Mitochondrial-Targeted Antioxidant Therapy Decreases Transforming Growth Factor-β–Mediated Collagen Production in a Murine Asthma Model

Abstract

Asthma is a disease of acute and chronic inflammation in which cytokines play a critical role in orchestrating the allergic inflammatory response. IL-13 and transforming growth factor (TGF)-b promote fibrotic airway remodeling, a major contributor to disease severity. Improved understanding is needed, because current therapies are inadequate for suppressing development of airway fibrosis. IL-13 is known to stimulate respiratory epithelial cells to produce TGF-b, but the mechanism through which this occurs is unknown. Here, we tested the hypothesis that reactive oxygen species (ROS) are a critical signaling intermediary between IL-13 or allergen stimulation and TGF-b-dependent airway remodeling. We used cultured human bronchial epithelial cells and an in vivo mouse model of allergic asthma to map a pathway where allergens enhanced mitochondrial ROS, which is an essential upstream signal for TGF-b activation and enhanced collagen production and deposition in airway fibroblasts. We show that mitochondria in airway epithelium are an essential source of ROS that activate TGF-b expression and activity. TGF-b from airway epithelium stimulates collagen expression in fibroblasts, contributing to an early fibrotic response to allergen exposure in cultured human airway cells and in ovalbumin-challenged mice. Treatment with the mitochondrialtargeted antioxidant, (2-(2,2,6,6-Tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl)triphenylphosphonium chloride (mitoTEMPO), significantly attenuated mitochondrial ROS, TGF-b, and collagen deposition in OVA-challenged mice and in cultured human epithelial cells. Our findings suggest that mitochondria are a critical source of ROS for promoting TGF-b activity that contributes to airway remodeling in allergic asthma. Mitochondrial-targeted antioxidants may be a novel approach for future asthma therapies.

Mitochondrial CaMKII inhibition in airway epithelium protects against allergic asthma

“…In subsequent studies, we found that mitochondrial-targeted antioxidant therapy protects against inflammation and fibrosis in OVA-challenged mice (10). These findings implicate both CaMKII and mitochondria in ROS-mediated pulmonary illnesses, including asthma.…”

“…in asthma; however, sources of these phenomena are unclear (6,7,(10)(11)(12)54). One potential clue is that mitochondrial CaMKII inhibition is protective in a variety of myocardial injury models linked to elevated ROS and mitochondrial dysfunction (7,20,55,56).…”

“…The rate of superoxide anion formation was determined in isolated mitochondria by lucigenin (bis-N-methylacridinium nitrate, catalog M8010, Sigma-Aldrich) as described previously (10,84). Briefly, 100 μl of substrate nicotinamide adenine dinucleotide phosphate reduced (100 μM) was added to 20 μg of mitochondrial protein lucigenin (5 μM).…”

Mitochondria in lung disease

“…While there has been considerable advancement in the development of mitochondria-targeted small molecule antioxidants (3) and alternative approaches to targeting mROS (133)(134)(135)(136)(137) appear promising, such mROS-targeted therapeutic approaches must be used with caution. mROS behave as a cytoprotective agent that leaves cells less susceptible to sub- …”

Oxidized CaMKII promotes asthma through the activation of mast cells

“…OVA-activated MMVVδ mast cells showed much lower levels of intracellular ROS compared with WT cells. Recent studies have suggested that mitochondrial ROS is an important source for promoting asthma phenotypes in OVA-challenged mice (38). We thus specifically detected mitochondrial ROS in these BMMCs using MitoTracker, a marker for mitochondrial localization, and MitoSOX, a fluorescent mitochondrial ROS reporter ( Figure 4H).…”