Alzheimer’s disease research has traditionally concentrated on major proteins such as amyloid and tau, along with the biological changes that accompany brain aging. A new study suggests that another, much smaller group of proteins may also deserve attention.

Scientists at the Salk Institute have created an extensive atlas of microproteins found in the human frontal cortex. These unusually small proteins have often been overlooked by conventional biological databases and analytical methods.

The new research identified more than 4,300 microproteins, including 1,067 with strong experimental evidence that were not present in reviewed protein records. The findings do not establish microproteins as a cause of Alzheimer’s disease. Instead, they provide a new molecular resource that could help researchers investigate previously hidden aspects of brain aging and neurodegeneration.

What Are Microproteins?

Microproteins are short proteins generally containing 150 or fewer amino acids. Many are produced from small open reading frames, known as smORFs, within genetic sequences that historically received less attention than conventional protein-coding regions.

Their small size makes them difficult to identify using some traditional genomic and proteomic approaches. As a result, certain proteins produced by human cells may be missing from standard reference databases.

The new study addresses this gap by combining transcriptomic information, mass spectrometry and computational analysis. Researchers also used ShortStop, an artificial-intelligence-powered tool developed in the Salk laboratory, to search existing biological datasets for evidence of previously overlooked microproteins.

A Detailed Map of the Aging Brain

The research examined more than 600 postmortem frontal-cortex samples from individuals with and without Alzheimer’s disease. The analysis produced evidence for 4,321 microproteins, while 1,067 previously uncharacterized molecules received particularly strong spectral support.

Mass spectrometry was important because it provided physical evidence of peptide fragments corresponding to the predicted microproteins. This helped distinguish experimentally supported molecules from proteins identified only through computer-based prediction.

The researchers found that hundreds of microproteins showed different abundance levels in Alzheimer’s disease samples. Some increased while others decreased, suggesting that these small proteins may participate in biological processes affected by neurodegeneration.

Microglia and Cellular Energy

One of the most notable findings involved microglia, the immune cells responsible for surveillance and maintenance within the brain. Microglial dysfunction is associated with aging and neurodegenerative conditions, making these cells an important area of Alzheimer’s research.

Researchers focused on a 63-amino-acid microprotein produced from the MKKS genetic region. The molecule, called micro-MKKS63, was the predominant detectable translation product at that location in the examined brain tissue.

Its abundance was reduced in Alzheimer’s disease samples. Additional experiments found that the microprotein was associated with mitochondria, the structures responsible for producing much of a cell’s usable energy. When researchers disrupted the microprotein in human microglial cells, measures of mitochondrial respiration, including oxygen consumption and ATP-linked respiration, were reduced.

These experiments suggest a connection between micro-MKKS63 and microglial energy metabolism. However, further research is required to determine precisely how the molecule functions and whether the observed changes contribute directly to Alzheimer’s disease.

Expert Insight

Alan Saghatelian, PhD, professor and Dr. Frederik Paulsen Chair at the Salk Institute, described the broader significance of the research: “We still do not fully understand the molecular mechanisms of healthy aging, and that is especially true for microproteins, which have been inadvertently overlooked for decades.”

What Comes Next?

Future studies can examine whether individual microproteins influence inflammation, mitochondrial activity, cellular communication or other processes involved in brain aging. Researchers can also investigate additional brain regions to determine whether similar molecular patterns occur throughout the brain.

The MKKS-derived microprotein provides an especially interesting research direction because its levels were reduced in Alzheimer’s disease and its disruption affected mitochondrial respiration in microglia. The findings do not establish a new cause or treatment for Alzheimer’s, but they reveal a previously underexplored layer of biology that could contribute to future research into brain aging and neurodegeneration.