Transient Brain Ischaemia Provokes Ca2+, PIP2 and Calpain Responses Prior to Delayed Neuronal Death in Monkeys

To clarify the mechanism of postischaemic delayed cornu Ammonis (CA)-1 neuronal death, we studied correlations among calpain activation and its subcellular localization, the immunoreactivity of phosphatidylinositol 4,5-bisphosphate (PIP₂) and Ca²⁺ mobilization in the monkey hippocampus by two independent experimental approaches: in vivo transient brain ischaemia and in vitro hypoxia-hypoglycaemia of hippocampal acute slices. The CA-1 sector undergoing 20 min of ischaemia in vivo showed microscopically a small number of neuronal deaths on day 1 and almost global neuronal loss on day 5 after ischaemia. Immediately after ischaemia, CA-1 neurons ultrastructurally showed vacuolation and/or disruption of the lysosomes. Western blotting using antibodies against inactivated or activated μ-calpain demonstrated μ-calpain activation specifically in the CA-1 sector immediately after ischaemia. This finding was confirmed in the perikarya of CA-1 neurons by immunohistochemistry. CA-1 neurons on day 1 showed sustained activation of μ-calpain, and increased immunostaining for inactivated and activated forms of μ- and m-calpains and for PIP₂. Activated μ-calpain and PIP₂ were found to be localized at the vacuolated lysosomal membrane or endoplasmic reticulum and mitochondrial membrane respectively, by immunoelectron microscopy. Calcium imaging data using hippocampal acute slices showed that hypoxia-hypoglycaemia in vitro provoked intense Ca²⁺ mobilization with increased PIP₂ immunostaining specifically in CA-1 neurons. These data suggest that transient brain ischaemia increases intracellular Ca²⁺ and PIP₂ breakdown, which will activate calpain proteolytic activity. Therefore, we suggest that activated calpain at the lysosomal membrane, with the possible release of biodegrading enzyme, will cause postischaemic CA-1 neuronal death.     

Differential effect of oestrogen on post‐exercise cardiac muscle myeloperoxidase and calpain activities in female rats

The effects of oestrogen administration on 1 h post‐exercise cardiac muscle myeloperoxidase (MPO) and calpain activities were determined in female rats. Rats were ovariectomized and implanted for 2 weeks with either oestrogen (25 mg 17‐oestradiol) or placebo pellets or left with ovaries intact. Rats were then run for 1 h at 21 m min^–1, 12% grade, killed 1 h post‐exercise and cardiac muscle and blood samples were removed. Control animals from each group were killed without prior exercise. Serum oestrogen levels in the order of the highest to lowest were; ovariectomized oestrogen replaced rats > intact ovaries rats > ovariectomized placebo rats. Oestrogen induced significant (P < 0.05) elevations in cardiac MPO activity at rest and at 1 h post‐exercise in ovariectomized rats. No significant elevations in cardiac MPO activity were evident in placebo ovariectomized or normal ovary rats at rest or post‐exercise. Cardiac calpain activities were similar in all unexercised groups. Ovariectomized placebo and intact ovary rats had significantly (P < 0.05) elevated cardiac calpain activities 1 h post‐exercise while calpain activity was not significantly elevated in hearts from ovariectomized oestrogen rats. These results demonstrate that oestrogen supplementation in ovariectomized rats induces elevations in cardiac muscle MPO activities at rest and at 1 h post‐exercise. This is opposite to the effect of oestrogen in post‐exercise skeletal muscle and implies a greater neutrophil infiltration into cardiac muscle caused by oestrogen. This effect cannot be explained by changes in 1 h post‐exercise cardiac muscle calpain activity, the elevation of which was suppressed by oestrogen administration. Oestrogen influences cardiac calpain activity similarly to its effect in skeletal muscle. Thus, oestrogen administration to ovariectomized rats induces elevations in cardiac MPO activity while suppressing cardiac calpain activity.     

Cleavage of integrin by mu-calpain during hypoxia in human endometrial cells

PROBLEM: The distribution and activation of mu-calpain and possible cleavage of integrin in human endometrial cells under hypoxic condition were investigated. METHOD OF STUDY: Human endometrial epithelial and stromal cells were subjected to hypoxia, and subsequently used for immunostaining and western blot analysis. RESULTS: The proform of mu-calpain was detected in the cytoplasm of normal cells, and displayed a substantial decrease after hypoxia. Conversely, the active form of mu-calpain was not detected in normal cells, but was abundant after hypoxia. The cytoplasmic domain of integrin beta3 was also detected in the cytoplasm of endometrial cells. Western blot analysis confirmed that both the proform of mu-calpain and the integrin beta3 cytoplasmic domain decreased during hypoxia. CONCLUSIONS: Mu-calpain is activated in human endometrial cells during hypoxia and that subsequent cleavage of the integrin beta3 cytoplasmic domain may give some adverse effects to the function of human endometrium.     

Brain-derived neurotrophic factor mediates neuroprotection against Aβ-induced toxicity through a mechanism independent on adenosine 2A receptor activation

Abstract

Brain-derived neurotrophic factor (BDNF) promotes neuronal survival through TrkB-FL activation. The activation of adenosine A_2A receptors (A_2AR) is essential for most of BDNF-mediated synaptic actions, such as synaptic plasticity, transmission and neurotransmitter release. We now aimed at evaluating the A_2AR influence upon BDNF-mediated neuroprotection against Aβ_25–35 toxicity in cultured neurons. Results showed that BDNF increases cell survival and reduces the caspase-3 and calpain activation induced by amyloid-β (Aβ) peptide, in a mechanism probably dependent on PLCγ pathway. This BDNF-mediated neuroprotection is not affected by A_2AR activation or inhibition. Moreover neither activation nor inhibition of A_2AR, per se, significantly influenced Aβ-induced neuronal death on calpain-mediated cleavage of TrkB induced by Aβ. In conclusion, these results suggest that, in opposition to the fast synaptic actions of BDNF, the neuroprotective actions of this neurotrophin against a strong Aβ insult do not require the activation of A_2AR.     

The physiological response of protease inhibition in dystrophic muscle

Duchenne muscular dystrophy (DMD) is caused by the production of a non‐functional dystrophin gene product and a failure to accumulate functional dystrophin protein in muscle cells. This leads to membrane instability, loss of Ca²⁺ homoeostasis and widespread cellular injury. Associated with these changes are increased protease activities in a variety of proteolytic systems. As such, there have been numerous investigations directed towards determining the therapeutic potential of protease inhibition. In this review, evidence from genetic and/or pharmacological inhibition of proteases as a treatment strategy for DMD is systematically evaluated. Specifically, we review the potential roles of calpain, proteasome, caspase, matrix metalloproteinase and serine protease inhibition as therapeutic approaches for DMD. We conclude that despite early results to the contrary, inhibition of calpain proteases is unlikely to be successful. Conversely, evidence suggests that inhibition of proteasome, matrix metalloproteinases and serine proteases does appear to decrease disease severity. An important caveat to these conclusions, however, is that the fundamental cause of DMD, dystrophin deficiency, is not corrected by this strategy. Hence, this should not be viewed as a cure, but rather, protease inhibitors should be considered for inclusion in a therapeutic cocktail. Physiological Relevance. Selective modulation of protease activity has the potential to profoundly change intracellular physiology resulting in a possible treatment for DMD. However, alteration of protease activities could also lead to worsening of disease progression by promoting the accumulation of substrates in the cell. The balance of benefit and potential damage caused by protease inhibition in human DMD patients is largely unexplored.     

钙激活中性蛋白酶介导雌激素增强MCF-7乳腺癌细胞的存活力

目的 探讨雌激素(E2)对MCF-7乳腺癌细胞钙激活中性蛋白酶1(CANP-1)基因表达和CANP蛋白酶活性的影响、以及CANP活性在E2增强细胞存活力中的作用.方法 以MCF-7乳腺癌细胞为研究模型、采用RT-PCR法检测mRNA表达、蛋白印迹法观察CANP特异性底物FAK蛋白剪切、血清饥饿诱导细胞死亡、锥虫蓝染色及细胞计数法检测细胞存活力.结果 E2(10 nmoL/L)可明显刺激乳腺癌细胞CANP-1基因表达上调,CANP抑制剂则可显著抑制E2诱导CANP-1基因上调;在无血清培养条件下,E2激活CANP活性及增加细胞存活力(14.3±4.9％,P＜0.05),而CANP抑制剂可显著抑制E2诱导CANP激活以及细胞存活力增强(19.2±3.9％,P＜0.05).结论 E2刺激MCF-7乳腺癌细胞CANP-1基因表达上调并增强CANP活性,后者可能参与介导血清饥饿时E2增强MCF-7细胞的存活力.     

脊髓损伤中钙蛋白酶的作用

脊髓损伤后可发生不同程度的神经坏死和组织变性,导致脊髓神经功能障碍。脊髓继发性损伤过程中钙蛋白酶(calpain)在脊髓损伤中发挥重要作用。Calpain为一Ca2+依赖性半胱氨酸蛋白酶,该酶包括2种同分异构体μ-calpain和m-calpain,分别由微摩尔和毫摩尔浓度的Ca2+激活。细胞内calpain以非活性酶原形式存在,细胞内游离Ca2+浓度升高后,calpain酶原被活化,引起calpain活化后一系列分子生物化学的改变,在脊髓引起细胞凋亡或损伤。应用calpain的特异性抑制剂进行干预后,脊髓calpain的表达和活性受到抑制,脊髓的病理改变和细胞凋亡得到缓解,神经功能得以保护。该文将calpain在脊髓损伤发展过程中的作用作一综述。     

钙蛋白酶参与tau蛋白过度磷酸化和截断的机制研究进展

阿尔茨海默病(AD)是最常见的神经退行性疾病之一,临床表现为认知和记忆功能障碍。钙蛋白酶(calpain)在细胞中广泛地被激活,钙蛋白酶的紊乱会引起AD病理学中tau蛋白过度磷酸化和tau蛋白的异常剪切。钙蛋白酶通过影响糖原合成酶激酶3和蛋白磷酸酶2A的活性,从而使tau蛋白多个位点发生异常过度磷酸化,并且介导tau蛋白单体的截断,诱导神经变性。钙蛋白酶有望成为AD药物治疗的潜在靶点。     

Systematic spatiotemporal mapping reveals divergent cell death pathways in three mouse models of hereditary retinal degeneration

Calcium (Ca²⁺) dysregulation has been linked to neuronal cell death, including in hereditary retinal degeneration. Ca²⁺ dysregulation is thought to cause rod and cone photoreceptor cell death. Spatial and temporal heterogeneities in retinal disease models have hampered validation of this hypothesis. We examined the role of Ca²⁺ in photoreceptor degeneration, assessing the activation pattern of Ca²⁺-dependent calpain proteases, generating spatiotemporal maps of the entire retina in the cpfl1 mouse model for primary cone degeneration, and in the rd1 and rd10 models for primary rod degeneration. We used Gaussian process models to distinguish the temporal sequences of degenerative molecular processes from other variability sources.In the rd1 and rd10 models, spatiotemporal pattern of increased calpain activity matched the progression of primary rod degeneration. High calpain activity coincided with activation of the calpain-2 isoform but not with calpain-1, suggesting differential roles for both calpain isoforms. Primary rod loss was linked to upregulation of apoptosis-inducing factor, although only a minute fraction of cells showed activity of the apoptotic marker caspase-3. After primary rod degeneration concluded, caspase-3 activation appeared in cones, suggesting apoptosis as the dominant mechanism for secondary cone loss. Gaussian process models highlighted calpain activity as a key event during primary rod photoreceptor cell death. Our data suggest a causal link between Ca²⁺ dysregulation and primary, nonapoptotic degeneration of photoreceptors and a role for apoptosis in secondary degeneration of cones, highlighting the importance of the spatial and temporal location of key molecular events, which may guide the evaluation of new therapies.     

Two region‐dependent pathways of eosinophilic neuronal death after transient cerebral ischemia

Various types of eosinophilic neurons (ENs) are found in the post‐ischemic brain. We examined the temporal profile of ENs in the core and peripheral regions of the ischemic cortex, and analyzed the relationship to the expression of various cell death‐related factors. Unilateral forebrain ischemia was induced in Mongolian gerbils by transient common carotid artery occlusions, and the brains from 3 h to 2 weeks post‐ischemia were prepared for morphometric and immunohistochemical analysis of ENs. ENs with minimally abnormal nuclei and swollen cell bodies appeared at 3 h in the ischemic core and at 12 h in the periphery. In both locations multiple cell death‐related factors including calcium, µ‐calpain, cathepsin D, 78 kDa glucose‐regulated protein (GRP78) and ubiquitin were activated. In the ischemic core, pyknosis and irregularly atrophic cytoplasm peaked at 12 h, which was associated with significant increases in staining for calcium and µ‐calpain. ENs with pyknosis and scant cytoplasm peaked at 4 days and were positive for TUNEL and calcium staining. In the ischemic periphery, ENs had slightly atrophic cytoplasm and sequentially developed pyknosis, karyorrhexis and karyolysis over 1 week. These cells were positive for TUNEL and calcium staining. All types of EN were negative for caspase 3. There may be two region‐dependent pathways of EN changes in the post‐ischemic brain: pyknosis with cytoplasmic shrinkage in the core, and nuclear disintegration with slightly atrophic cytoplasm in the periphery. This difference coordinates different activation patterns of cell death‐related factors in ENs.