Although cellular and molecular mechanisms during the course of bone healing have been
thoroughly investigated, the regulation of gene expression by microRNA during bone regen eration is still poorly understood. We hypothesized that nonunion formation is associated
with different microRNA expression patterns and that target proteins of these microRNAs
are differently expressed in callus tissue of nonunions compared to physiologically healing
bones. In a well-established femoral osteotomy model in CD-1 mice osteotomies were
induced which result either in healing or in nonunion formation. MicroRNA and target protein
expression was evaluated by microarray, quantitative real-time polymerase chain reaction
(qrt-PCR) and Western blot. Microarray analyses demonstrated 44 microRNAs to be rele vant for nonunion formation compared to physiological bone healing. In nonunions qrt-PCR
could validate a higher expression of microRNA-140-3p and microRNA-140-5p. This was
associated with a reduced expression of Dnpep and stromal cell-derived factor (SDF)-1α,
which are both known to be target proteins of microRNA-140 and also to be involved in the
process of bone healing. These data suggest that an increased expression of microRNA 140-3p and microRNA-140-5p markedly contributes to the development of nonunions, most
probably by affecting bone morphogenetic protein (BMP)-2 function during the early stage
of healing due to a reduced SDF-1α expression
