Distinct Roles of Sphingosine Kinase 1 and 2 in Murine Collagen-Induced Arthritis

Abstract

Sphingosine kinase (SphK) phosphorylates sphingosine into sphingosine-1-phosphate (S1P). S1P plays a critical role in angiogenesis, inflammation, and various pathologic conditions. To date, two mammalian isoenzymes, SphK1 and SphK2, have been identified. Although both SphK1 and SphK2 share overall homology and produce the common product, S1P, it has been proposed they display different unique and separate functions. In this study, we examined the role of SphK1 and SphK2 in a murine collagen-induced arthritis model by down-regulating each isoenzyme via specific small interfering RNA (siRNA). Prophylactic i.p. administration of SphK1 siRNA significantly reduced the incidence, disease severity, and articular inflammation compared with control siRNA recipients. Treatment of SphK1 siRNA also down-regulated serum levels of S1P, IL-6, TNF-α, IFN-γ, and IgG2a anti-collagen Ab. Ex vivo analysis demonstrated significant suppression of collagen-specific proinflammatory/Th1 cytokine (IL-6, TNF-α, IFN-γ) release in SphK siRNA-treated mice. Interestingly, mice received with SphK2 siRNA develop more aggressive disease; higher serum levels of IL-6, TNF-α, and IFN-γ; and proinflammatory cytokine production to collagen in vitro when compared with control siRNA recipients. Together, these results demonstrate the distinct immunomodulatory roles of SphK1 and SphK2 in the development of inflammatory arthritis by regulating the release of proinflammatory cytokines and T cell responses. These findings raise the possibility that drugs which specifically target SphK1 activity may play a beneficial role in the treatment of inflammatory arthritis.

Targeting the Metabolism and Receptors of Sphingosine-1- Phosphate for the Treatment of Rheumatoid Arthritis

“…Corroborating this observation, we reported that S1P protects synovial fibroblasts from ongoing apoptosis (Zhao et al, 2008). Using the mouse model of collagen-induced arthritis (CIA), Lai et al (2009) highlighted distinct roles for SphK1 and SphK2 in regulating cell growth and survival. The in vivo administration of SphK1 siRNA reduced inflammation whereas mice treated with SphK2 siRNA resulted in a more aggressive disease and greater secretion of proinflammatory cytokines (IL-6, TNF- and IFN-) by immune cells.…”

“…Manipulation of endogenous local and systemic amounts of bioactive S1P by inhibiting metabolic enzymes such as SphKs and SPL, by applying S1P-blocking agents such as FTY-720, VPC23019 and JTE-013 or anti-S1P antibodies is thus a promising approach for the treatment of RA. Studies targeting S1P metabolism and signalling for the treatment of RA are summarized in Table 1. 5.1 Targeting S1P metabolism 5.1.1 Reducing S1P formation with sphingosine kinase inhibitors Blockade of SphK1 activity in the mouse model of CIA significantly suppressed articular inflammation and joint destruction, reduced disease severity, and down-regulated proinflammatory cytokine production and inflammatory cell recruitment into the synovium (Lai et al, 2009). Decreasing S1P production by inhibiting SphK activity is, therefore, a promising therapeutic option in chronic inflammatory arthritis.…”

Sphingosine-1-Phosphate and Rheumatoid Arthritis: Pathological Implications and Potential Therapeutic Targets

“…This effect is due to an increased activity of SphK1 and an overproduction of S1P. In a murine experimental arthritis model, administration of SphK inhibitor, DMS, and of SphK1 siRNA significantly decreased the production of anticollagen IgG2a in the mouse serum [48,49]. S1P was also reported to induce chondrocyte proliferation through stimulation of COX-2 and PGE2 production and via activation of ERK [77,78], and was thus suggested to be able to modulate cartilage homeostasis.…”

“…Administration of the S1P receptor agonist FYT720, which down-regulates S1P receptors, in rat CIA and AIA models inhibits rat hind paw oedema and joint destruction and decreases lymphocyte invasion into the joints [93,94]. In addition to receptor modulation, non-specific inhibition of SphK with DMS in a murine CIA model has been shown to significantly reduce adjacent cartilage and bone erosion, synovial hyperplasia, and inflammatory infiltration into the joint compartment [48,49]. Moreover, suppression of SphK1 via siRNA knockdown results in similar reduction in joint pathology, serum levels of IL-6, TNF-α, IFN-γ and S1P, and the in vitro production of these proinflammatory mediators in response to collagen [48,49].…”

“…Suppression of SphK2 by siRNA results in a more aggressive disease and greater secretion of proinflammatory cytokines, such as IL-6, TNF-α and IFN-γ in a murine collagen-induced arthritis (CIA) model [49]. Of more interest, in a murine CIA model, administration of a pharmacological SphK inhibitor, N,N-dimethylsphingosine (DMS), and an siRNA approach to knockdown SphK1 isoform markedly suppressed joint pathologies such as adjacent cartilage and bone erosion, synovial hyperplasia, and inflammatory infiltration into the joint compartment [49].…”