title: Racemized and Isomerized Proteins in Aging Rat Teeth and Eye Lens.
abstract: The quantification of aspartic acid racemization in the proteins of nonmetabolically active tissues can be used as a measure of chronological aging in humans and other long-lived organisms. However, very few studies have been conducted in shorter-lived animals such as rodents, which are increasingly used as genetic and metabolic models of aging. An initial study had reported significant changes in the ratio of d- to l-aspartate in rat molars with age. Using a sensitive HPLC method for the determination of d- and l-aspartate from protein hydrolysates, we found no accumulation of d-aspartate in the molars of 17 rats that ranged in age from 2 to 44 months, and the amount of d-aspartate per molar did not correspond with molar eruption date as had been previously reported. However, developing an alternate approach, we found significant accumulation of isomerized aspartyl residues in eye lens proteins that are also formed by spontaneous degradation processes. In this study, we used the human protein l-isoaspartate/d-aspartate O-methyltransferase (PCMT1) as an analytical reagent in a sensitive and convenient procedure that could be used to rapidly examine multiple samples simultaneously. We found levels of isomerized aspartyl residues to be about 35 times higher in the lens extracts of 18-month-old rats versus 2-month-old rats, suggesting that isomerization may be an effective marker for biological aging in this range of ages. Importantly, we found that the accumulation appeared to plateau in rats of 18 months and older, indicating that potentially novel mechanisms for removing altered proteins may develop with age.
authors.affiliation: 1 Department of Chemistry and Biochemistry, The Molecular Biology Institute, University of California , Los Angeles, Los Angeles, California.
authors.forename: Rebeccah A
authors.initials: RA
authors.lastname: Warmack
authors.affiliation: 2 Tissue Engineering, Regenerative Medicine and Cell Therapies Laboratory, CUCAIBA, Buenos Aires Province Ministry of Public Health , Buenos Aires, Argentina .
authors.forename: Eduardo
authors.initials: E
authors.lastname: Mansilla
authors.affiliation: 3 Institute for Biochemical Research (INIBIOLP)-Cathedra of Histology B, Cathedra of Pathology B, School of Medicine, National University of La Plata , La Plata, Argentina .
authors.forename: Rodolfo G
authors.initials: RG
authors.lastname: Goya
authors.affiliation: 1 Department of Chemistry and Biochemistry, The Molecular Biology Institute, University of California , Los Angeles, Los Angeles, California.
authors.forename: Steven G
authors.initials: SG
authors.lastname: Clarke
mesh_terms: D000367:Age Factors; D000375:Aging / Q000378:metabolism*; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D005136:Eye Proteins / Q000737:chemistry / Q000378:metabolism*; D005260:Female; D006868:Hydrolysis; D007536:Isomerism; D007908:Lens, Crystalline / Q000378:metabolism*; D008963:Molar / Q000378:metabolism*; D026601:Protein D-Aspartate-L-Isoaspartate Methyltransferase / Q000378:metabolism; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D059748:Proteolysis; D017207:Rats, Sprague-Dawley
chemical_list: D015415:Biomarkers; D005136:Eye Proteins; D011506:Proteins; D001224:Aspartic Acid; C435725:PCMT1 protein, human; D026601:Protein D-Aspartate-L-Isoaspartate Methyltransferase