The Human ApoE4 Variant Reduces Functional Recovery and Neuronal Sprouting After Incomplete Spinal Cord Injury in Male Mice

Abstract

Spinal cord injury (SCI) is a devastating form of neurotrauma. Patients who carry one or two apolipoprotein E (ApoE)4 alleles show worse functional outcomes and longer hospital stays after SCI, but the cellular and molecular underpinnings for this genetic link remain poorly understood. Thus, there is a great need to generate animal models to accurately replicate the genetic determinants of outcomes after SCI to spur development of treatments that improve physical function. Here, we examined outcomes after a moderate contusion SCI of transgenic mice expressing human ApoE3 or ApoE4. ApoE4 mice have worse locomotor function and coordination after SCI. Histological examination revealed greater glial staining in ApoE4 mice after SCI associated with reduced levels of neuronal sprouting markers. Bulk RNA sequencing revealed that subcellular processes (SCPs), such as extracellular matrix organization and inflammatory responses, were highly ranked among upregulated genes at 7 days after SCI in ApoE4 variants. Conversely, SCPs related to neuronal action potential and neuron projection development were increased in ApoE3 mice at 21 days. In summary, our results reveal a clinically relevant SCI mouse model that recapitulates the influence of ApoE genotypes on post SCI function in individuals who carry these alleles and suggest that the mechanisms underlying worse recovery for ApoE4 animals involve glial activation and loss of sprouting and synaptic activity.

Assessing the impact of boldine on the gastrocnemius using multiomic profiling at 7 and 28 days post-complete spinal cord injury in young male mice

“…The copyright holder for this preprint this version posted August 17, 2022. ; https://doi.org/10.1101/2022.08.17.503230 doi: bioRxiv preprint d after a spinal cord isolation, a surgical procedure that creates an almost electrically silent muscle via spinal cord transection at two levels as well as bilateral dorsal rhizotomy between transection sites (14,55). Moderate to moderate-severe SCI (~50-80 kdyne injury force in mice) does not result in complete paralysis (56)(57)(58)(59). This potential for reloading of muscles in combination with pharmaceuticals has been recently shown to have some efficacy in improving muscle mass and locomotor recovery (57)(58)(59)(60).…”

Boldine modulates glial transcription and functional recovery in a murine model of contusion spinal cord injury

“…Tissue Harvest. At days 14 and 28 post SCI, 5 animals per group (Table1) were randomly selected to undergo perfusion-fixation under a deep anesthesia following an intraperitoneal injection of ketamine (100 mg/kg) and xylazine (30 mg/kg) as previously reported [30]. Briefly, mice were euthanized by transcardial perfusion with sterile saline followed by injection if ice-cold 4% paraformaldehyde (PFA).…”

“…Spinal Cord Injuries. A motor-incomplete contusion SCI was performed using an Infinite Horizons (IH) impactor (Precision Systems and Instrumentation) as previously reported [30]. Briefly, after induction of anesthesia by 3% isoflurane inhalation, animals were placed on heating pads warmed with recirculating water to 37 C. Hair was clipped over the cervical and thoracic spine areas.…”

“…Behavioral Testing. Locomotor recovery after SCI was tested as previously reported [30] using the Basso Mouse Scale (BMS) open-field test [32], and the horizontal ladder rung walk test (LRWT) [33], at specified timepoints (Figure 1). BMS is a well-established method for evaluating the severity of impairments in locomotor function after SCI by scoring locomotor milestones using a 9-point scale, with 0 being completely hindlimb paralysis and 9 being a normal healthy gait.…”

“…Detection of White Spared Matter. Transverse 10-micron sections of perfusion-fixed spinal cords were obtained with a cryostat (Leica) and used for immunofluorescence staining as previously reported [30].…”