SUMMARY Bone remodeling depends on the precise coordination of bone resorption and subsequent bone formation. Disturbances of this process are associated with skeletal diseases, such as Camurati-Engelmann disease (CED). We show using in vitro and animal models that active TGF-β1 released during bone resorption coordinates bone formation by inducing migration of bone marrow stromal cells, also known as bone mesenchymal stem cells (BMSCs) to the bone resorptive sites and that this process is mediated through SMAD signaling pathway. Analysis of a mouse model carrying a CED-derived TGF-β1 mutation, which exhibits the typical progressive diaphyseal dysplasia with tibial fractures, we found high levels of active TGF-β1 in the bone marrow. Treatment with a TGF-β type I receptor inhibitor partially rescued the uncoupled bone remodeling and prevented the fractures. Thus, as TGF-β1 functions to couple bone resorption and formation, modulation of TGF-β1 activity could be an effective treatment for the bone remodeling diseases.

The assembly of primary cilia is dependent on intraflagellar transport (IFT), which mediates the bidirectional movement of proteins between the base and tip of the cilium. In mice, congenic mutations disrupting genes required for IFT (e.g., Tg737 or the IFT kinesin Kif3a) are embryonic lethal, whereas kidney-specific disruption of IFT results in severe, rapidly progressing cystic pathology. Although the function of primary cilia in most tissues is unknown, in the kidney they are mechanosenstive organelles that detect fluid flow through the tubule lumen. The loss of this flow-induced signaling pathway is thought to be a major contributing factor to cyst formation. Recent data also suggest that there is a connection between ciliary dysfunction and obesity as evidenced by the discovery that proteins associated with human obesity syndromes such as Alström and Bardet-Biedl localize to this organelle. To more directly assess the importance of cilia in postnatal life, we utilized conditional alleles of two ciliogenic genes (Tg737 and Kif3a) to systemically induce cilia loss in adults. Surprisingly, the cystic kidney pathology in these mutants is dependent on the time at which cilia loss was induced, suggesting that cyst formation is not simply caused by impaired mechanosensation. In addition to the cystic pathology, the conditional cilia mutant mice become obese, are hyperphagic, and have elevated levels of serum insulin, glucose, and leptin. We further defined where in the body cilia are required for normal energy homeostasis by disrupting cilia on neurons throughout the central nervous system and on pro-opiomelanocortin-expressing cells in the hypothalamus, both of which resulted in obesity. These data establish that neuronal cilia function in a pathway regulating satiety responses.

Evidence suggests that the histone deacetylase, SIRT1, is a mediator of life span extension by calorie restriction; however, SIRT1 may paradoxically increase the risk of cancer. To better understand the relationship among SIRT1, energy balance, and cancer, two experiments were done. First, a transgenic mouse model of prostate cancer (transgenic adenocarcinoma of mouse prostate; TRAMP) was used to determine the role of energy balance on SIRT1 expression and the effect of cancer stage on SIRT1 and hypermethylated in cancer-1 (HIC-1). Second, immunohistochemistry was done on human prostate tumors to determine if SIRT1 was differentially expressed in tumor cells versus uninvolved cells. Results show that SIRT1 is not increased in the dorsolateral prostate (DLP) of calorierestricted mice during carcinogenesis. In contrast, when examined in the DLP as a function of pathologic score, SIRT1 was significantly elevated in mice with poorly differentiated adenocarcinomas compared with those with less-advanced disease. HIC-1, which has been shown to regulate SIRT1 levels, was markedly reduced in the same tumors, suggesting that a reduction in HIC-1 may be in part responsible for the increased expression of SIRT1 in prostatic adenocarcinomas. Furthermore, immunostaining of human prostate tumors showed that cancer cells had greater SIRT1 expression than uninvolved cells. In conclusion, DLP SIRT1 expression from calorie-restricted mice was not altered during carcinogenesis. However, SIRT1 expression was increased in mice with poorly differentiated adenocarcinomas and in human prostate cancer cells. Because SIRT1 may function as a tumor promoter, these results suggest that SIRT1 should be considered as a potential therapeutic target for prostate cancer. [Cancer Res 2007;67(14):6612-8]

In adults, visceral fat accumulation is associated with insulin resistance and dyslipidemia. The cause-and-effect nature of these relationships is not clear. The objective of the present study was to determine if similar relationships exist in prepubertal children. Specifically, we determined whether visceral fat was associated with fasting insulin, insulin sensitivity (Si), serum triglyceride (TG) concentration, or serum HDL cholesterol (HDL-C) concentration; whether visceral fat or Si was independently related to lipids; and whether ethnicity influenced the relationship between visceral fat and risk factors. Subjects were 61 prepubertal African-American and Caucasian children. Total body fat was determined by dual-energy X-ray absorptiometry, visceral fat by computed tomography, and insulin sensitivity by the tolbutamide-modified, frequently sampled intravenous glucose tolerance test with minimal modeling. In multiple linear regression analysis (adjusting for total fat, sex, and ethnicity), visceral fat was independently related to TG (P < 0.05) and fasting insulin (P < 0.001), but not Si (P = 0.425). Total body fat was independently related to Si (P < 0.001). Si was independently related to fasting insulin (P < 0.001) but not to TG or HDL-C (P = 0.941 and 0.201, respectively). Si in African-Americans was 42% lower than in Caucasians (0.50 +/- 0.05 vs. 0.86 +/- 0.11 x 10(-5) min(-1) x pmol(-1) x l, mean +/- SE after adjusting for total fat, P < 0.001). Nonetheless, ethnicity was not independently related to either TG or HDL-C (P = 0.075 and 0.619, respectively, after adjusting for total and visceral fat and sex). The slopes of the relationships of total and visceral fat with risk factors did not differ with ethnicity. In conclusion, visceral fat appears metabolically unique in children, being independently associated with elevated TG and insulin but not Si. Obese children and African-American children were more insulin resistant, independent of visceral fat accumulation. Lower Si was associated with higher, faster insulin, but not dyslipidemia. Thus, obesity, visceral fat accumulation, and ethnicity in children may confer negative, but independent, health risks.

NAGY, TIM R., AND ANNE-LAURE CLAIR. Precision and accuracy of dual-energy X-ray absorptiometry for determining in vivo body composition of mice. Obes Res. 2000;8:392-398. Objective: To evaluate the precision and accuracy of dualenergy X-ray absorptiometry (DXA) for the measurement of total-bone mineral density (TBMD), total-body bone mineral (TBBM), fat mass (FM), and bone-free lean tissue mass (LTM) in mice. Research Methods and Procedures: Twenty-five male C57BL/6J mice (6 to 11 weeks old; 19 to 29 g) were anesthetized and scanned three times (with repositioning between scans) using a peripheral densitometer (Lunar PIXImus). Gravimetric and chemical extraction techniques (Soxhlet) were used as the criterion method for the determination of body composition; ash content was determined by burning at 600°C for 8 hours. Discussion: These data show that the precision of DXA for measuring TBMD, TBBM, FM, and LTM in mice ranges from a low of 0.84% to a high of 2.20% (CV). DXA accurately measured bone ash content but overestimated carcass FM and underestimated LTM. However, because of the close relationship between DXA-derived data and chemical carcass analysis for FM and LTM, prediction equations can be derived to more accurately predict body composition.

Using dual-energy X-ray absorptiometry (DXA) as a standard method for determining body composition in children, we evaluated the accuracy of skinfold-thickness measurements (with the Slaughter et al equations, which are based on triceps and calf skinfold-thickness measurements), bioelectrical resistance (BR; with the Kushner el al equations and age-specific hydration constants), and other clinical measurements (individual skinfold thicknesses and body mass index) for the assessment of body fat in children. We studied a heterogenous group of 49 boys and 49 girls, aged 6.6 +/- 1.4 y and weighing 24.1 +/- 5.9 kg. Fat mass estimated by DXA was significantly lower than fat mass measured by skinfold thickness, even though fat mass measurements by these two techniques were strongly related to each other. Fat mass estimated by DXA was also significantly lower than fat mass measured by BR, and the model R2 and SEE were not as strong as for the skinfold-thickness technique. Fat mass estimated by DXA also correlated with other clinical indexes such as triceps skinfold thickness, body mass index, body weight, and subscapular skinfold thickness. In forward-regression analysis, subscapular skinfold thickness, body weight, triceps skinfold thickness, sex, and height2/resistance estimated the value for fat mass measured by DXA with a model R2 of 0.91 and an SEE of 0.94 kg fat mass. These studies suggest that existing techniques for assessing body fat in children may be inaccurate. We provide new anthropometric equations based on the use of DXA as a criterion that provide accurate and precise measures of body fat and fat-free mass in white children aged 4-9 y. This approach provides estimates of body fat standardized to a known laboratory standard of chemical analysis of carcasses.

The objective of this review was to compare and contrast the physiological and metabolic profiles of rodent white adipose fat pads with white adipose fat depots in humans. Human fat distribution and its metabolic consequences have received extensive attention, but much of what has been tested in translational research has relied heavily on rodents. Unfortunately, the validity of using rodent fat pads as a model of human adiposity has received less attention. There is a surprisingly lack of studies demonstrating an analogous relationship between rodent and human adiposity on obesity-related comorbidities. Therefore, we aimed to compare known similarities and disparities in terms of white adipose tissue (WAT) development and distribution, sexual dimorphism, weight loss, adipokine secretion, and aging. While the literature supports the notion that many similarities exist between rodents and humans, notable differences emerge related to fat deposition and function of WAT. Thus, further research is warranted to more carefully define the strengths and limitations of rodent WAT as a model for humans, with a particular emphasis on comparable fat depots, such as mesenteric fat.

Objective To investigate the variations in body weight, food intake and body composition of both male and female C57BL/6J mice during a diet-induced obesity (DIO) model with high-fat diet (HFD) feeding. Design and Methods Mice were individually housed and fed ad libitum either a low-fat diet (LFD, 10% calories from fat; n=15 male, n=15 female) or high-fat diet (HFD, 45% calories from fat; n=277 male, n=278 female) from 8 to 43 weeks of age. Body weight, food intake and body composition were routinely measured. Results Body weight was significantly increased with HFD (vs. LFD) in males from week 14 (p=0.0221) and in females from week 27 (P=0.0076). Fat mass and fat-free mass of all groups were significantly increased over time (all p<0.0001), with a large variation observed in fat mass. Baseline fat mass, fat-free mass and daily energy intake were significant predictors of future body weight for both sexes (p<0.0001). Baseline fat mass was a significant predictor of future body fat (p<0.0001). Conclusions Both males and females have large variations in fat mass, and this variability increases over time, while that of fat-free mass remains relatively stable. Sex differences exist in HFD responses and multivariate predicting models of body weight.