In rheumatoid arthritis (RA), fibroblast-like synoviocytes (FLS) that line joint synovial membranes aggressively invade the extracellular matrix, destroying cartilage and bone. As signal transduction in FLS is mediated through multiple pathways involving protein tyrosine phosphorylation, we sought to identify protein tyrosine phosphatases (PTPs) regulating the invasiveness of RA FLS. We describe that the transmembrane receptor PTP? (RPTP?), encoded by the transforming growth factor (TGF) ?-target gene, PTPRK, promotes RA FLS invasiveness.
PI3-kinases (PI3Ks) participate in nociception within spinal cord, dorsal root ganglion (DRG), and peripheral nerves. To extend our knowledge, we immunohistochemically stained for each of the 4 class I PI3K isoforms along with several cell-specific markers within the lumbar spinal cord, DRG, and sciatic nerve of naive rats. Intrathecal and intraplantar isoform specific antagonists were given as pretreatments before intraplantar carrageenan; pain behavior was then assessed over time. The ?-isoform was localized to central terminals of primary afferent fibers in spinal cord laminae IIi to IV as well as to neurons in ventral horn and DRG. The PI3K? isoform was the only class I isoform seen in dorsal horn neurons; it was also observed in DRG, Schwann cells, and axonal paranodes. The ?-isoform was found in spinal cord white matter oligodendrocytes and radial astrocytes, and the ?-isoform was seen in a subpopulation of IB4-positive DRG neurons. No isoform co-localized with microglial markers or satellite cells in naive tissue. Only the PI3K? antagonist, but none of the other antagonists, had anti-allodynic effects when administered intrathecally; coincident with reduced pain behavior, this agent completely blocked paw carrageenan-induced dorsal horn 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl) propanoic acid (AMPA) receptor trafficking to plasma membranes. Intraplantar administration of the ?-antagonist prominently reduced pain behavior. These data suggest that each isoform displays specificity with regard to neuronal type as well as to specific tissues. Furthermore, each PI3K isoform has a unique role in development of nociception and tissue inflammation.
Cartilage destruction mediated by invasive fibroblast-like synoviocytes (FLS) plays a central role in pathogenesis of rheumatoid arthritis (RA). Increased cell migration and degradation of extracellular matrix are fundamental to these processes. The class I PI3Ks control cell survival, proliferation, and migration, which might be involved in cartilage damage in RA. PI3K? isoform was recently identified as a key regulator of FLS growth and survival, suggesting that it could contribute to synoviocyte aggressive behavior. Therefore, we assessed the role of PI3K? in RA synoviocyte migration and invasion. We observed that PI3K? inhibition or small interfering RNA knockdown decreased platelet-derived growth factor (PDGF)-mediated migration and invasion of FLS. We then showed that PI3K? regulates the organization of actin cytoskeleton and lamellipodium formation during PDGF stimulation. To gain insight into molecular mechanisms, we examined the effect of PI3K? inhibition on Rac1/PAK, FAK, and JNK activation. Our studies suggest that Rac1/PAK is key target of PDGF-mediated PI3K? signaling, whereas FAK and JNK are not involved. Thus, PI3K? contributes to multiple aspects of the pathogenic FLS behavior in RA. These observations, together with previous findings that PI3K? regulates FLS growth and survival, suggest that PI3K? inhibition could be chondroprotective in RA by modulating synoviocyte growth, migration, and invasion.
Phosphoinositide 3-kinases ? and ? (PI3K? and PI3K?) are expressed in rheumatoid arthritis (RA) synovium and regulate innate and adaptive immune responses. We determined the effect of a potent PI3K?,? inhibitor, IPI-145, in two preclinical models of RA. IPI-145 was administered orally in rat adjuvant-induced arthritis (AA) and intraperitoneally in mouse collagen-induced arthritis (CIA). Efficacy was assessed by paw swelling, clinical scores, histopathology and radiography, and microcomputed tomography scanning. Gene expression and Akt phosphorylation in joint tissues were determined by quantitative real-time polymerase chain reaction and Western blot analysis. Serum concentrations of anti-type II collagen (CII) IgG and IgE were measured by immunoassay. T-cell responses to CII were assayed using thymidine incorporation and immunoassay. IPI-145 significantly reduced arthritis severity in both RA models using dosing regimens initiated before onset of clinical disease. Treatment of established arthritis with IPI-145 in AA, but not CIA, significantly decreased arthritis progression. In AA, histology scores, radiographic joint damage, and matrix metalloproteinase (MMP)-13 expression were reduced in IPI-145-treated rats. In CIA, joint histology scores and expression of MMP-3 and MMP-13 mRNA were lower in the IPI-145 early treatment group than in the vehicle group. The ratio of anti-CII IgG2a to total IgG in CIA was modestly reduced. Interleukin-17 production in response to CII was decreased in the IPI-145-treated group, suggesting an inhibitory effect on T-helper cell 17 differentiation. These data show that PI3K?,? inhibition suppresses inflammatory arthritis, as well as bone and cartilage damage, through effects on innate and adaptive immunity and that IPI-145 is a potential therapy for RA.
The fibroblast-like synoviocytes (FLS) in the synovial intimal lining of the joint are key mediators of inflammation and joint destruction in rheumatoid arthritis (RA). In RA, these cells aggressively invade the extracellular matrix, producing cartilage-degrading proteases and inflammatory cytokines. The behavior of FLS is controlled by multiple interconnected signal transduction pathways involving reversible phosphorylation of proteins on tyrosine residues. However, little is known about the role of the protein tyrosine phosphatases (PTPs) in FLS function. This study was undertaken to explore the expression of all of the PTP genes (the PTPome) in FLS.
The therapeutic utility of the targeting of B lymphocytes is currently being evaluated in a range of autoimmune diseases that include multiple sclerosis (MS). For MS, even though intrathecal immunoglobulin production is a hallmark of multiple sclerosis (MS), T cells have long been considered as the main effectors of pathogenesis. Recognition of the roles of autoreactive B cells has changed this conventional view of the disease and also provided a rationale for studies of anti-CD20 therapy in MS. Recent trials suggest that this approach may provide clinical benefits in some MS patients that equal or surpass currently approved approaches, yet not all patients may benefit. In this review we provide an overview on recent progress on these trials.
Rheumatoid arthritis (RA) remains a significant unmet medical need despite significant therapeutic advances. The pathogenesis of RA is complex and includes many cell types, including T cells, B cells, and macrophages. Fibroblast-like synoviocytes (FLS) in the synovial intimal lining also play a key role by producing cytokines that perpetuate inflammation and proteases that contribute to cartilage destruction. Rheumatoid FLS develop a unique aggressive phenotype that increases invasiveness into the extracellular matrix and further exacerbates joint damage. Recent advances in understanding the biology of FLS, including their regulation regulate innate immune responses and activation of intracellular signaling mechanisms that control their behavior, provide novel insights into disease mechanisms. New agents that target FLS could potentially complement the current therapies without major deleterious effect on adaptive immune responses.
Class I phosphoinositide 3 kinase (PI3K) ? is a promising therapeutic target for rheumatoid arthritis (RA) because of its contribution to leukocyte biology. However, its contribution in fibroblasts has not been studied as a mechanism that contributes to efficacy. We investigated the expression and function of PI3K? in synovium and cultured fibroblast-like synoviocytes (FLS). Immunohistochemistry demonstrated that PI3K? is highly expressed in RA synovium, especially in the synovial lining. Using quantitative PCR and Western blot analysis, we found that PI3K? mRNA and protein expression is higher in RA than in osteoarthritis (OA) synovium. PI3K? was also expressed in cultured FLS, along with PI3K? and PI3K?, whereas PI3K? was not detectable. PI3K? mRNA expression was selectively induced by inflammatory cytokines tumor necrosis factor (TNF) and interleukin-1 (IL-1) but not by growth factors platelet-derived growth factor (PDGF) and transforming growth factor ? (TGF?). The use of inhibitors that block individual PI3K isoforms, including the novel selective PI3K? inhibitor INK007, showed that PI3K? is required for PDGF- and TNF-induced Akt activation. PI3K? inhibition also diminished PDGF-mediated synoviocyte growth and sensitized cells to H(2)O(2)-induced apoptosis. These data are the first documentation of increased PI3K? expression in both RA synovium and cultured synoviocytes. Furthermore, these are the first data demonstrating that PI3K? is a major regulator of PDGF-mediated fibroblast growth and survival via Akt. Thus, targeting PI3K? in RA could modulate synoviocyte function via anti-inflammatory and disease-altering mechanisms.
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