High-resolution micro-computed tomography analyses of the abnormal trabecular bone structures in klotho gene mutant mice

Inactivation mutation of the recently discovered klotho gene in mice causes a syndrome resembling aging. Manifestations include short life span, ather osclerosis, gonadal atropy, skin atropy, emphysema, ataxia and ectopic calc ification. These mice also exhibit abnormally high bone density in the eyip hyses of their tibiae based on X-ray and histological analyses. However, mi crostructures of the trabecular bones in arbitrary two-dimensional planes o r three-dimensional regions are difficult to analyze by these techniques. T herefore, we applied high resolution micro-computed tomography (mu CT) to c haracterize the micro-structural abnormality in the trabecular bone in long bones as well as in vertebrae of four- to six-week-old klotho mutant mice. Two-dimensional mu CT analyses in the mid-sagittal plane as well as three- dimensional mu CT analyses indicated that the trabecular bone volume fracti on measured in the proximal metaphyses of the tibiae was increased more tha n twofold in klotho mutant mice compared with the wild-type mice. Similarly , the trabecular bone area fraction in the midsagittal plane of the lumbar vertebral bodies was also increased by about 80% at the proximal and distal ends. No significant difference was observed with regard to the cortical t hickness in the mid-shaft of femora between klotho mutant and wild-type mic e. Three-dimensional mu CT analyses also indicated that the trabecular numb er and thickness of the proximal metaphyses of the tibiae were increased by about 80% and 300% respectively in the klotho mutant mice, while trabecula r separation was 60% less in klotho mutant mice compared with the wild-type mice. These quantitative mu CT analyses indicate that the inactivation of klotho gene expression results in an increase in three-dimensional bone vol ume fraction, number and thickness of the trabecular bones in these mice.