Stromal cell-derived factor-1α attenuates oleate-induced acute lung injury in rabbits

CXCR3-independent role of CXCL10 in alveolar epithelial repair

The alveolar type II epithelial cells (AEC2s) act as stem cells in the lung for alveolar epithelial maintenance and repair. Chemokine C-X-C motif chemokine 10 (CXCL10) is expressed in injured tissues, modulating multiple cellular functions. AEC2s, previously reported to release chemokines to recruit leukocytes, were found in our study to secrete CXCL10 after bleomycin injury. We found that Sftpc-Cxcl10 transgenic mice were protected from bleomycin injury. The transgenic mice showed an increase in the AEC2 population in the lung by flow cytometry analysis. Both endogenous and exogenous CXCL10 promoted the colony formation efficiency of AEC2s in a three-dimensional (3-D) organoid growth assay. We identified that the regenerative effect of CXCL10 was CXCR3 independent using Cxcr3-deficient mice, but it was related to the TrkA pathway. Binding experiments showed that CXCL10 interacted with TrkA directly and reversibly. This study demonstrates a previously unidentified AEC2 autocrine signaling of CXCL10 to promote their regeneration and proliferation, probably involving a CXCR3-independent TrkA pathway.NEW & NOTEWORTHY CXCL10 may aid in lung injury recovery by promoting the proliferation of alveolar stem cells and using a distinct regulatory pathway from the classical one.

Regulation of the thrombin/protease-activated receptor 1 axis by chemokine (CXC motif) receptor 4

The chemokine receptor CXCR4, a G protein-coupled receptor (GPCR) capable of heteromerizing with other GPCRs, is involved in many processes, including immune responses, hematopoiesis, and organogenesis. Evidence suggests that CXCR4 activation reduces thrombin/protease-activated receptor 1 (PAR1)-induced impairment of endothelial barrier function. However, the mechanisms underlying cross-talk between CXCR4 and PAR1 are not well-understood. Using intermolecular bioluminescence resonance energy transfer and proximity ligation assays, we found that CXCR4 heteromerizes with PAR1 in the HEK293T expression system and in human primary pulmonary endothelial cells (hPPECs). A peptide analog of transmembrane domain 2 (TM2) of CXCR4 interfered with PAR1:CXCR4 heteromerization. In HTLA cells, the presence of CXCR4 reduced the efficacy of thrombin to induce β-arrestin-2 recruitment to recombinant PAR1 and enhanced thrombin-induced Ca²⁺ mobilization. Whereas thrombin-induced extracellular signal-regulated protein kinase 1/2 (ERK1/2) phosphorylation occurred more transiently in the presence of CXCR4, peak ERK1/2 phosphorylation was increased when compared with HTLA cells expressing PAR1 alone. CXCR4-associated effects on thrombin-induced β-arrestin-2 recruitment to and signaling of PAR1 could be reversed by TM2. In hPPECs, TM2 inhibited thrombin-induced ERK1/2 phosphorylation and activation of Ras homolog gene family member A. CXCR4 siRNA knockdown inhibited thrombin-induced ERK1/2 phosphorylation. Whereas thrombin stimulation reduced surface expression of PAR1, CXCR4, and PAR1:CXCR4 heteromers, chemokine (CXC motif) ligand 12 stimulation reduced surface expression of CXCR4 and PAR1:CXCR4 heteromers, but not of PAR1. Finally, TM2 dose-dependently inhibited thrombin-induced impairment of hPPEC monolayer permeability. Our findings suggest that CXCR4:PAR1 heteromerization enhances thrombin-induced G protein signaling of PAR1 and PAR1-mediated endothelial barrier disruption.

Natural and engineered chemokine (C-X-C motif) receptor 4 agonists prevent acute respiratory distress syndrome after lung ischemia-reperfusion injury and hemorrhage

We compared therapeutic properties of natural and engineered chemokine (C-X-C motif) receptor 4 (CXCR4) agonists in a rat acute respiratory distress syndrome (ARDS) model utilizing the PaO₂/FiO₂-ratio as a clinically relevant primary outcome criterion. Ventilated rats underwent unilateral lung ischemia from t = 0–70 min plus hemorrhage to a mean arterial blood pressure (MAP) of 30 mmHg from t = 40–70 min, followed by reperfusion/fluid resuscitation until t = 300 min. Natural CXCR4 agonists (CXCL12, ubiquitin) and engineered CXCL12 variants (CXCL12₁, CXCL2₂, CXCL12K27A/R41A/R47A, CXCL12 (3–68)) were administered within 5 min of fluid resuscitation. Animals treated with vehicle or CXCL12 (3–68) reached criteria for mild and moderate ARDS between t = 90–120 min and t = 120–180 min, respectively, and remained in moderate ARDS until t = 300 min. Ubiquitin, CXCL12, CXCL12₁ and CXCL12₂ prevented ARDS development. Potencies of CXCL12/CXCL12₁/CXCL12₂ were higher than the potency of ubiquitin. CXCL12K27A/R41A/R47A was inefficacious. CXCL12₁ > CXCL12 stabilized MAP and reduced fluid requirements. CXCR4 agonists at doses that preserved lung function reduced histological injury of the post-ischemic lung and reduced mortality from 55 to 9%. Our findings suggest that CXCR4 protein agonists prevent development of ARDS and reduce mortality in a rat model, and that development of new engineered protein therapeutics with improved pharmacological properties for ARDS is possible.

CXCR4 knockdown prevents inflammatory cytokine expression in macrophages by suppressing activation of MAPK and NF-κB signaling pathways

Background

Recent evidence has shown that C-X-C chemokine receptor type 4 (CXCR4) plays a crucial role in acute lung injury (ALI). Macrophages are key factors in the pathogenesis of ALI. The aim of this study was to investigate the role of CXCR4 in macrophages after lipopolysaccharide (LPS) stimulation and confirm that CXCR4 knockdown can inhibit inflammatory cytokines by suppressing mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) signaling pathway activation.

Results

In this study, we found that CXCR4 expression in lung tissue of ALI was significantly increased using immunofluorescence. We also found that the expression of CXCR4 in macrophages sorted from bronchoalveolar lavage fluid (BALF) of ALI was obviously upregulated through RT-qPCR. After CXCR4 knockdown using siRNA, we found that the expression of interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) was obviously down regulated in macrophages. Additionally, the phosphorylation of p38, Erk, and p65 was significantly decreased after CXCR4 knockdown through western blotting.

Conclusions

Taken together, the present study suggests that CXCR4 knockdown may inhibit inflammatory cytokine expression in macrophages by suppressing MAPK and NF-κB signaling pathway activation. Therefore, CXCR4 knockdown may have potential clinical value in treating ALI.

A case report on filamin A gene mutation and progressive pulmonary disease in an infant: A lung tissued derived mesenchymal stem cell study

RATIONALE

Mesenchymal stem cells (MSC) play a crucial role in both the maintenance of pulmonary integrity and the pathogenesis of lung disease. Lung involvement has been reported in patients with the filamin A (FLNA) gene mutation. Considering FLNA's role in the intrinsic mechanical properties of MSC, we characterized MSCs isolated from FLNA-defective lung tissue, in order to define their pathogenetic role in pulmonary damage.

PATIENT CONCERNS

A male infant developed significant lung disease resulting in emphysematous lesions and perivascular and interstitial fibrosis. He also exhibited general muscular hypotonia, bilateral inguinal hernia, and deformities of the lower limbs (pes tortus congenitalis and hip dysplasia). Following lobar resection, chronic respiratory failure occurred.

DIAGNOSIS

Genetic testing was performed during the course of his clinical care and revealed a new pathogenic variant of the FLNA gene c.7391_7403del; (p.Val2464AlafsTer5). Brain magnetic resonance imaging revealed periventricular nodular heterotopia.

INTERVENTIONS AND OUTCOMES

Surgical thoracoscopic lung biopsy was performed in order to obtain additional data on the pathological pulmonary features. A small portion of the pulmonary tissue was used for MSC expansion. Morphology, immunophenotype, differentiation capacity, and proliferative growth were evaluated. Bone marrow-derived mesenchymal stem cells (BM-MSC) were employed as a control. MSCs presented the typical MSC morphology and phenotype while exhibiting higher proliferative capacity (P <.001) and lower migration potential (P=.02) compared to control BM-MSC.

LESSONS

The genetic profile and altered features of the MSCs isolated from FLNA-related pediatric lung tissue could be directly related to defects in cell migration during embryonic lung development and pulmonary damage described in FLNA-defective patients.

Pathological roles of the homeostatic chemokine CXCL12

CXCL12 is a CXC chemokine that traditionally has been classified as a homeostatic chemokine. It contributes to physiological processes such as embryogenesis, hematopoiesis and angiogenesis. In contrast to these homeostatic functions, increased expression of CXCL12 in general, or of a specific CXCL12 splicing variant has been demonstrated in various pathologies. In addition to this increased or differential transcription of CXCL12, also upregulation of its receptors CXC chemokine receptor 4 (CXCR4) and atypical chemokine receptor 3 (ACKR3) contributes to the onset or progression of diseases. Moreover, posttranslational modification of CXCL12 during disease progression, through interaction with locally produced molecules or enzymes, also affects CXCL12 activity, adding further complexity. As CXCL12, CXCR4 and ACKR3 are broadly expressed, the number of pathologies wherein CXCL12 is involved is growing. In this review, the role of the CXCL12/CXCR4/ACKR3 axis will be discussed for the most prevalent pathologies. Administration of CXCL12-neutralizing antibodies or small-molecule antagonists of CXCR4 or ACKR3 delays disease onset or prevents disease progression in cancer, viral infections, inflammatory bowel diseases, rheumatoid arthritis and osteoarthritis, asthma and acute lung injury, amyotrophic lateral sclerosis and WHIM syndrome. On the other hand, CXCL12 has protective properties in Alzheimer's disease and multiple sclerosis, has a beneficial role in wound healing and has crucial homeostatic properties in general.

Effects of cognate, non-cognate and synthetic CXCR4 and ACKR3 ligands on human lung endothelial cell barrier function

Recent evidence suggests that chemokine CXCL12, the cognate agonist of chemokine receptors CXCR4 and ACKR3, reduces thrombin-mediated impairment of endothelial barrier function. A detailed characterization of the effects of CXCL12 on thrombin-mediated human lung endothelial hyperpermeability is lacking and structure-function correlations are not available. Furthermore, effects of other CXCR4/ACKR3 ligands on lung endothelial barrier function are unknown. Thus, we tested the effects of a panel of CXCR4/ACKR3 ligands (CXCL12, CXCL11, ubiquitin, AMD3100, TC14012) and compared the CXCR4/ACKR3 activities of CXCL12 variants (CXCL12α/β, CXCL12(3–68), CXCL12₁, CXCL12₂, CXCL12-S-S4V, CXCL12-R47E, CXCL12-K27A/R41A/R47A) with their effects on human lung endothelial barrier function in permeability assays. CXCL12α enhanced human primary pulmonary artery endothelial cell (hPPAEC) barrier function, whereas CXCL11, ubiquitin, AMD3100 and TC14012 were ineffective. Pre-treatment of hPPAEC with CXCL12α and ubiquitin reduced thrombin-mediated hyperpermeability. CXCL12α-treatment of hPPAEC after thrombin exposure reduced barrier function impairment by 70% (EC₅₀ 0.05–0.5nM), which could be antagonized with AMD3100; ubiquitin (0.03–3μM) was ineffective. In a human lung microvascular endothelial cell line (HULEC5a), CXCL12α and ubiquitin post-treatment attenuated thrombin-induced hyperpermeability to a similar degree. CXCL12(3–68) was inefficient to activate CXCR4 in Presto-Tango β-arrestin2 recruitment assays; CXCL12-S-S4V, CXCL12-R47E and CXCL12-K27A/R41A/R47A showed significantly reduced potencies to activate CXCR4. While the potencies of all proteins in ACKR3 Presto-Tango assays were comparable, the efficacy of CXCL12(3–68) to activate ACKR3 was significantly reduced. The potencies to attenuate thrombin-mediated hPPAEC barrier function impairment were: CXCL12α/β, CXCL12₁, CXCL12-K27A/R41A/R47A > CXCL12-S-S4V, CXCL12-R47E > CXCL12₂ > CXCL12(3–68). Our findings indicate that CXCR4 activation attenuates thrombin-induced lung endothelial barrier function impairment and suggest that protective effects of CXCL12 are dictated by its CXCR4 agonist activity and interactions of distinct protein moieties with heparan sulfate on the endothelial surface. These data may facilitate development of compounds with improved pharmacological properties to attenuate thrombin-induced vascular leakage in the pulmonary circulation.

Pharmacological modulation of C-X-C motif chemokine receptor 4 influences development of acute respiratory distress syndrome after lung ischaemia-reperfusion injury

Activation of C-X-C motif chemokine receptor 4 (CXCR4) has been reported to result in lung protective effects in various experimental models. The effects of pharmacological CXCR4 modulation on the development of acute respiratory distress syndrome (ARDS) after lung injury, however, are unknown. Thus, we studied whether blockade and activation of CXCR4 influences development of ARDS in a unilateral lung ischaemia-reperfusion injury rat model. Anaesthetized, mechanically ventilated animals underwent right lung ischaemia (series 1, 30 minutes; series 2, 60 minutes) followed by reperfusion for 300 minutes. In series 1, animals were treated with vehicle or 0.7 μmol/kg of AMD3100 (CXCR4 antagonist) and in series 2 with vehicle, 0.7 or 3.5 μmol/kg ubiquitin (non-cognate CXCR4 agonist) within 5 minutes of reperfusion. AMD3100 significantly reduced PaO₂ /FiO₂ ratios, converted mild ARDS with vehicle treatment into moderate ARDS (PaO₂ /FiO₂ ratio<200) and increased histological lung injury. Ubiquitin dose-dependently increased PaO₂ /FiO₂ ratios, converted moderate-to-severe into mild-to-moderate ARDS and reduced protein content of bronchoalveolar lavage fluid (BALF). Measurements of cytokine levels (TNFα, IL-6, IL-10) in lung homogenates and BALF showed that AMD3100 reduced IL-10 levels in homogenates from post-ischaemic lungs, whereas ubiquitin dose-dependently increased IL-10 levels in BALF from post-ischaemic lungs. Our findings establish a cause-effect relationship for the effects of pharmacological CXCR4 modulation on the development of ARDS after lung ischaemia-reperfusion injury. These data further suggest CXCR4 as a new drug target to reduce the incidence and attenuate the severity of ARDS after lung injury.

Predicted molecular signaling guiding photoreceptor cell migration following transplantation into damaged retina

To replace photoreceptors lost to disease or trauma and restore vision, laboratories around the world are investigating photoreceptor replacement strategies using subretinal transplantation of photoreceptor precursor cells (PPCs) and retinal progenitor cells (RPCs). Significant obstacles to advancement of photoreceptor cell-replacement include low migration rates of transplanted cells into host retina and an absence of data describing chemotactic signaling guiding migration of transplanted cells in the damaged retinal microenvironment. To elucidate chemotactic signaling guiding transplanted cell migration, bioinformatics modeling of PPC transplantation into light-damaged retina was performed. The bioinformatics modeling analyzed whole-genome expression data and matched PPC chemotactic cell-surface receptors to cognate ligands expressed in the light-damaged retinal microenvironment. A library of significantly predicted chemotactic ligand-receptor pairs, as well as downstream signaling networks was generated. PPC and RPC migration in microfluidic ligand gradients were analyzed using a highly predicted ligand-receptor pair, SDF-1α – CXCR4, and both PPCs and RPCs exhibited significant chemotaxis. This work present a systems level model and begins to elucidate molecular mechanisms involved in PPC and RPC migration within the damaged retinal microenvironment.