LPS and palmitate synergistically stimulate sphingosine kinase 1 and increase sphingosine 1 phosphate in RAW264.7 macrophages

Abstract

It has been well established that patients with diabetes or metabolic syndrome (MetS) have increased prevalence and severity of periodontitis, an oral infection initiated by bacteria and characterized by tissue inflammation and destruction. To understand the underlying mechanisms, we have shown that saturated fatty acid (SFA), which is increased in patients with type 2 diabetes or MetS, and LPS, an important pathogenic factor for periodontitis, synergistically stimulate expression of proinflammatory cytokines in macrophages by increasing ceramide production. However, the mechanisms by which increased ceramide enhances proinflammatory cytokine expression have not been well understood. Since sphingosine 1 phosphate (S1P) is a metabolite of ceramide and a bioactive lipid, we tested our hypothesis that stimulation of ceramide production by LPS and SFA facilitates S1P production, which contributes to proinflammatory cytokine expression. Results showed that LPS and palmitate, a major SFA, synergistically increased not only ceramide, but also S1P, and stimulated sphingosine kinase (SK) expression and membrane translocation in RAW264.7 macrophages. Results also showed that SK inhibition attenuated the stimulatory effect of LPS and palmitate on IL-6 secretion. Moreover, results showed that S1P enhanced the stimulatory effect of LPS and palmitate on IL-6 secretion. Finally, results showed that targeting S1P receptors using either S1P receptor antagonists or small interfering RNA attenuated IL-6 upregulation by LPS and palmitate. Taken together, this study demonstrated that LPS and palmitate synergistically stimulated S1P production and S1P in turn contributed to the upregulation of proinflammatory cytokine expression in macrophages by LPS and palmitate.

Ceramide and palmitic acid inhibit macrophage-mediated epithelial–mesenchymal transition in colorectal cancer

“…Consistent with previous reports, our data demonstrate that PA and Cer attenuate the M2-phenotype in macrophages. PA is a major saturated fatty acid and has been shown to stimulate pro-inflammatory cytokine expression by macrophages in vitro [28,45] and in pathologic processes like obesity. PA can directly bind to TLRs, or together with LPS they induce macrophages to express inflammatory cytokines [28,29].…”

Sphingosine-1-Phosphate and Macrophage Biology—How the Sphinx Tames the Big Eater

“…Also IL-1 signaling, another feed-forward NF-κB activator following microbial encounter, required SPHK1-dependent S1P as an intracellular cofactor (116). Besides TNF and IL-1β, SPHK1 is also rapidly activated downstream of other inducers of inflammatory macrophage activation, including LPS (117–119), and LPS in combination with palmitate (120), although it is unclear if SPHK1-derived S1P acts as a cofactor for intracellular LPS signaling. Stimulation of human THP-1 macrophages or mouse microglia with LPS required SPHK1 activity to produce IL-6, IL-1β, TNF-α, and/or NO (117, 118), whereas SPHK1 was dispensable for LPS, but not LPS/palmitate-induced IL-6 production, and TNF-α induced cyclooxygenase (COX)-2 expression in mouse RAW264.7 macrophages (119, 120).…”

“…Particularly, S1PR1 signaling promoted IL-6 production in a STAT3-dependent feedback loop, where IL-6 induced S1PR1 expression in mouse macrophages in vitro , in a model of sickle cell disease, and in dextran sodium sulfate (DSS)-induced colitis (124, 141). In RAW264.7 macrophages S1PR1 but also S1PR2 were involved in LPS and palmitate-induced IL-6 production (120). Moreover, S1PR1 signaling increased ARG1 activity in mouse macrophages to block the production of NO, which was induced by microbial stimuli in concert with IFN-γ, although the impact of STAT3 signaling in this context was not tested (137).…”

Cardiolipotoxicity, Inflammation, and Arrhythmias: Role for Interleukin-6 Molecular Mechanisms

“…Cardiac or systemic inflammation (or dysregulation of the innate immune system) is thought to be a function of the body’s non-specific response to injury (Pohl and Benseler, 2013). In obese and diabetic patients, the increased rates of infection and poor wound healing have been associated with immune cell dysfunction (Joshi et al, 1999; Ferrucci and Fabbri, 2018; Frydrych et al, 2018; Jin et al, 2018; van Niekerk and Engelbrecht, 2018). Importantly, macrophages are associated with heightened immune responses to infectious pathogens and tissue damage in diabetes (Mirza et al, 2009; Mirza and Koh, 2011; Das et al, 2018; Liu et al, 2018) and obesity (Lopez-Pascual et al, 2018; Ramos Muniz et al, 2018; Ding et al, 2018).…”