(22) Assessing Placental Autophagy in Response to Exercise

Erixberto Olivencia Álvarez¹, Elizabeth Padilla-Banks¹, Derek Yao^1,2, Breyana Robinson^1,3, and Carlos M. Guardia¹

1.     Placental Cell Biology Group, Reproductive & Developmental Laboratory, NIEHS, Durham, USA

2.     University of North Carolina at Chapel Hill, Chapel Hill, USA

3.     North Carolina Agricultural & Technical State University, Greensboro, USA


Abstract Text: Due to its effect on multiple metabolic pathways, exercise is essential for promoting physical health and overall wellness. Physical activity stress promotes tissue remodeling and nutrient flux, allowing cells to recycle resources through the autophagy pathway. The autophagosome is the main organelle in this pathway, it recruits and delivers targeted, and/or damaged cellular components to the lysosomes for posterior recycling and redistribution of resources. The process of organelle formation and cargo recruitment involves proteins like LC3, involved in substrate selection and autophagosome biogenesis, and BNIP3, responsible for the selective recruitment of mitochondrial components. Due to its role, autophagy is an intriguing mechanism when studying the placenta and its intertwined dynamics between the host and the offspring. This temporary organ develops during pregnancy along with the fetus and constantly communicates with the external environment while overseeing nutrient availability. Previous human studies showed that sustained, moderate to high intensity exercise during pregnancy stimulates placental growth, and increased vascularity, morphological changes in which autophagy is involved. Given the homeostatic role of this pathway during stress and the adaptability of the placenta, we hypothesize that autophagy in this organ is upregulated in response to physical activity, resulting in altered levels of cargo and autophagosome biogenesis proteins. 
To test this hypothesis, adult female mice were exposed to a voluntary running wheel protocol before and during pregnancy; this group was compared to sedentary animals at the same gestational age. Placental and fetal parameters were assessed, and placental tissue was frozen and fixed to examine autophagy response. After monitoring running wheel activity daily, we observed that physical activity declined as pregnancy progressed, indicating a prepartum behavior guided towards ensuring offspring safety. Immunoblot analysis from placental tissue showed increased LCII/LC3I protein ratio only in female exercised placentas when compared to their control, suggesting a sex dimorphic autophagy response. A decreased trend in BNIP3 was also observed, suggesting more mitophagy in the placenta. Histological analysis revealed an area reduction of the junctional zone in female placentas exposed to exercise when compared to male control placentas, while exercised male placentas showed a higher deposition of glycogen in that zone when compared to their control. To further analyze the autophagy flux, pregnant mice were dosed with chloroquine, a known autophagy inhibitor that disrupts the lysosome-autophagosome fusion, resulting in autophagosome accumulation. Expression of LC3II/LC3I protein was significantly higher only in male placentas is response to chloroquine, suggesting again a sex dimorphic response where more LC3 protein is being conjugated to the autophagosome membrane in response to exercise. Altogether, our study shows a significant role of placenta-specific autophagy in regulating fetal development during exercise. Targeting autophagy through exercise may offer therapeutic strategies to prevent placental dysfunction in pregnancy.