Calcaneal Tendon Collagen Fiber Morphometry and Aging

Fibrillar collagen in tendons and its natural development in rabbits are discussed in this paper. Achilles tendons from newborn (similar to 7 days) to elderly (similar to 38 months) rabbits were monitored in intact (n(tendons) = 24) and microtome sectioned (ntendons = 11) states with label-free second harmonic generation microscopy. After sectioning, the collagen fiber pattern was irregular for the younger animals and remained oriented parallel to the load axis of the tendon for the older animals. In contrast, the collagen fiber pattern in the intact samples followed the load axis for all the age groups. However, there was a significant difference in the tendon crimp pattern appearance between the age groups. The crimp amplitude (A) and wavelength (Lambda) started at very low values (A = 2.0 +/- 0.6 mu m, Lambda = 19 +/- 4 mu m) for the newborn animals. Both parameters increased for the sexually mature animals (>5 months old). When the animals were fully mature the amplitude decreased but the wavelength kept increasing. The results revealed that the microtome sectioning artifacts depend on the age of animals and that the collagen crimp pattern reflects the physical growth and development. The project was mainly supported by the Grant Agency of Charles University (grant no. GAUK 956213), Czech Science Foundation, grant no. 16-14758S, by the Ministry of Health of the Czech Republic, grant no. 16-28637A, by the Ministry of Education, Youth and Sports within National Sustainability Programme I, project no. LO1309, by MEYS (LM2015062 Czech-BioImaging), by ERDF OPPK Brain-View CZ.2.16/3.1.00/21544, and D.H. acknowledges the support from the Flemish Government and Hasselt University for a research stay at Hasselt University.