Modeling Neuronal Death and Degeneration in Mouse Primary Cerebellar Granule Neurons

Cerebellar granule neurons (CGNs) are a commonly used neuronal model, forming an abundant homogeneous population in the cerebellum. In light of their ...

Jewish General Hospital

McGill University

Defects in mitochondrial fission and cyclin dependent kinase 5 (CDK5) activation are early events that precede neuronal loss following NMDA-induced neuronal death. Here, we report that the cytoplasmic CDK5 tightly regulates mitochondrial morphology defects associated with NMDA-induced neuronal injury via regulation of the mitochondrial fission protein, dynamin-related protein 1 (DRP1). We show that DRP1 is a direct target of CDK5. CDK5-mediated phosphorylation of DRP1 at a conserved Serine residue, S585, is elevated at the mitochondria and is associated with increased mitochondrial fission. Ectopic expression of a cytoplasmic CDK5 or mutant DRP1-S585D results in increased mitochondrial fragmentation in primary neurons. Conversely, expression of a dominant negative form of cytoplasmic CDK5 or mutant DRP1-S585A results in elongated mitochondria. In addition, pharmacological inhibition of CDK5 by Roscovitine inhibits DRP1 phosphorylation and mitochondrial fission associated with NMDA-induced neuronal loss. Importantly, conditional deletion of CDK5 significantly attenuates DRP1 phosphorylation at S585 and rescues mitochondrial fission defects in neurons exposed to NMDA. Our studies delineate an important mechanism by which CDK5 regulates mitochondrial morphology defects associated with neuronal injury.

CDK5 phosphorylates DRP1 and drives mitochondrial defects in NMDA-induced neuronal death.

EGFRvIII-STAT3 signaling is important in glioblastoma pathogenesis. Here, we identified the cytokine receptor OSMR as a direct target gene of the transcription factor STAT3 in mouse astrocytes and human brain tumor stem cells (BTSCs). We found that OSMR functioned as an essential co-receptor for EGFRvIII. OSMR formed a physical complex with EGFRvIII, and depletion of OSMR impaired EGFRvIII-STAT3 signaling. Conversely, pharmacological inhibition of EGFRvIII phosphorylation inhibited the EGFRvIII-OSMR interaction and activation of STAT3. EGFRvIII-OSMR signaling in tumors operated constitutively, whereas EGFR-OSMR signaling in nontumor cells was synergistically activated by the ligands EGF and OSM. Finally, knockdown of OSMR strongly suppressed cell proliferation and tumor growth of mouse glioblastoma cells and human BTSC xenografts in mice, and prolonged the lifespan of these mice. Our findings identify OSMR as a critical regulator of glioblastoma tumor growth that orchestrates a feed-forward signaling mechanism with EGFRvIII and STAT3 to drive tumorigenesis.

Control of glioblastoma tumorigenesis by feed-forward cytokine signaling.

Chordoma is a rare primary bone cancer with limited treatment options. Surgical resection followed by radiotherapy has proven effective; however, when, in 30-40% of patients, tumours recur and metastasize, a high level of resistance to chemotherapies leaves these patients with a dearth of treatment options. Recent work published in the Journal of Pathology by Scheipl et al describing a focused compound drug screen highlights the significance of epidermal growth factor receptor (EGFR) signalling in chordoma, and shows potential for EGFR inhibitors as a way forward for developing an effective treatment for chordoma. Importantly, combining EGFR inhibitors with a MET inhibitor induces a synergistic effect on growth inhibition of resistant chordoma cells, highlighting the significance of combined EGFR and MET inhibitors as a potential avenue to defeat chemoresistance in chordoma patients. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

A focused compound screen highlights the significance of epidermal growth factor receptor signalling in chordoma pathogenesis.

Intellectual disability encompasses a large set of neurodevelopmental disorders of cognition that are more common in males than females. Although mutations in over 100 X-linked genes associated to intellectual disability have been identified, only a few X-linked intellectual disability proteins have been intensively studied. Hence, the molecular mechanisms underlying the majority of X-linked intellectual disability disorders remain poorly understood. A substantial fraction of X-linked intellectual disability genes encode nuclear proteins, suggesting that elucidating their functions in the regulation of transcription may provide novel insights into the pathogenesis of intellectual disability. Recent studies have uncovered mechanisms by which mutations of the gene encoding plant homeodomain (PHD)-like finger protein 6 (PHF6) contribute to the pathogenesis of the X-linked intellectual disability disorder Börjeson-Forssman-Lehmann syndrome (BFLS). PHF6 plays a critical role in the migration of neurons in the mouse cerebral cortex in vivo, and patient-specific mutations disrupt the ability of PHF6 to promote neuronal migration. Interestingly, PHF6 physically associates with the PAF1 transcriptional elongation complex and thereby drives neuronal migration in the cerebral cortex. PHF6 also interacts with the NuRD chromatin remodeling complex and with the nucleolar transcriptional regulator UBF, though the biological role of these interactions remains to be characterized. In other studies, PHF6 mRNA has been identified as the target of the microRNA miR-128 in the cerebral cortex, providing new insights into regulation of PHF6 function in neuronal migration. Importantly, deregulation of PHF6 function in neuronal migration triggers the formation of white matter heterotopias that harbor neuronal hyperexcitability, which may be relevant to the pathogenesis of intellectual disability and seizures in BFLS. Collectively, these studies are beginning to provide key insights into the molecular pathogenesis of BFLS.

Arezu Jahani-Asl

Lady Davis Institute for Medical Research

Jewish General Hospital

Modeling Neuronal Death and Degeneration in Mouse Primary Cerebellar Granule Neurons

Arezu Jahani-Asl

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Jewish General Hospital

Modeling Neuronal Death and Degeneration in Mouse Primary Cerebellar Granule Neurons

Lady Davis Institute for Medical Research