HSP70, The Cell's Repair Crew

Proteins need looking after

Every protein in your body is a long chain folded into a precise 3D shape. The shape is everything. A protein that loses its shape stops working, and worse, it can clump together with other misshapen proteins and cause damage.

Heat, lack of oxygen, toxins and oxidative stress can all knock proteins out of shape. So cells keep a team of helper proteins whose job is to protect other proteins, refold the ones that have gone wrong, and send the hopeless ones for recycling.

These helpers are called chaperones. One of the most important is HSP70.

Why it is called a "heat shock" protein

HSP stands for heat shock protein. The name comes from how they were discovered. Scientists noticed that when cells were briefly heated, they rapidly started making a specific set of proteins. Those proteins turned out to protect the cell from the heat damage.

The name stuck, but it is a bit misleading. Heat shock proteins are switched on by many kinds of stress, not just heat. Lack of oxygen is one of them.

HSP70 is named for its size, about 70 kilodaltons. The abstract describes it as a protective chaperone protein.

What HSP70 does for a stressed cell

When a cell is under stress, HSP70 helps in several ways:

• It grabs proteins that are starting to unfold and helps them refold correctly.
• It stops damaged proteins from clumping together.
• It helps steer badly damaged proteins toward the cell's recycling system.
• It is also involved in holding back the cell's self-destruct programme, giving the cell time to recover instead of giving up.

So more HSP70 after an injury is generally a good sign. It means the cell is actively defending itself.

What the study found

Here is the strongest result in the abstract. After three hours without oxygen and 24 hours of recovery, HSP70 had risen sharply in muscle cells treated with either hydrogen sulfide or SS-31.

The numbers reported, as relative levels, were:

The untreated normal-oxygen group is set at 1.00 as the reference point. Read the rest against that.

The injury alone nearly doubled HSP70, to about 1.88. That makes sense. Cells naturally switch on some HSP70 when they are stressed.

But cells pre-treated with either compound reached about four times the reference level. That is roughly double what the injury alone produced.

The authors summarise it simply: in the setting of simulated ischaemia-reperfusion injury, both hydrogen sulfide and SS-31 upregulate the protective chaperone protein HSP70.

Why this result is interesting

Remember from Part 3 how different these two compounds are. One is a signalling gas. The other is a peptide that sits on mitochondria.

Yet both pushed HSP70 to almost exactly the same level. That suggests they may be feeding into a shared protective response, even though they start from very different places.

For SS-31 specifically, this is a useful piece of the puzzle. Most research describes SS-31 as protecting mitochondria and reducing oxidative damage. This result adds something different: after the stress, cells treated with SS-31 had built up much more of their own repair machinery.

That fits a theme that appears in other SS-31 studies. In the brain bleed series, SS-31 restored the cell's own antioxidant enzymes rather than just acting as an antioxidant itself. Here, it is associated with a big rise in the cell's own repair crew. In both cases, the cell's own defences end up stronger.

How to read the numbers carefully

There are a couple of things worth noticing in that table.

The spreads are wide. SS-31's 4.25 has a plus or minus of 1.80, and hydrogen sulfide's 4.06 has 1.68. That means the individual results varied a lot from dish to dish. The averages are clearly higher than the untreated groups, but the exact size of the effect is uncertain.

The abstract does not give a p-value for the HSP70 result, and it does not say how many dishes were in each group. In a full paper, you would expect both. Without them, we can say the effect looks large, but we cannot say precisely how confident to be.

That does not cancel the finding. It means it is a strong early signal, not a precise measurement.

The bottom line on HSP70

In this experiment, muscle cells primed with SS-31 before losing oxygen came out of the recovery period with about twice as much of a key protective protein as cells that were not primed. Hydrogen sulfide did the same.

That is a clear, interesting result, and it is the main reason this abstract is worth reading.

Next, we look at the second measure, a death protein called Bad, and what it means to switch it off.

This series discusses a published conference abstract describing a laboratory study in cultured mouse cells. The results have not been shown in people. Nothing here is medical advice, and SS-31 is discussed for research purposes only.