Estradiol effects on intracellular Ca(2+) homeostasis in bovine brain-derived endothelial cells

Abstract

Estrogens diversely affect various physiological processes by genomic or non-genomic mechanisms, in both excitable and non-excitable cells. Additional to the trophic effects of estrogens promoting cell growth and differentiation, recent experimental evidence highlights their involvement in the regulation of intracellular Ca(2+) homeostasis. The effects of estrogens on excitable cells are well documented. However, these steroids also influence numerous physiological events in non-excitable cells, such as fibroblasts or vascular endothelial cells. We have focused our attention on an immortalized endothelial-like cell line derived from fetal bovine cerebellum. Estradiol (E(2)) effects on intracellular Ca(2+) homeostasis were tested by varying the exposure time to the hormone (8, 24, 48 h). Calcium measurements were performed with genetically encoded Ca(2+) probes (Cameleons) targeted to the main subcellular compartments involved in intracellular Ca(2+) homeostasis (cytosol, endoplasmic reticulum, mitochondria). Mitochondrial Ca(2+) uptake significantly decreased after 48-h exposure to E(2), whereas cytosolic and endoplasmic reticulum responses were unaffected. The effect of E(2) on mitochondrial Ca(2+) handling was blocked by ICI 182,780, a pure estrogen receptor antagonist, suggesting that the effect was estrogen-receptor-mediated. To evaluate whether the decrease of Ca(2+) uptake affected mitochondrial membrane potential (ΔΨm), cells were monitored in the presence of tetra-methyl-rhodamine-methylester; no significant changes were seen between cells treated with E(2) and controls. To investigate a mechanism of action, we assessed the possibile involvement of the permeability transition pore (PTP), an inner mitochondrial membrane channel influencing energy metabolism and cell viability. We treated cells with CyclosporinA (CsA), which binds to the matrix chaperone cyclophilin-D and regulates PTP opening. CsA reversed the effects of a 48-h treatment with E(2), suggesting a possible transcriptional modulation of proteins involved in the mitochondrial permeability transition process.