Non-Cell-Autonomous Reprogramming: Modulation of Damage Sensing Pathways as a Novel Approach in Cellular Reprogramming and Tissue Regeneration

Background

The Christophorou lab at the Babraham Institute has discovered a novel mechanism of somatic cell reprogramming that operates via non-cell autonomous signalling. This approach leverages extracellular factors released by non-reprogramming “bystander” cells and sensed by partially reprogrammed, emerging iPS (induced pluripotent stem) cells during a critical window in the reprogramming process, to enhance or even substitute for traditional cell-autonomous reprogramming methods. The researchers have additionally established that similar non-cell autonomous signals are released after tissue damage and are sensed by tissue progenitor cells, enhancing regeneration. The technology opens new avenues for regenerative medicine, tissue rejuvenation, and safer iPSC generation.

Technology Overview

Researchers identified a novel pathway via activation of Peptidylarginine Deiminase 4 (PADI4, PAD4), a nuclear enzyme that citrullinates histones and mediates chromatin externalization. They have demonstrated that downstream non-cell autonomous factors, such as extracellular histones, are sensed by partially reprogrammed cells during induced cell reprogramming and tissue regeneration and promote their plasticity.

In collaboration with the Francis Crick Institute, the researchers have developed a first-in-class, cell-permeable PADI4 activator— a cyclic peptide that allosterically activates PADI4 by stabilising its active conformation. This tool compound provides a unique opportunity to explore PADI4 activation for therapeutic and R&D use and serves as a launchpad for small-molecule drug discovery. Additionally, this work supports the repurposing of existing signalling agonists or the development of new ones for the enhancement of reprogramming and regeneration.

Publication: Bertran, M.T., Walmsley, R., Cummings, T. et al. A cyclic peptide toolkit reveals mechanistic principles of peptidylarginine deiminase IV regulation. Nat. Commun. _15_, 9746 (2024).

Stage of Development

Genetic and biochemical validation of target/pathway in in vitro, in vivo (induced cell reprogramming, tissue regeneration) and disease models.

Benefits

1. Novel reprogramming pathways: PADI4 activation triggers the downstream release of chromatin. Extracellular histones are shown to be a key non-cell autonomous factor and interact with sensing pathways (e.g., Toll-like receptors), eliciting cellular signalling and gene expression changes that promote cell plasticity and mediate reprogramming.
2. On target activating effect on PADI4, including its activation within cells, avoiding off-target effects.
3. Repurposes established signalling agonists for the enhancement of regenerative medicine approaches.
4. Has the potential to enhance chemical reprogramming technologies, which reduce the reliance on genetic modifications, minimizing the risk for adverse downstream effects, such as tumourigenesis.

Applications

• Regenerative medicine: Enhancing tissue repair and rejuvenation
• iPSC generation: Improving efficiency and safety of reprogramming
• Ex vivo cell therapy: Conditioning cells with non-cell autonomous factors
• Drug discovery: Targeting PADI4 or chromatin-sensing pathways for therapeutic modulation