Inhibiting CXCL12 blocks fibrocyte migration and differentiation and attenuates bronchiolitis obliterans in a murine heterotopic tracheal transplant model

Tamibarotene inhibit the accumulation of fibrocyte and alleviate renal fibrosis by IL-17A

Renal fibrosis is a common pathological process in the progression of chronic kidney disease. Accumulating evidence suggests that interleukin-17A (IL‐17A) and fibrocytes play crucial roles in the pathogenesis of fibrosis. However, the role of IL-17A in the regulation of renal fibrocytes in renal fibrosis has rarely been reported. Here, we report that the plasma IL-17A level is increased in immunoglobulin A nephropathy (IgAN) patients and is correlated with clinical parameters. Using a mouse model of unilateral ureteral obstruction (UUO), we found that both IL-17A expression and fibrocyte infiltration were increased in the kidneys of UUO mice. Besides, IL-17A enhanced fibrosis and fibrocyte-associated chemokine and activator expression in vitro. Furthermore, inhibition of IL-17A using Am80 (Tamibarotene) decreased fibrocytes and fibrocyte-associated chemokine and activator expression and significantly attenuated renal fibrosis in the UUO mice. Our findings suggest that Am80, which inhibits the accumulation of fibrocytes and alleviates renal fibrosis mediated by IL-17A, maybe a novel therapeutic drug for renal fibrosis.

Endothelial cell‑derived CCL15 mediates the transmigration of fibrocytes through the CCL15‑CCR1 axis in vitro

Wound healing is a complex physiological process in which fibrocytes serve a vital role. However, the mechanism underlying the recruitment of fibrocytes during wound healing remains largely unknown. The present study aimed to investigate whether endothelial cells are involved in the recruitment of fibrocytes in wound healing. To mimic the in vivo angiogenic process, a co‑culture system consisting of endothelial cells and fibrocytes was achieved using a permeable Transwell co‑culture system. The expression of chemokines produced by endothelial cells with or without co‑culture was then measured using a gene chip. Based on the dataset from chip analysis, chemokine ligand 15 (CCL15) produced by endothelial cells was identified, which likely serves a regulatory role in mediating the transmigration of fibrocytes. Overexpression of CCL15 in endothelial cells or chemokine receptor 1 (CCR1) in fibrocytes promoted the transmigration of fibrocytes, whilst silencing the expression of CCL15 in endothelial cells or that of CCR1 in fibrocytes attenuated the transmigration of fibrocytes. Results from the present study suggested that the CCL15‑CCR1 axis between endothelial cells and fibrocytes serves a vital role in mediating the recruitment of fibrocytes during wound healing.

A B cell-dependent pathway drives chronic lung allograft rejection after ischemia-reperfusion injury in mice

Chronic lung allograft dysfunction (CLAD) limits long-term survival after lung transplant (LT). Ischemia-reperfusion injury (IRI) promotes chronic rejection (CR) and CLAD, but the underlying mechanisms are not well understood. To examine mechanisms linking IRI to CR, a mouse orthotopic LT model using a minor alloantigen strain mismatch (C57BL/10 [B10, H-2^b ] → C57BL/6 [B6, H-2^b ]) and isograft controls (B6→B6) was used with antecedent minimal or prolonged graft storage. The latter resulted in IRI with subsequent airway and parenchymal fibrosis in prolonged storage allografts but not isografts. This pattern of CR after IRI was associated with the formation of B cell-rich tertiary lymphoid organs within the grafts and circulating autoantibodies. These processes were attenuated by B cell depletion, despite preservation of allograft T cell content. Our observations suggest that IRI may promote B cell recruitment that drives CR after LT. These observations have implications for the mechanisms leading to CLAD after LT.

TBX2 and TBX3 act downstream of canonical WNT signaling in patterning and differentiation of the mouse ureteric mesenchyme

The organized array of smooth muscle cells (SMCs) and fibroblasts in the walls of visceral tubular organs arises by patterning and differentiation of mesenchymal progenitors surrounding the epithelial lumen. Here, we show that the TBX2 and TBX3 transcription factors have novel and required roles in regulating these processes in the murine ureter. Co-expression of TBX2 and TBX3 in the inner mesenchymal region of the developing ureter requires canonical WNT signaling. Loss of TBX2/TBX3 in this region disrupts activity of two crucial drivers of the SMC program, Foxf1 and BMP4 signaling, resulting in decreased SMC differentiation and increased extracellular matrix. Transcriptional profiling and chromatin immunoprecipitation experiments revealed that TBX2/TBX3 directly repress expression of the WNT antagonists Dkk2 and Shisa2, the BMP antagonist Bmper and the chemokine Cxcl12 These findings suggest that TBX2/TBX3 are effectors of canonical WNT signaling in the ureteric mesenchyme that promote SMC differentiation by maintaining BMP4 and WNT signaling in the inner region, while restricting CXCL12 signaling to the outer layer of fibroblast-fated mesenchyme.

Sca-1+ cardiac fibroblasts promote development of heart failure

The causative effect of GM-CSF produced by cardiac fibroblasts to development of heart failure has not been shown. We identified the pathological GM-CSF-producing cardiac fibroblast subset and the specific deletion of IL-17A signaling to these cells attenuated cardiac inflammation and heart failure. We describe here the CD45^- CD31^- CD29⁺ mEF-SK4⁺ PDGFRα⁺ Sca-1⁺ periostin⁺ (Sca-1⁺ ) cardiac fibroblast subset as the main GM-CSF producer in both experimental autoimmune myocarditis and myocardial infarction mouse models. Specific ablation of IL-17A signaling to Sca-1⁺ periostin⁺ cardiac fibroblasts (Postn^Cre Il17ra^fl/fl ) protected mice from post-infarct heart failure and death. Moreover, Postn^Cre Il17ra^fl/fl mice had significantly fewer GM-CSF-producing Sca-1⁺ cardiac fibroblasts and inflammatory Ly6C^hi monocytes in the heart. Sca-1⁺ cardiac fibroblasts were not only potent GM-CSF producers, but also exhibited plasticity and switched their cytokine production profiles depending on local microenvironments. Moreover, we also found GM-CSF-positive cardiac fibroblasts in cardiac biopsy samples from heart failure patients of myocarditis or ischemic origin. Thus, this is the first identification of a pathological GM-CSF-producing cardiac fibroblast subset in human and mice hearts with myocarditis and ischemic cardiomyopathy. Sca-1⁺ cardiac fibroblasts direct the type of immune cells infiltrating the heart during cardiac inflammation and drive the development of heart failure.

The emerging role of fibrocytes in ocular disorders

The fibrocyte, which was first described in 1994, is a type of circulating mesenchymal progenitor cell in the peripheral blood. Fibrocytes play important roles in chronic inflammation, wound healing, tissue remodeling, and fibrosis. Emerging evidence indicates that fibrocytes are involved in a wide variety of ocular disorders associated with inflammation and fibrosis. In this review, we summarize recent advances regarding the general characteristic profile of fibrocytes, molecular mechanisms underlying the fibrocyte recruitment to target tissues, their differentiation into fibroblasts, and the potential role of fibrocytes in ocular disease. Given the critical role of fibrocytes in ocular disorders, fibrocytes may serve as a promising pharmaceutical target in the development of novel therapeutic strategies to treat ocular inflammation and fibrosis.

R1R2 peptide ameliorates pulmonary fibrosis in mice through fibrocyte migration and differentiation

Circulating fibrocytes play a key role in the pathogenesis of pulmonary fibrosis. Fibrocytes are bone marrow-derived leukocytes, which enter the lungs in response to their chemoattractant CXCL12 and differentiate into fibroblasts or myofibroblasts, leading to excess deposition of the collagen-rich extracellular matrix. Matrix metalloproteinase (MMP)-9 and MMP-2, secreted by fibrocytes, degrade the subendothelial basement membrane and promote fibrocyte influx into the lungs. Here, we demonstrate that R1R2, a novel peptide derived from the bacterial adhesin SFS, attenuates pulmonary fibrosis by preventing the differentiation of fibrocytes into myofibroblasts and by reducing the invasion of fibrocytes through basement membrane-like proteins. Moreover, our findings reveal dual regulation of R1R2 on MMP-9 through reduced enzymatic activity on gelatin and increased cleavage of CXCL12. These data suggest that R1R2 has potent anti-fibrotic effects against pulmonary fibrosis.

LTB4 and montelukast in transplantation-related bronchiolitis obliterans in rats

Background

Lung transplantation is the only effective treatment for end-stage lung diseases. Bronchiolitis obliterans, which is known as non-infectious chronic lung allograft dysfunction (CLAD) in the new classification, is the greatest threat to long-term survival after lung transplantation. This study investigated the role of leukotriene B4 (LTB4) and montelukast in transplantation-related bronchiolitis obliterans and discussed the pathophysiological significance of LTB4 in chronic rejection.

Methods

Rats were randomly divided into an experimental group (montelukast), a positive control group (dexamethasone), and a blank control group (normal saline solution; NS). Each piece of trachea removed from a F344 rat was transplanted into a Lewis rat through a 5-mm incision at the episternum by subcutaneous embedding. The recipients were treated with gastric lavage with 3 mg/kg · d montelukast suspension, 1 mg/kg · d dexamethasone, and 1 mL/kg · d NS, respectively, in each group. On Day 28, peripheral blood was drawn to measure the white blood cell counts and plasma LTB4 levels. The donor specimens were stained by H-E and Masson, and their organizational structure and extent of fibrosis were visually assessed. The measurement data were compared using one-way analysis of variance, and the categorical data were compared using the chi-square test. A P value of less than 0.05 was considered to indicate statistical significance.

Results

The white blood cell counts of the montelukast, dexamethasone, and NS groups were (16.0 ± 4.2) × 10⁹/L, (19.5 ± 11.6) × 10⁹/L, and (25.8 ± 3.6) × 10⁹/L; no statistical significance was found (P = 0.101). The concentrations of LTB4 were 2230 ± 592 pg/mL, 1961 ± 922 pg/mL, and 3764 ± 1169 pg/mL, and statistical significance was found between the NS group and each of the others (P = 0.009). The percentages of tracheal occlusion were 73.6% ± 13.8%, 23.4% ± 3.2%, and 89.9% ± 11.3%, and statistical significance was found among the three groups (P = 0.000).

Conclusions

The study established a model to simulate bronchiolitis obliterans after clinical lung transplantation. Oral administration of montelukast reduced plasma LTB4 levels in rats and played a preventive role against tracheal fibrosis after transplantation. This suggests that LTB4 may be involved in bronchiolitis obliterans after pulmonary transplantation. This study indicates a new direction for research into the prevention and treatment of bronchiolitis obliterans after lung transplantation.

Impact of Steroids on the Inflammatory Response after Ischemic Acute Kidney Injury in Rats

Inflammation plays a crucial role in acute kidney injury (AKI). The current study was designed to analyze the influence of prednisolone treatment on the inflammatory reaction during the first 96 h after AKI induction in a rat model. AKI was induced by unilateral clipping of the renal vessels. The treatment group received prednisolone 5 mg/kg s.c. daily. Infiltration rates of macrophages, leukocytes, and T-cells (24, 96 h) as well as plasma concentrations of the inflammatory markers intercellular adhesion molecule, interleukin-1 beta (IL-1β), IL-18, IL-6, and tumor necrosis factor-alpha (0, 6, 24, 96 h) were determined by fluorescence-activated cell sorting (FACS) analysis only. Ninety-six hours after AKI induction, the prednisolone group demonstrated significantly lower creatinine concentrations compared to the control group (P < 0.05). Twenty-four hours after induction of AKI, a significantly higher rate of infiltrating leukocytes was detectable with FACS analysis in the control group (P < 0.01) with a corresponding significantly higher rate of macrophages after 96 h (P < 0.01). IL-6 and IL-1β demonstrated a peak after 6 h with a significantly higher release in the control group (IL-6: P < 0.01; IL-1β: P < 0.05). In contrast to the control group, the prednisolone group demonstrated no further incline of IL-18 after 24 h. The results demonstrate the importance of stretching the observation period in an ischemia-reperfusion-induced AKI setting beyond the first 24 h. Despite the demonstrated protective effects of a continuous prednisolone application, it seems that this single anti-inflammatory agent will not be able to completely suppress the inflammatory response after an ischemia-reperfusion-induced AKI.

Circulating Fibrocytes Are Increased in Neonates with Bronchopulmonary Dysplasia

BACKGROUND

Bronchopulmonary dysplasia (BPD) is characterized by the aberrant remodeling of the lung parenchyma, resulting from accumulation of fibroblasts or myofibroblasts. Circulating fibrocytes are implied in pulmonary fibrosis, but whether these cells are associated with the development of BPD or the progressive fibrosis is unknown. The aim of the present study was to investigate the occurrence of fibrocytes in peripheral venous blood and explore whether these cells might be associated with severity of BPD.

METHODS

We investigated circulating fibrocytes in 66 patients with BPD, 23 patients with acute respiratory distress syndrome(ARDS) and 11 normal subjects. Circulating fibrocytes were defined and quantified as cells positive for CD45 andcollagen-1 by flow cytometry. Furthermore, serum SDF-1/CXCL12 and TGF-β1 were evaluated using ELISA methods. We also investigated the clinical value of fibrocyte counts by comparison with standard clinical parameters.

RESULTS

The patients with BPD had significantly increased numbers of fibrocytes compared to the controls (p < 0.01). Patients with ARDS were not different from healthy control subjects. There was a correlation between the number of fibrocytes and pulmonary hypertension or oxygen saturation (p < 0.05). Fibrocyte numbers were not correlated with other clinical or functional variables or radiologic severity scores. The fibrocyte attractant chemokine CXCL12 increased in plasma (p < 0.05) and was detectable in the bronchoalveolar lavage fluid of 40% of the patients but not in controls.

CONCLUSION

These findings indicate that circulating fibrocytes are increased in patients with BPD and may contribute to pulmonary fibrosis in BPD. Circulating fibrocytes, likely recruited through the CXCR4/CXCL12 axis, might contribute to the production of TGF-β1 for the expansion of fibroblast/myofibroblast population in BPD.

Organizing pneumonia in mice and men

BACKGROUND

Organizing pneumonia is a reaction pattern and an inflammatory response to acute lung injuries, and is characterized by intraluminal plugs of granulation tissue in distal airspaces. In contrast to other fibrotic pulmonary diseases, organizing pneumonia is generally responsive to corticosteroids. However, some patients do not respond to treatment, leading to respiratory failure and potentially death (up to 15 % of patients). In order to devise new therapeutic strategies, a better understanding of the disease's pathomechanisms is warranted. We previously generated a mouse model overexpressing CCL2, which generates organizing pneumonia-like changes, morphologically comparable to human patients. In this study, we investigated whether the histopathological similarities of human and murine pulmonary organizing pneumonia lesions also involve similar molecular pathways.

METHODS

We analyzed the similarities and differences of fibrosis-associated gene expression in individual compartments from patients with organizing pneumonia and transgenic (CCL2) mice using laser-assisted microdissection, real-time PCR and immunohistochemistry.

RESULTS

Gene expression profiling of human and murine organizing pneumonia lesions showed in part comparable expression levels of pivotal genes, notably of TGFB1/Tgfb1, TIMP1/Timp1, TIMP2/Timp2, COL3A1/Col3a1, CXCL12/Cxcl12, MMP2/Mmp2 and IL6/Il6. Hence, the transgenic CCL2 mouse model shows not only pathogenomic and morphological features of human organizing pneumonia but also a similar inflammatory profile.

CONCLUSIONS

We suggest that the CCL2-overexpressing transgenic mouse model (CCL2 Tg mice) is suitable for further investigation of fibrotic pulmonary remodeling, particularly of organizing pneumonia pathogenesis and for the search for novel therapeutic strategies.

Characterization of Lung Fibroblasts More than Two Decades after Mustard Gas Exposure

Purpose

In patients with short-term exposure to the sulfur mustard gas, the delayed cellular effects on lungs have not been well understood yet. The lung pathology shows a dominant feature consistent with obliterative bronchiolitis, in which fibroblasts play a central role. This study aims to characterize alterations to lung fibroblasts, at the cellular level, in patients with delayed respiratory complications after short-term exposure to the sulfur mustard gas.

Methods

Fibroblasts were isolated from the transbronchial biopsies of patients with documented history of exposure to single high-dose sulfur mustard during 1985–7 and compared with the fibroblasts of control subjects.

Results

Compared with controls, patients’ fibroblasts were thinner and shorter, and showed a higher population doubling level, migration capacity and number of filopodia. Sulfur mustard decreased the in vitro viability of fibroblasts and increased their sensitivity to induction of apoptosis, but did not change the rate of spontaneous apoptosis. In addition, higher expression of alpha smooth muscle actin showed that the lung's microenvironment in these patients is permissive for myofibroblastic differentiation.

Conclusions

These findings suggest that in patients under the study, the delayed pulmonary complications of sulfur mustard should be considered as a unique pathology, which might need a specific management by manipulation of cellular components.

Treg depletion attenuates irradiation-induced pulmonary fibrosis by reducing fibrocyte accumulation, inducing Th17 response, and shifting IFN-γ, IL-12/IL-4, IL-5 balance

Irradiation-induced pulmonary fibrosis results from thoracic radiotherapy and severely limits radiotherapy approaches. CD4(+) CD25(+) FoxP3(+) regulatory T cells (Tregs) are involved in experimentally induced murine lung fibrosis. However, the precise contribution of Tregs to irradiation-induced pulmonary fibrosis still remains unclear. We have previously established the mouse model of irradiation-induced pulmonary fibrosis and observed an increased frequency of Tregs during the process. This study aimed to investigate the effects of Treg depletion on irradiation-induced pulmonary fibrosis and on fibrocyte, Th17 cell response and production of multiple cytokines in mice. Treg-depleted mice were generated by intraperitoneal injection with anti-CD25 mAb 2h after 20 Gy (60)CO γ-ray thoracic irradiation and every 7 days thereafter. Pulmonary fibrosis was semi-quantitatively assessed using Masson's trichrome staining. The proportions of Tregs, fibrocyte and Th17 cells were detected by flow cytometry. Th1/Th2 cytokines were assessed by Luminex assays. We found that Treg depletion decelerated the process of irradiation-induced pulmonary fibrosis and hindered fibrocyte recruitment to the lung. In response to Treg depletion, the number of CD4(+) T lymphocytes and Th17 cells increased. Moreover, Th1/Th2 cytokine balance was disturbed into Th1 dominance upon Treg depletion. Our study demonstrates that Tregs are involved in irradiation-induced pulmonary fibrosis by promoting fibrocyte accumulation, attenuating Th17 response and regulating Th1/Th2 cytokine balance in the lung tissues, which suggests that Tregs may be therapeutically manipulated to decelerate the progression of irradiation-induced pulmonary fibrosis.

Local origin of mesenchymal cells in a murine orthotopic lung transplantation model of bronchiolitis obliterans

Bronchiolitis obliterans is the leading cause of chronic graft failure and long-term mortality in lung transplant recipients. Here, we used a novel murine model to characterize allograft fibrogenesis within a whole-lung microenvironment. Unilateral left lung transplantation was performed in mice across varying degrees of major histocompatibility complex mismatch combinations. B6D2F1/J (a cross between C57BL/6J and DBA/2J) (Haplotype H2b/d) lungs transplanted into DBA/2J (H2d) recipients were identified to show histopathology for bronchiolitis obliterans in all allogeneic grafts. Time course analysis showed an evolution from immune cell infiltration of the bronchioles and vessels at day 14, consistent with acute rejection and lymphocytic bronchitis, to subepithelial and intraluminal fibrotic lesions of bronchiolitis obliterans by day 28. Allografts at day 28 showed a significantly higher hydroxyproline content than the isografts (33.21 ± 1.89 versus 22.36 ± 2.33 μg/mL). At day 40 the hydroxyproline content had increased further (48.91 ± 7.09 μg/mL). Flow cytometric analysis was used to investigate the origin of mesenchymal cells in fibrotic allografts. Collagen I-positive cells (89.43% ± 6.53%) in day 28 allografts were H2Db positive, showing their donor origin. This novel murine model shows consistent and reproducible allograft fibrogenesis in the context of single-lung transplantation and represents a major step forward in investigating mechanisms of chronic graft failure.

Integration of proteomic and transcriptomic profiles identifies a novel PDGF-MYC network in human smooth muscle cells

Background

Platelet-derived growth factor-BB (PDGF-BB) has been implicated in the proliferation, migration and synthetic activities of smooth muscle cells that characterize physiologic and pathologic tissue remodeling in hollow organs. However, neither the molecular basis of PDGFR-regulated signaling webs, nor the extent to which specific components within these networks could be exploited for therapeutic benefit has been fully elucidated.

Results

Expression profiling and quantitative proteomics analysis of PDGF-treated primary human bladder smooth muscle cells identified 1,695 genes and 241 proteins as differentially expressed versus non-treated cells. Analysis of gene expression data revealed MYC, JUN, EGR1, MYB, RUNX1, as the transcription factors most significantly networked with up-regulated genes. Forty targets were significantly altered at both the mRNA and protein levels. Proliferation, migration and angiogenesis were the biological processes most significantly associated with this signature, and MYC was the most highly networked master regulator. Alterations in master regulators and gene targets were validated in PDGF-stimulated smooth muscle cells in vitro and in a model of bladder injury in vivo. Pharmacologic inhibition of MYC and JUN confirmed their role in SMC proliferation and migration. Network analysis identified the diaphanous-related formin 3 as a novel PDGF target regulated by MYC and JUN, which was necessary for PDGF-stimulated lamellipodium formation.

Conclusions

These findings provide the first systems-level analysis of the PDGF-regulated transcriptome and proteome in normal smooth muscle cells. The analyses revealed an extensive cohort of PDGF-dependent biological processes and connected key transcriptional effectors to their regulation, significantly expanding current knowledge of PDGF-stimulated signaling cascades. These observations also implicate MYC as a novel target for pharmacological intervention in fibroproliferative expansion of smooth muscle, and potentially in cancers in which PDGFR-dependent signaling or MYC activation promote tumor progression.

Tracking the elusive fibrocyte: identification and characterization of collagen-producing hematopoietic lineage cells during murine wound healing

Fibrocytes are a unique population of circulating cells reported to exhibit characteristics of both hematopoietic and mesenchymal cells, and play an important role in wound healing. However, putative fibrocytes have been found to lose expression of hematopoietic surface markers such as CD45 during differentiation, making it difficult to track these cells in vivo with conventional methodologies. In this study, to distinguish hematopoietic and nonhematopoietic cells without surface markers, we took advantage of the gene vav 1, which is expressed solely on hematopoietic cells but not on other cell types, and established a novel transgenic mouse, in which hematopoietic cells are irreversibly labeled with green fluorescent protein and nonhematopoietic cells with red fluorescent protein. Use of single-cell transcriptional analysis in this mouse model revealed two discrete types of collagen I (Col I) expressing cells of hematopoietic lineage recruited into excisional skin wounds. We confirmed this finding on a protein level, with one subset of these Col I synthesizing cells being CD45+ and CD11b+, consistent with the traditional definition of a fibrocyte, while another was CD45- and Cd11b-, representing a previously unidentified population. Both cell types were found to initially peak, then reduce posthealing, consistent with a disappearance from the wound site and not a loss of identifying surface marker expression. Taken together, we have unambiguously identified two cells of hematopoietic origin that are recruited to the wound site and deposit collagen, definitively confirming the existence and natural time course of fibrocytes in cutaneous healing.

Paracrine functions of fibrocytes to promote lung fibrosis

Fibrocytes are derived from the bone marrow and are found in the circulation. They can be recruited to sites of injury and contribute to repair/remodeling. In vitro evidence suggests that fibrocytes may differentiate into fibroblasts to promote lung fibrosis. However, in vivo evidence for this is sparse. This review summarizes recent literature which may suggest that fibrocytes function to promote fibrosis via paracrine actions. In this way, secretion of growth factors, proteases and matricellular proteins may strongly influence the actions of resident epithelial and mesenchymal cells to promote repair and resolution or to tip the scale toward pathologic remodeling.

Cytokine mediated tissue fibrosis

Acute inflammation is a recognised part of normal wound healing. However, when inflammation fails to resolve and a chronic inflammatory response is established this process can become dysregulated resulting in pathological wound repair, accumulation of permanent fibrotic scar tissue at the site of injury and the failure to return the tissue to normal function. Fibrosis can affect any organ including the lung, skin, heart, kidney and liver and it is estimated that 45% of deaths in the western world can now be attributed to diseases where fibrosis plays a major aetiological role. In this review we examine the evidence that cytokines play a vital role in the acute and chronic inflammatory responses that drive fibrosis in injured tissues. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Short-course rapamycin treatment preserves airway epithelium and protects against bronchiolitis obliterans

BACKGROUND

Damage to airway epithelium is closely related to the development of bronchiolitis obliterans (BO) in pulmonary transplantation. Rapamycin protects against BO development in a murine model, but its use in patients undergoing lung transplantation is limited by its side effects. We hypothesized that short-course rapamycin dosing could be used to prevent airway epithelium loss and protect against BO development in a murine model.

METHODS

A total alloantigenic mismatch, murine, heterotopic tracheal transplant model of BO was used. Animals were treated with either rapamycin or dimethyl sulfoxide (controls) according to one of three treatment regimens: (1) days 1 through 14 after transplantation, (2) days 3 through 7 after transplantation, or (3) days 14 through 28 after transplantation. Epithelial loss was assessed by use of hematoxylin and eosin stains 14 and 28 days after transplantation. Tracheal luminal obliteration was assessed at 28 days.

RESULTS

Early rapamycin treatment was protective against epithelial loss 14 days after transplantation in comparison with control animals (p < 0.001). Rapamycin treatment from days 1 to 14 was more effective at epithelial preservation (p = 0.002) and reducing luminal obliteration (p < 0.001) at 28 days than was rapamycin treatment from days 3 to 7. Late rapamycin treatment (days 14 to 28) allowed for recovery of the previously denuded epithelium at 28 days (92.5% epithelial loss to 35.6%) and a reduction in BO (p < 0.001).

CONCLUSIONS

Short-course rapamycin treatment protects against airway epithelium loss and subsequent development of BO in a murine model. Because of its immunosuppressive and antifibrotic effects, rapamycin may prove to be the ideal medication to prevent chronic rejection and BO in patients undergoing lung transplantation.

Rapamycin blocks fibrocyte migration and attenuates bronchiolitis obliterans in a murine model

BACKGROUND

Fibrocytes are integral in the development of fibroproliferative disease. The CXCL12/CXCR4 chemokine axis has been shown to play a central role in fibrocyte migration and the development of bronchiolitis obliterans (BO) after lung transplantation. Inhibition of the mammalian target of rapamycin (mTOR) pathway with rapamycin has been shown to decrease expression of both CXCR4 and its receptor agonist CXCL12. Thus, we hypothesized that rapamycin treatment would decrease fibrocyte trafficking into tracheal allografts and prevent BO.

METHODS

A total alloantigenic mismatch murine heterotopic tracheal transplant (HTT) model of BO was used. Animals were either treated with rapamycin or dimethyl sulfoxide (DMSO) for 14 days after tracheal transplantation. Fibrocyte levels were assessed by flow cytometry, and allograft neutrophil, CD3(+) T-cell, macrophage, and smooth muscle actin (SMA) levels were assessed by immunohistochemistry. Tracheal luminal obliteration was assessed on hematoxylin and eosin (H&E) stains.

RESULTS

Compared with DMSO-treated controls, rapamycin-treated mice showed a significant decrease in fibrocyte levels in tracheal allografts. Fibrocyte levels in recipient blood showed a similar pattern, although it was not statistically significant. Furthermore, animals treated with rapamycin showed a significant decrease in tracheal allograft luminal obliteration compared with controls. Based on immunohistochemical analyses, populations of α-SMA-positive (α-SMA(+)) cells, neutrophils, CD3(+) T cells, and macrophages were all decreased in rapamycin-treated allografts versus DMSO controls.

CONCLUSIONS

Rapamycin effectively reduces recruitment of fibrocytes into tracheal allografts and mitigates development of tracheal luminal fibrosis. Further studies are needed to determine the cellular and molecular mechanisms that mediate the protective effect of rapamycin against BO.

Fibrocytes in the Pathogenesis of Chronic Fibrotic Lung Disease

Fibrocytes were initially described in 1999 and since that time there has been a growing body of literature to suggest their importance in a number of chronic lung diseases. It is now well established that fibrocytes derive from the bone marrow and circulate within the peripheral blood. However, when injury occurs, fibrocytes can travel to the site of damage via chemokine-mediated recruitment. Recent studies suggest that fibrocyte numbers increase within the lung or circulation during numerous disease processes. Although fibrocytes readily differentiate into fibroblasts in vitro, whether they do so in vivo is still unknown. The variety of pro-fibrotic mediators that are secreted by fibrocytes makes it likely that they act via paracrine functions to influence the behavior of resident lung cells. This review summarizes recent insights regarding fibrocytes in asthma, scleroderma and IPF.