Objective: In recent years, microarray techniques have been used to characterize differences in mRNA populations between atherosclerotic plaques and normal arterial tissue. Because proteomics provide an attractive complementary approach to genomics, we used Western array technology as a global protein profiling method to identify differentially expressed proteins with potential pathobiological relevance in human atherosclerotic plaques.
Methods: Cell lysates from human carotid endarterectomy specimens and non-atherosclerotic mammary arteries were screened with monoclonal antibodies (823 in total) that were combined into unique cocktails. Hits were verified with traditional Western blotting.
Results: Seven proteins with a >5-fold relative expression difference were identified. One of the most apparent changes in human plaques was the downregulation of apoptosis-linked gene 2 (ALG-2), a positive mediator of apoptotic cell death. Differential expression of ALG-2 in human plaques relative to mammary arteries was not confirmed by real-time quantitative RT-PCR, suggesting post-transcriptional regulation. Uptake of aggregated LDL (agLDL) downregulated ALG-2 protein expression in THP-1 macrophages, but not in smooth muscle cells (SMCs). Transfection of THP-1 cells with ALG-2-specific small interfering RNA (siRNA) caused ALG-2 depletion and inhibited the execution phase of apoptosis (DNA fragmentation) but did not affect caspase-3 activation, annexin-V labeling and necrotic cell death.
Conclusion: Western array screening of carotid endarterectomy specimens revealed a strong downregulation of ALG-2 protein. Because ALG-2 has pro-apoptotic potential, our results point to a novel survival mechanism against cell death in human atherosclerotic plaques.