3034 – CYTOSTATIC STRESS CAUSES DEFECTS IN ACTIN-DEPENDENT AUTOPHAGY OF WNT5A-DELETED STROMAL CELLS

The support of hematopoiesis declines with age and it was previously shown that aging hematopoietic cells show cytoskeletal deregulation. Also, efficient autophagy is required to maintain cellular functions with age. Here, we describe a new mouse model with reduced support of hematopoiesis and age-related cytoskeletal changes in which the Wnt5a gene is deleted in Osterix (SP7)+ niche cells (O5AD/D mice). Considering that in these mice Wnt5a is deleted in niche cells, we here investigate niche cells from O5AD/D and control mice treated with 5-fluorouracil (5FU). We found that multipotent stromal cells (MSC) from the bone marrow of 5FU-treated O5AD/D mice show reduced CFU-F frequencies with preferential adipogenic differentiation. In these cells, the F-actin network is disorganized and associated with an elevated activity of the actin assembly-stimulating CDC42. Moreover, we found more and perinuclear accumulated ATG7+ and LC3+ autophagosomes in O5AD/D MSC. Also, LAMP1 expression was elevated and lysosomal diameters increased. But, we found no colocalization of LC3 and LAMP1 in O5AD/D MSC and concomitant autophagic flux, suggesting a defect in autophagy. Since in deregulated MSC from 5FU-treated O5AD/D mice CDC42 activity was increased and protein location was different, we additionally treated these mice with the CDC42 inhibitor CASIN. This treatment restored the CDC42 localization in O5AD/D MSCs and their F-actin stress fibers. Furthermore, LC3 and LAMP1 colocalization, mitochondrial and lysosomal diameters, and autophagic flux were restored. Most importantly, CASIN treatment restored the presence of the hematopoietic system and rescued the ability of O5AD/D mice to survive serial 5FU treatments.