Senolytic Peptides in Ageing Research: FOXO4-DRI, Humanin and SS-31

Cellular ageing begins with a simple idea: a cell stops dividing but does not die. Scientists call this state senescence. Senescent cells release inflammatory signalling molecules and tissue-remodelling enzymes, and their number rises in the tissues of older organisms. That is why researchers keep looking for tools that remove these cells selectively in an experimental model. This overview covers three peptides from the MOLEVIA range, each acting at a different point of the same biology: FOXO4-DRI as a senolytic, humanin as a mitochondria-derived peptide, and SS-31 as a ligand of cardiolipin. We describe each of them in the context of in vitro work and animal models.

Senescent cells: what researchers are looking for

Senescence is a defensive mechanism. DNA damage, telomere shortening or excessive oncogenic signalling halt cell division. The cell survives, but its secretory profile changes. This profile, known as the senescence-associated secretory phenotype, includes cytokines, growth factors and proteases. In small amounts it can be part of a normal tissue response. When senescent cells accumulate, they disturb the environment of their neighbours.

In the lab, two questions come up again and again. First, how do you detect senescent cells in culture and in tissue? Second, can you remove them selectively without harming cells that never entered that state? The second question is harder, because senescence has no single marker that separates these cells from all the others. For that reason, researchers design tools around a specific dependency of the cell on a protein, rather than around a general feature.

FOXO4-DRI: a senolytic aimed at FOXO4 and p53

FOXO4 belongs to the FOXO family of transcription factors. In senescent cells, FOXO4 binds the tumour suppressor p53 and keeps it in the nucleus in a way that prevents p53 from switching on the apoptosis programme. The cell survives when, under normal conditions, it should have died. This dependency is the target that senolytic tools are designed to exploit.

FOXO4-DRI is a D-retro-inverso peptide. Its sequence runs in reverse, and its amino acids are in the D configuration, which makes it harder for proteases to break down in culture. The peptide disrupts the binding of FOXO4 to p53. Once released, p53 moves into the nucleus and triggers apoptosis in senescent cells. In the reported in vitro studies, the effect was selective for senescent cells, while non-senescent cells responded much less.

The data come from cell cultures and animal models, where a reduction in senescent cells was described in selected tissues. These are not results in humans. For a laboratory, the main value of FOXO4-DRI is that it is a well-defined tool for asking how senescence depends on the FOXO4 and p53 axis. It is available in 2 mg and 10 mg vials.

Humanin: a peptide encoded in mitochondrial DNA

Humanin is a short peptide of 24 amino acids. Its gene sits in mitochondrial DNA, in the region that encodes 16S rRNA. This is an unusual origin, because most mitochondrial proteins are made from genes stored in the cell nucleus. Humanin acts mainly outside the cell, binding to membrane receptors. One of the receptors described in the literature is FPRL1, a formyl peptide receptor.

In cell cultures, humanin has been studied for its cytoprotective role, meaning its ability to protect cells against oxidative stress and toxins. Neuronal and cardiac muscle cell models are especially common. In animal models, researchers have described effects on glucose metabolism and on selected measures of cognitive function. These areas are actively investigated, and the answers to mechanistic questions keep evolving.

Working with humanin requires care during storage. Its methionine and cysteine residues are prone to oxidation, so the lyophilised material should be kept cold and away from light. It is available in a 10 mg size.

SS-31: a peptide that binds cardiolipin

SS-31, also known as elamipretide, is a tetrapeptide with the sequence D-Arg-Dmt-Lys-Phe-NH2. It belongs to the aromatic-cationic peptide family. Its positive charge and aromatic groups allow it to accumulate in the inner mitochondrial membrane. There it binds cardiolipin, a lipid typical of this membrane, and influences how the respiratory chain complexes are organised.

In vitro and animal studies have described effects of SS-31 on ATP production and on the level of reactive oxygen species. Elamipretide has also been tested in clinical studies, which makes it a widely referenced benchmark among mitochondria-targeted peptides. For a laboratory, this means access to a large body of methodological literature. SS-31 is available in 5 mg, 10 mg and 50 mg vials.

Comparison table

Feature	FOXO4-DRI	Humanin	SS-31
Molecule type	D-retro-inverso peptide	24 amino acid peptide	aromatic-cationic tetrapeptide
Main research focus	senescent cells, FOXO4 and p53 axis	cytoprotection, FPRL1 receptor	inner mitochondrial membrane, cardiolipin
Common models	cell cultures, animal models	neurons, heart cells, animal models	cell cultures, mitochondrial models
Research history	preclinical studies	preclinical studies	clinical studies of elamipretide
Molecular mass	confirmed by MS per batch	2687.2 Da	639.8 Da
Sizes in the shop	2 mg, 10 mg	10 mg	5 mg, 10 mg, 50 mg

How to plan the work in your lab

The right peptide depends on the research question. If the target is the senescent cell, FOXO4-DRI gives you a direct point of attack. If the question concerns extracellular signalling, humanin is the more natural choice. When membrane lipids and mitochondrial structure are the focus, SS-31 is the logical starting point.

Every batch from MOLEVIA is checked for:

• Purity of 99% or higher, confirmed by HPLC.
• Mass confirmed by MS, showing that the molecule matches its expected mass.

Before you start an experiment, record the batch number and the date the vial was opened. This makes it easier to compare results later. All products are sold as research reagents for laboratory use only (Research Use Only).

Ordering from the MOLEVIA shop

Orders placed before 14:00 on a working day ship the same day. InPost parcel lockers in Poland receive the parcel on the next working day, while DPD delivers to 29 European countries in 2-4 working days. Free shipping applies from 75 EUR, 65 GBP, 80 USD. Orders from 50 EUR (40 GBP, 55 USD) that include a peptide vial also get a free 10 ml vial of bacteriostatic water.

Quantity discounts apply automatically: 5% off for 2 items, 10% off for 3 items and 15% off for 5 items. Pay online by card, Apple Pay, Google Pay or BLIK (PLN only).

You can also browse the cellular ageing category for other peptides in this area of research.

Key takeaways

• FOXO4-DRI disrupts the binding of FOXO4 to p53, which in cell models leads to apoptosis of senescent cells.
• Humanin is a peptide encoded in mitochondrial DNA, studied for cytoprotection and signalling through the FPRL1 receptor.
• SS-31 binds cardiolipin in the inner mitochondrial membrane and has been studied in clinical trials of elamipretide.
• All three peptides require a clear research question, because each one acts on a different part of cell biology.
• Every batch is supplied with purity of 99% or higher (HPLC) and confirmed mass (MS).

Products covered in this overview: FOXO4-DRI, humanin and SS-31.