Medulloblastoma is the most common malignant paediatric brain tumour, with ~30% mediated by Sonic hedgehog signalling. Vismodegib-mediated inhibition of the Sonic hedgehog effector Smoothened ...inhibits tumour growth but causes growth plate fusion at effective doses. Here, we report a nanotherapeutic approach targeting endothelial tumour vasculature to enhance blood-brain barrier crossing. We use fucoidan-based nanocarriers targeting endothelial P-selectin to induce caveolin-1-dependent transcytosis and thus nanocarrier transport into the brain tumour microenvironment in a selective and active manner, the efficiency of which is increased by radiation treatment. In a Sonic hedgehog medulloblastoma animal model, fucoidan-based nanoparticles encapsulating vismodegib exhibit a striking efficacy and marked reduced bone toxicity and drug exposure to healthy brain tissue. Overall, these findings demonstrate a potent strategy for targeted intracranial pharmacodelivery that overcomes the restrictive blood-brain barrier to achieve enhanced tumour-selective penetration and has therapeutic implications for diseases within the central nervous system.
Mosaic mutant analysis, the study of cellular defects in scattered mutant cells in a wild-type environment, is a powerful approach for identifying critical functions of genes and has been applied ...extensively to invertebrate model organisms. A highly versatile technique has been developed in mouse: MASTR (mosaic mutant analysis with spatial and temporal control of recombination), which utilizes the increasing number of floxed alleles and simultaneously combines conditional gene mutagenesis and cell marking for fate analysis. A targeted allele (R26MASTR) was engineered; the allele expresses a GFPcre fusion protein following FLP-mediated recombination, which serves the dual function of deleting floxed alleles and marking mutant cells with GFP. Within 24 hr of tamoxifen administration to R26MASTR mice carrying an inducible FlpoER transgene and a floxed allele, nearly all GFP-expressing cells have a mutant allele. The fate of single cells lacking FGF8 or SHH signaling in the developing hindbrain was analyzed using MASTR, and it was revealed that there is only a short time window when neural progenitors require FGFR1 for viability and that granule cell precursors differentiate rapidly when SMO is lost. MASTR is a powerful tool that provides cell-type-specific (spatial) and temporal marking of mosaic mutant cells and is broadly applicable to developmental, cancer, and adult stem cell studies.
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► MASTR: a highly versatile technique for mosaic mutant analysis in mouse ► Combines FLPoER and conditional expression of GFPcre with deletion of floxed genes ► Useful in studies of mutant cell behaviors during development and in adult stem cells ► MASTR can be used to model sporadic human diseases and isolate mutant cells (GFP+)
Mosaic mutant analysis is a powerful technique for determining cell-autonomous and nonautonomous gene functions; however, the development of approaches in mouse has lagged behind other multicellular model organisms. Joyner and colleagues describe a new technique in mouse that utilizes any floxed allele and simultaneously combines conditional gene mutagenesis and cell marking to produce mosaic mutants. MASTR is a powerful tool that provides cell-type-specific and temporal control and is broadly applicable to developmental, cancer, and adult stem cell studies.
Dysregulated Hedgehog (Hh) signaling has been implicated in a growing number of human cancers. To date, most antagonists of this signaling pathway that have been developed target the Hh receptor ...Smoothened. However, these are predicted to have minimal effect when the pathway is activated as a result of dysregulation downstream of this receptor. In this issue of the JCI, Beauchamp and colleagues provide preclinical evidence that arsenic trioxide, a drug FDA approved for the treatment of acute promyelocytic leukemia, inhibits the growth of Ewing sarcoma and medulloblastoma cells by targeting GLI family zinc finger (GLI) proteins, which are Hh signaling pathway components downstream of Smoothened.
Pediatric high-grade gliomas, specifically diffuse midline gliomas, account for only 20% of clinical cases but are 100% fatal. A majority of the DMG cases are characterized by the signature K27M ...mutation in histone H3. The H3K27M mutation opposes the function of enhancer of zeste homolog 2 (EZH2), the methyltransferase enzyme of the polycomb repressor complex 2. However, the role of EZH2 in DMG pathogenesis is unclear. In this study, we demonstrate a tumor suppressor function for EZH2 using Ezh2 loss- and gain-of-function studies in H3WT DMG mouse models. Genetic ablation of Ezh2 increased cell proliferation and tumor grade while expression of an Ezh2 gain-of-function mutation significantly reduced tumor incidence and increased tumor latency. Transcriptomic analysis revealed that Ezh2 deletion upregulates an inflammatory response with upregulation of immunoproteasome genes such as Psmb8, Psmb9, and Psmb10. Ezh2 gain-of-function resulted in enrichment of the oxidative phosphorylation/mitochondrial metabolic pathway namely the isocitrate dehydrogenase Idh1/2/3 genes. Pharmacological inhibition of EZH2 augmented neural progenitor cell proliferation, supporting the tumor suppressive role of EZH2. In vivo 7-day treatment of H3K27M DMG tumor bearing mice with an EZH2 inhibitor, Tazemetostat, did not alter proliferation or significantly impact survival. Together our results suggest that EZH2 has a tumor suppressor function in DMG and warrants caution in clinical translation of EZH2 inhibitors to treat patients with DMG.
Abstract Mouse models have increased our understanding of the pathogenesis of medulloblastoma (MB), the most common malignant pediatric brain tumor that often forms in the cerebellum. A major goal of ...ongoing research is to better understand the early stages of tumorigenesis and to establish the genetic and environmental changes that underlie MB initiation and growth. However, studies of MB progression in mouse models are difficult due to the heterogeneity of tumor onset times and growth patterns and the lack of clinical symptoms at early stages. Magnetic resonance imaging (MRI) is critical for noninvasive, longitudinal, three-dimensional (3D) brain tumor imaging in the clinic but is limited in resolution and sensitivity for imaging early MBs in mice. In this study, high-resolution (100 μm in 2 hours) and high-throughput (150 μm in 15 minutes) manganese-enhanced MRI (MEMRI) protocols were optimized for early detection and monitoring of MBs in a Patched-1 ( Ptch1 ) conditional knockout (CKO) model. The high tissue contrast obtained with MEMRI revealed detailed cerebellar morphology and enabled detection of MBs over a wide range of stages including pretumoral lesions as early as 2 to 3 weeks postnatal with volumes close to 0.1 mm3 . Furthermore, longitudinal MEMRI allowed noninvasive monitoring of tumors and demonstrated that lesions within and between individuals have different tumorigenic potentials. 3D volumetric studies allowed quantitative analysis of MB tumor morphology and growth rates in individual Ptch1- CKO mice. These results show that MEMRI provides a powerful method for early in vivo detection and longitudinal imaging of MB progression in the mouse brain.
The fat mass and obesity-associated gene (FTO) codes for a DNA/RNA demethylase. Pathological variants in this gene are rare, with only three reports in the literature, all with mutations in the ...catalytic domain. We report the first biallelic human variant in fat mass and obesity-associated gene (c.287G>C, p.Arg96Pro/R96P) outside the catalytic site, causing numerous abnormalities across multiple organ systems, affecting respiratory, cardiovascular, and neurological function. Biochemical assays of cells with the patient’s variant were performed to further quantify the effect of the variant on function. Loss-of-function resulting from the patient’s R96P missense variant was demonstrated with in vitro biochemical characterization of demethylase activity, resulting in a 90% reduction in function of the fat mass and obesity-associated protein compared to wild-type. Our findings demonstrate a novel fat mass and obesity-associated gene non-catalytic site variant with a unique patient phenotype of bilateral multifocal epilepsy and multisystem congenital anomalies.
Subependymal giant cell astrocytomas are one of the three major intracranial lesions found in tuberous sclerosis complex. Subependymal giant cell astrocytomas are typically slow-growing tumors of ...mixed glioneuronal lineage which can become aggressive and cause obstructive hydrocephalus usually in older children and adolescents. Neonatal subependymal giant cell astrocytomas are extremely rare, and their natural history and prognosis are poorly understood. This report investigates an extremely large neonatal subependymal giant cell astrocytoma which was initially identified in utero at 19 weeks of gestation in a high-risk pregnancy with no family history of tuberous sclerosis complex.
Genomic rearrangements are a hallmark of most childhood tumors, including medulloblastoma, one of the most common brain tumors in children, but their causes remain largely unknown. Here, we show that ...PiggyBac transposable element derived 5 (Pgbd5) promotes tumor development in multiple developmentally accurate mouse models of Sonic Hedgehog (SHH) medulloblastoma. Most Pgbd5-deficient mice do not develop tumors, while maintaining normal cerebellar development. Ectopic activation of SHH signaling is sufficient to enforce cerebellar granule cell progenitor-like cell states, which exhibit Pgbd5-dependent expression of distinct DNA repair and neurodevelopmental factors. Mouse medulloblastomas expressing Pgbd5 have increased numbers of somatic structural DNA rearrangements, some of which carry PGBD5-specific sequences at their breakpoints. Similar sequence breakpoints recurrently affect somatic DNA rearrangements of known tumor suppressors and oncogenes in medulloblastomas in 329 children. This identifies PGBD5 as a medulloblastoma mutator and provides a genetic mechanism for the generation of oncogenic DNA rearrangements in childhood cancer.
Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-β (TGF-β) superfamily that play important roles in bone formation, embryonic patterning, and epidermal-neural cell ...fate decisions. BMPs signal through pathway specific mediators such as Smads1 and 5, but the upstream regulation of BMP-specific Smads has not been fully characterized. Here we report the identification of SANE (Smad1 AntagonisticEffector), a novel protein with significant sequence similarity to nuclear envelop proteins such as MAN1. SANE binds to Smad1/5 and to BMP type I receptors and regulates BMP signaling. SANE specifically blocks BMP-dependent signaling inXenopus embryos and in a mammalian model of bone formation but does not inhibit the TGF-β/Smad2 pathway. Inhibition of BMP signaling by SANE requires interaction between SANE and Smad1, because a SANE mutant that does not bind Smad1 does not inhibit BMP signaling. Furthermore, inhibition appears to be mediated by inhibition of BMP-induced Smad1 phosphorylation, blocking ligand-dependent nuclear translocation of Smad1. These studies define a new mode of regulation for intracellular BMP/Smad1 signaling.
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