Enhancement of osteogenesis post-splenectomy does not attenuate bone loss in ovariectomized rats

Functional Enrichment Analysis Identifying Regulatory Information Associated with Human Fracture

Dozens of loci associated with fracture have been identified by genome-wide association studies (GWASs). However, most of these variants are located in the noncoding regions including introns, long terminal repeats, and intergenic regions. Although combining regulation information helps to identify the causal SNPs and interpret the involvement of these variants in the etiology of human fracture, regulation information which was truly associated with fracture was unknown. A novel functional enrichment method GARFIELD (GWAS Analysis of Regulatory of Functional Information Enrichment with LD correction) was applied to identify fracture-associated regulation information, including transcript factor binding sites, expression quantitative trait loci (eQTLs), chromatin states, enhancer, promoter, dyadic, super enhancer and Epigenome marks. Fracture SNPs were significantly enriched in exon (Bonferroni correction, p value < 7.14 × 10-3) at two GWAS p value thresholds through GARFIELD. High level of fold-enrichment was observed in super enhancer of monocyte and the enhancer of chondrocyte (Bonferroni correction, p value < 4.45 × 10-3). eQTLs of 44 tissues/cells and 10 transcription factors (TFs) were identified to be associated with human fracture. These results provide new insight into the etiology of human fracture, which might increase the identification of the causal SNPs through the fine-mapping study combined with functional annotation, as well as polygenic risk score.

Megakaryocyte-driven changes in bone health: lessons from mouse models of myelofibrosis and related disorders

Over the years, numerous studies demonstrated reciprocal communications between processes of bone marrow hematopoiesis and bone remodeling. Megakaryocytes, rare bone marrow cells responsible for platelet production, were demonstrated to be involved in bone homeostasis. Myelofibrosis, characterized by an increase in pleomorphic megakaryocytes in the bone marrow, commonly leads to the development of osteosclerosis. In vivo, an increase in megakaryocyte number was shown to result in osteosclerosis in GATA-1^low, NF-E2^-/-, TPO^high, Mpll^f/f;PF4cre, Lnk^-/-, Mpig6b^-/-, Mpig6b^fl/fl;Gp1ba-Cr^+/KI, Pt-vWD mouse models. In vitro, megakaryocytes stimulate osteoblast proliferation and have variable effects on osteoclast proliferation and activity through soluble factors and direct cell-cell communications. Intriguingly, new studies revealed that the ability of megakaryocytes to communicate with bone cells is affected by the age and sex of animals. This mini-review summarises changes seen in bone architecture and bone cell function in mouse models with an elevated number of megakaryocytes and the effects megakaryocytes have on osteoblasts and osteoclasts in vitro, and discusses potential molecular players that can mediate these effects.

Histopathological, immunohistochemical, and biomechanical effects of splenectomy on Achilles tendon healing in rats

PURPOSE

This study aimed to assess Achilles tendon repair in rats following splenectomy to simulate patients with musculoskeletal system injury who had splenectomy after spleen injury, a situation often seen in orthopedics and traumatology practice.

MATERIALS AND METHODS

The study included 32 male Sprague-Dawley rats (10 months old; average weight, 394.5 ± 28.3 g). The rats were fed with standard rodent food ad libitum at 22°C in a dark environment for 12 h. They were divided into two groups, namely the splenectomy (total splenectomy and Achilles tendon repair) and control groups (only Achilles tendon repair; n = 16). Four weeks after the surgery, the rats were euthanized, and their Achilles tendons were examined histopathologically, immunohistochemically, and biomechanically.

RESULTS

In the splenectomy group, proinflammatory cytokines, such as interleukin-1β, tumor necrosis factor-α, and interferon-γ, showed significantly lower values than those in the control group (p ˂0.01); moreover, the levels of anti-inflammatory cytokines like vascular endothelial growth factor, transforming growth factor-β1, interleukin-2, interleukin-10, and hepatocyte growth factor were significantly higher than in the control group (p ˂ 0.001). The average ultimate tensile strengths were 2.58 ± 0.5 in the splenectomy and 2.78 ± 0.3 in the control group (p = 0.043). The average εUTS values were 0.33 ± 0.5 in the splenectomy and 0.44 ± 0.1 in the control group (p = 0.021).

CONCLUSION

Splenectomy may positively influence Achilles tendon healing through modification of the proinflammatory/anti-inflammatory ratio in favor of anti-inflammatory cytokines by causing a decrease in spleen-originated inflammatory cells.

Splenectomy may have more complications than currently proven

The spleen has been one of the least understood major organs for centuries. Its significance is relatively well-known today but it seems that all aspects of its activities are not fully understood. Persian medicine (PM) has special views on the function of spleen; many side effects were reported in PM due to spleen dysfunction. On the other hand nowadays splenectomy as a treatment strategy is recommended for some disorders and increasing risk of infections is considered as the most important long term side effect of that. In this study, we hypothesize that splenectomy may have more side effects than currently proven. According to PM, spleen is in close connection with liver, cardiovascular system, stomach, bone, brain and skin, and that is why any kind of spleen dysfunction leads to change in blood viscosity, appetite and bone strength, liver dysfunction, mood and skin disorders, cancer formation and fever. Considering this viewpoint it can be hypothesized such side effects may also occur after splenectomy. Proven complications of splenectomy include hypercoagulated state, cardiovascular events and infectious diseases but there is also some evidence about increased risk of cancer, skin disease like systemic lupus erythematosus, mood disorder such as depression, defective bone formation and impairment of immunity which can be considered as different levels of evidence to confirm the hypothesis. But for some others such as changes in appetite, there are no studies let alone convincing evidence. Future research about theses possible complications may lead to novel results.

miR-142-5p in Bone Marrow-Derived Mesenchymal Stem Cells Promotes Osteoporosis Involving Targeting Adhesion Molecule VCAM-1 and Inhibiting Cell Migration

Osteoporosis is a systemic bone metabolic disease that is highly prevalent in the elderly population, particularly in postmenopausal women, which results in enhanced bone fragility and an increased susceptibility to fractures. However, the underlying molecular pathogenesis mechanisms still remain to be further elucidated. In this study, in a rat ovariectomy- (OVX-) induced postmenopausal osteoporosis model, aberrant expression of a microRNA miR-142-5p and vascular cell adhesion molecule 1 (VCAM-1) was found by RNA sequencing analysis and qRT-PCR. Using a dual-luciferase reporter assay, we found that miR-142-5p can bind to and decrease expression of VCAM-1 mRNA. Such reduction was prohibited when the miR-142-5p binding site in VCAM-1 3′UTR was deleted, and Western blotting analyses validated the fact that miR-142-5p inhibited the expression of VCAM-1 protein. Bone marrow-derived mesenchymal stem cells (BMMSCs) transfected with miR-142-5p showed a significantly decreased migration ability in a Transwell migration assay. Collectively, these data indicated the important role of miR-142-5p in osteoporosis development involving targeting VCAM-1 and inhibiting BMMSC migration.

Short-Term Hypoxia Accelerates Bone Loss in Ovariectomized Rats by Suppressing Osteoblastogenesis but Enhancing Osteoclastogenesis

Background

Although it has been reported that hypoxic exposure can attenuate hypertension, heart disease, diabetes, and some other diseases, effects of hypoxia on osteoporosis are still unknown.

Material/Methods

The current study investigated whether short-term hypoxic exposure (in comparison with normoxic conditions) affects bone metabolism in normal or ovariectomized (OVX) adult female rats in an vivo study. Micro-computed tomography bone volume/structural analyses, histological examination, and serum bone turnover biochemical assays were used. In addition, the expressions of some associated major regulatory molecules were measured in osteoblastic cultures.

Results

While the 14-day hypoxic exposure did not change the bone-remodeling process in normal adult female rats, it decreased bone volume, osteoclast density, and serum bone formation marker (alkaline phosphatase) level, but increased osteoclast density and serum bone resorption marker (C-telopeptide of collagen) level in OVX rats. The bone marrow adipocyte number and serum fatty acid binding protein-4 level were increased in OVX-hypoxic rats compared with OVX-normoxic rats. Consistently, in human MG-63 osteoblastic cultures, the hypoxic condition suppressed protein expression of osteogenic transcriptional factors Runx2 and osterix, elevated protein expression of osteoclastogenic cytokine receptor activator of nuclear factor kappa-B ligand, but reduced that of osteoclastogenic inhibitor osteoprotegerin.

Conclusions

Our results suggest that, although no change occurred in the bone-remodeling process in normal adult female rats after hypoxic exposure, under the estrogen-deficient osteoporotic condition, the hypoxic condition can alter the bone microenvironment so that it may further impair osteoblastic differentiation and enhance osteoclastic formation, and thus reduce bone formation, enhance bone resorption, and accelerate bone loss.