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Peripheral blood miRNAs are associated with airflow below threshold in children with asthma

Abstract

Background

MicroRNAs (miRNAs) are crucial post-transcriptional regulators involved in inflammatory diseases, such as asthma. Poor lung function and airflow issues in childhood are linked to the development of chronic obstructive pulmonary disease (COPD) in adulthood.

Methods

We analyzed small RNA-Seq data from 365 peripheral whole blood samples from the Genetics of Asthma in Costa Rica Study (GACRS) for association with airflow levels measured by FEV1/FVC. Differentially expressed (DE) miRNAs were identified using DESeq2 in R, adjusting for covariates and applying a 10% false discovery rate (FDR). The analysis included 361 samples and 649 miRNAs. The two DE miRNAs were further tested for association with airflow obstruction in a study of adult former smokers with and without COPD.

Results

We found 1 upregulated and 1 downregulated miRNA in participants with airflow below the threshold compared to those above it. In the adult study, the same miRNAs were upregulated and downregulated in individuals with FEV1/FVC < 0.7 versus those with FEV1/FVC > 0.7, showing suggestive statistical evidence. The target genes of these miRNAs were enriched for PI3K-Akt, Hippo, WNT, MAPK, and focal adhesion pathways.

Conclusions

Two differentially expressed miRNAs were associated with airflow levels in children with asthma and airflow obstruction in adults with COPD. This suggests that shared genetic regulatory systems may influence childhood airflow and contribute to adulthood airflow obstruction.

Introduction

Asthma affects around 23 million people in the United States and over 300 million people globally [1]. The characteristic of asthma is an obstruction of airflow that is often, but not always, reversible. A fixed airflow obstruction that is not completely reversible is a characteristic of chronic obstructive pulmonary disease (COPD). The term “airflow obstruction” refers to the observation of a reduced expiratory airflow relative to the total volume of air exhaled. This is indicated by a decline in the ratio of forced expiratory volume in 1 s (FEV1) to forced vital capacity (FVC) [2]. The Dutch Hypothesis [3] proposed a genetic (or genomic) connection between asthma in childhood and COPD. Large-scale genome-wide association studies (GWASs) of asthma and COPD have illustrated an overall genetic correlation between asthma and COPD as well as multiple specific overlapping genomic loci with a concordant direction of effect [4]. However, despite strong evidence of partially overlapping genetic susceptibility to asthma and COPD, little research has centered on shared non-genetic omics drivers of airflow limitation or obstruction.

Recent findings have shown that mRNA regulation by microRNAs (miRNAs) may form part of the common genomic basis of asthma and COPD [5]. miRNAs are noncoding RNA molecules of 21–23 nucleotides that regulate gene expression by binding to 3’ untranslated target mRNA regions and triggering translation degradation or inhibition [6]. miRNAs play significant regulatory roles in immunological and inflammatory responses in several tissues and are thus potential therapeutic targets in asthma and COPD [7]. Earlier studies of miRNAs in asthma centered on asthma itself, such as circulating miRNA expression in children with asthma compared with healthy controls, regulation of IL-5 expression by miRNA, differential expression of miRNA in asthmatics and healthy controls, and differential expression of miRNA in epithelial and airway cells in asthmatics and healthy controls [8,9,10,11]. We have previously demonstrated shared miRNA regulation of asthma and COPD exacerbations [12]; however, exacerbations generally result from a complex interplay of external stimuli such as allergens or respiratory infections, social or economic factors influencing the availability and cost of exigent hospital care, and predisposing internal biology. This work identified five miRs (451b; 7-5p; 532-3p; 296-5p and 766-3p) associated with childhood asthma exacerbations and adult COPD exacerbations. Complex multigenic disorders such as asthma have had hundreds of DNA variants associated [13], and the genomic regulation is similarly complex and multi-genic [14]. Previous genetic studies [15, 16] of airflow obstruction and of asthma exacerbations have identified disparate loci, leading to separate insights into the underlying pathogenesis of asthma [17]. Peripheral blood miRNAs have not been investigated in airflow limitation or obstruction in children with asthma and makes an intriguing follow-up to prior work investigating exacerbations. Therefore, we hypothesized that peripheral blood miRNA, separate from those that regulate exacerbations, would regulate immunological and inflammatory responses associated with airflow levels in children with asthma and that these effects would be observable in adults with COPD. We tested this hypothesis in two well-characterized cohorts, one including children with asthma and another including current and former smoking adults with and without COPD.

Methods

Genetics of asthma in costa rica study

Subject recruitment and the study protocol for the Genetics of Asthma in Costa Rica Study (GACRS) have been previously reported [18, 19]. In brief, the GACRS included 1,165 asthmatic Costa Rican children with asthma aged 6 to 14 years who were recruited between February 2001 and July 2011. Asthma was defined as physician-diagnosed asthma and having either at least two respiratory symptoms (wheezing, coughing, or dyspnea) or a history of asthma attacks in the previous year. All study participants also had a high probability of having six great-grandparents born in Costa Rica’s Central Valley, as defined by a genealogist based on each parent’s paternal and maternal last names. Following American Thoracic Society guidelines, spirometry was performed using a Survey Tach Spirometer (Warren E. Collins, Braintree, Mass). Written parental informed consent and the child’s assent were obtained for all study participants. The study was approved by the Institutional Review Boards of the Hospital Nacional de Niños (San José, Costa Rica) and Brigham and Women’s Hospital (Boston, MA).

COPDGene

The study design and protocol for the COPDGene trial (NCT00608764 on ClinicalTrials.gov) were previously reported in detail [20]. In brief, COPDGene is a prospective study of both non-Hispanic white and African American current and former smokers with at least 10 pack-years of smoking, with and without spirometry-defined COPD. We included 439 individuals from the COPDGene 5-year follow-up visit with available peripheral whole blood small RNA sequencing data.

Primary outcome

In GACRS spirometry was performed at the initial visit according to ATS guidelines. Forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) were measured. Each subject performed spirometry tests to satisfaction three times, with the best being retained. These were converted to percent predicted FEV1 and FVC using Hankinson et al. [21] equations based on healthy Mexican Americans, which assesses airflow relative to a person’s age, sex, height, and race. Their ratio was used to define airflow level. In this cohort, the threshold for airflow was considered to be a predicted FEV1/FVC ratio of 100%. We chose this threshold primarily to increase statistical power: clinical airflow obstruction was rare in GACRS so choosing a threshold such as FEV1/FVC < 70% would lead to unbalanced cases vs. controls. Participants with an airflow A predicted FEV1/FVC of 100% represent the average for a healthy person of the appropriate age, sex, height, and race. This was treated as a binary variable and our primary outcome.

In the COPDGene study, post-bronchodilator spirometry was collected at the 5-year follow-up visit. In this cohort, we defined airflow obstruction as raw FEV1/FVC < 0.7, as it is the most relevant division in COPD, and this threshold is used as part of the diagnosis of COPD.

Other clinical and demographic data were compared between cases and controls using Chi-squared tests for discrete variables and Student’s t-test for continuous variables.

miRNA sequencing data and quality control

We used small RNA sequencing data previously sequenced on whole blood from 374 GACRS samples and 450 COPDGene samples [12]. GACRS blood samples were acquired at the time of phenotype assessment, between 2001 and 2005, and were stored at -80 degrees C until sequencing began in 2019. Small RNA-seq libraries were prepared using the NEXTflex Small RNA-Seq Kit v3 (PerkinElmer’s, Waltham, MA, USA), which has a maximum input of 10 uL (10 ng to 250 ng). First, adapters were ligated to the 3′ and 5′ ends of the RNA. Reverse transcription was then carried out to generate cDNA from the ligated RNA. Following reverse transcription, cDNA yield was amplified by PCR, utilizing a distinct barcoded PCR primer for each sample. Finally, the PCR product entered size selection using magnetic beads for libraries in the range of 140–160 bp, resulting in the isolation of the indexed miRNA libraries. Libraries were then pooled and sequenced on an Illumina NextSeq 550 high output flow cell, with a run length of 75 bp single reads, to generate ~ 10 M reads per sample. Briefly, we applied blockers for hemolysis-linked miRNAs hsa-miR-486-5p, hsa-miR-92a, and hsa-miR-451a (PerkinElmer, Waltham, MA) that were added to the input sample before library creation [22]. For quality control (QC) of the RNA-seq data, the COMPSRA [23] and BCBio small RNA-seq (https://github.com/bcbio/bcbio-nextgen) pipelines were implemented. miRNAs with less than five mapped reads in at least 50% of participants were removed before analysis. Raw and processed GACRS miRNA data is available in the Gene Expression Omnibus, accession GSE244036. No passing miRNA had any sample more than three standard deviations from the mean (log scale). In GACRS, we utilized the guided Principal Component Analysis (gPCA) [24] package to find batch effects. The PCA of COPDGene samples revealed an outlier batch that was eliminated from further analysis.

Identification of differentially expressed miRs

DESeq2 [25] version 1.30.0 (R version 4.0.3) with a Benjamini-Hochberg false discovery rate (FDR) correction for multiple testing was used to identify differentially expressed miRNAs (upregulated and downregulated miRNAs) between those with airflow above and below threshold in GACRS. DESeq2 uses raw count data and performs internal normalization and then negative binomial regression, a test appropriate to RNA-Seq count data [25]. A significance threshold of 10% FDR was used. This FDR threshold indicates that 10% of our declared significant miRNAs are likely to be false positives. The analysis was adjusted for age, sex, use of inhaled corticosteroids (ICS) in the prior year, maternal smoking, BMI, genotype PCs, and sequencing batch. Logistic regression was used to obtain estimates of effect size (Odds Ratios) for a doubling of miR counts. For consistency with the differential expression analysis, data for logistic regression was normalized using the DESeq2 method, which is based on the geometric mean of samples per gene [25]. Additionally, we conducted a permutation test to assess the difference in mean expression levels of top miRs between groups with airflow above and below the threshold. The permutation test randomly shuffled the miRNA values while preserving the group structure, allowing us to generate a null distribution of differences in means. This null distribution was obtained by repeating the permutation process ten thousand times. Subsequently, we compared the observed difference in means, calculated from the original data to this null distribution to determine its statistical significance. This approach enabled a robust assessment of group differences in top miRNA expression levels.

Similarly, in the COPDGene study, DESeq2 was used to assess the association of top DE miRNAs with airflow obstruction (FEV1/FVC < 0.70) while adjusting for age, sex, smoking history (current vs. former), pack-years of cigarette smoking, self-reported race (either non-Hispanic white or African American), and sequencing batch.

Functional annotation of differentially expressed miRNAs

The Micro T-CDS [26], TarBase [27], and Target Scan [28] databases were used to identify target mRNA transcripts for top DE miR between the above and below threshold airflow using the default parameters of the multiMiR package version 1.12 [29]. The clusterProfiler package version 3.18.1 was used to analyze the Kyoto Encyclopedia of Genes and Genomes (KEGG) [30] pathway using the union of each miR’s targets [31]. To show substantial enrichment of targeted genes for a pathway, we used an adjusted p-value threshold of 0.05 and a gene count of 3 or more.

The miRNA-target gene network and enrichment analysis for the top DE miRNAs were generated using the web-based tool miRNet 2.0 [32]. For network construction, miRNet takes the list of DE miRNAs and retrieves the predicted and validated putative gene targets from Tarbase-8.0 and miRTarBase-8.0. Functional enrichment was done using the KEGG database and a hypergeometric test, with an FDR threshold of 0.1 considered significant (Fig. 1).

Fig. 1
figure 1

Network of two differentially expressed miRs between children with airflow above and below threshold, and their gene targets. Nodes with different colors indicate genes in selected enriched KEGG pathways

The transcription factor (TF)-miRNA-Gene regulatory network for Hippo, PI3K-Akt, and MAPK signaling pathway-related validated target genes of DE miRNAs was reconstructed. The network contains three relations: TF - DE miRNA, TF - Target gene, and DE miRNA - target genes. We used TRRUST v2 [33] for TF - Target gene interactions, TransmiR v2.0 [34] for TF-miRNA interactions, and miRTarBase 7.0 [35] for experimentally validated (reporter assay or western blot) miRNA-target gene interactions. The transcription factors (TFs) were limited to those involved in the Hippo, PI3K-Akt, and MAPK signaling pathways, with genes shown that are jointly regulated by at least two miRs or transcription factors.

Results

Cohort characteristics

Peripheral whole-blood samples were available for 365 of the 1,165 children with asthma in the GACRS (31.33%). Children with airflow below the threshold were of similar age and weight to those above the threshold. Children below the threshold differed from those above thresholds mostly in spirometry, with greater FVC and lower FEV1, both pre-and post-bronchodilator administration (Table 1). Characteristics of participants undergoing small RNA sequencing in COPDGene are shown in Table 2.

Table 1 Baseline epidemiologic and clinical characteristics of the GACRS
Table 2 Baseline epidemiologic and clinical characteristics of COPDGene

Differentially expressed miRNAs

We had 361 samples and 649 miRNAs for DE analysis comparing the groups with airflow above (n = 220) and below (n = 141) threshold after quality control, filtering, and normalization.

In participants with airflow below threshold, we found one miRNA (let-7e-5p, p = 0.0001, FDR = 0.054; negative binomial regression odds ratio = 0.75, CI (0.64–0.87)) with higher expression and one miRNAs (miR-342-3p, p = 0.0002, FDR = 0.054; negative binomial regression odds ratio = 1.15, CI (1.07–1.23)) with lower expression (Table 3; Figs. 2 and 3). These two miRNAs were then tested for association with airflow obstruction (FEV1/FVC ratio < 0.7) in the COPDGene study, in which let-7e-5p was upregulated (p < 0.064) and miR-342-3p (p < 0.085) was downregulated in participants with FEV1/FVC < 0.7 (n = 196) compared to those with FEV1/FVC > 0.7 (n = 243) (Table 4).

Table 3 Significant up- and down-regulated miRNAs in GACRS. Mean counts: normalized mean counts in the reference group. Log2 FC: base-2-fold change from infrequent to frequent exacerbators. Odds ratio: computed with logistic regression. 95% CI: 95% confidence interval for odds ratio. P-value: for differential expression between above and below-threshold groups, computed with DESeq2. FDR: false discovery rate adjusted p-values, with FDR < 0.10 considered significant
Fig. 2
figure 2

Differential expression of peripheral blood miRNA between airflow above and below threshold in the GACRS. Benjamini-Hochberg adjusted p-values are shown. The mean expression is shown in the log2 scale. The vertical dotted lines correspond to a fold change up and down; the horizontal line represents an FDR < 10%

Fig. 3
figure 3

let-7e-5p (left) and miR-342-3p (right) are distributed above or below the airflow threshold in GACRS. X-Axis: FEV1/FVC ratio above (1) and below (0) threshold

Table 4 Replication of up-and down-regulated miRNAs between above and below FEV1/FVC threshold in COPDGene

Statistical significance of miR-342-3p and let-7e-5p were further assessed using a permutation test, with both showing strong evidence of no chance associations with airflow above or below threshold (miR-342-3p permutation p < 1e-04, let-7e-5p permutation p = 0.058). This test indicates that the observed difference in mean expression levels of miR-342-3p and let-7e-5p between the groups is extremely unlikely to have occurred by chance alone under the null hypothesis of no difference (Fig. 4).

Fig. 4
figure 4

Distribution of label-shuffling permutation test values for differential expression of hsa-miR-342-3p (a) and hsa-let-7e-5p (b). Red line: True test value for differential expression between above and below threshold FEV1/FVC ratio

To investigate potential pharmacogenomic effects on these two miRNAs, we then performed an analysis stratified by ICS use, and one also by SABA (Short-acting beta agonists) usage. We found that let-7e-5p was differentially expressed between higher and lower FEV1/FVC in the groups reporting regular SABA usage (p < 0.004) and the group reporting no recent ICS usage (p < 0.008), in each case being overexpressed in the higher FEV1/FVC group, consistent with our whole-cohort analysis.

These two miRNAs, therefore, showed the same direction of effect with airflow below threshold in childhood asthma (GACRS) and airflow obstruction in current and former smoking adults (COPDGene study).

Functional assessment of differentially expressed miRNAs

We performed a biological pathway enrichment analysis of putative gene targets of the 2 DE miRNAs using the clusterProfiler R package [31] (Fig. 5A). Phosphatidylinositol 3-kinase (PI3K) – protein kinase B (Akt), Hippo, Wingless-related integration site (WNT), Mitogen-activated protein kinase (MAPK), and focal adhesion signaling pathways were among the topmost enriched pathways. We also separately considered the targets of only the two miRNAs that were also associated with FEV1/FVC in the COPDGene study, where PI3K-Akt, MAPK, and Hippo signaling pathways were among the top five most enriched pathways (Fig. 5B). The targets of these two miRNAs are shown in Fig. 1, with a highlighting of genes participating in enriched pathways previously associated with asthma.

Fig. 5
figure 5

KEGG pathways enriched for target genes of two differentially expressed miRs between children with airflow above and below threshold (342-3p and let-7e-5p). Gene targets for miRs were identified using microT-CDS Diana, Target Scan & TarBase databases. Gene Ratio: genes of interest in the gene set over the total genes of interest

Transcription factor-miRNA-gene regulatory network reconstruction for specific pathways

To further understand the regulatory relationship between DE miRNAs, target genes, and transcription factors (TF) related to Hippo, PI3K-Akt, and MAPK signaling pathway, the TF-miRNA-Gene regulatory network was re-constructed as shown in Fig. 6 (A, B, and C; images abbreviated to show genes regulated by at least two elements). DE miRNA let-7e-5p had the highest connectivity in all three pathway-specific networks (Fig. 6). Moreover, the two DE miRNAs were predicted to have common targets in all three pathways, for example, CCND1, CCND2, and LIMD1 genes in the Hippo signaling pathway, IGF1R gene in MAPK signaling pathway, and (THBS1, MDM2, LAMC1, IGF1R, CCND1, CCND2) genes in PI3K-Akt signaling pathway, were found to be common targets for both DE miRNAs. Particularly, the MYC transcription factor regulates let-7e-5p expression in all three pathways.

Fig. 6
figure 6

Transcription factor (TF)-miRNA-Gene regulatory networks related to (A) Hippo, (B) PI3K-Akt and (C) MAPK signaling pathways, with regulation by both miR-342-3p and let-7e-5p

Discussion

We report that 2 miRNAs (let-7e-5p; miR-342-3p) are suggestively associated with airflow in a study of Costa Rican children with asthma. Of these two miRNAs, one was downregulated, and one was upregulated in participants with airflow below the threshold. miR-342-3p and let-7e-5p were observed to have the same direction of effect for differential expression related to airflow obstruction (FEV1/FVC ratio < 0.7) in COPDGene study participants, with suggestive statistical evidence.

Our choice of predicted FEV1/FVC ratio dichotomization at 100% represents a threshold chosen around the midpoint of the spectrum of observed airflow obstruction, or lack thereof, in GACRS. In healthy individuals, we would expect half of the subjects to be above 100% FEV1/FVC percent predicted. This contrasts with the 70% threshold chosen for replication in COPD, which represents a clinically meaningful level of obstruction in that disease. The GACRS cohort of children with mild asthma has low levels of fixed airflow obstruction, making a threshold of mild or no obstruction appropriate. Research has shown that poor lung function in childhood asthma can lead to adult COPD [36, 37], and while we don’t expect to see the same level of airflow obstruction in children as in COPD, identifying those with relatively poorer airflow compared to other children with asthma identifies those at greater risk of future clinical airflow obstruction.

We sought to generalize our childhood asthma miRNA airflow association to adult current and former smokers in the COPDGene study. Asthma is a major risk factor for COPD. However, airflow obstruction defined by reduced FEV1/FVC can occur through a variety of pathophysiologic mechanisms. Our work shows that airflow below the threshold in asthma and obstruction in adult current and former smokers share some regulatory precursors, which agrees with research showing that asthma and COPD have overlapping causes [3, 4]. These two miRNAs associated with airflow (FEV1/FVC) in both childhood asthma and current and former smoking adults have been previously associated with inflammation [38,39,40]. let-7e-5p has been linked to a proinflammatory role in asthma [41], and previously connected to the PI3-AKT, MAPK, Hippo, and Wnt signaling pathways, crucial regulatory pathways in asthma etiology [42,43,44]. In a murine model, miR-342-3p was linked to allergic airway disease, and it was also found to decrease inflammation in human macrophage THP-1 cells [40, 45]. Airflow obstruction in asthma is primarily linked to a distinctive form of airway inflammation that includes an increase in T cells (mainly CD4+) and eosinophils, as well as a thicker reticular layer of the epithelial basement membrane [46].

Some colleagues have previously investigated the association of serum miRNAs and FEV1/FVC in childhood asthma [10]. In a smaller study using 160 North American children with asthma on inhaled corticosteroids, Kho et al. [10]. identified 22 miRs associated with airway obstruction. We did not find an overlap between these 22 and our results here, but significant technical variations, as well as population differences and issues of statistical power, may have led to these results.

In vitro and in vivo studies have demonstrated that exogenous over-expression of miR-342-3p induced apoptosis and inhibited tumorigenicity, cell growth, invasion, and migration [47], cellular phenotypes which may be related to airway remodeling and lead to reduced FEV1/FVC. Another study reported the downregulated expression of miR-342-3p in COPD cases [48].

The Hippo pathway, which regulates organ size in the embryonic stages of development by encouraging apoptosis and regulating cell proliferation, is evolutionarily conserved throughout Drosophila melanogaster to humans [49, 50]. Yes-associated protein 1 (YAP1 or YAP) and transcriptional coactivator with PDZ-binding motif (TAZ), the main hippo effectors, are transcriptional coactivators that bind to transcription factors such as TEAD, SMAD, or TP73 when activated to influence the expression of various genes [51,52,53]. It was recently reported that YAP1 is abundantly expressed in embryonic and mature lung respiratory epithelial cells. Hippo/YAP1 signaling controls epithelial cell proliferation and differentiation, as well as embryonic lung development and postnatal airway homeostasis [54]. Furthermore, it has been revealed in mice that YAP1 is dynamically regulated during airway epithelial regeneration following lung damage, indicating a potential function for Hippo/YAP1 signaling in the etiology of acute and chronic lung disorders [55].

It is well accepted that YAP1 and TAZ function as downstream effectors of the Hippo pathway. They have emerged as important translational co-activators of a wide range of biological processes, and they play an important role in lung development and function. The YAP1/TAZ signaling pathway is dysregulated, which contributes to the development and progression of chronic lung conditions such as asthma, COPD, and lung infection. Therefore, owing to its critical functions, Chaulk et al. reported that cell density-mediating nuclear expression of YAP1/TAZ is required for high levels of Dicer to occur in MCF-10 A cell lines. Mechanistically, let-7 family members, which are well-validated as tumor suppressors, are significantly attenuated by nuclear YAP1/TAZ levels. Increased nuclear YAP1/TAZ can suppress the process of pre-miRNA conversion into mature let-7 miRNA by mediating the Dicer enzyme. However, let-7 biogenesis is dependent on cell density, rather than the expression of YAP1/TAZ [56, 57].

Genetic polymorphisms in FRMD6, an upstream activator of the Hippo pathway, have been linked to asthma and lung function [58]. Furthermore, genetic variations in the BIRC5 gene (also known as survivin), one of YAP1’s target genes, increased the risk of inflammatory disorders such as asthma. Furthermore, FRMD6 mRNA levels in sputum were considerably lower in asthmatic patients than in healthy controls, although BIRC5 levels were greater [58,59,60]. let-7e-5p and miR-342-3p, gene targets were enriched with Age-RAGE signaling pathway proteins, and this pathway is a major culprit in diabetic complications. Numerous researchers have discovered that the Receptor for Advanced Glycation End-products (RAGE) pathway expression is strongest in the lungs, and it has been identified as a driving factor for inflammation in pulmonary pathophysiology and associated with COPD [61,62,63]. Research has demonstrated a critical role of RAGE throughout the development of the Th-2 high allergic airway disease [64]. Taken together with our results, this supports a role for miRNA regulation of these RAGE-mediated processes leading to airway inflammation, airway remodeling, and later airflow obstruction.

The MAPK and PI3K-Akt signaling pathways, which have previously been related to asthma, were enriched in both gene targets of the two DE miRNAs and gene targets of the two miRNAs impacting both asthma and COPD lung function. The relationship between these two pathways to asthma was recently discussed in our previous study [12], which linked changes in miRNA expression to asthma exacerbations. The miRNA identified in that work also had mRNA targets significantly enriched for MAPK and PI3K-Akt pathway genes, and much of that discussion is also relevant to airway obstruction in asthma and COPD. MAPK and PI3K-Akt dysregulation can result in airway remodeling which can result in obstruction as well as a predisposition for increased exacerbations.

In addition to Th2-high eosinophilic asthma and Th2-low neutrophilic asthma, MAPK signaling may also play a role in COPD [46]. Smoke from cigarettes can activate the MAPK pathway in small airway epithelial cells, which results in the release of chemokines and inflammatory cytokines [65]. In Th2-low neutrophilic asthma and COPD, this kind of activation can result in airway remodeling, which lowers lung function and increases the chance of an exacerbation [66]. In allergic asthma, the PI3K-Akt pathway plays a regulatory role [67]. When PI3K-Akt is activated, other signaling molecules are activated downstream, one of which is NF-kB, a transcription factor that promotes inflammation. Inhibition of PI3K-Akt reduces the expression of proinflammatory cytokines IL-4, IL-6, and IL-8, as well as Tumor Necrosis Factor-alpha (TNF-a) and Immunoglobulin E (IgE); additionally, this pathway is regulated by other miRNA [68]. PI3K-Akt has also been implicated in inflammation in COPD and has been suggested as a possible therapeutic target in COPD [69].

let-7e-5p was also discovered to regulate an anti-inflammatory gene, archetypal dual-specificity phosphatase (DUSP1), which is involved in a feedback system that regulates the harmful inflammatory response caused by the MAPK cascade [70, 71]. Recent studies showed that among various proliferation pathways, the PI3K pathway is the key signaling route in asthmatic airway smooth muscle (ASM) proliferation while the ERK(MAPK) pathway provides a complementary signal required for the full mitogenic response [72, 73]. PI3K pathway gene, Phosphatase, and tensin homolog (PTEN) which was previously reported to regulate the proliferation and migration of ASM cells in Asthma [74,75,76] was found to be regulated by let-7e-5p. DUSP1 and PTEN gene expression were found to be regulated by the same transcription factor, TP53 (Fig. 6). Both target genes share the same transcriptional and post-transcriptional regulators, revealing the existence of complex crosstalk between the pathways targeted by the DE miRNAs, fine-tuning the expression of target genes and transcription factors for precise cellular response in Asthma.

We have previously investigated the regulation of asthma exacerbations [12] and bronchodilator response (BDR) [77] by blood and serum, respectively, miRNA in children. The two replicated miRNAs here, miR-342-3p and let-7e-5p, were not identified in those studies, as they did not meet multiple testing criteria for statistical significance. However, miR-342-3p miRNA was nominally associated with BDR at a p < 0.05 significance level, indicating that miR-342-3p may have a broader impact on childhood asthma. Further, miR-342-3p was not identified in a recent study of miRNAs associated with increased SABA usage [78]. We further investigated the pharmacogenomic effects of these two miRNAs in stratified analysis finding that only let-7e-5p showed evidence of differential expression when restricted to the no-ICS group and the SABA-usage group. These results are inconclusive and potentially provocative and should be investigated more in future work. We recognize that our study has several limitations. Our definition of airflow above or below the threshold in childhood asthma does not indicate clinical obstruction. Our definition was chosen because of concerns for statistical power in the GACRS cohort, where serious obstruction was rare. This expediency should bias us toward the null result of no miRNA associations. While the cohorts we interrogated to investigate childhood asthma and adult COPD have clinical differences, such as age, the history of smoking, and severity of disease, these differences would again bias toward the null hypothesis of no common miRNA associations. Because of differences in cohort demographics and causes of airway limitation in participants in GACRS and the COPDGene study, we would expect fewer miRNAs to replicate from one study to the other. Similarly, there was no cell composition data for the GACRS samples, and including these as covariates may provide additional insight. Additionally, we were unable to establish a strong temporal connection between airflow below the threshold and related miRNAs since the GACRS is cross-sectional.

Conclusion

Two miRNAs were linked to airflow levels in childhood asthma. These two miRNAs, hsa-miR-342-3p and hsa-let-7e-5p, show suggestive generalization.

with FEV1/FVC in current and former smoking adults. The miRNAs’ targets were shown to be highly enriched in several established asthma and COPD-related pathways, such as PI3-AKT, Hippo, and MAPK signaling. These findings suggest that the biology of airflow limitation and obstruction may be partially due to shared microRNA gene regulatory mechanisms regardless of host factors or disease context.

Data availability

Primary miRNA data can be downloaded from here https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE244036.

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Funding

This work received primary funding from NIH grants: R01 HL139634, R01 HL127332, R01 HL162570, R01 161362, P01 HL132825, R01 HL130512, U19 AI118608, R01 HL125734, K08 HL136928. Additional Grant support for COPDGene is from Award Number U01 HL089897 and Award Number U01 HL089856 from the National Heart, Lung, and Blood Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Heart, Lung, and Blood Institute or the National Institutes of Health. COPDGene is also supported by the COPD Foundation through contributions made to an Industry Advisory Board that has included AstraZeneca, Bayer Pharmaceuticals, Boehringer-Ingelheim, Genentech, GlaxoSmithKline, Novartis, Pfizer, and Sunovion.

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A.T., M.J.M., A.T.K., S.T.W., C.P.H., B.D.H., J.C.C., and K.G.T. designed the study. A.T., J.L., B.D.H, and R.S. performed the analysis. S.A. performed small RNA sequencing. A.T. compiled data and wrote the initial manuscript. A.T. and M.J.M. wrote the manuscript. All authors critically reviewed the manuscript drafts and approved the final version.

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Correspondence to Michael J. McGeachie.

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This study was conducted in accordance with the Declaration of Helsinki and was approved by the Institutional Review Board of Brigham and Women’s Hospital, IRB# 2017P001799, 7/29/2020. Additional approval for the Costa Rica cohort was obtained from the Hospital Nacional de Niños (San José, Costa Rica) and Brigham and Women’s Hospital (Boston, MA, USA). COPDGene Institutional Review Board (IRB) approval was obtained at each of the participating study centers before study initiation.

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Tiwari, A., Hobbs, B.D., Sharma, R. et al. Peripheral blood miRNAs are associated with airflow below threshold in children with asthma. Respir Res 26, 38 (2025). https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s12931-025-03116-w

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