Rat retinal ganglion cells upregulate the pro-apoptotic BH3-only protein Bim after optic nerve transection.
Increased expression of Bim, a pro-apoptotic member of the Bcl-2 family, has been shown to be critical for neuronal apoptosis. To study the involvement of Bim in injury-induced cell death in retina, Bim expression was studied in normal rat retina and in retina after optic nerve transection using quantitative RT-PCR and immunohistochemistry. As a complement to this, the apoptotic regulators Bax, Bcl-2, caspase-3 and phosphorylated c-jun were studied. The relative levels of Bim mRNA in retina were significantly higher 4 days after optic nerve transection and below normal levels at 14 days after transection. A parallel increase in the number of Bim-immunoreactive cells in the retinal ganglion cell layer could be seen. Bim-immunoreactivity localized to retrogradely True Blue-labeled retinal ganglion cells. The relative mRNA levels for both Bax and Bcl-2 were higher at 4 days after transection when compared to normal. Immunoreactivity for Bax, Bcl-2 as well as for caspase-3 and phosphorylated c-jun, indicative of cell death, localized to True Blue-identified retinal ganglion cells 4 days after injury. Bcl-2 immunoreactivity was also seen on other cells, most likely Müller glia cells. In addition, optic nerve transection caused an increase in Bim, Bax, and Bcl-2 mRNA levels in optic nerve and superior colliculus. Our results suggest that Bim is involved in injury-induced retinal ganglion cell death and indicate that the increase in Bim and Bax expression promote cell death of axotomized retinal ganglion cells whereas the elevation in Bcl-2 in retina may contribute to the control of the extent of apoptosis after the optic nerve transection.
Näpänkangas
Ulla
U
Department of Neuroscience, Units for Developmental Neuroscience, Uppsala University, S-75123 Uppsala, Sweden. ulla.napankangas@neuro.uu.se
Lindqvist
Niclas
N
Lindholm
Dan
D
Hallböök
Finn
F
D000818:Animals; D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; D001572:Benzofurans / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D005260:Female; D007150:Immunohistochemistry / Q000379:methods; D007211:Indoles / Q000378:metabolism; D008565:Membrane Proteins; D020221:Optic Nerve Injuries / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D012165:Retinal Ganglion Cells / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D013997:Time Factors; D015854:Up-Regulation / Q000235:genetics*; D051028:bcl-2-Associated X Protein
D051017:Apoptosis Regulatory Proteins; C494828:Bax protein, rat; D000072224:Bcl-2-Like Protein 11; C000606778:Bcl2l11 protein, rat; D001572:Benzofurans; D002352:Carrier Proteins; D007211:Indoles; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D051028:bcl-2-Associated X Protein; C007293:DAPI; C038675:true blue; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases