Abstract
The production and secretion of matrix proteins upon stimulation of fibroblasts by transforming growth factor‐beta (TGFβ) play a critical role in wound healing. How TGFβ supports the bioenergetic cost of matrix protein synthesis is not fully understood. Here, we show that TGFβ promotes protein translation at least in part by increasing the mitochondrial oxidation of glucose and glutamine carbons to support the bioenergetic demand of translation. Surprisingly, we found that in addition to stimulating the entry of glucose and glutamine carbon into the TCA cycle, TGFβ induced the biosynthesis of proline from glutamine in a Smad4‐dependent fashion. Metabolic manipulations that increased mitochondrial redox generation promoted proline biosynthesis, while reducing mitochondrial redox potential and/or ATP synthesis impaired proline biosynthesis. Thus, proline biosynthesis acts as a redox vent, preventing the TGFβ‐induced increase in mitochondrial glucose and glutamine catabolism from generating damaging reactive oxygen species (ROS) when TCA cycle activity exceeds the ability of oxidative phosphorylation to convert mitochondrial redox potential into ATP. In turn, the enhanced synthesis of proline supports TGFβ‐induced production of matrix proteins. Synopsis Transforming growth factor‐beta (TGFβ)‐induced fibroblast activation and matrix protein production is critical for wound healing; however exceeding nutrient utilization can also evoke detrimental oxidative stress. In this study, TGFβ is shown to protect cellular integrity by stimulating glutamine‐fueled proline biosynthesis, which acts as an electron sink and valve for reactive oxygen species accumulation. Stimulation of fibroblasts with TGFβ promotes glucose and glutamine uptake and their utilization for mitochondrial oxidation. Increased carbon oxidation supports the bioenergetic demand of TGFβ‐induced protein translation. TGFβ promotes proline biosynthesis from glutamine in a Smad4‐dependent fashion to support collagen production. Increased mitochondrial redox potential drives glutamine flux into proline biosynthesis. TGFβ stimulates glutamine metabolism to fuel proline and collagen synthesis, acting as a sink to prevent excessive ROS generation.