# Pathological calcification in canine tendon-derived cells is modulated by extracellular ATP

## TL;DR

This study developed an in vitro model to investigate calcification in canine tendons and found that extracellular ATP can modulate this process.

## Contribution

The study introduces a novel in vitro model for canine tendon calcification and identifies ATP as a modulator of this condition.

## Key findings

- 2 mM di-sodium phosphate and 2 mM calcium chloride induced optimal calcification in vitro.
- ATP treatment reduced calcium deposition and inhibited osteogenic gene expression.
- ATP increased cell viability and reversed calcification in a dose-dependent manner.

## Abstract

Tendon calcification is a commonly associated with degenerative tendinopathy of the Achilles tendons in dogs. It is characterised by the formation of calcific deposits and is refractory to treatment, often re-forming after surgical removal. Little is known about its pathogenesis and therefore the aims of this study were to develop an in vitro model of canine tendon calcification and use this model to investigate mechanisms driving calcification. Cells from the canine Achilles tendon were cultured with different calcifying media to establish which conditions were best able to induce specific, cell-mediated calcification. Once optimum calcification conditions had been established, the effect of ATP treatment on calcification was assessed. Results revealed that 2 mM di-sodium phosphate combined with 2 mM calcium chloride provided the optimum calcifying conditions, increasing calcium deposition and expression of osteogenic-related genes similar to those observed in tendon calcification in vivo. ATP treatment inhibited calcification in a dose-dependent manner, reducing calcium deposition and increasing cell viability, while osteogenic-related genes were no longer upregulated. In conclusion, the in vitro model of canine tendon calcification developed in this study provides the ability to study mechanisms driving tendon calcification, demonstrating that ATP plays a role in modulating tendon calcification that should be explored further in future studies.

The online version contains supplementary material available at 10.1007/s11259-024-10331-1.