A Metabolic Shift Fuels Stem Cell Dysfunction

Researchers publishing in the Nature journal Cell Discovery have described how the age-related attenuation of a key metabolic axis causes human adipose-derived stem cells (hASCs) to lose functional capabilities.

Pinpointing the loss of function

This paper begins by highlighting a core problem of using self-derived (autologous) stem cells for treatments in older people: the cells themselves have aged, leading to a loss of basic self-renewal and inability to fulfill their natural functions, harming rather than helping recipients [1].

The paper also notes that mesenchymal stem cells (MSCs), a group that includes hASCs, have aging that is associated with key changes in several metabolic components. Reduced glutathione (GSH) is associated with senescence in these cells [2]. N6-Methyladenosine (m6A), a key component of RNA modification that is necessary for cellular function, has also been found to be responsible for the fates of bone marrow MSCs [3], and its link to GSH processing has also been found to be connected to cellular senescence [4]. These researchers, therefore, sought to find out just how much m6A and its related pathways affect stem cell aging.

Older stem cells cannot perform

In their first experiment, the researchers compared aged and young hASCs to determine the extent to which aging affects these cells’ function. Unsurprisingly, despite being passaged the same number of times, hASCs derived from infants (I-hASCs) were far more able to proliferate and less likely to become senescent than hASCs derived from elderly people around the age of 80 (E-hASCs). The I-hASCs also had better cell morphology, faster migration, and greater viability, along with a greater expression of genes related to fat creation (adipogenesis), blood vessel creation (angiogenesis), metabolic function, wound healing, and overall activity.

The researchers tested these cells in a mouse model of injury and fat transplantation, comparing I-hASCs, E-hASCs, and a control group given no stem cells at all. Unsurprisingly, the mice given I-hASCs healed more quickly and had more angiogenesis in the transplanted fat, along with reduced inflammation, very few cysts or vacuoles, and nearly no fibrosis. However, even compared to the control group, the group given E-hASCs had intense inflammation, a large number of cysts and vacuoles, and intense fibrosis.

A closer look at gene expression using single-cell RNA sequencing revealed potential reasons why. The researchers were able to divide cells into five functional clusters: Cluster 1 (ACTA2+TAGLN+), which was most common in the I-hASCs, was associated with more angiogenesis, bone formation, and metabolic processes; further work found that this group had more stemness and more functional ability than the other groups. Cluster 2 was related to certain metabolic pathways specific to lipids. Cluster 3, which was abundant in E-hASCs, was related to senescence and aging along with the destruction of proteins and the dissolution of the extracellular matrix. Cluster 4 involved cell adhesion, while Cluster 5 involved division and the cell cycle.

Even among all of these various clusters, E-hASCs had more upregulated age-related pathways while I-hASCs had more gene expression related to the synthesis of amino acids and overall metabolism.

A crucial gene is methylated with age

The researchers also found that I-hASCs had more gene expression of a fundamental GSH-related pathway. An upregulation of IGF2BP3 allowed these cells to produce more enzymes that processed branched-chain amino acids (BCAAs) and glutamine, thus prompting these cells to have more GSH than their older counterparts. The expression of IGF2BP3 was also linked to a reduction in senescence-related gene expression and cellular death by apoptosis along with increases in cell proliferation and migration. IGF2BP3 was specifically identified as being downregulated by epigenetic alterations in aging: this gene is hypermethylated with age, preventing its expression.

A further experiment involving BCAA and glutamine found that supplementing these two molecules to mice was able to slightly restore the wound healing abilities of E-hASCs. According to the researchers, “these findings underscore the promise of metabolic modulation as a translational approach to mitigate cellular aging and improve regenerative therapies.”

While supplementation cannot fully reverse the effects of the dwindling IGF2BP3 with age, this metabolic approach provides a crucial starting point for potential near-term therapies. Further work will determine if such an approach will allow for autologous or other stem cell-related therapies to become more effective.

Literature

[1] Wang, B., Liu, Z., Chen, V. P., Wang, L., Inman, C. L., Zhou, Y., … & Xu, M. (2020). Transplanting cells from old but not young donors causes physical dysfunction in older recipients. Aging cell, 19(3), e13106.

[2] Benjamin, D. I., Brett, J. O., Both, P., Benjamin, J. S., Ishak, H. L., Kang, J., … & Rando, T. A. (2023). Multiomics reveals glutathione metabolism as a driver of bimodality during stem cell aging. Cell metabolism, 35(3), 472-486.

[3] Wu, Y., Xie, L., Wang, M., Xiong, Q., Guo, Y., Liang, Y., … & Yuan, Q. (2018). Mettl3-mediated m6A RNA methylation regulates the fate of bone marrow mesenchymal stem cells and osteoporosis. Nature communications, 9(1), 4772.

[4] Weng, H., Huang, F., Yu, Z., Chen, Z., Prince, E., Kang, Y., … & Chen, J. (2022). The m6A reader IGF2BP2 regulates glutamine metabolism and represents a therapeutic target in acute myeloid leukemia. Cancer cell, 40(12), 1566-1582.