Abstract
Diabetic (DM) patients have exacerbated atherosclerosis and high CVD burden. Changes in lipid metabolism, lipoprotein structure, and dysfunctional HDL are characteristics of diabetes. Our aim was to investigate whether serum ApoA-I, the main protein in HDL, was biochemically modified in DM patients. By using proteomic technologies, we have identified a 26 kDa ApoA-I form in serum. MS analysis revealed this 26 kDa form as a novel truncated variant lacking amino acids 1-38, ApoA-IΔ(1-38). DM patients show a 2-fold increase in ApoA-IΔ(1-38) over nondiabetic individuals. ApoA-IΔ(1-38) is found in LDL, but not in VLDL or HDL, with an increase in LDL3 and LDL4 subfractions. To identify candidate mechanisms of ApoA-I truncation, we investigated potentially involved enzymes by in silico data mining, and tested the most probable molecule in an established animal model of diabetes. We have found increased hepatic cathepsin D activity as one of the potential proteases involved in ApoA-I truncation. Cathepsin D-cleaved ApoA-I exhibited increased LDL binding affinity and decreased antioxidant activity against LDL oxidation. In conclusion, we show for the first time: a) presence of a novel truncated ApoA-I form, ApoA-IΔ(1-38), in human serum; b) ApoA-IΔ(1-38) is transported by LDL; c) ApoA-IΔ(1-38) is increased in dense LDL fractions of DM patients; and d) cathepsin D-ApoA-I truncation may lead to ApoA-IΔ(1-38) binding to LDLs, increasing their susceptibility to oxidation and contributing to the high cardiovascular risk of DM patients.
Highlights
Diabetic (DM) patients have exacerbated atherosclerosis and high CVD burden
This significant difference was not picked-up by ELISA determination of ApoA-I serum levels that gave significantly lower values in DM patients when compared with nonDM individuals (DM: 69.8 [59.8–83.5] mg/dl vs. nonDM: 139.7 [119.0– 155.3] mg/dl, P < 0.0001; Table 1)
Here we describe for the first time the presence of ApoA-I⌬(1-38) in serum, a form that is significantly increased in DM patients
Summary
Diabetic (DM) patients have exacerbated atherosclerosis and high CVD burden. Changes in lipid metabolism, lipoprotein structure, and dysfunctional HDL are characteristics of diabetes. A novel truncated form of apolipoprotein A-I transported by dense LDL is increased in diabetic patients. Several large clinical trials have demonstrated the importance of plasma lipoproteins in the pathogenesis of coronary artery disease (CAD) [3] It is well-known that high levels of LDLs are considered to be a key contributor to the initiation and progression of atherosclerosis [4], and are, one of the strongest predictors of CAD in both DM and nonDM patients [5]. ApoA-I transitions from lipid-free protein to spherical HDL particles through a particle remodeling process [10]. Levels of ApoA-I correlate with the protective effect of HDLs against atherosclerosis [16]
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