Mass Spectrometry Imaging Reveals Elevated Glomerular ATP/AMP in Diabetes/obesity and Identifies Sphingomyelin as a Possible Mediator

• MALDI-MSI revealed an increase in glomerular ATP/AMP ratio in the diabetic kidney.
• SM(d18:1/16:0) is increased in the glomeruli of diabetic and high-fat diet-fed mice.
• SM(d18:1/16:0) stimulated ATP production via enhanced aerobic glycolysis and reduced AMPK activity in mesangial cells.AMPK is known to be suppressed in states of high ATP/AMP ratio but the measurement of nucleotides in vivo has been difficult. Miyamoto et al. utilize matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to investigate the distribution of nucleotides and find an increase in glomerular ATP/AMP ratio in the diabetic kidney. Untargeted MALDI-MSI revealed that sphingomyelin(d18:1/16:0) is accumulated in the glomeruli of diabetic and high-fat diet-fed mice compared with controls. Sphingomyelin(d18:1/16:0) promotes ATP production in mesangial cells via activation of the glycolytic pathway. The inhibition of sphingomyelin(d18:1/16:0) synthesis may lead to novel therapeutic targets for the treatment of caloric-induced CKD.

AMP-activated protein kinase (AMPK) is suppressed in diabetes and may be due to a high ATP/AMP ratio, however the quantitation of nucleotides in vivo has been extremely difficult. Via matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to localize renal nucleotides we found that the diabetic kidney had a significant increase in glomerular ATP/AMP ratio. Untargeted MALDI-MSI analysis revealed that a specific sphingomyelin species (SM(d18:1/16:0)) accumulated in the glomeruli of diabetic and high-fat diet-fed mice compared with wild-type controls. In vitro studies in mesangial cells revealed that exogenous addition of SM(d18:1/16:0) significantly elevated ATP via increased glucose consumption and lactate production with a consequent reduction of AMPK and PGC1α. Furthermore, inhibition of sphingomyelin synthases reversed these effects. Our findings suggest that AMPK is reduced in the diabetic kidney due to an increase in the ATP/AMP ratio and that SM(d18:1/16:0) could be responsible for the enhanced ATP production via activation of the glycolytic pathway.

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