gms | German Medical Science

Objectives: Long bone fractures are a common injury pattern in multiple trauma patients and can often lead to joint stiffness and osteoarthritis over time. In this regard, fracture localisation and overall trauma severity may affect patient outcome, with local and systemic immune responses playing a central role. Recent studies have shown a direct association between the infrapatellar fat pad (IPFP) and arthrofibrotic lesions after trauma, although the exact biomolecular mechanism is not fully understood yet. MicroRNAs, key regulators of protein expression, may play important roles in the crosstalk between IPFP and trauma severity. The aim of this study was therefore to investigate the influence of an adjacent femur fracture and multiple trauma severity on microRNA (miRNA) expression patterns in IPFP.

Methods: Pigs were allocated to a minor-multiple trauma (MiMT, n=4; unilateral femur fracture, blunt chest trauma) or major-multiple trauma (MaMT, n=4; unilateral femur fracture, blunt chest trauma, haemorrhagic shock) group. After trauma induction and a 90-min shock phase, animals were operatively (external fixator) and medically stabilized and monitored in an ICU-setting for 72 h. After sacrificing, IPFP was harvested from the fractured and unfractured leg. MiRNAs were isolated, transcribed, and pooled for qPCR array analysis (miFinder miRCURY arrays) followed by bioinformatic analyses using Qiagen's GeneGlobe analysis platform and the ShinyGO V0.80 enrichment tool to identify mRNA targets of the deregulated miRNAs and their associated biomolecular pathways.

Results and conclusion: Compared to the unfractured leg of the MiMT group, the IPFP of the fractured leg showed upregulations of anti-inflammatory miRNAs (e.g., miR-16 and -23b), while the downregulated miRNA profile was pro-inflammatory (e.g., miR-21 and -223). Contrarily, miRNAs related to immune cell recruitment, activation and osteogenic differentiation were up-regulated in the IPFP from the fractured leg of the MaMT group. The downregulated miRNAs were anti-inflammatory. Compared to the unfractured leg of the MiMT group, the IPFP from the unfractured leg of the MaMT group showed increased expression of pro-inflammatory miRNAs. Bioinformatic analyses revealed various targets associated with post-traumatic immune response and tissue regeneration, such as toll-like receptors, several interleukins, and growth factors. Ongoing research focusses on mRNA target validations in the IPFP, and potential differences in synovial fluid and cartilage miRNA expression.

This study shows that miRNA expression in the IPFP is associated with both, adjacent femur fracture and overall trauma severity. Based on these different miRNA expression patterns associated with local and systemic responses, it can be suggested that the IPFP plays an active role in joint homeostasis after trauma. The results from this study warrant further research into the potential role of miRNAs and the IPFP in arthrofibrosis and osteoarthritis after trauma.