HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) All Versions of this Article: 287/1/E69    most recent 00461.2003v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (7) Citing Articles via Google Scholar Google Scholar Articles by Lee, F. N. Articles by Youn, J. H. Search for Related Content PubMed PubMed Citation Articles by Lee, F. N. Articles by Youn, J. H.

Insulin suppresses PDK-4 expression in skeletal muscle independently of plasma FFA

Department of Physiology and Biophysics, University of Southern California Keck School of Medicine, Los Angeles, California 90089

Submitted 13 October 2003 ; accepted in final form 9 March 2004

	ABSTRACT

TOP ABSTRACT METHODS RESULTS DISCUSSION GRANTS REFERENCES

 
Starvation and experimental diabetes induce a stable increase in pyruvate dehydrogenase kinase (PDK) activity in skeletal muscle, which is largely due to a selective upregulation of PDK-4 expression. Increased free fatty acid (FFA) level has been suggested to be responsible for the upregulation. Because these metabolic states are also characterized by insulin deficiency, the present study was designed to examine whether insulin has a significant effect to regulate PDK mRNA expression in rat skeletal muscle. In study 1, overnight-fasted rats received an infusion of saline or insulin for 5 h (n = 6 each). During the insulin infusion, plasma glucose was clamped at basal levels (euglycemic hyperinsulinemic clamp). A third group (n = 6) received Intralipid infusion during the clamp to prevent a fall in plasma FFA. PDK-2 mRNA level in gastrocnemius muscle was not altered by insulin or FFA (i.e., Intralipid infusion). In contrast, PDK-4 mRNA level was decreased 72% by insulin (P < 0.05), and Intralipid infusion prevented only 20% of the decrease. PDK-4 protein level was decreased 20% by insulin (P < 0.05), but this effect was not altered by Intralipid infusion. In study 2, overnight-fasted rats were refed or received an infusion of saline or nicotinic acid (NA, 30 µmol/h) for 5 h (n = 5 each). During the refeeding and NA infusion, plasma FFA levels were similarly (i.e., 60–70% vs. saline control) lowered. Muscle PDK-4 mRNA level decreased 77% after the refeeding (P < 0.05) but not after the NA infusion. In conclusion, the present data indicate that insulin had a profound effect to suppress PDK-4 expression in skeletal muscle and that, contrary to previous suggestions, circulating FFA had little impact on PDK-4 mRNA expression, at least within 5 h.

pyruvate dehydrogenase kinase; free fatty acid; insulin resistance; forkhead transcription factor

Previous studies have shown that starvation and experimental diabetes induce a stable increase in PDK activity in skeletal muscle (5, 7, 25), which explains the decreased activity of PDH and reduced glucose oxidation in these metabolic states. Skeletal muscle expresses two (i.e., PDK-2 and PDK-4) of the four PDK isoforms expressed in mammalian cells (PDK-1–4) (10, 24). The increase in PDK activity with starvation and diabetes was shown to be largely due to a selective upregulation of PDK-4 expression (29, 30). Because the plasma FFA level increases with starvation and diabetes, FFA has been suggested to stimulate PDK-4 expression in skeletal muscle (21, 28); FFA is an endogenous ligand for the peroxisome proliferator-activated receptor- (PPAR) (6, 9) and may increase PDK-4 expression by stimulating PPAR (11, 30). However, there are also large changes in other substrates and hormones in the blood during starvation or with diabetes. For example, the plasma insulin level decreases dramatically with starvation or diabetes. Insulin is known to have a profound effect to increase glucose oxidation, and it is therefore possible that the increase in PDK-4 expression (and decreased glucose oxidation) with starvation and diabetes is, at least in part, explained by insulin deficiency (5, 15, 30). However, few studies have examined directly whether insulin has a regulatory effect on PDK-4 expression in skeletal muscle. Majer et al. (15) showed that a hyperinsulinemic euglycemic clamp resulted in decreases in PDK mRNA levels in human skeletal muscle, suggesting a direct effect of insulin on PDK expression. However, this study, which employed a short exposure (i.e., 100 min) to insulin failed to demonstrate statistical significance for a small decrease in PDK-4 mRNA level while demonstrating a significant decrease in PDK-2 mRNA. Also, because plasma FFA level falls during hyperinsulinemic glucose clamps, the possibility cannot be excluded that insulin decreased PDK expression indirectly by decreasing plasma FFA. One goal of the present study was to examine whether insulin has a significant effect to regulate PDK-4 mRNA expression in rat skeletal muscle independently of plasma FFA. Another goal was to test whether changes in plasma FFA (in the absence of changes in plasma insulin) induced by an infusion of nicotinic acid (NA) (26) can alter PDK-4 mRNA expression in skeletal muscle.

	METHODS

TOP ABSTRACT METHODS RESULTS DISCUSSION GRANTS REFERENCES

 
Animals and catheterization. Male Wistar rats weighing 275–300 g were obtained from Simonsen (Gilroy, CA) and studied 5 days after arrival. Animals were housed under controlled temperature (22 ± 2°C) and lighting (12-h light, 0600–1800; 12-h dark, 1800–0600) with free access to water and standard rat chow. At least 4 days before the experiment, animals were placed in individual cages with tail restraint as previously described (1, 2, 13), which was required to protect tail blood vessel catheters during experiments. Animals were free to move about and were allowed unrestricted access to food and water. Two tail vein infusion catheters were placed the day before the experiment, and one tail artery blood sampling catheter was placed 4 h before the experiment (i.e., 0700). All procedures were approved by the Institutional Animal Care and Use Committee at the University of Southern California.

Experimental protocols. Experiments were conducted after an overnight fast; food was removed at 1700 on the day before the experiment. Two studies were carried out. In study 1, we determined the effects of plasma insulin, with and without Intralipid infusion to prevent a fall in plasma FFA, on skeletal muscle PDK-2 and PDK-4 mRNA expression. Animals received an infusion of porcine insulin (Eli Lilly, Indianapolis, IN) at a constant rate of 30 pmol·kg^–1·min^–1 for 5 h. During the insulin infusion, plasma glucose was clamped at basal levels by exogenous glucose infusion (hyperinsulinemic euglycemic clamp). The hyperinsulinemic euglycemic clamps were performed with (n = 6) or without (n = 6) a simultaneous infusion of Intralipid [Liposyn II (Abbott, North Chicago, IL); triglyceride emulsion, 20% wt/vol; 0.9 ml/h] and heparin (40 U/h, with 10 U as a priming bolus) (2). A third group of rats received only saline infusion (i.e., no insulin infusion; n = 6) for 5 h. At the end of the saline infusion or clamps, animals were anesthetized, and gastrocnemius muscles were rapidly dissected out, frozen immediately using liquid N₂-cooled aluminum blocks, and stored at –80°C for later analysis for PDK expression. In study 2, we tested in overnight-fasted rats the effects of refeeding and NA-induced decreases in plasma FFA on skeletal muscle PDK-2 and PDK-4 mRNA expression. One group of animals (n = 5) was refed for 5 h, and another group (n = 5) received a constant infusion of NA [30 µmol/h (26)] for 5 h to decrease plasma FFA similarly to the refed animals. During the NA infusion, small amounts of glucose were infused to prevent a fall in plasma glucose (26). A third group received only saline infusion (n = 5) for 5 h to serve as controls. At the end of the 5-h saline or NA infusion or refeeding, animals were anesthetized, and gastrocnemius muscles were taken as in study 1. In all of these experiments, blood samples were taken at various time points to measure plasma glucose, insulin, and FFA.

Northern blot analysis. Total RNA was extracted from frozen muscles using Tri Reagent from Molecular Research Center (Cincinnati, OH) according to the manufacturer's instructions. The total RNA preparations (25 µg each) were then loaded onto a 1% denaturing agarose gel, and electrophoresis was performed with 1x MOPS running buffer (Ambion, Austin, TX) at 50 V for 3.5 h. RNA was then capillary transferred overnight onto a positively charged nylon membrane (BrightStar-Plus, Ambion). cDNA probes for rat PDK-2 and PDK-4 were obtained by RT-PCR using an Advantage One Step RT-PCR kit from Clontech (Palo Alto, CA) and the following primers: PDK-4, 5'-CGTCGCCAGAATTAAAGCTC and 3'-CTGCCAGTTTCTCCTTCGAC; PDK-2, 5'-GTCAGCTAGGGGCCTTCTCT and 3'-CAGGACTATGCAGGCAGTGA. The cDNA probes were labeled with [³²P]dCTP (Perkin Elmer) using a DECAprime DNA labeling kit (Ambion). Hybridization was carried out using Ultrahyb solution (Ambion). After overnight hybridization at 42°C with the cDNA probes, the blots were then washed twice in 2x SSC (sodium chloride and sodium citrate buffer) for 15 min and twice in 0.1x SSC for 15 min. The autoradiograph was developed on Kodak BioMax MS film. Relative densities were quantified using the Bio-Rad Molecular Analyst. To control RNA loading, all blots were quantified for glyceraldehyde-3-phosphate dehydrogenase (G3PDH) by use of a probe included in the DECAprime DNA labeling kit (Ambion).

Western blot analysis. Frozen muscles (50 mg) were homogenized using a polytron at half-maximum speed (1 min, on ice) in 500 µl of buffer (20 mM Tris, pH 7.5, 5 mM EDTA, 10 mM Na₄P₂O₇, 100 mM NaF, 2 mM Na₃VO₄, 1% NP-40, 1 mM PMSF, 10 µg/ml aprotinin, and 10 µg/ml leupeptin). Muscle lysates were further solubilized by continuous stirring (4°C, 1 h) and centrifuged (14,000 g, 20 min). The supernatants (50 µg) were resolved by SDS-PAGE followed by electrophoretic transfer of proteins onto Hybond-P membranes (Amersham, Piscataway, NJ). The membranes were then probed with a rabbit antiserum (1:1,000) against PDK-4 (generous gift from Dr. R. A. Harris, Indiana University School of Medicine, Indianapolis, IN) and a secondary antibody (horseradish peroxidase-conjugated anti-rabbit IgG, Amersham). Signals were detected by an enhanced chemiluminescence method and quantified using the Bio-Rad Molecular Analyst.

Other assays. Plasma glucose was analyzed by a glucose oxidase method on a Beckman Glucose Analyzer II (Beckman, Fullerton, CA). Plasma insulin was measured by radioimmunoassay using a kit from Linco Research (St. Charles, MO). Plasma FFA was measured using an acyl-CoA oxidase-based colorimetric kit (Wako Pure Chemical Industries, Osaka, Japan).

Statistical analysis. Data are expressed as means ± SE. The significance of the differences in mean values among different treatment groups was evaluated using one-way ANOVA followed by ad hoc analysis using the Tukey test. P < 0.05 was considered statistically significant.

	RESULTS

TOP ABSTRACT METHODS RESULTS DISCUSSION GRANTS REFERENCES

 
Plasma insulin, glucose, and FFA levels during hyperinsulinemic euglycemic clamp with or without simultaneous infusion of Intralipid (study 1). Insulin infusion raised plasma insulin to 600 pM, and this level was slightly increased by Intralipid infusion (P < 0.05; Fig. 1). During the insulin infusion, plasma glucose was clamped at basal levels (6.0 mM). Plasma FFA levels decreased 65% during insulin infusion (P < 0.05), and this was prevented by Intralipid infusion. In fact, plasma FFA levels increased above basal during the combined infusion of insulin and Intralipid (P < 0.05). The glucose infusion rate (GINF) required to clamp plasma glucose, reflecting insulin's action to suppress hepatic glucose production and increase peripheral glucose uptake, increased rapidly during the 1st h and reached steady state within 2 h of initiation of the clamps. Elevation of plasma FFA via Intralipid infusion decreased GINF >50% at the end of the 5-h clamp (P < 0.05).

View larger version (17K): [in this window] [in a new window]   Fig. 1. Plasma insulin (A), glucose (B), and free fatty acid (FFA; C) concentrations and glucose infusion rate (GINF; D) during the 300-min saline infusion () or hyperinsulinemic euglycemic clamp with () or without () Intralipid infusion. Values are means ± SE for 6 experiments.

View larger version (42K): [in this window] [in a new window]   Fig. 2. Effects of insulin and Intralipid (FFA) infusions on pyruvate dehydrogenase kinase (PDK) mRNA expression in gastrocnemius muscle. A: representative Northern blots for PDK-2, PDK-4, and glyceraldehyde 3-phosphate dehydrogenase (G3PDH) mRNA expression in rats infused with saline (Basal), insulin (Insulin), or insulin and Intralipid (Insulin + FFA). B: Summary of PDK-2 and PDK-4 mRNA expression, normalized to G3PDH, for the 3 experimental groups. Values are means ± SE for 6 experiments. *P < 0.05 vs. basal; #P < 0.05 vs. insulin.

View larger version (30K): [in this window] [in a new window]   Fig. 3. Effects of insulin on PDK-4 and PDK-2 mRNA expression in soleus and gastrocnemius muscles. Northern blot analysis was performed on muscles of rats infused with saline or insulin for 5 h (n = 3 each).

View larger version (21K): [in this window] [in a new window]   Fig. 4. Effects of insulin on PDK-4 protein expression in gastrocnemius muscles. A: representative Western blots for PDK-4 protein expression in rats infused with saline (Basal), insulin (Insulin), or insulin and Intralipid (Insulin + FFA). B: summary of PDK-4 protein expression for the 3 experimental groups. Values are means ± SE for 5 experiments. *P < 0.05 vs. basal.

View larger version (17K): [in this window] [in a new window]   Fig. 5. Plasma glucose (A), insulin (B), and FFA (C) concentrations during the refeeding () or saline () or NA () infusion for 5 h. Values are means ± SE for 5 experiments.

View larger version (44K): [in this window] [in a new window]   Fig. 6. Effects of refeeding and nicotinic acid (NA) infusion on PDK mRNA expression in gastrocnemius muscle. A: representative Northern blots for PDK-2, PDK-4, and G3PDH mRNA expression. B: summary of PDK-2 and PDK-4 mRNA expression, normalized to G3PDH, for the 3 experimental groups. Values are means ± SE for 5 experiments. *P < 0.05 vs. control.

View larger version (28K): [in this window] [in a new window]   Fig. 7. Effects of overnight fasting, NA infusion, and 5-h refeeding on PDK-4 mRNA and protein expression in gastrocnemius muscle. A: representative Northern blots for PDK-2 and PDK-4 mRNA expression in muscles of fed, overnight-fasted, and 5-h-refed rats. B: representative Western blot and summary of PDK-4 protein expression in muscles of fed, overnight-fasted, NA-infused, and 5-h-refed rats. In B, values are means ± SE for 4 or 5 experiments. *P < 0.05 vs. overnight-fasted rats.

	DISCUSSION

TOP ABSTRACT METHODS RESULTS DISCUSSION GRANTS REFERENCES

Previous studies have shown that fasting induced a two- to fivefold increase in PDK-4 mRNA and protein expression in skeletal muscle (11, 18, 29, 30) and that these fasting effects were rapidly reversed during refeeding (29). Changes in FFA concentration during fasting and refeeding have been suggested to be responsible for this regulation (21, 28). In the present study a 5-h refeeding of overnight-fasted rats decreased muscle PDK-4 mRNA level by 77% (completely reversing the fasting-induced increases; Fig. 7), which was associated with a profound suppression of plasma FFA. However, a similar suppression of plasma FFA induced by NA infusion failed to alter muscle PDK-4 mRNA level. These data indicate that the changes in circulating FFA during refeeding cannot account for the rapid and profound decreases in muscle PDK-4 mRNA expression. In contrast, a 5-h insulin infusion caused a 72% decrease in muscle PDK-4 mRNA level, suggesting that insulin might be responsible for the changes in PDK-4 expression observed during refeeding. However, insulin concentrations during the insulin infusion (Fig. 1) were higher than those observed during the refeeding (Fig. 5); it is unclear whether insulin alone can fully account for the changes in PDK-4 expression during fasting and refeeding. Nonetheless, the present data clearly indicate that insulin has greater impact on skeletal muscle PDK-4 mRNA expression than FFA at least within the time frame (5 h) used in the present study.

PPAR has been suggested to play a major role in the regulation of PDK-4 expression with starvation or diabetes. First, WY-14643, a PPAR agonist, was shown to increase PDK-4 expression in rat gastrocnemius (fast glycolytic) muscle (30). Because FFA is an endogenous ligand for PPAR (6, 9) and FFA levels increase with starvation or diabetes, these data suggest that PDK-4 expression may be increased in these metabolic states as a result of increased PPAR stimulation by FFA. To support this concept, the upregulation of PDK-4 expression in hepatic, renal, and cardiac tissues associated with starvation was abolished (31) or attenuated (27) in PPAR-null mice. However, a more recent study (11) showed that the upregulation of PDK-4 expression with starvation was retained in oxidative muscles (soleus and tibialis anterior) of PPAR-null mice (unlike those observed in the fast glycolytic gastrocnemius muscles in earlier studies), indicating the presence of PPAR-independent mechanisms for regulation of PDK expression in these muscles. Also, it should be pointed out that PPAR-null mice, compared with control mice, showed substantially altered response to starvation (in terms of circulating substrate and hormone levels) (11). For example, we noted that the decrease in insulin during starvation was significantly less in PPAR-null mice compared with control mice, providing a possible explanation for attenuated PDK-4 response to starvation in some of previous studies with PPAR-null mice (27, 31).

Recent evidence indicates that PDK-4 is a target gene of the forkhead transcription factor Foxo1 (8, 14). Also, Akt/PKB, which is stimulated by insulin, has been shown to phosphorylate Foxo1 and cause its translocation from the nucleus into the cytosol, resulting in reduced transcriptional activity in transfected 293 cells (22, 23). Taken together, these data support the possibility that insulin suppresses PDK-4 expression in skeletal muscle by decreasing Foxo1 activity in the nucleus. In addition, Foxo1 gene expression was suggested to play a role in the regulation of PDK-4 gene expression (8). A more recent study (16) showed that insulin-induced phosphorylation and nuclear export of Foxo1 increased ubiquitination-mediated degradation of Foxo1 in Hep G2 cells. Our preliminary data show that Foxo1 content in gastrocnemius muscles significantly increased with overnight fasting and decreased after the 5-h insulin stimulation (data not shown). Whether insulin indeed regulates Foxo1 phosphorylation, translocation, and/or expression in skeletal muscle and, if so, whether it is causally related to the regulation of PDK-4 expression remain to be tested.

If insulin plays a major role in regulating muscle PDK-4 expression, it is tempting to speculate on the possibility that insulin's action to suppress PDK-4 expression is decreased in insulin-resistant states, which would result in increased PDK expression, leading to impaired glucose oxidation (15). Previous studies (12, 19) have shown that PDK-4 mRNA and protein expression increased in skeletal muscle with high-fat feeding, but it could not be inferred whether the increase was due to increased availability of fat or to a possible decrease in insulin's effect on PDK-4 expression in the insulin-resistant state. This important issue regarding the role of insulin resistance on skeletal muscle PDK-4 expression warrants further investigation.

In conclusion, our results indicate that insulin had a dramatic effect to suppress PDK-4 (but not PDK-2) mRNA expression in skeletal muscle independently of insulin's effect to decrease plasma FFA levels. In addition, and contrary to general belief, circulating FFA had little impact on PDK-4 mRNA expression in skeletal muscle. Our data suggest that the rapid and profound changes in PDK-4 mRNA expression during fasting or refeeding (or experimental diabetes) might be largely due to changes in circulating insulin rather than FFA.

	GRANTS

TOP ABSTRACT METHODS RESULTS DISCUSSION GRANTS REFERENCES

 
This study was supported by a research grant from the American Diabetes Association.

	ACKNOWLEDGMENTS

 
We thank Drs. Joyce Richey and Chin K. Sung for insightful comments on the manuscript.

	FOOTNOTES

 

Address for reprint requests and other correspondence: J. H. Youn, Dept. of Physiology and Biophysics, USC Keck School of Medicine, 1333 San Pablo St., MMR 626, Los Angeles, CA 90089-9142 (E-mail: youn{at}usc.edu).

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

	REFERENCES

TOP ABSTRACT METHODS RESULTS DISCUSSION GRANTS REFERENCES

 

1. Choi CS, Kim YB, Lee FN, Zabolotny JM, Kahn BB, and Youn JH. Lactate induces insulin resistance in skeletal muscle by suppressing glycolysis and impairing insulin signaling. Am J Physiol Endocrinol Metab 283: E233–E240, 2002.[Abstract/Free Full Text]
2. Choi CS, Lee FN, and Youn JH. Free fatty acids induce peripheral insulin resistance without increasing muscle hexosamine pathway product levels in rats. Diabetes 50: 418–424, 2001.[Abstract/Free Full Text]
3. Felber JP, Ferrannini E, Golay A, Meyer HU, Theibaud D, Curchod B, Maeder E, Jequier E, and DeFronzo RA. Role of lipid oxidation in pathogenesis of insulin resistance of obesity and type II diabetes. Diabetes 36: 1341–1350, 1987.[Abstract]
4. Felber JP, Meyer HU, Curchod B, Iselin HU, Rousselle J, Maeder E, Pahud P, and Jequier E. Glucose storage and oxidation in different degrees of human obesity measured by continuous indirect calorimetry. Diabetologia 20: 39–44, 1981.[CrossRef][ISI][Medline]
5. Feldhoff PW, Arnold J, Oesterling B, and Vary TC. Insulin-induced activation of pyruvate dehydrogenase complex in skeletal muscle of diabetic rats. Metabolism 42: 615–623, 1993.[CrossRef][ISI][Medline]
6. Forman BM, Chen J, and Evans RM. Hypolipidemic drugs, polyunsaturated fatty acids, and eicosanoids are ligands for peroxisome proliferator-activated receptors alpha and delta. Proc Natl Acad Sci USA 94: 4312–4317, 1997.[Abstract/Free Full Text]
7. Fuller SJ and Randle PJ. Reversible phosphorylation of pyruvate dehydrogenase in rat skeletal-muscle mitochondria. Effects of starvation and diabetes. Biochem J 219: 635–646, 1984.[ISI][Medline]
8. Furuyama T, Kitayama K, Yamashita H, and Mori N. Forkhead transcription factor FOXO1 (FKHR)-dependent induction of PDK4 gene expression in skeletal muscles during energy deprivation. Biochem J 375: 365–371, 2003.[CrossRef][ISI][Medline]
9. Gearing KL, Gottlicher M, Widmark E, Banner CD, Tollet P, Stromstedt M, Rafter JJ, Berge RK, and Gustafsson JA. Fatty acid activation of the peroxisome proliferator activated receptor, a member of the nuclear receptor gene superfamily. J Nutr 124, Suppl 8: 1284S–1288S, 1994.[Abstract/Free Full Text]
10. Gudi R, Bowker-Kinley MM, Kedishvili NY, Zhao Y, and Popov KM. Diversity of the pyruvate dehydrogenase kinase gene family in humans. J Biol Chem 270: 28989–28994, 1995.[Abstract/Free Full Text]
11. Holness MJ, Bulmer K, Gibbons GF, and Sugden MC. Up-regulation of pyruvate dehydrogenase kinase isoform 4 (PDK4) protein expression in oxidative skeletal muscle does not require the obligatory participation of peroxisome-proliferator-activated receptor alpha (PPARalpha). Biochem J 366: 839–846, 2002.[CrossRef][ISI][Medline]
12. Holness MJ, Kraus A, Harris RA, and Sugden MC. Targeted upregulation of pyruvate dehydrogenase kinase (PDK)-4 in slow-twitch skeletal muscle underlies the stable modification of the regulatory characteristics of PDK induced by high-fat feeding. Diabetes 49: 775–781, 2000.[Abstract]
13. Kim JK and Youn JH. Prolonged suppression of glucose metabolism causes insulin resistance in rat skeletal muscle. Am J Physiol Endocrinol Metab 272: E288–E296, 1997.[Abstract/Free Full Text]
14. Kwon HS, Haung B, Unterman TG, and Harris R. Protein kinase B- inhibits human pyruvate dehydrogenase kinase-4 gene induction by dexamethasone through inactivation of FOXO transcription factors. Diabetes 53: 899–910, 2004.[Abstract/Free Full Text]
15. Majer M, Popov KM, Harris RA, Bogardus C, and Prochazka M. Insulin downregulates pyruvate dehydrogenase kinase (PDK) mRNA: potential mechanism contributing to increased lipid oxidation in insulin-resistant subjects. Mol Genet Metab 65: 181–186, 1998.[CrossRef][ISI][Medline]
16. Matsuzaki H, Daitoku H, Hatta M, Tanaka K, and Fukamizu A. Insulin-induced phosphorylation of FKHR (Foxo1) targets to proteasomal degradation. Proc Natl Acad Sci USA 100: 11285–11290, 2003.[Abstract/Free Full Text]
17. Meyer HU, Curchod B, Maeder E, Pahud P, Jequier E, and Felber JP. Modifications of glucose storage and oxidation in nonobese diabetics, measured by continuous indirect calorimetry. Diabetes 29: 752–756, 1980.[Abstract]
18. Peters SJ, Harris RA, Heigenhauser GJ, and Spriet LL. Muscle fiber type comparison of PDH kinase activity and isoform expression in fed and fasted rats. Am J Physiol Regul Integr Comp Physiol 280: R661–R668, 2001.[Abstract/Free Full Text]
19. Peters SJ, Harris RA, Wu P, Pehleman TL, Heigenhauser GJ, and Spriet LL. Human skeletal muscle PDH kinase activity and isoform expression during a 3-day high-fat/low-carbohydrate diet. Am J Physiol Endocrinol Metab 281: E1151–E1158, 2001.[Abstract/Free Full Text]
20. Randle PJ. Regulatory interactions between lipids and carbohydrates: the glucose fatty acid cycle after 35 years. Diabetes Metab Rev 14: 263–283, 1998.[CrossRef][ISI][Medline]
21. Randle PJ, Priestman DA, Mistry S, and Halsall A. Mechanisms modifying glucose oxidation in diabetes mellitus. Diabetologia 37, Suppl 2: S155–S161, 1994.
22. Rena G, Guo S, Cichy SC, Unterman TG, and Cohen P. Phosphorylation of the transcription factor forkhead family member FKHR by protein kinase B. J Biol Chem 274: 17179–17183, 1999.[Abstract/Free Full Text]
23. Rena G, Woods YL, Prescott AR, Peggie M, Unterman TG, Williams MR, and Cohen P. Two novel phosphorylation sites on FKHR that are critical for its nuclear exclusion. EMBO J 21: 2263–2271, 2002.[CrossRef][ISI][Medline]
24. Rowles J, Scherer SW, Xi T, Majer M, Nickle DC, Rommens JM, Popov KM, Harris RA, Riebow NL, Xia J, Tsui LC, Bogardus C, and Prochazka M. Cloning and characterization of PDK4 on 7q21.3 encoding a fourth pyruvate dehydrogenase kinase isoenzyme in human. J Biol Chem 271: 22376–22382, 1996.[Abstract/Free Full Text]
25. Stace PB, Fatania HR, Jackson A, Kerbey AL, and Randle PJ. Cyclic AMP and free fatty acids in the longer-term regulation of pyruvate dehydrogenase kinase in rat soleus muscle. Biochim Biophys Acta 1135: 201–206, 1992.[Medline]
26. Stein DT, Esser V, Stevenson BE, Lane KE, Whiteside JH, Daniels MB, Chen S, and McGarry JD. Essentiality of circulating fatty acids for glucose-stimulated insulin secretion in the fasted rat. J Clin Invest 97: 2728–2735, 1996.[ISI][Medline]
27. Sugden MC, Bulmer K, Gibbons GF, Knight BL, and Holness MJ. Peroxisome-proliferator-activated receptor-alpha (PPARalpha) deficiency leads to dysregulation of hepatic lipid and carbohydrate metabolism by fatty acids and insulin. Biochem J 364: 361–368, 2002.[CrossRef][ISI][Medline]
28. Sugden MC, Bulmer K, and Holness MJ. Fuel-sensing mechanisms integrating lipid and carbohydrate utilization. Biochem Soc Trans 29: 272–278, 2001.[CrossRef][ISI][Medline]
29. Sugden MC, Kraus A, Harris RA, and Holness MJ. Fibre-type specific modification of the activity and regulation of skeletal muscle pyruvate dehydrogenase kinase (PDK) by prolonged starvation and refeeding is associated with targeted regulation of PDK isoenzyme 4 expression. Biochem J 346: 651–657, 2000.[CrossRef][ISI][Medline]
30. Wu P, Inskeep K, Bowker-Kinley MM, Popov KM, and Harris RA. Mechanism responsible for inactivation of skeletal muscle pyruvate dehydrogenase complex in starvation and diabetes. Diabetes 48: 1593–1599, 1999.[Abstract]
31. Wu P, Peters JM, and Harris RA. Adaptive increase in pyruvate dehydrogenase kinase 4 during starvation is mediated by peroxisome proliferator-activated receptor alpha. Biochem Biophys Res Commun 287: 391–396, 2001.[CrossRef][ISI][Medline]

This article has been cited by other articles:

				C. M. Schummer, U. Werner, N. Tennagels, D. Schmoll, G. Haschke, H.-P. Juretschke, M. S. Patel, M. Gerl, W. Kramer, and A. W. Herling Dysregulated pyruvate dehydrogenase complex in Zucker diabetic fatty rats Am J Physiol Endocrinol Metab, January 1, 2008; 294(1): E88 - E96. [Abstract] [Full Text] [PDF]

				U. A. White, A. A. Coulter, T. K. Miles, and J. M. Stephens The STAT5A-Mediated Induction of Pyruvate Dehydrogenase Kinase 4 Expression by Prolactin or Growth Hormone in Adipocytes Diabetes, June 1, 2007; 56(6): 1623 - 1629. [Abstract] [Full Text] [PDF]

				Y. I. Kim, F. N. Lee, W. S. Choi, S. Lee, and J. H. Youn Insulin Regulation of Skeletal Muscle PDK4 mRNA Expression Is Impaired in Acute Insulin-Resistant States. Diabetes, August 1, 2006; 55(8): 2311 - 2317. [Abstract] [Full Text] [PDF]

				A. E. Civitarese, M. K. C. Hesselink, A. P. Russell, E. Ravussin, and P. Schrauwen Glucose ingestion during exercise blunts exercise-induced gene expression of skeletal muscle fat oxidative genes Am J Physiol Endocrinol Metab, December 1, 2005; 289(6): E1023 - E1029. [Abstract] [Full Text] [PDF]

				L. J. Cluberton, S. L. McGee, R. M. Murphy, and M. Hargreaves Effect of carbohydrate ingestion on exercise-induced alterations in metabolic gene expression J Appl Physiol, October 1, 2005; 99(4): 1359 - 1363. [Abstract] [Full Text] [PDF]

				L. S. Golfman, C. R. Wilson, S. Sharma, M. Burgmaier, M. E. Young, P. H. Guthrie, M. Van Arsdall, J. V. Adrogue, K. K. Brown, and H. Taegtmeyer Activation of PPAR{gamma} enhances myocardial glucose oxidation and improves contractile function in isolated working hearts of ZDF rats Am J Physiol Endocrinol Metab, August 1, 2005; 289(2): E328 - E336. [Abstract] [Full Text] [PDF]

				E. A. Turvey, G. J. F. Heigenhauser, M. Parolin, and S. J. Peters Elevated n-3 fatty acids in a high-fat diet attenuate the increase in PDH kinase activity but not PDH activity in human skeletal muscle J Appl Physiol, January 1, 2005; 98(1): 350 - 355. [Abstract] [Full Text] [PDF]

				E. A. Turvey, G. J. F. Heigenhauser, M. Parolin, and S. J. Peters Elevated n-3 fatty acids in a high-fat diet attenuate the increase in PDH kinase activity but not PDH activity in human skeletal muscle J Appl Physiol, January 1, 2005; 98(1): 350 - 355. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) All Versions of this Article: 287/1/E69    most recent 00461.2003v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (7) Citing Articles via Google Scholar Google Scholar Articles by Lee, F. N. Articles by Youn, J. H. Search for Related Content PubMed PubMed Citation Articles by Lee, F. N. Articles by Youn, J. H.