The manipulation of cell state to produce positive outcomes via either electromagnetic fields or physical stimuli such as pressure are both understudied areas of cell biology, potentially applicable to the production of novel therapies, but with little concrete progress to that end goal. One of the challenges is that there are many, many different ways in which one can apply electromagnetic fields or physical stimuli to cells, and it seems fairly clear from a review of the fairly sparse literature on this topic that (a) most of the choices one can make in this large space of options will not produce the desired results, and (b) replication is hard because researchers do not adequately describe the exact protocol they are using. Small and even unintentional changes in the setup of the experiment can produce large differences in outcomes.
Today's open access paper is quite interesting. In it, researchers present evidence for the application of pulsed pressure to cells via low frequency ultrasound to be capable of reversing cellular senescence. Normally senescence is an irreversible transition, though in recent years researchers have found a few manipulations that can achieve this goal. Low frequency ultrasound is shown to affect mTOR signaling and boost autophagy. Pharmacological approaches to achieve this goal, such as use of rapamycin, do not reverse senescence. They do reduce the number of cells that become senescent, however, and thus allow the number of senescent cells in a tissue or in cell culture to become lower over time. Researchers tested the ultrasound approach in cell culture, but were careful to try to show that formerly senescent cells lost characteristics of senescence, it wasn't just a reduced onset of senescence. The researchers then tested the application of low frequency ultrasound to mice, and report a sizable gain in life span in mice treated with ultrasound throughout their lives, in the same ballpark as the use of senolytic drugs to clear senescent cells.
Rejuvenation of Senescent Cells, In Vitro and In Vivo, by Low-Frequency Ultrasound
Senescent cells, as rigorously defined by many markers, including the expression of β-galactosidase, can be mechanically rejuvenated by low frequency ultrasound (LFU) without transfection or other biochemical manipulations. The ultrasound pressure waves restore normal behavior irrespective of whether senescence is induced by chemical treatment or by repeated replication. There is no apoptosis with LFU, and videos of senescent cells show a dramatic increase in cell and mitochondrial motility, as well as in growth after LFU treatment. Many features of senescent cells are all reversed by LFU, including the increase in β-galactosidase activity, p16 and p21 expression, decreased telomere length, increased H3K9me3 levels, decreased 5mC levels, increased cell size, secretion of senescence-associated secretory phenotype (SASP), and inhibition of growth. Surprisingly, ultrasound treatment of normal cells causes secretion of growth-stimulating factors that partially restore normal behavior in senescent cells. Because replicatively senescent cells are restored to a normal phenotype by LFU, they can be cultured for longer periods to produce increased numbers of cells without major alteration in their phenotype.
It is perhaps surprising that fully senescent cells can be rejuvenated by pressure waves. This raises the question of how a senescent cell is defined. Cells that were made senescent by toxic compounds or repeated replications were incubated for long periods, and time-lapse video microscopy verified the absence of any growth. After such treatments, quiescent cells were not present since over 95% of the cells expressed β-galactosidase and many of the larger senescent cells grew and divided in the videos after LFU. By tracing individual cells, we were able to determine that growth was occurring in over 30% of the originally non-dividing cells after 4-5 days. Such robust growth is inconsistent with the growth of just a subpopulation of cells that are not senescent. Further, there is no apoptosis after LFU treatment of the senescent cells, and over fifteen characteristics of senescence are reversed. Thus, all of these objective criteria indicate that LFU reverses senescence, and we suggest that LFU actually rejuvenates senescent cells.
This opens many new possibilities in the aging research field, including the possibility of rejuvenating aged cells in vivo to inhibit age-dependent disorders, which appears to be true based on the results of the mouse studies reported here. 46 mice were treated over 300 days (some mice reached 3 years of age). In the five LFU-treated groups, the best survivors had the lowest doses of ultrasound with about 50% survival at 1000 days (~33 months of age) and 3 mice survived until 3 years. Autopsies of the mice that died revealed no tumors or obvious cause of death. In terms of the safety of LFU, half of the mice in the longevity study were treated daily with LFU for over 300 days without damage or evidence of harm from the LFU treatment. Further, the treated mice maintained a normal weight, whereas the weight of the sham mice was declining with age.
View the full article at FightAging
