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

Abstract

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.

The Warburg Effect in Diabetic Kidney Disease

“…In addition, in murine mesangial cells, we found that SM (d18:1/16:0) suppressed AMPK activity and reduced PGC-1α protein expression. 33 The liposomal SM (d18:1/16:0) treatment significantly increased lactate secretion in murine mesangial cells, suggesting that accumulation of SM and an increase in ATP in the diabetic kidney may be owing to the result of an increase in glycolysis. This was proved further by the treatment of glycolytic inhibitor 2-deoxy-D-glucose, which significantly inhibited ATP production, suggesting the potential role of SM (d18:1/16:0) in enhancing the glycolytic pathway to enhance ATP production and thus contribute to a Warburg type effect in glomeruli of the diabetic kidney (Fig.…”

“…The hypothesis of an enhanced glycolytic pathway in diabetes was supported by recent studies from our laboratory using mass spectrometry imaging (MSI)-based spatial metabolomics in DKD animal models and human kidney tissue. 33 We applied matrix-assisted laser desorption/ionization (MALDI)-MSI to localize and quantify renal nucleotides. 33 MALDI-MSI at 70-µmol/L resolution identified ATP, adenosine diphosphate, and AMP widely distributed throughout the kidney and showed a significant increase in ATP and decrease in AMP, leading to significantly increased ATP/AMP in glomeruli of diabetic mice when compared with nondiabetic ones.…”

“…33 We applied matrix-assisted laser desorption/ionization (MALDI)-MSI to localize and quantify renal nucleotides. 33 MALDI-MSI at 70-µmol/L resolution identified ATP, adenosine diphosphate, and AMP widely distributed throughout the kidney and showed a significant increase in ATP and decrease in AMP, leading to significantly increased ATP/AMP in glomeruli of diabetic mice when compared with nondiabetic ones. Furthermore, biochemical analysis of freshly extracted nucleotides from total kidney cortex showed a similar increase in total ATP levels in db/db diabetic mice compared with the db/m controls.…”

“…Mouse models of DKD and in vitro studies also are warranted to confirm and validate the human data. Furthermore, with the development of high sensitive technologies such as global DNA methylations, 80 singular-cell RNA sequencing, 81 RNA bar-coding based on single-molecule fluorescence in situ hybridization, 82 MALDI-MSI, 33 laser capture micro-dissection -omics, 83 and cytometry by time of flight, 84 it becomes feasible to measure multiomics (ie, genomics, transcriptomics, proteomics, and metabolomics/lipidomics) data in a single-cell or cell type. In the near future, we could link pathologic changes with multi-omics in glomeruli, podocytes, and tubules of DKD, which will allow in-depth understanding of DKD and pave the path for personalized kidney precision medicine.…”

Label-free molecular imaging of the kidney

“…81 Some of these include the study of anticancer drug distributions in mouse kidneys, 82 glomerular adenosine triphosphateadenosine monophosphate ratios in diabetic mouse models, 83 N -linked glycans in murine kidneys, 84 murine tubular lipid distributions in immunoglobulin A nephropathy, 85 region-specific sphingolipid metabolism in murine models of obesity, 86 sulfatide turnover in animal models of lipid storage disease, 87 sulfated lipid markers in polycystic kidney disease rats, 88 renal angiotensin metabolism in mice, 89 peptide classification and pathogenesis of amyloidosis in humans, 90 racial disparities in Wilms tumor incidence and human peptide biology, 91 rat protein biomarkers of gentamicin nephrotoxicity, 92 and assessing proteomic patterns of glomerulosclerosis for disease classification and prosclerotic mechanism determination in rats. 93 While it is impractical to provide a detailed description of all IMS renal research in this review, several recent reports are described below that highlight discoveries in areas of clear cell renal cell carcinoma, diabetic nephropathy (DN), preclinical renal drug toxicology, and infectious disease.…”