ABSTRACT
The antidiabetic drug metformin has been found to have beneficial effects in various neurological disorders; however, the molecular mechanisms underlying these effects remain unclear. Here we report that metformin protects neuronal cells from quinolinic acid (QUIN)-induced excitotoxicity. For this, we pretreated N18D3 neuronal cells with metformin prior to QUIN for 24 h. We found that pretreating the cells with metformin significantly improved cell survival rate in a concentration-dependent manner and reduced apoptotic cell death, as revealed by a MTT assay and DAPI staining, respectively. Calcium imaging using fluo-4 showed that metformin (100 µM) inhibited the intracellular calcium increase that was induced by QUIN. In addition, mRNA expression of pro-apoptotic genes, p21 and Bax, was decreased and of anti-apoptotic genes, Bcl-2 and Bcl-xl, was increased with metformin treatment compared to QUIN-induced cells. The immunoreactivity of phosphorylated ERK1/2 was elevated in cells treated with metformin, indicating the ERK1/2 signaling pathway in the neuroprotective effects of metformin in QUIN-induced cell death. Collectively, our data demonstrates that metformin exerts its neuroprotective effects by inhibiting intracellular calcium increases, allowing it to regulate ERK1/2 signaling and modulate cell survival and death genes.
ABSTRACT
Recent studies have shown that neuroblasts migrate from the subventricular zone (SVZ) into the injured area after ischemic brain insults. However, it is not well understood which mechanism mediates this ectopic migration and which types of cells migrate into the damaged region from the SVZ. The present study was designed to investigate the characteristics of the migration of nestin-positive neural stem cells toward the region of ischemic injury after focal cortical ischemia. Nestin-eGFP transgenic mice were used to effectively model the migration of SVZ cells. Photothrombotic ischemia was induced by injection of rose bengal (30 mg/kg) and exposure to cold light. Migration of nestin-positive cells was examined using 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) and bromodeoxyuridine (BrdU) labeling. The number of nestin-positive cells was increased significantly in the peri-infarct area at 5 and 7 days after photothrombosis. A subset of nestin-positive cells was co-labeled with DiI or BrdU. Some of the nestin-positive cells co-expressed doublecortin (DCX) and only a few nestin-positive cells co-labeled with anti-epidermal growth factor receptor (EGFr) antibody. However, no nestin-positive cells were immunoreactive for glial fibrillary acidic protein (GFAP). The inhibition of matrix metalloproteinases (MMPs) using the MMP inhibitor, FN-439, decreased nestin-positive cells in the peri-infarct region at 7 days after photothrombosis. Although MMP-9 was not co-expressed in the nestin-positive cells in the peri-infarct cortex, MMP-9 did co-localize with GFAP-positive astrocytes. These results suggest that nestin-positive neural progenitor cells migrate into the peri-infarct cortex after photothrombotic ischemia and that MMP-9 is involved in the migration.
