Novel in vitro co-culture methodology to investigate heterotypic cell-cell interactions

Cell-cell interactions are of crucial importance for the formation of tissues, homeostasis and regeneration processes as well as reactions on foreign bodies including implants. So far, however, the importance of heterotypic cell-cell interactions in the in vitro evaluation of implant surfaces has been largely neglected. This work aims to develop an in vitro methodology that enables the in-depth investigation of heterotypic cell-cell interactions in a mixed co-culture system, and to validate it with a primary adult human bone-derived osteoblast cells (HBCs) – abdominal fibroblasts (HAFs) system. The methodology proposed combines a simple live labelling step, semiautomated fluorescence image acquisition and analysis to characterize the interactions between different cell types (cell population dynamics) in co-culture in terms of cell proliferation and cell spatial distribution of each cell type. In this co-culture system, direct cell-cell contacts between the two cell types were permitted while the determination of cell-type specific responses could still be elucidated. We could show that HAF proliferation was reduced in a way negatively correlated with the seeding HBC/HAF ratio, i.e., a high proportion of HBC in the co-culture had an inhibitory effect on HAF proliferation. In all cultures segregation was found after 4 and 7 days of co-culture. HBCs were segregated at low ratios while HAFs were segregated at high ratios. Cell-cell distances depended on the total cell number in the co-culture but the dependence was different for each cell type

Mechanisms of disease: is osteoporosis the obesity of bone?

Osteoporosis and obesity, two disorders of body composition, are growing in prevalence. Interestingly, these diseases share several features including a genetic predisposition and a common progenitor cell. With aging, the composition of bone marrow shifts to favor the presence of adipocytes, osteoclast activity increases, and osteoblast function declines, resulting in osteoporosis. Secondary causes of osteoporosis, including diabetes mellitus, glucocorticoids and immobility, are associated with bone-marrow adiposity. In this review, we ask a provocative question: does fat infiltration in the bone marrow cause low bone mass or is it a result of bone loss? Unraveling the interface between bone and fat at a molecular and cellular level is likely to lead to a better understanding of several diseases, and to the development of drugs for both osteoporosis and obesity