023 - IUGR Alters Postnatal Murine Hippocampal Dentate Gyrus Microglial Morphology Which Is Tempered By Environmental Enrichment

Publication Number: 23.5769

Frank Strnad, University of Utah School of Medicine, South Salt Lake, UT, United States; Ashley Brown, University of Utah School of Medicine, salt lake, UT, United States; Matthew Wieben, University of Utah, Cottonwood Heights, UT, United States; Alejandra Bosco, University of Utah, Salt Lake City, UT, United States; Camille Fung, University of Utah, Dept. of Pediatrics, Salt Lake City, UT, United States

Background: In developed countries, hypertensive diseases of pregnancy (HDP) cause uteroplacental insufficiency (UPI) leading to intrauterine growth restriction (IUGR). IUGR offspring are at high risk for learning/memory deficits. Hippocampal dentate gyrus (DG) neurons receive cortical information to form memory. We have shown that IUGR DG neurons have decreased dendritic branching one month after birth. Given microglia’s role in dendritic pruning, we explored whether IUGR alters microglia. We determined if postnatal environmental enrichment (EE) would affect microglial response after IUGR.

Objective: To investigate IUGR’s impact on microglial number and morphology and determine if postnatal EE attenuates microglial response.

Design/Methods: We used a mouse model to generate sham or IUGR pups by implanting a micro-osmotic pump containing either vehicle or a TXA2-analog to mimic HDP/UPI in C57BL/6 pregnant dams at embryonic day E12.5 (term ~20 days). Pups remained in home cages or were placed in an enriched environment (EE) mimicking a playground daily for an hour from P21-P28, after which brains were harvested. We used Iba1 immunofluorescent staining for microglia and CD68 co-staining for activated microglia. We imaged at 20x magnification with fluorescent microscopy and counted the number of Iba1+ and Iba1+/CD68+ microglia and measured Iba1+ cell size using NIH ImageJ software. We used ANOVA with PLSD post hoc test for parametric data or Mann Whitney test for non-parametric data.

Results: Sham and IUGR DG had similar mean Iba1+ counts at P28 (n=38 brain sections from n=4/group, p=0.056, ANOVA). IUGR increased the number of Iba1+/CD68+ counts (p=0.028, Mann Whitney) and mean Iba1+ cell size (p=0.040, ANOVA). Postnatal EE decreased the baseline increase in activated microglia seen in IUGR (p=0.0007, Mann Whitney).

Conclusion(s): IUGR increases the number of activated microglia with larger cell sizes. We posit that these morphological changes could form the cellular basis for decreased dendritic branching and volume in our model. One week of postnatal EE, similar to early intervention in human infants, tempers the activated microglial response after IUGR. Future studies will ascertain these findings by increasing sample sizes, parsing out sex-specific differences, and determining if dendritic branching and volume are improved with postnatal EE.

Figure 1. Representative immunohistochemical images for microglia staining in P28 hippocampal dentate gyrus.
Representative images figure WSPR 2025.jpegIHC staining of microglia with Iba1+ (red) and Iba1+/CD68+ (red + blue = pink) of sham and IUGR with and without environmental enrichment (EE).