Exogenous α-calcitonin gene-related peptide attenuates lipopolysaccharide-induced acute lung injury in rats

RAMP1 Signaling Mitigates Acute Lung Injury by Distinctively Regulating Alveolar and Monocyte-Derived Macrophages

Acute respiratory distress syndrome (ARDS) is a life-threatening lung injury that induces cytokine hypersecretion. Receptor activity-modifying protein (RAMP) 1, a subunit of the calcitonin gene-related peptide (CGRP) receptor, regulates the production of cytokines. This study examined the role of RAMP1 signaling during lipopolysaccharide (LPS)-induced acute lung injury (ALI). LPS administration to wild-type (WT) mice depleted alveolar macrophages (AMs) and recruited monocyte-derived macrophages (MDMs) and neutrophils. RAMP1-deficient (RAMP1-/-) mice exhibited higher lung injury scores, cytokine levels, and cytokine-producing neutrophil infiltration. RAMP1-deficient AMs produced more cytokines in response to LPS than WT AMs. Adoptive transfer of RAMP1-deficient AMs to RAMP1-/- mice increased cytokine levels and neutrophil accumulation compared to the transfer of WT AMs. RAMP1-/- mice had reduced MDM recruitment and lower pro-inflammatory and reparative macrophage profiles. Cultured bone marrow (BM)-derived RAMP1-deficient macrophages stimulated with LPS showed decreased expression of pro-inflammatory and pro-repairing genes. CGRP administration to WT mice reduced cytokine production and neutrophil accumulation. These findings indicate that RAMP1 signaling mitigates LPS-induced ALI by inactivating AMs and promoting inflammatory and repair activities of MDMs. Targeting RAMP1 signaling presents a potential therapeutic approach for the treatment of ARDS.

Potential pharmaceuticals targeting neuroimmune interactions in treating acute lung injury

BACKGROUND AND MAIN BODY

Although interactions between the nervous and immune systems have been recognized decades ago, it has become increasingly appreciated that neuroimmune crosstalk is among the driving factors of multiple pulmonary inflammatory diseases including acute lung injury (ALI). Here, we review the current understanding of nerve innervations towards the lung and summarize how the neural regulation of immunity and inflammation participates in the onset and progression of several lung diseases, especially ALI. We then present advancements in the development of potential drugs for ALI targeting neuroimmune interactions, including cholinergic anti-inflammatory pathway, sympathetic-immune pathway, purinergic signalling, neuropeptides and renin-angiotensin system at different stages from preclinical investigation to clinical trials, including the traditional Chinese medicine.

CONCLUSION

This review highlights the importance of considering the therapeutic strategy of inflammatory diseases within a conceptual framework that integrates classical inflammatory cascade and neuroimmune circuits, so as to deepen the understanding of immune modulation and develop more sophisticated approaches to treat lung diseases represented by ALI.

KEY POINTS

The lungs present abundant nerve innervations. Neuroimmune interactions exert a modulatory effect in the onset and progression of lung inflammatory diseases, especially acute lung injury. The advancements of potential drugs for ALI targeting neuroimmune crosstalk at different stages from preclinical investigation to clinical trials are elaborated. Point out the direction for the development of neuroimmune pharmacology in the future.

Calcitonin gene-related peptide attenuated discogenic low back pain in rats possibly via inhibiting microglia activation

Discogenic low back pain (DLBP) is a multifactorial disease and associated with intervertebral disc degeneration. Calcitonin gene-related protein (CGRP) plays a critical role in pain processing, while the role in DLBP remains unclear. This study aims to investigate the anti-nociceptive role and related mechanisms of CGRP in DLBP. Here we established the DLBP rat and validated the model using histology and radiography. Minocycline, a microglial inhibitor, and CGRP were intrathecally injected and the behavioral test was performed to determine hyperalgesia. Further, BV2 microglial cells and microglial activation agent lipopolysaccharide (LPS) were employed for the in vitro experiment. We observed obvious lumbar intervertebral disc degeneration and hyperalgesia at 12 weeks postoperation in DLBP group, with significantly activated microglia in the spinal cord. CGRP treatment significantly inhibited the upregulation of proinflammatory cytokines and NLRP3/caspase-1 expression induced by LPS in BV2 cells, whereas treatment with CGRP alone had little effect on BV2 cells. The intrathecal injection of CGRP into DLBP rats relieved mechanical and thermal hyperalgesia, reverted the microglial activation and decreased the expression of NLRP3/caspase-1, similar to the effects produced by minocycline. Our results provide evidence that microglial activation in the spinal cord play a key role in hyperalgesia in DLBP rats. CGRP alleviates DLBP induced hyperalgesia and inhibits microglial activation in the spinal cord. Regulation of CGRP and microglial activation may provide a new strategy for ameliorating DLBP.

CGRP is essential for protection against alveolar epithelial cell necroptosis by activating the AMPK/L-OPA1 signaling pathway during acute lung injury

Alveolar epithelial cell (AEC) necroptosis is critical to disrupt the alveolar barrier and provoke acute lung injury (ALI). Here, we define calcitonin gene-related peptide (CGRP), the most abundant endogenous neuropeptide in the lung, as a novel modulator of AEC necroptosis in lipopolysaccharide (LPS)-induced ALI. Upon LPS-induced ALI, overexpression of Cgrp significantly mitigates the inflammatory response, alleviates lung tissue damage, and decreases AEC necroptosis. Similarly, CGRP alleviated AEC necroptosis under the LPS challenge in vitro. Previously, we identified that long optic atrophy 1 (L-OPA1) deficiency mediates mitochondrial fragmentation, leading to AEC necroptosis. In this study, we discovered that CGRP positively regulated mitochondrial fusion through stabilizing L-OPA1. Mechanistically, we elucidate that CGRP activates AMP-activated protein kinase (AMPK). Furthermore, the blockade of AMPK compromised the protective effect of CGRP against AEC necroptosis following the LPS challenge. Our study suggests that CRGP-mediated activation of the AMPK/L-OPA1 axis may have potent therapeutic benefits for patients with ALI or other diseases with necroptosis.

Irf7 regulates the expression of Srg3 and ferroptosis axis aggravated sepsis-induced acute lung injury

OBJECTIVE

To investigate the mechanism of action of Srg3 in acute lung injury caused by sepsis.

METHODS

First, a sepsis-induced acute lung injury rat model was established using cecal ligation and puncture (CLP). RNA sequencing (RNA-seq) was used to screen for highly expressed genes in sepsis-induced acute lung injury (ALI), and the results showed that Srg3 was significantly upregulated. Then, SWI3-related gene 3 (Srg3) was knocked down using AAV9 vector in vivo, and changes in ALI symptoms in rats were analyzed. In vitro experiments were conducted by establishing a cell model using lipopolysaccharide (LPS)-induced BEAS-2B cells and coculturing them with phorbol 12-myristate 13-acetate (PMA)-treated THP-1 cells to analyze macrophage polarization. Next, downstream signaling pathways regulated by Srg3 and transcription factors involved in regulating Srg3 expression were analyzed using the KEGG database. Finally, gain-of-loss functional validation experiments were performed to analyze the role of downstream signaling pathways regulated by Srg3 and transcription factors involved in regulating Srg3 expression in sepsis-induced acute lung injury.

RESULTS

Srg3 was significantly upregulated in sepsis-induced acute lung injury, and knocking down Srg3 significantly improved the symptoms of ALI in rats. Furthermore, in vitro experiments showed that knocking down Srg3 significantly weakened the inhibitory effect of LPS on the viability of BEAS-2B cells and promoted alternative activation phenotype (M2) macrophage polarization. Subsequent experiments showed that Srg3 can regulate the activation of the NF-κB signaling pathway and promote ferroptosis. Specific activation of the NF-κB signaling pathway or ferroptosis significantly weakened the effect of Srg3 knockdown. It was then found that Srg3 can be transcriptionally activated by interferon regulatory factor 7 (Irf7), and specific inhibition of Irf7 significantly improved the symptoms of ALI.

CONCLUSIONS

Irf7 transcriptionally activates the expression of Srg3, which can promote ferroptosis and activate classical activation phenotype (M1) macrophage polarization by regulating the NF-κB signaling pathway, thereby exacerbating the symptoms of septic lung injury.

The anti-inflammatory regulation of calcitonin gene-related peptide in mouse Aspergillus fumigatus keratitis

AIM

To analyze the impact of calcitonin gene-related peptide (CGRP) in mouse keratitis after Aspergillus fumigatus (A. fumigatus) infection.

METHODS

C57BL/6 mice were treated subconjunctivally with different concentrations of exogenous CGRP, and BALB/c mice were treated with CGRP8-37 (a CGRP antagonist) before corneas were infected with A. fumigatus. The cornea was assessed under the slit-lamp and the clinical score was recorded. The mRNA levels of IL-1β, TNF-α, IL-6, and MIP-2 were detected by quantitative real-time polymerase chain reaction (PCR), while the protein level of IL-1β was determined by Western blotting. In vitro, RAW264.7 cells were used to investigate NLRP3 and IL-1β expression induced by A. fumigatus after the pretreatment of exogenous CGRP or CGRP8-37. Cytokines expression in RAW264.7 cells was evaluated by real-time PCR and Western blotting.

RESULTS

Using exogenous CGRP resulted in down-regulated synthesis of IL-1β and MIP-2 stimulated by A. fumigatus in C57BL/6 mice keratitis, and the synthesis of IL-1β, MIP-2 and IL-6 was up-regulated in BALB/c mice corneas after the pretreatment with CGRP8-37. Pretreatment with exogenous CGRP and CGRP8-37 did not influence TNF-α mRNA levels either in BALB/c or C57BL/6 mice keratitis. The levels of NLRP3 and IL-1β were both reduced in A. fumigatus stimulated-macrophages after treatment with exogenous CGRP. And CGRP8-37 pretreatment would increase NLRP3 and IL-1β levels.

CONCLUSION

CGRP may alleviate the inflammatory reaction in mice keratitis after infection with A. fumigatus. The anti-inflammatory effect may be related to the inhibition of NLRP3 expression by CGRP.

Expression and role of calcitonin gene-related peptide in mouse Aspergillus fumigatus keratitis

AIM

To investigate the expression and role of calcitonin gene-related peptide (CGRP) in the mouse models induced by Aspergillus fumigatus (A. fumigatus).

METHODS

C57BL/6 mice were randomized into a control group and A. fumigatus keratitis group. The cornea photography was assessed under the slit lamp and the clinical score was recorded after infection. Western blot, real-time polymerase chain reaction (PCR) and immunohistofluorescence analysis were applied to detect CGRP expression in cornea of both groups. In vitro, tests were conducted with C57BL/6 mice macrophages to investigate CGRP expression after interaction with A. fumigatus. Cytokines expression induced by exogenous CGRP and the antagonist CGRP8-37 in A. fumigatus-exposed macrophages was evaluated by real-time PCR and ELISA.

RESULTS

The cornea expression of CGRP was significantly elevated in C57BL/6 mice corneas and macrophages after A. fumigatus infection. After treatment with exogenous CGRP, the levels of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α) and IL-6 were reduced, and IL-10 level was increased in the A. fumigatus stimulated-macrophages. However, IL-1β, TNF-α and IL-6 levels were upregulated after pretreatment of CGRP8-37. But the mRNA levels of MIP-2, TGF-β and IL-10 were not changed.

CONCLUSION

This study provides evidence that A. fumigatus increased CGRP expression. CGRP may play a protective role against inflammation in A. fumigatus keratitis.

Calcitonin gene‑related peptide induces IL‑6 expression in RAW264.7 macrophages mediated by mmu_circRNA_007893

Several circular RNAs (circRNAs) may have role important roles in biological processes, however, there is limited knowledge of circRNAs and their potential functions in RAW264.7 macrophages. The present study aimed to examine the expression of circRNAs and explore their effects on interleukin‑6 (IL‑6) expression induced by calcitonin gene‑related peptide (CGRP) in RAW264.7 macrophages. To identify circRNAs, the circRNA expression was measured in macrophages with or without CGRP stimulation. The interaction between circRNAs and microRNAs (miRs) were then identified using bioinformatic software and networks. In the current study, it was demonstrated that CGRP increased the expression of IL‑6 mRNA in a dose‑ and time‑dependent manner. Furthermore, mmu_circRNA_007893 was significantly increased in the CGRP‑stimulated macrophages. Silencing of mmu_circRNA_007893, IL‑6 mRNA expression was significantly decreased, whereas mmu‑miR‑485‑5p expression was markedly increased. Furthermore, when overexpression of mmu‑miR‑485‑5p, IL‑6 mRNA was markedly decreased. The results demonstrated that CGRP‑induced IL‑6 mRNA expression was mediated by mmu_circRNA_007893, and mmu_circRNA_007893 functioned as an endogenous mmu‑miR‑485‑5p sponge as part of induction of IL‑6 mRNA expression.

CGRP 8-37 enhances lipopolysaccharide-induced acute lung injury and regulating aquaporin 1 and 5 expressions in rats

Calcitonin gene-related peptide (CGRP) has been shown to play important roles in biological functions. However, there is very little evidence on the value of CGRP in lipopolysaccharide (LPS)-induced acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Therefore, this study aimed to investigate the role of CGRP in LPS-induced ALI in rats. In the experiment, Sprague-Dawley (SD) rats were randomized into control, an antagonist of α-calcitonin gene-related peptide receptor (CGRP8-37), LPS groups, and CGRP8-37 + LPS groups. ALI model was prepared through retrograde injection of LPS (10 mg/kg). At 6 and 12 h, bronchoalveolar lavage was performed and used to assess total cell count and levels of tumor necrosis factor-α, interleukin-1β, -6, and -10 by enzyme-linked immunosorbent assay (ELISA). Lung tissue was collected for assessing wet-to-dry (W/D) ratio, hematoxylin and eosin staining. Aquaporin (AQP)-1 and -5 expressions in lung tissues were detected by quantitative PCR and Western blot. The results showed that histological injury, total cell count, and W/D ratio significantly reduced in LPS group after 6 h. The levels of inflammatory cytokines in CGRP8-37 + LPS-treated rats were higher than that in LPS-treated rats (all, P < 0.001). Real-time RT-PCR analysis showed that levels of AQP-1 in rats from CGRP8-37 + LPS group was lower than that in LPS-treated rats (P = 0.005 and P < 0.001). Western blotting analysis showed that AQP-1 protein levels at 6 h significantly decreased in CGRP8-37 + LPS rats. Together, our data suggest that CGRP antagonists, CGRP8-37 could enhance ALI induced by LPS in the rat model, and regulate the expression levels of AQP-1 and AQP-5 by affecting inflammatory cytokines. Thereby, regulating endogenous CGRP may be a potential treatment for ALI/ARDS.

Role of the PKCα-c-Src tyrosine kinase pathway in the mediation of p120-catenin degradation in ventilator-induced lung injury

BACKGROUND AND OBJECTIVE

Ventilator-induced lung injury (VILI) is commonly associated with respiratory barrier dysfunction; however, the mechanisms have not been fully elucidated. This study aimed to determine the order and components of the signalling pathway that mediates the degradation of adherin junction of p120-catenin in VILI.

METHODS

For the in vivo study, C57BL/6 mice were pre-treated with inhibitors for 60 min prior to 4 h of mechanical ventilation. For the in vitro study, mouse lung epithelial 12 (MLE-12) cells were pre-treated with inhibitors for 60 min or small interfering RNA (siRNA) for 48 h prior to cyclic stretch at 20% for 4 h. The protein levels of protein kinase Cα (PKCα), activated c-Src and p120-catenin were determined via western blot analysis. Lung injury was determined via HE staining, immunofluorescence, wet/dry ratio and lung injury scores.

RESULTS

High tidal volume mechanical ventilation and 20% cyclic stretch resulted in the degradation of p120-catenin. Inhibitors of PKCα blocked c-Src kinase activation and p120-catenin degradation in VILI. Inhibitors of c-Src kinase or PP2 or siRNA blocked p120-catenin degradation but not PKCα activation.

CONCLUSION

The current findings demonstrates that PKCα and c-Src kinase participate in VILI. PKCα activation phosphorylates c-Src kinase and further decreases p120-catenin in VILI.