems is often time consuming, and requires expertise in the research area, limiting their application. To address this challenge, we developed GINtoSPN, an R package that automates the conversion of multi-omics molecular interaction network extracted from the Global Integrative Network (GIN) into Petri nets in GraphML format. These GraphML files can be directly used for Signaling Petri Net (SPN) simulation. To demonstrate the utility of this tool, we built a Petri net model for neurofibromatosis type I. Simulation of NF1 gene knockout, compared to normal skin fibroblast cells, revealed persistent accumulation of Ras-GTPs as expected. Additionally, we identified several other genes substantially affected by the loss of NF1’s function, exhibiting individual-specific variability. These results highlight the effectiveness of GINtoSPN in streamlining the modeling and simulation of complex biological systems.

Activation of MEK‐ERK‐c‐MYC signaling pathway promotes splenic M2-like macrophage polarization to inhibit PHcH-liver cirrhosis

IntroductionPortal hypertension combined with hypersplenism (PHcH) is the main cause of hypocytosis and esophagogastric variceal hemorrhage in patients with liver cirrhosis. Activated macrophages that destroy excess blood cells are the main cause of hypersplenism, but the activating pathway is not very clear. This study aims to investigate the activation types of splenic macrophages and their activation mechanisms, to provide experimental evidence for the biological treatment of splenomegaly, and to find a strategy to improve liver fibrosis and inflammation by intervening in splenic immune cells. This study revealed the occurrence of M2-like polarization of macrophages and upregulation of c-Myc gene expression in the PH spleen.MethodsRNAseq, protein chip, western blot, and chip-seq were performed on macrophages and the in vitro MEK inhibitor rafametinib was used. Carbon tetrachloride and thioacetamide induced mouse cirrhosis models were separately constructed.Resultsc-Myc gene knockout in splenic macrophages reduced M2-like polarization and exacerbated liver fibrosis inflammation. c-Myc activated the MAPK signaling pathway and upregulated the expression of IL-4 and M2-like related genes in PH hypersplenism through the MEK-ERK-c-Myc axis. In addition, the c-Myc gene exerted anti-inflammatory effects by upregulating IL-4-mediated signal transduction to promote M2-like differentiation and anti-inflammatory cytokine secretion.ConclusionsActivation of MEK‐ERK‐c‐MYC signaling pathway promotes splenic M2-like macrophage polarization to inhibit PHcH-liver cirrhosis. Therefore, the induction of macrophage depolarization might represent a new therapeutic approach in the cure of PH hypersplenism, making c-Myc a potential candidate for macrophage polarization therapy.