ABSTRACT
To determine whether reactive astrocytes stimulated by brain injury can transdifferentiate into functional new neurons, we labeled these cells by injecting a glial fibrillary acidic protein (GFAP) targeted enhanced green fluorescence protein plasmid (pGfa2-eGFP plasmid) into the striatum of adult rats immediately following a transient middle cerebral artery occlusion (MCAO) and performed immunolabeling with specific neuronal markers to trace the neural fates of eGFP-expressing (GFP(+)) reactive astrocytes. The results showed that a portion of striatal GFP(+) astrocytes could transdifferentiate into immature neurons at 1 week after MCAO and mature neurons at 2 weeks as determined by double staining GFP-expressing cells with ßIII-tubulin (GFP(+)-Tuj-1(+)) and microtubule associated protein-2 (GFP(+)-MAP-2(+)), respectively. GFP(+) neurons further expressed choline acetyltransferase, glutamic acid decarboxylase, dopamine receptor D2-like family proteins, and the N-methyl-D-aspartate receptor subunit R2, indicating that astrocyte-derived neurons could develop into cholinergic or GABAergic neurons and express dopamine and glutamate receptors on their membranes. Electron microscopy analysis indicated that GFP(+) neurons could form synapses with other neurons at 13 weeks after MCAO. Electrophysiological recordings revealed that action potentials and active postsynaptic currents could be recorded in the neuron-like GFP(+) cells but not in the astrocyte-like GFP(+) cells, demonstrating that new GFP(+) neurons possessed the capacity to fire action potentials and receive synaptic inputs. These results demonstrated that striatal astrocyte-derived new neurons participate in the rebuilding of functional neural networks, a fundamental basis for brain repair after injury. These results may lead to new therapeutic strategies for enhancing brain repair after ischemic stroke.
