Insulin-stimulated Akt kinase activity is reduced in skeletal muscle from NIDDM subjects.
The serine/threonine kinase Akt (PKB/Rac) has been implicated as playing a role in the insulin-signaling pathway to glucose transport. Little is known regarding the regulation of Akt kinase activity in insulin-sensitive tissues, such as skeletal muscle, or whether this regulation is altered in insulin-resistant states such as NIDDM. We examined the effect of insulin on Akt kinase activity in skeletal muscle from six NIDDM patients and six healthy subjects. Whole-body insulin sensitivity, assessed by the euglycemic-hyperinsulinemic clamp, was significantly lower in NIDDM subjects (P < 0.001), and this was accompanied by impaired in vitro insulin-stimulated glucose transport in skeletal muscle. In both groups, insulin induced a significant increase in Akt kinase activity, but the response to maximal insulin (60 nmol/l) was markedly reduced in skeletal muscle from NIDDM subjects (66% of control levels, P < 0.01). Impaired Akt kinase activity was not accompanied by decreased protein expression of Akt. Instead, a trend toward increased Akt expression was noted in skeletal muscle from NIDDM subjects (P < 0.1). These parallel defects in insulin-stimulated Akt kinase activity and glucose transport in diabetic skeletal muscle suggest that reduced Akt kinase activity may play a role in the development of insulin resistance in NIDDM.
Department of Clinical Physiology, Karolinska Hospital, Stockholm, Sweden. ankr@klinfys.ks.se
A
A
Krook
R A
RA
Roth
X J
XJ
Jiang
J R
JR
Zierath
H
H
Wallberg-Henriksson
D001692:Biological Transport / Q000187:drug effects; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology*; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000201:enzymology*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012016:Reference Values
D007328:Insulin; D011518:Proto-Oncogene Proteins; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D005947:Glucose