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Islet Society, AISG joint meeting 2015, Sydney
TRP Channels of Human Beta
Cells
Md. Shahidul Islam
Is.Islet society.
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3
Changes in P-glucose and insulin in human after mixed meals
Tsukuda K et al 2009 Diabetes Technol.Ther. 11:499
4Henquin J.C. et al 1994
Glucose induces electrical activity
in mouse beta cells
OFF
MODE
OFF
MODE
ON MODE
ON MODE
5J. V. Sanchez-Andres, A. et al J.Physiol 486:223-228, 1995.
In vivo and in vitro electrical activity in mouse islets
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Daily insulin secretion in human on three mixed meals
Insulin secretion
(nmol/day) Normal Obese
Basal 124 212
On three mixed meal 248 447
Polonsky K. S. et al, 1988, J Clin Invest. 81:435
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Human beta cells are in a READY mode
6 mM Glucose
Braun M et al, 2008, Diabetes 57:1618
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Mechanism of glucose-induced increase in [Ca2+] in the beta cells
KATP channels
(VGCCs
(T-, L-, P/Q type)
Closure of KATP channels depolarize membrane potential to the threshold for activation of L-type voltage gated Ca2+ channels
A. True
B. False
True
False
50%50%
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Na+
Ca2+K+
Closure of the KATP Channels does not depolarize
membrane potential to the threshold for
activation of the voltage-gated Ca2+ channels
“background current”
or “leak current”
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Insulin is the most life-threatening hormone
-hypoglycemia can kill
“KATP channel resembles the “handbrake of a car”
that is the beta cell; rather than its ignition”
-Paula. M. S. Heister. Thesis. University of Oxford. 2012
12Pearson,E.R. et al 2006. NEJM 355:467
Effect of glibenclamide on insulin secretion in
subjects with activating mutation in the KCNJ11
gene encoding Kir6.2 subunit of KATP
Without
glibenclamide
With glibenclamide
OFF mode
READY mode
ON mode
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KATP channels tune the beta cells
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Na+Ca2+ K+
Ashcroft and Rorsman 2004, Hum Mol Genet, 13:R21
Same magnitude of current (I) produces
greater change in membrane potential (DV)
when input resistance (R) is high
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Which ion channels mediate the “Background current”
or “Leak Current”
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Transient Receptor Potential
Baruch Minke
Craig Montell
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MCOLN1 = TRPML1
MCOLN3 = TRPML3
PKD2 = TRPP2
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1997
Bari M R et al, 2009,
J Cell Mol. Med. 13:3260
H2O2 + ACA
ACA= N-(p-amylcinnamoyl) anthranilic
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Whole cell currents
induced by H2O2 and
ADP ribose in INS-1E cells
Bari M R et al, 2009,
J Cell Mol. Med. 13:3260
INS1-E cells express functional TRPV1 channels
Fågelskiöld AJ 2012 Islets 4:56-63
P. Rabellato et al JOP. 15 (1):33-37, 2014
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No TRPV1 positive cells detected by IHC
in human islets or human insulinomas. Capsaicin does not increase
[Ca2+]i in human beta cells
Fågelskiöld AJ et al 2012
Islets 4:56-63
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Inhibition of TRPM5 inhibits insulin secretion in rat islets
K. Krishnan, et al 2014,
Pancreas 43 :597-604
TPPO=Triphenylphosphine oxide
23M. S. Islam. Adv.Exp.Med.Biol. 704:811-830, 2011.
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Immunohistochemistry images are not reliable without appropriate
positive and negative control experiments
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RNA-Seq data of human beta cells
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TRPC transcripts in human beta cells
Some features of TRPC1
Agonist-induced cation channel
Ca2+ permeable non-selective cation channel
May act as store-operated channel in some cells
Forms heteromeric TRPC channel tetramers
Is it a channel or a channel regulator?
(A. Dietrich et al Cells 3:939-962, 2014)
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TRPM5
in
non beta cells
TRPM transcripts in human beta cells
Some features of TRPM2
Activated by H2O2, alloxan
True agonist is ADP-ribose-2'-phosphate
B. Toth et al J.Gen.Physiol 145 (5):419-430, 2015.
Ca2+ permeable NSCC
Regulated by redox signals, “Sensor of Oxidative stress”
Involved in insulin secretion
Zn2+ release and cytotoxicity
P. T. Manna, et al Biochem.J. 466 (3):537-546, 2015.
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Some features of TRPM3
Many isoforms by alternative splicing
Ca2+ permeable channel
Activated by pregnenolone sulfate
Activated by PIPs
Activated by ATP
Activated by heat (noxious heat)
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1986
Marigo V 2009, Mol Cell Endocrinol 299: 1942009
TRPM4 in human beta cells
Some features of TRPM4
Ca2+ Activated Nonselective Cation Channel
Conducts monovalent cations but not diavalent cations
Regulated by Ca2+, PI(4,5)P2, Temperature
Associated with SUR1
Widely expressed, Heart, artery, neuronal cells,
Involved in the regulation of insulin secretion
Inhibited by 9-phenanthrol32
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Schematic figure of structure of TRPM7 “chenzyme”
Yee NS Cells 2014, 3, 751-777
Some features of TRPM7
Ubiquitously expressed
Permeable to Mg2+, Ca2+, and Zn2+, Ni2+, Cd2+, Ba2+, and
Sr2+
Constitutively active
Mg2+ absorption
Inhibited by intracellular Mg2+
Cell survival, proliferation, growth, differentiation, migration,
cancer development34
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MCOLN1 = TRPML1; MCOLN3 = TRPML3; PKD2 = TRPP1
TRPML and TRPP transcripts in human beta cells
Some features of TRPML1 (also called
MCOLN1)
Lysosomal Nonselective Cation Channel (Ca2+, Na+, Fe2+, Zn2+)
Ubiquitous expression
Activated by PI(3,5)P2
Involved in Autophagy, Vesicular Traficking and Biogenesis, Zn2+
Homeostasis
Mutation Causes Mucolipidosis Type IV
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Some features of TRPML3 (also called
MCOLN3)
Lysosomal mon-selective cation channel (Ca2+, Fe2+, Zn2+)
Regulates lysosome homeostasis, vesicular trafficking and
biogenesis, Exocytosis, Autophagy
Activated by PI (3,5) P2, inhibited by PI(4,5)P2
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Some features of TRPP1 (also called PKD2)
Non selective cation channel with Ca2+
permreability
Located on plasma membrane and
endoplasmic reticulum
Ca2+ induced intracellular Ca2+ release
channel (CICR)
Interacts with IP3R and RyR2
Inhibits RyR2 activity
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P. Koulen, et al Polycystin-2 is an intracellular calcium release
channel. Nat.Cell Biol. 4:191-197, 2002.
CICR is the language
of channel chatter
or TRPP1
CICR in the beta cells
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TRPV transcripts in beta cells
Take home messages
TRP channel(s) may mediate the “background current” and the
inward cationic current for depolarization of the plasma
membrane potential
Human beta cells express:
TRPC1,
TRPM2, TRPM3, TRPM4, TRPM7
TRPML1, TRPML3, TRPP1
Functions of TRP channels of beta cells need further studies
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