Polydatin attenuates AGEs-induced upregulation of fibronectin and ICAM-1 in rat glomerular mesangial cells and db/db diabetic mice kidneys by inhibiting the activation of the SphK1-S1P signaling pathway.

We previously demonstrated that activation of sphingosine kinase 1 (SphK1)- sphingosine 1- phosphate (S1P) signaling pathway by high glucose (HG) plays a pivotal role in increasing the expression of fibronectin (FN), an important fibrotic component, by promoting the DNA-binding activity of transcription factor activator protein 1 (AP-1) in glomerular mesangial cells (GMCs) under diabetic conditions. As a multi-target anti-oxidative drug, polydatin (PD) has been shown to have renoprotective effects on experimental diabetes. However, whether PD could resist diabetic nephropathy (DN) by regulating SphK1-S1P signaling pathway needs further investigation. Here, we found that PD significantly reversed the upregulated FN and ICAM-1 expression in GMCs exposed to AGEs. Simultaneously, PD dose-dependently inhibited SphK1 levels at the protein expression and kinase activity and attenuated S1P production under AGEs treatment conditions. In addition, PD reduced SphK activity in GMCs transfected with wild-type SphK(WT) plasmid and significantly suppressed SphK1-mediated increase of FN and ICAM-1 levels under normal conditions. Furthermore, we found that the AGEs-induced upregulation of phosphorylation of c-Jun at Ser63 and Ser73 and c-Fos at Ser32, DNA-binding activity and transcriptional activity of AP-1 were blocked by PD. In comparison with db/db model group, PD treatment suppressed SphK1 levels (mRNA, protein expression, and activity) and S1P production, reversed the upregulation of FN, ICAM-1, c-Jun, and c-Fos in the kidney tissues of diabetic mice, and finally ameliorated renal injury in db/db mice. These findings suggested that the downregulation of SphK1-S1P signaling pathway is probably a novel mechanism by which PD suppressed AGEs-induced FN and ICAM-1 expression and improved renal dysfunction of diabetic models.

Development of small-molecule inhibitors of sphingosine-1-phosphate signaling.

The pleiotropic sphingolipid mediator, sphingosine-1-phosphate, produced in cells by two sphingosine kinase isoenzymes, SphK1 and SphK2, regulates many cellular and physiological processes important for homeostasis and development and pathophysiology. Many of the actions of S1P are mediated by a family of five specific cell surface receptors that are ubiquitously and specifically expressed, although important direct intracellular targets of S1P have also recently been identified. S1P, SphK1, and or S1P receptors have been linked to onset and progression of numerous diseases, including many types of cancer, and especially inflammatory disorders, such as multiple sclerosis, asthma, rheumatoid arthritis, inflammatory bowel disease, and sepsis. S1P formation and signaling are attractive targets for development of new therapeutics. The effects of a number of inhibitors of SphKs and S1PRs have been examined in animal models of human diseases. The effectiveness of the immunosuppressant FTY720 (known as Fingolimod or Gilenya), recently approved for the treatment of multiple sclerosis, whose actions are mediated by downregulation of S1PR1, has become the gold standard for S1P-centric drugs. Here, we review S1P biology and signaling with an emphasis on potential therapeutic benefits of specific interventions and discuss recent development of small molecule antagonists and agonists that target specific subtypes of S1P receptors as well as inhibitors of SphKs.

Sphingosine-1-phosphate is a key regulator of proliferation and differentiation in retina photoreceptors.

PURPOSE: Identifying the cues required for the survival and development of photoreceptors is essential for treating retinal neurodegeneration. The authors previously established that glial-derived neurotrophic factor (GDNF) stimulates proliferation and that docosahexaenoic acid (DHA) promotes photoreceptor survival and differentiation. Later findings that ceramide triggers photoreceptor apoptosis suggested sphingolipids might also control photoreceptor development. The present study investigated whether sphingosine-1-phophate (S1P), which promotes survival and differentiation in several cell types, regulates photoreceptor proliferation and differentiation and whether it is a mediator in GDNF and DHA effects. METHODS: Rat retina neuronal cultures were supplemented at day 0 or 1 with S1P, GDNF, or DHA and were treated with DL-threo-dihydrosphingosine to inhibit S1P synthesis or with brefeldin A (BFA) to block intracellular trafficking. Proliferation was quantified to determine bromodeoxyuridine uptake and number of mitotic figures. Opsin, peripherin, and sphingosine kinase (SphK), the enzyme required for S1P synthesis, were quantified by immunocytochemistry and Western blot analysis. RESULTS: S1P increased the proliferation of photoreceptor progenitors. It also stimulated the formation of apical processes, enhanced opsin and peripherin expression, and promoted their localization in these processes; DHA had similar effects. BFA prevented S1P and DHA enhancement of apical process formation without affecting opsin expression. GDNF and DHA enhanced SphK expression in photoreceptors, while inhibiting S1P synthesis blocked GDNF mitogenic effects and DHA effects on differentiation. CONCLUSIONS: The authors propose S1P as a key regulator in photoreceptor development. GDNF and DHA might upregulate SphK levels to promote S1P synthesis, which would initially promote proliferation and then advance photoreceptor differentiation.

Itch-scratch responses induced by lysophosphatidic acid in mice.

The present investigation was conducted in order to determine whether lysophosphatidic acid (LPA) induces itch-scratch responses (ISRs) in mice. Intradermal administration of LPA induces ISRs; furthermore, the time course for LPA-induced ISRs was similar to that for histamine-induced responses. Comparative study of the pruritogenic activity revealed that histamine possessed a potent effect characterized by a dose-response relationship; however, prostaglandin D2 failed to induce this response. Pretreatment with ketotifen, a histamine H1 receptor antagonist, and capsaicin inhibited LPA-induced ISRs. Additionally, LPA-induced ISRs were abolished by Y-27632, an inhibitor of Rho-associated protein kinase (ROCK). These findings suggest that LPA-induced ISRs are attributable to histamine- and substance-P-mediated pathways. Moreover, the Rho/ROCK-mediated pathway may be involved.