Vitamin D3 regulation of stromelysin-1 (MMP-3) in chondrocyte cultures is mediated by protein kinase C

Histological Assessment of Endochondral Ossification and Bone Mineralization

Finely tuned cartilage mineralization, endochondral ossification, and normal bone formation are necessary for normal bone growth. Hypertrophic chondrocytes in the epiphyseal cartilage secrete matrix vesicles, which are small extracellular vesicles initiating mineralization, into the intercolumnar septa but not the transverse partitions of the cartilage columns. Bone-specific blood vessels invade the unmineralized transverse septum, exposing the mineralized cartilage cores. Many osteoblast precursors migrate to the cartilage cores, where they synthesize abundant bone matrices, and mineralize them in a process of matrix vesicle-mediated bone mineralization. Matrix vesicle-mediated mineralization concentrates calcium (Ca) and inorganic phosphates (Pi), which are converted into hydroxyapatite crystals. These crystals grow radially and are eventually get out of the vesicles to form spherical mineralized nodules, leading to collagen mineralization. The influx of Ca and Pi into the matrix vesicle is regulated by several enzymes and transporters such as TNAP, ENPP1, PiT1, PHOSPHO1, annexins, and others. Such matrix vesicle-mediated mineralization is regulated by osteoblastic activities, synchronizing the synthesis of organic bone material. However, osteocytes reportedly regulate peripheral mineralization, e.g., osteocytic osteolysis. The interplay between cartilage mineralization and vascular invasion during endochondral ossification, as well as that of osteoblasts and osteocytes for normal mineralization, appears to be crucial for normal bone growth.

Associations Between Vitamins C and D Intake and Cartilage Composition and Knee Joint Morphology Over 4 Years: Data From the Osteoarthritis Initiative

OBJECTIVE

To determine the cross-sectional and longitudinal associations of vitamin C and D intake with magnetic resonance imaging (MRI) measures of cartilage composition (T2) and joint structure (cartilage, meniscus, and bone marrow) using data from the Osteoarthritis Initiative (OAI) cohort.

METHODS

A total of 1,785 subjects with radiographic Kellgren/Lawrence knee grades 0-3 in the right knee were selected from the OAI database. Vitamins C and vitamin D intake (diet, supplements, and total) were assessed using the Block Brief 2000 Food Frequency Questionnaire at baseline. The MRI analysis protocol included 3T cartilage T2 quantification and semiquantitative joint morphology gradings (Whole-Organ Magnetic Resonance Imaging Score [WORMS]) at baseline and 4 years. Linear regression was used to assess the association between standardized baseline vitamin intake and both baseline WORMS scores and standardized cartilage T2 values.

RESULTS

Higher vitamin C intake was associated with lower average cartilage T2 values, medial tibia T2 values, and medial tibia WORMS scores (standardized coefficient range -0.07 to -0.05, P < 0.05). Higher vitamin D intake was associated with a lower cartilage WORMS sum score and medial femur WORMS score (standardized coefficient range -0.24 to -0.09, P < 0.05). Consistent use of vitamin D supplements of 400 IU at least once a week over 4 years was associated with significantly less worsening of cartilage, meniscus, and bone marrow abnormalities (odds ratio range 0.40-0.56, P < 0.05).

CONCLUSION

Supplementation with vitamin D over 4 years was associated with significantly less progression of knee joint abnormalities. Given the observational nature of this study, future longitudinal randomized controlled trials of vitamin D supplementation are warranted.

Ultrastructural and biochemical aspects of matrix vesicle-mediated mineralization

Matrix vesicle-mediated mineralization is an orchestrated sequence of ultrastructural and biochemical events that lead to crystal nucleation and growth. The influx of phosphate ions into the matrix vesicle is mediated by several proteins such as TNAP, ENPP1, Pit1, annexin and so forth. The catalytic activity of ENPP1 generates pyrophosphate (PPi) using extracellular ATPs as a substrate, and the resultant PPi prevents crystal overgrowth. However, TNAP hydrolyzes PPi into phosphate ion monomers, which are then transported into the matrix vesicle through Pit1. Accumulation of Ca²⁺ and PO₄³⁻ inside matrix vesicles then induces crystalline nucleation, with calcium phosphate crystals budding off radially, puncturing the matrix vesicle’s membrane and finally growing out of it to form mineralized nodules.

Role of vitamin D3 in treatment of lumbar disc herniation--pain and sensory aspects: study protocol for a randomized controlled trial

BACKGROUND

Vitamin D receptors have been identified in the spinal cord, nerve roots, dorsal root ganglia and glial cells, and its genetic polymorphism association with the development of lumbar disc degeneration and herniation has been documented. Metabolic effects of active vitamin D metabolites in the nucleus pulposus and annulus fibrosus cells have been studied. Lumbar disc herniation is a process that involves immune and inflammatory cells and processes that are targets for immune regulatory actions of vitamin D as a neurosteroid hormone. In addition to vitamin D's immune modulatory properties, its receptors have been identified in skeletal muscles. It also affects sensory neurons to modulate pain. In this study, we aim to study the role of vitamin D3 in discogenic pain and related sensory deficits. Additionally, we will address how post-treatment 25-hydroxy vitamin D3 level influences pain and sensory deficits severity. The cut-off value for serum 25-hydroxy vitamin D3 that would be efficacious in improving pain and sensory deficits in lumbar disc herniation will also be studied.

METHODS/DESIGN

We will conduct a randomized, placebo-controlled, double-blind clinical trial. Our study population will include 380 cases with one-level and unilateral lumbar disc herniation with duration of discogenic pain less than 8 weeks. Individuals who do not have any contraindications, will be divided into three groups based on serum 25-hydroxy vitamin D3 level, and each group will be randomized to receive either a single-dose 300,000-IU intramuscular injection of vitamin D3 or placebo. All patients will be under conservative treatment. Pre-treatment and post-treatment assessments will be performed with the McGill Pain Questionnaire and a visual analogue scale. For the 15-day duration of this study, questionnaires will be filled out during telephone interviews every 3 days (a total of five times). The initial and final interviews will be scheduled at our clinic. After 15 days, serum 25-hydroxy vitamin D3 levels will be measured for those who have received vitamin D3 (190 individuals).

TRIAL REGISTRATION

Iranian Registry for Clinical Trials ID: IRCT2014050317534N1 (trial registration: 5 June 2014).

Hypovitaminosis D and Cervical Disk Herniation among Adults Undergoing Spine Surgery

Study Design Single-center, retrospective study. Objective Suboptimal concentrations of vitamin D have been linked to hip and knee osteoarthritis in large, population-based cohort studies. We sought to examine the association of vitamin D levels with intervertebral disk disease. Methods From January 2010 through May 2011, 91 consecutive, eligible adult spine surgery patients who had undergone cervical magnetic resonance imaging (MRI) and preoperative serum 25-hydroxyvitamin D (s25D) measurement were retrospectively included. MRI was read for C2-T1 disk herniation and degeneration (grades I to V). Logistic regressions were performed. Results Compared with the 384 disks of nondeficient patients, 162 disks of vitamin D-deficient (< 20 ng/mL) patients were more frequently herniated (40% versus 27%, p = 0.004); deficiency was not predictive of individual disk grade (unadjusted odds ratio [uOR] = 0.98, p = 0.817). On regression analysis, deficiency was associated with increased number of herniations per patient (uOR = 2.17, 95% confidence interval [CI] = 1.22 to 3.87, p = 0.009; adjusted odds ratio [aOR] = 2.12, 95% CI = 1.11 to 4.03, p = 0.023). When disks were analyzed individually, and levels (e.g., C5 to C6), additionally controlled for, deficiency correlated with greater likelihood of herniation per disk (uOR = 1.81, 95% CI = 1.22 to 2.66, p = 0.003; aOR = 2.06, 95% CI = 1.25 to 3.41, p = 0.005). Conclusion Among adults undergoing spine surgery at our institution, vitamin D deficiency was associated with cervical disk herniation. Considering the current epidemics of vitamin D insufficiency and neck pain, further investigation is warranted, as these data were retrospectively collected and subject to sampling bias.

Does vitamin D affect femoral cartilage thickness? An ultrasonographic study

This study aims to investigate the association between vitamin D levels and distal femoral cartilage thickness in healthy subjects. Eighty patients who were admitted to our outpatient clinic between May and July 2013 were classified into three subgroups according to their 25-OH vitamin D levels of <10, 10-20, and ≥20 ng/mL. Distal femoral cartilage thickness was measured from the midpoints of the right medial condyle (RMC), right lateral condyle (RLC), right intercondylar area (RIA), left medial condyle (LMC), left lateral condyle (LLC), and left intercondylar area (LIA) by using musculoskeletal ultrasound (US). The group with severe vitamin D deficiency (<10 ng/mL) had thinner femoral cartilage thickness at LMC (p = 0.005). Positive correlations were determined only between vitamin D levels and US measurements in the severe vitamin D deficiency group at RLC (r = 444, p = 0.020), LMC (r = 357, p = 0.067), and LLC (r = 568, p = 0.002). Low levels of vitamin D seem to affect the femoral cartilage thickness, adversely. Further studies are necessary to ascertain the clinical relevance of this change in cartilage thickness and whether vitamin D supplementation can reverse the cartilage thinning process or the allied clinical symptoms in the course of knee osteoarthritis.

CD46: the 'multitasker' of complement proteins

Complement is undeniably quintessential for innate immunity by detecting and eliminating infectious microorganisms. Recent work, however, highlights an equally profound impact of complement on the induction and regulation of a wide range of immune cells. In particular, the complement regulator CD46 emerges as a key sensor of immune activation and a vital modulator of adaptive immunity. In this review, we summarize the current knowledge of CD46-mediated signalling events and their functional consequences on immune-competent cells with a specific focus on those in CD4(+) T cells. We will also discuss the promises and challenges that potential therapeutic modulation of CD46 may hold and pose.

Calcitriol modulates the CD46 pathway in T cells

The complement regulator CD46 is a costimulatory molecule for human T cells that induces a regulatory Tr1 phenotype, characterized by large amounts of IL-10 secretion. Secretion of IL-10 upon CD46 costimulation is largely impaired in T cells from patients with multiple sclerosis (MS). Vitamin D can exert a direct effect on T cells, and may be beneficial in several pathologies, including MS. In this pilot study, we examined whether active vitamin D (1,25(OH)(2)D(3) or calcitriol) could modulate the CD46 pathway and restore IL-10 production by CD46-costimulated CD4+ T cells from patients with MS. In healthy T cells, calcitriol profoundly affects the phenotype of CD46-costimulated CD4+ T cells, by increasing the expression of CD28, CD25, CTLA-4 and Foxp3 while it concomitantly decreased CD46 expression. Similar trends were observed in MS CD4+ T cells except for CD25 for which a striking opposite effect was observed: while CD25 was normally induced on MS T cells by CD46 costimulation, addition of calcitriol consistently inhibited its induction. Despite the aberrant effect on CD25 expression, calcitriol increased the IL-10:IFNγ ratio, characteristic of the CD46-induced Tr1 phenotype, in both T cells from healthy donors and patients with MS. Hence, we show that calcitriol affects the CD46 pathway, and that it promotes anti-inflammatory responses mediated by CD46. Moreover, it might be beneficial for T cell responses in MS.

Metabolic effects of vitamin D active metabolites in monolayer and micromass cultures of nucleus pulposus and annulus fibrosus cells isolated from human intervertebral disc

Intragenic polymorphisms in the vitamin D receptor gene are linked to disc degeneration features, suggesting that alterations in the vitamer-mediated signalling could be involved in the pathophysiology of the disc and that interaction of disc cells with vitamin D metabolites may be critical for disc health. The vitamer-mediated modulation of disc cells proliferation, metabolic activity, extracellular matrix (ECM) genes expression and proteins production was investigated. It was stated that disc cells express vitamin D receptor and are very sensitive to metabolic stimuli. In monolayer cultures, 1,25(OH)(2)D(3), but not 24,25(OH)(2)D(3), determined an inhibition of the proliferation and regulated also the ECM genes expression in nucleus pulposus and annulus fibrosus cells. Micromass cultures induced a more physiologic expression pattern of extracellular matrix genes. Cells Treatment with vitamin D metabolites did not result in relevant modifications of glycosaminoglycans production, except for annulus cells, whose production was reduced after 1,25(OH)(2)D(3) treatment. Moreover, a reduced glycosaminoglycans staining in both cell types and a significant reduced aggrecan gene expression in annulus cells treated with 1,25(OH)(2)D(3) were observed. A reduction of collagen I and II staining in annulus cells 1,25(OH)(2)D(3) treated, in accordance with a downregulation of collagen genes expression, was also registered. Finally, the vitamin D receptor gene expression did not show significant metabolite-mediated modification in monolayer or micromass cultures. These findings could enhance new insights on the biochemical mechanisms regulated by vitamin D in disc cartilage and possibly involved in the development of physiological/pathological modifications of the disc.

1Alpha,25-(OH)2D3 acts in the early phase of osteoblast differentiation to enhance mineralization via accelerated production of mature matrix vesicles

1Alpha,25-dihydroxyitamin D(3) (1,25D3) deficiency leads to impaired bone mineralization. We used the human pre-osteoblastic cell line SV-HFO, which forms within 19 days of culture an extracellular matrix that starts to mineralize around day 12, to examine the mechanism by which 1,25D3 regulates osteoblasts and directly stimulates mineralization. Time phase studies showed that 1,25D3 treatment prior to the onset of mineralization, rather than during mineralization led to accelerated and enhanced mineralization. This is supported by the observation of unaltered stimulation by 1,25D3 even when osteoblasts were devitalized just prior to onset of mineralization and after 1,25D3 treatment. Gene Chip expression profiling identified the pre-mineralization and mineralization phase as two strongly distinctive transcriptional periods with only 0.6% overlap of genes regulated by 1,25D3. In neither phase 1,25D3 significantly altered expression of extracellular matrix genes. 1,25D3 significantly accelerated the production of mature matrix vesicles (MVs) in the pre-mineralization. Duration rather than timing determined the extent of the 1,25D3 effect. We propose the concept that besides indirect effects via intestinal calcium uptake 1,25D3 directly accelerates osteoblast-mediated mineralization via increased production of mature MVs in the period prior to mineralization. The accelerated deposition of mature MVs leads to an earlier onset and higher rate of mineralization. These effects are independent of changes in extracellular matrix protein composition. These data on 1,25D3, mineralization, and MV biology add new insights into the role of 1,25D3 in bone metabolism and emphasize the importance of MVs in bone and maintaining bone health and strength by optimal mineralization status.

1alpha,25(OH)2-Vitamin D3 stimulation of secretion via chloride channel activation in Sertoli cells

Sertoli cell secretory activities are highly dependent on ion channel functions and critical to spermatogenesis. The steroid hormone 1alpha,25(OH)2-vitamin D3 (1,25(OH)2-D3) stimulates exocytosis in different cell systems by activating a nongenotropic vitamin D receptor (VDR). Here, we described 1,25(OH)2-D3 stimulation of secretion via Cl(-) channel activation in the mouse immature Sertoli cell line TM4. 1,25(OH)2-D3 potentiation of chloride currents was dependent on hormone concentration, and correlated with a significant increase in whole-cell capacitance within 20-40 min. In addition, Cl(-) currents were potentiated by the nongenomic VDR agonist 1alpha,25(OH)2 lumisterol D3 (JN), while 1,25(OH)2-D3 potentiation of channels was suppressed by nongenomic VDR antagonist 1beta,25(OH)2-vitamin D3 (HL). Treatment of TM4 cells with PKC and PKA activators PMA and forskolin respectively, increased Cl(-) currents significantly, while PKC and PKA inhibitors Go6983 and H-89, respectively, abolished 1,25(OH)2-D3 stimulation of Cl(-) currents, suggesting phosphorylation pathways in 1,25(OH))2-D3 mediated channel responses. RT-PCR demonstrated the expression of outwardly rectifying ClC-3 channels in TM4 cells. Taken together, our results demonstrate a PKA/PKC-dependent 1,25(OH)2-D3/VDR nongenotropic pathway leading to Cl(-) channel and exocytosis activation in Sertoli cells. We conclude that 1,25(OH)2-D3 appears to be a modulator of male reproductive functions at least in part by stimulating Sertoli cell secretory functions.

Role of matrix vesicles in biomineralization

BACKGROUND

Matrix vesicles have been implicated in the mineralization of calcified cartilage, bone and dentin for more than 40 years. During this period, their exact role, if any in the nucleation of hydroxyapatite mineral, and its subsequent association with the collagen fibrils in the organic matrix has been debated and remains controversial.

SCOPE OF REVIEW

This review summarizes studies spanning the whole history of matrix vesicles, but emphasizes recent findings and several hypotheses which have been recently introduced to explain in greater detail how matrix vesicles function in biomineralization.

MAJOR CONCLUSIONS

It is now generally accepted that matrix vesicles have some role(s) in mineralization; that they are the initial site of mineral formation; that MV bud from the plasma membrane of mineral forming cells, but that they take with them only a subset of the materials found in the parent membrane; that the three proteins, alkaline phosphatase, nucleotide pyrophosphatase phosphodiesterase and annexin V have important roles in the process and that matrix vesicles participate in regulating the concentration of PPi in the matrix. In contrast, many open questions remain to be answered.

GENERAL SIGNIFICANCE

Understanding the role of matrix vesicles in biomineralization will increase our knowledge of this important process.

Serum levels of vitamin D, sunlight exposure, and knee cartilage loss in older adults: the Tasmanian older adult cohort study

OBJECTIVE

To determine the associations between serum levels of vitamin D, sunlight exposure, and knee cartilage loss cross-sectionally and longitudinally in older adults.

METHODS

A total of 880 randomly selected subjects (mean age 61 years [range 51-79 years], 50% women) were studied at baseline, and 353 of these subjects were studied 2.9 years later. Serum levels of 25-hydroxyvitamin D (25[OH]D) were assessed by radioimmunoassay, and sunlight exposure was assessed by questionnaire. T1-weighted fat-suppressed magnetic resonance imaging (MRI) of the right knee was performed to determine knee cartilage volume and defects. Knee radiographic osteoarthritis (OA) and knee pain were also assessed.

RESULTS

The mean 25(OH)D serum level was 52.8 nmoles/liter at baseline (range 13-119 nmoles/liter). Winter sunlight exposure and serum 25(OH)D level were both positively associated with medial and lateral tibial cartilage volume, and a serum 25(OH)D level<50 nmoles/liter was associated with increased medial tibiofemoral joint space narrowing (all P<0.05). Longitudinally, baseline serum 25(OH)D level predicted change in both medial and lateral tibial cartilage volume (beta=+0.04% per annum per nmole/liter for both; P<0.05), and change in serum 25(OH)D level was positively associated with change in medial tibial cartilage volume. These associations were consistent in subjects with radiographic OA and knee pain and/or in women, but not in men or in subjects without radiographic OA or knee pain.

CONCLUSION

Sunlight exposure and serum 25(OH)D levels are both associated with decreased knee cartilage loss (assessed by radiograph or MRI). This is best observed using the whole range of 25(OH)D levels rather than predefined cut points and implies that achieving vitamin D sufficiency may prevent and/or retard cartilage loss in knee OA.

1,25-Dihydroxy vitamin D3 is an autocrine regulator of extracellular matrix turnover and growth factor release via ERp60-activated matrix vesicle matrix metalloproteinases

As growth plate chondrocytes mature and hypertrophy, they reorganize their proteoglycan-rich type II collagen extracellular matrix (ECM), involving 1,25(OH)(2)D(3)-dependent regulation of matrix metalloproteinases (MMPs). Stromelysin-1 (MMP-3) and 72-kD gelatinase (MMP-2) are found in extracellular matrix vesicles (MVs) and release and activate ECM-bound latent TGF-beta1 and TGF-beta2, respectively. 1,25(OH)(2)D(3) regulates incorporation of MMP-2 and MMP-3 into MVs and release of these enzymes in the ECM. Plasma membranes (PMs) and MVs contain the 1alpha,25(OH)(2)D(3) membrane receptor ERp60 (protein disulfide isomerase A3), phospholipase A(2) (PLA(2)), PLA(2)-activating protein, the nuclear vitamin D receptor and caveolin-1. 1,25(OH)(2)D(3) secreted by chondrocytes binds MV ERp60, activating PLA(2). Resulting lysophospholipids destabilize MV membranes, releasing active MMPs. We examined 1,25(OH)(2)D(3)-dependent activation of latent TGF-beta1 stored in cartilage ECM. Interestingly, TGF-beta1 regulates 1,25(OH)(2)D(3) production. 1alpha,25(OH)(2)D(3) activates PM protein kinase C (PKC)-alpha via ERp60-dependent PLA(2)-signaling, lysophospholipid production and phospholipase C-gamma. It also regulates distribution of phospholipids and PKC isoforms between MVs and PMs, enriching MVs in PKC-zeta. Direct activation of MV MMP-3 requires ERp60 based on blocking antibodies and PKC based on inhibitor studies. However, treatment of MVs with 1,25(OH)(2)D(3) decreases MV PKC-zeta activity, suggesting more complex feedback mechanisms, potentially involving MV lipid signaling. Our observations indicate that one role of MVs is to provide MMPs at sites distant from the cells. Chondrocytes secrete 1,25(OH)(2)D(3), which acts directly on MV-membranes via ERp60, releasing MMPs. MMP-specific ECM components are hydrolyzed, resulting in release and activation of growth factors that can act back on the cells.

1,25(OH)2-vitamin D3 inhibits proliferation and decreases production of monocyte chemoattractant protein-1, thrombopoietin, VEGF, and angiogenin by human annulus cells in vitro

STUDY DESIGN

Human lumbar anulus tissue and cultured human lumbar anulus cells were used in retrospective studies of the immunocytochemical localization of the vitamin D receptor (VDR) in disc tissue, and of the in vitro effects of the active metabolite of vitamin D, 1,25(OH)2D3, on anulus cell proliferation, cytokine, and proteoglycan (PG) production. 24,25-D3 was also analyzed. Studies were approved by the authors' Human Subjects Institutional Review Board. Discs were obtained from surgical specimens and from control donors.

OBJECTIVES

To determine if human anulus cells express the VDR in vivo, and to test the effect of in vitro exposure to 1,25(OH)2D3 and 24,25-D3 on anulus cell proteoglycan and cytokine production in 3-dimensional culture.

SUMMARY OF BACKGROUND DATA

Intragenic polymorphisms in the VDR gene have been associated with disc degeneration. 1,25(OH)2D3 has well-recognized effects on calcium homeostasis and bone mineralization, and is a negative growth regulator of a variety of normal and tumor cells. Its effects on human disc cells, however, are unexplored.

METHODS

Immunocytochemistry was performed on human lumbar disc anulus tissue from 19 subjects; human disc cells were cultured to test the effect of 1,25(OH)2D3 on proliferation of anulus cells from 5 subjects. A paired experimental design was used to determine proteoglycan production in control or 1,25(OH)2D3-treated cells, or in control or 24,25-D3-treated cells using the dimethylmethylene blue assay. A paired experimental design was also used to identify differences in cytokine production in conditioned media from control or 1,25(OH)2D3-treated cells, or in control or 24,25-D3-treated cells using ELISA assays.

RESULTS

Immunocytochemistry documented expression of the VDR in anulus cells. Young donor discs (aged newborn, 15 years) showed positive localization in all cells of the outer anulus, and some inner anulus cells. In adults (mean age, 38.9 years), some, but not all anulus cells, showed positive localization. Exposure to 10M 1,25(OH)2D3 in monolayer significantly reduced cell proliferation in vitro (P = 0.03). PG production in 3-dimensional was unchanged from control in both 1,25(OH)2D3- and 24,25-D3-treated cells. Cytokine production differed, however. 1,25(OH)2D3-treated cells showed significantly decreased production of vascular endothelial growth factor (VEGF) (P = 0.01), monocyte chemoattractant protein-1 (MCP-1) (P = 0.0006), angiogenin (P = 0.002), and thrombopoietin (P = 0.03) compared with controls. 24,25-D3-treated cells showed significantly elevated vascular endothelial growth factor-D (P = 0.01), beta-fibroblast growth factor (0.03), and significantly decreased interleukin-8, interferon-gamma, leptin, MCP-1, and TIMP-2 (tissue inhibitor of metalloproteinases-2) compared with controls (P <or= 0.01).

CONCLUSION

Data suggest that 1,25(OH)2D3 and 24,25-D3 may play roles as regulators of cell proliferation and production of specific cytokines in the lumbar anulus.

Synthesis and biological evaluation of new 6-s-cis locked 1,2,25-trihydroxyprevitamin D3 analogues

An efficient synthesis of several diastereomers of 2-hydroxy substituted 1alpha,25-dihydroxyprevitamin D3 derivatives was accomplished utilizing a practical route to the A-ring synthon. The biological activity of the analogues was evaluated in vitro. All the synthesized derivatives demonstrated low affinity for the vitamin D receptor and vitamin D-binding protein compared with 1alpha,25-dihydroxyvitamin D3, the natural hormone. 1alpha,2beta,25-trihydroxy-19-nor-pre-D3 was the most potent of the analogues in inhibiting proliferation of MCF-7 cells but requires higher EC50 concentrations than 1alpha,25-dihydroxyvitamin D3.

Update on biological actions of 1alpha,25(OH)2-vitamin D3 (rapid effects) and 24R,25(OH)2-vitamin D3

All biologic responses to vitamin D are now known to arise as a consequence of the metabolism of this seco-steroid into its two principal biologically active metabolites 1alpha,25(OH)(2)-vitamin D(3) (1ALPHA;,25(OH)(2)D(3)) and 24R,25(OH)(2)-vitamin D(3) (24R,25(OH)(2)D(3)). 1alpha,25(OH)(2)D(3) is the dominant metabolite and produces a wide array of biological responses via interacting both with the classical vitamin D nuclear receptor (VDR(nuc)) that regulates gene transcription in over 30 target organs and with a putative cell membrane receptor (VDR(mem1,25)) that mediates rapid (within seconds to minutes) biological responses. Ligand occupancy of VDR(mem1,25) is linked to signal transduction systems that can mediate the opening of Ca(2+) and chloride voltage gated channels as well as activation of MAP-kinase. MAP-kinase activation in some cells containing VDR(mem1,25)+VDR(nuc) then results in "cross-talk" from VDR(mem1,25) to VDR(nuc) which modulates transactivation of 1alpha,25(OH)(2)D(3) responsive gene promoters. The 24R,25(OH)(2)D(3) metabolite has been shown to be an essential hormone for the process of bone fracture healing. The activity of the enzyme responsible for the production of 24R,25(OH)(2)D(3), the renal 25(OH)D-24-hydroxylase, becomes elevated within 4-11 days after imposition of a tibial fracture, thereby increasing the blood concentrations of 24R,25(OH)(2)D(3) by threefold. The 24R,25(OH)(2)D(3) likely initiates its biological responses via binding to the ligand binding domain of a second cell membrane receptor, the VDR(mem24,25), which is stereospecific for 24R,25(OH)(2)D(3) in comparison with 24S,25(OH)(2)D(3) and 1alpha,25(OH)(2)D(3). This report summarizes the status of several current research frontiers in this arena of the vitamin D endocrine system.

1alpha,25(OH)2D3 regulates chondrocyte matrix vesicle protein kinase C (PKC) directly via G-protein-dependent mechanisms and indirectly via incorporation of PKC during matrix vesicle biogenesis

Matrix vesicles are extracellular organelles involved in mineral formation that are regulated by 1alpha,25(OH)(2)D(3). Prior studies have shown that protein kinase C (PKC) activity is involved in mediating the effects of 1alpha,25(OH)(2)D(3) in both matrix vesicles and plasma membranes. Here, we examined the regulation of matrix vesicle PKC by 1alpha,25(OH)(2)D(3) during biogenesis and after deposition in the matrix. When growth zone costochondral chondrocytes were treated for 9 min with 1alpha,25(OH)(2)D(3), PKCzeta in matrix vesicles was inhibited, while PKCalpha in plasma membranes was increased. In contrast, after treatment for 12 or 24 h, PKCzeta in matrix vesicles was increased, while PKCalpha in plasma membranes was unchanged. The effect of 1alpha,25(OH)(2)D(3) was stereospecific and metabolite-specific. Monensin blocked the increase in matrix vesicle PKC after 24 h, suggesting the secosteroid-regulated packaging of PKC. In addition, the 1alpha,25(OH)(2)D(3) membrane vitamin D receptor (1,25-mVDR) was involved, since a specific antibody blocked the 1alpha,25(OH)(2)D(3)-dependent changes in PKC after both long and short treatment times. In contrast, antibodies to annexin II had no effect, and there was no evidence for the presence of the nuclear VDR on Western blots. To investigate the signaling pathways involved in regulating matrix vesicle PKC activity after biosynthesis, matrix vesicles were isolated and then treated for 9 min with 1alpha,25(OH)(2)D(3) in the presence and absence of specific inhibitors. Inhibition of phosphatidylinositol-phospholipase C, phospholipase D, or G(i)/G(s) had no effect. However, inhibition of G(q) blocked the effect of 1alpha,25(OH)(2)D(3). The rapid effect of 1alpha,25(OH)(2)D(3) also involved the 1,25-mVDR. Moreover, arachidonic acid was found to stimulate PKC when added directly to isolated matrix vesicles. These results indicate that matrix vesicle PKC is regulated by 1alpha,25(OH)(2)D(3) at three levels: 1) during matrix vesicle biogenesis; 2) through direct action on the membrane; and 3) through production of other factors such as arachidonic acid.

Expression of vitamin D receptors and matrix metalloproteinases in osteoarthritic cartilage and human articular chondrocytes in vitro

OBJECTIVES

To examine the in situ distributions of vitamin D receptors (VDR) and matrix metalloproteinases (MMPs) in osteoarthritic cartilage for comparison with non-arthritic, normal cartilage; and to assess the in vitro effects of 1alpha,25 dihydroxyvitaminD(3)(1alpha,25(OH)(2)D(3)) on MMPs-1, -3 and -9 and prostaglandin E(2)(PGE(2)) production by cultures of human articular chondrocytes (HAC) shown to be VDR-positive.

METHODS

Using immunohistochemistry VDR expression in different specimens of osteoarthritic cartilage (N=11) was compared to that in normal cartilage (N=6), along with the immunodetection of MMPs-1, -3 and -9. The effects of 1alpha25(OH)(2)D(3)on MMP and PGE(2)production by HAC in vitro, with and without stimulation by TNFalpha or phorbol myristate acetate (PMA), was evaluated using ELISA methodology.

RESULTS

VDR was demonstrated in HAC of all specimens of osteoarthritic cartilage, especially the superficial zone, whereas only two of five normal cartilage specimens were VDR(+)for a minor proportion of HAC. Immunolocalization of MMPs-1, -3 and -9 was often seen in areas where chondrocytes were VDR(+), and dual immunolocalization has demonstrated individual chondrocytes positive for both VDR and MMP-3 in situ. In vitro, 1alpha25(OH)(2)D(3)alone had no effect on MMP-1, -9 and PGE(2)production by HAC, but MMP-3 production was up-regulated by 1alpha25(OH)(2)D(3)either with or without stimulation with TNFalpha or PMA. By contrast the increased production of MMP-9 and PGE(2)induced by PMA was significantly suppressed by concomitant treatment with 1alpha25(OH)(2)D(3).

CONCLUSIONS

The demonstration of VDR expression by HAC in osteoarthritic cartilage was often associated with sites where MMP expression was prevalent, observations in contrast to their virtual absence in normal age-matched cartilage. Together with HAC in vitro studies, the data suggests that 1alpha25(OH)(2)D(3)contributes to the regulation of MMP and PGE(2)production by HAC in osteoarthritic cartilage.

A new type of matrix vesicles is found in fetal bovine tracheal cartilage

Using 4-month-old fetal bovine tissue, the properties of the tibia epiphyseal cartilage matrix vesicles, a type of endochondral ossification tissue, were compared with those from tracheal cartilage. The matrix vesicle fractions, obtained by collagenase digestion and differential centrifugation, were subjected to sucrose-density-gradient centrifugation. Alkaline phosphatase activity, protease activity, and lacatate dehydrogenase activity were assayed for the marker enzyme of the matrix vesicles. Matrix vesicles containing alkaline phosphatase, metalloprotease, and lacatate dehydrogenase were found in the tibia epiphyseal cartilage at a density of 1.11 g/ml. In surprising contrast, we also found matrix vesicle-like vesicles with a high density of 1.24 g/ml in the tracheal cartilage. These also contained alkaline phosphatase and lactate dehydrogenase, but not metalloprotease. The electrophoretic profiles of the lactate dehydrogenase isoenzymes from the matrix vesicle and matrix vesicle-like vesicles were identical with those of chondrocyte cytosolic lactate dehydrogenase. Aldolase, aspartate: 2-oxoglutarate aminotransferase, alanine: 2-oxoglutarate aminotransferase, glucose-6-phosphatase, glutamate dehydrogenase, catalase, and cytosolic enzymes except for lactate dehydrogenase were not detected in these vesicles. These results suggest the presence of a mechanism for specific uptake of cytosolic lactate dehydrogenase in both vesicles. In this study, a new type of matrix vesicles without protease was found in the tracheal cartilage, a kind of permanent cartilage, but not in the tibia epiphyseal cartilage, which is replaced by bone tissue.

Different shapes of the steroid hormone 1alpha,25(OH)(2)-vitamin D(3) act as agonists for two different receptors in the vitamin D endocrine system to mediate genomic and rapid responses

Vitamin D(3) produces biologic responses as a consequence of its metabolism into 1alpha,25(OH)(2)-vitamin D(3) [1alpha,25(OH)(2)D(3)] and 24R,25(OH)(2)-vitamin D(3). The metabolic production of these two seco steroids and their generation of the plethora of biologic actions that are attributable to the parent vitamin D(3) are orchestrated via the integrated operation of the vitamin D endocrine system. This system is very similar in its organization to that of classic endocrine systems and is characterized by an endocrine gland (the kidney, the source of the two steroid hormones), target cells which possess receptors for the steroid hormones, and a feed-back loop involving changes in serum Ca(2+) that alter the secretion of parathyroid hormone (a stimulator of the renal 1-hydroxylase) which modulates the output by the kidney of the steroid hormones. There are, however, at least two unique aspects to the vitamin D endocrine system. (a) The chemical structures of vitamin D and its steroid hormones dictate that these be highly conformationally flexible molecules present a wide variety of shapes to their biologic environments. (b) It is now believed that 1alpha,25(OH)(2)D(3) produces biologic responses through two distinct receptors which recognize totally different shapes of the conformationally flexible 1alpha,25(OH)(2)D(3). Thus, the classic actions of 1alpha,25(OH)(2)D(3) to regulate gene transcription occur as a consequence of the stereospecific interaction of a modified 6-s-trans bowl-shape of 1alpha,25(OH)(2)D(3) with its nuclear receptor (VDR(nuc)). The ability of 1alpha,25(OH)(2)D(3) to generate a variety of rapid (seconds to minutes) biologic responses (opening of chloride channels, activation of PKC and MAP kinases) requires a planar 6-s-cis ligand shape which is recognized by a putative plasma membrane receptor (VDR(mem)) to initiate appropriate signal transduction pathways. This report summarizes the evidence for the specificity of different ligand shapes and the operation of the two receptor families for 1alpha,25(OH)(2)D(3).

Physiological importance of the 1,25(OH)2D3 membrane receptor and evidence for a membrane receptor specific for 24,25(OH)2D3

We have recently identified a membrane vitamin D receptor (mVDR) specific for 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and shown that it mediates the rapid activation of protein kinase C (PKC) in growth zone chondrocytes (GCs). In this study, we examine the role of the 1, 25(OH)2D3-mVDR in chondrocyte physiology and provide evidence for the existence of a specific membrane receptor for 24, 25-dihydroxyvitamin D3 (24,25(OH)2D3-mVDR). Fourth-passage cultures of growth plate chondrocytes at two distinct stages of endochondral development, resting zone (RC) and growth zone (GC) cells, were used to assess the role of the mVDR in cell proliferation, PKC activation, and proteoglycan sulfation. To preclude the involvement of the nuclear vitamin D receptor (nVDR), we used hybrid analogs of 1, 25(OH)2D3 with <0.1% affinity for the nVDR (2a, 1alpha-CH2OH-3beta-25D3; 3a, 1alpha-CH2OH-3beta-20-epi-22-oxa-25D3; and 3b, 1beta-CH2OH-3alpha-20-epi-22-oxa-25D3). To determine the involvement of the mVDR, we used an antibody generated against the highly purified 1,25(OH)2D3 binding protein from chick intestinal basolateral membranes (Ab99). Analog binding to the mVDR was demonstrated by competition with [3H]1,25(OH)2D3 using matrix vesicles (MVs) isolated from cultures of RC and GC cells. Specific recognition sites for 24,25(OH)2D3 in RC MVs were demonstrated by saturation binding analysis. Specific binding of 24,25(OH)2D3 was also investigated in plasma membranes (PMs) from RC and GC cells and GC MVs. In addition, we examined the ability of Ab99 to block the stimulation of PKC by analog 2a in isolated RC PMs as well as the inhibition of PKC by analog 2a in GC MVs. Like 1,25(OH)2D3, analogs 2a, 3a, and 3b inhibit RC and GC cell proliferation. The effect was dose dependent and could be blocked by Ab99. In GC cells, PKC activity was stimulated maximally by analogs 2a and 3a and very modestly by 3b. The effect of 2a and 3a was similar to that of 1, 25(OH)2D3 and was blocked by Ab99, whereas the effect of 3b was unaffected by antibody. In contrast, 2a was the only analog that increased PKC activity in RC cells, and this effect was unaffected by Ab99. Analog 2a had no effect on proteoglycan sulfation in RC cells, whereas analogs 3a and 3b stimulated it and this was not blocked by Ab99. Binding of [3H]1,25(OH)2D3 to GC MVs was displaced completely with 1,25(OH)2D3 and analogs 2a, 3a, and 3b, but 24, 25(OH)2D3 only displaced 51% of the bound ligand. 24,25(OH)2D3 displaced 50% of [3H]1,25(OH)2D3 bound to RC MVs, but 2a, 3a, and 3b displaced <50%. Scatchard analysis indicated specific binding of 24, 25(OH)2D3 to recognition sites in RC MVs with a Kd of 69.2 fmol/ml and a Bmax of 52.6 fmol/mg of protein. Specific binding for 24, 25(OH)2D3 was also found in RC and GC PMs and GC MVs. GC membranes exhibited lower specific binding than RC membranes; MVs had greater specific binding than PMs in both cell types. 2a caused a dose-dependent increase in PKC activity of RC PMs that was unaffected by Ab99; it inhibited PKC activity in GC MVs, and this effect was blocked by Ab99. The results indicate that the 1, 25(OH)2D3 mVDR mediates the antiproliferative effect of 1,25(OH)2D3 on chondrocytes. It also mediates the 1,25(OH)2D3-dependent stimulation of PKC in GC cells, but not the 2a-dependent increase in RC PKC activity, indicating that 24,25(OH)2D3 mediates its effects through a separate receptor. This is supported by the failure of Ab99 to block 2a-dependent stimulation of PKC in isolated PMs. The data demonstrate for the first time the presence of a specific 24, 25(OH)2D3 mVDR in endochondral chondrocytes and show that, although both cell types express mVDRs for 1,25(OH)2D3 and 24,25(OH)2D3, their relative distribution is cell maturation-dependent.

Hormone regulation of chondrocyte differentiation and endochondral bone formation

Endochondral bone formation, the formation of calcified bone on a cartilage scaffold, occurs during skeletal development, post natal growth and during bone remodelling and fracture repair. The epiphyseal growth plates represent classical tissues in which to study the ossification process, which requires two co-ordinated components; progressive chondrocyte differentiation and cartilage neovascularisation. Many gene knockout studies have produced new insights regarding how chondrocyte differentiation and angiogenesis are controlled at the molecular level. Additional genetic studies have produced new information regarding the role of hormones in the regulation of endochondral bone formation. The new challenge for the future is to determine how bone formation and turnover is physiologically regulated and co-ordinated to ensure that skeletal development and growth progresses correctly. This study reviews the emerging data in this quickly growing field which should ultimately provide fundamental insights into the normal control of endochondral ossification.

Serum vitamin D levels and incident changes of radiographic hip osteoarthritis: a longitudinal study. Study of Osteoporotic Fractures Research Group

OBJECTIVE

The purpose of this study was to determine the relationship of serum levels of 25-vitamin D and 1,25-vitamin D to incident changes of radiographic hip osteoarthritis (OA) among elderly white women.

METHODS

Baseline and followup hip radiographs of 237 subjects were obtained an average of 8 years apart. Hips were scored for individual radiographic features (IRF) and assigned a summary grade based on the number and type of IRF present. Serum 25- and 1,25-vitamin D levels from baseline samples were analyzed by radioimmunoassay. Logistic and linear regression were used to examine the association of 25- and 1,25-vitamin D levels with radiographic changes, adjusting for age, health status, physical activity, weight, vitamin D supplement use, and calcaneal bone mineral density.

RESULTS

The risk of incident hip OA defined as the development of definite joint space narrowing was increased for subjects who were in the middle (odds ratio [OR] 3.21, 95% confidence interval [95% CI] 1.06, 9.68) and lowest (OR 3.34, 95% CI 1.13, 9.86) tertiles for 25-vitamin D compared with subjects in the highest tertile. Vitamin D levels were not associated with incident hip OA defined as the development of definite osteophytes or new disease according to the summary grade. No association between serum 1,25-vitamin D and changes in radiographic hip OA was found.

CONCLUSION

Low serum levels of 25-vitamin D may be associated with incident changes of radiographic hip OA characterized by joint space narrowing.

Identification of a membrane receptor for 1,25-dihydroxyvitamin D3 which mediates rapid activation of protein kinase C

This paper is the first definitive report demonstrating a unique membrane receptor for 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) which mediates the rapid and nongenomic regulation of protein kinase C (PKC). Previous studies have shown that 1,25(OH)2D3 exerts rapid effects on chondrocyte membranes which are cell maturation-specific, do not require new gene expression, and do not appear to act via the traditional vitamin D receptor. We used antiserum generated to a [3H]1,25(OH)2D3 binding protein isolated from the basal lateral membrane of chick intestinal epithelium (Ab99) to determine if rat costochondral resting zone (RC) or growth zone (GC) cartilage cells contain a similar protein and if cell maturation-dependent differences exist. Immunohistochemistry demonstrated that both RC and GC cells express the protein, but levels are highest in GC. The binding protein is present in both plasma membranes and matrix vesicles and has a molecular weight of 66,000 Da. The 66 kDa protein in GC matrix vesicles has a Kd of 17.2 fmol/ml and Bmax of 124 fmol/mg of protein for [3H]1,25(OH)2D3. In contrast, the 66 kDa protein in RC matrix vesicles has a Kd of 27.7 fmol/ml and a Bmax of 100 fmol/mg of protein. Ab99 blocks the 1,25(OH)2D3-dependent increase in PKC activity in GC chondrocytes, indicating that the 1,25(OH)2D3-binding protein is indeed a receptor, linking ligand recognition to biologic function.

The effects of 17 beta-estradiol on chondrocyte differentiation are modulated by vitamin D3 metabolites

Both 17 beta-estradiol (17 beta) and the vitamin D metabolites, 1,25-(OH)2D3(1,25) and 24,25-(OH)2D3(24,25), regulate endochondral bone formation in vivo and in vitro. The effects of 17 beta are sex-specific and cell maturation-dependent. Similarly, the effects of 1,25 and 24,25 are cell maturation-dependent, with 1,25 affecting growth zone chondrocytes (GC) and 24,25 affecting resting zone chondrocytes (RC). This study examined whether the response of chondrocytes to 17 beta is altered after pretreatment with 1,25 or 24,25. Cells were isolated from the costochondral cartilage of male or female rats. Confluent, fourth-passage GC and RC cultures were pretreated with 1,25 or 24,25, respectively, for 24 or 48 h followed by treatment with 17 beta for an additional 24 h. At harvest, cell proliferation ([3H]-thymidine incorporation), differentiation (alkaline phosphatase specific activity [ALPase]), general metabolism ([3H]-uridine incorporation), and proteoglycan production ([35S]-sulfate incorporation) were determined. 1,25 enhanced the inhibitory effect of 17 beta on [3H]-thymidine incorporation by female GC cells; in contrast, no effect was observed in GC cells obtained from male rats. When male RC cells were treated with 17 beta, [3H]-thymidine incorporation was inhibited; however, when these cells were pretreated with 24,25 for 48 h, 17 beta stimulated [3H]-thymidine incorporation 24,25 had no effect on 17 beta-dependent [3H]-thymidine incorporation by female RC cells. 17 beta stimulated ALPase in female GC cells, but had no effect on male GC cells. 1,25 pretreatment of female GC cells inhibited the stimulatory effect of 17 beta on ALPase, but had no effect on ALPase in male GC cultures. 17 beta had no effect on male RC cell ALPase and stimulated ALPase in female RC cells. This was not affected by pretreatment with 24,25. Pretreatment with 1,25 increased the basal level of sulfate incorporation only in female GC. No effect was found in RC cells. These results indicate that pretreatment of rat costochondral chondrocytes with vitamin D metabolites modulate the effect of 17 beta. Although the effect of vitamin D metabolites alone on these chondrocytes is maturation-dependent and not sex-specific, the influence of preincubation with vitamin D metabolites on the effect of 17 beta is hormone-specific, sex-specific, and maturation-dependent.