We have previously reported that serotonin (5-hydroxytryptamine [SHT]) alters cultured bovine pulmonary artery smooth muscle cell (SMC) configuration through two different regulatory mechanisms. We now report that 5HT also regulates SMC growth through these same two mechanisms-a stimulatory event initiated intracellularly and inhibition of growth resulting from a cell surface action. 5HT (1 ,M) plus 0.1 mM iproniazid (a 5HT metabolic inhibitor) produced a severalfold stimulation of DNA synthesis (as measured by ['H]thymidine incorporation) of SMCs after a 17-24-hour incubation with only a slight elevation of cellular cAMP. This stimulatory effect responded synergistically with other growth factors including plateletderived growth factor, fibroblast growth factor, and epidermal growth factor and was effectively reversed by 5HT uptake inhibition. It was not produced by 5-hydroxyindoleacetic acid, a metabolite of 5HT. In the presence of 1 pM 5HT plus 0.1 mM isobutylmethylxanthine (IBMX), cAMP was elevated eightfold, dendritic formation occurred, and ['H]thymidine labeling of SMCs was inhibited. Inhibition of labeling by ['H]thymidine was mimicked by other agents that elevated cellular cAMP (10 ,uM histamine, 1 ,M isoproterenol plus 0.1 mM IBMX, and 10 ,uM forskolin) and by 1 mM dibutyryl cAMP. This inhibitory effect was not blocked by either inhibition of 5HT uptake or 5HT-receptor antagonists ketanserin (5HT2); methiothepin, spiperone, and mianserin (5HT1/5HT2); and 3-tropanyl-indole-3-carboxylate and 3-tropanyl-3,5-dichlorobenzoate (5HT3). However, similar to 5HT, the 5HT,A agonist, (+)-8-hydroxy-(+)- We have previously found that 5HT causes a configurational change (dendritic formation) of bovine pulmonary artery SMCs in culture through actions at two different locations of the cell, one that requires 5HT uptake into the cell'5 and another that by guest on May 9, 2018

ABSTRACT.We investigated the effect of erythropoietin (EPO) on differentiation and secretion of bone marrow-derived mesenchymal stem cells in an acute kidney injury microenvironment. Acute kidney injury mouse models were prepared. Both renal cortices were then immediately collected to produce the ischemia/reperfusion kidney homogenate supernatant. The morphological and ultrastructural changes in the cells were observed using an inverted microscope and a transmission electron microscope. Cytokeratin-18 was detected using flow cytometry. Bone morphogenetic protein-7 levels, hepatocyte growth factor, and vascular endothelial growth factor in the culture medium were detected using an enzyme-linked immunosorbent assay. The cells had high CD29 and CD44 expression, as well as low CD34 and CD45 expression. More round and oval cells with cobble-like appearances were observed after EPO treatment. In addition, an increase in the number of rough endoplasmic reticula, lysosomes, and mitochondria was observed in the cytoplasm; the intercellular junction peculiar to epithelial cells was also seen on the cell surface. After treatment with ischemia/reperfusion kidney homogenate supernatant, cytokeratin-18 expression increased significantly and EPO could magnify its expression. Bone morphogenetic protein-7 levels, hepatocyte growth factor, and vascular endothelial growth factor levels after treatment with ischemia/ reperfusion kidney homogenate supernatant significantly decreased, whereas EPO increased the cytokine secretion. The acute kidney injury microenvironment can induce the bone marrow-derived mesenchymal stem cells to partially differentiate into renal tubular epithelium-shaped cells, but weaken their secretion function. EPO intervention can boost up their differentiation function and reverse their low secretion effect.