Understanding the role of glial cells (astrocytes and oligodendrocytes) in maintaining the homeostasis of the optic nerve

Abstract

Purpose : There are many different types of optic nerve (ON) disorders and ON degeneration is the common feature amongst them. However, the role of glial cells in the pathophysiology of ON degeneration and the molecular mechanisms that regulate the maintenance of ON are not yet completely understood. We have identified a rat in which two separate mutations act synergistically to produce severe optic nerve degeneration. One mutation is in the Cryba1 gene encoding bA3/A1-crystallin (expressed in astrocytes) and the other is in Bckdk, the gene encoding branched-chain alpha-keto dehydrogenase kinase (expressed in oligodendrocytes and other cells). This study was undertaken to understand the role of glial cells in ON development and disease.

Methods : The ONs were dissected from wild type, Nuc1 (mutation in Cryba1), Frogleg (mutation in Bckdk) and Nuc1/Frogleg (mutations in both Cryba1 and Bckdk) rats at postnatal days 21 (P21), P60 and P150.They were processed conventionally for transmission electron microscopy (TEM) and immunofluorescent staining. The protein lysates of ON, brain stem and cortex from four different genotypes were analyzed by western analysis using antibodies against CNPase (2',3'-Cyclic-nucleotide 3'-phosphodiesterase) and MBP (myelin basic protein).

Results : At P60, TEM showed severe ON degeneration (axons and glial cells) in the double mutant rats (Nuc1/Frogleg) with profound demyelination compared to Nuc1, Frogleg or wild type (Fig. 1). However, at P21 there was no significant difference between Nuc1/Frogleg ON and the other genotypes. In addition, immunoblotting data showed that expression of mature oligodendrocyte marker proteins (CNPase and MBP) drastically declined in Nuc1/Frogleg ON at P150 relative to other genotypes, whereas no significant difference was seen in the cortex or brain stem. Moreover, there was no significant difference in expression of CNPase and MBP among the different genotypes at P21.

Conclusions : We have identified a spontaneous double mutant rat that has a severely affected glial population (astrocytes and oligodendrocytes) in the optic nerve. The demyelination is highly specific for the optic nerve, with no significant effect seen in the cortex or brain stem. This unique model will help to investigate the role of glial cells in the optic nerve during development and in neurodegenerative diseases.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.