The study of extracellular vesicles (EVs) from stem cells presents a novel approach in combating cellular senescence, a hallmark of aging. New research published in Aging Cell outlines how these vesicles, which are involved in intercellular signaling, can alter the behavior of senescent cells, suggesting a potential therapeutic pathway for age-related disorders.

A New Approach to Senescence

The researchers initiated their investigation by revisiting established strategies targeting senescence: senolytics and senomorphics. Senolytics are designed to induce death in senescent cells, while senomorphics modify their behavior. Historically, targeting cellular senescence with these compounds has been considered advantageous due to its apparent accessibility for therapeutic intervention, with notable examples including fisetin and the combination of dasatinib with quercetin. Interestingly, compounds like rapamycin have also demonstrated senomorphic properties [1].

However, the focus shifted to examining EVs, which contain signaling molecules capable of modulating cellular activities. Prior findings indicate that EVs have beneficial effects in various conditions, prompting researchers to delve deeper into their role in senescence, specifically isolating the impacts of micro-RNA strands (miRNAs) within these vesicles.

A Variety of EVs Demonstrate Benefits

The experimental design involved inducing senescence in fibroblasts via etoposide treatment for 48 hours, followed by a recovery period of six days. The study found that EVs derived from different stem cell types, such as embryonic stem cells, endothelial stem cells, and human liver stem cells, showed varying degrees of effectiveness in reducing senescence. A notable vesicle, AC83, was identified as particularly effective, reducing the senescent cell population from 100% to approximately 70% as quantified by the SA-β-gal assay.

Additional senescence biomarkers—including p16, p21, and inflammatory interleukins IL-1β and IL-6—were also assessed. While AC83 outperformed the other EVs in lowering p21 levels, the presence of a senomorphic effect was consistent across all tested EVs, with no significant reduction in total cell numbers.

Looking for the Right Combination

Shifting focus to the specific miRNAs present in the EVs, researchers utilized the miRNA Enrichment Analysis and Annotation Tool (miEAA) along with the age-related genetic database GenAge. Their goal was to identify beneficial miRNAs, deliberately excluding those present in EVs from non-stem cell sources. A total of eight miRNAs were identified as having significant positive impacts on senescent fibroblasts.

Interestingly, individual miRNAs did not yield comprehensive benefits. For instance, one miRNA reduced SA-β-gal but increased pro-inflammatory interleukins, while another did not affect SA-β-gal but showed a decrease in these interleukins. Ultimately, when tested in combinations, a quartet of these miRNAs, termed E5, demonstrated enhanced efficacy in reducing senescence and inflammation, surpassing the effectiveness of AC83.

Further genetic investigations suggested that the downregulation of genes PCAF and HIPK2 by E5 plays a crucial role in blocking senescence signals triggered by genetic damage. This combination also modulated other pathways, including those linked to inflammation, the mTOR pathway, and the cell cycle regulation.

Effectiveness in Mice

Preliminary studies indicated that all four miRNAs comprising E5 were less expressed in older mice compared to their younger counterparts. To evaluate therapeutic potential, the researchers administered E5 injections in two-year-old mice over a two-week period. Post-treatment analyses revealed decreased senescence markers and DNA damage in liver tissues, alongside a trend toward reduced inflammation markers.

Despite these promising findings, several limitations of the study were acknowledged. The researchers noted the need for exploration of the effects of these miRNAs on various cell types beyond fibroblasts, and recognized that a lifespan study had not been implemented to measure extended impacts. The possibility of utilizing targeted miRNA cocktails via mechanisms such as nanoparticles or genetically engineered EVs presents a novel frontier in aging research, calling for more in-depth evaluations to fully leverage the potential of miRNA in combating senescence.

Conclusion

The findings from this research open avenues for further exploration into the therapeutic applications of EVs and their miRNA compositions. By enhancing our understanding of how these signaling molecules interact with senescent cells, researchers may develop innovative treatments that offer not only longevity benefits but also improved quality of life for aging populations.

Literature Cited

[1] Selvarani, R., Mohammed, S., & Richardson, A. (2021). Effect of rapamycin on aging and age-related diseases—past and future. Geroscience, 43, 1135-1158.