Effect of 6-hydroxydopamine (6-OHDA) on proliferation of glial cells in the rat cortex and striatum: evidence for de-differentiation of resident astrocytes

Abstract

Reactive astrogliosis is the universal response to any brain insult. It is characterized by cellular hypertrophy, up-regulation of the astrocyte marker glial fibrillary acidic protein (GFAP), and proliferation. The source of these proliferating cells is under intense debate. Progenitor cells derived from the subventricular zone (SVZ), cells positive for chondroitin sulfate proteoglycan (NG2(+)), and de-differentiated astrocytes have been proposed as the origin of proliferating cells following injury. We have analyzed the effect of intraventricular-applied 6-hydroxydopamine (6-OHDA) on the proliferation and morphology of astrocytes in rat cortex and striatum by means of immunohistochemistry and confocal laser microscopy. At 4 days post-lesion, GFAP expression increased markedly. A subpopulation of the GFAP(+) cells co-expressed Ki-67, indicating that these cells were proliferating. To investigate whether these cells (1) arose from migrating SVZ progenitor cells, (2) derived from NG2(+) progenitor cells, or (3) de-differentiated from resident astrocytes, we studied the expression of the migration marker doublecortin (Dcx), the oligodendrocyte progenitor marker NG2, and the progenitor markers Nestin and Pax6. The proliferating Ki-67(+) cells co-expressed Nestin and Pax6, whereas no co-expression of Ki-67 with NG2 or the migration marker Dcx was observed. Thus, resident astrocytes de-differentiate, in response to the intraventricular application of 6-OHDA, to a phenotype resembling radial glia cells, which represent transient astrocyte precursors during development. An understanding of the mechanisms of the de-differentiation of mature astrocytes might be useful for designing new approaches to cell therapy in neurodegenerative diseases such as Parkinson's disease.

Original article Transcription factor Pax6 is expressed by astroglia after transient brain ischemia in the rat model

“…In physiological conditions, Pax6 plays an important role during CNS development, being characteristic of radial glia cells, responsible for neurogenesis, cells migration, brain patterning, neuronal specification, and growing of axonal projections [40,45,49]. Many authors regard Pax6 function as context-dependent and inhibiting cell proliferation, promoting neuronal differentiation and astrocyte maturation [46,55]. After completing development, Pax6 remains present in a relatively small group of progenitor cells, maintaining the proliferative properties and localized in the subventricular zone of lateral cerebral ventricles as well as in the subgranular zone of dentate gyrus in the hippocampal complex.…”

“…Reactive astrogliosis is an astrocytic response to different kinds of lesions [43,55]. Although the universal character of astrogliosis is accepted by many authors, there is evidence that various kinds of pa thological stimuli may evoke glial response, differentiated in morphological, biochemical and immunological profiles [3,35,51].…”

“…Activation by ischemia may result in re-appearing of Pax6 in the regions distant from the proliferative zones, but localized in ischemic penumbra, surrounding the necrotic core, which indicates changes of immunological characteristics of cells localized in the areas of reduced CBF. Pax6 up-regulation and astrocytic response were studied after activation by various stimuli like inflammation, brain injury, neurodegeneration and temperature injury [46,51,55]. However, Pax6 changes after transient cerebral ischemia are still only fragmentarily documented in the literature.…”

“…The most common signalling agents influencing this reaction include neurotransmitters and gliotransmitters (ATP, glutamate, noradrenalin), reactive oxygen species (nitric oxide; NO), cytokines and interleukins (IL-1α, IL-1β, IL-6, IL-10), tumour necrotic factor-α (TNF-α), tumour growth factor-β (TGF-β), lipopolysaccharide, Toll-like receptor ligands, endothelin-1 and β-amyloid [3,51]. Reactive gliotic response to various types of lesions is also concerned with up-regulation of numerous genes encoding markers characteristic of definite stages of glial and neuronal development, like progenitor and de-differentiation markers (nestin and Pax6), migration marker (doublecortin), cell division and proliferation marker (Ki-67) [55].…”

Astrocytes Role in Parkinson: A Double-Edged Sword

“…6-OHDA induces dopaminergic neuronal death by the increased generation of H 2 O 2 and quinones [92]. Additionally, it causes both microgliosis and astrogliosis, which is characterized by increased astrocytic proliferation in rat cortex and striatum accompanied by a marked expression of GFAP [92,93]. Taking into account that reactive astrocytes may produce various neurotrophic factors and antioxidant mole-cules targeting neuronal survival, it is possible that genetic manipulation of these functions in astrocytes may represent a promising strategy to improve dopaminergic neurons or neural progenitor cells survival [4,23].…”