Increased skeletal muscle expression of PKC-theta but not PKC-alpha mRNA in type 2 diabetes: inverse relationship with in-vivo insulin sensitivity.
BACKGROUND
Increases in PKC-theta (the major isoenzymic form of PKC in skeletal muscle) protein and isozyme activity have been reported in skeletal muscle from patients with type 2 diabetes mellitus (T2DM) and dietary-induced rodent models of insulin resistance, but the underlying biochemical mechanism is unclear and muscle PKC-theta mRNA expression has not been previously reported in patients with T2DM or in relation to in-vivo measurements of insulin sensitivity.


METHODS
Diet-only treated patients with T2DM (n=7) and healthy nondiabetic controls (n=7) of similar BMI attended the clinical research unit on two occasions, 1 week apart, for a skeletal muscle biopsy 2 h after a 75-g oral glucose load and measurement of whole-body insulin sensitivity using the euglycaemic hyperinsulinaemic clamp.


RESULTS
Type 2 DM patients were insulin resistant (M-value 3.0 +/- 0.4 vs. 8.6 +/- 0.8 mg glucose kg(-1) min(-1)) with fasting hyperinsulinaemia (306 +/- 116 vs. 34 +/- 9 pmol L(-1), P<0.001) and hypertriglyceridaemia (3.6 +/- 0.7 vs. 1.3 +/- 0.3 mmol L(-1), P<0.01) relative to controls. Semi-quantitative RT-PCR showed that expression of PKC-theta mRNA (relative to GAPDH mRNA) was 6-fold higher in T2DM subjects (0.63 + 0.25% vs. 0.09 + 0.07%, P<0.001), whereas there was no difference in expression of PKC-alpha mRNA between the two groups. Expression of PKC-theta mRNA was inversely correlated with insulin sensitivity (M) and positively correlated with fasting serum insulin concentration (P<0.02).


CONCLUSIONS
This is the first clinical study of PKC-theta mRNA expression in human diabetic skeletal muscle. The results indicate that transcriptional up-regulation of PKC-theta may at least partly contribute to the increased muscle PKC-theta signalling in T2DM, and that PKC-theta mRNA may be inversely related to in-vivo insulin sensitivity.
Gray
S
S
School of Medical & Surgical Sciences, Centre for Integrated Systems Biology and Medicine, University of Nottingham, Derby, UK.
Idris
I
I
Davis
K R
KR
Donnelly
R
R
D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology*; D006801:Humans; D007333:Insulin Resistance; D007527:Isoenzymes / Q000096:biosynthesis* / Q000235:genetics; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000201:enzymology*; D011493:Protein Kinase C / Q000096:biosynthesis* / Q000235:genetics; D051571:Protein Kinase C-alpha; D000074121:Protein Kinase C-theta; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015854:Up-Regulation
D007527:Isoenzymes; D012333:RNA, Messenger; C496628:PRKCA protein, human; C076233:PRKCQ protein, human; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D000074121:Protein Kinase C-theta