Desmin Regulates Airway Smooth Muscle Hypertrophy through Early Growth-responsive Protein-1 and MicroRNA-26a

Abstract

Bronchial biopsies of asthmatic patients show a negative correlation between desmin expression in airway smooth muscle cell (ASMC) and airway hyperresponsiveness. We previously showed that desmin is an intracellular load-bearing protein, which influences airway compliance, lung recoil, and airway contractile responsiveness (Shardonofsky, Asthma is a chronic lung disease with airway inflammation and abnormal airway smooth muscle contraction (bronchospasm), which is due to an intrinsic abnormality of the airway smooth muscle cells (ASMCs).F2 Airway remodeling and hyperresponsiveness are characteristic features of severe asthma and chronic obstructive pulmonary disease. Clinical studies show that both hypertrophy (increase in cell size) and hyperplasia (increase in cell number) of ASMCs play key roles in airway remodeling (1-5) and hyperresponsiveness in asthmatic patients (6). Moreover, a recent study in bronchial biopsies of asthmatic patients shows a correlation between airway hyperresponsiveness, predicted percentage of forced expiratory volume in 1 s, and airway responsiveness to deep inspiration and the levels of selective expression of ASMC proteins, including desmin (7). Desmin is a cytoskeleton protein and type III intermediate filament. All types of muscle cells, including ASMCs and alveolar ducts, express desmin (8 -12). Our physiologic data from desmin knock-out (Des Ϫ/Ϫ ) mice show that desmin is an intracellular load-bearing protein that influences airway compliance, lung recoil, and airway contractile responsiveness (13). These results suggest that desmin may play an important role in modulating ASMC phenotype.MicroRNAs (miRNAs) are now recognized as key regulators of gene expression and are associated with many human diseases. Recently, we have shown the role of miR-26a in the induction of hypertrophy in human ASMC (14). However, whether desmin can regulate the ASMC phenotype through a miRNA-regulated pathway is unknown. The aim of the present study is to investigate whether loss of desmin triggers induction of ASMC hypertrophy through a miR-26a-regulated pathway. Our results demonstrated that ASMCs of desmin null mice (ASMCs DesϪ/Ϫ ) showed hypertrophy and miR-26a up-regulation. Loss of desmin in mouse ASMCs activated Erk-1/2, which up-regulated miR-26a through Egr-1 (early growth responsive protein-1). The anti-hypertrophic protein glycogen synthase kinase-3␤ (GSK-3␤) is a target gene of miR-26a in ASMCs DesϪ/Ϫ . In addition, the siRNA-mediated knockdown of desmin protein in human ASMCs induced hypertrophy through the activation of the Egr-1/miR-26a/GSK-3␤ pathway. Overall, our data show that desmin is an essential intermediate filament for maintaining ASMC phenotype in both in vitro and in vivo systems. Our data also provide novel experimental evidence that desmin intermediate filaments are important in the regulation of microRNA. EXPERIMENTAL PROCEDURES

Epigenetics and miRNA emerge as key regulators of smooth muscle cell phenotype and function

“…Glycogen synthase kinase 3β, a recognized mediator of ASM hypertrophy in animal models [77], was consequently identified as a target of miR-26a-mediated silencing. Further studies have verified the role of miR-26a in hypertrophy using ASM cells isolated from desmin null mice, which exhibit hypertrophy and express upregulated miR-26a [78] and have established that the early growth responsive protein-1 activates the miR-26a promoter via ERK 1/2. The notion that mitogenic or inflammatory signaling pathways may transcriptionally or post-transcriptionally regulate miRNA expression in ASM cells is intriguing and is supported by recent studies of miR-146a regulation in ASM cells.…”

Airway smooth muscle in airway reactivity and remodeling: what have we learned?

“…Furthermore, in vitro studies using dissolution of different ECM proteins suggest that elastase exerts its functional effects by reducing parenchymal tethering, whereas collagenase reduces airway wall stiffness, thus differentially influencing the load on ASM during contraction (153). On the other hand, passive load on ASM can enhance expression of smooth muscle myosin heavy chain and decrease Akt signaling via integrins (58), whereas stretching of ASM results in increased TGF-␤ expression (mediated via multiple signaling mechanisms) (210) and induces ASM cell hypertrophy (211,212). Such stretch-induced hypertrophy may be mediated via miRNAs (e.g., miR-26a) (212), but Akt may also be important (183).…”

Genome-wide Mechanosensitive MicroRNA (MechanomiR) Screen Uncovers Dysregulation of Their Regulatory Networks in the mdm Mouse Model of Muscular Dystrophy

“…Subsequently, others have identified and demonstrated the role of individual mechanomiR in the pathogenicity of human diseases (24 -31). Interestingly, we have shown previously that loss of desmin protein in mice alters the miRNA expression profile and induces airway smooth muscle cell hypertrophy as a consequence of miR-26a up-regulation (32), suggesting a potential key role for the cytoskeletal protein in regulating miRNAs. It is important to note however that information on the genomewide expression profile of mechanomiRs and their target gene regulatory networks associated with human diseases, including MDs, is completely lacking.…”