Neuron Death and Disposal via Microglia and Astrocytes

For my STEAM project, I wanted to do something with neurons. As we have learned in class, neuron death can be considered more detrimental than death of other cells, due to their inability to reproduce as effectively as most other cells can. Neurons cannot go through mitosis, thus making the loss of neurons more worrying than the loss of another cell, like a skin cell. Neuron death is the process in which neuron cells cease to function. Our brains need neurons to perform all of its tasks, so with increased neuron death, comes decreased ability to complete those tasks. The loss of neurons has been found to cause cognitive impairment, and even neurodegenerative disorders such as Alzheimer’s (Avila et al., 2017). As we continue to age over time, so do our cells. If we are unable to effectively produce new brain cells, the loss of them can lead to some dysfunction, and this is one of the factors that contributes to the way in which Alzheimer’s disease develops. 

While we can easily recognize that neuron death can lead to problems, what does the process of neuron death look like? After sifting through some research articles, I found an article containing the first images of a neuron dying and promptly being “disposed of” (Damisah et al., 2020). I was personally interested in how such disposal happens. Because neurons are connected to each other in ways that other cells aren’t–through the connection via axons (DeSaix et al., 2013)–I imagined that it would be more difficult to dispose of dead neural cells. As it turns out, astrocytes and microglia are responsible for this task. Astrocytes are given the duty of breaking down and absorbing the dendrites and axons connected to a dead neuron, to get rid of the connections it shares to other neurons, whether they be dead or alive. Microglia, on the other hand, is responsible for the break down of the neuron cell itself. 

In my artwork, I portrayed a step-by-step process in which astrocytes and microglia break down a dead neuron cell. The blue neurons with smiley faces on them are still alive. However, the red neurons with frowny faces are dead. As you can see, there is some green coloring on the dead neuron, that eventually grows and covers the complete cell by the third step. As one might guess, the green coloring represents the microglia and astrocytes, as they gradually cover the cell and break it down, while severing the connections to the cells around it. This synaptic pruning is necessary to keep the brain functioning most optimally amidst the presence of dead brain cells, so I think that it is an important process to show.

References 

Avila J, Llorens-Martín M, Pallas-Bazarra N, et al. Cognitive Decline in Neuronal Aging and Alzheimer’s Disease: Role of NMDA Receptors and Associated Proteins. Front Neurosci. 2017;11:626. Published 2017 Nov 10. 

Damisah, E. C., Hill, R. A., Rai, A., Chen, F., Rothlin, C. V., Ghosh, S., & Grutzendler, J. (2020). Astrocytes and microglia play orchestrated roles and respect phagocytic territories during neuronal corpse removal in vivo. Science advances, 6(26).

DeSaix, P., Betts, J. G., Johnson, E., Johnson, J. E., Korol, O., Kruse, D. H., … & Young, K. A. (2013). Anatomy & Physiology: openStax.

Hart, M. (2020, July 14). Researchers Share First Captured Image of Dying Neuron. Nerdist. https://nerdist.com/article/dying-neuron-images/.

Yale Campus. (2020, June 26). Neurondeath [Video]. YouTube. https://www.youtube.com/watch?v=_BixMMfPkhU