Ablation of the calpain-targeted site in cardiac myosin binding protein-C is cardioprotective during ischemia-reperfusion injury

Cardiac myosin binding protein-C (cMyBP-C) phosphorylation is essential for normal heart function and protects the heart from ischemia-reperfusion (I/R) injury. It is known that protein kinase-A (PKA)-mediated phosphorylation of cMyBP-C prevents I/R-dependent proteolysis, whereas dephosphorylation of cMyBP-C at PKA sites correlates with its degradation. While sites on cMyBP-C associated with phosphorylation and proteolysis co-localize, the mechanisms that link cMyBP-C phosphorylation and proteolysis during cardioprotection are not well understood. Therefore, we aimed to determine if abrogation of cMyBP-C proteolysis in association with calpain, a calcium-activated protease, confers cardioprotection during I/R injury. Calpain is activated in both human ischemic heart samples and ischemic mouse myocardium where cMyBP-C is dephosphorylated and undergoes proteolysis. Moreover, cMyBP-C is a substrate for calpain proteolysis and cleaved by calpain at residues 272-TSLAGAGRR-280, a domain termed as the calpain-target site (CTS). Cardiac-specific transgenic (Tg) mice in which the CTS motif was ablated were bred into a cMyBP-C null background. These Tg mice were conclusively shown to possess a normal basal structure and function by analysis of histology, electron microscopy, immunofluorescence microscopy, Q-space MRI of tissue architecture, echocardiography, and hemodynamics. However, the genetic ablation of the CTS motif conferred resistance to calpain-mediated proteolysis of cMyBP-C. Following I/R injury, the loss of the CTS reduced infarct size compared to non-transgenic controls. Collectively, these findings demonstrate the physiological significance of calpain-targeted cMyBP-C proteolysis and provide a rationale for studying inhibition of calpain-mediated proteolysis of cMyBP-C as a therapeutic target for cardioprotection.

Electrical stimulation activates calpain 2 and subsequently upregulates collagens via the integrin β1/TGF-β1 signaling pathway

Stress urinary incontinence (SUI) is a public health issue attributed to weakened pelvic supporting tissues. Electrical stimulation (ES) is one of the first-line conservative treatments for SUI. However, the underlying mechanism of ES in the treatment of SUI is not clear. Here, we show that ES suppresses cell apoptosis and upregulates collagen expression by functioning as a cell growth inducer to activate the calpain 2/talin 1/integrin β1/transforming growth factor (TGF)-β1 axis. Specifically, ES promoted Ca²⁺ to flow into the cytoplasm through the calcium channel, Cav 3.2, thereby activating calpain 2. Then, the activated calpain 2 cleaved talin 1, which induced the activation of integrin β1 and upregulated the TGF-β1-mediated transcription of collagen I and III. Notably, blocking Cav 3.2 suppressed calcium influx and inhibited the activation of downstream proteins. Furthermore, the knockdown of calpain 2 resulted in the reduction of cleaved talin 1, and the shRNA-integrin β1 treatment downregulated the level of activated integrin β1 and the expression of TGF-β1-induced collagen I and III. An association of the ES-modulated collagen I and III upregulation with the therapeutic effect of the ES-Ca²⁺/calpain 2/talin 1/integrin β1/TGF-β1 axis was demonstrated in mouse fibroblast and mouse SUI models established through vaginal distension (VD). This outcome provides insight into clinical diagnosis and treatment.

Increased calpain-1 in mitochondria induces dilated heart failure in mice: role of mitochondrial superoxide anion

We and others have reported that calpain-1 was increased in myocardial mitochondria from various animal models of heart disease. This study investigated whether constitutive up-regulation of calpain-1 restricted to mitochondria induced myocardial injury and heart failure and, if so, whether these phenotypes could be rescued by selective inhibition of mitochondrial superoxide production. Transgenic mice with human CAPN1 up-regulation restricted to mitochondria in cardiomyocytes (Tg-mtCapn1/tTA) were generated and characterized with low and high over-expression of transgenic human CAPN1 restricted to mitochondria, respectively. Transgenic up-regulation of mitochondria-targeted CAPN1 dose-dependently induced cardiac cell death, adverse myocardial remodeling, heart failure, and early death in mice, the changes of which were associated with mitochondrial dysfunction and mitochondrial superoxide generation. Importantly, a daily injection of mitochondria-targeted superoxide dismutase mimetics mito-TEMPO for 1 month starting from age 2 months attenuated cardiac cell death, adverse myocardial remodeling and heart failure, and reduced mortality in Tg-mtCapn1/tTA mice. In contrast, administration of TEMPO did not achieve similar cardiac protection in transgenic mice. Furthermore, transgenic up-regulation of mitochondria-targeted CAPN1 induced a reduction of ATP5A1 protein and ATP synthase activity in hearts. In cultured cardiomyocytes, increased calpain-1 in mitochondria promoted mitochondrial permeability transition pore (mPTP) opening and induced cell death, which were prevented by over-expression of ATP5A1, mito-TEMPO or cyclosporin A, an inhibitor of mPTP opening. In conclusion, this study has provided direct evidence demonstrating that increased mitochondrial calpain-1 is an important mechanism contributing to myocardial injury and heart failure by disrupting ATP synthase, and promoting mitochondrial superoxide generation and mPTP opening.

Cell Death Mechanisms in a Mouse Model of Retinal Degeneration in Spinocerebellar Ataxia 7

Spino-cerebellar ataxia type 7 (SCA7) is a polyglutamine (polyQ) disorder characterized by neurodegeneration of the brain, cerebellum, and retina caused by a polyglutamine expansion in ataxin7. The presence of an expanded polyQ tract in a mutant protein is known to induce protein aggregation, cellular stress, toxicity, and finally cell death. However, the consequences of the presence of mutant ataxin7 in the retina and the mechanisms underlying photoreceptor degeneration remain poorly understood. In this study, we show that in a retinal SCA7 mouse model, polyQ ataxin7 induces stress within the retina and activates Muller cells. Moreover, unfolded protein response and autophagy are activated in SCA7 photoreceptors. We have also shown that the photoreceptor death does not involve a caspase-dependent apoptosis but instead involves apoptosis inducing factor (AIF) and Leukocyte Elastase Inhibitor (LEI/L-DNase II). When these two cell death effectors are downregulated by their siRNA, a significant reduction in photoreceptor death is observed. These results highlight the consequences of polyQ protein expression in the retina and the role of caspase-independent pathways involved in photoreceptor cell death.

LPS-Induced Inflammation Abolishes the Effect of DYRK1A on IkB Stability in the Brain of Mice

Down syndrome is characterized by premature aging and dementia with neurological features that mimic those found in Alzheimer's disease. This pathology in Down syndrome could be related to inflammation, which plays a role in other neurodegenerative diseases. We previously found a link between the NFkB pathway, long considered a prototypical proinflammatory signaling pathway, and the dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A). DYRK1A is associated with early onset of Alzheimer's disease in Down syndrome patients. Here, we sought to determine the role of DYRK1A on regulation of the NFkB pathway in the mouse brain. We found that over-expression of Dyrk1A (on a C57BL/6J background) stabilizes IκBα protein levels by inhibition of calpain activity and increases cytoplasmic p65 sequestration in the mouse brain. In contrast, Dyrk1A-deficient mice (on a CD1 background) have decreased IκBα protein levels with an increased calpain activity and decreased cytoplasmic p65 sequestration in the brain. Taken together, our results demonstrate a role of DYRK1A in regulation of the NFkB pathway. However, decreased IκBα and DYRK1A protein levels associated with an increased calpain activity were found in the brains of mice over-expressing Dyrk1A after lipopolysaccharide treatment. Although inflammation induced by lipopolysaccharide treatment has a positive effect on calpastatin and a negative effect on DYRK1A protein level, a positive effect on microglial activation is maintained in the brains of mice over-expressing Dyrk1A.

Calpain 1 in bronchoalveolar lavage fluid is associated with poor prognosis in lepidic predominant pulmonary adenocarcinoma

Calpain 1 is a proinflammatory calcium-activated cysteine protease, which can be partly externalized. Extracellular calpains limit inflammatory processes and promote tissue repair, through cell proliferation and migration. Toll like receptor (TLR) 2 has been identified as a target of extracellular calpains in lymphocytes. The aim was to investigate the externalization of calpain 1 and the release of soluble TLR2 during tumor progression of pulmonary lepidic predominant adenocarcinoma (LPA). Extracellular calpain 1, soluble fragment of TLR2 and cytokines were analyzed by ELISA in bronchoalveolar lavage fluid (BALF) supernatants from patients with LPA (n=68). Source of calpain was analyzed by immunohistochemistry and soluble TLR2 by flow cytometry on polymorphonuclear neutrophils (PMN) and human lung cancer cell lines. Extracellular calpain 1, secreted by tumor cells, was associated to tumor progression, neutrophilic inflammation, with a poor prognostic factor on survival (P=0.003). TLR2 was expressed on PMN and tumor cells and decreased after calpain exposure. Soluble fragment of TLR2 in BALF supernatants was correlated to the extracellular calpain 1 concentration (r=0.624; P<0.001), and its high level was associated with tumor progression and a pro-inflammatory environment. Extracellular calpain 1 secreted by tumor cells, could participate in inflammatory microenvironment and tumor progression through TLR2 in LPA.

Nimodipine attenuates the parkinsonian neurotoxin, MPTP-induced changes in the calcium binding proteins, calpain and calbindin

We have recently demonstrated neuroprotective abilities of nimodipine, an L-type voltage dependent calcium channel (VDCC) blocker in cellular and animal models of Parkinson's disease (PD). To understand the calcium regulatory mechanisms in the disease pathogenesis, the present study examined calcium regulatory proteins calbindin and calpain mRNA and protein levels employing quantitative PCR and western blot in 1-methyl-4-phenyl pyridinium ion (MPP⁺)-treated SH-SY5Y cell lines and in the striatum of mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). mRNA and protein levels of calbindin were lower, while that of calpain were higher in MPP⁺-treated SH-SY5Y cells and MPTP-treated mouse striatum as compared to their respective controls. Nimodipine pretreatment significantly attenuated these effects in the parkinsonian neurotoxin-treated SH-SY5Y cell line and in the mouse striatum. The activities of the apoptotic mediator, caspase-3 and calpain were increased in the neurotoxin-treated groups as compared to their respective controls, which was ameliorated by nimodipine pretreatment. These results suggest that parkinsonian neurotoxin-mediated dopaminergic neuronal death might involve defects in calcium regulatory proteins that control intracellular calcium homeostasis, and these could be corrected by inhibiting L-type VDCC activity. These findings support the notion that hypertensive patients who are on long-term intake of dihydropyridine have reduced risk for PD.

Calpain Purification Through Calpastatin and Calcium: Strategy and Procedures

This chapter describes the strategy and procedures for the calcium-mediated affinity purification of calpain. The affinity capture method exploits the reversible binding properties of calpain's intrinsically disordered protein (IDP) inhibitor, calpastatin. IDPs are easily produced in heterologous expression hosts and purified to homogeneity. Combining these properties with in vivo biotinylation leads to a simplified purification strategy whereby biotinylated human calpastatin domain 1 (hCSD1) can capture calpain efficiently from a complex biological mixture with only a single chromatographic step and in a considerably reduced time. Our approach is generally applicable through the in vivo biotinylation of any IDP of interest in order to capture its binding partner in a calcium- and chelator-based protocol.

The cAMP/PKA Pathway Inhibits Beta-amyloid Peptide Release from Human Platelets

The main component of Alzheimer's disease (AD) is the amyloid-beta peptide (Aβ), the brain of these patients is characterized by deposits in the parenchyma and cerebral blood vessels known as cerebral amyloid angiopathy (CAA). On the other hand, the platelets are the major source of the Aβ peptide in circulation and once secreted can activate the platelets and endothelial cells producing the secretion of several inflammatory mediators that finally end up unchaining the CAA and later AD. In the present study we demonstrate that cAMP/PKA pathway plays key roles in the regulation of calpain activation and secretion of Aβ in human platelets. We confirmed that inhibition of platelet functionality occurred when platelets were incubated with forskolin (molecule that rapidly increased cAMP levels). In this sense we found that platelets pre-incubated with forskolin (20 μM) present a complete inhibition of calpain activity and this effect is reversed using an inhibitor of protein kinase A. Consequentially, when platelets were inhibited by forskolin a reduction in the processing of the APP with the consequent decrease in the Aβ peptide secretion was observed. Therefore our study provides novel insight in relation to the mechanism of processing and release of the Aβ peptide from human platelets.

Calpain activation and neuronal death during early epileptogenesis

Epilepsy is a brain disorder characterized by a predisposition to suffer epileptic seizures. Acquired epilepsy might be the result of brain insults like head trauma, stroke, brain infection, or status epilepticus (SE) when one of these triggering injuries starts a transformative process known as epileptogenesis. There is some data to suggest that, during epileptogenesis, seizures themselves damage the brain but there is no conclusive evidence to demonstrate that spontaneous recurrent seizures themselves injure the brain. Our recent evidence indicates that calpain overactivation might be relevant for epileptogenesis. Here, we investigated if spontaneous recurrent seizures that occur during an early period of epileptogenesis show any correlation with the levels of calpain activation and/or expression. In addition, we also investigated a possible association between the occurrence of spontaneous seizures and increased levels of cell death, gliosis and inflammation (typical markers associated with epileptogenesis). We found that the number of spontaneous seizures detected prior to sample collection was correlated with altered calpain activity and expression. Moreover, the levels of hippocampal neurodegeneration were also correlated with seizure occurrence. Our findings suggest that, at least during early epileptogenesis, there is a correlation between seizure occurrence, calpain activity and neurodegeneration. Thus, this study opens the possibility that aberrant calpain reactivation by spontaneous seizures might contribute to the manifestation of future spontaneous seizures.

Inhibition of calpain delays early muscle atrophy after rotator cuff tendon release in sheep

Chronic rotator cuff (RC) tears are characterized by retraction, fat accumulation, and atrophy of the affected muscle. These features pose an intractable problem for surgical repair and subsequent recovery, and their prevention may be easier than reversal. Using an established ovine model, we tested the hypothesis that inhibition of the protease calpain mitigates m. infraspinatus atrophy by preservation of the myofibers' structural anchors in the sarcolemma (the costameres). Already 2 weeks of distal tendon release led to a reduction in muscle volume (-11.6 ± 9.1 cm3 , P = 0.038) and a 8.3% slow-to-fast shift of the fiber area (P = 0.046), which were both entirely abolished by chronic local administration of the calpain inhibitor calpeptin alone, and in combination with sildenafil. Calpain inhibition blunted the retraction of the muscle-tendon unit by 0.8-1.0 cm (P = 0.020) compared with the control group, and prevented cleavage of the costameric protein talin. Calpain 1 and 2 protein levels increased in the medicated groups after 4 weeks, counteracting the efficacy of calpeptin. Hence atrophic changes emerged after 4 weeks despite ongoing treatment. These findings suggest that the early muscular adaptations in the specific case of RC tear in the ovine model are indistinguishable from the atrophy and slow-to-fast fiber transformation observed with conventional unloading and can be prevented for 2 weeks. Concluding, calpain is a potential target to extend the temporal window for reconstruction of the ruptured RC tendon before recovery turns impossible.

Calpain Inhibition Increases SMN Protein in Spinal Cord Motoneurons and Ameliorates the Spinal Muscular Atrophy Phenotype in Mice

Spinal muscular atrophy (SMA), a leading genetic cause of infant death, is caused by the loss of survival motor neuron 1 (SMN1) gene. SMA is characterized by the degeneration and loss of spinal cord motoneurons (MNs), muscular atrophy, and weakness. SMN2 is the centromeric duplication of the SMN gene, whose numbers of copies determine the intracellular levels of SMN protein and define the disease onset and severity. It has been demonstrated that elevating SMN levels can be an important strategy in treating SMA and can be achieved by several mechanisms, including promotion of protein stability. SMN protein is a direct target of the calcium-dependent protease calpain and induces its proteolytic cleavage in muscle cells. In this study, we examined the involvement of calpain in SMN regulation on MNs. In vitro experiments showed that calpain activation induces SMN cleavage in CD1 and SMA mouse spinal cord MNs. Additionally, calpain 1 knockdown or inhibition increased SMN level and prevent neurite degeneration in these cells. We examined the effects of calpain inhibition on the phenotype of two severe SMA mouse models. Treatment with the calpain inhibitor, calpeptin, significantly improved the lifespan and motor function of these mice. Our observations show that calpain regulates SMN level in MNs and calpeptin administration improves SMA phenotype demonstrating the potential utility of calpain inhibitors in SMA therapy.

Creatine Monohydrate and Guanidinoacetic Acid Supplementation Affects the Growth Performance, Meat Quality, and Creatine Metabolism of Finishing Pigs

This study aimed to investigate the effects of creatine monohydrate (CMH) and guanidinoacetic acid (GAA) supplementation on the growth performance, meat quality, and creatine metabolism of finishing pigs. The pigs were randomly allocated to three treatment groups: the control group, CMH group, and GAA group. In comparison to the control group, CMH treatment increased average daily feed intake and GAA treatment increased average daily feed intake and average daily gain of pigs. In addition, CMH and GAA treatment increased pH_45 min, myofibrillar protein solubility, and calpain 1 mRNA expression level and decreased the drip loss and shear force value in longissimus dorsi or semitendinosus muscle. Moreover, CMH and GAA supplementation increased the concentrations of creatine and phosphocreatine and the mRNA expressions of guanidinoacetate N-methyltransferase and creatine transporter in longissimus dorsi muscle, semitendinosus muscle, liver, or kidneys and decreased the mRNA expressions of arginine:glycine amidinotransferase in kidneys. In conclusion, CMH and GAA supplementation could improve the growth performance and meat quality and alter creatine metabolism of finishing pigs.

A Calpain-Like Protein Is Involved in the Execution Phase of Programmed Cell Death of Entamoeba histolytica

Oxygen or nitrogen oxidative species and chemical stress induce the programmed cell death (PCD) of Entamoeba histolytica trophozoites. PCD caused by the aminoglycoside G418 is reduced by incubation with the cysteine protease inhibitor E-64; however, no typical caspases or metacaspases have been detected in this parasite. Calpain, a cysteine protease activated by calcium, has been suggested to be part of a specific PCD pathway in this parasite because the specific calpain inhibitor Z-Leu-Leu-Leu-al diminishes the PCD of trophozoites. Here, we predicted the hypothetical 3D structure of a calpain-like protein of E. histolytica and produced specific antibodies against it. We detected the protein in the cytoplasm and near the nucleus. Its expression gradually increased during incubation with G418, with the highest level after 9 h of treatment. In addition, a specific calpain-like siRNA sequence reduced the cell death rate by 65%. All these results support the hypothesis that the calpain-like protein is one of the proteases involved in the execution phase of PCD in E. histolytica. The hypothetical interactome of the calpain-like protein suggests that it may activate or regulate other proteins that probably participate in PCD, including those with EF-hand domains or other calcium-binding sites.

YC-1 alleviates bone loss in ovariectomized rats by inhibiting bone resorption and inducing extrinsic apoptosis in osteoclasts

Osteoporosis is a major health problem in postmenopausal women and the elderly that leads to fractures associated with substantial morbidity and mortality. Current osteoporosis therapies have significant drawbacks, and the risk of fragility fractures has not yet been eliminated. There remains an unmet need for a broader range of therapeutics. Previous studies have shown that YC-1 has important regulatory functions in the cardiovascular and nervous systems. Many of the YC-1 effector molecules in platelets, smooth muscle cells and neurons, such as cGMP and μ-calpain, also have important functions in osteoclasts. In this study, we explored the effects of YC-1 on bone remodeling and determined the potential of YC-1 as a treatment for postmenopausal osteoporosis. Micro-computed tomography of lumbar vertebrae showed that YC-1 significantly improved trabecular bone microarchitecture in ovariectomized rats compared with sham-operated rats. YC-1 also significantly reversed the increases in serum bone resorption and formation in these rats, as measured by enzyme immunoassays for serum CTX-1 and P1NP, respectively. Actin ring and pit formation assays and TRAP staining analysis showed that YC-1 inhibited osteoclast activity and survival. YC-1 induced extrinsic apoptosis in osteoclasts by activating caspase-3 and caspase-8. In osteoclasts, YC-1 stimulated μ-calpain activity and inhibited Src activity. Our findings provide proof-of-concept for YC-1 as a novel antiresorptive treatment strategy for postmenopausal osteoporosis, confirming an important role of nitric oxide/cGMP/protein kinase G signaling in bone.

Integrin α6 and EGFR signaling converge at mechanosensitive calpain 2

Cells sense and respond to mechanical cues from the extracellular matrix (ECM) via integrins. ECM stiffness is known to enhance integrin clustering and response to epidermal growth factor (EGF), but we lack information on when or if these mechanosensitive growth factor receptors and integrins converge intracellularly. Towards closing this knowledge gap, we combined a biomaterial platform with transcriptomics, molecular biology, and functional assays to link integrin-mediated mechanosensing and epidermal growth factor receptor (EGFR) signaling. We found that high integrin α6 expression controlled breast cancer cell adhesion and motility on soft, laminin-coated substrates, and this mimicked the response of cells to EGF stimulation. The mechanisms that drove both mechanosensitive cell adhesion and motility converged on calpain 2, an intracellular protease important for talin cleavage and focal adhesion turnover. EGF stimulation enhanced adhesion and motility on soft substrates, but required integrin α6 and calpain 2 signaling. In sum, we identified a new role for integrin α6 mechanosensing in breast cancer, wherein cell adhesion to laminin on soft substrates mimicked EGF stimulation. We identified calpain 2, downstream of both integrin α6 engagement and EGFR phosphorylation, as a common intracellular signaling node, and implicate integrin α6 and calpain 2 as potential targets to inhibit the migration of cancer cells in stiff tumor environments.

Effects of 10 weeks of regular running exercise with and without parallel PDTC treatment on expression of genes encoding sarcomere-associated proteins in murine skeletal muscle

Physical exercise can induce various adaptation reactions in skeletal muscle tissue, such as sarcomere remodeling. The latter involves degradation of damaged sarcomere components, as well as de novo protein synthesis and sarcomere assembly. These processes are controlled by specific protease systems in parallel with molecular chaperones that assist in folding of newly synthesized polypeptide chains and their incorporation into sarcomeres. Since acute exercise induces oxidative stress and inflammation, leading to activation of the transcription factor NFκB (nuclear factor kappa B), we speculated that this transcription factor might also play a role in the regulation of long-term adaptation to regular exercise. Thus, we studied skeletal muscle adaptation to running exercise in a murine model system, with and without parallel treatment with the NFκB-inhibitory, anti-oxidant and anti-inflammatory drug pyrrolidine dithiocarbamate (PDTC). In control mice, 10 weeks of uphill (15° incline) treadmill running for 60 min thrice a week at a final speed of 14 m/min had differential, but only minor effects on many genes encoding molecular chaperones for sarcomere proteins, and/or factors involved in the degradation of the latter. Furthermore, there were marked differences between individual muscles. PDTC treatment modulated gene expression patterns as well, both in sedentary and exercising mice; however, most of these effects were also modest and there was little effect of PDTC treatment on exercise-induced changes in gene expression. Taken together, our data suggest that moderate-intensity treadmill running, with or without parallel PDTC treatment, had little effect on the expression of genes encoding sarcomere components and sarcomere-associated factors in murine skeletal muscle tissue.

Basolateral amygdala calpain is required for extinction of contextual fear-memory

Extinction of fear-memory is essential for emotional and mental changes. However, the mechanisms underlying extinction of fear-memory are largely unknown. Calpain is a type of calcium-dependent protease that plays a critical role in memory consolidation and reconsolidation. Whether calpain functions in extinction of fear-memory is unknown, as are the molecular mechanisms. In this study, we investigated the pivotal role of calpain in extinction of fear-memory in mice, and assessed its mechanism. Conditioned stimulation/unconditioned stimulation-conditioned stimulation paradigms combined with pharmacological methods were employed to evaluate the action of calpain in memory extinction. Our data demonstrated that intraperitoneal or intra-basolateral amygdala (BLA) injection of calpain inhibitors could eliminate extinction of fear-memory in mice. Moreover, extinction of fear-memory paradigm-activated BLA calpain activity, which degraded suprachiasmatic nucleus circadian oscillatory protein (SCOP) and phosphatase and tensin homolog (PTEN), subsequently contributing to activation of a protein kinase B (AKT)-mammalian target of the rapamycin (mTor) signaling pathway. Additionally, cAMP-response element binding protein (CREB) phosphorylation was also augmented following extinction of fear-memory. Calpain inhibitor blocked the signaling pathway activation induced by extinction of fear-memory. Additionally, intra-BLA injection of rapamycin or cycloheximide also blocked the extinction of fear-memory. Conversely, intra-BLA injection of PTEN inhibitor, bpV, reversed the effect of calpeptin on extinction of fear-memory. Together, our data confirmed the function of BLA calpain in extinction of fear-memory, likely via degrading PTEN and activating AKT-mTor-dependent protein synthesis.

The zinc fingers of the small optic lobes calpain bind polyubiquitin

The small optic lobes (SOL) calpain is a highly conserved member of the calpain family expressed in the nervous system. A dominant negative form of the SOL calpain inhibited consolidation of one form of synaptic plasticity, non-associative facilitation, in sensory-motor neuronal cultures in Aplysia, presumably by inhibiting cleavage of protein kinase Cs (PKCs) into constitutively active protein kinase Ms (PKMs) (Hu et al. 2017a). SOL calpains have a conserved set of 5-6 N-terminal zinc fingers. Bioinformatic analysis suggests that these zinc fingers could bind to ubiquitin. In this study, we show that both the Aplysia and mouse SOL calpain (also known as Calpain 15) zinc fingers bind ubiquitinated proteins, and we confirm that Aplysia SOL binds poly- but not mono- or diubiquitin. No specific zinc finger is required for polyubiquitin binding. Neither polyubiquitin nor calcium was sufficient to induce purified Aplysia SOL calpain to autolyse or to cleave the atypical PKC to PKM in vitro. In Aplysia, over-expression of the atypical PKC in sensory neurons leads to an activity-dependent cleavage event and an increase in nuclear ubiquitin staining. Activity-dependent cleavage is partially blocked by a dominant negative SOL calpain, but not by a dominant negative classical calpain. The cleaved PKM was stabilized by the dominant negative classical calpain and destabilized by a dominant negative form of the PKM stabilizing protein KIdney/BRAin protein. These studies provide new insight into SOL calpain's function and regulation. Open Data: Materials are available on https://cos.io/our-services/open-science-badges/ https://osf.io/93n6m/.

Ingestion of soy protein isolate attenuates eccentric contraction-induced force depression and muscle proteolysis via inhibition of calpain-1 activation in rat fast-twitch skeletal muscle

OBJECTIVE

Eccentric contraction (ECC) is a contraction in which skeletal muscles are stretched while contracting. The aim of this study was to determine how ingestion of soy protein isolate (SPI) or animal-based proteins affect force deficit, calpain activation, and proteolysis of calcium ion (Ca²⁺)-regulatory proteins in rat fast-twitch muscles subjected to ECC.

METHODS

In the first experiment, male Wistar rats were randomly assigned to a control and an SPI group, which were fed a 20% casein and a 20% SPI diet, respectively, for 28 d before the ECC protocol. Anterior crural muscles underwent 200 repeated ECCs and were excised 3 d later. In the second experiment, half of the SPI rats were given water containing N^G-nitro-l-arginine-methyl ester (L-NAME), an inhibitor of nitric oxide synthase, for 3 d of recovery after ECC.

RESULTS

SPI ingestion attenuated ECC-induced force deficit, proteolysis of Ca²⁺-regulatory proteins, and autolysis of calpain-1. Co-ingestion of L-NAME inhibited SPI-associated increases in nitrite and nitrate levels and negated the force recovery effects of SPI.

CONCLUSION

These results suggest that SPI ingestion inhibits ECC-elicited force deficit and proteolysis of Ca²⁺ regulatory proteins, which is caused by inhibited activation of calpain-1 via increased nitric oxide production.

EphrinB/EphB signaling contributes to spinal nociceptive processing via calpain‑1 and caspase‑3

Previous studies have indicated that an important subfamily of receptor tyrosine kinases, ephrins and their receptors, are important in pain signaling, particularly in spinal nociceptive processing. In the present study, the role of the ephrin/Eph signaling pathway was confirmed, and it was shown that this signaling was also involved in spinal nociceptive processing through the actions of calpain‑1 and caspase‑3. First, the ephrinB ligands, ephrinB1‑Fc or ephrinB2‑Fc, were introduced into experimental mice via intrathecal injection, and it was found that this injection induced marked time‑ and dose‑dependent mechanical allodynia and thermal hyperalgesia, accompanied by increased levels of calpain‑1 and caspase‑3 in the spinal cord. MDL28170, an inhibitor of calpain‑1, reversed the behavioral effects and ameliorated the increases in calpain‑1 and caspase‑3. Second, it was found that the administration of EphB1 between L5 and L6 in mice inhibited the mechanical allodynia and thermal hyperalgesia induced by chronic constrictive injury. In addition, to demonstrate the cell phenotypes responsible for the increased levels of calpain‑1 and caspase‑3 in the spinal cord following injection with ephrinB2‑Fc, double immunofluorescent labeling was performed, which indicated that calpain‑1 and caspase‑3 were localized in neurons, but not in astrocytes or microglial cells. In conclusion, the present study suggested that ephrinB/EphB signaling contributes to spinal nociceptive processing via the actions of calpain‑1 and caspase‑3.

Phenol and chlorinated phenols exhibit different apoptotic potential in human red blood cells (in vitro study)

Phenol and chlorinated phenols are widely spread in the environment and human surrounding, which leads to a common environmental and occupational exposure of humans to these substances. The aim of this study was to assess eryptotic changes in human red blood cells treated with phenol, 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP). The erythrocytes were incubated with phenols studied in the concentrations ranging from 1 to 100 μg/mL for 24 h or 48 h. The results of the study revealed that all compounds studied caused phosphatidylserine translocation and increased cytosolic calcium ions level in human erythrocytes. It was also noticed that phenol and chlorophenols caused an increase in caspase-3 and calpain activation, which confirmed that they were capable of inducing suicidal death of erythrocytes. The results also revealed that PCP most strongly altered the parameters studied, while phenol exhibited the weakest eryptotic potential in the incubated cells.

Promoter interactome of human embryonic stem cell-derived cardiomyocytes connects GWAS regions to cardiac gene networks

Long-range chromosomal interactions bring distal regulatory elements and promoters together to regulate gene expression in biological processes. By performing promoter capture Hi-C (PCHi-C) on human embryonic stem cell-derived cardiomyocytes (hESC-CMs), we show that such promoter interactions are a key mechanism by which enhancers contact their target genes after hESC-CM differentiation from hESCs. We also show that the promoter interactome of hESC-CMs is associated with expression quantitative trait loci (eQTLs) in cardiac left ventricular tissue; captures the dynamic process of genome reorganisation after hESC-CM differentiation; overlaps genome-wide association study (GWAS) regions associated with heart rate; and identifies new candidate genes in such regions. These findings indicate that regulatory elements in hESC-CMs identified by our approach control gene expression involved in ventricular conduction and rhythm of the heart. The study of promoter interactions in other hESC-derived cell types may be of utility in functional investigation of GWAS-associated regions.

Delayed, oral pharmacological inhibition of calpains attenuates adverse post-infarction remodelling

 

Calpains activate during myocardial ischemia-reperfusion and contribute to reperfusion injury. Studies in transgenic animals with altered calpain/calpastatin system subjected to permanent ischemia suggest that calpains are also involved in post-infarction remodelling and heart failure.

Aims

To determine whether delayed oral administration of the calpain inhibitor SNJ-1945 reduces adverse myocardial remodelling and dysfunction following transient coronary occlusion.

Methods and results

Male Sprague-Dawley rats were subjected to 30 min of ischemia followed by 21 days of reperfusion and received the calpain inhibitor SNJ-1945 intraperitoneally at the onset of reperfusion (Acute group), orally starting after 24 h of reperfusion and for 14 days (Chronic group), or the combination of both treatments. Calpain-1 and calpain-2 protein content increased and correlated with higher calpain activity in control hearts. Administration of SNJ-1945 attenuated calpain activation, and reduced scar expansion, ventricular dilation and dysfunction in both acute and chronic groups. Acute treatment reduced infarct size in hearts reperfused for 24 h and inflammation measured after 3 days. Delayed, chronic oral administration of SNJ-1945 attenuated inflammation, cardiomyocyte hypertrophy and collagen infiltration in the non-infarcted myocardium at 21 days in correlation with increased levels of IĸB and reduced NF-ĸB activation. In cultured fibroblasts, SNJ-1945 attenuated TGF-β1-induced fibroblast activation.

Conclusions

Our data demonstrate for the first time that long-term calpain inhibition is possible with delayed oral treatment, attenuates adverse post-infarction remodelling, likely through prevention of NF-ĸB activation, and may be a promising therapeutic intervention to prevent adverse remodelling and heart failure in patients with acute myocardial infarction.

BmCalpains are involved in autophagy and apoptosis during metamorphosis and after starvation in Bombyx mori

Apoptosis and autophagy play crucial roles during Bombyx mori metamorphosis and in response to various adverse conditions, including starvation. Recently, calpain, one of the major intracellular proteases, has been reported to be involved in apoptosis and autophagy in mammals. BmATG5 and BmATG6 have been identified to mediate apoptosis following autophagy induced by 20-hydroxyecdysone and starvation in B. mori. However, B. mori calpains and their functions remain unclear. In this study, phylogenetic analysis of calpains from B. mori, Drosophila melanogaster and Homo sapiens were performed and the results showed distinct close relationships of BmCalpain-A/B with DmCalpain-A/B, BmCalpain-C with DmCalpain-C, and BmCalpain-7 with HsCalpain-7. Then, the expression profiles of BmCalpains were analyzed by quantitative real-time polymerase chain reaction, and results showed that expression of BmCalpain-A/B, BmCalpain-C and BmCalpain-7 was significantly increased during B. mori metamorphosis and induced in the fat body and midgut of starved larvae, which is consistent with the expression profiles of BmAtg5, BmAtg6 and BmCaspase-1. Moreover, the apoptosis-associated cleavage of BmATG6 in Bm-12 cells was significantly enhanced when BmCalpain-A/B and BmCalpain-7 were induced by starvation, and was partially inhibited by the inhibitor of either calpain or caspase, but completely inhibited when both types of inhibitors were applied together. Our results indicated that BmCalpains, including BmCalpain-A/B, -C and -7, may be involved in autophagy and apoptosis during B. mori metamorphosis and after starvation, and may also contribute to the apoptosis-associated cleavage of BmATG6.

Alpha 7 nicotinic receptors attenuate neurite development through calcium activation of calpain at the growth cone

The α7 nicotinic acetylcholine receptor (nAChR) is a ligand-gated ion channel that plays an important role in cellular calcium signaling contributing to synaptic development and plasticity, and is a key drug target for the treatment of neurodegenerative conditions such as Alzheimer's disease. Here we show that α7 nAChR mediated calcium signals in differentiating PC12 cells activate the proteolytic enzyme calpain leading to spectrin breakdown, microtubule retraction, and attenuation in neurite growth. Imaging in growth cones confirms that α7 activation decreases EB3 comet motility in a calcium dependent manner as demonstrated by the ability of α7 nAChR, ryanodine, or IP3 receptor antagonists to block the effect of α7 nAChR on growth. α7 nAChR mediated EB3 comet motility, spectrin breakdown, and neurite growth was also inhibited by the addition of the selective calpain blocker calpeptin and attenuated by the expression of an α7 subunit unable to bind Gαq and activate calcium store release. The findings indicate that α7 nAChRs regulate cytoskeletal dynamics through local calcium signals for calpain protease activity.

Capn4 contributes to tumor invasion and metastasis in clear cell renal cell carcinoma cells via modulating talin-focal adhesion kinase signaling pathway

Calpain small subunit 1 (Capn4) has been shown to correlate with the metastasis/invasion of clear cell renal cell carcinoma (ccRCC). This study aimed to further elucidate the molecular mechanisms underlying Capn4-mediated ccRCC progression. The mRNA expression levels in ccRCC cells were measured by quantitative real-time PCR. The effects of Capn4 on cell adhesion, invasion, and migration were examined by cell adhesion assay, cell invasion assay, and wound-healing assay, respectively. The protein levels were detected by western blot analysis. The effect of Capn4 on cancer metastasis in vivo was assessed in a nude mice xenograft model. It was found that Capn4 was up-regulated in the ccRCC cells, and Capn4 overexpression suppressed cell adhesion activity and increased cell invasion and migration in 786-O cells, while Capn4 silencing increased cell adhesion activity and impaired the invasion and migration ability of Caki-1 cells. Capn4 overexpression also increased the protein level of cleaved talin in 786-O cells, while Capn4 silencing decreased the protein level of cleaved talin in Caki-1 cells. The focal adhesion kinase (FAK)/AKT/MAPK signaling was activated by Capn4 overexpression in 786-O cells, and was inhibited by Capn4 down-regulation in Caki-1 cells. Capn4 overexpression increased the protein levels of matrix metalloproteinase 2 (MMP-2), vimentin, N-cadherin, and down-regulated E-cadherin in 786-O cells, while Capn4 silencing decreased the protein levels of MMP-2, vimentin, N-cadherin, and up-regulated E-cadherin in Caki-1 cells. Capn4 also promoted cancer metastasis in the in vivo nude mice xenograft model. Our results implicate the functional role of Capn4 in ccRCC invasion and migration, which may contribute to cancer metastasis in ccRCC.

Autosomal dominant calpainopathy due to heterozygous CAPN3 C.643_663del21

INTRODUCTION

A calpain-3 (CAPN3) gene heterozygous deletion (c.643_663del21) was recently linked to autosomal dominant (AD) limb-girdle muscular dystrophy. However, the possibility of digenic disease was raised. We describe 3 families with AD calpainopathy carrying this isolated mutation.

METHODS

Probands heterozygous for CAPN3 c.643_663del21 were identified by targeted next generation or whole exome sequencing. Clinical findings were collected for probands and families. Calpain-3 muscle Western blots were performed in 3 unrelated individuals.

RESULTS

Probands reported variable weakness in their 40s or 50s, with myalgia, back pain, or hyperlordosis. Pelvic girdle muscles were affected with adductor and hamstring sparing. Creatine kinase was normal to 1,800 U/L, independent of weakness severity. Imaging demonstrated lumbar paraspinal muscle atrophy. Electromyographic findings and muscle biopsies were normal to mildly myopathic. Muscle calpain-3 expression was reduced.

DISCUSSION

This study provides further evidence for AD calpainopathy associated with CAPN3 c.643_663del21. No pathogenic variants in other genes known to cause myopathy were detected. Muscle Nerve 57: 679-683, 2018.

Structures of human calpain-3 protease core with and without bound inhibitor reveal mechanisms of calpain activation

Limb-girdle muscular dystrophy type 2a arises from mutations in the Ca2+-activated intracellular cysteine protease calpain-3. This calpain isoform is abundant in skeletal muscle and differs from the main isoforms, calpain-1 and -2, in being a homodimer and having two short insertion sequences. The first of these, IS1, interrupts the protease core and must be cleaved for activation and substrate binding. Here, to learn how calpain-3 can be regulated and inhibited, we determined the structures of the calpain-3 protease core with IS1 present or proteolytically excised. To prevent intramolecular IS1 autoproteolysis, we converted the active-site Cys to Ala. Small-angle X-ray scattering (SAXS) analysis of the C129A mutant suggested that IS1 is disordered and mobile enough to occupy several locations. Surprisingly, this was also true for the apo version of this mutant. We therefore concluded that IS1 might have a binding partner in the sarcomere and is unstructured in its absence. After autoproteolytic IS1 removal from the active Cys129 calpain-3 protease core, we could solve its crystal structures with and without the cysteine protease inhibitors E-64 and leupeptin covalently bound to the active-site cysteine. In each structure, the active state of the protease core was assembled by the cooperative binding of two Ca2+ ions to the equivalent sites used in calpain-1 and -2. These structures of the calpain-3 active site with residual IS1 and with bound E-64 and leupeptin may help guide the design of calpain-3-specific inhibitors.

Interleukin-33 is activated by allergen- and necrosis-associated proteolytic activities to regulate its alarmin activity during epithelial damage

Interleukin (IL)-33 is an IL-1 family alarmin released from damaged epithelial and endothelial barriers to elicit immune responses and allergic inflammation via its receptor ST2. Serine proteases released from neutrophils, mast cells and cytotoxic lymphocytes have been proposed to process the N-terminus of IL-33 to enhance its activity. Here we report that processing of full length IL-33 can occur in mice deficient in these immune cell protease activities. We sought alternative mechanisms for the proteolytic activation of IL-33 and discovered that exogenous allergen proteases and endogenous calpains, from damaged airway epithelial cells, can process full length IL-33 and increase its alarmin activity up to ~60-fold. Processed forms of IL-33 of apparent molecular weights ~18, 20, 22 and 23 kDa, were detected in human lungs consistent with some, but not all, proposed processing sites. Furthermore, allergen proteases degraded processed forms of IL-33 after cysteine residue oxidation. We suggest that IL-33 can sense the proteolytic and oxidative microenvironment during tissue injury that facilitate its rapid activation and inactivation to regulate the duration of its alarmin function.

Calpain-2 as a therapeutic target for acute neuronal injury

INTRODUCTION

Calpains represent a family of neutral, calcium-dependent proteases, which modify the function of their target proteins by partial truncation. These proteases have been implicated in numerous cell functions, including cell division, proliferation, migration, and death. In the CNS, where calpain-1 and calpain-2 are the main calpain isoforms, their activation has been linked to synaptic plasticity as well as to neurodegeneration. This review will focus on the role of calpain-2 in acute neuronal injury and discuss the possibility of developing selective calpain-2 inhibitors for therapeutic purposes. Areas covered: This review covers the literature showing how calpain-2 is implicated in neuronal death in a number of pathological conditions. The possibility of developing new selective calpain-2 inhibitors for treating these conditions is discussed. Expert opinion: As evidence accumulates that calpain-2 activation participates in acute neuronal injury, there is interest in developing therapeutic approaches using selective calpain-2 inhibitors. Recent data indicate the potential use of such inhibitors in various pathologies associated with acute neuronal death. The possibility of extending the use of such inhibitors to more chronic forms of neurodegeneration is discussed.

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.

Hippocampal calpain is required for the consolidation and reconsolidation but not extinction of contextual fear memory

Memory consolidation, reconsolidation, and extinction have been shown to share similar molecular signatures, including new gene expression. Calpain is a Ca2+-dependent protease that exerts its effects through the proteolytic cleavage of target proteins. Neuron-specific conditional deletions of calpain 1 and 2 impair long-term potentiation in the hippocampus and spatial learning. Moreover, recent studies have suggested distinct roles of calpain 1 and 2 in synaptic plasticity. However, the role of hippocampal calpain in memory processes, especially memory consolidation, reconsolidation, and extinction, is still unclear. In the current study, we demonstrated the critical roles of hippocampal calpain in the consolidation, reconsolidation, and extinction of contextual fear memory in mice. We examined the effects of pharmacological inhibition of calpain in the hippocampus on these memory processes, using the N-Acetyl-Leu-Leu-norleucinal (ALLN; calpain 1 and 2 inhibitor). Microinfusion of ALLN into the dorsal hippocampus impaired long-term memory (24 h memory) without affecting short-term memory (2 h memory). Similarly, this pharmacological blockade of calpain in the dorsal hippocampus also disrupted reactivated memory but did not affect memory extinction. Importantly, the systemic administration of ALLN inhibited the induction of c-fos in the hippocampus, which is observed when memory is consolidated. Our observations showed that hippocampal calpain is required for the consolidation and reconsolidation of contextual fear memory. Further, the results suggested that calpain contributes to the regulation of new gene expression that is necessary for these memory processes as a regulator of Ca2+-signal transduction pathway.

Force-Induced Calpain Cleavage of Talin Is Critical for Growth, Adhesion Development, and Rigidity Sensing

Cell growth depends upon formation of cell-matrix adhesions, but mechanisms detailing the transmission of signals from adhesions to control proliferation are still lacking. Here, we find that the scaffold protein talin undergoes force-induced cleavage in early adhesions to produce the talin rod fragment that is needed for cell cycle progression. Expression of noncleavable talin blocks cell growth, adhesion maturation, proper mechanosensing, and the related property of EGF activation of motility. Further, the expression of talin rod in the presence of noncleavable full-length talin rescues cell growth and other functions. The cleavage of talin is found in early adhesions where there is also rapid turnover of talin that depends upon calpain and TRPM4 activity as well as the generation of force on talin. Thus, we suggest that an important function of talin is its control over cell cycle progression through its cleavage in early adhesions.

Contribution of PAR-1, PAR-4 and GPIbα in intracellular signaling leading to the cleavage of the β3 cytoplasmic domain during thrombin-induced platelet aggregation

Integrin αIIbβ3 plays a pivotal role in platelet aggregation by binding to fibrinogen. The β3 cytoplasmic domain of αIIbβ3 interacts with cytoskeletal and signaling proteins and is cleaved by µ-calpain, a calcium regulated cysteine protease. In the present study, we have investigated in more detail the cleavage of the β3 cytoplasmic domain during platelet aggregation induced by thrombin, TRAP-1 and TRAP-4. Our data show that β3 is cleaved in all three cases. The time course of β3 cleavage and the amount of cleaved β3 depends on the way platelets are activated and on the complete activation of µ-calpain, with a maximum of 90% of cleaved β3 obtained when thrombin is used. Furthermore, our results also show that the cleaved αIIbβ3 is mainly distributed in the Triton soluble fraction, indicating its inability to bind to the cytoskeleton. Interestingly, in the absence of GPIbα or following inhibition of thrombin binding to GPIbα, there is a reduction in the thrombin-induced calcium flux, β3 cleavage and µ-calpain activation. These results suggest that cleavage of the β3 cytoplasmic domain by µ-calpain might be an important step regulating the link between the cytoskeleton and αIIbβ3 during platelet aggregation, and that GPIbα could function as a cofactor for the complete activation of platelets by thrombin.

Concurrent assessment of calpain and caspase3 activities in brains of mice with acetaminophen-induced acute hepatic encephalopathy

To develop pharmacological therapy for acute hepatic encephalopathy (AHE), understanding the molecular basis for cell injury is essential. Excitotoxic neural cell injury mediated by calpain as a post- receptor mechanism has been proposed as a player in neuronal injury in AHE. Concurrent assessment of Calpain and Caspase3 activities in the brain of AHE mice in acetaminophen- induced mourine model was performed. After induction of AHE by acetaminophen in mice, the model was confirmed by histopathological, biochemical and behavioural studies. The brains were removed, western blot analysis was done and the relative activity of calpain and caspase was estimated and compared to control group calpain but not caspase 3 activity was significantly increased in the AHE group compared to the control brains. Experimentally, this finding is the first to report. Increased calpain activity in liver has been previously reported. To translate both finding it can be suggested that calpain inhibition can be an investigational intervention in saving lives in AHE. To confirm the results, besides more advanced toxicodynamic studies on acetaminophen, the results should be confirmed in other models of AHE in future.

The critical role of autophagy in cadmium-induced immunosuppression regulated by endoplasmic reticulum stress-mediated calpain activation in RAW264.7 mouse monocytes

Cadmium (Cd) has toxic and suppressive effects on the immune system, but the underlying mechanisms remain poorly understood. Here, we show that autophagy plays a critical role in regulation of Cd-induced immunosuppression in RAW264.7 cells. Cd decreased cell viability in a dose-dependent manner; cleaved caspase-8, caspase-3, and poly (ADP-ribose) polymerase (PARP)-1; increased DNA laddering; induced CCAAT-enhancer-binding protein homologous protein (CHOP); and reduced tumor necrosis factor (TNF)-α expression; indicating that caspase-dependent and endoplasmic reticulum (ER)-mediated apoptosis are involved in Cd-induced immunotoxicity. Furthermore, Cd induced autophagy, as demonstrated by microtubule-associated protein 1 light chain 3B (LC3B) plasmid DNA transfection and its conversion from LC3-I to the LC3-II form by autophagy inhibitors, via AMP-activated protein kinase (AMPK)-mammalian target of rapamycin (mTOR) signaling. Pharmacological and genetic inhibition of autophagy suppressed Cd-induced apoptosis, as evidenced by inhibition of caspase-8, caspase-3, and PARP-1 cleavage, indicating that autophagy promotes apoptosis. The pan-caspase inhibitor zVAD inhibited Cd-induced apoptosis, but increased autophagy and decreased cell viability, indicating that autophagy can compensate for reduced apoptotic cell death. Calpain inhibitors blocked Cd-induced apoptosis and autophagy, indicating that calpain plays a critical role in Cd cytotoxicity. Treatment with Ca²⁺ chelators completely recovered Cd-induced cell viability and inhibited Cd-induced apoptosis and autophagy. Treatment with N-acetyl-l-cysteine (NAC) suppressed Cd-induced antioxidant enzyme levels, apoptosis, and autophagy. Collectively, Cd-induced oxidative stress triggers ER stress, leading to Ca^2+-dependent calpain activation and subsequent activation of autophagy and apoptosis, resulting in immune suppression.

Mechanoregulation of SM22α/Transgelin

SM22α, also named transgelin, is an actin filament-associated protein in smooth muscle and fibroblasts. Three decades after its discovery, the biological function of SM22α remains under investigation. Here we report a novel finding that the expression and degradation of SM22α/transgelin are regulated by mechanical tension. Following a mass spectrometry identification of SM22α degradation in isolated and tension-unloaded mouse aorta, we developed specific monoclonal antibodies to study the regulation of SM22α in human fetal lung myofibroblast line MRC-5 and primary cultures of neonatal mouse skin fibroblasts. The level of SM22α is positively related to the mechanical tension in the cytoskeleton produced by the myosin II motor in response to the stiffness of the culture matrix. Quantitative reverse transcription polymerase chain reaction demonstrated that the expression of SM22α is regulated at the transcriptional level. This mechanical regulation resembles that of calponin 2, another actin filament-associated protein. Immunofluorescent staining co-localized SM22α with F-actin, myosin, and calponin 2 in mouse skin fibroblasts. The close phylogenetic relationship between SM22α and the calponin family supports that SM22α is a calponin-like regulatory protein. The level of SM22α is decreased in skin fibroblasts isolated from calponin 2 knockout mice, suggesting interrelated regulation and function of the two proteins. On the other hand, SM22α expression was maximized at a matrix stiffness higher than that for calponin 2 in the same cell type, indicating differentiated regulation and tension responsiveness. The novel mechanoregulation of SM22α/transgelin lays the groundwork for understanding its cellular functions.

Proteodynamics in aging human T cells - The need for its comprehensive study to understand the fine regulation of T lymphocyte functions

Cellular life depends mostly on the creation, modification, interactions and destruction of proteins. This is true for every cell, including human T lymphocytes. One way these cells can ascertain the fidelity and at least partial functionality of their proteomes under constant attack of irreversible modulations (e.g., ROS- or glycation-dependent) is proteostasis. However, with cellular aging proteostasis progressively fails and proteostenosis (decreased amounts and functionalities of remaining proteins) occurs. There are several mechanisms involved in the modulation and protection of the proteome in the T cells which include mainly multiple layers of vesicle-bound and cytoplasmic proteases (e.g., lysosomal and proteasomal ones) acting mostly by degradation of obsolete and age-modified proteins. Recently it was shown that another not yet so widely known system consisting of obligatorily calcium-dependent cysteine proteases, the calpains and their inhibitor, the calpastatin serves in T cells as a dual switch, either activating or inactivating different proteins depending on intracellular conditions. Thus the proteolytic elimination of altered proteins as well as modulation of activity of those remaining leads to dynamic change of proteome composition and function (proteodynamics) in aging lymphocytes, so far in an almost unknown way. Aging T cell proteodynamics requires further comprehensive analysis of the resulting lysoproteomic patterns and their changes.

The human blood parasite Schistosoma mansoni expresses extracellular tegumental calpains that cleave the blood clotting protein fibronectin

Schistosomes are intravascular, parasitic flatworms that cause debilitating disease afflicting >200 million people. Proteins expressed at the host-parasite interface likely play key roles in modifying the worm's local environment to ensure parasite survival. Proteomic analysis reveals that two proteases belonging to the calpain family (SmCalp1 and SmCalp2) are expressed in the Schistosoma mansoni tegument. We have cloned both; while highly conserved in domain organization they display just 31% amino acid sequence identity. Both display high relative expression in the parasite's intravascular life forms. Immunolocalization and activity based protein profiling experiments confirm the presence of the enzymes at the host-parasite interface. Living parasites exhibit surface calpain activity that is blocked in the absence of calcium and in the presence of calpain inhibitors (E64c, PD 150606 and calpastatin). While calpains are invariably reported to be exclusively intracellular (except in diseased or injured tissues), our data show that schistosomes display unique, constitutive, functional extracellular calpain activity. Furthermore we show that the worms are capable of cleaving the host blood clotting protein fibronectin and that this activity can be inhibited by E64c. We hypothesize that SmCalp1 and/or SmCalp2 perform this cleavage function to impede blood clot formation around the worms in vivo.

Influence of modified atmosphere packaging on protein oxidation, calpain activation and desmin degradation of beef muscles

BACKGROUND

Protein oxidation is widespread in biochemical systems. The objective of the study was to investigate the differences in protein oxidation, μ-calpain activity, desmin proteolysis and protein solubility of beef psoas major (PM) and semi-membranosus (SM) muscles under three packaging systems during postmortem ageing. At 24 h postmortem, beef muscles were packaged respectively in air-permeable film overwrap (AP), vacuum pack (VP) or modified atmosphere (MAP, 80% O₂ + 20% CO₂ ), and then displayed for 10 days at 4 °C.

RESULTS

Carbonyl group values and thiol group content were significantly influenced by packaging type and storage time. The SM muscles from AP and MAP showed greater μ-calpain activity compared to VP. Desmin of PM and SM from AP and MAP samples showed decreased proteolysis compared with VP.

CONCLUSION

The results suggested that the inhibition of μ-calpain activity of beef samples from AP and MAP could be closely associated with protein oxidation which further lowered the level of desmin degradation compared to VP. © 2017 Society of Chemical Industry.

Postmortem protein degradation is a key contributor to fresh pork loin tenderness

The objective of this study was to determine factors that influence tenderness independent of variation in pH, color, or marbling. To achieve the objective, 2 sample groups were chosen from a population of 159 pork loins aged 11 to 16 d. Predetermined ranges (ultimate pH, 5.54 to 5.86; marbling score, 1.0 to 3.0; percent total lipid, 1.61 to 3.37%) were defined for inclusion of individual loins in the study. The pork loins with the greatest ( = 12) and least ( = 12) Instron star probe values were assigned to 2 classification groups. The high star probe group had an average star probe that was 2.8 kg greater than the low star probe group (7.75 vs. 4.95 kg). Pork quality and sensory characteristics of pH, subjective and instrumental color values, cook loss, sensory tenderness, chewiness, juiciness, pork flavor, and off flavor were determined on fresh, never frozen pork chops. Lipid content, sarcomere length, myosin heavy-chain profile, and calpain autolysis were determined. Degradation of troponin-T, desmin, filamin, and titin were evaluated on the protein extracts from each sample. Pork loin pH, subjective color scores, Minolta L values, sarcomere length, and myosin heavy-chain composition were not different across groups. Chops from the low star probe group had a significantly greater marbling score (2.3 vs. 1.9) and lipid content (2.61 vs. 2.23%). Calpain-1 was completely autolyzed in both high and low star probe samples, demonstrating that calpain-1 potentially had been active in all samples. Low star probe whole-muscle protein extracts had more troponin-T ( < 0.01), desmin ( < 0.01), and filamin degradation ( < 0.01) than high star probe samples. Both classification groups showed degradation of titin. Remarkably, some high star probe samples still had observable intact bands of titin on SDS-PAGE gels. These results demonstrate that significant variation in instrumental tenderness is observed within a moderate pH range. Lipid content and proteolysis both appear to contribute to this variation.

The Shigella type III effector IpgD recodes Ca2+ signals during invasion of epithelial cells

The role of second messengers in the diversion of cellular processes by pathogens remains poorly studied despite their importance. Among these, Ca2+ virtually regulates all known cell processes, including cytoskeletal reorganization, inflammation, or cell death pathways. Under physiological conditions, cytosolic Ca2+ increases are transient and oscillatory, defining the so-called Ca2+ code that links cell responses to specific Ca2+ oscillatory patterns. During cell invasion, Shigella induces atypical local and global Ca2+ signals. Here, we show that by hydrolyzing phosphatidylinositol-(4,5)bisphosphate, the Shigella type III effector IpgD dampens inositol-(1,4,5)trisphosphate (InsP3) levels. By modifying InsP3 dynamics and diffusion, IpgD favors the elicitation of long-lasting local Ca2+ signals at Shigella invasion sites and converts Shigella-induced global oscillatory responses into erratic responses with atypical dynamics and amplitude. Furthermore, IpgD eventually inhibits InsP3-dependent responses during prolonged infection kinetics. IpgD thus acts as a pathogen regulator of the Ca2+ code implicated in a versatility of cell functions. Consistent with this function, IpgD prevents the Ca2+-dependent activation of calpain, thereby preserving the integrity of cell adhesion structures during the early stages of infection.

[Molecular and cellular mechanisms of damage to renal parenchyma in renal warm ischemia]

Warm ischemia of the renal parenchyma is a forced feature of laparoscopic partial nephrectomy. It is accompanied by oxygen deprivation of the organ and followed by re-oxygenation, which can cause additional damage to the renal tissue. This damage can result in acute functional and structural disorders of individual parts of the nephron, increasing the risk for a renal dysfunction. Timely diagnosis of the dysfunction is vital for the success of the treatment. The article provides an overview of current scientific data on the mechanisms of ischemic and reperfusion injuries at the molecular-cellular level and describes the current methods of their detection. Experimental and clinical study of the molecular-cellular mechanisms of ischemic-reperfusion injury of the renal tissue made it possible, first, to determine the main targets of alteration (cytolemma, mitochondria, lysosomes), and second, to establish its consequences, among which the most important are hypoergosis, DNA damage, simultaneous activation of intracellular systems of the suicidal program and induction of electrical breakdown of membranes of target nephrocytes; thirdly, to reveal the range of possibilities for limiting the consequences of hypoxia and/or re-oxygenation, among which interference in the metabolism of purines, measures ensuring the preservation of colloid osmotic pressure inside and outside the cell and membrane stabilization, antioxidant defense and inhibition of cysteine proteinases, etc. However, despite the advances in understanding the pathogenesis of cell damage, including ischemic-hypoxic injury, the problem of intraoperative ischemia-reperfusion safety remains relevant.

Regulation of cell wall genes in response to DEFECTIVE KERNEL1 (DEK1)-induced cell wall changes

Defective Kernel1 (DEK1) is a plant-specific calpain involved in epidermis specification and maintenance. DEK1 regulation of the epidermal cell wall is proposed to be key to ensure tissue integrity and coordinated growth. Changes in the expression of DEK1 are correlated with changes in the expression of cell wall-related genes. For example, we have found that Lipid transfer protein 3 (LTP3), EXPANSIN 11 (EXP11), and an AP2 transcription factor (AP2TF) are misexpressed in plants with constitutively altered levels of DEK1 activity. RT-qPCR studies show that LTP3 and AP2TF may respond to a DEK1-generated signal whereas EXP11 is not altered immediately after dexamethasone induction of CALPAIN suggesting it is not in the direct signaling pathway downstream of DEK1. Our data suggest these genes are regulated by a feedback mechanism in response to DEK1-induced changes in the cell wall, and contribute to the phenotypes seen in plants with altered DEK1 expression.

The neuroprotective effect of hesperidin in NMDA-induced retinal injury acts by suppressing oxidative stress and excessive calpain activation

We found that hesperidin, a plant-derived bioflavonoid, may be a candidate agent for neuroprotective treatment in the retina, after screening 41 materials for anti-oxidative properties in a primary retinal cell culture under oxidative stress. We found that the intravitreal injection of hesperidin in mice prevented reductions in markers of the retinal ganglion cells (RGCs) and RGC death after N-methyl-D-aspartate (NMDA)-induced excitotoxicity. Hesperidin treatment also reduced calpain activation, reactive oxygen species generation and TNF-α gene expression. Finally, hesperidin treatment improved electrophysiological function, measured with visual evoked potential, and visual function, measured with optomotry. Thus, we found that hesperidin suppressed a number of cytotoxic factors associated with NMDA-induced cell death signaling, such as oxidative stress, over-activation of calpain, and inflammation, thereby protecting the RGCs in mice. Therefore, hesperidin may have potential as a therapeutic supplement for protecting the retina against the damage associated with excitotoxic injury, such as occurs in glaucoma and diabetic retinopathy.

Regulation of platelet-activating factor-mediated protein tyrosine phosphatase 1B activation by a Janus kinase 2/calpain pathway

Atherosclerosis is a pro-inflammatory condition underlying many cardiovascular diseases. Platelet-activating factor (PAF) and interleukin 6 (IL-6) are actively involved in the onset and progression of atherosclerotic plaques. The involvement of monocyte-derived macrophages is well characterized in the installation of inflammatory conditions in the plaque, but less is known about the contribution of monocyte-derived dendritic cells (Mo-DCs). In the same way, the involvement of calcium, phospholipase C and A2 in PAF-induced IL-6 production, in different cells types, has been shown; however, the importance of the Jak/STAT pathway and its regulation by protein-tyrosine phosphatases in this response have not been addressed. In this study, we report that PAF stimulates PTP1B activity via Jak2, thereby modulating PAF-induced IL-6 production. Using HEK 293 cells stably transfected with the PAF receptor in order to discriminate the pathway components, our results suggest that Jak2 modulates PAF-induced IL-6 production via both positive and negative pathways. Jak2 kinase activity was necessary for maximal transactivation of the IL-6 promoter, as seen by luciferase assays, whereas the same kinase also downregulated this promoter transactivation through the activation of a calcium/calpain/PTP1B pathway. The same pathways were operational in monocyte-derived dendritic cells, since PAF-induced PTP1B activation negatively regulated PAF-induced IL-6 mRNA production and, in addition, Jak2 activated calpain, one of the components involved in PAF-induced PTP1B activation. Results obtained in this study indicate that Jak2 activation is important for maximal IL-6 promoter transactivation by PAF and that PTP1B is involved in the negative regulation of this transactivation. However, PTP1B does not directly regulate Jak2 activation, but rather Jak2 regulates PAF-induced PTP1B activation.

ER stress disturbs SR/ER-mitochondria Ca2+ transfer: Implications in Duchenne muscular dystrophy

Besides its role in calcium (Ca²⁺) homeostasis, the sarco-endoplamic reticulum (SR/ER) controls protein folding and is tethered to mitochondria. Under pathophysiological conditions the unfolded protein response (UPR) is associated with disturbance in SR/ER-mitochondria crosstalk. Here, we investigated whether ER stress altered SR/ER-mitochondria links, Ca²⁺ handling and muscle damage in WT (Wild Type) and mdx mice, the murine model of Duchenne Muscular Dystrophy (DMD). In WT mice, the SR/ER-mitochondria links were decreased in isolated FDB muscle fibers after injection of ER stress activator tunicamycin (TM). Ca²⁺ imaging revealed an increase of cytosolic Ca²⁺ transient and a decrease of mitochondrial Ca²⁺ uptake. The force generating capacity of muscle dropped after TM. This impaired contractile function was accompanied by an increase in autophagy markers and calpain-1 activation. Conversely, ER stress inhibitors restored SR/ER-mitochondria links, mitochondrial Ca²⁺ uptake and improved diaphragm contractility in mdx mice. Our findings demonstrated that ER stress-altered SR/ER-mitochondria links, disturbed Ca²⁺ handling and muscle function in WT and mdx mice. Thus, ER stress may open up a prospect of new therapeutic targets in DMD.

Effect of inhibition of μ-calpain on the myofibril structure and myofibrillar protein degradation in postmortem ovine muscle

BACKGROUND

Tenderness is considered to be one of the most important attributes of meat quality. Myofibrillar protein degradation contributes to meat tenderization during postmortem ageing. In this process, calpain is the primary enzyme catalyzing the proteolysis. To further understand the action of calpain in meat tenderization, a μ-calpain inhibitor, MDL-28170, was used and its effects on sarcomere structure and myofibrillar protein degradation were determined.

RESULTS

The results of the present study showed that inhibition of μ-calpain significantly reduced muscle myofibrillar fragmentation compared to the group without μ-calpain inhibitor. Meanwhile, the sarcomere structure of the μ-calpain inhibited muscle was only slightly broken and largely remained integral 48 h postmortem. Myosin heavy chain, actin, desmin, troponin T and troponin I were identified to be substrates of μ-calpain by liquid chromatography-tandem mass spectrocopy and western blotting, and were detected with a higher degradation degree in the control group compared to the μ-calpain inhibition group.

CONCLUSION

Comparatively, myosin heavy chain and actin were found to be less sensitive to μ-calpain compared to desmin, troponin T and troponin I. These findings provide a better understanding of the contribution of μ-calpain to the myofibril structure and myofibrillar protein degradation of ovine muscle. © 2016 Society of Chemical Industry.