Astrocytes
The stars of the brain
Credit: Art by Sam Esquillon. Set in motion by Dr. Emanuele Petretto. Words by Dr. Masia Maksymowicz. Project Coordinator: Dr. Masia Maksymowicz, Series Director: Dr. Radhika Patnala Sci-illustrate Endosymbiont
#Extraordinarycelltypes #sciart #lifescience
The silent heroes
The human brain is formed by many cell types, some of which we discussed previously. First are neurons, nerve cells that send information all over our bodies, stimulating specific body functions (e.g. breathing, moving). Another group of cells are glial cells, which provide physical and chemical support for neurons. Surprisingly, the most abundant among them are not neurons, but glial cells. Their number is linked to their function, which is to support other cells in the central (CNS) and peripheral nervous system (PNS), both physically and chemically (1). Thus, glial cells are the silent heroes of the nervous system, as their work is necessary for the proper work of the whole body. There are two glial cell types in the PNS: Schwann and satellite cells. In the CNS there are five glial cell types: astrocytes, oligodendrocytes, microglia, ependymal cells, and radial glia (1). Today we will focus on the most abundant glial cells, astrocytes.
The stars of our brains
Astrocytes (or astroglia) got their name from the Greek word astron meaning star, due to their star-shaped appearance (2). This star-like structure is formed by multiple projections that allow them to perform their functions in the nervous system. Classically, astrocytes were categorized according to their morphology and location inside the brain (2). Scientists used to recognise two types of astrocytes, one present in gray matter (protoplasmic astrocytes) and another one (fibrous astrocytes) in the white matter (3). Nowadays, thanks to transcriptomic analyses, we know that astrocytes are very heterogeneous cell type, and the differences in function and gene transcription between each subtype can be observed across the various cortical layers of the brain (4).
Interestingly, astrocytes present in primates and humans are larger and more complex in comparison to other vertebrates (5). This is especially important when studying functions of astrocytes, as although similar, commonly used mice astrocytes are different in many aspects to the human ones. Fortunately, it is possible to obtain astrocyte cell cultures using induced pluripotent stem cells (iPSC), which can be generated from somatic cells from skin or blood (6).
Keeping the brain clear
Inside the brain, astrocytes play multiple roles that overall result in proper homeostasis of this organ. First of all, they are involved in the formation and maintenance of the blood-brain barrier (BBB), a biological wall that separates the brain from the rest of the body. Astrocytes transport nutrients (e.g. glucose, which they store as glycogen or convert to lactate to feed neurons) and gases (e.g. oxygen) from blood vessels towards neurons, and can also sense and respond to inflammation, infection, or injury (4). They also give mechanical support to neurons (7). In fact, astrocytes form a network between blood vessels, neurons and other cells, which allows them to better regulate the BBB, limit the signaling at the synapses and help in cell communication (7).
Masters of relaxation
Astrocytes are also thought to be actively involved in circuit function by regulating the abundance of neurotransmitters, but also driving synapse formation and elimination (8). Recently, scientists discovered that binding with a neurotransmitter called norepinephrine has a different effect on astrocytes than neurons. While norepinephrine causes increased activation in neurons, for astrocytes it sends the information that they should help calm the neurons down (9). Since norepinephrine makes neurons alert, astrocytes help the brain to go back into a relaxed state.
When the waste control is affected
Another important function is removing waste and dead neurons from the brain, and maintaining the brain’s extracellular environment by recycling neurotransmitters and nutrients (3). In fact, astrocytes are a part of the glymphatic system (or glial-dependent lymphatic transport), a pseudo-lymphatic network formed by glial cells in the brain, that fuels and cleans the brain (10). Glymphatic system constantly removes toxins and waste from the brain, but it is only active during sleep. Disruption of the glymphatic system is linked to neurodegenerative diseases, like Alzheimer’s disease. Interestingly, our lifestyle choices (e.g. sleep position, exercising, omega-3 consumption, intermittent fasting, chronic stress) can also affect the work of the glymphatic system (10). While it is very humbling, how much our astrocytes can do for us, we clearly can also help them by leading a healthy lifestyle.
Recognizing and appreciating the labs working in this space
- Attwell Lab, UCL, London, UK https://www.ucl.ac.uk/biosciences/david-attwell
- Pękowska Lab, Nencki Institute of Experimental Biology PAS, Warsaw, Poland https://pekowskalab.nencki.edu.pl/about Twitter: @AleksandraPeko4
- Liddelow Lab, Neuroscience Institute, New York University, USA https://www.liddelowlab.com/ Twitter: @LiddelowSA
- Freeman Lab, Vollum Institute, Portland, USA https://www.ohsu.edu/freeman-lab
- Quintana Lab, Brigham and Women’s Hospital, Boston, USA, https://quintanalab.bwh.harvard.edu/ Twitter: @QuintanaLabHMS
- Herland Lab, Karolinska Institutet, Sweden https://www.herlandlab.com/
- Poskanzer Lab, Biochemistry & Biophysics Department, UCSF, USA, https://kiraposkanzerlab.org/research, Twitter: @KiraPoskanzer
- Sofroniew Lab, Department of Neurobiology, UCLA, USA https://neurobio.ucla.edu/people/michael-sofroniew-m-d-ph-d/
- Laboratory of astrocyte biology and CNS regeneration, University of Gothenburg, Sweden https://www.gu.se/en/research/laboratory-of-astrocyte-biology-and-cns-regeneration
- Eroglu Lab, Duke Neurobiology, Durham, USA https://www.neuro.duke.edu/research/faculty-labs/eroglu-lab
References
- Dellwo, Adrienne “What Are Glial Cells and What Do They Do?” (2023) https://www.verywellhealth.com/what-are-glial-cells-and-what-do-they-do-4159734#:~:text=Glial%20cells%20are%20a%20type,as%20neuroglia%20or%20just%20glia.
- Verkhratsky, Alexei, and Maiken Nedergaard. “Physiology of Astroglia.” Physiological reviews vol. 98,1 (2018): 239–389. doi:10.1152/physrev.00042.2016
- Sofroniew, Michael V, and Harry V Vinters. “Astrocytes: biology and pathology.” Acta neuropathologica vol. 119,1 (2010): 7–35. doi:10.1007/s00401–009–0619–8
- Hasel, Philip, and Shane A Liddelow. “Astrocytes.” Current biology : CB vol. 31,7 (2021): R326-R327. doi:10.1016/j.cub.2021.01.056
- Verkhratsky, Alexei et al. “Evolution of neuroglia.” Annals of the New York Academy of Sciences vol. 1518,1 (2022): 120–130. doi:10.1111/nyas.14917
- Voulgaris, Dimitrios et al. “Generation of Human iPSC-Derived Astrocytes with a mature star-shaped phenotype for CNS modeling.” Stem cell reviews and reports vol. 18,7 (2022): 2494–2512. doi:10.1007/s12015–022–10376–2
- Chiareli, Raphaela Almeida et al. “The Role of Astrocytes in the Neurorepair Process.” Frontiers in cell and developmental biology vol. 9 665795. 25 May. 2021, doi:10.3389/fcell.2021.665795
- Chung, Won-Suk et al. “Astrocytes Control Synapse Formation, Function, and Elimination.” Cold Spring Harbor perspectives in biology vol. 7,9 a020370. 6 Feb. 2015, doi:10.1101/cshperspect.a020370
- Reitman, Michael E et al. “Norepinephrine links astrocytic activity to regulation of cortical state.” Nature neuroscience vol. 26,4 (2023): 579–593. doi:10.1038/s41593–023–01284-w
- Reddy, Oliver Cameron, and Ysbrand D van der Werf. “The Sleeping Brain: Harnessing the Power of the Glymphatic System through Lifestyle Choices.” Brain sciences vol. 10,11 868. 17 Nov. 2020, doi:10.3390/brainsci10110868
About the author:
DR. MAŁGORZATA ‘MASIA’ MAKSYMOWICZ
Content Editor The League of Extraordinary Cell Types, Sci-Illustrate Stories
Dr. Maksymowicz did her Ph.D. in Cell Biology (IIMCB, Poland) studying the intracellular trafficking and inflammatory signalling of a cytokine receptor. She did a 1-year post-doc at Nencki Institute, Poland, studying the protein- and RNA-binding properties of proteins. Currently, she is doing a post-doc at Barts Cancer Institute, UK, studying the links between endocytosis and tumorigenesis. Dr. Maksymowicz is passionate about science and loves to combine different fields of biology, always trying to seek beauty in nature.
About the artist:
SAM ESQUILLON
Contributing Artist The League of Extraordinary Celltypes, Sci-Illustrate Stories
Sam worked for a couple of educational children’s shows as an illustrator, puppeteer, art director, and production designer. He still works as a production designer for international films and tv/ online streaming shows.
About the animator:
DR. EMANUELE PETRETTO
Animator The League of Extraordinary Cell Types, Sci-Illustrate Stories
Dr. Petretto received his Ph.D. in Biochemistry at the University of Fribourg, Switzerland, focusing on the behavior of matter at nanoscopic scales and the stability of colloidal systems. Using molecular dynamics simulations, he explored the delicate interaction among particles, interfaces, and solvents.
Currently, he is fully pursuing another delicate interaction: the intricate interplay between art and science. Through data visualization, motion design, and games, he wants to show the wonders of the complexity surrounding us.
About the series:
The League of Extraordinary Cell types
The team at Sci-Illustrate and Endosymbiont bring to you an exciting series where we dive deep into the wondrous cell types in our body, that make our hearts tick ❤.
