Proteomic Signature of Apolipoprotein J in the Early Phase of New-Onset Myocardial Infarction

Acute myocardial infarction (AMI) is one of the major causes of mortality and morbidity worldwide. Despite all the efforts, there is a lack of early markers for prevention, diagnosis, and treatment of ischemic syndromes. By applying a proteomic expression profiling approach to identify biomarkers of early stages of AMI, we have detected significant changes in Apolipoprotein J/clusterin (ApoJ) in patients with an acute new-onset myocardial infarction. ApoJ characterization by bidimensional electrophoresis (2-DE), followed by mass spectrometry (MALDI-TOF) depicted a cluster of 13 spots (pl, 4.5-5.0; M-w, 37.1-47.3 kDa) with a significantly different distribution between AMI-patients and controls. Specifically, spots 2, 3, 7, 10, and 13 showed a 2-fold increase in their intensity in AMI-patients (P = 0.001). Western-blot analysis (WB) for total serum ApoJ depicted two bands of 40-45 and 65-70 kDa. When only glycosylated forms were analyzed, the band of 65-70 kDa was the most predominant one. A 25% decrease (P = 0.05) of ApoJ glycosylated forms in AMI-patients was detected by 2-DE. Serum ApoJ levels, determined by a commercial ELISA, were significantly lower (P < 0.001) in AMI-patients (n = 39) immediately after the event than in controls (n = 60). In 60% of patients, the lowest ApoJ level was detected within 6 h after the onset of AMI. Between 72 and 96 h after admission, ApoJ values in AMI-patients had reached control levels. Our results demonstrate alterations in ApoJ proteomic profile, due to a differential glycosylation pattern, in AMI-patients within the first 6 h after the onset of the event. Therefore, the analysis of this isoform glycosylation shift in patients with AMI may be of better use to understand ApoJ function than the total serum levels of ApoJ and this isoform shift may become an early marker of AMI.