Project Summary/Abstract
Diabetes, a condition characterized by abnormally low insulin-stimulated glucose transport into skeletal
muscle, is a major threat to health. Activation of AMPK, such as by exercise, muscle contractions, or serum
starvation, provides a means to increase sensitivity of glucose transport to stimulation by insulin. While
enhanced phosphorylation of AS160 occurs concomitant with development of insulin sensitivity, the complete
molecular mechanisms underlying the increase in insulin-stimulated glucose transport remain unknown. We
aim to fill this important knowledge gap by testing the hypothesis that mTOR and ULK1 mediate AMPK-
induced insulin sensitivity. Our preliminary data show that inhibition of mTOR complex 1 (mTORC1) causes an
increase in insulin-stimulated glucose transport. We have also found that inhibition of ULK1 prevents insulin-
stimulated glucose uptake by serum-starved myotubes, while a pharmacological activator of ULK1 increases
AS160 phosphorylation. Finally, our data show that activation of AMPK causes an increase in mTORC2 activity
in myotubes, as demonstrated by increased phosphorylation of the mTORC2 substrate Akt. To test our
hypotheses, we propose three specific aims. For Aim 1, to determine the role of mTORC1 in insulin sensitivity,
we will test the hypothesis that inhibition of mTORC1 causes increased insulin sensitivity and mediates AMPK-
induced insulin sensitivity. Approaches for this aim will include determining whether inhibition of mTORC1 by
pharmacological and genetic means will increase insulin-stimulated glucose transport and whether activation of
mTORC1 by physiological and genetic means will prevent development of insulin sensitivity after activation of
AMPK, serum starvation, or exercise/muscle contractions. For Aim 2, to determine the role of ULK1 in insulin
sensitivity, we will test the hypothesis that activation of ULK1 is sufficient to increase insulin sensitivity and
necessary to induction of insulin sensitivity by AMPK. Approaches to this aim will include determining whether
pharmacological activation of ULK1 increases insulin-stimulated glucose transport and whether
pharmacological inhibition of ULK1 or expression of inactive or AMPK-insensitive mutants of ULK1 prevent
development of insulin sensitivity. For Aim 3, to determine the role of mTORC2 in AS160 phosphorylation and
insulin sensitivity, we will test the hypothesis that mTORC2 is an important mediator of AS160 phosphorylation
during development of insulin sensitivity. Approaches will include determining whether pharmacological or
genetic disruption of the mTORC2 complex will prevent the normal increase in AS160 phosphorylation after
serum starvation, activation of AMPK, or exercise/muscle contractions and whether prior activation of the
mTORC2 substrate Akt causes a later increase in insulin-stimulated glucose transport. Completion of the
specific aims will elucidate novel roles of mTOR and ULK1 in control of insulin sensitivity in skeletal muscle
and suggest future strategies to overcome insulin resistance.