Fractalkine functions as a chemoattractant for osteoarthritis synovial fibroblasts and stimulates phosphorylation of mitogen-activated protein kinases and Akt.
Fractalkine (FKN/CX3CL1) has been detected in synovial fluids from osteoarthritis (OA) patients. Additionally, low-level expression of the FKN receptor, CX3CR1, has been demonstrated in OA synovial lining. This study aimed to determine a biological function for this ligand/receptor pair in OA and to assess a potential signalling mechanism for FKN in this predominant synovial lining cell type, using chemotaxis assays, Western blotting and F-actin staining. Chemotaxis assays demonstrate that the chemokine domain of FKN effectively induces migration of OA fibroblasts. Consistent with this finding, visualization of F-actin demonstrates that 1 or 10 nM FKN induces noticeable reorganization of cytoskeletal structure in OA fibroblasts after 30 min stimulation with a maximal enhancement at approximately 2 h. In addition, Western blotting analysis demonstrates that FKN stimulates phosphorylation of the mitogen-activated protein (MAP) kinases p38, c-Jun N-terminal kinase (JNK) and extracellular-regulated kinase (ERK) 1/2 as well as the serine-threonine kinase Akt at Ser 473 and Thr 308. All these phosphorylation events occur in a time-dependent manner, with little or no activation within 1 min, and maximal activation occurring typically between 5 and 30 min. Moreover, inhibition of ERK 1/2 significantly reduces FKN-induced OA fibroblast migration. These results suggest that FKN is a novel chemoattractant for OA fibroblasts, consistent with FKN-induced alterations in cytoskeletal structure. In addition, FKN induces OA fibroblast signalling via the MAP kinases p38, JNK and ERK 1/2, as well as Akt.
Klosowska
K
K
Department of Microbiology and Immunology, Chicago College of Osteopathic Medicine, Chicago, IL 60515, USA.
Volin
M V
MV
Huynh
N
N
Chong
K K
KK
Halloran
M M
MM
Woods
J M
JM
D000199:Actins / Q000032:analysis; D000368:Aged; D015153:Blotting, Western / Q000379:methods; D000073883:CX3C Chemokine Receptor 1; D054428:Chemokine CX3CL1 / Q000378:metabolism* / Q000494:pharmacology; D002633:Chemotaxis; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010003:Osteoarthritis / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D018121:Receptors, Cytokine / Q000378:metabolism; D015728:Receptors, HIV / Q000378:metabolism; D013194:Staining and Labeling; D013583:Synovial Membrane / Q000737:chemistry / Q000378:metabolism* / Q000473:pathology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D000199:Actins; D000073883:CX3C Chemokine Receptor 1; D054428:Chemokine CX3CL1; D018121:Receptors, Cytokine; D015728:Receptors, HIV; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases