Yoshiko Onoe

Expression of Estrogen Receptor β in Rat Bone

A novel estrogen receptor, estrogen receptor beta (ERbeta), has recently been cloned from a rat prostate cDNA library. In bone, which is an important target tissue of estrogen, ER alpha has been reported to be present preferentially in osteoblasts, but the mechanism of action of estrogen in bone is still not known. In the present study, we examined expression of ERbeta mRNA in bone. Expression of ERbeta mRNA was evident in primary osteoblastic cells isolated from 1-day-old rat calvaria and rat osteosarcoma cells (ROS 17/2.8), and its level was higher than that of ER alpha mRNA. When osteoblastic cells were cultured for 28 days to induce differentiation into mature osteoblasts capable of forming bone nodules, ERbeta mRNA was constantly and highly expressed during the entire culture period. In contrast, the level of ER alpha mRNA was very low at the beginning of culture and it gradually increased during the differentiation of osteoblastic cells. Various tissues including bone were isolated from 8-week-old rats of both sexes, and total RNA was extracted to compare the tissue distribution of expression levels of ERbeta mRNA. In cancellous bone of the distal femoral metaphysis and lumbar vertebra, expression of ERbeta mRNA was obvious, and its level was equivalent to those in the uterus and testis, but lower than those in the ovary and prostate. The level of ERbeta mRNA in femoral cortical bone was lower than that in cancellous bone. There was no appreciable differences between female and male rats in the distribution and expression levels of ERbeta mRNA in bone. These results indicate that ERbeta mRNA is highly expressed in osteoblasts in rat bone, suggesting that there is a distinct mechanism of estrogen action mediated by ERbeta in bone.

Estrogen deficiency stimulates B lymphopoiesis in mouse bone marrow.

We have found that an estrogen deficiency causes a marked increase in bone marrow cells. To examine the effect of estrogen on hemopoiesis, we characterized the increased population of bone marrow cells after ovariectomy (OVX). In OVX mice, the percentage of myeloid cells and granulocytes was decreased, whereas that of B220-positive B lymphocytes was selectively increased 2-4 wk after surgery. The total number of myeloid cells and granulocytes did not change appreciably, but that of B220-positive cells was greatly increased by OVX. When OVX mice were treated with estrogen, the increased B lymphopoiesis returned to normal. B220-positive cells were classified into two subpopulations, B220low and B220high. The majority of the B220low cells were negative for the IgM mu chain, whereas most of the B220high cells were mu-positive. OVX selectively increased the precursors of B lymphocytes identified by B220low. mu-negative phenotype, suggesting that an estrogen deficiency stimulates accumulation of B lymphocyte precursors. When bone marrow-derived stromal cells (ST2) were pretreated with estrogen then co-cultured with bone marrow cells in the presence of estrogen, the stromal cell-dependent B lymphopoiesis was greatly inhibited. The present study suggests that estrogen plays an important role in the regulation of B lymphocyte development in mouse bone marrow.

Comparative Effects of Estrogen and Raloxifene on B Lymphopoiesis and Bone Loss Induced by Sex Steroid Deficiency in Mice

Estrogen deficiency caused by ovariectomy (OVX) results in a marked bone loss because of stimulated bone resorption. We have reported that OVX selectively stimulates B lymphopoiesis in mouse bone marrow, which is somehow related to bone resorption. Estrogen prevents both the increased B lymphopoiesis and the bone resorption caused by estrogen deficiency. Raloxifene also has a potent estrogenic activity for bone with minimal estrogenic activity for the uterus. To examine the effects of raloxifene on B lymphopoiesis and bone resorption, OVX mice were given either estrogen or raloxifene subcutaneously for 2–4 weeks using a miniosmotic pump. Reduced uterine weight in OVX mice was restored completely by 17β‐estradiol (E2). Some 300‐fold higher doses of raloxifene increased uterine weight of OVX mice, but only slightly. The number of B220‐ positive pre‐B cells was increased markedly in bone marrow after OVX. The increased B lymphopoiesis was prevented not only by E2 but by raloxifene. In OVX mice, the trabecular bone volume (BV) of the femoral distal metaphysis was reduced markedly, when measured by microcomputed tomography (μCT) scanning and dual‐energy X‐ray absorptiometry. Both E2 and raloxifene similarly restored it. Like estrogen deficiency, androgen deficiency induced by orchidectomy (ORX) also resulted in a marked bone loss and increased B lymphopoiesis. Both E2 and raloxifene prevented the changes in ORX mice. These results indicate that both estrogen deficiency and androgen deficiency similarly stimulate B lymphopoiesis in mouse bone marrow, which accompany bone loss. Raloxifene exhibits estrogenic actions in bone and bone marrow to prevent bone loss and regulate B lymphopoiesis without inducing estrogenic action in the uterus.

Effect of physical activity and nutrition on bone mineral density in young Japanese women

We explored factors that contributed to bone mineral density (BMD) in Japanese young women by quantifying the factors related to BMD. Between October 2003 and February 2004, we conducted a cross-sectional survey to study the status of nutritional intake and physical activity, and evaluated the various physical and serum parameters in relation to BMD. Subjects included 254 healthy female students who were 19–25 years old and were attending the Nursing School of Tokyo Womens Medical University, Japan. We measured the lumbar BMD (L2–L4) in these women. Multiple regression analysis was used to predict factors that contributed to current L2–L4 BMD. Our results showed that body mass index (BMI) (standardized regression coefficient = 0.45, P < 0.0001), past exercise habit (standardized regression coefficient = 0.15, P < 0.0059), and current total energy expenditure (standardized regression coefficient = 0.12, P < 0.03) were factors that significantly predicted the current L2–L4 BMD, with BMI as a key contributing factor. A BMI of 20.8 kg/m2 allowed acquisition of young adult mean (YAM) irrespective of the total energy expenditure. In subjects with low BMI, L2–L4 BMD increased with higher current energy expenditure. A BMI of 20.8 kg/m2 or greater and an energy expenditure of 32.9 METS-h/day or greater are required to acquire the YAM. We concluded that BMI and physical activity were factors that affected the BMD of Japanese young women.

Variations in Circulating Osteoprotegerin and Soluble RANKL during Diurnal and Menstrual Cycles in Young Women

Background/Aims:Physiological bone turnover shows diurnal variations and changes within the menstrual cycle. The aim of this study was to assess the variability of osteoprotegerin (OPG) and soluble RANKL (sRANKL) serum levels during diurnal and menstrual cycles. Method: Blood was collected from 15 young women at 6-hour intervals between 08.00 and 20.00 h during the follicular phase. Moreover, to compare the follicular and luteal phases, blood was also collected at 14.00 h during the luteal phase. Serum bone-specific alkaline phosphatase (BAP), N-telopeptide of type I collagen (NTX), OPG and free sRANKL were measured. Results: No diurnal variations in BAP, OPG, sRANKL and sRANKL/OPG ratio were detected. NTX was significantly higher in the morning than in the afternoon and at night (p = 0.02). There were no menstrual variations in either. Conclusions: The consistent absence of diurnal variations in circulating OPG and sRANKL levels may reflect the absence of diurnal variation in their expression in the bone microenvironment. In this case, the nocturnal rise and the fall in bone resorption in the luteal phase should be accounted for by other factors than RANKL/OPG-mediated factors. Timing of sampling is unlikely to influence the results of circulating OPG and sRANKL measurement.

Relationship between skipping breakfast and bone mineral density in young Japanese women.

UNLABELLED BACK GROUND AND AIMS: It is well known that insufficient nutrient intake leads to poor bone status. To find a simple evaluation method for prevention of nutrition intake disorder, a cross-sectional study with 275 healthy Japanese female students aged 19-25 was conducted. METHODS Anthropometric parameters, bone mineral density (BMD) at lumbar and total hip, bone metabolic markers and physical activity were measured in study participants and the frequency of skipping meals (breakfast, lunch, supper), and absolute values for nutrient intakes were assessed using a Diet History Questionnaire. RESULTS The frequency of skipping breakfast significantly correlate to total energy intake (ρ= -0.276, p<0.001). BMI, total intake of energy, intake of protein, intake of phosphate, and energy expenditure positively correlated significantly to BMD at lumbar and total hip (p<0.05) using simple linear regression. BMI (regression coefficient (b))=0.088, p<0.001), bone alkaline phosphatase (b= -0.050, p=0.012), total energy expenditure (b=0.019, p<0.001), and frequency of skipping breakfast (b= -0.018, p=0.048) were independent risk factors for lower total hip BMD by multiple regression analysis. The total hip BMD in participants who skipped breakfast three or more times was significantly lower than in those who did not skip breakfast (p=0.007). CONCLUSIONS In conclusion, managing the frequency of skipping breakfast and reducing it to <3 times per week may be beneficial for the maintenance of bone health in younger women.

Possible risk factor for postmenopausal women: postprandial hypertriglyceridemia.

Aim:  To explore the clinical implications of postprandial hypertriglyceridemia in postmenopausal Japanese women.