Astrocytes are known to provide support to gonadotropin releasing hormone (GnRH) neurons that control
the reproductive axis, for example by releasing prostaglandin E2 (PGE2) required for fertility. Astrocytes may
also play a critical role in the brain as metabolic sensors. In response to insulin, astrocytes increase glucose
uptake across the blood brain barrier and release metabolites and gliotransmitters to support neuronal
function. We have recently demonstrated a unique biological role for astrocytes in coupling fertility to energy
availability. We found that the absence of insulin signaling in astrocytes delays puberty, causes
hypogonadotropic hypogonadism, and dramatically reduces fertility. This finding is particularly exciting since
numerous studies have shown neuronal insulin sensing is unnecessary for reproduction. We have also found
that loss of astrocyte insulin sensing reduces PGE2 synthase levels, leading us to hypothesize that astrocyte
insulin sensing facilitates GnRH release by promoting astrocyte PGE2 release. New preliminary data suggest
that insulin signaling via FOXO pathways alter the transcription of enzymes in the PGE2 biosynthesis pathway,
such as COX-2. We will test our hypothesis by pursuing three specific aims. Aim 1) Define the relevant
temporal & spatial parameters of astrocyte insulin signaling. Using the tet-on genetic targeting system, we will
test whether astrocytes must sense insulin during adulthood or prior to puberty in order to permit normal
reproductive function. Astrocyte-specific viral cre administration will also determine the importance of
astrocyte insulin sensing in the arcuate nucleus and the rostral preoptic area. Aim 2) Determine the impact of
insulin signaling on astrocyte PGE2 gliotransmitter production proximal to reproductive circuits.
Measurement of regional PGE2 production will be complemented by AAV targeted disruption of Cox-2
production by astrocytes to determine its importance for fertility. Finally, we will determine whether Kiss1
neurons sense PGE2, leading to altered GnRH release. Aim 3) Determine the molecular role of the insulin/
FOXO pathway in astrocyte PGE2 synthesis. An astrocyte cell line will be used to systematically investigate the
major aspects of insulin/FOXO/COX signaling, including phosphorylation, localization, promoter occupancy,
and quantitative transcriptional activity measurements. Finally, we will ablate insulin signaling pathways in
astrocytes to determine their effect on fertility and PGE2 production. Collectively, these studies will identify
how insulin signaling in astrocytes sustains reproductive circuit function. This work will elucidate what may be
the dominant mechanism in the mammalian brain whereby insulin permits normal fertility and pubertal
maturation. Our results will advance our long-term goal of finding treatment targets for impaired fertility in
patients recovering from energy deficits, obese and diabetic populations, and others with idiopathic
hypogonadotropic hypogonadism.
