Site-specific glycations of apolipoprotein A-I lead to differentiated functional effects on lipid-binding and on glucose metabolism |
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Authors: | Joan Domingo-Espín Oktawia Nilsson Katja Bernfur Rita Del Giudice Jens O Lagerstedt |
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Institution: | 1. Department of Experimental Medical Science, Lund University, S-221 84 Lund, Sweden;2. Department of Biochemistry and Structural Biology, Lund University, S-221 84 Lund, Sweden |
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Abstract: | Prolonged hyperglycemia in poorly controlled diabetes leads to an increase in reactive glucose metabolites that covalently modify proteins by non-enzymatic glycation reactions. Apolipoprotein A-I (apoA-I) of high-density lipoprotein (HDL) is one of the proteins that becomes glycated in hyperglycemia. The impact of glycation on apoA-I protein structure and function in lipid and glucose metabolism were investigated.ApoA-I was chemically glycated by two different glucose metabolites (methylglyoxal and glycolaldehyde). Synchrotron radiation and conventional circular dichroism spectroscopy were used to study apoA-I structure and stability. The ability to bind lipids was measured by lipid-clearance assay and native gel analysis, and cholesterol efflux was measured by using lipid-laden J774 macrophages. Diet induced obese mice with established insulin resistance, L6 rat and C2C12 mouse myocytes, as well as INS-1E rat insulinoma cells, were used to determine in vivo and in vitro glucose uptake and insulin secretion.Site-specific, covalent modifications of apoA-I (lysines or arginines) led to altered protein structure, reduced lipid binding capability and a reduced ability to catalyze cholesterol efflux from macrophages, partly in a modification-specific manner. The stimulatory effects of apoA-I on the in vivo glucose clearance were negatively affected when apoA-I was modified with methylglyoxal, but not with glycolaldehyde. The in vitro data showed that both glucose uptake in muscle cells and insulin secretion from beta cells were affected. Taken together, glycation modifications impair the apoA-I protein functionality in lipid and glucose metabolism, which is expected to have implications for diabetes patients with poorly controlled blood glucose. |
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Keywords: | AGE advanced glycation end-product apoA-I apolipoprotein A-I CVD cardiovascular diseases CD circular dichroism DMPC 1 2-dimyristoyl-sn-glycero-3-phosphocholine ESI-MS/MS electrospray ionization tandem mass spectrometry GA glycolaldehyde GSIS glucose stimulated insulin secretion GTT glucose tolerance test HDL high-density lipoprotein HFD high fat diet i p intraperitoneally MG methylglyoxal MLV multilamellar vesicles MS mass spectroscopy rHDL recombinant HDL SRCD synchrotron radiation CD TNBSA 2 4 6-trinitrobenzene sulfonic acid WT wild type apoA-I High-density lipoprotein HDL Glycation Glucose metabolism Diabetes |
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