Temporal mechanically-induced signaling events in bone and dorsal root ganglion neurons after in vivo bone loading

• Published in: PloS one 2018-02, Vol.13 (2), p.e0192760-e0192760
• Main Authors: Bleedorn, Jason A, Hornberger, Troy A, Goodman, Craig A, Hao, Zhengling, Sample, Susannah J, Amene, Ermias, Markel, Mark D, Behan, Mary, Muir, Peter
• Format: Article
• Language: English
• Subjects: 1-Phosphatidylinositol 3-kinase; Adaptation; AKT protein; Animals; Biocompatibility; Biology and life sciences; Biomedical materials; Bone and Bones - metabolism; Bone growth; Bone mass; Bone remodeling; Bones; Brain; Brain-derived neurotrophic factor; c-Fos protein; c-Jun protein; Calcitonin; Calcitonin gene-related peptide; Cell culture; Cellular signal transduction; Dorsal root ganglia; Extracellular signal-regulated kinase; Funding; Ganglia; Ganglia, Spinal - cytology; Ganglia, Spinal - metabolism; Gene Expression; Genes; Health aspects; Intracellular signalling; JNK protein; Kinases; Laboratories; Limbs; Load; Male; MAP kinase; MAP Kinase Signaling System; Mechanical loading; Mechanical stimuli; Medical examination; Medical research; Medicine and Health Sciences; Nerve growth factor; Nervous system; Neurons; Neurons - metabolism; Osteogenesis; Phosphatidylinositol 3-Kinases - metabolism; Phosphorylation; Polymerase chain reaction; Proteins; Rapamycin; Rats; Rats, Sprague-Dawley; Rodents; Signal Transduction; Skeleton; Stress, Mechanical; Supervision; TOR Serine-Threonine Kinases - metabolism; Transcription factors; Ulna; Ulna - metabolism; Ulna - physiopathology; Veterinary colleges; Veterinary medicine
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0192760

Mechanical signals play an integral role in the regulation of bone mass and functional adaptation to bone loading. The osteocyte has long been considered the principle mechanosensory cell type in bone, although recent evidence suggests the sensory nervous system may play a role in mechanosensing. The specific signaling pathways responsible for functional adaptation of the skeleton through modeling and remodeling are not clearly defined. In vitro studies suggest involvement of intracellular signaling through mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt), and mammalian target of rapamycin (mTOR). However, anabolic signaling responses to bone loading using a whole animal in vivo model have not been studied in detail. Therefore, we examined mechanically-induced signaling events at five time points from 0 to 24 hours after loading using the rat in vivo ulna end-loading model. Western blot analysis of bone for MAPK's, PI3K/Akt, and mTOR signaling, and quantitative reverse transcription polymerase chain reaction (qRT-PCR) to estimate gene expression of calcitonin gene-related protein alpha (CGRP-α), brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), c-jun, and c-fos in dorsal root ganglion (DRG) of the brachial intumescence were performed. There was a significant increase in signaling through MAPK's including extracellular signal-related kinase (ERK) and c-Jun N-terminal kinase (JNK) in loaded limbs at 15 minutes after mechanical loading. Ulna loading did not significantly influence expression of the genes of interest in DRG neurons. Bone signaling and DRG gene expression from the loaded and contralateral limbs was correlated (SR>0.40, P