Role of calmodulin-calmodulin kinase II, cAMP/protein kinase A and ERK 1/2 on Aeromonas hydrophila-induced apoptosis of head kidney macrophages

Transcriptome analysis of host anti-Aeromonas hydrophila infection revealed the pathogenicity of A. hydrophila to American eels (Anguilla rostrata)

Aeromonas hydrophila is a commonly pathogenic bacterium in cultivated eels, but its pathogenicity to American eel (Anguilla rostrata) and the molecular mechanism of host anti-A. hydrophila infection remains uncertain. In this study, LD50 of A. hydrophila to American eels was determined and bacterial load in the liver and kidney of eels was assessed post 2.56 doses of LD50 of A. hydrophila infection. The results showed that the LD50 of A. hydrophila to American eels was determined to be 3.9 × 105 cfu/g body weight (7.8 × 106 cfu/fish), and the bacterial load peaked at 36 h post the infection (hpi) in the liver. Then, the histopathology was highlighted by congestion in splenic blood vessels, atrophied glomeruli, and necrotic hepatocytes. Additionally, the results of qRT-PCR revealed that 18 host immune-related genes showed significantly up or downregulated post-infection compare to that of pre-infection. Finally, results of the RNA-seq revealed 10 hub DEGs and 7 encoded proteins play essential role to the anti-A. hydrophila infection in American eels. Pathogenicity of A. hydrophila to American eels and RNA-seq of host anti-A. hydrophila infection were firstly reported in this study, shedding new light on our understanding of the A. hydrophila pathogenesis and the host immune response to the A. hydrophila infection strategies in gene transcript.

Aeromonas hydrophila inhibits autophagy triggering cytosolic translocation of mtDNA which activates the pro-apoptotic caspase-1/IL-1β-nitric oxide axis in headkidney macrophages

The molecular mechanisms underlying Aeromonas hydrophila-pathogenesis are not well understood. Using head kidney macrophages (HKM) of Clarias gariepinus, we previously reported the role of ER-stress in A. hydrophila-induced pathogenesis. Here, we report that PI3K/PLC-induced cytosolic-Ca²⁺ imbalance induces the expression of pro-apoptotic ER-stress marker, CHOP in A. hydrophila-infected HKM. CHOP promotes HKM apoptosis by inhibiting AKT activation and enhancing JNK signaling. Elevated mitochondrial ROS (mtROS) was recorded which declined significantly by ameliorating ER-stress and in the presence of ER-Ca²⁺ release modulators (2-APB and dantrolene) and mitochondrial-Ca²⁺ uptake inhibitor, Ru360, together suggesting the role of ER-mitochondrial Ca²⁺ dynamics in mtROS generation. Inhibiting mtROS production reduced HKM death implicating the pro-apoptotic role of mtROS in A. hydrophila-pathogenesis. The expression of autophagic proteins (LC3B, beclin-1, and atg 5) was suppressed in the infected HKM. Our results with autophagy-inducer rapamycin demonstrated that impaired autophagy favored the cytosolic accumulation of mitochondrial DNA (mtDNA) and the process depended on mtROS levels. Enhanced caspase-1 activity and IL-1β production was detected and transfection studies coupled with pharmacological inhibitors implicated mtROS/mtDNA axis to be crucial for activating the caspase-1/IL-1β cascade in infected HKM. RNAi studies further suggested the involvement of IL-1β in generating pro-apoptotic NO in A. hydrophila-infected HKM. Our study suggests a novel role of ER-mitochondria cross-talk in regulating A. hydrophila pathogenesis. Based on our observations, we conclude that A. hydrophila induces ER-stress and inhibits mitophagy resulting in mitochondrial dysfunction which leads to mtROS production and translocation of mtDNA into cytosol triggering the activation of caspase-1/IL-1β-mediated NO production, culminating in HKM apoptosis.

Wnt 5a mediated inflammatory injury of renal tubular epithelial cells dependent on calcium signaling pathway in Trichloroethylene sensitized mice

Patients with trichloroethene-induced Trichloroethylene hypersensitivity syndrome (THS) often present kidney injury. However, the role of Wnt 5a/Ca2+ pathway in renal tubular injury in Trichloroethylene (TCE) sensitized mice remains unclear. This study aimed to investigate how Wnt 5a/Ca2+ pathway induced renal tubular epithelial cell injury in TCE sensitized mice. A total of 84 female BALB/c Specific Pathogen Free mice aged 6-8 weeks were used to establish TCE sensitized mouse models. Renal histology and serum levels of α1-MG and β2-MG were used to assess the renal injury. The renal protein levels of Wnt 5a, ROR2, FZD5, PLC, p-CaMKII, IκB α, p-IκB α, NF-κB(p65), TNF α, IL 6 and IL 1β were measured. The levels of serum α1-MG and β2-MG and TNF α, IL 6 and IL 1β levels in the kidney tissue were significantly increased in TCE sensitized positive group. However, Box5 pretreatment inhibited the expression of PLC, p-CaMKII, p65 and attenuated the injury of renal tubular epithelial cells and suppressed the upregulated expression of the above cytokines. In addition, KN93 also reduced nuclear translocation of p65 and renal injury as well as the elevated cytokines by inhibiting CaMKII. These data identify Wnt 5a binding to ROR2 and FZD5, p65 nuclear translocation, and inflammatory cytokine release as a novel mechanism for renal tubular epithelial cells injury by sensitization with TCE. Box5 or KN93 pretreatment can block the expression of inflammatory cytokines and reduce the injury of renal tubular epithelial cells.

Th1-Th2 and M1-M2 interplay sculpt Aeromonas hydrophila pathogenesis in zebrafish (Danio rerio)

Aeromonas hydrophila is an important aquatic zoonotic pathogen that causes septicemia, necrotizing fasciitis and gastroenteritis in various aquatic and non-aquatic animals. However, the pathogenesis of A. hydrophila is not fully understood. Here, we examined the pathogenicity and histopathology of A. hydrophila in the zebrafish (Danio rerio) model system. We found that the intensity of symptoms and mortality is dose-dependent. Bacterial colonization studies demonstrated that A. hydrophila never cleared out from the fish body but stayed in a state of inactivity till it enters a fresh host. Reinfection studies showed that exposure to A. hydrophila provides immunity against future infection and hence improves fish survival. Gene expression studies revealed the crosstalk between T-helper cell and macrophage responses in fish immune system in response to A. hydrophila and infection memory. Histopathological studies showed that symptoms of tissue damage and inflammation lasted for less duration with less intensity in immunized fish when compared to non-immunized fish. Together, our results suggest that the zebrafish model is a useful system in studying the interplay between A. hydrophila pathogenesis, persistence and immunity.

mtROS Induced via TLR-2-SOCE Signaling Plays Proapoptotic and Bactericidal Role in Mycobacterium fortuitum-Infected Head Kidney Macrophages of Clarias gariepinus

The mechanisms underlying Mycobacterium fortuitum-induced mycobacteriosis remain unexplored. Using head kidney macrophages (HKM) from catfish (Clarias gariepinus), we report that Ca²⁺ surge across mitochondrial-Ca²⁺ uniporter (MICU), and consequent mitochondrial ROS (mtROS) production, is imperative for mycobactericidal activity. Inhibition of mtROS alleviated HKM apoptosis and enhanced bacterial survival. Based on RNA interference (RNAi) and inhibitor studies, we demonstrate that the Toll-like receptor (TLR)-2–endoplasmic reticulum (ER) stress–store-operated calcium entry (SOCE) axis is instrumental for activating the mt-Ca²⁺/mtROS cascade in M. fortuitum-infected HKM. Additionally, pharmacological inhibition of mtROS attenuated the expression of CHOP, STIM1, and Orai1, which suggests a positive feedback loop between ER-stress-induced SOCE and mtROS production. Elevated tumor necrosis factor alpha (TNF-α) levels and caspase-8 activity were observed in HKM consequent to M. fortuitum infection, and our results implicate that mtROS is crucial in activating the TNF-mediated caspase-8 activation. Our results for the first time demonstrate mitochondria as an innate immune signaling center regulating mycobacteriosis in fish. We conclude that M. fortuitum-induced persistent SOCE signaling leads to mtROS production, which in turn activates the TNF-α/caspase-8 axis culminating in HKM apoptosis and bacterial clearance.

Aeromonas sobria Induces Proinflammatory Cytokines Production in Mouse Macrophages via Activating NLRP3 Inflammasome Signaling Pathways

Aeromonas sobria, a common conditional pathogenic bacteria, is widely distributed in the environment and causes gastroenteritis in humans or septicemia in fish. Of all Aeromonas species, A. sobria is the most frequently isolated from human infections especially in immunocompromised subjects. Innate immunity is the first protection system of organism to resist non-specific pathogens invasion; however, the immune response process of hosts against A. sobria infection re\mains unexplored. The present study established an A. sobria infection model using primary mouse peritoneal macrophages (PMφs). The adherence and cytotoxicity of A. sobria on PMφs were determined by May-Grünwald Giemsa staining and LDH release measurement. Pro-inflammatory cytokine expression levels were measured using qPCR, western blotting, and ELISA methods. We also investigated the levels of ASC oligomerization and determined the roles of active caspase-1 in IL-1β secretion through inhibition assays and explored the activated pattern recognition receptors through immunofluorescence. We further elucidated the roles of activated inflammasome in regulating the host's inflammatory response through inhibition combined with ELISA assays. Our results showed that A. sobria induced lytic cell death and LDH release, whereas it had no adhesive properties on PMφs. A. sobria triggered various proinflammatory cytokine transcription level upregulation, and IL-1β occupied the highest levels. The pro-IL-1β protein expression levels increased in a dose-dependent manner with MOI ranging from 1 to 100. This process was regulated by ASC-dependent inflammasome, which cleavage pro-IL-1β into active IL-1β p17 with activated caspase-1 p20. Meanwhile, the expression levels of NLRP3 receptor significantly increased, location analysis revealed puncta-like surrounding nuclear, and inhibition of NLRP3 inflammasome downregulated caspase-1 activation and IL-1β secretion. Blocking of NLRP3 inflammasome activation through K⁺ efflux and cathepsin B or caspase approaches downregulated A. sobria-induced proinflammatory cytokine production. Overall, these data indicated that A. sobria induced proinflammatory cytokine production in PMφs through activating NLRP3 inflammasome signaling pathways.

TLR22-mediated activation of TNF-α-caspase-1/IL-1β inflammatory axis leads to apoptosis of Aeromonas hydrophila-infected macrophages

Toll-like receptors (TLRs) represent first line of host defence against microbes. Amongst different TLRs, TLR22 is exclusively expressed in non-mammalian vertebrates, including fish. The precise role of TLR22 in fish-immunity remains abstruse. Herein, we used headkidney macrophages (HKM) from Clarias gariepinus and deciphered its role in fish-immunity. Highest tlr22 expression was observed in the immunocompetent organ - headkidney; nonetheless expression in other tissues suggests its possible involvement in non-immune sites also. Aeromonas hydrophila infection up-regulates tlr22 expression in HKM. Our RNAi based study suggested TLR22 restricts intracellular survival of A. hydrophila. Inhibitor and RNAi studies further implicated TLR22 induces pro-inflammatory cytokines TNF-α and IL-1β. We observed heightened caspase-1 activity and our results suggest the role of TLR22 in activating TNF-α/caspase-1/IL-1β cascade leading to caspase-3 mediated apoptosis of A. hydrophila-infected HKM. We conclude, TLR22 plays critical role in immune-surveillance and triggers pro-inflammatory cytokines leading to caspase mediated HKM apoptosis and pathogen clearance.

Differential proteome profile of gill and spleen in three pathogen-infected Paralichthys olivaceus

BACKGROUND

Olive flounder (Paralichthys olivaceus) is one of the major cultured fish species in Asia including Korea. However, the mass mortality of olive flounder caused by various pathogens leads to huge economic loss. The pathogens that lead to fish mortality include parasites, bacteria, and viruses that can cause various kinds of diseases.

OBJECTIVE

The purpose of this study was to investigate the protein expression patterns in the gills and spleens of olive flounder after artificial infection. We hypothesized that proteomics levels in gills and spleen may be differentially expressed depending on infectious agents.

METHODS

To investigate the expression pattern of proteins in gills and spleens, olive flounders were experimentally infected with VHSV (virus), S. parauberis (bacteria), or M. avidus (pathogenic ciliate). Proteins were extracted from the gills and spleens of infected olive flounder. We used 2-DE analysis with LC-MS/MS to investigate proteome changes in infected olive flounders.

RESULTS

The results of the LC-MS/MS analyses showed different protein expression profiles depending on pathogenic sources and target organs. Proteins related to cytoskeletal structure like keratin, calmodulin and actin were mostly expressed in the infected gills. Proteins involved in the metabolism pathway like glycolysis were expressed mainly in the spleens. The protein profiles of S. parauberis and VHSV infection groups had many similarities, but the profile of the M. avidus infection group was greatly different in the gill and spleen.

CONCLUSION

Our results indicate that measures according to the characteristics of each pathogen are necessary for disease prevention and treatment of farmed fish.

Calmodulin downregulation in conditional knockout HeLa cells inhibits cell migration

The study of calmodulin (CaM) functions in living cells has been tackled up to date using cell-permeant CaM inhibitors or interference-RNA methods. CaM inhibitors may lack specificity and the siRNA interference approach is challenging, as all three CaM genes expressing an identical protein in mammals have to be blocked. Therefore, we recently introduced a novel genetic system using CRISPR/Cas9-mediated gene deletion and conditional CaM expression to study the function of CaM in HeLa cells. Here, we describe the effect of CaM downregulation on the basal and epidermal growth factor (EGF)-dependent 2D- and 3D-migration in HeLa cells. CaM downregulation inhibited cell migration on a 2D-surface in the absence but not in the presence of EGF. In contrast, CaM downregulation led to inhibition of 3D-migration across a porous membrane both in the absence and presence of EGF. CaM downregulation decreased the expression of Rac1, Cdc42 and RhoA, all known to play crucial roles in cell migration. These results show that EGF-dependent 2D- and 3D-migration utilize distinct CaM-regulated systems and identify several essential migratory proteins directly or indirectly regulated by CaM.

Low-dose methylmercury exposure impairs the locomotor activity of zebrafish: Role of intestinal inositol metabolism

Methylmercury (MeHg) is a ubiquitous environmental toxicant with neurotoxic effects. Although its neurotoxicity had been more studied, the role of gut microbiota remains unclear. In this study, adult zebrafish and larvae were exposed to MeHgCl at the dose of 0, 1 and 10 ng/mL. MeHgCl exposure impaired the locomotor activity via upregulation of apoptosis and autophagy related genes in the brain. Intestinal and cerebral metabolome indicated that phosphatidylinositol signaling system and inositol phosphate metabolism pathways were significantly impacted in adult zebrafish upon MeHgCl exposure. The levels of myo-inositol (MI) in the intestine and brain were decreased and positively correlated. 16 S rRNA sequencing data from adult zebrafish showed that MeHgCl exposure also shifted the structure of gut microbiota and reduced the relative abundance of Bacteroidetes and Proteobacteria, which were further identified at genus level as Aeromonas and Cetobacterium. Further functional analysis indicated that MeHgCl disrupted inositol phosphate metabolism of gut microbiota. Notably, MI supplementation restored the impairment of locomotor activity and inhibited the upregulation of apoptosis and autophagy related genes, such as bcl-2 and atg5. Thus, this study not only revealed the key role of gut microbiota in MeHgCl-mediated neurotoxicity but also gave new insights into antagonizing its toxicity.

A G-protein coupled receptor 39 agonist stimulates proliferation of keratinocytes via an ERK-dependent pathway

Keratinocyte proliferation serves as a crucial process in skin wound healing. The zinc-sensing G-protein coupled receptor 39 (GPR39), which is highly expressed in keratinocytes, has been shown to promote skin wound healing. The aim of this study was to investigate the effect of GPR39 activation on proliferation of keratinocytes and its underlying mechanism using immortalized human keratinocytes (HaCaT) as an in vitro model. GPR39 was functionally expressed in HaCaT cells. BrdU proliferation assays showed that treatment with GPR39 agonist TC-G 1008 (100 nM and 1 μM) increased cell proliferation. TC-G 1008 also enhanced ERK phosphorylation in time- and concentration-dependent manners. This effect was suppressed by co-treatment with wortmannin (PI3K inhibitor) and U0126 (MKK inhibitor). Of note, neither inhibition of Gα_q-phospholipase C (PLC)-[Ca²⁺]_i nor Gα_s-PKA pathway affected GPR39 stimulation-induced ERK phosphorylation. Similarly, barbadin, an inhibitor of G-protein-independent β-arrestin pathway, did not suppress ERK phosphorylation induced by GPR39 activation. Of particular importance, wortmannin, U0126, and FR180204 (ERK inhibitor) abrogated the effect of TC-G 1008-induced cell proliferation. Taken together, this study reveals novel insights into the role of GPR39 in regulating keratinocyte proliferation via a PI3K-MKK-ERK-dependent mechanism. GPR39 agonists may be used in enhancing keratinocyte proliferation, which may be beneficial for the cutaneous wound treatment.

Selenium Attenuates Chronic Heat Stress-Induced Apoptosis via the Inhibition of Endoplasmic Reticulum Stress in Mouse Granulosa Cells

Heat stress induces apoptosis in various cells. Selenium, an essential micronutrient, has beneficial effects in maintaining the cellular physiological functions. However, its potential protective action against chronic heat stress (CHS)-induced apoptosis in granulosa cells and the related molecular mechanisms are not fully elucidated. In this study, we investigated the roles of selenium in CHS-induced apoptosis in mouse granulosa cells and explored its underlying mechanism. The heat treatment for 6–48 h induced apoptosis, potentiated caspase 3 activity, increased the expression levels of apoptosis-related gene BAX and ER stress markers, glucose-regulated protein 78 (GRP78), and CCAAT/enhancer binding protein homologous protein (CHOP) in mouse granulosa cells. The treatment with ER stress inhibitor 4-PBA significantly attenuated the adverse effects caused by CHS. Selenium treatment significantly attenuated the CHS- or thapsigargin (Tg, an ER stress activator)-induced apoptosis, potentiation of caspase 3 activity, and the increased protein expression levels of BAX, GRP78, and CHOP. Additionally, treatment of the cells with 5 ng/mL selenium significantly ameliorated the levels of estradiol, which were decreased in response to heat exposure. Consistently, administering selenium supplement alleviated the hyperthermia-caused reduction in the serum estradiol levels in vivo. Together, our findings indicate that selenium has protective effects on CHS-induced apoptosis via inhibition of the ER stress pathway. The current study provides new insights in understanding the role of selenium during the process of heat-induced cell apoptosis.

Mechanism of AMPK-mediated apoptosis of rat gastric smooth muscle cells under high glucose condition

To observe changes in AMP-activated protein kinase (AMPK) activity and phosphorylation changes in AMPK signaling pathway in gastric smooth muscle cells of rats with diabetic gastroparesis (DGP), investigate the effect of AMPK on apoptosis and explore the underlying mechanism. After establishing rat model of DGP, rats were divided into normal control (NC) and DGP groups. The phosphorylation changes in AMPK pathway were detected by AMPK Signaling Phospho-Antibody Array, and the apoptosis-related proteins were determined. Rat gastric smooth muscle cells were cultured in vitro under different glucose conditions, and divided into normal and high glucose groups. The AMPK activity and intracellular Ca²⁺ changes in cells were observed. After AMPK silencing, cells were divided into high glucose-24h, high glucose-48h and high glucose-48h+siRNA groups. Changes in expression of apoptosis-related proteins were observed. AMPK activity and apoptosis rates were both increased in gastric smooth muscle tissues in DGP rats (P<0.05, P<0.001, respectively). A total of 14 apoptosis-related differentially phosphorylated proteins were identified. Under high-glucose condition, AMPK activity and intracellular Ca²⁺ concentrations in rat gastric smooth muscle cells were increased (both P<0.05). After AMPK silencing, p53 expression was decreased, Akt and p70 S6 ribosomal protein kinase (p70S6K) activities were were increased, Bcl-2 expression was increased, CaMKII activity was decreased in the high glucose-48h group. Under high-glucose condition, activated AMPK can directly or indirectly promote cells apoptosis by regulating the expression and activity of p53, Akt, p70S6K, Protein kinase A (PKA), Phospholipidol C (PLC)-β3, CaMKII, CaMKIV and eukaryotic translation initiation factor 4E binding protein1 (4E-BP1) in rat gastric smooth muscle cells.

TLR-2 mediated cytosolic-Ca2+ surge activates ER-stress-superoxide-NO signalosome augmenting TNF-α production leading to apoptosis of Mycobacterium smegmatis-infected fish macrophages

The implications of TLR-2 mediated alterations in cytosolic-Ca²⁺((Ca²⁺)_c) levels in M. smegmatis infections is not well known. Using headkidney macrophages (HKM) from Clarias gariepinus, we observed TLR-2 signalling is required in the phagocytosis of M. smegmatis. M. smegmatis induced caspase-dependent HKM apoptosis in MOI, time and growth-phase dependent manner. RNAi and inhibitor studies demonstrated critical role of TLR-2 in eliciting (Ca²⁺)_c-surge and c-Src-PI3K-PLC axis playing an intermediary role in the process. The (Ca²⁺)_c-surge triggered downstream ER-stress and superoxide (O₂⁻) generation. The cross-talk between ER-stress and O₂⁻ amplified TNF-α production, which led to HKM apoptosis and bacterial clearance. Release of nitric oxide (NO) was also observed and silencing the NOS2-NO axis enhanced intracellular bacterial survival and attenuated caspase activity. Pre-treatment with diphenyleneidonium chloride inhibited NO production implicating O₂^−–NO axis imperative in M. smegmatis-induced HKM apoptosis. NO positively impacted CHOP expression and TNF-α production in infected HKM. We conclude that, TLR-2 induced (Ca²⁺)_c-surge and ensuing cross-talk between ER-stress and O₂⁻ potentiates HKM pathology by amplifying pro-inflammatory TNF-α production. Moreover, the pro-oxidant environment triggers NO release which prolonged ER-stress and TNF-α production, culminating in HKM apoptosis and bacterial clearance. Together, our study suggests HKM an alternate model to study macrophage-mycobacteria interactions.

Interrelation of Ca2+ and PE_PGRS proteins during Mycobacterium tuberculosis pathogenesis

In today's era tuberculosis is a major threat to human population. The lethality of this disease is caused by very efficiently thrived bacteria Mycobacterium tuberculosis (M. tuberculosis). Ca²⁺ plays crucial role in maintenance of cellular homeostasis. Bacilli survival in human alveolar macrophages majorly depends on disruption in Ca²⁺ signaling. Bacilli sustainability in phagosome lies in the interruption of phagolysosomal fusion, which is possible because of low intracellular Ca²⁺ concentration. Bacilli contain various Ca²⁺ binding proteins which help in regulation of Ca²⁺ signaling for its own benefit. For the survival of pathogen, it requires alteration in normal Ca²⁺ concentration in healthy cell. In this review we aim to find the various Ca²⁺ binding domains which are present in several Ca²⁺ binding proteins of M. tuberculosis and variety of roles played by Ca²⁺ to survive bacilli within host cell. This manuscript emphasizes the Ca²⁺ binding domains present in PE_PGRS group of gene family and their functionality in M. tuberculosis survival and pathogenesis.

Silencing of spinal Trpv1 attenuates neuropathic pain in rats by inhibiting CAMKII expression and ERK2 phosphorylation

Accumulating evidence suggests a potential role of transient receptor potential vanilloid 1 (TRPV1) channels in inflammatory and cancer-related pain. However, the role of TRPV1 in the maintenance of neuropathic pain remains elusive. The current study investigated the effects of transient Trpv1 gene silencing using a small interference RNA (siRNA) on neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve in rats. Seven days after CCI, the TRPV1 siRNA was intrathecally administered (5 µg/15 µl, once daily for 2 days). TRPV1 and Ca²⁺/calmodulin-dependent protein kinase II (CAMKII) expression and extracellular signal-regulated kinase (ERK) phosphorylation in the spinal cord were detected using western blotting. The thresholds to mechanical and thermal stimuli were determined before and after intrathecal TRPV1 siRNA administration. TRPV1 and CAMKII expression and ERK2 phosphorylation in the spinal cord were upregulated after CCI. Intrathecal administration of the TRPV1 siRNA not only attenuated behavioural hyperalgesia but also reduced the expression of TRPV1 and CAMKII, as well as ERK2 phosphorylation. Based on these results, silencing of the TRPV1 gene in the spinal cord attenuates the maintenance of neuropathic pain by inhibiting CAMKII/ERK2 activation and suggests that TRPV1 represents a potential target in pain therapy.

Involvement of calpain in the neuropathogenesis of Alzheimer's disease

Alzheimer’s disease (AD) is the most common (60% to 80%) age‐related disease associated with dementia and is characterized by a deterioration of behavioral and cognitive capacities leading to death in few years after diagnosis, mainly due to complications from chronic illness. The characteristic hallmarks of the disease are extracellular senile plaques (SPs) and intracellular neurofibrillary tangles (NFTs) with neuropil threads, which are a direct result of amyloid precursor protein (APP) processing to Aβ, and τ hyperphosphorylation. However, many indirect underlying processes play a role in this event. One of these underlying mechanisms leading to these histological hallmarks is the uncontrolled hyperactivation of a family of cysteine proteases called calpains. Under normal physiological condition calpains participate in many processes of cells’ life and their activation is tightly controlled. However, with an increase in age, increased oxidative stress and other excitotoxicity assaults, this regulatory system becomes impaired and result in increased activation of these proteases involving them in the pathogenesis of various diseases including neurodegeneration like AD. Reviewed here is a pool of data on the implication of calpains in the pathogenesis of AD, the underlying molecular mechanism, and the potential of targeting these enzymes for AD therapeutics.

Mycobacterium fortuitum-induced ER-Mitochondrial calcium dynamics promotes calpain/caspase-12/caspase-9 mediated apoptosis in fish macrophages

Mycobacterium fortuitum is a natural fish pathogen. It induces apoptosis in headkidney macrophages (HKM) of catfish, Clarias sp though the mechanism remains largely unknown. We observed M. fortuitum triggers calcium (Ca²⁺) insult in the sub-cellular compartments which elicits pro-apototic ER-stress factor CHOP. Alleviating ER-stress inhibited CHOP and attenuated HKM apoptosis implicating ER-stress in the pathogenesis of M. fortuitum. ER-stress promoted calpain activation and silencing the protease inhibited caspase-12 activation. The study documents the primal role of calpain/caspase-12 axis on caspase-9 activation in M. fortuitum-pathogenesis. Mobilization of Ca²⁺ from ER to mitochondria led to increased mitochondrial Ca²⁺ (Ca²⁺)_m load,_, mitochondrial permeability transition (MPT) pore opening, altered mitochondrial membrane potential (ΔΨm) and cytochrome c release eventually activating the caspase-9/-3 cascade. Ultra-structural studies revealed close apposition of ER and mitochondria and pre-treatment with (Ca²⁺)_m-uniporter (MUP) blocker ruthenium red, reduced Ca²⁺ overload suggesting (Ca²⁺)_m fluxes are MUP-driven and the ER-mitochondria tethering orchestrates the process. This is the first report implicating role of sub-cellular Ca²⁺ in the pathogenesis of M. fortuitum. We summarize, the dynamics of Ca²⁺ in sub-cellular compartments incites ER-stress and mitochondrial dysfunction, leading to activation of pro-apoptotic calpain/caspase-12/caspase-9 axis in M. fortuitum-infected HKM.

Nalmefene attenuates malignant potential in colorectal cancer cell via inhibition of opioid receptor

Morphine is postulated a risk factor in promoting tumor growth and metastasis during the preoperative period, and high glycolysis of tumor cells is proved to accelerate tumor progression. In this study, we investigated whether nalmefene, an opioid receptor inhibitor, could inhibit CT26 colon cancer cell growth through influencing cell glycolysis. CCK8 and transwell migration assays showed that nalmefene inhibited CT26 cells viability and migration in a concentration-dependent manner. Extracellular acidification rate and oxygen consumption rate showed that nalmefene inhibited glycolysis of CT26 cells. Moreover, western blot analysis and quantitative real-time PCR revealed that nalmefene decreased the expressions of enzymes related to glycolysis. Flow cytometry results revealed that intracellular calcium (Ca2+) level was changed by nalmefene, western blot analysis showed that nalmefene decreased calmodulin expression and calcium/calmodulin dependent protein kinases II (CaMK II) phosphorylation, thus inhibiting the serine/threonine kinase (AKT)-glycogen synthase kinase-3β (GSK-3β) pathway. Furthermore, the effects of KN93, an inhibitor of CaMK II, were similar to the effects of nalmefene, and the anti-tumor effect of nalmefene could be counteracted by morphine. In conclusion, the anti-tumor effect of nalmefene may be achieved by inhibiting opioid receptor and down-regulating calmodulin expression and CaMK II phosphorylation, thus inhibiting AKT-GSK-3β pathway and the glycolysis of CT26 cells.

Aeromonas hydrophila-induced alterations in cytosolic calcium activate pro-apoptotic cPKC-MEK1/2-TNFα axis in infected headkidney macrophages of Clarias gariepinus

Alterations in intracellular-calcium (Ca²⁺)_i homeostasis is critical to Aeromonas hydrophila-induced headkidney macrophages (HKM) apoptosis of Clarias gariepinus, though the implications are poorly understood. Here, we describe the role of intermediate molecules of Ca^2+-signaling pathway that are involved in HKM apoptosis. We observed phosphoinositide-3-kinase/phospholipase C is critical for (Ca²⁺)_i release in infected HKM. Heightened protein kinase-C (PKC) activity and phosphorylation of MEK1/2-ERK1/2 was noted which declined in presence of 2-APB, Go6976 and PD98059, inhibitors to IP3-receptor, conventional PKC isoforms (cPKC) and MEK1/2 respectively implicating Ca²⁺/cPKC/MEK-ERK1/2 axis imperative in A. hydrophila-induced HKM apoptosis. Significant tumor necrosis factor-α (TNFα) production and its subsequent reduction in presence of MEK-ERK1/2 inhibitor U0126 suggested TNFα production downstream to cPKC-mediated signaling via MEK1/2-ERK1/2 pathway. RNAi and inhibitor studies established the role of TNFα in inducing caspase-8-mediated apoptosis of infected HKM. We conclude, alterations in A. hydrophila-induced (Ca²⁺)i alterations activate cPKC-MEK1/2-ERK1/2-TNFα signaling cascade triggering HKM apoptosis.

Intracellular Ca2+ homeostasis and JAK1/STAT3 pathway are involved in the protective effect of propofol on BV2 microglia against hypoxia-induced inflammation and apoptosis

BACKGROUND

Perioperative hypoxia may induce microglial inflammation and apoptosis, resulting in brain injury. The neuroprotective effect of propofol against hypoxia has been reported, but the underlying mechanisms are far from clear. In this study, we explored whether and how propofol could attenuate microglia BV2 cells from CoCl2-induced hypoxic injury.

METHODS

Mouse microglia BV2 cells were pretreated with propofol, and then stimulated with CoCl2. TNF-α level in the culture medium was measured by ELISA kit. Cell apoptosis and intracellular calcium concentration were measured by flow cytometry analysis. The effect of propofol on CoCl2-modulated expression of Ca2+/Calmodulin (CaM)-dependent protein kinase II (CAMKIIα), phosphorylated CAMKIIα (pCAMKIIα), STAT3, pSTAT3Y705, pSTAT3S727, ERK1/2, pERK1/2, pNFκB(p65), pro-caspase3, cleaved caspase 3, JAK1, pJAK1, JAK2, pJAK2 were detected by Western blot.

RESULTS

In BV2 cell, CoCl2 treatment time-dependently increased TNF-α release and induced apoptosis, which were alleviated by propofol. CoCl2 (500μmol/L, 8h) treatment increased intracellular Ca2+ level, and caused the phosphorylation of CAMKIIα, ERK1/2 and NFκB (p65), as well as the activation of caspase 3. More importantly, these effects could be modulated by 25μmol/L propofol via maintaining intracellular Ca2+ homeostasis and via up-regulating the phosphorylation of JAK1 and STAT3 at Tyr705.

CONCLUSION

Propofol could protect BV2 microglia from hypoxia-induced inflammation and apoptosis. The potential mechanisms may involve the maintaining of intracellular Ca2+ homeostasis and the activation of JAK1/STAT3 pathway.

Fluoride exposure abates pro-inflammatory response and induces in vivo apoptosis rendering zebrafish (Danio rerio) susceptible to bacterial infections

The present study describes the immunotoxic effect of chronic fluoride exposure on adult zebrafish (Danio rerio). Zebrafish were exposed to fluoride (71.12 mg/L; 1/10 LC₅₀) for 30 d and the expression of selected genes studied. We observed significant elevation in the detoxification pathway gene cyp1a suggesting chronic exposure to non-lethal concentration of fluoride is indeed toxic to fish. Fluoride mediated pro-oxidative stress is implicated with the downregulation in superoxide dismutase 1 and 2 (sod1/2) genes. Fluoride affected DNA repair machinery by abrogating the expression of the DNA repair gene rad51 and growth arrest and DNA damage inducible beta a gene gadd45ba. The upregulated expression of casp3a coupled with altered Bcl-2 associated X protein/B-cell lymphoma 2 ratio (baxa/bcl2a) clearly suggested chronic fluoride exposure induced the apoptotic cascade in zebrafish. Fluoride-exposed zebrafish when challenged with non-lethal dose of fish pathogen A. hydrophila revealed gross histopathology in spleen, bacterial persistence and significant mortality. We report that fluoride interferes with system-level output of pro-inflammatory cytokines tumour necrosis factor-α, interleukin-1β and interferon-γ, as a consequence, bacteria replicate efficiently causing significant fish mortality. We conclude, chronic fluoride exposure impairs the redox balance, affects DNA repair machinery with pro-apoptotic implications and suppresses pro-inflammatory cytokines expression abrogating host immunity to bacterial infections.

Inducible headkidney cytochrome P450 contributes to endosulfan immunotoxicity in walking catfish Clarias gariepinus

The effect of endosulfan metabolites on fish immune system is not well known. It is also not clear whether endosulfan accumulates in fish immune organs and undergoes metabolic biotransformation in situ. In the present study we investigated the role of headkidney (HK), an important fish immune organ on endosulfan metabolism and the long term effects of endosulfan metabolites on the fish immune system. C. gariepinus (walking catfish) were exposed to 2.884ppb of endosulfan (1/10th LC50) for 30d followed by their maintenance in endosulfan-free water for 30d for recovery. Endosulfan induced time-dependent reduction in the HK somatic index and histo-pathological changes in renal and hemopoietic components of the organ. At cellular level, exposure to endosulfan led to death of HK leucocytes. Gas-liquid-chromatography documented the presence of both α- and β-isomers of endosulfan along with the toxic metabolite endosulfan sulfate (ESS) in the HK of exposed fishes. We report that β-endosulfan accumulates more readily in the HK. Depuration studies suggested the persistence of ESS in the HK. Enzyme-immunoassay and qPCR results demonstrated direct relationship between cytochrome P450 1A (CYP1A) expression and ESS levels in the HK. Pre-treatment of HKL with CYP1A specific inhibitor α-Naphthoflavone (ANF) led to reduction in CYP1A mRNA, protein levels, and inhibited ESS formation together implicating the role of CYP1A on endosulfan metabolism. When the exposed fish were transferred to endosulfan-free water ('recovered fish') it was observed that after 30d of recovery period the concentration of endosulfan and its metabolite in the HK were significantly reduced, compared to 30-d exposed fish. We also observed improvement in HK histo-architecture but no significant recovery in HKL number and viability. Collectively, our findings suggest that HK plays an important role in endosulfan metabolism. We propose that endosulfan induces the activation of CYP1A in HK which led to the generation of persistent metabolite, ESS, resulting in immunotoxicity.

Pleiotropic roles of Ca+2/calmodulin-dependent pathways in regulating cadmium-induced toxicity in human osteoblast-like cell lines

The heavy metal cadmium is a widespread environmental contaminant that has gained public attention due to the global increase in cadmium-containing electronic waste. Human exposure to cadmium is linked to the pathogenesis of osteoporosis. We previously reported cadmium induces apoptosis and decreases alkaline phosphatase mRNA expression via extracellular signal-regulated protein kinase (ERK) activation in Saos-2 bone-forming osteoblasts. This study examines the mechanisms of cadmium-induced osteotoxicity by investigating roles of Ca⁺²/calmodulin-dependent protein kinase (CAMK) pathways. Saos-2 or MG-63 cells were treated for 24 or 48h with 5μM CdCl₂ alone or in combination with calmodulin-dependent phosphodiesterase (PDE) inhibitor CGS-9343β; calmodulin-dependent kinase kinase (CAMKK) inhibitor STO-609; or calmodulin-dependent kinase II (CAMKII) inhibitor KN-93. CGS-9343β protected against cadmium-induced toxicity and attenuated ERK activation; STO-609 enhanced toxicity and exacerbated ERK activation, whereas KN-93 had no detectable effect on cadmium-induced toxicity. Furthermore, CGS-9343β co-treatment attenuated cadmium-induced apoptosis; but CGS-9343β did not recover cadmium-induced decrease in ALP activity. The major findings suggest the calmodulin-dependent PDE pathway facilitates cadmium-induced ERK activation leading to apoptosis, whereas the CAMKK pathway plays a protective role against cadmium-induced osteotoxicity via ERK signaling. This research distinguishes itself by identifying pleiotropic roles for CAMK pathways in mediating cadmium's toxicity in osteoblasts.

Fluoride-induced headkidney macrophage cell apoptosis involves activation of the CaMKIIg-ERK 1/2-caspase-8 axis: the role of superoxide in initiating the apoptotic cascade

Fluoride is known to induce apoptosis though the mechanisms remain obscure. The aim of the present study was to understand the underlying molecular mechanisms of fluoride-induced apoptosis using fish headkidney macrophages (HKMs). Exposure to fluoride triggered HKM cell apoptosis as evidenced by Hoechst 333432 and AnnexinV-propidium iodide staining, the presence of an internucleosomal DNA ladder and the comet assay. Our results suggest the influx of extra-cellular Ca²⁺ to be an initial event in fluoride-induced HKM cell apoptosis. We observed persistently elevated levels of superoxide anions and our inhibitor studies with EGTA suggested the primal role of the Ca²⁺ flux in triggering superoxide production in fluoride-exposed HKM cells. Fluoride exposure led to elevated levels of Ca²⁺/CaM dependent protein kinase II gamma (CaMKIIg) and pre-treatment with the inhibitor KN-93 but not its inactive structural analogue KN-92 reduced the number of apoptotic cells establishing the pro-apoptotic role of CaMKIIg in fluoride-induced HKM cell apoptosis. We report that the sustained superoxide generation is primarily responsible for the increased CaMKIIg levels observed in fluoride-exposed HKM cells. Our inhibitor studies further implicated CaMKIIg in the activation of extracellular signal-regulated kinases 1 and 2 (ERK 1/2) culminating in caspase-8/caspase-3 mediated apoptosis of HKM cells. We conclude that fluoride-induced apoptosis is largely dependent on Ca²⁺ induced superoxide generation leading to elevation in CaMKIIg which in turn induces the phosphorylation of ERK 1/2 and downstream activation of extrinsic caspase cascade in HKM cells.

Lactobacillus acidophilus attenuates Aeromonas hydrophila induced cytotoxicity in catla thymus macrophages by modulating oxidative stress and inflammation

The pathogenesis of Aeromonas hydrophila, a potent fish pathogen, is attributed to its ability to cause motile aeromonad septicaemia leading to apoptosis in a myriad of fish species, including freshwater carp Catla catla. However, the underlying mechanism of antagonistic activity of probiotics against A. hydrophila induced apoptosis is not elucidated due to lack of appropriate in-vitro models. This study reported that the exposure of catla thymus macrophages (CTM) to A. hydrophila markedly induced cellular injuries as evidenced by elevated levels of reactive oxygen species (ROS), reactive nitrogen species (RNS), increased apoptosis, DNA damage and decreased cellular viability. Flow cytometry analysis and Annexin-V/propidium iodide assay further confirmed increased ROS positive cells leading to cell death after infection. The quantitative real-time PCR analysis, also revealed upregulation of inducible nitric-oxide synthase (iNOS), pro-inflammatory cytokine (TNFα), cyclooxygenase2 (COX-2) and downregulation of anti-inflammatory cytokine (IL-10). Pretreatment of cells with probiotic, Lactobacillus acidophilus attenuated A. hydrophila induced apoptosis as evident from the decrease in the levels of ROS, RNS and DNA damage. Significant increase (P≤0.05) in expression of TNFα and IL-10 and decrease in iNOS and COX-2 was observed on probiotic stimulation. In-vivo study using catla fingerlings confirmed similar pattern of ROS, iNOS, NO production and cytokine expression in thymus. This study provides a comprehensive insight into the mechanistic basis of L. acidophilus induced macrophage mediated inflammatory response against A. hydrophila in CTM cells. Further, it speculates the possibility of using cost-effective in-vitro models for screening probiotic candidates of therapeutic potential in aquaculture industry.

Calcium and Superoxide-Mediated Pathways Converge to Induce Nitric Oxide-Dependent Apoptosis in Mycobacterium fortuitum-Infected Fish Macrophages

Mycobacterium fortuitum causes ‘mycobacteriosis’ in wide range of hosts although the mechanisms remain largely unknown. Here we demonstrate the role of calcium (Ca⁺²)-signalling cascade on M. fortuitum-induced apoptosis in headkidney macrophages (HKM) of Clarias sp. M. fortuitum could trigger intracellular-Ca⁺² influx leading to the activation of calmodulin (CaM), protein kinase C alpha (PKCα) and Calmodulin kinase II gamma (CaMKIIg). Gene silencing and inhibitor studies established the role of CaM in M. fortuitum pathogenesis. We noted that CaMKIIg activation is regulated by CaM as well as PKCα-dependent superoxide anions. This is altogether first report of oxidised CaMKIIg in mycobacterial infections. Our studies with targeted-siRNA and pharmacological inhibitors implicate CaMKIIg to be pro-apoptotic and critical for the activation of extra-cellular signal regulated kinase 1/2 (ERK1/2). Inhibiting the ERK1/2 pathway attenuated nitric oxide synthase 2 (NOS2)-induced nitric oxide (NO) production. Conversely, inhibiting the NOS2-NO axis by specific-siRNA and inhibitors down-regulated ERK1/2 activation suggesting the crosstalk between ERK1/2 and NO is essential for pathogenesis induced by the bacterium. Silencing the NOS2-NO axis enhanced intracellular bacterial survival and attenuated caspase-8 mediated activation of caspase-3 in the infected HKM. Our findings unveil hitherto unknown mechanism of M. fortuitum pathogenesis. We propose that M. fortuitum triggers intracellular Ca⁺² elevations resulting in CaM activation and PKCα-mediated superoxide generation. The cascade converges in common pathway mediated by CaMKIIg resulting in the activation of ERK1/2-NOS2 axis. The crosstalk between ERK1/2 and NO shifts the balance in favour of caspase dependent apoptosis of M. fortuitum-infected HKM.

DAG/PKCδ and IP3/Ca²⁺/CaMK IIβ Operate in Parallel to Each Other in PLCγ1-Driven Cell Proliferation and Migration of Human Gastric Adenocarcinoma Cells, through Akt/mTOR/S6 Pathway

Phosphoinositide specific phospholipase Cγ (PLCγ) activates diacylglycerol (DAG)/protein kinase C (PKC) and inositol 1,4,5-trisphosphate (IP3)/Ca²⁺/calmodulin-dependent protein kinase II (CaMK II) axes to regulate import events in some cancer cells, including gastric adenocarcinoma cells. However, whether DAG/PKCδ and IP3/Ca²⁺/CaMK IIβ axes are simultaneously involved in PLCγ1-driven cell proliferation and migration of human gastric adenocarcinoma cells and the underlying mechanism are not elucidated. Here, we investigated the role of DAG/PKCδ or CaMK IIβ in PLCγ1-driven cell proliferation and migration of human gastric adenocarcinoma cells, using the BGC-823 cell line. The results indicated that the inhibition of PKCδ and CaMK IIβ could block cell proliferation and migration of BGC-823 cells as well as the effect of inhibiting PLCγ1, including the decrease of cell viability, the increase of apoptotic index, the down-regulation of matrix metalloproteinase (MMP) 9 expression level, and the decrease of cell migration rate. Both DAG/PKCδ and CaMK IIβ triggered protein kinase B (Akt)/mammalian target of rapamycin (mTOR)/S6 pathway to regulate protein synthesis. The data indicate that DAG/PKCδ and IP3/Ca²⁺/CaMK IIβ operate in parallel to each other in PLCγ1-driven cell proliferation and migration of human gastric adenocarcinoma cells through Akt/mTOR/S6 pathway, with important implication for validating PLCγ1 as a molecular biomarker in early gastric cancer diagnosis and disease surveillance.

Calmodulin is a stress and immune response gene in Chinese mitten crab Eriocheir sinensis

Calmodulin (CaM) is a multifunctional calcium sensor protein that participates in various cellular processes under normal, stress and pathological conditions. In crabs, however, the involvement of CaM in response to environmental stress and immune challenges has not been revealed yet. In the present study, a CaM cDNA (EsCaM) was identified from Chinese mitten crab Eriocheir sinensis and its mRNA expression patterns in response to ambient (salinity and pH) stress and immune challenges was examined. EsCaM encodes a 149-amino-acid protein with a calculated molecular mass of 16.8 kDa and an isoelectric point of 4.09. In unstimulated healthy E. sinensis, EsCaM mRNA transcript was detected in all tested tissues with predominant expression in hepatopancreas and the lowest expression in haemocytes. Ambient salinity (15‰ and 30‰ salinities) and pH (pH 6 and 8.5) stress significantly altered EsCaM mRNA expression in gill, hepatopancreas, haemocytes, intestine and muscle in Chinese mitten crab. In addition, EsCaM gene expression was significantly and rapidly induced as early as 2 h after LPS and Poly(I:C) immune stimulations in haemocytes in vitro. Furthermore, EsCaM expression was significantly up-regulated in E. sinensis haemocytes, gill, hepatopancreas, intestine and muscle in response to Edwardsiella tarda and Vibrio anguillarum challenges. Collectively, our findings suggest that EsCaM is an important stress and immune response gene in Chinese mitten crab.

Ameliorating ER-stress attenuates Aeromonas hydrophila-induced mitochondrial dysfunctioning and caspase mediated HKM apoptosis in Clarias batrachus

Endoplasmic reticulum (ER)-stress and unfolding protein response (UPR) has not been implied in Aeromonas hydrophila-pathogenicity. We report increased expression of the ER-stress markers: CHOP, BiP and phospho-eIF2α in A. hydrophila-infected headkidney macrophages (HKM) in Clarias batrachus. Pre-treatment with ER-stress inhibitor, 4-PBA alleviated ER-stress and HKM apoptosis suggesting ER-UPR critical for the process. The ER-Ca(2+) released via inositol-triphosphate and ryanodine receptors induced calpain-2 mediated superoxide ion generation and consequent NF-κB activation. Inhibiting NF-κB activation attenuated NO production suggesting the pro-apoptotic role of NF-κB on HKM pathology. Calpain-2 activated caspase-12 to intensify the apoptotic cascade through mitochondrial-membrane potential (ψm) dissipation and caspase-9 activation. Altered mitochondrial ultra-structure consequent to ER-Ca(2+) uptake via uniporters reduced ψm and released cytochrome C. Nitric oxide induced the cGMP/PKG-dependent activation of caspase-8 and truncated-Bid formation. Both the caspases converge onto caspase-3 to execute HKM apoptosis. These findings offer a possible molecular explanation for A. hydrophila pathogenicity.