Comparative proteomic profiling of plasma very-low-density and low-density lipoproteins

BackgroundLow-density lipoprotein (LDL) is a natural metabolite of very-low-density lipoprotein (VLDL) in the circulation. Systematic investigation of total protein components and dynamics might provide insights into this normal metabolic process.MethodsVLDL and LDL were purified from normolipidemia pooled plasma by gradient ultracentrifugation with either ionic or non-ionic media. The protein contents were compared by liquid chromatography tandem mass analyses based on isobaric tag for relative and absolute quantitation and two-dimensional gel electrophoresis.ResultsOur comparative lipoproteomes revealed 21 associated proteins. Combined with Western blot analysis, and on the basis of the differential expression levels we classified them into 3 groups: (i) VLDL > LDL [apolipoprotein (apo) A-IV, apo(a), apoCs, apoE, apoJ and serum amyloid A-4]; (ii) VLDL < LDL [albumin, α-1-antitrypsin, apoD, apoF, apoM, and paraoxonase-1]; and (iii) VLDL = LDL [apoA-I, apoA-II, apoB-100, apoL-I and prenylcysteine oxidase-1]. The apoA-I level positively correlated with PCYOX1 but negatively with apoM in VLDL and LDL. Furthermore, the two-dimensional maps displayed 5 apoA-I isoforms in which phosphorylation at Ser55, Ser166, Thr185, Thr221 and Ser252 residues were identified.ConclusionsThis study revealed the VLDL- and LDL lipoproteomes and the full-spectrum protein changes during physiological VLDL-to-LDL transition. It provides a valuable dataset VLDL and LDL proteomes potentially applied to the development of diagnostics.