The SGLT2 inhibitor ertugliflozin causes a switch of cardiac substrate utilization leading to reduced cardiac mTOR-signaling, unfolded protein response and apoptosis
Authors: Moellmann J , Mann P , Krueger K , Klinkhammer B , Boor P , Marx N , Lehrke M 
Published: October 2021

Abstract

Introduction
SGLT2 inhibitors reduce hospitalization for heart failure in patients with and without diabetes. The underlying mechanisms remain incompletely understood but might relate to the induction of a fasting like response with low blood glucose and insulin levels and increased ketone bodies. The study aimed to investigate underlying signaling pathways.

Methods and results
Cardiac hypertrophy was induced by transverse aortic constriction (TAC) surgery in 20-week-old C57Bl/6J mice. Mice were treated with the SGLT2 inhibitor ertugliflozin (225 mg/kg chow diet) or vehicle for a period of 10 weeks.
Ertugliflozin significantly improved left ventricular systolic and diastolic function (dp/dtmax: TAC ctrl.: 8900±3362 mmHg/s vs. TAC ertu.: 12051±1604 mmHg/s (p&lt;0.001) and dp/dtmin: TAC ctrl.: −7653±2770 mmHg/s vs. TAC ertu.: −10199±2463 mmHg/s (p&lt;0.01); by millar catheter with dobutamine stress) and reduced myocardial fibrosis (p=0.17) and hypertrophy (p=0.09). This was paralleled by the expected fasting like response with lower glucose and insulin levels (HOMA-IR p&lt;0.05) and increased ketone body concentrations (p&lt;0.05). As a consequence cardiac insulin signaling (AKT-phosphorylation at Thr(308), 0.39-fold (p&lt;0.01)) was reduced by ertugliflozin with less insulin-dependent glucose transporter GLUT4 expression (0.64-fold (p&lt;0.05)) while fatty acid transporter CD36 (2.12-fold (p&lt;0.001)) and the ketone body catabolizing key enzyme beta-hydroxybutyrate dehydrogenase BDH-1 were increased (1.59-fold (p&lt;0.01)) in addition to AMPK-signaling (AMPK-phosphorylation at Thr(172), 1.62-fold (p&lt;0.01)). This led to downstream inhibition of the mTOR pathway with reduced phosphorylation of p70S6K, 4E-BP1 and ULK1 (p70S6K-phosphorylation at Thr(389) (0.57-fold (p&lt;0.05)), 4E-BP1-phosphorylation at Ser(65) (0.74-fold (p&lt;0.05)) and ULK1-phosphorylation at Ser(757) (0.56-fold (p&lt;0.01))). MTOR signaling critically mediates cardiac hypertrophy, endoplasmic reticulum stress, unfolded protein response (UPR) and adverse cardiac remodeling. Consistently, we found ertugliflozin to reduce ATF6 (0.69-fold (p&lt;0.05)) and elf2α-phosphorylation at Ser(51) (0.66-fold (p=0.0611)) as well as downstream signaling (ATF4 0.58-fold (p&lt;0.01); CHOP 0.36-fold (p&lt;0.001)). This let to reduced caspase 3 (0.74-fold (p&lt;0.05)), collagen I (0.60-fold (p&lt;0.01)) and IL-1β (0.46-fold (p&lt;0.01)) expression indicating less apoptosis, fibrosis and left ventricular remodeling with consequential reduction of BNP expression (0.60-fold (p&lt;0.001)) in response to SGLT2 inhibition.

Conclusion
The SGLT2 inhibitor ertugliflozin improves left ventricular function in a murine model of cardiac hypertrophy. Mechanistically, this was associated with a metabolic switch of cardiac substrate utilization with reduced cardiac insulin- and increased cardiac AMPK-signaling leading to reduced cardiac mTOR-signaling, unfolded protein response and apoptosis.

Funding Acknowledgement
Type of funding sources: Private company. Main funding source(s): MSD