Toll-Like Receptor Ligands and CD154 Stimulate Microglia to Produce a Factor(s) That Promotes Excess Cholinergic Differentiation in the Developing Rat Basal Forebrain: Implications for Neurodevelopmental Disorders

Abstract

Maternal inflammation plays a role in the etiology of certain neurodevelopmental disorders including autism and schizophrenia. Because maternal inflammation can lead to activation of fetal microglia, we have examined effects of inflamed microglia on cultured neural progenitors from rat embryonic septal region and basal forebrain. These cells give rise to cholinergic neurons projecting to cortex and hippocampus. Microglia stimulated with lipopolysaccharide (LPS), peptidoglycan, Poly I:C and CD154 produce conditioned media (CM) that promotes excessive numbers of cholinergic neurons and levels of choline acetyltransferase (ChAT) activity 6 -8 times that of untreated cultures. Expression of the neural-specific transcription factor MATH1 increases substantially within 1 h of plating in LPS-CM. Untreated cultures do not attain equivalent levels until 6 h. By contrast, expression of glial-related transcription factors in LPS-CM-treated cultures never attains the elevated levels of untreated cultures. LPS-CM-treated clones derived from individual progenitors labeled with a LacZ-expressing retrovirus showed Ͼ2.5-fold increase in the percentage of cholinergic cells compared with untreated clones. Thus, CM from activated microglia prompts excess cholinergic differentiation from undifferentiated progenitors suggesting that microglial inflammation during critical stages can lead to aberrant brain development. (Pediatr Res 61: 15-20, 2007)

Maternal inflammation promotes fetal microglial activation and increased cholinergic expression in the fetal basal forebrain: role of interleukin-6

“…Culture studies have demonstrated that factors produced by activated microglia promote cholinergic differentiation of undifferentiated embryonic BF precursor cells (18)(19)(20). Whether MIA results in increased ChAT activity or increased numbers of cholinergic neurons in the fetal BF in vivo has not been investigated.…”

“…Studies from our laboratory and those of others have shown that a cocktail of factors released from stimulated microglia induces cholinergic differentiation of undifferentiated precursors from the mid-gestational basal forebrain (BF) (18)(19)(20). Moreover, activity of choline acetyltransferase (ChAT), the hallmark of cholinergic neurons, is elevated in the BFs of autistic subjects (21), and post-mortem analysis reveals an increased number and an enlargement of cholinergic BF neurons in autistic children (22).…”

“…In BF cultures, an increase in ChAT activity and cholinergic cell number is accompanied by a decrease in message for glutamic acid decarboxylase (GAD)65 (20). To determine whether a similar reduction occurs in vivo, RNA was extracted from E16.5 and P1 BFs of offspring of both saline-and poly(I:C)-injected mice.…”

“…ChAT activity in embryonic BF tissue was assayed as described by us previously (20) following the method of Fonnum (39). In this assay, endogenous ChAT converts Articles Pratt et al…”

TLR8: An Innate Immune Receptor in Brain, Neurons and Axons

“…18 In the CNS, TLR activation was shown to promote cholinergic differentiation from neural progenitors in the developing rat basal forebrain. 19 TLRs on neural progenitor cells (NPCs) were recently demonstrated to be directly involved in regulating adult hippocampal neurogenesis. 20 These observations have extended the function of TLRs in mammals from the realm of immunity to cellular development more generally.…”