Exercise and/or Cold Exposure Alters the Gene Expression Profile in the Fat Body and Changes the Heart Function in Drosophila

The major reason of human morbidity and mortality is obesity and related diseases. Brown adipose tissue (BAT) is associated with low total adipose tissue content and a lower risk of type 2 diabetes mellitus. Studies have shown that exercise and cold expose may induce browning. In this study, we verified (1) whether exercise and/or cold exposure can improve the expression level of ucp4c, serca, ampkα, camkII, sirt1, octβ3r, and hamlet; (2) if these interventions can save cardiac dysfunction induced by a high-fat diet (HFD) in Drosophila. w1118 (wild-type) virgin female flies collected within 8 h after eclosion were divided into eight groups: the normal feed control group (NFD-C), the normal feed exercise group (NFD-E), the normal feed cold exposure group (NFD-CA), the normal feed exercise/cold exposure group (NFD-EC), the HFD control group (HFD-C), the HFD exercise group (HFD-E), the HFD cold exposure group (HFD-CA), and the HFD exercise/cold exposure group (HFD-EC). After exercise and/or cold exposure for 7 days, the mRNA expression levels of ucp4c, serca, ampkα, camk II, sirt1, octβ3r, and hamlet were tested by qRT-PCR, and m-mode was used to assess cardiac function. In addition, we assessed the triacylglycerol (TAG) levels, motor ability, fat mass (by Oil Red O [ORO] staining), and morphological features. The results of TAG, ORO staining, and morphological features all indicate that after interventions, body size of Drosophila was smaller compared with the control group, irrespective of the feeding patterns. The mRNA expression levels of ucp4c, serca, octβ3r, hamlet, ampkα, camkII, and sirt1 were changed to varying degrees under different intervention states (exercise and/or cold exposure). Cold exposure and exercise/cold exposure partly improved cardiac function and the normal fruit flies' cardiac function and exercise ability. However, after exercise intervention, exercise ability and heart function were improved in both HFD and normal-fat diet (NFD) fruit flies. In conclusion, different intervention states (exercise and/or cold exposure) can change the mRNA expression levels of ucp4c, serca, octβ3r, hamlet, ampkα, camkII, and sirt1. Exercise is the most effective way to restore HFD-induced cardiac dysfunction.

Increase in cardiac myosin heavy-chain (MyHC) alpha protein isoform in hibernating ground squirrels, with echocardiographic visualization of ventricular wall hypertrophy and prolonged contraction

Deep hibernators such as golden-mantled ground squirrels (Callospermophilus lateralis) have multiple challenges to cardiac function during low temperature torpor and subsequent arousals. As heart rates fall from over 300 beats min(-1) to less than 10, chamber dilation and reduced cardiac output could lead to congestive myopathy. We performed echocardiography on a cohort of individuals prior to and after several months of hibernation. The left ventricular chamber exhibited eccentric and concentric hypertrophy during hibernation and thus calculated ventricular mass was ~30% greater. Ventricular ejection fraction was mildly reduced during hibernation but stroke volumes were greater due to the eccentric hypertrophy and dramatically increased diastolic filling volumes. Globally, the systolic phase in hibernation was ~9.5 times longer, and the diastolic phase was 28× longer. Left atrial ejection generally was not observed during hibernation. Atrial ejection returned weakly during early arousal. Strain echocardiography assessed the velocity and total movement distance of contraction and relaxation for regional ventricular segments in active and early arousal states. Myocardial systolic strain during early arousal was significantly greater than the active state, indicating greater total contractile movement. This mirrored the increased ventricular ejection fraction noted with early arousal. However, strain rates were slower during early arousal than during the active period, particularly systolic strain, which was 33% of active, compared with the rate of diastolic strain, which was 67% of active. As heart rate rose during the arousal period, myocardial velocities and strain rates also increased; this was matched closely by cardiac output. Curiously, though heart rates were only 26% of active heart rates during early arousal, the cardiac output was nearly 40% of the active state, suggesting an efficient pumping system. We further analyzed proportions of cardiac myosin heavy-chain (MyHC) isoforms in a separate cohort of squirrels over 5 months, including time points before hibernation, during hibernation and just prior to emergence. Hibernating individuals were maintained in both a 4°C cold room and a 20°C warm room. Measured by SDS-PAGE, relative percentages of cardiac MyHC alpha were increased during hibernation, at both hibernacula temperatures. A potential increase in contractile speed, and power, from more abundant MyHC alpha may aid force generation at low temperature and at low heart rates. Unlike many models of cardiomyopathies where the alpha isoform is replaced by the beta isoform in order to reduce oxygen consumption, ground squirrels demonstrate a potential cardioprotective mechanism to maintain cardiac output during torpor.

Is cold acclimation of benefit to hibernating rodents?

The thermal challenge associated with cold acclimation (CA) and hibernation requires effective cardio-respiratory function over a large range of temperatures. We examined the impact of acute cooling in a cold-naïve hibernator to quantify the presumed improvement in cardio-respiratory dysfunction triggered by CA, and estimate the role of the autonomic nervous system in optimising cardiac and respiratory function. Golden hamsters (Mesocricetus auratus) were held at a 12 h:12 h light:dark photoperiod and room temperature (21°C euthermic control) or exposed to simulated onset of winter in an environmental chamber, by progression to 1 h:23 h light:dark and 4°C over 4 weeks. In vivo acute cooling (core temperature Tb=25°C) in euthermic controls led to a hypotension and bradycardia, but preserved cardiac output. CA induced a hypertension at normothermia (Tb=37°C) but on cooling led to decreases in diastolic pressure below euthermic controls and a decrease in cardiac output, despite an increase in left ventricular conductance. Power spectral analysis of heart rate variability suggested a decline in vagal tone on cooling euthermic hamsters (Tb=25°C). Following CA, vagal tone was increased at Tb=37°C, but declined more quickly on cooling (Tb=25°C) to preserve vagal tone at levels similar to euthermic controls at Tb=37°C. For the isolated heart, CA led to concentric hypertrophy with decreased end-diastolic volume, but with no change in intrinsic heart rate at either 37 or 25°C. Mechanical impairment was noted at 37°C following CA, with peak developed pressure decreased by 50% and peak rate-pressure product decreased by 65%; this difference was preserved at 25°C. For euthermic hearts, coronary flow showed thermal sensitivity, decreasing by 65% on cooling (T=25°C). By contrast, CA hearts had low coronary flow compared with euthermic controls, but with a loss of thermal sensitivity. Together, these observations suggest that CA induced a functional impairment in the myocardium that limits performance of the cardiovascular system at euthermia, despite increased autonomic input to preserve cardiac function. On acute cooling this autonomic control was lost and cardiac performance declined further than for cold-naïve hamsters, suggesting that CA may compromise elements of cardiovascular function to facilitate preservation of those more critical for subsequent rewarming.