A novel isoform of prostate apoptosis response 4 (PAR-4) that co-distributes with F-actin and prevents apoptosis in neural stem cells

Neural stem cells injured by oxidative stress can be rejuvenated by GV1001, a novel peptide, through scavenging free radicals and enhancing survival signals

Oxidative stress is a well-known pathogenic mechanism of a diverse array of neurological diseases, and thus, numerous studies have attempted to identify antioxidants that prevent neuronal cell death. GV1001 is a 16-amino-acid peptide derived from human telomerase reverse transcriptase (hTERT). Considering that hTERT has a strong antioxidant effect, whether GV1001 also has an antioxidant effect is a question of interest. In the present study, we aimed to investigate the effects of GV1001 against oxidative stress in neural stem cells (NSCs). Primary culture NSCs were treated with different concentrations of GV1001 and/or hydrogen peroxide (H2O2) for various time durations. The H2O2 decreased the viability of the NSCs in a concentration-dependent manner, with 200μM H2O2 significantly decreasing both proliferation and migration. However, treatment with GV1001 rescued the viability, proliferation and migration of H2O2-injured NSCs. Consistently, free radical levels were increased in rat NSCs treated with H2O2, while co-treatment with GV1001 significantly reduced these levels, especially the intracellular levels. In addition, GV1001 restored the expression of survival-related proteins and reduced the expression of death-associated ones in NSCs treated with H2O2. In conclusion, GV1001 has antioxidant and neuroprotective effects in NSCs following treatment with H2O2, which appear to be mediated by scavenging free radicals, increasing survival signals and decreasing death signals.

Critical role of Spns2, a sphingosine-1-phosphate transporter, in lung cancer cell survival and migration

The sphingosine-1-phosphate (S1P) transporter Spns2 regulates myocardial precursor migration in zebrafish and lymphocyte trafficking in mice. However, its function in cancer has not been investigated. We show here that ectopic Spns2 expression induced apoptosis and its knockdown enhanced cell migration in non-small cell lung cancer (NSCLC) cells. Metabolically, Spns2 expression increased the extracellular S1P level while its knockdown the intracellular. Pharmacological inhibition of S1P synthesis abolished the augmented cell migration mediated by Spns2 knockdown, indicating that intracellular S1P plays a key role in this process. Cell signaling studies indicated that Spns2 expression impaired GSK-3β and Stat3 mediated pro-survival pathways. Conversely, these pathways were activated by Spns2 knockdown, which explains the increased cell migration since they are also crucial for migration. Alterations of Spns2 were found to affect several enzymes involved in S1P metabolism, including sphingosine kinases, S1P phosphatases, and S1P lyase 1. Genetically, Spns2 mRNA level was found to be reduced in advanced lung cancer (LC) patients as quantified by using a small scale qPCR array. These data show for the first time that Spns2 plays key roles in regulating the cellular functions in NSCLC cells, and that its down-regulation is a potential risk factor for LC.

It's a lipid's world: bioactive lipid metabolism and signaling in neural stem cell differentiation

Lipids are often considered membrane components whose function is to embed proteins into cell membranes. In the last two decades, studies on brain lipids have unequivocally demonstrated that many lipids have critical cell signaling functions; they are called "bioactive lipids". Pioneering work in Dr. Robert Ledeen's laboratory has shown that two bioactive brain sphingolipids, sphingomyelin and the ganglioside GM1 are major signaling lipids in the nuclear envelope. In addition to derivatives of the sphingolipid ceramide, the bioactive lipids discussed here belong to the classes of terpenoids and steroids, eicosanoids, and lysophospholipids. These lipids act mainly through two mechanisms: (1) direct interaction between the bioactive lipid and a specific protein binding partner such as a lipid receptor, protein kinase or phosphatase, ion exchanger, or other cell signaling protein; and (2) formation of lipid microdomains or rafts that regulate the activity of a group of raft-associated cell signaling proteins. In recent years, a third mechanism has emerged, which invokes lipid second messengers as a regulator for the energy and redox balance of differentiating neural stem cells (NSCs). Interestingly, developmental niches such as the stem cell niche for adult NSC differentiation may also be metabolic compartments that respond to a distinct combination of bioactive lipids. The biological function of these lipids as regulators of NSC differentiation will be reviewed and their application in stem cell therapy discussed.

The evolving biology of cell reprogramming

Modern stem cell biology has achieved a transformation that was thought by many to be every bit as unattainable as the ancient alchemists' dream of transforming base metals into gold. Exciting opportunities arise from the process known as 'cellular reprogramming' in which cells can be reliably changed from one tissue type to another. This is enabling novel approaches to more deeply investigate the fundamental basis of cell identity. In addition, new opportunities have also been created to study (perhaps even to treat) human genetic and degenerative diseases. Specific cell types that are affected in inherited disease can now be generated from easily accessible cells from the patient and compared with equivalent cells from healthy donors. The differences in cellular phenotype between the two may then be identified, and assays developed to establish therapies that prevent the development or progression of disease symptoms. Cellular reprogramming also has the potential to create new cells to replace those whose death or dysfunction causes disease symptoms. For patients suffering from inherited cases of degenerative diseases like Parkinson's disease or amyotrophic lateral sclerosis (also known as motor neuron disease), the future realization of such cell-based therapies would truly be worth its weight in gold. However, before this enormous potential can become a reality, several significant biological and technical challenges must be overcome. Furthermore, to maintain the credibility of the scientific community with the general public, it is important that hope-inspiring advances are not over-hyped. The papers in this issue of the Philosophical Transactions of the Royal Society B: Biological Sciences cover many areas relevant to this topic. In this Introduction, we provide an overall context in which to consider these individual papers.

Protection of murine neural progenitor cells by the Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin in the low nanomolar concentration range

Stem cell-based approaches provide hope as a potential therapy for neurodegenerative diseases and stroke. One of the major scientific hurdles for stem cell therapy is the poor survival rate of the newly formed or transplanted neural stem cells. In this study, we found that low-dose treatment with the Heat shock protein 90 (Hsp90) inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG), a heavily investigated anti-cancer drug, prevented neural progenitor cells from either naturally-occurring or stress-induced apoptosis, although it induced apoptosis at higher doses. This stress adaptation effect mediated by low-dose 17-AAG is accompanied by activation of multiple cell survival pathways, including the stress response pathway (induction of Hsp70), the MAPK pathway, and the PI3K/Akt pathway. When administered in vivo, 17-AAG led to Akt and glycogen synthase kinase 3β phosphorylation, and more 5-bromo-2'-deoxyuridine positive cells in the mouse brain. These findings could have profound implications in stem cell therapy for neurodegenerative diseases and stroke.

Ceramide in stem cell differentiation and embryo development: novel functions of a topological cell-signaling lipid and the concept of ceramide compartments

In the last two decades, the view on the function of ceramide as a sole metabolic precursor for other sphingolipids has completely changed. A plethora of studies has shown that ceramide is an important lipid cell-signaling factor regulating apoptosis in a variety of cell types. With the advent of new stem cell technologies and knockout mice for specific steps in ceramide biosynthesis, this view is about to change again. Recent studies suggest that ceramide is a critical cell-signaling factor for stem cell differentiation and cell polarity, two processes at the core of embryo development. This paper discusses studies on ceramide using in vitro differentiated stem cells, embryo cultures, and knockout mice with the goal of linking specific developmental stages to exciting and novel functions of this lipid. Particular attention is devoted to the concept of ceramide as a topological cell-signaling lipid: a lipid that forms distinct structures (membrane domains and vesicles termed “sphingosome”), which confines ceramide-induced cell signaling pathways to localized and even polarized compartments.

There is more to a lipid than just being a fat: sphingolipid-guided differentiation of oligodendroglial lineage from embryonic stem cells

Dr. Robert K. Yu's research showed for the first time that the composition of glycosphingolipids is tightly regulated during embryo development. Studies in our group showed that the glycosphingolipid precursor ceramide is also critical for stem cell differentiation and apoptosis. Our new studies suggest that ceramide and its derivative, sphingosine-1-phosphate (S1P), act synergistically on embryonic stem (ES) cell differentiation. When using neural precursor cells (NPCs) derived from ES cells for transplantation, residual pluripotent stem (rPS) cells pose a significant risk of tumor formation after stem cell transplantation. We show here that rPS cells did not express the S1P receptor S1P1, which left them vulnerable to ceramide or ceramide analog (N-oleoyl serinol or S18)-induced apoptosis. In contrast, ES cell-derived NPCs expressed S1P1 and were protected in the presence of S1P or its pro-drug analog FTY720. Consistent with previous studies, FTY720-treated NPCs differentiated predominantly toward oligodendroglial lineage as tested by the expression of the oligodendrocyte precursor cell (OPC) markers Olig2 and O4. As the consequence, a combined administration of S18 and FTY720 to differentiating ES cells eliminated rPS cells and promoted oligodendroglial differentiation. In addition, we show that this combination promoted differentiation of ES cell-derived NPCs toward oligodendroglial lineage in vivo after transplantation into mouse brain.

Two-state conformational equilibrium in the Par-4 leucine zipper domain

Prostate apoptosis response factor-4 (Par-4) is a pro-apoptotic and tumor-suppressive protein. A highly conserved heptad repeat sequence at the Par-4 C-terminus suggests the presence of a leucine zipper (LZ). This C-terminal region is essential for Par-4 self-association and interaction with various effector proteins. We have used nuclear magnetic resonance (NMR) spectroscopy to fully assign the chemical shift resonances of a peptide comprising the LZ domain of Par-4 at neutral pH. Further, we have investigated the properties of the Par-4 LZ domain and two point mutants under a variety of conditions using NMR, circular dichroism (CD), light scattering, and bioinformatics. Results indicate an environment-dependent conformational equilibrium between a partially ordered monomer (POM) and a predominantly coiled coil dimer (CCD). The combination of techniques used allows the time scales of the equilibrium to be probed and also helps to identify features of the amino acid sequence that may influence the equilibrium.

Intrinsic disorder and coiled-coil formation in prostate apoptosis response factor 4

Prostate apoptosis response factor-4 (Par-4) is an ubiquitously expressed pro-apoptotic and tumour suppressive protein that can both activate cell-death mechanisms and inhibit pro-survival factors. Par-4 contains a highly conserved coiled-coil region that serves as the primary recognition domain for a large number of binding partners. Par-4 is also tightly regulated by the aforementioned binding partners and by post-translational modifications. Biophysical data obtained in the present study indicate that Par-4 primarily comprises an intrinsically disordered protein. Bioinformatic analysis of the highly conserved Par-4 reveals low sequence complexity and enrichment in polar and charged amino acids. The high proteolytic susceptibility and an increased hydrodynamic radius are consistent with a largely extended structure in solution. Spectroscopic measurements using CD and NMR also reveal characteristic features of intrinsic disorder. Under physiological conditions, the data obtained show that Par-4 self-associates via the C-terminal domain, forming a coiled-coil. Interruption of self-association by urea also resulted in loss of secondary structure. These results are consistent with the stabilization of the coiled-coil motif through an intramolecular association.

The pro-apoptotic protein Par-4 facilitates vascular contractility by cytoskeletal targeting of ZIPK

Par-4 (prostate apoptosis response 4) is a pro-apoptotic protein and tumour suppressor that was originally identified as a gene product up-regulated during apoptosis in prostate cancer cells. Here, we show, for the first time, that Par-4 is expressed and co-localizes with the actin filament bundles in vascular smooth muscle. Furthermore, we demonstrate that targeting of ZIPK to the actin filaments, as observed upon PGF-2α stimulation, is inhibited by the presence of a cell permeant Par-4 decoy peptide. The same decoy peptide also significantly inhibits PGF-2α induced contractions of smooth muscle tissue. Moreover, knockdown of Par-4 using antisense morpholino nucleotides results in significantly reduced contractility, and myosin light chain and myosin phosphatase target subunit phosphorylation. These results indicate that Par-4 facilitates contraction by targeting ZIPK to the vicinity of its substrates, myosin light chain and MYPT, which are located on the actin filaments. These results identify Par-4 as a novel regulator of myosin light chain phosphorylation in differentiated, contractile vascular smooth muscle.

Smart drugs for smarter stem cells: making SENSe (sphingolipid-enhanced neural stem cells) of ceramide

Ceramide and its derivative sphingosine-1-phosphate (S1P) are important signaling sphingolipids for neural stem cell apoptosis and differentiation. Most recently, our group has shown that novel ceramide analogs can be used to eliminate teratoma (stem cell tumor)-forming cells from a neural stem cell graft. In new studies, we found that S1P promotes survival of specific neural precursor cells that undergo differentiation to cells expressing oligodendroglial markers. Our studies suggest that a combination of novel ceramide and S1P analogs eliminates tumor-forming stem cells and at the same time, triggers oligodendroglial differentiation. This review discusses recent studies on the function of ceramide and S1P for the regulation of apoptosis, differentiation, and polarity in stem cells. We will also discuss results from ongoing studies in our laboratory on the use of sphingolipids in stem cell therapy.