[Truncated abstract] Steroid receptors belong to the superfamily of nuclear receptors, and include the androgen receptor (AR), estrogen receptors (ER[alpha] and ER[beta], glucocorticoid receptor (GR), mineralocorticoid receptor (MR), and the progesterone receptors (PRA and PRB). Before binding ligand, the receptor undergoes biochemical and structural modifications through a series of interactions with molecular chaperones and cochaperones all within a receptor heterocomplex. The mature receptor complexes with the major chaperone Hsp90, the stabilising cochaperone p23, and one member of a group of cochaperones termed immunophilins. Steroid receptor-associated immunophilins include the cyclophilin, CyP40, two FK506-binding proteins, FKBP51 and FKBP52, and the protein phosphatase, PP5. Immunophilins are characterised by the presence of TPR domains which compete directly for the TPR-acceptor site within Hsp90. This leads to mutually exclusive, immunophilin-containing receptor complexes. While PP5 contains a C-terminal phosphatase domain, CyP40, FKBP51 and FKBP52 each contain an N-terminal peptidyl prolyl isomerase (PPIase) domain, which catalyses the cis/trans isomerisation of prolyl peptide bonds. FKBP52 has been demonstrated to potentiate the ligand-dependent activity of AR, GR and PR, but not ER[alpha]. Knowing that CyP40 is the preferred immunophilin associated with the ER[alpha] heterocomplex, it was hypothesised that this immunophilin plays a role in ER[alpha] function. ... As all mutants maintained this potentiating activity it was concluded that the five altered residues found within gpGR do not contribute to the altered interaction of FKBP52 and receptor. However, it cannot be discounted that FKBP51 is more competitive for gpGR. Immunophilins are hormonally regulated, with FKBP52 found to be essential for female fertility in mice. It was hypothesised that levels of immunophilins, associated with steroid receptors important in the menstrual cycle, would be regulated to reflect hormonal activity within cycling endometrium. Human pre-menopausal endometrial sections taken from different phases of the menstrual cycle were examined immunohistochemically for expression of CyP40, FKBP51, FKBP51 and PP5. Immunophilin levels peaked at the mid-secretory phase correlating with stromal decidualization, a process essential for eventual blastocyst implantation. The importance of immunophilins to steroid receptor action was therefore reinforced by the observation that immunophilins appear to be hormonally regulated in cycling pre-menopausal human endometrium. Further studies into the effects of immunophilin loss and knockdown on steroid receptor-mediated responses in specific mouse tissues, knockout-derived mouse embryo fibroblasts and cancer cell lines may contribute to our understanding of the receptor-selective and tissue-specific actions of the immunophilins. Elucidation of the mechanisms through which they modulate receptor function may provide opportunities for therapeutic intervention in steroid-related disease.

Understanding and studying the normal bone growth and development is causal. Bone and cartilage tissue provide in addition to their mechanical support, they provide a protection for vital organs such as heart, lung and brain. Longitudinal growth is regulated by the activity of chondrocytes in the epiphyseal growth plates of long bones. Many hormones and growth factors are involved in the regulation of this process. Among these, sex steroids are of crucial importance, especially during puberty. In long bones, endochondral bone formation occurs at the growth plate, a region of developing cartilage located between the epiphysis and the metaphysic. The process of endochondral ossification is regulated in part by sex steroid hormones. Androgens stimulate endochondral bone growth and elongation, while estrogen is known to suppress longitudinal bone growth and accelerate growth plate closure. Studies using rat costochondral growth plate chondrocytes as a model show that the effects of 17β-estradiol (E₂) on apoptosis are found in both male and female cells and the same mechanism is involved. In contrast, E₂ causes rapid activation of PKC in female cells but not in male cells. Dihydroxytestosterone (DHT) also has direct effects on growth plate chondrocytes, increasing matrix synthesis including sulfated glycosaminoglycan production, and enhancing cell maturation by increasing alkaline phosphatase enzymatic activity. Short stature and abnormally slow increase in height is one of the main reasons for referral to endocrinologist. Excessive growth and abnormally tall is also a problem, especially because it increase risk for the trunk abnormalities. Furthermore until now a few growth-promoting therapies are available for clinical use. Therefore future therapies for treating the growth disorders are essential. The overall goal of this project is to investigate the sexual-dimorphic effect of the sex steroid hormone in rat growth plate chondrocytes, the cellular signaling pathways mediating these actions, and their physiological role. The information gleaned from this study will provide new information about the role of sex steroid hormones in chondrogenesis and has implications in the development of new therapies for the treatment of bone fracture healing, and growth plate disorders. The central hypothesis was that sex steroid would play an important and sex-specific role in regulating chondrocytes as a main regulator of longitudinal bone growth.