Nano and micro biomechanical analyses of the nucleus pulposus after in situ immobilization in rats.

Immobilization can lead to intervertebral disc degeneration. The biomechanical characteristics of such discs have not so far been investigated at the micro- or nanoscale, the level at which cells sense and respond to the surrounding environment. This study aimed to characterize changes in the elastic modulus of the collagen fibrils in the nucleus pulposus at the nanoscale and correlate this with micro-biomechanical properties of the nucleus pulposus after immobilization, in addition to observation of tissue histology and its gene expressions. An immobilization system was used on the rat tail with an external fixation device. The elastic modulus was measured using both nano and micro probes for atomic force microscopy after 4 and 8 weeks of immobilization. Histology of the tissue was observed following hematoxylin and eosin staining. Gene expression in the annulus fibrosus tissue was quantified using real-time reverse transcription-polymerase chain reaction. The elastic modulus of the collagen fibrils in the nucleus pulposus at the nanoscale increased from 74.07 ± 17.06 MPa in the control to 90.06 ± 25.51 MPa after 8 weeks (P = 0.007), and from 33.51 ± 9.33 kPa to 43.18 ± 12.08 kPa at the microscale (P = 0.002). After immobilization for 8 weeks, a greater number of cells were observed by histology to be aggregated within the nucleus pulposus. Collagen II (P = 0.007) and aggrecan (P = 0.003) gene expression were downregulated whereas collagen I (P = 0.002), MMP-3 (P < 0.001), MMP-13 (P < 0.001) and ADAMTs-4 (P < 0.001) were upregulated. Immobilization not only influenced individual collagen fibrils at the nanoscale, but also altered the micro-biomechanics and cell response in the nucleus pulposus. These results suggest that significant changes occur in intervertebral discs at both scales after immobilization, a situation about which clinicians should be aware when immobilization has to be used clinically.

Sensory nerves protect from the progression of early stage osteoarthritis in mice.

PURPOSE: Osteoarthritis (OA) is a chronic degenerative joint disease. Sensory nerves play an important role in bone metabolism and in the progression of inflammation. This study explored the effects of sensory nerve on OA progression at early stage in mice. MATERIALS AND METHODS: OA was induced via destabilization of the medial meniscus (DMM) in C57BL/6 mice. Sensory denervation was induced by subcutaneous injection of capsaicin (90 mg/kg) one week prior to DMM. One week after capsaicin injection, sensory denervation in the tibia was confirmed by immunofluorescent staining. Four weeks after DMM, micro-CT scans, histological analysis, and RT-PCR tests were performed to evaluate OA progression. RESULTS: Subcutaneous injection of capsaicin successfully induced sensory denervation in tibia. The Osteoarthritis Research Society International (OARSI) score and synovitis score of the capsaicin+DMM group were significantly higher than the score of the vehicle+DMM group. The BV/TV of the tibial subchondral bone in the capsaicin+DMM group was significantly lower than in the vehicle+DMM group. In addition, the level of expression of inflammatory factors in the capsaicin+DMM group was significantly higher than in the vehicle+DMM group. CONCLUSIONS: Capsaicin-induced sensory denervation accelerated OA progression at early stage in mice. To put it another way, sensory nerve protects from OA progression at early stage in mice.

Acoustic-frequency vibratory stimulation regulates the balance between osteogenesis and adipogenesis of human bone marrow-derived mesenchymal stem cells.

Osteoporosis can be associated with the disordered balance between osteogenesis and adipogenesis of bone marrow-derived mesenchymal stem cells (BM-MSCs). Although low-frequency mechanical vibration has been demonstrated to promote osteogenesis, little is known about the influence of acoustic-frequency vibratory stimulation (AFVS). BM-MSCs were subjected to AFVS at frequencies of 0, 30, 400, and 800 Hz and induced toward osteogenic or adipogenic-specific lineage. Extracellular matrix mineralization was determined by Alizarin Red S staining and lipid accumulation was assessed by Oil Red O staining. Transcript levels of osteogenic and adipogenic marker genes were evaluated by real-time reverse transcription-polymerase chain reaction. Cell proliferation of BM-MSCs was promoted following exposure to AFVS at 800 Hz. Vibration at 800 Hz induced the highest level of calcium deposition and significantly increased mRNA expression of COL1A1, ALP, RUNX2, and SPP1. The 800 Hz group downregulated lipid accumulation and levels of adipogenic genes, including FABP4, CEBPA, PPARG, and LEP, while vibration at 30 Hz supported adipogenesis. BM-MSCs showed a frequency-dependent response to acoustic vibration. AFVS at 800 Hz was the most favorable for osteogenic differentiation and simultaneously suppressed adipogenesis. Thus, acoustic vibration could potentially become a novel means to prevent and treat osteoporosis.