Are lipid droplets the picnic basket of brain tumours?

Are lipid droplets (LDs) necessary to maintain the viability of brain tumour cells as they move to new nutrient-poor environments? In turn, could cancers be targeted by attacking what you might think of as the cancer cells' picnic basket? Lipid metabolism reprogramming, represented by increased lipid uptake, activation of de novo lipogenesis and increased lipid storage, is a newly identified hallmark of cancers. Recently, the presence of lipid droplets has been detected in several types of cancers, such as metastatic hepatocellular carcinoma, pancreatic and breast. LDs are storage organelles that provide a source of nutrients which may drive metastasis in different tumours. Currently, several roles of LDs have been posited in various tumours. This perspective aims to review and discuss the currently understood role of LDs in brain tumours.

The role of immunomodulators in treatment-resistant depression: case studies.

Depression is a common mental disorder affecting more than 264 million people worldwide. The first-line treatment for most cases of depression are selective serotonin reuptake inhibitors (SSRIs), such as sertraline, reboxetine and fluoxetine. Recently, it has been found that one-quarter of depressed patients have excessive activation of the immune system. This potentially warrants sub-categorisation of depressed patients into inflammatory and non-inflammatory subtypes. Such a sub-category of depression already exists for those not responding to various traditional antidepressants and is known as treatment-resistant depression. Those with treatment-resistant depression are far more likely to have raised inflammatory markers relative to those whose depression is treatment-responsive. Chronic, low-level inflammation seems to trigger depression via a multitude of mechanisms. These include kynurenine pathway and microglial cell activation, resulting in a reduction in hippocampal volume. Raised inflammatory cytokines also cause perturbations in monoaminergic signalling, which perhaps explains the preponderance of treatment resistance in those patients with inflammatory depression. Therefore, if treatment-resistant depression and inflammatory depression are semi-synonymous then it should follow that anti-inflammatory drugs will display high efficacy in both sub-types. Ketamine is a drug recently approved for use in depression in the USA and displays a particularly good response rate in those patients with treatment resistance. It has been suggested that the antidepressant efficacy of ketamine results from its anti-inflammatory effects. Ketamine seems to produce anti-inflammatory effects via polarisation of monocytes to M2 macrophages. Furthermore, another anti-inflammatory drug with potential use in treatment-resistant depression is Celecoxib. Celecoxib is a long-acting, selective COX-2 inhibitor. Early clinical trials show that Celecoxib has an adjuvant effect with traditional antidepressants in treatment-resistant patients. This paper highlights the importance of classifying depressed patients into inflammatory and non-inflammatory subtypes; and how this may lead to the development of more targeted treatments for treatment-resistant depression.

Role of MicroRNAs in the Development and Progression of the Four Medulloblastoma Subgroups.

Medulloblastoma is the most frequent malignant brain tumour in children. Medulloblastoma originate during the embryonic stage. They are located in the cerebellum, which is the area of the central nervous system (CNS) responsible for controlling equilibrium and coordination of movements. In 2012, medulloblastoma were divided into four subgroups based on a genome-wide analysis of RNA expression. These subgroups are named Wingless, Sonic Hedgehog, Group 3 and Group 4. Each subgroup has a different cell of origin, prognosis, and response to therapies. Wingless and Sonic Hedgehog medulloblastoma are so named based on the main mutation originating these tumours. Group 3 and Group 4 have generic names because we do not know the key mutation driving these tumours. Gene expression at the post-transcriptional level is regulated by a group of small single-stranded non-coding RNAs. These microRNA (miRNAs or miRs) play a central role in several cellular functions such as cell differentiation and, therefore, any malfunction in this regulatory system leads to a variety of disorders such as cancer. The role of miRNAs in medulloblastoma is still a topic of intense clinical research; previous studies have mostly concentrated on the clinical entity of the single disease rather than in the four molecular subgroups. In this review, we summarize the latest discoveries on miRNAs in the four medulloblastoma subgroups.

Alcohol-abuse drug disulfiram targets pediatric glioma via MLL degradation.

Pediatric gliomas comprise a broad range of brain tumors derived from glial cells. While high-grade gliomas are often resistant to therapy and associated with a poor outcome, children with low-grade gliomas face a better prognosis. However, the treatment of low-grade gliomas is often associated with severe long-term adverse effects. This shows that there is a strong need for improved treatment approaches. Here, we highlight the potential for repurposing disulfiram to treat pediatric gliomas. Disulfiram is a drug used to support the treatment of chronic alcoholism and was found to be effective against diverse cancer types in preclinical studies. Our results show that disulfiram efficiently kills pediatric glioma cell lines as well as patient-derived glioma stem cells. We propose a novel mechanism of action to explain disulfiram's anti-oncogenic activities by providing evidence that disulfiram induces the degradation of the oncoprotein MLL. Our results further reveal that disulfiram treatment and MLL downregulation induce similar responses at the level of histone modifications and gene expression, further strengthening that MLL is a key target of the drug and explaining its anti-oncogenic properties.

Elucidation of the BMI1 interactome identifies novel regulatory roles in glioblastoma.

Glioblastoma (GBM) is the most common and aggressive intrinsic brain tumour in adults. Epigenetic mechanisms controlling normal brain development are often dysregulated in GBM. Among these, BMI1, a structural component of the Polycomb Repressive Complex 1 (PRC1), which promotes the H2AK119ub catalytic activity of Ring1B, is upregulated in GBM and its tumorigenic role has been shown in vitro and in vivo. Here, we have used protein and chromatin immunoprecipitation followed by mass spectrometry (MS) analysis to elucidate the protein composition of PRC1 in GBM and transcriptional silencing of defining interactors in primary patient-derived GIC lines to assess their functional impact on GBM biology. We identify novel regulatory functions in mRNA splicing and cholesterol transport which could represent novel targetable mechanisms in GBM.

Correction to 'Elucidation of the BMI1 interactome identifies novel regulatory roles in glioblastoma'.

[This corrects the article DOI: 10.1093/narcan/zcab009.].

Can small molecular inhibitors that stop de novo serine synthesis be used in cancer treatment?

To sustain their malignancy, tumour cells acquire several metabolic adaptations such as increased oxygen, glucose, glutamine, and lipids uptake. Other metabolic processes are also enhanced as part of tumour metabolic reprogramming, for example, increased serine metabolism. Serine is a non-essential amino acid that supports several metabolic processes that are crucial for the growth and survival of proliferating cells, including protein, DNA, and glutathione synthesis. Indeed, increased activity of D-3-phosphoglycerate dehydrogenase (PHGDH), the enzyme rate-limiting de novo serine synthesis, has been extensively reported in several tumours. Therefore, selective inhibition of PHGDH may represent a new therapeutic strategy for over-expressing PHGDH tumours, owing to its downstream inhibition of essential biomass production such as one-carbon units and nucleotides. This perspective article will discuss the current status of research into small molecular inhibitors against PHGDH in colorectal cancer, breast cancer, and Ewing's sarcoma. We will summarise recent studies on the development of PHGDH-inhibitors, highlighting their clinical potential as new therapeutics. It also wants to shed a light on some of the key limitations of the use of PHGDH-inhibitors in cancer treatment which are worth taking into account.

Inositol treatment inhibits medulloblastoma through suppression of epigenetic-driven metabolic adaptation.

Deregulation of chromatin modifiers plays an essential role in the pathogenesis of medulloblastoma, the most common paediatric malignant brain tumour. Here, we identify a BMI1-dependent sensitivity to deregulation of inositol metabolism in a proportion of medulloblastoma. We demonstrate mTOR pathway activation and metabolic adaptation specifically in medulloblastoma of the molecular subgroup G4 characterised by a BMI1High;CHD7Low signature and show this can be counteracted by IP6 treatment. Finally, we demonstrate that IP6 synergises with cisplatin to enhance its cytotoxicity in vitro and extends survival in a pre-clinical BMI1High;CHD7Low xenograft model.

Regulation of Adult Neurogenesis in Mammalian Brain.

Adult neurogenesis is a multistage process by which neurons are generated and integrated into existing neuronal circuits. In the adult brain, neurogenesis is mainly localized in two specialized niches, the subgranular zone (SGZ) of the dentate gyrus and the subventricular zone (SVZ) adjacent to the lateral ventricles. Neurogenesis plays a fundamental role in postnatal brain, where it is required for neuronal plasticity. Moreover, perturbation of adult neurogenesis contributes to several human diseases, including cognitive impairment and neurodegenerative diseases. The interplay between extrinsic and intrinsic factors is fundamental in regulating neurogenesis. Over the past decades, several studies on intrinsic pathways, including transcription factors, have highlighted their fundamental role in regulating every stage of neurogenesis. However, it is likely that transcriptional regulation is part of a more sophisticated regulatory network, which includes epigenetic modifications, non-coding RNAs and metabolic pathways. Here, we review recent findings that advance our knowledge in epigenetic, transcriptional and metabolic regulation of adult neurogenesis in the SGZ of the hippocampus, with a special attention to the p53-family of transcription factors.

The C terminus of p73 is essential for hippocampal development.

The p53 family member p73 has a complex gene structure, including alternative promoters and alternative splicing of the 3' UTR. This results in a complex range of isoforms whose biological relevance largely remains to be determined. By deleting exon 13 (which encodes a sterile α motif) from the Trp73 gene, we selectively engineered mice to replace the most abundantly expressed C-terminal isoform, p73α, with a shorter product of alternative splicing, p73ß. These mice (Trp73Δ13/Δ13 ) display severe neurodevelopmental defects with significant functional and morphological abnormalities. Replacement of p73α with p73ß results in the depletion of Cajal-Retzius (CR) cells in embryonic stages, thus depriving the developing hippocampus of the pool of neurons necessary for correct hippocampal architecture. Consequently, Trp73Δ13/Δ13 mice display severe hippocampal dysgenesis, reduced synaptic functionality and impaired learning and memory capabilities. Our data shed light on the relevance of p73 alternative splicing and show that the full-length C terminus of p73 is essential for hippocampal development.

NPI-0052 and γ-radiation induce a synergistic apoptotic effect in medulloblastoma.

Medulloblastoma (MB) is the most common malignant solid paediatric brain tumour. The standard treatment for MB is surgical resection of the tumour, radiation and chemotherapy. This therapy is associated with high morbidity and adverse side effects. Hence, more targeted and less toxic therapies are vitally needed to improve the quality of life of survivors. NPI-0052 is a novel proteasome inhibitor that irreversibly binds the 20S proteasome subunit. This compound has anti-tumour activity in metastatic solid tumours, glioblastoma and multiple myeloma with a good safety profile. Importantly, NPI-0052 has a lipophilic structure and can penetrate the blood-brain barrier, making it a suitable treatment for brain tumours. In the present study, we performed an in silico gene expression analysis to evaluate the proteasome subunit expression in MB. To evaluate the anticancer activity of NPI-0052, we used a range of MB patient-derived MB cells and cell lines. The synergistic cell death of NPI-0052 with γ-radiation was evaluated in tumour organoids derived from patient-derived MB cells. We show that high expression of proteasome subunits is a poor prognostic factor for MB patients. Also, our preclinical work demonstrated that NPI-0052 can inhibit proteasome activity and activate apoptosis in MB cells. Moreover, we observe that NPI-0052 has a synergistic apoptotic effect with γ-radiation, a component of the current MB therapy. Here, we present compelling preclinical evidence that NPI-0052 can be used as an adjuvant treatment for p53-family-expressing MB tumours.

TET2 Regulates the Neuroinflammatory Response in Microglia.

Epigenomic mechanisms regulate distinct aspects of the inflammatory response in immune cells. Despite the central role for microglia in neuroinflammation and neurodegeneration, little is known about their epigenomic regulation of the inflammatory response. Here, we show that Ten-eleven translocation 2 (TET2) methylcytosine dioxygenase expression is increased in microglia upon stimulation with various inflammogens through a NF-κB-dependent pathway. We found that TET2 regulates early gene transcriptional changes, leading to early metabolic alterations, as well as a later inflammatory response independently of its enzymatic activity. We further show that TET2 regulates the proinflammatory response in microglia of mice intraperitoneally injected with LPS. We observed that microglia associated with amyloid ß plaques expressed TET2 in brain tissue from individuals with Alzheimer's disease (AD) and in 5xFAD mice. Collectively, our findings show that TET2 plays an important role in the microglial inflammatory response and suggest TET2 as a potential target to combat neurodegenerative brain disorders.

FASN activity is important for the initial stages of the induction of senescence.

Senescent cells accumulate in several tissues during ageing and contribute to several pathological processes such as ageing and cancer. Senescence induction is a complex process not well defined yet and is characterized by a series of molecular changes acquired after an initial growth arrest. We found that fatty acid synthase (FASN) levels increase during the induction of senescence in mouse hepatic stellate cells and human primary fibroblasts. Importantly, we also observed a significant increase in FASN levels during ageing in mouse liver tissues. To probe the central role of FASN in senescence induction, we used a small-molecule inhibitor of FASN activity, C75. We found that C75 treatment prevented the induction of senescence in mouse and human senescent cells. Importantly, C75 also reduced the expression of the signature SASP factors interleukin 1α (IL-1α), IL-1ß and IL-6, and suppressed the secretion of small extracellular vesicles. These findings were confirmed using a shRNA targeting FASN. In addition, we find that FASN inhibition induces metabolic changes in senescent cells. Our work underscores the importance of C75 as a pharmacological inhibitor for reducing the impact of senescent cell accumulation.

Sustained protein synthesis and reduced eEF2K levels in TAp73-\- mice brain: a possible compensatory mechanism.

The transcription factor p73 is a member of the p53 family, of which the transactivation domain containing isoform (TAp73) plays key roles in brain development and neuronal stem cells. TAp73 also facilitates homoeostasis and prevents oxidative damage in vivo by inducing the expression of its target genes. Recently, we found that in addition to its role in regulation of transcription, TAp73 also affects mRNA translation. In cultured cells, acute TAp73 depletion activates eEF2K, which phosphorylates eEF2 reducing mRNA translation elongation. As a consequence, there is a reduction in global proteins synthesis rates and reprogramming of the translatome, leading to a selective decrease in the translation of rRNA processing factors. Given the dramatic effects of Tap73 depletion in vitro it was important to determine whether similar effects were observed in vivo. Here, we report the surprising finding that in brains of TAp73 KO mice there is a reduced level of eEF2K, which allows protein synthesis rates to be maintained suggesting a compensation model. These data provide new insights to the role of TAp73 in translation regulation and the eEF2K pathway in the brain.

TAp73 contributes to the oxidative stress response by regulating protein synthesis.

TAp73 is a transcription factor that plays key roles in brain development, aging, and cancer. At the cellular level, TAp73 is a critical homeostasis-maintaining factor, particularly following oxidative stress. Although major studies focused on TAp73 transcriptional activities have indicated a contribution of TAp73 to cellular metabolism, the mechanisms underlying its role in redox homeostasis have not been completely elucidated. Here we show that TAp73 contributes to the oxidative stress response by participating in the control of protein synthesis. Regulation of mRNA translation occupies a central position in cellular homeostasis during the stress response, often by reducing global rates of protein synthesis and promoting translation of specific mRNAs. TAp73 depletion results in aberrant ribosomal RNA (rRNA) processing and impaired protein synthesis. In particular, polysomal profiles show that TAp73 promotes the integration of mRNAs that encode rRNA-processing factors in polysomes, supporting their translation. Concurrently, TAp73 depletion causes increased sensitivity to oxidative stress that correlates with reduced ATP levels, hyperactivation of AMPK, and translational defects. TAp73 is important for maintaining active translation of mitochondrial transcripts in response to oxidative stress, thus promoting mitochondrial activity. Our results indicate that TAp73 contributes to redox homeostasis by affecting the translational machinery, facilitating the translation of specific mitochondrial transcripts. This study identifies a mechanism by which TAp73 contributes to the oxidative stress response and describes a completely unexpected role for TAp73 in regulating protein synthesis.

p73 Regulates Primary Cortical Neuron Metabolism: a Global Metabolic Profile.

The transcription factor p73 has been demonstrated to play a significant role in survival and differentiation of neuronal stem cells. In this report, by employing comprehensive metabolic profile and mitochondrial bioenergetics analysis, we have explored the metabolic alterations in cortical neurons isolated from p73 N-terminal isoform specific knockout animals. We found that loss of the TAp73 or ΔNp73 triggers selective biochemical changes. In particular, p73 isoforms regulate sphingolipid and phospholipid biochemical pathway signaling. Indeed, sphinganine and sphingosine levels were reduced in p73-depleted cortical neurons, and decreased levels of several membrane phospholipids were also observed. Moreover, in line with the complexity associated with p73 functions, loss of the TAp73 seems to increase glycolysis, whereas on the contrary, loss of ΔNp73 isoform reduces glucose metabolism, indicating an isoform-specific differential effect on glycolysis. These changes in glycolytic flux were not reflected by parallel alterations of mitochondrial respiration, as only a slight increase of mitochondrial maximal respiration was observed in p73-depleted cortical neurons. Overall, our findings reinforce the key role of p73 in regulating cellular metabolism and point out that p73 exerts its functions in neuronal biology at least partially through the regulation of metabolic pathways.

TAp73 is a marker of glutamine addiction in medulloblastoma.

Medulloblastoma is the most common solid primary brain tumor in children. Remarkable advancements in the understanding of the genetic and epigenetic basis of these tumors have informed their recent molecular classification. However, the genotype/phenotype correlation of the subgroups remains largely uncharacterized. In particular, the metabolic phenotype is of great interest because of its druggability, which could lead to the development of novel and more tailored therapies for a subset of medulloblastoma. p73 plays a critical role in a range of cellular metabolic processes. We show overexpression of p73 in a proportion of non-WNT medulloblastoma. In these tumors, p73 sustains cell growth and proliferation via regulation of glutamine metabolism. We validated our results in a xenograft model in which we observed an increase in survival time in mice on a glutamine restriction diet. Notably, glutamine starvation has a synergistic effect with cisplatin, a component of the current medulloblastoma chemotherapy. These findings raise the possibility that glutamine depletion can be used as an adjuvant treatment for p73-expressing medulloblastoma.

How Does p73 Cause Neuronal Defects?

The p53-family member, p73, plays a key role in the development of the central nervous system (CNS), in senescence, and in tumor formation. The role of p73 in neuronal differentiation is complex and involves several downstream pathways. Indeed, in the last few years, we have learnt that TAp73 directly or indirectly regulates several genes involved in neural biology. In particular, TAp73 is involved in the maintenance of neural stem/progenitor cell self-renewal and differentiation throughout the regulation of SOX-2, Hey-2, TRIM32 and Notch. In addition, TAp73 is also implicated in the regulation of the differentiation and function of postmitotic neurons by regulating the expression of p75NTR and GLS2 (glutamine metabolism). Further still, the regulation of miR-34a by TAp73 indicates that microRNAs can also participate in this multifunctional role of p73 in adult brain physiology. However, contradictory results still exist in the relationship between p73 and brain disorders, and this remains an important area for further investigation.