Fig 1: The neurological and cognitive function of TBI rats was improved by CCR2 antagonist (RS504393) or p38 inhibitor (SB203580). (a) The mNSS score of TBI rats decreased after the application of high-dose CCR2 antagonists. (b) The mNSS score of TBI rats decreased after the application of high-dose p38 inhibitor. (c) The escape latency of TBI rats was reduced after the application of a high-dose CCR2 antagonist or p38 inhibitor. (d) The number of platform crossings of TBI rats increased after the application of high-dose CCR2 antagonist or p38 inhibitor. Values are expressed as mean ± SEM (n = 8/group). ***P < 0.001, *P < 0.05 vs. TBI + vehicle group. ###P < 0.001, ##P < 0.01, vs. sham group. TBI, traumatic brain injury; mNSS, modified neurological severity score.
Fig 2: TBI-induced upregulation of CCL2, CCR2, and p-p38 expression in the injured cortex of TBI rats. (a) Expression of CCL2 protein peaks on the third day after TBI, compared to sham group (n = 5/group). (b). Expression of CCR2 protein peaks on the third day after TBI, compared to sham group (n = 5/group). (c) The expression of p-p38 decreased after peaking on the first day after TBI (n = 3/group). Values are expressed as mean ± SEM. ***P < 0.001, **P < 0.01, *P < 0.05 vs. sham group. TBI, traumatic brain injury.
Fig 3: TRAF6 knockdown suppressed CCL2, CCR2, CXCL1, and CXCR2 expression at both mRNA and protein levels in injured cortex after TBI. (A–D) AAV9-TRAF6-RNAi downregulated (A,B) CCL2 and CCR2 mRNA, (C,D) CXCL1 and CXCR2 mRNA, (E,F) CCL2 and CCR2 protein, and (G,H) CXCL1 and CXCR2 protein expression in injured cortex on day 3 post-TBI. *P < 0.05, **P < 0.01, and ***P < 0.001 vs. AAV9-TRAF6-RNAi group. #P < 0.05, ##P < 0.01, and ###P < 0.001 vs. sham group.
Fig 4: Inhibitors of p-NF-κB and MAPKs reduced upregulation of CCL2, CCR2, CXCL1, and CXCR2 following TBI. A 25 mg/10 ml dose of the p-NF-κB inhibitor BAY117082, p-JNK inhibitor PD98059, p-ERK inhibitor SP600125, or p-p38 inhibitor SB203580 reduced CCL2 (A–D), CCR2 (E–H), CXCL1 (I–L), and CXCR2 (M–P) protein expression in the injured cortex as measured by ELISA, while lower doses (2.5 mg/10 ml) had no significant effect. *P < 0.05, **P < 0.01, and ***P < 0.001 vs. high dose group. ###P < 0.001 vs. sham group.
Fig 5: Schematic of the possible mechanism of neuroinflammation following TBI. TRAF6 expression is upregulated after TBI, which activates downstream MAPKs or NF-?B intracellular signaling pathways, induces the expression of chemokines CCL2 and CXCL1, and acts on the corresponding receptors CCR2 and CXCR2, contributes to neuroinflammation, and then leads to pathological changes such as neurologic function injury and nerve cell apoptosis.
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