Tim R. Nagy

TGF-β1―induced migration of bone mesenchymal stem cells couples bone resorption with formation

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 in vivo 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, to the bone resorptive sites and that this process is mediated through a SMAD signaling pathway. Analyzing mice carrying a CED-derived mutant TGFB1 (encoding TGF-β1), which show the typical progressive diaphyseal dysplasia seen in the human disease, 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 bone remodeling diseases.

Disruption of Intraflagellar Transport in Adult Mice Leads to Obesity and Slow-Onset Cystic Kidney Disease

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.

SIRT1 Is Significantly Elevated in Mouse and Human Prostate Cancer

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 calorie-restricted 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.

Prediction of intra-abdominal and subcutaneous abdominal adipose tissue in healthy pre-pubertal children

OBJECTIVE: To examine the relationship of intra-abdominal adipose tissue (IAAT) and subcutaneous abdominal adipose tissue (SAAT) with body composition and anthropometry in children.DESIGN: Cross-sectional data analysis.SUBJECTS: 113 healty Caucasian and African-American, pre-pubertal children aged 4–10 y.MEASUREMENTS: IAAT and SAAT by single slice computed tomography at the level of the umbilicus; total fat and trunk fat by dual energy X-ray absorptiometry (DEXA); anthropometric evaluation by skinfolds and circumferences.RESULTS: IAAT was most strongly correlated with abdominal skinfold (r=0.88) and trunk fat by DEXA (r=0.87), and SAAT with trunk fat by DEXA (r=0.96), total fat by DEXA (r=0.93) and waist circumference (r=0.93). In stepwise regression, IAAT was best predicted by trunk fat from DEXA, total fat from DEXA, and abdominal skinfold (R2=0.85); SAAT was best predicted by trunk fat from DEXA, body weight, waist circumference and abdominal skinfold (R2=0.96). In the absence of DEXA data, IAAT was best predicted by abdominal skinfold, ethnicity and subscapular skinfold (R2=0.82) and SAAT was best predicted by waist circumference subscapular skinfold, height and abdominal skinfold (R2=0.92). The prediction equations with and without DEXA were successfully cross-validated in an independent sample of 12 additional measures of IAAT and SAAT.CONCLUSION: These data provide useful information that can help in the interpretation of anthropometric data with regard to body fat distribution. IAAT and SAAT can be accurately estimated in Caucasian and African-American prepubertal children from anthropometry with and without the availability of DEXA data.

Physical activity related energy expenditure and fat mass in young children

OBJECTIVE: To examine whether body fat content in pre-pubertal children is influenced by physical activity related energy expenditure (AEE) and/or more qualitative aspects of physical activity. DESIGN: Cross-sectional study. SUBJECT: 101 pre-pubertal children were examined in Study 1: (age: 5.3±0.9 y; weight: 20.2±3.6 kg). In Study 2: 68 of the original children were re-examined (age: 6.3±0.9 y; weight: 23.6±5.0 y). MEASUREMENT: Fat mass (FM) and fat free mass (FFM) were determined by bioelectrical resistance and skinfolds; AEE was estimated from the difference between total energy expenditure (TEE) by doubly labeled water and post-prandial resting energy expenditure (REE) by indirect calorimetry; qualitative information on activity was derived by questionnaire. RESULTS: AEE was significantly correlated with FFM (r=0.32 in both Studies) and body weight (r=0.28 in Study 1; r=0.29 in Study 2), but not FM. There were no significant relationships between AEE and any of the variables from the activity questionnaire in children (including TV time, playing time, and an accumulated activity index in h/week). After adjusting for FFM, age, and gender, FM was inversely related to activity time in h/week (partial r=−0.24 in Study 1; partial r=−0.32 in Study 2) but not AEE (P>0.5). CONCLUSION: After adjusting for FFM, age, and gender, a small portion of the variance in body fat mass in children (∼10%) is explained by time devoted to recreational activity, whereas none of the variance is explained by the combined daily energy expenditure related to physical activity.

Differential effects of a centrally acting fatty acid synthase inhibitor in lean and obese mice

C75 is a potent inhibitor of fatty acid synthase that acts centrally to reduce food intake and body weight in mice; a single dose causes a rapid (>90%) decrease of food intake. These effects are associated with inhibition of fasting-induced up-regulation and down-regulation, respectively, of the expression of orexigenic (NPY and AgRP) and anorexigenic (POMC and CART) neuropeptide messages in the hypothalamus. Repeated administration of C75 at a submaximal level, however, differentially affected food intake of lean and obese mice. With lean mice, C75 suppressed food intake by ≈50% and, with obese mice (ob/ob and dietary-induced obesity), by 85–95% during the first day of treatment. Lean mice, however, became tolerant/resistant to C75 over the next 2–5 days of treatment, with food intake returning to near normal and rebound hyperphagia occurring on cessation of treatment. In contrast, ob/ob obese mice responded to C75 with a >90% suppression of food intake throughout the same period with incipient tolerance becoming evident only after substantial weight loss had occurred. Dietary-induced obese mice exhibited intermediate behavior. In all cases, a substantial loss of body weight resulted. Pair-fed controls lost 24–50% less body weight than C75-treated mice, indicating that, in addition to suppressing food intake, C75 may increase energy expenditure. The decrease in body weight by ob/ob mice was due primarily to loss of body fat. In contrast to the short-term effects of C75 on “fasting-induced” changes of hypothalamic orexigenic and anorexigenic neuropeptide mRNAs, repeated administration of C75 either had the inverse or no effect as tolerance developed.

Identification of Brown Adipose Tissue in Mice with Fat-Water IDEAL-MRI

To investigate the feasibility of using IDEAL (Iterative Decomposition with Echo Asymmetry and Least squares estimation) fat–water imaging and the resultant fat fraction metric in detecting brown adipose tissue (BAT) in mice, and in differentiating BAT from white adipose tissue (WAT).

Predicting body composition from anthropometry in pre-adolescent children

The objectives of this paper were to: a) evaluate the accuracy and precision of previously published pediatric body composition prediction equations and b) develop additional prediction equations from a large, heterogeneous group of Caucasian (n=133) and African-American (n=69) children. The combined cohort of 202 children included a wide range of ages (4.0–10.9 y), weights (14.0–70.8 kg), fat mass (FM: 1.2–28.5 kg) and percent body fat (% body fat: 6.2–49.6%). Skinfold measurements were obtained using a Lange caliper and body fat was measured with a Lunar DPX-L densitometer. The previously published equations of Slaughter et al and Goran et al did not accurately predict body fat. The entire cohort was randomly divided into two sub-groups for purposes of deriving and cross-validating a new prediction equation. In stepwise regression analysis in the development group (n=135), weight, triceps skinfold, gender, ethnicity and abdominal skinfold estimated FM measured by dual energy x-ray absorptiometry (DEXA) with a model R2 of 0.95. The new prediction equation was cross-validated in the control group (n=67) and each ethnic and gender subgroup. We conclude that a) the equations of Slaughter et al and Goran et al did not accurately predict FM in a heterogeneous group of children and b) a new anthropometric prediction equation is proposed that may provide accurate estimates of FM in both Caucasian and African-American children aged 4–10 y with a wide range of FM and body composition.

Strain variation in the response of body temperature to dietary restriction

Dietary restriction (DR, also referred to as calorie restriction, energy restriction, and food restriction) retards senescence and increases longevity in mammals. DR also lowers mean body temperature (T(b)), and thus mean T(b) might be useful as a covariate of DR-induced life extension. Indeed, lower T(b) could itself underlie some of the beneficial life-extension effects that occur during DR. To assess the relationship between lower T(b) during DR and life extension, we asked whether significant strain variation exists in the T(b) response of mice being fed 60% ad libitum (AL). Individually-housed, female mice from 28 strains, representing a genealogically diverse sample of the classical inbred strains, were directly compared. The mean T(b)s in response to DR exhibited highly significant strain variation, ranging from 1.5 degrees C below normal to a phenomenal 5 degrees C below normal. This variation was not explained by differences in loss of thermoregulation, AL adiposity, sensitivity to a nonadaptive hypothermia, motor activity, thermal arousal, absolute food intake, or efficacy of nutrient extraction. The variation in strain mean T(b) was also present in the absence of torpor. This strain variation could be used to critically test whether lower T(b) is a covariate of life extension during DR.

Mice Lacking Phosphatidylinositol Transfer Protein-α Exhibit Spinocerebellar Degeneration, Intestinal and Hepatic Steatosis, and Hypoglycemia

Phosphatidylinositol transfer proteins (PITPs) regulate the interface between lipid metabolism and cellular functions. We now report that ablation of PITPα function leads to aponecrotic spinocerebellar disease, hypoglycemia, and intestinal and hepatic steatosis in mice. The data indicate that hypoglycemia is in part associated with reduced proglucagon gene expression and glycogenolysis that result from pancreatic islet cell defects. The intestinal and hepatic steatosis results from the intracellular accumulation of neutral lipid and free fatty acid mass in these organs and suggests defective trafficking of triglycerides and diacylglycerols from the endoplasmic reticulum. We propose that deranged intestinal and hepatic lipid metabolism and defective proglucagon gene expression contribute to hypoglycemia in PITPα–/– mice, and that hypoglycemia is a significant contributing factor in the onset of spinocerebellar disease. Taken together, the data suggest an unanticipated role for PITPα in with glucose homeostasis and in mammalian endoplasmic reticulum functions that interface with transport of specific luminal lipid cargoes.