Cytochrome P450 Products and Arachidonic Acid–Induced, Non–Store-Operated, Ca2+Entry in Cultured Bovine Endothelial Cells

High Glucose Induces Mouse Mesangial Cell Overproliferation via Inhibition of Hydrogen Sulfide Synthesis in a TLR-4-Dependent Manner

Background/Aims: Overproliferation of mesangial cells was believed to play an important role in the progress of diabetic nephropathy, one of the primary complications of diabetes. Hydrogen sulfide (H2S), a well-known and pungent gas with the distinctive smell of rotten eggs, was discovered to play a protective role in diabetic nephropathy. Methods: MTT assay was used to examine the viability of mesangial cells. Small interfering RNA was used to knock down the expression of TLR4 while specific inhibitor LY294002 to suppress the function of PI3K. H2S generation rate was determined by a H2S micro-respiration sensor. Results: Glucose of 25mM induced significant mesangial cells proliferation, which was accomplished by significantly inhibited endogenous H2S synthesis. And exogenous H2S treatment by NaHS markedly mitigated the overproliferation of mouse mesangial cells. Furthermore, it was found that H2S deficiency could result in TLR4 activation. And H2S supplementation remarkably inhibited TLR4 expression and curbed the mesangial cell overproliferation. Besides, PI3K/Akt pathway inhibition also significantly ameliorated the cell overproliferation. Conclusion: High glucose (HG) induces mouse mesangial cell overproliferation via inhibition of hydrogen sulfide synthesis in a TLR-4-dependent manner. And PI3K/Akt pathway might also play a vital part in the HG-induced mesangial cell overproliferation.

Glucose enhances expression of TRPC1 and calcium entry in endothelial cells

Hyperglycemia is a major risk factor for endothelial dysfunction and vascular disease, and in the current study, the link to glucose-induced abnormal intracellular Ca(2+) (Ca(i)(2+)) homeostasis was explored in bovine aortic endothelial cells in high glucose (HG; 25 mmol/l) versus low glucose (LG; 5.5 mmol/l; control). Transient receptor potential 1 (TRPC1) ion channel protein, but not TRPC3, TRPC4, or TRPC6 expression, was significantly increased in HG versus LG at 72 h. HG for 4, 24, and 72 h did not change basal Ca(i)(2+) or ATP-induced Ca(i)(2+) release; however, the amplitude of sustained Ca(i)(2+) was significantly increased at 24 and 72 h and reduced by low concentration of the putative, but nonspecific, TRPC blockers, gadolinium, SKF-96365, and 2-aminoethoxydiphenyl borate. Treatment with TRPC1 antisense significantly reduced TRPC1 protein expression and ATP-induced Ca(2+) entry in bovine aortic endothelial cells. Although the link between HG-induced changes in TRPC1 expression, enhanced Ca(2+) entry, and endothelial dysfunction require further study, the current data are suggestive that targeting these pathways may reduce the impact of HG on endothelial function.

Ca2+-independent PLA2 controls endothelial store-operated Ca2+ entry and vascular tone in intact aorta

During an agonist stimulation of endothelial cells, the sustained Ca2+ entry occurring through store-operated channels has been shown to significantly contribute to smooth muscle relaxation through the release of relaxing factors such as nitric oxide (NO). However, the mechanisms linking Ca2+ stores depletion to the opening of such channels are still elusive. We have used Ca2+ and tension measurements in intact aortic strips to investigate the role of the Ca2+-independent isoform of phospholipase A2 (iPLA2) in endothelial store-operated Ca2+ entry and endothelium-dependent relaxation of smooth muscle. We provide evidence that iPLA2 is involved in the activation of endothelial store-operated Ca2+ entry when Ca2+ stores are artificially depleted. We also show that the sustained store-operated Ca2+ entry occurring during physiological stimulation of endothelial cells with the circulating hormone ATP is due to iPLA2 activation and significantly contributes to the amplitude and duration of ATP-induced endothelium-dependent relaxation. Consistently, both iPLA2 metabolites arachidonic acid and lysophosphatidylcholine were found to stimulate Ca2+ entry in native endothelial cells. However, only the latter triggered endothelium-dependent relaxation through NO release, suggesting that lysophosphatidylcholine produced by iPLA2 upon Ca2+ stores depletion may act as an intracellular messenger that stimulates store-operated Ca2+ entry and subsequent NO production in endothelial cells. Finally, we found that ACh-induced endothelium relaxation also depends on iPLA2 activation, suggesting that the iPLA2-dependent control of endothelial store-operated Ca2+ entry is a key physiological mechanism regulating arterial tone.

Effects of external ATP on Ca(2+) signalling in endothelial cells isolated from mouse islets

External ATP is believed to initiate and propagate Ca(2+) signals co-ordinating the insulin release pulses within and among the different islets in the pancreas. The possibility that islet endothelial cells participate in this process was evaluated by comparing the effects on [Ca(2+)](i) of purinoceptor activation in these cells with those in beta-cells. beta-Cell-rich pancreatic islets were isolated from ob/ob mice and dispersed into single cells/aggregates. After culture with or without endothelial cell growth supplement (ECGS), the cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) was measured with ratiometric fura-2 technique. Presence of ECGS or prolongation of culture (>5 days) resulted in proliferation of endothelial cells and altered their phenotype from rounded to elongated. Endothelial cells, preliminarily identified by attachment of Dynabeads coated with the Bandeiraea simplicifolia 1 lectin (BS-1), responded in a similar way as those stained with CD31 antibodies after measurements of [Ca(2+)](i). Spontaneous transients and oscillations of [Ca(2+)](i )were seen in beta-cells, but not in endothelial cells exposed to 20 mM glucose. Addition of ATP (10 microM) resulted in pronounced and more extended rise of [Ca(2+)](i) in endothelial cells than in beta-cells. The endothelial cells differed from the beta-cells by also responding with a rise of [Ca(2+)](i) to 10 microM UTP, but not to equimolar ADP and acetylcholine. The results support the idea of mutual interactions between islet endothelium and beta-cells based on ATP-induced Ca(2+) signals. It is suggested that the endothelial cells have a tonic inhibitory action on beta-cell P2 purinoceptors resulting in impaired synchronization of the insulin release pulses.

Econazole attenuates cytotoxicity of 1-methyl-4-phenylpyridinium by suppressing mitochondrial membrane permeability transition

Defects in mitochondrial function have been shown to participate in the induction of neuronal cell injury. The effect of econazole against the cytotoxicity of 1-methyl-4-phenylpyridinium (MPP(+)) in differentiated PC12 cells was assessed in relation to the mitochondrial membrane permeability changes. Treatment of PC12 cells with MPP(+) resulted in the nuclear damage, decrease in the mitochondrial transmembrane potential, cytosolic accumulation of cytochrome c, activation of caspase-3, increase in the formation of reactive oxygen species (ROS) and depletion of GSH. Econazole (0.25-2.5 microM) inhibited the cytotoxicity of MPP(+) or rotenone. The addition of econazole (0.5 microM) significantly attenuated the MPP(+)-induced mitochondrial damage, elevation of intracellular Ca(2+) level and cell death. However, because of the cytotoxicity, econazole at 5 microM did not attenuate the toxicity of MPP(+). The results show that econazole at the low concentrations may reduce the MPP(+)-induced viability loss in PC12 cells by suppressing the mitochondrial permeability transition, leading to activation of caspase-3 and the elevation of intracellular Ca(2+) levels, which are associated with the increased formation of ROS and depletion of GSH.