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Orthopedic and Rehabilitation Engineering

Orthopedic and Rehabilitation Engineering Lightning Talks

Linking Liver and Bone: Skeletal Fragility in Metabolic Dysfunction-Associated Steatotic Liver Disease

Saturday, October 26, 2024
8:44 AM - 8:51 AM EST
Location: Room 339

Introduction:  Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) is a disease marked by accumulation of fat in the liver which promotes organ malfunction, and is associated with an increased risk of fracture and osteoporosis. MASLD affects about 30 percent of the general population. Thus, it is critical to identify mechanisms behind the skeletal fragility connected to this disease to reduce harm and healthcare expenditure. To date, no established preclinical model exists for the study of the pathogenesis of skeletal fragility linked to MASLD. There is a critical data gap in our understanding of MASLD-associated osteoporosis and fracture. DIAMOND mice develop MASLD from diet alone, similar to humans, making them a uniquely suitable candidate for identifying mechanisms of skeletal fragility in MASLD. Exposure to a high-fat, high-carbohydrate diet causes hepatic steatosis, followed by steatohepatitis, cirrhosis, and spontaneous hepatocellular carcinoma. Without exposure to a high-fat diet, DIAMOND mice will retain normal liver and musculoskeletal structure and function. In humans, MASLD-associated osteopenia phenotypes exhibit sexual dimorphism. Biological males experience increased rates of osteoporosis and fracture, while females appear protected from this effect. We hypothesize DIAMOND mice follow the same pattern: males with MASLD have skeletal fragility while females with MASLD do not. Further, as in humans, skeletal fragility in DIAMOND mice worsens with MASLD severity.

Materials and

Methods:  DIAMOND mice were randomized to either a normal chow control diet (Harlan TD.7012) with normal water (CD/NW) or a high-fat, high-carbohydrate Western Diet (Harlan TD.88137) with sugar water (WD/SW) at 8 weeks of age. Mice were subdivided into 3 cohorts and sacrificed at 16, 36, and 48 weeks. Each cohort consisted of 20-40 mice, evenly composed of males and females (5-10 mice per sex/diet per cohort). Bone morphometry was longitudinally assessed by micro CT. Bone strength was measured by 3-point bending to failure (1 mm/min) by fracture. ANOVA was used to determine effects of sex and diet (2-WAY) or diet duration (1-WAY) on bone phenotype. Post-hoc analyses were conducted via Tukey’s method. Family-wise error rate was controlled using the Dunn-Sidak method. Significance was set at α < 0.05 for all comparisons after multiplicity adjustment.

Results, Conclusions, and Discussions: Longer exposure to Western Diet, correlating with a progressive MASLD phenotype, showed simultaneous bone loss in DIAMOND male mice. DIAMOND male mice on a control diet do not show bone loss. (Figure 1a-d) At the longest time point, 48 weeks, females on WD/SW are protected from bone loss, having similar bones to the females on CD/NW. (Figure 1e-h) Harmful changes in bone area and cortical thickness accumulated among male mice on WD/SW are significant at 48 weeks compared to CD/NW. (Figure 1a, 1b) These losses were not observed in females. (Figure 1e, 1f) Mechanical testing via 3-point bending of tibiae, specifically ultimate stress, supported results that males lost skeletal strength by 48 weeks, and females did not. (Figure 1c, 1g). Clinical observations of increased fracture incidence in males versus females with MASLD agree with these data.
Humans with MASLD--especially males--are more likely to be affected by osteoporosis and fracture. DIAMOND mice with MASLD from this study recapitulate the bone loss evident in humans. However, absence of analyses of human bone microarchitecture among persons with MASLD means the model fidelity cannot be fully assessed. We propose the DIAMOND mouse as a new preclinical candidate for investigating sexually dimorphic mechanisms of MASLD related bone loss. This model will aid in identifying new targets for therapeutic approaches which will reduce the increased morbidity and mortality among persons with MASLD, and lessen healthcare spending. These data support the hypothesis that male DIAMOND mice with MASLD will undergo bone loss and have reduced mechanical strength compared to the controls. These data also agree with the hypothesis that bone loss progresses with severity of MASLD, shown via duration diet exposure. Further studies on cellular and molecular mechanisms of this pathology are ongoing.

Acknowledgements (Optional):  This project was funded by the NSF Mechanobiology REU program and the Donahue Lab at Virginia Commonwealth University.