Rare missense variants of neuronal nicotinic acetylcholine receptor altering receptor function are associated with sporadic amyotrophic lateral sclerosis.
Sporadic amyotrophic lateral sclerosis (SALS) is a motor neuron degenerative disease of unknown etiology. Current thinking on SALS is that multiple genetic and environmental factors contribute to disease liability. Since neuronal acetylcholine receptors (nAChRs) are part of the glutamatergic pathway, we searched for sequence variants in CHRNA3, CHRNA4 and CHRNB4 genes, encoding neuronal nicotinic AChR subunits, in 245 SALS patients and in 450 controls. We characterized missense variants by in vitro mutagenesis, cell transfection and electrophysiology. Sequencing the regions encoding the intracellular loop of AChRs subunits disclosed 15 missense variants (6.1%) in 14 patients compared with only six variants (1.3%) in controls (P = 0.001; OR 4.48, 95% CI 1.7-11.8). The frequency of variants in exons encoding extracellular and transmembrane domains and in intronic regions did not differ. NAChRs formed by mutant alpha3 and alpha4 and wild-type (WT) beta4 subunits exhibited altered affinity for nicotine (Nic), reduced use-dependent rundown of Nic-activated currents (I(Nic)) and reduced desensitization leading to sustained intracellular Ca(2+) concentration, in comparison with WT-nAChR. The cellular loop has a crucial importance for receptor trafficking and regulating ion channel properties. Missense variants in this domain are significantly over-represented in SALS patients and alter functional properties of nAChR in vitro, resulting in increased Ca(2+) entry into the cells. We suggest that these gain-of-function variants might contribute to disease liability in a subset of SALS because Ca(2+) signals mediate nAChR's neuromodulatory effects, including regulation of glutamate release and control of cell survival.
Sabatelli
Mario
M
Istituto di Neurologia, Università Cattolica del Sacro Cuore, Roma, Italy.
Eusebi
Fabrizio
F
Al-Chalabi
Ammar
A
Conte
Amelia
A
Madia
Francesca
F
Luigetti
Marco
M
Mancuso
Irene
I
Limatola
Cristina
C
Trettel
Flavia
F
Sobrero
Fabrizia
F
Di Angelantonio
Silvia
S
Grassi
Francesca
F
Di Castro
Amalia
A
Moriconi
Claudia
C
Fucile
Sergio
S
Lattante
Serena
S
Marangi
Giuseppe
G
Murdolo
Marina
M
Orteschi
Daniela
D
Del Grande
Alessandra
A
Tonali
Pietro
P
Neri
Giovanni
G
Zollino
Marcella
M
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D016022:Case-Control Studies; D002460:Cell Line; D005260:Female; D014644:Genetic Variation; D006801:Humans; D008297:Male; D008875:Middle Aged; D016472:Motor Neuron Disease / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011978:Receptors, Nicotinic / Q000235:genetics / Q000378:metabolism*; D055815:Young Adult
D009419:Nerve Tissue Proteins; D011978:Receptors, Nicotinic; C447159:CHRNB4 protein, human