Actin dynamics in the regulation of the function of hematopoietic stem cells

• Applicant: Professor Dr. Robert A.J. Oostendorp
• Subject Area: Hematology, Oncology ; Cell Biology
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 424702342

In the previous funding period, we have found that in Wnt5a-haploinsufficient mice, HSCs are regenerated in normal numbers after transplantation. However, the regenerated HSCs (HSC-5a) are functionally defective and do not engraft secondary recipients. To understand this functional decline, we performed a transcriptome analysis. This analysis suggested that actin dynamics is deregulated in the HSC-5a, which was confirmed in experiments showing reduced adhesion, migration and homing. However, these diminished migratory properties do not explain the complete failure to engraft. Hence, in the current application, we propose to investigate how deregulation of actin dynamics drives the functional decline of HSCs. It is known that actin dynamics is not only required in migration, but also in endo- and exocytosis, as well as auto- and mitophagy. Indeed, our preliminary analyses showed an increased number of mitochondria in HSC-5a, suggestive of defective mitophagy. Here, we will test the hypothesis that HSC-5a suffer from a failure of an actin-dependent process to regulate the number of mitochondria. For this purpose, we will study mitochondrial mass and function in functionally deficient HSCs and their association with deregulated expression of the actin dynamics pathway. These HSCs will not only be generated in Wnt5a-haploinsuficient mice, but also isolated from Osx-Cre;Wnt5amice. Furthermore, we will modulate mitophagy, using small molecules inhibitors of actin dynamics or, alternatively, we will conditionally modulate the expression of actin dynamics genes which are upregulated in HSC-5a. Importantly, we will study whether these treatments or genetic manipulations will rescue in vitro behavior and repopulating HSC activity in vivo. These experiments will on the one hand increase our understanding of the coupling between actin dynamics, mitochondrial function, and HSC function, as well as identify additional actin dynamics pathway nodes which may facilitate normalization of mitochondria and rescue of HSC function. This knowledge may not only be of importance in understanding the functional decline of HSCs in normal regeneration and aging, but also in malignant disease associated with an aberrant niche such as aplastic anemia, chronic lymphocytic leukemia and myelodysplastic syndrome.

• DFG Programme: Research Grants