390 CCL2/CCR2 Signaling Axis Involving Activated Monocyte-Derived Macrophages Causes Spinal Cord Neuroinflammation and Nerve-Motor Pathology after Burn Injury

Infants and young children with major burns suffer with burn-induced systemic inflammation (BISI) and are at high risk of mortality. BISI triggers activation and migration of monocyte-derived macrophages (MD-MΦ). Migration of activated MD-MΦ in the spinal cord can cause neuroinflammation, affecting integrity of motor neurons and nerve-motor function. However, the migration of activated MD-MΦ through the CCL2/CCR2 axis and their effects on neuroinflammation in the spinal cord, leading to motor neurons damage and neuromotor dysfunction after burn injury have not been determined yet. Wild type (WT) and NEF-EYFP mice were used to produce ~25-30% scald burn injury for 1, 7 or 21 days. Cytokines were analyzed by Cytokine Antibody Array. Motor neuronal apoptosis in the spinal cord was identified by TUNEL assay. Nerve termini disintegration in NEF-EYFP mice were analyzed by fluorescent microscopy. Muscle strength in mice was determined by Hanging Wire Test. Our results showed that CCL2 release was significantly increased in the serum (> 2.3 folds) and in OSE (> 2 .4 folds) after burn injury and Ex-His insult, respectively, compared to respective controls. Migration of CCR2-containing MD-MΦ was higher in burned mice, as demonstrated by CCR2 positive cells, than in the sham burned mice. Depletion of MD-MΦ by Clophosomes prevented their migration to the spinal cord. TUNEL assay showed an increase in apoptotic cells and a decrease in EYFP neurons in the spinal cord, suggesting that the motor neuronal cells in the spinal cord were lost by apoptosis compared to non-burned mice. Microscopy showed that the nerve termini at neuromuscular junction were disintegrated after burn injury. Analysis of muscle strength by hanging wire test showed that the latency to fall was increased significantly in BISI (0.86 + 0.8 min) compared to sham burned (1.65 + 0.8 min) mice. Collectively, our results suggest CCL2/CCR2 signaling axis may be responsible for neuroinflammation in the spinal cord, which could lead to motor neuronal damage-associated neuromotor dysfunction. Thus, CCL2/CCR2 signaling axis involving MD-MΦ after burn injury would help us develop therapeutic measures to treat burned children. Dissecting the molecular and cellular mechanisms of neuroinflammation in spinal cord would benefit in clinical settings to understand burn pathology of the spinal cord.