Exercise substantially improves metabolic health, making the elicited mechanisms important targets for novel therapeutic strategies. Uncoupling protein 3 (UCP3) is a mitochondrial inner membrane protein highly selectively expressed in skeletal muscle. Here we report that moderate UCP3 overexpression (roughly 3-fold) in muscles of UCP3 transgenic (UCP3 Tg) mice acts as an exercise mimetic in many ways. UCP3 overexpression increased spontaneous activity (∼40%) and energy expenditure (∼5-10%) and decreased oxidative stress (∼15-20%), similar to exercise training in wild-type (WT) mice. The increase in complete fatty acid oxidation (FAO; ∼30% for WT and ∼70% for UCP3 Tg) and energy expenditure (∼8% for WT and 15% for UCP3 Tg) in response to endurance training was higher in UCP3 Tg than in WT mice, showing an additive effect of UCP3 and endurance training on these two parameters. Moreover, increases in circulating short-chain acylcarnitines in response to acute exercise in untrained WT mice were absent with training or in UCP3 Tg mice. UCP3 overexpression had the same effect as training in decreasing long-chain acylcarnitines. Outcomes coincided with a reduction in muscle carnitine acetyltransferase activity that catalyzes the formation of acylcarnitines. Overall, results are consistent with the conclusions that circulating acylcarnitines could be used as a marker of incomplete muscle FAO and that UCP3 is a potential target for the treatment of prevalent metabolic diseases in which muscle FAO is affected.

BackgroundIn utero undernutrition is associated with obesity and insulin resistance, although its effects on skeletal muscle remain poorly defined. Therefore, in the current study we explored the effects of in utero food restriction on muscle energy metabolism in mice.MethodsWe used an experimental mouse model system of maternal undernutrition during late pregnancy to examine offspring from undernourished dams (U) and control offspring from ad libitum fed dams (C). Weight loss of 10 wk old offspring on a 4 wk 40% calorie restricted diet was also followed. Experimental approaches included bioenergetic analyses in isolated mitochondria, intact (permeabilized) muscle and at the whole body level.ResultsU have increased adiposity and decreased glucose tolerance compared to C. Strikingly, when U are put on a 40% calorie restricted diet they lose half as much weight as calorie restricted controls. Mitochondria from muscle overall from U had decreased coupled (state 3) and uncoupled (state 4) respiration and increased maximal respiration compared to C. Mitochondrial yield was lower in U than C. In permeabilized fiber preparations from mixed fiber type muscle U had decreased mitochondrial content and decreased adenylate free leak respiration, fatty acid oxidative capacity, and state 3 respiratory capacity through complex I. Fiber maximal oxidative phosphorylation capacity did not differ between U and C but was decreased with calorie restriction.ConclusionsOur results reveal that in utero undernutrition alters metabolic physiology through a profound effect on skeletal muscle energetics and blunts response to a hypocaloric diet in adulthood. We propose that mitochondrial dysfunction links undernutrition in utero with metabolic disease in adulthood.

Cdk1 activity drives both mitotic entry and the metaphase-to-anaphase transition in all eukaryotes. The kinase Wee1 and the phosphatase Cdc25 regulate the mitotic activity of Cdk1 by the reversible phosphorylation of a conserved tyrosine residue. Mutation of cdc25 in Schizosaccharomyces pombe blocks Cdk1 dephosphorylation and causes cell cycle arrest. In contrast, deletion of MIH1, the cdc25 homolog in Saccharomyces cerevisiae, is viable. Although Cdk1-Y19 phosphorylation is elevated during mitosis in mih1D cells, Cdk1 is dephosphorylated as cells progress into G 1 , suggesting that additional phosphatases regulate Cdk1 dephosphorylation. Here we show that the phosphatase Ptp1 also regulates Cdk1 dephosphorylation in vivo and can directly dephosphorylate Cdk1 in vitro. Using a novel in vivo phosphatase assay, we also show that PP2A bound to Rts1, the budding yeast B56-regulatory subunit, regulates dephosphorylation of Cdk1 independently of a function regulating Swe1, Mih1, or Ptp1, suggesting that PP2A Rts1 either directly dephosphorylates Cdk1-Y19 or regulates an unidentified phosphatase.KEYWORDS Cdc25/Mih1; Cdk1; PP2A; Wee1/Swe1; mitosis M ITOTIC onset is regulated in all eukaryotes by an increase in Cdk1 activity caused by the dephosphorylation of Cdk1 on a conserved inhibitory tyrosine (tyrosine 19 in budding yeast) (Nurse 1990). The Wee1 kinase phosphorylates and inhibits Cdk1 (Gould and Nurse 1989; Parker et al. 1992), and the Cdc25 phosphatase acts as a mitotic inducer by dephosphorylating and activating Cdk1 (Dunphy and Kumagai 1991;Gautier et al. 1991). wee1 mutants in fission yeast shorten G 2 by prematurely activating Cdk1 (Nurse 1975;Russell and Nurse 1987), whereas cdc25 mutants cannot accumulate sufficient Cdk1 activity to enter mitosis and arrest (Russell and Nurse 1986). Both Wee1 and Cdc25 are the targets of numerous cell-cycle checkpoints, all of which delay mitotic entry by activating Wee1 or inhibiting Cdc25 (Kellogg 2003). In budding yeast, Swe1 (the Wee1 homolog) and Mih1 (the Cdc25 homolog) also function prior to mitosis (Russell et al. 1989;Harvey and Kellogg 2003;Pal et al. 2008), but our recent work revealed that overexpression of Swe1 or activation of a Swe1-dependent checkpoint arrests cells in metaphase .Deletion of cdc25 in fission yeast is lethal and arrests cells in G 2 , indicating the essential role of Cdk1-Y15 dephosphorylation in fission yeast (Russell and Nurse 1986). In contrast, although deletion of MIH1 exhibits high Cdk1-Y19 phosphorylation during mitosis, these cells have only mild delays in mitotic entry and anaphase onset and initiate Cdk1-Y19 dephosphorylation at anaphase onset (Russell et al. 1989;Pal et al. 2008;. This behavior argues that at least one additional phosphatase functions redundantly with Mih1.Russell and colleagues (Millar et al. 1992) identified the fission yeast Pyp3 as a phosphatase that functions redundantly with Cdc25. Increased expression of pyp3 or the budding yeast and mammalian homologs PTP1, PTP1B and TC-PTP1, respectively, suppress...