Tricolor Transgenic Murine Model for Studying Growth Plate Injury.

The cartilage growth plates in the bones of children enable limb lengthening but are weak relative to the bone, making them prone to fracturing when bones are overloaded. Better treatments for severely fractured growth plates are needed because the response to injury is a bony bridge that prematurely fuses the growth plate, leading to stunted and/or crooked limbs. Murine models of growth plate injury are advantageous for mechanistic studies, but are challenging because it is difficult to visualize and precisely injure the small growth plates in young mice. We describe here an improved growth plate injury model using transgenic mice with tri-lineage fluorescent reporters for collagen types I, II, and X. These mice show native fluorescence associated with the three primary substrata of the growth plate. A growth plate injury similar to a Salter-Harris Type II injury is created reproducibly with a bur using the hypertrophic section of the growth plate as a reference during live imaging under fluorescence stereo microscopy guidance. Frozen histology analysis of the native fluorescence simplifies assessing the cellular response to injury. This methodology represents a substantial leap in growth plate injury research, providing a detailed and reproducible method for investigating pathology and evaluating new therapeutic strategies.