Putative roles for phospholipase Cη enzymes in neuronal Ca2+ signal modulation

Associations of selenium exposure with blood lipids: Exploring mediating DNA methylation sites in general Chinese urban non-smokers

Selenium (Se) is widely distributed in the total environment and people are commonly exposed to Se, while the potential effects and mechanisms of Se exposure on blood lipids have not been well established. This study aimed to assess the associations of urinary Se (SeU) with blood lipids and explore the potential mediating DNA methylation sites. We included 2844 non-smoke participants from the second follow-up (2017-2018) of the Wuhan-Zhuhai cohort (WHZH) in this study. SeU and blood lipids [i.e., total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL), and high-density lipoprotein cholesterol (HDL)] for all participants were determined. The associations of SeU with blood lipids were analyzed by generalized linear models. Then, we conducted the blood lipids related epigenome-wide association studies (EWAS) among 221 never smokers, and the mediation analysis was conducted to explore the potential mediating cytosine-phosphoguanine (CpG) sites in the above associations. In this study, the SeU concentration of the participants in this study was 1.40 (0.94, 2.08) μg/mmol Cr. The SeU was positively associated with TC and LDL, and not associated with TG and HDL. We found 131, 3, and 1 new CpG sites related to TC, HDL, and LDL, respectively. Mediation analyses found that the methylation of cg06964030 (within MIR1306) and cg15824094 (within PLCH2) significantly mediated the positive association between SeU and TC. In conclusion, high levels of Se exposure were associated with increased TC and LDL among non-smokers, and the methylation of MIR1306 and PLCH2 partly mediated Se-associated TC increase. These findings provide new insights into the effects and mechanisms of Se exposure on lipids metabolism and highlight the importance of controlling Se exposure and intake for preventing high blood lipids.

Phospholipases in neuronal function: A role in learning and memory?

Despite the human brain being made of nearly 60% fat, the vast majority of studies on the mechanisms of neuronal communication which underpin cognition, memory and learning, primarily focus on proteins and/or (epi)genetic mechanisms. Phospholipids are the main component of all cellular membranes and function as substrates for numerous phospholipid-modifying enzymes, including phospholipases, which release free fatty acids (FFAs) and other lipid metabolites that can alter the intrinsic properties of the membranes, recruit and activate critical proteins, and act as lipid signalling molecules. Here, we will review brain specific phospholipases, their roles in membrane remodelling, neuronal function, learning and memory, as well as their disease implications. In particular, we will highlight key roles of unsaturated FFAs, particularly arachidonic acid, in neurotransmitter release, neuroinflammation and memory. In light of recent findings, we will also discuss the emerging role of phospholipase A₁ and the creation of saturated FFAs in the brain.

Modeling, dynamics and phosphoinositide binding of the pleckstrin homology domain of two novel PLCs: η1 and η2

PH domains mediate interactions involved in cell signaling, intracellular membrane transport regulation and cytoskeleton organization. Some PH domains bind phosphoinositides with different affinity and specificity. The two novel PLCη (1 and 2) possess an N-terminal PH domain (PHη1 and PHη2 respectively) that has been implicated in membrane association and induction of PLC activity. Understanding of the structure and dynamics is crucial for future modulation of lipid-protein interactions in PHη1, PHη2 and other PH domains. Therefore, the three-dimensional structure of PHη1 and PHη2 was modeled using ITASSER and phosphoinositides (IP3 and IP4) were docked in the inferred binding site using HADDOCK server. Molecular Dynamics simulations of unliganded and phosphoinositide bound PHη1 and PHη2 were performed using AMBER14 to study the mechanism of interaction, and conformational dynamics in response to phosphoinositide binding. The binding affinity was predicted using Kdeep server. The models of PHη1 and PHη2 had a conserved structural core consisting of seven β-strands and a C-terminal α-helix as seen in other PH domains. Sequence/structure analysis showed that phosphoinositide ligands bind PHη1 and PHη2 at the canonical binding site. Phosphoinositide binding induced movement of positively charged side chains towards the ligand, changes in the secondary structure especially at the β5-β6 loop and allosteric changes at the interface of β1-β2 and β5-β6 loops. Dynamics studies showed that the size of the binding site and differential affinity for IP3/IP4 binding is coordinated by the number, length, flexibility, secondary structure and allosteric interactions of the loops surrounding the phosphoinositide binding site.

Phospholipase C-η2 interacts with nuclear and cytoplasmic LIMK-1 during retinoic acid-stimulated neurite growth

Neurite growth is central to the formation and differentiation of functional neurons, and recently, an essential role for phospholipase C-η2 (PLCη2) in neuritogenesis was revealed. Here we investigate the function of PLCη2 in neuritogenesis using Neuro2A cells, which upon stimulation with retinoic acid differentiate and form neurites. We first investigated the role of the PLCη2 calcium-binding EF-hand domain, a domain that is known to be required for PLCη2 activation. To do this, we quantified neurite outgrowth in Neuro2A cells, stably overexpressing wild-type PLCη2 and D256A (EF-hand) and H460Q (active site) PLCη2 mutants. Retinoic acid-induced neuritogenesis was highly dependent on PLCη2 activity, with the H460Q mutant exhibiting a strong dominant-negative effect. Expression of the D256A mutant had little effect on neurite growth relative to the control, suggesting that calcium-directed activation of PLCη2 is not essential to this process. We next investigated which cellular compartments contain endogenous PLCη2 by comparing immunoelectron microscopy signals over control and knockdown cell lines. When signals were analyzed to reveal specific labeling for PLCη2, it was found to be localized predominantly over the nucleus and cytosol. Furthermore in these compartments (and also in growing neurites), a proximity ligand assay revealed that PLCη2 specifically interacts with LIMK-1 in Neuro2A cells. Taken together, these data emphasize the importance of the PLCη2 EF-hand domain and articulation of PLCη2 with LIMK-1 in regulating neuritogenesis.

The Novel Functions of the PLC/PKC/PKD Signaling Axis in G Protein-Coupled Receptor-Mediated Chemotaxis of Neutrophils

Chemotaxis, a directional cell migration guided by extracellular chemoattractant gradients, plays an essential role in the recruitment of neutrophils to sites of inflammation. Chemotaxis is mediated by the G protein-coupled receptor (GPCR) signaling pathway. Extracellular stimuli trigger activation of the PLC/PKC/PKD signaling axis, which controls several signaling pathways. Here, we concentrate on the novel functions of PLC/PKC/PKD signaling in GPCR-mediated chemotaxis of neutrophils.

The observation of plcA mutation and localization in Aspergillus nidulans

To know the function of the plcA gene, which encodes a putative phosphoinositide-specific phospholipase C, in a model filamentous fungus Aspergillus nidulans, it was disrupted thorough homologous recombination and examined. The germination rate of ΔplcA was reduced by approximately 65% and germination of ΔplcA at a lower temperature (25°C) was much slower than germination under normal conditions (37°C), suggesting the plcA is responsible for cold-sensitivity. The hyphal growth of ΔplcA was slightly reduced at 37°C and conspicuously reduced at 25°C. While germinating ΔplcA formed giant swollen spores, and generated short and thick hyphae. The results of the nuclear examination of ΔplcA showed nuclear division with missegregation, and the rate of nuclear division was lower than that of wild type at both 25°C and 37°C. The results of this study showed that plcA is localized to the nucleus through intracellular calcium signaling in A. nidulans. The abnormal nuclear division, resulting from plcA gene deletion, affects conidiation in asexual development. Taken together, these results suggested that plcA is required for normal vegetative growth, morphogenesis, conidiation, and nuclear division in A. nidulans.

The expanding roles of Gβγ subunits in G protein-coupled receptor signaling and drug action

Gβγ subunits from heterotrimeric G proteins perform a vast array of functions in cells with respect to signaling, often independently as well as in concert with Gα subunits. However, the eponymous term "Gβγ" does not do justice to the fact that 5 Gβ and 12 Gγ isoforms have evolved in mammals to serve much broader roles beyond their canonical roles in cellular signaling. We explore the phylogenetic diversity of Gβγ subunits with a view toward understanding these expanded roles in different cellular organelles. We suggest that the particular content of distinct Gβγ subunits regulates cellular activity, and that the granularity of individual Gβ and Gγ action is only beginning to be understood. Given the therapeutic potential of targeting Gβγ action, this larger view serves as a prelude to more specific development of drugs aimed at individual isoforms.

Phospholipase C-η2 is required for retinoic acid-stimulated neurite growth

Phospholipase C-η2 is a recently identified phospholipase C (PLC) implicated in the regulation of neuronal differentiation/maturation. PLCη2 activity is triggered by intracellular calcium mobilization and likely serves to amplify Ca²⁺ signals by stimulating further Ca²⁺ release from Ins(1,4,5)P₃-sensitive stores. The role of PLCη2 in neuritogenesis was assessed during retinoic acid (RA)-induced Neuro2A cell differentiation. PLCη2 expression increased two-fold during a 4-day differentiation period. Stable expression of PLCη2-targetted shRNA led to a decrease in the number of differentiated cells and total length of neurites following RA-treatment. Furthermore, RA response element activation was perturbed by PLCη2 knockdown. Using a bacterial two-hybrid screen, we identified LIM domain kinase 1 (LIMK1) as a putative interaction partner of PLCη2. Immunostaining of PLCη2 revealed significant co-localization with LIMK1 in the nucleus and growing neurites in Neuro2A cells. RA-induced phosphorylation of LIMK1 and cAMP-responsive element-binding protein was reduced in PLCη2 knock-down cells. The phosphoinositide-binding properties of the PLCη2 PH domain, assessed using a FRET-based assay, revealed this domain to possess a high affinity toward PtdIns(3,4,5)P₃. Immunostaining of PLCη2 together with PtdIns(3,4,5)P₃ in the Neuro2A cells revealed a high degree of co-localization, indicating that PtdIns(3,4,5)P₃ levels in cellular compartments are likely to be important for the spatial control of PLCη2 signaling.