Unravelling the Basic Calcium Phosphate crystal-dependent chondrocyte protein secretome; a role for TGF-ß signaling.

OBJECTIVE: Basic Calcium Phosphate (BCP) crystals play an active role in the progression of osteoarthritis (OA). However, the cellular consequences remain largely unknown. Therefore, we characterized for the first time the changes in the protein secretome of human OA articular chondrocytes as a result of BCP stimulation using two unbiased proteomic analysis methods. METHOD: Isolated human OA articular chondrocytes were stimulated with BCP crystals and examined by Quantitative Reverse Transcription PCR (RT-qPCR) and enzyme-linked immune sorbent assay (ELISA) after twenty-four and forty-eight hours. Forty-eight hours conditioned media were analyzed by label-free liquid chromatography-tandem mass spectrometry (LC-MS/MS) and an antibody array. The activity of BCP dependent Transforming Growth Factor Beta (TGF-ß) signaling was analyzed by RT-qPCR and luciferase reporter assays. The molecular consequences regarding BCP-dependent TGF-ß signaling on BCP-dependent Interleukin 6 (IL-6) were investigated using specific pathway inhibitors. RESULTS: Synthesized BCP crystals induced IL-6 expression and secretion upon stimulation of human articular chondrocytes. Concomitant induction of catabolic gene expression was observed. Analysis of conditioned media revealed a complex and diverse response with a large number of proteins involved in TGF-ß signaling, both in activation of latent TGF-ß and TGF-ß superfamily members, which were increased compared to non-stimulated OA chondrocytes. Activity of this BCP driven TGF-ß signaling was confirmed by increased activity of expression of TGF-ß target genes and luciferase reporters. Inhibition of BCP driven TGF-ß signaling resulted in decreased IL-6 expression and secretion with a moderate effect on catabolic gene expression. CONCLUSION: BCP crystal stimulation resulted in a complex and diverse chondrocyte protein secretome response. An important role for BCP-dependent TGF-ß signaling was identified in development of a pro-inflammatory environment.

Ribosomal RNA-based epitranscriptomic regulation of chondrocyte translation and proteome in osteoarthritis.

OBJECTIVE: Osteoarthritis-related cartilage extracellular matrix remodeling is dependent on changes in chondrocyte protein expression. Yet, the role of ribosomes in chondrocyte translation regulation is unknown. In this exploratory study, we investigated ribosomal RNA (rRNA) epitranscriptomic-based ribosome heterogeneity in human articular chondrocytes and its relevance for osteoarthritis. METHODS: Sequencing-based rRNA 2'-O-methylation profiling analysis (RiboMethSeq) was performed on non-OA primary human articular chondrocytes (n = 5) exposed for 14 days to osteoarthritic synovial fluid (14 donors, pooled, 20% v/v). The SW1353 SNORD71 KO cell pool was generated using LentiCRISPRv2/Cas9. The mode of translation initiation and fidelity were determined by dual-luciferase reporters. The cellular proteome was analyzed by LC-MS/MS and collagen type I protein expression was evaluated by immunoblotting. Loading of COL1A1 mRNA into polysomes was determined by sucrose gradient ultracentrifugation and fractionation. RESULTS: We discovered that osteoarthritic synovial fluid instigates site-specific changes in the rRNA 2'-O-me profile of primary human articular chondrocytes. We identified five sites with differential 2'-O-me levels. The 2'-O-me status of 5.8S-U14 (one of identified differential 2'-O-me sites; decreased by 7.7%, 95% CI [0.9-14.5%]) was targeted by depleting the level of its guide snoRNA SNORD71 (50% decrease, 95% CI [33-64%]). This resulted in an altered ribosome translation modus (e.g., CrPV IRES, FC 3, 95% CI [2.2-4.1]) and promoted translation of COL1A1 mRNA which led to increased levels of COL1A1 protein (FC 1.7, 95% CI [1.3-2.0]). CONCLUSIONS: Our data identify a novel concept suggesting that articular chondrocytes employ rRNA epitranscriptomic mechanisms in osteoarthritis development.

Development of a cyclic-inverso AHSG/Fetuin A-based peptide for inhibition of calcification in osteoarthritis.

OBJECTIVE: Ectopic calcification is an important contributor to chronic diseases, such as osteoarthritis. Currently, no effective therapies exist to counteract calcification. We developed peptides derived from the calcium binding domain of human Alpha-2-HS-Glycoprotein (AHSG/Fetuin A) to counteract calcification. METHODS: A library of seven 30 amino acid (AA) long peptides, spanning the 118 AA Cystatin 1 domain of AHSG, were synthesized and evaluated in an in vitro calcium phosphate precipitation assay. The best performing peptide was modified (cyclic, retro-inverso and combinations thereof) and evaluated in cellular calcification models and the rat Medial Collateral Ligament Transection + Medial Meniscal Tear (MCLT + MMT) osteoarthritis model. RESULTS: A cyclic peptide spanning AA 1-30 of mature AHSG showed clear inhibition of calcium phosphate precipitation in the nM-pM range that far exceeded the biological activity of the linear peptide variant or bovine Fetuin. Biochemical and electron microscopy analyses of calcium phosphate particles revealed a similar, but distinct, mode of action in comparison with bFetuin. A cyclic-inverso variant of the AHSG 1-30 peptide inhibited calcification of human articular chondrocytes, vascular smooth muscle cells and during osteogenic differentiation of bone marrow derived stromal cells. Lastly, we evaluated the effect of intra-articular injection of the cyclic-inverso AHSG 1-30 peptide in a rat osteoarthritis model. A significant improvement was found in histopathological osteoarthritis score and animal mobility. Serum levels of IFNγ were found to be lower in AHSG 1-30 peptide treated animals. CONCLUSIONS: The cyclic-inverso AHSG 1-30 peptide directly inhibits the calcification process and holds the potential for future application in osteoarthritis.

Direct comparison of non-osteoarthritic and osteoarthritic synovial fluid-induced intracellular chondrocyte signaling and phenotype changes.

OBJECTIVE: Since the joint microenvironment and tissue homeostasis are highly dependent on synovial fluid, we aimed to compare the essential chondrocyte signaling signatures of non-osteoarthritic vs end-stage osteoarthritic knee synovial fluid. Moreover, we determined the phenotypic consequence of the distinct signaling patterns on articular chondrocytes. METHODS: Protein profiling of synovial fluid was performed using antibody arrays. Chondrocyte signaling and phenotypic changes induced by non-osteoarthritic and osteoarthritic synovial fluid were analyzed using a phospho-kinase array, luciferase-based transcription factor activity assays, and RT-qPCR. The origin of osteoarthritic synovial fluid signaling was evaluated by comparing the signaling responses of conditioned media from cartilage, synovium, infrapatellar fat pad and meniscus. Osteoarthritic synovial fluid induced pathway-phenotype relationships were evaluated using pharmacological inhibitors. RESULTS: Compared to non-osteoarthritic synovial fluid, osteoarthritic synovial fluid was enriched in cytokines, chemokines and growth factors that provoked differential MAPK, AKT, NFκB and cell cycle signaling in chondrocytes. Functional pathway analysis confirmed increased activity of these signaling events upon osteoarthritic synovial fluid stimulation. Tissue secretomes of osteoarthritic cartilage, synovium, infrapatellar fat pad and meniscus activated several inflammatory signaling routes. Furthermore, the distinct pathway signatures of osteoarthritic synovial fluid led to accelerated chondrocyte dedifferentiation via MAPK/ERK signaling, increased chondrocyte fibrosis through MAPK/JNK and PI3K/AKT activation, an elevated inflammatory response mediated by cPKC/NFκB, production of extracellular matrix-degrading enzymes by MAPK/p38 and PI3K/AKT routes, and enabling of chondrocyte proliferation. CONCLUSION: This study provides the first mechanistic comparison between non-osteoarthritic and osteoarthritic synovial fluid, highlighting MAPKs, cPKC/NFκB and PI3K/AKT as crucial OA-associated intracellular signaling routes.

Celecoxib-mediated reduction of prostanoid release in Hoffa's fat pad from donors with cartilage pathology results in an attenuated inflammatory phenotype.

OBJECTIVE: The Hoffa's fat pad (HFP) is an intra-articular adipose tissue which is situated under and behind the patella. It contains immune cells next to adipocytes and secretes inflammatory factors during osteoarthritis (OA). In this study, we compared the release profile of prostanoids, which are involved in inflammation, of HFP from OA patients vs patients with a focal cartilage defect (CD) without evidence for OA on MRI and investigated the prostanoid modulatory anti-inflammatory action of celecoxib on HFP. DESIGN: Prostanoid release was analyzed in conditioned medium of HFP explant cultures from 17 osteoarthritic patients and 12 CD patients, in the presence or absence of celecoxib. Furthermore, gene expression of COX enzymes and expression of genes indicative of a pro-inflammatory or anti-inflammatory phenotype of HFP was analyzed. RESULTS: Prostanoid release by HFP from knee OA patients clustered in two subgroups with high and low prostanoid producers. HFP from high prostanoid producers released higher amounts of PGE2, PGF2α and PGD2 compared to HFP from CD patients. PGE2 release by OA HFP was positively associated with expression of genes known to be expressed by M1 macrophages, indicating a role for macrophages. Celecoxib modulated prostanoid release by HFP, and also modulated the inflammation ratio towards a more favorable anti-inflammatory M2 phenotype, most effectively in patients with higher prostanoid release profiles. CONCLUSION: In knee OA patients with inflamed HFP's, celecoxib may exert positive effects in the knee joint via decreasing the release of prostanoids produced by the HFP and by favorably modulating the anti-inflammatory marker expression in HFP.

Atmospheric nitrogen deposition on petals enhances seed quality of the forest herb Anemone nemorosa.

Elevated atmospheric input of nitrogen (N) is currently affecting plant biodiversity and ecosystem functioning. The growth and survival of numerous plant species is known to respond strongly to N fertilisation. Yet, few studies have assessed the effects of N deposition on seed quality and reproductive performance, which is an important life-history stage of plants. Here we address this knowledge gap by assessing the effects of atmospheric N deposition on seed quality of the ancient forest herb Anemone nemorosa using two complementary approaches. By taking advantage of the wide spatiotemporal variation in N deposition rates in pan-European temperate and boreal forests over 2 years, we detected positive effects of N deposition on the N concentration (percentage N per unit seed mass, increased from 2.8% to 4.1%) and N content (total N mass per seed more than doubled) of A. nemorosa seeds. In a complementary experiment, we applied ammonium nitrate to aboveground plant tissues and the soil surface to determine whether dissolved N sources in precipitation could be incorporated into seeds. Although the addition of N to leaves and the soil surface had no effect, a concentrated N solution applied to petals during anthesis resulted in increased seed mass, seed N concentration and N content. Our results demonstrate that N deposition on the petals enhances bioaccumulation of N in the seeds of A. nemorosa. Enhanced atmospheric inputs of N can thus not only affect growth and population dynamics via root or canopy uptake, but can also influence seed quality and reproduction via intake through the inflorescences.

Impairment of the chondrogenic phase of endochondral ossification in vivo by inhibition of cyclooxygenase-2.

Many studies have reported on the effects of cyclooxygenase-2 (COX-2) inhibition on osteogenesis. However, far less is known about the effects of COX-2 inhibition on chondrogenic differentiation. Previous studies conducted by our group show that COX-2 inhibition influences in vitro chondrogenic differentiation. Importantly, this might have consequences on endochondral ossification processes occurring in vivo, such as bone fracture healing, growth plate development and ectopic generation of cartilage. The goal of our study was to investigate, in vivo, the effect of COX-2 inhibition by celecoxib on the cartilaginous phase of three different endochondral ossification scenarios. 10 mg/kg/day celecoxib or placebo were orally administered for 25 d to skeletally-immature New Zealand White rabbits (n = 6 per group). Endochondral ossification during fracture healing of a non-critical size defect in the ulna, femoral growth plate and ectopically-induced cartilaginous tissue were examined by radiography, micro-computed tomography (µ-CT), histology and gene expression analysis. Celecoxib treatment resulted in delayed bone fracture healing, alterations in growth plate development and progression of mineralisation. In addition, chondrogenic differentiation of ectopically-induced cartilaginous tissue was severely impaired by celecoxib. In conclusion, we found that celecoxib impaired the chondrogenic phase of endochondral ossification.

Interacting effects of warming and drought on regeneration and early growth of Acer pseudoplatanus and A. platanoides.

Climate change is acting on several aspects of plant life cycles, including the sexual reproductive stage, which is considered amongst the most sensitive life-cycle phases. In temperate forests, it is expected that climate change will lead to a compositional change in community structure due to changes in the dominance of currently more abundant forest tree species. Increasing our understanding of the effects of climate change on currently secondary tree species recruitment is therefore important to better understand and forecast population and community dynamics in forests. Here, we analyse the interactive effects of rising temperatures and soil moisture reduction on germination, seedling survival and early growth of two important secondary European tree species, Acer pseudoplatanus and A. platanoides. Additionally, we analyse the effect of the temperature experienced by the mother tree during seed production by collecting seeds of both species along a 2200-km long latitudinal gradient. For most of the responses, A. platanoides showed higher sensitivity to the treatments applied, and especially to its joint manipulation, which for some variables resulted in additive effects while for others only partial compensation. In both species, germination and survival decreased with rising temperatures and/or soil moisture reduction while early growth decreased with declining soil moisture content. We conclude that although A. platanoides germination and survival were more affected after the applied treatments, its initial higher germination and larger seedlings might allow this species to be relatively more successful than A. pseudoplatanus in the face of climate change.

Hypertrophic differentiation during chondrogenic differentiation of progenitor cells is stimulated by BMP-2 but suppressed by BMP-7.

OBJECTIVE: Bone morphogenic protein (BMP)-2 and BMP-7 are clinically approved and their recombinant proteins are used for bone tissue regenerative purposes and widely evaluated for cartilage regeneration. Previous comparison of the in vitro chondrogenic characteristics of BMP-2 vs BMP-7 did not address hypertrophic differentiation and characterizing their chondrogenic properties with a focus in on chondrocyte hypertrophy was topic of investigation in this study. DESIGN: Equimolar concentrations of BMP-2 or BMP-7 were added to chondrogenic differentiating ATDC5, human bone marrow stem cells or rabbit periosteal explants. Expression of Col2a1, Sox9, Acan, Col10a1, Runx2, ALP, Mmp13, Mef2c and Bapx1/Nkx3.2 was determined by reverse transcription-quantitative PCR (RT-qPCR) and immunoblotting. Glycosaminoglycan content, cell proliferation capacity and ALP activity were analysed by colourimetric analyses. Expression of Bapx1/Nkx3.2 and Sox9 was targeted by transfection of target specific siRNA duplexes. RESULTS: BMP-2 dose-dependently increased chondrocyte hypertrophy during chondrogenic differentiation of progenitor cells, whereas BMP-7 acted hypertrophy-suppressive and chondro-promotive. Both BMPs did not influence cell proliferation, but they did increase total glycosaminoglycan content. In a candidate approach Bapx1/Nkx3.2 was found to be involved in the BMP-7 mediated suppression of chondrocyte hypertrophy in ATDC5 cells. CONCLUSIONS: BMP-2 and BMP-7 display opposing actions on the chondrogenic outcome of differentiating progenitor cells: BMP-2 acts a specific inducer of chondrocyte hypertrophy, while BMP-7 appears to increase or maintain chondrogenic potential and prevent chondrocyte hypertrophy. Our results pave the way for an application-dependent differential use of BMP-2 or BMP-7.

Redifferentiation of dedifferentiated human articular chondrocytes: comparison of 2D and 3D cultures.

OBJECTIVE: Three-dimensional (3D) cultures are widely used to redifferentiate chondrocytes. However, the rationale behind the choice for 3D above two-dimensional (2D) cultures is poorly systematically investigated and mainly based on mRNA expression and glycosaminoglycan (GAG) content. The objective was to determine the differential redifferentiation characteristics of human articular chondrocytes (HACs) in monolayer, alginate beads and pellet culture by investigating mRNA expression, protein expression, GAG content and cell proliferation. DESIGN: Dedifferentiated HACs from six individuals were redifferentiated in identical medium conditions for 7 days in monolayer, alginate beads or pellet culture. Read-out parameters were expression of chondrogenic and hypertrophic mRNAs and proteins, GAG content and cell proliferation. RESULTS: 3D cultures specifically expressed chondrogenic mRNAs [collagen type II (COL2A1), SRY (sex determining region Y)-box 9 (SOX9), aggrecan (ACAN)), whereas 2D cultures did not. Hypertrophic mRNAs (collagen type X (COL10A1), runt-related transcription factor 2 (RUNX2), matrix metalloproteinase 13 (MMP13), vascular endothelial growth factor A (VEGFA), osteopontin (OPN), alkaline phosphatase (ALP)) were highly increased in 2D cultures and lower in 3D cultures. Collagen type I (COL1A1) mRNA expression was highest in 3D cultures. Protein expression supports most of the mRNA data, although an important discrepancy was found between mRNA and protein expression of COL2A1 and SOX9 in monolayer culture, stressing on the importance of protein expression analysis. GAG content was highest in 3D cultures, whereas chondrocyte proliferation was almost specific for 2D cultures. CONCLUSIONS: For redifferentiation of dedifferentiated HACs, 3D cultures exhibit the most potent chondrogenic potential, whereas a hypertrophic phenotype is best achieved in 2D cultures. This is the first human study that systematically evaluates the differences between proliferation, GAG content, protein expression and mRNA expression of commonly used 2D and 3D chondrocyte culture techniques.

Inhibition of cyclooxygenase-2 impacts chondrocyte hypertrophic differentiation during endochondral ossification.

Skeletogenesis and bone fracture healing involve endochondral ossification, a process during which cartilaginous primordia are gradually replaced by bone tissue. In line with a role for cyclooxygenase-2 (COX-2) in the endochondral ossification process, non-steroidal anti-inflammatory drugs (NSAIDs) were reported to negatively affect bone fracture healing due to impaired osteogenesis. However, a role for COX-2 activity in the chondrogenic phase of endochondral ossification has not been addressed before. We show that COX-2 activity fulfils an important regulatory function in chondrocyte hypertrophic differentiation. Our data reveal essential cross-talk between COX-2 and bone morphogenic protein-2 (BMP-2) during chondrocyte hypertrophic differentiation. BMP-2 mediated chondrocyte hypertrophy is associated with increased COX-2 expression and pharmacological inhibition of COX-2 activity by NSAIDs (e.g., Celecoxib) decreases hypertrophic differentiation in various chondrogenic models in vitro and in vivo, while leaving early chondrogenic development unaltered. Our findings demonstrate that COX-2 activity is a novel factor partaking in chondrocyte hypertrophy in the context of endochondral ossification and these observations provide a novel etiological perspective on the adverse effects of NSAIDs on bone fracture healing and have important implications for the use of NSAIDs during endochondral skeletal development.

Meningioma of the cavernous sinus in a child: case report and review of the literature.

Meningiomas infrequently develop in children, and their clinical picture is somewhat different than in adults. We describe here a case of a meningioma in a 9-year-old girl unusual in two aspects. Firstly, it arose from the cavernous sinus what is exceptional in children. Secondly, despite the big tumor mass the child was almost asymptomatic. The only symptoms at presentation were a slight facial asymmetry and minimal laterodeviation of her mandible. Those symptoms had not been noticed by her parents and were detected during careful routine dental examination. The clinical course was quite aggressive and several neurosurgical interventions were necessary. This case underlines the importance of careful medical and dental examination during routine checkup consultations and undertaking necessary diagnostic procedures aimed at elucidating of all detected, even minimal abnormalities.