Therapeutic potential of genetically modified adult stem cells for osteopenia.

Adult stem cells have therapeutic potential because of their intrinsic capacity for self-renewal, especially for bone regeneration. The present study shows the utility of ex vivo modified mesenchymal stem cells (MSC) to enhance bone density in an immunocompetent mouse model of osteopenia. MSC were transduced ex vivo with a recombinant adeno-associated virus 2 (rAAV2) expressing bone morphogenetic protein 2 (BMP2) under the transcriptional control of collagen type-1alpha promoter. To enrich bone homing in vivo, we further modified the cells to transiently express the mouse alpha4 integrin. The modified MSC were systemically administered to ovariectomized, female C57BL/6 mice. Effects of the therapy were determined by dual-energy X-ray absorptiometry, 3D micro-CT, histology and immunohistochemistry for up to 6 months. Results indicated that mice transplanted with MSC expressing BMP2 showed significant increase in bone mineral density and bone mineral content (P < 0.001) with relatively better proliferative capabilities of bone marrow stromal cells and higher osteocompetent pool of cells compared to control animals. Micro-CT analysis of femora and other bone histomorphometric analyses indicated more trabecular bone following MSC-BMP2 therapy. Results obtained by transplanting genetically modified MSC from green fluorescent protein transgenic mouse suggested that production of BMP2 from transplanted MSC also influenced the mobilization of endogenous progenitors for new bone formation.

Leptin in postmenopausal women: influence of hormone therapy, insulin, and fat distribution.

Whether use of hormone-replacement therapy (HRT) influences menopause-related changes in body weight is unclear. HRT may affect energy balance by influencing synthesis of the adipocyte-derived hormone leptin. The objectives of this study were to: 1) identify factors influencing circulating leptin in postmenopausal women; 2) determine whether HRT influences serum leptin after adjusting for confounding factors; and, 3) identify potential independent effects of HRT or leptin on resting energy expenditure (REE). Subjects were 54 postmenopausal women, 45-55 yr old, 35 of whom used HRT (estrogen plus progestin). Total and regional body composition and fat distribution were determined by dual-energy x-ray absorptiometry and computed tomography; fasting serum leptin and insulin, by RIA; and REE, by indirect calorimetry. Stepwise multiple linear regression analysis indicated that serum leptin could best be predicted from total fat mass, fasting serum insulin, and total lean mass [log leptin = 1.08 x log fat mass) + (0.46 x log insulin) + (-1.25 x log lean mass) + 1.88; model R2 = 0.78, P < 0.001]. Multiple linear regression analysis indicated that visceral fat was independently related to leptin (parameter estimate = 0.23, P < 0.05), after adjusting for s.c. abdominal fat and leg fat, as well as lean mass and insulin. After adjusting for total fat mass, total lean mass, and fasting insulin, serum leptin did not differ between users and nonusers of HRT (21.7 +/- 1.0 vs. 20.2 +/- 1.3 ng/mL, P = 0.369, adjusted mean +/- SE, respectively). Serum estradiol was inversely correlated with (adjusted) leptin in non-HRT users (r = -0.50), suggesting that ovarian senescence may lead to an increase in leptin. Multiple linear regression analysis indicated that REE (adjusted for fat mass, fat-free mass, and ethnicity) was not associated with leptin (P = 0.298) or hormone use status (P = 0.999; 1323 +/- 31 vs. 1316 +/- 42 kcal/day, adjusted mean +/- SE for users and nonusers, respectively). These results indicate that, in postmenopausal women: 1) total fat mass, lean mass, and fasting insulin, but not HRT, are significant determinants of serum leptin; 2) visceral and s.c. fat contribute to serum leptin; and, 3) neither HRT nor leptin is independently related to REE.

Do hormonal indices of maturation explain energy expenditure differences in African American and Caucasian prepubertal children?

OBJECTIVE: To examine the relationships between hormonal indices of maturation and total, resting and physical activity-related energy expenditure (TEE, REE and AEE) in African American and Caucasian prepubertal children. DESIGN: Cross-sectional study. SUBJECTS: Sixty-four African American and 48 Caucasian prepubertal children. MEASUREMENTS: TEE (by doubly labeled water), REE (by indirect calorimetry), fat mass and fat-free mass (by dual-energy X-ray absorptiometry), fasting serum dehydroepiandrosterone-sulfate (DHEAS), androstenedione, and estrone-sulfate (by radioimmunoassay). RESULTS: Serum concentrations of hormones correlated significantly with REE and TEE (r values range from 0.33 to 0.76, P<0.001). Only androstenedione correlated significantly with AEE (r = 0.23, P<0.05). However, these correlations were no longer significant after adjusting energy expenditure components for fat-free mass. In multiple regression models, ethnicity was not a significant determinant of any energy expenditure component after adjusting for body composition and hormone concentrations. CONCLUSION: Hormonal indices of maturation do not influence energy expenditure in this group of African American and Caucasian prepubertal children.

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 (approximately 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.

Effect of photoperiod, testosterone, and estradiol on body mass, bifid claw size, and pelage color in collared lemmings (Dicrostonyx groenlandicus).

Collared lemmings undergo several photoperiod-mediated seasonal physiological changes. When exposed to short photoperiod, lemmings increase in size, develop a bifid claw, and molt to a white pelage. Previous data indicate that body mass, claw size, and pelage color are influenced by hormones of testicular origin, suggesting that, on a seasonal basis, changes in production of, or sensitivity to, testicular hormones may play a role in the development of the phenotype characteristic of the ambient photoperiod. The present study was designed to determine if the active testicular hormone(s) is testosterone (T) and/or estradiol (E2) and if seasonally changing physiological traits in female lemmings are also influenced by gonadal status. Fifty-day-old lemmings, reared in 22L:2D (long day), 16L:8D (intermediate day), or 8L:16D (short day), were either gonadectomized or sham operated and given either empty Silastic implants or implants containing T (4 or 10 mm; castrated males), E2 (4 mm undiluted or diluted 1:4 with cholesterol; ovariectomized females), the aromatase inhibitor ATD (androsta-1,4,6-triene-3,17-dione; 2 x 20 mm; intact animals of both sexes), or ATD plus a 10-mm T implant (castrated males). After a 6-week treatment period, changes in body mass, bifid claw width, pelage color stage, and serum prolactin (PRL) were assessed. The effects of gonadectomy and steroid treatment depended upon photoperiod. Whereas gonadectomy increased mass gained by both sexes under intermediate and short day, under long day only females showed the positive mass response to gonadectomy. Treatment with T and E2 reversed the effect of gonadectomy on body mass under intermediate day and decreased the amount of mass gained under short day. Treatment with ATD (males) and E2 (females) indicated that E2 was the hormone responsible for the tonic, inhibitory effect of the gonads on body mass in both sexes. Claw size was most sensitive to steroid manipulation in animals housed in long day, in which all treatments had a negative influence. Gonadectomy under short day resulted in the development of a whiter pelage in both sexes. The effect of gonadectomy on pelage in female lemmings, and its reversal by E2 treatment, may have been partially due to alteration of serum PRL.