Aging of human hematopoietic stem cells is linked to changes in Cdc42 activity

Abstract

In this study, we characterize age-related phenotypes of human hematopoietic stem cells (HSCs). We report increased frequencies of HSC, HPC and lineage negative cells in the elderly but a decreased frequency of multi-lymphoid progenitors. Aged human HSCs further exhibited a delay in initiating division ex vivo though without changes in their division kinetics. The activity of the small RhoGTPase Cdc42 was elevated in aged human hematopoietic cells and we identified a positive correlation between Cdc42 activity and the frequency of HSCs upon aging. The frequency of human HSCs polar for polarity proteins was, similar to the mouse, decreased upon aging, while inhibition of Cdc42 activity via the specific pharmacological inhibitor of Cdc42 activity, CASIN, resulted in re-polarisation of aged human HSCs with respect to Cdc42. Elevated activity of Cdc42 in aged HSCs thus contributed to age-related changes in HSCs. Xeno-transplants, using NBSGW mice as recipients, showed elevated chimerism in recipients of aged compared to young HSCs. Aged HSCs treated with CASIN ex vivo displayed an engraftment profile similar to recipients of young HSCs. Taken together, our work reveals strong evidence for a role of elevated Cdc42 activity in driving aging of human HSCs, and similar to mice, this presents a likely possibility for attenuation of aging in human HSCs.

Cdc42‐Borg4‐Septin7 axis regulates HSC polarity and function

“…The distribution of Septins in HSCs might therefore be regulated by the interaction of Septins with the Borg family of Cdc42 effector proteins (Sheffield et al , 2003 ; Farrugia & Calvo, 2016 ). We first tested whether a reduction of the elevated activity of Cdc42 in aged HSCs to the level reported for young HSCs with a specific inhibitor of Cdc42 activity termed CASIN (Florian et al , 2012 ; Grigoryan et al , 2018 ; Leins et al , 2018 ; Liu et al , 2019 ; Amoah et al , 2021 ) might influence distribution of Septin2, 6 or 7 in aged LT‐HSCs. Inhibition of Cdc42 activity increased the frequency of aged LT‐HSCs polar for Septin7 to the frequency reported for young LT‐HSCs (Fig 1 C and D) while the distribution of Septin2 and 6 was not affected by CASIN (Fig EV1 K–M).…”

“…The aging‐related changes in HSCs and hematopoiesis are caused by both cell intrinsic alterations in HSCs and extrinsic BM niche factors (Kamminga & de Haan, 2006 ; Geiger et al , 2007 ; Wang et al , 2011 ; Guidi et al , 2017 ; Saçma et al , 2019 ; Mejia‐Ramirez & Florian, 2020 ). An increase in the activity of the small RhoGTPase Cdc42 in aged HSCs causes the reduced frequency of polar HSCs upon aging and is also causative for HSC aging (Florian et al , 2012 ; Grigoryan et al , 2018 ; Leins et al , 2018 ; Liu et al , 2019 ; Amoah et al , 2021 ). Pharmacological attenuation of the aging‐related increase in the activity of Cdc42 by a specific small molecule inhibitor of Cdc42 activity termed CASIN resets the frequency of polar HSCs back to level reported for young HSCs and rejuvenates the function of chronologically aged HSC.…”

Postnatal conservation of human blood- and marrow-specific CD34+ hematopoietic phenotypes

“…Previous studies have reported altered frequencies of CD34+ lymphoid progenitors and HSCenriched phenotypes with advanced human age [16][17][18][19] . Therefore, we next asked if there might be specific age-or source-related shifts in the frequency of HSC and progenitor phenotypes across the eight sample groups analyzed here (Figure 2A, B).…”

“…Evidence of cell-intrinsic changes during aging include accumulated DNA damage, and metabolic and epigenetic alterations 15 . In contrast, less extensive analyses of BM cells from older humans have reported variably altered frequencies of certain CD34+ subsets with an increased proportion of those bearing an HSC phenotype and a reduced proportion of those with a more lymphoidrestricted phenotype [16][17][18][19] . However, a detailed comparison of the complete human CD34+ compartment in mobilized as well as normal PB and BM for over 7 decades of life has not yet been reported.…”

Reconstructing Boolean network ensembles from single-cell data for unraveling dynamics in the aging of human hematopoietic stem cells

“…In addition, Ikonomi et al also retrieved a single state attractor describing the same HSC population in young physiological conditions [5] . The increase in the number of attractors in the network reconstructed for young HSCs might be linked to their ability to promptly respond to stimulation and which is reduced in aged HSCs [60] . Together with our results from the structural analysis ( Fig.…”