What you will learn in this 9-minute webinar:
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How gliomas interface with the neuronal microenvironment and affect functional cognitive networks.
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How the hyperexcitable phenotype of neurons in the presence of glioma cells observed in vivo was recreated in vitro on the Maestro MEA platform.
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Demonstration of a multimodal approach combining clinical electrocorticography and magnetoencephalography data with in vitro data.
This presentation highlights data from a Nature paper by the author.
About the presenter:
Dr. Saritha Krishna
Brain Tumor Center
University of California, San Francisco
Dr. Saritha Krishna completed her PhD at the University of Georgia, where she studied the role of environmental triggers in the modulation of glial-neural communication in health and disease.
In her current role as a Research Specialist at the University of California, San Francisco, she focuses on understanding how glial cells influence brain physiology.
Transcript of the webinar:
Thank you for joining our coffee break webinar. Today’s topic is “Remodeling of human neural circuits by glioblastoma.”
Brain tumors are known to infiltrate healthy brain tissue and alter function. In glioblastoma, the most fatal type of adult brain tumor, this functional decline is particularly devastating. In this coffee break webinar, Dr. Krishna applies the principles of glial-neural communication to brain tumors and studies the mechanisms by which gliomas interface with the neuronal microenvironment and affect functional cognitive networks.
Dr. Saritha Krishna completed her PhD at the University of Georgia, where she studied the role of environmental triggers in the modulation of glial-neural communication in health and disease. In her current role as a Research Specialist at the University of California, San Francisco, she focuses on understanding how glial cells influence brain physiology.
Thank you for joining me. My name is Saritha Krishna, and I will be discussing a mechanism by which glioblastoma tumors remodel neural circuits to affect cognitive function, and how we’ve assessed this both in vitro and in vivo with clinical data from human patients.
Researchers have long known that brain tumors, especially gliomas, can affect a person’s cognitive and physical function. In glioblastoma, these infiltrating brain tumors were initially thought to impair normal brain functions by compressing the healthy brain tissue around the tumor mass and by potentially competing for blood supply from the adjacent healthy tissues. However, what exactly causes cognitive decline in glioblastoma patients is still unknown.
Preclinical studies have demonstrated a strong positive feedback loop between neurons and glioblastoma cells in the microenvironment, leading to neural hyperexcitability.
Beyond preclinical models, our group previously demonstrated in awake, resting patients that glioblastoma-infiltrated cortex exhibits increased neuronal excitability. While neurons within glioblastoma-infiltrated brain are hyperexcitable at rest, the extent of cognitive task-specific neuronal hyperexcitability and the mechanisms by which glioblastomas maintain the ability to engage with neuronal circuitry and alter cortical function remain incompletely understood. Deciphering the processes by which gliomas remodel neural circuits may uncover therapeutic targets for these lethal brain cancers.
To understand what this neuron-glioma feedback loop means for patients in terms of their cognitive and survival outcomes, our team recruited volunteers awaiting surgery whose tumors had infiltrated the brain region controlling speech and used intra-operative mapping during surgery to capture brain activity during different language tasks. In addition to finding increased neural activity in the specific brain areas responsible for language processing, we found activation in broader regions of the brain quite remote from known language zones of the brain. This unexpected finding shows that tumors can hijack and restructure connections in the brain tissue surrounding them and increase their activity. More importantly, we found that this functional integration of glioblastoma into neural circuits negatively influences patient’s cognitive performance and survival outcomes.
In order to understand the influence of gliomas on neural networks and investigate further into the mechanisms underlying this glioma-induced remodeling and hyperexcitability, we used a multimodal approach combining clinical electrocorticography and magnetoencephalography data with in vitro data.
During surgical tumor resection, we took primary patient glioblastoma biposies with varying functional connectivity. We then used the tumor biopsies from regions with high and low functional connectivity to the rest of the brain (HFC and LFC, respectively) and ran a series of in vitro experiments including RNA sequencing, primary patient-derived glioma culture, multi-electrode array (MEA), and patient-derived xenograft (PDX) mouse models.
Using both bulk and single-cell RNA sequencing and immunohistochemistry, we found that the HFC regions were enriched for synaptogenic genes, including thrombospondin 1 (TSP-1). TSP-1 is normally produced by healthy astrocytes in the brain and encourages the growth of new synapses, suggesting a mechanism for the observed glioma-induced neural circuit remodeling.
Co-cultured with neurons, HFC glioma cells exhibited a fivefold increase in proliferation rate and increased integration into neural organoids. By contrast, the LFC glioma in vitro cell proliferation index was unchanged by the presence of neurons in co-culture, and these cells had relatively low integration. These results indicate that the ability of HFC cells to proliferate and invade parenchymal tissue is contingent on the presence of neuronally secreted factors and that, in the absence of neuronal signals, they tend to acquire a dormant tumor phenotype. Interestingly, when TSP-1 was exogenously added to the LFC cells, they began behaving like the HFC glioma cells, suggesting that TSP-1 is critical for this neuron–glioma interaction.
Having established the neuronotrophic properties of HFC glioblastoma cells, we explored whether neuron-glioma integration recapitulated the hyperexcitability we observed in the brains of glioblastoma patients. To assess the functional electrophysiological responses in the neuron-glioma co-cultures, we used the Maestro MEA platform. The Maestro allowed us to characterize the functional phenotype of neurons co-cultured with either high- or low-functional connectivity glioma cells from patient tumor biopsies. Co-cultures with HFC tumor cells were significantly more active and synchronous than co-cultures with LFC tumor cells or cortical neurons, alone, reflecting the clinical data.
Finally, given the premise that HFC glioma cell-derived TSP-1 could serve as a molecular driver of this observed neuronal hyperexcitability, we targeted TSP-1 therapeutically using the FDA-approved drug, gabapentin (GBP). In HFC co-cultures, gabapentin treatment significantly reduced neural activity and synchrony, suggesting TSP-1 as a potential target for therapeutic development for glioblastoma.
In summary, we found that glioma-network integration negatively influences patient’s cognition and overall survival. We further found evidence of a glioma-derived mechanism, with malignant glioma cells remodeling the tumor microenvironment to promote neuronal hyperexcitability and tumor growth primarily through TSP-1 paracrine signaling. Finally, we demonstrated that inhibition of TSP-1 significantly decreases glioblastoma cell proliferation and network synchrony within the tumor microenvironment, identifying therapeutic vulnerabilities of glioma-network integration.
I would like to acknowledge and thank those who contributed to this work. Thank you for your attention.
And that is the conclusion for today's Coffee Break Webinar. If you have any questions you would like to ask regarding the research presented, or if you are interested in presenting your own research with microelectrode array technology or impedance-based assays, please forward them to coffeebreak at axionbio.com. For questions submitted for Saritha Krishna, she will be in touch with you shortly.
Thank you for joining in on today's Coffee Break Webinar and we look forward to seeing you again.
