In Situ Dividing and Phagocytosing Retinal Microglia Express Nestin, Vimentin, and NG2 In Vivo

Abstract

BackgroundFollowing injury, microglia become activated with subsets expressing nestin as well as other neural markers. Moreover, cerebral microglia can give rise to neurons in vitro. In a previous study, we analysed the proliferation potential and nestin re-expression of retinal macroglial cells such as astrocytes and Müller cells after optic nerve (ON) lesion. However, we were unable to identify the majority of proliferative nestin+ cells. Thus, the present study evaluates expression of nestin and other neural markers in quiescent and proliferating microglia in naïve retina and following ON transection in adult rats in vivo.Methodology/Principal FindingsFor analysis of cell proliferation and cells fates, rats received BrdU injections. Microglia in retinal sections or isolated cells were characterized using immunofluorescence labeling with markers for microglia (e.g., Iba1, CD11b), cell proliferation, and neural cells (e.g., nestin, vimentin, NG2, GFAP, Doublecortin etc.). Cellular analyses were performed using confocal laser scanning microscopy. In the naïve adult rat retina, about 60% of resting ramified microglia expressed nestin. After ON transection, numbers of nestin+ microglia peaked to a maximum at 7 days, primarily due to in situ cell proliferation of exclusively nestin+ microglia. After 8 weeks, microglia numbers re-attained control levels, but 20% were still BrdU+ and nestin+, although no further local cell proliferation occurred. In addition, nestin+ microglia co-expressed vimentin and NG2, but not GFAP or neuronal markers. Fourteen days after injury and following retrograde labeling of retinal ganglion cells (RGCs) with Fluorogold (FG), nestin+NG2+ microglia were positive for the dye indicating an active involvement of a proliferating cell population in phagocytosing apoptotic retinal neurons.Conclusions/SignificanceThe current study provides evidence that in adult rat retina, a specific resident population of microglia expresses proteins of immature neural cells that are involved in injury-induced cell proliferation and phagocytosis while transdifferentiation was not observed.

In vitro Differentiation of Adult Adipose Mesenchymal Stem Cells into Retinal Progenitor Cells

“…The morphological phase-contrast pattern observed in these cells (nuclear and cytoplasmic changes) indicates differentiation, which is supported by the specific immunofluorescent staining of specific cell lineage markers that match the different morphological changes [13,14]. A similar result was previously described by us for the differentiation of adult bone marrow-derived MSCs into neuroblasts.…”

Cell-replacement therapy and neural repair in the retina

“…Interestingly, nestin-expressing microglia have been demonstrated to exist even in the naive brain, in variable cell numbers in the various regions analyzed (Takamori et al 2009). More recently, we have demonstrated that a subpopulation of retinal microglia expressing neural markers nestin, NG2 and vimentin also exists in the naive adult rat retina (Wohl et al 2011), displaying a similar subcellular distribution of nestin filaments as that recently reported for the brain (Takamori et al 2009). Following ON transection, the microglial fraction expressing nestin proliferates in situ and we therefore conclude that microglial nestin expression probably plays a role in the physiological self-renewal of this endogenous cell population (Wohl et al 2010;Wohl et al 2011).…”

“…More recently, we have demonstrated that a subpopulation of retinal microglia expressing neural markers nestin, NG2 and vimentin also exists in the naive adult rat retina (Wohl et al 2011), displaying a similar subcellular distribution of nestin filaments as that recently reported for the brain (Takamori et al 2009). Following ON transection, the microglial fraction expressing nestin proliferates in situ and we therefore conclude that microglial nestin expression probably plays a role in the physiological self-renewal of this endogenous cell population (Wohl et al 2010;Wohl et al 2011). Since increasing evidence suggests that CNS injury can induce neural progenitor characteristics in activated microglia of non-neurogenic regions in vivo (Wu et al 2005;Yokoyama et al 2006), we propose that this specific retinal microglial subpopulation acts as an endogenous neural progenitor-like cell after injury.…”

Homeostasis of Microglia in the Adult Brain: Review of Novel Microglia Depletion Systems

“…Additionally, the BM-derived microglia that repopulate the brain after irradiation and depletion also express the nestin protein. Nestin expression in microglia could be shown, for example, in early stages of optic nerve injury [70] and traumatic brain injury [71], which indicates that nestin may be required for proliferation rather than serving as a stem cell marker. Importantly, as the study by Bruttger et al (2013) used the promoter of CX 3 CR1 as a cell fate-mapping system, they show that all repopulating cells are derived from CX 3 CR1 expressing progenitor cells.…”