Changes in FAT/CD36, UCP2, UCP3 and GLUT4 gene expression during lipid infusion in rat skeletal and heart muscle.
OBJECTIVE
It has been reported that an increased availability of free fatty acids (NEFA) not only interferes with glucose utilization in insulin-dependent tissues, but may also result in an uncoupling effect of heart metabolism. We aimed therefore to investigate the effect of an increased availability of NEFA on gene expression of proteins involved in transmembrane fatty acid (FAT/CD36) and glucose (GLUT4) transport and of the uncoupling proteins UCP2 and 3 at the heart and skeletal muscle level.


METHODS
Euglycemic hyperinsulinemic clamp was performed after 24 h Intralipid(R) plus heparin or saline infusion in lean Zucker rats. Skeletal and heart muscle glucose utilization was calculated by 2-deoxy-[1-(3)H]-D-glucose technique. Quantification of FAT/CD36, GLUT4, UCP2 and UCP3 mRNAs was obtained by Northern blot analysis or RT-PCR.


RESULTS
In Intralipid(R) plus heparin infused animals a significant decrease in insulin-mediated glucose uptake was observed both in the heart (22.62+/-2.04 vs 10.37+/-2.33 ng/mg/min; P<0.01) and in soleus muscle (13.46+/-1.53 vs 6.84+/-2.58 ng/mg/min; P<0.05). FAT/CD36 mRNA was significantly increased in skeletal muscle tissue (+117.4+/-16.3%, P<0.05), while no differences were found at the heart level in respect to saline infused rats. A clear decrease of GLUT4 mRNA was observed in both tissues. The 24 h infusion of fat emulsion resulted in a clear enhancement of UCP2 and UCP3 mRNA levels in the heart (99.5+/-15.3 and 80+/-4%) and in the skeletal muscle (291.5+/-24.7 and 146.9+/-12.7%).


CONCLUSIONS
As a result of the increased availability of NEFA, FAT/CD36 gene expression increases in skeletal muscle, but not at the heart level. The augmented lipid fuel supply is responsible for the depression of insulin-mediated glucose transport and for the increase of UCP2 and 3 gene expression in both skeletal and heart muscle.
Vettor
R
R
Internal Medicine, Department of Medical and Surgical Sciences, University of Padova, Padova, Italy. roberto.vettor@unipd.it
Fabris
R
R
Serra
R
R
Lombardi
A M
AM
Tonello
C
C
Granzotto
M
M
Marzolo
M O
MO
Carruba
M O
MO
Ricquier
D
D
Federspil
G
G
Nisoli
E
E
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D015152:Blotting, Northern; D018955:CD36 Antigens; D002352:Carrier Proteins / Q000235:genetics*; D005217:Fat Emulsions, Intravenous / Q000008:administration & dosage*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D015870:Gene Expression; D005947:Glucose / Q000378:metabolism; D015309:Glucose Clamp Technique; D051275:Glucose Transporter Type 4; D006493:Heparin / Q000008:administration & dosage; D007328:Insulin / Q000097:blood / Q000494:pharmacology; D007473:Ion Channels; D008297:Male; D008562:Membrane Glycoproteins / Q000235:genetics*; D026901:Membrane Transport Proteins; D024101:Mitochondrial Proteins; D009004:Monosaccharide Transport Proteins / Q000235:genetics*; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism; D027361:Organic Anion Transporters / Q000235:genetics*; D011506:Proteins / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D051381:Rats; D011924:Rats, Zucker; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000071246:Uncoupling Protein 2; D000071247:Uncoupling Protein 3
D001786:Blood Glucose; D018955:CD36 Antigens; D002352:Carrier Proteins; D005217:Fat Emulsions, Intravenous; D005230:Fatty Acids, Nonesterified; D051275:Glucose Transporter Type 4; D007328:Insulin; D007473:Ion Channels; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D024101:Mitochondrial Proteins; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D027361:Organic Anion Transporters; D011506:Proteins; D012333:RNA, Messenger; C495694:Slc2a4 protein, rat; C000604391:Ucp2 protein, rat; C000604394:Ucp3 protein, rat; D000071246:Uncoupling Protein 2; D000071247:Uncoupling Protein 3; D006493:Heparin; D005947:Glucose