CASIN (Cdc42 Activity-Specific INhibitor), also known as pyrlindole-related compound 2, is a compound that selectively inhibits the activity of Cdc42, a Rho GTPase protein involved in the regulation of several cellular functions such as cell cycle, cell migration, cell morphology and endocytosis.
During aging, expression and activity of Cdc42 in blood cells are associated with older adults and cardiovascular disease. Cdc42 can be used as a strong predictor of survival, and higher levels of Cdc42 have been associated with an increased risk of mortality. By inhibiting Cdc42, CASIN has shown able to rejuvenate aged hematopoietic stem cells (HSCs) in vitro and to reverse age-related phenotypes of HSCs in vivo.
Mechanism of action
CASIN binds to Cdc42-GDP with high affinity and inhibits the catalysed dissociation of GDP, decreasing Cdc42's activity. Cdc42 regulates actin organization, cell adhesion and cell movement and is essential for the retention of hematopoietic stem cells (HSCs) in the niche. However, increased mobilisation of HSCs from the bone marrow to peripheral blood might be beneficial for rejuvenation and aid in the treatment of blood diseases.
The mechanism of action of CASIN is related to the fact that by disrupting the exchange of guanine nucleotides necessary for the activation of Cdc42, CASIN suppresses the ability of Cdc42 to inhibit actin assembly and, as a result, prevents the cell membrane from wrinkling into actin-rich folds.
It has been found that due to changes in the levels of Cdc42 activity during aging, the volume and shape of the cell nucleus, as well as the localization of chromosome 11, can change. Reducing the age-associated increase of Cdc42 activity with CASIN can restore these age-related changes and rejuvenate the function of chronologically old hematopoietic stem cells.
Studies on health and lifespan
CASIN may in the future be used for the collection and transplantation of blood stem cells, since it promotes the release of functional hematopoietic stem cells and progenitor cells from the bone marrow into the peripheral blood at its doses that do not show toxicity nor affect the multilinear differentiation of blood cells. Since CASIN is able to prevent allergic airway inflammation, it might also be useful in the prevention and treatment of asthma.
Transplantation experiments of old-derived HSCs treated with CASIN have shown to functionally reverse to the function of young-derived HSCs, and can reduce or even reversing aging-associated immune dysfunction in older animals.
Moreover, aged human HSCs treated with CASIN ex vivo showed an engraftment profile similar to that observed in CASIN-treated mouse HSCs, suggesting it might be possible to similarly attenuate aging in human HSCs. However, it should be kept in mind that the function of ex vivo rejuvenated HSCs with CASIN in the case of transplantation to old recipients is limited by the old niche, at least partially due to the low level of the cytokine osteopontin in the old niches.
Treatment of old (75-week-old) female mice with CASIN for 4 consecutive days increased their mean lifespan by 10%. In the same study, elderly animals treated with CASIN showed a decrease in biological age as observed by their blood cells epigenetic clock.
Other studies have showed that treatment with CASIN can improve the regeneration of intestinal epithelium, by inhibiting the age-associated Cdc42 activity in intestinal crypts.  CASIN treatment of old hair follicle stem cells can also suppress canonical Wnt signaling in hair follicles and lead to hair follicle stem cell rejuvenation.
After a short systemic treatment with CASIN, transplanting aged hematopoietic stem cells (HSCs) from treated mice is sufficient to extend the healthspan and lifespan of aged immunocompromised mice without additional treatment. CASIN treatment improves strength and endurance of aged mice by increasing the myogenic regenerative potential of aged skeletal muscle stem cells. Furthermore, CASIN modifies niche localization and H4K16ac polarity of HSCs in vivo.
Side effects of CASIN
Although pharmacological reduction of Cdc42 activity by CASIN can improve the regeneration of aged intestinal epithelium, in particular in vivo crypt regeneration in aged mice, the prolonged inhibition of Cdc42 reduced colonic Lgr5+ intestinal epithelial stem cell regeneration and thus inhibited intestinal epithelial cell repair, leading to advanced mucosal inflammation (inflammatory bowel diseases), which could result in intestinal neoplasia. CASIN may also cause autoimmunity, mimicking regulatory T (Treg) cell-specific homozygous loss of Cdc42.
- CASIN Alters Epigenetic State to Produce Lasting Improvement in Aged Stem Cell Function. Fight aging.
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