Defining the role of endoplasmic reticulum in the initiation of paligenosis

Abstract

Reprogramming is crucial for cellular renewal in adult organs that lack dedicated stem cells for replacement of cell loss after injury. Because such cell plasticity is likely to be executed by a conserved cellular program, we have begun to identify the conserved cellular-molecular features of the process in which differentiated cells are recruited as progenitors. We have characterized three successive stages by which this occur with differentiated cells: 1) the cells downscale their organelle contents, 2) cells activate a progenitor-like gene network, and 3) cells reenter the cell cycle. We have given this conserved process the name paligenosis. Here, we investigate upstream triggers of paligenosis. Using a high-dose tamoxifen (HD-TAM) injury model to induce paligenosis in zymogenic chief cells of the murine stomach corpus, we observed ultrastructural changes in the endoplasmic reticulum (ER) during paligenosis initiation (e.g., swelling of ER lamellae, liberation of ribosomes from rough ER, and overall loss of ER). This led us to hypothesize that dynamic changes in ER were an upstream event in paligenosis. ER functioning is in part monitored by the Integrated Stress Response (ISR) with the paramount ER stress sensor being PERK, which then autophosphorylates and in turn phosphorylates the α subunit of the eukaryotic initiation factor 2 (eIF2α). Phospho-eIF2α halts global translation while upregulating a specific set of genes to restore homeostasis. Here, we go on to show that HD-TAM activates the ISR in paligenotic gastric chief cells, triggering global attenuation of protein synthesis. However, this “ER stress” ISR pathway must occur in a critical, temporally limited window early in paligenosis, as pharmaceutically-induced prolonged ER stress caused paligenosis to halt in early stages with cells failing to proliferate. Blocking the ISR also halted paligenosis in early stages. Ongoing experiments include the use of the glycosylation-inhibiting drug tunicamycin to determine if inducing the ISR via ER stress is sufficient to initiate paligenosis; and deleting PERK in chief cells during paligenosis using Perk flox/flox ; Mist1 CreERT2 mice. Our results provide initial insights on the dynamic functionality of the ER and its role and necessity during cellular regeneration. This work was supported by funding from the NIH through the National Institute of Diabetes and Digestive and Kidney Diseases and the National Cancer Institute. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.