Xiaobo Tang

20-Hydroxyeicosatetraenoic acid inhibits the apoptotic responses in pulmonary artery smooth muscle cells.

20-Hydroxyeicosatetraenoic acid (20-HETE), a omega-hydroxylation product of arachidonic acid catalyzed by cytochrome P450 4A (CYP4A), plays a role in vascular smooth muscle remodeling. Although its effects on angiogenic responses are known, it remains unclear whether 20-HETE acts on apoptosis of pulmonary arterial smooth muscle cells (PASMC), an important step in PASMC remodeling, and what pathways are involved in the process. Here we show evidence for the missing information. The effect of 20-HETE on PASMC apoptosis and the apoptosis-associated signaling pathways were determined with cell viability assay, Annexin V and propidium idodide binding, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL), mitochondrial potentials assay, caspase activity assay and Western blots. We found that exogenous 20-HETE suppressed the serum deprivation-induced loss of bovine PASMCs and prevented Annexin V binding, DNA nick end labeling and chromatin condensation. The effect was worsened by 17-octadecynoic acid (17-ODYA), which inhibited the production of endogenous 20-HETE. Furthermore, 20-HETE induced the expression of bcl-2, maintained the stability of mitochondria membrane, and relieved the activation of caspase-9 and caspase-3. Such effects were reversed in the presence of 17-ODYA. Thus, these findings indicate that 20-HETE protects PASMCs against apoptosis by acting on, at least in part, the intrinsic apoptotic pathway.

15-HETE suppresses K + channel activity and inhibits apoptosis in pulmonary artery smooth muscle cells

Abstract15-Hydroxyeicosatetraenoic acid (15-HETE) is an important hypoxic product from arachidonic acid (AA) in the wall of pulmonary vessels. Although its effects on pulmonary artery constriction are well known, it remains unclear whether 15-HETE acts on the apoptotic responses in pulmonary artery smooth muscle cells (PASMCs) and whether K+ channels participate in this process. These hypothesises were validated by cell viability assay, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling, mitochondrial potentials assay, caspase activity assay and western blot. We found that 15-HETE enhanced cell survival, suppressed the expression and activity of caspase-3, upregulated bcl-2 and attenuated mitochondrial depolarization, prevented chromatin condensation and partly reversed K+ channel opener-induced apoptosis in PASMCs under serum-deprived conditions. Our data indicated that 15-HETE inhibits the apoptosis in PASMCs through, at least in part, inactivating K+ channels.

Subacute hypoxia suppresses Kv3.4 channel expression and whole-cell K+ currents through endogenous 15-hydroxyeicosatetraenoic acid in pulmonary arterial smooth muscle cells

We have previously reported that subacute hypoxia activates lung 15-lipoxygenase (15-LOX), which catalyzes arachidonic acid to produce 15-HETE, leading to constriction of neonatal rabbit pulmonary arteries. Subacute hypoxia suppresses Kv3.4 channel expression and results in an inhibition of whole-cell K(+) currents (I(K)). Although the Kv channel inhibition is likely to be mediated through 15-HETE, direct evidence is still lacking. To reveal the role of the 15-LOX/15-HETE pathway in the hypoxia-induced down-regulation of Kv3.4 channel expression and inhibition of I(K), we performed studies using 15-LOX blockers, whole-cell patch-clamp, semi-quantitative PCR, ELISA and Western blot analysis. We found that Kv3.4 channel expression at the mRNA and protein levels was greatly up-regulated in pulmonary arterial smooth muscle cells after blockade of 15-LOX by CDC or NDGA. The 15-LOX blockade also partially restored I(K). In comparison, 15-HETE had a stronger effect than 12-HETE on the expression of Kv3.4 channels. 5-HETE had no noticeable effect on Kv3.4 channel expression. These data indicate that the 15-LOX pathway via its metabolite, 15-HETE, seems to play a role in the down-regulation of Kv3.4 expression and I(K) inhibition after subacute hypoxia.

Hypoxia suppresses KV1.5 channel expression through endogenous 15-HETE in rat pulmonary artery

Hypoxia initiated pulmonary vasoconstriction is due to the inhibition of voltage-gated K(+) (K(V)) channels. But the mechanism is unclear. We have evidence that hypoxia activates 15-lipoxygenase (15-LOX) in distal pulmonary arteries and increases the formation of 15-hydroxyeicosatetraenoate (15-HETE). 15-HETE-induced pulmonary artery constriction to be through the inhibition of K(V) channels (K(V)1.5, K(V)2.1 and K(V)3.4). However, no direct link among hypoxia, 15-HETE and inhibition of K(V) subtypes is established. Therefore, we investigated whether 15-LOX/15-HETE pathway contributes to the hypoxia-induced down-regulation of K(V) channels. As K(V)1.5 channel is O(2)-sensitive, it was chosen in the initial study. We found that inhibition of 15-LOX suppressed the response of hypoxic pulmonary artery rings to phenylephrine. The expressions of K(V)1.5 channel mRNA and protein was robustly up-regulated in cultured PASMC and pulmonary artery after blocking of 15-LOX by lipoxygenase inhibitors in hypoxia. The 15-LOX blockade also partly rescued the voltage-gated K(+) current (I(K(V))). 15-HETE contributes to the down-regulation of K(V)1.5 channel, inhibition of I(K(V)) and increase of native pulmonary artery tension after hypoxia. Hypoxia inhibits K(V)1.5 channel through 15-LOX/15-HETE pathway.

Source of the elevation Ca2+ evoked by 15-HETE in pulmonary arterial myocytes

We have previously reported that 15-hydroxyeicosatetraenoic acid (15-HETE), a metabolite of arachidonic acid by 15-lipoxygenase, causes pulmonary vasoconstriction via increasing the intracellular Ca(2+) concentration ([Ca(2+)]i). However, the multiple sources of Ca(2+) that contribute to Ca(2+) elevation during and after 15-HETE exposure have not been investigated. In the present study, pulmonary arterial ring technique and confocal laser scanning microscope were used to investigate the origin of Ca(2+). 15-HETE (1 microM) elicited an increase in [Ca(2+)]i in pulmonary artery smooth muscle cells in a time-dependent manner under both normal and hypoxic condition. The increases were composed of an initial rapid rise followed by a slow increase in the present of extracellular Ca(2+). The initial rapid phase was attenuated by inositol 1,4,5-triphosphate (IP(3)) receptor antagonist 2-aminoethoxydiphenyl borate (2-APB) and ryanodine receptor-operated Ca(2+) store depletion agent caffeine; the slow increasing phase and the constriction of pulmonary arterial ring were significantly inhibited by voltage-operated Ca(2+) channel blocker nifedipine or transient receptor potential canonical (TRPC) channel blocker La(3+), and almost completely diminished in Ca(2+)-free external solution, suggesting that the initial phase depends on intracellular Ca(2+) store and the second phase relies on extracellular Ca(2+). Interestingly, the effect of caffeine and La(3+) but not nifedipine were diminished in the present of 2-APB. Thus, these results suggest that 15-HETE mobilizes Ca(2+) signaling through: 1) Ca(2+) release immediately from Ca(2+) stores via activation of IP(3) receptor and, subsequently that of ryanodine receptor, 2) the depletion of Ca(2+) through CCE leading to the activation of TRPC, and 3) Ca(2+) entry through L-type Ca(2+) channels.

Role of protein kinase C in 15-HETE-induced hypoxic pulmonary vasoconstriction

The aim of the present study was to investigate the roles of protein kinase C (PKC) signal transduction pathway in the 15-hydroxyeicosatetraenoic acid (15-HETE)-induced down-regulation expression of K(V) 1.5, K(V) 2.1 and K(V) 3.4, and pulmonary vasoconstriction under hypoxia. Tension measurements on rat pulmonary artery (PA) rings, Western blots, semi-quantitative PCR and whole-cell patch-clamp technique were employed to investigate the effects of 15-HETE on PKC and K(V) channels. Hypericin (6.8 micromol/L), a PKC inhibitor, significantly attenuated the constriction of PA rings to 15-HETE under hypoxia. The down-regulation of K(V) 1.5, K(V) 2.1 and K(V) 3.4 channel expression and inhibition of whole-cell K currents (I(K)(V)) induced by 15-HETE were rescued and restored, respectively, by hypericin. These studies indicate that the PKC signal transduction pathway is involved in 15-HETE-induced rat pulmonary vasoconstriction under hypoxia. 15-HETE suppresses the expression of K(V) 1.5, K(V) 2.1 and K(V) 3.4 channels and inhibits I(K)(V) through the PKC signaling pathway in pulmonary arterial smooth muscle cells.

Carboxylesterase 2 is Downregulated in Colorectal Cancer Following Progression of the Disease

Expression of carboxylesterase 2 in colorectal tumor tissues and serum carboxylesterase 2 levels at different stages of the disease were investigated by Western blotting. Carboxylesterase 2 was decreasing in tumor tissues from TNM stages 0 through IV (n = 20); the expression of carboxylesterase 2 was similar between “normal” and tumor tissues (n = 20); serum carboxylesterase 2 levels were similar among patients at different stages of the disease. These results indicate that local expression of carboxylesterase 2 is downregulated following progression of the disease; carboxylesterase 2 expression is altered in histology “normal” tissues from stages I through IV before histopathological changes.

Hypoxia promotes rabbit pulmonary artery smooth muscle cells proliferation through a 15-LOX-2 product 15(S)-hydroxyeicosatetraenoic acid

The initial event of hypoxic pulmonary hypertension is acute hypoxic pulmonary vasoconstriction followed by remodeling of pulmonary arteries. Although 15(S)-hydroxyeicosatetraenoic acid [15(S)-HETE] is found to be able to induce hypoxic pulmonary vasoconstriction, role of 15(S)-HETE in pulmonary artery smooth muscle cells (PASMCs) proliferation has been studied less. We sought evidence for a role of 15(S)-HETE in the development of hypoxia-induced pulmonary hypertension. We found that hypoxia enhances 15-lipoxygenase-2 (15-LOX-2) expression and stimulates cultured rabbit PASMCs proliferation. 15(S)-HETE at concentration 0.1 μM stimulated proliferation of PASMCs and induced ERK 1/ERK 2 phosphorylation but had no effect on p38 kinase expression as assessed by Western blotting. 15(S)-HETE-stimulated PASMC proliferation was blocked by the MEK inhibitors PD-98059. Hypoxia (3% O(2))-stimulated PASMC proliferation was blocked by U0126, a MEK inhibitor, as well as by NDGA and CDC, inhibitors of 15-LOX, but not by the p38 MAPK inhibitor SB-202190. We conclude that 15-LOX-2 and its product, 15(S)-HETE, are important intermediates in hypoxia-induced rabbit PASMC proliferation and may participate in hypoxia-induced pulmonary hypertension.

Expression of 15-lipoxygenases in pulmonary arteries after hypoxia

Aims: We have previously reported that subacute hypoxia upregulates and activates the steady state expression of pulmonary artery 15‐lipoxygenase (15‐LOX). However, there are two 15‐LOX isoenzymes, 15‐LOX‐1 and 15‐LOX‐2, which are expressed in pulmonary arteries that have not been previously studied. In the present study, we identified the differential expression of the two isoenzymes in normoxic or hypoxic intrapulmonary arteries of rats, pulmonary artery endothelial cells (PAECs) and pulmonary artery smooth muscle cells (PASMCs) from the main branches of pulmonary artery of neonatal bovines. Methods: Immunohistochemistry, in situ hybridisation, RT‐PCR, and Western blotting were employed to identify the differential expression of the two isoenzymes. Results: 15‐LOX‐1 was expressed in both normoxic and hypoxic rat arteries. In contrast, 15‐LOX‐2 was hardly detectable in normoxic vessels by immunohistochemistry and Western blotting, but it was detected in hypoxic arteries. In cultured bovine pulmonary artery cells, 15‐LOX‐1 and 15‐LOX‐2 were found to be different in cellular distribution. The expression of 15‐LOX‐1 was stronger in PAECs than in PASMCs, whereas, 15‐LOX‐2 was weaker in PAECs than in PASMCs. Moreover, the expressions of both 15‐LOX isoenzymes increased dramatically after hypoxia. Conclusions: These results suggest that both isoenzymes of 15‐LOXs are upregulated after hypoxia.

Influence of the 15-HETE on cytosolic [ Ca2+] i of the rabbit pulmonary artery smooth muscle cells

Extracellular Ca2+ influx was blocked by L-type Ca2+ channel blocker nifedipine to observe the effects of 15-hydroxyeicosatetraenoic acid on the constriction of rabbit pulmonary artery rings and on the changes of Ca2+ level in the rabbit pulmonary artery smooth muscle cells, and further to investigate the mechanism of the calcium mobilization induced by the 15-HETE under hypoxic conditions. The effect of extracellular Ca2+ on tension of the rabbit PA rings was also studied. Nifedipine (10 µ mol/L) had no effect on 1 µ mol/L 15-hydroxyeicosatetraenoic acid induced vasoconstriction under normoxic and hypoxic conditions. Intracellular Ca2+ increased markedly in the 15-HETE group (cells were exposed to 1 µ mol/L 15-HETE for 8 min during culture) compared to the control group (P < 0.05). The study demonstrated that the 15-HETE could induce the elevation of Ca2+ in the pulmonary artery smooth muscle cells and the elevated calcium came from the release of the intracellular calcium.