How can neurons communicate with brain tumors and help them grow?
Yusha Sun was the lead author on this study. Yusha is a 6th year MD/PhD student in the lab of Hongjun Song who recently defended and is back in the clinic to finish his medical degree. He plans to pursue neuro-oncology and has a strong interest in studying brain tumors and the developing brain from the molecular, functional, and circuit levels. His research integrates circuit neuroscience and computational genomics to explore glioblastoma (GBM) biology and aims to leverage this understanding to bring therapies bench to bedside.
or technically,
Brain-wide neuronal circuit connectome of human glioblastoma
See Original Abstract on Pubmed
Authors of the study: Yusha Sun, Xin Wang, Daniel Y Zhang, Zhijian Zhang, Janardhan P Bhattarai, Yingqi Wang, Kristen H Park, Weifan Dong, Yun-Fen Hung, Qian Yang, Feng Zhang, Keerthi Rajamani, Shang Mu, Benjamin C Kennedy, Yan Hong, Jamie Galanaugh, Abhijeet Sambangi, Sang Hoon Kim, Garrett Wheeler, Tiago Gonçalves, Qing Wang, Daniel H Geschwind, Riki Kawaguchi, Angela N Viaene, Ingo Helbig, Sudha K Kessler, Ahmet Hoke, Huadong Wang, Fuqiang Xu, Zev A Binder, H Isaac Chen, Emily Ling-Lin Pai, Sara Stone, MacLean P Nasrallah, Kimberly M Christian, Marc Fuccillo, Nicolas Toni, Zhuhao Wu, Hwai-Jong Cheng, Donald M O'Rourke, Minghong Ma, Guo-Li Ming, Hongjun Song
Introduction
Over the past decade, new medical treatments have made many types of cancer easier to treat. However, glioblastoma (GBM)—a fast-growing and aggressive type of brain cancer—remains extremely difficult to cure. One major reason is that GBM tumors can communicate with neurons and recruit their assistance in tumor growth. Similar to a parasite, GBMs take advantage of the brain by stealing nutrients, invading other regions, and disrupting normal brain activity over time. To understand how GBM tumor cells communicate with neurons, Yusha Sun, an NGG graduate student in Hongjun Song’s lab, asked three key questions:
1) How and where do GBM tumor cells receive signals from neurons?
2) Which communication signals can GBM tumor cells respond to?
3) Do these signals have lasting effects on tumor fitness?
How and where do tumor cells receive signals from neurons?
To answer how GBM tumor cells connect with neurons, Yusha first studied what type of signal receivers (receptors) tumors had on their cell surfaces. Receptors are important for communication between cells and cells typically have many different types of receptors to receive different messages. This is similar to having social media apps — if someone has Instagram or Snapchat, you can message them there, but if you’re trying to message them on Snapchat when they don’t have an account, they won’t receive your message. In the same way, tumor cells need the right receptor to receive a signal from a neuron. Through a technique called RNA sequencing, which catalogs all the genes a cell has, Yusha analyzed the specific subset of genes that represent receptors, and found that tumor cells have many different types. This makes GBM challenging to treat because blocking one type of receptor may not stop the tumor growth—tumor cells can simply use other types of receptors to keep receiving signals from neurons.
Secondly, Yusha needed to understand which neurons sent signals to tumor cells and where those neurons were located. Yusha used retrograde monosynaptic tracing in GBM organoids, which are tiny tumor models grown from tumor cells taken from real patients. To perform retrograde monosynaptic training, Yusha implanted these organoids in the brains of live mice, then injected a fluorescent tracer virus into the organoid that traveled backwards from tumor cell to neuron, lighting up the signalling neurons. This works like a detective following clues backward from the crime scene to the culprit source.
Using this method revealed that depending on where the organoid’s tumor cell was located in the brain, it could receive signals from up to 18 neurons total - that’s a lot of connectivity! In addition, neurons from both nearby and distant regions were sending signals to tumor cells. Neurons seemed to establish connections with tumor cells rather rapidly - the tracer takes 2 days to visually label neurons after injection into the organoid, but could be seen in neurons as early as day 3. Overall, these results showed that tumor cells in organoids can connect extensively and rapidly with neurons.
Interestingly, Yusha performed these experiments using genetically distinct organoids from different patients, but they all showed similar patterns of widespread and rapid communication with neurons. This suggests that GBMs in other patients may have similar patterns of communication, which could help scientists find broader treatments for GBM.
What types of neurons are involved in neuron-tumor connections?
To understand which communication signals the tumor cells respond to, Yusha looked at the types of neurons connected with the tumor since different types of neurons send specific signals known as neurotransmitters, which are chemical messengers sent from neurons to other cells. Using labeling methods for specific cell types, Yusha found that neurons connected with the tumor consisted of various subtypes, including neurons that secreted neurotransmitters such as acetylcholine (ACh), serotonin, and dopamine.
Yusha found that tumors implanted in certain brain regions received many signals from neurons located in the basal forebrain, which is known to contain cholinergic neurons that are major producers of ACh. Yusha confirmed that these cholinergic neurons connected to tumor cells by performing anterograde tracing in mice, which tracks signals forward from neurons to the tumor.
Does ACh signalling have long-term effects on tumor fitness?
After identifying cholinergic neurons that release ACh, Yusha wanted to find out whether ACh causes long-term changes in tumor cells. To test this, they exposed GBM organoids grown in a lab dish to ACh and measured calcium levels inside the tumor cells. Calcium is important because it helps control how a cell behaves and functions, and changes in calcium levels can cause cells to turn different genes on or off. Yusha found that ACh stimulation increased calcium levels in tumor cells, and these levels stayed high even after the ACh was removed. Thus, he hypothesized that he would also find changes in gene expression since calcium levels changed. He used RNA sequencing to look for the specific subset of genes that changed their expression after ACh stimulation. Many of the genes that became more active after ACh stimulation were linked to tumor invasion and glioblastoma progression.
One gene that stood out was CHRM3, a receptor. When Yusha knocked down CHRM3, tumor cells showed much smaller calcium increases and reduced migration compared to normal cells. Together, these results indicate that ACh promotes tumor fitness through CHRM3, suggesting that blocking this receptor could be a promising GBM treatment strategy. Consistent with this result, the CHRM3 antagonist 4-DAMP (an agent that blocks CHRM3) produced effects similar to CHRM3 knockdown by reducing tumor fitness.
Conclusion and potential treatments
Overall, GBMs appear highly effective at receiving signals from diverse neuronal cell types and adapting their behavior to become more aggressive. Yusha showed that cholinergic neurons in the basal forebrain can send ACh to tumor cells and cause long-lasting tumor changes that increase fitness via the CHRM3 receptor. These findings highlight how closely connected GBMs are to neurons and provide a framework for studying how tumor cells respond to neuronal signals, advancing efforts to develop more effective treatments.
About the brief writer: Anna Kasper
Anna is a PhD candidate in Dr. Richard Phillips’ lab. Her research focuses on identifying the genetic regulators of immune cell infiltration in glioblastomas