CX3CR1 deficiency aggravates brain white matter injury and affects expression of the CD36/15LO/NR4A1 signal

Abstract

Objective: To study the effects of CX3CR1 on white matter injury, neurofunction, recognition, and expression of the CD36/15LO/NR4A1 signal in mice with traumatic brain injury (TBI).

Methods: CX3CR1^GFP/GFP, CX3CR1^GFP/+ and C57BL/6 male mice were randomly divided into 3 groups. We used a controlled cortical impact (CCI) to establish a TBI model and T2wt MRI to detect the TBI lesion. FA and DTI allowed for quantitative evaluation of the structural integrity of white matter tracts. Several behavior tests were used to investigate nerve function; a computer-based tracing system was used to trace and analyze dendrites and cell bodies of microglia and astrocytes in the peri-lesional brain areas. We also used RT-PCR and western blot to detect the effect of CX3CL1/CX3CR1 axis on CD36/15LO/NR4A1 signal.

Results: The fractional anisotropy (FA) at the corpus callosum area of brain was decreased at 3 days post TBI, the average lesion volume CX3CR1^GFP/GFP group was increased, and the neurologic deficit scores of mice of Cx3Cr1^GFP/+ and wild-type groups were significantly increased compared to Cx3Cr1^GFP/GFP group mice. In the Corner turn test, TBI induced impairments in forelimb function that were more severe than Cx3Cr11^GFP/+ and wild-type TBI mice. We operated the Y-maze at 3 days post-TBI and the NOR test at 28 days after TBI. There was a significant TBI effect induced in decreased percentage entries into the novel arm in Cx3Cr1^GFP/+ and wild-type TBI mice, compared with Cx3Cr1^GFP/GFP; Cx3Cr1^GFP/+. Wild-type mice showed decreased exploration time in new objects compared with Cx3Cr1^GFP/GFP. Those two behavior tests demonstrated that Cx3Cr1 knock-out increased the damage caused by TBI to memory. In the tail suspension and force swimming tests, there was no significant difference between those three groups. CD36 increased in Cx3Cr1^GFP/GFP compared with the other three groups at 3 days after TBI. TBI inhibited the expression of NR4A1 at 3 d after damage. Cx3Cr1 deficiency can induce high expression of 15LO, this was unaffected by TBI.

Conclusion: CX3CR1 deletion can enhance white matter injury. It increased the expression of CD36 and 15LO and increased expression of NR4A1. The lack of CX3CR1 can affect the recovery of nerve function.

Keywords: CX3CR1(GFP/GFP); TBI; The fractional anisotropy (FA); White matter injury.