AIF-1 expression modulates proliferation of human vascular smooth muscle cells by autocrine expression of G-CSF

Objective-Allograft inflammatory factor-1 (AIF-1) is associated with vascular smooth muscle cell (VSMC) activation and vascular injury. The purpose of this study was to characterize the molecular mechanism of AIF-1 growth-enhancing effects in human VSMC. Methods and Results-Primary human VSMCs were stably transduced with AIF-1 retrovirus (RV). Impact on cell growth was evaluated by the increase in cell number, and the effects on gene expression were determined by cDNA microarray analysis. AIF-RV overexpressing cells grew significantly more rapidly than empty-RV control cells in growth medium and serum-reduced medium (P<0.01 and 0.02, respectively). cDNA microarray analysis and Western blotting on serum-starved AIF-1-transduced VSMCs identified increased mRNA expression of several cell cycle proteins and, surprisingly, the cytokine G-CSF. Addition of G-CSF caused a 75% increase in proliferation of VSMCs in the absence of serum growth factors. The proliferative effects of AIF-1 were abrogated by neutralizing antibodies to G-CSF (P<0.05), and AIF-1-transduced VSMCs are chemotactic for human monocytes. Increased expression of G-CSF and colocalization with AIF-1 positive cells were seen in diseased, not normal human coronary arteries. Conclusions-This study indicates that AIF-1 enhances VSMC growth by autocrine production of G-CSF, and AIF-1 expression may influence VSMC-inflammatory cell communication.