RESUMEN
Osteomalacia is a bone-demineralizing disease of adulthood, often caused by hypovitaminosis D. Current animal models of the disease mimic osteomalacia as a consequence of gastric bypass or toxic exposure to metals, but a relevant model of diet-induced osteomalacia is lacking. For that purpose, 7-month-old female Sprague Dawley rats were randomly assigned into 2 weight-stratified groups and maintained for 4 months on synthetic diets containing negligible or normal levels of vitamin D. The dietary regimen resulted in vitamin D deficiency as measured by 25-hydroxyvitamin D serum levels; however, hypovitaminosis D per se did not affect biomarkers of calcium metabolism and bone turnover, nor did it result in increased osteoid. Thus, vitamin D depletion through the diet was found to be insufficient to induce an osteomalacia-like phenotype in the adult rat. After 4 months, the phosphate content of the vitamin D-depleted diet had decreased to 0.16% (calcium:phosphorus ratio of 5.85), resulting in an osteomalacic-like condition (trabecular osteoid surface/bone surface constituted 33%; CI, 26-40). The diet change also affected both metabolic and bone turnover biomarkers, including significantly suppressing serum fibroblast growth factor 23. Furthermore, decreased dietary phosphate in a vitamin D-depleted diet led to microarchitectural changes of trabecular and cortical bone, lower bone mass density, lower bone mass content and decreased bone strength, all indicating reduced bone quality. Taken together, our results show that osteomalacia can be induced in the adult female rat by depleting vitamin D and lowering phosphate content in the diet.
Asunto(s)
Hipofosfatemia/complicaciones , Osteomalacia/etiología , Deficiencia de Vitamina D/complicaciones , Animales , Remodelación Ósea , Huesos/metabolismo , Calcificación Fisiológica , Calcio/sangre , Calcio/orina , Femenino , Hipofosfatemia/metabolismo , Hipofosfatemia/patología , Osteomalacia/metabolismo , Osteomalacia/patología , Fosfatos/sangre , Fosfatos/orina , Fósforo/sangre , Fósforo/orina , Ratas , Ratas Sprague-Dawley , Vitamina D/análogos & derivados , Vitamina D/sangre , Deficiencia de Vitamina D/metabolismo , Deficiencia de Vitamina D/patologíaRESUMEN
The ionotropic ATP-gated P2X7 receptor (P2X7R) is involved in the regulation of many physiological functions including bone metabolism. Several studies on osteoblasts from rodents and human osteoblast-like cell lines have addressed the expression and function of P2X7R on these bone-forming cells however; its role in human primary osteoblasts has not yet been reported. The aim of this study was to assess the expression of the P2X7R in bone marrow-derived stromal cells and in primary human trabecular osteoblasts and to determine the function in bone formation and cell signaling. We report that osteoblasts derived from human trabecular explants express a functional P2X7R capable of agonist-induced increase in intracellular calcium concentration and a positive permeability to fluorescent dyes. These osteoblasts are fully differentiated cells with alkaline phosphatase activity and the ability to form mineralized nodules. We show that the transcriptional regulation of osteoblastic markers can be modulated by P2X7R activity or blockade thereby influencing the differentiation, proliferation and bone matrix formation by these primary human osteoblasts. Finally, we demonstrate that the P2X7R is involved in propagation of mechanically-induced intercellular signaling in addition to the known mechanisms involving calcium signaling via P2Y2 receptors and gap junction.
Asunto(s)
Osteoblastos/citología , Osteoblastos/metabolismo , Receptores Purinérgicos P2X7/metabolismo , Transducción de Señal , Fosfatasa Alcalina/metabolismo , Biomarcadores/metabolismo , Células de la Médula Ósea/citología , Calcificación Fisiológica , Señalización del Calcio , Hueso Esponjoso/citología , Muerte Celular , Proliferación Celular , Células Cultivadas , Perfilación de la Expresión Génica , Regulación de la Expresión Génica , Humanos , Células del Estroma/citología , Células del Estroma/metabolismoRESUMEN
Extracellular pyrimidines activate P2Y receptors on both smooth muscle cells and endothelial cells, leading to vasoconstriction and relaxation respectively. The aim of this study was to utilize P2Y knock-out (KO) mice to determine which P2Y receptor subtype are responsible for the contraction and relaxation in the coronary circulation and to establish whether P2Y receptors have different functions along the mouse coronary vascular tree. We tested stable pyrimidine analogues on isolated coronary arteries from P2Y2 and P2Y6 receptor KO mice in a myograph setup. In larger diameter segments of the left descending coronary artery (LAD) (lumen diameter~150µm) P2Y6 is the predominant contractile receptor for both UTP (uridine triphosphate) and UDP (uridine diphosphate) induced contraction. In contrast, P2Y2 receptors mediate endothelial-dependent relaxation. However, in smaller diameter LAD segments (lumen diameter~50µm), the situation is opposite, with P2Y2 being the contractile receptor and P2Y6 functioning as a relaxant receptor along with P2Y2. Immunohistochemistry was used to confirm smooth muscle and endothelial localization of the receptors. In vivo measurements of blood pressure in WT mice revealed a biphasic response to the stable analogue UDPßS. Based on the changes in P2Y receptor functionality along the mouse coronary arterial vasculature, we propose that UTP can act as a vasodilator downstream of its release, after being degraded to UDP, without affecting the contractile pyrimidine receptors. We also propose a model, showing physiological relevance for the changes in purinergic receptor functionality along the mouse coronary vascular tree.
Asunto(s)
Vasos Coronarios/metabolismo , Pirimidinas/metabolismo , Receptores Purinérgicos P2Y2/metabolismo , Receptores Purinérgicos P2/metabolismo , Animales , Presión Sanguínea/efectos de los fármacos , Endotelio/metabolismo , Femenino , Expresión Génica , Inmunohistoquímica , Masculino , Ratones , Ratones Noqueados , Modelos Biológicos , Miocitos del Músculo Liso/fisiología , Pirimidinas/farmacología , Receptores Purinérgicos P2/genética , Receptores Purinérgicos P2Y2/genética , Uridina Difosfato/metabolismo , Uridina Difosfato/farmacología , Vasoconstricción/efectos de los fármacosRESUMEN
Osteocytes are considered the primary mechanosensors of bone, but the signaling pathways they apply in mechanotransduction are still incompletely investigated and characterized. A growing body of data strongly indicates that P2 receptor signaling among osteoblasts and osteoclasts has regulatory effects on bone remodeling. Therefore, we hypothesized that ATP signaling is also applied by osteocytes in mechanotransduction. We applied a short fluid pulse on MLO-Y4 osteocyte-like cells during real-time detection of ATP and demonstrated that mechanical stimulation activates the acute release of ATP and that these acute ATP signals are fine-tuned according to the magnitude of loading. ATP release was then challenged by pharmacological inhibitors, which indicated a vesicular release pathway for acute ATP signals. Finally, we showed that osteocytes express functional P2X2 and P2X7 receptors and respond to even low concentrations of nucleotides by increasing intracellular calcium concentration. These results indicate that in osteocytes, vesicular ATP release is an acute mediator of mechanical signals and the magnitude of loading. These and previous results, therefore, implicate purinergic signaling as an early signaling pathway in osteocyte mechanotransduction.
Asunto(s)
Adenosina Trifosfato/metabolismo , Mecanotransducción Celular , Osteocitos/metabolismo , Animales , Remodelación Ósea , Señalización del Calcio , Línea Celular , Conexina 43/metabolismo , Conexinas/metabolismo , Expresión Génica , Ratones Endogámicos BALB C , Proteínas del Tejido Nervioso/metabolismo , Osteocitos/fisiología , Receptores Purinérgicos P2X/genética , Receptores Purinérgicos P2X/metabolismo , Sistemas de Mensajero SecundarioRESUMEN
The ATP receptor P2X7 (P2X7R or P2RX7) has a key role in inflammation and immunity, but its possible roles in cancer are not firmly established. In the present study, we investigated the effect of host genetic deletion of P2X7R in the mouse on the growth of B16 melanoma or CT26 colon carcinoma cells. Tumor size and metastatic dissemination were assessed by in vivo calliper and luciferase luminescence emission measurements along with postmortem examination. In P2X7R-deficient mice, tumor growth and metastatic spreading were accelerated strongly, compared with wild-type (wt) mice. Intratumoral IL-1ß and VEGF release were drastically reduced, and inflammatory cell infiltration was abrogated nearly completely. Similarly, tumor growth was also greatly accelerated in wt chimeric mice implanted with P2X7R-deficient bone marrow cells, defining hematopoietic cells as a sufficient site of P2X7R action. Finally, dendritic cells from P2X7R-deficient mice were unresponsive to stimulation with tumor cells, and chemotaxis of P2X7R-less cells was impaired. Overall, our results showed that host P2X7R expression was critical to support an antitumor immune response, and to restrict tumor growth and metastatic diffusion.
Asunto(s)
Neoplasias del Colon/genética , Inmunidad Innata/genética , Melanoma Experimental/genética , Receptores Purinérgicos P2X7/genética , Adenosina Trifosfato/metabolismo , Animales , Neoplasias del Colon/patología , Regulación Neoplásica de la Expresión Génica , Humanos , Interleucina-1beta/biosíntesis , Macrófagos/metabolismo , Macrófagos/patología , Melanoma Experimental/inmunología , Melanoma Experimental/patología , Ratones , Receptores Purinérgicos P2X7/deficiencia , Factor A de Crecimiento Endotelial Vascular/biosíntesisRESUMEN
Circulating interleukin (IL)-18 is elevated in obesity, but paradoxically causes hypophagia. We hypothesized that IL-18 may attenuate high-fat diet (HFD)-induced insulin resistance by activating AMP-activated protein kinase (AMPK). We studied mice with a global deletion of the α-isoform of the IL-18 receptor (IL-18R(-/-)) fed a standard chow or HFD. We next performed gain-of-function experiments in skeletal muscle, in vitro, ex vivo, and in vivo. We show that IL-18 is implicated in metabolic homeostasis, inflammation, and insulin resistance via mechanisms involving the activation of AMPK in skeletal muscle. IL-18R(-/-) mice display increased weight gain, ectopic lipid deposition, inflammation, and reduced AMPK signaling in skeletal muscle. Treating myotubes or skeletal muscle strips with IL-18 activated AMPK and increased fat oxidation. Moreover, in vivo electroporation of IL-18 into skeletal muscle activated AMPK and concomitantly inhibited HFD-induced weight gain. In summary, IL-18 enhances AMPK signaling and lipid oxidation in skeletal muscle implicating IL-18 in metabolic homeostasis.
Asunto(s)
Proteínas Quinasas Activadas por AMP/metabolismo , Resistencia a la Insulina/fisiología , Interleucina-18/metabolismo , Músculo Esquelético/enzimología , Aumento de Peso/fisiología , Proteínas Quinasas Activadas por AMP/genética , Animales , Composición Corporal/genética , Composición Corporal/fisiología , Calorimetría Indirecta , Femenino , Resistencia a la Insulina/genética , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Reacción en Cadena en Tiempo Real de la Polimerasa , Receptores de Interleucina-18/deficiencia , Receptores de Interleucina-18/genética , Aumento de Peso/genéticaRESUMEN
Parathyroid hormone (PTH) and PTH(1-34) have been shown to promote bone healing in several animal studies. It is known that the mechanical environment is important in fracture healing. Furthermore, PTH and mechanical loading has been suggested to have synergistic effects on intact bone. The aim of the present study was to investigate whether the effect of PTH(1-34) on fracture healing in rats was influenced by reduced mechanical loading. For this purpose, we used female, 25-week-old ovariectomized rats. Animals were subjected to closed midshaft fracture of the right tibia 10 weeks after ovariectomy. Five days before fracture, half of the animals received Botulinum Toxin A injections in the muscles of the fractured leg to induce muscle paralysis (unloaded group), whereas the other half received saline injections (control group). For the following 8 weeks, half of the animals in each group received injections of hPTH(1-34) (20 µg/kg/day) and the other half received vehicle treatment. Fracture healing was assessed by radiology, dual-energy X-ray absorptiometry (DXA), histology, and bone strength analysis. We found that unloading reduced callus area significantly, whereas no effects of PTH(1-34) on callus area were seen in neither normally nor unloaded animals. PTH(1-34) increased callus bone mineral density (BMD) and bone mineral content (BMC) significantly, whereas unloading decreased callus BMD and BMC significantly. PTH(1-34) treatment increased bone volume of the callus in both unloaded and control animals. PTH(1-34) treatment increased ultimate force of the fracture by 63% in both control and unloaded animals and no interaction of the two interventions could be detected. PTH(1-34) was able to stimulate bone formation in normally loaded as well as unloaded intact bone. In conclusion, the study confirms the stimulatory effect of PTH(1-34) on fracture healing, and our data suggest that PTH(1-34) is able to promote fracture healing, as well as intact bone formation during conditions of reduced mechanical loading.
Asunto(s)
Curación de Fractura/efectos de los fármacos , Hormona Paratiroidea/farmacología , Absorciometría de Fotón , Animales , Fenómenos Biomecánicos , Densidad Ósea/efectos de los fármacos , Callo Óseo/diagnóstico por imagen , Callo Óseo/efectos de los fármacos , Callo Óseo/patología , Callo Óseo/fisiopatología , Femenino , Fémur/diagnóstico por imagen , Fémur/efectos de los fármacos , Fémur/patología , Fémur/fisiopatología , Humanos , Movimiento/efectos de los fármacos , Tamaño de los Órganos/efectos de los fármacos , Ratas , Ratas Sprague-Dawley , Tibia/diagnóstico por imagen , Tibia/efectos de los fármacos , Tibia/patología , Tibia/fisiopatología , Soporte de PesoRESUMEN
PURPOSE: Adipose derived mesenchymal stem cells (ADMSCs) may be osteogenic, may generate neoangiogenisis and may be progenitors for differentiated osteoblast mineralization. Titanium granules may be suitable as carriers for these cells. The aim was to demonstrate the osteogenic potential of ADMSCs and the effect of porous non-oxidized (Ti) and oxidized titanium (TiO2) granules as carriers for ADMSCs mineralization in vitro. MATERIALS AND METHODS: ADMSCs were isolated, cultivated in osteoblast medium and evaluated for alkaline phosphatase (ALP) assay, RNA isolation, and ALP staining. Osteoblast in vitro mineralization cells without granules or seeded on Ti or TiO2 granules were evaluated for Alizarin Red assay and RNA isolation for later gene expressing. RESULTS: ADMSCs express osteoblastic lineage genes, CBFA-1 and stain strongly for ALP. Mineralization was significantly higher for cells seeded on TiO2 than on Ti granules or pure cells. Expression of ALPL and RUNX2 was significantly higher for cells seeded on TiO2 granules and expression of COL1α1 for pure cells was significantly higher than for cells seeded on granules. CONCLUSION: ADMSCs have osteogenic potential. Mineralization was significantly high when cells were seeded on TiO2 granules. TiO2 granules may be used as carriers for adipose derived mesenchymal osteoblastic cells from laboratory bench to the patient.
Asunto(s)
Tejido Adiposo/citología , Calcificación Fisiológica/fisiología , Células Madre Mesenquimatosas/fisiología , Osteoblastos/fisiología , Osteogénesis/fisiología , Andamios del Tejido/química , Titanio/química , Fosfatasa Alcalina/análisis , Animales , Antraquinonas , Materiales Biocompatibles/química , Técnicas de Cultivo de Célula , Diferenciación Celular/fisiología , Linaje de la Célula , Colágeno Tipo I/análisis , Cadena alfa 1 del Colágeno Tipo I , Colorantes , Subunidad alfa 1 del Factor de Unión al Sitio Principal/análisis , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos , Neovascularización Fisiológica/fisiología , PorosidadRESUMEN
The P2Y(2) receptor is a G-protein-coupled receptor with adenosine 5'-triphosphate (and UTP) as natural ligands. It is thought to be involved in bone physiology in an anti-osteogenic manner. As several non-synonymous single nucleotide polymorphisms (SNPs) have been identified within the P2Y(2) receptor gene in humans, we examined associations between genetic variations in the P2Y(2) receptor gene and bone mineral density (BMD) (i.e., osteoporosis risk), in a cohort of fracture patients. Six hundred and ninety women and 231 men aged ≥50 years, visiting an osteoporosis outpatient clinic at Maastricht University Medical Centre for standard medical follow-up after a recent fracture, were genotyped for three non-synonymous P2Y(2) receptor gene SNPs. BMD was measured at three locations (total hip, lumbar spine, and femoral neck) using dual-energy X-ray absorptiometry. Differences in BMD between different genotypes were tested using analysis of covariance. In women, BMD values at all sites were significantly different between the genotypes for the Leu46Pro polymorphism, with women homozygous for the variant allele showing the highest BMD values (0.05 > p > 0.01). The Arg312Ser and Arg334Cys polymorphisms showed no differences in BMD values between the different genotypes. This is the first report that describes the association between the Leu46Pro polymorphism of the human P2Y(2) receptor and the risk of osteoporosis.
Asunto(s)
Densidad Ósea/genética , Fracturas Óseas/epidemiología , Fracturas Óseas/genética , Osteoporosis/epidemiología , Osteoporosis/genética , Polimorfismo de Nucleótido Simple/genética , Receptores Purinérgicos P2Y2/genética , Absorciometría de Fotón , Anciano , Estudios de Cohortes , ADN/sangre , ADN/química , Femenino , Frecuencia de los Genes , Variación Genética , Genotipo , Haplotipos , Humanos , Masculino , Persona de Mediana Edad , Países Bajos/epidemiología , Medición de Riesgo , Saliva/químicaRESUMEN
The purinergic P2X7 receptor is expressed by bone cells and has been shown to be important in both bone formation and bone resorption. In this study we investigated the importance of the genetic background of the mouse strains on which the P2X7 knock-out models were based by comparing bone status of a new BALB/cJ P2X7(-/-) strain with a previous one based on the C57BL/6 strain. Female four-month-old mice from both strains were DXA scanned on a PIXImus densitometer; femurs were collected for bone strength measurements and serum for bone marker analysis. Bone-related parameters that were altered only slightly in the B6 P2X7(-/-) became significantly altered in the BALB/cJ P2X7(-/-) when compared to their wild type littermates. The BALB/cJ P2X7(-/-) showed reduced levels of serum C-telopeptide fragment (s-CTX), higher bone mineral density, and increased bone strength compared to the wild type littermates. In conclusion, we have shown that the genetic background of P2X7(-/-) mice strongly influences the bone phenotype of the P2X7(-/-) mice and that P2X7 has a more significant regulatory role in bone remodeling than found in previous studies.
RESUMEN
Macrophages from mouse strains with the naturally occurring mutation P451L in the purinergic receptor P2X7 have impaired responses to agonists (1). Because P2X7 receptors are expressed in bone cells and are implicated in bone physiology, we asked whether strains with the P451L mutation have a different bone phenotype. By sequencing the most common strains of inbred mice, we found that only a few strains (BALB, NOD, NZW, and 129) were harboring the wild allelic version of the mutation (P451) in the gene for the purinergic receptor P2X7. The strains were compared by means of dual energy X-ray absorptiometry (DXA), bone markers, and three-point bending. Cultured osteoclasts were used in the ATP-induced pore formation assay. We found that strains with the P451 allele (BALB/cJ and 129X1/SvJ) had stronger femurs and higher levels of the bone resorption marker C-telopeptide collagen (CTX) compared to C57Bl/6 (B6) and DBA/2J mice. In strains with the 451L allele, pore-formation activity in osteoclasts in vitro was lower after application of ATP. In conclusion, two strains with the 451L allele of the naturally occurring mutation P451L, have weaker bones and lower levels of CTX, suggesting lower resorption levels in these animals, which could be related to the decreased ATP-induced pore formation observed in vitro. The importance of these findings for the interpretation of the earlier reported effects of P2X7 in mice is discussed, along with strategies in developing a murine model for testing the therapeutic effects of P2X7 agonists and antagonists upon postmenopausal osteoporosis.
RESUMEN
Clopidogrel (Plavix), a selective P2Y(12) receptor antagonist, is widely prescribed to reduce the risk of heart attack and stroke and acts via the inhibition of platelet aggregation. Accumulating evidence now suggests that extracellular nucleotides, signaling through P2 receptors, play a significant role in bone, modulating both osteoblast and osteoclast function. In this study, we investigated the effects of clopidogrel treatment on (1) bone cell formation, differentiation, and activity in vitro; and (2) trabecular and cortical bone parameters in vivo. P2Y(12) receptor expression by osteoblasts and osteoclasts was confirmed using qPCR and Western blotting. Clopidogrel at 10 µM and 25 µM inhibited mineralized bone nodule formation by 50% and >85%, respectively. Clopidogrel slowed osteoblast proliferation with dose-dependent decreases in cell number (25% to 40%) evident in differentiating osteoblasts (day 7). A single dose of 10 to 25 µM clopidogrel to mature osteoblasts also reduced cell viability. At 14 days, ≥10 µM clopidogrel decreased alkaline phosphatase (ALP) activity by ≤70% and collagen formation by 40%, while increasing adipocyte formation. In osteoclasts, ≥1 µM clopidogrel inhibited formation, viability and resorptive activity. Twenty-week-old mice (n = 10-12) were ovariectomized or sham treated and dosed orally with clopidogrel (1 mg/kg) or vehicle (NaCl) daily for 4 weeks. Dual-energy X-ray absorptiometry (DXA) analysis showed clopidogrel-treated animals had decreases of 2% and 4% in whole-body and femoral bone mineral density (BMD), respectively. Detailed analysis of trabecular and cortical bone using micro-computed tomography (microCT) showed decreased trabecular bone volume in the tibia (24%) and femur (18%) of clopidogrel-treated mice. Trabecular number was reduced 20%, while trabecular separation was increased up to 15%. Trabecular thickness and cortical bone parameters were unaffected. Combined, these findings indicate that long-term exposure of bone cells to clopidogrel in vivo could negatively impact bone health.
Asunto(s)
Osteoblastos/efectos de los fármacos , Osteoblastos/metabolismo , Osteoclastos/efectos de los fármacos , Osteoclastos/metabolismo , Antagonistas del Receptor Purinérgico P2Y/farmacología , Ticlopidina/análogos & derivados , Fosfatasa Alcalina/metabolismo , Animales , Compuestos Azo , Biomarcadores/sangre , Densidad Ósea/efectos de los fármacos , Resorción Ósea/patología , Resorción Ósea/fisiopatología , Huesos/diagnóstico por imagen , Huesos/efectos de los fármacos , Huesos/patología , Huesos/fisiopatología , Recuento de Células , Supervivencia Celular/efectos de los fármacos , Células Cultivadas , Clopidogrel , Colágeno/metabolismo , AMP Cíclico/metabolismo , Regulación de la Expresión Génica/efectos de los fármacos , Espacio Intracelular/efectos de los fármacos , Espacio Intracelular/metabolismo , Ratones , Osteoblastos/patología , Osteoclastos/patología , Osteogénesis/efectos de los fármacos , Radiografía , Receptores Purinérgicos P2Y12/metabolismo , Solubilidad , Coloración y Etiquetado , Ticlopidina/farmacologíaRESUMEN
Long-term stability of titanium implants are dependent on a variety of factors. Nanocoating with organic molecules is one of the methods used to improve osseointegration. Therefore, the aim of this study is to evaluate the in vitro effect of nanocoating with pectic rhamnogalacturonan-I (RG-I) on surface properties and osteoblasts response. Three different RG-Is from apple and lupin pectins were modified and coated on amino-functionalized tissue culture polystyrene plates (aminated TCPS). Surface properties were evaluated by scanning electron microscopy, contact angle measurement, atomic force microscopy, and X-ray photoelectron spectroscopy. The effects of nanocoating on proliferation, matrix formation and mineralization, and expression of genes (real-time PCR) related to osteoblast differentiation and activity were tested using human osteoblast-like SaOS-2 cells. It was shown that RG-I coatings affected the surface properties. All three RG-I induced bone matrix formation and mineralization, which was also supported by the finding that gene expression levels of alkaline phosphatase, osteocalcin, and collagen type-1 were increased in cells cultured on the RG-I coated surface, indicating a more differentiated osteoblastic phenotype. This makes RG-I coating a promising and novel candidate for nanocoatings of implants.
Asunto(s)
Materiales Biocompatibles Revestidos/química , Nanoestructuras/química , Osteoblastos/fisiología , Pectinas/química , Prótesis e Implantes , Animales , Línea Celular , Materiales Biocompatibles Revestidos/metabolismo , Humanos , Lupinus/química , Malus/química , Ensayo de Materiales , Microscopía de Fuerza Atómica , Estructura Molecular , Oseointegración , Osteoblastos/citología , Pectinas/metabolismo , Espectroscopía de Fotoelectrones , Propiedades de SuperficieRESUMEN
The action of extracellular nucleotides is mediated by ionotropic P2X receptors and G-protein coupled P2Y receptors. The human genome contains 7 P2X and 8 P2Y receptor genes. Knockout mice strains are available for most of them. As their phenotypic analysis is progressing, bone abnormalities have been observed in an impressive number of these mice: distinct abnormalities in P2X7-/- mice, depending on the gene targeting construct and the genetic background, decreased bone mass in P2Y1-/- mice, increased bone mass in P2Y2-/- mice, decreased bone resorption in P2Y6-/- mice, decreased bone formation and bone resorption in P2Y13-/- mice. These findings demonstrate the unexpected importance of extracellular nucleotide signalling in the regulation of bone metabolism via multiple P2 receptors and distinct mechanisms involving both osteoblasts and osteoclasts.
Asunto(s)
Huesos/anomalías , Huesos/metabolismo , Fenotipo , Receptores Purinérgicos P2/genética , Transducción de Señal/genética , Animales , Densidad Ósea/genética , Resorción Ósea/genética , Espacio Extracelular/metabolismo , Ratones , Ratones Noqueados , Nucleótidos/metabolismoRESUMEN
The purinergic P2X7 receptor is implicated in both neuropathic and inflammatory pain, and has been suggested as a possible target in pain treatment. However, the specific role of the P2X7 receptor in bone cancer pain is unknown. We demonstrated that BALB/cJ P2X7 receptor knockout (P2X7R KO) mice were susceptible to bone cancer pain and moreover had an earlier onset of pain-related behaviours compared with cancer-bearing, wild-type mice. Furthermore, acute treatment with the selective P2X7 receptor antagonist, A-438079, failed to alleviate pain-related behaviours in models of bone cancer pain with and without astrocyte activation (BALB/cJ or C3H mice inoculated with 4T1 mammary cancer cells or NCTC 2472 osteosarcoma cells, respectively), suggesting that astrocytic P2X7 receptors play a negligible role in bone cancer pain. The results support the hypothesis that bone cancer pain is a separate pain state compared with those of neuropathic and inflammatory pain. However, the recent discovery of a P2X7 receptor splice variant expressed in the knockout mice used for this study complicates the interpretation of the results. The P2X7 splice variant receptor was detected in the spinal cord but not in osteoclasts of the P2X7R KO mouse. Further experiments are needed to elucidate the exact role of the P2X7 receptors in bone cancer pain.