Examining tissue composition, whole-bone morphology and mechanical behavior of Gorab^Prx1 mice tibiae: A mouse model of premature aging.

Abstract

Gerodermia osteodysplastica (GO) is a segmental progeroid disorder caused by loss-of-function mutations in the GORAB gene, associated with early onset osteoporosis and bone fragility. A conditional mouse model of GO (Gorab^Prx1) was generated in which the Gorab gene was deleted in long bones. We examined the biomechanical/functional relevance of the Gorab^Prx1 mutants as a premature aging model by characterizing bone composition, tissue-level strains, and whole-bone morphology and mechanical properties of the tibia. MicroCT imaging showed that Gorab^Prx1 tibiae had an increased anterior convex curvature and decreased cortical cross-sectional area, cortical thickness and moments of inertia, compared to littermate control (LC) tibiae. Fourier transform infrared (FTIR) imaging indicated a 34% decrease in mineral/matrix ratio and a 27% increase in acid phosphate content in the posterior metaphyseal cortex of the Gorab^Prx1 tibiae (p < .05), suggesting delayed mineralization. In vivo strain gauge measurement and finite element analysis showed ∼two times higher tissue-level strains within the Gorab^Prx1 tibiae relative to LC tibiae when subjected to axial compressive loads of the same magnitude. Three-point bending tests suggested that Gorab^Prx1 tibiae were weaker and more brittle, as indicated by decreasing whole-bone strength (46%), stiffness (55%), work-to-fracture (61%) and post-yield displacement (47%). Many of these morphological and biomechanical characteristics of the Gorab^Prx1 tibia recapitulated changes in other animal models of skeletal aging. Future studies are necessary to confirm how our observations might guide the way to a better understanding and treatment of GO.