Project description:Gliomas are highly aggressive brain tumors characterized by poor prognosis and composed of diffusely infiltrating tumor cells that intermingle with non-neoplastic cells in the tumor microenvironment, including neurons. Neurons are increasingly appreciated as important reactive components of the glioma microenvironment, due to their role in causing hallmark glioma symptoms, cognitive deficits, and seizures, as well as potentially driving glioma progression. Separately, mTOR signaling has been shown to have pleiotropic effects in the brain tumor microenvironment, including regulation of neuronal hyperexcitability. However, the local cellular level effects of mTOR inhibition on glioma-induced neuronal alterations are not well understood. Here we employed neuron-specific profiling of ribosome-bound mRNA via ‘Ribotag’, morphometric analysis, and intravital imaging, along with pharmacological mTOR inhibition to investigate the impact of glioma burden on excitatory neuronal pathophysiology as well as the impact of mTOR inhibition on these neuronal alterations. The Ribotag analysis of peritumoral excitatory neurons showed an upregulation in transcripts encoding for F-actin binding and other dendritic spine-enriched proteins. Light and electron microscopy analyses revealed marked decreases in dendritic spine density in peritumoral neurons. Intravital two-photon imaging in peritumoral excitatory neurons revealed progressive alterations in neuronal activity, both at the population and single neuron level, throughout tumor growth. Intravital two-photon imaging also revealed altered stimulus-evoked somatic calcium activity, both in rate and temporal alignment, which was most pronounced in neurons with high-tumor burden. A single acute dose of AZD8055, a mTORC1 and mTORC2 inhibitor reversed the translational effect of glioma on neurons, increased dendritic spine density, and functional neuronal alterations. These results point to mTOR-driven pathological plasticity in neurons at the infiltrative margin of glioma – manifested by alterations in ribosome-bound mRNA, dendritic spine morphology, and stimulus-evoked neuronal activity. Collectively, our work identifies the pathological changes that peritumoral neurons experience as both hyperlocal and reversible under the influence of mTOR inhibition, providing foundational knowledge for developing therapies targeting neuronal signaling in glioma.

Project description:Gray matter volume in the cerebral cortex has been consistently found to be decreased in patients with schizophrenia. The superior temporal gyrus (STG) is one of the cortical regions that exhibit the most pronounced volumetric reduction. This reduction is generally thought to reflect, at least in part, decreased number of synapses; the majority of these synapses are believed to be furnished by glutamatergic axon terminals onto the dendritic spines on pyramidal neurons. Pyramidal neurons in the cerebral cortex exhibit layer-specific connectional properties, providing neural circuit structures that support distinct aspects of higher cortical functions. For instance, dendritic spines on pyramidal neurons in layer 3 of the cerebral cortex are targeted by both local and long-range glutamatergic projections in a highly reciprocal fashion. Synchronized activities of pyramidal neuronal networks, especially in the gamma frequency band (i.e. 30-100 Hz), are critical for the integrity of higher cortical functions. Disturbances of these networks may contribute to the pathophysiology of schizophrenia by compromising gamma oscillation. This concept is supported by the following postmortem and clinical observations. First, the density of dendritic spines on pyramidal neurons in layer 3 of the cerebral cortex, including the STG, have been shown to be significantly decreased by 23-66% in subjects with schizophrenia. Second, consistent with these findings, the average somal area of these pyramidal cells is significantly smaller. Third, we have recently found that, in the prefrontal cortex, the density of glutamatergic axonal boutons, of which dendritic spines are their major targets, was significantly decreased by as much as 79% in layer 3 (but not layer 5) in subjects with schizophrenia. Finally, an increasing number of clinical studies have consistently demonstrated that gamma oscillatory synchrony is profoundly impaired in patients with schizophrenia. Furthermore, gamma impairment has been linked to the symptoms and cognitive deficits of the illness and the severity of these symptoms and deficits have in turn been associated with the magnitude of cortical gray matter reduction. Taken together, understanding the molecular underpinnings of pyramidal cell dysfunction will shed important light onto the pathophysiology of cortical dysfunction of schizophrenia. In order to gain insight into the molecular determinants of pyramidal cell dysfunction in schizophrenia, we combined LCM with Affymetrix microarray and high-throughput TaqManM-BM-.-based MegaPlex qRT-PCR approaches, respectively, to elucidate the alterations in messenger ribonucleic acid (mRNA) and microRNA (miRNA) expression profiles of these neurons in layer 3 of the STG. We found that transforming growth factor beta (TGFM-NM-2) and BMP (bone morphogenetic proteins) signaling pathways and many genes that regulate extracellular matrix (ECM), apoptosis and cytoskeleton were dysregulated in schizophrenia. In addition, we identified 10 miRNAs that were differentially expressed in this illness; interestingly, the predicted targets of these miRNAs included the dysregulated pathways and gene networks identified by microarray analysis. Together these findings provide a neurobiological framework within which we can begin to formulate and test specific hypotheses about the molecular mechanisms that underlie pyramidal cell dysfunction in schizophrenia. Gene epxression microarray from RNA isolated from pyramidal cells in layer III of the STG from 9 normal controls and 9 subjects with schizophrenia. There was no significant difference between diagnosis groups for age, sex, and post mortem interval (PMI).

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