Graft vascular disease (GVD) is the single greatest barrier to the long-term success of solid-organ transplantation. The lesions of GVD characteristically show concentric vascular intimal hyperplasia composed of smooth muscle-like cells (SMLCs) and associated extracellular matrix; this intimal expansion develops diffusely throughout the vasculature of transplanted organs, eventually limiting their arterial conduit function and causing graft ischemia and failure. Experimental allografts placed in Colony Stimulating Factor-1 (CSF- 1, also known as M-CSF)-deficient osteopetrotic (op) mice show greatly reduced accumulation of neointimal SMLCs compared to those placed in control recipients, suggesting that CSF-1, the principal mediator of macrophage differentiation, activation, and survival, has a significant role in GVD. In recent studies, we used op mice, reconstituted by transgenesis to express specific isoforms of CSF-1, as either donors or recipients in carotid arterial allograft transplantation. We found that lack of all CSF-1 in recipients significantly limited neointimal hyperplasia, while recipient expression of cell surface (cs) CSF-1 alone was sufficient for neointimal expansion. Surprisingly, absence of CSF-1 in donor tissue also impaired neointima formation; this reduction was also completely reversed when donor tissue expressed the cs isoform alone. Neointimal SMLCs expressed the CSF-1 receptor (CSF-1R) encoded by the c-fms oncogene, and antibody-mediated blockade of this receptor inhibited SMLC proliferation in vitro. Taken together, these findings suggest that CSF-1, expressed on the surface of both donor and recipient derived cells, can act in a local, autocrine/juxtacrine manner in GVD to stimulate chronic neointimal SMLC proliferation and eventual vascular obstruction. Based on these findings, we hypothesize that an essential function of CSF-1 signaling in GVD pathogenesis resides not only in its ability to stimulate its classical cellular target, the macrophage, but also in its effects on neointimal SMLCs that express the CSF-1R. To test this hypothesis and assess therapeutic opportunities that it suggests, we propose three aims: first, we will identify the essential cell type(s) through which CSF-1 drives GVD; second, we will test the effectiveness of pharmacologic CSF-1R inhibitors for prevention and regression of GVD in mouse transplantation models; and third, we will examine clinical transplant tissues, including grafts with advanced GVD, for evidence of expression and activation of the CSF-1 signaling pathway in human GVD. These studies will advance understanding of how CSF-1 signaling promotes GVD and evaluate its potential as a therapeutic target that can be readily translated into clinical practice to mitigate graft failure.

Public Health Relevance

Transplantation of hearts and kidneys is a proven life-saving intervention for patients suffering from end stage heart and renal failure. Unfortunately, the long term effectiveness of these procedures is limited by arteriosclerotic vascular disease that occurs in within the circulation of the transplanted organ. This problem affects almost all transplant recipients and is the major cause of eventual graft failure. There are currently no proven therapies that can prevent or reverse this vascular disease. Our studies address the role in this process of a cellular growth factor called CSF-1, and will evaluate the possibility that inhibitionof this factor may provide a novel strategy to decrease transplant vascular disease and prolong transplanted organ function.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Project (R01)
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Atherosclerosis and Inflammation of the Cardiovascular System Study Section (AICS)
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Adhikari, Bishow B
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Albert Einstein College of Medicine
United States
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Riascos-Bernal, Dario F; Sibinga, Nicholas E S; Kitsis, Richard N (2018) PDCD5 says no to NO. Proc Natl Acad Sci U S A 115:4535-4537