Mapping glucose metabolism pathways in the bovine lens using imaging mass spectrometry

Abstract

Purpose : To characterise the functionality of glucose metabolism pathways in the different regions of the lens by using imaging mass spectrometry (IMS) to spatially and temporally map the distribution of glucose and its metabolites in the bovine lens.

Methods : Bovine lenses were organ cultured in Artificial Aqueous Humor (AAH) then cryosectioned and coated with NEDC matrix. The samples were subsequently analysed by a MALDI-FTICR mass spectrometer (Bruker Solarix-XR 7T) in negative ion mode with MALDI IMS spatial resolution of 150mm. Data were imported into SCiLS Lab 2017a for analysis and visualisation of glucose and its metabolites. Expression of enzymes in glucose metabolism pathways in different regions of the lens were determined by Western blotting.

Results :
While glucose was detected throughout the bovine lens and was highest in the lens core, glucose metabolites and enzymes associated with the different glucose metabolism pathways where differentially distributed in different lens regions. The glucose metabolite fructose 1,6 bisphosphate, which is involved in glycolysis, was restricted to the outer cortex, while sorbitol and fructose-1-phosphate were highest in the core. Metabolites associated with the pentose phosphate pathway (6-phosphogluconolactone, 6-phosphogluconic acid, sedoheptulose 7 phosphate) were also concentrated in the lens inner cortex and core. UDP-glucose a precursor for glycogen was also accumulated in the outer cortex. Consistent with these regional differences in glucose metabolites, differential expression of the key enzymes involved in glucose metabolism were detected by Western blotting.

Conclusions :
Our imaging of the distribution of glucose and its metabolites and the detection of key enzymes involved in the different glucose metabolism pathways have shown that distinct metabolic compartments exist in the lens. Future work will use this IMS approach to monitor glucose uptake and metabolism pathways using stable isotopically-labelled glucose.

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