AMPK activation increases uncoupling protein-3 expression and mitochondrial enzyme activities in rat muscle without fibre type transitions

Abstract

The present study examined the effect of chronic activation of 5'-AMP-activated protein kinase (AMPK) on the metabolic profile, including uncoupling protein-3 (UCP-3) and myosin heavy chain (MHC)-based fibre phenotype of rodent fast-twitch tibialis anterior muscle. Sprague-Dawley rats were given daily injections of 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR), a known activator of AMPK, or vehicle (control) for 28 days. After AICAR treatment, UCP-3 expression at the mRNA level was elevated 1.6 +/- 0.1-fold (P < 0.006) and corresponded to a 3.3 +/- 0.2-fold increase in UCP-3 protein content (P < 0.0001). In addition, the activities of the mitochondrial reference enzymes citrate synthase (EC 4.1.3.7) and 3-hydroxyacyl-CoA-dehydrogenase (EC 1.1.1.35), which are known to increase in proportion to mitochondrial volume density, were elevated 1.6-fold (P < 0.006), while the activity of lactate dehydrogenase (EC 1.1.1.27) was reduced to 80 % of control (P < 0.02). No differences were detected after AICAR treatment in the activities of the glycolytic reference enzymes glyceraldehydephosphate dehydrogenase (EC 1.2.1.12) or phosphofructokinase (EC 2.7.1.11), nor were MHC-based fibre-type transitions observed, using immunohistochemical or electrophoretic analytical methods. These changes could not be attributed to variations in inter-organ signalling by metabolic substrates or insulin. We conclude that an AMPK-dependent pathway of signal transduction does mimic some of the metabolic changes associated with chronic exercise training, but does not affect expression of the MHC-based structural phenotype. Thus, the metabolic and MHC-based fibre types do not appear to be regulated in a co-ordinated way, but may be independently modified by different signalling pathways.

Creatine loading elevates the intracellular phosphorylation potential and alters adaptive responses of rat fast-twitch muscle to chronic low-frequency stimulation

“…( Table 2) were within the ranges of previous reports (Lowry et al 1978;Putman et al 2003Putman et al , 2004Gallo et al 2008). CLFS induced 89% and 34% increases (P < 0.01) in the respective maximum activities of CS and HADH in dextrose-CLFS and similar 77% and 58% increases (P < 0.01) in creatine-CLFS.…”

“…The CLFS-induced changes in glycolytic (i.e., GAPDH and PFK) and oxidative (i.e., CS and HADH) capacities observed in dextrose-CLFS were similar in magnitude to those observed in previous studies from our lab (Putman et al 2003(Putman et al , 2004(Putman et al , 2007 and others (for reviews see Pette and Staron 1997;Pette and Vrbová 1999) during a well-characterised phase of rapid fast-to-slow fibre type transitions. Abolishment of CLFS-induced reductions in the glycolytic reference enzymes PFK and GAPDH in creatine-CLFS suggests that regulatory events that are sensitive to fluctuations in the IPP may also exert control over the expression of PFK and GAPDH.…”

“…5) and mRNA (Fig. 6) levels, were similar to those previously reported (Putman et al 2003(Putman et al , 2004Martins et al 2012). Compared with voluntary running, which was used in our previous study (Gallo et al 2008) to investigate fast-to-slow fibre type transitions within plantaris of the same rat strain, CLFS induced more advanced fibre type conversion over a much shorter time period and proved to be a better experimental model.…”

“…Maximal activities of citrate synthase (CS, EC 2.3.3.1), 3-hydroxyacyl-CoA dehydrogenase (HADH, EC 1.1.1.35), phosphofructokinase (PFK, EC 2.7.1.11), glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) (Putman et al 2003(Putman et al , 2004Gallo et al 2008), and creatine kinase (CK, EC 2.7.3.2) were measured (Lowry et al 1978) as previously described.…”

The caloric restriction paradigm: Implications for healthy human aging

“…AMPK (AMP-activated protein kinase) is involved in the adaptive response to energy deficit. AMPK is also a PGC-1a activator that can induce mitochondrial biogenesis and increases activity of mitochondrial enzymes (Putman and others 2003; Zong and others 2002). The plant polyphenol resveratrol is an activator of AMPK that has been shown to produce CR-like alterations in gene transcription in multiple tissues in mice, although longevity does not appear to be extended in normally fed animals (Barger and others 2008a; Barger and others 2008b; Pearson and others 2008).…”