One story, four chapters

Each of the four studies on SS-31 looks at a different moment in the life of a stressed mitochondrion. Put them in order and you get something close to a full story, from a healthy cell to one that has decided to die.

Here is that story, told using all four papers.

Chapter one: the healthy power plant

A mitochondrion has two membranes, a smooth outer one and a heavily folded inner one. The folds, called cristae, are where energy is made. The more folds, the more energy.

Those folds are held in shape partly by a fat called cardiolipin, found almost only in mitochondria. The Wisconsin study explains that cardiolipin sits mainly in the inner membrane of healthy cells, helping keep the cristae stable.

This is where SS-31 lives. Several of these papers describe it as concentrating on the inner membrane and associating with cardiolipin. Its proposed job is to help keep that folded structure stable and working.

Healthy mitochondria also constantly split and merge, and the cell keeps building new ones. The diabetic liver study measured the proteins in charge of both: Drp1 and Fis1 for splitting, Mfn1, Mfn2 and Opa1 for merging, and PGC-1α, Nrf1, Nrf2 and TFAM for building new ones.

Chapter two: stress arrives

Then something goes wrong.

  • In the brain study, blood floods around the base of the brain.
  • In the liver study, blood sugar stays high for months.
  • In the muscle study, oxygen is cut off for three hours.
  • In the Wisconsin study, a chemical pushes cells toward death.

In every case, mitochondria come under pressure. They run harder or run short of oxygen, and they start leaking reactive oxygen species, unstable molecules that damage whatever they touch.

Chapter three: damage builds

The brain and liver studies both measured this damage directly.

In the brain, the marker of damaged membrane fats (MDA) rose, while the cell's own antioxidant enzymes (SOD and GPx) weakened.

In the liver, hydrogen peroxide rose, a different marker of damaged fats (HNE) rose, and ATP, the energy the mitochondria are supposed to produce, fell.

The liver study also showed the balance of splitting and merging tipping toward splitting, and the signals for building new mitochondria falling. More damage, fewer replacements.

In the muscle study, the cell's natural repair protein HSP70 rose a little after the injury, a sign the cell was trying to defend itself.

Chapter four: the decision to die

If stress continues, the cell reaches a decision point.

The brain study and the Wisconsin study both describe what happens next. A protein called BAX moves from the main fluid of the cell onto the outer membrane of the mitochondria. The membrane becomes leaky. Cytochrome c, a protein normally tucked inside the folds, escapes. That sets off a chain of enzymes, ending with caspase-3, which takes the cell apart.

The Wisconsin study adds detail on timing. BAX gathering takes about 20 to 30 minutes. Cytochrome c escapes almost the moment it starts. The mitochondria break into fragments once it finishes.

The muscle study touches this stage too, through a protein called Bad, which pushes cells toward death by tying up their protective proteins.

Where SS-31 stepped in

Now lay the SS-31 results over that story.

Chapter one, healthy structure. In the Wisconsin study, SS-31 helped mitochondria recover to larger, longer shapes faster.

Chapter three, damage. In the brain study, SS-31 lowered membrane damage and restored the antioxidant enzymes. In the liver study, it lowered hydrogen peroxide and membrane damage, raised ATP, restored the balance of splitting and merging, and boosted the signals for building new mitochondria. In the muscle study, it roughly doubled HSP70 compared with injured untreated cells.

Chapter four, the decision to die. In the brain study, measured as a snapshot at 24 hours, SS-31 reduced BAX on mitochondria, reduced cytochrome c release and reduced caspase-3. In the Wisconsin study, watched live, SS-31 did not stop BAX or cytochrome c once the process had started, and only slowed BAX slightly. In the muscle study, SS-31 was not reported to switch off Bad.

What the full story suggests

Read in order, a pattern appears. SS-31's clearest effects are in the earlier chapters: keeping structure intact, limiting damage, strengthening the cell's own defences. Its effects at the final decision point are much less clear.

That fits one sensible reading: SS-31 may protect cells mainly by keeping them away from the decision to die, rather than reversing that decision once it is made.

It is a more modest claim than "SS-31 blocks cell death". It is also the one the full set of evidence supports best.

Next, we look at exactly where the four labs agree.

This series discusses four laboratory studies in animals and cultured cells. None tested SS-31 in people. Nothing here is medical advice, and SS-31 is discussed for research purposes only.