The micro-RNA signature of hypertrophic callus-formation in bone fractures accompanied with traumatic brain injury.

Long-bone-fractures occasionally heal with hypertrophic callus formation when patients suffer a concomitant traumatic brain injury. Although this phenomenon is known for decades, the causal factors are still poorly understood and no feasible markers are currently available to predict the exuberant bone-mass-formation at an early timepoint after injury. In this study, we used small-RNA-seq, bioinformatic analyses and in vitro assays to identify a set of micro-RNAs in serum of hypertrophic callus patients that serve as potential biomarkers. The identified miRNAs are highly expressed in the human brain, primarily in the pituitary gland, they are differentially expressed during osteogenic differentiation of bone-marrow-derived mesenchymal stem cells and they regulate mRNA-targets, involved in bone-related pathways, such as RANK/RANKL, BMP/RUNX2, PI3K-AKT and Wnt/beta-catenin. Small RNA-seq profiling of human blood samples of four patient groups: fracture (Fx), traumatic brain injury (TBI), fracture accompanied with traumatic brain injury and normal bone healing (TBI+Fx) and fracture accompanied with traumatic brain injury and hypertrophic callus formation (TBI+Fx+Call). Blood sampling was performed 24h, 72h and 7 days after injury from three patients of each group.