Stem cells in alveolar regeneration: intrinsic or extrinsic?

Lead Research Organisation: King's College London
Department Name: Unlisted

Abstract

Most organs in the adult body cannot naturally repair damage, and disease often results. In emphysema, delicate microscopic air sacs in the lungs (named alveoli) become damaged. This reduces the surface area within the lungs for oxygen to cross into the bloodstream. Patients become breathless and may die of lung failure. By 2020 emphysema will be the 5th most prevalent disease worldwide and the 3rd most common cause of death. No cure currently exists. However, recent research has raised hopes for a future treatment to promote lung repair. Retinoic acid (RA) is known to be important in normal alveolar development, and appears to restart alveolar formation in adult mice with emphysematous lungs. In my project I aim to discover which cells respond to RA to produce new alveoli. Specific lung cells and blood-borne stem cells will be labelled before RA is given. Following alveolar regeneration, the lungs will be examined to reveal which cell label is present in the new alveoli. By increasing understanding of this process, this research field ultimately promises to find a cure for emphysema. Our results will also add to the growing understanding of how stem cells may be directed to repair other damaged adult organs.

Technical Summary

Emphysema is a chronic and debilitating destruction of the lungs for which there is no disease-modifying treatment. Almost uniquely, its incidence in the world is rapidly rising. Recent exciting results have been obtained which suggest that retinoic acid (RA), the metabolically active metabolite of vitamin A, can induce the regeneration of lung alveoli in several rat or mouse models of emphysema. If this were applicable to humans, then it would have a profound impact on human health. I wish to understand more about the cellular biology of regeneration in these models of emphysema and determine the source of cells for the regenerated lung alveoli. There are two potential cellular sources of regenerated tissue: intrinsic stem cells present in the lung; and haematopoietic stem cells from the blood. Experiments will be conducted using the dexamethasone treated mouse model of emphysema (developed in the Maden lab), which regenerates alveoli when treated with retinoic acid. The intrinsic stem cells already known to exist in the lung are the type II pneumocytes. This cell type is thought to be the progenitor of the type I pneumocyte, the cell which lines the walls of the alveoli. To test this possibility BrdU labelling studies will be conducted in the regeneration model currently in use in the Maden lab, the dexamethasone treated mouse. BrdU will be administered at frequent intervals after RA administration to induced regeneration followed by double labelled immunocytochemistry to determine the cell type which has incorporated BrdU and is therefore dividing. In addition a transgenic mouse which has green fluorescent protein (GFP) labelled type II pneumocytes will be used in the regeneration experiments - if type II cells are the source of regenerated cells then they should express GFP after regeneration. On the other hand, to test whether extrinsic blood borne haematopoietic stem cells are the source of regenerated tissue, dexamethasone treated chimaeric animals will be constructed whose blood cells express GFP. These animals will be treated with RA to induce regeneration and double labelling immunocytochemistry performed to determine whether or not the regenerated cells express GFP and therefore came from the blood. Granulocyte colony stimulating factor will also be tested as a potential regeneration-inducing molecule in the dexamethasone treated mouse model of emphysema. These experiments will determine the source of stem cells for the regenerated alveoli in a mouse model of emphysema, and add to the understanding of this potentially therapeutic process.

Publications


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Stinchcombe SV (2008) Retinoic acid induced alveolar regeneration: critical differences in strain sensitivity. in American journal of respiratory cell and molecular biology