ABSTRACT
OBJECTIVE: Aiming to delineate novel neuro-immune mechanisms for NGF/TrkA signalling in osteoarthritis (OA) pain, we evaluated inflammatory changes in the knee joints following injection of monoiodoacetate (MIA) in mice carrying a TrkA receptor mutation (P782S; TrkA KI mice). METHOD: In behavioural studies we monitored mechanical hypersensitivity following intra-articular MIA and oral prostaglandin D2 (PGD2) synthase inhibitor treatments. In immunohistochemical studies we quantified joint mast cell numbers, calcitonin gene-related peptide expression in synovia and dorsal root ganglia, spinal cord neuron activation and microgliosis. We quantified joint leukocyte infiltration by flow cytometry analysis, and PGD2 generation and cyclooxygenase-2 (COX-2) expression in mast cell lines by ELISA and Western blot. RESULTS: In TrkA KI mice we observed rapid development of mechanical hypersensitivity and amplification of dorsal horn neurons and microglia activation 7 days after MIA. In TrkA KI knee joints we detected significant leukocyte infiltration and mast cells located in the vicinity of synovial nociceptive fibres. We demonstrated that mast cells exposure to NGF results in up-regulation of COX-2 and increase of PGD2 production. Finally, we observed that a PGD2 synthase inhibitor prevented MIA-mechanical hypersensitivity in TrkA KI, at doses which were ineffective in wild type (WT) mice. CONCLUSION: Using the TrkA KI mouse model, we delineated a novel neuro-immune pathway and suggest that NGF-induced production of PGD2 in joint mast cells is critical for referred mechanical hypersensitivity in OA, probably through the activation of PGD2 receptor 1 in nociceptors: TrkA blockade in mast cells constitutes a potential target for OA pain.
Subject(s)
Osteoarthritis, Knee/etiology , Receptor, trkA/metabolism , Animals , Arthritis, Experimental/etiology , Arthritis, Experimental/physiopathology , Cartilage Diseases/pathology , Cartilage, Articular/drug effects , Cyclooxygenase 2/metabolism , Disease Models, Animal , Dose-Response Relationship, Drug , Drug Evaluation, Preclinical , Enzyme Inhibitors/administration & dosage , Enzyme Inhibitors/toxicity , Female , Injections, Intra-Articular , Intramolecular Oxidoreductases/antagonists & inhibitors , Iodoacetic Acid/administration & dosage , Iodoacetic Acid/toxicity , Lipocalins/antagonists & inhibitors , Macrophages/drug effects , Male , Mast Cells/drug effects , Mice, Inbred C57BL , Osteoarthritis, Knee/physiopathology , Prostaglandin D2/biosynthesis , Receptor, trkA/antagonists & inhibitors , Receptor, trkA/genetics , Stifle/metabolism , T-Lymphocytes/drug effects , Up-Regulation/physiologyABSTRACT
It has been suggested a role of fatty acid ethanolamides in control of feeding behavior. Among these, palmitoylethanolamide (PEA) has not been directly implicated in appetite regulation and weight gain. The aim of this study was to investigate the effect of PEA on food intake and body weight and the interaction between PEA and hypothalamic leptin signaling in ovariectomized rats. Ovariectomy produced hyperphagia and increased weight gain, making it an useful model of mild obesity. Ovariectomized rats were treated with PEA (30 mg/kg sc) for 5 weeks. Then, blood was collected, and hypothalamus and adipose tissue were removed for histological, cellular, and molecular measurements. We showed that PEA caused a reduction of food intake, body weight, and fat mass. The mechanisms underlying PEA effects involved an improvement in hypothalamic leptin signaling, through a raise in signal transducer and activator of transcription 3 phosphorylation. We also reported that PEA reduced AMP-activated protein kinase-α phosphorylation and modulated transcription of anorectic and orexigenic neuropeptides in the hypothalamus. Moreover, PEA increased AMP-activated protein kinase-α phosphorylation and carnitine palmitoyltransferase 1 transcription in adipose tissue, suggesting an increase in ATP-producing catabolic pathway. PEA also polarized adipose tissue macrophages to M2 lean phenotype, associated to a reduction of inflammatory cytokines/adipokines. To demonstrate the direct effect of PEA on leptin sensitivity without interference of adiposity loss, we obtained consistent data in PEA-treated sham-operated animals and in vitro in SH-SY5Y neuroblastoma cell line. Therefore, our data provide a rationale for the therapeutic use of PEA in obese postmenopausal woman.
Subject(s)
Eating/drug effects , Endocannabinoids/chemistry , Ethanolamines/chemistry , Leptin/metabolism , Obesity/metabolism , Palmitic Acids/chemistry , Adenosine Triphosphate/chemistry , Adipokines/metabolism , Amides/chemistry , Animals , Anti-Inflammatory Agents, Non-Steroidal/chemistry , Body Weight , Cell Line, Tumor , Cytokines/metabolism , Ethanol/chemistry , Fatty Acids/chemistry , Feeding Behavior , Female , Glucose Tolerance Test , Humans , Ovariectomy , Phosphorylation , Rats , Rats, Wistar , Signal Transduction , Weight GainABSTRACT
Non-dioxin-like polychlorinated biphenyls (PCBs) are stable and lipophilic chemicals that persist in the environment and tend to bioaccumulate in the food chains. In the present study, we have investigated the effect of PCBs 101, 153, and 180 on macrophage J774A.1 by assessing cell viability and apoptotic cell death. We have combined morphological techniques and biochemical ones to establish the relevance of apoptosis in macrophage cell death induced by PCBs, alone or in combination. Treatment with the examined PCBs caused the loss of cell viability and accelerated apoptosis in a concentration-dependent manner. Moreover, a synergistic effect on cell death and apoptosis was evidenced for all PCBs at concentrations which were inactive alone. The apoptosis induced by PCBs involved the increase of caspase-3 activity. Also, Bcl-2 and Bax proteins were assessed to elucidate the apoptosis machinery induced in macrophage cultures by PCBs. Our results indicate that the increase in PCB-induced apoptosis correlates with a reduction in the expression of antiapoptotic Bcl-2 and an increase in the expression of proapoptotic Bax. Interestingly, concentrations of PCBs inactive by themselves induce apoptosis when PCBs are combined. In conclusion, our findings suggest that, although less toxic than dioxin like congeners, the examined non-dioxin-like PCBs are equally dangerous as immunotoxic pollutants, also considering their presence as mixtures at higher levels than dioxin-like PCBs in biotic and abiotic matrices.
