MicroRNA-129-1-3p protects chicken granulosa cells from cadmium-induced apoptosis by down-regulating the MCU-mediated Ca2+ signaling pathway

Cadmium (Cd) is known as a female reproductive toxicant. Our previous study has shown that Cd can influence the proliferation and cell cycle of granulosa cells and induce apoptosis. MicroRNAs (miRNAs) play an important role in the regulation of Cd-induced granulosa cell damage in chickens. However, the mechanism remains unclear. In this study, we investigated the mechanisms by which microRNA-129-1-3p (miR-129-1-3p) regulates Cd-induced cytotoxicity in chicken granulosa cells. As anticipated, exposure to Cd resulted in the induction of oxidative stress in granulosa cells, accompanied by the downregulation of antioxidant molecules and/or enzymes of Nrf2, Mn-SOD, Cu-Zn SOD and CAT, and the upregulation of Keap1, GST, GSH-Px, GCLM, MDA, hydrogen peroxide and mitochondrial reactive oxygen species (mtROS). Further studies found that Cd exposure causes mitochondrial calcium ions (Ca2+) overload, provoking mitochondrial damage and apoptosis by upregulating IP3R, GRP75, VDAC1, MCU, CALM1, MFF, caspase 3, and caspase 9 gene and/or protein expressions and mitochondrial Ca2+ levels, while downregulating NCX1, NCLX and MFN2 gene and/or protein expressions and mitochondrial membrane potential (MMP). The Ca2+ chelator BAPTA-AM or the MCU inhibitor MCU-i4 significantly rescued Cd-induced mitochondrial dysfunction, thereby attenuating apoptosis. Additionally, a luciferase reported assay and western blot analysis confirmed that miR-129-1-3p directly target MCU. MiR-129-1-3p overexpression almost completely inhibited protein expression of MCU, increased the gene and protein expressions of NCLX and MFN2 downregulated by Cd, and attenuated mitochondrial Ca2+ overload, MMP depression and mitochondria damage induced by Cd. Moreover, the overexpression of miR-129-1-3p led to a reduction in mtROS and cell apoptosis levels, and a suppression of the gene and protein expressions of caspase 3 and caspase 9. As above, these results provided the evidence that IP3R-MCU signaling pathway activated by Cd plays a significant role in inducing mitochondrial Ca2+ overload, mitochondrial damage, and apoptosis. MiR-129-1-3p exerts a protective effect against Cd-induced granulosa cell apoptosis through the direct inhibition of MCU expression in the ovary of laying hens.

Gamma-aminobutyric acid (GABA) suppresses hemocyte phagocytosis by binding to GABA receptors and modulating corresponding downstream pathways in blood clam, Tegillarca granosa

Although accumulating data demonstrated that gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter, plays an important regulatory role in immunity of vertebrates, its immunomodulatory function and mechanisms of action remain poorly understood in invertebrates such as bivalve mollusks. In this study, the effect of GABA on phagocytic activity of hemocytes was evaluated in a commercial bivalve species, Tegillarca granosa. Furthermore, the potential regulatory mechanism underpinning was investigated by assessing potential downstream targets. Data obtained demonstrated that in vitro GABA incubation significantly constrained the phagocytic activity of hemocytes. In addition, the GABA-induced suppression of phagocytosis was markedly relieved by blocking of GABA_A and GABA_B receptors using corresponding antagonists. Hemocytes incubated with lipopolysaccharides (LPS) and GABA had significant higher K⁺-Cl^- cotransporter 2 (KCC2) content compared to the control. In addition, GABA treatment led to an elevation in intracellular Cl^-, which was shown to be leveled down to normal by blocking the ionotropic GABA_A receptor. Treatment with GABA_A receptor antagonist also rescued the suppression of GABA_A receptor-associated protein (GABARAP), KCC, TNF receptor associated factor 6 (TRAF6), inhibitor of nuclear factor kappa-B kinase subunit alpha (IKKα), and nuclear factor kappa B subunit 1 (NFκB) caused by GABA incubation. Furthermore, incubation of hemocytes with GABA resulted in a decrease in cAMP content, an increase in intracellular Ca²⁺, and downregulation of cAMP-dependent protein kinase (PKA), calmodulin kinase II (CAMK2), calmodulin (CaM), calcineurin (CaN), TRAF6, IKKα, and NFκB. All these above-mentioned changes were found to be evidently relieved by blocking the metabotropic G-protein-coupled GABA_B receptor. Our results suggest GABA may play an inhibitory role on phagocytosis through binding to both GABA_A and GABA_B receptors, and subsequently regulating corresponding downstream pathways in bivalve invertebrates.

Ca2+ participates in the regulation of microalgae triacylglycerol metabolism under heat stress

Microalgae are the largest CO₂ fixer and O₂ producer on the earth and occupy an increasingly important position in human life and production. Various environmental factors have a significant impact on the growth and metabolism of microalgae. As global warming intensifies, heat stress has become a crucial factor affecting the microalgae industry. However, till now, it has not been clear how microalgae sensed the temperature stress, transmitted stress signals and adjusted in intracellular metabolic pathways. In this study, the growth of microalgae Auxenochlorella protothecoides UTEX2341 was inhibited at 32 °C, but the single cell dry weight increased. The cell component analyses showed that both the carbohydrate and total protein content decreased significantly, while the lipid content increased by 158%. Meanwhile, the intracellular Ca²⁺ concentration increased continuously, with a maximum increase of 1.65 times. According to the transcriptome analyses, the up-regulation of Ca²⁺ influx channel protein mid1-complementing activity 1 (MCA1) gene and the down-regulation of efflux channel protein cation exchanger 1(CAX) and autoinhibited Ca²⁺-ATPase 1 (ACA1) genes in cytoplasmic membrane jointly facilitated the increase of Ca²⁺ in the cytoplasm. Coexpression network analysis indicated that the fluctuation of Ca²⁺ in the cytoplasm could activate the expression of transcription factors MYB3 and AP2-4 through calmodulin (CAM) and calcium-dependent protein kinase (CDPK), and then regulate glycerol-3-phosphate acyltransferases (GPAT) at the beginning of TAG synthesis and diacylglycerol acyltransferase (DGAT)/phospholipid: diacylglycerol acyltransferase (PDAT) in the last step of TAG synthesis. Furthermore, the addition of Ca²⁺ specific chelator BAPTA-AM inhibited the expression of GPAT, which was consistent with the decrease in microalgae lipid content. The results proved that Ca²⁺ participated in the regulation of microalgae TAG synthesis under heat stress, which provided a new view for the understanding of the microalgae lipid accumulation mechanism.

The leading role of adsorbed lead in PM2.5-induced hippocampal neuronal apoptosis and synaptic damage

Neurodegenerative diseases may be caused by air pollution, such as PM_2.5. However, particles still need to be elucidated the mechanism of synergistic neurotoxicity induced by pollutant-loading PM_2.5. In this study, we used a reductionist approach to study leading role of lead (Pb) in PM_2.5-induced hippocampal neuronal apoptosis and synaptic damage both in vivo and in vitro. Pb in PM_2.5 caused neurotoxicity: 1) by increasing ROS levels and thus causing apoptosis in neuronal cells and 2) by decreasing the expression of PSD95 via interfering with the calcium signaling pathway through cAMP/CREB/pCREB/BDNF/PSD95 pathway and reducing the synapse length by 50%. This study clarifies a key factor in PM_2.5-induced neurotoxicity and provides the experimental basis for reducing PM_2.5-induced neurotoxicity.

Modulatory function of calmodulin on phagocytosis and potential regulation mechanisms in the blood clam Tegillarca granosa

Unlike vertebrate species, invertebrates lack antigen-antibody mediated immune response and mainly rely on haemocyte phagocytosis to fight against pathogen infection. Recently, studies conducted in model vertebrates demonstrated that the multifunctional protein calmodulin (CaM) plays an important role in regulating immune responses. However, the intrinsic relation between CaM and phagocytosis process remains poorly understood in invertebrate species such as bivalve mollusks. Therefore, in the present study, the immunomodulatory function of CaM on haemocyte phagocytosis was verified in the blood clam, Tegillarca granosa, using the CaM-specific inhibitor N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7). Results obtained show that CaM inhibition significantly suppressed the phagocytic activity of haemocytes. In addition, CaM inhibition constrained intracellular Ca²⁺ elevation, hampered actin cytoskeleton assembly, suppressed calcineurin (CaN) activity, and disrupted NF-κB activation in haemocytes upon LPS induction. Furthermore, expression of seven selected genes from the actin cytoskeleton regulation- and immune-related pathways were significantly downregulated whereas those of CaM and CaN from the Ca²⁺-signaling pathway were significantly upregulated by in vitro incubation of haemocytes with W-7. For the first time, the present study demonstrated that CaM play an important role in phagocytosis modulation in bivalve species. In addition, the intracellular Ca²⁺ and downstream Ca²⁺-signaling-, actin cytoskeleton regulation-, and immune-related pathways offer candidate routes through which CaM modulates phagocytosis.

Acetylcholine suppresses phagocytosis via binding to muscarinic- and nicotinic-acetylcholine receptors and subsequently interfering Ca2+- and NFκB-signaling pathways in blood clam

Though immunomodulation via cholinergic neurotransmitter acetylcholine (ACh), an important part of neuroendocrine-immune (NEI) regulatory network, has been well established in vertebrate species, the mechanisms remain poorly understood in invertebrates. In the present study, the immunomodulatory effect of ACh on haemocyte phagocytosis was investigated in an invertebrate bivalve species, Tegillarca granosa. Data obtained showed that in vitro ACh incubation suppressed phagocytic activity of haemocytes along with a significant elevation in intracellular Ca²⁺. In addition, the expressions of genes from Ca²⁺ signaling pathway were significantly induced whereas those from NF-κB signaling pathway were significantly down-regulated by ACh incubation. Furthermore, these adverse impacts of ACh were significantly relieved by the blocking of muscarinic acetylcholine receptors (mAChRs) or nicotinic acetylcholine receptors (nAChRs) using corresponding antagonists. Our study suggests that ACh suppresses phagocytosis via binding to both mAChRs and nAChRs, which disrupts intracellular Ca²⁺ homeostasis and subsequently interferes with downstream Ca²⁺ and NF-κB signaling pathways.

The neutrophil serine protease PR3 induces shape change of platelets via the Rho/Rho kinase and Ca(2+) signaling pathways

INTRODUCTION

Proteinase 3 (PR3) is released from neutrophil azurophilic granules and exerts complex effects on the inflammatory process. PR3 catalyzes the degradation of a number of macromolecules, but the consequences on blood cells are less well defined. In the present study, the effect of PR3 on human platelets was thoroughly investigated.

METHODS

The experiments were performed on washed platelets freshly isolated from blood donated by healthy human volunteers. Platelets shape change and aggregation was measured on a Chrono-Log aggregometer. The phosphorylated form of MYPT1 was visualized by immunostaining. Platelet activation was further evaluated by flow cytometry.

RESULTS

PR3 induced platelet shape change but not aggregation. Flow cytometry analysis showed that PR3 induced no P-selectin expression or binding of fibrinogen to the platelets, and it did not change the activation in response to PAR1- or PAR4-activating peptides or to thrombin. Furthermore, Fura-2 measurement and immuno-blotting analysis, respectively, revealed that PR3 stimulated small intracellular Ca(2+) mobilization and Thr696-specific phosphorylation of the myosin phosphatase target subunit 1 (MYPT1). Separate treatment of platelets with the Rho/Rho kinase inhibitor Y-27632 and the intracellular Ca(2+) chelator BAPTA/AM reduced the shape change induced by PR3 whereas concurrent treatment completely inhibited it.

CONCLUSION

The data shows that the neutrophil protease PR3 is a direct modulator of human platelets and causes shape change through activation of the Rho/Rho kinase and Ca(2+) signaling pathways. This finding highlights an additional mechanism in the complex interplay between neutrophils and platelets.