Histone deacetylation mediates the rejuvenation of osteoblastogenesis by the combination of 25(OH)D3 and parathyroid hormone in MSCs from elders

Multiomics profiling reveals VDR as a central regulator of mesenchymal stem cell senescence with a known association with osteoporosis after high-fat diet exposure

The consumption of a high-fat diet (HFD) has been linked to osteoporosis and an increased risk of fragility fractures. However, the specific mechanisms of HFD-induced osteoporosis are not fully understood. Our study shows that exposure to an HFD induces premature senescence in bone marrow mesenchymal stem cells (BMSCs), diminishing their proliferation and osteogenic capability, and thereby contributes to osteoporosis. Transcriptomic and chromatin accessibility analyses revealed the decreased chromatin accessibility of vitamin D receptor (VDR)-binding sequences and decreased VDR signaling in BMSCs from HFD-fed mice, suggesting that VDR is a key regulator of BMSC senescence. Notably, the administration of a VDR activator to HFD-fed mice rescued BMSC senescence and significantly improved osteogenesis, bone mass, and other bone parameters. Mechanistically, VDR activation reduced BMSC senescence by decreasing intracellular reactive oxygen species (ROS) levels and preserving mitochondrial function. Our findings not only elucidate the mechanisms by which an HFD induces BMSC senescence and associated osteoporosis but also offer new insights into treating HFD-induced osteoporosis by targeting the VDR-superoxide dismutase 2 (SOD2)-ROS axis.

Identification of a clinical signature predictive of differentiation fate of human bone marrow stromal cells

BACKGROUND

Transplantation of human bone marrow stromal cells (hBMSCs) is a promising therapy for bone regeneration due to their ability to differentiate into bone forming osteoblastic cells. However, transplanted hBMSCs exhibit variable capacity for bone formation resulting in inconsistent clinical outcome. The aim of the study was to identify a set of donor- and cell-related characteristics that detect hBMSCs with optimal osteoblastic differentiation capacity.

METHODS

We collected hBMSCs from 58 patients undergoing surgery for bone fracture. Clinical profile of the donors and in vitro characteristics of cultured hBMSCs were included in uni- and multivariable analysis to determine their predictive value for osteoblastic versus adipocytic differentiation capacity assessed by quantification of mineralized matrix and mature adipocyte formation, respectively.

RESULTS

We identified a signature that explained > 50% of variation in osteoblastic differentiation outcome which included the following positive predictors: donor sex (male), absence of osteoporosis diagnosis, intake of vitamin D supplements, higher fraction of CD146+, and alkaline phosphate (ALP+) cells. With the exception of vitamin D and ALP+ cells, these variables were also negative predictors of adipocytic differentiation.

CONCLUSIONS

Using a combination of clinical and cellular criteria, it is possible to predict differentiation outcome of hBMSCs. This signature may be helpful in selecting donor cells in clinical trials of bone regeneration.

Association between histone deacetylase activity and vitamin D-dependent gene expressions in relation to sulforaphane in human colorectal cancer cells

BACKGROUND

It is relatively unknown as to how dietary bioactive compound sulforaphane (SFN) and vitamin D regulate gene expression in colorectal cancer. We hypothesized that a combination of SFN with vitamin D would prove beneficial in colorectal cancer. A combinatorial chemo-preventive strategy was employed to investigate the impact of SFN on chromatin remodeling in colorectal carcinoma. To understand the epigenetics-mediated changes in gene expression in response to SFN and vitamin D, Caco-2 cells were exposed for 24 h to vitamin D (100 nmol L^-1 ) either alone or in combination with SFN and trichostatin A (20 and 1 μmol L^-1 , respectively) at 70% confluency (proliferating) and after 13 days post-confluency (fully differentiated). Changes to VDR, CYP24A1, CYP27B1 and TRPV6 gene expressions were quantified using real-time PCR-based assays. Histone deacetylase (HDAC) inhibitor activity was assessed using HDAC I/II assay that measured global changes in acetylation status.

RESULTS

In differentiated Caco-2 cells, none of the genes had significant changes from D alone group. D + SFN (P = 0.99) demonstrated an opposing effect from D alone and decreased VDR expression. However, in proliferating Caco-2 cells, D + SFN (P < 0.04) increased VDR expression and decreased CYP27B1 (P < 0.01) more than D alone (P = 0.38 and 0.07, respectively). Although statistically significant, D + SFN (P = 0.01) effect on HDAC inhibitor activity was less than trichostatin A alone group (P < 0.0004) or SFN alone group (P < 0.0014).

CONCLUSIONS

The data suggest that colon cancer cells respond to dietary components differently under different conditions. The effect of vitamin D and SFN is selective and gene-specific in the complex multistep process of colorectal carcinogenesis in vitro. © 2020 Society of Chemical Industry.

Fibroblast growth factor 23 counters vitamin D metabolism and action in human mesenchymal stem cells

Chronic kidney disease (CKD) is associated with elevated circulating fibroblast growth factor 23 (FGF23), impaired renal biosynthesis of 1α,25-dihydroxyvitamin D (1α,25(OH)₂D), low bone mass, and increased fracture risk. Our previous data with human mesenchymal stem cells (hMSCs) indicated that vitamin D metabolism in hMSCs is regulated as it is in the kidney and promotes osteoblastogenesis in an autocrine/paracrine manner. In this study, we tested the hypothesis that FGF23 inhibits vitamin D metabolism and action in hMSCs. hMSCs were isolated from discarded marrow during hip arthroplasty, including two subjects receiving hemodialysis and a series of 20 subjects (aged 49-83 years) with estimated glomerular filtration rate (eGFR) data. The direct in vitro effects of rhFGF23 on hMSCs were analyzed by RT-PCR, Western immunoblot, and biochemical assays. Ex vivo analyses showed positive correlations for both secreted and membrane-bound αKlotho gene expression in hMSCs with eGFR of the subjects from whom hMSCs were isolated. There was downregulated constitutive expression of αKlotho, but not FGFR1 in hMSCs obtained from two hemodialysis subjects. In vitro, rhFGF23 countered vitamin D-stimulated osteoblast differentiation of hMSCs by reducing the vitamin D receptor, CYP27B1/1α-hydroxylase, biosynthesis of 1α,25(OH)₂D₃, and signaling through BMP-7. These data demonstrate that dysregulated vitamin D metabolism in hMSCs may contribute to impaired osteoblastogenesis and altered bone and mineral metabolism in CKD subjects due to elevated FGF23. This supports the importance of intracellular vitamin D metabolism in autocrine/paracrine regulation of osteoblast differentiation in hMSCs.

Obesity and leptin influence vitamin D metabolism and action in human marrow stromal cells

Obesity is associated with low serum 25-hydroxyvitamin D [s25(OH)D], high serum leptin, and generally high bone mineral density (BMD). Human Marrow Stromal Cells (hMSCs) differentiate to osteoblasts and are both a target and source of vitamin D metabolites in bone marrow. There is no information about the influence of obesity on vitamin D metabolism and osteoblastogenesis in hMSCs and little about direct effects of leptin on hMSCs. In this study, we tested the hypotheses that 1) obesity has an influence on the ex vivo constitutive expression of vitamin D-hydroxylase genes in hMSCs, and 2) recombinant human (rh) Leptin regulates the D-hydroxylases and promotes osteoblastogenesis in hMSCs. In a cohort of female subjects undergoing joint replacement surgery, the effects of Body Mass Index (BMI) and Fat Mass Index (FMI) on BMD T-scores and s25(OH)D were evaluated. hMSCs were isolated from bone tissues discarded during surgery. The direct effects of rh-Leptin on osteoblast differentiation and D-related genes in hMSCs were examined in vitro. There were positive correlations for BMD T-score of femoral neck and spine with BMI and FMI. Serum 25(OH)D levels in obese subjects were 71% of that in non-obese counterparts (p = 0.001). hMSCs from obese women had higher constitutive expression of CYP27A1/25-hydroxylase and vitamin D receptor. Those findings raised the mechanistic question of how obesity could influence vitamin D metabolism and osteoblast differentiation in hMSCs. Treating hMSCs with rh-Leptin in vitro significantly stimulated osteoblastogenesis. In addition, leptin downregulated CYP24A1 and upregulated CYP27B1, CYP27A1 and VDR, which play vital roles in vitamin D metabolism. Furthermore, co-treatment with leptin and vitamin D₃ metabolites promoted ALP activity compared with either alone. This research demonstrates links between obesity, vitamin D metabolism, and osteoblastogenesis by which leptin's direct effects on D-metabolism and osteoblast differentiation in hMSCs may protect bone from low s25(OH)D in obese subjects.

Synergistic effect of 1α,25-dihydroxyvitamin D3 and 17β-estradiol on osteoblast differentiation of pediatric MSCs

Vitamin D is essential for mineral homeostasis and contributes to bone metabolism by stimulating osteoblast differentiation of marrow stromal cells (MSCs). In this study, we used MSCs from pre-pubertal girls and boys to test the hypothesis that 1α,25(OH)₂D and 17β-estradiol have synergistic effects on these MSCs, and what mechanism is involved. With IRB approval, we isolated MSCs from discarded excess iliac marrow graft from children undergoing alveolar cleft repair. Plasma was available from 8 female (9.3±0.2years) and 8 male (9.6±0.1years) subjects for hormone assays [25(OH)D, total testosterone, 17β-estradiol, estrone, DHEA-S, Growth Hormone, IGF-I]. RT-PCR was used for gene expression. Alkaline phosphatase (ALP) activity was used to measure osteoblast differentiation at day 7; alizarin red was used to measure matrix mineralization at day 21. All subjects were pre-pubertal based on their hormone levels. Serum 25(OH)D levels ranged from 13.1 to 26.4ng/mL, with 75% below 20ng/mL. Constitutive gene expression of VDR and ERα, β varied from subject to subject with no association with sex or serum chemistries. In osteoblastogenic medium, 1α,25(OH)₂D₃ (10nM) increased ALP activity by 36% (p<0.05) in MSCs; 10nM of E2 was not stimulatory but the combination of 1α,25(OH)₂D₃ and E2 increased ALP 151% (p<0.05 vs. control) and by 84.5% (p<0.05 vs. 1α,25(OH)₂D3 alone). The combination of 1α,25(OH)₂D₃ and E2 significantly increased mineralization 11-fold, compared with either agent alone. Twenty-four hour treatment with 1α,25(OH)₂D₃ (10nM) or E2 (10nM) upregulated each other's receptor by as much as 5.8-fold for ERα and 2.9-fold for the VDR. In summary, 1α,25(OH)₂D3 stimulated osteoblast differentiation and matrix mineralization with MSCs from pre-pubertal subjects, with a synergistic effect of E2, mediated by upregulated receptor levels, at least in part. These studies add new information about the regulation of human osteoblast differentiation, effects of 1α,25(OH)₂D₃ and E2 on MSCs, and the importance of vitamin D for skeletal health.

Physiologic and pathophysiologic roles of extra renal CYP27b1: Case report and review

Although the kidney was initially thought to be the sole organ responsible for the production of 1,25(OH)₂D via the enzyme CYP27b1, it is now appreciated that the expression of CYP27b1 in tissues other than the kidney is wide spread. However, the kidney is the major source for circulating 1,25(OH)₂D. Only in certain granulomatous diseases such as sarcoidosis does the extra renal tissue produce sufficient 1,25(OH)₂D to contribute to the circulating levels, generally associated with hypercalcemia, as illustrated by the case report preceding the review. Therefore the expression of CYP27b1 outside the kidney under normal circumstances begs the question why, and in particular whether the extra renal production of 1,25(OH)₂D has physiologic importance. In this chapter this question will be discussed. First we discuss the sites for extra renal 1,25(OH)₂D production. This is followed by a discussion of the regulation of CYP27b1 expression and activity in extra renal tissues, pointing out that such regulation is tissue specific and different from that of CYP27b1 in the kidney. Finally the physiologic significance of extra renal 1,25(OH)₂D₃ production is examined, with special focus on the role of CYP27b1 in regulation of cellular proliferation and differentiation, hormone secretion, and immune function. At this point the data do not clearly demonstrate an essential role for CYP27b1 expression in any tissue outside the kidney, but several examples pointing in this direction are provided. With the availability of the mouse enabling tissue specific deletion of CYP27b1, the role of extra renal CYP27b1 expression in normal and pathologic states can now be addressed definitively.

MiR-351 negatively regulates osteoblast differentiation of MSCs induced by (+)-cholesten-3-one through targeting VDR

Our previous reports indicated that (+)-cholesten-3-one induces osteogenic differentiation of bone marrow mesenchymal stem cells (MSCs) by activating vitamin D receptor (VDR). However, whether and how miRNAs modulate osteogenic differentiation induced by (+)-cholesten-3-one have not been explored. In this study, miRNA array profiling and further validation by quantitative real-time PCR revealed that miR-351 was downregulated during (+)-cholesten-3-one-induced osteogenic differentiation of MSCs. Overexpression of miR-351 by miR-351 precursor transfection markedly inhibited the expression of osteoblast-specific genes, such as alkaline phosphatase (ALP), collagen type II, osteopontin (OPN), and runt-related transcription factor 2 (RUNX2), which consequently decreased a number of calcium mineralized nodules. Inhibition of miR-351 function by anti-miR-351 promoted expression of osteoblast-specific genes. Our results suggest that miR-351 is a negative regulator of osteoblast differentiation of MSCs induced by (+)-cholesten-3-one. Target prediction analysis tools and experimental validation by luciferase 3'UTR reporter assay identified VDR as a direct target of miR-351. miR-351 inhibited the expression of the VDR, which played a critical role in the control of osteogenic differentiation of MSCs. Importantly, overexpression of VDR significantly abolished the inhibitory effect of miR-351 on (+)-cholesten-3-one induced osteogenic differentiation. Taken together, our results demonstrate that miR-351 negatively regulates osteoblast differentiation of MSCs induced by (+)-cholesten-3-one through targeting VDR. These findings provid evidence that miR-351 can bea possible therapeutic target for bone repair and regeneration.

Chronic kidney disease and vitamin D metabolism in human bone marrow-derived MSCs

Vitamin D that is synthesized in the skin or is ingested undergoes sequential steps of metabolic activation via a cascade of cytochrome P450 enzymatic hydroxylations in the liver and kidney to produce 1α,25-dihydroxyvitamin D (1α,25(OH)2 D). There are many tissues that are able to synthesize 1α,25(OH)2 D, but the biological significance of extrarenal hydroxylases is unresolved. Human marrow-derived mesenchymal stem cells (marrow stromal cells, hMSCs) give rise to osteoblasts, and their differentiation is stimulated by 1α,25(OH)2 D. In addition to being targets of 1α,25(OH)2 D, hMSCs can synthesize it; on the basis of those observations, we further examined the local autocrine/paracrine role of vitamin D metabolism in osteoblast differentiation. Research with hMSCs from well-characterized subjects provides an innovative opportunity to evaluate the effects of clinical attributes on the regulation of hMSCs. Like the renal 1α-hydroxylase, the enzyme in hMSCs is constitutively decreased with age and chronic kidney disease (CKD); both are regulated by PTH1-34, insulin-like growth factor 1, calcium, 1α,25(OH)2 D, 25(OH)D, and fibroblast growth factor 23. CKD is associated with impaired renal biosynthesis of 1α,25(OH)2 D, low bone mass, and increased fracture risk. Studies with hMSCs from CKD patients or aged subjects indicate that circulating 25(OH)D may have an important role in osteoblast differentiation on vitamin D metabolism and action in hMSCs.

(+)-Cholesten-3-one induces osteogenic differentiation of bone marrow mesenchymal stem cells by activating vitamin D receptor

In our previous reports, it was revealed that steroids in traditional Chinese medicine (TCM) have the therapeutic potential to treat bone disease. In the present study, an in vitro model of a vitamin D receptor response element (VDRE) reporter gene assay in mesenchymal stem cells (MSCs) was used to identify steroids that enhanced osteogenic differentiation of MSCs. (+)-cholesten-3-one (CN), which possesses a ketone group that is modified in cholesterol and cholesterol myristate, effectively promoted the activity of the VDRE promoter. Phenotypic cellular analysis indicated that CN induced differentiation of MSCs into osteogenic cells and increased expression of specific osteogenesis markers, including alkaline phosphatase, collagen II and Runt-related transcription factor 2. Furthermore, CN significantly increased the expression of osteopontin, the target of the vitamin D receptor (VDR), which indicated that CN may activate vitamin D receptor signaling. Over-expression of VDR or knockdown studies with VDR-small interfering RNA revealed that the pro-differentiation effects induced by CN required VDR. Furthermore, the present study determined that the C-terminal region of the VDR is responsible for the action of CN. Taken together, the present findings demonstrated that CN induced osteogenic differentiation of MSCs by activating VDR. The present study explored the regulation of stem cells by using a series of similar steroids and provided evidence to support a potential strategy for the screening of novel drugs to treat bone disease in the future.

Paracrine effects of haematopoietic cells on human mesenchymal stem cells

Stem cell function decline during ageing can involve both cell intrinsic and extrinsic mechanisms. Bone and blood formation are intertwined in bone marrow, therefore haematopoietic cells and bone cells could be extrinsic factors for each other. In this study, we assessed the paracrine effects of extrinsic factors from haematopoietic cells on human mesenchymal stem cells (MSCs). Our data showed that haematopoietic cells stimulate proliferation, osteoblast differentiation and inhibit senescence of MSCs; TNF-α, PDGF-β, Wnt1, 4, 6, 7a and 10a, sFRP-3 and sFRP-5 are dominantly expressed in haematopoietic cells; the age-related increase of TNF-α in haematopoietic cells may perform as a negative factor in the interactions of haematopoietic cells on MSCs via TNF-α receptors and then activating NF-κB signaling or Wnt/β-catenin signaling to induce senescence and reduce osteoblast differentiation in MSCs. In conclusion, our data demonstrated that there are paracrine interactions of haematopoietic cells on human MSCs; immunosenescence may be one of the extrinsic mechanisms by which skeletal stem cell function decline during human skeletal ageing.

Epigenetic pathways regulating bone homeostasis: potential targeting for intervention of skeletal disorders

Epigenetic regulation utilizes different mechanisms to convey heritable traits to progeny cells that are independent of DNA sequence, including DNA silencing, post-translational modifications of histone proteins, and the post-transcriptional modulation of RNA transcript levels by non-coding RNAs. Although long non-coding RNAs have recently emerged as important regulators of gene imprinting, their functions during osteogenesis are as yet unexplored. In contrast, microRNAs (miRNAs) are well characterized for their control of osteogenic and osteoclastic pathways; thus, further defining how gene regulatory networks essential for skeleton functions are coordinated and finely tuned through the activities of miRNAs. Roles of miRNAs are constantly expanding as new studies uncover associations with skeletal disorders. The distinct functions of epigenetic regulators and evidence for integrating their activities to control normal bone gene expression and bone disease will be presented. In addition, potential for using "signature miRNAs" to identify, manage, and therapeutically treat osteosarcoma will be discussed in this review.

Vitamin D and gene networks in human osteoblasts

Bone formation is indirectly influenced by 1,25-dihydroxyvitamin D3 (1,25D3) through the stimulation of calcium uptake in the intestine and re-absorption in the kidneys. Direct effects on osteoblasts and bone formation have also been established. The vitamin D receptor (VDR) is expressed in osteoblasts and 1,25D3 modifies gene expression of various osteoblast differentiation and mineralization-related genes, such as alkaline phosphatase (ALPL), osteocalcin (BGLAP), and osteopontin (SPP1). 1,25D3 is known to stimulate mineralization of human osteoblasts in vitro, and recently it was shown that 1,25D3 induces mineralization via effects in the period preceding mineralization during the pre-mineralization period. For a full understanding of the action of 1,25D3 in osteoblasts it is important to get an integrated network view of the 1,25D3-regulated genes during osteoblast differentiation and mineralization. The current data will be presented and discussed alluding to future studies to fully delineate the 1,25D3 action in osteoblast. Describing and understanding the vitamin D regulatory networks and identifying the dominant players in these networks may help develop novel (personalized) vitamin D-based treatments. The following topics will be discussed in this overview: (1) Bone metabolism and osteoblasts, (2) Vitamin D, bone metabolism and osteoblast function, (3) Vitamin D induced transcriptional networks in the context of osteoblast differentiation and bone formation.

Vitamin D endocrine system and osteoblasts

The interaction between vitamin D and osteoblasts is complex. In the current review we will give an overview of the current knowledge of the vitamin D endocrine system in osteoblasts. The presence of the vitamin D receptor in osteoblasts enables direct effects of 1α,25dihydroxyvitamin D3 (1α,25D3) on osteoblasts, but the magnitude of the effects is subject to the presence of many other factors. Vitamin D affects osteoblast proliferation, as well as differentiation and mineralization, but these effects vary with the timing of treatment, dosage and origin of the osteoblasts. Vitamin D effects on differentiation and mineralization are mostly stimulatory in human and rat osteoblasts, and inhibitory in murine osteoblasts. Several genes and mechanisms are studied to explain the effects of 1α,25D3 on osteoblast differentiation and bone formation. Besides the classical VDR, osteoblasts also express a membrane-localized receptor, and in vitro studies have shown that osteoblasts are capable of the synthesis of 1α,25D3.

Vitamin D metabolism in human bone marrow stromal (mesenchymal stem) cells

There are many human extra-renal tissues and cells that biosynthesize 1α,25-dihydroxyvitamin D (1α,25(OH)(2)D) by the action of CYP27B1/1α-hydroxylase. Human marrow stromal cells (hMSCs), also known as mesenchymal stem cells, were isolated from marrow discarded from well-characterized, consented subjects during common orthopedic procedures. Human MSCs can give rise to osteoblasts, chondrocytes, adipocytes, and other lineages. Their in vitro differentiation to osteoblasts is stimulated by 1α,25(OH)(2)D, and recent evidence indicates that they have the capacity to metabolize vitamin D in a regulated manner. Human MSCs express the vitamin D receptor, 25-hydroxylases, 1α-hydroxylase, and 24-hydroxylase; stimulation of in vitro osteoblastogenesis by 25(OH)D depends on the activity of CYP27B1/1α-hydroxylase. The finding that hMSCs are a both a producer and target of 1α,25(OH)(2)D suggests a potential autocrine/paracrine role of vitamin D metabolism in osteoblast differentiation. Expression and enzyme activity of CYP27B1/1α-hydroxylase are upregulated by substrate 25(OH)D and Parathyroid Hormone (PTH) and are downregulated by 1α,25(OH)(2)D. With subject age, there are decreases in basal osteoblast potential and in stimulation of osteoblastogenesis by 1α,25(OH)(2)D, 25(OH)D, and PTH. In vitro treatment with a combination of 25(OH)D and PTH rejuvenated osteoblastogenesis with hMSCs from elders; this was attributable to increases in CYP27B1/1α-hydroxylase and in receptor for each hormone by the reciprocal factor. Other clinical variables beside age, i.e. low serum 25(OH)D or low estimated glomerular filtration rate, are correlated with reduced osteoblastogenesis. These studies suggest that osteoblastogenesis may not be optimal unless there is sufficient serum 25(OH)D substrate for hMSCs to synthesize and respond to local 1α,25(OH)(2)D.

Functional impairment of bone formation in the pathogenesis of osteoporosis: the bone marrow regenerative competence

The skeleton is a high-renewal organ that undergoes ongoing cycles of remodeling. The regenerative bone formation arm ultimately declines in the aging, postmenopausal skeleton, but current therapies do not adequately address this deficit. Bone marrow is the primary source of the skeletal anabolic response and the mesenchymal stem cells (MSCs), which give rise to bone matrix-producing osteoblasts. The identity of these stem cells is emerging, but it now appears that the term 'MSC' has often been misapplied to the bone marrow stromal cell (BMSC), a progeny of the MSC. Nevertheless, the changes in BMSC phenotype associated with age and estrogen depletion likely contribute to the attenuated regenerative competence of the marrow and may reflect alterations in MSC phenotype. Here we summarize current concepts in bone marrow MSC identity, and within this context, review recent observations on changes in bone marrow population dynamics associated with aging and menopause.