Ceramide-1-phosphate protection of cochlear hair cells against cisplatin ototoxicity

Ceramide kinase-mediated C1P metabolism attenuates acute liver injury by inhibiting the interaction between KEAP1 and NRF2

Acute liver injury is the basis of the pathogenesis of diverse liver diseases. However, the mechanism underlying liver injury is complex and not completely understood. In our study, we revealed that CERK, which phosphorylates ceramide to produce ceramide-1-phosphate (C1P), was the sphingolipid pathway-related protein that had the most significantly upregulated expression during acute liver injury. A functional study confirmed that CERK and C1P attenuate hepatic injury both in vitro and in vivo through antioxidant effects. Mechanistic studies have shown that CERK and C1P positively regulate the protein expression of NRF2, which is a crucial protein that helps maintain redox homeostasis. Furthermore, our results indicated that C1P disrupted the interaction between NRF2 and KEAP1 by competitively binding to KEAP1, which allowed for the nuclear translocation of NRF2. In addition, pull-down assays and molecular docking analyses revealed that C1P binds to the DGR domain of KEAP1, which allows it to maintain its interaction with NRF2. Importantly, these findings were verified in human primary hepatocytes and a mouse model of hepatic ischemia‒reperfusion injury. Taken together, our findings demonstrated that CERK-mediated C1P metabolism attenuates acute liver injury via the binding of C1P to the DGR domain of KEAP1 and subsequently the release and nuclear translocation of NRF2, which activates the transcription of cytoprotective and antioxidant genes. Our study suggested that the upregulation of CERK and C1P expression may serve as a potential antioxidant strategy to alleviate acute liver injury.

Estradiol protects hair cells from cisplatin-induced ototoxicity via Nrf2 activation

Cisplatin-induced ototoxicity is caused by reactive oxygen species. It has been recognized that estradiol (E2) regulates redox balance. However, little is known about the protective mechanisms of E2 against cisplatin-induced ototoxicity. In this study, we investigated the effect of E2 on nuclear factor erythroid 2-related factor 2 (Nrf2)-mediated hair cell protection using the organ of Corti isolated from mice. The organ of Corti collected from C57BL/6 mice at 3-5 postnatal days was used in all experiments. The organ of Corti was exposed to 20 μM cisplatin with/without 100 nM E2 to examine the effect of E2 on cisplatin-induced hair cell loss. The mRNA expression of Nrf2 and the phase II detoxification gene after E2 and cisplatin treatment was analyzed using quantitative real-time PCR. E2 significantly reduces cisplatin-induced cochlear hair cell death. In addition, 100 nM E2 increased the mRNA expression of Nrf2 and phase II detoxification genes in the organ of Corti under cisplatin treatment. Our results suggest that E2 activates Nrf2, phase II detoxification enzymes and exerts a protective effect against cisplatin-induced ototoxicity.

Implication of Ceramide Kinase/C1P in Cancer Development and Progression

Cancer cells rewire their metabolic programs to favor biological processes that promote cell survival, proliferation, and dissemination. Among this relevant reprogramming, sphingolipid metabolism provides metabolites that can favor or oppose these hallmarks of cancer. The sphingolipid ceramide 1-phosphate (C1P) and the enzyme responsible for its biosynthesis, ceramide kinase (CERK), are well established regulators of cell growth and survival in normal, as well as malignant cells through stress-regulated signaling pathways. This metabolite also promotes cell survival, which has been associated with the feedback regulation of other antitumoral sphingolipids or second messengers. C1P also regulates cancer cell invasion and migration of different types of cancer, including lung, breast, pancreas, prostate, or leukemia cells. More recently, CERK and C1P have been implicated in the control of inflammatory responses. The present review provides an updated view on the important role of CERK/C1P in the regulation of cancer cell growth, survival, and dissemination.

Ceramide Kinase Inhibition Blocks IGF-1-Mediated Survival of Otic Neurosensory Progenitors by Impairing AKT Phosphorylation

Sphingolipids are bioactive lipid components of cell membranes with important signal transduction functions in health and disease. Ceramide is the central building block for sphingolipid biosynthesis and is processed to form structurally and functionally distinct sphingolipids. Ceramide can be phosphorylated by ceramide kinase (CERK) to generate ceramide-1-phosphate, a cytoprotective signaling molecule that has been widely studied in multiple tissues and organs, including the developing otocyst. However, little is known about ceramide kinase regulation during inner ear development. Using chicken otocysts, we show that genes for CERK and other enzymes of ceramide metabolism are expressed during the early stages of inner ear development and that CERK is developmentally regulated at the otic vesicle stage. To explore its role in inner ear morphogenesis, we blocked CERK activity in organotypic cultures of otic vesicles with a specific inhibitor. Inhibition of CERK activity impaired proliferation and promoted apoptosis of epithelial otic progenitors. CERK inhibition also compromised neurogenesis of the acoustic-vestibular ganglion. Insulin-like growth factor-1 (IGF-1) is a key factor for proliferation, survival and differentiation in the chicken otocyst. CERK inhibition decreased IGF-1-induced AKT phosphorylation and blocked IGF-1-induced cell survival. Overall, our data suggest that CERK is activated as a central element in the network of anti-apoptotic pro-survival pathways elicited by IGF-1 during early inner ear development.

Novel signaling aspects of ceramide 1-phosphate

The bioactive sphingolipid ceramide 1-phosphate (C1P) regulates key physiologic cell functions and is implicated in a number of metabolic alterations and pathological processes. Initial studies using different types of fibroblasts and monocytes/macrophages revealed that C1P was mitogenic and that it promoted cell survival through inhibition of apoptosis. Subsequent studies implicated C1P in inflammatory responses with a specific role as pro-inflammatory agent. Specifically, C1P potently stimulated cytosolic phospholipase A₂ (cPLA₂) resulting in elevation of arachidonic acid and pro-inflammatory eicosanoid levels. However, increasing experimental evidence suggests that C1P can also exert anti-inflammatory actions in some cell types and tissues. Specifically, it has been demonstrated that C1P inhibits the release of pro-inflammatory cytokines and blocks activation of the pro-inflammatory transcription factor NF-κB in some cell types. Moreover, C1P was shown to increase the release of anti-inflammatory interleukin-10 in macrophages, and to overcome airway inflammation and reduce lung emphysema in vivo. Noteworthy, C1P stimulated cell migration, an action that is associated with diverse physiological cell functions, as well as with inflammatory responses and tumor dissemination. More recently, ceramide kinase (CerK), the enzyme that produces C1P in mammalian cells, has been shown to be upregulated during differentiation of pre-adipocytes into mature adipocytes, and that exogenous C1P, acting through a putative Gi protein-coupled receptor, negatively regulates adipogenesis. Although the latter actions seem to be contradictory, it is plausible that exogenous C1P may balance the adipogenic effects of intracellularly generated (CerK-derived) C1P in adipose tissue. The present review highlights novel signaling aspects of C1P and its impact in the regulation of cell growth and survival, inflammation and tumor dissemination.

Ceramide 1-Phosphate Protects Endothelial Colony–Forming Cells From Apoptosis and Increases Vasculogenesis In Vitro and In Vivo

Objective:

Ceramide 1-phosphate (C1P) is a bioactive sphingolipid highly augmented in damaged tissues. Because of its abilities to stimulate migration of murine bone marrow–derived progenitor cells, it has been suggested that C1P might be involved in tissue regeneration. In the present study, we aimed to investigate whether C1P regulates survival and angiogenic activity of human progenitor cells with great therapeutic potential in regenerative medicine such as endothelial colony–orming cells (ECFCs).

Approach and Results:

C1P protected ECFC from TNFα (tumor necrosis factor-α)-induced and monosodium urate crystal–induced death and acted as a potent chemoattractant factor through the activation of ERK1/2 (extracellular signal-regulated kinases 1 and 2) and AKT pathways. C1P treatment enhanced ECFC adhesion to collagen type I, an effect that was prevented by β1 integrin blockade, and to mature endothelial cells, which was mediated by the E-selectin/CD44 axis. ECFC proliferation and cord-like structure formation were also increased by C1P, as well as vascularization of gel plug implants loaded or not with ECFC. In a murine model of hindlimb ischemia, local administration of C1P alone promoted blood perfusion and reduced necrosis in the ischemic muscle. Additionally, the beneficial effects of ECFC infusion after ischemia were amplified by C1P pretreatment, resulting in a further and significant enhancement of leg reperfusion and muscle repair.

Conclusions:

Our findings suggest that C1P may have therapeutic relevance in ischemic disorders, improving tissue repair by itself, or priming ECFC angiogenic responses such as chemotaxis, adhesion, proliferation, and tubule formation, which result in a better outcome of ECFC-based therapy.

Modulatory Effects of Fingolimod (FTY720) on the Expression of Sphingolipid Metabolism-Related Genes in an Animal Model of Alzheimer's Disease

Sphingolipid signaling disturbances correlate with Alzheimer's disease (AD) progression. We examined the influence of FTY720/fingolimod, a sphingosine analog and sphingosine-1-phosphate (S1P) receptor modulator, on the expression of sphingolipid metabolism and signaling genes in a mouse transgenic AD model. Our results demonstrated that AβPP (V717I) transgene led with age to reduced mRNA expression of S1P receptors (S1PRs), sphingosine kinase SPHK2, ceramide kinase CERK, and the anti-apoptotic Bcl2 in the cerebral cortex and hippocampus, suggesting a pro-apoptotic shift in 12-month old mice. These changes largely emulated alterations we observed in the human sporadic AD hippocampus: reduced SPHK1, SPHK2, CERK, S1PR1, and BCL2. We observed that the responses to FTY720 treatment were modified by age and notably differed between control (APP^-) and AD transgenic (APP⁺) animals. AβPP (V717I)-expressing 12-month-old animals reacted to fingolimod with wide changes in the gene expression program in cortex and hippocampus, including increased pro-survival SPHKs and CERK. Moreover, BCL2 was elevated by FTY720 in the cortex at all ages (3, 6, 12 months) while in hippocampus this increase was observed at 12 months only. In APP^- mice, fingolimod did not induce any significant mRNA changes at 12 months. Our results indicate significant effect of FTY720 on the age-dependent transcription of genes involved in sphingolipid metabolism and pro-survival signaling, suggesting its neuroprotective role in AD animal model.