Intracellular redox-sensing proteins and redox signal transduction / 中国病理生理杂志

Many signaling proteins in mammalian cells are sensitive to the changes of redox environment ,which may specifically affect functions of these proteins ,thereby modulating their downstream effects.These signaling pro-teins are thought to be intracellular redox sensors.Redox-sensing functions have been observed in a variety of transcription factors,kinases,phosphatases,ion channels,and cytoskeletal/structural proteins,while the list is still expanding.We propose that many proteins with redox-sensing functions remain to be identified ,and our understanding on the complexity of the redox signaling network in cells is incomplete.In this article ,we provide an overview of some established mammalian intracellular redox sensors.It is suggested that ,when we study pathophysiological mechanisms of disease ,we should keep it in mind that oxidative damage to macromolecules is not the only consequence of increased reactive oxygen production. Rather,changes in redox balance may be linked to multiple specific pathways that are capable of transducing redox signals and regulating various fundamental cellular functions.Aberrant activation or inactivation of these redox signaling mecha-nisms may have significant contributions to the pathogenesis of diseases.

C/EBP homologous protein-mediated endoplasmic reticulum stress-related apoptosis pathway is involved in abdominal aortic constriction-induced myocardium hypertrophy in rats / 生理学报

Endoplasmic reticulum stress (ERS) is an adaptive process in response to circumstantial changes, but excessive and/or prolonged ERS can induce cell apoptosis. C/EBP homologous protein (CHOP) is a very important marker participating in ERS-associated cell apoptosis, while the role of the myocyte apoptosis induced by CHOP remains unclear in the development of hypertrophy. The present study aimed to investigate the effect of CHOP-mediated ERS-associated apoptosis on myocardial hypertrophy induced by abdominal aortic constriction in rats. Healthy male Wistar rats were randomly divided into model group (n=45) and control group (n=40). The rats in model group received abdominal aortic constriction. Hemodynamic changes, whole heart weight/body weight (HW/BW) and left ventricular weight/body weight (LVW/BW) were measured on 1 d, 3 d, 7 d, 14 d and 28 d after surgery, respectively. The mRNA expression of glucose-regulated protein 78 (GRP78), calreticulin (CRT) and CHOP, which are important markers of ERS, were detected by RT-PCR, and Western blot was used to assess the protein level of GRP78, CRT, CHOP, and apoptosis-associated proteins, Bax and Bcl-2. The results obtained were as follows. Compared with control group, the blood pressure, LVW/BW, and HW/BW of rats in model group increased significantly and cardiac function enhanced compensatively on 7 d after surgery, and increased progressively during the experiment. As early as 1 d after surgery, the mRNA level of CRT in model group increased by 136% (P< 0.01) compared with control, while the protein expression increased by 69.2% on 7 d after surgery (P<0.01). Both mRNA and protein expression of GRP78 increased by 20% and 186% (P<0.01) respectively on 7 d after surgery, and the expression sustained high level during the experiment afterwards. Correlation analysis indicated a positive correlation between +dp/dt(max) and CRT protein expression (r=0.780, P<0.01) as well as GRP78 protein expression (r=0.694, P<0.01). Prolonged ERS triggered myocyte apoptosis, as both the mRNA and protein level of CHOP in model group increased by 22.2% (P<0.01) and 76.0% (P<0.01) respectively compared with control on 7 d after hypertrophy (14 d after surgery), and meanwhile, the protein expression of pro-apoptotic Bax increased by 41.1% (P<0.01) and anti-apoptotic Bcl-2 protein expression decreased by 25.5% (P<0.01). Correlation analysis indicated a positive correlation between CHOP and Bax expression (r=0.654, P<0.01), and a negative correlation between CHOP and Bcl-2 expression (r=-0.671, P<0.01). These results suggest that abdominal aortic constriction induces a significant up-regulation in ER molecular chaperones at early stage of post-surgery, indicating that ERS response is activated in the rat heart; while prolonged ERS could lead to myocyte apoptosis, and CHOP-mediated ERS-associated apoptosis may contribute to myocardial hypertrophy. We speculate that cell apoptosis may take part in the regulation of myocardial hypertrophy and heart failure, and determine the progression of decompensated hypertrophy.

Calreticulin is involved in ischemic postconditioning-induced attenuation of ischemia/reperfusion injury in rat skeletal muscle / 生理学报

The present study was aimed to investigate the effect of ischemic postconditioning (I-postC) on ischemia/reperfusion (I/R) injury and whether calreticulin (CRT) is involved in its intracellular signal transduction both in vivo and in cultured skeletal muscle cells. I/R injury in the right hind limb of healthy male Wistar rats was induced by clamping the right femoral artery, and the rats were randomly divided into 3 groups (n=16): I/R group (4-hour ischemia/12- or 24-hour reperfusion), ischemic preconditioning (IPC) group (3 cycles of 1-minute ischemia/1-minute reperfusion) and I-postC group (3 cycles of 5-minute reperfusion/5-minute ischemia). The left hind limb was used as control. Lactate dehydrogenase (LDH) activity in blood plasma, wet/dry weight ratio (W/D) and ultramicrostructure of skeletal muscle were detected 12 h or 24 h after reperfusion. Cultured skeletal muscle cells from neonatal Sprague-Dawley (SD) rat were divided into 6 groups: hypoxia/reoxygenation (H/R) group, hypoxic postconditioning (H-postC) group, hypoxic preconditioning (HPC) group, cyclosporine A (CsA) + H-postC group, CsA + H/R group and control group. H/R was produced by 2-hour hypoxia/24-hour reoxygenation. The survival rate and apoptotic rate of skeletal muscle cells in each group were measured. Western blot was used to detect the expressions of CRT and calcineurin (CaN). The results were as follows: (1) During in vivo experiment, compared with I/R, I-postC significantly decreased LDH activity and W/D, attenuated the ultramicrostructure injury of skeletal muscle and the apoptosis of nucleolus. 12 h and 24 h after reperfusion, compared with that in I/R group, the expression of CRT in I-postC group increased by 439% and 102%, respectively (P<0.05), and the expression of CaN increased by 196% and 63%, respectively (P<0.05). Correlation analysis indicated a positive correlation between CRT and CaN expressions (r=0.865, P<0.01). (2) In cultured skeletal muscle cells, H-postC attenuated cell injury induced by H/R. Compared with those in H/R group, CRT and CaN expressions in H-postC increased by 31.8% (P<0.05) and 6.02%, respectively. The protection of H-postC and CaN up-regulation were eliminated when CsA, the inhibitor of CaN, was added before H-postC. Both in vivo and in vitro results indicate that I-postC, similar as IPC, can protect the skeletal muscle against I/R injury, and its effects may be mediated by CRT and CaN up-regulation. The inhibition of CaN expression may also attenuate the protective effects of I-postC.