Maria S. Johnson

Uncoupled and surviving: individual mice with high metabolism have greater mitochondrial uncoupling and live longer

Two theories of how energy metabolism should be associated with longevity, both mediated via free‐radical production, make completely contrary predictions. The ‘rate of living‐free‐radical theory’ ( Pearl, 1928 ; Harman, 1956 ; Sohal, 2002 ) suggests a negative association, the ‘uncoupling to survive’ hypothesis ( Brand, 2000 ) suggests the correlation should be positive. Existing empirical data on this issue is contradictory and extremely confused ( Rubner, 1908 ; Yan & Sohal, 2000 ; Ragland & Sohal, 1975 ; Daan et al., 1996 ; Wolf & Schmid‐Hempel, 1989 ]. We sought associations between longevity and individual variations in energy metabolism in a cohort of outbred mice. We found a positive association between metabolic intensity (kJ daily food assimilation expressed as g/body mass) and lifespan, but no relationships of lifespan to body mass, fat mass or lean body mass. Mice in the upper quartile of metabolic intensities had greater resting oxygen consumption by 17% and lived 36% longer than mice in the lowest intensity quartile. Mitochondria isolated from the skeletal muscle of mice in the upper quartile had higher proton conductance than mitochondria from mice from the lowest quartile. The higher conductance was caused by higher levels of endogenous activators of proton leak through the adenine nucleotide translocase and uncoupling protein‐3. Individuals with high metabolism were therefore more uncoupled, had greater resting and total daily energy expenditures and survived longest – supporting the ‘uncoupling to survive’ hypothesis.

Aerobic Fitness, Not Energy Expenditure, Influences Subsequent Increase in Adiposity in Black and White Children

Background. Low levels of energy expenditure and aerobic fitness have been hypothesized to be risk factors for obesity. Longitudinal studies to determine whether energy expenditure influences weight gain in whites have provided conflicting results. To date, no studies have examined this relationship in blacks or whether aerobic fitness influences weight gain in white or black children. Methods. One hundred fifteen children, 72 white (55 girls and 17 boys) and 43 black (24 girls and 19 boys) were recruited for this study. Aerobic fitness, resting, total, and activity-related energy expenditure and body composition were measured at baseline. The children returned annually for 3 to 5 repeated measures of body composition. The influence of the initial measures of energy expenditure and fitness on the subsequent rate of increase in adiposity was examined, adjusting for initial body composition, age, ethnicity, gender, and Tanner stage. Because 20 children did not attain maximum oxygen consumption, the sample size for the combined analysis was 95. Results. Initial fat mass was the main predictor of increasing adiposity in this cohort of children, with greater initial fat predicting a higher rate of increase of adiposity. There was also a significant negative relationship between aerobic fitness and the rate of increasing adiposity (F 1,82 = 3.92). With every increase of .1 L/minute of fitness, there was a decrease of .081 kg fat per kg of lean mass gained. None of the measures of energy expenditure significantly predicted increasing adiposity in white or black children. Conclusions. Initial fat mass was the dominant factor influencing increasing adiposity; however, aerobic fitness was also a significant independent predictor of increasing adiposity in this cohort of children. Resting, total, or activity-related energy expenditure did not predict increasing adiposity. It seems that aerobic fitness may be more important than absolute energy expenditure in the development of obesity in white or black children. energy expenditure, fitness, longitudinal, obesity.

The Functional Significance of Individual Variation in Basal Metabolic Rate

Basal metabolic rate (BMR) was established as a common reference point allowing comparable measures across different individuals and species. BMR is often regarded as a minimal rate of metabolism compatible with basic processes necessary to sustain life. One confusing aspect, however, is that BMR is highly variable, both within and between species. A potential explanation for this variability is that while individuals with high BMRs may suffer the disadvantage of having to feed for longer to cover the extra energy demands, this may be offset by advantages that accrue because of the high metabolic rate. One suggested advantage is that high levels of BMR are a consequence of maintaining a morphology that permits high rates of the maximal sustained rate of metabolism (SusMR)—the rate of metabolism that can be sustained for days or weeks. We have been studying the energetics of MF1 laboratory mice during peak lactation to investigate this idea. In this article, we review some of our work in connection with three particular predictions that derive from the hypothesised links among morphology, basal metabolism, and sustained metabolic rate. By comparing groups of individuals, for example, lactating and nonlactating individuals, the patterns that emerge are broadly consistent with the hypothesis that BMR and SusMR are linked by morphology. Lactating mice have bigger organs connected with energy acquisition and utilisation, greater resting metabolic rates in the thermoneutral zone, called RMRt (approximately equivalent to BMR), and high sustainable rates of maximal energy intake. However, when attempts are made to establish these relationships across individuals within lactating mice, the associations that are anticipated are either absent or very weak and depend on shared variation due to body mass. At this level there is very little support for the suggestion that variation in RMRt (and thus BMR) is sustained by associations with SusMR.

Limits to sustained energy intake VIII. Resting metabolic rate and organ morphology of laboratory mice lactating at thermoneutrality

SUMMARY We have previously shown that the food intake and milk production of MF1 laboratory mice lactating at 30°C, 21°C and 8°C increase as temperature declines. These data suggest that mice are not limited peripherally by the capacity of the mammary glands to produce milk but are limited by the capacity of the animal to dissipate body heat generated as a by-product of food processing and milk production. Here, we measure resting metabolic rate (RMR; prior to breeding and at peak lactation) and organ morphology (at peak lactation) in MF1 mice exposed to 30°C (thermoneutrality) and compare these traits with the same parameters measured previously in mice at 21°C and 8°C. The masses of visceral organs primarily responsible for energy flux (heart, lungs, stomach, small intestine, large intestine, liver, pancreas, spleen and kidneys) increased as temperature declined. The masses of all these organs differed between mice exposed to 8°C and 21°C, whereas only the masses of heart, liver and kidneys differed between mice at 21°C and 30°C. The increases in organ masses were paralleled by increases in RMR at peak lactation above the levels measured prior to breeding, with mice at 8°C and 21°C having significantly higher increases in RMR than mice at 30°C (29.6 kJ day–1, 25.5 kJ day–1 and 8.1 kJ day–1, respectively). The observed changes in visceral organs and RMR are consistent with both the heat dissipation and peripheral limit hypotheses. However, mice exposed to 8°C had substantially larger mammary glands than mice at 21°C or 30°C (2.450 g, 1.115 g and 0.956 g dry mass, respectively), which argues against the peripheral limitation hypothesis and is consistent with the heat dissipation limit hypothesis. In addition, cold exposure resulted in greater masses of brown adipose tissue, white adipose tissue, pelage and tail. We discuss these changes in the context of the potential thermoregulatory benefits from use of the heat generated as a by-product of milk synthesis.

Insulin Sensitivity and Blood Pressure in Black and White Children

Although insulin sensitivity is correlated with high blood pressure in adults, it is unclear whether such a relationship exists in children across ethnic groups. Therefore, the aims of the study were to establish (1) if body composition and insulin sensitivity were related to blood pressure in children, and (2) if any differences in blood pressure between white and black children were explained by body composition and/or insulin sensitivity. Insulin sensitivity and the acute insulin response were established by the minimal model and body composition by dual-energy X-ray absorptiometry. Blood pressure was recorded in the supine position. Body composition, fasting insulin (P <0.01), and the acute insulin response (P <0.05) were positively related to systolic blood pressure but not to diastolic blood pressure, and insulin sensitivity (P <0.001) was negatively related to systolic blood pressure but not to diastolic blood pressure. Insulin sensitivity was negatively associated with systolic and diastolic blood pressure after adjustment for body composition (P <0.01). Black children had higher systolic (110±9.2 versus 105±8.5 mm Hg, P =0.01) and diastolic (59±7.0 versus 54±8.0 mm Hg, P <0.01) blood pressure than did white children. The ethnic difference in blood pressure was not explained by body composition, fasting insulin, acute insulin response, or insulin sensitivity. In conclusion, the relationship between insulin sensitivity and systolic blood pressure is evident early in life. Black ethnicity and low insulin sensitivity contribute independently to higher blood pressure in children.

Effect of exercise and calorie restriction on biomarkers of aging in mice

Unlike calorie restriction, exercise fails to extend maximum life span, but the mechanisms that explain this disparate effect are unknown. We used a 24-wk protocol of treadmill running, weight matching, and pair feeding to compare the effects of exercise and calorie restriction on biomarkers related to aging. This study consisted of young controls, an ad libitum-fed sedentary group, two groups that were weight matched by exercise or 9% calorie restriction, and two groups that were weight matched by 9% calorie restriction + exercise or 18% calorie restriction. After 24 wk, ad libitum-fed sedentary mice were the heaviest and fattest. When weight-matched groups were compared, mice that exercised were leaner than calorie-restricted mice. Ad libitum-fed exercise mice tended to have lower serum IGF-1 than fully-fed controls, but no difference in fasting insulin. Mice that underwent 9% calorie restriction or 9% calorie restriction + exercise, had lower insulin levels; the lowest concentrations of serum insulin and IGF-1 were observed in 18% calorie-restricted mice. Exercise resulted in elevated levels of tissue heat shock proteins, but did not accelerate the accumulation of oxidative damage. Thus, failure of exercise to slow aging in previous studies is not likely the result of increased accrual of oxidative damage and may instead be due to an inability to fully mimic the hormonal and/or metabolic response to calorie restriction.

Mild Calorie Restriction Induces Fat Accumulation in Female C57BL/6J Mice

This study investigated the effects of mild calorie restriction (CR) (5%) on body weight, body composition, energy expenditure, feeding behavior, and locomotor activity in female C57BL/6J mice. Mice were subjected to a 5% reduction of food intake relative to baseline intake of ad libitum (AL) mice for 3 or 4 weeks. In experiment 1, body weight was monitored weekly and body composition (fat and lean mass) was determined at weeks 0, 2, and 4 by dual energy X‐ray absorptiometry. In experiment 2, body weight was measured every 3 days and body composition was determined by quantitative magnetic resonance weekly, and energy expenditure, feeding behavior, and locomotor activity were determined over 3 weeks in a metabolic chamber. At the end of both experiments, CR mice had greater fat mass (P < 0.01) and less lean mass (P < 0.01) compared with AL mice. Total energy expenditure (P < 0.05) and resting energy expenditure (P < 0.05) were significantly decreased in CR mice compared with AL mice over 3 weeks. CR mice ate significantly more food than AL mice immediately following daily food provisioning at 1600 hours (P < 0.01). These findings showed that mild CR caused increased fat mass, decreased lean mass and energy expenditure, and altered feeding behavior in female C57BL/6J mice. Locomotor activity or brown adipose tissue (BAT) thermogenic capacity did not appear to contribute to the decrease in energy expenditure. The increase in fat mass and decrease in lean mass may be a stress response to the uncertainty of food availability.

Cancer progression in the transgenic adenocarcinoma of mouse prostate mouse is related to energy balance, body mass, and body composition, but not food intake.

Calorie restriction can inhibit or delay carcinogenesis, reportedly due to a reduction in calorie intake rather than by concurrent changes in body mass and/or composition. Our objective was to test the hypothesis that body mass and/or composition have an important effect, independent of energy intake, on the benefits or hazards associated with calorie restriction or overeating, respectively. In the first experiment, transgenic mice that spontaneously develop prostate cancer [transgenic adenocarcinoma of mouse prostate (TRAMP)] were housed at 27 degrees C or 22 degrees C and pair fed the same diet for 21 weeks (95% of ad libitum intake at 27 degrees C). In the second experiment, TRAMP mice were housed at 27 degrees C or 22 degrees C and fed the same diet ad libitum for 21 weeks. Despite a similar calorie intake, pair-fed mice at 27 degrees C (PF27) were heavier (28.3 +/- 3.3 versus 17.6 +/- 1.6 g at 21 weeks; P < 0.001; mean +/- SD) and had greater fat (6.4 +/- 2.1 versus 1.9 +/- 0.3 g; P < 0.001) and lean mass (P < 0.001) than pair-fed mice at 22 degrees C. Furthermore, PF27 mice had greater levels of serum leptin (P < 0.001), lower levels of adiponectin (P < 0.05), and a greater frequency of prostatic adenocarcinoma (P < 0.05). In contrast, ad libitum-fed mice housed at 22 degrees C consumed approximately 30% more calories than ad libitum-fed mice at 27 degrees C, but there was no difference between groups in body composition or cancer progression. These results imply that the ability of calorie restriction to inhibit or delay cancer incidence and progression is mediated in part by changes in energy balance, body mass, and/or body composition rather than calorie intake per se, suggesting that excess calorie retention, rather than consumption, confers cancer risk.

Relationships between Resting Metabolic Rate and Morphology in Lactating Mice: What Tissues are the Major Contributors to Resting Metabolism?

We sought the relationship between resting metabolic rate (RMR) and gross tissue morphology in 59 lactating female MF1 mice. RMR was measured at peak lactation (Day 18 post partum) and the animals were then immediately killed and dissected into 18 separate components which were dried for 14 days at 60 °C. Individual variation in the RMR (CV) was 27%. The masses of the tissue components were similarly variable (CV ranging from 4.3% for the brain to around 150% for fat tissue). RMR was significantly related to overall body mass (r2 = 0.458) with a scaling exponent of 1.55. Similar significant relationships were evident between masses of most (16/18) of the tissues and overall body mass. Accordingly there were significant relationships between RMR and all the tissue masses with the exception of those tissues poorly related to overall body mass (specifically the lungs, small intestine, brain and kidneys). When the shared variation due to total body mass was eliminated there were no significant links between residual RMR and residual mass of any tissue. Re-describing the morphology using principal components analysis revealed a link between a general size component (PC 1) and RMR (r2 = 0.374) but this relationship disappeared when residual RMR was employed as the dependent variable. Despite other studies that indicate wide variations in the rates at which different tissues metabolise energy in vitro there was no indication in the present study that any particular component of the morphology was linked to high RMR in vivo.

Micro‐computed tomographic analysis of bone healing subsequent to graft placement

A micro-computed tomographic (muCT) analysis of bone healing subsequent to graft (tri calcium phosphate/TCP) placement in the maxillary sinus prior to dental endosteal implant placement was the focus of the current study. Ten trephined rod shaped human bone cores were obtained three months after the placement of particulate graft material. Using the muCT, samples were evaluated at 6 and 20 mum resolutions. The images exhibited regions of different grey scale (GL) magnitudes for bone and graft allowing a differentiation and quantification of the two sample regions. The GL threshold magnitudes at 20 mum resolution were determined to be less than 235 for organic and fluid, 235-450 for bone, 400-600 for bone and graft, and 600 and above for the graft material. The graft material was integrated with the bone showing the osteoconductivity of the TCP material, the mean bone volume was 25.50 (11.28) ranging from 5.66 to 37.9 and the mean graft volume was 0.42 (0.37) ranging from 0.01 to 1.17. The mean graft to bone volume ratio was 0.015 (0.01) with a range from 0.002 to 0.024. The structural data and observations from two- and three-dimensional images provided a valuable assessment of the graft distribution, its relation to modeling bone and also the anatomy of the healing bone. Thus this study demonstrated the capability to uniquely evaluate the status of healing bone associated with this TCP grafting biomaterial with opportunities for subsequent correlations with histomorphometrical studies and clinical outcomes of these type implant treatments.