Cross-talk between calpain and caspase proteolytic systems during neuronal apoptosis

Apoptosis and its role in postmortem meat tenderness: A comprehensive review

Tenderness is considered a crucial attribute of postmortem meat quality, directly influencing consumers' preferences and industrial economic benefits. The degradation of myofibrillar proteins by endogenous enzymes within muscle fibers is believed to be the most effective pathway for meat tenderization. After animals are slaughtered and exsanguinated, there is a significant accumulation of reactive oxygen species (ROS), and a dramatic depletion of adenosine triphosphate (ATP) in muscle, leading to inevitable cell death. Caspases are activated in postmortem muscle cells, which disrupt the cell structure and improve meat tenderness through protein hydrolysis. In this review, we systematically summarized the three primary types of cell death studied in postmortem muscle: apoptosis, autophagy and necrosis. Furthermore, we emphasized the molecular mechanisms of apoptosis and its corresponding apoptotic pathways (mitochondrial apoptosis, death receptors, and endoplasmic reticulum stress) that affect meat tenderness during muscle conversion to meat. Additionally, factors affecting apoptosis were comprehensively discussed, such as ROS, heat shock proteins, calcium (Ca2+)/calpains, and Bcl-2 family proteins. Finally, this comprehensive review of existing research reveals that apoptosis is mainly mediated by the mitochondrial pathway. This ultimately leads to myofibrillar proteins degradation through caspase activation, improving meat tenderness. This review summarizes the research progress on postmortem muscle apoptosis and its molecular mechanisms in meat tenderization. We hope this will enhance understanding of postmortem meat tenderness and provide a theoretical basis for meat tenderization techniques development in the future.

Therapeutic targeting and HSC proliferation by small molecules and biologicals

Hematopoietic stem cells (HSCs) have considerably therapeutic value on autologous and allogeneic transplantation for many malignant/non-malignant hematological diseases, especially with improvement of gene therapy. However, acquirement of limited cell dose from HSC sources is the main handicap for successful transplantation. Therefore, many strategies based on the utilization of various cytokines, interaction of stromal cells, modulation of several extrinsic and intrinsic factors have been developed to promote ex vivo functional HSC expansion with high reconstitution ability until today. Besides all these strategies, small molecules become prominent with their ease of use and various advantages when they are translated to the clinic. In the last two decades, several small molecule compounds have been investigated in pre-clinical studies and, some of them were evaluated in different stages of clinical trials for their safety and efficiencies. In this chapter, we will present an overview of HSC biology, function, regulation and also, pharmacological HSC modulation with small molecules from pre-clinical and clinical perspectives.

Metabolic, proteomic and microbial changes postmortem and during beef aging

The purpose of this review is to provide an overview of the current knowledge about proteomic and metabolic changes in beef, the microbiological alteration postmortem and during aging, and observe the influence on beef quality parameters, such as tenderness, taste and flavor. This review will also focus on the different aging types (wet- and dry-aging), the aging or postmortem time of beef and their effect on the proteome and metabolome of beef. The Ca2+ homeostasis and adenosine 5'-triphosphate breakdown are the main reactions in the pre-rigor phase. After rigor mortis, the enzymatic degradation of connective tissues and breakdown of energy metabolism dominate molecular changes in beef. Important metabolic processes leading to the formation of saccharides, nucleotides, organic acids (e.g. lactic acid), creatine and fatty acids are considered in this context as possible flavor precursors or formers of beef flavor and taste. Flavor precursors are substrates for lipid oxidation, Strecker degradation and Maillard reaction during cooking or roasting. The findings presented should serve as a basis for a better understanding of beef aging and its molecular effects and are intended to contribute to meeting the challenges of improving beef quality.

Calpain Inhibitors as Potential Therapeutic Modulators in Neurodegenerative Diseases

It is considered a significant challenge to understand the neuronal cell death mechanisms with a suitable cure for neurodegenerative disorders in the coming years. Calpains are one of the best-considered "cysteine proteases activated" in brain disorders. Calpain is an important marker and mediator in the pathophysiology of neurodegeneration. Calpain activation being the essential neurodegenerative factor causing apoptotic machinery activation, it is crucial to develop reliable and effective approaches to prevent calpain-mediated apoptosis in degenerating neurons. It has been recently seen that the "inhibition of calpain activation" has appeared as a possible therapeutic target for managing neurodegenerative diseases. A systematic literature review of PubMed, Medline, Bentham, Scopus, and EMBASE (Elsevier) databases was conducted. The present article reviews the basic pathobiology and role of selective calpain inhibitors used in various neurodegenerative diseases as a therapeutic target.

Sustained Energy Deficit Following Perinatal Asphyxia: A Shift towards the Fructose-2,6-bisphosphatase (TIGAR)-Dependent Pentose Phosphate Pathway and Postnatal Development

Labor and delivery entail a complex and sequential metabolic and physiologic cascade, culminating in most circumstances in successful childbirth, although delivery can be a risky episode if oxygen supply is interrupted, resulting in perinatal asphyxia (PA). PA causes an energy failure, leading to cell dysfunction and death if re-oxygenation is not promptly restored. PA is associated with long-term effects, challenging the ability of the brain to cope with stressors occurring along with life. We review here relevant targets responsible for metabolic cascades linked to neurodevelopmental impairments, that we have identified with a model of global PA in rats. Severe PA induces a sustained effect on redox homeostasis, increasing oxidative stress, decreasing metabolic and tissue antioxidant capacity in vulnerable brain regions, which remains weeks after the insult. Catalase activity is decreased in mesencephalon and hippocampus from PA-exposed (AS), compared to control neonates (CS), in parallel with increased cleaved caspase-3 levels, associated with decreased glutathione reductase and glutathione peroxidase activity, a shift towards the TIGAR-dependent pentose phosphate pathway, and delayed calpain-dependent cell death. The brain damage continues long after the re-oxygenation period, extending for weeks after PA, affecting neurons and glial cells, including myelination in grey and white matter. The resulting vulnerability was investigated with organotypic cultures built from AS and CS rat newborns, showing that substantia nigra TH-dopamine-positive cells from AS were more vulnerable to 1 mM of H2O2 than those from CS animals. Several therapeutic strategies are discussed, including hypothermia; N-acetylcysteine; memantine; nicotinamide, and intranasally administered mesenchymal stem cell secretomes, promising clinical translation.

Proteome profiling of different rat brain regions reveals the modulatory effect of prolonged maternal separation on proteins involved in cell death-related processes

Background

Early-life stress in the form of maternal separation can be associated with alterations in offspring neurodevelopment and brain functioning. Here, we aimed to investigate the potential impact of prolonged maternal separation on proteomic profiling of prefrontal cortex, hippocampus and cerebellum of juvenile and young adult rats. A special attention was devoted to proteins involved in the process of cell death and redox state maintenance.

Methods

Long-Evans pups were separated from their mothers for 3 h daily over the first 3 weeks of life (during days 2–21 of age). Brain tissue samples collected from juvenile (22-day-old) and young adult (90-day-old) rats were used for label-free quantitative (LFQ) proteomic analysis. In parallel, selected oxidative stress markers and apoptosis-related proteins were assessed biochemically and by Western blot, respectively.

Results

In total, 5526 proteins were detected in our proteomic analysis of rat brain tissue. Approximately one tenth of them (586 proteins) represented those involved in cell death processes or regulation of oxidative stress balance. Prolonged maternal separation caused changes in less than half of these proteins (271). The observed alterations in protein expression levels were age-, sex- and brain region-dependent. Interestingly, the proteins detected by mass spectrometry that are known to be involved in the maintenance of redox state were not markedly altered. Accordingly, we did not observe any significant differences between selected oxidative stress markers, such as the levels of hydrogen peroxide, reduced glutathione, protein carbonylation and lipid peroxidation in brain samples from rats that underwent maternal separation and from the corresponding controls. On the other hand, a number of changes were found in cell death-associated proteins, mainly in those involved in the apoptotic and autophagic pathways. However, there were no detectable alterations in the levels of cleaved products of caspases or Bcl-2 family members. Taken together, these data indicate that the apoptotic and autophagic cell death pathways were not activated by maternal separation either in adolescent or young adult rats.

Conclusion

Prolonged maternal separation can distinctly modulate expression profiles of proteins associated with cell death pathways in prefrontal cortex, hippocampus and cerebellum of juvenile rats and the consequences of early-life stress may last into adulthood and likely participate in variations in stress reactivity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40659-021-00327-5.

SARS-CoV-2: An Update on Potential Antivirals in Light of SARS-CoV Antiviral Drug Discoveries

Coronaviruses (CoVs) are a group of RNA viruses that are associated with different diseases in animals, birds, and humans. Human CoVs (HCoVs) have long been known to be the causative agents of mild respiratory illnesses. However, two HCoVs associated with severe respiratory diseases are Severe Acute Respiratory Syndrome-CoV (SARS-CoV) and Middle East Respiratory Syndrome-CoV (MERS-CoV). Both viruses resulted in hundreds of deaths after spreading to several countries. Most recently, SARS-CoV-2 has emerged as the third HCoV causing severe respiratory distress syndrome and viral pneumonia (known as COVID-19) in patients from Wuhan, China, in December 2019. Soon after its discovery, SARS-CoV-2 spread to all countries, resulting in millions of cases and thousands of deaths. Since the emergence of SARS-CoV, many research groups have dedicated their resources to discovering effective antivirals that can treat such life-threatening infections. The rapid spread and high fatality rate of SARS-CoV-2 necessitate the quick discovery of effective antivirals to control this outbreak. Since SARS-CoV-2 shares 79% sequence identity with SARS-CoV, several anti-SARS-CoV drugs have shown promise in limiting SARS-CoV-2 replication in vitro and in vivo. In this review, we discuss antivirals described for SARS-CoV and provide an update on therapeutic strategies and antivirals against SARS-CoV-2. The control of the current outbreak will strongly depend on the discovery of effective and safe anti-SARS-CoV-2 drugs.

Protective role of endothelial calpain knockout in lipopolysaccharide-induced acute kidney injury via attenuation of the p38-iNOS pathway and NO/ROS production

To explore the role of calpain and its signaling pathway in lipopolysaccharide (LPS)-induced acute kidney injury (AKI), animal models of endotoxemia were established by administration of LPS to mice with endothelial-specific Capn4 knockout (TEK/Capn4^−/−), mice with calpastatin (an endogenous calpain inhibitor) overexpression (Tg-CAST) and mice with myeloid-specific Capn4 knockout (LYZ/Capn4^−/−). Mouse pulmonary microvascular endothelial cells (PMECs) were used as a model of the microvascular endothelium and were stimulated with LPS. Renal function, renal inducible nitric oxide synthase (iNOS) and endothelial NOS (eNOS) expression, cellular apoptosis, plasma and renal levels of NO and reactive oxygen species (ROS), and phosphorylation of mitogen-activated protein kinase (MAPK) family members (p38, ERK1/2, and JNK1/2) were examined. Moreover, a calpain inhibitor, calpastatin overexpression adenoviruses and MAPK inhibitors were used. Significant renal dysfunction was induced by LPS stimulation, and recovery was observed in TEK/Capn4^−/− and Tg-CAST mice but not in LYZ/Capn4^−/− mice. Endothelial Capn4 knockout also abrogated the LPS-induced increases in renal iNOS expression, caspase-3 activity and apoptosis and plasma and renal NO and ROS levels but did not obviously affect renal eNOS expression. Moreover, LPS increased both calpain and caspase-3 activity, and only the expression of iNOS in PMECs was accompanied by increased phosphorylation of p38 and JNK. Inhibiting calpain activity or p38 phosphorylation alleviated the increased iNOS expression, NO/ROS production, and cellular apoptosis induced by LPS. These results suggest that endothelial calpain plays a protective role in LPS-induced AKI by inhibiting p38 phosphorylation, thus attenuating iNOS expression and further decreasing NO and ROS overproduction-induced endothelial apoptosis.

Therapies that inhibit the enzyme calpain could alleviate the effects of acute kidney injury according to researchers in China and Canada. Acute kidney injury is induced by endotoxemia, in which changes in the permeability of the intestine allow lipopolysaccharides (LPS) to pass from gut bacteria into the bloodstream. Calpain is known to be active during this process. Zhifeng Liu at the General Hospital of Guangzhou Military Command and co-workers induced endotoxemia in various mouse models by injecting them with LPS. The LPS induced significant kidney dysfunction and cell death, but these were alleviated in mice that were genetically modified to block calpain activity in the blood vessel lining, and in mice that overexpressed calpastatin, a calpain inhibitor. Blocking calpain reduces the expression of nitric oxide synthases that damage endothelial cells.

The Long-Term Impairment in Redox Homeostasis Observed in the Hippocampus of Rats Subjected to Global Perinatal Asphyxia (PA) Implies Changes in Glutathione-Dependent Antioxidant Enzymes and TIGAR-Dependent Shift Towards the Pentose Phosphate Pathways: Effect of Nicotinamide

We have recently reported that global perinatal asphyxia (PA) induces a regionally sustained increase in oxidized glutathione (GSSG) levels and GSSG/GSH ratio, a decrease in tissue-reducing capacity, a decrease in catalase activity, and an increase in apoptotic caspase-3-dependent cell death in rat neonatal brain up to 14 postnatal days, indicating a long-term impairment in redox homeostasis. In the present study, we evaluated whether the increase in GSSG/GSH ratio observed in hippocampus involves changes in glutathione reductase (GR) and glutathione peroxidase (GPx) activity, the enzymes reducing glutathione disulfide (GSSG) and hydroperoxides, respectively, as well as catalase, the enzyme protecting against peroxidation. The study also evaluated whether there is a shift in the metabolism towards the penthose phosphate pathway (PPP), by measuring TIGAR, the TP53-inducible glycolysis and apoptosis regulator, associated with delayed cell death, further monitoring calpain activity, involved in bax-dependent cell death, and XRCC1, a scaffolding protein interacting with genome sentinel proteins. Global PA was induced by immersing fetus-containing uterine horns removed by a cesarean section from on term rat dams into a water bath at 37 °C for 21 min. Asphyxia-exposed and sibling cesarean-delivered fetuses were manually resuscitated and nurtured by surrogate dams. Animals were euthanized at postnatal (P) days 1 or 14, dissecting samples from hippocampus to be assayed for glutathione, GR, GPx (all by spectrophotometry), catalase (Western blots and ELISA), TIGAR (Western blots), calpain (fluorescence), and XRCC1 (Western blots). One hour after delivery, asphyxia-exposed and control neonates were injected with either 100 μl saline or 0.8 mmol/kg nicotinamide, i.p., shown to protect from the short- and long-term consequences of PA. It was found that global PA produced (i) a sustained increase of GSSG levels and GSSG/GSH ratio at P1 and P14; (ii) a decrease of GR, GPx, and catalase activity at P1 and P14; (iii) a decrease at P1, followed by an increase at P14 of TIGAR levels; (iv) an increase of calpain activity at P14; and (v) an increase of XRCC1 levels, but only at P1. (vi) Nicotinamide prevented the effect of PA on GSSG levels and GSSG/GSH ratio, and on GR, GPx, and catalase activity, also on increased TIGAR levels and calpain activity observed at P14. The present study demonstrates that the long-term impaired redox homeostasis observed in the hippocampus of rats subjected to global PA implies changes in GR, GPx, and catalase, and a shift towards PPP, as indicated by an increase of TIGAR levels at P14.

The Effect of µ/m-Calpain on Protein Degradation of Chicken Breast Meat

This study was designed to determine the effects of µ/m-calpain on the degradation of cytoskeletal proteins in pectoralis major. Four chickens were slaughtered and the breasts were removed and stored for 12 hr at 4 °C. Each sample was divided into three groups and respectively immersed in control reagent, calpain inhibitor, and caspase inhibitor at 4 °C. The samples were used to evaluate troponin-T and desmin degradation, calpain activity, and myofibril ultrastructure at 12 hr, day 1, day 3, and day 7. Casein zymography revealed that µ-calpain could not be detected in all samples after 12 hr postmortem. The calpain inhibitor inhibited µ/m-calpain activity and reduced troponin-T and desmin degradation during 7 day postmortem. The caspase inhibitor inhibited µ/m-calpain activity and, troponin-T and desmin degradation before day 3 postmortem. The findings suggest that, µ/m-calpain had an effect on cytoskeletal protein degradation after 12 hr postmortem.

Interleukin-35 Attenuates D-Galactosamine/Lipopolysaccharide-Induced Liver Injury via Enhancing Interleukin-10 Production in Kupffer Cells

Interleukin (IL) -35 is an anti-inflammatory cytokine which exerts various beneficial effects on autoimmune diseases. However, whether IL-35 plays a role in endotoxin induced hepatitis demands clarification. This study aims to reveal the effect and mechanism of IL-35 on endotoxin induced liver injury. Acute hepatic injury was induced by D-galactosamine (D-GalN, 400 mg/kg) and lipopolysaccharide (LPS, 5 μg/kg) administration in mice. IL-35 treatment ameliorated D-GalN/LPS induced liver injury in a dose dependent manner as shown by histological examination, ALT determination and Caspase-3 activity assay. It also reduced production of pro-inflammatory cytokines, tumor necrosis factor (TNF)-α, IL-1β, and IL-6, and increased production of anti-inflammatory cytokines, IL-4, IL-10, and transforming growth factor (TGF)-β. This hepato-protective effect was proved mainly mediated by Kupffer cells (KC) via gadolinium chloride depletion and cell adoptive transfer experiment. In addition, IL-35 emolliated the cytotoxicity of LPS-triggered KCs to hepatocytes, suppressed nitric oxide (NO) and TNF-α production, and elevated IL-10 production in LPS stimulated KCs. Furthermore, IL-35 could not exert hepato-protective effect in IL-10-deficient mice in vivo and it could not suppress LPS induced NO and TNF-α production in IL-10-deficient KCs in vitro. In conclusion, IL-35 protects endotoxin-induced acute liver injury, which mainly acts thought increasing IL-10 production in KCs. This finding demonstrates a role of IL-35 in anti-infectious immunity and provides a potential therapeutic target in treating fulminant hepatitis.

JNK-mediated microglial DICER degradation potentiates inflammatory responses to induce dopaminergic neuron loss

Background

Amplified inflammation is important for the progression of Parkinson’s disease (PD). However, how this enhanced inflammation is regulated remains largely unknown. Deletion of DICER leads to progressive dopamine neuronal loss and induces gliosis. We hypothesized that the homeostasis of microglial DICER would be responsible for the amplified inflammation in the mouse model of PD.

Methods

The microglia or C57BL/6 mice were treated or injected with l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (MPTP) or 1-methyl-4-phenylpyridinium (MPP⁺), respectively, for the model establishment. Microglia and astrocytes sorted by fluorescence-activated cell sorter (FACS) were assayed by quantitative real-time PCR, Western blotting, immunoprecipitation, enzyme-linked immunosorbent assay (ELISA), immunohistofluorescence, and mass spectrometry.

Results

Microglial DICER was phosphorylated at serine 1456 by c-jun N-terminal kinase (JNK) and downregulated in response to 1-methyl-4-phenylpyridinium (MPP⁺), a causative agent in PD. Inhibition of JNK phosphorylation of DICER at serine 1456 rescued the MPP⁺-induced DICER degradation, suppressed microglial inflammatory process, and prevented the loss of tyrosine hydroxylase-expressing neurons in the mouse MPTP model.

Conclusions

JNK-mediated microglial DICER degradation potentiates inflammation to induce dopaminergic neuronal loss. Thus, preventing microglial DICER degradation could be a novel strategy for controlling neuroinflammation in PD.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1218-1) contains supplementary material, which is available to authorized users.

Mitochondrial BK Channel Openers CGS7181 and CGS7184 Exhibit Cytotoxic Properties

Potassium channel openers (KCOs) have been shown to play a role in cytoprotection through the activation of mitochondrial potassium channels. Recently, in several reports, a number of data has been described as off-target actions for KCOs. In the present study, we investigated the effects of BK_Ca channel openers CGS7181, CGS7184, NS1619, and NS004 in neuronal cells. For the purpose of this research, we used a rat brain, the mouse hippocampal HT22 cells, and the human astrocytoma U-87 MG cell line. We showed that CGS7184 activated the mitochondrial BK_Ca (mitoBK_Ca) channel in single-channel recordings performed on astrocytoma mitoplasts. Moreover, when applied to the rat brain homogenate or isolated rat brain mitochondria, CGS7184 increased the oxygen consumption rate, and can thus be considered a potentially cytoprotective agent. However, experiments on intact neuronal HT22 cells revealed that both CGS7181 and CGS7184 induced HT22 cell death in a concentration- and time-dependent manner. By contrast, we did not observe cell death when NS1619 or NS004 was applied. CGS7184 toxicity was not abolished by BK_Ca channel inhibitors, suggesting that the observed effects were independent of a BK_Ca-type channel activity. CGS7184 treatment resulted in an increase of cytoplasmic Ca²⁺ concentration that likely involved efflux from internal calcium stores and the activation of calpains (calcium-dependent proteases). The cytotoxic effect of the channel opener was partially reversed by a calpain inhibitor. Our data show that KCOs under study not only activate mitoBK_Ca channels from brain tissue, but also induce cell death when used in cellular models.

Protection against TBI-Induced Neuronal Death with Post-Treatment with a Selective Calpain-2 Inhibitor in Mice

Traumatic Brain Injury (TBI) is a major cause of death and disability worldwide. The calcium-dependent protease, calpain, has been shown to be involved in TBI-induced neuronal death. However, whereas various calpain inhibitors have been tested in several animal models of TBI, there has not been any clinical trial testing the efficacy of calpain inhibitors in human TBI. One important reason for this could be the lack of knowledge regarding the differential functions of the two major calpain isoforms in the brain, calpain-1 and calpain-2. In this study, we used the controlled cortical impact (CCI) model in mice to test the roles of calpain-1 and calpain-2 in TBI-induced neuronal death. Immunohistochemistry (IHC) with calpain activity markers performed at different time-points after CCI in wild-type and calpain-1 knock-out (KO) mice showed that calpain-1 was activated early in cortical areas surrounding the impact, within 0-8 h after CCI, whereas calpain-2 activation was delayed and was predominant during 8-72 h after CCI. Calpain-1 KO enhanced cell death, whereas calpain-2 activity correlated with the extent of cell death, suggesting that calpain-1 activation suppresses and calpain-2 activation promotes cell death following TBI. Systemic injection(s) of a calpain-2 selective inhibitor, NA101, at 1 h or 4 h after CCI significantly reduced calpain-2 activity and cell death around the impact site, reduced the lesion volume, and promoted motor and learning function recovery after TBI. Our data indicate that calpain-1 activity is neuroprotective and calpain-2 activity is neurodegenerative after TBI, and that a selective calpain-2 inhibitor can reduce TBI-induced cell death.

Molecular mechanisms underlying the α-tomatine-directed apoptosis in human malignant glioblastoma cell lines A172 and U-118 MG

In the present study, the molecular mechanisms involved in the α-tomatine-induced apoptosis in human glioblastoma cell lines A172 and U-118 MG were investigated. Wright staining and ApopTag assays were conducted to confirm the apoptosis induced by α-tomatine treatment. Fura-2 assay determined an enhancement in free Ca²⁺ intracellularly, indicating the occurrence of Ca²⁺-dependent apoptosis induction. Western blot experiments were also performed to predict the apoptosis by measuring the changes in the Bax:Bcl-2 ratio. Increase of calpain activity triggered caspase-12 expression, which in turn further activated caspase-9. In addition, an increase in the ratio of Bax:Bcl-2 accounted for the mitochondrial release of cytochrome c into the cytosol for caspase-3 and caspase-9 activation. Elevated activity of calpain and caspase-3 yielded spectrin breakdown products with 145 and 120 kDa, respectively. Caspase-3 activation further cleaved the inhibitor of caspase activated DNase, while the apoptosis-inducing factor detected in the cytosol suggested that apoptosis was independent of caspase. The apoptosis induction was further supported by decreased expression levels of nuclear factor-κB and increased expression of the inhibitor of nuclear factor, IκBα. In conclusion, the presented experimental results revealed the stimulation of different molecular mechanisms for α-tomatine-mediated apoptosis in A172 and U-118 MG human glioblastoma cell lines.

Inhibition of Calpains Protects Mn-Induced Neurotransmitter release disorders in Synaptosomes from Mice: Involvement of SNARE Complex and Synaptic Vesicle Fusion

Overexposure to manganese (Mn) could disrupt neurotransmitter release via influencing the formation of SNARE complex, but the underlying mechanisms are still unclear. A previous study demonstrated that SNAP-25 is one of substrate of calpains. The current study investigated whether calpains were involved in Mn-induced disorder of SNARE complex. After mice were treated with Mn for 24 days, Mn deposition increased significantly in basal nuclei in Mn-treated and calpeptin pre-treated groups. Behaviorally, less time spent in the center of the area and decreased average velocity significantly in an open field test after 24 days of Mn exposure. With the increase in MnCl₂ dosage, intracellular Ca²⁺ increased significantly, but pretreatment with calpeptin caused a dose-dependent decrease in calpains activity. There were fragments of N-terminal of SNAP-25 protein appearance in Mn-treated groups, but it is decreased with pretreatment of calpeptin. FM1-43-labeled synaptic vesicles also provided evidence that the treatment with Mn resulted in increasing first and then decreasing, which was consistent with Glu release and the 80 kDa protein levels of SNARE complexes. In summary, Mn induced the disorder of neurotransmitter release through influencing the formation of SNARE complex via cleaving SNAP-25 by overactivation of calpains in vivo.

Calpains and neuronal damage in the ischemic brain: The swiss knife in synaptic injury

The excessive extracellular accumulation of glutamate in the ischemic brain leads to an overactivation of glutamate receptors with consequent excitotoxic neuronal death. Neuronal demise is largely due to a sustained activation of NMDA receptors for glutamate, with a consequent increase in the intracellular Ca(2+) concentration and activation of calcium- dependent mechanisms. Calpains are a group of Ca(2+)-dependent proteases that truncate specific proteins, and some of the cleavage products remain in the cell, although with a distinct function. Numerous studies have shown pre- and post-synaptic effects of calpains on glutamatergic and GABAergic synapses, targeting membrane- associated proteins as well as intracellular proteins. The resulting changes in the presynaptic proteome alter neurotransmitter release, while the cleavage of postsynaptic proteins affects directly or indirectly the activity of neurotransmitter receptors and downstream mechanisms. These alterations also disturb the balance between excitatory and inhibitory neurotransmission in the brain, with an impact in neuronal demise. In this review we discuss the evidence pointing to a role for calpains in the dysregulation of excitatory and inhibitory synapses in brain ischemia, at the pre- and post-synaptic levels, as well as the functional consequences. Although targeting calpain-dependent mechanisms may constitute a good therapeutic approach for stroke, specific strategies should be developed to avoid non-specific effects given the important regulatory role played by these proteases under normal physiological conditions.

Proteolytic fragmentation of inositol 1,4,5-trisphosphate receptors: a novel mechanism regulating channel activity?

Inositol 1,4,5-trisphosphate receptors (IP3 Rs) are a family of ubiquitously expressed intracellular Ca(2+) release channels. Regulation of channel activity by Ca(2+) , nucleotides, phosphorylation, protein binding partners and other cellular factors is thought to play a major role in defining the specific spatiotemporal characteristics of intracellular Ca(2+) signals. These properties are, in turn, believed pivotal for the selective and specific physiological activation of Ca(2+) -dependent effectors. IP3 Rs are also substrates for the intracellular cysteine proteases, calpain and caspase. Cleavage of the IP3 R has been proposed to play a role in apoptotic cell death by uncoupling regions important for IP3 binding from the channel domain, leaving an unregulated leaky Ca(2+) pore. Contrary to this hypothesis, we demonstrate following proteolysis that N- and C-termini of IP3 R1 remain associated, presumably through non-covalent interactions. Further, we show that complementary fragments of IP3 R1 assemble into tetrameric structures and retain their ability to be regulated robustly by IP3 . While peptide continuity is clearly not necessary for IP3 -gating of the channel, we propose that cleavage of the IP3 R peptide chain may alter other important regulatory events to modulate channel activity. In this scenario, stimulation of the cleaved IP3 R may support distinct spatiotemporal Ca(2+) signals and activation of specific effectors. Notably, in many adaptive physiological events, the non-apoptotic activities of caspase and calpain are demonstrated to be important, but the substrates of the proteases are poorly defined. We speculate that proteolytic fragmentation may represent a novel form of IP3 R regulation, which plays a role in varied adaptive physiological processes.

Caspase-dependent degradation of MDMx/MDM4 cell cycle regulatory protein in amyloid β-induced neuronal damage

MDMx/MDM4 is a negative regulator of the p53 tumor suppressor protein and is necessary for survival in dividing cells. MDMx is also expressed in postmitotic neurons, with prosurvival roles that are independent of its extensively described roles in carcinogenesis. We and others have shown a role for MDMx loss in neuronal death in vitro and in vivo in several neurodegenerative diseases. Further, we have recently shown that MDMx is targeted for proteolytic degradation by calcium-dependent proteases, calpains, in neurons in vitro, and that MDMx overexpression provided partial neuroprotection in a model of HIV-associated neurodegeneration. Here, we assessed whether amyloid β (Aβ)-induced MDMx degradation occurred in Alzheimer's Disease (AD) models. Our data shows an age-dependent reduction in MDMx levels in cholinergic neurons within the cortex of adult mice expressing the swedish mutant of the amyloid precursor protein, APP in the Tg2576 murine model of AD. In vitro, Aβ treatment of primary cortical neurons led to the caspase-dependent MDMx degradation. Our findings suggest that MDMx degradation associated with neuronal death occurs via caspase activation in neurons, and that the progressive loss of MDMx protein represents a potential mechanism of Aβ-induced neuronal death during disease progression in AD.

Examining the Neural and Astroglial Protective Effects of Cellular Prion Protein Expression and Cell Death Protease Inhibition in Mouse Cerebrocortical Mixed Cultures

Overexpression of cellular prion protein, PrP(C), has cytoprotective effects against neuronal injuries. Inhibition of cell death-associated proteases such as necrosis-linked calpain and apoptosis-linked caspase are also neuroprotective. Here, we systematically studied how PrP(C) expression levels and cell death protease inhibition affect cytotoxic challenges to both neuronal and glial cells in mouse cerebrocortical mixed cultures (CCM). Primary CCM derived from three mouse lines expressing no (PrP(C) knockout mice (PrPKO)), normal (wild-type (wt)), or high (tga20) levels of PrP(C) were subjected to necrotic challenge (calcium ionophore A23187) and apoptotic challenge (staurosporine (STS)). CCM which originated from tga20 mice provided the most robust neuron-astroglia protective effects against necrotic and early apoptotic cell death (lactate dehydrogenase (LDH) release) at 6 h but subsequently lost its cytoprotective effects. In contrast, PrPKO-derived cultures displayed elevated A23187- and STS-induced cell death at 24 h. Calpain inhibitor SNJ-1945 protected against A23187 challenge at 6 h in CCM from all three mouse lines but protected only against A23187 and STS treatments by 24 h in the PrPKO line. In parallel, caspase inhibitor Z-D-DCB protected against pro-apoptotic STS challenge at 6 and 24 h. Furthermore, we also examined αII-spectrin breakdown products (primarily from neurons) and glial fibrillary acidic protein (GFAP) breakdown products (from astroglia) as cytoskeletal proteolytic biomarkers. Overall, it appeared that both neurons and astroglial cells were less vulnerable to proteolytic attack during A23187 and STS challenges in tga20-derived cultures but more vulnerable in PrPKO-derived cultures. In addition, calpain and caspase inhibitors provide further protection against respective protease attacks on these neuronal and glial cytoskeletal proteins in CCM regardless of mouse-line origin. Lastly, some synergistic cytoprotective effects between PrP(C) expression and addition of cell death-linked protease inhibitors were also observed.

Therapeutic Efficacy of E-64-d, a Selective Calpain Inhibitor, in Experimental Acute Spinal Cord Injury

This study aims to investigate the therapeutic effect of calpain inhibitor E-64-d on SCI and to find a new approach to treat SCI. When an SCI rat model was established, it was immediately administered with E-64-d. RT-PCR and Western blotting were used to determine the protein and mRNA levels of calpain 1 and 68-kD NFP. TUNEL staining and NeuN labeling were performed to analyze neuronal apoptosis in the lesion. Immunohistochemistry assay was carried out to observe the expressions of calpain 1 and GFAP. Cyclooxygenase-2 activity was measured to show the immune response status. Locomotor function was evaluated by inclined plane test and Basso, Beattie, and Bresnahan locomotor rating scale. The results showed that calpain 1 was activated after SCI occurred. Treatment with E-64-d decreased expressions of calpain 1 and GFAP, alleviated neuronal apoptosis, inhibited cyclooxygenase-2 activity, and resulted in the promoted locomotor function. Furthermore, combination of E-64-d and MP had better efficacy than did E-64-d or MP alone. E-64-d is expected to be applied to treat SCI, and its alliance with MP may provide a valid strategy for SCI therapy.

Caspase-1-mediated pathway promotes generation of thromboinflammatory microparticles

Extracellular ATP is a signal of tissue damage and induces macrophage responses that amplify inflammation and coagulation. Here we demonstrate that ATP signaling through macrophage P2X7 receptors uncouples the thioredoxin (TRX)/TRX reductase (TRXR) system and activates the inflammasome through endosome-generated ROS. TRXR and inflammasome activity promoted filopodia formation, cellular release of reduced TRX, and generation of extracellular thiol pathway-dependent, procoagulant microparticles (MPs). Additionally, inflammasome-induced activation of an intracellular caspase-1/calpain cysteine protease cascade degraded filamin, thereby severing bonds between the cytoskeleton and tissue factor (TF), the cell surface receptor responsible for coagulation activation. This cascade enabled TF trafficking from rafts to filopodia and ultimately onto phosphatidylserine-positive, highly procoagulant MPs. Furthermore, caspase-1 specifically facilitated cell surface actin exposure, which was required for the final release of highly procoagulant MPs from filopodia. Together, the results of this study delineate a thromboinflammatory pathway and suggest that components of this pathway have potential as pharmacological targets to simultaneously attenuate inflammation and innate immune cell-induced thrombosis.

Neuroprotective strategies against calpain-mediated neurodegeneration

Calpains are calcium-dependent proteolytic enzymes that have deleterious effects on neurons upon their pathological over-activation. According to the results of numerous studies to date, there is no doubt that abnormal calpain activation triggers activation and progression of apoptotic processes in neurodegeneration, leading to neuronal death. Thus, it is very crucial to unravel all the aspects of calpain-mediated neurodegeneration in order to protect neurons through eliminating or at least minimizing its lethal effects. Protecting neurons against calpain-activated apoptosis basically requires developing effective, reliable, and most importantly, therapeutically applicable approaches to succeed. From this aspect, the most significant studies focusing on preventing calpain-mediated neurodegeneration include blocking the N-methyl-d-aspartate (NMDA)-type glutamate receptor activities, which are closely related to calpain activation; directly inhibiting calpain itself via intrinsic or synthetic calpain inhibitors, or inhibiting its downstream processes; and utilizing the neuroprotectant steroid hormone estrogen and its receptors. In this review, the most remarkable neuroprotective strategies for calpain-mediated neurodegeneration are categorized and summarized with respect to their advantages and disadvantages over one another, in terms of their efficiency and applicability as a therapeutic regimen in the treatment of neurodegenerative diseases.

Human structural proteome-wide characterization of Cyclosporine A targets

MOTIVATION

Off-target interactions of a popular immunosuppressant Cyclosporine A (CSA) with several proteins besides its molecular target, cyclophilin A, are implicated in the activation of signaling pathways that lead to numerous side effects of this drug.

RESULTS

Using structural human proteome and a novel algorithm for inverse ligand binding prediction, ILbind, we determined a comprehensive set of 100+ putative partners of CSA. We empirically show that predictive quality of ILbind is better compared with other available predictors for this compound. We linked the putative target proteins, which include many new partners of CSA, with cellular functions, canonical pathways and toxicities that are typical for patients who take this drug. We used complementary approaches (molecular docking, molecular dynamics, surface plasmon resonance binding analysis and enzymatic assays) to validate and characterize three novel CSA targets: calpain 2, caspase 3 and p38 MAP kinase 14. The three targets are involved in the apoptotic pathways, are interconnected and are implicated in nephrotoxicity.

Role of calpastatin in the regulation of mRNA expression of calpain, caspase, and heat shock protein systems in bovine muscle satellite cells

Calpastatin participates in apoptotic cell death and cell signaling, but its role in skeletal myoblast development and molecular involvements in cell growth still remains unknown. The current study aimed to investigate the role of calpastatin on the expression patterns of calpains, caspases, and heat shock proteins (HSPs). In addition, the cell viability during myoblast growth under calpastatin silence condition was also investigated. Three small interference RNA sequences (siRNAs) were used to silence calpastatin gene and ligated into pSilencer plasmid vector to construct short hairpin RNA (shRNA) expression. The all three siRNAs significantly silence the calpastatin gene. Moreover, suppression of calpastatin significantly reduced the viability of myoblasts during growth phase when compared to control cells. Additionally, knockdown of calpastatin significantly increased the mRNA expression of μ-calpain, caspase-3, caspase-7, and caspase-9, as well as HSP-27, -70, and -90. The present study results suggested that the suppression of calpastatin resulted in the increased expression of μ-calpain, caspases, and HSPs which in turn regulate the apoptotic cell death. The present study throws light on the central role of calpastatin in the control of calpain activity, cell proliferation, cell survival, and apoptotic pathways.

Astragalus saponins modulates colon cancer development by regulating calpain-mediated glucose-regulated protein expression

Background

Glucose-regulated proteins (GRP) are induced in the cancer microenvironment to promote tumor survival, metastasis and drug resistance. AST was obtained from the medicinal plant Astragalus membranaceus, which possesses anti-tumor and pro-apoptotic properties in colon cancer cells and tumor xenograft. The present study aimed to investigate the involvement of GRP in endoplasmic reticulum (ER) stress-mediated apoptosis during colon cancer development, with focus on the correlation between AST-evoked regulation of GRP and calpain activation.

Methods

The effects of AST on GRP and apoptotic activity were assessed in HCT 116 human colon adenocarcinoma cells. Calpain activity was examined by using a fluorescence assay kit. Immunofluorescence staining and immunoprecipitation were employed to determine the localization and association between calpains and GRP. GRP78 gene silencing was performed to confirm the importance of GRP in anticancer drug activities. The modulation of GRP and calpains was also studied in nude mice xenograft.

Results

ER stress-mediated apoptosis was induced by AST, as shown by elevation in both spliced XBP-1 and CHOP levels, with parallel up-regulation of GRP. The expression of XBP-1 and CHOP continued to increase after the peak level of GRP was attained at 24 h. Nevertheless, the initial increase in calpain activity as well as calpain I and II protein level was gradually declined at later stage of drug treatment. Besides, the induction of GRP was partly reversed by calpain inhibitors, with concurrent promotion of AST-mediated apoptosis. The knockdown of GRP78 by gene silencing resulted in higher sensitivity of colon cancer cells to AST-induced apoptosis and reduction of colony formation. The association between calpains and GRP78 had been confirmed by immunofluorescence staining and immunoprecipitation. Modulation of GRP and calpains by AST was similarly demonstrated in nude mice xenograft, leading to significant inhibition of tumor growth.

Conclusions

Our findings exemplify that calpains, in particular calpain II, play a permissive role in the modulation of GRP78 and consequent regulation of ER stress-induced apoptosis. Combination of calpain inhibitors and AST could exhibit a more pronounced pro-apoptotic effect. These results help to envisage a new therapeutic approach in colon cancer by targeting calpain and GRP.

Electronic supplementary material

The online version of this article (doi:10.1186/1472-6882-14-401) contains supplementary material, which is available to authorized users.

Reduced syncytin-1 expression in choriocarcinoma BeWo cells activates the calpain1-AIF-mediated apoptosis, implication for preeclampsia

Placentas associated with preeclampsia are characterized by extensive apoptosis in trophoblast lineages. Syncytin-1 (HERVWE1) mediates the fusion of cytotrophoblasts to form syncytiotrophoblasts, which assume the placental barrier, fetal-maternal exchange and endocrine functions. While decreased syncytin-1 expression has been observed in preeclamptic placentas, it is not clear if this alteration is involved in trophoblast apoptosis. In the current study, we found that siRNA-mediated knockdown of syncytin-1 led to apoptosis in choriocarcinoma BeWo, a cell line of trophoblastic origin. Characterization of the apoptotic pathways indicated that this effect does not rely on the activation of caspases. Rather, decreased syncytin-1 levels activated the apoptosis inducing factor (AIF) apoptotic pathway by inducing the expression, cleavage, and nuclear translocation of AIF. Moreover, calpain1, the cysteine protease capable of cleaving AIF, was upregulated by syncytin-1 knockdown. Furthermore, treatment with calpain1 inhibitor MDL28170 effectively reversed AIF cleavage, AIF nuclear translocation, and cell apoptosis triggered by syncytin-1 downregulation, verifying the specific action of calpain1-AIF pathway in trophoblast apoptosis. We confirmed that preeclamptic placentas express lower levels of syncytin-1 than normal placentas, and observed an inverse correlation between syncytin-1 and AIF/calpain1 mRNA levels, a result consistent with the in vitro findings. Immunohistochemistry analyses indicated decreased syncytin-1 and increased AIF and calpain1 protein levels in apoptotic cells of preeclamptic placentas. These findings have for the first time revealed that decreased levels of syncytin-1 can trigger the AIF-mediated apoptosis pathway in BeWo cells. This novel mechanism may contribute to the structural and functional deficiencies of syncytium frequently observed in preeclamptic placentas.

CDK5 protects from caspase-induced Ataxin-3 cleavage and neurodegeneration

Spinocerebellar ataxia type 3 (SCA3) is one of at least nine inherited neurodegenerative diseases caused by an expansion of a polyglutamine tract within corresponding disease-specific proteins. In case of SCA3, mutation of Ataxin-3 results in aggregation of misfolded protein, formation of intranuclear as well as cytosolic inclusion bodies and cell death in distinct neuronal populations. Since cyclin-dependent kinase-5 (CDK5) has been shown to exert beneficial effects on aggregate formation and cell death in various polyglutamine diseases, we tested its therapeutic potential for SCA3. Our data show increased caspase-dependent Ataxin-3 cleavage, aggregation, and neurodegeneration in the absence of sufficient CDK5 activity. This disease-propagating effect could be reversed by mutation of the caspase cleavage site in Ataxin-3. Moreover, reduction of CDK5 expression levels by RNAi in vivo enhances SCA3 toxicity as assayed in a Drosophila model for SCA3. In summary, we present CDK5 as a potent neuroprotectant, regulating cleavage and thereby toxicity of Ataxin-3 and other polyglutamine proteins. We propose that increased caspase-dependent cleavage of mutated Ataxin-3, because of missing CDK5 shielding, leads to aggregation and cell death. Moreover, reduction of CDK5 expression levels by RNAi in vivo enhances SCA3 toxicity as assayed in a Drosophila model for SCA3. We think that CDK5 functions as a shield against cleavage-induced toxification and thereby is an interesting target for therapeutic intervention in polyQ disease in general.

Gallic acid selectively induces the necrosis of activated hepatic stellate cells via a calcium-dependent calpain I activation pathway

AIMS

The activation of hepatic stellate cells (HSCs) in response to liver injury is critical to the development of liver fibrosis, thus, the blockage of the activation of HSCs is considered as a rational approach for anti-fibrotic treatment. In this report, we investigated the effects and the underlying mechanisms of gallic acid (GA) in interfering with the activation of HSCs.

MAIN METHODS

The primary cultured rat HSCs were treated with various doses of GA for different time intervals. The morphology, viability, caspase activity, calcium ion flux, calpain I activity, reactive oxygen species generation and lysosomal functions were then investigated.

KEY FINDINGS

GA selectively killed HSCs in both dose- and time-dependent manners, while remained no harm to hepatocytes. Besides, caspases were not involved in GA-induced cell death of HSCs. Further results showed that GA toxicity was associated with a rapid burst of reactive oxygen species (ROS) and a subsequent increase of intracellular Ca(2+) and calpain activity. Addition of calpain I but not calpain II inhibitor rescued HSCs from GA-induced death. In parallel, pretreatment with antioxidants or an intracellular Ca(2+) chelator eradicated GA responses, implying that GA-mediated cytotoxicity was dependent on its pro-oxidative properties and its effect on Ca(2+) flux. Furthermore, application of ROS scavengers also reversed Ca(2+) release and the disruption of lysosomal membranes in GA-treated HSCs.

SIGNIFICANCE

These results provide evidence for the first time that GA causes selective HSC death through a Ca(2+)/calpain I-mediated necrosis cascade, suggesting that GA may represent a potential therapeutic agent to combat liver fibrosis.

Functional validation of a human CAPN5 exome variant by lentiviral transduction into mouse retina

Exome sequencing indicated that the gene encoding the calpain-5 protease, CAPN5, is the likely cause of retinal degeneration and autoimmune uveitis in human patients with autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV, OMIM #193235). To explore the mechanism of ADNIV, a human CAPN5 disease allele was expressed in mouse retinas with a lentiviral vector created to express either the wild-type human (h) CAPN5 or the ADNIV mutant hCAPN5-R243L allele under a rhodopsin promoter with tandem green fluorescent protein (GFP) expression. Vectors were injected into the subretinal space of perinatal mice. Mouse phenotypes were analyzed using electroretinography, histology and inflammatory gene expression profiling. Mouse calpain-5 showed high homology to its human ortholog with >98% sequence identity that includes the ADNIV mutant residue. Calpain-5 protein was expressed in the inner and outer segments of the photoreceptors and in the outer plexiform layer. Expression of the hCAPN5-R243L allele caused loss of the electroretinogram b-wave, photoreceptor degeneration and induction of immune cell infiltration and inflammatory genes in the retina, recapitulating major features of the ADNIV phenotype. Intraocular neovascularization and fibrosis were not observed during the study period. Our study shows that expression of the hCAPN5-R243L disease allele elicits an ADNIV-like disease in mice. It further suggests that ADNIV is due to CAPN5 gain-of-function rather than haploinsufficiency, and retinal expression may be sufficient to generate an autoimmune response. Genetic models of ADNIV in the mouse can be used to explore protease mechanisms in retinal degeneration and inflammation as well as preclinical therapeutic testing.

Regulation of axon degeneration after injury and in development by the endogenous calpain inhibitor calpastatin

Axon degeneration is widespread both in neurodegenerative disease and in normal neural development, but the molecular pathways regulating these degenerative processes and the extent to which they are distinct or overlapping remain incompletely understood. We report that calpastatin, an inhibitor of calcium-activated proteases of the calpain family, functions as a key endogenous regulator of axon degeneration. Calpastatin depletion was observed in degenerating axons after physical injury, and maintaining calpastatin inhibited degeneration of transected axons in vitro and in the optic nerve in vivo. Calpastatin depletion also occurred in a caspase-dependent manner in trophic factor-deprived sensory axons and was required for this in vitro model of developmental degeneration. In vivo, calpastatin regulated the normal pruning of retinal ganglion cell axons in their target field. These findings identify calpastatin as a key checkpoint for axonal survival after injury and during development, and demonstrate downstream convergence of these distinct pathways of axon degeneration.

Pea3 transcription factor family members Etv4 and Etv5 mediate retrograde signaling and axonal growth of DRG sensory neurons in response to NGF

Nerve growth factor (NGF) is a target-derived neurotrophic growth factor that controls many aspects of sensory and sympathetic neuronal development. The identification of transcription factors and downstream target genes that mediate NGF-dependent neuronal differentiation and target field innervation is currently a major challenge. Here, we show that the Pea3 transcription factor family members Etv4 and Etv5 are expressed by developing TrkA-positive dorsal root ganglion (DRG) neurons during the period of target innervation. Real-time PCR assays indicated that Etv4 and Etv5 mRNAs are significantly induced by NGF in different neuronal cells, suggesting that they could be involved in the biological responses induced by this neurotrophin. Interestingly, distal axon application of NGF in compartmentalized cultures of rat DRG sensory neurons was sufficient to induce a significant increase in Etv4 and Etv5 mRNA expression. Pharmacological assays also revealed that activation of MEK/ERK (MAPK) pathway is required for Etv4 and Etv5 gene induction in response to NGF. Downregulation of Etv4 and Etv5 using small interference RNA knockdown experiments inhibited NGF-induced neurite outgrowth of rat sensory neurons, while overexpression of full-length Etv4 or Etv5 potentiated neuronal differentiation in response to this neurotrophin. Together, these data establish Etv4 and Etv5 as essential molecules of the transcriptional program linking neurotrophin signaling to sensory neuronal differentiation, and suggest that they can be involved in NGF-mediated target innervation.

Transcriptional mechanisms underlying sensitization of peripheral sensory neurons by granulocyte-/granulocyte-macrophage colony stimulating factors

BACKGROUND

Cancer-associated pain is a major cause of poor quality of life in cancer patients and is frequently resistant to conventional therapy. Recent studies indicate that some hematopoietic growth factors, namely granulocyte macrophage colony stimulating factor (GMCSF) and granulocyte colony stimulating factor (GCSF), are abundantly released in the tumor microenvironment and play a key role in regulating tumor-nerve interactions and tumor-associated pain by activating receptors on dorsal root ganglion (DRG) neurons. Moreover, these hematopoietic factors have been highly implicated in postsurgical pain, inflammatory pain and osteoarthritic pain. However, the molecular mechanisms via which G-/GMCSF bring about nociceptive sensitization and elicit pain are not known.

RESULTS

In order to elucidate G-/GMCSF mediated transcriptional changes in the sensory neurons, we performed a comprehensive, genome-wide analysis of changes in the transcriptome of DRG neurons brought about by exposure to GMCSF or GCSF. We present complete information on regulated genes and validated profiling analyses and report novel regulatory networks and interaction maps revealed by detailed bioinformatics analyses. Amongst these, we validate calpain 2, matrix metalloproteinase 9 (MMP9) and a RhoGTPase Rac1 as well as Tumor necrosis factor alpha (TNFα) as transcriptional targets of G-/GMCSF and demonstrate the importance of MMP9 and Rac1 in GMCSF-induced nociceptor sensitization.

CONCLUSION

With integrative approach of bioinformatics, in vivo pharmacology and behavioral analyses, our results not only indicate that transcriptional control by G-/GMCSF signaling regulates a variety of established pain modulators, but also uncover a large number of novel targets, paving the way for translational analyses in the context of pain disorders.

Inhibition of aberrant cyclin-dependent kinase 5 activity attenuates isoflurane neurotoxicity in the developing brain

Aberrant CDK5 activity is implicated in a number of neurodegenerative disorders. Isoflurane exposure leads to neuronal apoptosis, and subsequent learning and memory defects in the developing brain. The present study was designed to examine whether and how CDK5 activity plays a role in developmental isoflurane neurotoxicity. Rat pups and hippocampal neuronal cultures were exposed to 1.5% isoflurane for 4 h. The protein and mRNA levels of CDK5, p35 and p25 were detected by western blot and QReal-Time PCR. CDK5 activity was evaluated in vitro using Histone H1 as a substrate. Roscovitine (an inhibitor of CDK5) was applied before isoflurane treatment, cleaved Caspase-3, Bcl-2, Bax, MEF2 and phospho-MEF2A-Ser-408 expressions were determined. Dominant-Negative CDK5 was transfected before isoflurane treatment. Neuronal apoptosis was evaluated by Flow cytometry (FCM) and TUNEL-staining. Cognitive functions were assessed by Morris water maze. We found that isoflurane treatment led to an aberrant CDK5 activation due to its activator p25 that was cleaved from p35 by calpain. Inhibition of CDK5 activity with Roscovitine enhanced Bcl-2, and decreased cleaved Caspase-3 and Bax expressions. In addition, isoflurane exposure resulted in a decrease of MEF2 and increase of phospho-MEF2A-Ser-408, which were rescued by Roscovitine or Dominant-Negative CDK5 transfection. Dominant-Negative CDK5 transfection also decreased the percentage of TUNEL-positive cells in isoflurane neurotoxicity. Moreover, Roscovitine remarkably alleviated the learning and memory deficits induced by postnatal isoflurane exposure. These results indicated that aberrant CDK5 activity-dependent MEF2 phosphorylation mediates developmental isoflurane neurotoxicity. Inhibition of CDK5 overactivation contributes to the relief of isoflurane neurotoxicity in the developing brain.

The effects of Capn1 gene inactivation on skeletal muscle growth, development, and atrophy, and the compensatory role of other proteolytic systems

Myofibrillar protein turnover is a key component of muscle growth and degeneration, requiring proteolytic enzymes to degrade the skeletal muscle proteins. The objective of this study was to investigate the role of the calpain proteolytic system in muscle growth development using μ-calpain knockout (KO) mice in comparison with control wild-type (WT) mice, and evaluate the subsequent effects of silencing this gene on other proteolytic systems. No differences in muscle development between genotypes were observed during the early stages of growth due to the up regulation of other proteolytic systems. The KO mice showed significantly greater m-calpain protein abundance (P < 0.01) and activity (P < 0.001), and greater caspase 3/7 activity (P < 0.05). At 30 wk of age, KO mice showed increased protein:DNA (P < 0.05) and RNA:DNA ratios (P < 0.01), greater protein content (P < 0.01) at the expense of lipid deposition (P < 0.05), and an increase in size and number of fast-twitch glycolytic muscle fibers (P < 0.05), suggesting that KO mice exhibit an increased capacity to accumulate and maintain protein in their skeletal muscle. Also, expression of proteins associated with muscle regeneration (neural cell adhesion molecule and myoD) were both reduced in the mature KO mice (P < 0.05 and P < 0.01, respectively), indicating less muscle regeneration and, therefore, less muscle damage. These findings indicate the concerted action of proteolytic systems to ensure muscle protein homeostasis in vivo. Furthermore, these data contribute to the existing evidence of the importance of the calpain system's involvement in muscle growth, development, and atrophy. Collectively, these data suggest that there are opportunities to target the calpain system to promote the growth and/or restoration of skeletal muscle mass.

Calpain cleaves methionine aminopeptidase-2 in a rat model of ischemia/reperfusion

Ischemic stroke results in multiple injurious signals within a cell including dysregulation of calcium homeostasis. Consequently, there is an increase in the enzymatic activity of the calpains, calcium dependent proteases that are thought to contribute to neuronal injury. In addition, cellular stress due to ischemia/reperfusion also triggers a decrease in protein translation through activation of the unfolded protein response (UPR). In the present study we found that methionine aminopeptidase 2 (MetAP2), a critical component of the translation initiation complex, is a calpain substrate. In vitro calpain assays demonstrated that while MetAP2 has autoproteolytic activity, calpain also produces a stable proteolytic fragment at 50kDa using recombinant MetAP2. This 50kDa fragment, in addition to a 57kDa fragment was present in in vitro digestions of rat brain homogenates. Production of these fragments was inhibited by calpastatin, the endogenous and specific inhibitor of calpain. Using an in vivo middle cerebral artery occlusion (MCAO) model only the 57kDa fragment of MetAP2 was observed. These data suggest that calpain activation in stroke may regulate MetAP2-mediated protein translation giving calpains a larger role in the cellular stress response than previously determined.

Caspase-3 in the central nervous system: beyond apoptosis

Caspase-3 has been identified as a key mediator of neuronal programmed cell death. This protease plays a central role in the developing nervous system and its activation is observed early in neural tube formation and persists during postnatal differentiation of the neural network. Caspase-3 activation, a crucial event of neuronal cell death program, is also a feature of many chronic neurodegenerative diseases. This traditional apoptotic function of caspase-3 is challenged by recent studies that reveal new cell death-independent roles for mitochondrial-activated caspase-3 in neurite pruning and synaptic plasticity. These findings underscore the need for further research into the mechanism of action and functions of caspase-3 that may prove useful in the development of novel pharmacological treatments for a diverse range of neurological disorders.

Effects of inhibitors on the synergistic interaction between calpain and caspase-3 during post-mortem aging of chicken meat

Calpain has been considered to be the most important protease involved in tenderization during the conversion of muscle into meat. However, recent evidence suggests the possible involvement of the key apoptosis protease, caspase, on post-mortem tenderization. This study used inhibitors of calpain and caspase-3 to treat chicken muscle immediately after slaughter and followed the changes in caspase-3 and calpain activities together with their expression during 5 days of aging. Addition of calpain inhibitors to the system resulted in significantly higher caspase-3 activities (p < 0.01) during storage. Western blot analysis of pro-caspase-3 and α-spectrin cleavage of the 120 kDa peptide (SBDP 120) showed that the addition of calpain inhibitors resulted in the formation of higher amounts of the active form of caspase-3 compared with the control (p < 0.01). Inclusion of inhibitors of caspase-3 led to lower calpain activities (p < 0.01) and dramatically reduced the expression of calpain-1 and calpain-2 (p < 0.01). Concomitantly, this inhibition resulted in greater calpastatin expression compared with the control (p < 0.01). The findings of this investigation show that calpain prevented the activation of caspase-3, whereas caspase-3 appeared to enhance the calpain activity during post-mortem aging through inhibition of calpastatin. It is therefore suggested that there is a relationship between caspase-3 and calpain which contributes to the tenderizing process during the conversion of muscle tissue into meat.

Proximal giant neurofilamentous axonopathy in mice genetically engineered to resist calpain and caspase cleavage of α-II spectrin

We use 1,2-diacetylbenzene (1,2-DAB) to probe molecular mechanisms of proximal giant neurofilamentous axonopathy (PGNA), a pathological hallmark of amyotrophic lateral sclerosis. The spinal cord proteome of rodents displaying 1,2-DAB PGNA suggests a reduction in the abundance of α-II spectrin (Spna2), a key protein in the maintenance of axonal integrity. Protein immunoblotting indicates that this reduction is due to Spna2 degradation. We investigated the importance of such degradation in 1,2-DAB PGNA. Spna2 mutant mice lacking a calpain- and/or caspase-sensitive domain (CSD), thus hypothetically resistant to 1,2-DAB, and wild-type littermates, were treated with 1,2-DAB, 35 mg/kg/day, or saline control, for 3 weeks. 1,2-DAB induced motor weakness and PGNA, irrespective of the genotype. Spna2-calpain breakdown products were not detected in mutant mice, which displayed a normal structure of the nervous system under saline treatment. Intriguingly, treatment with 1,2-DAB reduced the abundance of the caspase-specific 120-kDa Spna2 breakdown products. Our findings indicate that degradation of Spna2 by calpain- and/or caspase is not central to the pathogenesis of 1,2-DAB axonopathy. In addition, the Spna2-CSD seems to be not required for the maintenance of the cytoskeleton integrity. Our conceptual framework offers opportunities to study the role of calpain-caspase cross talk, including that of the protease degradomics, in models of axonal degeneration.

Aeromonas hydrophila induced head kidney macrophage apoptosis in Clarias batrachus involves the activation of calpain and is caspase-3 mediated

The mechanism of macrophage cytotoxicity induced by Aeromonas hydrophila is yet unresolved. We observed A. hydrophila induces Head Kidney Macrophage (HKM) apoptosis in Clarias batrachus, as evident from Hoechst 33342 and AnnexinV-Propidium Iodide staining and presence of oligonucleosomal DNA ladder. Initiation of apoptosis required the bacteria to be alive, be actively phagocytosed into HKM and was dependent on host proteins. Elevated cytosolic calcium and consequent calpain activity that declined following pre-incubation with EGTA, verapamil and nifedipine implicates the role of calcium influx through voltage gated calcium channels and calpain in A. hydrophila-induced HKM apoptosis. Though, calpain-1 and -2 were involved, calpain-2 appeared to be more important in the process. EGTA, verapamil, nifedipine and calpain-2 inhibitor reduced caspase-3 activity and apoptosis. We conclude that A. hydrophila alters cytosolic calcium homeostasis initiating the activation of calpains, more specifically calpain-2, which leads to caspase-3 mediated HKM apoptosis in C. batrachus.