Capital Normal University Researchers Identify How Stem Cells Remove Differentiation Signals

Researchers in China have identified how stem cells maintain their original state without differentiating. The study found that autophagy, the cell’s intracellular digestive system, removes signals that induce differentiation.

On the 13th, a research team led by Professor Li Zhouhua of the School of Life Sciences at Capital Normal University published the findings in the international journal Autophagy.

The team conducted a large-scale genetic screen in adult Drosophila intestinal stem cells and identified several subunits of V-ATPase. Among them, Vha68-2 (ATP6V1A) was found to be essential for stem cell proliferation and differentiation, as well as tissue regeneration.

When Vha68-2 function was lost, structures derived from the cell membrane accumulated in autophagosomes and lysosomes. The process was found to be mediated by the proteins Atg16 and Rab5.

In particular, stem cells lacking Vha68-2 differentiated immediately as Notch signaling became abnormally activated. The team explained that Vha68-2 maintains stem cell fate by drawing Notch receptors into the cell and degrading them in autophagic lysosomes.

In the absence of Vha68-2, truncated Notch products lacking the extracellular domain accumulated in autophagic lysosomes. These accumulated Notch products were found to undergo further cleavage and induce stem cell differentiation.

The team said that the roles of Vha68-2 in autophagy and stem cell maintenance are evolutionarily conserved. The findings offer a new mechanism for how autophagy contributes to stem cell maintenance under physiological conditions.

Adult tissues rely on resident stem cells to replace damaged cells. An imbalance between stem cell proliferation and differentiation can lead to excessive proliferation or premature differentiation, potentially causing diseases such as cancer and aging-related conditions.

The Drosophila midgut is widely used in stem cell biology research because its cellular composition, development and regulatory mechanisms are similar to those of mammals. Intestinal stem cells produce differentiated cells while renewing themselves through asymmetric division, a process regulated by Notch signaling.

After a Notch receptor binds to a ligand on the membrane of a signaling cell, it undergoes two rounds of proteolysis. Its intracellular domain then moves into the nucleus and regulates gene expression. When Notch signaling disappears in intestinal stem cells, proliferation increases and differentiation is suppressed, leading to tumors; conversely, sustained activation causes stem cells to be lost.

The team explained, “Although Notch receptors are highly expressed in stem cells, signaling is completely blocked under normal conditions. Whether autophagy is involved in this process had not been established.”

Autophagy is the process by which protein aggregates and organelles are enclosed in double-membrane structures called autophagosomes, which then fuse with lysosomes for degradation. Basal autophagy maintains cellular homeostasis and is rapidly activated in response to stresses such as nutrient deprivation.

V-ATPase consists of a cytoplasmic V1 sector and a membrane-bound V0 sector, and plays a key role in creating an acidic environment in lysosomes and intracellular vesicles. However, it is known not to be required for the fusion of autophagosomes and lysosomes.

The study is significant because it is the first to identify the specific mechanism by which V-ATPase regulates intestinal stem cell proliferation and differentiation. The findings are expected to contribute to understanding stem cell maintenance and developing treatment strategies for related diseases.