Endocannabinoid Signaling in the Prefrontal Cortex in Schizophrenia
Transcript of Endocannabinoid Signaling in the Prefrontal Cortex in Schizophrenia
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DAVID VOLK, MD, PHDTRANSLATIONAL NEUROSCIENCE PROGRAM
UNIVERSITY OF PITTSBURGH
Exploring the Relationship Between Cannabis Use, Cognitive Deficits and
Schizophrenia: Role of the Endogenous Cannabinoid System
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Cannabis Use and Schizophrenia
Associated with worse clinical outcome
Kavanagh Drugs 2002
Prefrontal cortex-related cognitive impairments
Solowoji JAMA 2002
Exacerbates cognitive impairments in
schizophrenia
D’Souza BiolPsych 2005
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Endocannabinoid (eCB) System
CB1 receptor is located on inhibitory axon terminals
Activation of the CB1 receptor suppresses the release of GABA
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Endocannabinoid (eCB) System and Schizophrenia
GABA signaling is already impaired in the PFC in schizophrenia which contributes to cognitive deficits in schizophrenia
Cannabis use may worsen cognitive deficits in schizophrenia by aggravating pre-existing deficits in GABA signaling
Alterations in eCB signaling may worsen impairments in GABA signaling in schizophrenia
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What is the status of eCB signaling in schizophrenia?
Lower CB1 receptor mRNA and protein levels in the PFC in schizophrenia (Eggan ArchGenPsych 2008)
Knowing the status of eCB signaling requires knowledge of the regulation of the eCB ligands that bind to the CB1 receptor
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2-AG: The Brain’s Own Cannabis
2-AG (2-arachidonyloglycerol) is an endogenous cannabinoid
2-AG is synthesized by diacylglycerol lipase (DAGL)
2-AG is metabolized by monoglyceride lipase (MGL)
2-AG activates CB1 receptors and reduces the release of GABA
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Endocannabinoid Signaling Suppresses GABA Release
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Subject Demographics
Control Schizophrenia T Value(df=82)
P Value
N 42 42
Sex 31M/11F 31M/11F
Race 34W/8B 29W/13B
Age (years) 48 ± 13 47 ± 13 0.4 p=0.69
PMI (hours) 17.8 ± 5.9
18.1 ± 8.7 .17 p=0.86
Storage (mo)
97 ± 43 97 ± 46 .02 p=0.98
pH 6.7 ± 0.2 6.6 ± 0.4 1.67 p=.10
RIN 8.3 ± 0.6 8.2 ± 0.7 1.2 p=.23
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Project Design
Real-time reverse transcription PCR (quantitative PCR)
RNA isolated from PFC area 9RNA is reversed transcribed to cDNAQuantitative PCR performed with SYBR Green and
gene-specific primersGene expression levels normalized to 3 reference
genes
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2-AG Synthesizing and Metabolizing Enzymes
DAGLα DAGLβ MGL
ANCOVA F Stat
P Value
F Stat P Value F Stat P Value
F1,38 .019 .89 .018 .90 .841 .37
Relative Expression Level in Control Subjects
Rela
tive
Exp
ress
ion
Leve
l in
Sch
iz
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Metabolizing Enzyme for Anandamide FAAH
ANCOVA F Stat
P Value
F1,38 1.1 .30
Rela
tive
Exp
ress
ion
Leve
l in
Sch
iz
Relative Expression Level in Control Subjects
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Group I Metabotropic Glutamate Receptors
mGluR1α mGluR5
ANCOVA F Stat P Value F Stat P Value
F1,38 9.2 .004 3.5 .07
+12.4% +4.3%
Rela
tive
Exp
ress
ion
Leve
l in
Sch
iz
Relative Expression Level in Control Subjects
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Summary of Findings
No change in 2-AG or anandamide synthesizing or metabolizing enzyme mRNA expression levels in PFC area 9 in schizophrenia. However, we do not know if changes may be still be
present at the protein level (i.e. amount and/or activity of enzyme).
Elevated mGluR1α mRNA expression levels in the PFC in schizophrenia.
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Validation of Results with Additional Primers
Primer Set % Change in Schiz
Unpaired (F1,16) Paired (F1,8)
F P F P
mGluR1α_1 +38.8% 38.5 .000 37.6 .000
mGluR1α_2 +39.9% 39.1 .000 91.3 .000
mGluR1α_3 +30.7% 26.8 .000 57.2 .000
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Interpreting Elevated mGluR1α mRNA Expression in Schizophrenia
Elevated signaling through mGluR1α receptors may increase 2-AG signaling, resulting in a further deleterious reduction in GABA neurotransmission in the PFC in schizophrenia.
Are elevated mGluR1α mRNA levels associated with enhanced signaling through the receptor? Elevated mGluR1α protein levels (and no change in mGluR5)
previously reported in the PFC in schizophrenia (Gupta Synapse 2005).
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RGS4 and mGluR1α in Schizophrenia
RGS4 (Regulator of G Protein Signaling) reduces the duration of signaling from some G protein coupled receptors, including mGluR1α (Saugstad JNeurosci 1998).
Lower RGS4 mRNA levels have been reported in the PFC in schizophrenia (Mirnics MolPsych 2001, Erdely Synapse 2006).
Lower RGS4 and higher mGluR1α levels may together further enhance signaling through mGluR1α receptors in the PFC.
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RGS4 mRNA Expression in Schizophrenia
ANCOVA F Stat
P Value
F1,38 29.4 .000
-16.1%R
ela
tive
Exp
ress
ion
Leve
l in
Sch
izop
hre
nia
Relative Expression Level in Control Subjects
*8 pairs previously studied
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Interpreting Elevated mGluR1α mRNA Expression in Schizophrenia
Are elevated mGluR1α mRNA levels associated with enhanced signaling through the receptor? Elevated mGluR1α protein levels (and no change in mGluR5)
previously reported in the PFC in schizophrenia (Gupta Synapse 2005).
The combination of lower RGS4 and higher mGluR1α levels may together further enhance signaling through mGluR1α receptors in the PFC.
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Novel Treatment Approaches for Schizophrenia
mGluR1α antagonist may reduce eCB-mediated suppression of GABA signaling mGluR1α /5 activation induces LTP/LTD of AMPA and NMDA
receptors (Ireland and Abraham JNeuroPhys 2009)
DAGL inhibitor would reduce suppression of GABA releaseSpecific for 2-AG and not other eCB ligands
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Acknowledgements
David Lewis, MD, Director of the Translational Neuroscience Program
Translational Neuroscience Program Faculty and Staff
Liz Sengupta
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Questions and Comments?
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Future Studies
Cannabis use during adolescence is a risk factor for schizophrenia
Moore Lancet 2007
Mechanism of increased sensitivity to the effects of cannabis during adolescence is not understood
Knowledge of the development of the eCB system in the PFC may provide insights into mechanisms that lead to a period of increased sensitivity to cannabis