The origin of neointimal smooth muscle cells in transplant arteriosclerosis from recipient bone-marrow cells in rat aortic allograft

N-octanoyl Dopamine Attenuates the Development of Transplant Vasculopathy in Rat Aortic Allografts Via Smooth Muscle Cell Protective Mechanisms

BACKGROUND

Transplant vasculopathy (TV) is a major cause for late graft loss after cardiac transplantation. Endothelial damage and T cell infiltration play a pivotal role in the development of TV. Because N-octanoyl dopamine (NOD) inhibits vascular inflammation and suppresses T cell activation in vitro, we here tested the hypothesis that NOD treatment ameliorates TV.

METHODS

Aortic grafts were orthotopically transplanted in the Dark Agouti to Brown Norway strain combination. Recipient rats were treated with NOD or vehicle administered via osmotic minipumps. Histology and quantitative polymerase chain reaction (qPCR) were performed on nontransplanted aortas and grafts explanted 2 and 4 weeks after transplantation to assess the degree of TV, inflammation, apoptosis, and number of (proliferating) α smooth muscle actin (αSMA) neointimal cells. In vitro analyses of human aortic smooth muscle cells were performed to test the effect of NOD on proliferation (WST-1 assay), cell cycle (flow cytometry and qPCR), and cytokine-induced apoptosis (flow cytometry).

RESULTS

Allografts from vehicle-treated recipients developed neointimal lesions predominantly consisting of αSMA-expressing cells. NOD treatment significantly reduced neointima formation and neointimal αSMA cells. In situ, smooth muscle cell proliferation (Ki67) was not influenced by NOD. Macrophage (CD68), T (CD3), and Natural Killer (ANK61) cell infiltration as well as intragraft TNFα and IFNγ mRNA expression were similar in both groups. Medial apoptosis (cleaved caspase-3) was significantly reduced by NOD. In vitro, NOD inhibited proliferation of human aortic smooth muscle cells by causing a G1-arrest and protected from TNFα-induced apoptosis.

CONCLUSIONS

This study identified NOD as potential treatment modality to attenuate TV. Our data clearly support a vasculoprotective effect of NOD by reducing smooth muscle cell proliferation and inflammation-induced apoptosis.

MicroRNA-155 Promotes the Directional Migration of Resident Smooth Muscle Progenitor Cells by Regulating Monocyte Chemoattractant Protein 1 in Transplant Arteriosclerosis

OBJECTIVE

Smooth muscle-like cells are major cell components of transplant arteriosclerosis lesions. This study investigated the origin of the smooth muscle-like cells, the mechanisms responsible for their accumulation in the neointima, and the factors that drive these processes.

APPROACH AND RESULTS

A murine aortic transplantation model was established by transplanting miR-155(-/-) bone marrow cells into miR-155(+/+) mice. MicroRNA-155 was found to play a functional role in the transplant arteriosclerosis. Moreover, we found that the nonbone marrow-derived progenitor cells with markers of both early differentiated smooth muscles and stem cells in the allograft adventitia were smooth muscle progenitor cells. Purified smooth muscle progenitor cells expressed a mature smooth muscle cell marker when induced by platelet-derived growth factor-BB in vitro. In vivo, these cells could migrate into the intima from the adventitia and could contribute to the neointimal hyperplasia. The loss of microRNA-155 in bone marrow-derived cells decreased the concentration gradient of monocyte chemoattractant protein 1 between the intima and the adventitia of the allografts, which reduced the migration of smooth muscle progenitor cells from the adventitia into the neointima.

CONCLUSIONS

This study demonstrated that microRNA-155 promoted the directional migration of smooth muscle progenitor cells from the adventitia by regulating the monocyte chemoattractant protein 1 concentration gradient, which aggravated transplant arteriosclerosis.

Effects of exogenous peripheral-blood-derived endothelial progenitor cells or unfractionated bone-marrow-derived cells on neointimal formation and inflammation in cholesterol-fed, balloon-denuded, and radiated iliac arteries of inbred rabbits

BACKGROUND

Injection of bone marrow cells (BMC) and endothelial progenitor cells (EPC) or application of stem-cell-mobilizing factors has been associated both with reduction or exacerbation of atherosclerosis and with unstable plaque phenotype. The discrepancies may reflect the cell type, dosing, duration, and route of administration of cells in these studies. The aim of this study was to determine the effects of peripheral-blood-derived endothelial progenitor cells (PBEPC) or unfractionated BMC obtained from inbred siblings on neointimal formation and inflammation in cholesterol-fed, balloon-denuded, and radiated rabbit iliac arteries.

METHODS

Rabbits were fed a 1.0% cholesterol diet for 14 days, followed by endothelial denudation in both iliac arteries, and continued on a 0.15% cholesterol diet. On day 42, denuded areas were radiated, and animals were randomized. The first group received PBEPC (n=5), the second group received BMC (n=4), and the third group received heparinized (20 IU) saline (Control; n=3). PBEPC were characterized by flow cytometry. Cells (5x10(6)) or saline was administered twice through the ear vein: the first time at 1 h after radiation and the second time at 2 weeks after radiation. Four weeks after radiation, the animals were sacrificed, and arterial segments were processed for morphometry.

RESULTS

Administration of BMC or PBEPC from inbred siblings had no adverse effect. Lumen area (0.93+/-0.53 mm(2)), neointimal area (0.65+/-0.29 mm(2)), percent stenosis (44+/-21), and macrophage score (0.6+/-0.3) in controls were similar to those in cell-treated groups.

CONCLUSION

This study demonstrates that, in the current animal model, either PBEPC or BMC failed to affect neointimal formation or inflammation.