Age-related changes in human meniscal glycosaminoglycans

Introduction With an increased human lifespan, a major challenge is now to ensure a concomitant increase in healthspan. Meniscal damage and degradation are common and are strongly correlated with subsequent osteoarthritis. Indeed, meniscal damage has been identified in about 60% of people over 60. Markers of pathology will facilitate intervention but first require normal age‐related changes to be established. Methods Undamaged vascular and avascular regions of medial and lateral human menisci were comminuted and the tissue extracted into 4‐m GuHCl and subject to associative CsCl density gradient centrifugation. Aggrecan and the small leucine rich PGs (SLRPs) were isolated and their GAG profiles examined by HPAEC fingerprinting, following enzyme depolymerization, and by an NMR spectroscopy. Results and discussion Analysis of aggrecan and the SLRPs show that there is a complex and dynamic pattern of KS, CS and DS abundance and distribution within human menisci, which changes with age. The abundance of SLRPs is higher in the avascular than vascular tissues, however, this is not reflected in the abundance of aggrecan which is present at similar levels in both tissue regions. The data show no other significant differences between medial and lateral and between vascular and avascular tissue regions. Analysis of the sulfation pattern of CS following digestion by ACII lyase, shows that in both aggrecan and SLRPs the 4‐sulfation level falls with age from 20 to 35% in young tissues to 10–20% in older. Subsequent analyses following ABC lyase depolymerization, to include DS, shows very significant change with age from CS + DS 4‐sulfation levels of ca. 40–55% in young tissue to ca. 15–30% in older. The difference between these datasets represents the contribution made by 4‐sulfated DS. Thus, analysis of the difference suggests that DS makes a decreasing contribution to the CS/DS profile with age. Indeed, this is confirmed by an NMR analysis of these samples. Analysis of the resonances in the region 1.95–2.2 p.p.m. (ref to TSP) allows the estimation of the contribution made by DS, CS and KS. These data show that, in aggrecan, the contribution made by DS chains falls from ca. 10% in younger tissues to ca. 2–4% in older tissues. NMR analysis also shows that KS levels fall with age from ca. 15–20% in younger tissues to 5–10% in older tissues. Analysis of the structure of the KS chains shows chains with a structure similar to that of in articular cartilage but that at all ages there are very low levels of fucosylation (ca. 1–5%). Previous studies of age‐related changes in CS/DS and KS structures have shown significant changes in the first 17 years of life, with only modest nonpathological changes after that time. These data from meniscal tissues do not show such a dramatic halting of normal age‐related changes. Indeed, the data show gradual age‐related changes in DS, CS and KS abundance and structure throughout life. These baseline age‐related changes data will now allow the analysis of pathology‐related changes.     

Age-related changes in the glycosaminoglycans of human meniscal aggrecan

Introduction Meniscal damage and degradation, which are strongly correlated with subsequent OA, have been identified in approximately 60% of people over 60 years of age. Age‐related changes in articular cartilage glycosaminoglycans (GAGs) have been described, and used to facilitate the study of pathology‐related changes ( Plass et al. 1998 ). However, such data do not yet exist for the meniscus. Materials and methods Undamaged human menisci were obtained following leg amputations, and the vascular and avascular zones of each lateral and medial meniscus were extracted into 4 m GuHCl. Aggrecan was recovered in the A1 fraction following CsCl density gradient centrifugation, and the relative abundance of chondroitin, dermatan and keratan sulphates (CS, DS and KS) was examined by NMR spectroscopy at 400 MHz and 43 °C. Results Human meniscal aggrecan was shown to contain CS, DS and KS, and our data show age‐related changes in the relative abundance of these GAGs. The change was similar for medial and lateral menisci and for the vascular and avascular zones within these. The KS abundance in aggrecan from young menisci (<15 years) was found to be 15–20% of the total GAGs. However, in older samples, it comprised only 7–12% of the GAGs. We have confirmed the presence of DS in human meniscal aggrecan and show that the abundance of DS gradually falls from approximately 16% at 10 years to 2–4% at 75 years. There is some variability between humans, although the trend is clear and for each human there is good agreement between medial and lateral menisci and vascular and avascular locations. The levels of CS comprise the remainder of the GAG attached to aggrecan and contribute the remainder of the GAG abundance. This can be seen to increase from 67 to 72% at 10 years to approximately 90% at 75 years. Discussion Our data show a clear age‐related change in the relative abundance CS, DS and KS from human meniscal aggrecan. The data show a decrease in the abundance of KS and DS and a concomitant increase in CS levels. These observations differ from those widely seen for articular cartilage, in which the levels of CS are seen to fall with age. We have confirmed that DS is a component of human meniscal aggrecan in agreement with previous work ( McNicol & Roughley 1980 ). However, previously reported levels of DS, approximately 20%, are those found only in younger menisci. Absolute levels of these GAGs have not yet been determined, and hence the mechanisms which bring about this relative increase in CS with age may include either changes in biosynthetic output and/or widespread GAG loss in which KS and DS loss increases with age.     

Endocrine roles of vitamin K-dependent- osteocalcin in the relation between bone metabolism and metabolic disorders

Reviews in Endocrine and Metabolic Disorders - Obesity and diabetes are important metabolic diseases and a major public health problem among the world, they have serious health and economic...