Skip to main content
Premium Trial:

Request an Annual Quote

Single-Cell Study Finds Mutations Accumulate in Human B Lymphocytes With Age

NEW YORK (GenomeWeb) – Mutations accumulate in human B lymphocytes with increasing age, according to a new single-cell sequencing study.

This buildup of somatic DNA mutations is thought to be a driver of both cancer and aging. To examine this, researchers from the US and China sequenced human B lymphocytes isolated from healthy people ranging in age from a few months to more than 100 years.

Newborns, they reported yesterday in the Proceedings of the National Academy of Sciences, have fewer than 500 somatic mutations per cell compared to more than 3,000 per cell in centenarians. The mutational signatures that arose within B cells with age were also similar to those found among B cell tumors, suggesting that these somatic mutations contribute to the increased cancer risk that goes along with aging.

"[T]his comprehensive characterization of the landscape of somatic mutations in B lymphocytes across the entire human age range shows a highly significant age-related increase of mutations," senior author Jan Vijg from Albert Einstein College of Medicine and his colleagues wrote.

He and his colleagues applied the single-cell multiple displacement amplification (SCMDA) approach they developed — the method aims to address issues common among single-cell sequencing techniques — to analyze the genomes of 56 single B lymphocytes from 14 individuals. The average sequencing depth for these single cells was 28X, with more than half the genome covered at a depth of 20X or greater.

The researchers also sequenced bulk DNA from peripheral blood mononuclear cells from these individuals to an average 25X depth.

After filtering out germline variants, as identified from the match bulk sequencing data, the researchers identified between 237 and 5,862 SNVs per cell.

The number of SNVs varied, though, with age. Cells from newborns harbored a median 463.4 mutations, while cells from 27- to 30-year olds contained a median 1,181.9 mutations, cells from 52- to 75-year olds contained a median 2,101.7 mutations, and cells from 97- to 106-year olds contained a median 3,127.0 mutations.

Most mutations, the researchers noted, were unique to each cell, though about two dozen were recurrent and shared among cells from the same individual, suggesting the cells arose from a common ancestor. Additionally, though most mutations were scattered throughout the genome, the researchers uncovered some hotspots, including some near Ig gene regions.

The researchers unearthed mutational signatures of aging within these cells, signatures they noted were similar to mutational signatures observed in human cancers. For instance, the B signature of aging the researchers uncovered was akin to the mutation signature of pilocytic astrocytoma, a childhood cancer, while their signature D was similar to one found in lymphocytic leukemia and malignant B cell lymphoma.

This, the researchers said, highlights the role of aging in cancer risk.

By combining their single-cell sequencing data with exome and ATAC-sequencing data, they found mutations within transcription factor binding domains increased with age, as did the number of mutations in active open chromatin regions with age. This indicated to them that these alterations might have functional consequences.

The researchers further estimated that the median number of mutations affecting the functional part of the B cell genome increased from a median 27 per cell in newborns to 85.1 per cell in people over the age of 97 years. But as compared to the rest of the genome, they noted that the pace of mutations accumulating in these regions was lower, suggesting these mutations were subject to negative selection.

The researchers added that their study sets the stage for further ones into the mechanisms and ramifications of aging. "Our present results provide the foundation for finally testing the somatic mutation theory of aging by studying multiple human organs and tissues for the accumulation of potentially functional mutations and their causal relationship to age-related functional decline and disease," they wrote.