Regulatory Role of IL-6 on Fracture Healing, and MASH Progression in a Murine Western Diet Model

• Applicants: Dr. Benedikt Kaufmann; Dr. Tanja Carina Maisenbacher
• Subject Area: Orthopaedics, Traumatology, Reconstructive Surgery ; General and Visceral Surgery
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 566272247

Nonunion is a serious complication of fracture healing, requiring complex treatment strategies and imposing a significant socioeconomic burden. Despite extensive research, the development of nonunion remains incompletely understood. Impaired fracture healing is associated with risk factors such as obesity, metabolic syndrome, associated steatotic liver disease or steatohepatitis (MASLD / MASH), and pre-/diabetes. In Germany, 49% of adults are overweight or obese, with MASLD/MASH prevalence estimated at 21% and diabetes affecting 7-10%. These conditions are characterized by chronic inflammation due to increased cytokine release (e.g., IL-6, TNF-α, GM-CSF) and an increase in neutrophil recruitment. Bone fractures induce acute inflammation, and this inflammation may exacerbate the conditions above, leading to disease progression and impaired fracture healing. It is assumed that local bone inflammation is reduced which delays fracture healing, as well as the egress of neutrophils from the bone marrow, and their tissue recruitment is expected to be increased, which in turn fosters inflammation and fibrosis in tissues, e.g. liver, muscle, or subcutaneous fat. Targeting the inflammatory cascade may offer benefits in preventing MASH and pre-/diabetes from progressing, while also enhancing fracture healing. This project aims to investigate Il-6 as a key regulator of inflammation as a potential target to disrupt this cycle of mutual reinforcement and to identify possible clinical applications. Methods: Male C57BL/6J mice will be fed either Standard Diet (SD / N=130) or Western Diet (WD / N=130) ad libitum for 15 weeks, starting at 8 weeks of age. The WD contains 60% fat, 20% carbohydrates (fructose), and 20% protein, effectively inducing MAFLD/MASH and insulin resistance. Blood glucose and insulin tolerance will be assessed post-preconditioning. A standardized closed femur fracture will occur one week later, with half of the animals (N = 65 in each SD & WD group) receiving an injection with 2.0 mg/kg BW neutralizing anti-murine IL-6 antibody 30 min and 48 h post-surgery. Mice will be euthanized at intervals (2, 7, 14, and 28 days), collecting blood and tissue (bone, muscle, fat tissue, liver) for analysis. Bones will be evaluated via X-ray, µCT, and bending tests; histopathological changes will be assessed, and neutrophil granules analyzed. Gene expression, neutrophil mobilization, and IL-6 and insulin signaling in tissues will be evaluated, with findings later verified in patient blood samples. Summary: To optimally analyze the interplay of inflammation, obesity, and diabetes in liver and bone, this project aims to integrate the expertise of both traumatology and visceral surgery. This multidisciplinary approach ensures a translational perspective on this complex and clinically crucial area of research, ultimately providing innovative insights into the role of inflammation in the context of metabolic diseases and fracture healing.

• DFG Programme: Research Grants