Abstract 550: Nuclear Targeting of Apelin in Vascular Smooth Muscle Cells: Implications in Cell Proliferation and Atherosclerotic Plaque Formation?
Background: The main circulatory form of Apelin is a highly conserved 13 amino acid hypotensive peptide derived from a 77 amino acid prepropeptide. The very low plasma levels suggest autocrine, paracrine and possibly intracrine functions of Apelin. It is synthesized in smooth muscle cells (SMCs), and we found a nuclear expression in rhomboid type (R), poorly differentiated SMCs. The biological features of R-SMCs (i.e. enhanced proliferative and migratory activities) explain their capacity to accumulate in the intima.
Objectives: Investigate the role of intracrine Apelin in SMC phenotypic change, a process characteristic of atherosclerotic plaque formation.
Methods and Results: As shown in our previous work, a 3’-shift in translation can lead to N-truncated peptides with new address sequences (FASEB J. 20(6): 732-4, 2006). P-SORT software analysis of preproApelin sequence suggests that N-terminal truncated Apelin may target the nucleus, and we confirm this in many cell types by overexpression of mutated preproApelin-EGFP and preproApelin-His-tag. Transfection of mutated preproApelin-His-tag encoding plasmid in differentiated spindle-shaped (S) SMCs induces a transition towards a R-phenotype associated with increased proliferative activity, as well as downregulation of SMC differentiation markers (i.e. α-smooth muscle actin) and increased nuclear expression of S100A4 (a marker typical of R-SMCs). In contrast, transfection of S-SMCs with wild type preproApelin-His-tag encoding plasmid does not induce nuclear targeting of Apelin or S100A4, and does not change the S-phenotype. Stimulation of S-SMCs with PDGF-BB also induces nuclear targeting of both Apelin and S100A4 and transition to the R-phenotype. In vivo, Apelin is expressed in SMC nuclei of stent-induced intimal thickening, while its expression in SMCs of the media is mainly cytoplasmic.
Conclusions: Altogether, theses preliminary studies provide evidence for nuclear targeting of Apelin in SMCs and suggest actions on gene expression, proliferation, and differentiation. The pathophysiological consequences of this retargeting could be of importance in the understanding of artherosclerosis.
- © 2012 by American Heart Association, Inc.