Abstract
Purpose: :
Several studies uncovered alterations of the genome and the proteome in glaucomatous tissues, thus providing new insights into processes involved into glaucomatous neurodegeneration. However, up to now nothing is known about the constitution and lipid composition of neuronal membranes in glaucoma patients. Facing the fact that cell membranes represent an important link to the extracellular space and their involved in important signaling pathways, we conducted a study comparing the lipid composition of optic nerve tissues from healthy subjects and glaucoma patients.
Methods: :
Lipidomic analysis of human optic nerve tissue samples (CTRL: N=5; glaucoma: N=5) was performed using a high performance MALDI-Imaging approach. Optic nerve cryo sections were embedded into HCCA matrix using ImagePrep robotic station. Local distribution of lipids within the tissue was analyzed using a solariX 12 T FTMS (Bruker Daltonics), reaching a spatial distribution of 40 µm. Lipids were detected within a mass range m/z 400-1500. Data analysis and quantification of lipid abundances was performed using DataAnalysis 4.0 and FlexImaging 3.0 (Bruker Daltonics). For detection of lipids with differential abundances in glaucomatous tissues principal component analysis was performed. Findings were validated using immunohistochemistry.
Results: :
Using MALDI-Imaging technology we enabled a high-resolution insight into the spatial distribution of different lipid species in human optic nerve tissues. Further the comparison of healthy and glaucomatous subjects revealed a strong alteration of the lipid composition of cells within the optic nerve of glaucoma patients. Several lipids were found to be strongly in increased in glaucomatous tissues. E.g. C18:1 sphingomyelin revealed a 2.5 fold increase (CTRL: ME=0.3E-07±0.2E-07; glaucoma: ME=0.8E-07±0.25E-07). Other, so far unidentified lipids (881.75 Da; 928.83 Da) could only be detected in tissue sections of healthy subjects and are completely absent from optic nerve sections from glaucoma patients.
Conclusions: :
The increase of sphingomyelin in glaucomatous tissues suggests an involvement of the sphingomyelin/ceramide pathway. This pathway is triggered by external stresses such as oxidative stress or messenger proteins like Il-1 and heat shock proteins. Downstream signaling involves proteins like Bad/BCL-2, Erk-1 and 14-3-3 - proteins which are well known to be involved in glaucomatous neurodegeneration. In summary this pathway could provide an additional link in glaucoma pathogenesis, bringing together and explaining findings from several previous studies.
Keywords: proteomics • lipids • imaging/image analysis: non-clinical