Expression Profile and Role of EphrinA1 Ligand After Spinal Cord Injury

Abstract

Spinal cord injury (SCI) triggers the re-expression of inhibitory molecules present in early stages of development, contributing to prevention of axonal regeneration. Upregulation of EphA receptor tyrosine kinases after injury suggest their involvement in the nervous system's response to damage. However, the expression profile of their ephrinA ligands after SCI is unclear. In this study, we determined the expression of ephrinA ligands after contusive SCI. Adult Sprague-Dawley female rats were injured using the MASCIS impactor device at the T10 vertebrae, and levels of ephrinA mRNA and protein determined at different time points. Identification of the cell phenotype expressing the ephrin ligand and colocalization with Eph receptors was performed with immunohistochemistry and confocal microscopy. Behavioral studies were made, after blocking ephrinA1 expression with antisense (AS) oligonucleotides, to assess hindlimb locomotor activity. Real-time PCR demonstrated basal mRNA levels of ephrin (A1, A2, A3, and A5) in the adult spinal cord. Interestingly, ephrinA1 was the only ligand whose mRNA levels were significantly altered after SCI. Although ephrinA1 mRNA levels increased after 2 weeks and remain elevated, we did not observe this pattern at the protein level as revealed by western blot analysis. Immunohistochemical studies showed ephrinA1 expression in reactive astrocytes, axons, and neurons and also their colocalization with EphA4 and A7 receptors. Behavioral studies revealed worsening of locomotor activity when ephrinA1 expression was reduced. This study suggests that ephrinA1 ligands play a role in the pathophysiology of SCI.

Evidence That the EphA2 Receptor Exacerbates Ischemic Brain Injury

“…We found that isolated cortical neurons do indeed express the EphA2 receptor and its ligands (ephrin-A1–A3) (Fig. 5A, B, C, D, E and F), and that expressions of ephrin-A1 and ephrin-A3 was greater than that of ephrin-A2 in these cells, consistent with previous reports [5], [6], [23]. Furthermore, expression of all four proteins appeared to be increased in primary cortical neurons following 24 h of glucose deprivation (GD) in vitro (Fig.…”

“…These findings are particularly relevant for ischemic stroke, in which damage to cerebral endothelium and disruption of tight junctions leads to altered blood-brain barrier (BBB) permeability, contributing to post-stroke inflammation and edema. In addition, expression of both the EphA2 receptor and ephrin-A1 are known to be upregulated in various models of CNS injury [5], [6], [23]. However, it is unknown whether the EphA2 receptor plays a role in stroke-induced BBB breakdown and injury.…”

Replicating infant astrocyte behavior in the adult after brain injury improves outcomes

“…Here we reveal that age-dependent ephrin-A1 treatment on reactive astrocytes post-injury leads to reduced glial scar severity observed in infants following a brain injury [10], contributing to improved neuronal sparing. This is supported by prior evidence that reactive astrocyte-associated ephrin-A1 signaling contributes to functional recovery after spinal cord injury in rodents [21]. Additionally, ephrin-A1 signaling can be recapitulated following brain injury in adults to attenuate scarring and improve outcomes.…”

“…For example, ephrin-A1 and -A5 treatment elicited identical outcomes in both human and marmoset astrocytes in vitro, which differed from that observed in rodents [38]. Our conclusions highlight that ephrin-A1 signaling on reactive astrocytes [21] is required for improved functional recovery after CNS injury. Importantly the rh-ephrin-A1-fc infusion tempered rather than abrogated glial scarring in adults, providing further evidence that glial scarring is a necessary component and prerequisite to repair [12].…”

“…A wealth of evidence has linked these guidance cues with the pathophysiology and pathogenesis of CNS injury. Specifically, Eph/ ephrin signaling is a crucial regulator of astrocyte reactivity in rodents [20][21][22][23][24], nonhuman primates [10,25] and human [26]. Furthermore, the Eph/ ephrins have been the target of a number of preclinical treatment studies [27,28].…”