CDC42 Inhibition via CASIN as a Possible Approach to Rejuvenation of Hematopoietic Stem Cell Function
CDC42 inhibition looks promising as a way to rejuvenate immune function via reversing the age-related disruption of hematopoiesis in bone marrow. At some point hematopoietic stem cells become so damaged that no amount of tinkering with their regulatory functions will help, but the evidence to date suggests that this doesn't occur until quite a way past middle age. In older mice, a single treatment of CDC42 inhibitor CASIN extends life span. Here, researchers report on further evaluations of the ability of CASIN to improve hematopoietic stem cell function, extending the work from mouse cells to human cells.
Aging is associated with tissue degeneration, aging-related diseases, and an increased susceptibility to infections. These hallmarks of aging have been linked to aging-related changes within somatic stem cell compartments, and primarily investigated in animal models like mice. One of the most extensively studied somatic stem cell-based system is the hematopoietic system.
Hematopoietic stem cells (HSCs) maintain blood homeostasis and show an age-related decline in overall function in mice, which includes an increase in myelopoiesis, accumulation of DNA damage, changes in epigenomic and transcriptional programs, decreased cell polarity and aberrant activity of the small RhoGTPase Cdc42. Although significant progress has been achieved in elucidating mechanisms of aging of murine HSCs, it remains unclear whether these mechanisms can be simply extrapolated to other species, including humans. For these reasons, novel studies into understanding mechanisms of aging of human HSCs are warranted and are a prerequisite to bolster the transition of this knowledge into the clinic.
In this study, we characterize age-related phenotypes of human hematopoietic stem cells (HSCs). We report increased frequencies of HSC, hematopoetic progenitor cells (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. Xenotransplantation of human HSCs into immunodeficient mice showed elevated chimerism in recipients of aged compared to young HSCs, indicating a worse function in aged HSCs. Aged HSCs treated with CASIN ex vivo displayed an engraftment profile similar to recipients of young HSCs, however.
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.
"At some point hematopoietic stem cells become so damaged that no amount of tinkering with their regulatory functions will help" - this is the old school thinking that sens and their zealots preached forever. Meanwhile, real science shows something else.
What about other stem cells as well? Cdc42 work on them too?
Even off there's a hard limit at the current live expectancy we are far from it. Of course, at some point we will need cell line replacement but only after fixing many other issues first
During somatic embryogenesis (https://en.wikipedia.org/wiki/Somatic_embryogenesis), the renewal of the cell line is possible without the sexual process (due to which some trees live for thousands of years). It is much more difficult to renew the intercellular matrix - this is now the "bottleneck problem". (https://en.wikipedia.org/wiki/Extracellular_matrix).
See more about CASIN in my article in ru.wikipedia: https://ru.wikipedia.org/wiki/CASIN
Hi Dmitry! Just a 2 cents.
''Applying this C57BL/6-trained DNA methylation marker panel to blood cells from aged animals treated with CASIN 9 weeks after treatment, we observed that epigenetic age predictions did not correlate anymore to the chronological age as in aged control animals, but resulted in a biological age prediction that was on average 9 weeks younger than their chronological age (Figure 1i). These data imply that epigenetic changes underlie the extended longevity of aged CASIN-treated mice, while reinforcing the necessity to mechanistically validate tissues, cells, and biological pathways involved in the extension of longevity...
Cdc42 activity-specific inhibitor (CASIN) for 4 consecutive days significantly extends average and maximum lifespan. Moreover, aged CASIN-treated animals displayed a youthful level of the aging-associated cytokines IL-1β, IL-1α, and INFγ in serum and a significantly younger epigenetic clock as based on DNA methylation levels in blood cells.''
This is nearly 100% proof that epigenetic clock reversal is the reason why the mouse live longer.
Epigenetic aging dictates maximum lifespan. A 1980s Russian study had shown that the epigenome loses all its 5-methylcytosine content in the lifetime of an animal. Demonstrating that the faster the epigenome 'empties'/demethylates the faster the animal biologically 'ages' (a mouse lost its residues 50-100x faster than a human, and thus why it lives 2-4 years; a cow lost it 4-5 times faster (it lives 25 years), while a horse lost 2-3 times faster (it lives 50 years)), that is because demethylation allows 'gene activation/gene unsilencing', while methylation is what allows gene silencing (mainly, keeping the 'inflammatory genes silenced', i.e. INF, TNF, IL-6 p53...most of them immunity related inflammation genes meant to destroy cancer by immune system).
I used to think programming/the program was what dictates longevity (not healthspan but maximal lifespan)...then, it was damages...now, I'm back to believing programming is the largest decider of longevity; and that damages are only a 'premature limiting' byproduct, not The product that dictates longevity; that's the program. There is an exact correlation between how much more the mouse lived after CASIN and how much less the clock went down, thus biological epiclock is the main dictator of -all- animals maximal longevity. It is not (just) 'correlative', it is The causation.
(DNA damage can be untangled from the clock; dna damage does nothing to the intrinsic clock, maybe the extrinsic clock (health related) is affected; not the intrinsic one (aging related)).
How so? Well, just check reprogrammed iPSCs, they have reversed epigenetic age to 0...they can continue differentiating, their telomeres are tall again, they are spindle shape again, etc...their damages? repaired. their residues? Most - gone. These residues of age - are possibly removed...by autophagy but some can't be phagocited/broken down; like lipofuscin a pigment that can't be destroyed; but it Can be 'diluted' out of the cells as cell cycling continues (to not end up transfered from the old mother cell to the new young daughter cell in division; so that the daughter cell is intact with none in it; because right now, daughter cells accumulate mounting aging pigments over time/replications, and taht is due to 'parental transfer' during replication).
Babies can have 100% scar-free healing of a deep flesh gash injury, with no macro-granulation (scar formation), adults don't have this capacity anymore in their skin/flesh; I believe that epigenetic reversal 'somehow' changes the microarchitecture of the ECM (extra-cellular matrix) too - it is rebuilt; the ECM does not stay the same, it's built up again 'from scratch' - as such, residues are removed/diluted away (possible glucosepane/crosslinks, AGEs, ALEs..), the main reconstructors are the matrix metalloproteinase (MMPs); thus, we might not be able to reverse the residues accumulating inthe ECM, but epigenetic age reversal seems to affect that too. With that said, if we Can't reverse ECM problems...then we can 'stall them' indefinitely...that is better than letting them continue their course 'piling on and on' until 'clogged'; as in, epiage reversal would not reverse ECM residues but, at least, it would stop new ones from accumulating/and contributing to the total cumul/mass.. or they would accumulate to a 'crawl'/in speed; if we divide by a 1000 the speed at which ECM residues accumulate then it is 'like' stopping aging too, to a 'standstill';
and that's just as valuable as completely removing/reversing every ECM residue. The only goal of all of this, is to 'stop' aging, or in this case, 'freeze it' to a standstill. Of course, we would prefer going back to 20 years old clock...but if that is not truly 100% entirely possible (as in, we do reverse to 20 years old...but our ECM does not and residues still there...after reversal, they are not gone), then we have the ECM problem, so we need to 'freeze it', if we freeze it, we will be a 'false 20',
meaning we are reversed to 20 years old but our body still carried ECM residues from when we were older; thus, we are not a True 20 (true reversal...only partial/false 'sort of' reversal),...-and that can be Sufficient in itself; we would then be a 'partial 20' and this would 'freeze' further ECM residue accumulation down a near stand-still; ECM residues will still accumulate, but 1000x times slower; thus, resiudes accumulation will be quasi-nill/0...if you accumulate 0.0000000000000000001 units of ECM residues/day..then it might take you 10000 years to accumulate anything worthwhile to end life (because we know that 'clogging up the ECM over teh decades of residues in it' is a 'limiting' factor of why we don't live more than 122; but if ECM not clogged ever...then, that limit is gone).
Just a 2 cents.
Actually yes, we have also shown in hair follicle stem cells that Cdc42 activity is elevated upon aging and by treating with casin, the growth phase (anagen) was induced once more in aged mice.
You can check out the paper here DOI: 10.21203/rs.3.rs-95907/v1