Astrocytes promote TNF-mediated toxicity to oligodendrocyte precursors

Abstract

Neuroinflammation and increased production of tumor necrosis factor (TNF) in the CNS have been implicated in many neurological diseases including white matter disorders periventricular leukomalacia and multiple sclerosis. However, the exact role of TNF in these diseases and how it mediates oligodendrocyte injury remain unclear. Previously, we demonstrated that lipopolysaccharide (LPS) selectively kills oligodendrocyte precursors (preOLs) in a non-cell autonomous fashion through the induction of TNF in mixed glial cultures. Here, we report that activation of oligodendroglial, but not astroglial and microglial, TNFR1 is required for LPS toxicity, and that astrocytes promote TNF-mediated preOL death through a cell contact-dependent mechanism. Microglia were the sole source for TNF production in LPS-treated mixed glial cultures. Ablation of TNFR1 in mixed glia completely prevented LPS-induced death of preOLs. TNFR1-expressing preOLs were similarly susceptible to LPS treatment when seeded into wildtype and TNFR1 Using an in vitro model for inflammatory injury to preOLs, we demonstrated that LPS induces selective preOL death indirectly by activating microglia (Li et al. , 2008. We further identified that peroxynitrite underlies the potent direct killing capability of activated microglia and that astrocytes can shift the killing mechanism to one dependent on TNF signaling (Li et al. 2008). However, neither the cellular source for TNF production nor the TNF receptor mediating preOL death was identified. As primary glial cells all express TNF receptors (Dopp et al. 1997), they can all engage in TNF signaling. Here, we systematically dissected the cellular source for TNF production, determined the TNF receptor required for LPS toxicity, and further identified an essential role for oligodendroglial TNFR1 in TNF-mediated killing of preOLs in mixed glial cultures. Most importantly, we provided the first evidence demonstrating that astrocytes sensitize preOLs to TNF toxicity in a contact-dependent manner. Materials and methodsAnimals and reagents Wildtype B6.129SF2/J and C57BL/6J mice, transgenic eGFP mice (003291, background C57BL/6J), and TNF (background B6.129SF2/J) and TNFR1 (background C57BL/6J) knockout mice were obtained from the Jackson Laboratory (Bar Harbor, ME, USA). Recombinant TNF was obtained from R&D Systems (Minneapolis, MN, USA). Platelet-derived growth factor and basic fibroblast growth factor were from PeproTech (Rocky Hill, NJ, USA). Recombinant green fluorescent protein (GFP) adenovirus was from Gene Transfer Vector Core, University of Iowa. Rabbit polyclonal antibodies against Iba1 were purchased from Wako Chemicals (Richmond, VA, USA). Rat anti-mouse TNF (clone MP6-XT22) was obtained from eBioscience (San Diego, CA, USA). Olig2 antibody was a generous gift from Dr. Richard Lu (University of Texas Southwestern Medical Center). Lactate dehydrogenase (LDH) cytotoxicity kit was from Roche Applied Science (Indianapolis, IN, USA). Unless specified otherwise, all other reagents were from Sigma (St. Lou...

Direct and Indirect Effects of Immune and Central Nervous System–Resident Cells on Human Oligodendrocyte Progenitor Cell Differentiation

“…Indeed, TNF-a was demonstrated to cause degeneration of oligodendrocytes in the MS brain (4,24). Previous reports suggested that TNF-a inhibits survival and differentiation of OPCs in a model of spinal cord injury (SCI) (25), enhances oxidative stress-induced oligodendrocyte apoptosis (26), and mediates oligodendrocyte cell death through a TNFR1-dependent mechanism (27). Although our data support the previous work implicating TNF-a as a key cytokine that can dramatically influence oligodendrocyte biology (Fig.…”

General Control Nonderepressible 2 (GCN2) Kinase Protects Oligodendrocytes and White Matter during Branched-chain Amino Acid Deficiency in Mice

“…Oxidative stress and pro-inflammatory cytokines are found to contribute to demyelination and axonal damage in cultured cerebellar cells and promote oligodendrocyte progenitor cell death in microglia treated with LPS (46,47). It is also reported that microglia and astrocytes produce and secrete TNF␣, inhibiting the survival and differentiation of oligodendrocyte precursor cells (48,49). Consistent with these reports, a marked increase in Tnf␣ mRNA level was detected in GBDK brains, suggesting a proinflammatory environment.…”

Activation of oligodendroglial Stat3 is required for efficient remyelination

“…Mixed glial cultures and oligodendrocyte precursor cells (OPCs) were isolated with the differential attachment method as described previously (Chen et al, 2007; Kim et al, 2011; Li et al, 2008). In brief, the brains of P1–2 rat or mouse pups were isolated and placed in ice cold HBSS, followed by meninges removal under a dissection microscope.…”