Présentation de Arnaud Monteil réalisée durant le cours du réseau international des instituts Pasteur de "Médecine Génomique: du diagnostic à la thérapie " (17-21 octobre 2016)

1. Etude des canaux ioniques: intérêts pour la physiopathologie et
le traitement des troubles de la motricité
Cours international: médecine génomique, du diagnostic à la thérapie
17-21 octobre 2016-Institut Pasteur de Tunis
Arnaud Monteil
arnaud.monteil@igf.cnrs.fr

2. Ion channels
- Ion channels are gated pores that permit the passive flow of ions down their electrochemical
gradients.
- More than 400 genes are known that encode ion channel subunits.
- Alternative splicing and heteromeric assembly of different subunits increase the diversity of ion
channels.
- Such many channels are needed to accomplish very complex cellular functions.
- Dysfunction of ion channels are key events in many pathological processes.
- Ion channels are target of importance in a pathological context.

3. Ion channel classes
Ashcroft, 2006

4. Some examples of currents
Piezo2 (mechano-gated) Nav1.3 (voltage-gated)
nAChR (Ligand-gated, direct) NALCN (Ligand-gated through GPCRs)

5. 3D models depicting VGNCs in 3 different states
Kim, 2014

6. Introduction

7. Introduction

8. Skeletal muscle channelopathies
1- Mutations in AchR subunits causes myasthenia (muscle weakness) by preventing binding of acetylcholine.
2- Loss of presynaptic K+-channel function (KV1.1, KCNA1) leads to increased transmitter release and enhanced muscle contraction.
3- Downregulation of presynaptic Ca2+ channels causes myasthenia by preventing neurotransmitter release.
4- Gain-of-function mutations in the muscle Na+ channel (Nav1.4, SCN4A) cause hyperexcitability and myotonia.
5- Loss-of-function mutations in ClC channels cause hyperexcitability and myotonia.
6- Loss-of- function mutations in Kir1.1 cause hyperexcitability and myotonia.
7- Mutations in muscle CaV channels (Cav1.1, CACNA1S) impair Ca2+ release from intracellular stores, producing malignant hyperthermia or
paralysis.
8- RYR channels impair Ca2+ release from intracellular stores, producing malignant hyperthermia or paralysis.
Ashcroft, 2006

9. Skeletal muscle channelopathies

10. Kim, 2014
Skeletal muscle channelopathies
Cannon, 2015

11. • Recurrent episodes of weakness, lasting minutes to hours, with
spontaneous full recovery.
• Provocation of attacks by environmental stresses:
- Rest after a period of vigorous exercise.
- Carbohydrate-rich meals.
- Shifts of serum potassium (high or low).
- Exposure to cold.
- Emotional stress.
- Pregnancy.
• Over times, some patients develop a slowly permanent weakness.
Periodic Paralysis

12. • The transient loss of muscle excitability during an attack of weakness is
caused by depolarization of the resting membrane potential.
• Three different mechanisms have been identified.
- A persistent Na+ caused by a defect of inactivation (1-2% remains open), other defects in
gain-of-function mutants (gating, inactivation, hyperpolarized shift of activation).
- Loss-of-function changes for inward rectifier potassium channels (Kir2.1, Kir2.6, Kir3.4).
- « Gating pore » current.
Periodic Paralysis
Rudel et al, 1984

13. Hypokalemic Periodic Paralysis (CACNA1S, SCN4A)

14. Hyperkalemic Periodic Paralysis (SCN4A)

15. Hyperkalemic Periodic Paralysis (SCN4A)

16. Hyperkalemic Periodic Paralysis (SCN4A)

17. Therapeutic management of periodic paralysis
• Acetazolamide is beneficial for about 50% of HypoPP patients with Cav1.1
but not Nav1.4 mutations.
• K+-supplements (HypoPP).
• Avoidance of large carbohydrate-rich meals (HypoPP).
• KATP openers (cromakalin; HypoPP).
• Na+-K+-Cl- co-transporter (NKCC) inhibitor (bumetanide; HypoPP).
• Avoidance of K+-rich food (Nav1.4 - HyperPP).
• Carbohydrate snack to truncate an episode (Nav1.4 - HyperPP).
• Promote kaliuresis with diuretics (Nav1.4 - HyperPP).
• Carbonic anhydrase inhibitors (acetazolamide, dichlorphenamide; Nav1.4 -
HyperPP).

18. • Inability of muscle to relax after voluntary effort.
• The after-contractions may persist for many seconds.
• With repeated movements, the intensity of myotonia diminishes over
seconds to minutes and may even become asymptomatic.
• Conversely, some affected individuals have paradoxical worsening of
myotonic stiffness with repeated effort (paramyotonia). This process is
aggravated by muscle cooling.
• Additional triggers have been associated with worsering myotonia:
- Potassium administration.
- Emotional stress.
- Pregnancy.
- Hypothyroidism.
- Depolarizing general anesthetics.
- Cold exposure.
Myotonia

19. Myotonia
• Two different mechanisms have been identified:
- Reduction of the resting chloride conductance.
- Gain-of-function changes to the voltage-dependent gating of Nav1.4 sodium channels.

20. Myotonia congenita (CLCN-1)
- Divided into dominant (Thomsen disease) and recessive (Becker disease) forms.
- Over 200 mutations in the CLCN1 gene have been reported.
some cases can be total, a direct treatment tar- ingchannel openingofclosed, drug-boundchan-
FIGURE 2. Localization of missense mutations. The approximate position of recessive (blue squares), dominant (red
circles), semi-dominant (red-blue hexagons), and sporadic (green squares) mutations is shown in a topology model of the
primary protein sequence. The length of the various segments is approximately to scale. The topology was chosen ac-
cording to Schmidt-Rose and Jentsch [1997].
Pusch, 2002

21. Popponen et al, 2008
Myotonia congenita (recessive mutations of CLCN-1)
Kubisch et al, 1998

22. Myotonia congenita (dominant mutations of CLCN-1)
Kubisch et al, 1998

23. Myotonia congenita (SCN4A)

24. Paramyotonia congenita (SCN4A)

25. • Avoidance of cold environments.
• Voltage-gated sodium channels blockers (tocainimide, mexitetine,
flecainimide).
• Acetazolamide (carbonic anhydrase inhibitor)?
Therapeutic management of Myotonia congenita

26. Disease Channel Protein Gene
Cognitive impairment with or
without cerebellar ataxia
Nav1.6: sodium channel, voltage-gated, type VIII, α
subunit
SCN8A
Episodic ataxia type 1 Kv1.1: potassium channel, voltage-gated, shaker-related
subfamily, member 1
KCNA1
Episodic ataxia type 2 Cav2.1: calcium channel, voltage-gated, P/Q type, α1A
subunit
CACNA1A
Episodic ataxia type 5 Cavβ4: calcium channel, voltage-gated, β4 subunit CACNB4
Spinocerebellar ataxia type 6 Cav2.1: calcium channel, voltage-gated, P/Q type, α1A
subunit
CACNA1A
Spinocerebellar ataxia type 13 Kv3.3: potassium channel, voltage-gated, Shaw-related
subfamily, member 3
KCNC3
Autosomal-Dominant Cerebellar
Ataxia
Cav3.1: calcium channel, voltage-gated, T type, α1G
subunit
CACNA1G
CLIFAHDD syndrome (dominant) NALCN: sodium channel, leak, α subunit NALCN
Infantile hypotonia with
psychomotor retardation and
characteristic facies (IHPRF,
recessive)
NALCN: sodium channel, leak, α subunit NALCN
Channelopathies-related ataxia

27. Snutch & Monteil, Neuron. 2007 May 24;54(4):505-7.
Cladogram of α Subunits for the 4-Domain Ion Channel Family
- Central Nervous System
- Heart
- Adrenal Gland
- Thyroid Gland
- Salivary Gland
- Mammary Gland
- Islets of Langerhans

28. Dominant-Negative Effects of Misfolded Mutants of VGCC
Mezghrani et al, 2008

29. NALCN regulates the neuronal resting membrane potential
Hippocampal neurons
M. musculus
(Lu et al, 2007, Cell)
RPeD1 neurons
L. stagnalis
(Lu et al, 2011, Plos ONE)
Premotor interneurons
C. elegans
(Xie et al, 2013, Neuron)
Retrotrapezoid nucleus neurons
M. musculus
(Shi et al, 2016, J. Neurosci.)
C4 nerve root recordings from brain stem spinal cord
M. musculus
(Lu et al, 2007, Cell)

30. Congenital contractures of limbs and face, hypotonia and developmental delay
(Chong et al, 2015, Am J Hum Genet; Aoyagi et al, 2015, Hum Mutat; Wang et al,
2016, Clin Genet; Fukai et al, 2016, J Hum Genet; Karakaya et al, 2016,
Neuropediatrics; Sivaraman et al, 2016, J Clin Neurosci; Bend et al, 2016, Neurology)
Infantile neuroaxonal dystrophy (Köroglu et al, 2013, J Med Genet)
Infantile hypotonia with psychomotor retardation and characteristic facies (Al-
Sayed et al, 2013, Am J Hum Genet ; Gal et al, 2016, Eur J Med Genet)
NALCN in human diseases

31. Dominant-negative effect of NALCN mutations (CLIFFAHDD)
Chong et al, 2015

32. Aoyagi et al, 2015
An animal model for the CLIFFAHDD syndrome

33. Correction of NALCN deficiency by acting on other channels
Kasap et al, 2016

34. Correction of NALCN deficiency by acting on other channels
(4-AP: inhibitor of voltage-gated K+ channels)

35. Correction of NALCN deficiency by acting on other channels
(Quinine: inhibitor of voltage-gated K+ channels)

36. Correction of NALCN deficiency by acting on other channels

37. Correction of NALCN deficiency by acting on other channels
(FPL-64176: activator of voltage-gated Ca2+ channels)

38. Correction of NALCN deficiency by acting on other channels
(CBNX: activator of Gap Junctions)

39. Correction of NALCN deficiency by acting on other channels
(MFQ: activator of Gap Junctions)

41. • Akinésie: L'akinésie est une lenteur d'initiation des mouvements avec une tendance à l'immobilité
(mouvements volontaires, mouvements associés, mouvements d'ajustement postural,
mouvements d'expression gestuelle et émotionnelle), et ce, en l'absence de paralysie. Cela est dû à
un problème d'activation de zones du cerveau (atteinte de la voie nigro-striée entraînant un déficit
en dopamine).
• Dyskinésie: la dyskinésie activité motrice involontaire, lente et stéréotypée affectant
préférentiellement la face (langue, lèvres, mâchoire) s’étendant au tronc et aux membres.
• Dysplasie: Une dysplasie est une malformation ou déformation résultant d'une anomalie du
développement d'un tissu ou d'un organe, qui survient au cours de la période embryonnaire ou
après la naissance.
• Myotonie: une myotonie se caractérise par une décontraction lente et difficile d'un muscle à la
suite d'une contraction volontaire.
• Paralysie périodique: Les paralysies périodiques sont un groupe de maladies génétiques rares qui
conduisent à une faiblesse musculaire ou une paralysie (rarement la mort) à partir de facteurs
déclenchant courants tels que le froid, la chaleur, des repas riches en glucides, le jeûne, le stress,
l'excitation et l'activité physique de toute nature.
• Ataxie: l'ataxie est une pathologie neuromusculaire qui consiste en un manque de coordination fine
des mouvements volontaires. Elle n'est pas liée à une déficience physique des muscles mais plutôt
à une atteinte du système nerveux. Le trouble de la coordination est partiellement corrigé par le
contrôle visuel.
Définitions