Pathophysiology of bronchoconstriction: role of oxidatively damaged DNA repair

Abstract

Purpose of review: To provide an overview on the present understanding of roles of oxidative DNA damage repair in cell signaling underlying bronchoconstriction common to, but not restricted to various forms of asthma and chronic obstructive pulmonary disease.

Recent findings: Bronchoconstriction is a tightening of smooth muscle surrounding the bronchi and bronchioles with consequent wheezing and shortness of breath. Key stimuli include air pollutants, viral infections, allergens, thermal and osmotic changes, and shear stress of mucosal epithelium, triggering a wide range of cellular, vascular, and neural events. Although activation of nerve fibers, the role of G-proteins, protein kinases and Ca++, and molecular interaction within contracting filaments of muscle are well defined, the overarching mechanisms by which a wide range of stimuli initiate these events are not fully understood. Many, if not all, stimuli increase levels of reactive oxygen species, which are signaling and oxidatively modifying macromolecules, including DNA. The primary reactive oxygen species target in DNA is guanine, and 8-oxoguanine is one of the most abundant base lesions. It is repaired by 8-oxoguanine DNA glycosylase1 during base excision repair processes. The product, free 8-oxo-7,8-dihydro-2'-deoxyguanosine base, is bound by 8-oxoguanine DNA glycosylase1 with high affinity, and the complex then functions as an activator of small guanosine triphosphatases, triggering pathways for inducing gene expression and contraction of intracellular filaments in mast and smooth muscle cells.

Summary: Oxidative DNA damage repair-mediated cell activation signaling result in gene expression that 'primes' the mucosal epithelium and submucosal tissues to generate mediators of airway smooth muscle contractions.

Figure 1. Associations of OGG1-BER with cell activation signaling and bronchoconstriction

Repair is initiated by 8-oxoG extraction from the DNA helix and excision as a base. OGG1 then cleaves the DNA phosphate backbone at the abasic site, resulting in formation of 3′-phospho-α,β-unsaturated aldehyde (3′dRP) and 5′-phosphate termini. The 3′-phospho-α,β-unsaturated aldehyde is removed by AP endonuclease1 (APE1). DNA polymerase β, then incorporates guanine and the resulting nicks are sealed by a DNA ligase. The free 8-oxoG bound by cytoplasmic OGG1 (OGG1:8-oxoG complex = OGG1-GEF), which is functioning now as a guanine nucleotide exchange factor (GEF) and activates small GTPases. Signaling downstream from RAS and RHO family GTPases, changes in the expression of genes encoding pro-inflammatory mediators, regulatory and structural proteins shown to be involved in bronchoconstriction. GEF, guanine nucleotide exchange factor; OGG1, 8-oxoguanine DNA glycosylase; OGG1-GEF (OGG1: 8-oxoG complex); 8-oxoG, 8-oxo-7, 8-dihydroguanine; AP, apurinic/apyrimidinic; RAC1, Ras-related C3 botulinum toxin substrate 1; RHO, Mammalian Rous sarcoma virus homology proteins; GDP, guanosine diphosphate; GTP, guanosine triphosphate.

Figure 2. Gene expression mediating biological processes associated with bronchoconstriction upon OGG1-BER

A, Schematic illustration of experimental design. Lungs were challenged three times at 48-h intervals with 8-oxoG base to mimic intermittent OGG1-BER, and RNAs were isolated at 0, 30, 60 and 120 min. A single challenge was applied as a control. RNA pools from 4–5 mice were subjected to RNA sequencing by using an Illumina HiSeq 1000 sequencing system (Illumina Inc., San Diego, CA). B, Visual depiction of 8-oxoG-induced gene expression associated with bronchoconstriction. C, Gene Ontology enRIchment anaLysis and visuaLizAtion (GOrilla) database-defined system processes. Significance levels of processes are color-coded. D, Biological processes and their P-values was identified by GOrilla analysis software.

Figure 3. 8-Oxoguanine DNA glycosylase1-driven DNA base excision repair-induced gene expression involved in mast cell activation and degranulation

A, Visual depiction of changes in gene expressions involved in mast cell degranulation. B, Biological processes identified by utilizing the GOrilla GO analysis tool. C,D, OGG1 silencing decreased the release of biogenic amines from mast cells. GO, gene ontology; GOx, glycose oxidase; Ogg1, 8-oxoguanine DNA glycosylase1