MicroRNA-145 and -212 regulate astrocytic function after spinal cord injury

Abstract

Astrogliosis is essential for tissue repair after spinal cord injury (SCI) since astrocytes play supporting roles for neurons and form glial scar as a physical barrier to prohibit the expansion of secondary injury Deregulated microRNAs (miRNAs) have been reported to contribute to CNS neurodegeneration and damages In this study we present that mir-145 a miRNA species enriched in rat neurons and astrocytes was downregulated at the lesion site at 1 week (subacute) and 1 month (chronic) after SCI The in vitro studies showed that potent inflammagen lipopolysaccharide (LPS) inhibited astrocytic mir-145 expression via p38 MAPK or ERK1/2 pathway We used lentivirus-mediated pre-miRNA delivery system using the promoter of glial fibrillary acidic protein (GFAP) an astrocyte-specific intermediate filament to induce astrocyte-specific overexpression of mir-145 at the lesion site The results indicated that astrocytic mir-145 overexpression attenuated the pileup of astrocytes at the lesion border and reduced their process density along with the increased accumulation of activated microglia In parallel overexpression of mir-145 reduced astrocytic cell size and the number of astrocytic cell processes Astrocytic cell proliferation and migration were diminished after mir-145 overexpression Through 3’-UTR luciferase reporter assay and western blot analysis we identified that GFAP and c-Myc were the direct targets of mir-145 in astrocytes These findings demonstrate that mir-145 regulates astrocytic dynamics partly via the downregulation of GFAP and c-Myc In addition we identified that astrocytic glutamate transporter GLAST was one of mir-145 targets In the regard to mir-212 the miRNA was observed to be expressed in neurons mainly but in astrocytes and oligodendrocytes to some degree Its level was also reduced at the lesion site after SCI After exposure of astrocytes to LPS astrocytic mir-212 was downregulated Overexpression of mir-212 caused the morphological change of astrocytes into elongated process-bearing shapes which might be due to mir-212 induced repression of β-actin expression Together the results from the study as described above point to the novel role of mir-145 and mir-212 in the regulation of astrocytic dynamics Moreover the findings reveal that the downregulation of mir-145 and mir-212 in astrocytes after SCI might be critical for astrogliosis after SCI

Date of Award	2015 Jan 21
Original language	English
Supervisor	Shun-Fen Tzeng (Supervisor)