Se Hwa Kim

Peripheral Effect of α-Melanocyte-stimulating Hormone on Fatty Acid Oxidation in Skeletal Muscle

To study the peripheral effects of melanocortin on fuel homeostasis in skeletal muscle, we assessed palmitate oxidation and AMP kinase activity in α-melanocyte-stimulating hormone (α-MSH)-treated muscle cells. After α-MSH treatment, carnitine palmitoyltransferase-1 and fatty acid oxidation (FAO) increased in a dose-dependent manner. A strong melanocortin agonist, NDP-MSH, also stimulated FAO in primary culture muscle cells and C2C12 cells. However, [Glu6]α-MSH-ND, which has ample MC4R and MC3R agonistic activity, stimulated FAO only at high concentrations (10–5 m). JKC-363, a selective MC4R antagonist, did not suppress α-MSH-induced FAO. Meanwhile, SHU9119, which has both antagonistic activity on MC3R and MC4R and agonistic activity on both MC1R and MC5R, increased the effect of α-MSH on FAO in both C2C12 and primary muscle cells. Small interference RNA against MC5R suppressed the α-MSH-induced FAO effectively. cAMP analogues mimicked the effect of α-MSH on FAO, and the effects of both α-MSH and cAMP analogue-mediated FAO were antagonized by a protein kinase A inhibitor (H89) and a cAMP antagonist ((Rp)-cAMP). Acetyl-CoA carboxylase activity was suppressed by α-MSH and cAMP analogues by phosphorylation through AMP-activated protein kinase activation in C2C12 cells. Taken together, these results suggest that α-MSH increases FAO in skeletal muscle, in which MC5R may play a major role. Furthermore, these results suggest that α-MSH-induced FAO involves cAMP-protein kinase A-mediated AMP-activated protein kinase activation.

The forkhead transcription factor Foxc2 stimulates osteoblast differentiation

The forkhead box C2 (Foxc2) protein is a member of the family of winged helix/forkhead transcription factors. Foxc2-deficient mice display defective formation of the aortic arches, multiple craniofacial bones, and vertebral columns. To investigate the role of Foxc2 in osteoblast differentiation, DNA containing Foxc2 was transfected into the developing cranial suture mesenchymal cells by electroporation. Compared to the controls, alkaline phosphatase (ALP) and bone sialoprotein were expressed strongly in suture mesenchymal cells in the Foxc2 overexpressed calvaria. After Foxc2-siRNA transfection, ALP staining was rarely observed in the suture mesenchyme and adjacent parietal bone of the calvaria. Meanwhile, overexpression of Foxc2 increased protein levels of beta-catenin and stimulated TCF/LEF transcriptional activity. The protein kinase A inhibitor H-89 suppressed Foxc2-mediated increases in TCF/LEF transcriptional activity (-40%, P<0.01). In conclusion, our results demonstrated that Foxc2 stimulated osteoblast differentiation of mesenchymal cells and preosteoblasts. Activation of canonical Wnt-beta-catenin signals might be involved in the Foxc2-mediated stimulation of osteoblast differentiation.

The forkhead transcription factor Foxc2 promotes osteoblastogenesis via up-regulation of integrin β1 expression

The forkhead box C2 (Foxc2) protein, a member of the forkhead/winged helix transcription factor family, plays an important role in regulation of metabolism, arterial specification, and vascular sprouting. Foxc2-null mutants die prenatally or perinatally, and they exhibit hypoplasia of the vertebrae and insufficient chondrification or ossification of medial structures. However, the role of Foxc2 in osteoblastogenesis is not yet fully understood. According to the degree of differentiation of osteoblasts, we found that Foxc2 expression was gradually increased and dose-dependently up-regulated by well-known bone anabolic agents, such as hPTH(1-34) and BMP2. In ex vivo mouse calvarial organ culture, a significant reduction of the basal expression of Foxc2 induced by siFoxc2 remarkably suppressed cell proliferation and differentiation and induced cell death. Knockdown of Foxc2 expression using siFoxc2 in both MC3T3-E1 and primary mouse calvarial cells also resulted in a significant suppression of proliferation and differentiation, and induced cell death, supporting the ex vivo observations. In addition, the resistance to apoptosis induced by serum deprivation and phosphorylation of both Akt and ERK was significantly reduced after siFoxc2 treatment. Conversely, overexpression of Foxc2 increased the proliferation of MC3T3-E1 and primary mouse calvarial cells. Furthermore, we found that Foxc2 enhanced the expression of integrin β1, an important modulator of osteoblastogenesis, by direct binding to a Forkhead-binding element in its promoter. Taken together, these results indicate that Foxc2 plays an important role in osteoblastogenesis by promoting osteoblast proliferation, survival and differentiation through up-regulation of integrin β1 in response to stimuli which induce bone formation.

The adaptation and relationship of FGF-23 to changes in mineral metabolism in Graves' disease.

Objective  The aim of this study was to observe the changes in bone and mineral metabolism and to confirm the regulation of fibroblast growth factor‐23 (FGF‐23) in untreated Graves’ disease.

Modifications of T-scores by quantitative ultrasonography for the diagnosis of osteoporosis in koreans.

To identify a proper T-score threshold for the diagnosis of osteoporosis in Koreans using quantitative ultrasonography (QUS), normative data from 240 females and 238 males (ages 20-29 yr) were newly generated. Then, the osteoporosis prevalence estimate for men and women over 50 yr of age was analyzed using previous World Health Organization (WHO) methods and heel QUS. T-scores were calculated from the normative data. There were definite negative correlations between age and all of the QUS parameters, such as speed of sound (SOS), broadband ultrasound attenuation (BUA), and estimated heel bone mineral density (BMD) (p<0.0001). After applying the recently determined prevalence of incident vertebral fracture in Koreans over 50 yr of age (11.6% and 9.1%, female vs male, respectively) to the diagnosis of osteoporosis by T-scores from heel BMD as measured by QUS, it was revealed that applicable T-scores for women and men were -2.25 and -1.85, respectively. These data suggest that simply using a T-score of -2.5, the classical WHO threshold for osteoporosis, underestimates the true prevalence when using peripheral QUS. Further prospective study of the power of QUS in predicting the absolute risk of fracture is needed.

Increased sclerostin levels after further ablation of remnant estrogen by aromatase inhibitors.

Background Sclerostin is a secreted Wnt inhibitor produced almost exclusively by osteocytes, which inhibits bone formation. Aromatase inhibitors (AIs), which reduce the conversion of steroids to estrogen, are used to treat endocrine-responsive breast cancer. As AIs lower estrogen levels, they increase bone turnover and lower bone mass. We analyzed changes in serum sclerostin levels in Korean women with breast cancer who were treated with an AI. Methods We included postmenopausal women with endocrine-responsive breast cancer (n=90; mean age, 57.7 years) treated with an AI, and compared them to healthy premenopausal women (n=36; mean age, 28.0 years). The subjects were randomly assigned to take either 5 mg alendronate with 0.5 µg calcitriol (n=46), or placebo (n=44) for 6 months. Results Postmenopausal women with breast cancer had significantly higher sclerostin levels compared to those in premenopausal women (27.8±13.6 pmol/L vs. 23.1±4.8 pmol/L, P<0.05). Baseline sclerostin levels positively correlated with either lumbar spine or total hip bone mineral density only in postmenopausal women (r=0.218 and r=0.233; P<0.05, respectively). Serum sclerostin levels increased by 39.9%±10.2% 6 months after AI use in postmenopausal women; however, no difference was observed between the alendronate and placebo groups (39.9%±10.2% vs. 55.9%±9.13%, P>0.05). Conclusion Serum sclerostin levels increased with absolute deficiency of residual estrogens in postmenopausal women with endocrine-responsive breast cancer who underwent AI therapy with concurrent bone loss.

Association Between Body Mass Index and the Risk of Hip Fracture by Sex and Age: A Prospective Cohort Study: BODY MASS INDEX AND HIP FRACTURE

The association between body mass index (BMI) and hip fracture may differ by ethnic group. We examined the association between BMI and hip fracture according to sex and age and to identify BMI ranges associated with the lowest risk in Korean men and women. We followed up 288,068 Korean adults (aged 50 to 80 years), who underwent health examinations in 2002–03 to 2013; we examined national hospital discharge records. Hazard ratios (HRs) were calculated using Cox proportional hazard models after adjusting for confounders. During a mean follow‐up period of 10.5 years, 1502 men and 2432 women suffered a hip fracture. Nonlinear associations were observed between BMI and hip fracture: a U‐curve for women and a reverse J‐curve for men. Men with BMIs of 27.5 to 29.9 kg/m2 and women with BMIs of 25 to 27.4 kg/m2 showed the lowest incidence of hip fracture. The multivariate‐adjusted HRs for hip fracture per 5 kg/m2 decrease in BMI were 2.09 (95% confidence interval [CI] 1.83–2.38) and 1.34 (95% CI 1.19–1.51) in men and women with BMI <25 kg/m2. The HRs were generally highest in the age group of 50 to 59 years (HR = 3.42 in men and 2.27 in women) and thereafter decreased with age. Among participants with BMI ≥25 kg/m2, the HRs for hip fracture per 5 kg/m2 increase in BMI were 1.26 (95% CI 1.08–1.47) in women and 0.91 (95% CI 0.62–1.33) in men. In conclusion, the overweight range of BMI was associated with the lowest risk of hip fracture. Lower BMI was a risk factor for hip fracture, whereas obesity was associated with an increased risk of hip fracture, particularly in women. Overweight may be protective against hip fracture in Asian adults but not obesity.