Cardioprotective mechanism of calreticulin up-regulation induced by hypoxic postconditioning / 生理学报

Calreticulin (CRT) is an essential Ca(2+)-binding chaperone existing in endoplasmic reticulum (ER) or sarcoplasmic reticulum (SR), and is involved in intracellular Ca(2+) homeostasis and protein folding. Ischemic postconditioning (I-postC), a newly discovered endogenous protective phenomenon, induces CRT up-regulation. The present study aimed to investigate the cardioprotective mechanism of CRT up-regulation induced by hypoxic postconditioning (H-postC). Primary cultured neonatal rat cardiomyocytes were exposed to 2 h of hypoxia followed by 24 h of reoxygenation. Postconditioning was carried out by two cycles of 10 min of reoxygenation and 20 min of rehypoxia after 2 h of hypoxia. Antisense oligodeoxynucleotides (AS-ODNs) were used to inhibit CRT expression 36 h before hypoxia. Cardiomyocytes were randomly divided into 6 groups as follows (n=4): control, hypoxia/reoxygenation (H/R), H-postC, AS, AS + H/R, and AS + H-postC. Morphological studies, lactate dehydrogenase (LDH) activity assay in culture medium, and flow cytometry were used to detect cardiomyocyte necrosis and apoptosis. Intracellular Ca(2+) concentration was detected by fluorescent Fluo-3/AM staining through laser confocal microscope, and p-nitrophenyl phosphate (PNPP) was used as substrate to measure calcineurin (CaN) activity. The expression of CRT, CaN, nuclear factor kappa B (NFκB) and apoptosis-related proteins, such as Bcl-2, Bax and C/EBP homologous protein (CHOP) were detected by Western blot. The results were as follows. (1) H-postC protected neonatal cardiomyocytes from H/R injury. Compared with H/R group, cell survival rate increased by 17.1%, apoptotic rate and LDH leakage decreased by 6.67% and 27.9% in H-postC group, respectively (P<0.05). (2) H-postC induced mild up-regulation of CRT expression. Inhibition of CRT by AS-ODNs attenuated the cardioprotection of H-postC partly. Compared with H-postC group, cell survival rate decreased by 8.98%, and apoptotic rate and LDH leakage increased by 1.74% and 13.6% in AS + H-postC group, respectively (P<0.05), but intracellular Ca(2+) concentration, CaN activity, and expression of CaN and NFκB did not change significantly (P>0.05), suggesting that CRT participates in endogenous protection, not through Ca(2+)-CaN pathway. (3) H-postC inhibited the expression of pro-apoptosis proteins such as Bax and CHOP, but induced up-regulation of anti-apoptosis protein Bcl-2. Inhibition of CRT by AS-ODNs partly inhibited the changes in apoptosis-related proteins expression induced by H-postC, suggesting that CRT participates in the anti-apoptosis effect of H-postC through regulating expression of apoptosis-related proteins. These results indicate that CRT up-regulation induced by H-postC is involved in the cardioprotection through regulating expression of apoptosis-related proteins, not through Ca(2+)-CaN pathway in neonatal cardiomyocytes.

Down-regulation of perlecan expression contributes to the inhibition of rat cardiac microvascular endothelial cell proliferation induced by hypoxia / 生理学报

Exposure of endothelial cells (ECs) to hypoxia leads to a decrease in EC proliferation. However, the mechanism by which hypoxia inhibits EC proliferation is unclear. Perlecan has been reported to play an important role in regulating EC proliferation. We hypothesized that perlecan was involved in the hypoxia-induced inhibition of EC proliferation. To test this hypothesis, rat cardiac microvascular ECs were cultured under normoxic or hypoxic conditions for 12 h and harvested for determination of perlecan mRNA expression using real-time reverse transcription-polymerase chain reaction (RT-PCR). The results showed that exposure of ECs to hypoxia for 12 h induced a decrease in perlecan mRNA expression (61.72%, P<0.05). Concomitantly, the down-regulation of endogenous perlecan induced by hypoxia or the neutralization of endogenous perlecan with anti-perlecan antibody significantly inhibited EC proliferation and responsiveness to basic fibroblast growth factor (bFGF), and decreased focal adhesion kinase (FAK) expression and extracellular signal-regulated kinase 1/2 (ERK1/2) activation. These data indicate that down-regulation of perlecan expression contributes to hypoxia-induced inhibition of rat cardiac microvascular EC proliferation by suppressing FAK-mediated and ERK1/2-dependent growth signals.

Hypoxic preconditioning induces endoplasmic reticulum stress-related cardioprotection mediated by p38 mitogen-activated protein kinase / 生理学报

Calreticulin (CRT), an important Ca(2+)-binding molecular chaperone in the endoplasmic reticulum (ER), and caspase-12, a pivotal molecule mediating ER-initiated apoptosis, are involved in the ER stress (ERS). Using primary cultured neonatal cardiomyocytes, CRT and caspase-12 expression and activation during hypoxic preconditioning (HPC) and hypoxia/reoxygenation (H/R) were studied to explore the role of ERS in cardioprotection by HPC. And by using SB203580 and SP600125 [the specific inhibitors of p38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase (JNK)] separately, the role of p38 MAPK in HPC-induced ERS was also detected. Neonatal cardiomyocytes were prepared from Sprague-Dawley rats aged 24 h, and cultured in DMEM medium containing 10% fetal bovine serum, and then randomly divided into six groups as follows: H/R, HPC+H/R, SB203580+HPC+H/R, SP600125+HPC+H/R, HPC and control groups. H/R was produced by 2-hour hypoxia/14-hour reoxygenation, and HPC by 20-minute hypoxia/24-hour reoxygenation. Morphological studies, estimation of lactate dehydrogenase (LDH) leakage and flow cytometry were employed to assess cell apoptosis and necrosis. CRT and caspase-12 expression and activation, levels of phospho-p38 MAPK and phospho-JNK were detected by Western blot. All experiments were repeated at least four separate times. The results obtained are as follows: (1) HPC relieved the cell injury caused by H/R. Compared with that in H/R group, cellso survival rate in HPC+H/R group increased by 6.4%, and the apoptosis rate and LDH leakage in the cell culture medium decreased by 6.6% and 70.0%, respectively. (2) H/R induced caspase-12 activation (33.2-fold increase in comparison with control) and CRT expression (8.1-fold increase in comparison with control). HPC itself resulted in mild CRT up-regulation (2.6-fold increase in comparison with control), but the extent of up-regulation was lower than that induced by H/R. HPC before H/R was found to relieve the over-expression of CRT induced by H/R (72.4% decrease), and to inhibit the activation of caspase-12 (59.6% decrease). (3) The protection of HPC and HPC-induced up-expression of CRT and inhibition of caspase-12 activation were almost eliminated when the inhibitor of p38 MAPK, not of JNK, was present before HPC. These results suggest that HPC protects the neonatal cardiomyocytes from severe ERS-induced apoptosis during sustained H/R through pre-invoking proper ERS response. Mild up-expression of CRT and inhibition of caspase-12 activation induced by HPC, which are important protection factors, are mediated by p38 MAPK, not by JNK.

Effects of human urotensin II on pia mater microcirculation in rats / 中国应用生理学杂志

<p><b>AIM</b>To investigate the effects of human urotensin II (hUII) on in vivo pia mater microcirculation in rats.</p><p><b>METHODS</b>Adult SD rats were randomly assigned to the following groups: control, sodium chloride injection (NS), UII(10(-6) mol/L), noradrenaline (NA, 10(-6) mol/L), and UII (10(-6) mol/L) + NA (10(-6) mol/L) groups. For recording of microcirculation images in pia mater, skull windows were performed and mounted on the stage of an intravital microscope equipped with a TV camera. Video images of microcirculation were stored by a video cassette recorder. Temporal changes in internal diameter and microcirculatory velocity of microvessels were measured by computer using the Image Pro software. The blood flow in cerebral tissues were measured with PIMII laser Doppler perfusion Imager (Lisca, Sweden).</p><p><b>RESULTS</b>The internal diameters of arterioles and venules in control group were (35.4 +/- 3.6) microm and (40.6 +/- 8.5) microm, respectively. In UII group, the arterioles and venules contracted immediately after treated with UII and up to the peak at 1 min, the internal diameters of arterioles and venules were (25.6 +/- 3.4) microm and (23.4 +/- 3.3) microm, respectively (P < 0.05). Both microcirculatory velocity in arterioles and venules had no significant changes in UII group (P > 0.05). The blood flow in meninges increased 1 min after treated with UII and up to high peak at 5 min (3.5 +/- 0.4 perfusion unit vs. control 2.3 +/- 0.6, P < 0.05).</p><p><b>CONCLUSION</b>hUII can contract microvessels in pia mater of rats and increase microcirculatory blood perfusion to cerebral tissue involved.</p>

Role of hypoxia-inducible factor-1alpha in the prevention of cardiomyocyte injury induced by hypoxic preconditioning / 生理学报

In order to understand the intracellular mechanism of preconditioning, we investigated the relationship among activities of extracellular signal-regulated protein kinases (ERKs), the expression of hypoxia-inducible factor -1alpha (HIF-1alpha) and the effect of hypoxic preconditioning (HPC) on cell injury induced by hypoxia-reoxygenation in cultured neonatal rat cardiomyocytes 24 h after brief hypoxia. Cultured cardiomyocytes of neonatal Sprague-Dawley rats were divided into four groups: hypoxia/reoxygenation (H/R), hypoxia preconditioning (HPC), hypoxia preconditioning + mitogen-activated protein kinase (MAPK) inhibitor PD98059 (HPC+PD98059), and control (C). We measured the survival rate and apoptosis rate of cardiomyocytes at 6 or 12 h after hypoxia/reoxygenation, activities of extracellular signal-regulated protein kinases (ERKs), and expression of hypoxia-inducible factor-1alpha (HIF-1alpha). We found that the survival rate of cardiomyocytes in hypoxic preconditioning group increased by 6.08% and 7.91% at 6 and 12 h after hypoxia/reoxygenation (n=6, P<0.05), respectively, and the apoptotic rate decreased by 10.92% and 14.34% (n=6, P<0.05) respectively. Hypoxic preconditioning increased the abundance of phospho-ERK1/2 by 3-folds and expression of HIF-1alpha by 1-fold in whole cell extracts from hypoxic preconditioned cardiomyocytes. PD98059, an inhibitor of the upstream kinase of ERKs, abolished the anti-injury effect, ERKs activation, and expression of HIF-1alpha induced by hypoxic preconditioning. Statistical analysis indicated that there was negative correlation between apoptotic rate and activities of ERKs or expression of HIF-1alpha, and positive correlation between activities of ERKs and expression of HIF-1alpha. It is concluded that hypoxic preconditioning protects cardiomyocytes from hypoxia/reoxygenation-induced injury and that upregulation of HIF-1alpha through ERKs pathway mediates the cardioprotection of hypoxic preconditioning.