Project Summary/Abstract
Glaucoma is the leading cause of irreversible blindness and is projected to affect 112 million people worldwide
by 2040. Women represent 59% of the glaucoma population, highlighting the need to understand sex-specific
risk factors for glaucoma. In addition, altered estrogen levels, signaling, or metabolism play a role in glaucoma
in both sexes. In women, estrogen receptor polymorphisms are associated with ocular hypertension (an
important causal risk factor for glaucoma). Moreover, post-menopausal women have a 1-3 mmHg higher
intraocular pressure (IOP) than pre-menopausal women, while hormone therapy containing estrogen reduces
IOP. These data suggest that menopause and estrogen levels influence IOP, but the mechanism is unknown.
IOP is affected by many factors, but aqueous outflow resistance is the key determinant, which in turn is primarily
controlled by trabecular meshwork (TM) function. Intriguingly, outflow resistance correlates with TM stiffness,
and it is known that menopause and estrogen levels affect stiffness of many tissues outside the eye, suggesting
a possible mechanism by which altered estrogen levels affect IOP. Menopause also alters gene expression, with
many genes affected by menopause known to influence aqueous outflow resistance. Thus, it is hypothesized
that menopause increases aqueous outflow resistance by stiffening the TM, thus increasing a woman’s
risk of developing glaucoma, and that these effects are mediated by altered gene expression profiles in
the aqueous outflow pathway. This proposal addresses the hypothesis in an animal model of menopause as
follows: Aim 1 will measure IOP and aqueous outflow resistance. Aim 2 will measure TM stiffness using Atomic
Force Microscopy. Aim 3 will assess gene expression in aqueous outflow pathway tissues using RNAseq.
This proposal achieves these aims using several approaches: (A) It employs a well-established model of
menopause, ovariectomy (OVX), in female Brown Norway rats (9-10 months of age); and (B) It will determine if
topical estrogen therapy mitigates the effects of OVX. This proposal will also investigate whether topical estrogen
therapy affects IOP and aqueous outflow resistance in male rats (9-10 months of age), with an eye towards
eventual clinical translation. In all animals, IOP will be measured using rebound tonometry for 8 weeks, followed
by measurement of outflow resistance (via iPerfusion) and TM stiffness (via atomic force microscopy) in one
eye. Contralateral eyes will be used to assess: (1) estrogen levels, (2) TM structure and composition, or (3) gene
expression. Preliminary data support this hypothesis, showing that IOP and aqueous outflow resistance are
increased by OVX. This proposal will build on these data and expects to demonstrate that menopause increases
TM stiffness and alters gene expression in aqueous outflow pathway tissues, and that topical estrogen therapy
prevents these changes. These findings will provide functional and mechanistic insight into the association
between menopause and glaucoma, and the benefits of topical estrogen therapy as a treatment for glaucoma.