Activation of microglia/macrophages determines the fate of retinal ganglion cell survival in rat chronic ocular hypertension model

Abstract

Although it has been demonstrated that microglia/macrophages produce neuroprotective effects in acute injury, whether they do the same in chronic neurodegeneration such as glaucoma is largely unknown. Using a laser-induced chronic ocular hypertension (COH) model, we systematically studied the influences of microglia in RGC loss. Adult female SD rats were anesthetized with intra-peritoneal injection of a ketamine/xylazine mixture. Proparacaine hydrochloride was applied to the eyes as topical anesthetics. The limbal vein and the three radial episcleral aqueous humor drainage veins of the right eye were photocoagulated twice with a 7-day interval using an Argon laser. While a small number of microglial cells (10 3 ) did not produce significant influence, injection of large number of microglial cells (10 5 ) into the vitreous significantly increased RGC loss. Appropriate quantity (10 4 ) microglial cells per intraocular injection markedly reduced RGC loss in the COH model. Monocyte chemoattractant protein 1 at low concentration (10 and 100 ng), but not at high concentration (1,000 ng), provided significant neuroprotective effect on RGCs, which may attribute to the chemoattractive property on microglia/macrophages to the retina. Immunocytochemical staining on flat mounted retinas displayed high immunoreactivity for ionized calcium binding adapter molecular 1 (Iba1), indicating high number of microglia/macrophages. Potent stimulation of micro glia/macrophages by lipopolysaccharide (LPS) significantly increased the death of RGCs in the COH model. Iba1-immunoreactive positive microglia/macrophages in the LPS group were activated with enlarged cell body and thickened short process. These results advance our understanding of the roles of microglia in chronic neurodegeneration. Our results can demonstrate that microglia/macrophages can be either protective or harmful depending on the stimulation in chronic neurological disorder like glaucoma. Acknowledgement: The study is supported by The American Health Assistant Foundation to R.C.C. Chang and K.-F. So.