Submitted on January 31, 2007
Accepted on October 12, 2007
Shear Stress and 17
-Estradiol Modulate Cerebral Microvascular Endothelial Na-K-Cl Cotransporter and Na/H Exchanger Protein Levels
Elaine Chang1, Martha E. O'Donnell2, and Abdul I. Barakat1*
1 Mechanical and Aeronautical Engineering, University of California-Davis, Davis, California, United States
2 Physiology and Membrane Biology, University of California-Davis, Davis, California, United States
* To whom correspondence should be addressed. E-mail: abarakat{at}ucdavis.edu.
Ion transporters of blood brain barrier (BBB) endothelial cells play an important role in regulating movement of ions between the blood and brain. During ischemic stroke, reduction in cerebral blood flow is accompanied by transport of Na and Cl from blood into brain with consequent brain edema formation. We have shown previously that a BBB Na-K-Cl cotransporter (NKCC) participates in ischemia-induced brain Na and water uptake and that a BBB Na/H exchanger (NHE) may also participate. While abrupt reduction of blood flow is a prominent component of ischemia, the effects of flow on BBB NKCC and NHE are not known. In the present study we examined the effects of changes in shear stress on NKCC and NHE protein levels in cerebral microvascular endothelial cells (CMEC). We have shown previously that estradiol attenuates both ischemia-induced cerebral edema and CMEC NKCC activity. Thus, in the present study we also examined the effects of estradiol on NKCC and NHE protein levels in CMEC. Exposing CMEC to steady shear stress (19 dyne/cm2) increased abundance of both NKCC and NHE. Estradiol abolished the shear stress-induced increase in NHE but not NKCC. Abrupt reduction of shear stress did not alter NKCC or NHE abundance in the absence of estradiol but decreased NKCC abundance in estradiol-treated cells. Our results indicate that changes in shear stress modulate BBB NKCC and NHE protein levels. They also support the hypothesis that estradiol attenuates edema formation in ischemic stroke in part by reducing abundance of BBB NKCC protein.
