Lgals3 governs muscle satellite cell quiescence and regeneration via Drp1-dependent mitochondrial dynamics

Every muscle in the human body holds a hidden reserve of repair crews, waiting in the shadows of healthy tissue. These are muscle satellite cells, a specialized population of stem cells that lie dormant until an injury strikes. When a muscle is damaged, these cells wake up, multiply rapidly, and transform into new muscle fibers to patch the wound. Once the repair is complete, some of these cells return to their dormant state to ensure the body is ready for the next injury, while others fuse together to rebuild the tissue. This delicate balance between waking up to fix damage and staying asleep to preserve the supply is critical; if the system fails, muscles cannot heal, leading to weakness and wasting diseases. For decades, scientists have known that this process requires precise energy management and careful control of the cell's internal machinery, but the specific molecular switches that decide when a cell should divide, when it should rest, and when it should become new muscle have remained largely a mystery.

A recent study published by researchers at Chongqing Medical University and its affiliated hospital has shed light on one of these crucial switches. The team focused on a protein called Lgals3, which had been suspected of playing a role in muscle health but whose exact function in these stem cells was unclear. To find the answer, the scientists created a unique model using mice that lacked the gene for Lgals3 specifically in their muscle satellite cells. They then injured the leg muscles of these mice and watched how the tissue tried to heal. The results were striking: without Lgals3, the muscle regeneration process faltered significantly. The injured muscles failed to grow back to their normal size, and the new muscle fibers that did form were smaller and fewer in number. This indicated that Lgals3 is not just a bystander but a necessary conductor for the orchestra of muscle repair.

Digging deeper into the cells themselves, the researchers observed a clear timeline for when this protein appears. In a healthy, resting muscle, the satellite cells are asleep and contain no detectable Lgals3. However, the moment the cells are activated by injury, the protein appears rapidly. It rises as the cells begin to multiply and stays present as they start to turn into muscle. When the scientists removed Lgals3, the cells struggled to wake up and divide. They remained stuck in a dormant state, unable to generate enough new cells to repair the damage. Surprisingly, the absence of this protein also changed the cells' behavior in a way that favored staying asleep rather than becoming muscle. The cells that lacked Lgals3 were more likely to return to a resting state and less likely to fuse into new muscle fibers, effectively clogging the repair pipeline.

To understand why this happened, the team looked inside the cells at their power plants, the mitochondria. These tiny structures generate the energy required for the cell to grow and divide. The researchers found that in normal cells, Lgals3 helps manage the shape of these mitochondria, keeping them connected in a healthy, branching network. In cells without Lgals3, the mitochondria broke apart into small, fragmented pieces. This fragmentation was linked to a specific protein called Drp1, which acts as a cutter that splits mitochondria. The study showed that Lgals3 physically interacts with Drp1 to regulate this process. Without Lgals3, the interaction went awry, causing excessive splitting of the mitochondria. This structural chaos led to a drop in the cell's energy production and triggered a cleanup process called autophagy, where the cell eats its own damaged parts. While this cleanup is usually helpful, in this case, it seemed to signal the cell to stop dividing and stay quiet, rather than pushing forward to rebuild the muscle.

The study concludes that Lgals3 acts as a molecular switch that guides muscle stem cells through the complex journey of repair. By controlling the interaction with Drp1, it ensures that mitochondria remain healthy and energetic enough to support rapid cell division and muscle formation. When this switch is missing, the cells lose their energy, their internal structures break down, and they retreat into dormancy instead of healing the injury. This discovery provides a clearer picture of how muscle regeneration works at a fundamental level, highlighting a specific mechanism that could one day be targeted to help people with muscle-wasting conditions or age-related decline. The work confirms that the ability of our muscles to heal depends not just on the presence of stem cells, but on the precise molecular signals that tell them when to wake up, how to power themselves, and when to finish the job.