ABSTRACT
Hematopoietic stem cells (HSCs) regenerate blood and immune cells throughout life. However, aging HSCs
exhibit reduced self-renewal activity, diminished regenerative capacity, and myeloid-biased differentiation that
contribute to an increased incidence of immune dysfunction, bone marrow failure, anemia, clonal hematopoiesis,
and cancer in older adults. Translational control has emerged as fundamentally and preferentially important for
stem cells. Young adult HSCs have lower protein synthesis rates than other hematopoietic cells and increases
in protein synthesis impair HSC function by increasing the biogenesis of misfolded proteins and disrupting protein
homeostasis (proteostasis). In preliminary studies, we found that old HSCs preserve low protein synthesis rates,
but increase the biogenesis of misfolded proteins, raising the possibility that translation fidelity declines in HSCs
during aging and contributes to age-related HSC dysfunction by disrupting proteostasis. The goal of this proposal
is to test if young adult HSCs have elevated translation fidelity as compared to restricted progenitors and old
HSCs, and to determine if enhancing translation fidelity increases HSC fitness and longevity. To our knowledge,
translation fidelity has not yet been studied in a cell-type- or age-specific manner in vivo, and interventions that
specifically boost translation fidelity in mammals have not been reported. To overcome these limitations, we
developed a single cell assay to quantify relative translation fidelity, and developed a new genetic mouse model
with high-fidelity ribosomes (Rps23K60R) that enhances translation fidelity and reduces proteostasis stress in
aging HSCs. In Aim 1, we will use translation fidelity reporter mice to quantify relative translation fidelity in HSCs
and progenitors in vivo, and will determine if genetically or environmentally increasing protein synthesis reduces
fidelity in HSCs. Furthermore, we will test if enhancing translation fidelity in Rps23K60R mice protects HSCs from
the proteostasis disrupting effects associated with increased protein synthesis. In Aim 2, we will test if translation
fidelity declines in HSCs during aging, and if enhancing fidelity delays/mitigates age-related declines in HSC
function. We will also determine if enhancing translation fidelity delays/prevents stem cell exhaustion in serial
transplantation assays and extends organismal healthspan and lifespan. Finally, in Aim 3, we will determine the
effects of enhancing translation fidelity on proteostasis using a suite of single cell assays to investigate proteome
quality and quantitative proteomics to investigate proteome content throughout life. We will also test if enhancing
fidelity alleviates the need to activate proteotoxic stress response pathways to preserve HSC fitness during
aging. These studies will elucidate if cell-type-specific differences in translation fidelity are employed to confer
stem cell longevity and will reveal if modulating translation fidelity is a potential therapeutic strategy to enhance
stem cell fitness and organismal longevity by preventing age-related proteostasis disruption. Overall, this work
will open new directions for extending human healthspan and longevity.