O‐GlcNAc Transferase Regulates Growth Factor Signaling and Extracellular Matrix Composition in Idiopathic Pulmonary Fibrosis

Abstract

RationaleIdiopathic pulmonary fibrosis (IPF) is a chronic disease that affects the lungs. The scarring and progressive fibrosis, mediated by communication from the intracellular network and the extracellular matrix (ECM), results in impaired lung function causing respiratory failure and mortality. Over the years, IPF has been documented as a metabolic and age‐related disease. Several hallmarks of aging have been studied, including dysregulated nutrient sensing, altered metabolism, and intracellular communication. Interestingly, dysregulated nutrient sensing, via altered glucose utilization, has been shown to drive metabolic reprogramming in myofibroblasts. O‐linked N‐Acetylglucosamine (O‐GlcNAc) transferase (OGT) is a metabolic ‘stress sensor’ and is responsible for the O‐GlcNAc modification of proteins involved in many cellular processes including metabolism, intracellular communication, and growth factor signaling. However, the potential role of OGT/O‐GlcNAc on growth factor signaling, intracellular communication, and ECM changes during transdifferentiation has not been studied.MethodsLung tissue from individuals with IPF or controls was subjected to immunohistochemistry (IHC) staining to assess O‐GlcNAc modification. In addition, the role of OGT on transforming growth factor beta 1 (TGFb1) induced fibroblast to myofibroblast transition (FMT) was assessed on primary human lung fibroblasts cultured in the presence or absence of an OGT inhibitor, OSMI‐1. Alpha smooth muscle actin (a‐SMA), type 1 collagen (COL1a1), and Smad3 phosphorylation following TGFb1 stimulation with and without OSMI‐1 was examined by Western blot analysis.ResultsIn human lung tissue sections, O‐GlcNAc levels were increased in IPF lung tissue compared to control human lungs as determined by IHC staining. In primary human lung fibroblast, TGFb1 administration resulted an increase in fibroblast transdifferentiation, which was determined by higher COL1a1 and a‐SMA expression. Interestingly, inhibition of OGT by OSMI‐1 following TGFb1 administration reduced expression of COL1a1 and a‐ SMA. Furthermore, OGT inhibition was shown to alter Smad3 phosphorylation upon treatment with TGFb1 (up to 2 hours) in the human lung fibroblasts.ConclusionCollectively, these data suggest that the metabolic sensor, OGT, and the O‐GlcNAc protein modification may have a role in regulating the expression of ECM proteins including COL1a1 by altering TGFb1 signaling during FMT. More importantly, the OGT/O‐GlcNAc axis may be directly involved in the pathogenesis of IPF and regulation of cellular transdifferentiation through TGFb1 signaling and overall ECM composition. Determining the mechanistic role of the O‐GlcNAc modification of proteins on these processes is needed, and may help to identify novel therapies for the treatment of IPF or any other fibrotic diseases.