Hyun Joon Sohn

αB-Crystallin is Expressed in Myelinating Oligodendrocytes of the Developing and Adult Avian Retina

It is well known that the expression of αB-crystallin (aBC) is increased in neurons and glia under pathologic conditions. However, the expression of aBC during the normal development of the central nervous system has not been reported. This study aimed to clarify the cell type in the chick retina in which aBC is expressed and timing of aBC expression in this cell type during development. Double immunofluorescence with cell-specific markers demonstrated that aBC was selectively expressed in oligodendrocytes (OLs) in the embryonic day 20 (E20) chick retina. A small number of aBC-expressing OLs first appeared in the nerve fiber layer of the central and peripheral retina at E16. Faint aBC expression was also observed in myelin sheaths near cell bodies in the central retina. The number of aBC-expressing OLs and intensity of aBC expression in myelin sheaths were increased in the periphery as well as in the center of the E19 retina. aBC signals in the post-hatching day 120 retina were observed in the entire nerve fiber layer. The spatiotemporal expression pattern of aBC was identical to that of myelin basic protein. These data indicate that aBC-expressing OLs are myelinating OLs among OL-lineage cells. Besides, intrayolk injection of tocopherol, an antioxidant, provoked a decrease in the levels of aBC expression in myelinating OLs. These data suggest that aBC expression in myelinating OLs responds to the change of physiological oxidative stress.

Differential expression of αB-crystallin causes maturation-dependent susceptibility of oligodendrocytes to oxidative stress

Oligodendrocyte precursor cells (OPCs) are most susceptible to oxidative stress in the brain. However, the cause of differences in susceptibility to oxidative stress between OPCs and mature oligodendrocytes (mOLs) remains unclear. Recently, we identified in vivo that αB-crystallin (aBC) is expressed in mOLs but not in OPCs. Therefore, we examined in the present study whether aBC expression could affect cell survival under oxidative stress induced by hydrogen peroxide using primary cultures of OPCs and mOLs from neonatal rat brains. Expression of aBC was greater in mOLs than in OPCs, and the survival rate of mOLs was significantly higher than that of OPCs under oxidative stress. Suppression of aBC by siRNA transfection resulted in a decrease in the survival rate of mOLs under oxidative stress. These data suggest that higher susceptibility of OPCs than mOLs to oxidative stress is due, at least in part, to low levels of aBC expression. [BMB Reports 2013; 46(10): 501-506]

Sequential accumulation of iron in glial cells during chicken cerebellar development

Iron is an essential, but potentially harmful, metal in the brain. In normal brain, iron has been reported to accumulate mainly in glial cells and occasionally in neurons in some particular nuclei. However, the majority of investigations have targeted the adult brain. Here, we investigated spatiotemporal localization of iron in developing and adult chicken cerebellum using iron histochemistry. Iron reactivity was not detected in the chick cerebellum until embryonic day 12. Iron accumulation was first found in mature myelinating oligodendrocytes located in the inner part of the cerebellar folium at embryonic day 14. From embryonic day 20, iron-positive mature myelinating oligodendrocytes were localized in the white matter and the granular layer. From post-hatching day 2, iron accumulation was observed in Bergmann glia in the Purkinje cell layer as well as in mature myelinating oligodendrocytes. Iron accumulation in microglia was observed in the granular and molecular layers at post-hatching month 12. Our data indicate that during cerebellar development iron is accumulated in a unique sequence according to individual requirements or microenvironmental demands.

Characterization of the antigenic phenotype of αB-crystallin-expressing peripapillary glial cells in the developing chick retina

Radial glia are transdifferentiated into astrocytes within the developing brain and spinal cord. The neural retina contains Müller cells, which are retinal radial glia. Some of the cells that surround the optic nerve head among Müller cells in the chicken retina are called peripapillary glial cells (PPGCs). PPGCs express different molecules compared to typical Müller cells. However, an antigenic PPGC phenotype has not yet been clearly established. In this study, we classified the antigenic PPGC phenotypes and identified the differentiation stages of these cells. At embryonic day (E)8, αB-crystallin-positive PPGCs had a bipolar shape with long processes that traversed entire layers of the retina. Pax2 and vimentin were expressed in αB-crystallin-positive PPGCs. Glial fibrillary acidic protein (GFAP) immunoreactivity was not observed in PPGCs. At E18, αB-crystallin immunoreactivity disappeared from the vitread processes of PPGCs. However, the PPGC cell bodies and ventricular processes contained αB-crystallin protein, and the PPGCs retained the same Pax2-positive/vimentin-positive/GFAP-negative profile as that seen at E8. At post-hatch day 120, αB-crystallin and Pax2 immunoreactivity was not observed, but vimentin and GFAP expression was clearly observed in the presumptive location of the PPGCs. Furthermore, these two proteins overlapped within that location. Considering that vimentin expression is prolonged until the post-hatching period in chicken brain, these findings suggest that Pax2-negative/vimentin-positive/GFAP-positive PPGCs are phenotypically identical to mature astrocytes in this avian species.