Rui-Hao Zhang1, Xiao-Bo Zhang1, Yu-Bao Lu2, Yi-Cun Hu1, Xiang-Yi Chen1, De-Chen Yu1, Jin-Tao Shi1, Wen-Huan Yuan3, Jing Wang4, Hai-Yu Zhou5. 1. Department of Orthopedics, Lanzhou University Second Hospital, Lanzhou, Gansu, 730000, PR China; Key Laboratory of Bone and Joint Disease Research of Gansu Province, Lanzhou, 730000, PR China. 2. Department of Spine Surgery, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510000, PR China. 3. Baotou First Affiliated Hospital of Inner Mongolia University of Science and Technology, Baotou, 014000, PR China. 4. The People's Hospital of Baoan District, Shenzhen, 518000, PR China. Electronic address: wangjing1mail@163.com. 5. Department of Orthopedics, Lanzhou University Second Hospital, Lanzhou, Gansu, 730000, PR China; Lanzhou Xigu District People's Hospital, Lanzhou, Gansu, 730000, PR China. Electronic address: zhouhy@lzu.edu.cn.
Abstract
OBJECTIVES: Postmenopausal osteoporosis (PMO) and osteoporotic fracture seriously impair human health in developed countries. The present study aims to explore whether sensory nerves, calcitonin gene-related peptide (CGRP), and brain-derived serotonin are related to bone loss in ovariectomized (OVX) rats. METHODS: Female rats were grouped into the ovariectomized (OVX) and sham surgery (SHAM) groups. Immunocytochemistry, western blotting, and qPCR were performed to detect CGRP expression in the femurs. The expression levels of serotonin and CGRP in the spinal cord and brainstem were estimated using western blotting, immunofluorescence, and qPCR. ELISA was used to evaluate the serum biomarkers of bone formation and resorption. Bone mineral density was measured using dual-energy X-ray (DXA) analysis. Femur microstructure was imaged by Micro CT. P values less than 0.05 were considered statistically significant. RESULTS: ELISA showed that serum bone alkaline phosphatase (BALP), tartrate-resistant acid phosphatase (TRAP), β-crosslaps, and β-ctx were increased in the OVX group. In the OVX group, in vivo bone mineral density, trabecular bone mineral density, bone volume fraction (BV/TV), and trabecular number (Tb. N) were significantly decreased, while trabecular spacing (Tb. Sp) and trabecular bone pattern factor (Tb. Pf) were markedly increased. In the OVX group, the expression levels of CGRP of the femur were significantly downregulated. In contrast, CGRP and serotonin expression was increased in the spinal cord of the OVX group. Serotonin expression was increased in the brainstem, brainstem nucleus raphe magnus (RMG), and nucleus raphe dorsalis (DRN). CONCLUSION: Our results indicated that the activation of osteoclast triggered the release of CGRP from nociceptive sensory nerve fibers and transmitted this painful stimulus to the dorsal horn of the spinal cord to release increased CGRP. The descending serotonergic inhibitory system was activated by increased CGRP levels of the spinal cord and promoted serotonin release in the brainstem RMG, DRN, and the spinal cord, contributing to the decreased CGRP level in bone tissue, which revealed a novel mechanism of bone loss in PMO.
OBJECTIVES: Postmenopausal osteoporosis (PMO) and osteoporotic fracture seriously impair human health in developed countries. The present study aims to explore whether sensory nerves, calcitonin gene-related peptide (CGRP), and brain-derived serotonin are related to bone loss in ovariectomized (OVX) rats. METHODS: Female rats were grouped into the ovariectomized (OVX) and sham surgery (SHAM) groups. Immunocytochemistry, western blotting, and qPCR were performed to detect CGRP expression in the femurs. The expression levels of serotonin and CGRP in the spinal cord and brainstem were estimated using western blotting, immunofluorescence, and qPCR. ELISA was used to evaluate the serum biomarkers of bone formation and resorption. Bone mineral density was measured using dual-energy X-ray (DXA) analysis. Femur microstructure was imaged by Micro CT. P values less than 0.05 were considered statistically significant. RESULTS: ELISA showed that serum bone alkaline phosphatase (BALP), tartrate-resistant acid phosphatase (TRAP), β-crosslaps, and β-ctx were increased in the OVX group. In the OVX group, in vivo bone mineral density, trabecular bone mineral density, bone volume fraction (BV/TV), and trabecular number (Tb. N) were significantly decreased, while trabecular spacing (Tb. Sp) and trabecular bone pattern factor (Tb. Pf) were markedly increased. In the OVX group, the expression levels of CGRP of the femur were significantly downregulated. In contrast, CGRP and serotonin expression was increased in the spinal cord of the OVX group. Serotonin expression was increased in the brainstem, brainstem nucleus raphe magnus (RMG), and nucleus raphe dorsalis (DRN). CONCLUSION: Our results indicated that the activation of osteoclast triggered the release of CGRP from nociceptive sensory nerve fibers and transmitted this painful stimulus to the dorsal horn of the spinal cord to release increased CGRP. The descending serotonergic inhibitory system was activated by increased CGRP levels of the spinal cord and promoted serotonin release in the brainstem RMG, DRN, and the spinal cord, contributing to the decreased CGRP level in bone tissue, which revealed a novel mechanism of bone loss in PMO.