Increased c-Jun-NH2-kinase signaling in neurofibromatosis-1 heterozygous microglia drives microglia activation and promotes optic glioma proliferation

Visual Deficits and Diagnostic and Therapeutic Strategies for Neurofibromatosis Type 1: Bridging Science and Patient-Centered Care

Neurofibromatosis type 1 (NF1) is an inherited autosomal dominant disorder primarily affecting children and adolescents characterized by multisystemic clinical manifestations. Mutations in neurofibromin, the protein encoded by the Nf1 tumor suppressor gene, result in dysregulation of the RAS/MAPK pathway leading to uncontrolled cell growth and migration. Neurofibromin is highly expressed in several cell lineages including melanocytes, glial cells, neurons, and Schwann cells. Individuals with NF1 possess a genetic predisposition to central nervous system neoplasms, particularly gliomas affecting the visual pathway, known as optic pathway gliomas (OPGs). While OPGs are typically asymptomatic and benign, they can induce visual impairment in some patients. This review provides insight into the spectrum and visual outcomes of NF1, current diagnostic techniques and therapeutic interventions, and explores the influence of NF1-OPGS on visual abnormalities. We focus on recent advancements in preclinical animal models to elucidate the underlying mechanisms of NF1 pathology and therapies targeting NF1-OPGs. Overall, our review highlights the involvement of retinal ganglion cell dysfunction and degeneration in NF1 disease, and the need for further research to transform scientific laboratory discoveries to improved patient outcomes.

Role of the Microenvironment in Glioma Pathogenesis

Gliomas are a diverse group of primary central nervous system tumors that affect both children and adults. Recent studies have revealed a dynamic cross talk that occurs between glioma cells and components of their microenvironment, including neurons, astrocytes, immune cells, and the extracellular matrix. This cross talk regulates fundamental aspects of glioma development and growth. In this review, we discuss recent discoveries about the impact of these interactions on gliomas and highlight how tumor cells actively remodel their microenvironment to promote disease. These studies provide a better understanding of the interactions in the microenvironment that are important in gliomas, offer insight into the cross talk that occurs, and identify potential therapeutic vulnerabilities that can be utilized to improve clinical outcomes.

Pediatric low-grade glioma models: advances and ongoing challenges

Pediatric low-grade gliomas represent the most common childhood brain tumor class. While often curable, some tumors fail to respond and even successful treatments can have life-long side effects. Many clinical trials are underway for pediatric low-grade gliomas. However, these trials are expensive and challenging to organize due to the heterogeneity of patients and subtypes. Advances in sequencing technologies are helping to mitigate this by revealing the molecular landscapes of mutations in pediatric low-grade glioma. Functionalizing these mutations in the form of preclinical models is the next step in both understanding the disease mechanisms as well as for testing therapeutics. However, such models are often more difficult to generate due to their less proliferative nature, and the heterogeneity of tumor microenvironments, cell(s)-of-origin, and genetic alterations. In this review, we discuss the molecular and genetic alterations and the various preclinical models generated for the different types of pediatric low-grade gliomas. We examined the different preclinical models for pediatric low-grade gliomas, summarizing the scientific advances made to the field and therapeutic implications. We also discuss the advantages and limitations of the various models. This review highlights the importance of preclinical models for pediatric low-grade gliomas while noting the challenges and future directions of these models to improve therapeutic outcomes of pediatric low-grade gliomas.

Review: therapeutic approaches for circadian modulation of the glioma microenvironment

High-grade gliomas are malignant brain tumors that are characteristically hard to treat because of their nature; they grow quickly and invasively through the brain tissue and develop chemoradiation resistance in adults. There is also a distinct lack of targeted treatment options in the pediatric population for this tumor type to date. Several approaches to overcome therapeutic resistance have been explored, including targeted therapy to growth pathways (ie. EGFR and VEGF inhibitors), epigenetic modulators, and immunotherapies such as Chimeric Antigen Receptor T-cell and vaccine therapies. One new promising approach relies on the timing of chemotherapy administration based on intrinsic circadian rhythms. Recent work in glioblastoma has demonstrated temporal variations in chemosensitivity and, thus, improved survival based on treatment time of day. This may be due to intrinsic rhythms of the glioma cells, permeability of the blood brain barrier to chemotherapy agents, the tumor immune microenvironment, or another unknown mechanism. We review the literature to discuss chronotherapeutic approaches to high-grade glioma treatment, circadian regulation of the immune system and tumor microenvironment in gliomas. We further discuss how these two areas may be combined to temporally regulate and/or improve the effectiveness of immunotherapies.

Neurofibromin 1 mutations impair the function of human induced pluripotent stem cell-derived microglia

Neurofibromatosis type 1 (NF1) is an autosomal dominant condition caused by germline mutations in the neurofibromin 1 (NF1) gene. Children with NF1 are prone to the development of multiple nervous system abnormalities, including autism and brain tumors, which could reflect the effect of NF1 mutation on microglia function. Using heterozygous Nf1-mutant mice, we previously demonstrated that impaired purinergic signaling underlies deficits in microglia process extension and phagocytosis in situ. To determine whether these abnormalities are also observed in human microglia in the setting of NF1, we leveraged an engineered isogenic series of human induced pluripotent stem cells to generate human microglia-like (hiMGL) cells heterozygous for three different NF1 gene mutations found in patients with NF1. Whereas all NF1-mutant and isogenic control hiMGL cells expressed classical microglia markers and exhibited similar transcriptomes and cytokine/chemokine release profiles, only NF1-mutant hiMGL cells had defects in P2X receptor activation, phagocytosis and motility. Taken together, these findings indicate that heterozygous NF1 mutations impair a subset of the functional properties of human microglia, which could contribute to the neurological abnormalities seen in children with NF1.

Optimizing preclinical pediatric low-grade glioma models for meaningful clinical translation

Pediatric low-grade gliomas (pLGGs) are the most common brain tumor in young children. While they are typically associated with good overall survival, children with these central nervous system tumors often experience chronic tumor- and therapy-related morbidities. Moreover, individuals with unresectable tumors frequently have multiple recurrences and persistent neurological symptoms. Deep molecular analyses of pLGGs reveal that they are caused by genetic alterations that converge on a single mitogenic pathway (MEK/ERK), but their growth is heavily influenced by nonneoplastic cells (neurons, T cells, microglia) in their local microenvironment. The interplay between neoplastic cell MEK/ERK pathway activation and stromal cell support necessitates the use of predictive preclinical models to identify the most promising drug candidates for clinical evaluation. As part of a series of white papers focused on pLGGs, we discuss the current status of preclinical pLGG modeling, with the goal of improving clinical translation for children with these common brain tumors.

The Neuroimmune Regulation and Potential Therapeutic Strategies of Optic Pathway Glioma

Optic pathway glioma (OPG) is one of the causes of pediatric visual impairment. Unfortunately, there is as yet no cure for such a disease. Understanding the underlying mechanisms and the potential therapeutic strategies may help to delay the progression of OPG and rescue the visual morbidities. Here, we provide an overview of preclinical OPG studies and the regulatory pathways controlling OPG pathophysiology. We next discuss the role of microenvironmental cells (neurons, T cells, and tumor-associated microglia and macrophages) in OPG development. Last, we provide insight into potential therapeutic strategies for treating OPG and promoting axon regeneration.

The Present and Future of Optic Pathway Glioma Therapy

Optic pathway gliomas (OPGs) encompass two distinct categories: benign pediatric gliomas, which are characterized by favorable prognosis, and malignant adult gliomas, which are aggressive cancers associated with a poor outcome. Our review aims to explore the established standards of care for both types of tumors, highlight the emerging therapeutic strategies for OPG treatment, and propose potential alternative therapies that, while originally studied in a broader glioma context, may hold promise for OPGs pending further investigation. These potential therapies encompass immunotherapy approaches, molecular-targeted therapy, modulation of the tumor microenvironment, nanotechnologies, magnetic hyperthermia therapy, cyberKnife, cannabinoids, and the ketogenic diet. Restoring visual function is a significant challenge in cases where optic nerve damage has occurred due to the tumor or its therapeutic interventions. Numerous approaches, particularly those involving stem cells, are currently being investigated as potential facilitators of visual recovery in these patients.

MicroRNA-217 aggravates breast cancer through activation of NF1-mediated HSF1/ATG7 axis and c-Jun/ATF3/MMP13 axis

Application of microRNA-mediated mRNA expression in treatment of diverse cancers has been documented. The current study was explored to study the role of miR-217 in breast cancer (BC) progression and the related downstream factors. Clinical tissue samples, BC cell lines and the established xenograft models were prepared for ectopic expression and depletion experiments to discern the regulatory roles of miR-217-mediated NF1 in BC cell proliferation, metastasis and chemoresistance as well as tumorigenic ability of BC cells in nude mice. miR-217 was upregulated in BC, which was a predictor of poor prognosis of BC patients. NF1 could be targeted by miR-217. miR-217 promoted malignant characteristics of BC cells through enhancing ATF3-MMP13 interaction by inhibiting NF1. miR-217 repressed sensitivity against anti-cancer drugs by inducing autophagy of BC cells through the NF1/HSF1/ATG7 axis. Also, miR-217 could inhibit NF1 to facilitate tumorigenic ability of BC cells in vivo. Our study emphasized that miR-217 could potentially inhibit NF1 expression to activate the c-Jun, thus enhancing the expression and interaction of ATF3/MMP13 and promoting the malignant features of BC cells. Furthermore, miR-217 conferred chemoresistance on BC by enhancing BC cell autophagy, which was achieved by limiting NF1 expression to induce the HSF1/ATG7 pathway.

Wasl is crucial to maintain microglial core activities during glioblastoma initiation stages

Microglia actively promotes the growth of high-grade gliomas. Within the glioma microenvironment an amoeboid microglial morphology has been observed, however the underlying causes and the related impact on microglia functions and their tumor promoting activities is unclear. Using the advantages of the larval zebrafish model, we identified the underlying mechanism and show that microglial morphology and functions are already impaired during glioma initiation stages. The presence of pre-neoplastic HRasV12 expressing cells induces an amoeboid morphology of microglia, increases microglial numbers and decreases their motility and phagocytic activity. RNA sequencing analysis revealed lower expression levels of the actin nucleation promoting factor wasla in microglia. Importantly, a microglia specific rescue of wasla expression restores microglial morphology and functions. This results in increased phagocytosis of pre-neoplastic cells and slows down tumor progression. In conclusion, we identified a mechanism that de-activates core microglial functions within the emerging glioma microenvironment. Restoration of this mechanism might provide a way to impair glioma growth.

Neuronal hyperexcitability drives central and peripheral nervous system tumor progression in models of neurofibromatosis-1

Neuronal activity is emerging as a driver of central and peripheral nervous system cancers. Here, we examined neuronal physiology in mouse models of the tumor predisposition syndrome Neurofibromatosis-1 (NF1), with different propensities to develop nervous system cancers. We show that central and peripheral nervous system neurons from mice with tumor-causing Nf1 gene mutations exhibit hyperexcitability and increased secretion of activity-dependent tumor-promoting paracrine factors. We discovered a neurofibroma mitogen (COL1A2) produced by peripheral neurons in an activity-regulated manner, which increases NF1-deficient Schwann cell proliferation, establishing that neurofibromas are regulated by neuronal activity. In contrast, mice with the Arg1809Cys Nf1 mutation, found in NF1 patients lacking neurofibromas or optic gliomas, do not exhibit neuronal hyperexcitability or develop these NF1-associated tumors. The hyperexcitability of tumor-prone Nf1-mutant neurons results from reduced NF1-regulated hyperpolarization-activated cyclic nucleotide-gated (HCN) channel function, such that neuronal excitability, activity-regulated paracrine factor production, and tumor progression are attenuated by HCN channel activation. Collectively, these findings reveal that NF1 mutations act at the level of neurons to modify tumor predisposition by increasing neuronal excitability and activity-regulated paracrine factor production.

Neuronal activity is emerging as a driver of nervous system tumors. Here, the authors show in mouse models of Neurofibromatosis-1 (NF1) that Nf1 mutations differentially drive both central and peripheral nervous system tumor growth in mice through reduced hyperpolarization-activated cyclic nucleotide-gated (HCN) channel function.

RAS and beyond: the many faces of the neurofibromatosis type 1 protein

Neurofibromatosis type 1 is a rare neurogenetic syndrome, characterized by pigmentary abnormalities, learning and social deficits, and a predisposition for benign and malignant tumor formation caused by germline mutations in the NF1 gene. With the cloning of the NF1 gene and the recognition that the encoded protein, neurofibromin, largely functions as a negative regulator of RAS activity, attention has mainly focused on RAS and canonical RAS effector pathway signaling relevant to disease pathogenesis and treatment. However, as neurofibromin is a large cytoplasmic protein the RAS regulatory domain of which occupies only 10% of its entire coding sequence, both canonical and non-canonical RAS pathway modulation, as well as the existence of potential non-RAS functions, are becoming apparent. In this Special article, we discuss our current understanding of neurofibromin function.

Targeted genetic and molecular therapies in neurofibromatosis - A review of present therapeutic options and a glimpse into the future

Neurofibromatosis type 1, the most common phakomatoses, can present with a host of signs and symptoms, usually involving the skin and the peripheral nervous system. It is characterized by a mutation in the neurofibromatosis type 1 gene on chromosome 17q11.2 that codes for the protein neurofibromin. Neurofibromin acts as a tumor suppressor gene by inhibiting rat sarcoma (Ras) activity and its deficiency leads to increased Ras activity, cellular proliferation and tumor formation. This review was conducted to analyze the various targeted therapies at the genetic and molecular level employed to manage the tumors and other clinical presentations associated with neurofibromatosis type 1. Twenty-eight studies of treatment modalities for the conditions associated with neurofibromatosis and which involved either targeted gene therapy or molecular level therapies, including the latest advances, were included in this review. Mitogen-activated protein kinase kinase inhibition, mammalian target of Rapamycin inhibition and Tyrosine kinase inhibition, represent some of the newer treatment options in this category. Although there are a number of trials for providing therapeutic options at the genetic and molecular level for the various physical and psychological morbidities associated with neurofibromatosis type 1, most of them are in the preclinical stage. Increased clinical trials of the molecules and gene therapies could significantly help in managing the various chronic and sometimes, life-threatening conditions associated with neurofibromatosis 1 and these will probably represent the preferred treatment direction of the future.

Reimagining Pilocytic Astrocytomas in the Context of Pediatric Low-Grade Gliomas

Pediatric low-grade gliomas (pLGGs) are the most common brain tumor in children, and are associated with life-long clinical morbidity. Relative to their high-grade adult counterparts or other malignant childhood brain tumors, there is a paucity of authenticated preclinical models for these pediatric low-grade gliomas and an incomplete understanding of their molecular and cellular pathogenesis. While large scale genomic profiling efforts have identified the majority of pathogenic driver mutations, which converge on the MAPK/ERK signaling pathway, it is now appreciated that these events may not be sufficient by themselves for gliomagenesis and clinical progression. In light of the recent World Health Organization reclassification of pLGGs, and pilocytic astrocytoma (PA) in particular, we review our current understanding of these pediatric brain tumors, provide a conceptual framework for future mechanistic studies, and outline the challenges and pressing needs for the pLGG clinical and research communities.

Implications of new understandings of gliomas in children and adults with NF1: report of a consensus conference

Gliomas are the most common primary central nervous system tumors occurring in children and adults with neurofibromatosis type 1 (NF1). Over the past decade, discoveries of the molecular basis of low-grade gliomas (LGGs) have led to new approaches for diagnosis and treatments. However, these new understandings have not been fully applied to the management of NF1-associated gliomas. A consensus panel consisting of experts in NF1 and gliomas was convened to review the current molecular knowledge of NF1-associated low-grade “transformed” and high-grade gliomas; insights gained from mouse models of NF1-LGGs; challenges in diagnosing and treating older patients with NF1-associated gliomas; and advances in molecularly targeted treatment and potential immunologic treatment of these tumors. Next steps are recommended to advance the management and outcomes for NF1-associated gliomas.

Immune biology of glioma-associated macrophages and microglia: functional and therapeutic implications

CNS immune defenses are marshaled and dominated by brain resident macrophages and microglia, which are the innate immune sentinels and frontline host immune barriers against various pathogenic insults. These myeloid lineage cells are the predominant immune population in gliomas and can constitute up to 30-50% of the total cellular composition. Parenchymal microglial cells and recruited monocyte-derived macrophages from the periphery exhibit disease-specific phenotypic characteristics with spatial and temporal distinctions and are heterogeneous subpopulations based on their molecular signatures. A preponderance of myeloid over lymphoid lineage cells during CNS inflammation, including gliomas, is a contrasting feature of brain immunity relative to peripheral immunity. Herein we discuss glioma-associated macrophage and microglia immune biology in the context of their identity, molecular drivers of recruitment, nomenclature and functional paradoxes, therapeutic reprogramming and polarization strategies, relevant challenges, and our perspectives on therapeutic modulation.

A biopolymer-based and inflammation-responsive nanodrug for rheumatoid arthritis treatment via inhibiting JAK-STAT and JNK signalling pathways

Rheumatoid arthritis (RA) is a common chronic autoimmune disease associated with progressive disability, systemic complications, and poor prognosis. The improved understanding of the roles of immune signaling pathway inhibitors has shed light on designing new and more effective approaches for RA treatment. In this work, an inflammation-responsive and molecularly targeted drug system has been developed for RA therapy. The drug carrier was synthesized by covalently grafting hydrophobic cholesterol (Chol) molecules onto a hydrophilic chondroitin sulfate (CS) chain via the inflammation-responsive diselenide bonds (SeSe). The resultant amphiphilic polymer CSSeSeChol readily forms nanoparticles (NPs) and encapsulates two kinase inhibitors tofacitinib and SP600125 in aqueous media. Upon administration into the RA mouse model, the nanodrug accumulates in RA lesions and releases the inhibitors for regulating the JAK-STAT and JNK pathways. As a result, the nanodrug exhibits satisfactory efficacy in RA treatment by suppressing the expression of relevant pro-inflammatory cytokines, blocking the activation of osteoclasts and providing protection for cartilage and joints.

JAM-A functions as a female microglial tumor suppressor in glioblastoma

BACKGROUND

Glioblastoma (GBM) is the most aggressive primary brain tumor and has a dismal prognosis. Previously, we identified that junctional adhesion molecule A (JAM-A), a cell adhesion molecule, is highly elevated in human GBM cancer stem cells and predicts poor patient prognosis. While JAM-A is also highly expressed in other cells in the tumor microenvironment, specifically microglia and macrophages, how JAM-A expression in these cells affects tumor growth has yet to be determined. The goal of this study was to understand the role of microenvironmental JAM-A in mediating GBM growth.

METHODS

Male and female wild-type (WT) and JAM-A-deficient mice were transplanted intracranially with the syngeneic glioma cell lines GL261 and SB28 and were assessed for differences in survival and microglial activation in tumors and in vitro. RNA-sequencing was performed to identify differentially regulated genes among all genotypes, and differences were validated in vitro and in vivo.

RESULTS

We found that JAM-A-deficient female mice succumbed to GBM more quickly compared with WT females and JAM-A-deficient and male WT mice. Analysis of microglia in the tumors revealed that female JAM-A-deficient microglia were more activated, and RNA-sequencing identified elevated expression of Fizz1 and Ifi202b specifically in JAM-A-deficient female microglia.

CONCLUSIONS

Our findings suggest that JAM-A functions to suppress pathogenic microglial activation in the female tumor microenvironment, highlighting an emerging role for sex differences in the GBM microenvironment and suggesting that sex differences extend beyond previously reported tumor cell-intrinsic differences.

The impact of host immune cells on the development of neurofibromatosis type 1: The abnormal immune system provides an immune microenvironment for tumorigenesis

AbstractThe immune system plays an essential role in the development of tumors, which has been demonstrated in multiple types of cancers. Consistent with this, immunotherapies with targets that disrupt these mechanisms and turn the immune system against developing cancers have been proven effective. In neurofibromatosis type 1 (NF1), an autosomal dominant genetic disorder, the understanding of the complex interactions of the immune system is incomplete despite the discovery of the pivotal role of immune cells in the tumor microenvironment. Individuals with NF1 show a loss of the NF1 gene in nonneoplastic cells, including immune cells, and the aberrant immune system exhibits intriguing interactions with NF1. This review aims to provide an update on recent studies showing the bilateral influences of NF1 mutations on immune cells and how the abnormal immune system promotes the development of NF1 and NF1-related tumors. We then discuss the immune receptors major histocompatibility complex class I and II and the PD-L1 mechanism that shield NF1 from immunosurveillance and enable the immune escape of tumor tissues. Clarification of the latest understanding of the mechanisms underlying the effects of the abnormal immune system on promoting the development of NF1 will indicate potential future directions for further studies and new immunotherapies.

Translating current basic research into future therapies for neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is a hereditary tumour syndrome that predisposes to benign and malignant tumours originating from neural crest cells. Biallelic inactivation of the tumour-suppressor gene NF1 in glial cells in the skin, along a nerve plexus or in the brain results in the development of benign tumours: cutaneous neurofibroma, plexiform neurofibroma and glioma, respectively. Despite more than 40 years of research, only one medication was recently approved for treatment of plexiform neurofibroma and no drugs have been specifically approved for the management of other tumours. Work carried out over the past several years indicates that inhibiting different cellular signalling pathways (such as Hippo, Janus kinase/signal transducer and activator of transcription, mitogen-activated protein kinase and those mediated by sex hormones) in tumour cells or targeting cells in the microenvironment (nerve cells, macrophages, mast cells and T cells) might benefit NF1 patients. In this review, we outline previous strategies aimed at targeting these signalling pathways or cells in the microenvironment, agents that are currently in clinical trials, and the latest advances in basic research that could culminate in the development of novel therapeutics for patients with NF1.

Microglia/Brain Macrophages as Central Drivers of Brain Tumor Pathobiology

One of the most common brain tumors in children and adults is glioma or astrocytoma. There are few effective therapies for these cancers, and patients with malignant glioma fare poorly, even after aggressive surgery, chemotherapy, and radiation. Over the past decade, it is now appreciated that these tumors are composed of numerous distinct neoplastic and non-neoplastic cell populations, which could each influence overall tumor biology and response to therapy. Among these noncancerous cell types, monocytes (microglia and macrophages) predominate. In this Review, we discuss the complex interactions involving microglia and macrophages relevant to glioma formation, progression, and response to therapy.

The Sociobiology of Brain Tumors

Brain tumors are complex cellular ecosystems, composed of populations of both neoplastic and non-neoplastic cell types. While the contributions of the cancer cells in low-grade and high-grade gliomas have been extensively studied, there is comparatively less known about the contributions of the non-neoplastic cells in these tumors. As such, a large proportion of the non-neoplastic cells in gliomas are resident brain microglia, infiltrating circulating macrophages, and T lymphocytes. These immune system-like stromal cells are recruited into the evolving tumor through the elaboration of chemokines, and are reprogrammed to adopt new cellular identities critical for glioma formation, maintenance, and progression. In this manner, these populations of tumor-associated microglia and macrophages produce growth factors that support gliomagenesis and continued tumor growth. As we begin to characterize these immune cell contributions, future therapies might emerge as adjuvant approaches to glioma treatment.

Brain tumors in Neurofibromatosis type 1

As a cancer predisposition syndrome, individuals with neurofibromatosis type 1 (NF1) are at increased risk for the development of both benign and malignant tumors. One of the most common locations for these cancers is the central nervous system, where low-grade gliomas predominate in children. During early childhood, gliomas affecting the optic pathway are most frequently encountered, whereas gliomas of the brainstem and other locations are observed in slightly older children. In contrast, the majority of gliomas arising in adults with NF1 are malignant cancers, typically glioblastoma, involving the cerebral hemispheres. Our understanding of the pathogenesis of NF1-associated gliomas has been significantly advanced through the use of genetically engineered mice, yielding new targets for therapeutic drug design and evaluation. In addition, Nf1 murine glioma models have served as instructive platforms for defining the cell of origin of these tumors, elucidating the critical role of the tumor microenvironment in determining tumor growth and vision loss, and determining how cancer risk factors (sex, germline NF1 mutation) impact on glioma formation and progression. Moreover, these preclinical models have permitted early phase analysis of promising drugs that reduce tumor growth and attenuate vision loss, as an initial step prior to translation to human clinical trials.

Microglia as Dynamic Cellular Mediators of Brain Function

Originally hypothesized to function solely as immunologic responders within the central nervous system (CNS), emerging evidence has revealed that microglia have more complex roles in normal brain development and in the context of disease. In health, microglia influence neural progenitor fate decisions, astrocyte activation, neuronal homeostasis, and synaptogenesis. In the setting of brain disease, including autism, brain tumors, and neurodegenerative disorders, microglia undergo substantial morphological, molecular, and functional changes, which establish new biological states relevant to disease pathogenesis and progression. In this review, we discuss the function of microglia in health and disease and outline a conceptual framework for elucidating their specific contributions to nervous system pathobiology.

KIAA1549-BRAF Expression Establishes a Permissive Tumor Microenvironment Through NFκB-Mediated CCL2 Production

KIAA1549-BRAF is the most frequently identified genetic mutation in sporadic pilocytic astrocytoma (PA), creating a fusion BRAF (f-BRAF) protein with increased BRAF activity. Fusion-BRAF-expressing neural stem cells (NSCs) exhibit increased cell growth and can generate glioma-like lesions following injection into the cerebella of naïve mice. Increased Iba1⁺ monocyte (microglia) infiltration is associated with murine f-BRAF-expressing NSC-induced glioma-like lesion formation, suggesting that f-BRAF-expressing NSCs attract microglia to establish a microenvironment supportive of tumorigenesis. Herein, we identify Ccl2 as the chemokine produced by f-BRAF-expressing NSCs, which is critical for creating a permissive stroma for gliomagenesis. In addition, f-BRAF regulation of Ccl2 production operates in an ERK- and NFκB-dependent manner in cerebellar NSCs. Finally, Ccr2-mediated microglia recruitment is required for glioma-like lesion formation in vivo, as tumor do not form in Ccr2-deficient mice following f-BRAF-expressing NSC injection. Collectively, these results demonstrate that f-BRAF expression creates a supportive tumor microenvironment through NFκB-mediated Ccl2 production and microglia recruitment.

Graph complexity analysis identifies an ETV5 tumor-specific network in human and murine low-grade glioma

Conventional differential expression analyses have been successfully employed to identify genes whose levels change across experimental conditions. One limitation of this approach is the inability to discover central regulators that control gene expression networks. In addition, while methods for identifying central nodes in a network are widely implemented, the bioinformatics validation process and the theoretical error estimates that reflect the uncertainty in each step of the analysis are rarely considered. Using the betweenness centrality measure, we identified Etv5 as a potential tissue-level regulator in murine neurofibromatosis type 1 (Nf1) low-grade brain tumors (optic gliomas). As such, the expression of Etv5 and Etv5 target genes were increased in multiple independently-generated mouse optic glioma models relative to non-neoplastic (normal healthy) optic nerves, as well as in the cognate human tumors (pilocytic astrocytoma) relative to normal human brain. Importantly, differential Etv5 and Etv5 network expression was not directly the result of Nf1 gene dysfunction in specific cell types, but rather reflects a property of the tumor as an aggregate tissue. Moreover, this differential Etv5 expression was independently validated at the RNA and protein levels. Taken together, the combined use of network analysis, differential RNA expression findings, and experimental validation highlights the potential of the computational network approach to provide new insights into tumor biology.

Insights into optic pathway glioma vision loss from mouse models of neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is a common cancer predisposition syndrome caused by mutations in the NF1 gene. The NF1-encoded protein (neurofibromin) is an inhibitor of the oncoprotein RAS and controls cell growth and survival. Individuals with NF1 are prone to developing low-grade tumors of the optic nerves, chiasm, tracts, and radiations, termed optic pathway gliomas (OPGs), which can cause vision loss. A paucity of surgical tumor specimens and of patient-derived xenografts for investigative studies has limited our understanding of human NF1-associated OPG (NF1-OPG). However, mice genetically engineered to harbor Nf1 gene mutations develop optic gliomas that share many features of their human counterparts. These genetically engineered mouse (GEM) strains have provided important insights into the cellular and molecular determinants that underlie mouse Nf1 optic glioma development, maintenance, and associated vision loss, with relevance by extension to human NF1-OPG disease. Herein, we review our current understanding of NF1-OPG pathobiology and describe the mechanisms responsible for tumor initiation, growth, and associated vision loss in Nf1 GEM models. We also discuss how Nf1 GEM and other preclinical models can be deployed to identify and evaluate molecularly targeted therapies for OPG, particularly as they pertain to future strategies aimed at preventing or improving tumor-associated vision loss in children with NF1.

Athymic mice reveal a requirement for T-cell-microglia interactions in establishing a microenvironment supportive of Nf1 low-grade glioma growth

Murine Neurofibromatosis-1 (Nf1) optic low-grade glioma (LGG) stem cells (o-GSCs) form glioma-like lesions in wild-type, but not athymic, mice following transplantation. Here, Pan et al. show that the inability of athymic mice to support o-GSC engraftment results from impaired brain microglia/macrophage function, including reduced expression of Ccr2 and Ccl5, both of which are required for o-GSC engraftment and Nf1 optic glioma growth.

Pediatric low-grade gliomas (LGGs) frequently do not engraft in immunocompromised mice, limiting their use as an experimental platform. In contrast, murine Neurofibromatosis-1 (Nf1) optic LGG stem cells (o-GSCs) form glioma-like lesions in wild-type, but not athymic, mice following transplantation. Here, we show that the inability of athymic mice to support o-GSC engraftment results from impaired microglia/macrophage function, including reduced expression of Ccr2 and Ccl5, both of which are required for o-GSC engraftment and Nf1 optic glioma growth. Impaired Ccr2 and Ccl5 expression in athymic microglia/macrophages was restored by T-cell exposure, establishing T-cell–microglia/macrophage interactions as critical stromal determinants that support NF1 LGG growth.

Neurofibromatosis type 1 and optic pathway glioma: Molecular interplay and therapeutic insights

Children with neurofibromatosis type 1 (NF1) are predisposed to develop central nervous system neoplasms, the most common of which are low-grade gliomas (LGGs). The absence of human NF1 associated LGG-derived cell lines, coupled with an inability to generate patient-derived xenograft models, represents barriers to profile molecularly targeted therapies for these tumors. Thus, genetically engineered mouse models have been identified to evaluate the interplay between Nf1-deficient tumor cells and nonneoplastic stromal cells to evaluate potential therapies for these neoplasms. Future treatments might also consider targeting the nonneoplastic cells in NF1-LGGs to reduce tumor growth and neurologic morbidity in affected children.

Tumor initiating cells induce Cxcr4-mediated infiltration of pro-tumoral macrophages into the brain

It is now clear that microglia and macrophages are present in brain tumors, but whether or how they affect initiation and development of tumors is not known. Exploiting the advantages of the zebrafish (Danio rerio) model, we showed that macrophages and microglia respond immediately upon oncogene activation in the brain. Overexpression of human AKT1 within neural cells of larval zebrafish led to a significant increase in the macrophage and microglia populations. By using a combination of transgenic and mutant zebrafish lines, we showed that this increase was caused by the infiltration of peripheral macrophages into the brain mediated via Sdf1b-Cxcr4b signaling. Intriguingly, confocal live imaging reveals highly dynamic interactions between macrophages/microglia and pre-neoplastic cells, which do not result in phagocytosis of pre-neoplastic cells. Finally, depletion of macrophages and microglia resulted in a significant reduction of oncogenic cell proliferation. Thus, macrophages and microglia show tumor promoting functions already during the earliest stages of the developing tumor microenvironment.

β1 integrin- and JNK-dependent tumor growth upon hypofractionated radiation

Radiation therapy is an effective cancer treatment modality although tumors invariably become resistant. Using the transgenic adenocarcinoma of mouse prostate (TRAMP) model system, we report that a hypofractionated radiation schedule (10 Gy/day for 5 consecutive days) effectively blocks prostate tumor growth in wild type (β1^wt /TRAMP) mice as well as in mice carrying a conditional ablation of β1 integrins in the prostatic epithelium (β1^pc-/- /TRAMP). Since JNK is known to be suppressed by β1 integrins and mediates radiation-induced apoptosis, we tested the effect of SP600125, an inhibitor of c-Jun amino-terminal kinase (JNK) in the TRAMP model system. Our results show that SP600125 negates the effect of radiation on tumor growth in β1^pc-/- /TRAMP mice and leads to invasive adenocarcinoma. These effects are associated with increased focal adhesion kinase (FAK) expression and phosphorylation in prostate tumors in β1^pc-/- /TRAMP mice. In marked contrast, radiation-induced tumor growth suppression, FAK expression and phosphorylation are not altered by SP600125 treatment of β1^wt /TRAMP mice. Furthermore, we have reported earlier that abrogation of insulin-like growth factor receptor (IGF-IR) in prostate cancer cells enhances the sensitivity to radiation. Here we further explore the β1/IGF-IR crosstalk and report that β1 integrins promote cell proliferation partly by enhancing the expression of IGF-IR. In conclusion, we demonstrate that β1 integrin-mediated inhibition of JNK signaling modulates tumor growth rate upon hypofractionated radiation.

Neurofibromin 1 Impairs Natural Killer T-Cell-Dependent Antitumor Immunity against a T-Cell Lymphoma

Neurofibromin 1 (NF1) is a tumor suppressor gene encoding a Ras GTPase that negatively regulates Ras signaling pathways. Mutations in NF1 are linked to neurofibromatosis type 1, juvenile myelomonocytic leukemia and Watson syndrome. In terms of antitumor immunity, CD1d-dependent natural killer T (NKT) cells play an important role in the innate antitumor immune response. Generally, Type-I NKT cells protect (and Type-II NKT cells impair) host antitumor immunity. We have previously shown that CD1d-mediated antigen presentation to NKT cells is regulated by cell signaling pathways. To study whether a haploinsufficiency in NF1 would affect CD1d-dependent activation of NKT cells, we analyzed the NKT-cell population as well as the functional expression of CD1d in Nf1^+/− mice. Nf1^+/− mice were found to have similar levels of NKT cells as wildtype (WT) littermates. Interestingly, however, reduced CD1d expression was observed in Nf1^+/− mice compared with their WT littermates. When inoculated with a T-cell lymphoma in vivo, Nf1^+/− mice survived longer than their WT littermates. Furthermore, blocking CD1d in vivo significantly enhanced antitumor activity in WT, but not in Nf1^+/− mice. In contrast, a deficiency in Type-I NKT cells increased antitumor activity in Nf1^+/− mice, but not in WT littermates. Therefore, these data suggest that normal NF1 expression impairs CD1d-mediated NKT-cell activation and antitumor activity against a T-cell lymphoma.

Optic Pathway Gliomas in Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1) is one of the most common brain tumor predisposition syndromes, in which affected children are prone to the development of low-grade gliomas. While NF1-associated gliomas can be found in several brain regions, the majority arise in the optic nerves, chiasm, tracts, and radiations (optic pathway gliomas; OPGs). Owing to their location, 35-50% of affected children present with reduced visual acuity. Unfortunately, despite tumor stabilization following chemotherapy, vision does not improve in most children. For this reasons, more effective therapies are being sought that reflect a deeper understanding of the NF1 gene and the use of authenticated Nf1 genetically-engineered mouse strains. The implementation of these models for drug discovery and validation has galvanized molecularly-targeted clinical trials in children with NF1-OPG. Future research focused on defining the cellular and molecular factors that underlie optic glioma development and progression also has the potential to provide personalized risk assessment strategies for this pediatric population.

Dissecting Clinical Heterogeneity in Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1) is a common neurogenetic disorder in which affected children and adults are predisposed to the development of benign and malignant nervous system tumors. Caused by a germline mutation in the NF1 tumor suppressor gene, individuals with NF1 are prone to optic gliomas, malignant gliomas, neurofibromas, and malignant peripheral nerve sheath tumors, as well as behavioral, cognitive, motor, bone, cardiac, and pigmentary abnormalities. Although NF1 is a classic monogenic syndrome, the clinical features of the disorder and their impact on patient morbidity are variable, even within individuals who bear the same germline NF1 gene mutation. As such, NF1 affords unique opportunities to define the factors that contribute to disease heterogeneity and to develop therapies personalized to a given individual (precision medicine). This review highlights the clinical features of NF1 and the use of genetically engineered mouse models to define the molecular and cellular pathogenesis of NF1-associated nervous system tumors.

Whole tumor RNA-sequencing and deconvolution reveal a clinically-prognostic PTEN/PI3K-regulated glioma transcriptional signature

The concept that solid tumors are maintained by a productive interplay between neoplastic and non-neoplastic elements has gained traction with the demonstration that stromal fibroblasts and immune system cells dictate cancer development and progression. While less studied, brain tumor (glioma) biology is likewise influenced by non-neoplastic immune system cells (macrophages and microglia) which interact with neoplastic glioma cells to create a unique physiological state (glioma ecosystem) distinct from that found in the normal tissue. To explore this neoplastic ground state, we leveraged several preclinical mouse models of neurofibromatosis type 1 (NF1) optic glioma, a low-grade astrocytoma whose formation and maintenance requires productive interactions between non-neoplastic and neoplastic cells, and employed whole tumor RNA-sequencing and mathematical deconvolution strategies to characterize this low-grade glioma ecosystem as an aggregate of cellular and acellular elements. Using this approach, we demonstrate that optic gliomas generated by altering the germline Nf1 gene mutation, the glioma cell of origin, or the presence of co-existing genetic alterations represent molecularly-distinct tumors. However, these optic glioma tumors share a 25-gene core signature, not found in normal optic nerve, that is normalized by microglia inhibition (minocycline), but not conventional (carboplatin) or molecularly-targeted (rapamycin) chemotherapy. Lastly, we identify a genetic signature conferred by Pten reduction and corrected by PI3K inhibition. This signature predicts progression-free survival in patients with either low-grade or high-grade glioma. Collectively, these findings support the concept that gliomas are composite ecological systems whose biology and response to therapy may be best defined by examining the tumor as a whole.

Neurofibromatosis type 1

Neurofibromatosis type 1 is a complex autosomal dominant disorder caused by germline mutations in the NF1 tumour suppressor gene. Nearly all individuals with neurofibromatosis type 1 develop pigmentary lesions (café-au-lait macules, skinfold freckling and Lisch nodules) and dermal neurofibromas. Some individuals develop skeletal abnormalities (scoliosis, tibial pseudarthrosis and orbital dysplasia), brain tumours (optic pathway gliomas and glioblastoma), peripheral nerve tumours (spinal neurofibromas, plexiform neurofibromas and malignant peripheral nerve sheath tumours), learning disabilities, attention deficits, and social and behavioural problems, which can negatively affect quality of life. With the identification of NF1 and the generation of accurate preclinical mouse strains that model some of these clinical features, therapies that target the underlying molecular and cellular pathophysiology for neurofibromatosis type 1 are becoming available. Although no single treatment exists, current clinical management strategies include early detection of disease phenotypes (risk assessment) and biologically targeted therapies. Similarly, new medical and behavioural interventions are emerging to improve the quality of life of patients. Although considerable progress has been made in understanding this condition, numerous challenges remain; a collaborative and interdisciplinary approach is required to manage individuals with neurofibromatosis type1 and to develop effective treatments.

The role of the immune system in neurofibromatosis type 1-associated nervous system tumors

With the recent development of new anticancer therapies targeting the immune system, it is important to understand which immune cell types and cytokines play critical roles in suppressing or promoting tumorigenesis. The role of mast cells in promoting neurofibroma growth in neurofibromatosis type 1 (NF1) patients was hypothesized decades ago. More recent experiments in mouse models have demonstrated the causal role of mast cells in neurofibroma development and of microglia in optic pathway glioma development. We review here what is known about the role of NF1 mutation in immune cell function and the role of immune cells in promoting tumorigenesis in NF1. We also review the therapies targeting immune cell pathways and their promise in NF1 tumors.

Challenges in Drug Discovery for Neurofibromatosis Type 1-Associated Low-Grade Glioma

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder that results from germline mutations of the NF1 gene, creating a predisposition to low-grade gliomas (LGGs; pilocytic astrocytoma) in young children. Insufficient data and resources represent major challenges to identifying the best possible drug therapies for children with this tumor. Herein, we summarize the currently available cell lines, genetically engineered mouse models, and therapeutic targets for these LGGs. Conspicuously absent are human tumor-derived cell lines or patient-derived xenograft models for NF1-LGG. New collaborative initiatives between patients and their families, research groups, and pharmaceutical companies are needed to create transformative resources and broaden the knowledge base relevant to identifying cooperating genetic drivers and possible drug therapeutics for this common pediatric brain tumor.

Associations between allergic conditions and pediatric brain tumors in Neurofibromatosis type 1

Individuals with Neurofibromatosis type 1 (NF1) are at increased risk for pediatric brain tumors (PBTs), especially optic gliomas; however, factors influencing their development are largely unknown. Extensive research suggests that allergic conditions protect against brain tumors, particularly gliomas in individuals without NF1. In this large cross-sectional study, we employed two different data sources to evaluate evidence for the hypothesis that allergic conditions (allergies, asthma, and eczema) may protect against PBT development in individuals with NF1. We used self- and parent/legal guardian reported questionnaire data from participants in the NF1 Patient Registry Initiative (NPRI, n = 1660) born from 1933 to 2014 to ascertain allergic condition and PBT diagnosis histories. Medical records (MRs) of 629 NF1 patients at a large medical center born from 1930 to 2012 were also reviewed for PBT and allergic condition diagnoses to evaluate additional evidence for our hypothesis. We used logistic regression to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for associations between allergic condition diagnoses and PBTs. Both data sources provided limited to no support for a protective effect of allergies or eczema on PBT development. Non-significant inverse associations between asthma and PBTs were observed (NPRI: OR = 0.80, 95% CI 0.55-1.17; MR: OR = 0.71, 95% CI 0.40-1.28) with stronger associations for optic gliomas specifically. Additionally, a significant inverse association was observed in an NPRI subgroup analysis where the reported asthma diagnosis age was younger than the reported PBT diagnosis age (OR = 0.57; 95% CI 0.36-0.89). Our study supports the hypothesis that asthma protects against PBT development in NF1.

Estrogen activation of microglia underlies the sexually dimorphic differences in Nf1 optic glioma-induced retinal pathology

Children with neurofibromatosis type 1 (NF1) develop low-grade brain tumors throughout the optic pathway. Nearly 50% of children with optic pathway gliomas (OPGs) experience visual impairment, and few regain their vision after chemotherapy. Recent studies have revealed that girls with optic nerve gliomas are five times more likely to lose vision and require treatment than boys. To determine the mechanism underlying this sexually dimorphic difference in clinical outcome, we leveraged Nf1 optic glioma (Nf1-OPG) mice. We demonstrate that female Nf1-OPG mice exhibit greater retinal ganglion cell (RGC) loss and only females have retinal nerve fiber layer (RNFL) thinning, despite mice of both sexes harboring tumors of identical volumes and proliferation. Female gonadal sex hormones are responsible for this sexual dimorphism, as ovariectomy, but not castration, of Nf1-OPG mice normalizes RGC survival and RNFL thickness. In addition, female Nf1-OPG mice have threefold more microglia than their male counterparts, and minocycline inhibition of microglia corrects the retinal pathology. Moreover, pharmacologic inhibition of microglial estrogen receptor-β (ERβ) function corrects the retinal abnormalities in female Nf1-OPG mice. Collectively, these studies establish that female gonadal sex hormones underlie the sexual dimorphic differences in Nf1 optic glioma-induced retinal dysfunction by operating at the level of tumor-associated microglial activation.

RNA Sequencing of Tumor-Associated Microglia Reveals Ccl5 as a Stromal Chemokine Critical for Neurofibromatosis-1 Glioma Growth

Solid cancers develop within a supportive microenvironment that promotes tumor formation and growth through the elaboration of mitogens and chemokines. Within these tumors, monocytes (macrophages and microglia) represent rich sources of these stromal factors. Leveraging a genetically engineered mouse model of neurofibromatosis type 1 (NF1) low-grade brain tumor (optic glioma), we have previously demonstrated that microglia are essential for glioma formation and maintenance. To identify potential tumor-associated microglial factors that support glioma growth (gliomagens), we initiated a comprehensive large-scale discovery effort using optimized RNA-sequencing methods focused specifically on glioma-associated microglia. Candidate microglial gliomagens were prioritized to identify potential secreted or membrane-bound proteins, which were next validated by quantitative real-time polymerase chain reaction as well as by RNA fluorescence in situ hybridization following minocycline-mediated microglial inactivation in vivo. Using these selection criteria, chemokine (C-C motif) ligand 5 (Ccl5) was identified as a chemokine highly expressed in genetically engineered Nf1 mouse optic gliomas relative to nonneoplastic optic nerves. As a candidate gliomagen, recombinant Ccl5 increased Nf1-deficient optic nerve astrocyte growth in vitro. Importantly, consistent with its critical role in maintaining tumor growth, treatment with Ccl5 neutralizing antibodies reduced Nf1 mouse optic glioma growth and improved retinal dysfunction in vivo. Collectively, these findings establish Ccl5 as an important microglial growth factor for low-grade glioma maintenance relevant to the development of future stroma-targeted brain tumor therapies.

Contextual signaling in cancer

The formation and maintenance of an organism are highly dependent on the orderly control of cell growth, differentiation, death, and migration. These processes are tightly regulated by signaling cascades in which a limited number of molecules dictate these cellular events. While these signaling pathways are highly conserved across species and cell types, the functional outcomes that result from their engagement are specified by the context in which they are activated. Using the Neurofibromatosis type 1 (NF1) cancer predisposition syndrome as an illustrative platform, we discuss how NF1/RAS signaling can create functional diversity at multiple levels (molecular, cellular, tissue, and genetic/genomic). As such, the ability of related molecules (e.g., K-RAS, H-RAS) to activate distinct effectors, as well as cell type- and tissue-specific differences in molecular composition and effector engagement, generate numerous unique functional effects. These variations, coupled with a multitude of extracellular cues and genomic/genetic changes that each modify the innate signaling properties of the cell, enable precise control of cellular physiology in both health and disease. Understanding these contextual influences is important when trying to dissect the underlying pathogenic mechanisms of cancer relevant to molecularly-targeted therapeutics.

The role of microglia and macrophages in glioma maintenance and progression

There is a growing recognition that gliomas are complex tumors composed of neoplastic and non-neoplastic cells, which each individually contribute to cancer formation, progression and response to treatment. The majority of the non-neoplastic cells are tumor-associated macrophages (TAMs), either of peripheral origin or representing brain-intrinsic microglia, that create a supportive stroma for neoplastic cell expansion and invasion. TAMs are recruited to the glioma environment, have immune functions, and can release a wide array of growth factors and cytokines in response to those factors produced by cancer cells. In this manner, TAMs facilitate tumor proliferation, survival and migration. Through such iterative interactions, a unique tumor ecosystem is established, which offers new opportunities for therapeutic targeting.

Neurofibromatosis type 1 associated low grade gliomas: A comparison with sporadic low grade gliomas

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder, associated with a variable clinical phenotype including café-au-lait spots, intertriginous freckling, Lisch nodules, neurofibromas, optic pathway gliomas and distinctive bony lesions. NF1 is caused by a mutation in the NF1 gene, which codes for neurofibromin, a large protein involved in the MAPK- and the mTOR-pathway through RAS-RAF signalling. NF1 is a known tumour predisposition syndrome, associated with different tumours of the nervous system including low grade gliomas (LGGs) in the paediatric population. The focus of this review is on grade I pilocytic astrocytomas (PAs), the most commonly observed histologic subtype of low grade gliomas in NF1. Clinically, these PAs have a better prognosis and show different localisation patterns than their sporadic counterparts, which are most commonly associated with a KIAA1549:BRAF fusion. In this review, possible mechanisms of tumourigenesis in LGGs with and without NF1 will be discussed, including the contribution of different signalling pathways and tumour microenvironment. Furthermore we will discuss how increased understanding of tumourigenesis may lead to new potential targets for treatment.

RASopathies: unraveling mechanisms with animal models

RASopathies are developmental disorders caused by germline mutations in the Ras-MAPK pathway, and are characterized by a broad spectrum of functional and morphological abnormalities. The high incidence of these disorders (∼1/1000 births) motivates the development of systematic approaches for their efficient diagnosis and potential treatment. Recent advances in genome sequencing have greatly facilitated the genotyping and discovery of mutations in affected individuals, but establishing the causal relationships between molecules and disease phenotypes is non-trivial and presents both technical and conceptual challenges. Here, we discuss how these challenges could be addressed using genetically modified model organisms that have been instrumental in delineating the Ras-MAPK pathway and its roles during development. Focusing on studies in mice, zebrafish and Drosophila, we provide an up-to-date review of animal models of RASopathies at the molecular and functional level. We also discuss how increasingly sophisticated techniques of genetic engineering can be used to rigorously connect changes in specific components of the Ras-MAPK pathway with observed functional and morphological phenotypes. Establishing these connections is essential for advancing our understanding of RASopathies and for devising rational strategies for their management and treatment.

Summary: Developmental disorders caused by germline mutations in the Ras-MAPK pathway are called RASopathies. Studies with animal models, including mice, zebrafish and Drosophila, continue to enhance our understanding of these diseases.

NF1 germline mutation differentially dictates optic glioma formation and growth in neurofibromatosis-1

Neurofibromatosis type 1 (NF1) is a common neurogenetic condition characterized by significant clinical heterogeneity. A major barrier to developing precision medicine approaches for NF1 is an incomplete understanding of the factors that underlie its inherent variability. To determine the impact of the germline NF1 gene mutation on the optic gliomas frequently encountered in children with NF1, we developed genetically engineered mice harboring two representative NF1-patient-derived Nf1 gene mutations (c.2542G>C;p.G848R and c.2041C>T;p.R681X). We found that each germline Nf1 gene mutation resulted in different levels of neurofibromin expression. Importantly, only R681X(CKO) but not G848R(CKO), mice develop optic gliomas with increased optic nerve volumes, glial fibrillary acid protein immunoreactivity, proliferation and retinal ganglion cell death, similar to Nf1 conditional knockout mice harboring a neomycin insertion (neo) as the germline Nf1 gene mutation. These differences in optic glioma phenotypes reflect both cell-autonomous and stromal effects of the germline Nf1 gene mutation. In this regard, primary astrocytes harboring the R681X germline Nf1 gene mutation exhibit increased basal astrocyte proliferation (BrdU incorporation) indistinguishable from neo(CKO) astrocytes, whereas astrocytes with the G848R mutation have lower levels of proliferation. Evidence for paracrine effects from the tumor microenvironment were revealed when R681X(CKO) mice were compared with conventional neo(CKO) mice. Relative to neo(CKO) mice, the optic gliomas from R681X(CKO) mice had more microglia infiltration and JNK(Thr183/Tyr185) activation, microglia-produced Ccl5, and glial AKT(Thr308) activation. Collectively, these studies establish that the germline Nf1 gene mutation is a major determinant of optic glioma development and growth through by both tumor cell-intrinsic and stromal effects.

3-D imaging mass spectrometry of protein distributions in mouse Neurofibromatosis 1 (NF1)-associated optic glioma

Neurofibromatosis type 1 (NF1) is a common neurogenetic disorder, in which affected individuals develop tumors of the nervous system. Children with NF1 are particularly prone to brain tumors (gliomas) involving the optic pathway that can result in impaired vision. Since tumor formation and expansion requires a cooperative tumor microenvironment, it is important to identify the cellular and acellular components associated with glioma development and growth. In this study, we used 3-D matrix assisted laser desorption ionization imaging mass spectrometry (MALDI IMS) to measure the distributions of multiple molecular species throughout optic nerve tissue in mice with and without glioma, and to explore their spatial relationships within the 3-D volume of the optic nerve and chiasm. 3-D IMS studies often involve extensive workflows due to the high volume of sections required to generate high quality 3-D images. Herein, we present a workflow for 3-D data acquisition and volume reconstruction using mouse optic nerve tissue. The resulting 3-D IMS data yield both molecular similarities and differences between glioma-bearing and wild-type (WT) tissues, including protein distributions localizing to different anatomical subregions.

BIOLOGICAL SIGNIFICANCE

The current work addresses a number of challenges in 3-D MALDI IMS, driven by the small size of the mouse optic nerve and the need to maintain consistency across multiple 2-D IMS experiments. The 3-D IMS data yield both molecular similarities and differences between glioma-bearing and wild-type (WT) tissues, including protein distributions localizing to different anatomical subregions, which could then be targeted for identification and related back to the biology observed in gliomas of the optic nerve.

Pediatric gliomas as neurodevelopmental disorders

Brain tumors represent the most common solid tumor of childhood, with gliomas comprising the largest fraction of these cancers. Several features distinguish them from their adult counterparts, including their natural history, causative genetic mutations, and brain locations. These unique properties suggest that the cellular and molecular etiologies that underlie their development and maintenance might be different from those that govern adult gliomagenesis and growth. In this review, we discuss the genetic basis for pediatric low-grade and high-grade glioma in the context of developmental neurobiology, and highlight the differences between histologically-similar tumors arising in children and adults.