Obesity impairs apoptotic cell clearance in asthma

Abstract

Background

Asthma in obese adults is typically more severe and less responsive to glucocorticoids than asthma in nonobese adults.

Objective

We sought to determine whether the clearance of apoptotic inflammatory cells (efferocytosis) by airway macrophages was associated with altered inflammation and reduced glucocorticoid sensitivity in obese asthmatic patients.

Methods

We investigated the relationship of efferocytosis by airway (induced sputum) macrophages and blood monocytes to markers of monocyte programming, in vitro glucocorticoid response, and systemic oxidative stress in a cohort of adults with persistent asthma.

Results

Efferocytosis by airway macrophages was assessed in obese (n = 14) and nonobese (n = 19) asthmatic patients. Efferocytosis by macrophages was 40% lower in obese than nonobese subjects, with a mean efferocytic index of 1.77 (SD, 1.07) versus 3.00 (SD, 1.25; P < .01). A similar reduction of efferocytic function was observed in blood monocytes of obese participants. In these monocytes there was also a relative decrease in expression of markers of alternative (M2) programming associated with efferocytosis, including peroxisome proliferator-activated receptor δ and CX3 chemokine receptor 1. Macrophage efferocytic index was significantly correlated with dexamethasone-induced mitogen-activated protein kinase phosphatase 1 expression (ρ = 0.46, P < .02) and baseline glucocorticoid receptor α expression (ρ = 0.44, P < .02) in PBMCs. Plasma 4-hydroxynonenal levels were increased in obese asthmatic patients at 0.33 ng/mL (SD, 0.15 ng/mL) versus 0.16 ng/mL (SD, 0.08 ng/mL) in nonobese patients (P = .006) and was inversely correlated with macrophage efferocytic index (ρ = −0.67, P = .02).

Conclusions

Asthma in obese adults is associated with impaired macrophage/monocyte efferocytosis. Impairment of this anti-inflammatory process is associated with altered monocyte/macrophage programming, reduced glucocorticoid responsiveness, and systemic oxidative stress.

Obesity induces a systemic inflammatory state marked by increased oxidative stress^1,2 and enhanced expression of inflammatory mediators (eg, TNF-α) that have been implicated in the development of metabolic syndrome and insulin resistance.^3,4 Of note, oxidative stress and several of these same proinflammatory cytokines have been implicated in the initiation, maintenance, and progression of asthma, as well as important clinical phenotypes, such as the development of glucocorticoid insensitivity.^5–15 Furthermore, much of the inflammation in obesity is attributed to pathologic recruitment, classical activation (M1 skewing), or both, of macrophages in adipose tissue, as well as other tissues, including liver and muscle.^3,16,17 Similarly, in patients with severe or glucocorticoid-insensitive asthma, M1 skewing of blood monocytes and alveolar macrophages has been documented.^18–20 These links suggest a possible intersection of obesity and asthma at the level of airway macrophage activation and function. So-called “alternatively activated” or M2 macrophages help to control and resolve inflammation, in part through the recognition and removal of dying cells in a unique phagocytic process called efferocytosis.^21,22 M2 programming of macrophages is required for their expression of efferocytic receptors and bridge molecules.^23–26 Notably, glucocorticoids further enhance macrophage efferocytic capability.^27–29 Not only is efferocytosis important for clearance of dying cells before phlogistic disintegration,³⁰ it leads macrophages to produce anti-inflammatory mediators, such as IL-10, TGF-β, and prostaglandin E₂, which potently suppress inflammation.^31–33 Impaired efferocytosis is increasingly recognized in patients with chronic airway inflammatory disorders, including severe asthma, chronic obstructive pulmonary disease, and cystic fibrosis, and is hypothesized to contribute to persistent inflammation.^29,34,35 For instance, airway macrophages from patients with severe asthma have reduced ability to efferocytose apoptotic cells, a function that can be increased approximately 3-fold by glucocorticoids.²⁹

In light of the parallels in oxidative stress, proinflammatory cytokines, and macrophage programming between obesity and glucocorticoid-insensitive or more severe asthma phenotypes, we hypothesized that airway macrophage dysfunction, specifically impaired efferocytosis, might play an important role with regard to the effect of obesity on airway inflammation in patients with asthma. This hypothesis was tested in a cross-sectional study in obese and nonobese adults with persistent asthma.

METHODS

Study population

Adults with mild-to-moderate persistent asthma³⁶ (n = 33) were enrolled. All participants were recruited from a single site (National Jewish Health) during participation in the run-in period of 2 National Heart, Lung, and Blood Institute–sponsored asthma clinical trials.³⁷ The inclusion and exclusion criteria and design of the common run-in period have been reported previously and are included in the Methods section in this article’s Online Repository at www.jacionline.org.³⁷ All participants were being treated with inhaled corticosteroid (hydrofluoroalkane beclomethasone dipropionate, 80 µg twice daily). Lung function, airway hyperresponsiveness, and fraction of exhaled nitric oxide were measured by using standard techniques.^38–40 Induced sputum was obtained from all participants, and cytospin preparations were prepared by using standard techniques.⁴¹ A separate healthy control population (n = 25) was comprised of nonsmoking adult participants with normal lung function. In these subjects cytologic preparations from bronchoalveolar lavage specimens⁴² were also prepared as above.⁴¹ Obesity was defined by using standard criteria⁴³ as a body mass index (BMI) of 30 kg/m² or greater. All participants provided written informed consent, and all protocols were approved by the National Jewish Health Institutional Review Board.

Efferocytosis and apoptotic cells in induced sputum

By using validated methodology,^34,35 cytospin preparations of lower airway cells were viewed in triplicate for assessment of in vivo efferocytosis and apoptotic cells by using light microscopy according to a methodology described previously (see Fig E1, A, in this article’s Online Repository at www.jacionline.org). Random fields were read in a blinded fashion by a single reader for apoptotic cells and efferocytosis until a minimum of 500 macrophages were counted. Previous measures of intraobserver and interobserver variance within the laboratory demonstrate correlations of 0.92 and 0.91, respectively. The efferocytic index, as a measure of overall clearance, was calculated by multiplying the percentage of macrophages that had phagocytosed apoptotic bodies by the average number of apoptotic bodies per macrophage.⁴⁴ Apoptotic inflammatory cells were determined by the appearance of pyknotic nuclear morphology.⁴⁴

Efferocytosis by blood monocytes in vitro

Blood monocytes were isolated from a representative subset of the asthmatic patients (n = 9 obese and 15 nonobese, see Table E1 in this article’s Online Repository at www.jacionline.org). Blood was phlebotomized into CPT tubes (Becton Dickinson, Franklin Lakes, NJ), followed by negative selection with magnetic beads (Miltenyi Biotec, Auburn, Calif). Monocytes (7 × 10⁴ per well in a 96-well plate) were plated in X-VIVO 15 (10% pooled human serum; Lonza, Basel, Switzerland) for 2 hours before testing for efferocytosis. Five-micrometer carboxylated beads (Bangs Laboratories, Fishers, Ind), serving as apoptotic cell mimics, were added at a ratio of 2 beads per monocyte for 1 hour.³¹ After vigorous washing to remove free beads, efferocytosis of the beads was determined by means of visual inspection (see Fig E1, B). A minimum of 200 monocytes were counted, and the efferocytic index was calculated as above. Correlations of 0.95 and 0.91 for intraobserver and interobserver variance, respectively, have been documented for monocyte uptake within the laboratory.

Reverse transcribed quantitative PCR

Total RNA was extracted from freshly isolated blood monocytes and reverse transcribed to cDNA by using standard techniques. PCR was performed (7900H; Applied Biosystems, Foster City, Calif) with commercially available primers for a panel of candidate M1 and M2 programming markers and efferocytic receptors, including arginase 1, a disintegrin and metalloproteinase domain–containing protein (ADAM) 8, peroxisome proliferator-activated receptor (PPAR) δ, PPARγ, macrophage mannose receptor, CX3C chemokine receptor 1, adiponectin receptor, TGF-β receptor, and GP132 receptor.^44–53 Glyceraldehyde-3-phosphate dehydrogenase or 18s RNA served as endogenous controls.

Assessment of oxidative stress

Assays for 4-hydroxynonenal (4HNE), a product of lipid peroxidation and a marker of systemic oxidative stress, were performed by using previously reported methods of gas chromatography/mass spectrometry.⁵⁴

Assessment of in vitro glucocorticoid responsiveness

PBMCs were isolated and stimulated with 10⁻⁷ mol/L dexamethasone for 4 hours. Mitogen-activated protein kinase phosphatase 1 (MKP-1) expression was determined by using RT-PCR in cells treated with medium alone and medium plus dexamethasone, as described previously.⁵⁵ Expression of glucocorticoid receptor (GCR) α was determined as described previously.⁵⁶

Statistical methods

All data were described as means ± SDs. Between-group differences (BMI category) were evaluated by using the Mann-Whitney U test. Continuous relationships between parameters were analyzed by using unadjusted linear regression. Nonparametric Spearman ρ correlation coefficient was used to determine correlations between parameters.

RESULTS

Baseline characteristics of study participants with asthma (n = 33) are presented in Table I. Obese (n = 14) and nonobese (n = 19) asthmatic patients were well matched for demographics and markers of asthma severity and inflammation. Significant differences between the obese and nonobese asthmatic patients were demonstrated for markers associated with obesity, including leptin and high-sensitivity C-reactive protein. Cytospin preparations of induced sputum (Table II) indicated that the percentage of airway macrophages was increased in obese asthmatic patients. Airway macrophage percentages were positively correlated with BMI (Spearman ρ = 0.47, P = .01). The percentage of inflammatory cells demonstrating apoptotic features did not differ between nonobese and obese asthmatic patients and was not correlated with BMI (ρ = −0.2, P = .2). The percentages of sputum eosinophils and neutrophils did not differ between the 2 groups.

TABLE I.

Characteristics of the study population

	Nonobese subjects	Obese subjects	P value
No.	19	14	—
Age (y)	39 (10)	38 (14)	.7
Female sex (no.)	9 (48)	5 (36)	.5
African American (no.)	4 (25)	4 (33)	.8
BMI (kg/m2)	23.6 (2.8)	37.2 (5.1)	<.01
FEV1 (L [before albuterol])	2.7 (0.8)	2.7 (0.9)	.8
FEV1 (L [after albuterol])	3.0 (0.8)	3.2 (0.8)	.5
FVC (L [before albuterol])	3.8 (1.1)	4.3 (0.9)	.9
FVC (L [after albuterol])	4.0 (1.1)	4.4 (0.9)	.9
FEV1/FVC ratio	0.7 (0.1)	0.7 (0.1)	.5
PC20 FEV1 (mg/mL methacholine)	2.2 (2.4)	1.6 (1.3)	.8
Feno (ppb)	23 (12)	23 (21)	.3
Adiponectin (µg/mL)	8.9 (6.3)	8.4 (4.9)	.7
Leptin (ng/mL)	8.4 (12.5)	29.2 (11.4)	<.01
IL-6 (pg/mL)	1.4 (1.8)	1.5 (0.8)	.06
TNF-α (pg/mL)	1.6 (1.0)	1.5 (0.6)	.8
hs-CRP (mg/mL)	2.6 (4.5)	4.8 (3.3)	<.01

Data are presented as counts (percentages of population) or means (SDs).

Feno, Fraction of exhaled nitric oxide; hs-CRP, high-sensitivity C-reactive protein.

TABLE II.

Induced sputum cell differential counts in nonobese and obese participants

	Nonobese subjects	Obese subjects	P value
Eosinophils (%)	3.4 (4.6)	1.3 (2.5)	.07
Neutrophil (%)	55.6 (20.7)	39.5 (21.9)	.06
Macrophages (%)	28.1 (15.0)	42.1 (19.7)	.02
Lymphocytes (%)	0.8 (0.9)	0.7 (0.7)	.90
Apoptotic cells (%)	31.6 (18.9)	22.9 (16.6)	.26

Data are presented as means (SDs).

Although the percentage of airway macrophages containing 1 or more engulfed apoptotic bodies was similar in nonobese and obese asthmatic patients (2.3% [SD, 1.23%] vs 2.0% [SD, 1.6%]), the number of apoptotic bodies per macrophage was lower in the obese asthmatic patients at 1.07 (SD, 0.14) versus 1.29 (SD, 0.34) in nonobese asthmatic patients (P = .05, Table III). Represented as the efferocytic index, uptake by airway macrophages of obese asthmatic patients was 40% lower than in nonobese asthmatic patients at 1.77 (SD, 1.07) versus 3.00 (SD, 1.25; P < .01, Table III). In healthy nonasthmatic control participants an opposite trend was observed, with an increased efferocytic index in obese control subjects (n = 6; BMI, 34 kg/m² [SD, 2.6 kg/m²]) versus nonobese control subjects (n = 19; BMI, 24.5 kg/m² [SD, 3.0 kg/m²]) at 3.73 (0.95) and 2.42 (0.87), respectively (P = .005).

TABLE III.

Efferocytosis by airway macrophages and peripheral blood monocytes in nonobese and obese asthmatic participants

	Nonobese subjects	Obese subjects	P value
Airway macrophages
No. of apoptotic bodies per macrophage	1.29 (0.34)	1.07 (0.14)	.05
Efferocytic index	3.00 (1.25)	1.77 (1.07)	<.01
Apoptotic cells (%)/airway macrophage (%) ratio	1.04 (1.07)	0.44 (0.6)	.02
Peripheral blood monocytes
No. of engulfed beads per monocyte	3.2 (1.2)	2.1 (0.6)	<.01
Efferocytic index	165.6 (89.2)	98.6 (83.0)	.03

Data are presented as means (SDs).

When expressed as a ratio (ie, the percentage of inflammatory cells that were apoptotic divided by the percentage of inflammatory cells that were macrophages), values for nonobese asthmatic patients were higher than for obese asthmatic patients (1.04 [SD, 1.07] vs 0.44 [SD, 0.6], P = .02). However, the percentage of inflammatory cells characterized as apoptotic was not correlated with the efferocytic index (ρ = −0.07, P = .7), suggesting that the proportion of inflammatory cells undergoing apoptosis was not tightly coupled to overall clearance. When BMI was treated as a continuous variable, the efferocytic index inversely correlated with BMI (ρ = −0.51, P = .003) in asthmatic patients, suggesting a dose-response aspect to the categorical differences reported above. As with the categorical analyses above, nonasthmatic participants showed an opposite relationship between BMI and airway macrophage efferocytosis, with a positive correlation between BMI and efferocytic index (ρ = 0.46, P = .02).

We then sought to directly determine whether blood monocytes (inflammatory macrophage precursors)⁵⁷ of obese asthmatic patients demonstrated impaired efferocytic capability in vitro. In a subset of asthmatic participants, 9 obese and 15 nonobese and similar in characteristics to the main cohort (group characteristics reported in Table E1), blood monocytes were isolated and tested for their ability to take up carboxylated beads (apoptotic cell mimics, see the Methods section). The percentage of monocytes taking up 1 or more carboxylated beads was similar for both groups at 49.9% (SD, 15.9%) for nonobese asthmatic patients versus 44.2% (SD, 27.8%) for obese asthmatic patients (P = .4), but substantially fewer beads were taken up by monocytes of obese asthmatic patients compared with nonobese asthmatic patients at 2.1 (SD, 0.6) versus 3.2 (SD, 1.2; P < .01, Table III). Accordingly, when expressed as the efferocytic index, efferocytosis of bead targets was significantly reduced in obese asthmatic patients relative to that seen in nonobese asthmatic patients at 98.6 (SD, 83.0) versus 165.6 (SD, 89.2; P = .03, Table III), indicating a similar 40% reduction in efferocytosis by blood monocytes. When BMI was treated as a continuous variable, a trend toward an inverse relationship of efferocytosis by blood monocytes was noted (ρ = −0.37, P = .07), but no significant correlation between efferocytosis by airway macrophages and blood monocytes was demonstrated (ρ = 0.26, P = .35).

Programming differences in blood monocytes from obese and nonobese asthmatic participants were then evaluated. Candidate markers of M2 programming were evaluated by using real-time quantitative PCR (Table IV). Of these, expressions of PPARδ and ADAM8 were inversely correlated with BMI (ρ = −0.41 and P < .05 for PPARδ; ρ = −0.61 and P < .01 for ADAM8), suggesting diminished M2 programming with increasing obesity in asthmatic patients. Expression of CX3 chemokine receptor 1, which is implicated in efferocytosis,⁵⁰ was also diminished in obese asthmatic patients (ρ = −0.56, P < .05). Arginase 1 and GP132 receptor expression correlated significantly with monocyte efferocytic index. Neither PPARγ nor macrophage mannose receptor, both of which are reported to be expressed at very low levels in human monocytes before differentiation into macrophages,⁴⁶ were correlated with either BMI or efferocytic index. None of the markers were significantly correlated with efferocytosis by airway macrophages. When the specific M1 programming candidate markers IL-8, monocyte chemotactic protein 1, IL-6, and TNF-α were assessed, none were found to be associated with obesity or related to the efferocytic capability of monocytes or airway macrophages. Serum leptin levels were inversely correlated with the efferocytic index of airway macrophages (ρ = −0.32, P < .05) and blood monocytes (ρ = −0.43, P < .05). However, when adjusted for BMI, these relationships with serum leptin were no longer significant.

TABLE IV.

Correlation of M2 programming/efferocytosis markers in blood monocytes with BMI and EI

M2/efferocytic markers	ρ vs BMI	P value	ρ vs monocyte EI	P value
PPARδ	−0.41	.04	0.38	.06
ADAM8	−0.61	<.01	0.37	.07
CX3CR1	−0.56	.02	0.43	.07
PPARγ	0.01	.98	0.29	.16
MMR	−0.29	.18	0.34	.10
Arginase 1	−0.20	.33	0.42	.04
Adiponectin receptor	−0.13	.55	0.38	.06
TGF-β receptor	−0.09	.67	0.39	.06
GP132 receptor	−0.22	.30	0.51	.01

CX3CR1, CX3 chemokine receptor 1; EI, efferocytic index; MMR, macrophage mannose receptor.

To explore the relationship between obesity, efferocytic function, and markers of oxidative stress, we assayed concentrations of plasma 4HNE, a product of lipid peroxidation and a biomarker of systemic oxidative stress. 4HNE levels were significantly increased in obese asthmatic patients (n = 10) at 0.33 ng/mL (SD, 0.15 ng/mL) versus 0.17 ng/mL (SD, 0.08 ng/mL) in nonobese asthmatic patients (n = 10, P = .006, Fig 1). 4HNE levels were significantly and inversely correlated with the efferocytic index in airway macrophages (ρ = −0.67, P = .02, n = 11, Table V) but not in blood monocytes, which demonstrated a similar trend that did not achieve statistical significance (ρ = −0.53, P = .18).

FIG 1.

4HNE concentrations in the plasma of nonobese (n = 10) and obese (n = 10) asthmatic patients.

TABLE V.

Correlation (unadjusted) of sputum efferocytic index with markers of oxidative stress and glucocorticoid response

	ρ	P value
4HNE vs EI in airway macrophages	−0.67	.02
MKP-1 expression vs EI in airway macrophages	0.56	.003
GCRα expression vs EI in airway macrophages	0.49	.009

EI, Efferocytic index.

Because glucocorticoids are reported to enhance efferocytosis,^27–29 the relationship of efferocytosis by airway macrophages to in vitro markers of glucocorticoid responsiveness was then investigated in asthmatic participants. Efferocytosis in airway macrophages was significantly correlated with both the induction of MKP-1 expression by dexamethasone (ρ = 0.56, P = .003) and GCRα expression (ρ = 0.49, P = .009) in PBMCs (Table V). When adjusted for BMI in a standard least-squares model, these relationships remained significant (r = 0.61 and P = .002 for MKP-1; r = 0.49 and P = .01 for GCRα). There was no relationship between airway macrophage efferocytosis and GCRβ, which was expressed at very low levels. No relationship between these markers of glucocorticoid response and efferocytosis in blood monocytes was demonstrated (ρ = 0.03 and P = .9 for MKP-1; ρ = −0.1 and P = .7 for GCRα).

DISCUSSION

Asthma and obesity are major public health issues, and there is increasing evidence of interaction of these 2 disorders in both adults and children.^58–63 Studies suggest that asthma in obese persons can be characterized by both increased severity and reduced glucocorticoid responsiveness demonstrated both in vivo and in vitro, although not uniformly so.^{55,60,61,63–65} Traditional markers of T_H2-type inflammation, such as fraction of exhaled nitric oxide and airway eosinophil numbers, are not increased in obese compared with nonobese patients with asthma,⁶⁰ and the basis of this harder-to-control phenotype is not well understood.

In an attempt to begin to identify the underlying mechanisms, we report the first data comparing efferocytosis by airway macrophages and peripheral blood monocytes in obese and nonobese participants with asthma. This difference was not observed in subjects without asthma, suggesting that interactions between these 2 diseases result in the observed impairment in efferocytosis. The findings in obese asthmatic patients occur in the context of decreased expression of certain markers of alternative (M2) macrophage programming and are significantly related to in vitro assessment of glucocorticoid response, with the degree of impaired efferocytosis increasing as glucocorticoid responsiveness decreased. Furthermore, we demonstrate a significant relationship between efferocytic capacity and degree of systemic oxidative stress, suggesting a possible role of oxidative stress in modulating these pathways. Given these findings, we hypothesize that impaired efferocytosis by airway macrophages contributes to increased severity of asthma in the setting of obesity.

Given the increased numbers of activated macrophages found in adipose tissue and muscle in patients with obesity associated with insulin resistance,^3,47,66,67 it is reasonable to hypothesize that lung macrophages might be a key inflammatory cell in patients with asthma complicated by obesity. On the basis of inflammatory cell differentials for induced sputum, the percentage of airway macrophages was increased in obese asthmatic patients. The lack of absolute macrophage quantification is a shortcoming of our current approach, although to our knowledge, no studies to date have shown that absolute numbers of airway macrophages are greater in obese patients with asthma. This question is relevant for future investigation.

Notably, there were no differences in the percentages of apoptotic cells between obese and nonobese asthmatic patients. However, there was a decrease in the percentage of apoptotic cells to the percentage of macrophages expressed as a ratio for obese asthmatic patients. Direct assessment of isolated sputum macrophages “fed” exogenous apoptotic cells will be required to determine whether impaired efferocytosis by airway macrophages of obese subjects is due to limited apoptotic target availability. Direct assessment of sputum macrophages was not performed in this study and is technically challenging. Importantly, direct assessment of blood monocyte efferocytic capacity mirrored findings in the airway macrophages, suggesting that phagocytic functional alterations are systemic in obese asthmatic patients.

Our results suggest that monocyte/macrophage programming is altered in obese asthmatic patients. We demonstrated evidence of diminished M2 programming, which is typically required for efficient efferocytosis. Monocyte mRNA expression of the M2 markers (eg, the nuclear receptor PPARδ and ADAM8) correlated inversely with BMI, and several of the target markers were positively associated with monocyte efferocytic capability (Table IV). As such, assessments of the programming and functions of monocytes, as precursors of tissue macrophages and as cells exposed to the same systemic inflammatory milieu, might serve as biomarkers, reflecting the status of macrophages in inflamed airways. Nonetheless, we acknowledge that investigation of blood monocytes as a surrogate for airway macrophages is a potential limitation of this report in that resident macrophages in tissues can demonstrate both phenotypic and functional differences when compared with circulating blood monocytes.⁶⁸

There is controversy regarding M1 markers in human subjects versus murine models in obesity,^16,17,69 and we were unable to demonstrate an increase in expression of candidate M1-related markers in monocytes of our obese study participants with asthma. Nonetheless, some evidence of M1 programming of airway macrophages¹⁸ and, to a limited extent, monocytes²⁰ has been described in patients with severe steroid-resistant asthma and, in turn, associated with reduced MKP-1 induction.⁷⁰ Thus it is possible that the reduced MKP-1 induction and low GCRα expression observed herein can be considered a functional readout reflective of disproportionate M1 programming, explaining significant correlation between these markers of glucocorticoids response and impaired efferocytosis by airway macrophages. In our earlier work we demonstrated that impaired glucocorticoid responsiveness in vitro required a disease-by-disease interaction; it was demonstrated only in obese asthmatic patients and not subjects with obesity alone. Our data from this disparate study population suggest that this same interaction is also required for the impairment of efferocytosis.

Finally, although not conclusive, our data also suggest that oxidative stress might be an important mechanistic link between obesity, macrophage programming and function, and glucocorticoid insensitivity in asthmatic patients. Obesity is known to be associated with increases in systemic oxidative stress,² and increased oxidant production by macrophages inhibits the ability of macrophages to recognize, phagocytose, and clear apoptotic cells, particularly after stimulation with TNF-α.^71,72 Thus the systemic proinflammatory environment in obese patients might affect asthma through proinflammatory cytokines and associated increases in oxidative stress. These, in turn, impair macrophage/monocyte function in ways that are critical to the maintenance or resolution of airway inflammation, while also altering glucocorticoid response pathways.

Taken together, these data point to the need for future investigations designed to improve our understanding of airway macrophage programming and function in asthma complicated by obesity, with the goal of identifying novel therapeutic targets. Given that the nuclear receptors PPARδ and PPARγ are both robustly implicated in M2 programming of macrophages and efferocytosis, as well as suppression of inflammation and enhanced systemic insulin sensitivity,^23,44,66,67 targeting these pathways might constitute a novel and relevant clinical therapeutic approach in the treatment of obese asthmatic patients.

Key message.

• Airway macrophages from obese asthmatic adults demonstrate impaired efferocytosis that is associated with increased oxidants, altered monocyte programming, and reduced glucocorticoid responsiveness.

Abbreviations used

ADAM

A disintegrin and metalloproteinase domain–containing protein

BMI

Body mass index

GCR

Glucocorticoid receptor

4HNE

4-Hydroxynonenal

MKP-1

Mitogen-activated protein kinase phosphatase 1

PPAR

Peroxisome proliferator-activated receptor