Regulating G protein activity by lipase-independent functions of phospholipase C

Levodopa-induced dyskinesia: interplay between the N-methyl-D-aspartic acid receptor and neuroinflammation

Parkinson's disease (PD) is a common neurodegenerative disorder of middle-aged and elderly people, clinically characterized by resting tremor, myotonia, reduced movement, and impaired postural balance. Clinically, patients with PD are often administered levodopa (L-DOPA) to improve their symptoms. However, after years of L-DOPA treatment, most patients experience complications of varying severity, including the "on-off phenomenon", decreased efficacy, and levodopa-induced dyskinesia (LID). The development of LID can seriously affect the quality of life of patients, but its pathogenesis is unclear and effective treatments are lacking. Glutamic acid (Glu)-mediated changes in synaptic plasticity play a major role in LID. The N-methyl-D-aspartic acid receptor (NMDAR), an ionotropic glutamate receptor, is closely associated with synaptic plasticity, and neuroinflammation can modulate NMDAR activation or expression; in addition, neuroinflammation may be involved in the development of LID. However, it is not clear whether NMDA receptors are co-regulated with neuroinflammation during LID formation. Here we review how neuroinflammation mediates the development of LID through the regulation of NMDA receptors, and assess whether common anti-inflammatory drugs and NMDA receptor antagonists may be able to mitigate the development of LID through the regulation of central neuroinflammation, thereby providing a new theoretical basis for finding new therapeutic targets for LID.

Protein nanoparticle-induced osmotic pressure gradients modify pulmonary edema through hyperpermeability in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS), caused by noncardiogenic pulmonary edema (PE), contributes significantly to Coronavirus 2019 (COVID-19)-associated morbidity and mortality. We explored the effect of transmembrane osmotic pressure (OP) gradients in PE using a fluorescence resonance energy transfer-based Intermediate filament (IF) tension optical probe. Angiotensin-II- and bradykinin-induced increases in intracellular protein nanoparticle (PN)-OP were associated with inflammasome production and cytoskeletal depolymerization. Intracellular protein nanoparticle production also resulted in cytomembrane hyperpolarization and L-VGCC-induced calcium signals, which differed from diacylglycerol-induced calcium increment via TRPC6 activation. Both pathways involve voltage-dependent cation influx and OP upregulation via SUR1-TRPM4 channels. Meanwhile, intra/extracellular PN-induced OP gradients across membranes upregulated pulmonary endothelial and alveolar barrier permeability. Attenuation of intracellular PN, calcium signals, and cation influx by drug combinations effectively relieved intracellular OP and pulmonary endothelial nonselective permeability, and improved epithelial fluid absorption and PE. Thus, PN-OP is pivotal in pulmonary edema in ARDS and COVID-19, and transmembrane OP recovery could be used to treat pulmonary edema and develop new drug targets in pulmonary injury.

Graphical Abstract

Effect of Electro-acupuncture on Vasomotor Symptoms in Rats with Acute Cerebral Infarction Based on Phosphatidylinositol System

Objective

To investigate the effect of electro-acupuncture (EA) on vasomotor symptoms in rats with acute cerebral infarction, by observing the changes in the expression of factors related to the phosphatidylinositol (PI) system.

Methods

Forty-two Wistar rats were randomly divided into 3 groups by a random number table: the control group (n=6), the model group (n=18) and the EA group (n=18). The EA group was given EA treatment at Shuigou (GV 26) instantly after modeling with middle cerebral artery occlusion (MCAO) method, while the model and control groups were not given any treatment. The degrees of neurological deficiency were evaluated using neurological severity scores (NSS) and the brain blood flow was evaluated by a laser scanning confocal microscope. Western blot analysis was conducted to detect the expression levels of G-protein subtype (Gq) and calmodulin (CaM). Competition for protein binding was conducted to detect the expression level of inositol triphosphate (IP3). Thin layer quantitative analysis was conducted to detect the expression level of diacylglycerol (DAG). The expression level of intracellular concentration of free calcium ion ([Ca²⁺]_i) was detected by flow cytometry.

Results

The NSS of the model group was significantly higher than the control group at 3 and 6 h after MCAO (P<0.01), while the EA group was significantly lower than the model group at 6 h (P<0.01). The cerebral blood flow in the model group was significantly lower than the control group at 1, 3 and 6 h after MCAO (P<0.01), while for the EA group it was remarkably higher than the model group at the same time points (P<0.01). The expressions of Gq, CaM, IP3, DAG and [Ca²⁺]_i in the model group were significantly higher than the control group (P<0.05 or P<0.01), and those in the EA group were significantly lower than the model group at the same time points (P<0.05 or P<0.01).

Conclusion

EA treatment at GV 26 can effectively decrease the over-expression of related factors of PI system in rats with acute cerebral infarction, improve cerebral autonomy movement, and alleviate cerebral vascular spasm.

HIV infection of astrocytes compromises inter-organelle interactions and inositol phosphate metabolism: A potential mechanism of bystander damage and viral reservoir survival

HIV-associated neurological dysfunction is observed in more than half of the HIV-infected population, even in the current antiretroviral era. The mechanisms by which HIV mediates CNS dysfunction are not well understood but have been associated with the presence of long-lasting HIV reservoirs. In the CNS, macrophage/microglia and a small population of astrocytes harbor the virus. However, the low number of HIV-infected cells does not correlate with the high degree of damage, suggesting that mechanisms of damage amplification may be involved. Here, we demonstrate that the survival mechanism of HIV-infected cells and the apoptosis of surrounding uninfected cells is regulated by inter-organelle interactions among the mitochondria/Golgi/endoplasmic reticulum system and the associated signaling mediated by IP₃ and calcium. We identified that latently HIV-infected astrocytes had elevated intracellular levels of IP₃, a master regulator second messenger, which diffuses via gap junctions into neighboring uninfected astrocytes resulting in their apoptosis. In addition, using laser capture microdissection, we confirmed that bystander apoptosis of uninfected astrocytes and the survival of HIV-infected astrocytes were dependent on mitochondrial function, intracellular calcium, and IP₃ signaling. Blocking gap junction channels did not prevent an increase in IP₃ or inter-organelle dysfunction in HIV-infected cells but reduced the amplification of apoptosis into uninfected neighboring cells. Our data provide a mechanistic explanation for bystander damage induced by surviving infected cells that serve as viral reservoirs and provide potential targets for interventions to reduce the devastating consequences of HIV within the brain.

Transduction and Adaptation Mechanisms in the Cilium or Microvilli of Photoreceptors and Olfactory Receptors From Insects to Humans

Sensing changes in the environment is crucial for survival. Animals from invertebrates to vertebrates use both visual and olfactory stimuli to direct survival behaviors including identification of food sources, finding mates, and predator avoidance. In primary sensory neurons there are signal transduction mechanisms that convert chemical or light signals into an electrical response through ligand binding or photoactivation of a receptor, that can be propagated to the olfactory and visual centers of the brain to create a perception of the odor and visual landscapes surrounding us. The fundamental principles of olfactory and phototransduction pathways within vertebrates are somewhat analogous. Signal transduction in both systems takes place in the ciliary sub-compartments of the sensory cells and relies upon the activation of G protein-coupled receptors (GPCRs) to close cyclic nucleotide-gated (CNG) cation channels in photoreceptors to produce a hyperpolarization of the cell, or in olfactory sensory neurons open CNG channels to produce a depolarization. However, while invertebrate phototransduction also involves GPCRs, invertebrate photoreceptors can be either ciliary and/or microvillar with hyperpolarizing and depolarizing responses to light, respectively. Moreover, olfactory transduction in invertebrates may be a mixture of metabotropic G protein and ionotropic signaling pathways. This review will highlight differences of the visual and olfactory transduction mechanisms between vertebrates and invertebrates, focusing on the implications to the gain of the transduction processes, and how they are modulated to allow detection of small changes in odor concentration and light intensity over a wide range of background stimulus levels.

Activation of Bombyx mori neuropeptide G protein-coupled receptor A19 by neuropeptide RYamides couples to Gq protein-dependent signaling pathways

RYamides constitute a novel family of neuropeptides newly identified in insects, and play important roles in regulating a variety of physiological processes. However, the signaling characteristics and physiological actions of RYamide signaling system remain largely unknown. In the present study, we cloned the full-length complementary DNA of the RYamide receptor BNGR-A19 from Bombyx mori larvae. After expression in mammalian HEK293T and insect Sf9 cells, functional assays revealed that BNGR-A19 was activated by synthetic RYamide peptides, triggering a significant increase in cAMP-response element controlled luciferase activity and Ca²⁺ mobilization in a G_q inhibitor-sensitive manner. Upon activation by RYamide peptides, BNGR-A19 elicited ERK1/2 phosphorylation via a G_q -PLC-PKC pathway, and also underwent a rapid internalization from the cell surface to the cytoplasm. Further cross-activity analysis indicated that BNGR-A19 exhibited very weak response upon stimulation by high concentration (1 μM) of Bombyx sulfakinin-1, neuropeptide F-1, and short neuropeptide F-1, and vice versa, Bombyx RYamides also showed slight potency for activating Bombyx NPF receptor (BNGR-A4) and sNPF receptor (BNGR-A11). In addition, the quantitative reverse-transcription polymerase chain reaction results showed that the high-level expression of BNGR-A19 was detected in the hindgut and testis, suggesting that the RYamide signaling is likely involved in the regulation of feeding, water homeostasis and testis development. This study provides the first in-depth information on the insect RYamide signaling system, facilitating the further clarification of its endocrinological roles in insect physiology.

A journey into the world of insect lipid metabolism

Lipid metabolism is fundamental to life. In insects, it is critical, during reproduction, flight, starvation, and diapause. The coordination center for insect lipid metabolism is the fat body, which is analogous to the vertebrate adipose tissue and liver. Fat body contains various different cell types; however, adipocytes and oenocytes are the primary cells related to lipid metabolism. Lipid metabolism starts with the hydrolysis of dietary lipids, absorption of lipid monomers, followed by lipid transport from midgut to the fat body, lipogenesis or lipolysis in the fat body, and lipid transport from fat body to other sites demanding energy. Lipid metabolism is under the control of hormones, transcription factors, secondary messengers and posttranscriptional modifications. Primarily, lipogenesis is under the control of insulin-like peptides that activate lipogenic transcription factors, such as sterol regulatory element-binding proteins, whereas lipolysis is coordinated by the adipokinetic hormone that activates lipolytic transcription factors, such as forkhead box class O and cAMP-response element-binding protein. Calcium is the primary-secondary messenger affecting lipid metabolism and has different outcomes depending on the site of lipogenesis or lipolysis. Phosphorylation is central to lipid metabolism and multiple phosphorylases are involved in lipid accumulation or hydrolysis. Although most of the knowledge of insect lipid metabolism comes from the studies on the model Drosophila; other insects, in particular those with obligatory or facultative diapause, also have great potential to study lipid metabolism. The use of these models would significantly improve our knowledge of insect lipid metabolism.

The Role of Peptide Hormones in Insect Lipid Metabolism

Lipids are the primary storage molecules and an essential source of energy in insects during reproduction, prolonged periods of flight, starvation, and diapause. The coordination center for insect lipid metabolism is the fat body, which is analogous to the vertebrate adipose tissue and liver. The fat body is primarily composed of adipocytes, which accumulate triacylglycerols in intracellular lipid droplets. Genomics and proteomics, together with functional analyses, such as RNA interference and CRISPR/Cas9-targeted genome editing, identified various genes involved in lipid metabolism and elucidated their functions. However, the endocrine control of insect lipid metabolism, in particular the roles of peptide hormones in lipogenesis and lipolysis are relatively less-known topics. In the current review, the neuropeptides that directly or indirectly affect insect lipid metabolism are introduced. The primary lipolytic and lipogenic peptide hormones are adipokinetic hormone and the brain insulin-like peptides (ILP2, ILP3, ILP5). Other neuropeptides, such as insulin-growth factor ILP6, neuropeptide F, allatostatin-A, corazonin, leucokinin, tachykinins and limostatin, might stimulate lipolysis, while diapause hormone-pheromone biosynthesis activating neuropeptide, short neuropeptide F, CCHamide-2, and the cytokines Unpaired 1 and Unpaired 2 might induce lipogenesis. Most of these peptides interact with one another, but mostly with insulin signaling, and therefore affect lipid metabolism indirectly. Peptide hormones are also involved in lipid metabolism during reproduction, flight, diapause, starvation, infections and immunity; these are also highlighted. The review concludes with a discussion of the potential of lipid metabolism-related peptide hormones in pest management.

Hydrostatic pressure promotes endothelial tube formation through aquaporin 1 and Ras-ERK signaling

Vascular tubulogenesis is tightly linked with physiological and pathological events in the living body. Endothelial cells (ECs), which are constantly exposed to hemodynamic forces, play a key role in tubulogenesis. Hydrostatic pressure in particular has been shown to elicit biophysical and biochemical responses leading to EC-mediated tubulogenesis. However, the relationship between tubulogenesis and hydrostatic pressure remains to be elucidated. Here, we propose a specific mechanism through which hydrostatic pressure promotes tubulogenesis. We show that pressure exposure transiently activates the Ras/extracellular signal-regulated kinase (ERK) pathway in ECs, inducing endothelial tubulogenic responses. Water efflux through aquaporin 1 and activation of protein kinase C via specific G protein–coupled receptors are essential to the pressure-induced transient activation of the Ras/ERK pathway. Our approach could provide a basis for elucidating the mechanopathology of tubulogenesis-related diseases and the development of mechanotherapies for improving human health.

Yoshino et al. investigate the mechanism by which exposure to pressure promotes endothelial cells to form tubes and find that Aquaporin-mediated water efflux activates the Ras-ERK pathway via PKC and GPCR activation. These findings may be relevant to understand how blood pressure affects vascular tubulogenesis.

Role of lysophosphatidic acid in vascular smooth muscle cell proliferation

Lysophosphatidic acid (LPA) is an important lipid molecule for signal transduction in cell proliferation. Although the effects of LPA on vascular smooth muscle (VSM) cell growth have been reported previously, the underlying mechanisms of its action are not fully understood. The present study was undertaken to investigate the effects of some inhibitors of different protein kinases and other molecular targets on LPA-induced DNA synthesis as well as gene expression in the aortic VSM cells. The DNA synthesis was studied by the [³H]thymidine incorporation method and the gene expression was investigated by the real-time PCR technique. It was observed that the LPA-induced DNA synthesis was attenuated by inhibitors of protein kinase C (PKC) (staurosporine, calphostin C, and bisindolylmaleimide), phosphoinositide 3-kinase (PI3K) (wortmannin and LY294002), and ribosomal p70S6 kinase (p70S6K) (rapamycin). The inhibitors of guanine protein coupled receptors (GPCR) (pertussis toxin), phospholipase C (PLC) (U73122 and D609), and sodium-hydrogen exchanger (NHE) (amiloride and dimethyl amiloride) were also shown to depress the LPA-induced DNA synthesis. Furthermore, gene expressions for PLC β1 isoform, PKC δ and ε isoforms, casein kinase II β isoform, and endothelin-1A receptors were elevated by LPA. These results suggest that the LPA-induced proliferation of VSM cells is mediated through the activation of GPCR and multiple protein kinases as well as gene expressions of some of their specific isoforms.

Ethanolic Extract of Folium Sennae Mediates the Glucose Uptake of L6 Cells by GLUT4 and Ca2

In today’s world, diabetes mellitus (DM) is on the rise, especially type 2 diabetes mellitus (T2DM), which is characterized by insulin resistance. T2DM has high morbidity, and therapies with natural products have attracted much attention in the recent past. In this paper, we aimed to study the hypoglycemic effect and the mechanism of an ethanolic extract of Folium Sennae (FSE) on L6 cells. The glucose uptake of L6 cells was investigated using a glucose assay kit. We studied glucose transporter 4 (GLUT4) expression and AMP-activated protein kinase (AMPK), protein kinase B (PKB/Akt), and protein kinase C (PKC) phosphorylation levels using western blot analysis. GLUT4 trafficking and intracellular Ca²⁺ levels were monitored by laser confocal microscopy in L6 cells stably expressing IRAP-mOrange. GLUT4 fusion with plasma membrane (PM) was observed by myc-GLUT4-mOrange. FSE stimulated glucose uptake; GLUT4 expression and translocation; PM fusion; intracellular Ca²⁺ elevation; and the phosphorylation of AMPK, Akt, and PKC in L6 cells. GLUT4 translocation was weakened by the AMPK inhibitor compound C, PI3K inhibitor Wortmannin, PKC inhibitor Gö6983, G protein inhibitor PTX/Gallein, and PLC inhibitor U73122. Similarly, in addition to PTX/Gallein and U73122, the IP3R inhibitor 2-APB and a 0 mM Ca²⁺-EGTA solution partially inhibited the elevation of intracellular Ca²⁺ levels. BAPTA-AM had a significant inhibitory effect on FSE-mediated GLUT4 activities. In summary, FSE regulates GLUT4 expression and translocation by activating the AMPK, PI3K/Akt, and G protein–PLC–PKC pathways. FSE causes increasing Ca²⁺ concentration to complete the fusion of GLUT4 vesicles with PM, allowing glucose uptake. Therefore, FSE may be a potential drug for improving T2DM.

Presynaptic increase in IP3 receptor type 1 concentration in the early phase of hippocampal synaptic plasticity

The inositol 1,4,5-trisphosphate receptor (IP₃R) subtype IP₃R1 is highly enriched in the brain, including hippocampal neurons. It plays an important function in regulating intracellular calcium concentrations. Residing on the smooth endoplasmic reticulum (sER), the IP₃R1 mobilizes calcium into the cytosol upon binding the intracellular signaling molecule IP₃, whose concentration is increased by stimulating certain metabotropic glutamate receptors. Increased calcium may mediate synaptic changes occurring during long-term plasticity, which includes molecular mechanisms underlying memory encoding. The exact synaptic localization of IP₃R1 in the central nervous system (CNS) remains unclear. We hypothesized that IP₃R1, in addition to its known expression in soma and dendritic shafts of hippocampal CA1 pyramidal neurons, also may be present in postsynaptic spines. Moreover, we hypothesized that IP₃R1 may be present in presynaptic terminals as well, given the importance of calcium in regulating presynaptic neurotransmitter exocytosis. To test these two hypotheses, we used IP₃R1 immunocytochemistry at the light and electron microscopical levels in the CA1 area of the hippocampus. Furthermore, we hypothesized that induction of long-term potentiation (LTP) would be accompanied by an increase in synaptic IP₃R1 concentrations, thereby facilitating synaptic mechanisms of long term plasticity. To investigate this, we used quantitative immunogold electron microscopy to determine possible changes in IP₃R1 concentration in sub-synaptic compartments before and five minutes after high frequency tetanizations. Firstly, our data confirm localization of IP₃R1 in both presynaptic terminals and postsynaptic spines. Secondly, the concentration of IP₃R1 after tetanization was significantly increased in the presynaptic compartment, suggesting a presynaptic role of IP₃R1 in early phases of synaptic plasticity. It is therefore possible that IP₃R1 is involved in modulating neurotransmitter release by regulating calcium homeostasis presynaptically.

CAPA periviscerokinin-mediated activation of MAPK/ERK signaling through Gq-PLC-PKC-dependent cascade and reciprocal ERK activation-dependent internalized kinetics of Bom-CAPA-PVK receptor 2

Bombyx mori neuropeptide G protein-coupled receptor (BNGR)-A27 is a specific receptor for B. mori capability (CAPA) periviscerokinin (PVK), that is, Bom-CAPA-PVK receptor 2. Upon stimulation of Bom-CAPA-PVK-1 or -PVK-2, Bom-CAPA-PVK receptor 2 significantly increases cAMP-response element-controlled luciferase activity and Ca²⁺ mobilization in a Gq inhibitor-sensitive manner. However, the underlying mechanism(s) for CAPA/CAPA receptor system mediation of extracellular signal-regulated kinases1/2 (ERK1/2) activation remains to be explained further. Here, we discovered that Bom-CAPA-PVK receptor 2 stimulated ERK1/2 phosphorylation in a dose- and time-dependent manner in response to Bom-CAPA-PVK-1 or -PVK-2 with similar potencies. Furthermore, ERK1/2 phosphorylation can be inhibited by Gq inhibitor UBO-QIC, PLC inhibitor U73122, protein kinase C (PKC) inhibitor Go 6983, phospholipase D (PLD) inhibitor FIPI and Ca²⁺ chelators EGTA and BAPTA-AM. Moreover, Bom-CAPA-PVK-R2-induced activation of ERK1/2 was significantly attenuated by treatment with the Gβγ-specific inhibitors, phosphatidylinositol 3-kinase (PI3K)-specific inhibitor Wortmannin and Src-specific inhibitor PP2. Our data also demonstrate that receptor tyrosine kinase (RTK) transactivation pathways are involved in the mechanisms of Bom-CAPA-PVK receptor to ERK1/2 phosphorylation. In addition, β-arrestin1/2 is not involved in Bom-CAPA-PVK-R2-mediated ERK1/2 activation but required for the agonist-independent, ERK1/2 activation-dependent internalization of the G protein-coupled receptor (GPCR).

Agonist-mediated activation of Bombyx mori diapause hormone receptor signals to extracellular signal-regulated kinases 1 and 2 through Gq-PLC-PKC-dependent cascade

Diapause is a developmental strategy adopted by insects to survive in challenging environments such as the low temperatures of a winter. This unique process is regulated by diapause hormone (DH), which is a neuropeptide hormone that induces egg diapause in Bombyx mori and is involved in terminating pupal diapause in heliothis moths. An G protein-coupled receptor from the silkworm, B. mori, has been identified as a specific cell surface receptor for DH. However, the detailed information on the DH-DHR system and its mechanism(s) involved in the induction of embryonic diapause remains unknown. Here, we combined functional assays with various specific inhibitors to elucidate the DHR-mediated signaling pathways. Upon activation by DH, B. mori DHR is coupled to the Gq protein, leading to a significant increase of intracellular Ca(2+) and cAMP response element-driven luciferase activity in an UBO-QIC, a specific Gq inhibitor, sensitive manner. B. mori DHR elicited ERK1/2 phosphorylation in a dose- and time-dependent manner in response to DH. This effect was almost completely inhibited by co-incubation with UBO-QIC and was also significantly suppressed by PLC inhibitor U73122, PKC inhibitors Gö6983 and the Ca(2+) chelator EGTA. Moreover, DHR-induced activation of ERK1/2 was significantly attenuated by treatment with the Gβγ specific inhibitors gallein and M119K and the PI3K specific inhibitor Wortmannin, but not by the Src specific inhibitor PP2. Our data also demonstrates that the EGFR-transactivation pathway is not involved in the DHR-mediated ERK1/2 phosphorylation. Future efforts are needed to clarify the role of the ERK1/2 signaling pathway in the DH-mediated induction of B. mori embryonic diapause.

Decoding Gαq signaling

Gαq signals with phospholipase C-β (PLC-β) to modify behavior in response to an agonist-bound GPCR. While the fundamental steps which prime Gαq to interact with PLC-β have been identified, questions remain concerning signal strength with PLC-β and other effectors. Gαq is generally viewed to function as a simple ON and OFF switch for its effector, dependent on the binding of GTP or GDP. However, Gαq does not have a single effector, Gαq has many different effectors. Furthermore, select effectors also regulate Gαq activity. PLC-β is a lipase and a GTPase activating protein (GAP) selective for Gαq. The contribution of G protein regulating activity to signal amplitude remains unclear. The unique PLC-β coiled-coil domain is essential for maximum Gαq response, both lipase and GAP. Nonetheless, coiled-coil domain associations necessary to maximum response have not been revealed by the structural approach. This review discusses progress towards understanding the basis for signal strength with PLC-β and other effectors. Shared and effector-specific interactions have been identified. Finally, the evidence for allosteric regulation of lipase stimulation by protein kinase C, the membrane, phosphatidic acid, phosphatidylinositol-4, 5-bisphosphate and GPCR is explored. Endogenous allosteric regulators can suppress or enhance maximum lipase stimulation dependent on the PLC-β coiled-coil domain. A better understanding of allosteric modulation may therefore identify a wealth of new targets to regulate signal strength and behavior.