Osteogenic capacity of mesenchymal stem cells from patients with osteoporotic hip fractures in vivo

PURPOSE

Human mesenchymal stem cells (MSCs) have the ability to differentiate into bone-forming osteoblasts. The aim of this study was to elucidate if MSCs from patients with OP show a senescent phenotype and explore their bone-forming ability in vivo.

MATERIALS AND METHODS

MSCs from patients with OP and controls with osteoarthritis (OA) were implanted into the subcutaneous tissue of immunodeficient mice for histological analysis and expression of human genes by RT-PCR. The expression of senescence-associated phenotype (SASP) genes, as well as p16, p21, and galactosidase, was studied in cultures of MSCs.

RESULTS

In vivo bone formation was evaluated in 103 implants (47 OP, 56 OA). New bone was observed in 45% of the implants with OP cells and 46% of those with OA cells (p = 0.99). The expression of several bone-related genes (collagen, osteocalcin, alkaline phosphatase, sialoprotein) was also similar in both groups. There were no differences between groups in SASP gene expression, p16, and p21 expression, or in senescence-associated galactosidase activity.

CONCLUSION

Senescence markers and the osteogenic capacity in vivo of MSCs from patients with OP are not inferior to that of cells from controls of similar age with OA. This supports the interest of future studies to evaluate the potential use of autologous MSCs from OP patients in bone regeneration procedures.

Influence of hyperbaric oxygen therapy on bone metabolism in patients with neoplasm

Background

Hyperbaric oxygen therapy (HBOT) is useful in the treatment of complications due to radiotherapy in patients with neoplasm. Its effects on bone metabolism are unclear. In our study, we analyzed the effects of HBOT on bone remodeling in oncological patients with radiotherapy.

Materials and methods

Prospective clinical study in 23 patients with neoplasms undergoing treatment with HBOT due to complications of radiotherapy (hemorrhagic cystitis, proctitis or radionecrosis) and 25 patients with chronic anal fissure. The average number of HBOT sessions was 20 ± 5 (100% oxygen, 2.3 atmospheres and 90 min per day). Serum levels of aminoterminal propeptide of type I collagen (P1NP), C terminal telopeptide of type I collagen (CTX), alkaline phosphatase (AP), 25hydroxyvitamin D (25-OHD), parathyroid hormone (PTH), were measured at 3 time points: T0 (before beginning HBOT), T1 (at the end of HBOT) and T2 (6 months after HBOT).

Results

At baseline, the patients with neoplasm have higher bone turnover than those with anal fissure. These differences were 41% in CTX (0.238 ± 0.202 ng/mL in neoplasm and 0.141 ± 0.116 ng/mL in fissure; p = 0.04), 30% for PTH (46 ± 36 pg/mL in neoplasm and 32 ± 17 pg/mL in fissure; p = 0.04) and 15% for alkaline phosphatase (80 ± 24 U/L in neoplasm and 68 ± 16 U/L in fissure; p = 0.04). In the group with neoplasm, the values of P1NP decreased 6% after HBOT (T0: 49 ± 31 ng/mL, T2: 46 ± 12 ng/mL; p = 0.03). Also, there were non-significant decreases in PTH (-34%) and CTX (-30%).

Conclusions

Patients with neoplasm and complications with radiotherapy have an increase in bone remodeling that may be diminished after HBOT.

Methylation of the Sclerostin (SOST) Gene in Serum Free DNA: A New Bone Biomarker?

Introduction: Cell-free DNA (cfDNA) methylation is an important molecular biomarker, which provides information about the regulation of gene expression in the tissue of origin. There is an inverse correlation between SOST gene methylation and expression levels. Methods: We analyzed SOST promoter methylation in cfDNA from serum, and compared it with DNA from blood and bone cells from patients undergoing hip replacement surgery. We also measured cfDNA methylation in 28 osteoporotic patients at baseline and after 6 months of antiosteoporotic therapy (alendronate, teriparatide, or denosumab). Results: SOST gene promoter methylation levels in serum cfDNA were very similar to those of bone-derived DNA (79% ± 12% and 82% ± 7%, respectively), but lower than methylation levels in blood cell DNA (87% ± 10%). Furthermore, there was a positive correlation between an individual's SOST DNA methylation values in serum and bone. No differences in either serum sclerostin levels or SOST methylation were found after 6-months of therapy with antiosteoporotic drugs. Conclusions: Our results suggest that serum cfDNA does not originate from blood cells, but rather from bone. However, since we did not confirm changes in this marker after therapy with bone-active drugs, further studies examining the correlation between bone changes of SOST expression and SOST methylation in cfDNA are needed to confirm its potential role as a bone biomarker.

Long Noncoding RNAs as Bone Marrow Stem Cell Regulators in Osteoporosis

Long noncoding RNAs (lncRNAs) contribute toward regulating gene expression and cell differentiation and may be involved in the pathogenesis of several diseases. The objective of this study was to determine the expression patterns of lncRNAs in bone marrow mesenchymal stem cells (BMSCs) derived from patients with osteoporotic fractures and their relevance to osteogenic function. The BMSCs were isolated from the femoral head of patients with hip fractures (FRX) and controls with osteoarthritis (OA). We found 74 differentially expressed genes between FRX and OA, of which 33 were of the lncRNA type. Among them, 52 genes (20 lncRNAs) were replicated in another independent dataset. The differentially expressed lncRNAs were over-represented among those correlated with differentially expressed protein-coding genes. In addition, the comparison of pre- and post-differentiated paired samples revealed 163 differentially expressed genes, of which 99 were of the lncRNA type. Among them, the overexpression of LINC00341 induced an upregulation of typical osteoblastic genes. In conclusion, the analysis of lncRNA expression in BMSCs shows specific patterns in patients with osteoporotic fractures, as well as changes associated with osteogenic differentiation. The regulation of bone genes through lncRNAs might bring new opportunities for designing bone anabolic therapies in systemic and localized bone disorders.

Epigenetics of Skeletal Diseases

PURPOSE OF REVIEW

Epigenetic mechanisms modify gene activity in a stable manner without altering DNA sequence. They participate in the adaptation to the environment, as well as in the pathogenesis of common complex disorders. We provide an overview of the role of epigenetic mechanisms in bone biology and pathology.

RECENT FINDINGS

Extensive evidence supports the involvement of epigenetic mechanisms (DNA methylation, post-translational modifications of histone tails, and non-coding RNAs) in the differentiation of bone cells and mechanotransduction. A variety of epigenetic abnormalities have been described in patients with osteoporosis, osteoarthritis, and skeletal cancers, but their actual pathogenetic roles are still unclear. A few drugs targeting epigenetic marks have been approved for neoplastic disorders, and many more are being actively investigated. Advances in the field of epigenetics underscore the complex interactions between genetic and environmental factors as determinants of osteoporosis and other common disorders. Likewise, they help to explain the mechanisms by which prenatal and post-natal external factors, from nutrition to psychological stress, impact our body and influence the risk of later disease.

Differential analysis of genome-wide methylation and gene expression in mesenchymal stem cells of patients with fractures and osteoarthritis

Insufficient activity of the bone-forming osteoblasts leads to low bone mass and predisposes to fragility fractures. The functional capacity of human mesenchymal stem cells (hMSCs), the precursors of osteoblasts, may be compromised in elderly individuals, in relation with the epigenetic changes associated with aging. However, the role of hMSCs in the pathogenesis of osteoporosis is still unclear. Therefore, we aimed to characterize the genome-wide methylation and gene expression signatures and the differentiation capacity of hMSCs from patients with hip fractures. We obtained hMSCs from the femoral heads of women undergoing hip replacement due to hip fractures and controls with hip osteoarthritis. DNA methylation was explored with the Infinium 450K bead array. Transcriptome analysis was done by RNA sequencing. The genomic analyses revealed that most differentially methylated loci were situated in genomic regions with enhancer activity, distant from gene bodies and promoters. These regions were associated with differentially expressed genes enriched in pathways related to hMSC growth and osteoblast differentiation. hMSCs from patients with fractures showed enhanced proliferation and upregulation of the osteogenic drivers RUNX2/OSX. Also, they showed some signs of accelerated methylation aging. When cultured in osteogenic medium, hMSCs from patients with fractures showed an impaired differentiation capacity, with reduced alkaline phosphatase activity and poor accumulation of a mineralized matrix. Our results point to 2 areas of potential interest for discovering new therapeutic targets for low bone mass disorders and bone regeneration: the mechanisms stimulating MSCs proliferation after fracture and those impairing their terminal differentiation.