TGF-β Coordinates Alanine Synthesis and Import for Myofibroblast Differentiation in Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease marked by aberrant fibroblast-to-myofibroblast differentiation, a process that requires metabolic reprogramming. We identify alanine as a critical metabolite that confers metabolic flexibility to support differentiation. TGF-β increases alanine by activating both its synthesis and import in normal and IPF lung fibroblasts. Alanine is synthesized primarily by GPT2, which is regulated by a glutamine–glutamate–α-ketoglutarate axis. Inhibiting GPT2 depletes alanine and suppresses TGF-β-induced expression of α-SMA and COL1A1, an effect reversed by alanine supplementation. We also identify SLC38A2 as a key transporter of both alanine and glutamine that is upregulated by TGF-β and alanine deprivation. Together, SLC38A2 and GPT2 activities converge to maintain intracellular alanine levels to support myofibroblast differentiation. Mechanistically, alanine deficiency suppresses glycolysis and depletes tricarboxylic acid cycle intermediates, while supplementation provides carbon and nitrogen for intracellular glutamate and proline biosynthesis, particularly in the absence of glutamine. Combined inhibition of GPT2 and SLC38A2 suppresses fibrogenic responses in fibroblasts and in human precision-cut lung slices, highlighting a potential therapeutic strategy for fibrotic lung disease.