A supplement‐free osteoclast–osteoblast co‐culture for pre‐clinical application

Abstract

There is increasing demand for efficient and physiological in vitro cell culture systems suitable for testing new pharmaceutical drugs or for evaluating materials for tissue regeneration. In particular, co-cultures of two or more tissue-relevant cell types have the advantage to study the response of cells on diverse parameters in a more natural environment with respect to physiological complexity. We developed a direct bone cell co-culture system using human peripheral blood monocytes (hPBMC) and human bone marrow stromal cells (hBMSC) as osteoclast/osteoblast precursor cells, respectively, strictly avoiding external supplements for the induction of differentiation. The sophisticated direct hPBMC/hBMSC co-culture was characterized focusing on osteoclast function and was compared with two indirect approaches. Only in the direct co-culture, hPBMC were triggered by hBMSC into osteoclastogenesis and became active resorbing osteoclasts. Bisphosphonates and sulfated glycosaminoglycans were used to examine the suitability of the co-culture system for evaluating the influence of certain effectors on bone healing and bone regeneration and the contribution of each cell type thereby. The results show that the investigated substances had more pronounced effects on both osteoblasts and osteoclasts in the co-culture system than in respective monocultures.

Impact of Culture Medium on Cellular Interactions in in vitro Co-culture Systems

“…Both molecules are naturally produced by osteoblasts (Boyce and Xing, 2007). Thus, in a co-culture with osteoblasts, no additional cytokines may be needed for osteoclast formation (Schulze et al, 2018;Zhu et al, 2018).…”

Osteoclast Formation within a Human Co-Culture System on Bone Material as an In Vitro Model for Bone Remodeling Processes

“…In contrast to the study of Schulze et al, [52] we assume differentiation factors such as M-CSF and RANKL were not sufficiently expressed in our culture set-ups to create active OCs on BS without further supplementation. Only in model III, including M-CSF and RANKL in the media, characteristic actin formation, the expression of cathepsin K, and CD51/61 in multinuclear cells, as well as resorption pits, were seen on BS.…”

“…A recent study by Schulze et al presents a direct co-culture of hMSCs and hMCs on a SaOS-2-derived extracellular matrix [52]. This matrix was introduced as an alternative material for testing bone resorption activity of osteoclasts [53,54].…”

From the Clinical Problem to the Basic Research—Co-Culture Models of Osteoblasts and Osteoclasts

“…Primary human osteoblasts should be the cells of choice to be used in all areas of in vitro bone biology research. However, human mesenchymal stem/stromal cells (MSCs) and human peripheral blood monocytes (PBMCs) are a good alternative for the co-culture systems, which are targeted at the interaction between osteoblast and osteoclast, avoiding the use of external supplements to induce the appropriate differentiation [110]. MSCs have the property to differentiate into different cell types, like osteoblasts, chondrocytes and adipocytes [111].…”

“…Simply by using the conditioned medium of differentiating primary osteoblasts, mononuclear cells can be differentiated into osteoclastic cells [51,52]. On the other hand, to avoid diverse supplements from interfering with the differentiation process of the other cell type in co-culture, Schulze presented a direct co-culture model of human B-MSCs and PBMCs without exogenous cytokines, which is suitable to mimic bone-remodeling [110]. …”