Although originally characterised as proteins involved in the control of reproductive function, activins, and to a lesser degree inhibins, are also important regulators of homeostasis in extragonadal tissues. Accordingly, disrupted inhibin/activin expression can have detrimental effects not only for fertility and fecundity, but also for the regulation of muscle, fat and bone mass. Indeed, only recently, two complementary mouse models of inhibin designed to lack bioactivity/responsiveness, revealed that inhibin A/B deficiency during pregnancy, restricts embryo and foetal survival. Conversely, hyper elevated levels of activin A/B, as are frequently observed in patients with advanced cancers, can not only promote gonadal tumour growth but also cancer-cachexia. As such, it is not surprising that inhibin/activin genetic variations or altered circulating levels have been linked to reproductive disorders and cancer. Whilst some of the detrimental health effects associated with disrupted inhibin/activin levels can be attributed to accompanied changes in circulating follicle stimulating hormone (FSH) levels, there is now abundant evidence that activins, in particular, have fundamental FSH-independent tissue homeostatic roles. Increased understanding of inhibin/activin activity, garnered over several decades, has enabled the development of targeted therapies with applications for both reproductive and extra-gonadal tissues. Inhibin- or activin-targeted technologies have been shown not just to enhance fertility and fecundity, but also to reduce disease severity in models of cancer cachexia. Excitingly, these technologies are likely to benefit human medicine and be highly valuable to animal breeding and veterinary programs.
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Adam Hagg, Eliza O'Shea, Craig A. Harrison, and Kelly Louise Walton
Yao Wang, Peter K Nicholls, Peter G Stanton, Craig A Harrison, Mai Sarraj, Robert B Gilchrist, Jock K Findlay, and Paul G Farnworth
Growth differentiation factor 9 (GDF9) produced within the ovary plays an essential role during follicle maturation through actions on granulosa cells, but extra-ovarian expression, signalling and actions of GDF9 are less well characterised. The present studies confirm GDF9 expression in the mouse testis, pituitary gland and adrenocortical cancer (AC) cells, and establish its expression in LβT2 gonadotrophs, and in mouse adrenal glands, particularly foetal and neonatal cortical cells. AC, LβT2, TM3 Leydig and TM4 Sertoli cells express the requisite GDF9 binding signalling components, particularly activin receptor-like kinase (ALK) 5 and the bone morphogenetic protein (BMP)/GDF type II receptor, BMPRII (BMPR2). We therefore compared GDF9 activation of these potential extra-ovarian target cell types with its activation of granulosa cells. Recombinant mouse GDF9 stimulated expression of activin/transforming growth factor-β-responsive reporters, pGRAS-luc or pAR3-lux, in TM4 and AC cells (IC50=145 ng/ml in the latter case), and two granulosa cell lines, KGN and COV434. The ALK4/5/7 inhibitor, SB431542, blocked GDF9 activity in each case. By contrast, GDF9 lacked specific effects on TM3 cells and rat primary pituitary and mouse LβT2 gonadotrophs. Our findings show that GDF9 regulates the expression of R-SMAD2/3-responsive reporter genes through ALK4, 5 or 7 in extra-ovarian (adrenocortical and Sertoli) cells with similar potency and signalling pathway to its actions on granulosa cells, but suggest that expression of BMPRII, ALK5 (TGFBR1) and R-SMADs 2 and 3 may not be sufficient for a cell to respond to GDF9.