Sphingosine kinase 1/S1P pathway involvement in the GDNF-induced GAP43 transcription

The role of sphingosine-1-phosphate in the development and progression of Parkinson's disease

Parkinson's disease (PD) could be viewed as a proteinopathy caused by changes in lipids, whereby modifications in lipid metabolism may lead to protein alterations, such as the accumulation of alpha-synuclein (α-syn), ultimately resulting in neurodegeneration. Although the loss of dopaminergic neurons in the substantia nigra is the major clinical manifestation of PD, the etiology of it is largely unknown. Increasing evidence has highlighted the important role of lipids in the pathophysiology of PD. Sphingosine-1-phosphate (S1P), a signaling lipid, has been suggested to have a potential association with the advancement and worsening of PD. Therefore, better understanding the mechanisms and regulatory proteins is of high interest. Most interestingly, S1P appears to be an important target to offers a new strategy for the diagnosis and treatment of PD. In this review, we first introduce the basic situation of S1P structure, function and regulation, with a special focus on the several pathways. We then briefly describe the regulation of S1P signaling pathway on cells and make a special focused on the cell growth, proliferation and apoptosis, etc. Finally, we discuss the function of S1P as potential therapeutic target to improve the clinical symptoms of PD, and even prevent the progression of the PD. In the context of PD, the functions of S1P modulators have been extensively elucidated. In conclusion, S1P modulators represent a novel and promising therapeutic principle and therapeutic method for PD. However, more research is required before these drugs can be considered as a standard treatment option for PD.

Genes critical for development and differentiation of dopaminergic neurons are downregulated in Parkinson's disease

We performed transcriptome analysis using RNA sequencing on substantia nigra pars compacta (SNpc) from mice after acute and chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment and from Parkinson's disease (PD) patients. Acute and chronic exposure to MPTP resulted in decreased expression of genes involved in sodium channel regulation. However, upregulation of pro-inflammatory pathways was seen after single dose but not after chronic MPTP treatment. Dopamine biosynthesis and synaptic vesicle recycling pathways were downregulated in PD patients and after chronic MPTP treatment in mice. Genes essential for midbrain development and determination of dopaminergic phenotype such as, LMX1B, FOXA1, RSPO2, KLHL1, EBF3, PITX3, RGS4, ALDH1A1, RET, FOXA2, EN1, DLK1, GFRA1, LMX1A, NR4A2, GAP43, SNCA, PBX1, and GRB10 were downregulated in human PD and overexpression of GFP tagged LMX1B rescued MPP⁺ induced death in SH-SY5Y neurons. Downregulation of gene ensemble involved in development and differentiation of dopaminergic neurons indicate their potential involvement in pathogenesis and progression of human PD.

Combination of midostaurin and ATRA exerts dose-dependent dual effects on acute myeloid leukemia cells with wild type FLT3

Background

Midostaurin combined with chemotherapy is currently used to treat newly diagnosed acute myeloid leukemia (AML) patients with FMS-like tyrosine kinase 3 (FLT3)-mutations. However, midostaurin acts as an antagonist to some chemotherapeutic agents in leukemia cell lines without FLT3 mutations. All-trans retinoic acid (ATRA) induces apoptosis when used in combination with midostaurin in FLT3-mutated AML cells. This combination has been shown to be safe in AML patients. However, the effect of this combination has not been investigated in AML without FLT3 mutations.

Methods

Cell proliferation was assessed by a cell counting assay. Cell death was evaluated by cell viability and Annexin-V assays. Cell differentiation was assessed by CD11b expression profiling and morphological analysis. To explore the underlying mechanisms, we studied the role of caspase3/7, Lyn, Fgr, Hck, RAF, MEK, ERK, AKT, PU.1, CCAAT/enhancer binding protein β (C/EBPβ) and C/EBPε by Western blot analysis and immunoprecipitation assays. Antitumor activity was also confirmed in mouse xenograft models established with AML cells.

Results

In this study, 0.1 − 0.25 μM midostaurin (mido(L)) combined with ATRA induced differentiation while 0.25 − 0.5 μM midostaurin (mido(H)) combined with ATRA triggered apoptosis in some AML cell lines without FLT3-mutations. Midostaurin combined with ATRA (mido-ATRA) also exhibited antitumor activity in mouse xenograft models established with AML cells. Mechanistically, mido(H)-ATRA-induced apoptosis was dependent on caspase-3/7. Mido(L)-ATRA inhibited Akt activation which was associated with decreased activity of Lyn/Fgr/Hck, resulted in dephosphorylation of RAF S259, activated RAF/MEK/ERK, along with upregulating the protein levels of C/EBPβ, C/EBPε and PU.1. A MEK specific inhibitor was observed to suppress mido(L)-ATRA-induced increases in the protein levels of C/EBPs and PU.1 and mido(L)-ATRA-induced differentiation. Furthermore, inhibition of Akt activity promoted mido(L)-ATRA-induced downregulation of RAF S259 phosphorylation and mido(L)-ATRA-induced differentiation. Therefore, Lyn/Fgr/Hck-associated Akt inhibition activated RAF/MEK/ERK and controlled mido(L)-ATRA-induced differentiation by upregulation of C/EBPs and PU.1. Mido(L)-ATRA also promoted assembly of the signalosome, which may facilitate RAF activation.

Conclusions

Midostaurin combined with ATRA exerts antitumor activity against AML with wild-type FLT3 mutations in vitro and in vivo. These findings may provide novel therapeutic strategies for some AML patients without FLT3 mutations and imply a new target of midostaurin.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09828-2.

Recent Insights into the Interplay of Alpha-Synuclein and Sphingolipid Signaling in Parkinson's Disease

Molecular studies have provided increasing evidence that Parkinson’s disease (PD) is a protein conformational disease, where the spread of alpha-synuclein (ASN) pathology along the neuraxis correlates with clinical disease outcome. Pathogenic forms of ASN evoke oxidative stress (OS), neuroinflammation, and protein alterations in neighboring cells, thereby intensifying ASN toxicity, neurodegeneration, and neuronal death. A number of evidence suggest that homeostasis between bioactive sphingolipids with opposing function—e.g., sphingosine-1-phosphate (S1P) and ceramide—is essential in pro-survival signaling and cell defense against OS. In contrast, imbalance of the “sphingolipid biostat” favoring pro-oxidative/pro-apoptotic ceramide-mediated changes have been indicated in PD and other neurodegenerative disorders. Therefore, we focused on the role of sphingolipid alterations in ASN burden, as well as in a vast range of its neurotoxic effects. Sphingolipid homeostasis is principally directed by sphingosine kinases (SphKs), which synthesize S1P—a potent lipid mediator regulating cell fate and inflammatory response—making SphK/S1P signaling an essential pharmacological target. A growing number of studies have shown that S1P receptor modulators, and agonists are promising protectants in several neurological diseases. This review demonstrates the relationship between ASN toxicity and alteration of SphK-dependent S1P signaling in OS, neuroinflammation, and neuronal death. Moreover, we discuss the S1P receptor-mediated pathways as a novel promising therapeutic approach in PD.

Lysophospholipids and Their G-Coupled Protein Signaling in Alzheimer's Disease: From Physiological Performance to Pathological Impairment

Lysophospholipids (LPLs) are bioactive signaling lipids that are generated from phospholipase-mediated hydrolyzation of membrane phospholipids (PLs) and sphingolipids (SLs). Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are two of the best-characterized LPLs which mediate a variety of cellular physiological responses via specific G-protein coupled receptor (GPCR) mediated signaling pathways. Considerable evidence now demonstrates the crucial role of LPA and S1P in neurodegenerative diseases, especially in Alzheimer’s disease (AD). Dysfunction of LPA and S1P metabolism can lead to aberrant accumulation of amyloid-β (Aβ) peptides, the formation of neurofibrillary tangles (NFTs), neuroinflammation and ultimately neuronal death. Summarizing LPA and S1P signaling profile may aid in profound health and pathological processes. In the current review, we will introduce the metabolism as well as the physiological roles of LPA and S1P in maintaining the normal functions of the nervous system. Given these pivotal functions, we will further discuss the role of dysregulation of LPA and S1P in promoting AD pathogenesis.

Sphingosine Kinase 1 Regulates the Survival of Breast Cancer Stem Cells and Non-stem Breast Cancer Cells by Suppression of STAT1

Cancer stem cells (CSCs) represent rare tumor cell populations capable of self-renewal, differentiation, and tumor initiation and are highly resistant to chemotherapy and radiotherapy. Thus, therapeutic approaches that can effectively target CSCs and tumor cells could be the key to efficient tumor treatment. In this study, we explored the function of SPHK1 in breast CSCs and non-CSCs. We showed that RNAi-mediated knockdown of SPHK1 inhibited cell proliferation and induced apoptosis in both breast CSCs and non-CSCs, while ectopic expression of SPHK1 enhanced breast CSC survival and mammosphere forming efficiency. We identified STAT1 and IFN signaling as key regulatory targets of SPHK1 and demonstrated that an important mechanism by which SPHK1 promotes cancer cell survival is through the suppression of STAT1. We further demonstrated that SPHK1 inhibitors, FTY720 and PF543, synergized with doxorubicin in targeting both breast CSCs and non-CSCs. In conclusion, we provide important evidence that SPHK1 is a key regulator of cell survival and proliferation in breast CSCs and non-CSCs and is an attractive target for the design of future therapies.

Dasatinib synergizes with ATRA to trigger granulocytic differentiation in ATRA resistant acute promyelocytic leukemia cell lines via Lyn inhibition-mediated activation of RAF-1/MEK/ERK

All-trans retinoic acid (ATRA) resistance has been a critical problem in acute promyelocytic leukemia (APL) relapsed patients. In this study, dasatinib synergized with ATRA to trigger differentiation in ATRA-resistant APL cell lines. The combined treatment activated RAF-1, MEK and ERK as well as enhanced ATRA-promoted up-regulation of the protein level of PU.1, C/EBPβ and C/EBPε. U0126 (MEK specific inhibitor) and sorafenib tosylate (RAF-1 specific inhibitor) suppressed the combined treatment-induced differentiation, ERK phosphorylation and the up-regulation of C/EBPs and PU.1. Sorafenib tosylate also attenuated the MEK activity. However, the combined treatment did not enhance Ras activity and Ras inhibitor neither blocked MEK activation nor inhibited differentiation. Therefore, the combined treatment induced differentiation via Ras independent RAF-1/MEK/ERK. Earlier than RAF-1 activation, dasatinib suppressed Lyn activity, the predominant activated Src family kinase (SFK) and dephosphorylated RAF-1 at S259. Furthermore, SFK inhibitor, PP2 did suppress Lyn activity and mimicked the effect of dasatinib on ATRA-induced differentiation as well as decreased phosphorylation of RAF-1 at S259. Thus, it was suggested that Lyn inhibition might activate RAF-1 by the dephosphorylation of RAF at S259 and lead to differentiation. In conclusion, the combination of dasatinib and ATRA could overcome ATRA resistance through Lyn inhibition-mediated activation of RAF-1/MEK/ERK.

Sphingosine 1-phosphate - A double edged sword in the brain

The physiological functions of sphingosine 1-phosphate (S1P) and its pathological roles in various diseases are increasingly being elucidated. Particularly, a growing body of literature has implicated S1P in the pathogenesis of brain related disorders. With the deciphering of more intricate aspects of S1P signalling, there is also a need to reconsider the notion of S1P only as a determinant of cell survival and proliferation. Further the concept of 'S1P-ceramide' balance as the controlling switch of cellular fate and functions needs to be refined. In this review, we focus on the brain related functions of S1P with special focus on its role in synaptic transmission, neuronal autophagy and neuroinflammation. The review also attempts to bring out the multi-faceted nature of S1P signalling aspects that makes it a 'double edged sword'. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

GDNF From Human Periodontal Ligament Cells Treated With Pro-Inflammatory Cytokines Promotes Neurocytic Differentiation of PC12 Cells

Glial cell line-derived neurotrophic factor (GDNF) is known to mediate multiple biological activities such as promotion of cell motility and proliferation, and morphogenesis. However, little is known about its effects on periodontal ligament (PDL) cells. Recently, we reported that GDNF expression is increased in wounded rat PDL tissue and human PDL cells (HPDLCs) treated with pro-inflammatory cytokines. Here, we investigated the associated expression of GDNF and the pro-inflammatory cytokine interleukin-1 beta (IL-1β) in wounded PDL tissue, and whether HPDLCs secrete GDNF which affects neurocytic differentiation. Rat PDL cells near the wounded area showed intense immunoreactions against an anti-GDNF antibody, where immunoreactivity was also increased against an anti-IL-1β antibody. Compared with untreated cells, HPDLCs treated with IL-1β or tumor necrosis factor-alpha showed an increase in the secretion of GDNF protein. Conditioned medium of IL-1β-treated HPDLCs (IL-1β-CM) increased neurite outgrowth of PC12 rat adrenal pheochromocytoma cells. The expression levels of two neural regeneration-associated genes, growth-associated protein-43 (Gap-43), and small proline-rich repeat protein 1A (Sprr1A), were also upregulated in IL-1β-CM-treated PC12 cells. These stimulatory effects of IL-1β-CM were significantly inhibited by a neutralizing antibody against GDNF. In addition, U0126, a MEK inhibitor, inhibited GDNF-induced neurite outgrowth of PC12 cells. These findings suggest that an increase of GDNF in wounded PDL tissue might play an important role in neural regeneration probably via the MEK/ERK signaling pathway. J. Cell. Biochem. 118: 699-708, 2017. © 2016 Wiley Periodicals, Inc.

C/EBPβ and C/EBPδ transcription factors: Basic biology and roles in the CNS

CCAAT/enhancer binding protein (C/EBP) β and C/EBPδ are transcription factors of the basic-leucine zipper class which share phylogenetic, structural and functional features. In this review we first describe in depth their basic molecular biology which includes fascinating aspects such as the regulated use of alternative initiation codons in the C/EBPβ mRNA. The physical interactions with multiple transcription factors which greatly opens the number of potentially regulated genes or the presence of at least five different types of post-translational modifications are also remarkable molecular mechanisms that modulate C/EBPβ and C/EBPδ function. In the second part, we review the present knowledge on the localization, expression changes and physiological roles of C/EBPβ and C/EBPδ in neurons, astrocytes and microglia. We conclude that C/EBPβ and C/EBPδ share two unique features related to their role in the CNS: whereas in neurons they participate in memory formation and synaptic plasticity, in glial cells they regulate the pro-inflammatory program. Because of their role in neuroinflammation, C/EBPβ and C/EBPδ in microglia are potential targets for treatment of neurodegenerative disorders. Any strategy to reduce C/EBPβ and C/EBPδ activity in neuroinflammation needs to take into account its potential side-effects in neurons. Therefore, cell-specific treatments will be required for the successful application of this strategy.

Enhanced axon outgrowth and improved long-distance axon regeneration in sprouty2 deficient mice

Sprouty (Spry) proteins are negative feedback inhibitors of receptor tyrosine kinase signaling. Downregulation of Spry2 has been demonstrated to promote elongative axon growth of cultured peripheral and central neurons. Here, we analyzed Spry2 global knockout mice with respect to axon outgrowth in vitro and peripheral axon regeneration in vivo. Neurons dissociated from adult Spry2 deficient sensory ganglia revealed stronger extracellular signal-regulated kinase activation and enhanced axon outgrowth. Prominent axon elongation was observed in heterozygous Spry2(+/-) neuron cultures, whereas homozygous Spry2(-/-) neurons predominantly exhibited a branching phenotype. Following sciatic nerve crush, Spry2(+/-) mice recovered faster in motor but not sensory testing paradigms (Spry2(-/-) mice did not tolerate anesthesia required for nerve surgery). We attribute the improvement in the rotarod test to higher numbers of myelinated fibers in the regenerating sciatic nerve, higher densities of motor endplates in hind limb muscles and increased levels of GAP-43 mRNA, a downstream target of extracellular regulated kinase signaling. Conversely, homozygous Spry2(-/-) mice revealed enhanced mechanosensory function (von Frey's test) that was accompanied by an increased innervation of the epidermis, elevated numbers of nonmyelinated axons and more IB4-positive neurons in dorsal root ganglia. The present results corroborate the functional significance of receptor tyrosine kinase signaling inhibitors for axon outgrowth during development and nerve regeneration and propose Spry2 as a novel potential target for pharmacological inhibition to accelerate long-distance axon regeneration in injured peripheral nerves.

Combined staurosporine and retinoic acid induces differentiation in retinoic acid resistant acute promyelocytic leukemia cell lines

All-trans retinoic acid (ATRA) resistance has been a critical problem in acute promyelocytic leukemia (APL) relapsed patients. In ATRA resistant APL cell lines NB4-R1 and NB4-R2, the combination of staurosporine and ATRA synergized to trigger differentiation accompanied by significantly enhanced protein level of CCAAT/enhancer binding protein ε (C/EBPε) and C/EBPβ as well as the phosphorylation of mitogen-activated protein (MEK) and extracellular signal-regulated kinase (ERK). Furthermore, attenuation of the MEK activation blocked not only the differentiation but also the increased protein level of C/EBPε and C/EBPβ. Taken together, we concluded that the combination of ATRA and staurosporine could overcome differentiation block via MEK/ERK signaling pathway in ATRA-resistant APL cell lines.

Sphingosine-1-phosphate receptor-3 signaling up-regulates epidermal growth factor receptor and enhances epidermal growth factor receptor-mediated carcinogenic activities in cultured lung adenocarcinoma cells

Sphingosine-1-phosphate (S1P) regulates a wide array of biological functions. However, the role of S1P signaling in tumorigenesis remains to be elucidated. In this study, we show that S1P receptor subtype 3 (S1P₃) is markedly up-regulated in a subset of lung adenocarcinoma cells compared to normal lung epithelial cells. Specific knockdown of S1P₃ receptors inhibits proliferation and anchorage-independent growth of lung adenocarcinoma cells. Mechanistically, we demonstrate that S1P₃ signaling increases epidermal growth factor receptor (EGFR) expression via the Rho kinase (ROCK) pathway in lung adenocarcinoma cells. Nuclear run-off analysis indicates that S1P/S1P₃ signaling transcriptionally increases EGFR expression. Knockdown of S1P₃ receptors diminishes the S1P-stimulated EGFR expression in lung adenocarcinoma cells. Moreover, S1P treatment greatly enhances EGF-stimulated colony formation, proliferation and invasion of lung adenocarcinoma cells. Together, these results suggest that the enhanced S1P₃-EGFR signaling axis may contribute to the tumorigenesis or progression of lung adenocarcinomas.