Abstract
Purpose:
To evaluate the neuropathological and biochemical changes in the optic nerve and the total number of retinal ganglion cell (RGC) at 3 weeks post repetitive mild traumatic brain injury in a mouse model.
Methods:
Adult male C57BL/6 mice (10-12 weeks old) were subjected to either r-mTBI (n =5) or repetitive sham (r-sham; n = 5), according to an established protocol. Mice were sacrificed and optic nerves extracted and processed for paraffin embedding at 3 weeks post injury. Cellularity of the optic nerve and myelination was estimated after staining with H&E and Luxol Fast Blue and RGC numbers were counted in flatmounts. Proteomic and lipidomic analysis was carried out by LC/MS and UPLC.
Results:
Regions of focal demyelination and increased cellularity were observed in the optic nerves after r-mTBI compared to r-sham or naive mice paralleled by a 25% decrease the total number of Brna-3a-positicve RGCs. Proteomic analysis of optic nerve tissue demonstrated various changes consistent with a negative effect of r-mTBI on major cellular processes like depolymerization of microtubules, disassembly of filaments and quantity of neurons, manifested by the downregulation of several protein classes, like neurofilaments (NEFH, NEFM, NEFL), tubulin (TUBB2A, TUBA4A), microtubule-associated proteins (MAP1A, MAP1B), collagen (COL6A1, COL6A3) and the upregulation of other proteins, like heat shock proteins (HSP90B1, HSPB1), APOE, cathepsin D, etc. Lipidomic analysis showed up- or downregulation of several phospholipid species. Notably, several lysophosphatidylcholine (LPC) species, including 1-palmitoyl LPC (16:0), a phospholipid specie with known pro-inflammatory and demyelinating properties, were upregulated.
Conclusions:
Results from the biochemical analysis correlated with changes detected by histological and immunohistochemical methods and indicate the involvement of several important pathways, indicating the possibility for identifying therapeutic targets for improving the visual consequences of mTBI.