The signaling mechanisms mediating myocardial
glucose transport are not fully understood.
Sucrose nonfermenting AMP-activated
protein kinase (AMPK)-related
kinase (SNARK) is an AMPK-related
protein kinase that is expressed in the heart and has been implicated in contraction-stimulated
glucose transport in mouse skeletal muscle. We first determined if SNARK is phosphorylated on Thr208 , a site critical for SNARK activity. Mice were treated with exercise,
ischemia, submaximal
insulin, or maximal
insulin. Treadmill exercise slightly, but significantly increased SNARK Thr208 phosphorylation.
Ischemia also increased SNARK Thr208 phosphorylation, but there was no effect of submaximal or maximal
insulin. HL1 cardiomyocytes were used to overexpress wild-type (WT) SNARK and to knockdown endogenous SNARK. Overexpression of WT SNARK had no effect on
ischemia-stimulated
glucose transport; however, SNARK knockdown significantly decreased
ischemia-stimulated
glucose transport. SNARK overexpression or knockdown did not alter
insulin-stimulated
glucose transport or
glycogen concentrations. To study SNARK function in vivo, SNARK heterozygous knockout mice (SNARK+/- ) and WT littermates performed treadmill exercise. Exercise-stimulated
glucose transport was decreased by ~50% in hearts from SNARK+/- mice. In summary, exercise and
ischemia increase SNARK Thr208 phosphorylation in the heart and SNARK regulates exercise-stimulated and
ischemia-stimulated
glucose transport. SNARK is a novel mediator of
insulin-independent
glucose transport in the heart.