Abstract
Purpose: :
Glutamate is the major excitatory neurotransmitter in the retina, but its role is not limited to synaptic transmission. Glutamate is also implicated in the maintenance and function of the blood–brain–barrier. Glutamate signaling in endothelial cells modulates vascular permeability of the blood–brain–barrier via mGluR1α. Recent data in the DBA/2 mouse model of closed–angle glaucoma reveals an increase in vascular permeability, where dextran–leakage increases with increasing age. Here we examined the expression and localization of mGluR1α to determine its potential as a modulator of vascular permeability in this retina.
Methods: :
All experiments were conducted with age–matched DBA/2 mice for which intraocular pressure (IOP) was measured using the Tono–pen XL beginning at three months of age. We used PCR to screen mRNA from whole retina for expression of mGluR1α as a function of age and IOP. To examine changes in mGluR1α protein levels, we used Western blots to probe protein isolated from the whole retina as a function of age and IOP. Localization of the mGluR1α protein was performed by immunocytochemistry with aldehyde–fixed whole–mount preparations and retinal sections for mice between the ages of three and six months with varying IOPs.
Results: :
The expression of the mGluR1α gene remained stable with age and with varying IOP. However, Western blotting suggested that protein levels of mGluR1α increased with increasing age and IOP. Immunolocalization of mGluR1α revealed qualitative changes in its spatial distribution that correlated with vessel size, age and IOP. As age increased, the number of vessels expressing mGluR1α also increased. Increased IOP differentially altered the number and size of vessels expressing mGluR1α with respect to age.
Conclusions: :
Changes in mGluR1α expression correlate with age and IOP, two significant risk factors for glaucoma. These data suggest that changes in mGluR1α expression are regulated at the protein level rather than the mRNA level, where we observed no change in expression. Together, our studies indicate that mGluR1α may play a role in vascular changes and potential increases in vascular permeability associated with disease progression in the DBA/2 mouse model.
Keywords: vascular cells • neurotransmitters/neurotransmitter systems • receptors