Induction of lipogenic differentiation and alveolar regeneration in emphysema via PPARG and SREBP

Introduction

Emphysema is a respiratory disease characterized by chronic alveolar destruction. Lipofibroblasts (LIF) play a key role in the stem cell niche surrounding alveolar type II (AT2) cells and may contribute to alveolar regeneration. We have previously shown that senescent cell elimination induces alveolar regeneration, increased LIF numbers and activation of the sterol regulatory binding protein (SREBP) and peroxisome proliferator-activated receptor gamma (PPARG) pathways [1]. However, it remains unclear whether the activation of these pathways can increase fibroblast stem cell niche properties and promote alveolar regeneration during emphysema.

Methods

Human lung tissue slides were obtained from patients with or without emphysema and immunofluorescent staining was performed to identify LIF (ADRP+Vimentin+). Both human primary fibroblasts and primary AT2 cells were isolated from lobectomies through the explant method and magnetic sorting (HT2-280+) respectively. Fibroblasts were treated with Rosiglitazone and T0901317 for 72 hours. LIF phenotype acquisition was evaluated through IF staining, qPCR and lipidomic analysis. Stem cell niche properties were evaluated by performing alveolar organoid formation assay by co-culturing treated fibroblasts with H-441 cells or primary AT2 cells. Adult C57BL6 mice received intra-tracheal injection of either Elastase or PBS. From D₂₁ mice were treated by intraperitoneal injections of Rosiglitazone (5 μg/g/d), T0901317 (10 μg/g/d) or vehicule, 5/7 days. Lungs were collected at D₉₀. Left lung was fixated for morphological analysis.

Results

Our study showed a decrease in LIF populations among patients with emphysema compared to controls. Furthermore, Rosiglitazone, a PPARG agonist, and T0901317, a SREBP agonist, can induce lipogenic differentiation in human lung fibroblasts. Activation of both pathways increased the expression of ADRP and the activation of the SREBP pathway induced the accumulation of neutral lipids in the fibroblasts. Using an organoid model of alveolar regeneration, we show that activating these pathways increases the stem cell niche properties of fibroblasts and enhances the number of organoids formed with either H441 cells or primary AT2. Lastly, in a murine mode of elastase-induced emphysema, we show that Rosiglitazone partially reverts emphysema.

Conclusion

Activation of PPARG and SREBP pathways promotes lipogenic differentiation of fibroblasts, enhances human alveolar organoid formation and partially reverts emphysema in vivo. These results provide insight into potential therapeutic strategies for promoting alveolar regeneration in patients with emphysema.