Older women deposit bone with less collagen cross-linking and glycosaminoglycan content than bone made by younger women — ASN Events
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  3. Older women deposit bone with less collagen cross-linking and glycosaminoglycan content than bone made by younger women

Older women deposit bone with less collagen cross-linking and glycosaminoglycan content than bone made by younger women (#21)

Mary Louise Fac 1 2 , Haniyeh Hemmatian 2 , Ingrid Poulton 2 , Natalie Sims 1 2
  1. Department of Medicine at St. Vincent's Hospital, The University of Melbourne, Fitzroy, Victoria, Australia
  2. Bone Cell Biology and Disease Unit, St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia

Cortical bone is a heterogeneous material containing osteons at different stages of mineral accrual. With ageing, bone material quality degenerates, but whether this includes deposition of new bone with poor composition is unknown. We previously observed, by Fourier-Transform Infrared Microspectroscopy (FTIRM), that new bone deposited by older women contains collagen that is more compressed than that of younger women. To identify contributors to this age-related difference in collagen quality, we here assessed the same specimens by Raman spectroscopy.

Femoral midshaft cortical bone from 10 young (20-40 year-old) and 10 old (77-95 year-old) women were obtained from the Melbourne Femur Research Collection. Osteons at early and late stages of mineral accrual were identified by histology, calcium content (quantitative backscattered electron imaging), and phosphate:amide I gradient (FTIRM). The osteonal wall was imaged by Raman at 1µm resolution in ~10 early-stage and ~20 late-stage osteons per age group. A piecewise linear mixed model was used to determine differences in matrix maturation in the most recently deposited bone (25µm closest to osteonal pore).

In young women, early-stage osteons (containing osteoid and with an increasing mineral:matrix ratio) exhibited a significant decline in collagen crosslinks (slope=-0.0016), glycosaminoglycan (GAG) content (slope=-0.22), and nanoporosity (slope=-0.02) with increasing distance from the osteonal pore. In old women, their early-stage osteons also showed declines in collagen crosslinks and GAG content, but these began at a lower level than in young women near the osteonal pore, and had 25% and 75% flatter slopes, respectively, compared to young women. In late-stage osteons of young and old women, these maturation processes were not observed: levels were consistently low across the entire osteonal wall. There were no differences in mineral content or crystallinity between osteons of young and old women.

In summary, newly formed osteons still undergoing mineral accrual in young women are also undergoing a process where collagen crosslinks, GAG content and nanoporosity reduce as bone matures. In old women, these parameters are already low in newly deposited bone, resembling mature tissue in young women. We conclude that this more mature collagen material deposited by older women may contribute to age-related bone fragility.