Estrogen and glucocorticoid receptors in adult canine articular cartilage

Abstract

The cytoplasmic and crude nuclear fractions of adult mongrel dog articular cartilage contained estradi-01-and dexamethasone-binding components which had properties of physiologic steroid receptors. The equilibrium dissociation constants averaged 0.37 nM for estradiol and 2.27 nM for dexamethasone. The concentrations of estrogen receptors ranged from below 6 to 101 fmolhg protein in the cytosols and from below 2.8 to 17.5 fmol/pg DNA in the nuclear fractions. Glucocorticoid receptors were detected in only 4 of 13 cytosols (range: 61.2-132 fmolhg protein), whereas 10 of 13 nuclear fractions contained 0.8 to 46.8 femtomoles of the receptors for each microgram of DNA. There appeared to be no marked difference between the contents of either steroid receptor in female or male dog cartilage. No receptors were detected for androgen and progesterone.Cartilage has recently been found to bear cellular receptors for both insulin and glucocorticoids ( I ,2). Whether articular cartilage is a target organ for estrogen, which is known to increase the mechanical strength of the cartilage growth plate in rats (3). is not known. Studies in vivo have shown chondrocyte hypertrophy, decreased )'SO4 incorporation, and decreased turnover of proteoglycan in response to estrogen administration (4.5). The mechanism of estrogen's action on chondrocytes is unknown; blockade of somatomedin effects has been postulated as a mechanism (43). Srudies in vitro have yielded conflicting results about "SO4 uptake (4). We have previously demonstrated that changes of cartilage matrix in vitro. especially enhancement of hyaluronic acid synthesis, are mediated by the dibutyryl analog of cyclic adenosine monophosphate (6). A recent study of mouse skin revealed enhanced hyaluronic acid synthesis in response to estrogen: the response was proportional to the number of estrogen receptors present in the male mouse skin used (7).Other studies have revealed that testosterone and cortisol also affect cartilage in vivo by enhancing hyaluronic acid synthesis and depressing 35S04 incorporation in vivo. respectively; the mechanisms are under investigation (4). This study was designed to determine if receptors for estrogen, progestin. androgen, and cortisol exist in adult canine cartilage, and, if so, the relative number and cellular compartmentalization of those found. MATERIALS AND METHODSBuffers. Two buffers were used in this study. Buffer pH 7.6 at 4°C. 7.4 at 25°C. Buffer B was buffer A that contained 10% glycerol.Tissues. Cartilage was collected in iced buffer A from

Hormone receptors in the epiphysial cartilage

“…Unlike the articular cartilage which contains oestrogen (Rosner, Manni, Malemud et al 1982;Young & Stack, 1982) as well as glucocorticoid (Young & Stack, 1982) binding sites, the present study detected only the specific binding of dexamethasone but not oestrogen in epiphysial chondrocytes, indicating an indirect action of oestrogen on this tissue. The high affinity dexamethasone binding component has a dissociation constant and a displacement by steroids in a manner similar to that shown for cytosol binding sites in embryonic chick cartilage (Kd 7-4 nmol/1) (Lee, Hicks, Hughes et al 1978) and dog articular cartilage (Kd 1-3 nmol/1) (Young & Stack, 1982).…”

“…The high affinity dexamethasone binding component has a dissociation constant and a displacement by steroids in a manner similar to that shown for cytosol binding sites in embryonic chick cartilage (Kd 7-4 nmol/1) (Lee, Hicks, Hughes et al 1978) and dog articular cartilage (Kd 1-3 nmol/1) (Young & Stack, 1982). The level of receptor (1740 sites/cell) is low compared to rabbit articular chondrocytes monolayer (40000 sites/cell) (Blondelon, Adolphe, Zizine & Lechat, 1980).…”

Protective effect of androgens against inflammation induced cartilage degradation in male rodents.

“…To our knowledge only oestradiol receptors have been described in articular chondrocytes. '3 14 These receptors were found in small amounts but showed high affinity, which may justify saturation at physiological concentrations. It should also be noted that the lower concentrations used in our in vitro studies correspond approximately to physiological concentrations of free sex steroids, given that these hormones are bound to carrier proteins in excess of 90%.…”

Evidence for Receptors Specific for 17β-Estradiol and Testosterone in Chondrocyte Cultures

“…It was found that growth induced by sex hormones was not always associated with increases in serum GH or IGF-1.6.7 In addition, receptors for 17P-estradiol have been found in the epiphyses of mouse tibiae,sI cultured normal human osteoblast-like ~ells,l6~5* osteoblast-like osteosarcoma cells,23 and avian osteoclasts,53 as well as in fracture healing.54 Moreover, estradiol receptors have been found in articular cartilage. [55][56][57][58][59] Testosterone, which is the most abundant androgen, is metabolized in target tissues to dihydrotestosterone (DHT) or androstenedione by 5-alpha reductase before binding to its receptor. -3 This also appears to occur in chondrocytes from epiphyseal and articular cartilage.64.65 Recently, receptors for DHT were also found in osteoblasts24.66 and epiphyseal chondrocytes.38 However, some tissues do not have the appropriate enzymes to convert testosterone to DHT and testosterone functions dire~tly.57.…”