Role of the Chondroitin Sulfate Proteoglycan, Neurocan, in Inhibition of Sensory Neurite Regeneration

In the adult mammalian brain and spinal cord, neuronal injury results in failed neurite regeneration, in part due to the up-regulation of chondroitin sulfate proteoglycans (CSPGs). CSPGs are molecules consisting of a protein core with covalently bound glycosaminoglycans (GAGS), specifically, chondroitin sulfate side-chains. The majority of CSPGs produced after injury originate from reactive astrocytes found in the glial scar surrounding the injury site. Although this milieu is very complex and involves more than just CSPGs, axonal regrowth may be improved if the expression of specific, highly inhibitory CSPGs produced after injury were attenuated selectively. Neurocan is one type of CSPG that is upregulated after injury and inhibits neurite regeneration. The over-arching goal of this study is to focus on the response and growth of sensory neurons in the presence of astrocytes that express neurocan, in relation to those astrocytes in which neurocan has been “knocked down” by shRNA transfection. In order to perform this analysis, the conditions needed for the co-culture experiment of chick astrocytes and chick neurons were optimized. A series of preliminary tests were performed on chick astrocytes, including a test to monitor the upregulation of CSPGs after treatment with Transforming Growth Factor-β (TGF-β), previously shown to mimic injury in an In vitro setting in rat astrocytes (G. Curinga et. al, 2008), and a test to demonstrate that chick astrocytes express Glial Fibrillary Acidic Protein (GFAP) in culture. Through these optimizations, co-culture analysis will be used to evaluate neuronal responses to neurocan. Other techniques used were tissue culture, immunofluorescence, and neurite outgrowth analyses

Novel Influences of Sex and \u3ci\u3eAPOE\u3c/i\u3e Genotype on Spinal Plasticity and Recovery of Function after Spinal Cord Injury

Spinal cord injuries can abolish both motor and sensory function throughout the body. Spontaneous recovery after injury is limited and can vary substantially between individuals. Despite an abundance of therapeutic approaches that have shown promise in preclinical models, there is currently a lack of effective treatment strategies that have been translated to restore function after SCI in the human population. We hypothesized that sex and genetic background of injured individuals could impact how they respond to treatment strategies, presenting a barrier to translating therapies that are not tailored to the individual. One gene of particular interest is APOE, which has been extensively studied in the brain due to its allele-specific influences on synaptic plasticity, metabolism, inflammation, and neurodegeneration. Despite its prominence as a therapeutic target in brain injury and disease, little is known about how it influences neural plasticity and repair processes in the spinal cord. Utilizing humanized mice, we examined how the ε3 and ε4 alleles of APOE influence the efficacy of therapeutic intermittent hypoxia (IH) in inducing spinally-mediated plasticity after cervical SCI. IH is sufficient to enhance plasticity and restore motor function after experimental SCI in genetically similar rodent populations, but its effect in human subjects is more variable (Golder, 2005; Hayes et al., 2014). Our results demonstrate that both sex and APOE genotype determine the extent of respiratory motor plasticity that is elicited by IH, highlighting the importance of considering these clinically relevant variables when translating therapeutic approaches for the SCI community. Significance Statement There is currently a critical need for therapeutics that restore motor and sensory function effectively after cervical spinal cord injury. Although many therapeutic approaches, including intermittent hypoxia, are being investigated for their potential to enhance spinal plasticity and improve motor outcomes after SCI, it is unknown whether the efficacy of these treatment strategies is influenced by individuals’ genetic background. Here we show that APOE genotype and sex both play a role in determining the propensity for motor plasticity in humanized mice after cervical SCI. These results indicate that sex and genetic background dictate how individuals respond to therapeutic approaches, thereby emphasizing the importance of developing personalized medicine for the diverse SCI population