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Glucosepane Is Associated with Changes to Structural and Physical Properties of Collagen Fibrils

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Glucosepane Is Associated with Changes to Structural and Physical Properties of Collagen Fibrils Article Glucosepane is associated with changes to structural and physical properties of collagen fibrils Anthony Nash 1, Maria Notou 2, Andrea F. Lopez-Clavijo 3, Laurent Bozec 4, Nora H. de Leeuw 5 and Helen L. Birch University College London, Institute of Orthopaedics and Musculoskeletal Science, Stanmore Campus, Royal National Orthopaedic Hospital, Stanmore HA7 4LP, UK Correspondence to Helen L. Birch: [email protected], [email protected], [email protected], [email protected], [email protected] https://doi.org/10.1016/j.mbplus.2019.100013 Abstract Collagen glycation, and in particular the formation of advanced glycation end-product (AGE) crosslinks, plays a central role in the ageing process and in many of the long-term complications of diabetes. Glucosepane, the most abundant and relevant AGE crosslink, has been suggested to increase the stiffness of tissue and reduce its solubility, although no evidence is available concerning the mechanisms. We have used a combination of computational and experimental techniques to study a collagen-rich tissue with a relatively simple organisation to further our understanding of the impact of glucosepane on the structural and physical properties of collagen fibrils. Our work shows that glucosepane levels increase dramatically in aged tendon tissue and are associated with the reduced density of collagen packing and increased porosity to water molecules. Our studies provide the basis to understand many of the tissue dysfunctions associated with ageing and diabetes across a range of different tissues types. © 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). Introduction crosslinks has been known about for almost forty years [5], the AGE crosslink glucosepane was only Glucosepane has emerged as the most abundant identified relatively recently [6]. In the case of and clinically relevant advanced glycation end- glucosepane, its formation is initiated by the amino product (AGE) crosslink in type I collagen-rich group of a lysine residue undergoing a nucleophilic tissues [1] and it is associated with many of the attack by a reactive carbonyl group of glucose in a long-term complications of diabetes, including ne- reaction commonly known as the Maillard reaction. phropathy, neuropathy and retinopathy [2]. More The product of this reaction undergoes a rearrange- recently, increases in glucosepane have been ment to form the more stable Amadori product. This correlated with the progression of the age-related is followed by a series of reactions, where the degenerative disease osteoarthritis [3]. Despite the carbonyl group is passed down the backbone of the association of glucosepane with severe tissue glucose molecule before cyclisation takes place; dysfunction, the mechanism by which these chang- further reaction with the amino group on an arginine es are imposed on the tissue remains largely residue side-chain then forms the glucosepane unexplored. crosslink [6,7]. Like all AGE crosslinks, glucosepane is formed Glucosepane is generating much interest, partic- following a series of spontaneous adventitious ularly with respect to the mechanisms of ageing, modifications to the amino group on the side-chain although the complex chemistry of glucosepane has of lysine and arginine residues in protein polypep- hindered progress in assessing its impact on tide chains [4]. Although the formation of AGE function [8]. Glucosepane levels were first measured 0022-2836/© 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons. org/licenses/by-nc-nd/4.0/). (2019) 4, 100013 2 Glucosepane is associated with changes to collagen fibrils Fig. 1. Human tendon tissue was subjected to sequential enzymatic digestion to release glucosepane, which was separated and quantified using LC Q-TOF MS (a). Relative levels of glucosepane in Achilles and anterior tibialis tendon tissue against patient age. Red squares represent anterior tibialis tendon tissue (dark red = male, light red = female), blue diamonds represent Achilles tendon tissue (dark blue = male, light blue = female) (b). The fragmentation pattern of glucosepane in the tissue sample matched that of the glucosepane standard preparation (c). in human dermal collagen and glomerular basement predictor of future microvascular complications in membrane in diabetic and non-diabetic subjects [9]. diabetic patients [10]. Furthermore, plasma levels of Levels of glucosepane in dermal collagen were glucosepane were found to be increased sixfold in found to increase significantly with increasing age in patients with advanced osteoarthritis relative to non-diabetic samples and to be significantly higher healthy controls [3]. Disease progression is thought in diabetic skin samples [9]. To our knowledge, to be manifested by an AGE crosslink-induced glucosepane levels have not been quantified in other stiffening of the tissue and reduced susceptibility to collagen-rich human tissues such as tendon, liga- proteolytic degradation; both factors are also asso- ment, bone, cartilage and blood vessels, although it ciated with advancing chronological age. has been shown robustly that glucosepane levels in Tendon tissue is one of the most collagen-rich dermal collagen are associated with micro-vascular tissues in the body. Tendons are rope-like struc- disease in other organs [9] and they are an accurate tures, connecting muscletobone,whichare Glucosepane is associated with changes to collagen fibrils 3 Fig. 2. Crystallographic dimensions of lengths and angles (a) accompanied by a cross-section representation of the unit cell periodically replicated (insert). Single collagen protein surface area (b), the number of inter-polypeptide hydrogen bonds found across a single collagen protein (c), the radius of gyration of a single collagen protein (d) and a systemic protein density plot (e). responsible for transmitting tensile forces generated function [12,13]. These properties stem from the by muscle contraction to the bony skeleton to bring precise arrangement of collagen throughout the about movement around a joint. The high tensile hierarchical structure of the tissue from collagen strength required for their function is provided by molecules to fibrils, fibres, fascicles and finally the type I collagen, which forms the majority (about 80%) whole tendon (for a review of tendon structure see of the dry weight of tendon [11]. In addition to high Thorpe and Screen (2016) [14]). tensile strength, the stiffness and elasticity of tendon Collagen in tendon has a long half-life, estimated are highly tuned and tendon-specific for efficient to be around 200 years in equine flexor tendon 4 Glucosepane is associated with changes to collagen fibrils tissue [11], with almost no turnover in human collagen molecule packing within the fibril. MD Achilles tendon [15]; as a result, the collagen is simulations were carried out using GROMACS vulnerable to glycation and crosslinking. Indeed, 5.1.2 [22] with a collagen-like peptide in a unit cell other more easily quantified measures of AGE repeated via periodic boundary conditions in all three formation, such as collagen-linked fluorescence dimensions (Fig. 2a). Three models were created for and the AGE crosslink pentosidine [11], show a study; a wild-type, which is effectively an extension significant positive correlation with donor age, to the unit-cell of the 4Z1R crystal structure of a providing evidence of an accumulation of age- collagen-like peptide; the same structure but modi- related post-translational modifications to collagen fied with a lysine and arginine side chain substituted and suggesting that glucosepane is highly likely to between two polypeptide chains at residue positions accumulate in tendon tissue. Interestingly, the 17 and 49, respectively (pre-cross-link formation); incidence of tendon injury is well known to increase and the structure modified with a glucosepane cross- with older age in human [16–18] and equine [19–21] link between two polypeptide chains of the same species, suggesting a decline in the mechanical collagen molecule, at positions 17 and 49. In the pre- competence of tendon with ageing. cross-linked and cross-linked models, only one Given the high content of type I collagen mole- collagen molecule from the eight was modified in cules in tendon and its relatively simple parallel the final extended unit cell. Each system was arrangement into fibrillar structures, tendon has the subjected to a series of equilibrium simulation potential to provide an ideal model to study the steps, as described in the methodology. After impact of increasing glucosepane levels on collagen equilibration, each system was simulated for 20 ns structural and molecular properties. In this study, we using the NPT ensemble. The initial 10 ns of have used a combination of computer simulations equilibration were discarded and all analyses were and experimental work on ex vivo human tissue to performed over the remaining 10 ns trajectories. determine the impact of glucosepane crosslinks on Structural changes to the collagen molecule were the material properties of tendon tissue at a nano- investigated first by using a rolling sphere with a scale level. radius of 1.2 nm to calculate the total solvent- accessible surface area (SASA) [23] of the peptide backbone atoms for each of the three models. Each Results and discussion set of surface area values were shown to remain consistent (Fig. 2b) providing evidence suggesting a well-equilibrated system. The addition of an arginine Glucosepane levels in tendon tissue and lysine sidechain contributed to a 7.5 nm2 increase in surface area compared to the wild-type, In our studies, we have used human Achilles and whereas the surface area increased by 9.8 nm2 as a anterior tibialis tendon tissue from young (16.7 ± result of the inclusion of a glucosepane crosslink. 2.7 years, n = 6) and old (71.2 ± 6.0 years, n = 6) The increase in SASA is indicative of backbone groups of donors to quantify the levels of glucosepane access increasing in the presence of glucosepane, and determine changes in levels with age (Fig.
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