The Role of TNFα and Sphingolipid Signaling in Cardiac Hypoxia: Evidence that Cardiomyocytes Release TNFα and Sphingosine

Sphingosine (SPH) is a naturally occurring signaling molecule thought to be responsible for the negative inotropic and cardiotoxic effects of the pro-inflammatory cytokine, TNFα. When subjected to hypoxia and acidosis, Langendorff perfused adult rabbit hearts generate SPH, and isolated adult rat cardiomyocytes released TNFα and SPH into the cell-conditioned media under hypoxic conditions before hypoxia-induced cell permeabilization associated with necrosis. Cardiomyocyte SPH production in response to hypoxia was blocked by TNFRII:Fc which interferes with TNFα binding to its membrane-bound receptor, suggesting that hypoxiatriggered SPH production was TNFα dependent. Extracellular SPH was rapidly converted almost exclusively to S1P by an active sphingosine kinase present in blood components, as seen in vitro and in Langendorff-perfused rat hearts. These results indicate that cardiacderived TNFα and its sphingolipid mediator, SPH, may be important extracellular signals in the heart that contribute to the pathogenesis of cardiac ischemia

Antibodies against Lysophosphatidic Acid Protect against Blast-Induced Ocular Injuries

Exposure to blast overpressure waves is implicated as the major cause of ocular injuries and resultant visual dysfunction in veterans involved in recent combat operations. No effective therapeutic strategies have been developed so far for blast-induced ocular dysfunction. Lysophosphatidic acid (LPA) is a bioactive phospholipid generated by activated platelets, astrocytes, choroidal plexus cells, and microglia and is reported to play major roles in stimulating inflammatory processes. The levels of LPA in the cerebrospinal fluid have been reported to increase acutely in patients with traumatic brain injury (TBI) as well as in a controlled cortical impact (CCI) TBI model in mice. In the present study, we have evaluated the efficacy of a single intravenous administration of a monoclonal LPA antibody (25 mg/kg) given at 1 h post-blast for protection against injuries to the retina and associated ocular dysfunctions. Our results show that a single 19 psi blast exposure significantly increased the levels of several species of LPA in blood plasma at 1 and 4 h post-blast. The anti-LPA antibody treatment significantly decreased glial cell activation and preserved neuronal cell morphology in the retina on day 8 after blast exposure. Optokinetic measurements indicated that anti-LPA antibody treatment significantly improved visual acuity in both eyes on days 2 and 6 post-blast exposure. Anti-LPA antibody treatment significantly increased rod photoreceptor and bipolar neuronal cell signaling in both eyes on day 7 post-blast exposure. These results suggest that blast exposure triggers release of LPAs, which play a major role promoting blast-induced ocular injuries, and that a single early administration of anti-LPA antibodies provides significant protection

Anti-Lysophosphatidic Acid Antibodies Improve Traumatic Brain Injury Outcomes

BACKGROUND: Lysophosphatidic acid (LPA) is a bioactive phospholipid with a potentially causative role in neurotrauma. Blocking LPA signaling with the LPA-directed monoclonal antibody B3/Lpathomab is neuroprotective in the mouse spinal cord following injury. FINDINGS: Here we investigated the use of this agent in treatment of secondary brain damage consequent to traumatic brain injury (TBI). LPA was elevated in cerebrospinal fluid (CSF) of patients with TBI compared to controls. LPA levels were also elevated in a mouse controlled cortical impact (CCI) model of TBI and B3 significantly reduced lesion volume by both histological and MRI assessments. Diminished tissue damage coincided with lower brain IL-6 levels and improvement in functional outcomes. CONCLUSIONS: This study presents a novel therapeutic approach for the treatment of TBI by blocking extracellular LPA signaling to minimize secondary brain damage and neurological dysfunction

Intracellular S1P Generation Is Essential for S1P-Induced Motility of Human Lung Endothelial Cells: Role of Sphingosine Kinase 1 and S1P Lyase

Earlier we have shown that extracellular sphingosine-1-phosphate (S1P) induces migration of human pulmonary artery endothelial cells (HPAECs) through the activation of S1P(1) receptor, PKCε, and PLD2-PKCζ-Rac1 signaling cascade. As endothelial cells generate intracellular S1P, here we have investigated the role of sphingosine kinases (SphKs) and S1P lyase (S1PL), that regulate intracellular S1P accumulation, in HPAEC motility

Sphingosine 1-phosphate protects mouse EDL skeletal muscle during fatigue

Sphingomyelin derivatives exert various second messenger actions in numerous tissues. Sphingosine (SPH) and sphingosine 1-phosphate (S1P) are two major sphingomyelin derivatives present at high levels in blood. The aim of the present work was to investigate whether S1P and SPH exert relevant actions in mouse skeletal muscle contractility and fatigue. Exogenous S1P and SPH administration caused a significant reduction of tension decline during fatigue of extensor digitorum longus muscle. Final tension after the fatiguing protocol was 40% higher than in untreated muscle. Interestingly, N,N-dimethylsphingosine, an inhibitor of SPH kinase (SK), abolished the effect of supplemented SPH but not that of S1P, suggesting that SPH acts through its conversion to S1P. Moreover, SPH was not effective in Ca(2+)-free solutions, in agreement with the hypothesis that SPH action is dependent on its conversion to S1P by the Ca(2+)-requiring enzyme SK. In contrast to SPH, S1P produced its positive effects on fatigue in Ca(2+)-free conditions, indicating that S1P action does not require Ca(2+) entry and most likely is receptor mediated. The effects of S1P could be ascribed in part to its ability to prevent the reduction (-20 mV) of action potential amplitude caused by fatigue. In conclusion, these results indicate that extracellular S1P has protective effects during the development of muscle fatigue and that the extracellular conversion of SPH to S1P may represent a rheostat mechanism to protect skeletal muscle from possible cytotoxic actions of SPH

Sphingosine 1-phosphate signaling through its receptor S1P5 promotes chromosome segregation and mitotic progression

International audienceSphingosine kinase 1 (SphK1) promotes cell proliferation and survival, and its abundance is often increased in tumors. SphK1 produces the signaling lipid sphingosine 1-phosphate (S1P), which activates signaling cascades downstream five G protein-coupled receptors (S1P1-5) to modulate vascular and immune system function and promote proliferation. We identified a new function of the SphK1-S1P pathway specifically in the control of mitosis. SphK1 depletion in HeLa cells caused prometaphase arrest, whereas its overexpression or activation accelerated mitosis. Increasing the abundance of S1P promoted mitotic progression, overrode the spindle assembly checkpoint (SAC), and led to chromosome segregation defects. S1P was secreted through the transporter SPNS2 and stimulated mitosis by binding to and activating S1P5 on the extracellular side, which then activated the intracellular phosphatidylinositol 3-kinase (PI3K)-AKT pathway. Knockdown of S1P5 prevented the S1P-induced spindle defect phenotype. RNA interference assays revealed that the mitotic kinase Polo-like kinase 1 (PLK1) was an important effector of S1P-S1P5 signaling-induced mitosis in HeLa cells. Our findings identify an extracellular signal and the downstream pathway that promotes mitotic progression and may indicate potential therapeutic targets to inhibit the proliferation of cancer cells