Role of transcriptional elongation in dermal fat development

Summary: Abstract Body: Dermal white adipose tissue (dWAT) is vital for skin regeneration, wound healing, and tissue repair. It supports hair follicle regeneration, fights infections, and regulates extracellular matrix through free fatty acid signaling. Dermal fibroblasts (dFbs) maintain dWAT by generating adipocyte precursors and playing a key role in adipogenesis. PDGFRA+ fibroblasts contribute to adipocyte progenitors and can differentiate into adipocytes, but the mechanisms of their transition to dWAT remain unclear. dWAT development may involve gene expression regulation via transcription elongation, a process controlled by the negative elongation factor (NELF) and RNA Polymerase II (Pol II). NELF stabilizes paused RNA Pol II, preventing premature termination. Phosphorylation of NELF, Pol II CTD Ser residues, and DSIF promotes Pol II release, enabling transcription elongation. To determine whether transcriptional elongation plays any role in dWAT development or maintenance, we generated Nelfb deficient mice by deleting Nelfb in PDGFRA+ dermal fibroblasts. Loss of Nelfb led to no dermal fat formation, perinatal lethality, and reduced adipogenic regulators. Nelfb promotes adipogenesis by binding to the transcription start site of regulators that promote adipocyte differentiation such as Pparg, Cebpa, Krox20, and Stat3 to turn on their expression (CUT&Run assay). Its loss destabilizes RNA Pol II at those regions and causes chromatin closure resulting in silencing of key adipogenic genes. Notably, retroviral expression of Pparg in Nelfb deleted cells could restore adipocyte differentiation suggesting that Nelfb regulates Pparg expression, a critical mediator of adipogenesis. In addition, treatment of Nelfb deficient mice with PPARG agonist (Rosiglitazone) restored dWAT formation and increased their lifespan. These findings highlight Nelfb's critical role in promoting the expression of Pparg, Cebpa, Krox20, and Stat3 which are necessary for adipogenesis and dWAT formation. Samiksha Mahapatra¹, Yifang Chen¹, Julian Gomez¹, Celia Fernandez-Mendez¹, Uyanga Batzorig¹, Ye Liu¹, George Sen¹ 1. University of California San Diego, La Jolla, CA, United States. Stem Cell Biology, Tissue Regeneration and Wound Healing