Impaired regulation of the TNF-alpha converting enzyme/tissue inhibitor of metalloproteinase 3 proteolytic system in skeletal muscle of obese type 2 diabetic patients: a new mechanism of insulin resistance in humans.
OBJECTIVE
TNF-alpha levels are increased in obesity and type 2 diabetes. The regulation of TNF-alpha converting enzyme (TACE) and its inhibitor, tissue inhibitor of metalloproteinase 3 (TIMP3), in human type 2 diabetes is unknown.


METHODS
We examined TACE/TIMP3 regulation: (1) in lean and obese normal glucose tolerant (NGT) individuals and in type 2 diabetes patients; (2) following 6 h of lipid/saline infusion in NGT individuals; and (3) in cultured human myotubes from lean NGT individuals incubated with palmitate. Insulin sensitivity was assessed by a euglycaemic clamp and TACE/TIMP3 was evaluated by confocal microscopy, RT-PCR, western blotting and an in vitro activity assay. Circulating TNF-alpha, TNF-alpha-receptor 1 (TNFR1), TNF-alpha-receptor 2 (TNFR2), IL-6 receptor (IL-6R), vascular cell adhesion molecule (VCAM) and intercellular adhesion molecule (ICAM) levels were evaluated.


RESULTS
TIMP3 levels were reduced and TACE enzymatic activity was increased in type 2 diabetes skeletal muscle. TACE expression, and TACE, TNF-alpha, TNFR1 and IL-6R levels were increased in type 2 diabetes, and positively correlated with insulin resistance. A 6 h lipid infusion into NGT individuals decreased insulin-stimulated glucose metabolism by 25% with increased TACE, decreased expression of the gene encoding TIMP3 and increased IL-6R release. Palmitate induced a dramatic reduction of TIMP3 and increased the TACE/TIMP3 ratio in cultured myotubes.


CONCLUSIONS
TACE activity was increased in skeletal muscle of obese type 2 diabetes patients and in lipid-induced insulin resistance. We propose that dysregulation of membrane proteolysis by TACE/TIMP3 of TNF-alpha and IL-6R is an important factor for the development of skeletal muscle insulin resistance in obese type 2 diabetes patients by a novel autocrine/paracrine mechanism.
Monroy
A
A
Department of Medicine, University of Texas Health Science Center at San Antonio, 78229-3900, USA.
Kamath
S
S
Chavez
A O
AO
Centonze
V E
VE
Veerasamy
M
M
Barrentine
A
A
Wewer
J J
JJ
Coletta
D K
DK
Jenkinson
C
C
Jhingan
R M
RM
Smokler
D
D
Reyna
S
S
Musi
N
N
Khokka
R
R
Federici
M
M
Tripathy
D
D
DeFronzo
R A
RA
Folli
F
F
D051722:ADAM Proteins / Q000235:genetics / Q000378:metabolism*; D000072198:ADAM17 Protein; D000328:Adult; D015153:Blotting, Western; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D007333:Insulin Resistance / Q000235:genetics / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D019947:Receptors, Interleukin-6 / Q000235:genetics / Q000378:metabolism; D019717:Tissue Inhibitor of Metalloproteinase-3 / Q000235:genetics / Q000378:metabolism*
D019947:Receptors, Interleukin-6; D019717:Tissue Inhibitor of Metalloproteinase-3; D051722:ADAM Proteins; D000072198:ADAM17 Protein; C000606462:ADAM17 protein, human