Extracellular Vesicles from Young Cardiac Progenitor Cells Produce Benefits in Old Mice

The signaling environment in the body is generated by cells, communication mediated by the molecules that cells release and take up, many of which are packaged into extracellular vesicles. This signaling changes profoundly between development and adult life, and then again in important ways with advancing age. In principle, providing aged tissues with the signals passed back and forth during embryonic development will spur greater maintenance and regeneration. In practice, tissues are systems of great and only partially understood complexity, and attempts to beneficially manipulate signaling in this way are still very much a work in progress, even after decades of effort.

The transplantation of forms of stem cell is perhaps the most successful approach to date when it comes to manipulation of cell signaling for benefit. Stem cells die off following transplantation, but while they survive, their signals influence surrounding tissues. Yet these therapies are as yet nowhere near as reliable or successful as desired, again a matter of complexity: which cells; how to culture them; how to deliver them; how to replicate winning strategies. Deriving extracellular vesicles from stem cell populations will likely run into many of the same issues, but this approach is at least less logistically complex, and thus less costly. Just as researchers produce evidence for benefits in animal models derived from transplantation of embryonic stem cells, they also demonstrate that extracellular vesicles can produce interesting results. This remains some way from clinical application in the mainstream, though increasingly available via medical tourism.

Today's open access paper is an example of the transition from cell therapy to extracellular vesicle therapy. The authors use a population of progenitor cells derived from the embryonic heart to produce vesicles, and demonstrate positive results in old rats following injection of these vesicles into the heart. This delivery of embryonic signaling may or may not be reducing harmful cellular senescence via reprogramming; it is a little early to say whether or not the reduction in senescence results from that mechanism. It is, however, quite interesting to see benefits throughout the body resulting from an injection of vesicles into the heart.

Rejuvenating effects of young extracellular vesicles in aged rats and in cellular models of human senescence

Cardiosphere-derived cells (CDCs) are cardiac progenitor cells with broad-ranging bioactivity in preclinical and clinical studies. Recently, we found that transplantation of young CDCs exerts anti-aging effects in old rodents, improving heart function. Although we specifically targeted the heart in that study, multiple systemic benefits were evident, hinting that soluble factors might play a prominent role. In vitro experiments revealed that extracellular vesicles (EVs) from CDCs (CDC-EVs) mimicked the anti-senescent effects of CDCs, at least partially through activation of the telomerase-telomere axis. Together with the anti-tumorigenic effects of CDC-EVs in old rats with spontaneous leukemia, it seems reasonable to hypothesize that anti-senescent properties of CDC-EVs may underlie the benefits. If so, EVs might be logical therapeutic candidates for a variety of aging-related diseases.

Treatment with young CDC-EVs induce structural and functional improvements in the heart, lungs, skeletal muscle, and kidneys of old rats, while favorably modulating glucose metabolism and anti-senescence pathways. Repeated systemic administration of young CDC-EVs in aged rodents triggered broad-ranging functional improvements, with concordant structural changes in different organs and associated evidence of tissue rejuvenation. The beneficial effects of CDC-EVs were maintained over mid-term follow-up, with prolongation of survival of treated animals. But, beyond longevity, the changes we observed in heart and kidney function, glucose metabolism, and exercise tolerance have the potential to improve quality of life, which is an important goal of anti-aging therapies.

Using a single cell-free therapeutic agent, young CDC-EVs, we demonstrated that multiple pathologies can be favorably modulated. Moreover, tissue fibrosis contributing to organ dysfunction was broadly ameliorated (heart, lungs, skeletal muscle, and kidneys exhibited less interstitial fibrosis) in CDC-EV treated rats. Based on these findings, CDC-EVs emerge as a strategy capable of targeting pathophysiologic mechanisms underlying many age-related chronic conditions. Both MiR-146 and miR-92a highly enriched in CDC-EVs known to be implicated in aging-related pathways may have played a role in rejuvenating effects observed in our study.

Cellular senescence is thought to contribute to progressive age-related organ dysfunction. Previously, we described an anti-senescent effect of young CDC-EVs in vitro. Here, we confirm that cellular rejuvenation, conceived as partial or total reversal of senescence, can be also achieved in vivo in old animals injected with young CDC-EVs. Benefits include telomere elongation in heart cells, less-active DNA damage response (represented by phosphorylated γH2AX), lower IL-6 levels, and changes in protein levels suggestive of enhanced mitochondrial biogenesis in skeletal muscle. Extensive transcriptomic differences in treated versus control groups were consistent with the observed upregulation of the transcription factor NANOG and extracellular signal-regulated kinase ERK 1/2. Both are recognized regulators and stabilizers of the pluripotency gene regulatory network. Accordingly, we speculate that the mechanism of action of young CDC-EVs is related in part to the control of the dynamic state of pluripotency and reprogramming, a strategy that has been touted in pursuit of rejuvenation.