MicroRNA-145 as one negative regulator of astrogliosis

Astrogliosis occurs at the lesion site within days to weeks after spinal cord injury (SCI) and involves the proliferation and hypertrophy of astrocytes, leading to glia scar formation. Changes in gene expression by deregulated microRNAs (miRNAs) are involved in the process of central nervous system neurodegeneration. Here, we report that mir-145, a miRNA enriched in rat spinal neurons and astrocytes, was downregulated at 1 week and 1 month after SCI. Our in vitro studies using astrocytes prepared from neonatal spinal cord tissues indicated that potent inflammagen lipopolysaccharide downregulated mir-145 expression in astrocytes, suggesting that SCI-triggered inflammatory signaling pathways could play the inhibitory role in astrocytic mir-145 expression. To induce overexpression of mir-145 in astrocytes at the spinal cord lesion site, we developed a lentivirus-mediated pre-miRNA delivery system using the promoter of glial fibrillary acidic protein (GFAP), an astrocyte-specific intermediate filament. The results indicated that astrocyte-specific overexpression of mir-145 reduced astrocytic cell density at the lesion border of the injured spinal cord. In parallel, overexpression of mir-145 reduced the size of astrocytes and the number of related cell processes, as well as cell proliferation and migration. Through a luciferase reporter system, we found that GFAP and c-myc were the two potential targets of mir-145 in astrocytes. Together, the findings demonstrate the novel role of mir-145 in the regulation of astrocytic dynamics, and reveal that the downregulation of mir-145 in astrocytes is a critical factor inducing astrogliosis after SCI. GLIA 2015;63:194-205.