Transmembrane signaling through phospholipase C-beta in the developing human prefrontal cortex

PLCβ1 by-passes early growth response -1 to induce the differentiation of neuronal cells

The Gαq/phospholipase C-β (PLCβ) signaling system mediates calcium responses to a variety of hormones and neurotransmitters. Recent studies suggest that PLCβ1 expression plays a role in the differentiation of two types of cultured neuronal cells (PC12 and SK-N-SH) through a mechanism independent of Gαq. Here, we show that, similar to that observed in PC12 and SK-N-SH cells, PLCβ1 expression increases when human NT2 cells are induced to differentiate either through cytosine-β-D-arabinofuranoside or retinoic acid. Preventing this increase, abolishes differentiation, and down-regulating PLCβ1 in rat primary astrocytes causes cells to adapt an undifferentiated morphology. Surprisingly, transfecting PLCβ1 into undifferentiated PC12 or NT2 cells induces differentiation without the need for differentiating agents. Studies to uncover the underlying mechanism focused on the transcription factor early growth response 1 (Egr-1) which mediates PLCβ1 expression early in differentiation. Over-expressing PLCβ1 in HEK293 cells enhances Egr-1 expression and induces morphological changes. We show that increased levels of cytosolic PLCβ1 in undifferentiated PC12 cells disrupts the association between Egr-1 and its cytosolic binding partner (Tar RNA binding protein), promoting relocalization of Egr-1 to the nucleus, which promotes transcription of proteins needed for differentiation. These studies show a novel mechanism through which differentiation can be modulated.

A muscarinic, GIRK channel-mediated inhibition of inspiratory-related XII nerve motor output emerges in early postnatal development in mice

In neonatal rhythmic medullary slices, muscarinic acetylcholine receptor (mAChR) activation of hypoglossal (XII) motoneurons that innervate the tongue has a net excitatory effect on XII inspiratory motor output. Conversely, during rapid eye movement sleep in adult rodents, XII motoneurons experience a loss of excitability partly due to activation of mAChRs. This may be mediated by activation of G-protein-coupled inwardly rectifying potassium (GIRK) channels. Therefore, this study was designed to evaluate whether muscarinic modulation of XII inspiratory motor output in mouse rhythmic medullary slices includes GIRK channel-mediated inhibition and, if so, when this inhibitory mechanism emerges. Local pressure injection of the mAChR agonist muscarine potentiated inspiratory bursting by 150 ± 28% in postnatal day (P)0-P5 rhythmic medullary slice preparations. In the absence of muscarine, pharmacological GIRK channel block by Tertiapin-Q did not affect inspiratory burst parameters, whereas activation with ML297 decreased inspiratory burst area. Blocking GIRK channels by local preapplication of Tertiapin-Q revealed a developmental change in muscarinic modulation of inspiratory bursting. In P0-P2 rhythmic medullary slices, Tertiapin-Q preapplication had no significant effect on muscarinic potentiation of inspiratory bursting (a negligible 6% decrease). However, preapplication of Tertiapin-Q to P3-P5 rhythmic medullary slices caused a 19% increase in muscarinic potentiation of XII inspiratory burst amplitude. Immunofluorescence experiments revealed expression of GIRK 1 and 2 subunits and M1, M2, M3, and M5 mAChRs from P0 to P5. Overall, these data support that mechanisms underlying muscarinic modulation of inspiratory burst activity change postnatally and that potent GIRK-mediated inhibition described in adults emerges early in postnatal life.NEW & NOTEWORTHY Muscarinic modulation of inspiratory bursting at hypoglossal motoneurons has a net excitatory effect in neonatal rhythmic medullary slice preparations and a net inhibitory effect in adult animals. We demonstrate that muscarinic modulation of inspiratory bursting undergoes maturational changes from postnatal days 0 to 5 that include emergence of an inhibitory component mediated by G-protein-coupled inwardly rectifying potassium channels after postnatal day 3 in neonatal mouse rhythmic medullary slice preparations.

Multiple functions of phospholipase Cβ1 at a glance

Phospholipase Cβ (PLCβ) is the main effector of the Gq family of heterotrimeric G proteins that transduces signals from hormones and neurotransmitters into Ca2+ signals. While PLCβ is critical for Ca2+ responses, recent studies have suggested that PLCβ has additional roles independent of its lipase activity. These novel functions are carried out by a cytosolic population of PLCβ that binds and inhibits the component 3 promoter of RNA-induced silencing complex (C3PO) to impact cytosolic RNA populations. Additionally, cytosolic PLCβ binds to stress granule proteins, keeping them dispersed and thus inhibiting stress granule formation. Upon activation of the Gα subunit of Gq (Gαq), cytosolic PLCβ relocalizes to the membrane, releasing C3PO and stress granule proteins, which in turn promotes activation of C3PO and RNA processing, as well as sequestration of specific transcripts into newly formed stress granules. As highlighted in this Cell Science at a Glance and the accompanying poster, the link between Gαq signaling, increased intracellular Ca2+ and changes in RNA processing impacts neuronal cell differentiation and may also affect neuronal development and dysfunction.

Design and validation of recombinant protein standards for quantitative Western blot analysis of cannabinoid CB1 receptor density in cell membranes: an alternative to radioligand binding methods

Background

Replacement of radioligand binding assays with antibody-antigen interaction-based approaches for quantitative analysis of G protein-coupled receptor (GPCR) levels requires the use of purified protein standards containing the antigen. GPCRs in general and cannabinoid CB₁ receptor in particular show a progressive tendency to aggregate and precipitate in aqueous solution outside of their biological context due to the low solubility that the hydrophobic nature imprinted by their seven transmembrane domains. This renders full-length recombinant GPCRs useless for analytical purposes, a problem that can be overcome by engineering soluble recombinant fragments of the receptor containing the antigen.

Results

Here we generated highly soluble and stable recombinant protein constructs GST-CB1_414–472 and GST-CB1_414-442 containing much of the human CB₁ receptor C-terminal tail for use as standard and negative control, respectively, in quantitative Western blot analysis of CB₁ receptor expression on crude synaptosomes of the adult rat brain cortex. To this end we used three different antibodies, all raised against a peptide comprising the C-terminal residues 443–473 of the mouse CB₁ receptor that corresponds to residues 442–472 in the human homolog. Estimated values of CB₁ receptor density obtained by quantitative Western blot were of the same order of magnitude but slightly higher than values obtained by the radioligand saturation binding assay.

Conclusions

Collectively, here we provide a suitable Western blot-based design as a simple, cost-effective and radioactivity-free alternative for the quantitative analysis of CB₁ receptor expression, and potentially of any GPCR, in a variety of biological samples. The discrepancies between the results obtained by quantitative Western blot and radioligand saturation binding techniques are discussed in the context of their particular theoretical bases and methodological constraints.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01914-1.

Fit-for-purpose based testing and validation of antibodies to amino- and carboxy-terminal domains of cannabinoid receptor 1

Specific and selective anti-CB₁ antibodies are among the most powerful research tools to unravel the complex biological processes mediated by the CB₁ receptor in both physiological and pathological conditions. However, low performance of antibodies remains a major source of inconsistency between results from different laboratories. Using a variety of techniques, including some of the most commonly accepted ones for antibody specificity testing, we identified three of five commercial antibodies against different regions of CB₁ receptor as the best choice for specific end-use purposes. Specifically, an antibody against a long fragment of the extracellular amino tail of CB₁ receptor (but not one against a short sequence of the extreme amino-terminus) detected strong surface staining when applied to live cells, whereas two different antibodies against an identical fragment of the extreme carboxy-terminus of CB₁ receptor (but not one against an upstream peptide) showed acceptable performance on all platforms, although they behaved differently in immunohistochemical assays depending on the tissue fixation procedure used and showed different specificity in Western blot assays, which made each of them particularly suitable for one of those techniques. Our results provide a framework to interpret past and future results derived from the use of different anti-CB₁ antibodies in the context of current knowledge about the CB₁ receptor at the molecular level, and highlight the need for an adequate validation for specific purposes, not only before antibodies are placed on the market, but also before the decision to discontinue them is made.

Serum metallome in pregnant women and the relationship with congenital malformations of the central nervous system: a case-control study

BACKGROUND

Congenital malformations of the central nervous system (CNS) consist of a wide range of birth defects of multifactorial origin.

METHODS

Concentrations of 44 metals were determined by Inductively Coupled Plasma Mass Spectrometry in serum of 111 mothers in the second trimester of pregnancy who carried a malformed fetus and compared them with serum concentrations of the same metals in 90 mothers with a normally developed fetus at the same week of pregnancy. Data are reported as means ± standard deviations.

RESULTS

We found a direct relationship between congenital defects of the CNS and maternal serum concentration of aluminum: it was statistically higher in women carrying a fetus with this class of malformation, compared both to mothers carrying a fetus with another class of malformation (6.45 ± 15.15 μg/L Vs 1.44 ± 4.21 μg/L, p < 0.0006) and to Controls (i.e. mothers carrying a normally-developed fetus) (6.45 ± 15.15 μg/L Vs 0.11 ± 0.51 μg/L, p < 0.0006). Moreover, Aluminum abundances were below the limit of detection in the majority of control samples.

CONCLUSION

CAluminum may play a role in the onset of central nervous system malformations, although the exact Aluminum species and related specific type of malformation needs further elucidation.

Phospholipase C Beta 1: a Candidate Signature Gene for Proneural Subtype High-Grade Glioma

Phospholipase C beta 1 (PLCβ1) expresses in gliomas and cultured glial cells, but its expression is barely detectable in normal glial cells. We analyzed data from Gene Expression Omnibus (GEO-GDSxxx), The Cancer Genome Atlas (TCGA), and the Repository for Molecular Brain Neoplasia Data (REMBRANDT) to explore the potential role of PLCβ1 as a biomarker in high-grade glioma (HGG). PLCβ1 expression is significantly higher in grade III gliomas than that in grade IV gliomas from GDS1815 (n = 24 vs. 76), GDS1962 (n = 19 vs. 81), and GDS1975 (n = 26 vs. 59). In GDS1815, PLCβ1 expression correlates with several known proneural (PN) signature genes; its expression from PN subtype (n = 15) is significantly higher than that from mesenchymal (Mes) subtype (n = 33) HGG. In GDS1962, PLCβ1 expression is the highest in nontumor brain tissue (n = 23) and is significantly higher than its expression in grade II gliomas [astrocytomas (n = 7) and oligodendrogliomas (n = 37)]. A Kaplan-Meier survival curve from a REMBRANDT cohort demonstrates that glioma patients with intermediate PLCβ1 expression (n = 103) survived significantly longer than PLCβ1 downregulated (2X) groups (n = 226). From TCGA data, PLCβ1 RNA-Seq signal inversely correlates with the pathological grades, and PLCβ1 expression in PN (n = 8) is of significantly higher levels than that in Mes (n = 8) subtypes of glioblastoma. The top 50 % of PLCβ1 expression subgroup (n = 294) of gliomas (grades II to IV merged) survived significantly longer than the low 50 percentile of the PLCβ1 expression subgroup (n = 293). p values are less than 0.05 for all these analyses. We conclude that PLCβ1 is a candidate signature gene for PN subtype HGG, and its expression inversely correlates with glioma pathological grade and is a potential prognostic factor.

Nuclear phospholipase C-β1 and diacylglycerol LIPASE-α in brain cortical neurons

Phosphoinositide (PtdIns) signaling involves the generation of lipid second messengers in response to stimuli in a receptor-mediated manner at the plasma membrane. In neuronal cells of adult brain, the standard model proposes that activation of metabotropic receptors coupled to Phospholipase C-β1 (PLC-β1) is linked to endocannabinoid signaling through the production of diacylglycerol (DAG), which could be systematically metabolized by 1,2-diacylglycerol Lipases (DAGL) to produce an increase of 2-arachidonoyl-glycerol (2-AG), the most abundant endocannabinoid in the brain. However, the existence of a nuclear PtdIns metabolism independent from that occurring elsewhere in the cell is now widely accepted, suggesting that the nucleus constitutes both a functional and a distinct compartment for PtdIns metabolism. In this review, we shall highlight the main achievements in the field of neuronal nuclear inositol lipid metabolism with particular attention to progress made linked to the 2-AG biosynthesis. Our aim has been to identify potential sites of 2-AG synthesis other than the neuronal cytoplasmic compartment by determining the subcellular localization of PLC-β1 and DAGL-α, which is much more abundant than DAGL-β in brain. Our data show that PLC-β1 and DAGL-α are detected in discrete brain regions, with a marked predominance of pyramidal morphologies of positive cortical cells, consistent with their role in the biosynthesis and release of 2-AG by pyramidal neurons to control their synaptic inputs. However, as novelty, we showed here an integrated description of the localization of PLC-β1 and DAGL-α in the neuronal nuclear compartment. We discuss our comparative analysis of the expression patterns of PLC-β1 and DAGL-α, providing some insight into the potential autocrine role of 2-AG production in the neuronal nuclear compartment that probably subserve additional roles to the recognized activation of the CB1 cannabinoid receptor.

Phosphoinositide pathway and the signal transduction network in neural development

The development of the nervous system is under the strict control of a number of signal transduction pathways, often interconnected. Among them, the phosphoinositide (PI) pathway and the related phospholipase C (PI-PLC) family of enzymes have been attracting much attention. Besides their well-known role in the regulation of intracellular calcium levels, PI-PLC enzymes interact with a number of molecules belonging to further signal transduction pathways, contributing to a specific and complex network in the developing nervous system. In this review, the connections of PI signalling with further transduction pathways acting during neural development are discussed, with special regard to the role of the PI-PLC family of enzymes.

Cellular neurochemical characterization and subcellular localization of phospholipase C β1 in rat brain

The present study describes a complete and detailed neuroanatomical distribution map of the phospholipase C beta1 (PLCβ1) isoform along the adult rat neuraxis, and defines the phenotype of cells expressing PLCβ1, along with its subcellular localization in cortical neurons as assessed by double-immunofluorescence staining and confocal laser scanning. Immunohistochemical labeling revealed a considerable morphological heterogeneity among PLCβ1-positive cells in the cortex, even though there was a marked predominance of pyramidal morphologies. As an exception to the general non-matching distribution of GFAP and PLCβ1, a high degree of co-expression was observed in radial glia-like processes of the spinal cord white matter. In the somatosensory cortex, the proportion of GABAergic neurons co-stained with PLCβ1 was similar (around 2/3) in layers I, II-III, IV and VI, and considerably lower in layer V (around 2/5). Double immunofluorescence against PLCβ1 and nuclear speckle markers SC-35 and NeuN/Fox3 in isolated nuclei from the rat cortex showed a high overlap of both markers with PLCβ1 within the nuclear matrix. In contrast, there was no apparent co-localization with markers of the nuclear envelope and lamina. Finally, to assess whether the subcellular expression pattern of PLCβ1 involved specifically one of the two splice variants of PLCβ1, we carried out Western blot experiments in cortical subcellular fractions. Notably, PLCβ1a/1b ratios were statistically higher in the cytoplasm than in the nuclear and plasma membrane fractions. These results provide a deeper knowledge of the cellular distribution of the PLCβ1 isoform in different cell subtypes of the rat brain, and of its presence in the neuronal nuclear compartment.

Alpha-cobratoxin inhibits T-type calcium currents through muscarinic M4 receptor and Gο-protein βγ subunits-dependent protein kinase A pathway in dorsal root ganglion neurons

The long-chain neurotoxic protein, alpha-cobratoxin (α-CTx), has been shown to have analgesic effects. However, the underlying mechanisms still remain unclear. In this study, we examined the effects of α-CTx on T-type calcium channel currents (T-currents) and elucidated the relevant mechanisms in mouse dorsal root ganglion (DRG) neurons. Our results showed that α-CTx reversibly inhibited T-currents in a dose-dependent manner. This inhibitory effect was blocked by the selective muscarinic M4 receptor antagonist tropicamide, while methyllycaconitine, a specific antagonist for the α7 subtype of nicotinic receptor had no effect. siRNA targeting the M4 receptor in small DRG neurons abolished α-CTx-induced T-current inhibition. Intracellular application of GDP-β-S or a selective antibody against the G(o)α-protein, as well as pretreatment of the cells with pertussis toxin, abolished the inhibitory effects of α-CTx. The M4 receptor-mediated response was blocked by dialyzing cells with QEHA peptide or anti-G(β) antibody. Pretreatment of the cells with protein kinase A (PKA) inhibitor H89 or intracellular application of PKI 6-22 abolished α-CTx-induced T-current inhibition in small DRG neurons, whereas inhibition of phosphatidylinositol 3-kinase or PKC elicited no such effects. In addition, α-CTx significantly increased PKA activity in DRG neurons, whereas pretreatment of the cells with tropicamide abolished this effect. In summary, our results suggest that activation of muscarinic M4 receptor by α-CTx inhibits T-currents via the G(βγ) of G(o)-protein and PKA-dependent pathway. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Activation of M3 muscarinic receptors inhibits T-type Ca(2+) channel currents via pertussis toxin-sensitive novel protein kinase C pathway in small dorsal root ganglion neurons

Cobrotoxin (CbT), a short-chain postsynaptic α-neurotoxin, has been reported to play a role in analgesia. However, to date, the detailed mechanisms still remain unknown. In the present study, we identify a novel functional role of CbT in modulating T-type Ca(2+) channel currents (T-currents) in small dorsal root ganglia (DRG) neurons as well as pain behaviors in mice. We found that CbT inhibited T-currents in a dose-dependent manner. CbT at 1μM reversibly inhibited T-currents by ~26.3%. This inhibitory effect was abolished by the non-selective muscarinic acetylcholine receptor (mAChR) antagonist atropine, or the selective M3 mAChR antagonist 4-DAMP, while naloxone, an opioid receptor antagonist had no effect. Intracellular infusion of GDP-β-S or pretreatment of the cells with pertussis toxin (PTX) completely blocked the inhibitory effects of CbT. Using depolarizing prepulse, we found the absence of direct binding between G-protein βγ subunits and T-type Ca(2+) channels in CbT-induced T-current inhibition. CbT responses were abolished by the phospholipase C inhibitor U73122 (but not the inactive analog U73343). The classical and novel protein kinase C (nPKC) antagonist chelerythrine chlorid or GF109203X abolished CbT responses, whereas the classical PKC antagonist Ro31-8820 or inhibition of PKA elicited no such effects. Intrathecal administration of CbT (5μg/kg) produced antinociceptive effects in mechanical, thermal, and inflammatory pain models. Moreover, CbT-induced antinociception could be abrogated by 4-DAMP. Taken together, these results suggest that CbT acting through M3 mAChR inhibits T-currents via a PTX-sensitive nPKC pathway in small DRG neurons, which could contribute to its analgesic effects in mice.

Molecular characterization of a phospholipase C beta potentially involved in moth olfactory transduction

To clarify the role of phospholipase C (PLC) in insect olfactory transduction, we have undertaken its molecular identification in the moth Spodoptera littoralis. From the analysis of a male antennal expressed sequence tag library, we succeeded in cloning a full-length cDNA encoding a PLC that belongs to the cluster of PLC-beta subtypes. In adult males, the PLC-beta transcript was located predominantly in brain and antennae where its presence was detected in the olfactory sensilla trichodea. Moreover, PLC-beta was expressed in antennae at the beginning of the pupal stage, then reached a maximum at the end of this stage and was maintained at this level during the adult period. Taken together, these results provided molecular evidence for the putative participation of a PLC-beta in signaling pathways responsible for the establishment and the functioning of insect olfactory system.

Differential regulation of phospholipase C-beta2 activity and membrane interaction by Galphaq, Gbeta1gamma2, and Rac2

We combined fluorescence recovery after photobleaching (FRAP) beam-size analysis with biochemical assays to investigate the mechanisms of membrane recruitment and activation of phospholipase C-beta(2) (PLCbeta(2)) by G protein alpha(q) and betagamma dimers. We show that activation by alpha(q) and betagamma differ from activation by Rac2 and from each other. Stimulation by alpha(q) enhanced the plasma membrane association of PLCbeta(2), but not of PLCbeta(2)Delta, which lacks the alpha(q)-interacting region. Although alpha(q) resembled Rac2 in increasing the contribution of exchange to the FRAP of PLCbeta(2) and in enhancing its membrane association, the latter effect was weaker than with Rac2. Moreover, the membrane recruitment of PLCbeta(2) by alpha(q) occurred by enhancing PLCbeta(2) association with fast-diffusing (lipid-like) membrane components, whereas stimulation by Rac2 led to interactions with slow diffusing membrane sites. On the other hand, activation by betagamma shifted the FRAP of PLCbeta(2) and PLCbeta(2)Delta to pure lateral diffusion 3- to 5-fold faster than lipids, suggesting surfing-like diffusion along the membrane. We propose that these different modes of PLCbeta(2) membrane recruitment may accommodate contrasting functional needs to hydrolyze phosphatidylinositol 4,5-bisphosphate (PtdInsP(2)) in localized versus dispersed populations. PLCbeta(2) activation by Rac2, which leads to slow lateral diffusion and much faster exchange, recruits PLCbeta(2) to act locally on PtdInsP(2) at specific domains. Activation by alpha(q) leads to lipid-like diffusion of PLCbeta(2) accompanied by exchange, enabling the sampling of larger, yet limited, areas prior to dissociation. Finally, activation by betagamma recruits PLCbeta(2) to the membrane by transient interactions, leading to fast "surfing" diffusion along the membrane, sampling large regions for dispersed PtdInsP(2) populations.

A kinetic model for calcium dynamics in RAW 264.7 cells: 1. Mechanisms, parameters, and subpopulational variability

Calcium (Ca(2+)) is an important second messenger and has been the subject of numerous experimental measurements and mechanistic studies in intracellular signaling. Calcium profile can also serve as a useful cellular phenotype. Kinetic models of calcium dynamics provide quantitative insights into the calcium signaling networks. We report here the development of a complex kinetic model for calcium dynamics in RAW 264.7 cells stimulated by the C5a ligand. The model is developed using the vast number of measurements of in vivo calcium dynamics carried out in the Alliance for Cellular Signaling (AfCS) Laboratories. Ligand binding, phospholipase C-beta (PLC-beta) activation, inositol 1,4,5-trisphosphate (IP(3)) receptor (IP(3)R) dynamics, and calcium exchange with mitochondria and extracellular matrix have all been incorporated into the model. The experimental data include data from both native and knockdown cell lines. Subpopulational variability in measurements is addressed by allowing nonkinetic parameters to vary across datasets. The model predicts temporal response of Ca(2+) concentration for various doses of C5a under different initial conditions. The optimized parameters for IP(3)R dynamics are in agreement with the legacy data. Further, the half-maximal effect concentration of C5a and the predicted dose response are comparable to those seen in AfCS measurements. Sensitivity analysis shows that the model is robust to parametric perturbations.

A kinetic model for calcium dynamics in RAW 264.7 cells: 2. Knockdown response and long-term response

This article addresses how quantitative models such as the one proposed in the companion article can be used to study cellular network perturbations such as knockdowns and pharmacological perturbations in a predictive manner. Using the kinetic model for cytosolic calcium dynamics in RAW 264.7 cells developed in the companion article, the calcium response to complement 5a (C5a) for the knockdown of seven proteins (C5a receptor; G-beta-2; G-alpha,i-2,3; regulator of G-protein signaling-10; G-protein coupled receptor kinase-2; phospholipase C beta-3; arrestin) is predicted and validated against the data from the Alliance for Cellular Signaling. The knockdown responses provide insights into how altered expressions of important proteins in disease states result in intermediate measurable phenotypes. Long-term response and long-term dose response have also been predicted, providing insights into how the receptor desensitization, internalization, and recycle result in tolerance. Sensitivity analysis of long-term response shows that the mechanisms and parameters in the receptor recycle path are important for long-term calcium dynamics.