title: Glycation-altered proteolysis as a pathobiologic mechanism that links dietary glycemic index, aging, and age-related disease (in nondiabetics).
abstract: Epidemiologic studies indicate that the risks for major age-related debilities including coronary heart disease, diabetes, and age-related macular degeneration (AMD) are diminished in people who consume lower glycemic index (GI) diets, but lack of a unifying physiobiochemical mechanism that explains the salutary effect is a barrier to implementing dietary practices that capture the benefits of consuming lower GI diets. We established a simple murine model of age-related retinal lesions that precede AMD (hereafter called AMD-like lesions). We found that consuming a higher GI diet promotes these AMD-like lesions. However, mice that consumed the lower vs. higher GI diet had significantly reduced frequency (P < 0.02) and severity (P < 0.05) of hallmark age-related retinal lesions such as basal deposits. Consuming higher GI diets was associated with > 3 fold higher accumulation of advanced glycation end products (AGEs) in retina, lens, liver, and brain in the age-matched mice, suggesting that higher GI diets induce systemic glycative stress that is etiologic for lesions. Data from live cell and cell-free systems show that the ubiquitin-proteasome system (UPS) and lysosome/autophagy pathway [lysosomal proteolytic system (LPS)] are involved in the degradation of AGEs. Glycatively modified substrates were degraded significantly slower than unmodified substrates by the UPS. Compounding the detriments of glycative stress, AGE modification of ubiquitin and ubiquitin-conjugating enzymes impaired UPS activities. Furthermore, ubiquitin conjugates and AGEs accumulate and are found in lysosomes when cells are glycatively stressed or the UPS or LPS/autophagy are inhibited, indicating that the UPS and LPS interact with one another to degrade AGEs. Together, these data explain why AGEs accumulate as glycative stress increases.
authors.affiliation: Laboratory for Nutrition and Vision Research, USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA.
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Uchiki
authors.forename: Karen A
authors.initials: KA
authors.lastname: Weikel
authors.forename: Wangwang
authors.initials: W
authors.lastname: Jiao
authors.forename: Fu
authors.initials: F
authors.lastname: Shang
authors.forename: Andrea
authors.initials: A
authors.lastname: Caceres
authors.forename: Dorota
authors.initials: D
authors.lastname: Pawlak
authors.forename: James T
authors.initials: JT
authors.lastname: Handa
authors.forename: Michael
authors.initials: M
authors.lastname: Brownlee
authors.forename: Ram
authors.initials: R
authors.lastname: Nagaraj
authors.forename: Allen
authors.initials: A
authors.lastname: Taylor
mesh_terms: D000375:Aging / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001343:Autophagy; D002474:Cell-Free System; D004032:Diet / Q000009:adverse effects*; D004195:Disease Models, Animal; D005947:Glucose / Q000009:adverse effects; D017127:Glycation End Products, Advanced / Q000378:metabolism; D038321:Glycemic Index; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D008268:Macular Degeneration / Q000209:etiology / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D012160:Retina / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D012720:Severity of Illness Index; D025801:Ubiquitin / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism
chemical_list: D017127:Glycation End Products, Advanced; D025801:Ubiquitin; D044763:Ubiquitin-Conjugating Enzymes; D046988:Proteasome Endopeptidase Complex; D005947:Glucose