SUN-466 Gestational Diabetes Alters Hypothalamic Development, Microglial Activation, and Insulin Signaling in Offspring

Gestational diabetes mellitus (GDM) is characterized by maternal insulin resistance during pregnancy, leading to high blood glucose levels. Offspring of a GDM pregnancy often have high birth weight that continues through life. GDM influence on developing hypothalamic tanycytes may underlie this outcome. Tanycytes line the third ventricle and project into the median eminence (ME). They are a major component of hypothalamic nutrient sensing, particularly of glucose. Tanycytes are also capable of giving rise to hypothalamic neurons that regulate energy homeostasis and are known to proliferate postnatally in response to diet. We hypothesized that GDM would lead to changes in the tanycyte and ME cell populations of offspring. To study this, we utilized a leptin receptor mutant mouse model, Lepr (+/db), that develops GDM during pregnancy. We looked at three potential mechanisms by which GDM could affect the hypothalamus: tanycyte proliferation, insulin signaling, and microglial activation. First, to examine proliferation, we injected wildtype and Lepr (+/db) dams with BrdU on embryonic days 16.5, 17.5, and 18.5, corresponding with the onset of GDM. Cells immunopositive for BrdU on the day of birth are either minimally proliferating at the time of injection or newly born afterward. We observed significantly fewer positive cells in the α and β1 tanycyte region and in the ME of GDM offspring compared to controls. Fewer cells proliferating in these regions could hinder adaptability to changing metabolic needs. Second, we examined the impact of maternal GDM on insulin signaling in offspring after birth. Brain slices from P9 control and GDM offspring were incubated with vehicle or insulin and immunostained for phospho-AKT (pAKT). While insulin exposure induced pAKT similarly in all offspring, basal pAKT was significantly higher in GDM offspring than controls. pAKT was confined to tanycytes and their projections within the ME. This suggests that GDM offspring have hyperactive insulin signaling when nutrient conditions do not warrant it, particularly in nutrient-sensing tanycytes. Third, we examined microglial activation since GDM causes systemic inflammation in the mothers, and hypothalamic microglia, the brain’s resident immune system, have been shown to play an important role in the development of obesity. We immunostained for Iba-1 in offspring from control and GDM dams on P0 to assess the number and activity state of microglial cells. Compared to offspring of control mothers, offspring born to GDM mothers have more active microglia near α and β1 tanycytes and in the ME. Since microglial activation induced by overnutrition is linked to obesity in adults, a similar mechanism may act on GDM offspring. Taken together, our data suggest that being born to a mother with GDM results in alterations to the tanycyte population and ME, which could play major roles in disordered feeding.