PROJECT SUMMARY.
Type 2 diabetes currently affects >25.8 million Americans, creating an economic burden totaling over
$245 billion dollars per year. It is a progressive metabolic disease characterized by hyperglycemia, hyper-
insulinemia, and insulin resistance in skeletal muscle, the primary site of insulin-mediated glucose disposal.
Importantly, while insulin-induced muscle glucose uptake is impaired in type 2 diabetes, the ability of insulin-
independent stimuli such as exercise to increase muscle glucose uptake and lower blood glucose levels remains
functional. Thus, increasing muscle glucose uptake via an exercise-dependent mechanism(s) is an effective
strategy to treat hyperglycemia in type 2 diabetes. Unfortunately, those mechanisms are not well understood.
Glucose transporter 4 (GLUT4) is the glucose transporter responsible for increasing skeletal muscle glucose
uptake in response to both insulin and acute muscle contraction. Surprisingly, results from our lab have now
found that chronic muscle loading, a model of resistance exercise training, increases muscle glucose uptake
independent of both insulin and GLUT4. Thus, chronic muscle loading increases glucose uptake via a
unique/alternative mechanism, and one which could represent a novel intracellular target for enhancing muscle
glucose uptake in type 2 diabetes. Unfortunately, that mechanism is currently not known. Preliminary data from
our lab indicate that glucose transporter 1 (GLUT1) and the Ca2+-activated, serine/threonine kinase, Ca2+/
calmodulin-dependent protein kinase kinase ¿ (CaMKK¿) could be important proteins connecting chronic muscle
loading to increased skeletal muscle glucose uptake. Thus, the specific objectives of this proposal are to
determine if expression of GLUT1 in skeletal muscle is necessary for the regulation of basal or overload-induced
muscle glucose uptake and/or growth (AIM 1), and to determine if CaMKK¿ regulates muscle glucose uptake in
a GLUT4-dependent or independent manner (AIM 2). To achieve these objectives, a combination of innovative
and state-of-the-art approaches and methodologies will be utilized including the newly created chemical GLUT1
inhibitor, BAY-876; generation of an inducible muscle-specific GLUT1 knockout mouse; in vivo muscle gene
transfer/electroporation to allow for the rapid, transient expression of genes in mouse muscle; cultured mouse
muscle cells that stably express exofacially labeled GLUT4; and a cell membrane impermeant bis-glucose
photolabel, BIO-LC-ATB-BGPA, to examine cell surface GLUT4 localization in adult mouse skeletal muscle. It is
anticipated that the proposed research will identify the glucose transporters responsible for chronic muscle
loading/overload-induced and constitutively active CaMKKa-induced skeletal muscle glucose uptake. The
significance of this research is that it represents a critical first step towards the development of new type 2
diabetes therapies designed to enhance insulin-independent skeletal muscle glucose uptake.
