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.
