Vitamin D controls the capacity of human dendritic cells to induce functional regulatory T cells by regulation of glucose metabolism

Tolerogenic dendritic cells (tolDCs) instruct regulatory T cells (Tregs) to dampen autoimmunity. Active vitamin D₃ (1α,25-dihydroxyvitamin D₃; 1α,25(OH)₂D₃) imprints human monocyte-derived DCs with tolerogenic properties by reprogramming their glucose metabolism. Here we identify the glycolytic enzyme 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 4 (PFKFB4) as a critical checkpoint and direct transcriptional target of 1α,25(OH)₂D₃ in determining the tolDC profile. Using tracer metabolomics, we show that PFKFB4 activity is essential for glucose metabolism, especially for glucose oxidation, which is elevated upon 1α,25(OH)₂D₃ exposure. Pharmacological inhibition of PFKFB4 reversed the 1α,25(OH)₂D₃-mediated shift in metabolism, DC profile and function, as determined by expression of inhibitory surface markers and secretion of regulatory cytokines and factors. Moreover, PFKFB4 inhibition in 1α,25(OH)₂D₃-treated DCs blocked their hallmark capacity to induce suppressive Tregs. This work demonstrates that alterations in the bioenergetic metabolism of immune cells are central to the immunomodulatory effects induced by 1α,25(OH)₂D₃.

Metabolism of selective 20-epi-vitamin D3 analogs in rat osteosarcoma UMR-106 cells: Isolation and identification of four novel C-1 fatty acid esters of 1α,25-dihydroxy-16-ene-20-epi-vitamin D3

Analogs of 1α,25-dihydroxyvitamin D₃ (S1) with 20-epi modification (20-epi analogs) possess unique biological properties. We previously reported that 1α,25-dihydroxy-20-epi-vitamin D₃ (S2), the basic 20-epi analog is metabolized into less polar metabolites (LPMs) in rat osteosarcoma cells (UMR-106) but not in a perfused rat kidney. Furthermore, we also noted that only selective 20-epi analogs are metabolized into LPMs. For example, 1α,25-dihydroxy-16-ene-20-epi-vitamin D₃ (S4), but not 1α,25-dihydroxy-16-ene-23-yne-20-epi-vitamin D₃ (S5) is metabolized into LPMs. In spite of these novel findings, the unequivocal identification of LPMs has not been achieved to date. We report here on a thorough investigation of the metabolism of S4 in UMR-106 cells and isolated two major LPMs produced directly from the substrate S4 itself and two minor LPMs produced from 3-epi-S4, a metabolite of S4 produced through C-3 epimerization pathway. Using GC/MS, ESI-MS and ¹H NMR analysis, we identified all the four LPMs of S4 as 25-hydroxy-16-ene-20-epi-vitamin D₃-1-stearate and 25-hydroxy-16-ene-20-epi-vitamin D₃-1-oleate and their respective C-3 epimers. We report here for the first time the elucidation of a novel pathway of metabolism in UMR-106 cells in which both 1α,25(OH)₂-16-ene-20-epi-D₃ and 1α,25(OH)₂-16-ene-20-epi-3-epi-D₃ undergo C-1 esterification into stearic and oleic acid esters.

The phenotype and function of murine bone marrow-derived dendritic cells is not affected by the absence of VDR or its ability to bind 1α,25-dihydroxyvitamin D3

The nuclear vitamin D receptor (VDR) is generally recognized as a ligand-dependent transcription factor that mediates the actions of its natural ligand, 1α,25-dihydroxyvitamin D₃ (1α,25(OH)₂D₃) on multiple target genes involved in mineral homeostasis, bone development, as well as immune reactivity. As the VDR is widely distributed in nearly all cells of the body, it implies that the vitamin D endocrine system may regulate many cell types and functions. Experiments in VDR null mice established that the VDR has intrinsically critical roles in skin and keratinocyte biology but not in immune responses. Oppositely, absence of the VDR ligand is linked to susceptibility to autoimmunity, illustrating a potential role for the unliganded VDR in the immune system. This discrepancy stimulated us to further investigate the impact of the VDR on the phenotype and function of myeloid dendritic cells (DCs) generated ex vivo from bone marrow precursors of VDR null (with a truncated VDR) and VDR ΔAF2 mice (with a mutated C-terminal activation factor 2 domain thus rendering ligand-induced gene transcription impossible). Absent or unliganded VDR did not affect bone marrow-derived myeloid DC generation. DCs obtained from VDR null and VDR ΔAF2 bone marrow cells had comparable MHC-II, and costimulatory molecule CD86, CD80 and CD40 expression than DCs from wild-type bone marrow cells. Additionally, an unliganded VDR did not affect the cytokine production nor the antigen-specific T cell stimulatory capacity of bone marrow-derived DCs. In conclusion, we showed that although clear effects of 1α,25-dihydroxyvitamin D₃ are described on DC generation, absence of VDR or presence of an unliganded VDR does not affect the profile and function of ex vivo generated bone marrow-derived DCs.

MART-10, the new brand of 1α,25(OH)2D3 analog, is a potent anti-angiogenic agent in vivo and in vitro

BACKGROUND

Angiogenesis is the hall marker for cancer growth and metastasis. Thus, anti-angiogenesis emerges as a new way to treat cancer. 1α,25(OH)2D3 is recently getting popular due to the non-mineral functions, which have been applied fore cancer treatment. The newly-synthesized 1α,25(OH)2D3 analog, MART-10, has been proved to be much more potent than 1α,25(OH)2D3 regarding inhibiting cancer cells growth and metastasis without inducing hypercalcemia in vivo. In this study, we aimed to investigate the effect of MART-10 and 1α,25(OH)2D3 on angiogenesis in vitro and in vivo.

METHODS AND RESULTS

MART-10 and 1α,25(OH)2D3 were able to repress VEGFA-induced human umbilical vein endothelial cells (HUVECs) migration, invasion and tube formation, but not proliferation, with MART-10 much more potent than 1α,25(OH)2D3. The Chick Chorioallantoic Membrane (CAM) assay and matrigeal angiogenesis assay further confirmed the in vivo more potent anti-angiogenesis effect of MART-10. MART-10 inhibited the VEGFA-induced HUVECs angiogenesis process through downregulation of Akt and Erk 1/2 phosphorylation. The VEGFA-VEGFR2 (VEGF receptor 2) axis is the main signal transducing pathway to stimulate angiogenesis. A positive autocrine manner was found for the first time in HUVECs as treated by VEGFA, which induced VEGFA expression and secretion, and VEGFR2 expression. MART-10 and 1α,25(OH)2D3 were demonstrated to be able to repress this positive autocrine manner, thus inhibiting angiogenesis.

CONCLUSIONS

MART-10 and 1α,25(OH)2D3 both are effective anti-angiogenesis agents. Given MART-10 is much more potent than 1α,25(OH)2D3 and active in vivo without obvious side effect, MART-10 should be deemed as a promising anti-cancer agent.

Histochemical examination of adipose derived stem cells combined with β-TCP for bone defects restoration under systemic administration of 1α,25(OH)2D3

The purpose of this study was to evaluate the effects of osteogenic differentiated adipose-derived stem cell (ADSC) loaded beta-tricalcium phosphate (β-TCP) in the restoration of bone defects under intraperitoneal administration of 1α,25-dihydroxyvitamin D3(1α,25(OH)2D3). ADSCs were isolated from the fat tissue of 8 week old Wister rats and co-cultured with β-TCP for 21 days under osteogenic induction. Then the ADSC-β-TCP complexes were implanted into bone defects in the femora of rats. 1α,25(OH)2D3 (VD) or normal saline (NS) was administrated intraperitoneally every other day after the surgery. Femora were harvested at day 7, day 14 and day 28 post-surgery. There were 4 groups for all specimens: β-TCP-NS group; β-TCP-ADSC-NS group; β-TCP-VD group and β-TCP-ADSC-VD group. Alkaline phosphatase (ALP) was up-regulated obviously in ADSC groups compared with non-ADSC groups at day 7, day 14 and day 28, although high expression of runt-related transcription factor 2 (RUNX2) was only seen at day 7. Furthermore, the number of TRAP-positive osteoclasts and the expression of cathepsin K (CK) were significantly decreased in VD groups compared with non-VD groups at day 7 and day 14. As a most significant finding, the β-TCP-ADSC-VD group showed the highest BV/TV ratio compared with the other three groups at day 28. Taken together, ADSC-loaded β-TCP under the administration of 1α,25(OH)2D3 made a promising therapy for bone defects restoration.

1α,25(OH)2D3 differentially regulates miRNA expression in human bladder cancer cells

Bladder cancer is the fourth most commonly diagnosed cancer in men and eighth leading cause of cancer-related death in the US. Epidemiological and experimental studies strongly suggest a role for 1α,25(OH)2D3 in cancer prevention and treatment. The antitumor activities of 1α,25(OH)2D3 are mediated by the induction of cell cycle arrest, apoptosis, differentiation and the inhibition of angiogenesis and metastasis. miRNAs play important regulatory roles in cancer development and progression. However, the role of 1α,25(OH)2D3 in the regulation of miRNA expression and the potential impact in bladder cancer has not been investigated. Therefore, we studied 1α,25(OH)2D3-regulated miRNA expression profiles in human bladder cancer cell line 253J and the highly tumorigenic and metastatic derivative line 253J-BV by miRNA qPCR panels. 253J and 253J-BV cells express endogenous vitamin D receptor (VDR), which can be further induced by 1α,25(OH)2D3. VDR target gene 24-hydroxylase was induced by 1α,25(OH)2D3 in both cell lines, indicating functional 1α,25(OH)2D3 signaling. The miRNA qPCR panel assay results showed that 253J and 253J-BV cells have distinct miRNA expression profiles. Further, 1α,25(OH)2D3 differentially regulated miRNA expression profiles in 253J and 253J-BV cells in a dynamic manner. Pathway analysis of the miRNA target genes revealed distinct patterns of contribution to the molecular functions and biological processes in the two cell lines. In conclusion, 1α,25(OH)2D3 differentially regulates the expression of miRNAs, which may contribute to distinct biological functions, in human bladder 253J and 253J-BV cells. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

Membrane-mediated actions of 1,25-dihydroxy vitamin D3: a review of the roles of phospholipase A2 activating protein and Ca(2+)/calmodulin-dependent protein kinase II

The secosteroid 1α,25-dihydroxy vitamin D3 [1α,25(OH)2D3] acts on cells via classical steroid hormone receptor-mediated gene transcription and by initiating rapid membrane-mediated signaling pathways. In its membrane-initiated pathway, after 1α,25(OH)2D3 interacts with protein disulfide isomerase, family A, member 3 (Pdia3) in caveolae, phospholipase A2 (PLA2) and protein kinase C (PKC) are activated. Recent efforts to determine the signaling proteins involved in the 1α,25(OH)2D3 signal from Pdia3 to PLA2 have indicated that phospholipase A2 activating protein (PLAA) and Ca(2+)/calmodulin-dependent kinase II (CaMKII) are required. PLAA is located in caveolae, where it interacts with Pdia3 and caveolin-1 (Cav-1) to initiate rapid signaling via CaMKII, activating PLA2, leading to activation of protein kinase C (PKC) and PKC-dependent responses.

Cell cycle arrest and apoptosis induced by 1α,25(OH)2D3 and TX 527 in Kaposi sarcoma is VDR dependent

We have previously shown that 1α,25(OH)2-Vitamin D3 [1α,25(OH)2D3] and its less calcemic analog TX 527 inhibit the proliferation of endothelial cells transformed by the viral G protein-coupled receptor associated to Kaposi sarcoma (vGPCR) and this could be partially explained by the inhibition of the NF-κB pathway. In this work, we further explored the mechanism of action of both vitamin D compounds in Kaposi sarcoma. We investigated whether the cell cycle arrest and subsequent apoptosis of endothelial cells (SVEC) and SVEC transformed by vGPCR (SVEC-vGPCR) elicited by 1α,25(OH)2D3 and TX 527 were mediated by the vitamin D receptor (VDR). Cell cycle analysis of SVEC and SVEC-vGPCR treated with 1α,25(OH)2D3 (10nM, 48h) revealed that 1α,25(OH)2D3 increased the percentage of cells in the G0/G1 phase and diminished the percentage of cells in the S phase of the cell cycle. Moreover, the number of cells in the S phase was higher in SVEC-vGPCR than in SVEC due to vGPCR expression. TX 527 exerted similar effects on growth arrest in SVEC-vGPCR cells. The cell cycle changes were suppressed when the expression of the VDR was blocked by a stable transfection of shRNA against VDR. Annexin V-PI staining demonstrated apoptosis in both SVEC and SVEC-vGPCR after 1α,25(OH)2D3 and TX 527 treatment (10nM, 24h). Cleavage of caspase-3 detected by Western blot analysis was increased to a greater extent in SVEC than in SVEC-vGPCR cells, and this effect was also blocked in VDR knockdown cells. Altogether, these results suggest that 1α,25(OH)2D3 and TX 527 inhibit the proliferation of SVEC and SVEC-vGPCR and induce apoptosis by a mechanism that involves the VDR.

Novel roles of 1α,25(OH)2D3 on DNA repair provide new strategies for breast cancer treatment

Breast cancers classified as triple-negative (TNBC) and BRCA1-deficient, are particularly aggressive and difficult to treat. A major breakthrough was the finding that these tumors are exquisitely sensitive to inhibitors of poly(ADP-ribose) polymerase (PARPi). Phase II clinical trials have shown encouraging outcomes, with tolerable side effects. However, a significant fraction of these cancers acquire resistance. Elegant studies demonstrated that loss of the DNA repair protein 53BP1 contributes to the resistance of BRCA1-deficient cells and tumors to PARPi. Thus, raising the levels of 53BP1 in these aggressive tumors could potentially restore their sensitivity to PARPi and other genotoxic agents. We will review here our studies revealing that 1α,25(OH)2D3, an active form of vitamin D, stabilizes 53BP1 levels in tumor cells. Breast tumor cells that become BRCA1-deficient activate cathepsin L-mediated degradation of 53BP1 to ensure genome stability and proliferation. Importantly, 1α,25(OH)2D3 treatment restores the levels of 53BP1 as efficiently as cathepsin L inhibitors, which results in increased genomic instability in response to PARPi or radiation, and reduced proliferation. Furthermore, analysis of human breast tumors identified nuclear cathepsin L as a positive biomarker for TNBC, which correlates inversely with 53BP1 when vitamin D receptor (VDR) nuclear levels are low. The major findings of these studies are: (1) identification of a new pathway contributing to breast cancers with the poorest prognosis; (2) discovery of the ability of 1α,25(OH)2D3 to inhibit this pathway; and (3) discovery of a triple biomarker signature for identification of patients that could benefit from the treatment. This article is part of a Special Issue entitled '16th Vitamin D Workshop'.

New insights on membrane mediated effects of 1α,25-dihydroxy vitamin D3 signaling in the musculoskeletal system

1α,25-Dihydroxy vitamin D3 [1α,25(OH)2D3] acts on cells via classical steroid hormone receptor-mediated gene transcription and by initiating rapid membrane-mediated signaling pathways. Two receptors have been implicated to play roles in 1α,25(OH)2D3 mediated rapid signaling, the classical nuclear vitamin D receptor (VDR) and protein disulfide isomerase, family A, member 3 (Pdia3). Long term efforts to investigate the roles of these two receptors demonstrated thatPdia3 is located in caveolae, where it interacts with phospholipase A2 (PLA2) activating protein (PLAA) and caveolin-1 (Cav-1) to initiate rapid signaling via Ca(++)/calmodulin-dependent protein kinase II (CaMKII), PLA2, phospholipase C (PLC), protein kinase C (PKC), and ultimately the ERK1/2 family of mitogen activated protein kinases (MAPK). VDR is present on the plasma membrane, and it is required for 1α,25(OH)2D3 induced rapid activation of Src. PDIA3+/- mice demonstrate an impaired musculoskeletal phenotype. Moreover, our studies examining mineralization of pre-osteoblasts in 3D culture have shown the physiological importance of Pdia3 and VDR interaction: knockdown of Pdia3 or VDR is characterized by impaired mineralization of the constructs.

Anti-proliferative activity of 25-hydroxyvitamin D3 in human prostate cells

1α-Hydroxylation of 25-hydroxyvitamin D3 is believed to be essential for its biological effects. In this study, we evaluated the biological activity of 25(OH)D3 itself comparing with the effect of cell-derived 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3). First, we measured the cell-derived 1α,25(OH)2D3 level in immortalized human prostate cell (PZ-HPV-7) using [(3)H]-25(OH)D3. The effects of the cell-derived 1α,25(OH)2D3 on vitamin D3 24-hydroxylase (CYP24A1) mRNA level and the cell growth inhibition were significantly lower than the effects of 25(OH)D3 itself added to cell culture. 25-Hydroxyvitamin D3 1α-hydroxylase (CYP27B1) gene knockdown had no significant effects on the 25(OH)D3-dependent effects, whereas vitamin D receptor (VDR) gene knockdown resulted in a significant decrease in the 25(OH)D3-dependent effects. These results strongly suggest that 25(OH)D3 can directly bind to VDR and exerts its biological functions. DNA microarray and real-time RT-PCR analyses suggest that semaphorin 3B, cystatin E/M, and cystatin D may be involved in the antiproliferative effect of 25(OH)D3.