Cardiometabolic rewiring in the context of doxorubicin-induced cardiotoxicity: fuel preference changes from fatty acids to glucose oxidation
Authors: Russo M , Guerra G , Priolo R , Riganti C , Reano S , Filigheddu N , Hirsch E , Ghigo A 
Published: November 2023

Abstract

Background
Doxorubicin (DOX) is a chemotherapeutic drug administered to treat a wide spectrum of tumours. However, its clinical use is hampered by the onset of cardiotoxic effects, with a reduction of LVEF that occurs within the first year from the treatment initiation. Recently it has been demonstrated that DOX accumulates into mitochondria, with metabolic perturbation and energetic imbalance. We previously described that phosphoinositide 3-kinase γ (PI3Kγ) contributes to DOX-induced cardiotoxicity, with the inhibition of autophagy and accumulation of damaged mitochondria into cardiac cells.

Objective
Here we intend to better understand the maladaptive metabolic rewiring occurring in DOX-treated hearts and the contribution of PI3Kg signalling to this process.

Methods
10 weeks-old wild-type (WT) and knock-in mice expressing a kinase-inactive PI3Kγ (kinase-dead; KD) were treated with DOX (4 mg/Kg) at day 0, 7 and 14 (cumulative dose 12 mg/Kg). To explore the contribution of PI3Kγ on the early cardiac metabolic rewiring, metabolomic analysis were performed on animals sacrificed at day 3. Mitochondria respiration capacity and glycolytic enzymes activity were evaluated at day 3 and 42. To investigate the role of autophagy, 8 weeks-old mice were infected with an adeno-associated virus 9 (AAV9) carrying a vector expressing a short-hairpin RNA against ATG7 (ATG7sh). To test the role of PI3Kγ in glycolysis regulation, glucose uptake and plasma membrane exposure of GLUT-4 were measured in neonatal mouse cardiomyocytes (NMCs) with DOX acute treatment (1µM for 3h). To evaluate oxygen consumption with the administration of different substrates OROBOROS analysis were performed on myocardial slices from mice sacrificed at day 3.

Results
Metabolomic analysis of DOX-treated hearts revealed an accumulation of TCA cycle metabolites, with reduced levels of pyruvate, unchanged abundance of lactate but increased quantity of Acetyl-CoA, indicative of increased glucose oxidation and accelerated TCA cycle flux. Moreover, the activity of glycolytic enzymes was upregulated and fatty acid oxidation downregulated after DOX. In agreement, oxygen consumption was significantly increased in DOX-treated WT after pyruvate supplementation, with the formation of cytotoxic ROS rather than energy production. These metabolic changes were fully prevented in KD hearts. Interestingly, they failed to increase glucose oxidation in response to DOX even with autophagy inhibition, indicating that PI3Kγ likely controls the fuel preference after DOX through an autophagy-independent mechanism. In vitro experiments showed that genetic and pharmacological inhibition of PI3Kγ significantly prevented DOX-induced mobilization of GLUT-4-carrying vesicles to the plasma membrane and reduced glucose uptake.

Conclusion
These results demonstrate that PI3Kγ promotes a maladaptive metabolic rewiring in the heart in response to DOX, with an increased glucose utilization via a GLUT4-dependent mechanism.