Evidence for cell‐specific changes with age in expression of oestrogen receptor (ER) α and β in bone fractures from men and women

Abstract

Oestrogen is recognized as important for maintaining bone mass in men and women. Oestrogen receptor (ER) alpha and the recently described ER-beta are both expressed in bone cells, but have different affinities for oestrogen agonists and plant oestrogens, which could be important in developing treatments for bone loss in both men and women. It is unclear, however, which isoform predominates in bone; cell type and age may influence their relative expression. The present study has compared ER-alpha and ER-beta expression in serial sections of human fracture callus from males (n = 19, age range 5-72 years) and females (n = 15, age range 3-86 years) by indirect immunoperoxidase. Fracture callus was used as it can be readily obtained from individuals over a wide age range and contains a variety of bone cells. Antibody specificity was confirmed by western blotting and comparison of immunoreactivity in sections of breast tumour and benign prostate hyperplasia. No gender difference in ER expression was found in bone from individuals less than 40 years old. Proliferative chondrocytes were positive for both isoforms, but few larger hypertrophic cells were immunoreactive. ER-alpha and ER-beta were co-expressed in osteoclasts, suggesting that oestrogen may act directly on these cells. Osteoblasts, osteocytes, and mesenchymal cells also expressed both isoforms. In women over 40 years of age, however, relatively fewer biopsies contained osteocytes positive for ER-alpha and ER-beta. Likewise, the proportions of osteoblasts and mesenchymal cells expressing ER-beta were reduced but ER-alpha remained unaffected. In contrast, in men over 40 years, only the proportion of biopsies containing ER-beta-positive mesenchymal cells was lower. In these older men and women, ER-alpha and ER-beta expression was retained by the small proliferative chondrocytes. These results demonstrate that gender, age, and cell type are important determinants of ER isoform expression in skeletal cells.

The aromatase inhibitor letrozole increases epiphyseal growth plate height and tibial length in peripubertal male mice

“…Prompted by studies indicating a direct regulatory role of androgens and estrogens in the growth plate (Lubahn et al 1993, Kusek et al 1998, Kennedy et al 1999, Nilsson et al 1999, Braidman et al 2001, Van der Eerden et al 2002a, Batra et al 2003), we investigated the effect of the highly selective nonsteroidal aromatase inhibitor, letrozole, on growth in peripubertal male mice. To prove that letrozole inhibits aromatase activity, we first examined its effect on granulosa cells from ovaries of female mice.…”

Morphology, mechanisms and pathology of musculoskeletal ageing

“…In addition to a fall in oestrogen levels with age, osteocytes and osteoblasts become less responsive to oestrogen in men and women due to decreased oestrogen receptor synthesis initiated at the RNA level [48,49]. Thus, there is accumulating evidence that reduced oestrogen bioavailability explains the osteopenia and poor fracture healing that accompanies ageing in both men and women [50].…”

Runx2 Integrates Estrogen Activity in Osteoblasts

“…1B). Therefore, these easily obtained and well characterized osteoblast cultures can be made estrogen responsive in vitro, replicating the hormone-sensitive status of osteoblasts that occur in more mature organisms in vivo (43)(44)(45)(46). Importantly, this osteoblast cell culture model provides a sensitive system to examine specific aspects of ER␣ on osteoblast activity uncomplicated by the presence of endogenous ERs.…”

“…We chose to avoid possible complications from antibiotic toxicity, unknown effects from stable gene integration, and phenotypic drift by cells in continuous culture with our approach. Even so, it is difficult to know how the level of ER␣ expression in any transfected cell model compares with that in adult bone because, even in vivo, levels of ER␣ vary considerably with age and with anatomical bone location (43)(44)(45)(46). However, expression of ER␣ by transient gene transfection seemed appropriate and predictable, because the ability of estrogen to driven reporter gene expression by ERE was steroid- FIG.…”