Sustained regulation of hypothalamus-pituitary-ovary hormones with tissue-engineered ovarian constructs as a treatment for osteoporosis in females

点击翻译按钮获取中文摘要

SUSTAINED REGULATION OF HYPOTHALAMUS-PITUITARY-OVARY HORMONES WITH TISSUE- ENGINEERED OVARIAN CONSTRUCTS AS A TREATMENT FOR OSTEOPOROSIS IN FEMALES PROJECT SUMMARY/ABSTRACT Females are disproportionately affected by osteoporosis and osteoporotic fracture. In the U.S., approximately 40 million women have or are at risk of developing osteoporosis and the majority (~ 60%) of the 2 million osteoporotic bone fractures (direct costs > $20 billion per year) occur in women. Women have a 1-in-2 lifetime chance of having an osteoporotic fracture and a 4-fold higher rate of osteoporosis than men. A key underlying cause is ovarian failure due to menopause or other conditions that lead to loss of ovarian hormones with concomitant disruption of the hypothalamus-ovary-pituitary (HPO) axis. Until 2002, traditional pharmacological hormone therapy (pHT) was widely used due to its perceived ability to reduce risk of osteoporosis and, importantly, osteoporotic fracture. The Women’s Health Initiative (WHI) verified this long-held belief, demonstrating that pHT reduced incidence of osteoporotic fracture. However, the WHI also indicated that the risks of hormone therapy, such as cardiovascular disease and certain types of cancer, outweighed the benefits of reduced levels of osteoporosis. Follow-on studies indicate that risks may be higher in women older than 60 years of age and/or more than 10 years post-menopause, suggesting that hormone therapy may still be effective if given at lower, safer doses and via suitable delivery platforms. We propose biomimetic, ovarian cell constructs as a tissue engineering approach to hormone delivery (cellular hormone therapy; cHT) in the treatment of osteoporosis. The hypothesis guiding this research is that cHT can achieve better bone health and safety outcomes than pharmacological agents, such as pHT or the bisphosphonates, in ovarian failure because it mimics native ovarian structure and function. Our cHT approach uses a spatial arrangement of two key ovarian cell types (granulosa and theca cells) that mimics native ovarian follicle structure while avoiding pitfalls of whole ovarian tissue encapsulation such as oocyte (egg) expulsion and loss of function with time. Our system has achieved sustained and physiologically- relevant levels of ovarian hormone secretion. We have demonstrated that the encapsulated ovarian cells participate in the HPO axis, as evidenced by regulation of follicle stimulating hormone (FSH) and luteinizing hormone (LH) levels from the anterior pituitary. There are fundamental differences between our cHT constructs and the native ovary (e.g., lack of oocytes in our constructs) but ovarian, pituitary, and possibly hypothalamic hormones are regulated in a manner similar to a pre-ovarian failure state. These cell-based constructs also release other hormones naturally secreted by native ovaries but not present in pHT. More importantly, cHT achieved beneficial bone outcomes in a manner that was safer than pHT. The long-term goal of this research is to develop a cell-based therapy that can be used in humans for the prevention of osteoporosis associated with loss of ovarian function in women. In our preliminary studies, we have assessed cHT by using isogeneic cells in a rat model. However, to achieve clinical translation it is necessary to (1) understand how the cHT dose and timing of implantation affects safety and bone health, (2) identify suitable human, allogeneic, and/or xenogeneic cell sources for cHT and (3) understand how cHT achieves its effects at both a cellular and systemic level. We will also determine the maximum duration of time that cHT can secrete ovarian hormones and regulate other hormones of the HPO axis. The proposed experiments will be conducted primarily in a rat surgical model of ovarian failure to induce osteoporosis (ovariectomy; ovx). However, as a first step towards clinical translation we also propose the use of a larger, rabbit model of ovarian failure and osteoporosis (ovx with glucocorticoid delivery). cHT will be directly compared to pHT and to alendronate, a bisphosphonate drug widely prescribed to treat osteoporosis. We will also compare cHT (and controls) to untreated ovx animals and to rats that have not received an ovx (healthy, age-matched rats). We will propose three experimental aims: Aim 1. Determine effect of isogeneic cHT dose and implant timing on HPO hormone levels, safety and bone health in rat ovx model. Aim 2. Assess HPO hormone levels, immune response, safety and bone health in two ovarian failure models of osteoporosis with isogeneic, allogeneic or human cHT treatment. Aim 3. Determine differential gene expression (DGE) profiles for isogeneic, allogeneic, and human cHT to identify key functional pathways and any time-dependent changes in vitro and in a rat ovx model. Completion of these studies will demonstrate the safety and efficacy of these tissue-engineered constructs as a potential treatment for osteoporosis and provide information on their mechanisms of action.