New signalling pathway involved in the anti-proliferative action of vitamin D3 and its analogues in human neuroblastoma cells. A role for ceramide kinase

Sphingolipid classes and the interrelationship with pediatric asthma and asthma risk factors

BACKGROUND

While dysregulated sphingolipid metabolism has been associated with risk of childhood asthma, the specific sphingolipid classes and/or mechanisms driving this relationship remain unclear. We aimed to understand the multifaceted role between sphingolipids and other established asthma risk factors that complicate this relationship.

METHODS

We performed targeted LC-MS/MS-based quantification of 77 sphingolipids in plasma from 997 children aged 6 years from two independent cohorts (VDAART and COPSAC2010 ). We examined associations of circulatory sphingolipids with childhood asthma, lung function, and three asthma risk factors: functional SNPs in ORMDL3, low vitamin D levels, and reduced gut microbial maturity. Given racial differences between these cohorts, association analyses were performed separately and then meta-analyzed together.

RESULTS

We observed elevations in circulatory sphingolipids with asthma phenotypes and risk factors; however, there were differential associations of sphingolipid classes with clinical outcomes and/or risk factors. While elevations from metabolites involved in ceramide recycling and catabolic pathways were associated with asthma and worse lung function [meta p-value range: 1.863E-04 to 2.24E-3], increased ceramide levels were associated with asthma risk factors [meta p-value range: 7.75E-5 to .013], but not asthma. Further investigation identified that some ceramides acted as mediators while some interacted with risk factors in the associations with asthma outcomes.

CONCLUSION

This study demonstrates the differential role that sphingolipid subclasses may play in asthma and its risk factors. While overall elevations in sphingolipids appeared to be deleterious overall; elevations in ceramides were uniquely associated with increases in asthma risk factors only; while elevations in asthma phenotypes were associated with recycling sphingolipids. Modification of asthma risk factors may play an important role in regulating sphingolipid homeostasis via ceramides to affect asthma. Further function work may validate the observed associations.

Interplay between Vitamin D and Sphingolipids in Cardiometabolic Diseases

Sphingolipids (SLs) are structural, bioactive molecules with several key cellular roles, whereas 1,25-dihydroxyvitamin D (1,25(OH)D), the active form of vitamin D, is considered the major regulator of calcium homeostasis, although it also exerts other extraskeletal effects. Many studies reported the physiological connection between vitamin D and SLs, highlighting not only the effects of vitamin D on SL metabolism and signaling but also the influence of SLs on vitamin D levels and function, thus strongly suggesting a crosstalk between these molecules. After a brief description of 1,25(OH)D and SL metabolism, this review aims to discuss the preclinical and clinical evidence on the crosstalk between SLs and 1,25(OH)D, with a special focus on cardiometabolic diseases.

Vitamin D Status in Children With High-risk Neuroblastoma

BACKGROUND

Vitamin D deficiency has become a matter of concern in pediatric cancer patients. A relationship between neuroblastoma and Vitamin D signaling pathways has been revealed with interest in the antiproliferative and antiinvasive properties of vitamin D. Our aim is to describe the prevalence of Vitamin D deficiency among children with high-risk neuroblastoma (HR-NB) and to explore its association with disease status.

MATERIALS AND METHODS

In all, 182 patients with HR-NB were managed at our center from 2017 to 2021. Serum 25(OH)D levels were tested at the first blood analysis performed and correlated with clinical data and disease status.

RESULTS

One hundred forty-eight (81.4%) had low 25(OH)D levels (48.4% categorized as deficiency (25(OH)D below 20 ng/mL) and 33.0% as insufficiency (25(OH)D 20 to 30 ng/mL). Median Vitamin D level was 20.2 ng/mL. Vitamin D levels were not associated with race or sex. Although malnourished patients had lower median 25(OH)D levels(11.1 ng/mL), no statistical association was observed with Vitamin D deficiency. There was no association between Vitamin D levels and disease status. An inverse correlation was found between age and vitamin D levels ( P =0.0040).

CONCLUSION

A concerning high prevalence of low Vitamin D levels affects more than two-thirds of patients with HR-NB in our cohort, regardless of the disease status at the time of evaluation. Older children are at a higher risk for deficient levels of vitamin D.

Developing New Cyclodextrin-Based Nanosponges Complexes to Improve Vitamin D Absorption in an In Vitro Study

Vitamin D plays an important role in numerous cellular functions due to the ability to bind the Vitamin D receptor (VDR), which is present in different tissues. Several human diseases depend on low vitamin D3 (human isoform) serum level, and supplementation is necessary. However, vitamin D3 has poor bioavailability, and several strategies are tested to increase its absorption. In this work, the complexation of vitamin D3 in Cyclodextrin-based nanosponge (CD-NS, in particular, βNS-CDI 1:4) was carried out to study the possible enhancement of bioactivity. The βNS-CDI 1:4 was synthesized by mechanochemistry, and the complex was confirmed using FTIR-ATR and TGA. TGA demonstrated higher thermostability of the complexed form. Subsequently, in vitro experiments were performed to evaluate the biological activity of Vitamin D3 complexed in the nanosponges on intestinal cells and assess its bioavailability without cytotoxic effect. The Vitamin D3 complexes enhance cellular activity at the intestinal level and improve its bioavailability. In conclusion, this study demonstrates for the first time the ability of CD-NS complexes to improve the chemical and biological function of Vitamin D3.

Immunohistochemical Detection of the Presence of Vitamin D Receptor in Childhood Solid Tumors

Background: Our previous work has shown a correlation between lower vitamin D levels in children with cancer and adverse prognosis. It suggests that supplying vitamin D is reasonable. VDR expression in childhood solid tumors has been linked to tumor characteristics and patient survival in only a few studies. Methods: For this study, 177 children with solid tumors were selected whose biopsies and tumor tissue formalin-fixed, paraffin-embedded tissue blocks were available for immunohistochemical analysis at Semmelweis University, Budapest (Hungary). Results: We found that non-significant VDR expression was associated with a significantly less favorable prognosis (p = 0.0061) in the examined childhood solid tumors. There was a clinically significant association; non-significant VDR expression had more than 14-fold odds of an unfavorable prognosis (OR = 14.74). The rate of VDR expression differed significantly between tumor types (p < 0.0001). Conclusion: In conclusion, VDR expression measured by IHC staining is inversely associated with aggressive characteristics in different childhood cancers. The downregulation of VDR expression in more aggressive childhood cancers suggests that functional vitamin D activity may slow or block cancer progression.

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.

Control of Skeletal Muscle Atrophy Associated to Cancer or Corticosteroids by Ceramide Kinase

Apart from cytokines and chemokines, sphingolipid mediators, particularly sphingosine-1-phosphate (S1P) and ceramide 1-phosphate (C1P), contribute to cancer and inflammation. Cancer, as well as other inflammatory conditions, are associated with skeletal muscle (SkM) atrophy, which is characterized by the unbalance between protein synthesis and degradation. Although the signaling pathways involved in SkM mass wasting are multiple, the regulatory role of simple sphingolipids is limited. Here, we report the impairment of ceramide kinase (CerK), the enzyme responsible for the phosphorylation of ceramide to C1P, associated with the accomplishment of atrophic phenotype in various experimental models of SkM atrophy: in vivo animal model bearing the C26 adenocarcinoma or Lewis lung carcinoma tumors, in human and murine SkM cells treated with the conditioned medium obtained from cancer cells or with the glucocorticoid dexamethasone. Notably, we demonstrate in all the three experimental approaches a drastic decrease of CerK expression. Gene silencing of CerK promotes the up-regulation of atrogin-1/MAFbx expression, which was also observed after cell treatment with C8-ceramide, a biologically active ceramide analogue. Conversely, C1P treatment significantly reduced the corticosteroid's effects. Altogether, these findings provide evidence that CerK, acting as a molecular modulator, may be a new possible target for SkM mass regulation associated with cancer or corticosteroids.

Ceramide/protein phosphatase 2A axis is engaged in gap junction impairment elicited by PCB153 in liver stem-like progenitor cells

The widespread environmental pollutant 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153) is a non-dioxin-like toxicant. It is a potential carcinogen compound able to induce gap junction (GJ) intercellular communication impairment, probably the first non-genomic event leading to tumor promotion. Although PCBs have been known for many years, the molecular mode of PCB153 action is still unclear. Recent studies from our research group have shown that the toxicant elicits a transient modulation of connexin (Cx) 43-formed GJs in hepatic stem-like WB-F344 cells involving sphingosine 1-phosphate (S1P) path. Taking into account that other strictly related bioactive sphingolipids, such as ceramide (Cer), may have different effects from S1P, here we aim to clarify the signaling paths engaged by PCB153 in the control of GJs, focusing primarily on the role of Cer. Accordingly, we have achieved a combined biomolecular and electrophysiological analysis of GJs in cultured WB-F344 cells treated with PCB153 at different time points. We have found that the toxicant elicited a time-dependent regulation of GJs formed by different Cx isoforms, through a transient modulation of Cer/Cer kinase (CerK) axis and, in turn, of protein phosphatase 2A (PP2A). Our new findings demonstrate the existence of a specific molecular mechanism downstream to Cer, which distinctly affects the voltage-dependent and -independent GJs in liver stem-like cells, and open new opportunities for the identification of additional potential targets of these environmental toxicants.

Role of bioactive sphingolipids in physiology and pathology

Sphingolipids are a class of complex lipids containing a backbone of sphingoid bases, namely the organic aliphatic amino alcohol sphingosine (Sph), that are essential constituents of eukaryotic cells. They were first described as major components of cell membrane architecture, but it is now well established that some sphingolipids are bioactive and can regulate key biological functions. These include cell growth and survival, cell differentiation, angiogenesis, autophagy, cell migration, or organogenesis. Furthermore, some bioactive sphingolipids are implicated in pathological processes including inflammation-associated illnesses such as atherosclerosis, rheumatoid arthritis, inflammatory bowel disease (namely Crohn's disease and ulcerative colitis), type II diabetes, obesity, and cancer. A major sphingolipid metabolite is ceramide, which is the core of sphingolipid metabolism and can act as second messenger, especially when it is produced at the plasma membrane of cells. Ceramides promote cell cycle arrest and apoptosis. However, ceramide 1-phosphate (C1P), the product of ceramide kinase (CerK), and Sph 1-phosphate (S1P), which is generated by the action of Sph kinases (SphK), stimulate cell proliferation and inhibit apoptosis. Recently, C1P has been implicated in the spontaneous migration of cells from some types of cancer, and can enhance cell migration/invasion of malignant cells through interaction with a Gi protein-coupled receptor. In addition, CerK and SphK are implicated in inflammatory responses, some of which are associated with cancer progression and metastasis. Hence, targeting these sphingolipid kinases to inhibit C1P or S1P production, or blockade of their receptors might contribute to the development of novel therapeutic strategies to reduce metabolic alterations and disease.

Cholesterol and Sphingolipid Enriched Lipid Rafts as Therapeutic Targets in Cancer

Lipid rafts are critical cell membrane lipid platforms enriched in sphingolipid and cholesterol content involved in diverse cellular processes. They have been proposed to influence membrane properties and to accommodate receptors within themselves by facilitating their interaction with ligands. Over the past decade, technical advances have improved our understanding of lipid rafts as bioactive structures. In this review, we will cover the more recent findings about cholesterol, sphingolipids and lipid rafts located in cellular and nuclear membranes in cancer. Collectively, the data provide insights on the role of lipid rafts as biomolecular targets in cancer with good perspectives for the development of innovative therapeutic strategies.

Down-regulation of ceramide kinase via proteasome and lysosome pathways in PC12 cells by serum withdrawal: Its protection by nerve growth factor and role in exocytosis

Ceramide kinase (CerK) phosphorylates ceramide to ceramide-1-phosphate (C1P). CerK is highly expressed in the brain, and its association with the neuronal function has been reported. Previous reports showed that the activity of CerK is regulated by post-translational modifications including phosphorylation, whereas the cellular fate of CerK protein and its role in neuronal functions have not been clearly elucidated. Therefore, we investigated these issues in PC12 cells. Treatment with nerve growth factor (NGF) for 6 h increased the formation of C1P but not CerK mRNA. Knockdown of CerK and overexpression of HA-tagged CerK down- and up-regulated the formation of C1P, respectively. In PC12-CerK-HA cells, serum withdrawal caused ubiquitination of CerK-HA protein and down-regulated both CerK-HA protein and C1P formation within 6 h, and these down-regulations were abolished by co-treatments with NGF or proteasome inhibitors such as MG132 and clasto-lactacystin. Microscopic analysis showed that treatment with the proteasome inhibitors increased CerK-HA in puncture structures, possibly endosomes and/or vesicles, in cells. Treatment with the lysosome inhibitors reduced serum withdrawal-induced down-regulation of CerK-HA protein but not C1P formation. When knockdown or overexpression of CerK was performed, Ca²⁺-induced release of [³H] noradrenaline was reduced or enhanced, respectively, but neurite extension was not modified. There was a positive correlation between noradrenaline release and formation of C1P and/or CerK-HA levels in NGF- and clasto-lactacystin-treated cells. These results suggest that levels of CerK were down-regulated by the ubiquitin/proteasome and lysosome pathways and the former pathway-sensitive pool of CerK was suggested to be linked with exocytosis in PC12 cells.

The Genetic Variations Associated With Time to Aseptic Loosening After Total Joint Arthroplasty

BACKGROUND

Total joint arthroplasty (TJA) is one of the most frequent surgical procedures performed in modern hospitals, and aseptic loosening is the most common indication for revision surgeries. We conducted a systemic exploration of potential genetic determinants for early aseptic loosening.

METHODS

Data from 423 patients undergoing TJA were collected and analyzed. Three analytical groups were formed based on joint arthroplasty status. Group 1 were TJA patients without symptoms of aseptic loosening of at least 1 year, group 2 were patients with primary TJA, and group 3 were patients receiving revision surgery because of aseptic loosening. Genome-wide genotyping comparing genotype frequencies between patients with and without aseptic loosening (group 3 vs groups 1 and 2) was conducted. A case-control association analysis and linear modeling were applied to identify the impact of the identified genes on implant survival with time to the revision as an outcome measure.

RESULTS

We identified 52 single-nucleotide polymorphisms (SNPs) with a genome-wide suggestive P value less than 10^-5 to be associated with the implant loosening. The most remarkable odds ratios (OR) were found with the variations in the IFIT2/IFIT3 (OR, 21.6), CERK (OR, 12.6), and PAPPA (OR, 14.0) genes. Variations in the genotypes of 4 SNPs-rs115871127, rs16823835, rs13275667, and rs2514486-predicted variability in the time to aseptic loosening. The time to aseptic loosening varied from 8 to 16 years depending on the genotype, indicating a substantial effect of genetic variance.

CONCLUSION

Development of the aseptic loosening is associated with several genetic variations and we identified at least 4 SNPs with a significant effect on the time for loosening. These data could help to develop a personalized approach for TJA and loosening management.

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.

Targeting lipid mediators in cancer biology

Bioactive lipids are essential components of human cells and tissues. As discussed in this review, the cancer lipidome is diverse and malleable, with the ability to promote or inhibit cancer pathogenesis. Targeting lipids within the tumor and surrounding microenvironment may be a novel therapeutic approach for treating cancer patients. Additionally, the emergence of a novel super-family of lipid mediators termed specialized pro-resolving mediators (SPMs) has revealed a new role for bioactive lipid mediators in the resolution of inflammation in cancer biology. The role of SPMs in cancer holds great promise in our understanding of cancer pathogenesis and can ultimately be used in future cancer diagnostics and therapy.

Phosphorylation and inhibition of ceramide kinase by protein kinase C-β: Their changes by serine residue mutations

Ceramide kinase (CerK) phosphorylates ceramide to ceramide-1-phosphate (C1P), and various roles for the CerK/C1P pathway in the regulation of cellular/biological functions have been demonstrated. CerK is constitutively phosphorylated at several serine (Ser, S) residues, however, the roles of Ser residues, including their phosphorylation, in CerK activity, have not yet been elucidated in detail. Therefore, we conducted the present study to investigate this issue. In A549 cells expressing wild-type CerK, a treatment with phorbol 12-myristate 13-acetate (PMA) decreased the formation of C1P in a protein kinase C (PKC)-βI/II-mediated manner. In the Phos-tag SDS-PAGE analysis, CerK existed in its phosphorylated form and was further phosphorylated by the PMA treatment in a PKC-βI/II-mediated manner. We examined the effects of the displacement of Ser residues (72/300/340/403/408/427) in CerK by alanine (Ala, A) on its activity and phosphorylation. Triple mutations (S340/408/427A), but not a single or double mutations (S340/408A), in CerK significantly decreased the formation of C1P. PMA-induced phosphorylation levels in S340/408A- and S340/408/427A-CerK were significantly and maximally reduced, respectively, but were similar in CerK with a single mutation and wild-type CerK. Ser residue mutations tested, including six mutations, did not affect PMA-induced decreases in C1P formation more than expected. Treatments with the protein phosphatase inhibitors, okadaic acid and cyclosporine A, decreased the formation of C1P. These results demonstrated that the activity of CerK was regulated in a phosphorylation-dependent manner in cells.

The Role of Ceramide 1-Phosphate in Tumor Cell Survival and Dissemination

Ceramide 1-phosphate (C1P) is a pleiotropic bioactive sphingolipid metabolite capable of regulating key physiologic cell functions and promoting pathologic processes. Concerning pathology, C1P or ceramide kinase (CerK), the enzyme responsible for its biosynthesis in mammalian cells, has been implicated in cancer cell growth, survival, and dissemination and is involved in inflammatory responses associated with different types of cancer cells. The mechanisms or signaling pathways mediating these C1P actions have only been partially described. This chapter reviews recent progress in identifying signal transduction pathways involved in the promotion of cancer cell growth, survival, and dissemination by CerK and C1P.

Identification of an acid sphingomyelinase ceramide kinase pathway in the regulation of the chemokine CCL5

Acid sphingomyelinase (ASM) hydrolyzes sphingomyelin to produce the biologically active lipid ceramide. Previous studies have implicated ASM in the induction of the chemokine CCL5 in response to TNF-α however, the lipid mediator of this effect was not established. In the present study, we identified a novel pathway connecting ASM and ceramide kinase (CERK). The results show that TNF-α induces the formation of ceramide 1-phosphate (C-1-P) in a CERK-dependent manner. Silencing of CERK blocks CCL5 production in response to TNF-α. Interestingly, cells lacking ASM have decreased C-1-P production following TNF-α treatment, suggesting that ASM may be acting upstream of CERK. Functionally, ASM and CERK induce a highly concordant program of cytokine production and both are required for migration of breast cancer cells. Taken together, these data suggest ASM can produce ceramide which is then converted to C-1-P by CERK, and that C-1-P is required for production of CCL5 and several cytokines and chemokines, with roles in cell migration. These results highlight the diversity in action of ASM through more than one bioactive sphingolipid.

The Role of Sphingosine-1-Phosphate and Ceramide-1-Phosphate in Inflammation and Cancer

Inflammation is part of our body's response to tissue injury and pathogens. It helps to recruit various immune cells to the site of inflammation and activates the production of mediators to mobilize systemic protective processes. However, chronic inflammation can increase the risk of diseases like cancer. Apart from cytokines and chemokines, lipid mediators, particularly sphingosine-1-phosphate (S1P) and ceramide-1-phosphate (C1P), contribute to inflammation and cancer. S1P is an important player in inflammation-associated colon cancer progression. On the other hand, C1P has been recognized to be involved in cancer cell growth, migration, survival, and inflammation. However, whether C1P is involved in inflammation-associated cancer is not yet established. In contrast, few studies have also suggested that S1P and C1P are involved in anti-inflammatory pathways regulated in certain cell types. Ceramide is the substrate for ceramide kinase (CERK) to yield C1P, and sphingosine is phosphorylated to S1P by sphingosine kinases (SphKs). Biological functions of sphingolipid metabolites have been studied extensively. Ceramide is associated with cell growth inhibition and enhancement of apoptosis while S1P and C1P are associated with enhancement of cell growth and survival. Altogether, S1P and C1P are important regulators of ceramide level and cell fate. This review focuses on S1P and C1P involvement in inflammation and cancer with emphasis on recent progress in the field.

Vascular endothelial growth factor mediates ceramide 1-phosphate-stimulated macrophage proliferation

The bioactive sphingolipid ceramide 1-phosphate (C1P) regulates cell division in a variety of cell types including macrophages. However, the mechanisms involved in this action are not completely understood. In the present work we show that C1P stimulates the release of vascular endothelial growth factor (VEGF) in RAW264.7 macrophages, and that this growth factor is essential for stimulation of cell proliferation by C1P. The stimulation of VEGF release was dependent upon activation of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB-1 also known as Akt-1), and mitogen-activated protein kinase-kinase (MEK)/extracellularly regulated kinase-2 (ERK-2) pathways, as inhibition of these kinases with selective pharmacological inhibitors or with specific gene silencing siRNA, abrogated VEGF release. A key observation was that sequestration of VEGF with a neutralizing antibody, or treatment with VEGF siRNA abolished C1P-stimulated macrophage growth. Also, inhibition of the pathways involved in C1P-stimulated VEGF release inhibited the stimulation of macrophage growth by C1P. Moreover, blockade of VEGF receptor-2 (VEGFR-2), which is the primary receptor for VEGF, with the pharmacological inhibitor DMH4, or with specific VEGFR-2 siRNA, substantially inhibited C1P-stimulated cell growth. It can be concluded that stimulation of VEGF release is a key factor in the promotion of macrophage proliferation by C1P.

Crosstalk between sphingolipids and vitamin D3: potential role in the nervous system

Sphingolipids are both structural and bioactive compounds. In particular, ceramide and sphingosine 1-phosphate regulate cell fate, inflammation and excitability. 1-α,25-dihydroxyvitamin D3 (1,25(OH)₂ D₃ ) is known to play an important physiological role in growth and differentiation in a variety of cell types, including neural cells, through genomic actions mediated by its specific receptor, and non-genomic effects that result in the activation of specific signalling pathways. 1,25(OH)₂ D₃ and sphingolipids, in particular sphingosine 1-phosphate, share many common effectors, including calcium regulation, growth factors and inflammatory cytokines, but it is still not known whether they can act synergistically. Alterations in the signalling and concentrations of sphingolipids and 1,25(OH)₂ D₃ have been found in neurodegenerative diseases and fingolimod, a structural analogue of sphingosine, has been approved for the treatment of multiple sclerosis. This review, after a brief description of the role of sphingolipids and 1,25(OH)₂ D₃ , will focus on the potential crosstalk between sphingolipids and 1,25(OH)₂ D₃ in neural cells.

Vitamin D3 protects against Aβ peptide cytotoxicity in differentiated human neuroblastoma SH- SY5Y cells: A role for S1P1/p38MAPK/ATF4 axis

Besides its classical function of bone metabolism regulation, 1alpha, 25-dihydroxyvitamin D3 (1,25(OH)₂D₃), acts on a variety of tissues including the nervous system, where the hormone plays an important role as neuroprotective, antiproliferating and differentiating agent. Sphingolipids are bioactive lipids that play critical and complex roles in regulating cell fate. In the present paper we have investigated whether sphingolipids are involved in the protective action of 1,25(OH)₂D_3. We have found that 1,25(OH)₂D₃ prevents amyloid-β peptide (Aβ(1-42)) cytotoxicity both in differentiated SH-SY5Y human neuroblastoma cells and in vivo. In differentiated SH-SY5Y cells, Aβ(1-42) strongly reduces the sphingosine-1-phosphate (S1P)/ceramide (Cer) ratio while 1,25(OH)₂D₃ partially reverts this effect. 1,25(OH)₂D₃ reverts also the Aβ(1-42)-induced reduction of sphingosine kinase activity. We have also studied the crosstalk between 1,25(OH)₂D₃ and S1P signaling pathways downstream to the activation of S1P receptor subtype S1P1. Notably, we found that 1,25(OH)₂D₃ prevents the reduction of S1P1 expression promoted by Aβ(1-42) and thereby it modulates the downstream signaling leading to ER stress damage (p38MAPK/ATF4). Similar effects were observed by using ZK191784. In addition, chronic treatment with 1,25(OH)₂D₃ protects from aggregated Aβ(1-42)-induced damage in the CA1 region of the rat hippocampus and promotes cell proliferation in the hippocampal dentate gyrus of adult mice. In conclusion, these results represent the first evidence of the role of 1,25(OH)₂D₃ and its structural analogue ZK191784 in counteracting the Aβ(1-42) peptide-induced toxicity through the modulation of S1P/S1P1/p38MAPK/ATF4 pathway in differentiated SH-SY5Y cells.

Nuclear Lipids in the Nervous System: What they do in Health and Disease

In the last 20 years it has been widely demonstrated that cell nucleus contains neutral and polar lipids localized in nuclear membranes, nucleoli, nuclear matrix and chromatin. Nuclear lipids may show specific organization forming nuclear lipid microdomains and have both structural and functional roles. Depending on their localization, nuclear lipids play different roles such as the regulation of nuclear membrane and nuclear matrix fluidity but they also can act as platforms for vitamin and hormone function, for active chromatin anchoring, and for the regulation of gene expression, DNA duplication and transcription. Crosstalk among different kinds of lipid signalling pathways influence the physiopathology of numerous cell types. In neural cells the nuclear lipids are involved in cell proliferation, differentiation, inflammation, migration and apoptosis. Abnormal metabolism of nuclear lipids might be closely associated with tumorigenesis and neurodegenerative diseases such as Alzheimer disease and Parkinson disease among others.

Protective effects of 1α,25-Dihydroxyvitamin D3 on cultured neural cells exposed to catalytic iron

Recent studies have postulated a role for vitamin D and its receptor on cerebral function, and anti‐inflammatory, immunomodulatory and neuroprotective effects have been described; vitamin D can inhibit proinflammatory cytokines and nitric oxide synthesis during various neurodegenerative insults, and may be considered as a potential drug for the treatment of these disorders. In addition, iron is crucial for neuronal development and neurotransmitter production in the brain, but its accumulation as catalytic form (Fe³⁺) impairs brain function and causes the dysregulation of iron metabolism leading to tissue damage due to the formation of toxic free radicals (ROS). This research was planned to study the role of vitamin D to prevent iron damage in neuroblastoma BE(2)M17 cells. Mechanisms involved in neurodegeneration, including cell viability, ROS production, and the most common intracellular pathways were studied. Pretreatment with calcitriol (the active form of vitamin D) reduced cellular injury induced by exposure to catalytic iron.

Non-dioxin-like organic toxicant PCB153 modulates sphingolipid metabolism in liver progenitor cells: its role in Cx43-formed gap junction impairment

The non-dioxin-like environmental toxicant 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153), member of a group of persistent organic pollutants wide-spread throughout the environment, reduces gap junction intercellular communication (GJIC), an event possibly associated with tumor promotion. Since very few studies have investigated the signaling effectors and mode(s) of action of PCB153, and it is known that the gap junction (GJ) protein Cx43 can be regulated by the bioactive sphingolipid (SL) sphingosine 1-phosphate (S1P), this in vitro study mainly addresses whether SL metabolism is affected by PCB153 in rat liver epithelial WB-F344 cells. PCB153 treatment obtained significant changes in the S1P/ceramide (Cer) ratio, known to be crucial in determining cell fate. In particular, an increase in S1P at 30 min and a decrease of the bioactive lipid at 3 h were observed, whereas Cer level increased at 1 h and 24 h. Notably, a time-dependent modulation of sphingosine kinase (SphK), the enzyme responsible for S1P synthesis, and of its regulators, ERK1/2 and protein phosphatase PP2A, supports the involvement of these signaling effectors in PCB153 toxicity. Electrophysiological analyses, furthermore, indicated that the lipophilic environmental toxicant significantly reduced GJ biophysical properties, affecting both voltage-dependent (such as those formed by Cx43 and/or Cx32) and voltage-independent channels, thereby demonstrating that PCB153 may act differently on GJs formed by distinct Cx isoforms. SphK down-regulation alone induced GJIC impairment, and, when combined with PCB153, the acute effect on GJ suppression was additive. Moreover, after enzyme-specific gene silencing, the SphK1 isoform appears to be responsible for down-regulating Cx43 expression, while being the target of PCB153 at short-term exposure. In conclusion, we provide the first evidence of novel effectors in PCB153 toxic action in rat liver stem-like cells, leading us to consider SLs as potential markers for preventing GJIC deregulation and, thus, the tumorigenic action elicited by this environmental toxicant.

Role of sphingosine kinase/S1P axis in ECM remodeling of cardiac cells elicited by relaxin

The initiation and progression of heart failure is linked to adverse cardiac remodeling of the extracellular matrix (ECM) during disease mainly through the deregulation of myocardial metalloproteinases (MMPs). Relaxin (RLX), a peptide hormone acting as a physiological cardiac effector, is a key regulator of ECM remodeling in reproductive and nonreproductive tissues. Studying primary cultures of mouse cardiac muscle cells and rat H9c2 cardiomyoblasts, we have obtained evidence for a new signaling pathway activated by RLX to induce ECM remodeling that involves the bioactive sphingolipids sphingosine-1-phosphate (S1P) and ceramide. In both cell populations, recombinant human RLX increased sphingosine kinase activity and S1P formation, whereas sphingomyelin and ceramide content were decreased in [(3)H]serine-labeled cells. According to the literature, RLX promoted MMP-2 and MMP-9 expression/release. Pharmacological inhibition of sphingolipid metabolism and silencing of sphingosine kinase 1, the enzyme responsible for S1P formation, were able to prevent MMP expression/release elicited by the hormone and induce the expression of tissue inhibitor of MMPs. In addition, we found that sphingolipid signaling is required for the regulation of connective tissue growth factor, a member of the CCN 1-3 family of genes that are involved in cell proliferation and differentiation. Finally, the induction of cardiomyoblast maturation induced by RLX was also found to be counteracted by inhibition of S1P formation. In conclusion, these findings provide a novel mechanism by which RLX acts on cardiac ECM remodeling and cardiac cell differentiation and offer interesting therapeutic options to prevent heart fibrosis and to favor myocardial regeneration.

Control of inflammatory responses by ceramide, sphingosine 1-phosphate and ceramide 1-phosphate

Inflammation is a network of complex processes involving a variety of metabolic and signaling pathways aiming at healing and repairing damage tissue, or fighting infection. However, inflammation can be detrimental when it becomes out of control. Inflammatory mediators involve cytokines, bioactive lipids and lipid-derived metabolites. In particular, the simple sphingolipids ceramides, sphingosine 1-phosphate, and ceramide 1-phosphate have been widely implicated in inflammation. However, although ceramide 1-phosphate was first described as pro-inflammatory, recent studies show that it has anti-inflammatory properties when produced in specific cell types or tissues. The biological functions of ceramides and sphingosine 1-phosphate have been extensively studied. These sphingolipids have opposing effects with ceramides being potent inducers of cell cycle arrest and apoptosis, and sphingosine 1-phosphate promoting cell growth and survival. However, the biological actions of ceramide 1-phosphate have only been partially described. Ceramide 1-phosphate is mitogenic and anti-apoptotic, and more recently, it has been demonstrated to be key regulator of cell migration. Both sphingosine 1-phosphate and ceramide 1-phosphate are also implicated in tumor growth and dissemination. The present review highlights new aspects on the control of inflammation and cell migration by simple sphingolipids, with special emphasis to the role played by ceramide 1-phosphate in controlling these actions.

Inhibitors for the Vitamin D Receptor-Coregulator Interaction

The vitamin D receptor (VDR) belongs to the superfamily of nuclear receptors and is activated by the endogenous ligand 1,25-dihydroxyvitamin D3. The genomic effects mediated by VDR consist of the activation and repression of gene transcription, which includes the formation of multiprotein complexes with coregulator proteins. Coregulators bind many nuclear receptors and can be categorized according to their role as coactivators (gene activation) or corepressors (gene repression). Herein, different approaches to develop compounds that modulate the interaction between VDR and coregulators are summarized. This includes coregulator peptides that were identified by creating phage display libraries. Subsequent modification of these peptides including the introduction of a tether or nonhydrolyzable bonds resulted in the first direct VDR-coregulator inhibitors. Later, small molecules that inhibit VDR-coregulator inhibitors were identified using rational drug design and high-throughput screening. Early on, allosteric inhibition of VDR-coregulator interactions was achieved with VDR antagonists that change the conformation of VDR and modulate the interactions with coregulators. A detailed discussion of their dual agonist/antagonist effects is given as well as a summary of their biological effects in cell-based assays and in vivo studies.

Epigenetic and Immune Regulation of Colorectal Cancer Stem Cells

Colorectal cancer stem cells (CSCs) were initially considered to be a subset of undifferentiated tumor cells with well-defined phenotypic and molecular markers. However, emerging evidence indicates instead that colorectal CSCs are heterogeneous subsets of tumor cells that are continuously reshaped by the dynamic interactions between genetic, epigenetic, and immune factors in the tumor microenvironment. Thus, the colorectal CSC phenotypes and responsiveness to therapy may not only be a tumor cell-intrinsic feature, but also depend on tumor-extrinsic microenvironmental factors. Furthermore, emerging evidence also implicates colorectal CSCs in potential immune evasion. Therefore, understanding how colorectal CSC-intrinsic mechanisms cooperate with the extrinsic microenvironmental factors to dynamically shape colorectal CSC resistance to chemotherapy and immunotherapy holds great promise for development of targeted CSC therapies of advanced human CRC.

Nutraceutical properties of chestnut flours: beneficial effects on skeletal muscle atrophy

Plants contain a wide range of non-nutritive phytochemicals, many of which have protective or preventive properties for human diseases. The aim of the present work has been to investigate the nutraceutical properties of sweet chestnut flour extracts obtained from fruits collected from 7 geographic areas of Tuscany (Italy), and their ability in modulating skeletal muscle atrophy. We found that the cultivars from different geographic areas are characterized by the composition and quantity of various nutrients and specific bioactive components, such as tocopherols, polyphenols and sphingolipids. The nutraceutical properties of chestnut sweet flours have been evaluated in C2C12 myotubes induced to atrophy by serum deprivation or dexamethasone. We found that the pretreatment with both total extracts of tocopherols and sphingolipids is able to counterbalance cell atrophy, reducing the decrease in myotube size and myonuclei number, and attenuating protein degradation and the increase in expression of MAFbx/atrogin-1 (a muscle-specific atrophy marker). By contrast, polyphenol extracts were not able to prevent atrophy. Since we also found that γ-tocopherol is the major form of tocopherol in sweet flour and its content differs depending on the procedure of sweet flour preparation, the mechanisms by which γ-tocopherol as well as sphingolipids affect skeletal muscle cell atrophy have been also investigated. This is the first evidence that chestnut sweet flour is a natural source of specific bioactive components with a relevant role in the prevention of cell degeneration and maintenance of skeletal muscle mass, opening important implications in designing appropriate nutritional therapeutic approaches to skeletal muscle atrophy.

Sphingomyelinase D/ceramide 1-phosphate in cell survival and inflammation

Sphingolipids are major constituents of biological membranes of eukaryotic cells. Many studies have shown that sphingomyelin (SM) is a major phospholipid in cell bilayers and is mainly localized to the plasma membrane of cells, where it serves both as a building block for cell architecture and as a precursor of bioactive sphingolipids. In particular, upregulation of (C-type) sphingomyelinases will produce ceramide, which regulates many physiological functions including apoptosis, senescence, or cell differentiation. Interestingly, the venom of some arthropodes including spiders of the genus Loxosceles, or the toxins of some bacteria such as Corynebacterium tuberculosis, or Vibrio damsela possess high levels of D-type sphingomyelinase (SMase D). This enzyme catalyzes the hydrolysis of SM to yield ceramide 1-phosphate (C1P), which promotes cell growth and survival and is a potent pro-inflammatory agent in different cell types. In particular, C1P stimulates cytosolic phospholipase A2 leading to arachidonic acid release and the subsequent formation of eicosanoids, actions that are all associated to the promotion of inflammation. In addition, C1P potently stimulates macrophage migration, which has also been associated to inflammatory responses. Interestingly, this action required the interaction of C1P with a specific plasma membrane receptor, whereas accumulation of intracellular C1P failed to stimulate chemotaxis. The C1P receptor is coupled to Gi proteins and activates of the PI3K/Akt and MEK/ERK1-2 pathways upon ligation with C1P. The proposed review will address novel aspects on the control of inflammatory responses by C1P and will highlight the molecular mechanisms whereby C1P exerts these actions.

Mesenchymal stromal cell secreted sphingosine 1-phosphate (S1P) exerts a stimulatory effect on skeletal myoblast proliferation

Bone-marrow-derived mesenchymal stromal cells (MSCs) have the potential to significantly contribute to skeletal muscle healing through the secretion of paracrine factors that support proliferation and enhance participation of the endogenous muscle stem cells in the process of repair/regeneration. However, MSC-derived trophic molecules have been poorly characterized. The aim of this study was to investigate paracrine signaling effects of MSCs on skeletal myoblasts. It was found, using a biochemical and morphological approach that sphingosine 1-phosphate (S1P), a natural bioactive lipid exerting a broad range of muscle cell responses, is secreted by MSCs and represents an important factor by which these cells exert their stimulatory effects on C2C12 myoblast and satellite cell proliferation. Indeed, exposure to conditioned medium obtained from MSCs cultured in the presence of the selective sphingosine kinase inhibitor (iSK), blocked increased cell proliferation caused by the conditioned medium from untreated MSCs, and the addition of exogenous S1P in the conditioned medium from MSCs pre-treated with iSK further increased myoblast proliferation. Finally, we also demonstrated that the myoblast response to MSC-secreted vascular endothelial growth factor (VEGF) involves the release of S1P from C2C12 cells. Our data may have important implications in the optimization of cell-based strategies to promote skeletal muscle regeneration.

Re-configuration of sphingolipid metabolism by oncogenic transformation

The sphingolipids are one of the major lipid families in eukaryotes, incorporating a diverse array of structural variants that exert a powerful influence over cell fate and physiology. Increased expression of sphingosine kinase 1 (SPHK1), which catalyses the synthesis of the pro-survival, pro-angiogenic metabolite sphingosine 1-phosphate (S1P), is well established as a hallmark of multiple cancers. Metabolic alterations that reduce levels of the pro-apoptotic lipid ceramide, particularly its glucosylation by glucosylceramide synthase (GCS), have frequently been associated with cancer drug resistance. However, the simple notion that the balance between ceramide and S1P, often referred to as the sphingolipid rheostat, dictates cell survival contrasts with recent studies showing that highly potent and selective SPHK1 inhibitors do not affect cancer cell proliferation or survival, and studies demonstrating higher ceramide levels in some metastatic cancers. Recent reports have implicated other sphingolipid metabolic enzymes such as acid sphingomyelinase (ASM) more strongly in cancer pathogenesis, and highlight lysosomal sphingolipid metabolism as a possible weak point for therapeutic targeting in cancer. This review describes the evidence implicating different sphingolipid metabolic enzymes and their products in cancer pathogenesis, and suggests how newer systems-level approaches may improve our overall understanding of how oncogenic transformation reconfigures sphingolipid metabolism.