CXCL12/CXCR4 Signaling Contributes to the Pathogenesis of Opioid Tolerance: A Translational Study.

BACKGROUND: Long-term opioid therapy for chronic pain may lead to analgesic tolerance, especially when administered intrathecally, thus preventing adequate pain relief. Discovering drug targets to treat opioid tolerance using a mechanism-based approach targeting opioid-induced neuroinflammation provides new therapeutic opportunities. In this study, we provide translational evidence that CXCL12/CXCR4 signaling contributes to the pathogenesis of opioid tolerance. METHODS: The CXCL12 levels in the cerebrospinal fluid of opioid-tolerant patients were compared with those of opioid-naive subjects. For further investigation, a rodent translational study was designed using 2 clinically relevant opioid delivery paradigms: daily intraperitoneal morphine injections and continuous intrathecal morphine infusion. We measured rats' tail flick responses and calculated the percentage of maximum possible effects (%MPE) to demonstrate opioid acute antinociception and the development of analgesic tolerance. The effects of exogenous CXCL12, CXCL12 neutralizing antibody, and receptor antagonist AMD3100 were investigated by intrathecal administration. Data were presented as mean ± SEM. RESULTS: CXCL12 was significantly upregulated in the cerebrospinal fluid of opioid-tolerant patients for 892 ± 34 pg/mL (n = 27) versus 755 ± 33 pg/mL (n = 10) in naive control subjects (P = .03). Furthermore, after 2 and 5 days of intrathecal morphine infusion, rat lumbar spinal cord dorsal horn CXCL12 messenger RNA levels were significantly upregulated by 3.2 ± 0.7 (P = .016) and 3.4 ± 0.3 (P = .003) fold, respectively. Results from the daily intraperitoneal morphine injection experiments revealed that administering an intrathecal infusion of CXCL12 for 24 hours before the first morphine injection did not decrease antinociception efficacy on day 1 but accelerated tolerance after day 2 (%MPE 49.5% vs 88.1%, P = .0003). In the intrathecal morphine coinfusion experiments, CXCL12 accelerated tolerance development (%MPE 9.4% vs 43.4% on day 1, P < .0001), whereas coadministration with CXCL12 neutralizing antibody attenuated tolerance (72.5% vs 43.4% on day 1, P < .0001; 47.6% vs 17.5% on day 2, P < .0001). Coadministration of receptor antagonist AMD 3100 can persistently preserve morphine analgesic effects throughout the study period (27.9% ± 4.1% vs 0.9% ± 1.6% on day 5, P = .03). CONCLUSIONS: The CXCL12/CXCR4 pathway contributes to the pathogenesis of opioid tolerance. Our study indicates that intervening with CXCL12/CXCR4 signaling has therapeutic potential for opioid tolerance.

Role of spinal CXCL1 (GROα) in opioid tolerance: a human-to-rodent translational study.

BACKGROUND: The pivotal role of glial activation and up-regulated inflammatory mediators in the opioid tolerance has been confirmed in rodents but not yet in humans. Here, the authors investigated the intraspinal cytokine and chemokine profiles of opioid-tolerant cancer patients; and to determine if up-regulated chemokines could modify opioid tolerance in rats. METHODS: Cerebrospinal fluid samples from opioid-tolerant cancer patients and opioid-naive subjects were compared. The cerebrospinal fluid levels of tumor necrosis factor-alpha, CXCL1, CXCL10, CCL2, and CX3CL1 were assayed. The rat tail flick test was utilized to assess the effects of intrathecal CXCL1 on morphine-induced acute antinociception and analgesic tolerance. RESULTS: CXCL1 level in cerebrospinal fluid was significantly up-regulated in the opioid-tolerant group (n = 30, 18.8 pg/ml vs. 13.2 pg/ml, P = 0.02) and was positively correlated (r = 0.49, P < 0.01) with opioid dosage. In rat experiment, after induction of tolerance by morphine infusion, the spinal cord CXCL1 messenger RNA was up-regulated to 32.5 ± 11.9-fold. Although CXCL1 infusion alone did not affect baseline tail-flick latency, the analgesic efficacy of a single intraperitoneal injection of morphine dropped significantly on day 1 to day 3 after intrathecal infusion of CXCL1. After establishing tolerance by intrathecal continuous infusion of morphine, its development was accelerated by coadministration of CXCL1 and attenuated by coadministration of CXCL1-neutralizing antibody or CXCR2 antagonist. CONCLUSIONS: CXCL1 is up-regulated in both opioid-tolerant patients and rodents. The onset and extent of opioid tolerance was affected by antagonizing intrathecal CXCL1/CXCR2 signaling. Therefore, the CXCL1/CXCR2 signal pathway may be a novel target for the treatment of opioid tolerance.

Involvement of 15-lipoxygenase in the inflammatory arthritis.

15-Lipoxygenase (15-LOX) is involved in many pathological processes. The aim of this study is to examine the role of 15-LOX in the matrix metalloproteinase (MMP) expression and inflammatory arthritis. It was found that treatment of 15-LOX downstream product of 15-(S)-HETE (15-S-hydroxyeicosatetraenoic acid) increased the mRNA and protein levels of MMP-2 in rheumatoid arthritis synovial fibroblast (RASF) derived from rheumatoid arthritis patients. The enhancement effect of 15-(S)-HETE was antagonized by the addition of LY294002 (PI3K inhibitor) and PDTC (NF-κB inhibitor). Treatment of 15-(S)-HETE increased the phosphorylation of AKT, nuclear translocation of p65 and the breakdown of IκBα. TNF-α and IL-1ß are the key cytokines involved in arthritis and also increase the activity of MMP-2 in RASF, which was antagonized by pretreatment with 15-LOX inhibitor PD146176 or knockdown of 15-LOX. It was also found that these two cytokines increased the expression of 15-LOX in RASF. Treatment of glucocorticoid but not NSAIDs inhibited 15-(S)-HETE-induced expression of MMP-2. In comparison with wild-type mice, adjuvant-induced arthritis and MMP-2 expression in synovial membrane were markedly inhibited in 15-LOX knockout (KO) mice. These results indicate that 15-LOX plays an important role in the disease progression of arthritis and may be involved in the inflammatory action induced by TNF-α and IL-1ß. 15-LOX is thus a good target for developing drugs in the treatment of inflammatory arthritis.

Transcriptomic, Protein-DNA Interaction, and Metabolomic Studies of VosA, VelB, and WetA in Aspergillus nidulans Asexual Spores.

In filamentous fungi, asexual development involves cellular differentiation and metabolic remodeling leading to the formation of intact asexual spores. The development of asexual spores (conidia) in Aspergillus is precisely coordinated by multiple transcription factors (TFs), including VosA, VelB, and WetA. Notably, these three TFs are essential for the structural and metabolic integrity, i.e., proper maturation, of conidia in the model fungus Aspergillus nidulans To gain mechanistic insight into the complex regulatory and interdependent roles of these TFs in asexual sporogenesis, we carried out multi-omics studies on the transcriptome, protein-DNA interactions, and primary and secondary metabolism employing A. nidulans conidia. RNA sequencing and chromatin immunoprecipitation sequencing analyses have revealed that the three TFs directly or indirectly regulate the expression of genes associated with heterotrimeric G-protein signal transduction, mitogen-activated protein (MAP) kinases, spore wall formation and structural integrity, asexual development, and primary/secondary metabolism. In addition, metabolomics analyses of wild-type and individual mutant conidia indicate that these three TFs regulate a diverse array of primary metabolites, including those in the tricarboxylic acid (TCA) cycle, certain amino acids, and trehalose, and secondary metabolites such as sterigmatocystin, emericellamide, austinol, and dehydroaustinol. In summary, WetA, VosA, and VelB play interdependent, overlapping, and distinct roles in governing morphological development and primary/secondary metabolic remodeling in Aspergillus conidia, leading to the production of vital conidia suitable for fungal proliferation and dissemination.IMPORTANCE Filamentous fungi produce a vast number of asexual spores that act as efficient propagules. Due to their infectious and/or allergenic nature, fungal spores affect our daily life. Aspergillus species produce asexual spores called conidia; their formation involves morphological development and metabolic changes, and the associated regulatory systems are coordinated by multiple transcription factors (TFs). To understand the underlying global regulatory programs and cellular outcomes associated with conidium formation, genomic and metabolomic analyses were performed in the model fungus Aspergillus nidulans Our results show that the fungus-specific WetA/VosA/VelB TFs govern the coordination of morphological and chemical developments during sporogenesis. The results of this study provide insights into the interdependent, overlapping, or distinct genetic regulatory networks necessary to produce intact asexual spores. The findings are relevant for other Aspergillus species such as the major human pathogen Aspergillus fumigatus and the aflatoxin producer Aspergillus flavus.

Cytochrome P450 Monooxygenase-Mediated Metabolic Utilization of Benzo[a]Pyrene by Aspergillus Species.

Soil-dwelling fungal species possess the versatile metabolic capability to degrade complex organic compounds that are toxic to humans, yet the mechanisms they employ remain largely unknown. Benzo[a]pyrene (BaP) is a pervasive carcinogenic contaminant, posing a significant concern for human health. Here, we report that several Aspergillus species are capable of degrading BaP. Exposing Aspergillus nidulans cells to BaP results in transcriptomic and metabolic changes associated with cellular growth and energy generation, implying that the fungus utilizes BaP as a growth substrate. Importantly, we identify and characterize the conserved bapA gene encoding a cytochrome P450 monooxygenase that is necessary for the metabolic utilization of BaP in Aspergillus We further demonstrate that the fungal NF-κB-type velvet regulators VeA and VelB are required for proper expression of bapA in response to nutrient limitation and BaP degradation in A. nidulans Our study illuminates fundamental knowledge of fungal BaP metabolism and provides novel insights into enhancing bioremediation potential.IMPORTANCE We are increasingly exposed to environmental pollutants, including the carcinogen benzo[a]pyrene (BaP), which has prompted extensive research into human metabolism of toxicants. However, little is known about metabolic mechanisms employed by fungi that are able to use some toxic pollutants as the substrates for growth, leaving innocuous by-products. This study systemically demonstrates that a common soil-dwelling fungus is able to use benzo[a]pyrene as food, which results in expression and metabolic changes associated with growth and energy generation. Importantly, this study reveals key components of the metabolic utilization of BaP, notably a cytochrome P450 monooxygenase and the fungal NF-κB-type transcriptional regulators. Our study advances fundamental knowledge of fungal BaP metabolism and provides novel insight into designing and implementing enhanced bioremediation strategies.

Regulation of the maturation of osteoblasts and osteoclastogenesis by glutamate.

Glutamate, an important central excitatory neurotransmitter, is also secreted by osteoblasts and may be involved in the regulation of bone metabolism. Glutamate receptors for N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) are demonstrated in bone cells. Here we investigated the in vivo effects of glutamate by local injection of AMPA, NMDA, and their antagonists into tibia as well as their in vitro effects on the maturation of osteoblasts and formation of osteoclasts. AMPA receptor antagonist CNQX and NMDA receptor antagonist MK-801 significantly inhibited the maturation and mineralization of osteoblasts in high-glutamate alpha-MEM. On the other hand, AMPA and NMDA up-regulated the mineralized deposition and osteocalcin mRNA expression of primary osteoblasts cultured in glutamate-free DMEM. AMPA and NMDA induced the phosphorylation of extracellular signal-related kinases (ERK) in osteoblasts within 15 min. In addition, NMDA but not AMPA up-regulated the number of osteoclasts while MK801 antagonized this potentiating effect. To explore the action of glutamate agonists on bone formation in animal model, AMPA was locally injected into tibia and it was found that the bone volume in secondary spongiosa significantly increased and co-treatment of CNQX antagonized the enhancing effect of AMPA. These results suggest that glutamate may play a physiological role in regulating the maturation of osteoblasts and osteoclastogenesis. Activation of both AMPA and NMDA receptors regulates the maturation of osteoblasts. NMDA but not AMPA affects receptor for activation of NF-kappaB ligand (RANKL)-induced osteoclastogenesis.

Systematic Dissection of the Evolutionarily Conserved WetA Developmental Regulator across a Genus of Filamentous Fungi.

Asexual sporulation is fundamental to the ecology and lifestyle of filamentous fungi and can facilitate both plant and human infection. In Aspergillus, the production of asexual spores is primarily governed by the BrlA→AbaA→WetA regulatory cascade. The final step in this cascade is controlled by the WetA protein and governs not only the morphological differentiation of spores but also the production and deposition of diverse metabolites into spores. While WetA is conserved across the genus Aspergillus, the structure and degree of conservation of the wetA gene regulatory network (GRN) remain largely unknown. We carried out comparative transcriptome analyses of comparisons between wetA null mutant and wild-type asexual spores in three representative species spanning the diversity of the genus Aspergillus: A. nidulans, A. flavus, and A. fumigatus We discovered that WetA regulates asexual sporulation in all three species via a negative-feedback loop that represses BrlA, the cascade's first step. Furthermore, data from chromatin immunoprecipitation sequencing (ChIP-seq) experiments in A. nidulans asexual spores suggest that WetA is a DNA-binding protein that interacts with a novel regulatory motif. Several global regulators known to bridge spore production and the production of secondary metabolites show species-specific regulatory patterns in our data. These results suggest that the BrlA→AbaA→WetA cascade's regulatory role in cellular and chemical asexual spore development is functionally conserved but that the wetA-associated GRN has diverged during Aspergillus evolution.IMPORTANCE The formation of resilient spores is a key factor contributing to the survival and fitness of many microorganisms, including fungi. In the fungal genus Aspergillus, spore formation is controlled by a complex gene regulatory network that also impacts a variety of other processes, including secondary metabolism. To gain mechanistic insights into how fungal spore formation is controlled across Aspergillus, we dissected the gene regulatory network downstream of a major regulator of spore maturation (WetA) in three species that span the diversity of the genus: the genetic model A. nidulans, the human pathogen A. fumigatus, and the aflatoxin producer A. flavus Our data show that WetA regulates asexual sporulation in all three species via a negative-feedback loop and likely binds a novel regulatory element that we term the WetA response element (WRE). These results shed light on how gene regulatory networks in microorganisms control important biological processes and evolve across diverse species.

WetA bridges cellular and chemical development in Aspergillus flavus.

Bridging cellular reproduction and survival is essential for all life forms. Aspergillus fungi primarily reproduce by forming asexual spores called conidia, whose formation and maturation is governed by the central genetic regulatory circuit BrlA→AbaA→WetA. Here, we report that WetA is a multi-functional regulator that couples spore differentiation and survival, and governs proper chemical development in Aspergillus flavus. The deletion of wetA results in the formation of conidia with defective cell walls and no intra-cellular trehalose, leading to reduced stress tolerance, a rapid loss of viability, and disintegration of spores. WetA is also required for normal vegetative growth, hyphal branching, and production of aflatoxins. Targeted and genome-wide expression analyses reveal that WetA exerts feedback control of brlA and that 5,700 genes show altered mRNA levels in the mutant conidia. Functional category analyses of differentially expressed genes in ΔwetA RNA-seq data indicate that WetA contributes to spore integrity and maturity by properly regulating the metabolic pathways of trehalose, chitin, α-(1,3)-glucan, ß-(1,3)-glucan, melanin, hydrophobins, and secondary metabolism more generally. Moreover, 160 genes predicted to encode transcription factors are differentially expressed by the absence of wetA, suggesting that WetA may play a global regulatory role in conidial development. Collectively, we present a comprehensive model for developmental control that bridges spore differentiation and survival in A. flavus.

5-Lipoxygenase inhibitors attenuate TNF-α-induced inflammation in human synovial fibroblasts.

The lipoxygenase isoform of 5-lipoxygenase (5-LOX) is reported to be overexpressed in human rheumatoid arthritis synovial tissue and involved in the progress of inflammatory arthritis. However, the detailed mechanism of how 5-lipoxygenase regulates the inflammatory response in arthritis synovial tissue is still unclear. The aim of this study was to investigate the involvement of lipoxygenase pathways in TNF-α-induced production of cytokines and chemokines. Human synovial fibroblasts from rheumatoid patients were used in this study. 5-LOX inhibitors and shRNA were used to examine the involvement of 5-LOX in TNF-α-induced cytokines and chemokines expression. The signaling pathways were examined by Western Blotting or immunofluorescence staining. The effect of 5-LOX inhibitor on TNF-α-induced chemokine expression and paw edema was also explored in vivo in C57BL/6 mice. Treatment with 5-LOX inhibitors significantly decreased TNF-α-induced pro-inflammatory mediators including interleukin-6 (IL-6) and monocyte chemo-attractant protein-1 (MCP-1) in human synovial fibroblasts. Knockdown of 5-LOX using shRNA exerted similar inhibitory effects. The abrogation of NF-κB activation was involved in the antagonizing effects of these inhibitors. Furthermore, 5-LOX inhibitor decreased TNF-α-induced up-regulation of serum MCP-1 level and paw edema in mouse model. Our results provide the evidence that the administration of 5-LOX inhibitors is able to ameliorate TNF-α-induced cytokine/chemokine release and paw edema, indicating that 5-LOX inhibitors may be developed for therapeutic treatment of inflammatory arthritis.

Enhancement of PLGF production by 15-(S)-HETE via PI3K-Akt, NF-κB and COX-2 pathways in rheumatoid arthritis synovial fibroblast.

Metabolites from arachidonic acids play the pivotal roles in inflammatory arthritis. Arachidonic acid could be metabolized by cyclooxygenase (COX) and lipoxygenase (LOX) to produce the bioactive eicosanoids. Although the down-stream products of COX including prostaglandin E2 are well-known inflammatory stimulators, the role of LOX products in inflammatory arthritis is still unclear. Here we found that the downstream product of 15-LOX, 15-S-hydroxyeicosatetraenoic acid (15-(S)-HETE), can enhance the expression of placenta growth factor (PLGF), which is recently considered to play an important role in rheumatoid arthritis. 15-(S)-HETE increased the expression of PLGF in human rheumatoid arthritis synovial fibroblasts in a time-dependent and concentration-dependent manner. PI3K-Akt, NF-κB signaling pathways were involved in the potentiation effects of 15-(S)-HETE. In addition, COX-2 was up-regulated by the treatment of 15-(S)-HETE and the increase of COX-2 expression participated in 15-(S)-HETE-induced PLGF expression, which was confirmed by COX-2 shRNA or pharmacological COX-2 inhibitor. Moreover, it was found that treatment of prostaglandin E2 (PGE2), which was the main down-stream metabolite of COX-2, increased the expression of PLGF. EP1, EP2, EP3 and EP4 agonists could up-regulate PLGF as well. In animal studies, we found that the adjuvant-induced expression of PLGF and COX-2 was inhibited in 15-LOX knockout mice. These results indicated that PLGF up-regulation by 15-LOX downstream product may be involved in inflammatory arthritis.