AIBP Regulates TRPV1 Activation in Chemotherapy-Induced Peripheral Neuropathy by Controlling Lipid Raft Dynamics and Proximity to TLR4 in Dorsal Root Ganglion Neurons

Nociceptive afferent signaling evoked by inflammation and nerve injury is mediated by the opening of ligand-gated and voltage-gated receptors or channels localized to cholesterol-rich lipid raft membrane domains. Dorsal root ganglion (DRG) nociceptors express high levels of toll-like receptor 4 (TLR4), which also localize to lipid rafts. Genetic deletion or pharmacologic blocking of TLR4 diminishes pain associated with chemotherapy-induced peripheral neuropathy (CIPN). In DRGs of mice with paclitaxel-induced CIPN, we analyzed DRG neuronal lipid rafts, expression of TLR4, activation of transient receptor potential cation channel subfamily V member 1 (TRPV1), and TLR4-TRPV1 interaction. Using proximity ligation assay, flow cytometry, and whole-mount DRG microscopy, we found that CIPN increased DRG neuronal lipid rafts and TLR4 expression. These effects were reversed by intrathecal injection of apolipoprotein A-I binding protein (AIBP), a protein that binds to TLR4 and specifically targets cholesterol depletion from TLR4-expressing cells. Chemotherapy-induced peripheral neuropathy increased TRPV1 phosphorylation, localization to neuronal lipid rafts, and proximity to TLR4. These effects were also reversed by AIBP treatment. Regulation of TRPV1-TLR4 interactions and their associated lipid rafts by AIBP covaried with the enduring reversal of mechanical allodynia otherwise observed in CIPN. In addition, AIBP reduced intracellular calcium in response to the TRPV1 agonist capsaicin, which was increased in DRG neurons from paclitaxel-treated mice and in the naïve mouse DRG neurons incubated in vitro with paclitaxel. Together, these results suggest that the assembly of nociceptive and inflammatory receptors in the environment of lipid rafts regulates nociceptive signaling in DRG neurons and that AIBP can control lipid raft-associated nociceptive processing

ApoA-I binding protein (AIBP) decreases mechanical hypersensitivity after plantar incision in a rat model of post-operative pain

https://openworks.mdanderson.org/sumexp22/1090/thumbnail.jp

Lipid rafts in glial cells: role in neuroinflammation and pain processing Thematic Review Series: Biology of Lipid Rafts

Activation of microglia and astrocytes secondary to inflammatory processes contributes to the development and perpetuation of pain with a neuropathic phenotype. This pain state presents as a chronic debilitating condition and affects a large population of patients with conditions like rheumatoid arthritis and diabetes, or after surgery, trauma, or chemotherapy. Here, we review the regulation of lipid rafts in glial cells and the role they play as a key component of neuroinflammatory sensitization of central pain signaling pathways. In this context, we introduce the concept of an inflammaraft (i-raft), enlarged lipid rafts harboring activated receptors and adaptor molecules and serving as an organizing platform to initiate inflammatory signaling and the cellular response. Characteristics of the inflammaraft include increased relative abundance of lipid rafts in inflammatory cells, increased content of cholesterol per raft, and increased levels of inflammatory receptors, such as toll-like receptor (TLR)4, adaptor molecules, ion channels, and enzymes in lipid rafts. This inflammaraft motif serves an important role in the membrane assembly of protein complexes, for example, TLR4 dimerization. Operating within this framework, we demonstrate the involvement of inflammatory receptors, redox molecules, and ion channels in the inflammaraft formation and the regulation of cholesterol and sphingolipid metabolism in the inflammaraft maintenance and disruption. Strategies for targeting inflammarafts, without affecting the integrity of lipid rafts in noninflammatory cells, may lead to developing novel therapies for neuropathic pain states and other neuroinflammatory conditions

Role of ERK1/2 activation and nNOS uncoupling on endothelial dysfunction induced by lysophosphatidylcholine

Background and aims: Lysophosphatidylcholine (LPC) - a main component of oxidized LDL -is involved in endothelial dysfunction that precedes atherosclerosis, with an increased superoxide anions and a reduced NO production via endothelial NO synthase (eNOS) uncoupling. However, there is no evidence about the mechanisms involved in neuronal NOS (nNOS) uncoupling. Extracellular signal-regulated kinase (ERK) is related to the control of NO production and inflammatory gene transcription activation in atherosclerosis. Our aim was to investigate the role of nNOS/ERK1/2 pathway on endothelial dysfunction induced by LPC, in mouse aorta and human endothelial cells. Methods: Thoracic aorta from wild type mice was used to perform vascular reactivity studies in the presence or absence of LPC. Human endothelial cells were used to investigate the effect of LPC on expression of nNOS and his products NO and H2O2. Results: LPC reduced acetylcholine (ACh)-induced vasodilation in mouse aorta (Emax(CT/LPC) = similar to 95 +/- 2/ 62 +/- 3%, p = 0.0004) and increased phenylephrine-induced vasoconstriction (Emax(CT/LPC) = similar to 4 +/- 0,1/ 6 +/- 0,1 mN/mm, p = 0.0002), with a reduction in NO (fluorescence intensity(CT/LPC) = 91 +/- 3/62 +/- 2 x 10(3), p = 0.0002) and H2O2 (fluorescence intensityCT/LPC = similar to 16 +/- 0,8/10 +/- 0,7 x 10(3), p = 0.0041) production evocated by ACh. An inhibition of nNOS by TRIM (Emax(CT/CT+TRIM) = similar to 93 +/- 1/43 +/- 3%, p = 0,0048; Emax(LPC/LPC+TRIM) = similar to 62 +/- 3/65 +/- 3%) or H2O2 degradation by catalase (Emax(CT/CT+cat) = similar to 93 +/- 1/46 +/- 2%, p < 0,001; Emax(LPC/LPC+cat) = similar to 62,8 +/- 3,2/60,5 +/- 4,7%) reduced the relaxation in the control but not in LPC group. PD98059, an ERK1/2 inhibitor, abolished the increase in vasoconstriction in LPC-treated vessels (Emax(LPC/LPC+PD) = similar to 6 +/- 0,1/3 +/- 0,1 mN/mm, p = 0.0001). LPC also reduced the dimer/monomer proportion and increased nNOS(ser852) phosphorylation. Conclusions: LPC induced nNOS uncoupling and nNOS(Ser852) phosphorylation, reduced NO and H2O2 production and improved superoxide production by modulating ERK1/2 activity in human and murine endothelial cells. (C) 2016 Elsevier Ireland Ltd. All rights reserved

Normalization of cholesterol metabolism in spinal microglia alleviates neuropathic pain.

Neuroinflammation is a major component in the transition to and perpetuation of neuropathic pain states. Spinal neuroinflammation involves activation of TLR4, localized to enlarged, cholesterol-enriched lipid rafts, designated here as inflammarafts. Conditional deletion of cholesterol transporters ABCA1 and ABCG1 in microglia, leading to inflammaraft formation, induced tactile allodynia in naive mice. The apoA-I binding protein (AIBP) facilitated cholesterol depletion from inflammarafts and reversed neuropathic pain in a model of chemotherapy-induced peripheral neuropathy (CIPN) in wild-type mice, but AIBP failed to reverse allodynia in mice with ABCA1/ABCG1-deficient microglia, suggesting a cholesterol-dependent mechanism. An AIBP mutant lacking the TLR4-binding domain did not bind microglia or reverse CIPN allodynia. The long-lasting therapeutic effect of a single AIBP dose in CIPN was associated with anti-inflammatory and cholesterol metabolism reprogramming and reduced accumulation of lipid droplets in microglia. These results suggest a cholesterol-driven mechanism of regulation of neuropathic pain by controlling the TLR4 inflammarafts and gene expression program in microglia and blocking the perpetuation of neuroinflammation