Role of T-cells in Post-Menopausal Osteoporosis

Estrogen (E) deficiency is a major cause of post-menopausal osteoporosis. The mechanisms by
which E deficiency causes osteoporosis has been recently linked to regulation of two key
osteoclastic cytokines: RANKL and TNFα (TNF) , , produced by the T-cell in the bone
micro-environment. TNF is a cytokine that has long been associated with bone destruction
during E deficiency in both animal and human models. However, the cellular sources of TNF
and its exact mechanism of action are poorly understood. Previous studies in animal models
has demonstrated that in marked contrast to responses in wild type (WT) mice, ovariectomy
(ovx) failed to induce bone loss and did not stimulate osteoclast (OC) formation in T-cell
deficient mice. This phenomenon is reversed by T cell reconstitution with WT T cells but
not with T cells from TNF -/- mice2,4. These findings established T-cells and T-cell
produced TNF as essential mediators of the bone-wasting effects of E deficiency in vivo.
TNF further enhances OC formation by up regulating the stromal cell production of RANKL and
M-CSF and by augmenting the responsiveness of OC precursors to RANKL4. The mechanisms by
which E deficiency leads to enhanced levels of T-cell derived TNF involve a realignment of
the adaptive immune response that ultimately leads to an expansion in the pool of TNF
secreting T-cells. Dr. Pacifici's group showed that these pathways in mouse models involve
the up-regulation of antigen presentation by macrophages and dendritic cells, leading to T
cell activation and peripheral expansion of TNF producing T cells. They also showed that E
deficiency causes a rebound in thymic T cell output that contributes to both the T cell
expansion and the bone loss induced by ovx in young adult mice .

The objective of this study is to translate these critical findings in the mouse for the
first time to E deficient women following ovx. If this work defines an important role for
T-cells in E deficiency-induced bone loss, this could stimulate the development of novel
therapies designed to block T-cell expansion or their contribution to cytokine production
and thus prevent or attenuate bone loss in this common clinical setting. The hypothesis of
the research plan is that T-cells derived from women, rendered E deficient after undergoing
ovx, exhibit: 1) increased T-cell activation, and proliferation; 2) enhanced production of
pro-osteoclastogenic cytokines RANKL and TNF; and 3) demonstrate increased T-cell output
from the thymus that together cause bone loss.

Inclusion Criteria:

- Women between the age of 18-55, pre-menopausal by history (regular spontaneous
menstrual bleeding every 21-35 days) or documented FSH <10, no current estrogen
therapy, undergoing hysterectomy with (ovx) or without ovariectomy (control group)
for benign gynecologic disease (fibroid uterus, endometriosis, dysfunctional uterine
bleeding, chronic pelvic pain) or for prophylaxis against ovarian cancer (BRCA
positive).

Exclusion Criteria:

- History of an active cancer including breast and uterine cancer, treatment with
chemotherapy or glucocorticoids

- History of an immune deficiency syndrome including HIV infection

- History of severe anemia with hematocrit < 25.