Astronauts live in a practically weightless environment, scientifically known as microgravity. The effects of microgravity on the human body are various and fascinating—some of them damaging, some redeeming. New research finds a therapeutic purpose for the impact of microgravity on human stem cells.

From the brain shifting upward to muscles shrinking, veins swelling, and astronauts' faces getting puffy, the effects of microgravity on the human body are fascinating, to say the least.

But how do weightless conditions affect the heart? Because this vital organ doesn't need to pump as much blood throughout the body as it would under gravity, over time, blood vessels tend to become less elastic and thicker, which raises the risk of heart disease.

As a counterpoint to these negative consequences, however, scientists are uncovering more and more potentially therapeutic effects of spaceflight on the human heart.

For instance, studies have shown that microgravity simulated in the lab affects progenitor heart cells differently depending on their age. Progenitor cells are "early descendants of stem cells that can differentiate to form one or more kinds of cell."

Other studies on embryonic mouse cells have shown that simulating spaceflight affects the stemness and differentiation of stem cells, helping them to differentiate more quickly into cardiac muscle cells.

So, researchers from Loma Linda University in Loma Linda, CA, wondered if stem cells thus modified could be used for cardiac repair.

To answer this question, Jonathan Baio and colleagues simulated the molecular changes that would happen under microgravity and explored their implications for boosting the therapeutic potential of cardiovascular progenitor cells.

The researchers published their findings in a special issue of the journal Stem Cells and Development.

Microgravity changes calcium signaling

Baio and team simulated microgravity for 6–7 days on NASA's International Space Station and cultured neonatal cardiac progenitor cells for 12 days in the National Laboratory aboard the space station.

The scientists looked for changes in gene expression and found that the microgravity environment "induced the expression of genes that are typically associated with an earlier state of cardiovascular development."

After 6–7 days, the scientists found changes in calcium signaling pathways which, they say, could be used to improve stem-cell–based therapies for cardiac repair.

After 30 days, a calcium-dependent protein kinase, or enzyme, called C alpha was activated. To further "explore the effect of calcium induction in neonatal [cardiac progenitor cells]," the researchers activated the protein kinase on Earth by increasing calcium signaling.

The changes noted made the researchers conclude that "manipulating calcium signaling on Earth [presents] a novel therapeutic opportunity for cell-based cardiac repair."

What the findings mean for cardiac repair

As the authors note, there are already early-phase clinical trials that are using heart stem cells to treat patients with ischemic cardiomyopathy or to help people recover from a heart attack.

While the results of these trials are promising, sometimes cell engraftment fails and scientists are still debating what type of cell is best for the transplant.

"Therefore, the application of findings from [microgravity] experiments to Earth-based experiments may help overcome the shortcomings of current clinical trials involving the use of [cardiac progenitor cells] for cardiac repair," write the authors.

Baio and colleagues conclude:

"[M]anipulating the normal gravity environment of early [cardiac progenitor cells] may highlight important mechanisms by which early cardiac progenitors develop or expand. Such insights may be applied to further understand cardiovascular development and enhance the outcomes of stem-cell–based regenerative therapies."

Graham C. Parker, PhD—who is affiliated with the Wayne State University School of Medicine in Detroit, MI, and is the Editor-in-Chief of the journal Stem Cell and Development—also comments on the findings.

He says, "This paper provides an important proof-of-concept for combining space- and ground-based experimental design and informs cardiac therapeutic development both for spaceflight and here on Earth."