optogenetics: a bright future for voltage gated ion channels...annamaria mauro laura confalonieri...
TRANSCRIPT
Viviana Agus Axxam S.p.A., Milano, Italy
Optogenetics: A Bright Future for
Voltage Gated Ion Channels
Presentation Summary
2
• Hamamatsu and AXXAM: FDSS µCELL demo period
Cav1.3 and ChR2 assay
• Optogenetics: overview and advantages
• Channelrhodopsin2 to modulate cell membrane voltage
• Activation of Cav1.3 by ChR2: recombinant assay setup
• Validation of “light protocol” at FDSS µCELL: test of reference compounds
• Comparison with “K+ protocol” and patch-clamp data
• Conclusions and future perspectives
FDSS μCELL DEMO @ AXXAM
Ca2+ assay (fluorescent dyes,
luminescent photoprotein)
• CCKAR (GPCR)
• GLP1R (GPCR)
• ADORA1 (GPCR)
• DRD1-DRD2 (GPCR)
• Enzymatic assay
Glow Luminescence assay:
• PPARα, PPARδ (NHR)
• Promoter assay
Genetically encoded sensor
• TMEM16A (EYFP)
Optogenetics
• Cav1.3 (ChR2)
Fluo8 LED (blue light)
MPdye LED (green light)
Hybrid Camera
(Fluo & Lumi)
3
Optogenetics: overview
4
Optogenetics is a technology that combines:
1) A «genetic» component, able to target specific neuron types
2) An «optical» component, able to interact specifically with the genetic component
to achieve fast control of well-defined events in specific cells of living tissue
The starting point was the idea to have
a system available to control the
activity of specific neuron types in the
brain in a better way
Method of the year 2010
Rhodopsins: Light-gated ion channels
5
Opsins:
• Seven-transmembrane, light-responsive proteins
• Rapidly translocate specific ions across the membranes of the cells in which they are expressed
• Contain the Vitamin-A derived chromophore all-trans-retinal as a light capture molecule
• Studied since the 1970s for their fascinating biophysical properties
• Used by several different life forms that use light as energy source or sensory cue
Structural simplicity, fast kinetics ► attractive tool for a rapid control of specific cellular processes, such as, for example, modulation of membrane voltage and neuronal action potentials propagation Light as activating stimulus ► more physiological, compared to other hyperpolarizing or depolarizing stimulus (for example K+ injection) Possibility to target their expression to specific cell types ► genetically defined modulation of cellular processes
• Seven transmembrane opsin (eyespot of unicellular alga Chlamydomonas reinhardtii)
• Activated by blue light (470 nm): the light causes a conformational change in the light sensitive
molecule (retinal), which in turn causes a conformational change and the opening of the
channelrhodopsin protein
• Non-selective cation channel (Na+, K+, Ca2+, H+): the flow of ions changes the electrical potential
across the cell membrane which might, if sufficiently large, cause the neuron to fire
• Widely used to depolarize neurons and generate action potential firing: very good expression in different cell hosts
From: Wong J, J Mech Phys Solids 2012 Jun 1; 60(6) 1158-1178
From Ed Boyden Lab.
6
Channelrhodopsin-2
CLOSED OPEN INACTIVE
State-dependent blocker
• L-type calcium channel
• High Voltage Activated (HVA)
• α1 (pore) + α2δ, β, γ (accessory) subunits
• Therapeutic target: Cardiovascular, hormone
secretion, CNS (Parkinson’s, Alzheimer’s disease)
• Drug need: Cav1.2 selectivity; state-dependent
Optogenetic control of Cav1.3
KIR2.3 Low [K+]o High [K+]o
ChR2 DARK BLUE LIGHT
7
Cav1.3 optogenetic assay
α1
α2
δ1 β3
Na+ K+
Ca2+
Ca2+
Na+
K+ Na+
K+
Na+
K+ K+ Ca2+
Ca2+ Ca2+
Ca2+
Ca2+
Fluo-8,NW
K+
K+
K+
K+
K+ K+
K+
K+
Human
KIR2.3
Ca2+
ChR2
(D156A)
Human Cav1.3
(α1,β3,α2δ1)
HEK-293 cells
470nm
8
KEY QUESTIONS
• Is it possible to adapt the assay to the FDSS
µCELL optics for use in HTS?
• Can ChR2 be used to depolarize cells, such
as HEK293, avoiding the artificial
depolarization protocols such as KCl
injection?
• Does the exposure of the cells to blue light of
adequate intensity induce a ChR2 dependent
cellular depolarization with subsequent
activation of the transfected target?
• Does the ion flux through ChR2 alter the
detection of the transfected target?
Channelrhodopsin-2 and cell based assays
POTENTIAL ISSUES
• The light produced by the instrument LED
system might not have the adequate intensity
for ChR2 activation
• The ion flux through the ChR2 might be not
sufficient to induce membrane depolarization
• The membrane depolarization induced might be
not sufficient to drive the activation of
transfected voltage gated channels.
• ChR2 is not permeable to Ca2+ in the presence
of extracellular Na+; therefore Cav channels are
ideal targets to be modulated with optogenetics,
since their activity can be monitored by the use
of a Ca2+ sensitive dye GOAL
Generate stable cell lines co-expressing a
Voltage Gated ion channel of interest and ChR2
without altering the ion channel pharmacology
9
ChR2 induced membrane depolarization
• FDSS µCELL LED efficiently
activates ChR2 D156A
(minimum light intensity required for wild-type
ChR2 activation: 1mW/mm2; Aravanis, 2007)
Blue light ( = 480 nm; 0.013 mW/mm2)
• Membrane depolarization
half-recovered after ≈ 10 min
(t-off 6.9 min)
50%
repolarization
10
Cav1.3 half-inactivation protocol
50%
inactivated
• Cav1.3 efficiently activated by ChR2
• 50% recovery from inactivation after 10 min
Fluo 8 dye
(4 mM K+; 2µM retinal)
Blue light
5 - 45 min
Blue light • ChR2
• Fluo8
LIGHT
K+
Fluo 8 dye 50%
inactivated
• Cav1.3 efficiently activated by K+
• 50% Cav1.3 inactivation in 16mM K+
75mM K+ 0mM - 75 mM K+
INACTIVE RESTING
11
1 1 0 1 0 0 1 0 0 0
-1 0 0
-8 0
-6 0
-4 0
-2 0
0
2 0
[ K+
] m M
Vr (
mV
)
R T /z F = 5 2 .2 2
K ir2 .3 C u rre n t C la m p
R T /z F = 5 4 .7 6
K ir2 .3 V o lta g e C la m p
T h e o ry
H E K 2 9 3 W T V o lta g e C la m p
C a v 1 .3 C lo n e K 2 .8 C u rre n t C la m p
R T /z F = 5 8 .7 3
R T /z F = 5 8 .9 0K ir 2 .3 (c u rre n t c la m p )
K ir 2 .3 (v o lta g e c la m p )
C a V 1 .3 (c u rre n t c la m p )
T h e o r y
H e k 2 9 3 (v o lta g e c la m p )
State-dependent blockers with «Light protocol»
ISRADIPINE dose-response @ µCELL
Read interval 0.1s
Exp.: 0.03s; Sens.: 3
RESTING STATE
Fluo 8 dye
(4 mM K+; 2µM retinal)
Blue light
10 min
Blue light Blocker DR
HALF-INACTIVATED STATE
Fluo 8 dye
(4 mM K+; 2µM retinal)
Blue light
5 min
Blocker DR
• Very nice Cav1.3 activation by ChR2
• State dependency well detected by
Light inactivation protocol
12
Light protocol vs. K+ protocol vs. qPatch
• “Light protocol” well suitable for state-dependent
blockers studies
• Good correlation with classical “K+ protocol”
(less physiological)
• Good correlation with patch-clamp
1 0 -9 1 0 -8 1 0 -7 1 0 -6 1 0 -5
0
2 5
5 0
7 5
1 0 0
Is ra d ip in e [M ]
% R
em
ain
ing
IC
av
1.3
C lo s e d (H P = -9 0 m V )
In a c tiv a te d (H P = -6 0 m V )
I C 5 0 = 3 6 2 n M
I C 5 0 = 3 2 .2 n M
C a v 1 .3 /C h R 2 @ q P a tc h 1 6 x
C lo s e d (H P = -9 0 m V ): IC 5 0 3 6 2 n M
H a lf-in a c t (H P = -6 0 m V ): IC 5 0 3 2 n M
1 0 -1 0 1 0 -9 1 0 -8 1 0 -7 1 0 -6 1 0 -5 1 0 -4
0
2
4
6
8
C a v 1 .3 s ta te -d e p e n d e n t
b lo c k e r p h a r m a c o lo g y
L ig h t v s . K+ p ro to c o l
Is ra d ip in e [M ]
F
/F0
(F
luo
,8-N
W)
1.369e-007
9.502e-008
1.146e-008
1.746e-008
R e s tin g (D a rk )
H a lf- in a c tiv a te d (B lu e L ig h t = > 1 0 m in )
R e s tin g (4 m M K+
)
H a lf- in a c tiv a te d (1 6 m M K+
)
IC 5 0 1 3 7 n M (R e s tin g ; lig h t)
IC 5 0 9 5 n M (R e s tin g ; K+)
R e s tin g (d a rk ): IC 5 0 1 3 7 n M
R e s tin g (4 m M K+): IC 5 0 9 5 n M
H a lf- in a c t (B lu e lig h t 10 m in ): IC 5 0 1 2 n M
H a lf- in a c t (1 6 m M K+): IC 5 0 1 4 n M
13
Summary and conclusions
Isradipine IC50 “K+ protocol” “Light protocol” qPatch 16x Literature
Resting 95 nM 137 nM 362 nM 300 nM (-90mV)
Half-inactivated 14 nM 12 nM 32 nM 30 nM (-50mV)
RATIO 6.8 11.4 11.3 10
MAIN ACHIEVEMENTS:
• FDSS µCELL optics is well suitable for ChR2 activation
• A “Light protocol” was set up at the FDSS µCELL to study the Cav1.3 channel either in resting or
inactivated state
• The pharmacology of known state dependent blockers has been successfully validated, showing a
good agreement with the classical “K+ protocol”, patch clamp experiments and literature data
HIGHLIGHTS:
• First time ChR2 used for optical control of recombinant voltage-gated calcium channel assay
• Physiological, robust, precise activation of Cav1.3 channel
FUTURE PERSPECTIVES:
• Light modulation of other voltage-gated ion channel target is ongoing
14
Aknowledgments
AXXAM:
Alberto di Silvio cell line generation
Sara Tremolada cell line validation
Jean-Francois Rolland patch-clamp
Katharina Montag clonings
Loredana Redaelli cell biology head
Lia Scarabottolo discovery services
director
Stefan Lohmer overall strategies
Hamamatsu team:
Jean Marc d'Angelo
Annamaria Mauro
Laura Confalonieri
Via Meucci 3
20091, Bresso (Milan, Italy)
phone + 39 02 210561
fax + 39 02 2105602
www.axxam.com