Annexin 5 overexpression increased articular chondrocyte apoptosis induced by basic calcium phosphate crystals

Inhibiting Lysyl Oxidases prevents pathologic cartilage calcification

Lysyl oxidases (LOX(L)) are enzymes that catalyze the formation of cross-links in collagen and elastin fibers during physiologic calcification of bone. However, it remains unknown whether they may promote pathologic calcification of articular cartilage, an important hallmark of debilitating arthropathies. Here, we have studied the possible roles of LOX(L) in cartilage calcification, related and not related to their cross-linking activity. We first demonstrated that inhibition of LOX(L) by β-aminoproprionitrile (BAPN) significantly reduced calcification in murine and human chondrocytes, and in joint of meniscectomized mice. These BAPN's effects on calcification were accounted for by different LOX(L) roles. Firstly, reduced LOX(L)-mediated extracellular matrix cross-links downregulated Anx5, Pit1 and Pit2 calcification genes. Secondly, BAPN reduced collagen fibrotic markers Col1 and Col3. Additionally, LOX(L) inhibition blocked chondrocytes hypertrophic differentiation (Runx2 and COL10), pro-inflammatory IL-6 release and reactive oxygen species (ROS) production, all triggers of chondrocyte calcification. Through unbiased transcriptomic analysis we confirmed a positive correlation between LOX(L) genes and genes for calcification, hypertrophy and extracellular matrix catabolism. This association was conserved throughout species (mouse, human) and tissues that can undergo pathologic calcification (kidney, arteries, skin). Overall, LOX(L) play a critical role in the process of chondrocyte calcification and may be therapeutic targets to treat cartilage calcification in arthropathies.

Crystal arthropathies and osteoarthritis-where is the link?

Osteoarthritis (OA) is one of the leading causes of disability worldwide. As our understanding of OA progressively has moved from a purely mechanical "wear and tear" concept toward a complex multi-tissue condition in which inflammation plays a central role, the possible role of crystal-induced inflammation in OA incidence and progression may be relevant. In addition to gout, which affects 4% of the US population, basic calcium phosphate and calcium pyrophosphate deposition both may induce joint inflammation and may play a role in pain in OA. This narrative review article discusses the possible mechanisms underlying the associations between crystal-induced arthropathies and OA, and the important implications of these for clinical practice and future research.

Cartilage calcification in osteoarthritis: mechanisms and clinical relevance

Pathological calcification of cartilage is a hallmark of osteoarthritis (OA). Calcification can be observed both at the cartilage surface and in its deeper layers. The formation of calcium-containing crystals, typically basic calcium phosphate (BCP) and calcium pyrophosphate dihydrate (CPP) crystals, is an active, highly regulated and complex biological process that is initiated by chondrocytes and modified by genetic factors, dysregulated mitophagy or apoptosis, inflammation and the activation of specific cellular-signalling pathways. The links between OA and BCP deposition are stronger than those observed between OA and CPP deposition. Here, we review the molecular processes involved in cartilage calcification in OA and summarize the effects of calcium crystals on chondrocytes, synovial fibroblasts, macrophages and bone cells. Finally, we highlight therapeutic pathways leading to decreased joint calcification and potential new drugs that could treat not only OA but also other diseases associated with pathological calcification.

The Gasotransmitter Hydrogen Sulfide (H2S) Prevents Pathologic Calcification (PC) in Cartilage

Pathologic calcification (PC) is a painful and disabling condition whereby calcium-containing crystals deposit in tissues that do not physiologically calcify: cartilage, tendons, muscle, vessels and skin. In cartilage, compression and inflammation triggered by PC leads to cartilage degradation typical of osteoarthritis (OA). The PC process is poorly understood and treatments able to target the underlying mechanisms of the disease are lacking. Here we show a crucial role of the gasotransmitter hydrogen sulfide (H₂S) and, in particular, of the H₂S-producing enzyme cystathionine γ-lyase (CSE), in regulating PC in cartilage. Cse deficiency (Cse KO mice) exacerbated calcification in both surgically-induced (menisectomy) and spontaneous (aging) murine models of cartilage PC, and augmented PC was closely associated with cartilage degradation (OA). On the contrary, Cse overexpression (Cse tg mice) protected from these features. In vitro, Cse KO chondrocytes showed increased calcification, potentially via enhanced alkaline phosphatase (Alpl) expression and activity and increased IL-6 production. The opposite results were obtained in Cse tg chondrocytes. In cartilage samples from patients with OA, CSE expression inversely correlated with the degree of tissue calcification and disease severity. Increased cartilage degradation in murine and human tissues lacking or expressing low CSE levels may be accounted for by dysregulated catabolism. We found higher levels of matrix-degrading metalloproteases Mmp-3 and -13 in Cse KO chondrocytes, whereas the opposite results were obtained in Cse tg cells. Finally, by high-throughput screening, we identified a novel small molecule CSE positive allosteric modulator (PAM), and demonstrated that it was able to increase cellular H₂S production, and decrease murine and human chondrocyte calcification and IL-6 secretion. Together, these data implicate impaired CSE-dependent H₂S production by chondrocytes in the etiology of cartilage PC and worsening of secondary outcomes (OA). In this context, enhancing CSE expression and/or activity in chondrocytes could represent a potential strategy to inhibit PC.

AnnexinA5 Might Suppress the Phenotype of Human Gastric Cancer Cells via ERK Pathway

Gastric cancer is one of the most fatal diseases around the world. However, the mechanism of the development of gastric cancer is still not clarified. In addition, the anticancer drugs have cytotoxicity with different degrees. AnnexinA5, a member of the annexin family, has a great binding ability with the membrane phospholipid in a calcium dependent manner and is involved in the development of various cancers. This study aims to explore the influence of annexinA5 on human gastric cancer cells and whether it has the potential to be an auxiliary treatment to gastric cancer. In this study, the role of annexinA5 was detected from both the endogenous and the exogenous aspects on the gastric cancer cell lines MGC-803 and MKN-45. The cells were divided into a knockdown group in which RNA interference technique was used to suppress annexinA5 expression and a protein-supplementing group in which annexinA5 protein was added in the culture supernatant. After the suppression ratio of RNA interference was determined and the IC50 of annexinA5 protein was decided respectively, the cells' proliferation was detected by MTT assay, colony formation assay, and the expression of PCNA. FCM assay and PI staining methods were applied to test cell apoptosis and necrosis. To investigate whether ANXA5 influence cell metastasis, wound healing assay and transwell assay were employed. To further detect the mechanism of annexinA5 action, the signal pathway was examined with Western Blot method. When ANXA5 gene was knocked down, cell proliferation and metastasis were promoted, while cell apoptosis was suppressed. On the other hand, after the annexinA5 protein was applied to the gastric cancer cells, cell proliferation and metastasis were inhibited, while cell apoptosis and necrosis were promoted. AnnexinA5 played its role via ERK signal pathway. ANXA5 acted as tumor suppressor gene in the gastric cancer by suppressing ERK signal pathway and has the potentiality to be an auxiliary anticancer agent.

Apoptosis in the Extraosseous Calcification Process

Extraosseous calcification is a pathologic mineralization process occurring in soft connective tissues (e.g., skin, vessels, tendons, and cartilage). It can take place on a genetic basis or as a consequence of acquired chronic diseases. In this last case, the etiology is multifactorial, including both extra- and intracellular mechanisms, such as the formation of membrane vesicles (e.g., matrix vesicles and apoptotic bodies), mitochondrial alterations, and oxidative stress. This review is an overview of extraosseous calcification mechanisms focusing on the relationships between apoptosis and mineralization in cartilage and vascular tissues, as these are the two tissues mostly affected by a number of age-related diseases having a progressively increased impact in Western Countries.

Adrenomedullin and truncated peptide adrenomedullin(22-52) affect chondrocyte response to apoptotis in vitro: downregulation of FAS protects chondrocyte from cell death

Chondrocyte apoptosis may have a pivotal role in the development of osteoarthritis. Interest has increased in the use of anti-apoptotic compounds to protect against osteoarthritis development. In this work, we investigated the effect of adrenomedullin (AM), a 52 amino-acid hormone peptide, and a 31 amino-acid truncated form, AM(22-52), on chondrocyte apoptosis. Bovine articular chondrocytes (BACs) were cultured under hypoxic conditions to mimic cartilage environment and then treated with Fas ligand (Fas-L) to induce apoptosis. The expression of AM and its calcitonin receptor-like receptor (CLR)/receptor activity-modifying protein (RAMP) (receptor/co-receptor) was assessed by immunostaining. We evaluated the effect of AM and AM(22-52) on Fas-L-induced chondrocyte apoptosis. FAS expression was appreciated by RT-qPCR and immunostainings. The expression of hypoxia-inducible factor 1α (HIF-1α), CLR and one co-receptor (RAMP2) was evidenced. With BACs under hypoxia, cyclic adenosine monophosphate production increased dose-dependently with AM stimulation. AM significantly decreased caspase-3 activity (mean 35% decrease; p = 0.03) as a marker of Fas-L-induced apoptosis. Articular chondrocytes treated with AM showed significantly reduced cell death, along with downregulated Fas expression and production, as compared with AM(22-52). AM decreased articular chondrocyte apoptosis by downregulating a Fas receptor. These findings may pave the way for novel therapeutic approaches in osteoarthritis.

Galectin 3 Deficiency Alters Chondrocyte Primary Cilium Formation and Exacerbates Cartilage Destruction via Mitochondrial Apoptosis

Mechanical overload and aging are the main risk factors of osteoarthritis (OA). Galectin 3 (GAL3) is important in the formation of primary cilia, organelles that are able to sense mechanical stress. The objectives were to evaluate the role of GAL3 in chondrocyte primary cilium formation and in OA in mice. Chondrocyte primary cilium was detected in vitro by confocal microscopy. OA was induced by aging and partial meniscectomy of wild-type (WT) and Gal3-null 129SvEV mice (Gal3^−/−). Primary chondrocytes were isolated from joints of new-born mice. Chondrocyte apoptosis was assessed by Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), caspase 3 activity and cytochrome c release. Gene expression was assessed by qRT-PCR. GAL3 was localized at the basal body of the chondrocyte primary cilium. Primary cilia of Gal3^−/− chondrocytes were frequently abnormal and misshapen. Deletion of Gal3 triggered premature OA during aging and exacerbated joint instability-induced OA. In both aging and surgery-induced OA cartilage, levels of chondrocyte catabolism and hypertrophy markers and apoptosis were more severe in Gal3^−/− than WT samples. In vitro, Gal3 knockout favored chondrocyte apoptosis via the mitochondrial pathway. GAL3 is a key regulator of cartilage homeostasis and chondrocyte primary cilium formation in mice. Gal3 deletion promotes OA development.

Proteomic changes of aryl hydrocarbon receptor (AhR)-silenced porcine granulosa cells exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a toxic man-made chemical compound contaminating the environment and affecting human/animal health and reproduction. Intracellular TCDD action usually involves the activation of aryl hydrocarbon receptor (AhR). The aim of the current study was to examine TCDD-induced changes in the proteome of AhR-silenced porcine granulosa cells. The AhR-silenced cells were treated with TCDD (100 nM) for 3, 12 or 24 h. Total protein was isolated, labeled with cyanines and next, the samples were separated by isoelectric focusing and SDS-PAGE. Proteins of interest were identified by MALDI-TOF/TOF mass spectrometry (MS) analysis and confirmed by western blotting and fluorescence immunocytochemistry. The AhR-targeted siRNA transfection reduced the granulosal expression level of AhR by 60–70%. In AhR-silenced porcine granulosa cells, TCDD influenced the abundance of only three proteins: annexin V, protein disulfide isomerase and ATP synthase subunit beta. The obtained results revealed the ability of TCDD to alter protein abundance in an AhR-independent manner. This study offers a new insight into the mechanism of TCDD action and provide directions for future functional studies focused on molecular effects exerted by TCDD.

Calcium-Containing Crystals and Osteoarthritis: an Unhealthy Alliance

PURPOSE OF REVIEW

Osteoarthritis (OA) is the most common form of joint disease globally and is associated with significant morbidity and disability. Increasing evidence points to an important inflammatory component in the development and progression of OA. The precise pathways involved in OA inflammatory processes remain to be clarified. Basic calcium phosphate (BCP) and calcium pyrophosphate dihydrate (CPP) crystals can induce inflammation and arthritis and recent studies point to a potential pathogenic role in OA. In the light of this evidence, we explore the relationship and potential mechanistic pathways linking calcium-containing crystals and OA.

RECENT FINDINGS

CPP crystals induce inflammation through the NLRP3 inflammasome while BCP crystals mediate both NLRP3 dependent and independent effects. BCP crystals have been demonstrated to induce key mitogenic and inflammatory pathways and contribute to cartilage degradation. Calcium-containing crystals induce key inflammatory pathways and may represent an attractive novel target in OA, a condition devoid of effective treatments.

Annexin A5 overexpression might suppress proliferation and metastasis of human uterine cervical carcinoma cells

BACKGROUND

Annexin A5 (ANXA5) is a kind of Ca2+-dependent phospholipid binding protein which is involved in cell membrane dynamics and organization. Recent data showed that ANXA5 might involve in tumorigenesis.

OBJECTIVE

To explore what role ANXA5 play in human uterine cervical carcinoma.

MATERIALS AND METHODS

In this study, a recombined ANXA5 plasmid was constructed and uterine cervical carcinoma cell lines HeLa and SiHa were transfected with it. After ANXA5 overexpression was determined by Western Blot, cell proliferation test was detected by MTT assay and colony formation assay respectively. FACS assay and Hochest33258 staining methods were employed to detect cell apoptosis. To further investigate whether ANXA5 influence cell migration and invasion, wound healing assay and transwell assay were applied. At the same time, the relative mechanism was investigated.

RESULTS

When ANXA5 expression increased, cell proliferation was inhibited by regulating the expression of bcl-2 and bax while cell metastasis was suppressed by regulating E-cadherin and MMP-9 expression.

CONCLUSION

ANXA5 overexpression in the uterine cervical carcinoma might play important roles in cell proliferation and metastasis of uterine cervical cancer cells and act as an anti-cancer gene in uterine cervical cancer.

ASIC2a overexpression enhances the protective effect of PcTx1 and APETx2 against acidosis-induced articular chondrocyte apoptosis and cytotoxicity

Acid hydrarthrosis is another important pathological character in rheumatoid arthritis (RA), and acid-sensing ion channel 1a (ASIC1a) plays a destructive role in acidosis-induced articular chondrocyte cytotoxicity. Recently, ASIC2a has been reported to possess neuroprotective effect on acidosis-induced injury of neuronal cells. However, whether ASIC2a has an enhanced effect on the protective effect of blocking ASIC1a and ASIC3 against acid-induced chondrocyte apoptosis is still unclear. The aim of present study was to investigate the chondroprotective effect of ASIC2a with PcTx1 (ASIC1a specific blocker) and APETx2 (ASIC3 specific blocker) on acidosis-induced chondrocyte apoptosis. Our results revealed that acid (pH 6.0) decreased the cell viability and induced apoptosis of articular chondrocytes. PcTx1 and APETx2 combination significantly attenuated acidosis-induced chondrocyte cytotoxicity due to inhibit apoptosis, and this role could be enhanced by ASIC2a overexpression compared with the PcTx1 and APETx2 combination alone group. Moreover, both the [Ca²⁺]_i levels and the levels of phosphorylated ERK1/2 as well as p38 were further reduced in acidosis-induced chondrocytes after ASIC2a overexpression in the presence of PcTx1 and APETx2. Furthermore, ASIC2a overexpression also reduced acid-induced the expression of ASIC1a. In addition, ASIC2a overexpression further promoted the PcTx1 and APETx2-increased levels of type II collagen in acidosis-induced chondrocytes. Taken together, the current data suggested that ASIC2a overexpression might enhance the anti-apoptotic and protective role of PcTx1 and APETx2 against acid-induced rat articular chondrocyte apoptosis by regulating ASIC1a expression and the [Ca²⁺]_i levels and at least in part, suppressing p38 and ERK1/2 MAPK signaling pathways.

Time-dependent proteomic and genomic alterations in Toll-like receptor-4-activated human chondrocytes: increased expression of lamin A/C and annexins

Activation of Toll-like receptor-4 (TLR-4) in articular chondrocytes increases the catabolic compartment and leads to matrix degradation during the development of osteoarthritis. In this study, we determined the proteomic and genomic alterations in human chondrocytes during lipopolysaccharide (LPS)-induced inflammation to elucidate the underlying mechanisms and consequences of TLR-4 activation. Human chondrocytes were cultured with LPS for 12, 24, and 36 h to induce TLR-4 activation. The TLR-4-induced inflammatory response was confirmed by real-time PCR analysis of increased interleukin-1 beta (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α) expression levels. In TLR-4-activated chondrocytes, proteomic changes were determined by two-dimensional electrophoresis and matrix-assisted laser desorption/ionization-mass spectroscopy analysis, and genomic changes were determined by microarray and gene ontology analyses. Proteomics analysis identified 26 proteins with significantly altered expression levels; these proteins were related to the cytoskeleton and oxidative stress responses. Gene ontology analysis indicated that LPS treatment altered specific functional pathways including ‘chemotaxis’, ‘hematopoietic organ development’, ‘positive regulation of cell proliferation’, and ‘regulation of cytokine biosynthetic process’. Nine of the 26 identified proteins displayed the same increased expression patterns in both proteomics and genomics analyses. Western blot analysis confirmed the LPS-induced increases in expression levels of lamin A/C and annexins 4/5/6. In conclusion, this study identified the time-dependent genomic, proteomic, and functional pathway alterations that occur in chondrocytes during LPS-induced TLR-4 activation. These results provide valuable new insights into the underlying mechanisms that control the development and progression of osteoarthritis.

Interleukin-6 and chondrocyte mineralisation act in tandem to promote experimental osteoarthritis

OBJECTIVES

Basic calcium phosphate (BCP) crystal and interleukin 6 (IL-6) have been implicated in osteoarthritis (OA). We hypothesise that these two factors may be linked in a reciprocal amplification loop which leads to OA.

METHODS

Primary murine chondrocytes and human cartilage explants were incubated with hydroxyapatite (HA) crystals, a form of BCP, and the modulation of cytokines and matrix-degrading enzymes assayed. The ability of IL-6 to stimulate chondrocyte calcification was assessed in vitro. The mechanisms underlying the effects of HA on chondrocytes were investigated using chemical inhibitors, and the pathways mediating IL-6-induced calcification characterised by quantifying the expression of genes involved in chondrocyte mineralisation. The role of calcification in vivo was studied in the meniscectomy model of murine OA (MNX), and the link between IL-6 and cartilage degradation investigated by histology.

RESULTS

In chondrocytes, BCP crystals stimulated IL-6 secretion, further amplified in an autocrine loop, through signalling pathways involving Syk and PI3 kinases, Jak2 and Stat3 molecules. Exogenous IL-6 promoted calcium-containing crystal formation and upregulation of genes involved in calcification: the pyrophosphate channel Ank, the calcium channel Annexin5 and the sodium/phosphate cotransporter Pit-1. Treatment of chondrocytes with IL-6 inhibitors significantly inhibited IL-6-induced crystal formation. In meniscectomised mice, increasing deposits of BCP crystals were observed around the joint and correlated with cartilage degradation and IL-6 expression. Finally, BCP crystals induced proteoglycan loss and IL-6 expression in human cartilage explants, which were reduced by an IL-6 inhibitor.

CONCLUSIONS

BCP crystals and IL-6 form a positive feedback loop leading to OA. Targeting calcium-containing crystal formation and/or IL-6 are promising therapeutic strategies in OA.

Recombinant Human Annexin A5 Can Repair the Disrupted Cardiomyocyte Adherens Junctions in Endotoxemia

Recombinant human annexin A5 (Anx5) is known to protect cardiac function during endotoxemia, although the underlying mechanisms have yet to be elucidated. In this study, we demonstrated that Anx5 could repair the disrupted cardiomyocyte adherens junctions and improve the myocardial contractile function in lipopolysaccharide (LPS)-induced endotoxemia. Mechanistic studies revealed that Anx5 could antagonize the disassociation between p120-catenin (p120) and N-cadherin as well as the dephosphorylation of p120 in LPS-treated cardiomyocytes. Small interference RNA and specific inhibitors experiment demonstrated that Anx5 regulated p120 functions by inhibition of p21-activated kinase 5 in a protein kinase Cα-dependent way. Moreover, Anx5 could inhibit nuclear factor κB activation and downregulate the level of inflammatory cytokines, such as tumor necrosis factor α and interleukin 1β, which contributed to improving tissue pathological damage in LPS-induced mouse endotoxemia model. Taken together, Anx5 could protect cardiomyocytes adherens junctions and improve myocardial contractile function via regulation of p120 and anti-inflammation in LPS-induced endotoxemia. This study provided novel insights in the prevention and treatment of septic shock.

Effects of laser treatment on the expression of cytosolic proteins in the synovium of patients with osteoarthritis

BACKGROUND AND OBJECTIVE

Low level laser therapy (LLLT) has been developed for non-invasive treatment of joint diseases. We have previously shown that LLLT influenced synovial protein expression in rheumatoid arthritis (RA). The aim of this study was to assess the effects of laser irradiation on osteoarthritic (OA) synovial protein expression.

STUDY DESIGN/MATERIALS AND METHODS

The synovial membrane samples removed from the knees of 6 OA patients were irradiated ex vivo using near infrared diode laser (807-811 nm; 25 J/cm(2) ). An untreated sample taken from the same patient served as control. Synovial protein separation and identification were performed by two-dimensional differential gel electrophoresis and mass spectrometry, respectively.

RESULTS

Eleven proteins showing altered expression due to laser irradiation were identified. There were three patients whose tissue samples demonstrated a significant increase (P < 0.05) in mitochondrial heat shock 60 kD protein 1 variant 1. The expression of the other proteins (calpain small subunit 1, tubulin alpha-1C and beta 2, vimentin variant 3, annexin A1, annexin A5, cofilin 1, transgelin, and collagen type VI alpha 2 chain precursor) significantly decreased (P < 0.05) compared to the control samples.

CONCLUSIONS

A single diode laser irradiation of the synovial samples of patients with osteoarthritis can statistically significantly alter the expression of some proteins in vitro. These findings provide some more evidence for biological efficacy of LLLT treatment, used for osteoarthritis.

Fetuin-A and albumin alter cytotoxic effects of calcium phosphate nanoparticles on human vascular smooth muscle cells

Calcification is a detrimental process in vascular ageing and in diseases such as atherosclerosis and arthritis. In particular, small calcium phosphate (CaP) crystal deposits are associated with inflammation and atherosclerotic plaque de-stabilisation. We previously reported that CaP particles caused human vascular smooth muscle cell (VSMC) death and that serum reduced the toxic effects of the particles. Here, we found that the serum proteins fetuin-A and albumin (≥ 1 µM) reduced intracellular Ca2+ elevations and cell death in VSMCs in response to CaP particles. In addition, CaP particles functionalised with fetuin-A, but not albumin, were less toxic than naked CaP particles. Electron microscopic studies revealed that CaP particles were internalised in different ways; via macropinocytosis, membrane invagination or plasma membrane damage, which occurred within 10 minutes of exposure to particles. However, cell death did not occur until approximately 30 minutes, suggesting that plasma membrane repair and survival mechanisms were activated. In the presence of fetuin-A, CaP particle-induced damage was inhibited and CaP/plasma membrane interactions and particle uptake were delayed. Fetuin-A also reduced dissolution of CaP particles under acidic conditions, which may contribute to its cytoprotective effects after CaP particle exposure to VSMCs. These studies are particularly relevant to the calcification observed in blood vessels in patients with kidney disease, where circulating levels of fetuin-A and albumin are low, and in pathological situations where CaP crystal formation outweighs calcification-inhibitory mechanisms.

Annexin A6 interacts with p65 and stimulates NF-κB activity and catabolic events in articular chondrocytes

OBJECTIVE

ANXA6, the gene for annexin A6, is highly expressed in osteoarthritic (OA) articular chondrocytes but not in healthy articular chondrocytes. This study was undertaken to determine whether annexin A6 affects catabolic events in these cells.

METHODS

Articular chondrocytes were isolated from Anxa6-knockout mice, wild-type (WT) mice, and human articular cartilage in which ANXA6 was overexpressed. Cells were treated with interleukin-1β (IL-1β) or tumor necrosis factor α (TNFα), and expression of catabolic genes and activation of NF-κB were determined by real-time polymerase chain reaction and luciferase reporter assay. Anxa6(-/-) and WT mouse knee joints were injected with IL-1β or the medial collateral ligament was transected and partial resection of the medial meniscus was performed to determine the role of Anxa6 in IL-1β-mediated cartilage destruction and OA progression. The mechanism by which Anxa6 stimulates NF-κB activity was determined by coimmunoprecipitation and immunoblot analysis of nuclear and cytoplasmic fractions of IL-1β-treated Anxa6(-/-) and WT mouse chondrocytes for p65 and Anxa6.

RESULTS

Loss of Anxa6 resulted in decreased NF-κB activation and catabolic marker messenger RNA (mRNA) levels in IL-1β- or TNFα-treated articular chondrocytes, whereas overexpression of ANXA6 resulted in increased NF-κB activity and catabolic marker mRNA levels. Annexin A6 interacted with p65, and loss of Anxa6 caused decreased nuclear translocation and retention of the active p50/p65 NF-κB complex. Cartilage destruction in Anxa6(-/-) mouse knee joints after IL-1β injection or partial medial meniscectomy was reduced as compared to that in WT mouse joints.

CONCLUSION

Our data define a role of annexin A6 in the modulation of NF-κB activity and in the stimulation of catabolic events in articular chondrocytes.

Role of annexin A5 in cisplatin-induced toxicity in renal cells: molecular mechanism of apoptosis

Annexin A5 belongs to a large family of calcium-binding and phospholipid-binding proteins and may act as an endogenous regulator of various pathophysiological processes. There is increasing evidence that annexin A5 is related to cytotoxicity, but the precise function of this protein has yet to be elucidated. In this study, we aimed to verify the function of annexin A5 in the apoptosis of renal epithelial cells. Real-time PCR and Western blot analysis, together with immunofluorescence analysis, showed that the expression of annexin A5 significantly increased in the presence of cisplatin in both human and rat renal epithelial cells. With regard to the mechanism of cisplatin-induced apoptosis, apoptosis-inducing factor (AIF) release into the cytosol was observed, and the underlying mechanism was identified as voltage-dependent anion channel (VDAC) oligomerization. Mitochondrial membrane potential (Δψm) was found to be greatly disrupted in cisplatin-treated cells. Moreover, cisplatin strongly induced translocation of annexin A5 into mitochondria. To understand the functional significance of annexin A5 in renal cell death, we used a siRNA-mediated approach to knock down annexin A5. Annexin A5 depletion by siRNA led to decreased annexin A5 translocation into mitochondria and significantly reduced VDAC oligomerization and AIF release. Annexin A5 siRNA also increased cell viability compared with the control. Moreover, expression of annexin A5 was induced by other nephrotoxicants such as CdCl2 and bacitracin. Taken together, our data suggest that annexin A5 may play a crucial role in cisplatin-induced toxicity by mediating the mitochondrial apoptotic pathway via the induction and oligomerization of VDAC.

Annexin a5 as a new potential biomarker for Cisplatin-induced toxicity in human kidney epithelial cells

Cisplatin is a member of platinum-containing anti-cancer drugs that causes cross-linking of DNA and ultimately cancer cell apoptosis. The therapeutic function of cisplatin on various types of cancers has been widely reported but the side effects have been discovered together and nephrotoxicity has been regarded as major side effect of cisplatin. To select candidates for new sensitive nephrotoxicity biomarker, we performed proteomic analysis using 2-DE/MALDI-TOF-MS followed by cisplatin treatment in human kidney cell line, HK-2 cells, and compared the results to the gene profi le from microarray composed of genes changed in expression by cisplatin from formerly reported article. Annexin A5 has been selected to be the most potential candidate and it has been identifi ed using Western blot, RT-PCR and cell viability assay whether annexin A5 is available to be a sensitive nephrotoxic biomarker. Treatment with cisplatin on HK-2 cells caused the increase of annexin A5 expression in protein and mRNA levels. Overexpression of annexin A5 blocked HK-2 cell proliferation, indicating correlation between annexin A5 and renal cell toxicity. Taken together, these results suggest the possibility of annexin A5 as a new biomarker for cisplatin-mediated nephrotoxicity.

Amorphous calcium phosphate nanoparticles could function as a novel cancer therapeutic agent by employing a suitable targeted drug delivery platform

Employment of nanovehicular system for delivering apoptogenic agent to cancer cells for inducing apoptosis has widely been investigated. Loading efficacy and controlled release of the agents are of the inseparable obstacles that hamper the efforts in reaching an efficacious targeted cancer therapy method. When the carrier itself is apoptogenic, then there is no need to load the carrier with apoptogenic agent and just delivering of the particle to the specific location matters. Hence, we hypothesize that amorphous calcium phosphate nanoparticle (ACPN) is a potent candidate for apoptosis induction, although encapsulation in liposome shell, and surface decoration with targeting ligand (TL), and cell-penetrating peptide (CPP) plays a pivotal role in the employment of this agent. It is well understood that elevation in cytosolic Ca2+ ([Ca2+]c) would result in the induction of apoptosis. ACPN has the potential to cause imbalance in this medium by elevating [Ca2+]c. Owning to the fact that the nanoparticles should be delivered into cytosol, it is necessary to trap them in a liposomal shell for evading endocytosis. It was demonstrated that employment of the trans-activator of transcription (TAT) as CPP eminently enhances the efficacy of endosomal escape; therefore, the platform is designed in a way that TAT is positioned on the surface of the liposome. Due to the fact that the apoptosis should be induced in sole cancer cells, Folate as TL is also attached on the surface of the liposome. This hypothesis heralds the new generation of chemotherapeutic agents and platforms which could have less side effect than the most common ones, in addition to other advantages they have.

Fetuin-A-containing calciprotein particles reduce mineral stress in the macrophage

The formation of fetuin-A-containing calciprotein particles (CPP) may facilitate the clearance of calcium phosphate nanocrystals from the extracellular fluid. These crystals may otherwise seed extra-osseous mineralization. Fetuin-A is a partially phosphorylated glycoprotein that plays a critical role in stabilizing these particles, inhibiting crystal growth and aggregation. CPP removal is thought to be predominantly mediated by cells of the reticuloendothelial system via type I and type II class A scavenger receptor (SR-AI/II). Naked calcium phosphate crystals are known to stimulate macrophages and other cell types in vitro, but little is known of the effect of CPP on these cells. We report here, for the first time, that CPP induce expression and secretion of tumour necrosis factor (TNF)-α, interleukin (IL)-1β in murine RAW 264.7 macrophages. Importantly, however, CPP induced significantly lower cytokine secretion than hydroxyapatite (HAP) crystals of equivalent size and calcium content. Furthermore, CPP only had a modest effect on macrophage viability and apoptosis, even at very high levels, compared to HAP crystals, which were strongly pro-apoptotic at much lower levels. Fetuin-A phosphorylation was found to modulate the effect of CPP on cytokine secretion and apoptosis, but not uptake via SR-AI/II. Prolonged exposure of macrophages to CPP was found to result in up-regulated expression of SR-AI/II. CPP formation may help protect against some of the pro-inflammatory and harmful effects of calcium phosphate nanocrystals, perhaps representing a natural defense system for calcium mineral stress. However, in pathological states where production exceeds clearance capacity, these particles may still stimulate pro-inflammatory and pro-apoptotic cascades in macrophages, which may be important in the pathogenesis of vascular calcification.

Pathogenic role of basic calcium phosphate crystals in destructive arthropathies

BACKGROUND

basic calcium phosphate (BCP) crystals are commonly found in osteoarthritis (OA) and are associated with cartilage destruction. BCP crystals induce in vitro catabolic responses with the production of metalloproteases and inflammatory cytokines such as interleukin-1 (IL-1). In vivo, IL-1 production induced by BCP crystals is both dependant and independent of NLRP3 inflammasome. We aimed to clarify 1/ the role of BCP crystals in cartilage destruction and 2/ the role of IL-1 and NLRP3 inflammasome in cartilage degradation related to BCP crystals.

METHODOLOGY PRINCIPAL FINDINGS

synovial membranes isolated from OA knees were analysed by alizarin Red and FTIR. Pyrogen free BCP crystals were injected into right knees of WT, NLRP3 -/-, ASC -/-, IL-1α -/- and IL-1β-/- mice and PBS was injected into left knees. To assess the role of IL-1, WT mice were treated by intra-peritoneal injections of anakinra, the IL-1Ra recombinant protein, or PBS. Articular destruction was studied at d4, d17 and d30 assessing synovial inflammation, proteoglycan loss and chondrocyte apoptosis. BCP crystals were frequently found in OA synovial membranes including low grade OA. BCP crystals injected into murine knee joints provoked synovial inflammation characterized by synovial macrophage infiltration that persisted at day 30, cartilage degradation as evidenced by loss of proteoglycan staining by Safranin-O and concomitant expression of VDIPEN epitopes, and increased chondrocyte apoptosis. BCP crystal-induced synovitis was totally independent of IL-1α and IL-1β signalling and no alterations of inflammation were observed in mice deficient for components of the NLRP3-inflammasome, IL-1α or IL-1β. Similarly, treatment with anakinra did not prevent BCP crystal effects. In vitro, BCP crystals elicited enhanced transcription of matrix degrading and pro-inflammatory genes in macrophages.

CONCLUSIONS SIGNIFICANCE

intra-articular BCP crystals can elicit synovial inflammation and cartilage degradation suggesting that BCP crystals have a direct pathogenic role in OA. The effects are independent of IL-1 and NLRP3 inflammasome.

Intracellular calcium oscillations in articular chondrocytes induced by basic calcium phosphate crystals lead to cartilage degradation

OBJECTIVE

Basic calcium phosphate (BCP) crystals, including octacalcium phosphate (OCP), carbonated-apatite (CA) and hydroxyapatite (HA) crystals are associated with destructive forms of osteoarthritis. Mechanisms of BCP-induced cartilage breakdown remain incompletely understood. We assessed the ability of BCP to induce changes in intracellular calcium (iCa(2+)) content and oscillations and the role of iCa(2+) in BCP-induced cartilage degradation.

METHODS

Bovine articular chondrocytes (BACs) and bovine cartilage explants (BCEs) were stimulated with BCP or monosodium urate (MSU) crystals. iCa(2+) levels were determined by spectrofluorimetry and oscillations by confocal microscopy. mRNA expression of matrix metalloproteinase 3 (MMP-3), a disintegrin and metalloprotease with thrombospondin-like motifs 4 (ADAMTS-4) and ADAMTS-5 was assessed by quantitative real-time PCR. Glycosaminoglycan (GAG) release was measured in the supernatants of BCE cultures.

RESULTS

All three BCP crystals significantly increased iCa(2+) content. OCP also induced iCa(2+) oscillations. Rate of BACs displaying iCa(2+) oscillations increased over time, with a peak after 20 min of stimulation. OCP-induced iCa(2+) oscillations involved both extracellular Ca(2+) (eCa(2+)) influx and iCa(2+) stores. Indeed, OCP-induced iCa(2+) oscillations decreased rapidly in Ca(2+)-free medium. Both voltage- and non-voltage-dependent Ca(2+) channels were involved in eCa(2+) influx. BCP crystal-induced variation in iCa(2+) content was associated with BCP crystal-induced cartilage matrix degradation. However, iCa²(+) was not associated with OCP crystal-induced mRNA expression of MMP-3, ADAMTS-4 or ADAMTS-5.

CONCLUSION

BCP crystals can induce variation in iCa(2+) content and oscillations in articular chondrocytes. Furthermore, BCP crystal-induced changes in iCa(2+) content play a pivotal role in BCP catabolic effects on articular cartilage.

Adrenomedullin(22-52) combats inflammation and prevents systemic bone loss in murine collagen-induced arthritis

OBJECTIVE

Adrenomedullin(22-52) is a truncated peptide derived from adrenomedullin, a growth factor with antiapoptotic and immunoregulatory properties. It can act as an agonist or an antagonist depending on cell type. Its in vivo effects are unknown, but adrenomedullin(22-52) could possess immunomodulatory properties. This study was undertaken to evaluate the effect of adrenomedullin(22-52) in a mouse model of arthritis.

METHODS

DBA/1 mice with collagen-induced arthritis (CIA) were treated with 1.2 μg/gm adrenomedullin(22-52) , adrenomedullin, or saline at arthritis onset. Bone mineral density was measured at the beginning of the experiment and when mice were killed. Mouse joints were processed for histologic analysis and protein studies, and spleens were examined for Treg cell expression. Cytokine expression was studied in mouse joint tissue and serum.

RESULTS

In mice with CIA, adrenomedullin and adrenomedullin(22-52) reduced clinical and histologic arthritis scores and shifted the pattern of articular and systemic cytokine expression from Th1 to Th2, as compared to untreated mice with CIA (controls). Tumor necrosis factor α, interleukin-6 (IL-6), and IL-17A levels were significantly decreased in the joints of mice with CIA treated with adrenomedullin or adrenomedullin(22-52) as compared to controls, whereas IL-4 and IL-10 levels were increased. Adrenomedullin(22-52) was more effective than adrenomedullin in modulating cytokine content and enhanced Treg cell function without changing Treg cell expression compared to controls. Adrenomedullin receptor binding and transcriptional adrenomedullin receptor expression were markedly increased in joints from controls, whereas adrenomedullin receptor binding was considerably decreased in treated animals. Mice with CIA treated with adrenomedullin or adrenomedullin(22-52) had considerably fewer apoptotic chondrocytes and diminished cartilage degradation. Adrenomedullin(22-52) completely prevented systemic bone loss by preserving osteoblastic activity, but without changes in osteoclastic activity.

CONCLUSION

Our findings indicate that adrenomedullin(22-52) , which has no vasoactive or tumor-inducing effects, is a potent antiinflammatory and bone-protective agent in this arthritis model.

Phosphate-dependent stimulation of MGP and OPN expression in osteoblasts via the ERK1/2 pathway is modulated by calcium

Inorganic phosphate (Pi) acts as a signaling molecule in bone-forming cells, affecting cell functions and gene expression. Particularly, Pi stimulates the expression of mineralization-associated genes such as matrix gla protein (MGP) and osteopontin (OPN) through the ERK1/2 pathway. With respect to the presence of elevated extracellular calcium and Pi levels during bone remodeling, we questioned whether calcium might play a role in the Pi-dependent effects in osteoblasts. We first showed by Western blot and real-time PCR that the concomitant presence of 10 mM Pi and 1.8 mM calcium is required to stimulate ERK1/2 phosphorylation and MGP/OPN genes expression. The mechanisms involved in the cellular effects of calcium in the presence of Pi were subsequently examined. Firstly, the use of the calcium-sensing receptor (CaSR) agonist gadolinium and the G-protein inhibitor pertussis toxin enabled us to determine that a CaSR mechanism is not involved in the Pi and calcium mediated cellular effects. By transmission electron microscopy, we next demonstrated that adding 10mM Pi to the culture medium containing 1.8mM calcium led to the formation calcium phosphate precipitates (CaPp). Moreover, treatment of osteoblasts with exogenous pre-synthesized CaPp stimulated ERK1/2 phosphorylation and MGP/OPN genes expression. In spite of high extracellular calcium and Pi concentrations, this stimulation was blunted in the presence of phosphocitrate, an inhibitor of crystal formation. Finally, we showed that despite that CaPp are not endocytosed, their effect on ERK1/2 phosphorylation and MGP/OPN genes expression were dependent on lipid rafts integrity. In summary, we showed that calcium is required for Pi-dependent ERK1/2 phosphorylation and regulation of mineralization-associated genes in osteoblasts and that its effect could originate from extracellular-related effects of CaPp that are dependent on the integrity of lipid rafts.

Inorganic phosphate stimulates apoptosis in murine MO6-G3 odontoblast-like cells

OBJECTIVE

Dental pathologies such as caries are the most prevalent disease worldwide with infectious and social complications. During the process of caries formation, the tooth is degraded and demineralization of enamel and dentine leads to the release of large amounts of inorganic phosphate (Pi) within dental tubuli. As Pi has been shown to induce apoptosis in skeletal cells, including osteoblasts and chondrocytes, we questioned whether high concentrations of Pi could affect odontoblast viability, proliferation and apoptosis.

DESIGN

Using the odontoblast-like MO6-G3 cell line as a model, we used cell counting and MTS-based colorimetric assays to measure cell viability and proliferation. Apoptosis was assessed using Hoechst nuclei staining and detection of the early apoptotic markers annexin V and Apo2.7.

RESULTS

We show for the first time that a high Pi concentration (7 mM) induced a decrease in odontoblast viability and proliferation together with a large increase in apoptosis. These effects were blunted in calcium-free medium, possibly due to the formation of calcium-phosphate crystals in the presence of high Pi concentrations.

CONCLUSION

This study contributes to clarifying the effect of Pi on odontoblast viability and apoptosis, which may improve our understanding of the role of Pi during caries formation.

Octacalcium phosphate crystals induce inflammation in vivo through interleukin-1 but independent of the NLRP3 inflammasome in mice

OBJECTIVE

To determine the mechanisms involved in inflammatory responses to octacalcium phosphate (OCP) crystals in vivo.

METHODS

OCP crystal-induced inflammation was monitored using a peritoneal model of inflammation in mice with different deficiencies affecting interleukin-1 (IL-1) secretion (IL-1α(-/-) , IL-1β(-/-) , ASC(-/-) , and NLRP3(-/-) mice) or in mice pretreated with IL-1 inhibitors (anakinra [recombinant IL-1 receptor antagonist] and anti-IL-1β). The production of IL-1α, IL-1β, and myeloid-related protein 8 (MRP-8)-MRP-14 complex was determined by enzyme-linked immunosorbent assay. Peritoneal neutrophil recruitment and cell viability were determined by flow cytometry. Depletion of mast cells or resident macrophages was performed by pretreatment with compound 48/80 or clodronate liposomes, respectively.

RESULTS

OCP crystals induced peritoneal inflammation, as demonstrated by neutrophil recruitment and up-modulation of IL-1α, IL-1β, and MRP-8-MRP-14 complex, to levels comparable with those induced by monosodium urate monohydrate crystals. This OCP crystal-induced inflammation was both IL-1α- and IL-1β-dependent, as shown by the inhibitory effects of anakinra and anti-IL-1β antibody treatment. Accordingly, OCP crystal stimulation resulted in milder inflammation in IL-1α(-/-) and IL-1β(-/-) mice. Interestingly, ASC(-/-) and NLRP3(-/-) mice did not show any alteration in their inflammation status in response to OCP crystals. Depletion of the resident macrophage population resulted in a significant decrease in crystal-induced neutrophil infiltration and proinflammatory cytokine production in vivo, whereas mast cell depletion had no effect. Finally, OCP crystals induced apoptosis/necrosis of peritoneal cells in vivo.

CONCLUSION

These data indicate that macrophages, rather than mast cells, are important for initiating and driving OCP crystal-induced inflammation. Additionally, OCP crystals induce IL-1-dependent peritoneal inflammation without requiring the NLRP3 inflammasome.

Basic calcium phosphate crystals induce monocyte/macrophage IL-1β secretion through the NLRP3 inflammasome in vitro

Basic calcium phosphate (BCP) crystals are associated with severe osteoarthritis and acute periarticular inflammation. Three main forms of BCP crystals have been identified from pathological tissues: octacalcium phosphate, carbonate-substituted apatite, and hydroxyapatite. We investigated the proinflammatory effects of these BCP crystals in vitro with special regard to the involvement of the NLRP3-inflammasome in THP-1 cells, primary human monocytes and macrophages, and mouse bone marrow-derived macrophages (BMDM). THP-1 cells stimulated with BCP crystals produced IL-1β in a dose-dependent manner. Similarly, primary human cells and BMDM from wild-type mice also produced high concentrations of IL-1β after crystal stimulation. THP-1 cells transfected with short hairpin RNA against the components of the NLRP3 inflammasome and mouse BMDM from mice deficient for NLRP3, apoptosis-associated speck-like protein, or caspase-1 did not produce IL-1β after BCP crystal stimulation. BCP crystals induced macrophage apoptosis/necrosis as demonstrated by MTT and flow cytometric analysis. Collectively, these results demonstrate that BCP crystals induce IL-1β secretion through activating the NLRP3 inflammasome. Furthermore, we speculate that IL-1 blockade could be a novel strategy to inhibit BCP-induced inflammation in human disease.

Proteomic analysis by two-dimensional electrophoresis to identify the normal human chondrocyte proteome stimulated by tumor necrosis factor alpha and interleukin-1beta

OBJECTIVE

To determine the intracellular proteome of normal human chondrocytes stimulated with interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha) and to ascertain differences in the protein expression patterns of these 2 cytokines.

METHODS

Normal human knee cartilage chondrocytes were incubated for 48 hours without stimulation or stimulated with IL-1beta (5 ng/ml) or with TNFalpha (10 ng/ml). For each culture condition, protein extracts from 4 normal subjects were pooled and resolved using 2-dimensional electrophoresis. Protein spots were visualized with Sypro stain, and qualitative and quantitative analyses were performed using PDQuest software. Protein spots were then identified by mass spectrometry, using matrix-assisted laser desorption ionization-time-of-flight/time-of-flight technology.

RESULTS

We identified 37 spots by mass spectrometry (MS) or by MS/MS, corresponding to 35 different proteins. In IL-1beta-stimulated chondrocytes, IL-1beta was found to modulate 22 proteins, as compared with unstimulated chondrocytes. All of these proteins except connective tissue growth factor (CCND2) were up-regulated. Proteins involved in cellular metabolism and energy (23%) that were up-regulated or induced by IL-1beta included nicotinamide phosphoribosyltransferase, long-chain fatty acid-coenzyme A ligase 4, delta-aminolevulinic acid dehydratase, triosephosphate isomerase, and an isoform of glyceraldehyde-3-phosphate dehydrogenase. In TNFalpha-stimulated chondrocytes, TNFalpha was found to modulate 20 proteins, as compared with unstimulated chondrocytes. All of these except chitinase 3-like 1 (cartilage glycoprotein 39), proteasome activator complex subunit 2, and G3PDH, were up-regulated. Eighteen proteins were differently modulated by IL-1beta and TNFalpha. Of these, 45% were related to metabolism.

CONCLUSION

IL-1beta and TNFalpha induce different profiles of intracellular protein expression in healthy human chondrocytes. Most of the proteins that are differently regulated are proteins that are implicated in the generation of cellular energy and in glycolysis.

Advances in understanding calcium-containing crystal disease

PURPOSE OF REVIEW

Calcium pyrophosphate dihydrate and basic calcium phosphate crystals are the two most common calcium-containing crystals involved in rheumatic diseases. Recent literature concerning their role in the pathogenesis of osteoarthritis is reviewed.

RECENT FINDINGS

In some instances, these calcium crystals might worsen osteoarthritis cartilage destruction. Laboratory investigations have identified determinants of cartilage calcification, especially a better characterization of matrix vesicle content and a better understanding of the regulation of inorganic pyrophosphate and phosphate concentration. In-vitro studies have highlighted new pathogenic mechanisms of calcium crystal-induced cell activation. Several intracellular signalling pathways are activated by calcium crystals. Recent studies suggested the implication of the inflammasome complex and a pivotal role for IL-1 in pseudogout attacks and chondrocyte apoptosis in basic calcium phosphate crystal-related arthropathies.

SUMMARY

Animal models of osteoarthritis and in-vitro studies using calcium pyrophosphate dihydrate and basic calcium phosphate crystals will improve our knowledge of these common crystals and could suggest new targets for drugs, as these common diseases are 'orphan' with respect to therapy.

Counterpoint: Hydroxyapatite crystal deposition is not intimately involved in the pathogenesis and progression of human osteoarthritis

The association of hydroxyapatite deposition with osteoarthritis pathogenesis and progression remains controversial, even after decades of study. Hydroxyapatite crystals are found in osteoarthritis in advanced disease only. Even then, hydroxyapatite crystals are found in such small amounts that special analytical techniques are required to detect the crystals. Further, the osteoarthritic joint fluid appears noninflammatory, suggesting that such hydroxyapatite crystals have very small effect on the pathologic process. Formal histopathologic evidence is scant, but hydroxyapatite crystal deposition within osteoarthritic synovium or cartilage is a rare event. Hydroxyapatite crystals may be present at end-stage osteoarthritis, but in insufficient amounts to contribute significantly to osteoarthritis pathogenesis or progression. This review critically examines the evidence from osteoarthritic synovial fluids, imaging, and histopathology to determine whether the well-characterized in vitro cellular reactions to hydroxyapatite apply to the pathogenesis of human osteoarthritis.