Bi-directional modulation of cellular interactions in an in vitro co-culture model of tendon-to-bone interface

Objectives This work aimed at studying in vitro interactions between human tendon-derived cells (hTDCs) and pre-osteoblasts (pre-OBs) that may trigger a cascade of events involved in enthesis regeneration. Materials and methods The effect of 5 osteogenic medium (OM) conditions over the modulation of hTDCs and pre-OBs towards the tenogenic and osteogenic phenotypes, respectively, was studied. Three different medium conditions were chosen for subsequently establishing a direct co-culture system in order to study the expression of bone, tendon and interface-related markers. Results A higher matrix mineralization and ALP activity was observed in co-cultures in the presence of OM. Higher transcription levels of bone- (ALPL, RUNX2, SPP1) and interface-related genes (ACAN, COMP) were found in co-cultures. The expression of aggrecan was influenced by the presence of OM and cell-cell interactions occurring in co-culture. Conclusions The present work assessed both the influence of OM on cell phenotype modulation and the importance of co-culture models while promoting cell-cell interactions and the exchange of soluble factors in triggering an interface-like phenotype to potentially modulate enthesis regeneration.