Ismael Galve-Roperh

Anti-tumoral action of cannabinoids: Involvement of sustained ceramide accumulation and extracellular signal-regulated kinase activation

Δ9-Tetrahydrocannabinol, the main active component of marijuana, induces apoptosis of transformed neural cells in culture. Here, we show that intratumoral administration of Δ9-tetrahydrocannabinol and the synthetic cannabinoid agonist WIN-55,212-2 induced a considerable regression of malignant gliomas in Wistar rats and in mice deficient in recombination activating gene 2. Cannabinoid treatment did not produce any substantial neurotoxic effect in the conditions used. Experiments with two subclones of C6 glioma cells in culture showed that cannabinoids signal apoptosis by a pathway involving cannabinoid receptors, sustained ceramide accumulation and Raf1/extracellular signal-regulated kinase activation. These results may provide the basis for a new therapeutic approach for the treatment of malignant gliomas.

Δ9-Tetrahydrocannabinol induces apoptosis in C6 glioma cells

Δ9‐Tetrahydrocannabinol (THC), the major active component of marijuana, induced apoptosis in C6.9 glioma cells, as determined by DNA fragmentation and loss of plasma membrane asymmetry. THC stimulated sphingomyelin hydrolysis in C6.9 glioma cells. THC and N‐acetylsphingosine, a cell‐permeable ceramide analog, induced apoptosis in several transformed neural cells but not in primary astrocytes or neurons. Although glioma C6.9 cells expressed the CB1 cannabinoid receptor, neither THC‐induced apoptosis nor THC‐induced sphingomyelin breakdown were prevented by SR141716, a specific antagonist of that receptor. Results thus show that THC‐induced apoptosis in glioma C6.9 cells may rely on a CB1 receptor‐independent stimulation of sphingomyelin breakdown.

The endocannabinoid system drives neural progenitor proliferation

The discovery of multipotent neural progenitor (NP) cells has provided strong support for the existence of neurogenesis in the adult brain. However, the signals controlling NP proliferation remain elusive. Endocannabinoids, the endogenous counterparts of marijuana‐derived cannabinoids, act as neuromodulators via presynaptic CB1 receptors and also control neural cell death and survival. Here we show that progenitor cells express a functional endocannabinoid system that actively regulates cell proliferation both in vitro and in vivo. Specifically, NPs produce endocannabinoids and express the CB1 receptor and the endocannabinoid‐inactivating enzyme fatty acid amide hydrolase (FAAH). CB1 receptor activation promotes cell proliferation and neurosphere generation, an action that is abrogated in CB1‐deficient NPs. Accordingly, proliferation of hippocampal NPs is increased in FAAH‐deficient mice. Our results demonstrate that endocannabinoids constitute a new group of signaling cues that regulate NP proliferation and thus open novel therapeutic avenues for manipulation of NP cell fate in the adult brain.

Microglial CB2 cannabinoid receptors are neuroprotective in Huntington's disease excitotoxicity

Cannabinoid-derived drugs are promising agents for the development of novel neuroprotective strategies. Activation of neuronal CB(1) cannabinoid receptors attenuates excitotoxic glutamatergic neurotransmission, triggers prosurvival signalling pathways and palliates motor symptoms in animal models of neurodegenerative disorders. However, in Huntingtons disease there is a very early downregulation of CB(1) receptors in striatal neurons that, together with the undesirable psychoactive effects triggered by CB(1) receptor activation, foster the search for alternative pharmacological treatments. Here, we show that CB(2) cannabinoid receptor expression increases in striatal microglia of Huntingtons disease transgenic mouse models and patients. Genetic ablation of CB(2) receptors in R6/2 mice, that express human mutant huntingtin exon 1, enhanced microglial activation, aggravated disease symptomatology and reduced mice lifespan. Likewise, induction of striatal excitotoxicity in CB(2) receptor-deficient mice by quinolinic acid administration exacerbated brain oedema, microglial activation, proinflammatory-mediator state and medium-sized spiny neuron degeneration. Moreover, administration of CB(2) receptor-selective agonists to wild-type mice subjected to excitotoxicity reduced neuroinflammation, brain oedema, striatal neuronal loss and motor symptoms. Studies on ganciclovir-induced depletion of astroglial proliferation in transgenic mice expressing thymidine kinase under the control of the glial fibrillary acidic protein promoter excluded the participation of proliferating astroglia in CB(2) receptor-mediated actions. These findings support a pivotal role for CB(2) receptors in attenuating microglial activation and preventing neurodegeneration that may pave the way to new therapeutic strategies for neuroprotection in Huntingtons disease as well as in other neurodegenerative disorders with a significant excitotoxic component.

Control of the cell survival/death decision by cannabinoids

Abstract. Cannabinoids, the active components of Cannabissativa (marijuana), and their derivatives produce a wide spectrum of central and peripheral effects, some of which may have clinical application. The discovery of specific cannabinoid receptors and a family of endogenous ligands of those receptors has attracted much attention to cannabinoids in recent years. One of the most exciting and promising areas of current cannabinoid research is the ability of these compounds to control the cell survival/death decision. Thus cannabinoids may induce proliferation, growth arrest, or apoptosis in a number of cells, including neurons, lymphocytes, and various transformed neural and nonneural cells. The variation in drug effects may depend on experimental factors such as drug concentration, timing of drug delivery, and type of cell examined. Regarding the central nervous system, most of the experimental evidence indicates that cannabinoids may protect neurons from toxic insults such as glutamaergic overstimulation, ischemia and oxidative damage. In contrast, cannabinoids induce apoptosis of glioma cells in culture and regression of malignant gliomas in vivo. Breast and prostate cancer cells are also sensitive to cannabinoid-induced antiproliferation. Regarding the immune system, low doses of cannabinoids may enhance cell proliferation, whereas high doses of cannabinoids usually induce growth arrest or apoptosis. The neuroprotective effect of cannabinoids may have potential clinical relevance for the treatment of neurodegenerative disorders such as multiple sclerosis, Parkinsons disease, and ischemia/stroke, whereas their growth-inhibiting action on transformed cells might be useful for the management of malignant brain tumors. Ongoing investigation is in search for cannabinoid-based therapeutic strategies devoid of nondesired psychotropic effects.

Non-psychoactive CB2 cannabinoid agonists stimulate neural progenitor proliferation

Cannabinoids, the active components of marijuana and their endogenous counterparts, act on the brain and many other organs through the widely expressed CB1 cannabinoid receptor. In contrast, the CB2 cannabinoid receptor is abundant in the immune system and shows a restricted expression pattern in brain cells. CB2‐selective agonists are, therefore, very attractive therapeutic agents as they do not cause CB1‐mediated psychoactive effects. CB2 receptor expression in brain has been partially examined in differentiated cells, while its presence and function in neural progenitor cells remain unknown. Here we show that the CB2 receptor is expressed, both in vitro and in vivo, in neural progenitors from late embryonic stages to adult brain. Selective pharmacological activation of the CB2 receptor in vitro promotes neural progenitor cell proliferation and neurosphere generation, an action that is impaired in CB2‐deficient cells. Accordingly, in vivo experiments evidence that hippocampal progenitor proliferation is increased by administration of the CB2‐selective agonist HU‐308. Moreover, impaired progenitor proliferation was observed in CB2‐deficient mice both in normal conditions and on kainate‐induced excitotoxicity. These findings provide a novel physiological role for the CB2 cannabinoid receptor and open a novel therapeutic avenue for manipulating neural progenitor cell fate.—Palazuelos, J., Aguado, T., Egia, A., Mechoulam, R., Guzmán, M., Galve‐Roperh, I. Non‐psychoactive CB2 cannabinoid agonists stimulate neural progenitor proliferation. FASEB J. 20, E1773–E1779 (2006)

Endocannabinoid signaling controls pyramidal cell specification and long-range axon patterning

Endocannabinoids (eCBs) have recently been identified as axon guidance cues shaping the connectivity of local GABAergic interneurons in the developing cerebrum. However, eCB functions during pyramidal cell specification and establishment of long-range axonal connections are unknown. Here, we show that eCB signaling is operational in subcortical proliferative zones from embryonic day 12 in the mouse telencephalon and controls the proliferation of pyramidal cell progenitors and radial migration of immature pyramidal cells. When layer patterning is accomplished, developing pyramidal cells rely on eCB signaling to initiate the elongation and fasciculation of their long-range axons. Accordingly, CB1 cannabinoid receptor (CB1R) null and pyramidal cell-specific conditional mutant (CB1Rf/f,NEX-Cre) mice develop deficits in neuronal progenitor proliferation and axon fasciculation. Likewise, axonal pathfinding becomes impaired after in utero pharmacological blockade of CB1Rs. Overall, eCBs are fundamental developmental cues controlling pyramidal cell development during corticogenesis.

The Endocannabinoid System Promotes Astroglial Differentiation by Acting on Neural Progenitor Cells

Endocannabinoids exert an important neuromodulatory role via presynaptic cannabinoid CB1 receptors and may also participate in the control of neural cell death and survival. The function of the endocannabinoid system has been extensively studied in differentiated neurons, but its potential role in neural progenitor cells remains to be elucidated. Here we show that the CB1 receptor and the endocannabinoid-inactivating enzyme fatty acid amide hydrolase are expressed, both in vitro and in vivo, in postnatal radial glia (RC2+ cells) and in adult nestin type I (nestin+GFAP+) neural progenitor cells. Cell culture experiments show that CB1 receptor activation increases progenitor proliferation and differentiation into astroglial cells in vitro. In vivo analysis evidences that, in postnatal CB1−/− mouse brain, progenitor proliferation and astrogliogenesis are impaired. Likewise, in adult CB1-deficient mice, neural progenitor proliferation is decreased but is increased in fatty acid amide hydrolase-deficient mice. In addition, endocannabinoid signaling controls neural progenitor differentiation in the adult brain by promoting astroglial differentiation of newly born cells. These results show a novel physiological role of endocannabinoids, which constitute a new family of signaling cues involved in the regulation of neural progenitor cell function.

De novo-synthesized ceramide signals apoptosis in astrocytes via extracellular signal-regulated kinase

ABSTRACT Recent observations support the importance of ceramide synthesis de novo in the induction of apoptosis. However, the downstream targets of de novo‐synthesized ceramide are unknown. Here we show that palmitate incorporated into ceramide and induced apoptotic DNA fragmentation in astrocytes. These effects of palmitate were exacerbated when fatty acid breakdown was uncoupled and were not evident in neurons, which show a very low capacity to take up and metabolize palmitate. Palmitate‐induced apoptosis of astrocytes was prevented by L‐cycloserine and fumonisin B1, two inhibitors of ceramide synthesis de novo, and by PD098059, an inhibitor of the extracellular signal‐regulated kinase (ERK) cascade. Accordingly, palmitate activated ERK by a process that was dependent on ceramide synthesis de novo and Raf‐1, but independent of kinase suppressor of Ras. Other potential targets of ceramide in the control of cell fate, namely, c‐Jun amino‐terminal kinase, p38 mitogen‐activated protein kinase, and protein kinase B, were not significantly affected in astrocytes exposed to palmitate. Results show that the Raf‐1/ERK cascade is the selective downstream target of de novo‐synthesized ceramide in the induction of apoptosis in astrocytes and also highlight the importance of ceramide synthesis de novo in apoptosis of astrocytes, which might have pathophysiological relevance.—Blázquez, C., Galve‐Roperh, I., Guzmán, M. De novo‐synthesized ceramide signals apoptosis in astrocytes via extracellular signal‐regulated kinase. FASEB J. 14, 2315‐2322 (2000)

Sphingosine-1-phosphate phosphohydrolase in regulation of sphingolipid metabolism and apoptosis

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite that regulates diverse biological processes by binding to a family of G protein–coupled receptors or as an intracellular second messenger. Mammalian S1P phosphatase (SPP-1), which degrades S1P to terminate its actions, was recently cloned based on homology to a lipid phosphohydrolase that regulates the levels of phosphorylated sphingoid bases in yeast. Confocal microscopy surprisingly revealed that epitope-tagged SPP-1 is intracellular and colocalized with the ER marker calnexin. Moreover, SPP-1 activity and protein appeared to be mainly enriched in the intracellular membranes with lower expression in the plasma membrane. Treatment of SPP-1 transfectants with S1P markedly increased ceramide levels, predominantly in the intracellular membranes, diminished survival, and enhanced apoptosis. Remarkably, dihydro-S1P, although a good substrate for SPP-1 in situ, did not cause significant ceramide accumulation or increase apoptosis. Ceramide accumulation induced by S1P was completely blocked by fumonisin B1, an inhibitor of ceramide synthase, but only partially reduced by myriocin, an inhibitor of serine palmitoyltransferase, the first committed step in de novo synthesis of ceramide. Furthermore, S1P, but not dihydro-S1P, stimulated incorporation of [3H]palmitate, a substrate for both serine palmitoyltransferase and ceramide synthase, into C16-ceramide. Collectively, our results suggest that SPP-1 functions in an unprecedented manner to regulate sphingolipid biosynthesis and is poised to influence cell fate.