Regulation of liver glucokinase activity in rats with fructose-induced insulin resistance and impaired glucose and lipid metabolism.
We evaluated the relative role of different regulatory mechanisms, particularly 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase (PFK2/FBPase-2), in liver glucokinase (GK) activity in intact animals with fructose-induced insulin resistance and impaired glucose and lipid metabolism. We measured blood glucose, triglyceride and insulin concentration, glucose tolerance, liver triglyceride content, GK activity, and GK and PFK2 protein and gene expression in fructose-rich diet (FRD) and control rats. After 3 weeks, FRD rats had significantly higher blood glucose, insulin and triglyceride levels, and liver triglyceride content, insulin resistance, and impaired glucose tolerance. FRD rats also had significantly higher GK activity in the cytosolic fraction (18.3 +/- 0.35 vs. 11.27 +/- 0.34 mU/mg protein). Differences in GK protein concentration (116% and 100%) were not significant, suggesting a potentially impaired GK translocation in FRD rats. Although GK transcription level was similar, PFK2 gene expression and protein concentration were 4- and 5-fold higher in the cytosolic fraction of FRD animals. PFK2 immunological blockage significantly decreased GK activity in control and FRD rats; in the latter, this blockage decreased GK activity to control levels. Results suggest that increased liver GK activity might participate in the adaptative response to fructose overload to maintain glucose/triglyceride homeostasis in intact animals. Under these conditions, PFK2 increase would be the main enhancer of GK activity.
Francini
Flavio
F
CENEXA / Center for Experimental and Applied Endocrinology (UNLP-CONICET, PAHO/WHO Collaborating Center for Diabetes), National University of La Plata, School of Medicine, 1900 La Plata, Argentina. f_francini@yahoo.com
Castro
María C
MC
Gagliardino
Juan J
JJ
Massa
María L
ML
D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001786:Blood Glucose / Q000032:analysis; D015153:Blotting, Western; D005632:Fructose / Q000009:adverse effects*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D005941:Glucokinase / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D005951:Glucose Tolerance Test; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance; D050356:Lipid Metabolism / Q000187:drug effects*; D008099:Liver / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D008297:Male; D025481:Phosphofructokinase-2 / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014280:Triglycerides / Q000378:metabolism
D000911:Antibodies, Monoclonal; D001786:Blood Glucose; D007328:Insulin; D014280:Triglycerides; D005632:Fructose; D025481:Phosphofructokinase-2; D005941:Glucokinase; D005947:Glucose