L-Glutamine (Gln) functions physiologically to balance tissue requirements of carbon and nitrogen. It has been proposed that in cancer cells undergoing aerobic glycolysis, accelerated anabolism is sustained by Gln-derived carbons, which replenish the tricarboxylic acid (TCA) cycle (anaplerosis). However, it is shown here that in glioblastoma (GBM) cells, almost half of the Gln-derived glutamate (Glu) is secreted and does not enter the TCA cycle and, that inhibiting glutaminolysis does not affect proliferation. Moreover, Gln-starved cells are not rescued by TCA cycle replenishment. Instead, the conversion of Glu to Gln by Glutamine Synthetase (GS) (cataplerosis) confers Gln prototrophy, and fuels de novo purine biosynthesis. In both orthotopic GBM models and in patients, 13C-glucose tracing showed that GS produces Gln from TCA cycle-derived carbons. Finally, while it is contributed only marginally by the circulation, the Gln required for the growth of GBM tumours is either autonomously synthesized by GS-positive glioma cells, or supplied by astrocytes.

Astrocytes are the major glial cell of the central nervous system (CNS), providing both metabolic and physical support to other neural cells. After injury, astrocytes become reactive and express a continuum of phenotypes which may be supportive or inhibitory to CNS repair. This review will focus on the ability of astrocytes to influence myelination in the context of specific secreted factors, cytokines and other neural cell targets within the CNS. In particular, we focus on how astrocytes provide energy and cholesterol to neurons, influence synaptogenesis, affect oligodendrocyte biology and instigate cross-talk between the many cellular components of the CNS.

Spinal cord injury (SCI) is a devastating condition with limited capacity for repair. Cell transplantation is a potential strategy to promote SCI repair with cells from the olfactory system being promising candidates. Although transplants of human olfactory mucosa (OM) are already ongoing in clinical trials, the repair potential of this tissue remains unclear. Previously, we identified mesenchymal-like stem cells that reside in the lamina propria (LP-MSCs) of rat and human OM. Little is known about these cells or their interactions with glia such as olfactory ensheathing cells (OECs), which would be co-transplanted with MSCs from the OM, or endogenous CNS glia such as oligodendrocytes. We have characterized, purified, and assessed the repair potential of human LP-MSCs by investigating their effect on glial cell biology with specific emphasis on CNS myelination in vitro. Purified LP-MSCs expressed typical bone marrow MSC (BM-MSC) markers, formed spheres, were clonogenic and differentiated into bone and fat. LP-MSC conditioned medium (CM) promoted oligodendrocyte precursor cell (OPC) and OEC proliferation and induced a highly branched morphology. LP-MSC-CM treatment caused OEC process extension. Both LP and BM-MSCs promoted OPC proliferation and differentiation, but only myelinating cultures treated with CM from LP and not BM-MSCs had a significant increase in myelination. Comparison with fibroblasts and contaminating OM fibroblast like-cells showed the promyelination effect was LP-MSC specific. Thus LP-MSCs harvested from human OM biopsies may be an important candidate for cell transplantation by contributing to the repair of SCI.

Olfactory mucosal (OM) tissue, a potential source of stem cells, is currently being assessed in the clinic as a candidate tissue for transplant‐mediated repair of spinal cord injury. We examined the ability of embryonic rat OM tissue to generate stem cells using culture conditions known to promote neural stem cell proliferation. Primary spheres formed that proliferated and exhibited two main morphologies: (a) CNS neurosphere‐like (OM‐I) and (b) small, tight spheroid‐like (OM‐II). The OM‐I spheres expressed the neural stem cell marker nestin but also markers of peripheral glia, neurons, and connective tissue. Further studies demonstrated the presence of multipotential mesenchymal‐like stem cells within OM‐I spheres that differentiated into bone, adipose, and smooth muscle cells. In contrast, the OM‐II spheres contained mainly cytokeratin‐expressing cells. Immunolabeling of rat olfactory tissue with Stro‐1, CD90, and CD105 showed the presence of multipotent mesenchymal cells in the lamina propria, whereas cytokeratin was expressed by the epithelial cells of the olfactory epithelium. In addition, a comparable pattern of immunoreactivity was detected in human tissue using Stro‐1 and cytokeratin, suggesting the presence of similar cells in this tissue. The identification of a nonepithelial multipotent cell in the OM may explain the varied reports on olfactory stem cell differentiation capacity in vitro and in vivo and illustrates the cellular complexity of this tissue as a potential source of stem cells for transplantation and translation to the clinic. STEM CELLS 2009;27:2196–2208

The initial step in directed cell movement is lamellipodial protrusion, an action driven by actin polymerization. Enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) family proteins are key regulators of this actin polymerization and can control lamellipodial protrusion rate. Ena/VASP proteins are substrates for modification by cyclic-nucleotide-dependent protein kinases at a number of sites. Phosphorylation of Ser239 of VASP in vitro inhibits its anti-capping and filament-bundling activity but the effects of this modification on lamellipodial structure and function are unknown. To examine the functional effects of this modification in living cells, we studied VASP phosphorylation at Ser239 by nitric oxide (NO) stimulation of cGMP-dependent protein kinase. Using live cell imaging of primary cells transfected with GFP-VASP constructs, we found that NO produced rapid retraction of lamellipodia together with cell rounding that was dependent on guanylate cyclase and type II cGMP-dependent protein kinase. In cells expressing a mutant VASP (Ser239Ala) lacking the site preferentially phosphorylated by this kinase, NO had no effect. Phosphorylation of Ser239 of VASP results in loss of lamellipodial protrusions and cell rounding, and is a powerful means of controlling directed actin polymerization within lamellipodia.