ABSTRACT
OBJECTIVE: Pathological findings in neonatal brain injury associated with preterm birth include focal and/or diffuse white matter injury (WMI). Despite the heterogeneous nature of this condition, reactive astrogliosis and microgliosis are frequently observed. Thus, molecular mechanisms by which glia activation contribute to WMI were investigated. METHODS: Postmortem brains of neonatal brain injury were investigated to identify molecular features of reactive astrocytes. The contribution of astrogliosis to WMI was further tested in a mouse model in genetically engineered mice. RESULTS: Activated STAT3 signaling in reactive astrocytes was found to be a common feature in postmortem brains of neonatal brain injury. In a mouse model of neonatal WMI, conditional deletion of STAT3 in astrocytes resulted in exacerbated WMI, which was associated with delayed maturation of oligodendrocytes. Mechanistically, the delay occurred in association with overexpression of transforming growth factor (TGF)ß-1 in microglia, which in healthy controls decreased with myelin maturation in an age-dependent manner. TGFß-1 directly and dose-dependently inhibited the maturation of purified oligodendrocyte progenitors, and pharmacological inhibition of TGFß-1 signaling in vivo reversed the delay in myelin development. Factors secreted from STAT3-deficient astrocytes promoted elevated TGFß-1 production in cultured microglia compared to wild-type astrocytes. INTERPRETATION: These results suggest that myelin development is regulated by a mechanism involving crosstalk between microglia and oligodendrocyte progenitors. Reactive astrocytes may modify this signaling in a STAT3-dependent manner, preventing the pathological expression of TGFß-1 in microglia and the impairment of oligodendrocyte maturation.
Subject(s)
Astrocytes/metabolism , Brain Injuries/complications , Brain Injuries/pathology , Gliosis/etiology , Myelin Sheath/metabolism , STAT3 Transcription Factor/metabolism , Age Factors , Animals , Animals, Newborn , Astrocytes/chemistry , Astrocytes/drug effects , Benzamides/pharmacology , Benzamides/therapeutic use , Cell Differentiation/drug effects , Cell Differentiation/genetics , Cell Proliferation/drug effects , Cells, Cultured , Culture Media, Conditioned/pharmacology , Dioxoles/pharmacology , Dioxoles/therapeutic use , Disease Models, Animal , Enzyme-Linked Immunosorbent Assay , Female , Gene Expression Regulation, Developmental/drug effects , Glial Fibrillary Acidic Protein/metabolism , Gliosis/drug therapy , Humans , Infant , Infant, Newborn , Lipopolysaccharides/toxicity , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Postmortem Changes , Receptors, Transforming Growth Factor beta/antagonists & inhibitors , STAT3 Transcription Factor/deficiency , Signal Transduction/drug effects , Signal Transduction/genetics , Smad2 Protein/metabolism , Stem Cells/drug effects , Transforming Growth Factor beta1/metabolismABSTRACT
In the intestine, interaction between epithelial cells and macrophages (MΦs) create a unique immunoregulatory microenvironment necessary to maintain local immune and tissue homeostasis. Human intestinal epithelial cells (IECs) have been shown to express interleukin (IL)-10, which keeps epithelial integrity. We have demonstrated that bacterial signaling through Toll-like receptor (TLR) 4 induces 15-deoxy-Δ-12,14-prostaglandin J2 (15d-PGJ2) synthesis in intestinal MΦs by cyclooxygenase (Cox)-2 expression. Here, we show that TLR4 signaling generates crosstalk between IECs and MΦs that enhances IL-10 expression in IECs. Direct stimulation of TLR4 leads to the expression of IL-10 in IECs, while the presence of MΦs in a Transwell system induces another peak in IL-10 expression in IECs at a later time point. The second peak of the IL-10 expression is two times greater than the first peak. This late induction of IL-10 depends on the nuclear receptor peroxisome proliferator-activated receptor (PPAR) γ that is accumulated in IECs by TLR4-mediated inhibition of the ubiquitin-proteasomal pathway. TLR4 signaling in MΦs in turn synthesizes 15d-PGJ2 through p38 and ERK activation and Cox-2 induction, which activates PPARγ in IECs. These results suggest that TLR4 signaling maintains IL-10 production in IECs by generating epithelial-MΦs crosstalk, which is an important mechanism in the maintenance of intestinal homeostasis mediated through host-bacterial interactions.