Umeå University's logo

BACKGROUND: In COPD, the balance between matrix metalloproteinases (MMPs) and their natural inhibitors [tissue inhibitors of metalloproteinases (TIMPs)] is shifted towards excessive degradation, reflected in bronchoalveolar lavage (BAL) as increased MMP concentrations. Because of their critical role in lung homeostasis, MMP activity is tightly regulated, but to what extent this regulation occurs through epigenetic mechanisms remains unknown.

METHODS: To explore the interplay between MMPs, TIMPs, and DNA methylation (DNAm) we (1) analysed MMP-9, -12, and TIMP-1 concentrations in BAL fluid, and profiled DNAm in BAL cells from 18 COPD and 30 control subjects, (2) estimated protein-COPD relationships using multivariable regression, (3) identified protein quantitative trait methylation loci (pQTMs) with COPD as a potential modifier in a separate interaction model, and (4) integrated significant interactions with a previous COPD GWAS meta-analysis.

RESULTS: COPD was associated with higher levels of BAL MMP-12 (p = 0.016) but not with MMP-9 or TIMP-1. Further examination of MMP-12 identified association with DNAm at 34 loci (pQTMs), with TGFBR2 (p = 2.25 × 10^-10) and THBS4 (p = 1.11 × 10^-9) among the top ten pQTM genes. The interaction model identified 66 sites where the DNAm-MMP-12 association was significantly different in COPD compared to controls. Of these, one was colocalized with SNPs previously associated with COPD.

CONCLUSIONS: Our findings indicate that airway MMP-12 may partially be regulated by epigenetic mechanisms and that this regulation is disrupted in COPD. Furthermore, integration with COPD GWAS data suggests that this dysregulation is influenced by a combination of environmental factors, disease processes, and genetics, with the latter potentially playing a lesser role.

Objectives: There is a lack of knowledge about whether occupational exposures increase the risk of emphysema, especially in never-smokers. Our objective was to determine if occupational exposures are associated with emphysema and impaired diffusing capacity.

Methods: In the Swedish CArdioPulmonary bioImage Study (SCAPIS), persons from the general population aged 50–64 answered a questionnaire and underwent CT of the lung as well as assessment of the diffusing capacity of their lungs for carbon monoxide (DLCO), presented as DLCO<lower limit of normal (LLN). Emphysema was defined as emphysema in any part of the lungs. Occupational exposures were assessed by a job exposure matrix based on longest held job. ORs with 95% CIs were calculated using logistic multivariable models.

Results: In this cross-sectional study (27370 persons including 13981 never-smokers), occupational exposure to inorganic dust was associated with emphysema (OR 1.25, 95% CI 1.07 to 1.47), also among never-smokers, (OR 1.46, 95% CI 1.00 to 2.11). There were associations with DLCO<LLN for occupational exposure to inorganic dust and vapour and gases. With all exposures in the same model, inorganic dust was associated with emphysema (OR 1.30, 95% CI 1.08 to 1.57), and vapour and gases were associated with DLCO<LLN (OR 1.17, 95% CI 1.00 to 1.38). In those with emphysema and impaired DLCO, there was an association with inorganic dust (OR 1.65, 95% CI 1.20 to 2.28), also among never-smokers (OR 3.79, 95% CI 1.35 to 10.63).

Conclusions: Occupational exposures to inorganic dust are associated with emphysema. The association is stronger in those with the combination of emphysema and impaired DLCO indicating serious exposure effects in the alveoli.

BACKGROUND: Low lung function has been consistently associated with increased cardiovascular disease (CVD) risk, with emerging evidence suggesting a potential causal relationship. However, underlying biological mechanisms remain unclear. AIM: To investigate relationships between CVD-associated plasma proteins and lung function.

METHODS: We analysed plasma protein profiles in two Swedish population-based cohorts: the Swedish CArdioPulmonary bioImage Study (SCAPIS) (n = 4,982, mean age 57.6 years) as the discovery cohort and the SCAPIS pilot study (n = 1,054, mean age 57.7 years) for replication. Multiple linear regression models were used to assess associations between 92 CVD-associated proteins and z-scores of FEV1, FVC, and FEV1/FVC, adjusting for known confounders. P-values were corrected using the Benjamini-Hochberg method (5% FDR). Significantly associated proteins were validated in the replication cohort. R

ESULTS: A total of 69 proteins were associated with FEV1, 57 with FVC, and 9 with FEV1/FVC. Several inflammatory proteins and adipokines, including leptin, interleukin-6, fatty acid-binding protein (adipocyte), were consistently linked to lower lung function. Leptin had the strongest negative association (FEV1: β = -0.50, 95 % CI: [-0.69, -0.31], p < 0.001; FVC: β = -0.52, 95 % CI: [-0.68, -0.35], p < 0.001 per-SD increase).

CONCLUSIONS: Multiple CVD-associated proteins, mainly reflecting inflammatory and metabolic processes, were associated with reduced FEV1 and FVC, supporting a link between systemic inflammation, adipokine metabolism and impaired lung function. Leptin had the strongest association, suggesting that its effects on lung function may extend beyond adiposity. Further research is needed to clarify the mechanisms driving these associations and to assess whether these proteins could serve as early biomarkers or intervention targets.

Rationale: Postbronchodilator spirometry is used for the diagnosis of chronic obstructive pulmonary disease. However, prebronchodilator reference values are used for spirometry interpretation.

Objectives: To compare the resulting prevalence rates of abnormal spirometry and study the consequences of using preor postbronchodilator reference values generated within SCAPIS (Swedish CArdioPulmonary bioImage Study) when interpreting postbronchodilator spirometry in a general population.

Methods: SCAPIS reference values for postbronchodilator and prebronchodilator spirometry were based on 10,156 and 1,498 never-smoking, healthy participants, respectively. We studied the associations of abnormal spirometry, defined by using pre- or postbronchodilator reference values, with respiratory burden in the SCAPIS general population (28,851 individuals).

Measurements and Main Results: Bronchodilation resulted in higher predicted medians and lower limits of normal (LLNs) for FEV₁/FVC ratios. The prevalence of postbronchodilator FEV₁/FVC ratio lower than the prebronchodilator LLN was 4.8%, and that of postbronchodilator FEV₁/FVC lower than the postbronchodilator LLN was 9.9%, for the general population. An additional 5.1% were identified as having an abnormal postbronchodilator FEV₁/FVC ratio, and this group hadmore respiratory symptoms, emphysema (13.5% vs. 4.1%; P < 0.001), and self-reported physician-diagnosed chronic obstructive pulmonary disease (2.8% vs. 0.5%, P < 0.001) than subjects with a postbronchodilator FEV₁/FVC ratio greater than the LLN for both pre- and postbronchodilation.

Conclusions: Pre- and postbronchodilator spirometry reference values differ with regard to FEV₁/FVC ratio. Use of postbronchodilator reference values doubled the population prevalence of airflow obstruction; this was related to a higher respiratory burden. Using postbronchodilator reference values when interpreting postbronchodilator spirometry might enable the identification of individuals with mild disease and be clinically relevant.

Background: Chronic obstructive pulmonary disease (COPD) is a heterogenous and chronic inflammatory syndrome with the lungs as its main target organ. Clinically, COPD is characterized by airflow limitation, chronic respiratory symptoms, and many extrapulmonary comorbidities. Tobacco smoke is the main environmental risk factor, but pollutants and smoke from biomass fuel are also major contributors. 

Why some, but not all, smokers develop the disease is a key but largely unresolved research question. Genetic factors seem to explain 40—60% of COPD susceptibility, but what additional role epigenetic factors such as DNA methylation might play has not been thoroughly investigated.

Immune cells are of vital importance in the COPD pathogenesis. Among airway lymphocytes, cytotoxic CD8+ T cells are the ones most often found to be involved in the disease, but other lymphocyte populations are not as well studied.

Among patients with manifest COPD, the rate of decline in lung function differs widely. Smoking cessation decreases the rate, but beyond that, it is not well understood why some patients experience a more rapid and some a much slower disease progression. Rapid decline is associated with a poor prognosis and has been recognized as a separate phenotype of COPD. 

Aim: The overall aim of this thesis was to examine the immunologic and epigenetic features of COPD with a focus on the rapid decline phenotype, using flow cytometry and measurement of DNA methylation in cells from bronchoalveolar lavage (BAL) fluid together with clinical characteristics such as rate of decline in lung function, use of inhaled corticosteroids and smoking status. The studies included in this thesis were all part of the Respiratory and Cardiovascular Effects in COPD (“KOLIN”) study.

Methods: The study population was the same for all studies in this thesis. Subjects were recruited from the Obstructive Lung Disease in Northern Sweden (OLIN) COPD study according to predetermined criteria. OLIN COPD also provided the longitudinal data needed for classification of rapid/non-rapid decliners (decline in forced expiratory volume in the first second [FEV1] ≥60 or ≤30 mL/year respectively). BAL fluid was analyzed for cell type composition using flow cytometry. DNA methylation in BAL cells was measured using the Illumina MethylationEPIC BeadChip. 

In the statistical analysis, flow cytometry data was analyzed using group-wise comparisons and multivariable regression models. DNA methylation data was analyzed for association with COPD and accelerated epigenetic aging (defined as the difference between chronological and epigenetic age) using multilinear regression models. Differentially methylated positions and regions associated with COPD were analyzed for gene association and pathway enrichment and integrated with data from previous gene expression and genome-wide association studies.

Results: Paper I: in this first paper based on flow cytometry, we focused on cytotoxic lymphocytes and found that Natural Killer (NK) cells in BAL were increased in COPD while invariant Natural Killer T (iNKT) and Natural Killer T-like (NKT-like) cells increased with smoking but not with COPD. NK cells were also higher when comparing ex-smokers with and without COPD. No significant differences were found between COPD subjects with a rapid vs. a non-rapid decline in lung function.

Paper II: regulatory immune cells were investigated in this second flow cytometry-based paper. We found that FoxP3+ regulatory T cells (Tregs) were significantly lower in COPD subjects with a rapid decline in lung function compared to those with a non-rapid decline. This result was significant before as well as after adjustments for inhaled corticosteroids (ICS) usage and smoking. None of the investigated regulatory immune cell populations (T helper cells, activated T helper cells, and FoxP3+ Tregs) displayed significant differences associated with either COPD or smoking.

Paper III: measurements of BAL cell DNA methylation revealed epigenome-wide differential methylation in COPD; 1,155 differentially methylated positions (DMPs) and 7,097 differentially methylated regions. Functional analysis using Kyoto Encyclopedia of Genes and Genomes and Gene Ontology databases identified biologically plausible pathways and gene relationships, including enrichment for transcription factor activity. No correlation was found between COPD and accelerated aging. For 79 unique DMPs, DNA methylation correlated significantly with gene expression in BAL. Thirty-nine percent of DMPs were co-located with single nucleotide polymorphisms (SNPs) associated with COPD.

Conclusions: Among cytotoxic cell types, the NK cell population stood out as it 1) was increased in COPD; and 2) did not normalize in COPD subjects that had quit smoking. This indicates that NK cells might contribute to the continued disease progression in COPD even after smoking cessation.

COPD subjects with a rapid decline in lung function had significantly lower levels of Fox P3+ Tregs in BAL. Further longitudinal research is needed to establish the causal direction of this relationship, but based on the evidence available to date, I deem it more plausible that a low expression of Fox P3+ Tregs would lead to a rapid decline in lung function, than the other way around.

Our epigenome-wide association study (EWAS) identified widespread differential methylation in COPD, and many DMPs displayed a strong correlation with gene expression. Somewhat less than half of DMPs were located in close proximity to COPD-associated SNPs, suggesting that these might be sites where genetic factors regulate methylation status. In sum, our findings suggest strong associations between epigenetic factors and COPD. As this was the first ever published EWAS of COPD based on BAL cells, results must be validated in future studies.

Rationale: Spirometry is essential for diagnosis and assessment of prognosis in COPD.

Objectives: To identify FEV1 trajectories and their determinants, based on annual spirometry measurements among individuals with and without airway obstruction. Furthermore, to assess mortality in relation to trajectories.

Methods: In 2002-04, individuals with airway obstruction (AO) (FEV1/VC<0.70, n=993) and age- and sex-matched non-obstructive (NO) referents were recruited from population-based cohorts. Annual spirometries until 2014 were utilized in joint-survival Latent Class Mixed Models to identify lung function trajectories. Mortality data were collected during 15 years of follow-up.

Results: Three trajectories were identified among the AO-cases and two among the NO referents. Trajectory membership was driven by baseline FEV1%predicted (%pred) in both groups and additionaly, pack-years in AO and current smoking in NO. Longitudinal FEV1%pred level depended on baseline FEV1%pred, pack-years and obesity. The trajectories were distributed: 79.6% T1AO FEV1-high with normal decline, 12.8% T2AO FEV1-high with rapid decline, and 7.7% T3AO FEV1-low with normal decline (mean 27, 72 and 26 mL/year) among AO-individuals, and 96.7% T1NO FEV1-high with normal decline and 3.3% T2NO FEV1-high with rapid decline (mean 34 and 173 mL/year) among referents. Hazard for death was increased for T2AO (HR1.56) and T3AO (HR3.45) vs. T1AO, and for T2NO (HR2.99) vs. T1NO.

Conclusions: Three different FEV1 trajectories were identified among those with airway obstruction and two among the referents, with different outcomes in terms of FEV1-decline and mortality. The FEV1 trajectories among airway obstructive and the relationship between low FVC and trajectory outcome are of particular clinical interest.

DNA methylation patterns in chronic pulmonary obstructive disease (COPD) might offer new insights into disease pathogenesis. To assess methylation profiles in the main COPD target organ, we performed an epigenome-wide association study on BAL cells. Bronchoscopies were performed in 18 subjects with COPD and 15 control subjects (ex- and current smokers). DNA methylation was measured using the Illumina MethylationEPIC BeadChip Kit, covering more than 850,000 CpGs. Differentially methylated positions (DMPs) were examined for 1) enrichment in pathways and functional gene relationships using the Kyoto Encyclopedia of Genes and Genomes and Gene Ontology, 2) accelerated aging using Horvath's epigenetic clock, 3) correlation with gene expression, and 4) colocalization with genetic variation. We found 1,155 Bonferroni-significant (P < 6.74 × 10-8) DMPs associated with COPD, many with large effect sizes. Functional analysis identified biologically plausible pathways and gene relationships, including enrichment for transcription factor activity. Strong correlation was found between DNA methylation and chronological age but not between COPD and accelerated aging. For 79 unique DMPs, DNA methylation correlated significantly with gene expression in BAL cells. Thirty-nine percent of DMPs were colocalized with COPD-associated SNPs. To the best of our knowledge, this is the first epigenome-wide association study of COPD on BAL cells, and our analyses revealed many differential methylation sites. Integration with mRNA data showed a strong functional readout for relevant genes, identifying sites where DNA methylation might directly affect expression. Almost half of DMPs were colocated with SNPs identified in previous genome-wide association studies of COPD, suggesting joint genetic and epigenetic pathways related to disease.

Chronic airflow limitation (CAL) can be defined as fixed ratio of forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) < 0.70 after bronchodilation. It is unclear which is the most optimal ratio in relation to respiratory morbidity. The aim was to investigate to what extent different ratios of FEV1/FVC were associated with any respiratory symptom. In a cross‐sectional general population study, 15,128 adults (50–64 years of age), 7,120 never‐smokers and 8,008 ever‐smokers completed a respiratory questionnaire and performed FEV1 and FVC after bronchodilation. We calculated different ratios of FEV1/FVC from 0.40 to 1.0 using 0.70 as reference category. We analysed odds ratios (OR) between different ratios and any respiratory symptom using adjusted multivariable logistic regression. Among all subjects, regardless of smoking habits, the lowest odds for any respiratory symptom was at FEV1/FVC = 0.82, OR 0.48 (95% CI 0.41–0.56). Among never‐smokers, the lowest odds for any respiratory symptom was at FEV1/FVC = 0.81, OR 0.53 (95% CI 0.41–0.70). Among ever‐smokers, the odds for any respiratory symptom was lowest at FEV1/FVC = 0.81, OR 0.43 (95% CI 0.16–1.19), although the rate of inclining in odds was small in the upper part, that is FEV1/FVC = 0.85 showed similar odds, OR 0.45 (95% CI 0.38–0.55). We concluded that the odds for any respiratory symptoms continuously decreased with higher FEV1/FVC ratios and reached a minimum around 0.80–0.85, with similar results among never‐smokers. These results indicate that the optimal threshold associated with respiratory symptoms may be higher than 0.70 and this should be further investigated in prospective longitudinal studies.

Background: Differences in the expression of regulatory T cells (Tregs) have been suggested to explain why some smokers develop COPD and some do not. Upregulation of Tregs in response to smoking would restrain airway inflammation and thus the development of COPD; while the absense of such upregulation would over time lead to chronic inflammation and COPD. We hypothesized that—among COPD patients—the same mechanism would affect rate of decline in lung function; specifically, that a decreased expression of Tregs would be associated with a more rapid decline in FEV1.

Methods: Bronchoscopy with BAL was performed in 52 subjects recruited from the longitudinal OLIN COPD study; 12 with COPD and a rapid decline in lung function (loss of FEV1 ≥ 60 ml/year), 10 with COPD and a non-rapid decline in lung function (loss of FEV1 ≤ 30 ml/year), 15 current and ex-smokers and 15 non-smokers with normal lung function. BAL lymphocyte subsets were determined using flow cytometry.

Results: The proportions of Tregs with regulatory function (FoxP3+/CD4+CD25bright) were significantly lower in COPD subjects with a rapid decline in lung function compared to those with a non-rapid decline (p = 0.019). This result was confirmed in a mixed model regression analysis in which adjustments for inhaled corticosteroid usage, smoking, sex and age were evaluated. No significant difference was found between COPD subjects and smokers or non-smokers with normal lung function.

Conclusions: COPD subjects with a rapid decline in lung function had lower proportions of T cells with regulatory function in BAL fluid, suggesting that an inability to suppress the inflammatory response following smoking might lead to a more rapid decline in FEV1.