dsrtf webinar: dr. h. craig heller, stanford university
TRANSCRIPT
Down Syndrome Research and Treatment Foundation
Today’s Agenda
Overview of DSRTF: Carolyn Cronin, DSRTF Executive Director
Sleep’s Impact on Learning and Memory: Dr. Craig Heller, Stanford University
How You Can Help
E-mail: [email protected]
Down Syndrome Research and Treatment Foundation
Down Syndrome Research andTreatment Foundation Mission
• Stimulate and fund cognition research to improve learning, memory, and speech for individuals with Down syndrome
• Translation of research to deliver treatments to allow individuals to:
• Participate more successfully in school
• Lead more active and independent lives
• Prevent or delay early cognitive decline
Down Syndrome Research and Treatment Foundation
Why Cognition Research?
• Cognitive challenges present throughout life
• Generally, mild to moderate cognitive impairment
• Significant presence of neuropathology of Alzheimer’s disease by the age of 40
Down Syndrome Research and Treatment Foundation
FOCUSPioneer in stimulating cognition research
RESOURCESLeaders in funding and executing Ds-specific research strategy
COLLABORATIONInterdisciplinary coordination and communication
TRANSLATIONAccelerate the move from research to treatments
DSRTF Strategy
Down Syndrome Research and Treatment Foundation
2003 Down Syndrome Research
• No evidence of what causes impaired cognition in people with Down syndrome
• No targets on which to focus efforts
• Minimal government funding
• Few researchers focused on DS cognition
Down Syndrome Research and Treatment Foundation
Research Results
• Eight drug targets
Areas of the brain that work differently —“mechanisms”
• Three candidate drugs — and more work in this area
• Two clinical trials — and investment in tests for efficacy
Down Syndrome Research and Treatment Foundation
Government Funding:NIH Per Capita Investment
30,00030,00030,000
17,500
45,000400,000400,000400,000
1,500,000
Number of Individuals affected in the U.S.
1,500,000
2X
5X
6X13X 27X
3X
39X
52X
28X
Progress Towards Improving Cognition in
Individuals with Down Syndrome
Craig Heller and Craig GarnerCo-directors Down Syndrome Center
Stanford University
DSRTF Webinar, January 29, 2013
Clinical Assessment
• Caused by the triplication of Chromosome 21 (~250 genes).
• Common Disorder: 1/700 Births: Incidence higher when mothers are over 35
• 350,000 afflicted in US; 500,000 Europe; > 3 Million world wide
• Cognitive impairment, mild-severe (IQ 20-80)
• Progressive cognitive decline
• Deficits in speech and language skills
• Deficits in short- and long-term memory
• Propensity for early onset Alzheimer Disease (~30 years of age)
Down Syndrome
Current Treatment Strategies for
Cognitive Impairment in DS
Drug Description Trial Outcome Adverse
Vitamin
supplement
Antioxidants, folinic
acid, vitamins A, C, E…
and more
Numerous, including
placebo-controlled
No significant benefit
Vasopressin Peptide hormone One trial: short,
placebo-controlled
No significant benefit N/A
Piracetam Nootropic, GABA
derivative. Site of
action unknown.
One trial: placebo-
controlled
No significant benefit Various,
common
Donepezil Acetylcholinesterase
inhibitor
Various. DS + AD,
adults, children.
Large trial ongoing
Mixed. No clear
significant benefit for
non-AD.
Various,
common
Rivastigmine Cholinesterase
inhibitor.
2 trials: DS + AD
placebo-controlled;
adolescents open
label
No benefit DS + AD,
small improvement
adolescents
7/11 in
adolescents
None have been shown to be effective
Our strategy
• Define what is wrong in
humans.
• Explore animal models that
reflect the problems.
• Discover the underlying
mechanisms.
• Develop rationale drug
therapies to fix these
mechanisms.
Developing Therapies for Cognitive
Impairment due to Down Syndrome
Neuropsychological Assessment of Learning and
Memory in Down Syndrome
• (see Lynn Nadel, Genes,Brain and Behavior 2:156 2003)
– Learning is normal in very young subjects <6 month, but declines
progressively in the first year.
– A second decline occurs in adulthood as the risk of early onset
Alzheimer disease takes it toll.
– Disproportionately affected are memory processes that involve
the hippocampus and prefrontal cortex.
– Impairments are mostly seen in declarative memory, though
procedural memory is also affected.
– Impairments affect speech, language and verbal short term
memory and IQ.
The hippocampus is important for
memory
Henry Molaison (HM)
1926-2008
The Ts65Dn Mouse Model of DS
TS Mouse WT or 2N Mouse
Karyotype analysis
(visual display of the chromosomes grouped by their size,
number and shape)
Synapses and synaptic plasticity in DS mice
– Brain anatomy is altered.
– Synaptic plasticity is impaired.
–Electrophysiological studies indicate that
excessive inhibition is suppressing
synaptic plasticity in neural circuits critical
for memory processing.
Inhibition is under-emphasized in models of how the brain works.
Over-inhibition could impair the transfer Short Term Memory to Long Term.
Major inhibitory system in brain is GABA… (very much involved in Sleep
and Circadian Rhythms).
Can GABA antagonists restore learning and memory in TS mice?
If so, is the action through modulation of sleep and/or circadian systems?
A working hypothesis:
Intellectual disability is due to over-inhibition in the CNS
Fabian Fernandez
A mouse model of Down syndrome shows poor
learning and memory performance
A mouse model of Down syndrome shows poor
learning and memory performance
Fernandez & Garner, 2007
Normal mice
DS mice
Study Design: Evaluation of chronic treatment
with GABA antagonists on learning and memory.
Day 1
Training/testing trials
carried out at various
times after treatment
ends.
Day 17
Daily drug treatment
Object recognition
testing
Object recognition
training
Drugs Used:
Picrotoxin
Bilobilide
Pentylenetetrazole
Flumasinil
Drugs given during the light phase
Fabian Fernandez, Damien Colas, Bayara
Chuluun, Craig Heller, Craig Garner, et al.
Memory improvement is long-lasting after daily
pentylenetetrazole (PTZ) dose
1 week post-treatment 2 months post-treatment
Normal mice
DS mice
Fernandez & Garner, 2007
GABAA Receptor Antagonists Tested and Shown
to be Efficacious
• Picrotoxin:
– Pros: Potent compound (IC50 1uM), excellent bioavailability
– Cons: narrow therapeutic window
• Bilobalide:
– Pros: Potent compound (IC50 2uM), excellent bioavailability, good therapeutic window
– Cons: currently available in plant extract only (Gingko Biloba), difficult synthesis.
• Pentylenetetrazole:
– Pros: Excellent pharmacokinetic values, oral delivery, excellent bioavailability, good therapeutic window, long history in humans
– Cons: Currently not approved by FDA
• Alpha5 inverse agonist:
– Pros: Excellent pharmacokinetic values, oral delivery, excellent bioavailability, good therapeutic window. Specific for a subset of hippocampal GABAA receptors.
– Cons: currently not approved by FDA
• Flumazenil:
– Pros: Excellent pharmacokinetic values, good therapeutic window, approved by FDA for the treatment of benzodiazepine overdose
– Cons: poor oral bioavailability, acute IV administration
Goals of recent studies
• Preclinical development of PTZ
– Dose, safety, age, pharmacokinetics
• Investigation of mechanism of drug therapy
– Dosing strategy
– Developing New Biometrics
– Understand Mechanism
Lea
rnin
g in
dex (
%)
Colas & Chuluun
25
50
75
2N NaCl 2N PTZ TS NaCl TS PTZ
24 hrs
0 hrs
0.03 mg/kg dose
PTZ is effective at very low dose levels
PTZ is effective at all ages: not a
developmental effect.
24 hrs
0 hrs
8 months
Lea
rnin
g in
dex
(%)
25
50
75
TS NaCl TS PTZ TS NaCl TS PTZ
12 months
Colas & Chuluun
Damian Colas
Assessing Safety: Continuous EEG
monitoring before, after and during PTZ treatment
1000hr of continuous EEG monitoring:
no evidence of seizure events
PTZ regimen also does not increase seizure threshold
LI (%
)
2N Ts65Dn**
* 24 hrs
0 hrs
Treatment during the dark phase (wake)
Lea
rnin
g in
dex (
%)
0
20
PTZ
40
80
PTZ
Colas & Chuluun
These effects are circadian phase dependent.
GABA antagonists can rescue the learning disability of Down
Syndrome……… BUT,
A model system for research on circadian rhythms and photoperiodicity.
Time of Day (h) Circadian Time (h)
Phase
Shift
(h)
Aschoff’s Rule Phase Response Curve
Siberian hamsters have normal circadian behavior
Ruby et al.
Time of Day (h)
Reentrainment: ± 3 h
Normal re-entrainment to short shifts in photocycle
Ruby et al.
But, if we try to phase shift the
hamster’s circadian rhythm by 5
or 6 hours – a disastrous result!
Total Arrhythmia for the rest of their lives!
Time of Day (h)
Ruby et al. 1996
And, hamsters made arrhythmic with such a phase shift
are learning impaired!
Time
5 min 5 min
Familiarization Phase Testing Phase
Novel object recognition (NOR)
Spontaneous alternation (SA): spatial working memory
Zeitgeber Time (h)D
iscrim
ina
tio
n In
de
x
Memory deficits in SA and NOR
Ruby et al. 2008
Memory is rescued by the chronic treatment protocol with the GABAA receptor antagonist PTZ
Dis
crim
ina
tion
Ind
ex
Ruby et al. unpublished
The circadian clock mechanism releases GABA.
Is a continuously active circadian clock interfering with memory formation?
SCN Lesion (SCNx) Disruptive Phase Shift (DPS)
Arrhythmia Can Also Be Induced by Ablation of the Circadian Clock in the Brain (the SCN)
Ruby et al. unpublished
SCN ablation has no effect on SA or NOR
Ruby et al. unpublished
Can SCN ablation rescue memory in DPS hamsters?
DPS
SCNx
Ruby et al. unpublished
SCN ablation rescues memory in arrhythmic hamsters
Ruby et al. unpublished
Evidence that the SCN actively suppresses neuroplasticity at a particular
circadian phase.
Why????
25
50
75
Dis
cri
min
ati
on
In
dex (%
)
Dark 12 hr Dark 24 hr Light 12 hr Light 24 hr
training testing
Memory Consolidation Requires a Sleep Phase(C57Bl6 mice)
Does Memory Consolidation Require a Certain Quality of Sleep?
Chuluun, Colas et al.
Using Optogenetics to Fragment Sleep Without Altering
Total Sleep Duration to see Effects on Memory
Training 5 min
Testing 5 min
Optogenetic stimulation – 4 hrs
0 12 24
Time (hrs)
Mice trained early in light phase and then stimulated optogenetically at
30, 60, 120, or 240 sec intervals for 4 hrs, or sleep deprived, or left undisturbed.
Testing 24 hrs after training.
Rolls, Colas et al. 2011
Stimulation results in a greater number of brief episodes of
wake, but does not decrease total sleep time!
Rolls, Colas, et al 2011.
Lower delta, higher theta
Major Finding: Memory consolidation requires minimal
quanta of NREM sleep
Rolls, Colas, et al. 2011
Animals are trained in the Dark phase and
tested 24 hrs later in the Dark phase.
Learning is normal.
Sleep fragmentation only interferes with learning when
delivered during the light phase
Rolls, Collas, et al. 2011
But, still a circadian component --
NOR training
0H
NOR testing
24H
Baseline
4 hr sleep deprivation before training
25
35
45
55
65
75
85
2N BL TS BL 2N SD TS SD
0H
24H
50%
**
**
**
DI
(%)
n=8 n=11
The Converse: Enhancing SWA in Ts65Dn mice
improves their learning and memory without GABA
antagonists.
Sleep deprivation for 4 hrs
prior to training.Normalization
of delta power
following SD
Colas et al.
A Bold Hypothesis
When short term memory is being
transferred to long term memory during
sleep, the circadian system suppresses
neuroplasticity to protect the fidelity of the
memory transcripts.
Could circadian suppression of neuroplasticity be too
great in DS?
Could the sleep related processes of memory
consolidation be impaired by high levels of GABA
activity?
Conclusions (tentative)
• Tonic over-inhibition via GABAergic mechanisms can
produce learning disability.
• Inhibitory tone can be reset long-term with a short-term
treatment with GABAA antagonists at the proper
circadian phase.
• PTZ is an excellent candidate for clinical trials. It’s
efficacy is not age dependent.
• Quality sleep is needed for memory consolidation and for
efficacy of GABAA antagonist treatment.
• The circadian system suppresses neural plasticity during
consolidation via GABAergic mechanisms. The
functional significance may be to stabilize memory
transcripts.
Acknowledgements
Garner Laboratory
Craig C. Garner
Fabian Fernandez
Martina Blank
Deepti Warrier
Jackie Rodriguez
Dan Wetmore
Funding Support NSF, NIH, Stanford Spark Program, Coulter
Foundation, DSRTF, Fidelity Foundation, Stanford
Neuroscience Institute
Heller Laboratory
H. Craig Heller
Bayara Chuluun
Damien Colas
Norman Ruby
Grace Hagiwara
Thanks!
Down Syndrome Research and Treatment Foundation
Ways You Can Help
• Increase awareness of DSRTF and the promise and progress of cognitive research
• Tell us how we can provide additional value and information
• Participate online and invite others to join to continue to grow the DSRTF/plus15 community
• Invite us to share our mission with other groups with whom you are affiliated
• Increase the funding we can make available for research