Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2023 Feb 24:7:100087.
doi: 10.1016/j.yjsbx.2023.100087. eCollection 2023.

Heterotopic mineral deposits in intact rat Achilles tendons are characterized by a unique fiber-like structure

Maria Pierantoni  1 , Malin Hammerman  1   2 , Isabella Silva Barreto  1 , Linnea Andersson  1 , Vladimir Novak  3 , Hanna Isaksson  1 , Pernilla Eliasson  2   4
Affiliations

Heterotopic mineral deposits in intact rat Achilles tendons are characterized by a unique fiber-like structure

Maria Pierantoni et al. J Struct Biol X. .

Abstract

Heterotopic mineralization entails pathological mineral formation inside soft tissues. In human tendons mineralization is often associated with tendinopathies, tendon weakness and pain. In Achilles tendons, mineralization is considered to occur through heterotopic ossification (HO) primarily in response to tendon pathologies. However, refined details regarding HO deposition and microstructure are unknown. In this study, we characterize HO in intact rat Achilles tendons through high-resolution phase contrast enhanced synchrotron X-ray tomography. Furthermore, we test the potential of studying local tissue injury by needling intact Achilles tendons and the relation between tissue microdamage and HO. The results show that HO occurs in all intact Achilles tendons at 16 weeks of age. HO deposits are characterized by an elongated ellipsoidal shape and by a fiber-like internal structure which suggests that some collagen fibers have mineralized. The data indicates that deposition along fibers initiates in the pericellular area, and propagates into the intercellular area. Within HO deposits cells are larger and more rounded compared to tenocytes between unmineralized fibers, which are fewer and elongated. The results also indicate that multiple HO deposits may merge into bigger structures with time by accession along unmineralized fibers. Furthermore, the presence of unmineralized regions within the deposits may indicate that HOs are not only growing, but mineral resorption may also occur. Additionally, phase contrast synchrotron X-ray tomography allowed to distinguish microdamage at the fiber level in response to needling. The needle injury protocol could in the future enable to elucidate the relation between local inflammation, microdamage, and HO deposition.

Keywords: Calcification; Collagen; Fibers; HO, Heterotopic Ossification; Pathological mineralization; Phase contrast enhanced synchrotron X-ray tomography.

PubMed Disclaimer

Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

None
Graphical abstract
Fig. 1
Fig. 1
HO deposits in intact Achilles tendons are characterized by a fiber-like structure. A) Volume rendering showing the location of the HO deposit in the whole tendon (from bone to muscle junction). B) Volume rendering of one deposit of HO. Longitudinal (C) and cross-section (D) slices showing the internal fiber-like structure of the HO deposit. E) magnification of the area in the square in C) and F) magnification showing the transition from collagen fibers to mineralized fibers in the tendon tissue. Arrowheads indicate cell-like lacunae within the deposit and the arrows show how the fiber structure is maintained moving from the soft collagen tissue into the mineralized deposit.
Fig. 2
Fig. 2
HO deposits containing unmineralized gaps. A) Tendon cross-section showing the location of the HO deposit within the tendon margins (arrowheads). B) Longitudinal view showing three gaps within one HO deposit. C) Tendon cross-section showing the HO deposit bulging out from the tendon margins (arrowheads) into the surrounding tissue. D) Gap within a deposit containing adipocyte-like structures (arrowheads) similar to adipose tissue found outside the tendon (arrows). Inserts: longitudinal views showing the position of the deposits from the calcaneus bone on A) the bottom anterior and C) lateral views, the circle indicates the deposit shown in the main panel.
Fig. 3
Fig. 3
Microdamage in the collagen structure induced by the needling was visible after 4 weeks. A) 5 times needled tendon and B) 20 times needled tendon. The arrows indicate the beginning and end of the damaged region. In both tendons HO deposits in the proximity of the needled regions were observed.
Fig. 4
Fig. 4
Merging deposits of HO. A) Volume rendering showing the location of three merging HO deposits in a 5 times needled tendon. B) Volume rendering magnification of the three merging deposits in A. C-D) Longitudinal magnifications showing the merging (arrows) between the top and middle deposits (C) and between the middle and bottom deposit (D).
Fig. 5
Fig. 5
Formation of an HO deposit in a tendon needled 5 times. From left to right: cross-sectional, left and right views of the deposit showing that HO may start around cells (arrowheads) and propagates along the fibers in between them (arrow). Scale bars = 25 µm.
Fig. 6
Fig. 6
Histology of HO deposits in intact tendons. The tendons were stained with Alcian blue (A-D) or Picro Sirius Red (E-G). A and E) overview of the whole tendon, B and F) the HO deposit (*) was located at the distal side of the tendon close the surface. The mineralized region was denser and characterized by areas which were darker than the unmineralized fibers. The arrows indicate the presence of adipose tissue around the tendon. C) An increased number of cells is present in the HO (*) compared to the surrounding tissue (arrowhead). D) Within the mineralized region rounded cells (*) were observed. These cells were bigger than the elongated tenocytes (arrowhead) present in between unmineralized fibers. G) Within the HO deposit a fiber-like structure was preserved but the fibers are more disorganized and discontinuous (*) than the highly oriented unmineralized fibers (arrowhead). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

References

    1. Asai S., Otsuru S., Candela M.E., Cantley L., Uchibe K., Hofmann T.J., Zhang K., Wapner K.L., Soslowsky L.J., Horwitz E.M., Enomoto-Iwamoto M. Stem Cells. 2014;32:3266–3277. - PMC - PubMed
    1. Bogaerts S., Carvalho C.D.B., Scheys L., Desloovere K., D’hooge J., Maes F., Suetens P., Peers K. PLoS One. 2017;12:e0181364. - PMC - PubMed
    1. Chan E.D., Morales D.V., Welsh C.H., McDermott M.T., Schwarz M.I. Am. J. Respir. Crit. Care Med. 2002;165:1654–1669. - PubMed
    1. Chen G., Jiang H., Tian X., Tang J., Bai X., Zhang Z., Wang L. Mol. Med. Rep. 2017;16:5901–5907. - PMC - PubMed
    1. Cloetens P., Ludwig W., Baruchel J., Van Dyck D., Van Landuyt J., Guigay J.P., Schlenker M. Appl. Phys. Lett. 1999;75:2912–2914.