Somatic stem cells (SCs) are responsible for replenishing damaged cells within tissue. SCs can either self-renewal to maintain the SC population or differentiate to generate specialized cells. Proper regulation of SC division is crucial for tissue repair and regeneration, and aberrant SC behavior can lead to SC depletion, failure in tissue homeostasis and function, and/or disease and cancers. As the animal ages, SCs become more prone to behavioral defects, but the mechanisms driving this decline have only recently been begun to be understood. Our previous work and preliminary data have shown that, in Drosophila, inflammation caused by age-associated increased levels of the Unpaired cytokines (Upd; homologous to mammalian IL-6) and JAK/STAT signaling activity causes behavior defects in intestinal stem cells (ISCs), ultimately leading to tissue metaplasia and death. However, the cause of chronic inflammation in aging-animals is poorly understood. This proposal aims to identify protein(s) that contribute towards this phenomenon and to determine whether manipulating these levels restores stem cell behavior and extends tissue function in aging animals. To address this, we utilize dual model systems: the Drosophila gastrointestinal (GI) tract and the mouse trachea. The midgut is highly compartmentalized, which enables clear distinction of ISC behavior in vivo. The accessibility and high-throughput turn out of the fly allows us to test our hypotheses in a comparably rapid manner. We will then test these results in the mouse model for a more direct relevance to humans. The mouse tracheal epithelium shares similar organization to the fly GI tract and the lineage of basal cells, the stem cells of the trachea, is nearly identical to the lineage of fly ISCs. These similarities ofer us the opportunity to utilize the advantages of both model systems. LaminB is a strong candidate to influence inflammation-associated SC dysfunction in aging animals. LaminB has been previously shown to decline in the aging fly and cause GI dysfunction. In addition, defects in lamins have shown to cause Hutchinson-Gilford progeria syndrome, a disorder that manifests at an early age to cause symptoms resembling premature aging. We hypothesize that LaminB decline causes GI dysfunction by increasing Upd expression and JAK/STAT activity. This will then cause aberrant ISC activity leading to metaplasia. To test this hypothesis in flies, we will () determine whether depleting LaminB in young animals will mimic Upd levels, JAK/STAT activity, and ISC/GI tract dysfunction in older animals, and (ii) whether overexpressing LaminB in older animals will decrease Upd and JAK/STAT levels, restore ISC behavior and GI function, and extend lifespan. Finally, we will (iii) determine whether these lamin-associated effects on inflammation, SC behavior, and tissue morphology are conserved in the mouse trachea, using knockout and knockin models. Altogether, this study will be among the first to identify a cause for inflammation-associated SC dysfunction and will have important implications for human aging and age-associated diseases.
Somatic stem cells directly generate cells in damaged tissue and are crucial for tissue regeneration, but their function declines as the animal ages, leading to failure in tissue maintenance and repair. Using the combined efficiency of Drosophila genetics and the human relevancy of mouse models, this proposal aims to identify mechanisms driving age-associated decline in stem cell function. These findings will provide valuable insight into the molecular mechanisms of the aging process and contribute towards understanding and developing therapeutic strategies for age-associated diseases.
