Introduction

Postprandial hyperglycaemic spikes are a major risk factor for cardiovascular risk in diabetes. We hypothesized that hyperglycaemic spikes increase circulating monocyte levels and atherosclerosis through receptor for advanced glycation endproducts (RAGE) signaling on monocyte precursors.

Methods

We injected wildtype female C57Bl/6 (WT) mice 4 subsequent times with glucose to induce hyperglycaemic spikes (~15-20mmol/l) and sacrificed them after 1 and 7 days of normoglycaemia. We quantified common myeloid (CMP) and granulocyte-monocyte precursors (GMP) and circulating monocyte subsets (Ly6C^{hi and lo}) with flow cytometry. To examine the role of haematopoietic RAGE, we transplanted Rage^-/- bone marrow into irradiated WT mice. To determine if this translated into accelerated atherosclerosis, we induced weekly hyperglycaemic spikes for 10 weeks in Apoe^-/- mice or Rage^-/-Apoe^-/- mice.

Results

We found in the bone marrow that the CMP and GMP were increased 2.2 and 1.3 fold after 1 day and normalized 7 days after glucose spiking. This translated to a significant increase in monocytes after 7 days (especially Ly6C^hi subset). Interestingly, 1 day after glucose spiking, the expression of the RAGE ligand S100A8/A9 in white blood cells and expression of RAGE on CMPs were increased. Subsequently, we transplanted mice with Rage^-/- bone marrow and found that they were protected against monocytosis induced by hyperglycaemic spikes. Using a novel small molecule inhibitor of S100A8/A9 conferred protection against hyperglycemic spikes. Hyperglycaemic spikes increased atherosclerotic burden in the aortic arch by 2-fold, this was abolished by the deletion of RAGE.

Conclusion

These results reveal the potential harm of hyperglycaemic spikes by acting on haematopoietic progenitors, stimulating monocyte production. This is dependent on RAGE signaling, with S100A8/A9 as a likely ligand. Preventing hyperglycaemic spikes or dampening RAGE signaling may reduce cardiovascular risk in people with diabetes.