Ex Vivo Organ Cultures as Models to Study Bone Biology

Abstract

The integrity of the skeleton is maintained by the coordinated and balanced activities of the bone cells. Osteoclasts resorb bone, osteoblasts form bone, and osteocytes orchestrate the activities of osteoclasts and osteoblasts. A variety of in vitro approaches has been used in an attempt to reproduce the complex in vivo interactions among bone cells under physiological as well as pathological conditions and to test new therapies. Most cell culture systems lack the proper extracellular matrix, cellular diversity, and native spatial distribution of the components of the bone microenvironment. In contrast, ex vivo cultures of fragments of intact bone preserve key cell–cell and cell–matrix interactions and allow the study of bone cells in their natural 3D environment. Further, bone organ cultures predict the in vivo responses to genetic and pharmacologic interventions saving precious time and resources. Moreover, organ cultures using human bone reproduce human conditions and are a useful tool to test patient responses to therapeutic agents. Thus, these ex vivo approaches provide a platform to perform research in bone physiology and pathophysiology. In this review, we describe protocols optimized in our laboratories to establish ex vivo bone organ cultures and provide technical hints and suggestions. In addition, we present examples on how this technical approach can be employed to study osteocyte biology, drug responses in bone, cancer‐induced bone disease, and cross‐talk between bone and other organs © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Feasibility of Cell Lines for In Vitro Co-Cultures Models for Bone Metabolism

“…Trabecular core cultures are also used to investigate biocompatibility of materials [103], or cancer-dependent effects on bone [90]. The possibility to generate these ex vivo cultures from human bone slices or biopsies, even allows investigating molecular mechanisms in metabolic bone diseases [111,112].…”

Use of in vitro bone models to screen for altered bone metabolism, osteopathies, and fracture healing: challenges of complex models

“…Therefore, trabecular core cultures represent a great model to investigate alterations in bone metabolism and biocompatibility of materials. The possibility to generate these ex vivo cultures from human bone slices or biopsies further allows investigation of molecular mechanisms in metabolic bone diseases, when the bone samples are obtained from patients with the underlying disease (Bellido and Delgado-Calle 2020 ; Owen and Reilly 2018 ). When the models should be used for screening approaches, one has to keep in mind the metabolism of the different drugs within the body, e.g., first path effects and metabolism in the liver.…”

Trends in Bone Metastasis Modeling

“…These first models were used to study bone growth, bone and cartilage matrix turnover, and the effects of cancer in bone [150][151][152]. More recently, this system has been employed to study mechanical loading, interactions between different bone cell types, the molecular steps involved in bone resorption/formation, and cancer progression [137]. In the past decades, a variety of creative assays have been developed to efficaciously model an in situ bone environment.…”

“…Bellido and colleagues further developed this model, switching to a rotating culture system. This allowed a direct contact of freshly bisected postnatal calvariae and tumor cells, in order to stimulate bone-tumor cell interactions [137]. A recent work has extended this model to a more accurate system that is focused on the human bone-tumor niche, by replacing rodents' samples with human ones [158].…”