GLP-1 Drug Exendin-4 Reverses Macrophage Aging to Heal Spinal Cord Injuries

Spinal cord injury (SCI) triggers a cascade of secondary damage driven in part by immune cells called macrophages that rush to the injury site to clean up myelin debris (MD). While this cleanup is initially beneficial, new evidence from this study reveals a dangerous consequence: macrophages that engulf too much lipid-rich MD transform into dysfunctional, senescent foam cells that actively worsen the injury environment.

Using a mouse T10 contusion SCI model and bone marrow-derived macrophage cultures, researchers demonstrated that MD-overloaded macrophages acquire hallmarks of cellular senescence—elevated β-galactosidase activity, DNA damage markers (γH2AX), cell cycle arrest (elevated p21/p16), and a pro-inflammatory senescence-associated secretory phenotype (SASP). Critically, these senescent macrophages showed severely impaired efferocytosis, the process by which immune cells clear apoptotic (dying) neurons. This failure allowed dead neurons to accumulate, amplifying inflammation, promoting astrocytic scar formation, and blocking axonal regeneration—a triple threat to neural repair.

The study then tested exendin-4 (Ex-4), a GLP-1 receptor agonist, as a countermeasure. Ex-4 treatment significantly reduced senescence markers in MD-challenged macrophages, restored their efferocytotic capacity, and reduced neuronal apoptosis and astrocyte activation in co-culture experiments. Mechanistically, Ex-4 activated AMPK phosphorylation, which upregulated Gas6 (growth arrest-specific 6), a secreted protein that binds and activates the Axl receptor on macrophage surfaces—a known efferocytosis checkpoint. Molecular docking and dynamics simulations confirmed direct GLP-1R–AMPK interactions. Macrophage-specific knockdown of Gas6 (via AAV-shRNA driven by an F4/80 promoter) abolished Ex-4's protective effects, confirming this pathway's necessity.

In live mice, Ex-4 administered for seven days post-SCI enhanced remyelination (assessed by MBP staining), supported axonal sprouting (NF200 immunofluorescence), reduced glial scarring (GFAP), and produced measurable improvements in hindlimb motor function on BMS behavioral scoring. Single-cell RNA sequencing analysis of published SCI datasets (GSE162610) corroborated in vivo findings, showing that macrophage clusters at the injury site had elevated senescence-related gene scores and depressed efferocytosis-related gene scores peaking around 3–7 days post-injury.

These findings are significant for the longevity and medicine communities on multiple levels. First, they establish macrophage senescence as a previously overlooked pathological driver of SCI progression—not just an aging phenomenon but an acute stress response triggered by lipid overload. Second, they position GLP-1R agonists, a drug class already widely prescribed for metabolic disease, as candidate neurological therapeutics. Caveats include the exclusive use of male mice, short observation windows, and the lack of pharmacokinetic data on CNS bioavailability of Ex-4.