Expression of AMPK, SIRT1, and ACC Differs between Winter- and Summer-Acclimatized Djungarian Hamsters.

The wintering strategy of the Djungarian hamster (Phodopus sungorus) includes a naturally occurring decrease in food intake and body mass. Our aim was to investigate the conceivable role of the metabolic regulators, AMP-activated protein kinase (AMPK) and sirtuin 1 (SIRT1), in the seasonal adaptation of the Djungarian hamster. In addition, a rate-limiting enzyme in fatty acid synthesis and oxidation, acetyl CoA carboxylase (ACC), was studied. Relative protein expressions and phosphorylated forms (pAMPK and pACC) were determined by Western blot from subcutaneous white adipose tissues (sWAT), abdominal white adipose tissues (aWAT), interscapular brown adipose tissues (iBAT), skeletal muscle, and hypothalamus of winter- and summer-acclimatized hamsters. The winter group had higher AMPK expression in sWAT, aWAT, and iBAT, but the relative amount of phosphorylated protein (pAMPK/AMPK ratio) was lower in these tissues. Furthermore, ACC expression was higher in sWAT and iBAT of the winter animals. pACC (inactive form) levels were higher in all adipose tissues, yet a lower pACC/ACC ratio was detected in iBAT of the winter hamsters. Muscle AMPK expression was lower but pAMPK/AMPK ratio higher in the winter group. SIRT1 expression was higher in muscle and all adipose tissues of the winter hamsters. Hypothalamic protein expressions did not differ between the groups. Higher expressions of AMPK, ACC, and SIRT1 in WAT and iBAT of the winter hamsters suggest a role in the regulation of lipid reserves and increased thermogenic capacity characteristic to the winter-adapted Djungarian hamsters.

Effects of wintertime fasting and seasonal adaptation on AMPK and ACC in hypothalamus, adipose tissue and liver of the raccoon dog (Nyctereutes procyonoides).

The raccoon dog (Nyctereutes procyonoides) is a canid with autumnal fattening and passive wintering strategy. We examined the effects of wintertime fasting and seasonality on AMP-activated protein kinase (AMPK), a regulator of metabolism, and its target, acetyl-CoA carboxylase (ACC) on the species. Twelve farmed raccoon dogs (eleven females/one male) were divided into two groups: half were fasted for ten weeks in December-March (winter fasted) and the others were fed ad libitum (winter fed). A third group (autumn fed, eight females) was fed ad libitum and sampled in December. Total AMPK, ACC and their phosphorylated forms (pAMPK, pACC) were measured from hypothalamus, liver, intra-abdominal (iWAT) and subcutaneous white adipose tissues (sWAT). The fasted animals lost 32% and the fed 20% of their body mass. Hypothalamic AMPK expression was lower and pACC levels higher in the winter groups compared to the autumn fed group. Liver pAMPK was lower in the winter fasted group, with consistently decreased ACC and pACC. AMPK and pAMPK were down-regulated in sWAT and iWAT of both winter groups, with a parallel decline in pACC in sWAT. The responses of AMPK and ACC to fasting were dissimilar to the effects observed previously in non-seasonal mammals and hibernators. Differences between the winter fed and autumn fed groups indicate that the functions of AMPK and ACC could be regulated in a season-dependent manner. Furthermore, the distinctive effects of prolonged fasting and seasonal adaptation on AMPK-ACC pathway could contribute to the wintering strategy of the raccoon dog.

Maintenance of skeletal muscle energy homeostasis during prolonged wintertime fasting in the raccoon dog (Nyctereutes procyonoides).

The raccoon dog (Nyctereutes procyonoides) is a canid species with autumnal fattening and prolonged wintertime fasting. Nonpathological body weight cycling and the ability to tolerate food deficiency make this species a unique subject for studying physiological mechanisms in energy metabolism. AMP-activated protein kinase (AMPK) is a cellular energy sensor regulating energy homeostasis. During acute fasting, AMPK promotes fatty acid oxidation and enhances glucose uptake. We evaluated the effects of prolonged fasting on muscle energy metabolism in farm-bred raccoon dogs. Total and phosphorylated AMPK and acetyl-CoA carboxylase (ACC), glucose transporter 4 (GLUT 4), insulin receptor and protein kinase B (Akt) protein expressions of hind limb muscles were determined by Western blot after 10 weeks of fasting. Plasma insulin, leptin, ghrelin, glucose and free fatty acid levels were measured, and muscle myosin heavy chain (MHC) isoform composition analyzed. Fasting had no effects on AMPK phosphorylation, but total AMPK expression decreased in m. rectus femoris, m. tibialis anterior and m. extensor digitorum longus resulting in a higher phosphorylation ratio. Decreased total expression was also observed for ACC. Fasting did not influence GLUT 4, insulin receptor or Akt expression, but Akt phosphorylation was lower in m. flexor digitorum superficialis and m. extensor digitorum longus. Three MHC isoforms (I, IIa and IIx) were detected without differences in composition between the fasted and control animals. The studied muscles were resistant to prolonged fasting indicating that raccoon dogs have an effective molecular regulatory system for preserving skeletal muscle function during wintertime immobility and fasting.

Specific effects of endurance and sprint training on protein expression of calsequestrin and SERCA in mouse skeletal muscle.

Calsequestrin (CSQ) is the main Ca²âº binding protein inside the sarcoplasmic reticulum (SR) of skeletal and cardiac muscle. The present study demonstrates the specific effects of different training regimens on CSQ isoform 1 (CSQ1, the primary isoform) and SR Ca²âº-ATPase (SERCA1, 2) expression in various skeletal muscles of mouse. CSQ1, SERCA1, and SERCA2 protein expression was determined with Western blot in m. soleus (SOL), m. extensor digitorum longus (EDL), m. gastrocnemius (GAS), m. rectus femoris (RF), and m. tibialis anterior (TA) muscles after completing a 6-week endurance or sprint training program. Endurance training induced decrease in CSQ1 concentration in SOL (p < 0.001) and in SERCA1 levels in GAS (p < 0.05), whereas increase in CSQ1 expression was detected in EDL (p < 0.01). After sprint training the concentration of CSQ1 increased in GAS (p < 0.01) and EDL (p < 0.01). Additionally, sprint exercise induced an increase in SERCA1 in GAS (p < 0.001) and a decline in TA (p < 0.05). SERCA2 was up-regulated with sprint training in GAS (p < 0.01). Myosin heavy chain (MHC) based fibre type composition altered differently depending on the muscle and the training regimen.These results indicate that (1) diverse training strategies used affect differently CSQ1 and SERCA1 concentrations in the skeletal muscle, (2) the regulation of CSQ1 and SERCA1 does not necessary follow the fast-slow definition despite the correlation between MHC isoforms, and (3) the changes in CSQ1 concentration occur prior to SERCA1 or SERCA2.