RESUMEN
Quantitative and microscopic tracking of Borrelia afzelii transmission from infected Ixodes ricinus nymphs has shown a transmission cycle different from that of Borrelia burgdorferi and Ixodes scapularisBorrelia afzelii organisms are abundant in the guts of unfed I. ricinus nymphs, and their numbers continuously decrease during feeding. Borrelia afzelii spirochetes are present in murine skin within 1 day of tick attachment. In contrast, spirochetes were not detectable in salivary glands at any stage of tick feeding. Further experiments demonstrated that tick saliva is not essential for B. afzelii infectivity, the most important requirement for successful host colonization being a change in expression of outer surface proteins that occurs in the tick gut during feeding. Spirochetes in vertebrate mode are then able to survive within the host even in the absence of tick saliva. Taken together, our data suggest that the tick gut is the decisive organ that determines the competence of I. ricinus to vector B. afzelii We discuss possible transmission mechanisms of B. afzelii spirochetes that should be further tested in order to design effective preventive and therapeutic strategies against Lyme disease.
Asunto(s)
Vectores Arácnidos/microbiología , Grupo Borrelia Burgdorferi/fisiología , Ixodes/microbiología , Enfermedad de Lyme/transmisión , Animales , Vectores Arácnidos/fisiología , Femenino , Humanos , Ixodes/fisiología , Enfermedad de Lyme/microbiología , Ratones , Ratones Endogámicos C3H , Ninfa/microbiologíaRESUMEN
Aberrant fibroblast growth factor (FGF) signaling disturbs chondrocyte differentiation in skeletal dysplasia, but the mechanisms underlying this process remain unclear. Recently, FGF was found to activate canonical WNT/ß-catenin pathway in chondrocytes via Erk MAP kinase-mediated phosphorylation of WNT co-receptor Lrp6. Here, we explore the cellular consequences of such a signaling interaction. WNT enhanced the FGF-mediated suppression of chondrocyte differentiation in mouse limb bud micromass and limb organ cultures, leading to inhibition of cartilage nodule formation in micromass cultures, and suppression of growth in cultured limbs. Simultaneous activation of the FGF and WNT/ß-catenin pathways resulted in loss of chondrocyte extracellular matrix, expression of genes typical for mineralized tissues and alteration of cellular shape. WNT enhanced the FGF-mediated downregulation of chondrocyte proteoglycan and collagen extracellular matrix via inhibition of matrix synthesis and induction of proteinases involved in matrix degradation. Expression of genes regulating RhoA GTPase pathway was induced by FGF in cooperation with WNT, and inhibition of the RhoA signaling rescued the FGF/WNT-mediated changes in chondrocyte cellular shape. Our results suggest that aberrant FGF signaling cooperates with WNT/ß-catenin in suppression of chondrocyte differentiation.
Asunto(s)
Cartílago/efectos de los fármacos , Diferenciación Celular/efectos de los fármacos , Condrocitos/efectos de los fármacos , Factores de Crecimiento de Fibroblastos/farmacología , Receptores de Factores de Crecimiento de Fibroblastos/metabolismo , Proteínas Wnt/metabolismo , beta Catenina/metabolismo , Animales , Western Blotting , Cartílago/citología , Cartílago/metabolismo , Diferenciación Celular/genética , Línea Celular Tumoral , Células Cultivadas , Condrocitos/metabolismo , Sinergismo Farmacológico , Factor 2 de Crecimiento de Fibroblastos/farmacología , Células HEK293 , Humanos , Esbozos de los Miembros/efectos de los fármacos , Esbozos de los Miembros/embriología , Esbozos de los Miembros/metabolismo , Proteína-6 Relacionada a Receptor de Lipoproteína de Baja Densidad/genética , Proteína-6 Relacionada a Receptor de Lipoproteína de Baja Densidad/metabolismo , Microscopía Confocal , Modelos Biológicos , Ratas , Receptores de Factores de Crecimiento de Fibroblastos/genética , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Transducción de Señal/efectos de los fármacos , Transducción de Señal/genética , Transcriptoma/efectos de los fármacos , Transcriptoma/genética , Proteínas Wnt/genética , Proteínas Wnt/farmacología , Proteína Wnt3A/farmacología , beta Catenina/genéticaRESUMEN
Receptor tyrosine kinase signaling cooperates with WNT/ß-catenin signaling in regulating many biological processes, but the mechanisms of their interaction remain poorly defined. We describe a potent activation of WNT/ß-catenin by FGFR2, FGFR3, EGFR and TRKA kinases, which is independent of the PI3K/AKT pathway. Instead, this phenotype depends on ERK MAP kinase-mediated phosphorylation of WNT co-receptor LRP6 at Ser1490 and Thr1572 during its Golgi network-based maturation process. This phosphorylation dramatically increases the cellular response to WNT. Moreover, FGFR2, FGFR3, EGFR and TRKA directly phosphorylate ß-catenin at Tyr142, which is known to increase cytoplasmic ß-catenin concentration via release of ß-catenin from membranous cadherin complexes. We conclude that signaling via ERK/LRP6 pathway and direct ß-catenin phosphorylation at Tyr142 represent two mechanisms used by various receptor tyrosine kinase systems to activate canonical WNT signaling.