PDH activation during in vitro muscle contractions in PDH kinase 2 knockout mice: effect of PDH kinase 1 compensation

Abstract

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...

Role of pyruvate dehydrogenase kinase 4 in regulating PDH activation during acute muscle contraction

“…To investigate this possibility, we compared our data with previous data from our lab in fed WT mice that underwent the same experimental protocol (Dunford et al 2011). Comparing these groups offers three levels of PDK4 content: basal (fed WT), elevated (fasted WT), and absent (PDK4-KO) (Wu et al 1999;Jeoung et al 2006).…”

“…Our lab has previously shown that an inability to sufficiently activate PDHa during muscle contraction leads to a decrease in muscle force production at 40 Hz (Dunford et al 2011), which could suggest that the rate of muscle glucose oxidation may limit the ability of muscle to produce higher forces. This is supported by previous research in single mouse flexor brevis muscle fibres that demonstrated muscle fatigue during contraction occurred with a reduced availability of glucose, even in the absence of any measurable changes in muscle viability (Allen et al 2002).…”

“…Additional data in fed WT mice from previous research in our lab with the same investigators (and incubation and stimulation protocols) were used for comparison purposes only (Dunford et al 2011).…”

“…Comparison of PDHa activity of fasted WT and PDK4-KO mice with PDHa activity of fed WT mice acquired from previous data in our lab(Dunford et al 2011). *: Different from fasted WT within a stimulus.…”

Pyruvate Dehydrogenase Kinases in the Nervous System: Their Principal Functions in Neuronal-glial Metabolic Interaction and Neuro-metabolic Disorders

“…Pyruvate dehydrogenase complex (PDC) having a predominant role in the regulation of mammalian metabolism represents the point-of-no-return regarding the utilization of carbohydrate, plays a leading role in maintaining glucose homoeostasis and is immensely involved in the metabolic pathway required for energy production and movement [1][2][3]. PDC is entirely nuclear encoded and consists of multiple copies of three structurally distinct, but functionally interdependent, enzymes (E 1 through E 3 ) [4].…”