We investigated the relationships among M1 monocytes, M2 monocytes, osteoclast (OC) differentiation ability, and clinical characteristics in patients with rheumatoid arthritis (RA).
Peripheral blood ...mononuclear cells (PBMCs) were isolated from RA patients and healthy donors, and we then investigated the number of M1 monocytes or M2 monocytes by fluorescence-activated cell sorting. We also obtained and cultured CD14-positive cells from PBMCs from RA patients and healthy donors to investigate OC differentiation
.
Forty RA patients and 20 healthy donors were included. Twenty-two patients (55%) were anticitrullinated protein antibody (ACPA) positive. The median M1/M2 ratio was 0.59 (0.31-1.11, interquartile range). There were no significant differences between the RA patients and healthy donors. There was a positive correlation between the M1/M2 ratio and the differentiated OC number
in RA patients (ρ = 0.81,
< 0.001). The ACPA-positive patients had significantly higher M1/M2 ratios
(
= 0.028) and significantly greater numbers of OCs
(
= 0.005) than the ACPA-negative patients. Multivariable regression analysis revealed that the M1/M2 ratio was the sole significant contribution factor to
osteoclastogenesis. RA patients with M1/M2 ratios >1 (having relatively more M1 monocytes) had higher C-reactive protein and erythrocyte sedimentation rates than RA patients with M1/M2 ratios ≤1. M1-dominant monocytes
produced higher concentrations of interleukin-6 upon stimulation with lipopolysaccharide than M2 monocytes.
M1/M2 monocytes imbalance strongly contributes to osteoclastogenesis of RA patients. Our findings cast M1 and M2 monocyte subsets in a new light as a new target of treatments for RA to prevent progression of osteoclastic bone destruction.
Serum calcium levels are tightly controlled by an integrated hormone-controlled system that involves active vitamin D 1,25(OH)(2)D, which can elicit calcium mobilization from bone when intestinal ...calcium absorption is decreased. The skeletal adaptations, however, are still poorly characterized. To gain insight into these issues, we analyzed the consequences of specific vitamin D receptor (Vdr) inactivation in the intestine and in mature osteoblasts on calcium and bone homeostasis. We report here that decreased intestinal calcium absorption in intestine-specific Vdr knockout mice resulted in severely reduced skeletal calcium levels so as to ensure normal levels of calcium in the serum. Furthermore, increased 1,25(OH)(2)D levels not only stimulated bone turnover, leading to osteopenia, but also suppressed bone matrix mineralization. This resulted in extensive hyperosteoidosis, also surrounding the osteocytes, and hypomineralization of the entire bone cortex, which may have contributed to the increase in bone fractures. Mechanistically, osteoblastic VDR signaling suppressed calcium incorporation in bone by directly stimulating the transcription of genes encoding mineralization inhibitors. Ablation of skeletal Vdr signaling precluded this calcium transfer from bone to serum, leading to better preservation of bone mass and mineralization. These findings indicate that in mice, maintaining normocalcemia has priority over skeletal integrity, and that to minimize skeletal calcium storage, 1,25(OH)(2)D not only increases calcium release from bone, but also inhibits calcium incorporation in bone.
The analysis of mice that lack systemically the actions of the active form of vitamin D, 1,25(OH)2 D, has shown that 1,25(OH)2 D is an essential regulator of calcium homeostasis and that its actions ...are aimed at maintaining serum calcium levels within narrow limits. Especially the stimulation of intestinal calcium transport by 1,25(OH)2 D is important for calcium and bone homeostasis. The involved transporters are however still elusive. The targeted deletion of 1,25(OH)2 D action in chondrocytes has provided compelling evidence for a paracrine control of bone development and endocrine regulation of phosphate homeostasis by 1,25(OH)2 D. Targeting vitamin D receptor (VDR) function in other tissues will further enhance our understanding of the cell-type specific action of 1,25(OH)2 D. In this review, we will discuss the current understanding and remaining questions concerning the calcemic actions of 1,25(OH)2 D in the intestine, kidney and bone, with special focus on the evidence obtained by the use of transgenic mouse models.
Highlights • The physiological role of vitamin D depends on calcium supply and calcium balance. • When the calcium balance is normal, the major target of vitamin D is intestine. • Vitamin D ...stimulates mainly active intestinal calcium transport mechanism. • During a negative calcium balance, bone effects of vitamin D become dominant. • The role of vitamin D in maintaining normocalcemia has priority over skeletal integrity.
•Calcium status required for bone protections by milk basic protein (MBP) was studied.•Systemic- or intestine-specific vitamin D receptor knockout mice were used.•In severe hyperparathyroidism, MBP ...failed to rescue impaired bone mineralization.•Contrary to the parathyroid hormone, MBP inhibited osteoclast differentiation responding to the receptor activator of nuclear factor κB ligand–osteoprotegerin axis.•Normal calcium homeostasis is essential for the functional threshold of dietary MBP.
Milk provide protective effects against bone loss caused by an impaired calcium balance. Although the effects of some elements have previously been confirmed, the involvement of milk basic protein (MBP) in bone mineral metabolism remains poorly characterized. Moreover, the importance of mineral nutrition sufficiency to establish the effect of MBP must be evaluated.
First, to evaluate the physiological conditions required for MBP activity, we examined the bone and mineral phenotypes of mice that suffer from insufficient calcium absorption due to a lack of intestinal vitamin D signaling. Second, to determine whether vitamin D signaling affects the effect of MBP on bone resorption, in vitro osteoclastogenesis were assessed using bone marrow cells.
In mice with systemic vitamin D receptor (Vdr) inactivation, dietary MBP supplementation was unable to normalize hypercalcemia and hyperparathyroidism and failed to rescue bone mineralization impairments. In contrast, calcium and bone homeostasis responded to MBP supplementation when Vdr inactivation was restricted to the intestines. Hyperparathyroidism in intestine-specific Vdr knockout mice was also improved by MBP supplementation, along with a decrease in bone resorption in response to the level of serum tartrate-resistant acid phosphatase 5b. These results corresponded with a reduction in tartrate-resistant acid phosphatase-stained osteoclast numbers and the eroded surface on the tibia. MBP treatment dose-dependently suppressed osteoclastogenesis in cultured bone marrow macrophages regardless of vitamin D activity. These effects of MBP were blunted when parathyroid hormone was added to the culture medium, which is in line with the in vivo phenotype observed with systemic Vdr inactivation and suggests that severe hyperparathyroidism limits MBP activity in the bone.
Therefore, adaptive calcium homeostasis is an essential requirement when MBP exerts protective effects through the inhibition of bone resorption.
Osteoclasts are multinucleated cells responsible for bone resorption. Src homology 3 (SH3) domain‐containing protein‐2 (SH3P2)/osteoclast‐stimulating factor‐1 regulates osteoclast differentiation, ...but its exact role remains elusive. Here, we show that SH3P2 suppresses osteoclast differentiation. SH3P2 knockout (KO) mice displayed decreased femoral trabecular bone mass and enhanced localization of osteoclasts on the tibial trabecular bone surface, suggesting that SH3P2 suppresses bone resorption by osteoclasts. Osteoclast differentiation based on cellular multinuclearity induced by macrophage colony‐stimulating factor and receptor activator of nuclear factor‐κB ligand (RANKL) was enhanced in bone marrow‐derived macrophages lacking SH3P2. RANKL induced SH3P2 dephosphorylation, which increased the association of actin‐dependent motor protein myosin 1E (Myo1E) with SH3P2 and thereby prevented Myo1E localization to the plasma membrane. Consistent with this, Myo1E in the membrane fraction increased in SH3P2‐KO cells. Together with the attenuated osteoclast differentiation in Myo1E knocked down cells, SH3P2 may suppress osteoclast differentiation by preventing their cell‐to‐cell fusion depending on Myo1E membrane localization.
RANKL on the one hand increases Myo1E expression and on the other hand decreases SH3P2 phosphorylation, which interferes with its association with Myo1E. The balance between these two pathways, which apparently mediate opposite effects on membrane localization of Myo1E, may be a critical determinant of RANKL‐induced osteoclast differentiation.
Abstract The active form of vitamin D, 1,25(OH)2 D, is a crucial regulator of calcium homeostasis, especially through stimulation of intestinal calcium transport. Lack of intestinal vitamin D ...receptor (VDR) signaling does however not result in hypocalcemia, because the increased 1,25(OH)2 D levels stimulate calcium handling in extra-intestinal tissues. Systemic VDR deficiency, on the other hand, results in hypocalcemia because calcium handling is impaired not only in the intestine, but also in kidney and bone. It remains however unclear whether low intestinal VDR activity, as observed during aging, is sufficient for intestinal calcium transport and for mineral and bone homeostasis. To this end, we generated mice that expressed the Vdr exclusively in the gut, but at reduced levels. We found that ~ 15% of intestinal VDR expression greatly prevented the Vdr null phenotype in young-adult mice, including the severe hypocalcemia. Serum calcium levels were, however, in the low-normal range, which may be due to the suboptimal intestinal calcium absorption, renal calcium loss, insufficient increase in bone resorption and normal calcium incorporation in the bone matrix. In conclusion, our results indicate that low intestinal VDR levels improve intestinal calcium absorption compared to Vdr null mice, but also show that 1,25(OH)2 D-mediated fine-tuning of renal calcium reabsorption and bone mineralization and resorption is required to maintain fully normal serum calcium levels.
Gamma-glutamyl carboxylase (GGCX) gene mutation causes GGCX syndrome (OMIM: 137167), which is characterized by pseudoxanthoma elasticum (PXE)-like symptoms and coagulation impairment. Here, we ...present a 55-year-old male with a novel homozygous deletion mutation, c.2,221delT, p.S741LfsX100, in the GGCX gene. Histopathological examination revealed calcium deposits in elastic fibers and vessel walls, and collagen accumulation in the mid-dermis. Studies of dermal fibroblasts from the patient (GGCX dermal fibroblasts) demonstrated that the mutated GGCX protein was larger, but its expression level and intracellular distribution were indistinguishable from those of the wild-type GGCX protein. Immunostaining and an enzyme-linked immunosorbent assay showed an increase in undercarboxylated matrix gamma-carboxyglutamic acid protein (ucMGP), a representative substrate of GGCX and a potent calcification inhibitor, indicating that mutated GGCX was enzymatically inactive. Under osteogenic conditions, calcium deposition was exclusively observed in GGCX dermal fibroblasts. Furthermore, GGCX dermal fibroblast cultures contained 23- and 7.7-fold more alkaline phosphatase (ALP)-positive cells than normal dermal fibroblast cultures (n = 3), without and with osteogenic induction, respectively. Expression and activity of ALP were higher in GGCX dermal fibroblasts than in normal dermal fibroblasts upon osteogenic induction. mRNA levels of other osteogenic markers were also higher in GGCX dermal fibroblasts than in normal dermal fibroblasts, which including bone morphogenetic protein 6, runt-related transcription factor 2, and periostin (POSTN) without osteogenic induction; and osterix, collagen type I alpha 2, and POSTN with osteogenic induction. Together, these data indicate that GGCX dermal fibroblasts trans-differentiate into the osteogenic lineage. This study proposes another mechanism underlying aberrant calcification in patients with GGCX syndrome.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The increasing number of osteoporosis patients is a pressing issue worldwide. Osteoporosis frequently causes fragility fractures, limiting activities of daily life and increasing mortality. Many ...osteoporosis patients take numerous medicines due to other health issues; thus, it would be preferable if a single medicine could ameliorate osteoporosis and other conditions. Here, we screened 96 randomly selected drugs targeting various diseases for their ability to inhibit differentiation of osteoclasts, which play a pivotal role in development of osteoporosis, and identified methotrexate (MTX), as a potential inhibitor. MTX is currently used to treat sarcomas or leukemic malignancies or auto-inflammatory diseases such as rheumatoid arthritis (RA) through its anti-proliferative and immunosuppressive activities; however, a direct effect on osteoclast differentiation has not been shown. Here, we report that osteoclast formation and expression of osteoclastic genes such as
NFATc1
and
DC
-
STAMP
, which are induced by the cytokine RANKL, are significantly inhibited by MTX. We found that RANKL-dependent calcium (Ca) influx into osteoclast progenitors was significantly inhibited by MTX. RA patients often develop osteoporosis, and osteoclasts are reportedly required for joint destruction; thus, MTX treatment could have a beneficial effect on RA patients exhibiting high osteoclast activity by preventing both osteoporosis and joint destruction.
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