Proteomics of Deep Cervical Lymph Nodes After Experimental Traumatic Brain Injury

Traumatic brain injury (TBI) damages the glymphatic-lymphatic system. We hypothesized that brain injury associated with trauma results in the enrichment of brain-relevant proteins in deep cervical lymph nodes (DCLNs), the end station of meningeal lymphatic vessels, and that some of these proteins will present mechanistic tissue biomarkers for TBI. Proteomes of rat DCLNs were investigated in the left DCLN (ipsilateral to injury) and right DCLN at 6.5 months after severe TBI induced by lateral fluid percussion injury or after sham operation. DCLN proteomes were identified using sequential window acquisition of all theoretical mass spectra. Group comparisons, together with functional protein annotation analyses, were used to identify regulated protein candidates for further validation and pathway analyses. Validation of a selected candidate was assessed using enzyme-linked immunosorbent assay. Analysis comparing post-TBI animals with sham-operated controls revealed 25 upregulated and 16 downregulated proteins in the ipsilateral DCLN and 20 upregulated and 28 downregulated proteins in the contralateral DCLN of post-TBI animals. Protein class and function analyses highlighted the dysregulation of enzymes and binding proteins. Pathway analysis indicated an increase in autophagy. Biomarker analysis suggested that a subgroup of post-TBI animals had an increase in zonula occludens-1 coexpressed with proteins linked to molecular transport and amyloid precursor protein. We propose here that, after TBI, a subgroup of animals exhibit dysregulation of the TBI-relevant protein interactome in DCLNs, and that DCLNs might thus serve as an interesting biomarker source in future studies aiming to elucidate pathological brain functioning.