Effect of exercise on age-related changes in collagen fibril diameter distributions in the common digital extensor tendons of young horses

Connective tissues are biological composites comprising of collagen fibrils embedded in (and reinforcing) the hydrated proteoglycan-rich (PG) gel within the extracellular matrices (ECMs). Age-related changes to the mechanical properties of tissues are often associated with changes to the structure of the ECM, namely, fibril diameter. However, quantitative attempts to correlate fibril diameter to mechanical properties have yielded inconclusive evidence. Here, we described a novel approach that was based on the rule of mixtures for fiber composites to evaluate the dependence of age-related changes in tendon tensile strength (σ) and stiffness (E) on the collagen fibril cross-sectional area fraction (ρ), which is related to the fibril volume fraction. Tail tendons from C57BL6 mice from age groups 1.6–35.3months old were stretched to failure to determine σ and E. Parallel measurements of ρ as a function of age were made using transmission electron microscopy. Mathematical models (rule of mixtures) of fibrils reinforcing a PG gel in tendons were used to investigate the influence of ρ on ageing changes in σ and E. The magnitudes of σ, E, and ρ increased rapidly from 1.6monthsto4.0months (P-values <0.05) before reaching a constant (age independent) from 4.0monthsto29.0months (P-values >0.05); this trend continued for E and ρ (P-values >0.05) from 29.0monthsto35.3months, but not for σ, which decreased gradually (P-values <0.05). Linear regression analysis revealed that age-related changes in σ and E correlated positively to ρ (P-values <0.05). Collagen fibril cross-sectional area fraction ρ is a significant predictor of ageing changes in σ and E in the tail tendons of C57BL6 mice.

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Collagen Fibril Diameter Distributions in Ligaments and Tendons of the Carpal Region of the Horse

Connective Tissue Research ◽

10.3109/03008209609028889 ◽

1996 ◽

Vol 34 (1) ◽

pp. 11-21 ◽

Cited By ~ 11

Author(s):

S. P. Davankar ◽

N. J. Deane ◽

A. S. Davies ◽

E. C. Firth ◽

H. Hodge ◽

...

Keyword(s):

Collagen Fibril ◽

Fibril Diameter ◽

Diameter Distributions

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Bimodal collagen fibril diameter distributions direct age-related variations in tendon resilience and resistance to rupture

Journal of Applied Physiology ◽

10.1152/japplphysiol.00258.2012 ◽

2012 ◽

Vol 113 (6) ◽

pp. 878-888 ◽

Cited By ~ 43

Author(s):

K. L. Goh ◽

D. F. Holmes ◽

Y. Lu ◽

P. P. Purslow ◽

K. E. Kadler ◽

...

Keyword(s):

Collagen Fibril ◽

Strain Energy ◽

Age Groups ◽

Bimodal Distribution ◽

Tensile Tests ◽

Age Related ◽

Transmission Electron ◽

Rupture Energy ◽

Tail Tendon ◽

Fibril Diameter

Scaling relationships have been formulated to investigate the influence of collagen fibril diameter ( D) on age-related variations in the strain energy density of tendon. Transmission electron microscopy was used to quantify D in tail tendon from 1.7- to 35.3-mo-old (C57BL/6) male mice. Frequency histograms of D for all age groups were modeled as two normally distributed subpopulations with smaller ( DD1) and larger ( DD2) mean Ds, respectively. Both DD1 and DD2 increase from 1.6 to 4.0 mo but decrease thereafter. From tensile tests to rupture, two strain energy densities were calculated: 1) uE [from initial loading until the yield stress (σ Y)], which contributes primarily to tendon resilience, and 2) uF [from σ Y through the maximum stress (σ U) until rupture], which relates primarily to resistance of the tendons to rupture. As measured by the normalized strain energy densities uE/σ Y and uF/σ U, both the resilience and resistance to rupture increase with increasing age and peak at 23.0 and 4.0 mo, respectively, before decreasing thereafter. Multiple regression analysis reveals that increases in uE/σ Y (resilience energy) are associated with decreases in DD1 and increases in DD2, whereas uF/σ U (rupture energy) is associated with increases in DD1 alone. These findings support a model where age-related variations in tendon resilience and resistance to rupture can be directed by subtle changes in the bimodal distribution of Ds.

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On Collagen Fibril Diameter Distributions

Connective Tissue Research ◽

10.3109/03008209109152160 ◽

1991 ◽

Vol 26 (1-2) ◽

pp. 11-21 ◽

Cited By ~ 11

Author(s):

P. N. Jones

Keyword(s):

Collagen Fibril ◽

Fibril Diameter ◽

Diameter Distributions

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Hypercapnia-induced shear-mediated dilation in the internal carotid artery is blunted in healthy older adults

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00335.2018 ◽

2018 ◽

Vol 315 (5) ◽

pp. H1279-H1286 ◽

Cited By ~ 5

Author(s):

Erika Iwamoto ◽

Joshua M. Bock ◽

Darren P. Casey

Keyword(s):

Older Adults ◽

Shear Rate ◽

Carotid Arteries ◽

Internal Carotid ◽

Healthy Adults ◽

Age Related ◽

The Common ◽

Internal Carotid Arteries ◽

Age Related Changes ◽

Important Stimulus

This study aimed to elucidate the effect of aging on shear-mediated dilation of the common and internal carotid arteries (CCA and ICA, respectively). Hypercapnia-induced shear-mediated dilation in the CCA and ICA were assessed in 10 young (5 women and 5 men, 23 ± 1 yr) and 10 older (6 women/4 men, 68 ± 1 yr) healthy adults. Shear-mediated dilation was induced by two levels of hypercapnia (target end-tidal Pco2, +5 and +10 mmHg from individual baseline values) and was calculated as the percent rise in peak diameter from baseline diameter. There were no differences in shear-mediated dilation between young and older adults in either artery under lower levels of hypercapnia (CCA: 2.8 ± 0.6 vs. 2.0 ± 0.3%, P = 0.35; ICA: 4.6 ± 0.8 vs 3.6 ± 0.4%, P = 0.37). However, shear-mediated dilation in response to higher levels of hypercapnia was attenuated in older compared with young adults in the ICA (4.5 ± 0.5 vs. 7.9 ± 1.2%, P < 0.01) but not in the CCA (3.7 ± 0.6 vs. 4.5 ± 0.8%, P = 0.35). Shear-mediated dilation was significantly correlated to the percent change in shear rate in the ICA (young: r = 0.55, P = 0.01; older: r = 0.49, P = 0.03) but not in the CCA in either young or older adults (young: r = −0.30, P = 0.90; older: r = 0.16, P = 0.50). These data indicate that aging attenuates shear-mediated dilation of the ICA in response to higher levels of hypercapnia, and shear rate is an important stimulus for hypercapnic vasodilation of the ICA in both young and older adults. The present results may provide insights into age-related changes in the regulation of cerebral circulation in healthy adults. NEW & NOTEWORTHY We explored the effect of aging on shear-mediated dilation in the common and internal carotid arteries (CCA and ICA, respectively) in healthy adults. Our findings suggest that 1) aging attenuates shear-mediated dilation of the ICA but not the CCA and 2) shear rate is an important stimulus for hypercapnic vasodilation of the ICA in young and older adults. These findings may provide insights into the age-related changes in cerebrovascular regulation of healthy adults.

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