VMA21 deficiency causes an autophagic myopathy by compromising V-ATPase activity and lysosomal acidification.
X-linked myopathy with excessive autophagy (XMEA) is a childhood-onset disease characterized by progressive vacuolation and atrophy of skeletal muscle. We show that XMEA is caused by hypomorphic alleles of the VMA21 gene, that VMA21 is the diverged human ortholog of the yeast Vma21p protein, and that like Vma21p it is an essential assembly chaperone of the V-ATPase, the principal mammalian proton pump complex. Decreased VMA21 raises lysosomal pH, which reduces lysosomal degradative ability and blocks autophagy. This reduces cellular free amino acids, which upregulates the mTOR pathway and mTOR-dependent macroautophagy, resulting in proliferation of large and ineffective autolysosomes that engulf sections of cytoplasm, merge together, and vacuolate the cell. Our results uncover macroautophagic overcompensation leading to cell vacuolation and tissue atrophy as a mechanism of disease.
Ramachandran
Nivetha
N
Program in Genetics and Genome Biology, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.
Munteanu
Iulia
I
Wang
Peixiang
P
Aubourg
Pauline
P
Rilstone
Jennifer J
JJ
Israelian
Nyrie
N
Naranian
Taline
T
Paroutis
Paul
P
Guo
Ray
R
Ren
Zhi-Ping
ZP
Nishino
Ichizo
I
Chabrol
Brigitte
B
Pellissier
Jean-Francois
JF
Minetti
Carlo
C
Udd
Bjarne
B
Fardeau
Michel
M
Tailor
Chetankumar S
CS
Mahuran
Don J
DJ
Kissel
John T
JT
Kalimo
Hannu
H
Levy
Nicolas
N
Manolson
Morris F
MF
Ackerley
Cameron A
CA
Minassian
Berge A
BA
D001343:Autophagy; D050172:Genes, X-Linked; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D009135:Muscular Diseases / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D025262:Vacuolar Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism*
D008565:Membrane Proteins; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; C091909:VMA21 protein, S cerevisiae; C540401:VMA21 protein, human; D025262:Vacuolar Proton-Translocating ATPases