Fetuin-a in the developing brain

The serum protein fetuin-A is essential for mineral homeostasis and shows immunomodulatory functions, for example by binding to TGF superfamily proteins. It proved neuroprotective in a rat stroke model and reduced lethality after systemic lipopolysaccharide challenge in mice. Serum fetuin-A concentrations are highest during intrauterine life. Different species show intrauterine cerebral fetuin-A immunoreactivity, suggesting a contribution to brain development. We therefore aimed at specifying fetuin-A immunoreactivity in brains of newborn rats (age P0-P28) and human neonates (20-40 weeks of gestation). In humans and rats, fetuin-A was found in cortex, white matter, subplate, hippocampus, subventricular zone, and ependymal cells which supports a global role for brain function. In rats, overall fetuin-A immunoreactivity decreased with age. At P0 fetuin-A immunoreactivity affected most brain structures. Thereafter, it became increasingly restricted to distinct cells of the hippocampus, cingular gyrus, periventricular stem cell layer, and ependyma. In ependymal cells the staining pattern complied with active transependymal transport from cerebrospinal fluid. Double immunofluorescence studies revealed colocalization with NeuN (mature neurons), beta III tubulin (immature neurons), GFAP (astrocytes), and CD68 (activated microglia). This points to a role of fetuin-A in different brain functional systems. In human neonatal autopsy cases, frequently affected from severe neurological and non-neurological diseases, fetuin-A immunoreactivity was heterogeneous and much less associated with age than in healthy tissues studied earlier, suggesting an impact of exogeneous noxious factors on fetuin-A regulation. Further research on the role of fetuin-A in the neonatal brain during physiological and pathological conditions is recommended.