Prolonged Upright Posture Induces Calcified Hypertrophy in the Cartilage End Plate in Rat Lumbar Spine

Study Design. Both forelimbs of rats were amputated and these rats were kept in the custom-made cages to keep prolonged and repeated upright posture. Changes of bone were observed in the lumbar vertebrae at three different time points after the surgery. Objective. To investigate the effect of prolonged and repeated upright posture on the cartilage end plate of rat lumbar vertebrae. Summary of Background Data. Previous studies show calcified hypertrophy is related to mechanical stress, but there are no clear evidences to indicate whether or not long-term and repeated assumption of the upright posture could result in calcified hypertrophy in cartilage end plate of rat lumbar spine. Methods. The forelimbs of 30 rats were amputated when they were 1 month old. These rats were kept in the custom-made cages and were forced to stand upright on their hind-limbs and tails to obtain water and food. Normal rats of the same ages kept in regular cages were used as control. The rats were killed at 5, 7, and 9 months after the surgery and lumbar vertebrae samples were harvested for micro-CT, histologic, and immunohistochemical studies. Total RNA isolated from these samples were used for real-time RT-PCR of type X collagen (Col10 alpha 1), vascular endothelial growth factor (VEGF), and transforming growth factor beta 1 (TGF-beta 1). Results. Micro-CT showed increased inner part of cartilage end plate. Histologic revealed peripheral hypertrophy of disc after the surgery. Immunostaining and real-time RT-PCR showed increased protein and mRNA expression of type X collagen, VEGF, and TGF-beta 1. Conclusion. Prolonged upright posture induces cartilage end plate calcification and hypertrophy in rat lumbar spine.