Functional Role of the Hippo Pathway Coactivator Taz in the Aging of Hematopoietic Stem Cells

• Applicant: Dr. Björn von Eyss
• Subject Area: Cell Biology
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 409619902

Aging is a highly complex and poorly understood process, as we are just beginning to decipher the molecular basis of aging. The hematopoietic system is particularly affected by aging, as it leads to a decreased function at all levels of the cellular hierarchy (from the differentiated to the most immature progenitors). Previous work has shown that hematopoietic stem cells (HSCs) have an age-related loss of functionality. In our preliminary work, we identified Taz as a promising candidate that is transcriptionally upregulated specifically in HSCs in aging mice. Taz is a transcriptional coactivator that acts as the critical downstream regulator of the Hippo pathway. Interestingly, our RNA sequencing experiments revealed that not only is Taz up-regulated in aging, but also that this enhanced Taz expression contributes to the altered age-specific gene expression profile of HSCs. Thus, we want to address four important questions with this application:A) What is the functional consequence of enhanced Taz expression for HSCs?B) What are the critical target genes of Taz during aging?C) Which molecular processes are responsible for the enhanced Taz expression in aging?D) Which transcription factors recruit Taz to its critical target genes?To address question A), transplant models in the mouse will used. Here, old HSCs are isolated from mice and the Taz expression is up-regulated or down-regulated by lentiviral constructs. After transplantation into primary recipients or retransplantation into secondary recipients, the effect of altered Taz expression in HSCs on the peripheral blood will be examined. Here, we will address if altered Taz expression has an effect on described age-associated HSC defects - e.g. myeloid skewing. Through our preliminary work, we were able to identify a manageable number of age-related Taz target genes in HSCs. These target genes will be functionally tested by a focused shRNA screen in a transplantation model (question B). By combining in vitro and in vivo studies, we want to identify factors (such as altered signal transduction processes and/ or changes in the epigenome) that are causal for the enhanced Taz expression in aging HSCs (question C). To identify the critical transcription factors for Taz function in aging HSCs, we will conduct targeted and proteome-wide interaction studies for Taz. Thus, this proposal aims to investigate Taz as a critical factor in the aging of HSCs and to reveal the critical signaling pathways upstream and downstream of Taz.

• DFG Programme: Research Grants