Functional Variant in the Autophagy-Related 5 Gene
Promotor is Associated with Childhood Asthma
Lisa J. Martin1., Jayanta Gupta1., Soma S. S. K. Jyothula2, Melinda Butsch Kovacic1, Jocelyn M. Biagini
Myers1, Tia L. Patterson1, Mark B. Ericksen1, Hua He1, Aaron M. Gibson1, Tesfaye M. Baye1,
Sushil Amirisetty1, Anna M. Tsoras1, Youbao Sha2, N. Tony Eissa2, Gurjit K. Khurana Hershey1*
1Department of Pediatrics, Cincinnati Children’s Hospital Medical Center, University of Cincinnati, Cincinnati, Ohio, United States of America, 2Department of Medicine,
Baylor College of Medicine, Houston, Texas, United States of America
Rationale and Objective: Autophagy is a cellular process directed at eliminating or recycling cellular proteins. Recently, the
autophagy pathway has been implicated in immune dysfunction, the pathogenesis of inflammatory disorders, and response
to viral infection. Associations between two genes in the autophagy pathway, ATG5 and ATG7, with childhood asthma were
Methods: Using genetic and experimental approaches, we examined the association of 13 HapMap-derived tagging SNPs in
ATG5 and ATG7 with childhood asthma in 312 asthmatic and 246 non-allergic control children. We confirmed our findings
by using independent cohorts and imputation analysis. Finally, we evaluated the functional relevance of a disease
Measurements and Main Results: We demonstrated that ATG5 single nucleotide polymorphisms rs12201458 and rs510432
were associated with asthma (p=0.00085 and 0.0025, respectively). In three independent cohorts, additional variants in
ATG5 in the same LD block were associated with asthma (p,0.05). We found that rs510432 was functionally relevant and
conferred significantly increased promotor activity. Furthermore, Atg5 expression was increased in nasal epithelium of acute
asthmatics compared to stable asthmatics and non-asthmatic controls.
Conclusion: Genetic variants in ATG5, including a functional promotor variant, are associated with childhood asthma. These
results provide novel evidence for a role for ATG5 in childhood asthma.
Citation: Martin LJ, Gupta J, Jyothula SSSK, Butsch Kovacic M, Biagini Myers JM, et al. (2012) Functional Variant in the Autophagy-Related 5 Gene Promotor is
Associated with Childhood Asthma. PLoS ONE 7(4): e33454. doi:10.1371/journal.pone.0033454
Editor: Dominik Hartl, University of Tu ¨bingen, Germany
Received October 26, 2011; Accepted February 15, 2012; Published April 20, 2012
Copyright: ? 2012 Martin et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was funded by National Institutes of Health grants U19 AI070235 (GKKH and LJM) and U19 AI07041209 (NTE). The funders had no role in
study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: Gurjit.Khurana.Hershey@cchmc.org
. These authors contributed equally to this work.
Asthma is a chronic, inflammatory disease of the respiratory
airways leading to episodes of wheezing, shortness of breath, chest
tightness and cough. About 300 million people are affected by
asthma globally, with 20 million people in the United States
suffering from the condition [1,2] including 10 million children
(13.8%) . Parental asthma is a strong predictor of childhood
asthma, suggesting a strong genetic basis . However, genes that
have been associated with asthma account for only a minor
portion of disease heritability  suggesting that undiscovered
genetic variants likely exist in understudied pathways relevant to
Autophagy is a cellular process directed at recycling of cellular
proteins and removal of intracellular microorganisms. Though
traditionally thought to be a mechanism directed at survival
during starvation, evidence suggests that autophagy has a role in
innate and adaptive immune responses . In fact, autophagy has
been linked to B lymphocyte development , antigen presenta-
tion , and antiviral immunity . More recently, autophagy has
been implicated in the lung, with increased autophagy and
activation of autophagy proteins in lung tissue from chronic
obstructive pulmonary disease patients . In fact, the autophagy
pathway has been reported to respond to cigarette smoke exposure
and has been postulated to be a key component of the lung tissue
injury response to chronic smoke exposure [10,11]. If bronchial
epithelial cells deficient in an autophagy protein are hyperrespon-
sive to methacholine exposure, it is conceivable that autophagy
gene dysregulation results in changes in the epithelial factors
released; these epithelial factors may then contribute to smooth
muscle hyperreactivity in asthmatics.
Given the evidence implicating autophagy in immune responses
and inflammation, we examined whether variants in autophagy
genes were associated with asthma. We focused on autophagy-
related 5 gene (ATG5) and autophagy-related 7 gene (ATG7) because
ATG5 is essential for autophagosome formation , and ATG7 has
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been previously shown to be associated with airway hyperrespon-
siveness in animal models . We hypothesized that ATG5 and
ATG7 polymorphisms and/or dysregulated expression of these
genes are associated with childhood asthma. To test our
hypothesis, we genotyped tagging single nucleotide polymorphisms
(SNPs) in 312 asthmatic and 246 non-asthmatic non-allergic
children and supported our findings using additional cohorts of
children and adults. We identified 2 SNPs in ATG5 associated with
asthma, including one in the putative promotor, which we
demonstrate to be functionally relevant.
The study protocol was approved by the Cincinnati Children’s
Hospital Medical Center Institutional Review Board. Parents gave
written informed consent for the children’s participation, and
children gave their assent.
The primary analysis cohort included children aged 4–17 years
from the greater Cincinnati, Ohio metro area who were enrolled
in either the Greater Cincinnati Pediatric Clinic Repository
(GCPCR) or the Genomic Control Cohort (GCC) [13,14]. Due to
sample size considerations, analyses were restricted to individuals
where self-reported race was white/Caucasian. Asthma cases
(N=312) were derived from the GCPCR, a clinic-based pediatric
repository. Asthma was diagnosed according to American
Thoracic Society (ATS) guidelines . PFT data was available
for 220 children with asthma. Non-asthmatic non-allergic control
subjects were derived from both the GCPCR and the GCC, the
latter being a population-based cohort representative of the
Greater Cincinnati area. Controls had no personal history of
allergies or asthma and no family history of asthma (N=246). For
simplicity, this case control cohort is referred to as the GCPCR
Genetic data from two additional cohorts, the Childhood
Asthma Management Program (CAMP) and the Childhood
Asthma Research and Education (CARE) studies, were extracted
from the database of Genotypes and Phenotypes (dbGaP)
(http://www.ncbi.nlm.nih.gov/gap) with permission. Our analy-
sis included 334 family trios of European ancestry from CAMP
and 95 trios of European ancestry from CARE with Affymetrix
6.0 genotyping data. In addition to CAMP and CARE, we also
evaluated genetic associations in 71 GCC participants with
parent-reported asthma and 211 adults from the Cincinnati
Control Cohort  with no personal or family history of
asthma, all of which had Affymetrix 6.0 genotyping data
available. These case/control cohorts are referred to together
as the ‘‘CINCY’’ cohort for these analyses.
Selection of SNPs and Genotyping Procedures
For the GCPCR cohort, European descent population (CEU)
tagging SNPs were selected based on HapMap NCBI Build 35
(http://www.hapmap.org) using the pair-wise Tagger algorithm
(r2,0.8, minor allele frequency (MAF).0.05) . Eight tagging
SNPs were identified in ATG5, but due to power concerns and low
MAF (,0.1), only four tagging SNPs (rs3804329, rs671116,
rs12201458, rs573775) were included in the analysis from our
custom Illumina GoldenGate assay. Likewise, 10 tagging SNPs
were identified in ATG7, but 7 (rs1499082, rs2606742, rs2606750,
rs346078, rs4684787, rs3856794, rs2305295) were analyzed due to
low MAF. Additionally, ATG5 SNPs located in the 59 untranslated
region (UTR) (rs510432) and 39 UTR/flanking region (rs1322178)
were genotyped. Thirty ancestry informative markers (AIMs) were
also genotyped . Genotyping was performed according to
manufacturer’s protocol (http://www.illumina.com) and assigned
using BeadStudio (V3.2, Illumina, San Diego, CA). Call rates were
.99%. All SNPs were in Hardy-Weinberg equilibrium (HWE).
Five asthmatic (2 M, 3 F) children were excluded due to missing
call rates greater than 20%.
Gene Expression Studies
Microarray data were derived from previously published data
. Briefly, nasal mucosal cells were collected from asthmatic
and control participants using a CytoSoft Brush (Medical
Packaging Corp, Camarilo, CA). The methods for sample
collection, sample processing, RNA isolation, and microarray
hybridization using the HG-U133A GeneChip (Affymetrix, Santa
Clara, CA) have been described previously . The cells were
largely comprised (.92%) of respiratory epithelial cells. Several
genes identified using this approach have been implicated in
asthma pathogenesis in other studies, validating this approach
Cloning of Atg5 Promotor Fragments and Determination
of Promotor Activity
In order to examine the potential impact of rs510432 (located
335bp upstream of the putative human ATG5 transcription start
site) on promotor function, we determined the effect of this SNP
on promotor activity. Human genomic deoxyribonucleic acid
(DNA) was isolated from peripheral blood mononuclear cells
isolated from Buffy coats obtained from local blood bank using
Ficoll Hyperpaque method (Stem Cell Technologies). Genomic
DNA was subjected to PCR amplification using primers
[Fragment 1 Sense AGAGACCTGCTTTCGGCCTG (Location
–6081 to –377), Fragment 2 Sense TGCTAATGGCAGTG-
CATCTCA (Location –4532 to –377), Fragment 3 Sense
CAAGTGATGGTTAGGGTTCATGG (Location –3555 to –
377) & Fragment 4 Sense TGGAGGAAATGGTAAGGCCAA
(Location –2749 to–377),
GCCCTCCGTGTTCTGCCTAA] designed to generate four
fragments containing the Atg5 promotor. Sequence analysis
confirmed that the promotor fragments contained the non-variant
allele for rs510432. The resulting promotor fragments were
purified and sub-cloned into PGL4.20 Firefly Luciferase vector
and co-transfected into HEK293 cells along with PGL4.73 Renilla
transfection control vector. Briefly, we transfected 0.8 million
HEK cells with 2 mg of construct plasmid and 0.08 mg PGL4.73
plasmid (transfection control) simultaneously. This serves as an
internal control for transfection efficiency and also eliminates the
need for viability testing. After 16 hours, the cells were lysed and
Firefly and Renilla Luciferase activities were determined. Promo-
Table 1. Characteristics of the GCPCR population.
Total children, N317246
Children after exclusions, Na
Mean age (years) 6 SD10.04 6 3.44b
11.79 6 3.40
FEV1 (% predicted 6 SD)100.5 6 14.5–
aIndicates sample passing quality control.
bIndicates significant differences (p,0.05) with non-allergic control children.
ATG5 Variants in Asthma
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tor activity was assessed using dual Luciferase assay kit according
to the manufacturer’s instructions (Promega corp). Site-directed
mutagenesis was done using PCR Strategy (Primer Sense:
TACTTTGTTG) to generate the rs510432 allelic variants and
were confirmed by sequencing. In each independent experiment
performed, the average value of Firefly luciferase activity and
Renilla luciferase activity was calculated. The fold difference was
measured using the Renilla luciferase as denominator. PGL4.20
empty vector fold ratio was empirically valued at 1 and rest of the
fold ratios were normalized to PGL4.20. The values for each of the
three independent experiments were tabulated. The final results
are presented as mean with error bars (+/– 1 SD). Paired two
tailed student’s t-test was performed to test differences by allelic
variant, with an alpha of 0.05 set as statistical significance.
Data were analyzed using SAS (V9.1, SAS Inc., Cary, NC) and
PLINK (V1.05; http://pngu.mgh.harvard.edu/purcell/plink/).
Differences in age and sex in disease and control groups were
tested using t-tests and chi-square tests. To ensure genotyping
quality, SNPs exhibiting deviations in HWE (p , 0.0001) were
excluded. Population stratification was assessed using EIGEN-
STRAT and 30 AIMs . There was no evidence of population
stratification (l = 1), thus no adjustment was applied.
To test for association with asthma, we used logistic regression
based on an underlying additive genetic model including age and
sex as covariates. To test association with PFTs, we used linear
regression based on an underlying additive model and included
age and sex as covariates. Results in GCPCR were evaluated after
correcting for multiple testing using a Bonferroni adjustment
taking into account the average linkage disequilibrium (LD)
correlation of 0.239 among 13 SNPs (p-value ,0.007) using the
freely available Simple Interactive Statistical Analyses Software
(http://www.quantitativeskills.com/sisa/). LD was examined us-
ing Haploview (V4.1 (http://www.broadinstitute.org/scientific-
haploview/haploview). Given the small sample sizes of our
additional cohorts (CAMP, CARE, CINCY), we evaluated
evidence of association at the nominal level as we were seeking
replicate findings from the GCPCR.
Based on HapMap CEU results (release 22), imputation was
performed after filtering out SNPs with genotyping call rates ,
90%, MAF , 10%, and HWE p-value , 0.0001 with MACH
. To ensure data quality, imputed genotypes with r2,0.3 were
removed . Imputed SNPs were then tested for association with
asthma using PLINK. Meta-analysis of the results from imputed
SNPs was performed with a weighted Z score (Stouffer’s Ztrend) as
implemented in METAL with the sample weights taken as the
square root of the sample size . Evidence of association was
evaluated using the same significance threshold as our discovery
Analysis of mRNA Expression
To analyze Affymetrix gene expression, we applied Robust
Multi-array Analysis (RMA), in GeneSpring (V7.3.1, Agilent
Technologies, Lexington, MA). Briefly, RMA adjusts for chip
background, normalizes across chips, and summarizes the data.
Expression levels were estimated by using the MicroArraySuite 5.0
algorithm (Affymetrix, Santa Clara, California). Intensities were
normalized to the median expression level of the control samples
. We then performed a one-way analysis of variance
(ANOVA) followed by a Tukey-Kramer post-hoc test (for pairwise
statistical significance between the acute asthmatics, stable
asthmatics, and non-asthmatics) using PRISM (GraphPad Soft-
ware Inc., La Jolla, CA).
The mean age of asthmatic and non-allergic groups was 10.0
and 11.8 years, respectively (Table 1) with the non-allergic group
being slightly, but significantly older. There were no significant
differences in sex between cases and controls.
Table 2. Genotyped SNPs and their minor allele frequencies (MAF) in the GCPCR cohort.
GeneSNPAlleles Minor Allele locationType
Hapmap CEU MAF - cases MAF - controls
ATG5 rs1322178C/TT 10663178139 UTR0.21 0.22 0.17
rs12201458A/CA 106642688intron 0.090.090.16a
rs3804329 A/GG 106686428intron 0.220.220.17
rs671116C/TC 106760598intron0.40 0.390.33
rs573775C/TT106764867 intron 0.300.32 0.27
rs510432 A/GG10677403159 UTR0.46 0.510.42b
rs2606750 A/GA11347151intron0.41 0.360.36
rs2606742C/TC 11366717Intron0.15 0.200.17
ap=0.00085; OR=0.52, 95% CI, 0.36–0.77.
bp=0.0025; OR=1.47, 95% CI, 1.14–1.88.
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Genetic Associations between ATG5 and Childhood
Two variants in ATG5 were significantly associated with asthma
in the GCPCR (Table 2, Figure 1). The minor allele (A) of ATG5
rs12201458 was associated with a decreased risk of asthma
(p=0.00085; OR=0.52, 95% CI, 0.36–0.77), while the minor
allele (G) of ATG5 rs510432 was associated with increased asthma
risk (p=0.0025; OR=1.47, 95% CI, 1.14–1.88). The pattern of
LD and haploype block formation within the ATG5 gene is
displayed in Figure 2. Haploview defined one 133 kb haplotype
block within the gene region consisting of 5 SNPs using the
Confidence Interval method31. Interestingly, rs510432 and
rs12201458 were not in the same haplotype block. There were
Figure 1. Identification of association between asthma and ATG5 SNPs. Negative log10p value of the associations in GCPCR, CAMP, CARE,
and CINCY cohorts are presented as well as the meta analysis (METAL). Black circles represent genotyped SNPs and grey triangles represent imputed
SNPs. The dotted line represents significance (p=0.007 for GCPCR and METAL after correction for multiple comparisons, p=0.05 for CAMP, CARE,
ATG5 Variants in Asthma
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no significant disease associations with any of the ATG7 SNPs
Among asthma cases, we next examined whether ATG5 or
ATG7 SNPs were associated with pulmonary function tests,
including FEV1 (% predicted) and FEV1/FVC (% predicted).
There was no evidence of association (p.0.38) between ATG5 and
pulmonary function within the asthmatic group (data not shown).
For ATG7 SNPs, a single SNP exhibited nominal association
To detect additional ATG5 SNP associations with asthma in the
GCPCR cohort, we imputed 112 SNPs located on chromosome 6
between 106734603 and 106885077 base pairs where ATG5 is
located. One hundred and four SNPs passed our imputation
criteria and 15 were associated with asthma after correction for
multiple comparisons (p,0.007) (Figure 1). Importantly, the MAF
in the controls were consistent with HapMap CEU MAF. Further,
there was 99% agreement between genotyped SNPs and the
corresponding imputed SNPs indicating good imputation quality.
We next examined associations of ATG5 SNPs with asthma in
three additional independent cohorts: CAMP, CARE and CINCY
(Figure 1) using available genome-wide SNP data. In each cohort,
ATG5 SNPs were nominally associated with asthma (p,0.05).
Further, using meta-analysis, we identified four SNPs (rs12212740,
p=0.0036; rs12201458, p=0.0015; rs2299863, p=0.0038; and
rs11751513, p=0.00086) associated with asthma at our multiple
testing correction p-value of 0.007. Interestingly, in the meta-
analysis, our most strongly associated SNP from the discovery
cohort (rs510432) did not exhibit significant evidence of
association across the studies. However, failure of this association
was driven by the CAMP cohort. If the direction of association was
not incorporated into the meta analysis, this SNP would have
reached significance after multiple testing correction (Stouffer’s z
Asthma-associated rs510432 SNP G Variant Allele Confers
Enhanced ATG5 Promotor Activity
The ATG5 rs510432 SNP is located upstream of ATG5’s first
exon in the putative promotor region. Thus, we examined the
potential functionality of this SNP. Human genomic DNA was
isolated from peripheral blood mononuclear cells and was
subjected to PCR amplification in order to generate four
fragments of different lengths containing the Atg5 promotor
(Figure 3). All promotor fragments resulted in enhanced luciferase
activity. Maximal activity was shown for fragments 2,417 bp and
3,239 bp (–3555 to –377 and –2749 to –377, respectively). Larger
fragments containing upstream sequences (–6081 to –377 and –
4532 to –377, respectively) resulted in relative reduction of
promotor activity, suggesting the presence of upstream regulatory
elements. Because fragment 3,239 bp represented the largest
promotor fragment with maximal activity, this fragment was used
as a template for introduction of base change from A to G (asthma
genotype) at rs510432. The variant ‘‘G’’ allele resulted in
significantly enhanced promotor activity by 23% compared to
the non-variant ‘‘A’’ allele (p,0.007) (Figure 3B). Further, we
queried the TRANSFAC database for transcription factor binding
sites which include rs510432 and identified two transcription
factors, STAT1 and C-Fos, which have been associated with
Atg5 mRNA Expression Increased in Acute Asthma
Based on our results thus far, we hypothesized that ATG5
expression would be increased in patients with asthma. Therefore,
we compared Atg5 gene expression in nasal mucosal cells (.92%
airway epithelial cells) isolated from children with acute or stable
asthma, as well as from non-asthmatic control children. ATG5
expression was significantly increased in the nasal cells derived
from children with acute asthma compared to non-allergic
controls with two distinct probe sets (202511_s_at, p=0.0057;
210639_s_at, p=0.021) (Figure 4). Notably, stable asthmatics had
an intermediate expression level, but were not significantly
different from controls.
Our data support a role for the autophagy pathway, and
specifically ATG5 but not ATG7, in childhood asthma. We
identified two variants in the ATG5 gene that are associated with
asthma using a genetic association study and uncovered additional
novel associations using genotypes inferred through imputation.
We investigated the biologic relevance of the ATG5 rs510432 SNP
and found that the disease-associated allelic variant confers
enhanced ATG5 promotor activity. When we queried the
TRANSFAC database for transcription factor binding sites that
include rs510432, we identified two transcription factors, STAT1
and C-Fos, which have been associated with asthma and may be
mediating the functional differences observed. Further, we
demonstrated that Atg5 mRNA expression is up-regulated in
human nasal epithelial cells during an acute asthma attack.
Collectively, our results suggest a novel function for ATG5 in
By screening the autophagy genes ATG5 and ATG7, we found
of ATG5 as a candidate gene for asthma based on searches using
Figure 2. LD plot and identification of haplotype block in the
ATG5 gene. The position of the 6 SNPs within the ATG5 gene are
shown above the plot. D’ values, indicating extent of LD between SNPs,
are noted on the squares. Higher color intensity of the squares indicates
higher LD between SNPs. The inverted black triangle represents a single
haplotype block (estimated by Gabriel’s 90% bounds on D’30).
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Figure 3. Asthma-associated rs510432 SNP G variant allele confers enhanced promotor activity. A. ATG5 promotor fragments generated
from genomic DNA isolated from human peripheral blood mononuclear cells. B, C. Luciferase activity of promotor assay vectors. In the mutant the
corresponding sites of the two strands of the DNA were mutated from A to G. Promotor activities (corrected for transfection efficiency) are presented
as fold increase relative to empty vector (PGL4.20). The fold ratio of empty PGL4.20 Firefly Luciferase plasmid to PGL4.73 Renilla transfection control
vector was normalized to 1. Mean 6 SD, n=3 independent experiments.
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Genome-Wide Association Studies (http://www.genome.gov/
variant rs510432 was associated with childhood asthma in the
promotor variant had functional effects, the promotor activity of
had higher promotor activity than the A allele. The increased
(G) is consistent with our gene expression studies showing increased
gene expression of ATG5 in asthmatics. Further, the increased
obstructive pulmonary disease patients .
Several other ATG5 SNPs were found to be associated with
childhood asthma. The genotyped ATG5 rs12201458 SNP is
located in intron 7, the last intron in the gene. This SNP is
predicted to be an intronic enhancer with a low predicted risk of
functional effects using FASTSNP . As, the SNPs genotyped
for ATG5 were predominantly tagging, the identified association
with rs122201458 may be due to linkage disequilibrium with
functional variants. Thus, the genotypes at markers that had not
been genotyped in this study were imputed using a reference
panel. Imputation can permit the comparison of studies which
focused on different SNPs. Using meta-analysis, four SNPs
exhibited significant association across the studies.
We found Atg5 expression to be up-regulated in nasal epithelium
from acute asthmatics. While there have been no previous studies
investigating Atg5 expression in asthmatics, there is evidence of
increased expression of autophagic proteins, including Atg5, in
lung tissue from patients with chronic obstructive pulmonary
disease . The respiratory tract is divided into the upper airway
(UA; the portion from the nose to the vocal cords) and the lower
airway (LA; below the vocal cords). Epidemiologic and biologic
evidence support this concept of a ‘‘united airway’’ in which the
UA reflects pathophysiologic changes occurring in the LA and vice
versa through biological cross-talk. Studies have demonstrated that
comparable inflammatory processes underlie rhinitis and asthma
[28,29]; and not only does nasal allergen challenge initiate
pulmonary inflammation , but lung allergen challenge induces
inflammation in bronchial and nasal mucosa . The autophagy
pathway is responsive to cigarette smoke exposure  and viral
infection [9,33], important cofactors for asthma, further support-
ing a role of autophagy in respiratory disease.
While, Atg5 is necessary for antigen presentation  and can
lead to increased viral clearance , autophagy machinery can
also be hijacked to increase viral replication . Atg5, though
indispensible for autophagy, has functions independent of
autophagy including a role in apoptosis and regulation of
interferon (IFN) responses against viral infections [9,35]. Indeed,
the Atg12-Atg5 conjugate has been shown to negatively regulate
the type I IFN modulating pathway . Thus, in contrast to anti-
pathogenic properties of autophagic processes, Atg5 also has the
capacity to promote RNA virus replication by inhibiting innate
anti-virus immune responses, a rather paradoxical role for Atg5.
These non-canonical roles for Atg5 in regulation of apoptosis and
IFN production could have significance in asthma pathology in
relation to immune responses to viral infections. Our data has
demonstrated amplified Atg5 expression in acute asthmatics.
Consistent with previous studies indicating that asthmatics have
slower viral clearance , increased Atg5 expression could lead
to augmented viral replication, greater virus production and thus
prolonged viral clearance. Taken together, these studies provide a
potential mechanism for a role of ATG5 in asthma. Future
studies are required to determine if ATG5 has a causal role in
asthma or if these differences are due to inflammation and related
Figure 4. ATG5 expression enhanced in nasal mucosal samples from children with acute asthma. Data are presented as normalized
expression from Affymetrix array data using (A) 202511_s_at and (B) 210639_s_at ATG5 probesets. Intensities were normalized to the median
expression level of the control samples.
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A major strength of our study is the use of functional
investigations to complement the genetic associations. Indeed,
many genetic association studies have reported associations with
asthma, but few have characterized functional effects . Our
data provide strong evidence for association of a functional
promotor SNP in ATG5 with childhood asthma. Our study is
limited in that we utilized adult controls in one of the cohorts.
Although many studies prefer to match cases and controls on age,
studies have utilized adults as controls for childhood asthma as
they represent a truly asthma-free population, whereas similarly
aged child controls may go on to develop asthma . While this
has a potential to create bias, this cohort was used only to confirm
findings and therefore the risk of incorrect inference is minimal.
Some of the cohorts were of modest size, but it is important to note
that both the CAMP and CARE cohorts have extremely well
characterized subjects with detailed phenotypic data. However,
replication in additional cohorts is warranted.
In summary, several independent investigators have linked
autophagy to various aspects of the innate and adaptive immunity.
ATG5 is a key component of the autophagy machinery and has
functions in viral clearance. We have demonstrated that ATG5
variants are associated with childhood asthma, including a variant
that confers enhanced promotor activity and that Atg5 expression
is dysregulated in children with asthma. Additional studies are
necessary to further elucidate biological roles of autophagy and
autophagy-related antiviral defense in asthma pathogenesis.
We thank the physicians, nurses and staff of Cincinnati Children’s Hospital
Medical Center clinics (Allergy and Immunology, Pulmonary, Dermatol-
ogy, Headache Center, Dental, Orthopedic) and Emergency Department
as well as the investigators and staff of the Genomic Control and Cincinnati
Control Cohorts. We thank the patients and their families who participated
in this study. CAMP and CARE datasets were obtained from dbGaP
accession number phs000166.v2.p1.
Conceived and designed the experiments: GKKH NTE. Performed the
experiments: SJ MBE. Analyzed the data: LJM HH JG SJ SA. Contributed
reagents/materials/analysis tools: TLP AMG AMT SA. Wrote the paper:
LJM JG MBK JBM GKKH NTE YS SJ TMB.
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