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Activity and protein localization of multiple glutamate transporters in gestation day 14 vs. day 20 rat placenta
J C Matthews1, M J Beveridge, M S Malandro
1Department of Pediatrics, University of Florida College of Medicine, Gainesville 32610, USA.
Insights
Glutamate transporters in the placenta increase with fetal development, enhancing nutrient absorption crucial for fetal growth. This study tracks key transporters, showing greater placental glutamate uptake capacity by day 20.
Area of Science:
- Reproductive biology
- Neuroscience
- Biochemistry
Background:
- Placental glutamate uptake is vital for fetal development.
- System X-AG transporters (GLAST1, GLT1, EAAC1, EAAT4) mediate this uptake.
- Understanding transporter expression changes during gestation is key.
Purpose of the Study:
- To investigate the expression and activity of glutamate transporters (system X-AG) in the developing rat placenta.
- To compare transporter levels and function between gestational days 14 and 20.
- To correlate mRNA and protein expression with placental glutamate transport capacity.
Main Methods:
- Quantitative analysis of steady-state mRNA levels for GLAST1, GLT1, EAAC1, and EAAT4.
- Immunohistochemistry to determine protein expression and localization of transporters.
- Measurement of Na(+)-dependent glutamate uptake to assess system X-AG activity in placental membrane subdomains.
Main Results:
- mRNA levels for all evaluated transporters were higher on day 20 compared to day 14.
- GLAST1, GLT1, and EAAC1 protein expression increased by day 20, showing asymmetric cellular localization.
- System X-AG activity, responsible for most glutamate uptake, was significantly greater in day 20 placenta, particularly in basal membranes.
Conclusions:
- Placental glutamate transport capacity increases significantly during late gestation.
- The expression and localization of key transporters like EAAC1 and GLAST1 are upregulated to meet fetal demands.
- These findings highlight the dynamic adaptation of placental function for optimal fetal development.
Abstract:
Concentrative absorption of glutamate by the developing placenta is critical for proper fetal development. The expression of GLAST1, GLT1, EAAC1, and EAAT4, known to be capable of D-aspartate-inhibitable and Na(+)-coupled glutamate transport (system X-AG), was evaluated in day 14 vs. day 20 rat chorioallantoic placenta. Steady-state mRNA levels were greater at day 20 for all transporters. Immunohistochemistry determined that the expression of GLAST1, GLT1, and EAAC1 was greater throughout the day 20 placenta and was asymmetric with respect to cellular localization. EAAT4 protein was not detected. System X-AG activity was responsible for most of the Na(+)-dependent glutamate uptake and was greater in day 20 than in day 14 apical and basal membrane subdomains of the labyrinth syncytiotrophoblast. Greater quantities of EAAC1 and GLAST1 protein were identified on day 20, and quantities were greater in basal than in apical membranes. GLT1 expression, unchanged in apical membranes, was decreased in basal membranes. These data correlate transporter mRNA and protein content with transport activity and demonstrate an increasing capacity for glutamate absorption by the developing placenta.
