Non-alcoholic fatty liver disease in mice with heterozygous mutation in TMED2
August
Non-alcoholic fatty liver disease in mice with heterozygous mutation in TMED2
Wenyang Hou 0 1 2
Swati Gupta 0 1 2
Marie-Claude Beauchamp 0 1 2
Libin Yuan 0 1 2
Loydie A. Jerome-Majewska 0 1 2
0 Current address: Department of Pathology, Yale School of Medicine , New Haven, Connecticut , United States of America
1 Department of Human Genetics, McGill University , Montreal, QueÂbec , Canada , 2 Department of Pediatrics, McGill University Health Centre Glen Site , Montreal, QueÂbec , Canada , 3 Department of Anatomy and Cell Biology, McGill University , Strathcona Anatomy and Dentistry Building, QueÂbec , Canada
2 Editor: Arun Rishi, Wayne State University , UNITED STATES
The transmembrane emp24 domain/p24 (TMED) family are essential components of the vesicular transport machinery. Members of the TMED family serve as cargo receptors implicated in selection and packaging of endoplasmic reticulum (ER) luminal proteins into coatomer (COP) II coated vesicles for anterograde transport to the Golgi. Deletion or mutations of Tmed genes in yeast and Drosophila results in ER-stress and activation of the unfolded protein response (UPR). The UPR leads to expression of genes and proteins important for expanding the folding capacity of the ER, degrading misfolded proteins, and reducing the load of new proteins entering the ER. The UPR is activated in non-alcoholic fatty liver disease (NAFLD) in human and mouse and may contribute to the development and the progression of NAFLD. Tmed2, the sole member of the vertebrate Tmed β subfamily, exhibits tissue and temporal specific patterns of expression in embryos and developing placenta but is ubiquitously expressed in all adult organs. We previously identified a single point mutation, the 99J mutation, in the signal sequence of Tmed2 in an N-ethyl-N-nitrosourea (ENU) mutagenesis screen. Histological and molecular analysis of livers from heterozygous mice carrying the 99J mutation, Tmed299J/+, revealed a requirement for TMED2 in liver health. We show that Tmed299J/+ mice had decreased levels of TMED2 and TMED10, dilated endoplasmic reticulum membrane, and increased phosphorylation of eIF2α, indicating ER-stress and activation of the UPR. Increased expression of Srebp1a and 2 at the newborn stage and increased incidence of NAFLD were also found in Tmed299J/+ mice. Our data establishes Tmed299J/+ mice as a novel mouse model for NAFLD and supports a role for TMED2 in liver health.
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Data Availability Statement: All relevant data are
within the paper and its Supporting Information
files.
Funding: This work was supported by the Natural
Sciences and Engineering Research Council of
Canada (NSERC), http://www.nserc-crsng.gc.ca/
index_eng.asp, RGPIN-2015-06699.
Competing interests: The authors have declared
that no competing interests exist.
Introduction
The ten TMED proteins in mouse and human are subdivided into four subfamilies based on
sequence similarity [
1
]: three belong to the α subfamily (TMED4, 9, 11); one to the β family
(TMED2); five to the γ subfamily (TMED1, 3, 5, 6, 7); and one to the δ family (TMED10).
TMED proteins were found to form monomers, dimers and heterodimers [
2
]and to regulate
the stability of each other [
3
]. Thus, loss of one member of a subfamily resulted in loss of
TMED proteins in other subfamilies [
2, 4, 5
].
Members of the TMED family serve as cargo receptors implicated in selection and
packaging of endoplasmic reticulum (ER) luminal proteins into COP II coated vesicles for
anterograde transport to the Golgi. TMED putative cargos include WNTs and
glycosylphosphatidylinositol-anchored proteins (GPI-AP)[
3
]. Deletion or mutations of Tmed
genes in yeast and Drosophila resulted in ER-stress and activation of the unfolded protein
response (UPR)[
6, 7
].The UPR leads to expression of genes and proteins important for
expanding the folding capacity of the ER, degrading misfolded proteins, and reducing the load
of new proteins entering the ER [8].
Tmed2, the sole member of the vertebrate Tmedβ subfamily exhibits tissue and temporal
specific patterns of expression in embryos and developing placenta [
5, 9, 10
] but was
ubiquitously expressed in all adult organs [
11
]. Our group identified a point mutation in the signal
sequence of Tmed2 in a mutant mouse line, 99J, generated in a mutagenesis screen with
Nethyl-N-nitrosourea (ENU). We showed that the 99J mutation results in decreased TMED2
protein levels in heterozygous (Tmed299J/+) embryos and loss of TMED2 protein in
homozygous mutant embryos (Tmed299J/99J)[
5
]. Tmed2 is required for morphogenesis of the embryo
and its associated placenta, and consequently Tmed299J/99J embryos arrest at mid-gestation,
shortly after embryonic day (E)10.5 [
5
]. Similarly, Tmed10, the sole member of the Tmed δ
family is required for embryonic development and, Tmed10 homozygous mutant embryos
arrest early in development, before E3.5 [
4
]. Furthermore, Tmed10 heterozygous mice showed
di (...truncated)