P2Y receptors activated by diadenosine polyphosphates reestablish Ca(2+) transients in achondroplasic chondrocytes

Extracellular Nucleotides Selectively Induce Migration of Chondrocytes and Expression of Type II Collagen

The migration of chondrocytes from healthy to injured tissues is one of the most important challenges during cartilage repair. Additionally, maintenance of the chondrogenic phenotype remains another limitation, especially during monolayer culture in vitro. Using both the differentiated and undifferentiated chondrogenic ATDC5 cell line, we showed that extracellular nucleotides are able to increase the migration rate of chondrocytes without affecting their chondrogenic phenotype. We checked the potency of natural nucleotides (ATP, ADP, UTP, and UDP) as well as their stable phosphorothioate analogs, containing a sulfur atom in the place of one nonbridging oxygen atom in a phosphate group. We also detected P2y1, P2y2, P2y4, P2y6, P2y12, P2y13, and P2y14 mRNA transcripts for nucleotide receptors, demonstrating that P2y1 and P2y13 are highly upregulated in differentiated ATDC5 cells. We showed that ADPβS, UDPβS, and ADP are the best stimulators of migration of differentiated chondrocytes. Additionally, ADP and ADPβS positively affected the expression of type II collagen, a structural component of the cartilage matrix.

Purinergic Signalling: Therapeutic Developments

Purinergic signalling, i.e., the role of nucleotides as extracellular signalling molecules, was proposed in 1972. However, this concept was not well accepted until the early 1990's when receptor subtypes for purines and pyrimidines were cloned and characterised, which includes four subtypes of the P1 (adenosine) receptor, seven subtypes of P2X ion channel receptors and 8 subtypes of the P2Y G protein-coupled receptor. Early studies were largely concerned with the physiology, pharmacology and biochemistry of purinergic signalling. More recently, the focus has been on the pathophysiology and therapeutic potential. There was early recognition of the use of P1 receptor agonists for the treatment of supraventricular tachycardia and A2A receptor antagonists are promising for the treatment of Parkinson's disease. Clopidogrel, a P2Y12 antagonist, is widely used for the treatment of thrombosis and stroke, blocking P2Y12 receptor-mediated platelet aggregation. Diquafosol, a long acting P2Y2 receptor agonist, is being used for the treatment of dry eye. P2X3 receptor antagonists have been developed that are orally bioavailable and stable in vivo and are currently in clinical trials for the treatment of chronic cough, bladder incontinence, visceral pain and hypertension. Antagonists to P2X7 receptors are being investigated for the treatment of inflammatory disorders, including neurodegenerative diseases. Other investigations are in progress for the use of purinergic agents for the treatment of osteoporosis, myocardial infarction, irritable bowel syndrome, epilepsy, atherosclerosis, depression, autism, diabetes, and cancer.

A critical look at the function of the P2Y11 receptor

The P2Y11 receptor is a member of the purinergic receptor family. It has been overlooked, somewhat due to the lack of a P2ry11 gene orthologue in the murine genome, which prevents the generation of knockout mice, which have been so helpful for defining the roles of other P2Y receptors. Furthermore, some of the studies reported to date have methodological shortcomings, making it difficult to determine the function of P2Y11 with certainty. In this review, we discuss the lack of a murine "P2Y11-like receptor" and highlight the limitations of the currently available methods used to investigate the P2Y11 receptor. These methods include protein recognition with antibodies that show very little specificity, gene expression studies that completely overlook the existence of a fusion transcript between the adjacent PPAN gene and P2RY11, and agonists/antagonists reported to be specific for the P2Y11 receptor but which have not been tested for activity on numerous other adenosine 5'-triphosphate (ATP)-binding receptors. We suggest a set of criteria for evaluating whether a dataset describes effects mediated by the P2Y11 receptor. Following these criteria, we conclude that the current evidence suggests a role for P2Y11 in immune activation with cell type-specific effects.

The impact of polyphenols on chondrocyte growth and survival: a preliminary report

Background

Imbalances in the functional binding of fibroblast growth factors (FGFs) to their receptors (FGFRs) have consequences for cell proliferation and differentiation that in chondrocytes may lead to degraded cartilage. The toxic, proinflammatory, and oxidative response of cytokines and FGFs can be mitigated by dietary polyphenols.

Objective

We explored the possible effects of polyphenols in the management of osteoarticular diseases using a model based on the transduction of a mutated human FGFR3 (G380R) in murine chondrocytes. This mutation is present in most cases of skeletal dysplasia and is responsible for the overexpression of FGFR3 that, in the presence of its ligand, FGF9, results in toxic effects leading to altered cellular growth.

Design

Different combinations of dietary polyphenols derived from plant extracts were assayed in FGFR3 (G380R) mutated murine chondrocytes, exploring cell survival, chloride efflux, extracellular matrix (ECM) generation, and grade of activation of mitogen-activated protein kinases.

Results

Bioactive compounds from Hibiscus sabdariffa reversed the toxic effects of FGF9 and restored normal growth, suggesting a probable translation to clinical requests in humans. Indeed, these compounds activated the intracellular chloride efflux, increased ECM generation, and stimulated cell proliferation. The inhibition of mitogen-activated protein kinase phosphorylation was interpreted as the main mechanism governing these beneficial effects.

Conclusions

These findings support the rationale behind the encouragement of the development of drugs that repress the overexpression of FGFRs and suggest the dietary incorporation of supplementary nutrients in the management of degraded cartilage.

Purinergic signalling in the musculoskeletal system

It is now widely recognised that extracellular nucleotides, signalling via purinergic receptors, participate in numerous biological processes in most tissues. It has become evident that extracellular nucleotides have significant regulatory effects in the musculoskeletal system. In early development, ATP released from motor nerves along with acetylcholine acts as a cotransmitter in neuromuscular transmission; in mature animals, ATP functions as a neuromodulator. Purinergic receptors expressed by skeletal muscle and satellite cells play important pathophysiological roles in their development or repair. In many cell types, expression of purinergic receptors is often dependent on differentiation. For example, sequential expression of P2X5, P2Y1 and P2X2 receptors occurs during muscle regeneration in the mdx model of muscular dystrophy. In bone and cartilage cells, the functional effects of purinergic signalling appear to be largely negative. ATP stimulates the formation and activation of osteoclasts, the bone-destroying cells. Another role appears to be as a potent local inhibitor of mineralisation. In osteoblasts, the bone-forming cells, ATP acts via P2 receptors to limit bone mineralisation by inhibiting alkaline phosphatase expression and activity. Extracellular ATP additionally exerts significant effects on mineralisation via its hydrolysis product, pyrophosphate. Evidence now suggests that purinergic signalling is potentially important in several bone and joint disorders including osteoporosis, rheumatoid arthritis and cancers. Strategies for future musculoskeletal therapies might involve modulation of purinergic receptor function or of the ecto-nucleotidases responsible for ATP breakdown or ATP transport inhibitors.

Using antibodies against P2Y and P2X receptors in purinergic signaling research

The broad expression pattern of the G protein-coupled P2Y receptors has demonstrated that these receptors are fundamental determinants in many physiological responses, including neuromodulation, vasodilation, inflammation, and cell migration. P2Y receptors couple either G(q) or G(i) upon activation, thereby activating different signaling pathways. Ionotropic ATP (P2X) receptors bind extracellular nucleotides, a signal which is transduced within the P2X protein complex into a cation channel opening, which usually leads to intracellular calcium concentration elevation. As such, this family of proteins initiates or shapes several cellular processes including synaptic transmission, gene expression, proliferation, migration, and apoptosis. The ever-growing range of applications for antibodies in the last 30 years attests to their major role in medicine and biological research. Antibodies have been used as therapeutic tools in cancer and inflammatory diseases, as diagnostic reagents (flow cytometry, ELISA, and immunohistochemistry, to name a few applications), and in widespread use in biological research, including Western blot, immunoprecipitation, and ELISPOT. In this article, we will showcase several of the advances that scientists around the world have achieved using the line of antibodies developed at Alomone Labs for P2Y and P2X receptors.

Effects of diadenosine tetraphosphate on FGF9-induced chloride flux changes in achondroplastic chondrocytes

Achondroplasia, the most common type of dwarfism, is characterized by a mutation in the fibroblast growth factor receptor 3 (FGFR3). Achondroplasia is an orphan pathology with no pharmacological treatment so far. However, the possibility of using the dinucleotide diadenosine tetraphosphate (Ap(4)A) with therapeutic purposes in achondroplasia has been previously suggested. The pathogenesis involves the constitutive activation of FGFR3, resulting in altered biochemical and physiological processes in chondrocytes. Some of these altered processes can be influenced by changes in cell volume and ionic currents. In this study, the action of mutant FGFR3 on chondrocyte size and chloride flux in achondroplastic chondrocytes was investigated as well as the effect of the Ap(4)A on these processes triggered by mutant FGFR3. Stimulation with the fibroblast growth factor 9 (FGF9), the preferred ligand for FGFR3, induced an enlarged achondroplastic chondrocyte size and an increase in the intracellular chloride concentration, suggesting the blockade of chloride efflux. Treatment with the Ap(4)A reversed the morphological changes triggered by FGF9 and restored the chloride efflux. These data provide further evidence for the therapeutic potential of this dinucleotide in achondroplasia treatment.

Boron and fish oil have different beneficial effects on strength and trabecular microarchitecture of bone

An experiment was performed to determine whether boron deprivation would adversely affect vertebra (trabecular) bone microarchitecture, and whether any adverse effect would be modified by dietary fatty acid composition. Female rats were fed diets containing 0.1mg (9 micromol) boron/kg in a factorial arrangement with variables of supplemental boron at 0 (boron-deprived) or 3 (boron-adequate) mg (278 micromol)/kg and fat sources of 75 g safflower oil/kg or 65 g fish (menhaden)oil/kg plus 10 g linoleic acid/kg. After 6 weeks, six females per treatment were bred. Dams and pups continued on their respective diets through gestation, lactation, and after weaning. At age 21 weeks, the microarchitecture of the fourth lumbar vertebrae from 12 randomly selected pups from each treatment was determined by microcomputed tomography. Boron deprivation decreased bone volume fraction and increased trabecular separation and structural model index. Boron deprivation decreased trabecular thickness when the dietary oil was safflower. A three-point bending test for bone strength found that boron deprivation decreased the maximum force needed to break the femur. Feeding fish oil instead of safflower oil decreased connectivity density in vertebrae of boron-deficient but not in boron-adequate rats. Fish oil instead of safflower oil increased the maximum force to break and the bending moment of the femur, especially in rats fed adequate boron. The findings confirm that boron and fish oil are beneficial to cortical bone strength, and show that nutritional intakes of boron are beneficial for trabecular bone microarchitecture and influence the beneficial effects of fish oil on bone.