Biomedical subjects

Anke Witting

Publications and source records attributed to Anke Witting.

7 recordsLinked to original sources

PubMed2006

Experimental autoimmune encephalomyelitis disrupts endocannabinoid-mediated neuroprotection.

Focal cerebral ischemia and traumatic brain injury induce an escalating amount of cell death because of harmful mediators diffusing from the original lesion site. Evidence suggests that healthy cells surrounding these lesions attempt to protect themselves by producing endocannabinoids (eCBs) and activating cannabinoid receptors, the molecular target for marijuana-derived compounds. Indeed, activation of cannabinoid receptors reduces the production and diffusion of harmful mediators. Here, we provide evidence that an exception to this pattern is found in experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. We show that cell damage induced by EAE does not lead to increase in eCBs, even though cannabinoid receptors are functional because synthetic cannabinoid agonists are known to confine EAE-induced lesions. This lack of eCB increase is likely due to IFN-gamma, which is released by primed T cells invading the CNS. We show that IFN-gamma disrupts the functionality of purinergic P2X7 receptors, a key step controlling eCB production by microglia, the main source of eCBs in brain. Accordingly, induction of EAE in P2X7-/- mice results in even lower eCB levels and more pronounced cell damage than in wild-type mice. Our data suggest that the high level of CNS IFN-gamma associated with EAE disrupts eCB-mediated neuroprotection while maintaining functional cannabinoid receptors, thus providing additional support for the use of cannabinoid-based medicine to treat multiple sclerosis.

Animals↗

PubMed2006

The endocannabinoid anandamide protects neurons during CNS inflammation by induction of MKP-1 in microglial cells.

Endocannabinoids are released after brain injury and believed to attenuate neuronal damage by binding to CB(1) receptors and protecting against excitotoxicity. Such excitotoxic brain lesions initially result in primary destruction of brain parenchyma, which attracts macrophages and microglia. These inflammatory cells release toxic cytokines and free radicals, resulting in secondary neuronal damage. In this study, we show that the endocannabinoid system is highly activated during CNS inflammation and that the endocannabinoid anandamide (AEA) protects neurons from inflammatory damage by CB(1/2) receptor-mediated rapid induction of mitogen-activated protein kinase phosphatase-1 (MKP-1) in microglial cells associated with histone H3 phoshorylation of the mkp-1 gene sequence. As a result, AEA-induced rapid MKP-1 expression switches off MAPK signal transduction in microglial cells activated by stimulation of pattern recognition receptors. The release of AEA in injured CNS tissue might therefore represent a new mechanism of neuro-immune communication during CNS injury, which controls and limits immune response after primary CNS damage.

Adult↗

PubMed2005

Cannabinol delays symptom onset in SOD1 (G93A) transgenic mice without affecting survival.

Therapeutic options for amyotrophic lateral sclerosis (ALS), the most common adult-onset motor neuron disorder, remain limited. Emerging evidence from clinical studies and transgenic mouse models of ALS suggests that cannabinoids, the bioactive ingredients of marijuana (Cannabis sativa) might have some therapeutic benefit in this disease. However, Delta(9)-tetrahydrocannabinol (Delta(9)-THC), the predominant cannabinoid in marijuana, induces mind-altering effects and is partially addictive, compromising its clinical usefulness. We therefore tested whether cannabinol (CBN), a non-psychotropic cannabinoid, influences disease progression and survival in the SOD1 (G93A) mouse model of ALS. CBN was delivered via subcutaneously implanted osmotic mini-pumps (5 mg/kg/day) over a period of up to 12 weeks. We found that this treatment significantly delays disease onset by more than two weeks while survival was not affected. Further research is necessary to determine whether non-psychotropic cannabinoids might be useful in ameliorating symptoms in ALS.

Age Factors↗

PubMed2004

P2X7 receptors control 2-arachidonoylglycerol production by microglial cells.

Endogenous cannabinoid ligands (endocannabinoids) produced by neurons, astrocytes, and microglial cells activate cannabinoid receptors, the molecular target for marijuana's bioactive ingredient Delta(9)-tetrahydrocannabinol. The molecular mechanism underlying the production of the most abundant endocannabinoid, 2-arachidonoylglycerol (2-AG), is unclear. A prevalent hypothesis proposes that activation of metabotropic receptors coupled to the phosphatidylinositol-specific phospholipase C and diacylglycerol (DG) lipase pathway will systematically lead to increases in 2-AG production. Here, we show that ATP increases 2-AG production by cultured microglial cells in a phosphatidylinositol-specific phospholipase C and DG lipase-dependent manner. However, efficacious activation of metabotropic P2Y purinergic receptors coupled to phosphatidylinositol-specific phospholipase C does not increase 2-AG production. This suggests that ionotropic, and not metabotropic, purinergic receptors control 2-AG production at an unexpected enzymatic step of its metabolic pathway. We show that activation of P2X(7) ionotropic receptors, which are highly permeable to calcium, is necessary and sufficient to increase 2-AG production in microglial cells. We also show that the sustained rise in intracellular calcium induced by activation of P2X(7) receptors directly increases DG lipase activity while inhibiting the activity of monoacylglycerol lipase, the enzyme that degrades 2-AG. This inverse sensitivity of DG lipase and monoacylglycerol lipase to calcium constitutes an original and efficient modality for sustained accumulation of 2-AG. Because prolonged increases in 2-AG amounts in brain parenchyma are thought to orchestrate neuroinflammation, the enzymatic steps involved in 2-AG synthesis and degradation by microglial cells constitute appealing targets for therapy aimed at controlling exacerbated neuroinflammation.

Adenosine Triphosphate↗

PubMed2004

Endocannabinoids accumulate in spinal cord of SOD1 G93A transgenic mice.

Approximately 2% of amyotrophic lateral sclerosis (ALS) cases are caused by mutations in the super oxide dismutase 1 (SOD1) gene and transgenic mice for these mutations recapitulate many features of this devastating neurodegenerative disease. Here we show that the amount of anandamide (AEA) and 2-arachidonoylglycerol (2-AG), two endocannabinoids that have neuroprotective properties, increase in spinal cord of SOD1(G93A) transgenic mice. This increase occurs in the lumbar section of spinal cords, the first section to undergo neurodegeneration, and is significant before overt motor impairment. Our results show that chronic neurodegeneration induced by a genetic mutation increases endocannabinoid production possibly as part of an endogenous defense mechanism.

Age Factors↗

PubMed2003

Nonpsychotropic cannabinoid receptors regulate microglial cell migration.

During neuroinflammation, activated microglial cells migrate toward dying neurons, where they exacerbate local cell damage. The signaling molecules that trigger microglial cell migration are poorly understood. In this paper, we show that pathological overstimulation of neurons by glutamate plus carbachol dramatically increases the production of the endocannabinoid 2-arachidonylglycerol (2-AG) but only slightly increases the production of anandamide and does not affect the production of two putative endocannabinoids, homo-gamma-linolenylethanolamide and docosatetraenylethanolamide. We further show that pathological stimulation of microglial cells with ATP also increases the production of 2-AG without affecting the amount of other endocannabinoids. Using a Boyden chamber assay, we provide evidence that 2-AG triggers microglial cell migration. This effect of 2-AG occurs through CB2 and abnormal-cannabidiol-sensitive receptors, with subsequent activation of the extracellular signal-regulated kinase 1/2 signal transduction pathway. It is important to note that cannabinol and cannabidiol, two nonpsychotropic ingredients present in the marijuana plant, prevent the 2-AG-induced cell migration by antagonizing the CB2 and abnormal-cannabidiol-sensitive receptors, respectively. Finally, we show that microglial cells express CB2 receptors at the leading edge of lamellipodia, which is consistent with the involvement of microglial cells in cell migration. Our study identifies a cannabinoid signaling system regulating microglial cell migration. Because this signaling system is likely to be involved in recruiting microglial cells toward dying neurons, we propose that cannabinol and cannabidiol are promising nonpsychotropic therapeutics to prevent the recruitment of these cells at neuroinflammatory lesion sites.

Animals↗

PubMed2002

Astrocytes in culture produce anandamide and other acylethanolamides.

Anandamide (arachidonylethanolamide) is an endocannabinoid that belongs to the acylethanolamide lipid family. It is produced by neurons in a calcium-dependent manner and acts through cannabinoid CB1 receptors. Other members of the acylethanolamide lipid family are also produced by neurons and act through G-protein-coupled receptors: homo-gamma-linolenylethanolamide (HEA) and docosatetraenylethanolamide (DEA) act through CB1 receptors, palmitylethanolamide (PEA) acts through CB2-like receptors, and oleylethanolamide (OEA) acts through receptors that have not yet been cloned. Although it is clear that anandamide and other acylethanolamides play a major role in neuronal signaling, whether astrocytes also produce these lipids is unknown. We developed a chemical ionization gas chromatography/mass spectrometry method that allows femtomole detection and quantification of anandamide and other acylethanolamides. Using this method, we unambiguously detected and quantified anandamide, HEA, DEA, PEA, and OEA in mouse astrocytes in culture. Stimulation of mouse astrocytes with ionomycin, a calcium ionophore, enhanced the production of anandamide, HEA, and DEA, whereas PEA and OEA levels were unchanged. Endothelin-1, a peptide known to act on astrocytes, enhanced the production of anandamide, without affecting the levels of other acylethanolamides. These results show that astrocytes produce anandamide, HEA, and DEA in a calcium-dependent manner and that anandamide biosynthesis can be selectively stimulated under physiologically relevant conditions. The relative levels of acylethanolamides in astrocytes from rat and human were different from the relative levels of acylethanolamides in mouse astrocytes, indicating that the production of these lipids differs between species. Because astrocytes are known to express CB1 receptors and inactivate endocannabinoids, our finding strongly suggests the existence of a functional endocannabinoid signaling system in these cells.

Amides↗