Visceral obesity and metabolic syndrome have been recognized to be a leading cause of cardiovascular disease, and chronic inflammation. Adipose tissue remodeling and malfunctioning has been suggested to play a central role in obesity. Adipose tissue contains multiple cell types including stromal cells: adipocytes, macrophages, and endothelial cells, and their interaction is important in obese adipose tissue remodeling including angiogenesis, and adipogenesis, thus leading to a dysfunction at the tissue level. However, little is known about the detailed mechanisms of these cell-cell interactions, because much of the structural and functional integrity of the tissue is lost when it is fixed, processed and sectioned. A visualization technique, based on laser confocal microscopy, was therefore developed that made it possible to precisely evaluate the three-dimensional structures in living tissue, and the cell dynamics in vivo with a high time and spatial resolution. These findings demonstrated a close spatial and temporal interrelationship between blood vessel development and adipogenesis, and both were augmented in animal models of obesity. In obesity, close interactions of activated platelets, leukocytes, and endothelial cells in the vessel walls of adipose tissue was also observed by in vivo imaging. The activating status of the macrophages that infiltrated the adipose tissue was altered, and the expression of adhesion molecules in adipose tissue increased in the macrophages as well as in endothelial cells. Platelets were activated locally in obesity, and the vascular permeability also increased. Such abnormal cell-cell interactions could be a cause of obese adipose tissue remodeling and, as a result, they could be a potentially useful therapeutic target.
We herein demonstrate the rapid effect of progesterone (PROG) on the intracellular Ca2+ ([Ca2+]i) dynamics in GT1-7 cells. The cells were loaded with Calcium Green-1 AM and single-cell Ca2+ imaging was performed by digital microscopic imaging. The frequency of spontaneous Ca2+ oscillation was 0.09 Hz. A 20-min incubation with 1 μM PROG significantly suppressed the Ca2+ oscillation down to 54% of the control frequency. The inhibitor of the classical PROG receptor, RU-486, completely blocked this PROG-induced suppression of Ca2+ oscillation. The Ca2+ oscillation was completely blocked by the treatment with nicardipine, an inhibitor of the voltage-sensitive Ca2+ channel, but not blocked by the treatment with thapsigargin, an inhibitor of the Ca2+ pump of microsomes. Therefore, the PROG-induced suppression of the Ca2+ oscillation may be due to modulation of the voltage-dependent Ca2+ channel. These results imply that PROG rapidly (within 20 min) drives Ca2+ signaling via the nongenomic pathway dependent on classical PROG receptors. The existence of the PROG receptor was confirmed by a Western blot analysis.