Ulla Näpänkangas

The growth factor response in ischemic rat retina and superior colliculus after brimonidine pre-treatment

The alpha-2-adrenergic receptor agonist brimonidine has been shown to increase survival of retinal ganglion cells following ischemic injury to the rat retina. Increased expression of growth factors has been suggested to be involved in this action. We investigated expressional changes of growth factors and their receptors following transient retinal ischemia induced by selective ligature of ophthalmic vessels in rats pre-treated with vehicle or 0.5% brimonidine. In addition, analysis of expression in retinal samples following unilateral administration of brimonidine to normal tissue was performed. Tissue samples of retina and superior colliculus were collected at time points between 6h and 14 days of retinal reperfusion. Analysis of mRNA levels of the ligands BDNF, NT3, CNTF, FGF1, FGF2, FGF9 and HGF; as well as the receptors TrkB, TrkC, p75(NTR), CNTFRalpha, FGFR1, FGFR3, FGFR4 and HGFR were performed using qRT-PCR. The cell specific markers Thy1 and GFAP were analysed. We report transiently increased retinal levels of BDNF, NT3, p75(NTR), FGFR1 and HGFR and decreased levels of FGF9, HGF, TrkB, TrkC, FGFR4 and Thy1 following ischemia. The decreases were counteracted by brimonidine. Brimonidine treatment gave an increase in BDNF, NT3 and CNTF levels compared to the vehicle treated group. In superior colliculus increased levels of growth factor mRNA were found. In conclusion, transient ischemia has a profound effect on gene expression in rat retina. Alterations can also be seen in the superior colliculus but are smaller. Brimonidine pre-treatment attenuates an acute injury-induced response by decreasing the expression of several genes, among them p75(NTR). Brimonidine also causes a prolonged increase of several growth factors as well as receptors in retina and superior colliculus compared to the ischemic situation. The increased expression of several growth factors represents a coordinated growth factor system response that differs from the ischemia-induced changes and is likely part of the neuroprotective activity that is elicited by BMD pre-treatment.

Multiple receptor tyrosine kinases are expressed in adult rat retinal ganglion cells as revealed by single-cell degenerate primer polymerase chain reaction

Abstract Background. To achieve a better understanding of the repertoire of receptor tyrosine kinases (RTKs) in adult retinal ganglion cells (RGCs) we performed polymerase chain reaction (PCR), using degenerate primers directed towards conserved sequences in the tyrosine kinase domain, on cDNA from isolated single RGCs univocally identified by retrograde tracing from the superior colliculi. Results. All the PCR-amplified fragments of the expected sizes were sequenced, and 25% of them contained a tyrosine kinase domain. These were: Axl, Csf-1R, Eph A4, Pdgfrβ, Ptk7, Ret, Ros, Sky, TrkB, TrkC, Vegfr-2, and Vegfr-3. Non-RTK sequences were Jak1 and 2. Retinal expression of Axl, Csf-1R, Pdgfrβ, Ret, Sky, TrkB, TrkC, Vegfr-2, and Vegfr-3, as well as Jak1 and 2, was confirmed by PCR on total retina cDNA. Immunodetection of Csf-1R, Pdgfrα/β, Ret, Sky, TrkB, and Vegfr-2 on retrogradely traced retinas demonstrated that they were expressed by RGCs. Co-localization of Vegfr-2 and Csf-1R, of Vegfr-2 and TrkB, and of Csf-1R and Ret in retrogradely labelled RGCs was shown. The effect of optic nerve transection on the mRNA level of Pdgfrβ, Csf-1R, Vegfr-2, Sky, and Axl, and of the Axl ligands Gas6 and ProteinS, was analysed. These analyses show transection-induced changes in Axl and ProteinS mRNA levels. Conclusions. The repertoire of RTKs expressed by RGCs is more extensive than previously anticipated. Several of the receptors found in this study, including Pdgfrβ, Csf-1R, Vegfr-2, Sky, and Axl, and their ligands, have not previously been primarily associated with retinal ganglion cells.