Age-related changes in hydroxylysylglycosides of human glomerular basement membrane collagen

Correlation between single nephron glomerular filtration rate and filtration area in superficial glomeruli of developing rats

Single nephron glomerular filtration rate (SNGFR) was correlated to the area of the glomerular basement membrane (GBM) determined by stereological techniques in rats between 20 and 40 days of age. Single nephron glomerular filtration rate increased 8.4 times in parallel with a twofold increase in GBM area. The much greater postnatal increase in SNGFR than in GBM area demonstrates that the increase in GBM area cannot account for the entire increase in SNGFR. Instead a combination of other factors influencing SNGFR most likely determines the largest part of the increase in SNGFR during this period. Thus, the drop in vascular resistance known to occur during maturation will increase the renal blood flow and may cause the filtration process to turn from a state of filtration equilibrium to or close to disequilibrium, thereby increasing GFR. Additional increase in GFR may be due to an increased net driving force for filtration and/or changed hydraulic permeability.

Age-related changes in non-enzymatic glycosylation of human basement membranes

Age and diabetes-related changes in the extent of non-enzymatic glycosylation of two anatomically distinct human basement membranes were examined. The amount of glucose in ketoamine linkage to glomerular basement membrane, measured by the thiobarbituric acid reaction, correlated positively and significantly with age. For analysis of lens capsule basement membrane, adsorption to agarose-linked phenylboronate was used. The ability of this resin to completely discriminate non-glycosylated from glycosylated residues was first documented by separating synthetic preparations of radioactive glucitol-lysine and glucitol-hydroxylysine, the glucosylamines formed with non-enzymatic glycosylation of collagen, from the respective free amino acids by affinity chromatography on and batch adsorption to phenylboronate. The extent of non-enzymatic glycosylation of lens capsule basement membranes correlated with age in both non-diabetic and diabetic samples, and the slopes of the lines for age versus glycosylation were similar in both groups. The calculated line for diabetic specimens, however, was displaced about 15 years to the left, compatible with premature aging. The results indicate that non-enzymatic glycosylation can be accurately assessed in minute amounts of tissue by phenylboronate adsorption, and provide evidence that human basement membrane is subject to increased glycosylation with aging and diabetes.

Age-related changes in sulfation of basement membrane glycosaminoglycans

Alterations in heparan sulfate, the principal glycosaminoglycan species in glomerular basement membrane, have been proposed as contributory to permeability changes in nephropathic disorders. In the present study, the extent of sulfation of glycosaminoglycans isolated from pronase digests of human glomerular basement membrane, obtained from subjects 15-89 years old, was examined. The sulfate to hexuronic acid ratio significantly diminished as a function of increasing age. These results suggest that decreased sulfation of glycosaminoglycans and consequent reduction in net negative charge alters permselective properties of the glomerular basement membrane with aging.

Age-related changes in rat glomerular basement membrane

1. The yield of GBM from rat kidney increased with rat age and the membrane became more collagen-like, as judged by the glycine, hydroxyproline, hydroxylysine content and the degree of glycosylation. 2. GBM became progressively less soluble in sodium dodecyl sulphate (SDS) and 2-mercaptoethanol with age. An increase in the lower molecular weight subunits of membranes prepared from older rats was demonstrated by polyacrylamide gel electrophoresis.

Chemical characterization of glomerular and tubular basement membranes of men of different age

Pairs of glomerular and tubular basement membrane preparations were obtained from kidneys of individuals of premature age up to 80 years. The purity of the preparations was established with light and electron microscopy and by estimating the total phosphorus content. The amino acid and carbohydrate composition was determined and statistically evaluated for 33 to 38 preparations divided over five age groups. Comparison of glomerular and tubular basement membranes from the same kidneys showed that regardless of age glomerular basement membranes contain more 3-hydroxyproline and more of the heteropolysaccharide constituents neuraminic acids and mannose. These differences cannot be ascribed solely to the presence of a minor amount of interstitial collagen. The chemical composition of the two types of basement membranes changes with age. For the first few years after birth the contents of glycine and total imino acids increase and those of collagen-nonspecific amino acids decrease, whereas constituents of the heteropolysaccharide units do not change markedly. These results suggest that proportions of collagenous and noncollagenous peptide moieties gradually change with age in both glomerular and tubular basement membranes. In addition, the extent of hydroxylation of proline and lysine increases significantly with age, reaching an adult level for glomerular basement membranes after 4 to 7 months of age and for tubular basement membranes during late childhood. The contents of glucose and galactose rise with age to an extent comparable with that of hydroxylysine. The age-related changes in basement membrane composition may influence functional properties of these extracellular renal structures.