Inhibition of AIF-1 expression by constitutive siRNA expression reduces macrophage migration, proliferation, and signal transduction initiated by atherogenic stimuli.
Allograft inflammatory factor-1 (AIF-1) is a cytoplasmic, calcium-binding, inflammation-responsive scaffold protein. Several studies have reported increased AIF-1 expression in activated macrophages and have implicated AIF-1 as a marker of activated macrophages. However, the function of AIF-1 in macrophages and the mechanism whereby it participates in macrophage activation are unknown at this time. Immunohistochemical analysis colocalized AIF-1 expression with CD68-positive macrophages in atherosclerotic human coronary arteries. Subsequent experiments were designed to determine a role for AIF-1 in macrophage activation in response to atherogenic stimuli. Stimulation of human and murine macrophages with oxidized LDL significantly increased AIF-1 expression above basal levels. Stable transfection of AIF-1 small interfering RNA (siRNA) in macrophages reduced AIF-1 protein expression by 79% and reduced macrophage proliferation by 52% (P < 0.01). Inhibition of proliferation was not due to induction of apoptosis. Sequences that did not knock down AIF-1 expression had no effect on proliferation. AIF-1 siRNA expression reduced macrophage migration by 60% (P < 0.01). Both proliferation and migration of siRNA-expressing macrophages could be restored by adenoviral expression of AIF-1 (P < 0.001 and 0.005, respectively), suggesting a tight association between AIF-1 expression and macrophage activation. Phosphorylation of Akt, p44/42 MAPK, and p38 kinase were significantly reduced in siRNA macrophages challenged with oxidized LDL (P < 0.05). Phosphorylation of p38 kinase was significantly inhibited in siRNA macrophages stimulated with T lymphocyte conditioned medium (P < 0.05). These data indicate that AIF-1 mediates atherogenesis-initiated signaling and activation of macrophages.
Tian
Ying
Y
Department of Physiology, Cardiovascular Research Center, Temple University School of Medicine, Rm. 810, MRB, 3420 N. Broad St., Philadelphia, PA 19140, USA.
Kelemen
Sheri E
SE
Autieri
Michael V
MV
D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D015214:Antigens, Differentiation, Myelomonocytic / Q000378:metabolism; D050197:Atherosclerosis; D002135:Calcium-Binding Proteins; D002465:Cell Movement / Q000502:physiology*; D049109:Cell Proliferation; D003331:Coronary Vessels / Q000166:cytology / Q000378:metabolism / Q000473:pathology; D017077:Culture Media, Conditioned / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008077:Lipoproteins, LDL / Q000494:pharmacology; D008262:Macrophage Activation; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008840:Microfilament Proteins; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D000097382:CD68 Molecule
D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D002135:Calcium-Binding Proteins; D017077:Culture Media, Conditioned; D004268:DNA-Binding Proteins; D008077:Lipoproteins, LDL; D008840:Microfilament Proteins; D020928:Mitogen-Activated Protein Kinases; D051057:Proto-Oncogene Proteins c-akt; D034741:RNA, Small Interfering; C112986:AIF1 protein, human; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C099252:oxidized low density lipoprotein