Dunford EC, Herbst EA, Jeoung NH, Gittings W, Inglis JG, Vandenboom R, LeBlanc PJ, Harris RA, Peters SJ. PDH activation during in vitro muscle contractions in PDH kinase 2 knockout mice: effect of PDH kinase 1 compensation. Am J Physiol Regul Integr Comp Physiol 300: R1487-R1493, 2011. First published March 16, 2011 doi:10.1152/ajpregu.00498.2010.-Pyruvate dehydrogenase (PDH) plays an important role in regulating carbohydrate oxidation in skeletal muscle. PDH is deactivated by a set of PDH kinases (PDK1, PDK2, PDK3, PDK4), with PDK2 and PDK4 being the most predominant isoforms in skeletal muscle. Although PDK2 is the most abundant isoform, few studies have examined its physiological role. The role of PDK2 on PDH activation (PDHa) at rest and during muscle stimulation at 10 and 40 Hz (eliciting low-and moderate-intensity muscle contractions, respectively) in isolated extensor digitorum longus muscles was studied in PDK2 knockout (PDK2KO) and wild-type (WT) mice (n ϭ 5 per group). PDHa activity was unexpectedly 35 and 77% lower in PDK2KO than WT muscle (P ϭ 0.043), while total PDK activity was nearly fourfold lower in PDK2KO muscle (P ϭ 0.006). During 40-Hz contractions, initial force was lower in PDK2KO than WT muscle (P Ͻ 0.001) but fatigued similarly to ϳ75% of initial force by 3 min. There were no differences in initial force or rate of fatigue during 10-Hz contractions. PDK1 compensated for the lack of PDK2 and was 1.8-fold higher in PDK2KO than WT muscle (P ϭ 0.019). This likely contributed to ensuring that resting PDHa activity was similar between the groups and accounts for the lower PDH activation during muscle contraction, as PDK1 is a very potent inhibitor of the PDH complex. Increased PDK1 expression appears to be regulated by hypoxia inducible factor-1␣, which was 3.5-fold higher in PDK2KO muscle. It is clear that PDK2 activity is essential, even at rest, in regulation of carbohydrate oxidation and production of reducing equivalents for the electron transport chain. In addition, these results underscore the importance of the overall kinetics of the PDK isoform population, rather than total PDK activity, in determining transformation of the PDH complex and PDHa activity during muscle contraction. pyruvate dehydrogenase 4; pyruvate dehydrogenase 1; carbohydrate oxidation; hypoxia inducible factor-1␣; E1␣; E2 THE PYRUVATE DEHYDROGENASE (PDH) complex plays a major role in the regulation of glucose homeostasis by catalyzing the decarboxylation of pyruvate to acetyl-CoA. PDH links glycolysis to the tricarboxylic acid (TCA) cycle, as PDH controls carbohydrate oxidation by regulating the entrance of carbohydrate-derived acetyl units into the TCA cycle (10). PDH activation is regulated through reversible phosphorylation and dephosphorylation carried out by intrinsic regulatory enzymes. Sequential phosphorylation of E1 at three specific serine residues, serine 264 (site 1), serine 271 (site 2), and serine 203 (site 3), by a family of PDH kinases (PDK1, PDK2, PDK3, PDK4) renders the complex inactive (42, 43), w...

The oxidation of carbohydrates in mammals is regulated by the pyruvate dehydrogenase (PDH) complex, which is covalently regulated by four PDH kinases (PDK1-4) and two PDH phosphatases (PDP1-2) unique to the PDH complex. To investigate the role that PDK4 plays in regulating PDH activation (PDHa) during muscle contraction, mouse extensor digitorum muscle was removed from wild type (WT) and PDK4-knockout (PDK4-KO) mice after a 24 h fast and stimulated for 3 min either at 10 Hz (low-intensity contraction), 40 Hz (moderate-intensity contraction), or allowed to rest. Force was recorded and muscle PDHa activity and metabolite concentrations were measured. PDHa activity was ∼2.5-fold higher at rest in PDK4-KO mice than WT mice (P = 0.009) and ∼2-fold higher in PDK4-KO mice at both 10 Hz (P < 0.001) and 40 Hz (P < 0.001). Force relative to muscle weight was similar at 10 Hz, but was 5.8 ± 0.7 mN·g(-1) in PDK4-KO mice and 3.5 ± 0.7 mN·g(-1) in WT mice at 40 Hz (P < 0.001), with a similar rate of fatigue in both genotypes. From these results it was concluded that PDK4 plays a role in reducing PDHa activity during low to moderate-intensity muscle stimulation, and that absence of PDK4 and the subsequent changes in carbohydrate utilization may alter force production.