Maternal suboptimal selenium intake and low-level lead exposure affect offspring's microglial immune profile and its reactivity to a subsequent inflammatory hit.

Micronutrients such as selenium (Se) are essentials since prenatal life to support brain and cognitive development. Se deficiency, which affects up to 1 billion people worldwide, can interact with common adverse environmental challenges including (Pb), exacerbating their toxic effects. Exploiting our recently validated rat model of maternal Se restriction and developmental low Pb exposure, our aims were to investigate: (i) the early consequences of suboptimal Se intake and low-Pb exposure on neuroinflammation in neonates' whole brains; (ii) the potential priming effect of suboptimal Se and low-Pb exposure on offspring's glial reactivity to a further inflammatory hit. To these aims female rats were fed with suboptimal (0.04 mg/kg; Subopt) and optimal (0.15 mg/kg; Opt) Se dietary levels throughout pregnancy and lactation and exposed or not to environmentally relevant Pb dose in drinking water (12.5 µg/mL) since 4 weeks pre-mating. We found an overall higher basal expression of inflammatory markers in neonatal brains, as well as in purified microglia and organotypic hippocampal slice cultures, from the Subopt Se offspring. Subopt/Pb cultures were highly activated than Subopt cultures and showed a higher susceptibility to the inflammatory challenge lipopolysaccharide than cultures from the Opt groups. We demonstrate that even a mild Se deficiency and low-Pb exposure during brain development can influence the neuroinflammatory tone of microglia, exacerbate the toxic effects of Pb and prime microglial reactivity to subsequent inflammatory stimuli. These neuroinflammatory changes may be responsible, at least in part, for adverse neurodevelopmental outcomes.

Docosahexaenoic acid promotes oligodendrocyte differentiation via PPAR-γ signalling and prevents tumor necrosis factor-α-dependent maturational arrest.

Docosahexaenoic acid (DHA) is an essential omega-3 fatty acid known to be neuroprotective in several models of human diseases, including multiple sclerosis. The protective effects of DHA are largely attributed to its ability to interfere with the activity of transcription factors controlling immune and inflammatory responses, including the agonist-dependent transcription factor peroxisome proliferator-activated receptor-γ (PPAR-γ). In this study, we used primary oligodendrocyte progenitor (OP) cultures from neonatal rat brain to investigate whether DHA could influence OP maturation and directly promote myelination, as previously reported for selective PPAR-γ agonists. We show that, similarly to the selective PPAR-γ agonist pioglitazone (PGZ), DHA promotes OP maturation and counteracts the maturational arrest induced by TNF-α, used to mimic inflammatory conditions. The PPAR-γ antagonist GW9662 prevented both DHA-induced OP maturation and PPAR-γ nuclear translocation, supporting the hypothesis that DHA acts through the activation of PPAR-γ. In addition, both PGZ and DHA induced the phosphorylation of extracellular signal-regulated-kinase 1-2 (ERK1/2), in a PPAR-γ-dependent manner. ERK1/2 activity is known to regulate the transition from OPs to immature oligodendrocytes and the presence of specific inhibitors of ERK1/2 phosphorylation (U0126 or PD98059) prevented the differentiating effects of both DHA and PGZ. These results indicate that DHA might influence the process of OP maturation through its PPAR-γ agonistic activity and provide novel molecular mechanisms for the action of this dietary fatty acid, further supporting the nutritional intervention in demyelinating diseases such as multiple sclerosis.