Donor and recipient cell surface colony stimulating factor-1 promote neointimal formation in transplant-associated arteriosclerosis

PLX3397, a CSF1 receptor inhibitor, limits allotransplantation-induced vascular remodelling

AIMS

Graft vascular disease (GVD), a clinically important and highly complex vascular occlusive disease, arises from the interplay of multiple cellular and molecular pathways. While occlusive intimal lesions are composed predominantly of smooth-muscle-like cells (SMLCs), the origin of these cells and the stimuli leading to their accumulation in GVD are uncertain. Macrophages have recently been identified as both potential drivers of intimal hyperplasia and precursors that undergo transdifferentiation to become SMLCs in non-transplant settings. Colony-stimulating factor-1 (CSF1) is a well-known regulator of macrophage development and differentiation, and prior preclinical studies have shown that lack of CSF1 limits GVD. We sought to identify the origins of SMLCs and of cells expressing the CSF1 receptor (CSF1R) in GVD, and to test the hypothesis that pharmacologic inhibition of CSF1 signalling would curtail both macrophage and SMLC activities and decrease vascular occlusion.

METHODS AND RESULTS

We used genetically modified mice and a vascular transplant model with minor antigen mismatch to assess cell origins. We found that neointimal SMLCs derive from both donor and recipient, and that transdifferentiation of macrophages to SMLC phenotype is minimal in this model. Cells expressing CSF1R in grafts were identified as recipient-derived myeloid cells of Cx3cr1 lineage, and these cells rarely expressed smooth muscle marker proteins. Blockade of CSF1R activity using the tyrosine kinase inhibitor PLX3397 limited the expression of genes associated with innate immunity and decreased levels of circulating monocytes and intimal macrophages. Importantly, PLX3397 attenuated the development of GVD in arterial allografts.

CONCLUSION

These studies provide proof of concept for pharmacologic inhibition of the CSF1/CSF1R signalling pathway as a therapeutic strategy in GVD. Further preclinical testing of this pathway in GVD is warranted.

PI3Kγ promotes vascular smooth muscle cell phenotypic modulation and transplant arteriosclerosis via a SOX9-dependent mechanism

Background

Transplant arteriosclerosis (TA) remains the major cause of chronic graft failure in solid organ transplantation. The phenotypic modulation of vascular smooth muscle cells (VSMCs) is a key event for the initiation and progression of neointimal formation and TA. This study aims to explore the role and underlying mechanism of phosphoinositide 3-kinases γ (PI3Kγ) in VSMC phenotypic modulation and TA.

Methods

The rat model of aortic transplantation was established to detect PI3Kγ expression and its role in neointimal formation and vascular remodeling in vivo. PI3Kγ shRNA transfection was employed to knockdown PI3Kγ gene. Aortic VSMCs was cultured and treated with TNF-α to explore the role and molecular mechanism of PI3Kγ in VSMC phenotypic modulation.

Findings

Activated PI3Kγ/p-Akt signaling was observed in aortic allografts and in TNF-α-treated VSMCs. Lentivirus-mediated shRNA transfection effectively inhibited PI3Kγ expression in medial VSMCs while restoring the expression of VSMC contractile genes, associated with impaired neointimal formation in aortic allografts. In cultured VSMCs, PI3Kγ blockade with pharmacological inhibitor or genetic knockdown markedly abrogated TNF-α-induced downregulation of VSMC contractile genes and increase in cellular proliferation and migration. Moreover, SOX9 located in nucleus competitively inhibited the interaction of Myocardin and SRF, while PI3Kγ inhibition robustly reduced SOX9 expression and its nuclear translocation and repaired the Myocardin/SRF association.

Interpretation

These results suggest that PI3Kγ plays a critical role in VSMC phenotypic modulation via a SOX9-dependent mechanism. Therefore, PI3Kγ in VSMCs may represent a promising therapeutic target for the treatment of TA.

Fund

National Natural Science Foundation of China.

Cross talk between inflammatory cytokines and granulocyte-macrophage colony-stimulating factor in transplant vasculopathy

BACKGROUND

Transplant vasculopathy limits the clinical results of solid organ transplantation.

MATERIALS AND METHODS

Thirty-three arterial grafts were implanted in the abdominal aorta of Lewis rats. The animals were humanely sacrificed 4 wk after surgery. The study groups had 15 arterial isografts and 18 arterial allografts. Growth factors and inflammatory cytokines, released by the removed grafts, were studied in organ culture. The released growth factors were analyzed in vitro to assess their effect on the proliferation of endothelial, smooth muscle cells and fibroblasts.

RESULTS

In arterial isogenic and allogenic grafts, platelet-derived growth factor and basic fibroblastic growth factor release was minimal (P < 0.01). There was a significant release of granulocyte-macrophage colony-stimulating factor and tumor necrosis factor-α (TNF-α; P < 0.001) in allografts. GM-CSF and TNF-α, at concentrations in the allograft organ cultures, stimulated significantly the growth of smooth muscle cells. The simultaneous action of TNF-α and GM-CSF had an exponential growth effect on endothelial cells and smooth muscle cells. Interleukin (IL)-1, IL-2, and IL-9 were released in high quantities by allografts. In vitro, IL-1, IL-2, and IL-9 facilitated the growth effect of GM-CSF and TNF-α.

CONCLUSIONS

Transplant vasculopathy depends on the simultaneous and complementary additive effects of several growth factors and cytokines, which have a continuous "cross talk."

Growth factors and experimental arterial grafts

BACKGROUND

The production of growth factors from several experimental arterial conduits was determined.

METHODS

We implanted 105 experimental arterial grafts that were 1 cm long in the abdominal aorta of Lewis rats (average weight, 250 g). Five different types of grafts were analyzed: arterial isografts, vein grafts, arterial allografts, and polytetrafluoroethylene (PTFE) grafts with normal or decreased compliance. Animals were killed humanely 4 weeks after surgery and the production of platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF), transforming growth factor-β, tumor necrosis factor-α, and interleukin-1 was analyzed.

RESULTS

Myointimal hyperplasia (MH) was evident in vein grafts, arterial allografts, and PTFE grafts, but not in arterial isografts. Growth factor production was increased for grafts prone to develop MH like vein, PTFE grafts, and arterial allografts. PDGF and bFGF were increased significantly for PTFE and vein grafts, but not for arterial allografts. The importance of bFGF and PGDF was confirmed by the capability of antibody to PDGF and to bFGF to reduce the mitogenic activity of smooth muscle cells, in vivo and in vitro, for PTFE and vein grafts, but not for arterial allografts, in which a predominant role was played by interleukin-1 and tumor necrosis factor-α.

CONCLUSIONS

Agents able to neutralize this increased production of growth factors, either directly or by competition with their receptors, can prevent MH formation.

Role of macrophage colony-stimulating factor in the development of neointimal thickening following arterial injury

Evidence suggests that macrophage colony-stimulating factor (M-CSF) participates critically in atherosclerosis; little is known about the role of M-CSF in the development of neointimal hyperplasia following mechanical vascular injury. We examined the expression of M-CSF and its receptor, c-fms, in rodent and rabbit models of arterial injury. Injured rat carotid arteries expressed 3- to 10-fold higher levels of M-CSF and c-fms mRNA and protein following balloon injury as compared to uninjured arteries. In the rabbit, M-CSF protein expression was greatest in neointimal smooth muscle cells (SMCs) postinjury, with some expression in medial SMCs. M-CSF-positive SMCs exhibited markers of proliferation. At 30days postinjury, neointimal SMCs in the adjacent healed area near the border between injured and uninjured zone lost both proliferative activity and overexpression of M-CSF. The presence of induced M-CSF and c-fms expression correlated with the initiation of SMCs proliferation. M-CSF stimulated incorporation of [(3)H] thymidine in human aortic smooth muscle cells in a concentration-dependent manner. Serum-free conditioned medium from aortic SMCs also promoted DNA synthesis, and this effect was blocked by M-CSF specific antibody. To test further the role of M-CSF in vivo, we induced arterial injury by placing a periadventitial collar around the carotid arteries in compound mutant mice lacking apolipoprotein apoE (apoE(-/-)) and M-CSF. Loss of M-CSF abolished the neointimal hyperplastic response to arterial injury in apoE(-/-) mice. Local delivery of M-CSF to the injured artery restored neointimal proliferation, suggesting a critical role of M-CSF for the development of neointimal thickening following arterial injury.

Cell-Surface and Secreted Isoforms of CSF-1 Exert Opposing Roles in Macrophage-Mediated Neural Damage in Cx32-Deficient Mice

Previous studies in myelin-mutant mouse models of the inherited and incurable nerve disorder, Charcot-Marie-Tooth (CMT) neuropathy, have demonstrated that low-grade secondary inflammation implicating phagocytosing macrophages amplifies demyelination, Schwann cell dedifferentiation and perturbation of axons. The cytokine colony stimulating factor-1 (CSF-1) acts as an important regulator of these macrophage-related disease mechanisms, as genetic and pharmacologic approaches to block the CSF-1/CSF-1R signaling result in a significant alleviation of pathological alterations in mutant peripheral nerves. In mouse models of CMT1A and CMT1X, as well as in human biopsies, CSF-1 is predominantly expressed by endoneurial fibroblasts, which are closely associated with macrophages, suggesting local stimulatory mechanisms. Here we investigated the impact of cell-surface and secreted isoforms of CSF-1 on macrophage-related disease in connexin32-deficient (Cx32def) mice, a mouse model of CMT1X. Our present observations suggest that the secreted proteoglycan isoform (spCSF-1) is predominantly expressed by fibroblasts, whereas the membrane-spanning cell-surface isoform (csCSF-1) is expressed by macrophages. Using crossbreeding approaches to selectively restore or overexpress distinct isoforms in CSF-1-deficient (osteopetrotic) Cx32def mice, we demonstrate that both isoforms equally regulate macrophage numbers dose-dependently. However, spCSF-1 mediates macrophage activation and macrophage-related neural damage, whereas csCSF-1 inhibits macrophage activation and attenuates neuropathy. These results further corroborate the important role of secondary inflammation in mouse models of CMT1 and might identify specific targets for therapeutic approaches to modulate innate immune reactions.

SIGNIFICANCE STATEMENT

Mouse models of Charcot-Marie-Tooth neuropathy have indicated that low-grade secondary inflammation involving phagocytosing macrophages amplifies demyelination, Schwann cell dedifferentiation, and perturbation of axons. The recruitment and pathogenic activation of detrimental macrophages is regulated by CSF-1, a cytokine that is mostly expressed by fibroblasts in the diseased nerve and exists in three isoforms. We show that the cell-surface and secreted isoforms of CSF-1 have opposing effects on macrophage activation and disease progression in a mouse model of CMT1X. These insights into opposing functions of disease-modulating cytokine isoforms might enable the development of specific therapeutic approaches.