Gene expression of intracortical bone demonstrates loading-induced increases in Wnt1 and Ngf and inhibition of bone remodeling processes

AUTHORS

Taylor L.Harris, Matthew J.Silva

ABSTRACT

Osteocytes are the primary mechanosensitive cells in bone. However, their location in mineralized matrix has limited the in vivo study of osteocytic genes induced by mechanical loading. Laser Capture Microdissection (LCM) allows isolation of intracortical bone (Intra-CB), enriched for osteocytes, from bone tissue for gene expression analysis. We used microarray to analyze gene expression from mouse tibial Intra-CB dissected using LCM 4 h after a single loading bout or after 5 days of loading. Osteocyte enrichment was supported by greater expression of Sost, Dmp1, Dkk1, and Mepe in Intra-CB regions vs. Mixed regions containing periosteum and muscle (fold-change (FC) = 3.4, 2.2, 5.1, 3.0, respectively). Over 150 differentially expressed genes (DEGs) due to loading (loaded vs. contralateral control) in Intra-CB were found on Day 1 and Day 5, but only 10 genes were differentially expressed on both days, including Ngf (Day 1 FC = 13.5, Day 5 FC = 11.1) and Wnt1 (Day 1 FC = 1.5, Day 5 FC = 5.1). The expression of Ngf and Wnt1 within Intra-CB was confirmed by in situ hybridization, and a significant increase in number of Wnt1 mRNA molecules occurred on day 1. We also found changes in extracellular matrix remodeling with Timp1 (FC = 3.1) increased on day 1 and MMP13 (FC = 0.3) decreased on day 5. Supporting this result, IHC for osteocytic MMP13 demonstrated a marginal decrease due to loading on day 5. Gene Ontology (GO) biological processes for loading DEGs indicated regulation of vasculature, neuronal and immune processes while cell-type specific gene lists suggested regulation of osteoclast, osteoblast, and endothelial related genes. In summary, microarray analysis of microdissected Intra-CB revealed differential regulation of Ngf, Wnt1, and MMP13 due to loading in osteocytes.

Adenine-induced chronic kidney disease induces a similar skeletal phenotype in male and female C57BL/6 mice with more severe deficits in cortical bone properties of male mice

AUTHORS

Corinne E. Metzger, Elizabeth A. Swallow, Alexander J. Stacy, Matthew R. Allen

ABSTRACT

Chronic kidney disease (CKD) causes bone loss, particularly in cortical bone, through formation of cortical pores which lead to skeletal fragility. Animal models of CKD have shown variability in the skeletal response to CKD between males and females suggesting sex may play a role in this variation. Our aim was to compare the impact of adenine-induced CKD on cortical parameters in skeletally mature male and female C57Bl/6 mice. After 10-weeks of adenine-induced CKD, both male and female adenine mice had high serum parathyroid hormone (PTH), high bone turnover, and cortical porosity compared to non-CKD controls. Both sexes had lower cortical thickness, but only male mice had lower cortical bone area. CKD imparted greater deficits in mechanical properties of male mice compared to female mice. These data demonstrate that both male and female mice develop high PTH/high bone turnover in response to adenine-induced CKD and that cortical bone phenotypes are slightly more severe in males, particularly in mechanical properties deficits.

Cigarette smoke-associated inflammation impairs bone remodeling through NFκB activation

AUTHORS

Yi Lu, Yuanpu Peter Di, Ming Chang, Xin Huang, Qiuyan Chen, Ni Hong, Beth A. Kahkonen, Marissa E. Di, Chunyan Yu, Evan T. Keller & Jian Zhang

ABSTRACT

Background

Cigarette smoking constitutes a major lifestyle risk factor for osteoporosis and hip fracture. It is reported to impair the outcome of many clinical procedures, such as wound infection treatment and fracture healing. Importantly, although several studies have already demonstrated the negative correlation between cigarette consume and impaired bone homeostasis, there is still a poor understanding of how does smoking affect bone health, due to the lack of an adequately designed animal model. Our goal was to determine that cigarette smoke exposure impairs the dynamic bone remodeling process through induction of bone resorption and inhibition of bone formation.

Methods

We developed cigarette smoke exposure protocols exposing mice to environmental smoking for 10 days or 3 months to determine acute and chronic smoke exposure effects. We used these models, to demonstrate the effect of smoking exposure on the cellular and molecular changes of bone remodeling and correlate these early alterations with subsequent bone structure changes measured by microCT and pQCT. We examined the bone phenotype alterations in vivo and ex vivo in the acute and chronic smoke exposure mice by measuring bone mineral density and bone histomorphometry. Further, we measured osteoclast and osteoblast differentiation gene expression levels in each group. The function changes of osteoclast or osteoblast were evaluated.

Results

Smoke exposure caused a significant imbalance between bone resorption and bone formation. A 10-day exposure to cigarette smoke sufficiently and effectively induced osteoclast activity, leading to the inhibition of osteoblast differentiation, although it did not immediately alter bone structure as demonstrated in mice exposed to smoke for 3 months. Cigarette smoke exposure also induced DNA-binding activity of nuclear factor kappaB (NFκB) in osteoclasts, which subsequently gave rise to changes in bone remodeling-related gene expression.

Conclusions

Our findings suggest that smoke exposure induces RANKL activation-mediated by NFκB, which could be a “smoke sensor” for bone remodeling.

Exosomal transfer of osteoclast-derived miRNAs to chondrocytes contributes to osteoarthritis progression

AUTHORS

Jin Liu, Xiaohao Wu, Jun Lu, Guangxin Huang, Lei Dang, Huarui Zhang, Chuanxin Zhong, Zongkang Zhang, Dijie Li, Fangfei Li, Chao Liang, Yuanyuan Yu, Bao-Ting Zhang, Lin Chen, Aiping Lu & Ge Zhang

ABSTRACT

Osteoarthritis (OA) is a prevalent aging-related joint disease lacking disease-modifying therapies. Here, we identified an upregulation of circulating exosomal osteoclast (OC)-derived microRNAs (OC-miRNAs) during the progression of surgery-induced OA in mice. We found that reducing OC-miRNAs by Cre-mediated excision of the key miRNA-processing enzyme Dicer or blocking the secretion of OC-originated exosomes by short interfering RNA-mediated silencing of Rab27a substantially delayed the progression of surgery-induced OA in mice. Mechanistically, the exosomal transfer of OC-miRNAs to chondrocytes reduced the resistance of cartilage to matrix degeneration, osteochondral angiogenesis and sensory innervation during OA progression by suppressing tissue inhibitor of metalloproteinase-2 (TIMP-2) and TIMP-3. Furthermore, systemic administration of a new OC-targeted exosome inhibitor (OCExoInhib) blunted the progression of surgery-induced OA in mice. We suggest that targeting the exosomal transfer of OC-miRNAs to chondrocytes represents a potential therapeutic avenue to tackle OA progression.

Peptidomimetic inhibitor of L-plastin reduces osteoclastic bone resorption in aging female mice

AUTHORS

Hanan Aljohani, Joseph P. Stains, Sunipa Majumdar, Deepa Srinivasan, Linda Senbanjo & Meenakshi A. Chellaiah

ABSTRACT

L-plastin (LPL) was identified as a potential regulator of the actin-bundling process involved in forming nascent sealing zones (NSZs), which are precursor zones for mature sealing zones. TAT-fused cell-penetrating small molecular weight LPL peptide (TAT- MARGSVSDEE, denoted as an inhibitory LPL peptide) attenuated the formation of NSZs and impaired bone resorption in vitro in osteoclasts. Also, the genetic deletion of LPL in mice demonstrated decreased eroded perimeters and increased trabecular bone density. In the present study, we hypothesized that targeting LPL with the inhibitory LPL peptide in vivo could reduce osteoclast function and increase bone density in a mice model of low bone mass. We injected aging C57BL/6 female mice (36 weeks old) subcutaneously with the inhibitory and scrambled peptides of LPL for 14 weeks. Micro-CT and histomorphometry analyses demonstrated an increase in trabecular bone density of femoral and tibial bones with no change in cortical thickness in mice injected with the inhibitory LPL peptide. A reduction in the serum levels of CTX-1 peptide suggests that the increase in bone density is associated with a decrease in osteoclast function. No changes in bone formation rate and mineral apposition rate, and the serum levels of P1NP indicate that the inhibitory LPL peptide does not affect osteoblast function. Our study shows that the inhibitory LPL peptide can block osteoclast function without impairing the function of osteoblasts. LPL peptide could be developed as a prospective therapeutic agent to treat osteoporosis.

Simvastatin loaded chitosan guided bone regeneration membranes stimulate bone healing

AUTHORS

Vishnu Priya Murali, Fernanda D. Guerra, Najib Ghadri, James M. Christian, Sidney H. Stein, Jessica A. Jennings, Richard A. Smith, Joel D. Bumgardner

ABSTRACT

Background and Objective

Electrospun chitosan membranes (ESCM) modified with short-chain fatty acids have the ability to control the release of simvastatin (SMV), an anti-cholesterol drug with osteogenic potential, for guided bone regeneration (GBR) applications. This study evaluated in vivo osteogenic effects of rapid short release of SMV (4 weeks) vs long sustained release (8 weeks) from acetic anhydride (AA)—and hexanoic anhydride (HA)-modified ESCMs, respectively.

Methods

AA ESCMs loaded with 10 or 50 µg SMV and HA ESCMs loaded with 50 µg SMV were evaluated for biocompatibility and bone formation at 4 and 8 weeks, in 5 mm critical size rat calvarial defects, using histological evaluation and micro-CT analysis.

Results

No severe inflammatory response was noticed around the ESCMs. Less hydrophobic AA membranes showed signs of resorption by week 4 and were almost completely resorbed by week 8 whereas the more hydrophobic HA membranes resorbed slowly, remaining intact over 8 weeks. In micro-CT analysis, 10 µg SMV-loaded AA membranes did not show significant bone formation as compared to non-loaded AA membranes at either evaluation time points. 50 µg SMV-loaded AA membranes stimulated significantly more bone formation than non-loaded AA membranes by week 4 (%bone = 31.0 ± 5.9% (AA50) vs 18.5 ± 13.7% (AA0)) but showed no difference at week 8. HA membranes with 50 µg SMV showed significantly more bone formation as compared to corresponding non-loaded membranes by week 8 (%bone = 61.7 ± 8.9% (HA50) vs 33.9 ± 29.7% (HA0)), though such an effect was not significant at week 4.

Conclusion

These results indicate that modified ESCMs may be used to control the release of SMV and promote bone healing in GBR applications.