Abstract 18818: Sodium Glucose Co-Transporter 1 (SGLT1) is a Novel Contributor to Cardiac Ischemia/Reperfusion (I/R) Injury Through PKC- and ERK-Dependent Mechanisms
Introduction: We have shown that AMP-activated protein kinase (AMPK) upregulates SGLT1, which contributes to cardiac ischemia/reperfusion (I/R) injury by activating NADPH oxidase 2 (Nox2). AMPK is known to interact with MAPK/ERK pathway. Studies in non-cardiac cells have suggested that SGLT1 stabilizes EGFR, which in turns activates PKC. PKC leads to phosphorylation of p47 phox, a regulatory subunit of Nox2.
Hypothesis: ERK mediates upregulation of SGLT1 by AMPK, and EGFR mediates activation of Nox2 by SGLT1 in cardiac I/R injury.
Methods and Results: Ex vivo studies: We constructed two transgenic mouse models: (1) cardiomyocyte-specific knockdown of SGLT1 (TGSGLT1-DOWN), using transgenic RNAi technology; and (2) cardiomyocyte-specific doxycycline-suppressible conditional overexpression of SGLT1 (TGSGLT1-ON). Isolated perfused hearts from TGSGLT1-DOWN mice, TGSGLT1-ON mice, and wildtype (WT) littermates were subjected to 20 min global no-flow ischemia followed by 20 min reperfusion. Compared to WT hearts, TGSGLT1-DOWN and TGSGLT1-ON hearts respectively showed less and greater impairment of cardiac contractility following I/R (peak left ventricular systolic pressure [LVSP]: WT, 77±9; TGSGLT1-DOWN, 130 ±17; TGSGLT1-ON, 63±10 mmHg; P<0.05). Phosphorylation of PKC and p47 phox was decreased in TGSGLT1-DOWN hearts following I/R. Compared to WT hearts, TGSGLT1-ON hearts exhibited greater PKC activation (0.380±0.047 vs 0.650±0.028 arbitrary units, P<0.05). Compared to WT hearts, PKC α and β expression was decreased in TGSGLT1-DOWN hearts and increased in TGSGLT1-ON hearts, but PKC ε expression was increased in TGSGLT1-DOWN hearts and decreased in TGSGLT1-ON hearts. Co-immunoprecipitation showed interactions between SGLT1 and EGFR, and between EGFR and PKC, but not between SGLT1 and PKC. In vitro studies: Cultured HL-1 cells were treated with vehicle, metformin (AMPK activator), U0126 (ERK inhibitor) or metformin+U0126 for 18h. Metformin treatment increased AMPK phosphorylation and SGLT1 expression, an effect that was abrogated by U0126.
Conclusions: AMPK upregulates SGLT1 through the MAPK/ERK pathway. PKC α and β may be downstream effectors of SGLT1 in cardiac I/R injury. EGFR may mediate activation of PKC α and β by SGLT1.
Author Disclosures: Z. Li: None. L. Gifford: None. F. Ahmad: None.
- © 2016 by American Heart Association, Inc.