The Role of Mitochondria in Glioma Pathophysiology

microRNA 21 and long non-coding RNAs interplays underlie cancer pathophysiology: A narrative review

Non-coding RNAs (ncRNAs) are a diverse group of functional RNA molecules that lack the ability to code for proteins. Despite missing this traditional role, ncRNAs have emerged as crucial regulators of various biological processes and have been implicated in the development and progression of many diseases, including cancer. MicroRNAs (miRNAs) and long non-coding RNAs (lncRNAs) are two prominent classes of ncRNAs that have emerged as key players in cancer pathophysiology. In particular, miR-21 has been reported to exhibit oncogenic roles in various forms of human cancer, including prostate, breast, lung, and colorectal cancer. In this context, miR-21 overexpression is closely associated with tumor proliferation, growth, invasion, angiogenesis, and chemoresistance, whereas miR-21 inactivation is linked to the regression of most tumor-related processes. Accordingly, miR-21 is a crucial modulator of various canonical oncogenic pathways such as PTEN/PI3K/Akt, Wnt/β-catenin, STAT, p53, MMP2, and MMP9. Moreover, interplays between lncRNA and miRNA further complicate the regulatory mechanisms underlying tumor development and progression. In this regard, several lncRNAs have been found to interact with miR-21 and, by functioning as competitive endogenous RNAs (ceRNAs) or miRNA sponges, can modulate cancer tumorigenesis. This work presents and discusses recent findings highlighting the roles and pathophysiological implications of the miR-21-lncRNA regulatory axis in cancer occurrence, development, and progression. The data collected indicate that specific lncRNAs, such as MEG3, CASC2, and GAS5, are strongly associated with miR-21 in various types of cancer, including gastric, cervical, lung, and glioma. Indeed, these lncRNAs are well-known tumor suppressors and are commonly downregulated in different types of tumors. Conversely, by modulating various mechanisms and oncogenic signaling pathways, their overexpression has been linked with preventing tumor formation and development. This review highlights the significance of these regulatory pathways in cancer and their potential for use in cancer therapy as diagnostic and prognostic markers.

Mitochondrial Changes in Rat Brain Endothelial Cells Associated with Hepatic Encephalopathy: Relation to the Blood-Brain Barrier Dysfunction

The mechanisms underlying cerebral vascular dysfunction and edema during hepatic encephalopathy (HE) are unclear. Blood-brain barrier (BBB) impairment, resulting from increased vascular permeability, has been reported in acute and chronic HE. Mitochondrial dysfunction is a well-documented result of HE mainly affecting astrocytes, but much less so in the BBB-forming endothelial cells. Here we review literature reports and own experimental data obtained in HE models emphasizing alterations in mitochondrial dynamics and function as a possible contributor to the status of brain endothelial cell mitochondria in HE. Own studies on the expression of the mitochondrial fusion-fission controlling genes rendered HE animal model-dependent effects: increase of mitochondrial fusion controlling genes opa1, mfn1 in cerebral vessels in ammonium acetate-induced hyperammonemia, but a decrease of the two former genes and increase of fis1 in vessels in thioacetamide-induced HE. In endothelial cell line (RBE4) after 24 h ammonia and/or TNFα treatment, conditions mimicking crucial aspects of HE in vivo, we observed altered expression of mitochondrial fission/fusion genes: a decrease of opa1, mfn1, and, increase of the fission related fis1 gene. The effect in vitro was paralleled by the generation of reactive oxygen species, decreased total antioxidant capacity, decreased mitochondrial membrane potential, as well as increased permeability of RBE4 cell monolayer to fluorescein isothiocyanate dextran. Electron microscopy documented enlarged mitochondria in the brain endothelial cells of rats in both in vivo models. Collectively, the here observed alterations of cerebral endothelial mitochondria are indicative of their fission, and decreased potential of endothelial mitochondria are likely to contribute to BBB dysfunction in HE.

Awake Craniotomy for a Frontal Astrocytoma: A Case Report

Awake craniotomy is a surgical procedure that has been gaining significance over the past decades. Neuronavigation is an intraoperative technology that locates tumors and monitors the brain cortex during awake craniotomy. The presence of cerebral low-grade gliomas in the frontal lobe creates a risk of affecting vital centers of the brain cortex during surgery. We present a clinical case of a 42-year-old male patient who entered the neurosurgery clinic with a clinical manifestation of headache for two months. MRI showed evidence of the recurrence of a left frontal glioma. Differential diagnoses of frontal gliomas include metastases, abscesses, and cysts. The pathophysiologic background of the disease is the mutation of neuroglial cells, which leads to an abnormal and uncontrollable proliferation. Under sleep-awake anesthesia, operative treatment was performed through left frontal awake craniotomy under neuronavigation. As a result, a total excision was achieved. Motor functions of the right limbs and speech have been preserved. The patient was mobilized on the day after the intervention. Surgery-related complications were not observed. The patient had relief from the symptoms and was discharged on the fifth day. Awake craniotomy combined with neuronavigation was the most efficient and the least harmful method for the excision of the tumor. For low-grade gliomas localized in the frontal area of the encephalon, awake craniotomy is the only secure option for surgery.

The role of long noncoding RNA DGCR5 in cancers: Focus on molecular targets

Long noncoding RNAs (lncRNAs) are major components of cellular transcripts that are emerging as important players in various biological pathways. Due to their specific expression and functional diversity in a variety of cancers, lncRNAs have promising applications in cancer diagnosis, prognosis, and therapy. Studies have shown that lncRNA DiGeorge syndrome critical region gene 5 (DGCR5) with high specificity and accuracy has the potential to become biomarkers in cancers. LncRNA DGCR5 can be noninvasively extracted from body fluids, tissues, and cells, and can be used as independent or auxiliary biomarkers to improve the accuracy of diagnosis or prognosis. Now, the underlying mechanisms of lncRNAs such as DGCR5 were explored as therapeutic targets, which have been investigated in clinical trials of several cancers. The DGCR5 lacks an appropriate animal model, which is necessary to gain greater knowledge of their functions. While some studies on the uses of DGCR5 have been carried out, the small sample size makes them unreliable. In this review, we presented a compilation of recent publications addressing the potential of lncRNA DGCR5 that could be considered as biomarkers or therapeutic targets, with the hopes of providing promised implications for future cancer therapy.

Cuproptosis facilitates immune activation but promotes immune escape, and a machine learning-based cuproptosis-related signature is identified for predicting prognosis and immunotherapy response of gliomas

AIMS

Cell death, except for cuproptosis, in gliomas has been extensively studied, providing novel targets for immunotherapy by reshaping the tumor immune microenvironment through multiple mechanisms. This study aimed to explore the effect of cuproptosis on the immune microenvironment and its predictive power in prognosis and immunotherapy response.

METHODS

Eight glioma cohorts were included in this study. We employed the unsupervised clustering algorithm to identify novel cuproptosis clusters and described their immune microenvironmental characteristics, mutation landscape, and altered signaling pathways. We verified the correlation among FDX1, SLC31A1, and macrophage infiltration in 56 glioma tissues. Next, based on multicenter cohorts and 10 machine learning algorithms, we constructed an artificial intelligence-driven cuproptosis-related signature named CuproScore.

RESULTS

Our findings suggested that glioma patients with high levels of cuproptosis had a worse prognosis owing to immunosuppression caused by unique immune escape mechanisms. Meanwhile, we experimentally validated the positive association between cuproptosis and macrophages and its tumor-promoting mechanism in vitro. Furthermore, our CuproScore exhibited powerful and robust prognostic predictive ability. It was also capable of predicting response to immunotherapy and chemotherapy drug sensitivity.

CONCLUSIONS

Cuproptosis facilitates immune activation but promotes immune escape. The CuproScore could predict prognosis and immunotherapy response in gliomas.

RICH2 decreases the mitochondrial number and affects mitochondrial localization in diffuse low-grade glioma-related epilepsy

Epilepsy, a common complication of diffuse low-grade gliomas (DLGGs; diffuse oligodendroglioma and astrocytoma collectively), severely compromises the quality of life of patients. DLGG epileptogenicity may primarily be generated by interactions between the tumor and the neocortex. Neuronal uptake of dysfunctional mitochondria from the extracellular environment can lead to abnormal neuronal discharge. Mitochondrial dysfunction is frequently observed in gliomas that can transmigrate across the plasma membranes. Here, we examined the role of the Rho GTPase-activating protein 44 (RICH2) in mitochondrial dynamics and DLGG-related epilepsy. We investigated the association between mitochondrial and RICH2 expression in human DLGG tissues using immunohistochemistry. We examined the association between RICH2 and epilepsy in nude mouse glioma models by electrophysiology. The effect of RICH2 on mitochondrial morphology and calcium motility were assessed by single cell fluorescence microscopy. Quantitative RT-PCR (qRT-PCR) and Western blot analysis were performed to characterize RICH2 induced expression changes in the genes related to mitochondrial dynamics, mitogenesis and mitochondrial function. We found that RICH2 expression was higher in oligodendroglioma than in astrocytoma and was correlated with better prognosis and higher epilepsy rate in patients. The expression of mitochondria may be associated with clinical DLGG-related epilepsy and reduced by RICH2 overexpression. And RICH2 could promote DLGG-related epilepsy in tumorigenic nude mice. RICH2 overexpression decreased calcium flow and the mitochondria released from glioma cells (SW1088 and U251) into the extracellular environment, potentially via downregulation of MFN-1/MFN-2 levels which suggests reduced mitochondrial fusion. In addition, we observed decreased mitochondrial trafficking into neurons (released from glioma cells and trafficked into neurons), which could explain the higher incidence of DLGG-related epilepsy due to reduced neuroprotection. Furthermore, RICH2 downregulated MAPK/ERK/HIF-1 pathway. In conclusion, these results suggest that RICH2 could promote epilepsy by (i) inhibiting mitochondrial fusion via MFN downregulation and Drp-1 upregulation; (ii) altering the MAPK/ERK/Hif-1 signaling axis. RICH2 may be a potential target in the treatment of DLGG-related epilepsy.

Mass Spectrometry Imaging Reveals Abnormalities in Cardiolipin Composition and Distribution in Astrocytoma Tumor Tissues

Cardiolipin (CL) is a mitochondrial lipid with diverse roles in cellular respiration, signaling, and organelle membrane structure. CL content and composition are essential for proper mitochondrial function. Deranged mitochondrial energy production and signaling are key components of glial cell cancers and altered CL molecular species have been observed in mouse brain glial cell xenograft tumors. The objective of this study was to describe CL structural diversity trends in human astrocytoma tumors of varying grades and correlate these trends with histological regions within the heterogeneous astrocytoma microenvironment. To this aim, we applied desorption electrospray ionization coupled with high field asymmetric ion mobility mass spectrometry (DESI-FAIMS-MS) to map CL molecular species in human normal cortex (N = 29), lower-grade astrocytoma (N = 19), and glioblastoma (N = 28) tissues. With this platform, we detected 46 CL species and 12 monolysocardiolipin species from normal cortex samples. CL profiles detected from glioblastoma tissues lacked diversity and abundance of longer chain polyunsaturated fatty acid containing CL species when compared to CL detected from normal and lower-grade tumors. CL profiles correlated with trends in tumor viability and tumor infiltration. Structural characterization of the CL species by tandem MS experiments revealed differences in fatty acid and double bond isomer composition among astrocytoma tissues compared with normal cortex and glioblastoma tissues. The GlioVis platform was used to analyze astrocytoma gene expression data from the CGGA dataset. Decreased expression of several mitochondrial respiratory enzyme encoding-genes was observed for higher-grade versus lower-grade tumors, however no significant difference was observed for cardiolipin synthesis enzyme CRLS1.

Pre-clinical and clinical importance of miR-21 in human cancers: Tumorigenesis, therapy response, delivery approaches and targeting agents

The field of non-coding RNA (ncRNA) has made significant progress in understanding the pathogenesis of diseases and has broadened our knowledge towards their targeting, especially in cancer therapy. ncRNAs are a large family of RNAs with microRNAs (miRNAs) being one kind of endogenous RNA which lack encoded proteins. By now, miRNAs have been well-coined in pathogenesis and development of cancer. The current review focuses on the role of miR-21 in cancers and its association with tumor progression. miR-21 has both oncogenic and onco-suppressor functions and most of the experiments are in agreement with the tumor-promoting function of this miRNA. miR-21 primarily decreases PTEN expression to induce PI3K/Akt signaling in cancer progression. Overexpression of miR-21 inhibits apoptosis and is vital for inducing pro-survival autophagy. miR-21 is vital for metabolic reprogramming and can induce glycolysis to enhance tumor progression. miR-21 stimulates EMT mechanisms and increases expression of MMP-2 and MMP-9 thereby elevating tumor metastasis. miR-21 is a target of anti-cancer agents such as curcumin and curcumol and its down-regulation impairs tumor progression. Upregulation of miR-21 results in cancer resistance to chemotherapy and radiotherapy. Increasing evidence has revealed the role of miR-21 as a biomarker as it is present in both the serum and exosomes making them beneficial biomarkers for non-invasive diagnosis of cancer.

Identification of a novel cuproptosis-related gene signature and integrative analyses in patients with lower-grade gliomas

Background

Cuproptosis is a newly discovered unique non-apoptotic programmed cell death distinguished from known death mechanisms like ferroptosis, pyroptosis, and necroptosis. However, the prognostic value of cuproptosis and the correlation between cuproptosis and the tumor microenvironment (TME) in lower-grade gliomas (LGGs) remain unknown.

Methods

In this study, we systematically investigated the genetic and transcriptional variation, prognostic value, and expression patterns of cuproptosis-related genes (CRGs). The CRG score was applied to quantify the cuproptosis subtypes. We then evaluated their values in the TME, prognostic prediction, and therapeutic responses in LGG. Lastly, we collected five paired LGG and matched normal adjacent tissue samples from Sun Yat-sen University Cancer Center (SYSUCC) to verify the expression of signature genes by quantitative real-time PCR (qRT-PCR) and Western blotting (WB).

Results

Two distinct cuproptosis-related clusters were identified using consensus unsupervised clustering analysis. The correlation between multilayer CRG alterations with clinical characteristics, prognosis, and TME cell infiltration were observed. Then, a well-performed cuproptosis-related risk model (CRG score) was developed to predict LGG patients' prognosis, which was evaluated and validated in two external cohorts. We classified patients into high- and low-risk groups according to the CRG score and found that patients in the low-risk group showed significantly higher survival possibilities than those in the high-risk group (P<0.001). A high CRG score implies higher TME scores, more significant TME cell infiltration, and increased mutation burden. Meanwhile, the CRG score was significantly correlated with the cancer stem cell index, chemoradiotherapy sensitivity-related genes and immune checkpoint genes, and chemotherapeutic sensitivity, indicating the association with CRGs and treatment responses. Univariate and multivariate Cox regression analyses revealed that the CRG score was an independent prognostic predictor for LGG patients. Subsequently, a highly accurate predictive model was established for facilitating the clinical application of the CRG score, showing good predictive ability and calibration. Additionally, crucial CRGs were further validated by qRT-PCR and WB.

Conclusion

Collectively, we demonstrated a comprehensive overview of CRG profiles in LGG and established a novel risk model for LGG patients' therapy status and prognosis. Our findings highlight the potential clinical implications of CRGs, suggesting that cuproptosis may be the potential therapeutic target for patients with LGG.

Double face of cytochrome c in cancers by Raman imaging

Cytochrome c (Cyt c) is a key protein that is needed to maintain life (respiration) and cell death (apoptosis). The dual-function of Cyt c comes from its capability to act as mitochondrial redox carrier that transfers electrons between the membrane-embedded complexes III and IV and to serve as a cytoplasmic apoptosis-triggering agent, activating the caspase cascade. However, the precise roles of Cyt c in mitochondria, cytoplasm and extracellular matrix under normal and pathological conditions are not completely understood. To date, no pathway of Cyt c release that results in caspase activation has been compellingly demonstrated in any invertebrate. The significance of mitochondrial dysfunctionality has not been studied in ductal carcinoma to the best of our knowledge. We used Raman spectroscopy and imaging to monitor changes in the redox state of the mitochondrial cytochromes in ex vivo surgically resected specimens of human breast tissues, and in vitro human breast cells of normal cells (MCF 10A), slightly malignant cells (MCF7) and highly aggressive cells (MDA-MB-231). We showed that Raman imaging provides insight into the biology of human breast ductal cancer. Here we show that proper concentration of monounsaturated fatty acids, saturated fatty acids, cardiolipin and Cyt c is critical in the correct breast ductal functioning and constitutes an important parameter to assess breast epithelial cells integrity and homeostasis. We look inside human breast ducts by Raman imaging answering fundamental questions about location and distribution of various biochemical components inside the lumen, epithelial cells of the duct and the extracellular matrix around the cancer duct during cancer development in situ. Our results show that human breast cancers demonstrate a redox imbalance compared to normal tissue. The reduced cytochrome c is upregulated in all stages of cancers development. The results of the paper shed light on a largely non-investigated issues regarding cytochromes and mitochondrial function in electron transfer chain. We found in histopathologically controlled breast cancer duct that Cyt c, cardiolipin, and palmitic acid are the main components inside the lumen of cancerous duct in situ. The presented results show direct evidence that Cyt c is released to the lumen from the epithelial cells in cancerous duct. In contrast the lumen in normal duct is empty and free of Cyt c. Our results demonstrate how Cyt c is likely to function in cancer development. We anticipate our results to be a starting point for more sophisticated in vitro and in vivo animal models. For example, the correlation between concentration of Cyt c and cancer grade could be tested in various types of cancer. Furthermore, Cyt c is a target of anti-cancer drug development and a well-defined and quantitative Raman based assay for oxidative phosphorylation and apoptosis will be relevant for such developments.

Somatic mitochondrial DNA mutations in different grades of glioma

Aim: Mitochondrial DNA (mtDNA) alterations play an important role in the multistep processes of cancer development. Gliomas are among the most diagnosed brain cancer. The relationship between mtDNA alterations and different grades of gliomas are still elusive. This study aimed to elucidate the profile of somatic mtDNA mutations in different grades of gliomas and correlate it with clinical phenotype. Materials & methods: Forty histopathologically confirmed glioma tissue samples and their matched blood were collected and subjected for mtDNA sequencing. Results & conclusion: About 75% of the gliomas harbored at least one somatic mutation in the mtDNA gene, and 45% of these mutations were pathogenic. Mutations were scattered across the mtDNA genome, and the commonest nonsynonymous mutations were located at complex I and IV of the mitochondrial respiratory chain. These findings may have implication for future research to determine the mitochondrial energetics and its downstream metabolomics on gliomas.

GRPEL2 Knockdown Exerts Redox Regulation in Glioblastoma

Malignant brain tumors are responsible for catastrophic morbidity and mortality globally. Among them, glioblastoma multiforme (GBM) bears the worst prognosis. The GrpE-like 2 homolog (GRPEL2) plays a crucial role in regulating mitochondrial protein import and redox homeostasis. However, the role of GRPEL2 in human glioblastoma has yet to be clarified. In this study, we investigated the function of GRPEL2 in glioma. Based on bioinformatics analyses from the Cancer Gene Atlas (TCGA) and the Chinese Glioma Genome Atlas (CGGA), we inferred that GRPEL2 expression positively correlates with WHO tumor grade (p < 0.001), IDH mutation status (p < 0.001), oligodendroglial differentiation (p < 0.001), and overall survival (p < 0.001) in glioma datasets. Functional validation in LN229 and GBM8401 GBM cells showed that GRPEL2 knockdown efficiently inhibited cellular proliferation. Moreover, GRPEL2 suppression induced cell cycle arrest at the sub-G1 phase. Furthermore, GRPEL2 silencing decreased intracellular reactive oxygen species (ROS) without impending mitochondria membrane potential. The cellular oxidative respiration measured with a Seahorse XFp analyzer exhibited a reduction of the oxygen consumption rate (OCR) in GBM cells by siGRPEL2, which subsequently enhanced autophagy and senescence in glioblastoma cells. Taken together, GRPEL2 is a novel redox regulator of mitochondria bioenergetics and a potential target for treating GBM in the future.

Silencing LINC00294 Restores Mitochondrial Function and Inhibits Apoptosis of Glioma Cells under Hypoxia via the miR-21-5p/CASKIN1/cAMP Axis

Glioma is a type of malignant intracranial tumor. Extensive research has identified the participation of long noncoding RNAs (lncRNAs) in glioma progression. This study investigated the mechanism of LINC00294 in mitochondrial function and glioma cell apoptosis. Glioma miRNA and mRNA microarray datasets were obtained, and differentially expressed lncRNAs in glioma were screened through various databases. The LINC00294 expression in glioma patients and glioma cells was detected. Glioma cells were treated under hypoxic conditions and transfected with LINC00294 silencing. The apoptosis and mitochondrial function of glioma cells were measured. The expressions of and relations among miR-21-5p, CASKIN1, and cAMP in glioma cells were analyzed. Under hypoxic conditions and LINC00294 silencing, the apoptosis and mitochondrial function of glioma cells were detected after inhibiting miR-21-5p or overexpressing CASKIN1. Our results indicated that LINC00294 was downregulated in glioma. LINC00294 silencing inhibited glioma cell apoptosis under hypoxia. LINC00294 silencing reversed the inhibition of hypoxia on mitochondrial function under hypoxia. LINC00294 promoted the CASKIN1 expression by sponging miR-21-5p and activated the cAMP pathway. Inhibition of miR-21-5p or overexpression of CASKIN1 annulled the effects of LINC00294 silencing on mitochondrial function and glioma cell apoptosis under hypoxia. In conclusion, LINC00294 elevated the CASKIN1 expression by sponging miR-21-5p and activating the cAMP signaling pathway, thus inhibiting mitochondrial function and facilitating glioma cell apoptosis.

Multifunctional lipidic nanocarriers for effective therapy of glioblastoma: recent advances in stimuli-responsive, receptor and subcellular targeted approaches

Background

Glioblastoma, or glioblastoma multiforme (GBM), remains a fatal cancer type despite the remarkable progress in understanding the genesis and propagation of the tumor. Current treatment modalities, comprising mainly of surgery followed by adjuvant chemoradiation, are insufficient for improving patients' survival owing to existing hurdles, including the blood–brain barrier (BBB). In contemporary practice, the prospect of long-term survival or cure continues to be a challenge for patients suffering from GBM. This review provides an insight into the drug delivery strategies and the significant efforts made in lipid-based nanoplatform research to circumvent the challenges in optimal drug delivery in GBM.

Area covered

Owing to the unique properties of lipid-based nanoplatforms and advancements in clinical translation, this article describes the application of various stimuli-responsive lipid nanocarriers and tumor subcellular organelle-targeted therapy to give an idea about the strategies that can be applied to enhance site-specific drug delivery for GBM. Furthermore, active targeting of drugs via surface-modified lipid-based nanostructures and recent findings in alternative therapeutic platforms such as gene therapy, immunotherapy, and multimodal therapy have also been overviewed.

Expert opinion

Lipid-based nanoparticles stand out among the other nanocarriers explored for GBM drug delivery, as they support both passive and active drug targeting by crossing/bypassing the BBB at the same time minimizing toxicity and projects better pharmacological parameters. Although these nanocarriers could be a plausible choice for treating GBM, in-depth research is essential to advance neuro-oncology research and enhance outcomes in patients with brain tumors.

Complementary Nuclear Magnetic Resonance-Based Metabolomics Approaches for Glioma Biomarker Identification in a Drosophila melanogaster Model

Human malignant gliomas are the most common type of primary brain tumor. Composed of glial cells and their precursors, they are aggressive and highly invasive, leading to a poor prognosis. Due to the difficulty of surgically removing tumors and their resistance to treatments, novel therapeutic approaches are needed to improve patient life expectancy and comfort. Drosophila melanogaster is a compelling genetic model to better understanding human neurological diseases owing to its high conservation in signaling pathways and cellular content of the brain. Here, glioma has been induced in Drosophila by co-activating the epidermal growth factor receptor and the phosphatidyl-inositol-3 kinase signaling pathways. Complementary nuclear magnetic resonance (NMR) techniques were used to obtain metabolic profiles in the third instar larvae brains. Fresh organs were directly studied by ¹H high resolution-magic angle spinning (HR-MAS) NMR, and brain extracts were analyzed by solution-state ¹H-NMR. Statistical analyses revealed differential metabolic signatures, impacted metabolic pathways, and glioma biomarkers. Each method was efficient to determine biomarkers. The highlighted metabolites including glucose, myo-inositol, sarcosine, glycine, alanine, and pyruvate for solution-state NMR and proline, myo-inositol, acetate, and glucose for HR-MAS show very good performances in discriminating samples according to their nature with data mining based on receiver operating characteristic curves. Combining results allows for a more complete view of induced disturbances and opens the possibility of deciphering the biochemical mechanisms of these tumors. The identified biomarkers provide a means to rebalance specific pathways through targeted metabolic therapy and to study the effects of pharmacological treatments using Drosophila as a model organism.

Ketogenic Metabolic Therapy, Without Chemo or Radiation, for the Long-Term Management of IDH1-Mutant Glioblastoma: An 80-Month Follow-Up Case Report

Background: Successful treatment of glioblastoma (GBM) remains futile despite decades of intense research. GBM is similar to most other malignant cancers in requiring glucose and glutamine for growth, regardless of histological or genetic heterogeneity. Ketogenic metabolic therapy (KMT) is a non-toxic nutritional intervention for cancer management. We report the case of a 32-year-old man who presented in 2014 with seizures and a right frontal lobe tumor on MRI. The tumor cells were immunoreactive with antibodies to the IDH1 (R132H) mutation, P53 (patchy), MIB-1 index (4–6%), and absent ATRX protein expression. DNA analysis showed no evidence of methylation of the MGMT gene promoter. The presence of prominent microvascular proliferation and areas of necrosis were consistent with an IDH-mutant glioblastoma (WHO Grade 4).

Methods: The patient refused standard of care (SOC) and steroid medication after initial diagnosis, but was knowledgeable and self-motivated enough to consume a low-carbohydrate ketogenic diet consisting mostly of saturated fats, minimal vegetables, and a variety of meats. The patient used the glucose ketone index calculator to maintain his Glucose Ketone Index (GKI) near 2.0 without body weight loss.

Results: The tumor continued to grow slowly without expected vasogenic edema until 2017, when the patient opted for surgical debulking. The enhancing area, centered in the inferior frontal gyrus, was surgically excised. The pathology specimen confirmed IDH1-mutant GBM. Following surgery, the patient continued with a self-administered ketogenic diet to maintain low GKI values, indicative of therapeutic ketosis. At the time of this report (May 2021), the patient remains alive with a good quality of life, except for occasional seizures. MRI continues to show slow interval progression of the tumor.

Conclusion: This is the first report of confirmed IDH1-mutant GBM treated with KMT and surgical debulking without chemo- or radiotherapy. The long-term survival of this patient, now at 80 months, could be due in part to a therapeutic metabolic synergy between KMT and the IDH1 mutation that simultaneously target the glycolysis and glutaminolysis pathways that are essential for GBM growth. Further studies are needed to determine if this non-toxic therapeutic strategy could be effective in providing long-term management for other GBM patients with or without IDH mutations.

An integrative analysis of the age-associated multi-omic landscape across cancers

Age is the most important risk factor for cancer, as cancer incidence and mortality increase with age. However, how molecular alterations in tumours differ among patients of different age remains largely unexplored. Here, using data from The Cancer Genome Atlas, we comprehensively characterise genomic, transcriptomic and epigenetic alterations in relation to patients' age across cancer types. We show that tumours from older patients present an overall increase in genomic instability, somatic copy-number alterations (SCNAs) and somatic mutations. Age-associated SCNAs and mutations are identified in several cancer-driver genes across different cancer types. The largest age-related genomic differences are found in gliomas and endometrial cancer. We identify age-related global transcriptomic changes and demonstrate that these genes are in part regulated by age-associated DNA methylation changes. This study provides a comprehensive, multi-omics view of age-associated alterations in cancer and underscores age as an important factor to consider in cancer research and clinical practice.

Overexpression of Annexin A2 promotes proliferation by forming a Glypican 1/c-Myc positive feedback loop: prognostic significance in human glioma

In order to set up a reliable prediction system for the tumor grade and prognosis in glioma patients, we clarify the complicated crosstalk of Annexin A2 (ANXA2) with Glypican 1 (GPC1) and demonstrate whether combined indexes of ANXA2 and GPC1 could improve the prognostic evaluation for glioma patients. We found that ANXA2-induced glioma cell proliferation in a c-Myc-dependent manner. ANXA2 increased the expression of GPC1 via c-Myc and the upregulated GPC1 further promoted the c-Myc level, forming a positive feedback loop, which eventually led to enhanced proliferation of glioma cells. Both mRNA and protein levels of ANXA2 were upregulated in glioma tissues and coincided with the overexpression of GPC1. Besides, we utilized tissue microarrays (TMAs) and immunohistochemistry to demonstrate that glioma patients with both high expression of ANXA2 and GPC1 tended to have higher rate of tumor recurrence and shorter overall survival (OS). In conclusion, the overexpression of ANXA2 promotes proliferation of glioma cells by forming a GPC1/c-Myc positive feedback loop, and ANXA2 together with its downstream target GPC1 could be a potential "combination biomarker" for predicting prognosis of glioma patients.

Paris saponin H inhibits the proliferation of glioma cells through the A1 and A3 adenosine receptor‑mediated pathway

Paris saponin H (PSH) is a type of steroid saponin derived from Rhizoma Paridis (RP; the rhizome of Paris). In our previous studies, saponins from RP exerted antiglioma activity in vitro. However, the effects of PSH on glioma have not been elucidated. The aim of the present study was to evaluate the effects of PSH on U251 glioblastoma cells and elucidate the possible underlying mechanism. The cells were treated with PSH at various concentrations for 48 h, and the cell viability, invasion, apoptosis and cycle progression were assessed using specific assay kits. The activation of Akt, 44/42‑mitogen‑activated protein kinase (MAPK) and the expression levels of A1 adenosine receptor (ARA1) and ARA3 were assessed by western blotting. The results demonstrated that PSH inhibited cell viability, migration and invasion, and induced apoptosis. Treatment of U251 cells with PSH induced the upregulation of p21 and p27, and the downregulation cyclin D1 and S‑phase kinase associated protein 2 protein expression levels, which induced cell cycle arrest at the G1 phase. The results also demonstrated that PSH inhibited the expression of ARA1, and the agonist of ARA1, 2‑chloro‑N6‑cyclopentyladenosine, reversed the effects of PSH. Hypoxia induced increases in the ARA3, hypoxia‑inducible factor‑1α (HIF‑1α) and vascular endothelial growth factor (VEGF) protein expression levels, which were associated with the activation of the Akt and P44/42 MAPK pathways. Compared with the hypoxia group, PSH inhibited the expression levels of ARA3, HIF‑1α and VEGF, as well as the phosphorylation levels of Akt and 44/42 MAPK, and repressed HIF‑1α transcriptional activity. Furthermore, the results demonstrated that PSH inhibited the expression of HIF‑1α by inhibiting the phosphorylation of Akt and 44/42 MAPK mediated by ARA3. Taken together, these results suggested that PSH reduced U251 cell viability via the inhibition of ARA1 and ARA3 expression, and further inhibited Akt and 44/42 MAPK phosphorylation, induced apoptosis and cell cycle arrest.

Current Progress of Phytomedicine in Glioblastoma Therapy

Glioblastoma multiforme, an intrusive brain cancer, has the lowest survival rate of all brain cancers. The chemotherapy utilized to prevent their proliferation and propagation is limited due to modulation of complex cancer signalling pathways. These complex pathways provide infiltrative and drug evading properties leading to the development of chemotherapy resistance. Therefore, the development and discovery of such interventions or therapies that can bypass all these resistive barriers to ameliorate glioma prognosis and survival is of profound importance. Medicinal plants are comprised of an exorbitant range of phytochemicals that have the broad-spectrum capability to target intrusive brain cancers, modulate anti-cancer pathways and immunological responses to facilitate their eradication, and induce apoptosis. These phytocompounds also interfere with several oncogenic proteins that promote cancer invasiveness and metastasis, chemotherapy resistance and angiogenesis. These plants are extremely vital for promising anti-glioma therapy to avert glioma proliferation and recurrence. In this review, we acquired recent literature on medicinal plants whose extracts/bioactive ingredients are newly exploited in glioma therapeutics, and also highlighted their mode of action and pharmacological profile.

LncRNA DGCR5 plays a tumor-suppressive role in glioma via the miR-21/Smad7 and miR-23a/PTEN axes

Glioma is one of the most commonly diagnosed brain malignancies with a high cancer-related death rate in humans. The prognosis of glioma patients is still unsatisfactory. In the present study, we attempted to identify lncRNAs and miRNAs that might be related to NF-κB-mediated epithelial-mesenchymal transition in glioma cells based on online microarray expression profiles, and investigate the specific effects of lncRNA-miRNA-mRNA axes on glioma cell phenotypes. Herein, we identified lncRNA DGCR5 as a downregulated lncRNA in glioma that was negatively regulated by NF-κB1 in an NF-κB1 RE-dependent manner. LncRNA DGCR5 overexpression significantly inhibited the capacity of glioma cells to proliferate, migrate, and invade, whereas promoted the apoptosis of glioma cells. Moreover, lncRNA DGCR5 overexpression upregulated the epithelial marker E-cadherin while downregulating the mesenchymal marker VIM, as well as Snai2 and TWIST. Regarding the underlying molecular mechanisms, lncRNA DGCR5 could inhibit miR-21 and miR-23a expression, and miR-21 or miR-23a overexpression significantly reversed the tumor-suppressive effects of lncRNA DGCR5 overexpression. LncRNA DGCR5 exerted its tumor-suppressive effects through the DGCR5/miR-21/Smad7 and DGCR5/miR-23a/PTEN axes. In conclusion, lncRNA DGCR5 suppresses the capacity of glioma cells to migrate and invade via miR-21/Smad7, whereas it inhibits the proliferation and enhances the apoptosis of glioma cells through miR-23a/PTEN.

Cytochrome C Oxidase Subunit 4 (COX4): A Potential Therapeutic Target for the Treatment of Medullary Thyroid Cancer

The nuclear-encoded subunit 4 of cytochrome c oxidase (COX4) plays a role in regulation of oxidative phosphorylation and contributes to cancer progression. We sought to determine the role of COX4 in differentiated (DTC) and medullary (MTC) thyroid cancers. We examined the expression of COX4 in human thyroid tumors by immunostaining and used shRNA-mediated knockdown of COX4 to evaluate its functional contributions in thyroid cancer cell lines. In human thyroid tissue, the expression of COX4 was higher in cancers than in either normal thyroid (p = 0.0001) or adenomas (p = 0.001). The level of COX4 expression correlated with tumor size (p = 0.04) and lymph-node metastases (p = 0.024) in patients with MTCs. COX4 silencing had no effects on cell signaling activation and mitochondrial respiration in DTC cell lines (FTC133 and BCPAP). In MTC-derived TT cells, COX4 silencing inhibited p70S6K/pS6 and p-ERK signaling, and was associated with decreased oxygen consumption and ATP production. Treatment with potassium cyanide had minimal effects on FTC133 and BCPAP, but inhibited mitochondrial respiration and induced apoptosis in MTC-derived TT cells. Our data demonstrated that metastatic MTCs are characterized by increased expression of COX4, and MTC-derived TT cells are vulnerable to COX4 silencing. These data suggest that COX4 can be considered as a novel molecular target for the treatment of MTC.

MYC-activated lncRNA HNF1A-AS1 overexpression facilitates glioma progression via cooperating with miR-32-5p/SOX4 axis

Mounting literatures have revealed the crucial effects of long noncoding RNA (lncRNA) in various cancers, including glioma. HNF1A‐AS1, a novel lncRNA, is reported to modulate tumorigenesis and development of multiple cancers. However, the tumorigenic function of lncRNA HNF1A‐AS1 in glioma remains largely unknown. quantitative reverse transcription and polymerase chain reaction and western blot assays were applied to evaluate the expression of relevant mRNAs and proteins. 5‐Ethynyl‐2’‐ deoxyuridine, terminal deoxynucleotidyl transferase dUTP nick‐end labeling, flow cytometry, and transwell assays were conducted for examining the influence of HNF1A‐AS1 on glioma cell functions. The relationship among RNAs was investigated by mechanical experiments. The results demonstrated that HNF1A‐AS1 was predominantly highly expressed in glioma cell lines compared with nontumor glial epithelial cell, which was associated with the stimulation of transcription factor myelocytomatosis oncogene. Knockdown of HNF1A‐AS1 remarkably inhibited glioma cells proliferation, migration, and invasion, while accelerating cell apoptosis in vitro. Mechanically, HNF1A‐AS1 served as a miR‐32‐5p sponge. Moreover, SOX4 was discovered as a target of miR‐32‐5p. Inhibited miR‐32‐5p or upregulated SOX4 could markedly counteract the inhibitory effects of silencing HNF1A‐AS1 on glioma malignant biological behaviors. HNF1A‐AS1 exerted oncogenic property in glioma progression via upregulating miR‐32‐5p–mediated SOX4 expression, suggesting potential novel therapeutic target for future glioma treatment.

SNHG9/miR-199a-5p/Wnt2 Axis Regulates Cell Growth and Aerobic Glycolysis in Glioblastoma

Aerobic glycolysis is a characteristic in cancers that is important for cancer cell proliferation. Emerging evidence shows that long non-coding RNA (LncRNA) participates in glucose metabolism and cell proliferation in cancer. This study explored the effect of LncRNA: SNHG9 in glioblastoma. The mRNA expression of SNHG9 in human glioma tissues and glioblastoma cell lines was measured by qRT-PCR. Glioblastoma cell lines (U87 and U251) were transfected with miR-199a-5p or SNHG9-expressing plasmid and cell viability as well as concentrations of glucose and lactate were measured. The extracellular acidification was evaluated by glycolysis stress test. The Wnt2 levels were determined by qRT-PCR and Western blot. Results showed that the mRNA expression of SNHG9 was elevated in glioblastoma tissues. The elevated SNHG9 expression was related to lower survival rate in patients with glioma. SNHG9 could downregulate miR-199a-5p and upregulate Wnt2 in glioblastoma cells. Overexpression of SNHG9 in glioblastoma cells promoted aerobic glycolysis and cell proliferation, which could be attenuated by miR-199a-5p. Results of this study indicated an effect of SNHG9/miR-199a-5p/Wnt2 axis in regulating cell growth and aerobic glycolysis in glioblastoma.

Principal component analysis on LC‑MS/MS and 2DE‑MALDI‑TOF in glioblastoma cell lines reveals that mitochondria act as organelle sensors of the metabolic state in glioblastoma

Glioblastoma is a difficult disease to diagnose. Proteomic techniques are commonly applied in biomedical research, and can be useful for early detection, making an accurate diagnosis and reducing mortality. The relevance of mitochondria in brain development and function is well known; therefore, mitochondria may influence the development of glioblastoma. The T98G (with oxidative metabolism) and U87MG (with glycolytic metabolism) cell lines are considered to be useful glioblastoma models for studying these tumors and the role of mitochondria in key aspects of this disease, such as prognosis, metastasis and apoptosis. In the present study, principal component analysis of protein abundance data identified by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF) from 2D gels indicated that representative mitochondrial proteins were associated with glioblastoma. The selected proteins were organized into T98G- and U87MG-specific protein-protein interaction networks to demonstrate the representativeness of both proteomic techniques. Gene Ontology overrepresentation analysis based on the relevant proteins revealed that mitochondrial processes were associated with metabolic changes, invasion and metastasis in glioblastoma, along with other non-mitochondrial processes, such as DNA translation, chaperone responses and autophagy. Despite the lower resolution of 2D electrophoresis, principal component analysis yielded information of comparable quality to that of LC-MS/MS. The present analysis pipeline described a specific and more complete metabolic status for each cell line, defined a clear mitochondrial performance for distinct glioblastoma tumors, and introduced a useful strategy to understand the heterogeneity of glioblastoma.

LINC00668 Modulates SOCS5 Expression Through Competitively Sponging miR-518c-3p to Facilitate Glioma Cell Proliferation

Glioma is a common invasive cancer with unfavorable prognosis in patients. Long non-coding RNAs (lncRNAs) exert significant functions in carcinogenesis of various cancers including glioma. Among them, long intergenic non-coding RNA 668 (LINC00668) was reported to function as oncogene in various cancers, but its molecular mechanism in glioma has not been thoroughly researched. Our current study aimed to investigate the role and molecular mechanism of LINC00668 in glioma cells. We initially found out that LINC00668 was up-regulated in glioma cells. Through a series of function assays, LINC00668 was verified to facilitate cell proliferation and inhibit apoptosis in glioma. Then, by means of online databases, RNA pull down assay and RIP assay, we verified the binding relation between LINC00668 and miR-518c-3p. Also, the next function assays exposed that miR-518c-3p was the tumor suppressor in glioma cells. Similarly, SOCS5 (suppressor of cytokine signaling 5) was found to bind with miR-518c-3p, which repressed glioma tumorigenesis by targeting SOCS5. Moreover, rescue assays manifested that LINC00668 modulated expression of SOCS5 in a miR-518c-3p-dependent way and further regulated glioma tumorigenesis. Overall, LINC00668 modulates SOCS5 expression through competitively sponging miR-518c-3p to facilitate glioma cell proliferation.

Anesthesia and brain tumor surgery: technical considerations based on current research evidence

PURPOSE OF REVIEW

Anesthetics may influence cancer recurrence and metastasis following surgery by modulating the neuroendocrine stress response or by directly affecting cancer cell biology. This review summarizes the current evidence on whether commonly used anesthetics potentially affect postoperative outcomes following solid organ cancer surgery with particular focus on neurological malignancies.

RECENT FINDINGS

Despite significant improvement in diagnostic and therapeutic technology over the past decades, mortality rates after cancer surgery (including brain tumor resection) remains high. With regards to brain tumors, interaction between microglia/macrophages and tumor cells by multiple biological factors play an important role in tumor progression and metastasis. Preclinical studies have demonstrated an association between anesthetics and brain tumor cell biology, and a potential effect on tumor progression and metastasis has been revealed. However, in the clinical setting, the current evidence is inadequate to draw firm conclusions on the optimal anesthetic technique for brain tumor surgery.

SUMMARY

Further work at both the basic science and clinical level is urgently needed to evaluate the association between perioperative factors, including anesthetics/technique, and postoperative brain tumor outcomes.

High expression of ALDH1A3 might independently influence poor progression-free and overall survival in patients with glioma via maintaining glucose uptake and lactate production

Recent studies have found that the acetaldehyde dehydrogenase 1A3 (ALDH1A3) gene is a marker of glioma stem cells. A total of 115 brain glioma specimens were collected and classified into grade I-IV, while non-tumor brain tissue specimens, taken from 12 patients of vascular malformation surgery, were used as control. ALDH1A3 gene promoter methylation in glioma tissues was detected by pyrosequencing, while immunohistochemistry and western blot were used to detect ALDH1A3 protein expressions in different grades of glioma tissues and normal brain tissues. The expression of ALDH1A3 in the glioma cell line U87 was detected by quantitative real-time polymerase chain reaction and RNA-Seq technology was applied to investigate differentially expressed genes before and after silencing the ALDH1A3 gene. Among the 115 glioma tissue specimens, 50 (43.48%) showed low and 65 (56.52%) high expression of ALDH1A3, but no expression was detected in the control. Univariate and multivariate COX regression analyses showed that the patient's tumor pathological grade, the methylation status of ALDH1A3 promoter, and the expression of ALDH1A3 protein were risk factors for progression-free survival (PFS) and overall survival (OS) (all P < 0.05) and the OS of mice with silenced ALDH1A3 in a glioma nude mouse model was prolonged. U87 experiments revealed that ALDH1A3 expression had significant effects on apoptosis, proliferation, cell cycle, mitochondrial membrane potential, glucose consumption, lactate production, invasion ability, and expression of the pyruvate kinase M2 (PKM2) and hexokinase 2 (HK2) in glioma cells. ALDH1A3 protein expression is a marker for poor PFS and OS in glioma patients.

lncRNA LINC01494 Promotes Proliferation, Migration And Invasion In Glioma Through miR-122-5p/CCNG1 Axis

Background

Long noncoding RNAs (lncRNAs) are recognized as key effectors in tumor, including glioma. LINC01494 is an uncharacterized novel lncRNA. In this research, we aimed to investigate the function of LINC01494 in glioma.

Methods

Gene relative expression was analyzed by qRT-PCR method. CCK8, colony formation and Transwell assay was used to determine cell proliferation, migration and invasion. Bioinformatics analyses were used to predict the target of LINC01494 and miR-122-5p. Luciferase reporter assay was utilized to validate the interactions between LINC01494 and miR-122-5p or CCNG1 and miR-122-5p.

Results

LINC01494 was identified as a significantly upregulated lncRNA in glioma through bioinformatics analysis. Furthermore, LINC01494 upregulation indicated poor prognosis. Meanwhile, in vitro investigation indicated that silencing LINC01494 with siRNAs obviously inhibited the proliferation, cell cycle, migration and invasion of glioma cells. Besides, it is found that LINC01494 expression was negatively correlated with miR-122-5p. We demonstrated that LINC01494 inhibited miR-122-5p to upregulate CCNG1 expression through direct interaction. Rescue assay further demonstrated that LINC01494/miR-122-5p/CCNG1 signaling cascade plays a critical role in regulating glioma cell proliferation, migration and invasion.

Conclusion

Taken together, our findings demonstrated the essential function and molecular mechanism of LINC01494 in glioma progression.

Integrated Approach Reveals Role of Mitochondrial Germ-Line Mutation F18L in Respiratory Chain, Oxidative Alterations, Drug Sensitivity, and Patient Prognosis in Glioblastoma

Glioblastoma is the most common and malignant primary brain tumour in adults, with a dismal prognosis. This is partly due to considerable inter- and intra-tumour heterogeneity. Changes in the cellular energy-producing mitochondrial respiratory chain complex (MRC) activities are a hallmark of glioblastoma relative to the normal brain, and associate with differential survival outcomes. Targeting MRC complexes with drugs can also facilitate anti-glioblastoma activity. Whether mutations in the mitochondrial DNA (mtDNA) that encode several components of the MRC contribute to these phenomena remains underexplored. We identified a germ-line mtDNA mutation (m. 14798T > C), enriched in glioblastoma relative to healthy controls, that causes an amino acid substitution F18L within the core mtDNA-encoded cytochrome b subunit of MRC complex III. F18L is predicted to alter corresponding complex III activity, and sensitivity to complex III-targeting drugs. This could in turn alter reactive oxygen species (ROS) production, cell behaviour and, consequently, patient outcomes. Here we show that, despite a heterogeneous mitochondrial background in adult glioblastoma patient biopsy-derived cell cultures, the F18L substitution associates with alterations in individual MRC complex activities, in particular a 75% increase in MRC complex II_III activity, and a 34% reduction in CoQ10, the natural substrate for MRC complex III, levels. Downstream characterisation of an F18L-carrier revealed an 87% increase in intra-cellular ROS, an altered cellular distribution of mitochondrial-specific ROS, and a 64% increased sensitivity to clomipramine, a repurposed MRC complex III-targeting drug. In patients, F18L-carriers that received the current standard of care treatment had a poorer prognosis than non-carriers (373 days vs. 415 days, respectively). Single germ-line mitochondrial mutations could predispose individuals to differential prognoses, and sensitivity to mitochondrial targeted drugs. Thus, F18L, which is present in blood could serve as a useful non-invasive biomarker for the stratification of patients into prognostically relevant groups, one of which requires a lower dose of clomipramine to achieve clinical effect, thus minimising side-effects.

Long noncoding RNA DLEU1 aggravates glioma progression via the miR-421/MEF2D axis

Background

Long noncoding RNA (lncRNA) deleted in lymphocytic leukemia 1 (DLEU1) was reported to be involved in the development and progression of multiple cancers. However, the accurate expression pattern, biological function and potential molecular mechanism of DLEU1 in glioma are not yet known. The present study investigated the role of DLEU in the development and progression of glioma, as well as the potential mechanism played by DLEU1 in glioma.

Materials and methods

The levels of DLEUI in glioma tissues and cell lines were examined using quantitative real-time PCR. The potential effects of DLEU1 on the proliferation, mobility, invasion and apoptosis of glioma cells were evaluated using corresponding in vitro experiments. The association between DLEU1 and microRNA (miR)-421 was also determined using luciferase reporter activity and RNA immunoprecipitation (RIP) assays.

Results

The results revealed that DLEU1 was significantly upregulated in glioma tissues and cell lines. Increased DLEU1 was positively associated with the high-grade carcinoma (III-IV). Functional studies revealed that knockdown of DLEU1 expression by siRNA led to decreased proliferation, migration and invasion and increased apoptosis in human glioma cells. Furthermore, luciferase reporter activity and RIP assays confirmed that DLEUI could act as a competing endogenous RNA (ceRNA) for miR-421 that functioned as a tumor suppressor in glioma. Moreover, inhibition miR-421 partially restored the effect of DLEU1 knockdown on the glioma cells. DLEU1 could regulate myocyte enhancer factor 2D (MEF2D) expression, a known target of miR-421 in glioma cells.

Conclusion

Taken together, these findings suggested that DLEU1 regulated MEF2D expression to promote glioma progression by sponging miR-421 and that DLEU1 might be a potential therapeutic target for glioma.

Provocative Question: Should Ketogenic Metabolic Therapy Become the Standard of Care for Glioblastoma?

No major advances have been made in improving overall survival for glioblastoma (GBM) in almost 100 years. The current standard of care (SOC) for GBM involves immediate surgical resection followed by radiotherapy with concomitant temozolomide chemotherapy. Corticosteroid (dexamethasone) is often prescribed to GBM patients to reduce tumor edema and inflammation. The SOC disrupts the glutamate-glutamine cycle thus increasing availability of glucose and glutamine in the tumor microenvironment. Glucose and glutamine are the prime fermentable fuels that underlie therapy resistance and drive GBM growth through substrate level phosphorylation in the cytoplasm and the mitochondria, respectively. Emerging evidence indicates that ketogenic metabolic therapy (KMT) can reduce glucose availability while elevating ketone bodies that are neuroprotective and non-fermentable. Information is presented from preclinical and case report studies showing how KMT could target tumor cells without causing neurochemical damage thus improving progression free and overall survival for patients with GBM.

Long noncoding RNA 00460 (LINC00460) promotes glioma progression by negatively regulating miR-320a

Objective

Long noncoding RNA 00460 (LINC00460) has been reported to contribute to tumorigenesis in multiple types of human malignancies. However, the biological role and the underlying molecular mechanism of LINC00460 in glioma remain unclear. The aim of this study was to investigate the clinical value, the biological function, and the potential mechanism of LINC00460 in glioma.

Methods

The expression level of LINC00460 in glioma tissues and cell lines was examined by quantitative real‐time polymerase chain reaction (qRT‐PCR). Cell Counting Kit‐8, flow cemetery, wound healing, and transwell invasion assays were used to explore the effect of LINC00460 on glioma cell proliferation, apoptosis, migration, and invasion. qRT‐PCR and reporter assays were used to further verify the regulatory mechanism of LINC00460 in glioma progression.

Results

LINC00460 expression was upregulated in glioma tissues and cell lines compared with non–tumor brain samples and astrocyte cell line (NHA), respectively. Moreover, increased LINC00460 expression was closely associated with glioma tumor grade. Loss‐of‐function assays revealed that knockdown of LINC00460 significantly inhibited glioma cell proliferation, induced cell apoptosis, and suppressed migration and invasion. The mechanistic assays disclosed that LINC00460 binded to miR‐320a in a sequence‐specific manner and regulated its expression. Moreover, miR‐320 inhibition partially attenuated LINC00460 knockdown‐mediated suppressive effects on glioma cell proliferation, migration, and invasion.

Conclusion

These findings suggested that LINC00460 might function as an oncogenic lncRNA in glioma development and could be explored as a potential therapeutic target for glioma.

LncRNA UCA1 sponges miR-204-5p to promote migration, invasion and epithelial-mesenchymal transition of glioma cells via upregulation of ZEB1

Long non-coding RNA urothelial carcinoma associated 1 (lncRNA UCA1) promotes cancer progression and enhances chemoresistance through miR-204-5p in a few cancers. However, no studies have investigated whether UCA1 regulates glioma metastasis through miR-204-5p and its target. In the present study, cell migration, invasion and epithelial-mesenchymal transition (EMT) were evaluated in glioma cells overexpressing UCA1. The relationships among UCA1, miR-204-5p and ZEB1 were examined by real-time PCR, western blotting and dual-luciferase reporter assays. The effect of UCA1 knockdown on xenograft tumor growth was investigated. The levels of miR-204-5p, fibronectin, COL5 A1 and ZEB1 in tumor tissues were also determined. The results showed that UCA1 overexpression promoted cell migration, invasion and EMT. UCA1 interacted with miR-204-5p and decreased its level. ZEB1 was identified as a direct target of miR-204-5p and miR-204-5p negatively regulated ZEB1 expression. Moreover, UCA1 sponged miR-204-5p and partially rescued the inhibitory effect of miR-204-5p on ZEB1. In our in vivo studies, UCA1 knockdown reduced tumor volume and tumor weight. In addition, the levels of fibronectin, COL5 A1 and ZEB1 were decreased, while miR-204-5p level was increased. The present study provides the first evidence that UCA1 promotes glioma metastasis through the miR-204-5p/ZEB1 axis, contributing to the understanding of the pathogenesis of glioma.

Temozolomide, sirolimus and chloroquine is a new therapeutic combination that synergizes to disrupt lysosomal function and cholesterol homeostasis in GBM cells

Glioblastoma (GBM) cells are characterized by high phagocytosis, lipogenesis, exocytosis activities, low autophagy capacity and high lysosomal demand are necessary for survival and invasion. The lysosome stands at the cross roads of lipid biosynthesis, transporting, sorting between exogenous and endogenous cholesterol. We hypothesized that three already approved drugs, the autophagy inducer, sirolimus (rapamycin, Rapa), the autophagy inhibitor, chloroquine (CQ), and DNA alkylating chemotherapy, temozolomide (TMZ) could synergize against GBM. This repurposed triple therapy combination induced GBM apoptosis in vitro and inhibited GBM xenograft growth in vivo. Cytotoxicity is caused by induction of lysosomal membrane permeabilization and release of hydrolases, and may be rescued by cholesterol supplementation. Triple treatment inhibits lysosomal function, prevents cholesterol extraction from low density lipoprotein (LDL), and causes clumping of lysosome associated membrane protein-1 (LAMP-1) and lipid droplets (LD) accumulation. Co-treatment of the cell lines with inhibitor of caspases and cathepsin B only partially reverse of cytotoxicities, while N-acetyl cysteine (NAC) can be more effective. A combination of reactive oxygen species (ROS) generation from cholesterol depletion are the early event of underling mechanism. Cholesterol repletion abolished the ROS production and reversed the cytotoxicity from QRT treatment. The shortage of free cholesterol destabilizes lysosomal membranes converting aborted autophagy to apoptosis through either direct mitochondria damage or cathepsin B release. This promising anti-GBM triple therapy combination severely decreases mitochondrial function, induces lysosome-dependent apoptotic cell death, and is now poised for further clinical testing and validation.

Development and Characterization of Methylene Blue Oleate Salt-Loaded Polymeric Nanoparticles and their Potential Application as a Treatment for Glioblastoma

Glioblastoma (GBM) is an aggressive, grade IV brain tumor that develops from astrocytes located within the cerebrum, resulting in poor prognosis and survival rates following an accepted treatment regimen of surgery, radiation, and temozolomide. Thus, development of new therapeutics is necessary. During the last two decades, methylene blue (MB) has received increased attention as a potential neurotherapeutic due to its duality in brain cancers and neurodegenerative diseases. While MB is capable of easily permeating the blood-brain barrier, its therapeutic concentrations in GBM are known to induce off-target cytotoxicity and thus, another mode of drug delivery must be considered. To this end, encapsulation of formerly unusable compounds into nanoparticles (NPs) made from the biodegradable/biocompatible, FDA approved co-polymer poly (lactide-co-glycolide) (PLGA) has been more commonplace when developing novel therapeutics. In this study, we formulated and characterized Pluronic F68-coated PLGA NPs containing a sodium oleate conjugate of MB (MBOS) via solvent displacement. Conjugation of sodium oleate to MB was shown to reduce its release from PLGA NPs compared to unmodified MB, leading to potential improvements in drug accumulation and therapeutic effectiveness. Our drug-loaded NP preparations, which were ~170 nm in size and had drug loading values of ~2%, were shown to reduce cell viability and cell compartment-specific, as well as overall cell, functions equivalenty, if not more so, when compared to free drug in two GBM cell lines. Following bio-distribution analysis of free MBOS compared to its nano-encapsulated counterpart, drug-loaded NPs were shown to more effectively permeate the BBB, which could lead to improvements in therapeutic effectiveness upon further examination in a tumor-bearing mouse model. Based on these results, we believe that the further development and eventual utilization of this nanoformulation could lead to an effective GBM therapy that could extend patient survival rates.

Evaluation of mitochondrial respiratory function in highly glycolytic glioma cells reveals low ADP phosphorylation in relation to oxidative capacity

High-grade gliomas are aggressive and intensely glycolytic tumors. In the present study, we evaluated the mitochondrial respiratory function of glioma cells (T98G and U-87MG) and fresh human glioblastoma (GBM) tissue. To this end, measurements of oxygen consumption rate (OCR) were performed under various experimental conditions. The OCR of T98G and U-87MG cells was well coupled to ADP phosphorylation based on the ratio of ATP produced per oxygen consumed of ~2.5. In agreement, the basal OCR of GBM tissue was also partially associated with ADP phosphorylation. The basal respiration of intact T98G and U-87MG cells was not limited by the supply of endogenous substrates, as indicated by the increased OCR in response to a protonophore. These cells also displayed a high affinity for oxygen, as evidenced by the values of the partial pressure of oxygen when respiration is half maximal (p ₅₀). In permeabilized glioma cells, ADP-stimulated OCR was only approximately 50% of that obtained in the presence of protonophore, revealing a significant limitation in oxidative phosphorylation (OXPHOS) relative to the activity of the electron transport system (ETS). This characteristic was maintained when the cells were grown under low glucose conditions. Flux control coefficient analyses demonstrated that the impaired OXPHOS was associated with the function of both mitochondrial ATP synthase and the adenine nucleotide translocator, but not the phosphate carrier. Altogether, these data indicate that the availability and metabolism of respiratory substrates and mitochondrial ETS are preserved in T98G and U-87MG glioma cells even though these cells possess a relatively restrained OXPHOS capability.

Mitochondrial DNA Mutations in Grade II and III Glioma Cell Lines Are Associated with Significant Mitochondrial Dysfunction and Higher Oxidative Stress

The role of mitochondria in tumorigenesis has regained much attention as it could dysregulate cellular energetics, oxidative stress and apoptosis. However, the role of mitochondria in different grade gliomasis still unknown. This study aimed to identify mitochondrial DNA (mtDNA) sequence variations that could possibly affect the mitochondrial functions and also the oxidative stress status. Three different grades of human glioma cell lines and a normal human astrocyte cell line were cultured in-vitro and tested for oxidative stress biomarkers. Relative oxidative stress level, mitochondria activity, and mitochondrial mass were determined by live cell imaging with confocal laser scanning microscope using CM-H₂DCFDA, MitoTracker Green, and MitoTracker Orange stains. The entire mitochondrial genome was sequenced using the AffymetrixGeneChip Human Mitochondrial Resequencing Array 2.0. The mitochondrial sequence variations were subjected to phylogenetic haplogroup assessment and pathogenicity of the mutations were predicted using pMUT and PolyPhen2. The Grade II astrocytoma cells showed increased oxidative stress wherea high level of 8-OHdG and oxidative stress indicator were observed. Simultaneously, Grade II and III glioma cells showed relatively poor mitochondria functions and increased number of mutations in the coding region of the mtDNA which could be due to high levels of oxidative stress in these cells. These non-synonymous mtDNA sequence variations were predicted to be pathogenic and could possibly lead to protein dysfunction, leading to oxidative phosphorylation (OXPHOS) impairment, mitochondria dysfunction and could create a vicious cycle of oxidative stress. The Grade IV cells had no missense mutation but preserved intact mitochondria and excellent antioxidant defense mechanisms thus ensuring better survival. In conclusion, Grade II and III glioma cells demonstrated coding region mtDNA mutations, leading to mitochondrial dysfunction and higher oxidative stress.

Antagonist activity of the antipsychotic drug lithium chloride and the antileukemic drug imatinib mesylate during glioblastoma treatment in vitro

OBJECTIVES

Glioblastoma (GBM), the most common primary tumour of the central nervous system, is characterised by a high malignancy and poor prognosis. The aims of this study were to investigate whether the combination of imatinib mesylate (IM) and lithium chloride (LiCl) exhibited a synergistic effect in treatment and to determine whether midkine (MK) affected the fate of this treatment in vitro.

METHODS

Monolayer and spheroid cultures of the T98G human GBM cell line were treated with an IM and LiCl combination for 72 h. The cell proliferation index, apoptotic index, cell cycle distribution, apoptotic and anti-apoptotic protein levels, and cAMP level as well as the cellular morphology and ultrastructure were evaluated.

RESULTS

All applications inhibited cell proliferation and induced apoptosis. The most substantial decreases in cell proliferation and the caspase-3, epidermal growth factor receptor (EGFR), platelet derived growth factor receptor-alpha (PDGFR-α), multidrug resistance protein-1 (MRP-1), aquaporin-4 (AQP-4) and cAMP levels were induced by the LiCl treatment, which exhibited more pronounced effects compared with the combination treatment. LiCl was less effective in decreasing the MK and B cell lymphoma-2 (Bcl-2) levels compared with the combination treatment. The most substantial decrease in the p170 levels was identified following the combination treatment, whereas IM induced the second greatest decrease. LiCl alone had no effect on the p170 levels. IM induced the most substantial decrease in the phospho-glycogen synthase kinase 3-beta (p-GSK-3β)/glycogen synthase kinase 3-beta (GSK-3β) ratio, and LiCl induced the second most substantial decrease. Both LiCl and the combination treatment induced G2 + M arrest, whereas IM induced G0 + G1 arrest after 72 h of exposure. An apoptotic appearance and autophagic vacuoles were commonly identified in the LiCl, combination and IM groups, respectively.

CONCLUSIONS

The combination of IM and LiCl exhibited an antagonist effect, and MK had a role at this antagonism.

The Actual Role of LDH as Tumor Marker, Biochemical and Clinical Aspects

Lactate dehydrogenase (LDH) among many biochemical parameters represents a very valuable enzyme in patients with cancer with possibility for easy routine measurement in many clinical laboratories. Previous studies where mostly based on investigated LDH in serum of patients with cancer with aims to estimate their clinical significance. The new directions in investigation of LDH where based on the principle that tumor cells release intracellular enzymes trough damaged cell membrane, that is mostly consequence in intracellular mitochondrial machinery alteration, and apoptosis deregulation. This consideration can be used not only in-vitro assays, but also in respect to clinical characteristics of tumor patients. Based on new techniques of molecular biology it is shown that intracellular characteristics of LDH enzyme are very sensitive indicators of the cellular metabolic state, aerobic or anaerobic direction of glycolysis, activation status and malignant transformation. Using different molecular analyses it is very useful to analyzed intracellular LDH activity in different cell line and tumor tissues obtained from patients, not only to understanding complexity in cancer biochemistry but also in early clinical diagnosis. Based on understandings of the LDH altered metabolism, new therapy option is created with aims to blocking certain metabolic pathways and stop tumors growth.

Mitochondrial Dysfunction in Gliomas: Pharmacotherapeutic Potential of Natural Compounds

Gliomas are the most common primary brain tumors either benign or malignant originating from the glial tissue. Glioblastoma multiforme (GBM) is the most prevalent and aggressive form among all gliomas, associated with decimal prognosis due to it`s high invasive nature. GBM is also characterized by high recurrence rate and apoptosis resistance features which make the therapeutic targeting very challenging. Mitochondria are key cellular organelles that are acting as focal points in diverse array of cellular functions such as cellular energy metabolism, regulation of ion homeostasis, redox signaling and cell death. Eventual findings of mitochondrial dysfunction include preference of glycolysis over oxidative phosphorylation, enhanced reactive oxygen species generation and abnormal mitochondria mediated apoptotic machinery are frequently observed in various malignancies including gliomas. In particular, gliomas harbor mitochondrial structure abnormalities, genomic mutations in mtDNA, altered energy metabolism (Warburg effect) along with mutations in isocitrate dehydrogenase (IDH) enzyme. Numerous natural compounds have shown efficacy in the treatment of gliomas by targeting mitochondrial aberrant signaling cascades. Some of the natural compounds directly target the components of mitochondria whereas others act indirectly through modulating metabolic abnormalities that are consequence of the mitochondrial dysfunction. The present review offers a molecular insight into mitochondrial pathology in gliomas and therapeutic mechanisms of some of the promising natural compounds that target mitochondrial dysfunction. This review also sheds light on the challenges and possible ways to overcome the hurdles associated with these natural compounds to enter into the clinical market.

ATP5A1 and ATP5B are highly expressed in glioblastoma tumor cells and endothelial cells of microvascular proliferation

Glioblastoma (GBM) is the most common primary malignant brain tumor. Microvascular proliferation is one of the characteristic pathologic features of GBM. Mitochondrial dysfunction plays an important role in the pathogenesis of GBM. In this study, microvascular proliferation from GBM and normal brain blood vessels were laser microdissected and total RNA was isolated from these microvasculatures. The difference of mRNA expression profiles among GBM microvasculature, normal brain blood vessels and GBM tumor cells was evaluated by mitochondria and metabolism PCR gene arrays. It was found that the mRNA levels of ATP5A1 and ATP5B in GBM tumor cells as well as microvascular proliferation were significantly higher compared with normal brain blood vessels. Immunohistochemical stains with anti-ATP5A1 antibody or anti-ATP5B antibody were performed on tissue microarray, which demonstrated strongly positive expression of ATP5A1 and ATP5B in GBM tumor cells and GBM microvascular proliferation while normal blood vessels were negative. By analyzing The Cancer Genome Atlas data sets for GBM and other cancers, genomic DNA alterations (mutation, amplification or deletion) were less likely the reason for the high expression of ATP5A1 and ATP5B in GBM. Our miRNA microarray data showed that miRNAs that target ATP5A1 or ATP5B were down-regulated, which might be the most likely reason for the high expression of ATP5A1 and ATP5B in GBM tumor cells and microvascular proliferation. These findings help us better understand the pathogenesis of GBM, and agents against ATP5A1 and/or ATP5B might effectively kill both tumor cells and microvascular proliferation in GBM. MiRNAs, such as Let-7f, miR-16, miR-23, miR-100 and miR-101, that target ATP5A1 or ATP5B, might be potential therapeutic agents for GBM.

Identification and functional prediction of mitochondrial complex III and IV mutations associated with glioblastoma

Background

Glioblastoma (GBM) is the most common primary brain tumor in adults, with a dismal prognosis. Treatment is hampered by GBM's unique biology, including differential cell response to therapy. Although several mitochondrial abnormalities have been identified, how mitochondrial DNA (mtDNA) mutations contribute to GBM biology and therapeutic response remains poorly described. We sought to determine the spectrum of functional complex III and IV mtDNA mutations in GBM.

Methods

The complete mitochondrial genomes of 10 GBM cell lines were obtained using next-generation sequencing and combined with another set obtained from 32 GBM tissues. Three-dimensional structural mapping and analysis of all the nonsynonymous mutations identified in complex III and IV proteins was then performed to investigate functional importance.

Results

Over 200 mutations were identified in the mtDNAs, including a significant proportion with very low mutational loads. Twenty-five were nonsynonymous mutations in complex III and IV, 9 of which were predicted to be functional and affect mitochondrial respiratory chain activity. Most of the functional candidates were GBM specific and not found in the general population, and 2 were present in the germ-line. Patient-specific maps reveal that 43% of tumors carry at least one functional candidate.

Conclusions

We reveal that the spectrum of GBM-associated mtDNA mutations is wider than previously thought, as well as novel structural-functional links between specific mtDNA mutations, abnormal mitochondria, and the biology of GBM. These results could provide tangible new prognostic indicators as well as targets with which to guide the development of patient-specific mitochondrially mediated chemotherapeutic approaches.

Metabolic therapy: a new paradigm for managing malignant brain cancer

Little progress has been made in the long-term management of glioblastoma multiforme (GBM), considered among the most lethal of brain cancers. Cytotoxic chemotherapy, steroids, and high-dose radiation are generally used as the standard of care for GBM. These procedures can create a tumor microenvironment rich in glucose and glutamine. Glucose and glutamine are suggested to facilitate tumor progression. Recent evidence suggests that many GBMs are infected with cytomegalovirus, which could further enhance glucose and glutamine metabolism in the tumor cells. Emerging evidence also suggests that neoplastic macrophages/microglia, arising through possible fusion hybridization, can comprise an invasive cell subpopulation within GBM. Glucose and glutamine are major fuels for myeloid cells, as well as for the more rapidly proliferating cancer stem cells. Therapies that increase inflammation and energy metabolites in the GBM microenvironment can enhance tumor progression. In contrast to current GBM therapies, metabolic therapy is designed to target the metabolic malady common to all tumor cells (aerobic fermentation), while enhancing the health and vitality of normal brain cells and the entire body. The calorie restricted ketogenic diet (KD-R) is an anti-angiogenic, anti-inflammatory and pro-apoptotic metabolic therapy that also reduces fermentable fuels in the tumor microenvironment. Metabolic therapy, as an alternative to the standard of care, has the potential to improve outcome for patients with GBM and other malignant brain cancers.

Conditioned media from human adipose tissue-derived mesenchymal stem cells and umbilical cord-derived mesenchymal stem cells efficiently induced the apoptosis and differentiation in human glioma cell lines in vitro

Human mesenchymal stem cells (MSCs) have an intrinsic property for homing towards tumor sites and can be used as tumor-tropic vectors for tumor therapy. But very limited studies investigated the antitumor properties of MSCs themselves. In this study we investigated the antiglioma properties of two easily accessible MSCs, namely, human adipose tissue-derived mesenchymal stem cells (ASCs) and umbilical cord-derived mesenchymal stem cells (UC-MSCs). We found (1) MSC conditioned media can significantly inhibit the growth of human U251 glioma cell line; (2) MSC conditioned media can significantly induce apoptosis in human U251 cell line; (3) real-time PCR experiments showed significant upregulation of apoptotic genes of both caspase-3 and caspase-9 and significant downregulation of antiapoptotic genes such as survivin and XIAP after MSC conditioned media induction in U 251 cells; (4) furthermore, MSCs conditioned media culture induced rapid and complete differentiation in U251 cells. These results indicate MSCs can efficiently induce both apoptosis and differentiation in U251 human glioma cell line. Whereas UC-MSCs are more efficient for apoptosis induction than ASCs, their capability of differentiation induction is not distinguishable from each other. Our findings suggest MSCs themselves have favorable antitumor characteristics and should be further explored in future glioma therapy.

Interactions among mitochondrial proteins altered in glioblastoma

Mitochondrial dysfunction is putatively central to glioblastoma (GBM) pathophysiology but there has been no systematic analysis in GBM of the proteins which are integral to mitochondrial function. Alterations in proteins in mitochondrial enriched fractions from patients with GBM were defined with label-free liquid chromatography mass spectrometry. 256 mitochondrially-associated proteins were identified in mitochondrial enriched fractions and 117 of these mitochondrial proteins were markedly (fold-change ≥2) and significantly altered in GBM (p ≤ 0.05). Proteins associated with oxidative damage (including catalase, superoxide dismutase 2, peroxiredoxin 1 and peroxiredoxin 4) were increased in GBM. Protein–protein interaction analysis highlighted a reduction in multiple proteins coupled to energy metabolism (in particular respiratory chain proteins, including 23 complex-I proteins). Qualitative ultrastructural analysis in GBM with electron microscopy showed a notably higher prevalence of mitochondria with cristolysis in GBM. This study highlights the complex mitochondrial proteomic adjustments which occur in GBM pathophysiology.

Antidepressant drugs as a complementary therapeutic strategy in cancer

In the last decade, it has been increasingly recognized that antidepressant drugs may exert a range of effects, in addition to their well-documented ability to modulate neurotransmission. Although as a group they act on monoaminergic systems and receptors in different ways, a number of studies have demonstrated that at least some antidepressants might have other properties in common, including immunomodulatory, cyto/neuroprotective, analgesic and anti-inflammatory activities. These properties are partly related to the influence of antidepressants on glial cell function. Recently, emerging information about the possible anticancer properties of antidepressants has sparked increased interest within scientific community, and there is now evidence that these drugs affect the key cellular mechanisms of carcinogenesis. This review examines the putative cellular targets for the anticancer action of antidepressant drugs, and presents examples of the interaction between antidepressants and anticancer drugs. By reviewing the current state of research in this area, we hope to focus the attention of oncologists and researchers engaged in the study of cancer on the role that antidepressant drugs could play in the complementary therapy of cancer.

Light-controlled inhibition of malignant glioma by opsin gene transfer

Glioblastomas are aggressive cancers with low survival rates and poor prognosis because of their highly proliferative and invasive capacity. In the current study, we describe a new optogenetic strategy that selectively inhibits glioma cells through light-controlled membrane depolarization and cell death. Transfer of the engineered opsin ChETA (engineered Channelrhodopsin-2 variant) gene into primary human glioma cells or cell lines, but not normal astrocytes, unexpectedly decreased cell proliferation and increased mitochondria-dependent apoptosis, upon light stimulation. These optogenetic effects were mediated by membrane depolarization-induced reductions in cyclin expression and mitochondrial transmembrane potential. Importantly, the ChETA gene transfer and light illumination in mice significantly inhibited subcutaneous and intracranial glioma growth and increased the survival of the animals bearing the glioma. These results uncover an unexpected effect of opsin ion channels on glioma cells and offer the opportunity for the first time to treat glioma using a light-controllable optogenetic approach.