Disruption of the Aldehyde Dehydrogenase 2 Gene Results in No Increase in Trabecular Bone Mass Due to Skeletal Loading in Association with Impaired Cell Cycle Regulation Through p21 Expression in the Bone Marrow Cells of Mice

Approximately 45% of people of East Asian descent have the inactive aldehyde dehydrogenase 2 (ALDH2) phenotype. The enzyme defect of ALDH2 has been found to adversely influence the risk of osteoporosis. The aim of this study was to clarify the effect of skeletal loading on trabecular bone structure and dynamics in Aldh2-disrupted mice in the absence of alcohol consumption. Four-week-old male Aldh2(-/-) (KO) and Aldh2(+/+) (WT) mice were divided into a ground control (GC) group and a climbing exercise (CE) group in each genotype. The trabecular bone mineral density of the distal femur measured by peripheral quantitative computed tomography in the wild-type CE (WTCE) group was significantly higher than that in the wild-type GC (WTGC) group; however, there was no significant difference between the knockout CE (KOCE) and knockout GC (KOGC) groups. Bone histomorphometry revealed that osteogenic parameters were significantly increased in the WTCE group compared with the WTGC group, but not increased in the KOCE group compared with the KOGC group. Quantitative reverse transcriptase polymerase chain reaction and flow cytometry revealed that mRNA and protein expression levels of p21 were significantly decreased in the WTCE group compared with those in the WTGC group, while these differences were not observed between the KOGC and KOCE groups. This study provides the first in vivo evidence that p21 expression in the bone marrow is not decreased after skeletal loading and osteoblast differentiation is impaired in the absence of Aldh2 gene.