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

Short-range interactions between fibrocytes and CD8+ T cells in COPD bronchial inflammatory response

Bronchi of chronic obstructive pulmonary disease (COPD) are the site of extensive cell infiltration, allowing persistent contact between resident cells and immune cells. Tissue fibrocytes interaction with CD8⁺ T cells and its consequences were investigated using a combination of in situ, in vitro experiments and mathematical modeling. We show that fibrocytes and CD8⁺ T cells are found in the vicinity of distal airways and that potential interactions are more frequent in tissues from COPD patients compared to those of control subjects. Increased proximity and clusterization between CD8⁺ T cells and fibrocytes are associated with altered lung function. Tissular CD8⁺ T cells from COPD patients promote fibrocyte chemotaxis via the CXCL8-CXCR1/2 axis. Live imaging shows that CD8⁺ T cells establish short-term interactions with fibrocytes, that trigger CD8⁺ T cell proliferation in a CD54- and CD86-dependent manner, pro-inflammatory cytokines production, CD8⁺ T cell cytotoxic activity against bronchial epithelial cells and fibrocyte immunomodulatory properties. We defined a computational model describing these intercellular interactions and calibrated the parameters based on our experimental measurements. We show the model's ability to reproduce histological ex vivo characteristics, and observe an important contribution of fibrocyte-mediated CD8⁺ T cell proliferation in COPD development. Using the model to test therapeutic scenarios, we predict a recovery time of several years, and the failure of targeting chemotaxis or interacting processes. Altogether, our study reveals that local interactions between fibrocytes and CD8⁺ T cells could jeopardize the balance between protective immunity and chronic inflammation in the bronchi of COPD patients.

SOCS3 overexpression in T cells ameliorates chronic airway obstruction in a murine heterotopic tracheal transplantation model

PURPOSE

Suppressor of cytokine signaling-3 (SOCS3) is a negative feedback inhibitor of cytokine signaling with T-cell-mediated immunosuppressive effects on obliterative bronchiolitis (OB). In this study, we aimed to investigate the impact of T-cell-specific overexpression of SOCS3 using a murine heterotopic tracheal transplantation (HTT) model.

METHODS

Tracheal allografts from BALB/c mice were subcutaneously transplanted into wild-type C57BL/6J (B6; WT) mice and SOCS3 transgenic B6 (SOCS3TG) mice. Tracheal allografts were analyzed by immunohistochemistry and quantitative polymerase chain reaction assays at days 7 and 21.

RESULTS

At day 21, allografts in SOCS3TG mice showed significant amelioration of airway obstruction and epithelial loss compared with allografts in WT mice. The intragraft expression of IFN-γ and CXCL10 was suppressed, while that of IL-4 was enhanced in SOCS3TG mice at day 7. The T-bet levels were lower in SOCS3TG allografts than in WT allografts at day 7.

CONCLUSION

We revealed that the overexpression of SOCS3 in T cells effectively ameliorates OB development in a murine HTT model by inhibiting the Th1 phenotype in the early phase. Our results suggest that the regulation of the T-cell response, through the modulation of SOCS expression, has potential as a new therapeutic strategy for chronic lung allograft dysfunction.

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.

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.

Rapamycin prevents bronchiolitis obliterans through increasing infiltration of regulatory B cells in a murine tracheal transplantation model

OBJECTIVE

B lymphocytes are generally considered to be activators of the immune response; however, recent findings have shown that a subtype of B lymphocytes, regulatory B lymphocytes, play a role in attenuating the immune response. Bronchiolitis obliterans remains the major limitation to modern-day lung transplantation. The role of regulatory B lymphocytes in bronchiolitis obliterans has not been elucidated. We hypothesized that regulatory B lymphocytes play a role in the attenuation of bronchiolitis obliterans.

METHODS

We performed a standard heterotopic tracheal transplant model. Tracheas from Balb/c mice were transplanted into C57BL/6 recipients. Rapamycin treatment and dimethyl sulfoxide control groups were each treated for the first 14 days after the transplant. Tracheas were collected on days 7, 14, and 28 post-transplantation. Luminal obliteration was evaluated by hematoxylin-eosin staining and Picrosirius red staining. Immune cell infiltration and characteristics, and secretion of interleukin-10 and transforming growth factor-β1 were accessed by immunohistochemistry. Cytokines and transforming growth factor-β1 were measured using the Luminex assay (Bio-Rad, Hercules, Calif).

RESULTS

The results revealed that intraperitoneal injection of rapamycin for 14 days after tracheal transplantation significantly reduced luminal obliteration on day 28 when compared with the dimethyl sulfoxide control group (97.78% ± 3.63% vs 3.02% ± 2.14%, P < .001). Rapamycin treatment markedly induced regulatory B lymphocytes (B220(+)IgM(+)IgG(-)IL-10(+)TGF-β1(+)) cells when compared with dimethyl sulfoxide controls. Rapamycin treatment inhibited interleukin-1β, 6, 13, and 17 on days 7 and 14. Rapamycin also greatly increased interleukin-10 and transforming growth factor-β1 production in B cells and regulatory T lymphocytes infiltration on day 28.

CONCLUSIONS

Mammalian target of rapamycin inhibition decreases the development of bronchiolitis obliterans via inhibition of proinflammatory cytokines and increasing regulatory B lymphocytes cell infiltration, which subsequently produces anti-inflammatory cytokines and upregulates regulatory T lymphocyte cells.

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.

Rapamycin promotes Schwann cell migration and nerve growth factor secretion

Rapamycin, similar to FK506, can promote neural regeneration in vitro. We assumed that the mechanisms of action of rapamycin and FK506 in promoting peripheral nerve regeneration were similar. This study compared the effects of different concentrations of rapamycin and FK506 on Schwann cells and investigated effects and mechanisms of rapamycin on improving peripheral nerve regeneration. Results demonstrated that the lowest rapamycin concentration (1.53 nmol/L) more significantly promoted Schwann cell migration than the highest FK506 concentration (100μmol/L). Rapamycin promoted the secretion of nerve growth factors and upregulated growth-associated protein 43 expression in Schwann cells, but did not significantly affect Schwann cell proliferation. Therefore, rapamycin has potential application in peripheral nerve regeneration therapy.

Rapamycin attenuates pulmonary allergic vasculitis in murine model by reducing TGF-β production in the lung

BACKGROUND

Rapamycin has been reported to inhibit mesenchymal cell proliferation in a murine model of pulmonary fibrosis. In the present study, we examined the effects of rapamycin on vascular remodeling including intraluminal myofibroblast proliferation in a murine model of allergic vasculitis with eosinophil infiltration.

METHODS

C57BL/6 mice were sensitized with ovalbumin (OVA) and alum. The positive controls were exposed to aerosolized OVA daily for 7 days. The other group of mice was administered with rapamycin (1mg/kg) intraperitoneally, in parallel with daily exposure to aerosolized OVA for 7 days. On the 3rd and 7th day, bronchoalveolar lavage (BAL) was performed and the lungs were excised for pathological analysis. Cell differentials were determined and concentrations of IL-4, IL-5, IL-13 and TGF-β in the BAL fluid (BALF) were measured. Semi-quantitative analysis of pathological changes in the pulmonary arteries was evaluated according to the severity of vasculitis.

RESULTS

The number of eosinophils in BALF was reduced significantly in the mice treated with rapamycin compared to the positive control. There was a significant decrease in the TGF-β concentration of the BALF in the rapamycin-treated group compared to that of the positive control. The pathological scores were reduced significantly in the rapamycin-treated group compared to the positive control group. Intraluminal myofibroblasts in pulmonary arteries were reduced dramatically in the rapamycin-treated group compared to the positive control group.

CONCLUSIONS

Rapamycin suppressed pulmonary vascular remodeling in a murine model of allergic vasculitis with eosinophil infiltration through reducing eosinophil infiltration and TGF-β production in the lung and inhibition against biological action of TGF-β.

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.