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Lysophosphatidic acid directly activates TRPV1 through a C-terminal binding site
Abstract and Figures
Since 1992, there has been growing evidence that the bioactive phospholipid lysophosphatidic acid (LPA), whose amounts are increased upon tissue injury, activates primary nociceptors resulting in neuropathic pain. The TRPV1 ion channel is expressed in primary afferent nociceptors and is activated by physical and chemical stimuli. Here we show that in control mice LPA produces acute pain-like behaviors, which are substantially reduced in Trpv1-null animals. Our data also demonstrate that LPA activates TRPV1 through a unique mechanism that is independent of G protein-coupled receptors, contrary to what has been widely shown for other ion channels, by directly interacting with the C terminus of the channel. We conclude that TRPV1 is a direct molecular target of the pain-producing molecule LPA and that this constitutes, to our knowledge, the first example of LPA binding directly to an ion channel to acutely regulate its function.
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... While LPA is known to activate metabotropic receptors (G-protein-coupled receptors), it has also been shown to activate or potentiate ionotropic receptors, including TRPV1 (refs. 10,15,16). Indeed, LPA activates recombinant TRPV1 channels in reconstituted liposomes 7 and elicits TRPV1-dependent pain-related behavior in mice 10 . Thus, we are interested in determining how this endogenous pro-algesic lipid binds to TRPV1, and whether and how this involves interaction with the vanilloid site. ...
... 10,15,16). Indeed, LPA activates recombinant TRPV1 channels in reconstituted liposomes 7 and elicits TRPV1-dependent pain-related behavior in mice 10 . Thus, we are interested in determining how this endogenous pro-algesic lipid binds to TRPV1, and whether and how this involves interaction with the vanilloid site. ...
... Previous electrophysiological studies showed that the charge-reversal mutation, K710D, abrogates LPA-evoked responses, leading to the conclusion that K710, a residue located on the periphery of TRPV1 at the membrane-protein interface, is key in mediating the binding of LPA 10 . However, our cryo-EM data place the binding of LPA in the VBP, about 25 Å away from K710. ...
TRP ion channels are modulated by phosphoinositide lipids, but the underlying structural mechanisms remain unclear. The capsaicin- and heat-activated receptor, TRPV1, has served as a model for deciphering lipid modulation, which is relevant to understanding how pro-algesic agents enhance channel activity in the setting of inflammatory pain. Identification of a pocket within the TRPV1 transmembrane core has provided initial clues as to how phosphoinositide lipids bind to and regulate the channel. Here we show that this regulatory pocket in rat TRPV1 can accommodate diverse lipid species, including the inflammatory lipid lysophosphatidic acid, whose actions are determined by their specific modes of binding. Furthermore, we show that an empty-pocket channel lacking an endogenous phosphoinositide lipid assumes an agonist-like state, even at low temperature, substantiating the concept that phosphoinositide lipids serve as negative TRPV1 modulators whose ejection from the binding pocket is a critical step toward activation by thermal or chemical stimuli.
... Importantly, LPA can directly activate the TRPV1 channel to induce acute pain response via a positively charged residue (lysine 710, K710), which is located in the C-terminal TRP domain that is critical for TRPV1 channel gating [23,35]. This LPA-induced pain response is independent of the classical LPA receptors [39,41]. Mutagenesis studies have demonstrated that replacing TRPV1 K710 with a neutral glutamine (K710Q) or a negatively charged aspartic acid (K710D) significantly reduces the TRPV1 current response to LPA [7,41]. ...
... This LPA-induced pain response is independent of the classical LPA receptors [39,41]. Mutagenesis studies have demonstrated that replacing TRPV1 K710 with a neutral glutamine (K710Q) or a negatively charged aspartic acid (K710D) significantly reduces the TRPV1 current response to LPA [7,41]. Additionally, our recent study revealed that mice with a TRPV1 K710N in vivo mutation, where K710 is replaced with a neutral asparagine (K710N), were resistant to LPA analogue (Brp-LPA)-induced pain responses [23]. ...
... LPA has been shown to directly activate rat TRPV1 at the site of K710 and produce pain by acting on nociceptors [41]. In our recent study, we generated TRPV1 K710N knock-in mice using CRISPR/Cas9 technology and observed reduced pain sensitivity in this transgenic mouse model [23]. ...
Lysophosphatidic acid (LPA) is a bioactive phospholipid that plays a crucial role in cardiovascular diseases. Here, we question whether LPA contributes to myocardial ischemia/reperfusion (I/R) injury by acting on transient receptor potential vanilloid 1 (TRPV1) in spinal cord. By ligating the left coronary artery to establish an in vivo I/R mouse model, we observed a 1.57-fold increase in LPA level in the cerebrospinal fluid (CSF). The I/R-elevated CSF LPA levels were reduced by HA130, an LPA synthesis inhibitor, compared to vehicle treatment (4.74 ± 0.34 vs. 6.46 ± 0.94 μg/mL, p = 0.0014). Myocardial infarct size was reduced by HA130 treatment compared to the vehicle group (26 ± 8% vs. 46 ± 8%, p = 0.0001). To block the interaction of LPA with TRPV1 at the K710 site, we generated a K710N knock-in mouse model. The TRPV1K710N mice were resistant to LPA-induced myocardial injury, showing a smaller infarct size relative to TRPV1WT mice (28 ± 4% vs. 60 ± 7%, p < 0.0001). Additionally, a sequence-specific TRPV1 peptide targeting the K710 region produced similar protective effects against LPA-induced myocardial injury. Blocking the K710 region through K710N mutation or TRPV1 peptide resulted in reduced neuropeptides release and decreased activity of cardiac sensory neurons, leading to a decrease in cardiac norepinephrine concentration and the restoration of intramyocardial pro-survival signaling, namely protein kinase B/extracellular regulated kinase/glycogen synthase kinase-3β pathway. These findings suggest that the elevation of CSF LPA is strongly associated with myocardial I/R injury. Moreover, inhibiting the interaction of LPA with TRPV1 by blocking the K710 region uncovers a novel strategy for preventing myocardial ischemic injury.
... LPA also binds to other G-protein-coupled receptors (GPCRs), including GPPR87 [45], GPPR35 [46] and P2Y10 [47], to induce Ca 2+ release and subcellular signalling. Moreover, different LPA species interact with non-GPCRs such as the receptor for advanced glycation end products (RAGE) to induce AKT/cyclin D1 signalling [48] and the cation channel transient receptor potential vanilloid 1 (TRPV1)-an ion channel-to promote the release of intracellular Ca 2+ [49]. Finally, peroxisome proliferator-activated receptor γ (PPARγ) is the only intracellular LPA receptor identified thus far. ...
Lysophosphatidic acid (LPA) is a phospholipid that displays potent signalling activities that are regulated in both an autocrine and paracrine manner. It can be found both extra- and intracellularly, where it interacts with different receptors to activate signalling pathways that regulate a plethora of cellular processes, including mitosis, proliferation and migration. LPA metabolism is complex, and its biosynthesis and catabolism are under tight control to ensure proper LPA levels in the body. In cancer patient specimens, LPA levels are frequently higher compared to those of healthy individuals and often correlate with poor responses and more aggressive disease. Accordingly, LPA, through promoting cancer cell migration and invasion, enhances the metastasis and dissemination of tumour cells. In this review, we summarise the role of LPA in the regulation of critical aspects of tumour biology and further discuss the available pre-clinical and clinical evidence regarding the feasibility and efficacy of targeting LPA metabolism for effective anticancer therapy.
... While this example of programmed cell death was attributed to elevations in ethylene signaling, it remains possible that it also involves signaling contributions from SA. LysoPC treatments have also been shown to elevate [Ca 2+ ] cyt in both yeast and human cell lines(Chaudhuri et al., 2003;Rimola et al., 2020), suggesting the same might occur in plants. In human cells, LysoPC elevates [Ca 2+ ] cyt by activating two Ca 2+ channels(Rimola et al., 2020), likely by interacting with their cytosolic C-terminal tails(Nieto- Posadas et al., 2011). LysoPC is also known to activate P-type ATPases involved in H + transport by disrupting the autoinhibitory functions of their cytosolic C-terminal tail(Palmgren et al., 1988;Wielandt et al., 2015), raising the potential for similar regulation of12 of 15 DAVIS ET AL. ...
P4 ATPases (i.e . , lipid flippases) are eukaryotic enzymes that transport lipids across membrane bilayers. In plants, P4 ATPases are named Aminophospholipid ATPases (ALAs) and are organized into five phylogenetic clusters. Here we generated an Arabidopsis mutant lacking all five cluster‐2 ALAs ( ala8/9/10/11/12 ), which is the most highly expressed ALA subgroup in vegetative tissues. Plants harboring the quintuple knockout (KO) show rosettes that are 2.2‐fold smaller and display chlorotic lesions. A similar but less severe phenotype was observed in an ala10/11 double KO. The growth and lesion phenotypes of ala8/9/10/11/12 mutants were reversed by expressing a NahG transgene, which encodes an enzyme that degrades salicylic acid (SA). A role for SA in promoting the lesion phenotype was further supported by quantitative PCR assays showing increased mRNA abundance for an SA‐biosynthesis gene ISOCHORISMATE SYNTHASE 1 ( ICS1 ) and two SA‐responsive genes PATHOGENESIS‐RELATED GENE 1 ( PR1 ) and PR2. Lesion phenotypes were also reversed by growing plants in liquid media containing either low calcium (~0.1 mM) or high nitrogen concentrations (~24 mM), which are conditions known to suppress SA‐dependent autoimmunity. Yeast‐based fluorescent lipid uptake assays revealed that ALA10 and ALA11 display overlapping substrate specificities, including the transport of LysoPC signaling lipids. Together, these results establish that the biochemical functions of ALA8–12 are at least partially overlapping, and that deficiencies in cluster‐2 ALAs result in an SA‐dependent autoimmunity phenotype that has not been observed for flippase mutants with deficiencies in other ALA clusters.
... However, activation of TRPV4 by LPA18:1 and LPC18:1 occurs with different open probabilities (higher Po for LPC than for LPA) but with different single-channel conductances (lower for LPC), suggesting that this happens through a mechanism in which these agonists promote different open states. A similar phenomenon was observed by our group for LPA18:1 and TRPV1, where LPA18:1 activates the channel, partially through interactions with residue K710 in the TRP box of the channel [176], but also leads to a different conformational open state with higher conductance, as compared to the one produced by capsaicin [177]. ...
The members of the superfamily of Transient Receptor Potential (TRP) ion channels are physiologically important molecules that have been studied for many years and are still being intensively researched. Among the vanilloid TRP subfamily, the TRPV4 ion channel is an interesting protein due to its involvement in several essential physiological processes and in the development of various diseases. As in other proteins, changes in its function that lead to the development of pathological states, have been closely associated with modification of its regulation by different molecules, but also by the appearance of mutations which affect the structure and gating of the channel. In the last few years, some structures for the TRPV4 channel have been solved. Due to the importance of this protein in physiology, here we discuss the recent progress in determining the structure of the TRPV4 channel, which has been achieved in three species of animals (Xenopus tropicalis, Mus musculus, and Homo sapiens), highlighting conserved features as well as key differences among them and emphasizing the binding sites for some ligands that play crucial roles in its regulation.
... It has been shown that urolithin and its many structural analogs inhibit AGE-BSA/sRAGE interactions and its RAGE inhibition is like that of Azeliragon (Guérin et al., 2021) [ Table 3]. (Bresnick et al., 2015;Cristóvaõ and Gomes, 2019;Leclerc et al., 2009;Santamaria-Kisiel et al., 2006) 3. LPA V, C2 Glycerophospholipid Activation of protein kinases (PI3K/ AKT) and ERK GPCR,RAGE,Transient receptor potential vanilloid (TRPV1) (Lee et al., 2019;Nieto-Posadas et al., 2011;Smyth et al., 2020;Tian et al., 2021;Ueda et al., 2018) 4. Aβ V Hydrolytic cleavage of APP protein RAGE expression is higher in AD, induces oxidative stress in neurons, and, produces cytokines in microglia by stimulating NADPH oxidase RAGE & more (Askarova et al., 2011;Karran et al., 2011;Deane et al., 2003;Murphy and Levine, 2010;Sturchler et al., 2008) 5. Phosphatidylserine -Plasma membrane ...
According to the facts and figures 2023stated that 6.7 million Americans over the age of 65 have Alzheimer's disease (AD). The scenario of AD has reached up to the maximum, of 4.1 million individuals, 2/3rd are female patients, and approximately 1 in 9 adults over the age of 65 have dementia with AD dementia. The fact that there are now no viable treatments for AD indicates that the underlying disease mechanisms are not fully understood. The progressive neurodegenerative disease, AD is characterized by amyloid plaques and neurofibrillary tangles (NFTs) of abnormally hyperphosphorylated tau protein and senile plaques (SPs), which are brought on by the buildup of amyloid beta (Aβ). Numerous attempts have been made to produce compounds that interfere with these characteristics because of significant research efforts into the primary pathogenic hallmark of this disorder. Here, we summarize several research that highlights interesting therapy strategies and the neuroprotective effects of GLP-1, Sigma, and, AGE-RAGE receptors in pre-clinical and clinical AD models.
... These cascades induce changes in the gating characteristics of ion channels such as TRPV1, TRPA1, Nav1.7, Nav1.8, and Nav1.9 through processes like phosphorylation [11,12]. The outcome of these changes is enhanced neuronal firing, contributing to heightened pain sensitivity. ...
This review explores the link between immune interactions and chronic pain, offering new perspectives on treatment. It focuses on Janus kinase (JAK) inhibitors’ potential in pain management. Immune cells’ communication with neurons shapes neuroinflammatory responses, and JAK inhibitors’ effects on pain pathways are discussed, including cytokine suppression and microglial modulation. This review integrates studies from rheumatoid arthritis (RA) pain and central sensitization to highlight connections between immune interactions and pain. Studies on RA joint pain reveal the shift from cytokines to sensitization. Neurobiological investigations into central sensitization uncover shared pathways in chronic pain. Clinical evidence supports JAK inhibitors’ efficacy on pain-related outcomes and their effects on neurons and immune cells. Challenges and future directions are outlined, including interdisciplinary collaboration and dosing optimization. Overall, this review highlights JAK inhibitors’ potential to target immune-mediated pain pathways, underscoring the need for more research on immune–pain connections.
According to the facts and figures 2023 on Alzheimer’s disease (AD) stated that 6.7 million Americans over the age of 65 have AD. The scenario of AD has reached up to the maximum, of 4.1 million individuals, 2/3rd are female patients, and approximately 1 in 9 adults over the age of 65 have dementia with AD dementia. The fact that there are now no viable treatments for AD indicates that the underlying disease mechanisms are not fully understood. The progressive neurodegenerative illness AD is characterized by amyloid plaques and NFTs of abnormally hyperphosphorylated tau protein and senile plaques (SPs), which are brought on by the buildup of amyloid beta (Aβ). Numerous attempts have been made to produce compounds that interfere with these characteristics because of significant research efforts into the primary pathogenic hallmark of this disorder. Here, we summarize several research that highlights interesting therapy strategies and the neuroprotective effects of GLP-1, Sigma, and, AGE-RAGE receptors in pre-clinical and clinical AD models.
Background: Chemotherapy-induced peripheral neuropathy (CIPN) is a serious therapy-limiting side effect of commonly used anticancer drugs. Previous studies suggest that lipids may play a role in CIPN. Therefore, the present study aimed to identify the particular types of lipids that are regulated as a consequence of paclitaxel administration and may be associated with the occurrence of post-therapeutic neuropathy.
Methods: High resolution mass spectrometry lipidomics was applied to quantify d = 255 different lipid mediators in the blood of n = 31 patients drawn before and after paclitaxel therapy for breast cancer treatment. A variety of supervised statistical and machine-learning methods was applied to identify lipids that were regulated during paclitaxel therapy or differed among patients with and without post-therapeutic neuropathy.
Results: Twenty-seven lipids were identified that carried relevant information to train machine learning algorithms to identify, in new cases, whether a blood sample was drawn before or after paclitaxel therapy with a median balanced accuracy of up to 90%. One of the top hits, sphinganine-1-phosphate (SA1P), was found to induce calcium transients in sensory neurons via the transient receptor potential vanilloid 1 (TRPV1) channel and sphingosine-1-phosphate receptors.SA1P also showed different blood concentrations between patients with and without neuropathy.
Conclusions: Present findings suggest an important role for sphinganine-1-phosphate in paclitaxel-induced biological changes associated with neuropathic side effects. The identified SA1P, through its receptors, provides a potential drug target for co-therapy with paclitaxel to reduce one of its major and therapy-limiting side effects.
The molecular basis of the thermal sensitivity of temperature-sensitive channels appears to arise from a specific protein domain rather than integration of global thermal effects. Using systematic chimeric analysis, we show that the N-terminal region that connects ankyrin repeats to the first transmembrane segment is crucial for temperature sensing in heat-activated vanilloid receptor channels. Changing this region both transformed temperature-insensitive isoforms into temperature-sensitive channels and significantly perturbed temperature sensing in temperature-sensitive wild-type channels. Swapping other domains such as the transmembrane core, the C terminus, and the rest of the N terminus had little effect on the steepness of temperature dependence. Our results support that thermal transient receptor potential channels contain modular thermal sensors that confer the unprecedentedly strong temperature dependence to these channels.
Autotaxin (ATX, also known as ectonucleotide pyrophosphatase/phosphodiesterase-2, ENPP2) is a secreted lysophospholipase D that generates the lipid mediator lysophosphatidic acid (LPA), a mitogen and chemoattractant for many cell types. ATX-LPA signaling is involved in various pathologies including tumor progression and inflammation. However, the molecular basis of substrate recognition and catalysis by ATX and the mechanism by which it interacts with target cells are unclear. Here, we present the crystal structure of ATX, alone and in complex with a small-molecule inhibitor. We have identified a hydrophobic lipid-binding pocket and mapped key residues for catalysis and selection between nucleotide and phospholipid substrates. We have shown that ATX interacts with cell-surface integrins through its N-terminal somatomedin B-like domains, using an atypical mechanism. Our results define determinants of substrate discrimination by the ENPP family, suggest how ATX promotes localized LPA signaling and suggest new approaches for targeting ATX with small-molecule therapeutic agents.
Although a large number of ion channels are now believed to be regulated by phosphoinositides, particularly phosphoinositide 4,5-bisphosphate (PIP2), the mechanisms involved in phosphoinositide regulation are unclear. For the TRP superfamily of ion channels, the role and mechanism of PIP2 modulation has been especially difficult to resolve. Outstanding questions include: is PIP2 the endogenous regulatory lipid; does PIP2 potentiate all TRPs or are some TRPs inhibited by PIP2; where does PIP2 interact with TRP channels; and is the mechanism of modulation conserved among disparate subfamilies? We first addressed whether the PIP2 sensor resides within the primary sequence of the channel itself, or, as recently proposed, within an accessory integral membrane protein called Pirt. Here we show that Pirt does not alter the phosphoinositide sensitivity of TRPV1 in HEK-293 cells, that there is no FRET between TRPV1 and Pirt, and that dissociated dorsal root ganglion neurons from Pirt knock-out mice have an apparent affinity for PIP2 indistinguishable from that of their wild-type littermates. We followed by focusing on the role of the C terminus of TRPV1 in sensing PIP2. Here, we show that the distal C-terminal region is not required for PIP2 regulation, as PIP2 activation remains intact in channels in which the distal C-terminal has been truncated. Furthermore, we used a novel in vitro binding assay to demonstrate that the proximal C-terminal region of TRPV1 is sufficient for PIP2 binding. Together, our data suggest that the proximal C-terminal region of TRPV1 can interact directly with PIP2 and may play a key role in PIP2 regulation of the channel.
It has been demonstrated that lysophosphatidic acid (LPA) released from injury tissue and transient receptor potential vanilloid 1 (TRPV1) receptor are implicated in the induction of chronic pain. In the present study we examined whether an interaction between LPA receptor LPA(1) and TRPV1 in dorsal root ganglion (DRG) neurons contributes to the development of bone cancer pain.
Bone cancer was established by injection of mammary gland carcinoma cells into the rat tibia. Following the development of bone cancer pain, the TRPV1 expression and capsaicin-evoked currents were up-regulated in rat DRG neurons at L(4-6) segments. Immunohistochemistry staining revealed a high co-localization of LPA(1) with TRPV1 in DRG neurons. In isolated DRG neurons, whole-cell patch recording showed that capsaicin-induced currents were potentiated by LPA in a dose-dependent manner. The potentiation was blocked by either LPA(1) antagonist, protein kinase C (PKC) inhibitor or PKCε inhibitor, but not by protein kinase A (PKA) inhibitor or Rho inhibitor. In the behavioral tests, both mechanical allodynia and thermal hyperalgesia in bone cancer rats were attenuated by LPA(1) antagonist.
LPA potentiates TRPV1 current via a PKCε-dependent pathway in DRG neurons of rats with bone cancer, which may be a novel peripheral mechanism underlying the induction of bone cancer pain.
Lysophospholipids are cell membrane-derived lipids that include both glycerophospholipids such as lysophosphatidic acid (LPA) and sphingoid lipids such as sphingosine 1-phosphate (S1P). These and related molecules can function in vertebrates as extracellular signals by binding and activating G protein-coupled receptors. There are currently five LPA receptors, along with a proposed sixth (LPA₁-LPA₆), and five S1P receptors (S1P₁-S1P₅). A remarkably diverse biology and pathophysiology has emerged since the last review, driven by cloned receptors and targeted gene deletion ("knockout") studies in mice, which implicate receptor-mediated lysophospholipid signaling in most organ systems and multiple disease processes. The entry of various lysophospholipid receptor modulatory compounds into humans through clinical trials is ongoing and may lead to new medicines that are based on this signaling system. This review incorporates IUPHAR Nomenclature Committee guidelines in updating the nomenclature for lysophospholipid receptors ( http://www.iuphar-db.org/DATABASE/FamilyMenuForward?familyId=36).
The activity and intracellular localization of protein kinase C (PKC) family members are controlled by phosphorylation at three highly conserved sites in the catalytic kinase domain, In the case of the novel PKCepsilon isoform, these are Thr(566) in the activation loop. Thr(710) in the turn motif and Ser(729) in the C-terminal hydrophobic motif. In the present study. we analysed the contribution of the phosphoinositide-dependent kinase 1 (PDK-1) and PKCepsilon kinase activity in controlling the phosphorylation of Thr(566) and Ser(729). In NIH 3T3 fibroblasts, PKCepsilon migrated as a single band, and stimulation with platelet-derived growth factor resulted in the appearance of a second band with a slower electrophoretic mobility, concomitant with an increase in phosphorylation of Thr(566) and Ser(729). Cells transfected with an active PDK-1 allele also resulted in increased PKCepsilon Thr(566) and Ser(729) phosphorylation. whereas an active myristoylated PKCepsilon mutant was constitutively phosphorylated at these sites. Protein kinase-inactive mutants of PKCepsilon were not phosphorylated at Ser(729) in cells, and phosphorylation of this site leads to dephosphorylation of the activation-loop Thr(566), an effect which can be reversed with either okadaic acid or co-transfection with active PDK-1. In vitro, PDK-1 catalysed the phosphorylation of purified PKCepsilon in the presence of mixed micelles containing either diacylglycerol or PtdIns(3,4,5)P-3, concomitant with an increase in Ser(729) phosphorylation. These studies reveal that the mechanism of phosphorylation of a novel PKC is the same as that for conventional PKCs: PDK-1 phosphorylation of the activation loop triggers autophosphorylation of the hydrophobic motif. However, the regulation of this phosphorylation is different for novel and conventional PKCs. Specifically, the phosphorylation of novel PKCs is regulated rather than constitutive.
The nociception by intraplantar (i.pl.) lysophosphatidic acid (LPA) injection was significantly, but partially blocked when mice received intrathecal (i.t.) antisense oligodeoxynucleotide treatment for the vzg-1 type LPA-receptor. The residual LPA-nociception observed under the condition of pertussis toxin-treatment, which is expected to block presynaptic contribution, was abolished by diphenhydramine (i.pl.), an H1-type histamine receptor antagonist. Taking into account that vzg-1 mRNA was detected in the dorsal root ganglion by RT-PCR method, these findings suggest that the LPA-induced nociception is attributed to the mechanism through vzg-1 receptor on nociceptor endings, and to that through unidentified LPA-receptor on peripheral, possibly mast cells.
Autotaxin (ATX, also known as Enpp2) is a secreted lysophospholipase D that hydrolyzes lysophosphatidylcholine to generate lysophosphatidic acid (LPA), a lipid mediator that activates G protein-coupled receptors to evoke various cellular responses. Here, we report the crystal structures of mouse ATX alone and in complex with LPAs with different acyl-chain lengths and saturations. These structures reveal that the multidomain architecture helps to maintain the structural rigidity of the lipid-binding pocket, which accommodates the respective LPA molecules in distinct conformations. They indicate that a loop region in the catalytic domain is a major determinant for the substrate specificity of the Enpp family enzymes. Furthermore, along with biochemical and biological data, these structures suggest that the produced LPAs are delivered from the active site to cognate G protein-coupled receptors through a hydrophobic channel.
J. Neurochem. (2010) 115, 643–653.
We recently demonstrated that de novo lysophosphatidic acid (LPA) production in the spinal cord occurs in the early phase after nerve injury or LPA injection, and underlies the peripheral mechanisms of neuropathic pain. In this study, we examined the possible involvement of spinal cord microglia in such LPA-mediated functions. Intrathecal LPA injection rapidly increased the gene expression of CD11b and protein expression of phosphor-p38, accompanied by a morphological change of microglia from a ramified to amoeboid shape. Although early treatment with minocycline significantly inhibited LPA-induced neuropathic pain-like behavior and microglial activation, late treatment did not. Early treatment with minocycline also blocked LPA-evoked de novo LPA production and the increased activation of cytosolic phospholipase A2, an LPA synthesis-related enzyme. Similar results were observed when the sciatic nerve was partially injured: early, but not late, treatment with minocycline significantly inhibited the injury-induced neuropathic pain, microglial activation, de novo LPA production and the underlying increased activation of cytosolic phospholipase A2 as well as calcium-independent phospholipase A2, another LPA synthesis-related enzyme. These findings suggest that the early phase of microglial activation is involved in de novo LPA production, and that this underlies the initial mechanisms of nerve injury-induced neuropathic pain.