Matrix Softness Induces an Afibrogenic Lipofibroblast Phenotype in Fibroblasts from Patients with Idiopathic Pulmonary Fibrosis

Contractile myofibroblasts immersed in stiffened remodeled extracellular matrix characterize fibrotic lesions in idiopathic pulmonary fibrosis. Lipofibroblasts are lipid droplet-containing interstitial fibroblasts that support functional homeostasis of the developing and adult lung. We show that stiff substrates augment myofibroblast differentiation and extracellular matrix production <i>in vitro</i> under basal conditions and following TGF-β1 (transforming growth factor-β1) incubation when cultured on tissue culture plastic, whereas culture in soft microenvironments (as spheroids or on soft collagen-coated substrate) redirects myofibroblasts to a lipofibroblast-like phenotype (identified by expression of ADRP [adipose differentiation-related protein] and intracellular lipid droplets), with reduced basal α-SMA (α-smooth muscle actin), collagen I, vimentin, and fibronectin expression. The fibrogenic effects of TGF-β1 are prevented in fibroblasts cultured in soft settings. Global proteomics showed similar numbers of TGF-β1-induced differentially expressed proteins in stiff and soft settings (271 and 436, respectively). Of these, only 33 were similarly altered by TGF-β1; 200 were exclusively altered by TGF-β1 in the stiff setting and 365 in the soft setting; 38 showed opposite responses. Reductions in YAP/TAZ, β-catenin, and SMAD expression and their limited nuclear levels in soft settings may explain the "afibrogenic" characteristic of these lipofibroblasts. Thus, in spheroids of lipofibroblasts, TGF-β1 intracellular signaling is redirected and uncoupled from fibrogenesis, including YAP/TAZ, β-catenin, and SMAD. Understanding the proximal causal mechanotransduction signaling networks that are differentially active in soft and stiff microenvironments may reveal novel drug targets for fibrosis treatment.