ABSTRACT
The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor whose physiological function is poorly understood. The AhR is highly expressed in barrier organs such as the skin, intestine, and lung. The lungs are continuously exposed to environmental pollutants such as cigarette smoke (CS) that can induce cell death mechanisms such as apoptosis, autophagy, and endoplasmic reticulum (ER) stress. CS also contains toxicants that are AhR ligands. We have previously shown that the AhR protects against apoptosis, but whether the AhR also protects against autophagy or ER stress is not known. Using cigarette smoke extract (CSE) as our in vitro surrogate of environmental tobacco exposure, we first assessed the conversion of LC3I to LC3II, a classic feature of both autophagic and ER stress-mediated cell death pathways. LC3II was elevated in CSE-exposed lung structural cells [mouse lung fibroblasts (MLFs), MLE12 and A549 cells] when AhR was absent. However, this heightened LC3II expression could not be explained by increased expression of key autophagy genes (Gabarapl1, Becn1, Map1lc3b), upregulation of upstream autophagic machinery (Atg5-12, Atg3), or impaired autophagic flux, suggesting that LC3II may be autophagy independent. This was further supported by the absence of autophagosomes in Ahr-/- lung cells. However, Ahr-/- lung cells had widespread ER dilation, elevated expression of the ER stress markers CHOP and GADD34, and an accumulation of ubiquitinated proteins. These findings collectively illustrate a novel role for the AhR in attenuating ER stress by a mechanism that may be autophagy independent.
Subject(s)
Endoplasmic Reticulum Stress , Fibroblasts/metabolism , Gene Expression Regulation , Lung/metabolism , Microtubule-Associated Proteins/biosynthesis , Receptors, Aryl Hydrocarbon/metabolism , Animals , Autophagy , Mice , Mice, Knockout , Microtubule-Associated Proteins/genetics , Protein Phosphatase 1/genetics , Protein Phosphatase 1/metabolism , Receptors, Aryl Hydrocarbon/genetics , Transcription Factor CHOP/genetics , Transcription Factor CHOP/metabolismABSTRACT
Childhood tuberculosis (TB) has hitherto been treated through estimation of pediatric doses through the crushing of adult pills, but the bitter taste of the pills and the inaccuracy of this dosing method presents a challenge for both patients and healthcare providers, leading to poor treatment outcomes. The TB Alliance therefore launched the Speeding Treatments to End Pediatric-Tuberculosis (STEP-TB) project to incentivize the introduction of pediatric Fixed-Dose Combinations (FDCs) of TB drugs. This case study describes the elements of this project, evaluates its impact, and highlights future challenges for pediatric TB treatment. The impact assessment incorporates both market impact as well as projected public health impact, evaluating the availability, affordability, and quality of the FDCs, and lastly providing a projection of lives saved as a result of scale-up of the FDCs to near-universal availability and utilization, based on a publicly available pediatric TB-specific model. STEP-TB resulted in the development of two child-friendly FDCs that were successfully brought to market and made available in 20 of the project's 22 high-burden countries. On the basis of a country-specific projection of pediatric TB mortality in Kenya, scale-up to near-universal availability and utilization of the new FDCs could reduce pediatric TB-associated mortality by 2660 cases over the next 5 years. Future challenges include maintaining affordable prices for the FDCs and considering mechanisms to incentivize their introduction among high-risk groups in low-burden countries.
