Autophagy contributed to integrin turnover during axon regrowth in cultured mouse neurons
Autophagy contributed to integrin turnover during axon regrowth in cultured mouse neurons
On August 6, Anda Cimpian, Jessica C. F. Kwok, James Fawcett, and Pavla Jendelova published a preprint on axon regeneration. Using cultured adult mouse sensory neurons, the authors tracked changes in autophagic vesicles and β1-integrin-containing vesicles after axotomy.
An axon is a long projection of a neuron. Its growing tip adds new membrane and attaches to the surrounding extracellular matrix, a protein network around cells. Integrins are cell-surface receptors that mediate this attachment. Autophagy encloses cellular components in vesicles, delivers them to lysosomes for degradation, and returns reusable material to cellular circulation.
The authors severed axons in dorsal root ganglion explants and tracked vesicle movement near the distal end of each axon for 2 minutes. Immediately after injury, every axon showed an increase in the number of autophagic and β1-integrin-containing vesicles, while vesicle movement slowed. After 2 hours, the number of autophagic vesicles returned to its preinjury level in axons that had resumed growth. In the distal segments of these axons, β1-integrin-containing vesicles were more likely to remain stationary. Among moving vesicles, those labeled with both β1-integrin and an autophagy marker were more likely to travel toward the neuronal cell body.
Over 2 hours, about 80% of axons grew in the control culture, with each axon extending by an average of 30 micrometers. After axotomy, about 40% resumed growth, and the new processes reached an average length of 35 micrometers. Integrins help the growing axon tip maintain its attachment to the extracellular matrix, so the authors included their localization within the distal segment in their model of axon growth.
The researchers then used drugs to alter autophagy. 3-MA, which inhibits the formation of autophagic vesicles, reduced the proportion of growing and regenerating axons and limited their extension. After 3 hours of treatment, rapamycin increased the proportion of axons that began to regenerate. It also increased the number of β1-integrin-containing vesicles near the distal segment. Among moving vesicles, those labeled with both β1-integrin and an autophagy marker were more likely to travel toward the cell body. The authors observed the same pattern in regrowing axons.
The authors propose a testable model in which autophagy changes the fate of a specific cargo, β1-integrin. Integrins, in turn, alter the maturation and transport of autophagic vesicles. This reciprocal relationship provides a way to test how receptor localization near the growing axon tip affects axon regrowth.