Channels • 2021 • Volume 6 • Number 1 Page 3 downregulation of miRNAs that control the Treg response also causes inflammation and autoimmunity to increase. Heightened inflammation and dysregulated immune response lead to development of autoimmune disorders such as rheumatoid arthritis, multiple sclerosis, psoriasis, inflammatory bowel disease, and systemic lupus (Liu et al., 2018). Analysis MicroRNA Expression in Healthy Astrocytes MicroRNA (miRNA) plays an important part in maintaining the normal functions of the central nervous system (Sun et al., 2019), and they often have an inhibitory function. Although its role is still not completely clear, an accumulating collection of evidence indicates that miRNA is a key part of many of the roles and tasks of the astrocyte. For instance, miRNA seems to be necessary in the formation of synapses. Research has shown that increased levels of CCL5, a target of miRNA, caused deficiencies in synapse formation (Sun et al., 2019). In addition, this research further supported the theory that miRNA plays a pivotal role in regulating the activation of astrocytes. When an astrocyte becomes activated, it gains the ability to secrete various signaling substances that regulate neuron development, function, and connectivity (Jovicic & Gitler, 2017). Among these substances are exosomes carrying miRNA shown to be significantly different from the miRNA that remains inside the cell. The miRNA carried by exosomes provide a mechanism for differentiating the function of various miRNAs within the cell. Also, while not much is yet known about this exosomal miRNA, recent evidence shows that miRNA plays a key role in the inflammatory response, diminishing the activity of target neurons and downregulating the transcription of proteins required for neuronal excitability (Chaudhuri et al., 2018). In fact, miRNA likely plays a major role in the neurogenic stress response (Luarte et al., 2017). For this reason, certain miRNA could be a good biomarker for central nervous system inflammation and stress points (Lafourcade et al., 2016). Finally, there is no one fast and easy way to tell what a healthy expression of miRNA in astrocytes is since the answer will depend on many factors, such as age and anatomical location. Researchers find a high expression of miRNA in the fetal germinal matrix, likely for developmental purposes (Rao et al., 2016). There is a higher expression of miRNA in adult white matter than in fetal white matter, while in grey matter the two seem comparable. Also, similar overall levels of miRNA exist between adult white and grey matter; however, different levels of various miRNA appear to be expressed in each (Rao et al., 2016). MicroRNA Expression in Glioblastoma MiRNAs have a close relation to the biological features of the glioblastoma stem cells (GSCs) and predict the survival in glioblastoma patients. Fifty-one miRNAs are associated with glioblastoma’s stem-like phenotype, and nine were identified to be strongly upregulated in GSCs: miR-9-3p, miR93-3p, miR-93-5p, miR-106b-5p, miR-124-3p, miR-153-3p, miR-301a-3p, miR-345-5p, and miR652-3p (Sana et al., 2018). Both miR-9-3p and the hairpin counterpart miR-9-5p are expressed in the brain. These miRNAs affect the Notch signaling pathways, which surprisingly promotes differentiation of neural stem cells. Furthermore, this affected Notch pathway appears to induce
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