Expression of Allograft Inflammatory Factor-1 Is a Marker of Activated Human Vascular Smooth Muscle Cells and Arterial Injury

Abstract

Abstract-The cytokine-induced activation and proliferation of medial vascular smooth muscle cells (VSMCs) leading to intimal hyperplasia is one of the most critical cellular events in the formation of transplant arteriopathy and balloon angioplasty-induced restenosis. Allograft inflammatory factor-1 (AIF-1) is a calcium-binding protein that we have previously shown to be expressed in balloon angioplasty-injured rat carotid arteries. We hypothesized that AIF-1 expression may be associated with the VSMC response to injury. In this study, we examined AIF-1 expression in immunologic and mechanical models of arterial injury. Reverse transcription-polymerase chain reaction and Western analysis demonstrated that AIF-1 is acutely and transiently expressed in aortic medial smooth muscle cells of rat cardiac allografts, with mRNA and protein peaking at 3 to 7 days after transplant and declining by 10 days after transplant. Immunohistochemical analysis identified abundant AIF-1 in the medial VSMCs of these vessels. Immunohistochemical analysis of balloon angioplasty-injured swine coronary arteries also demonstrates an acute AIF-1 expression detectable by 24 hours and continuing up to 14 days after the procedure. AIF-1 in these vessels also localizes to the medial VSMCs and cells of the developing neointima. AIF-1 protein is not expressed in quiescent cultured human VSMCs but is induced in cells challenged with various inflammatory cytokines, primarily by interferon-␥, interleukin-1␤, and T-cell-conditioned media. Transfection and overexpression of AIF-1 in human VSMCs result in enhanced growth of these cells. Taken together, these data indicate that AIF-1 expression is associated with vascular trauma and suggest that this protein may play a role in VSMC activation subsequent to arterial injury.

Allograft inflammatory factor-1 augments macrophage phagocytotic activity and accelerates the progression of atherosclerosis in ApoE−/− mice

“…AIF-1 expression regulates the proliferation of VSMC (8,31). Thus, AIF-1 appears to be involved in the pathogenesis of atherosclerosis through not only macrophage activation but also vascular regeneration in the lesion and we were able to demonstrate that AIF-1 Tg ApoE -/-mice exhibited significantly increased areas of atherosclerotic lesions as compared to those in ApoE -/-mice.…”

“…AIF-1 is expressed in cells of a monocyte/macrophage lineage and augmented by interferon (IFN)-γ, suggesting a novel molecular involvement in allogeneic responses. AIF-1 expression has also been demonstrated in macrophages and microglial cells during experimental autoimmune inflammation (3,4) and cerebral infarction (5), as well as in devascularized skeletal muscle tissues (6), vascular smooth muscle cells (VSMC) at the site of injury with balloon angioplasty (7,8) and activated T cells (9). Thus, AIF-1 may play a pivotal role not only in immune responses to alloantigens but also in various host responses to inflammatory stimuli.…”

“…Inhibition of AIF-1 expression by small interfering (si) RNA reduced macrophage migration and proliferation (17). Moreover, the findings that oxidized lowdensity lipoprotein (LDL) induces AIF-1 expression (17) and that AIF-1 expression regulates the proliferation of VSMC (8), suggest that AIF-1 is critically involved in the pathogenesis of atherosclerosis, a disease related to inflammation (18).…”

Allograft Inflammatory Factor-1 Expression Correlates With Cardiac Rejection and Development of Cardiac Allograft Vasculopathy

“…8 We have previously reported the acute and transient expression of AIF-1 in medial and intimal VSMC in several models of arterial injury in rat and swine. 11,12 Although constitutively expressed in leukocytes, AIF-1 is not expressed in unstimulated cultured human VSMC but is strongly induced in response to inflammatory cytokines and T-lymphocyte conditioned media. 12 We have also shown that overexpression of AIF-1 in VSMC leads to a more rapid growth and deregulated expression of cell cycle proteins, suggesting that one function of AIF-1 might be in the regulation of VSMC proliferation.…”

“…11,12 Although constitutively expressed in leukocytes, AIF-1 is not expressed in unstimulated cultured human VSMC but is strongly induced in response to inflammatory cytokines and T-lymphocyte conditioned media. 12 We have also shown that overexpression of AIF-1 in VSMC leads to a more rapid growth and deregulated expression of cell cycle proteins, suggesting that one function of AIF-1 might be in the regulation of VSMC proliferation. 12,13 Standard morphological features of endomyocardial biopsy specimens do not necessarily correlate with the development CAV, 14 and a specific, reliable, objective, and rapidly quantitative surrogate is needed to detect the early development of CAV.…”