Microglial activation induces cell death, inhibits neurite outgrowth and causes neurite retraction of differentiated neuroblastoma cells

Abstract

Activation of glial cells has been proposed to contribute to neuronal dysfunction and neuronal cell death in Alzheimer's disease. In this study, we attempt to determine some of the effects of secreted factors from activated murine N-11 microglia on viability and morphology of neurons using the differentiated neuroblastoma cell line Neuro2a. Microglia were activated either by lipopolysaccharide (LPS), bacterial cell wall proteoglycans, or advanced glycation endproducts (AGEs), protein-bound sugar oxidation products. At high LPS or AGE concentrations, conditioned medium from microglia caused neuronal cell death in a dose-dependent manner. At sublethal LPS or AGE concentrations, conditioned media inhibited retinoic acid-induced neurite outgrowth and stimulated retraction of already extended neurites. Among the many possible secreted factors, the contribution of NO or NO metabolites in the cytotoxicity of conditioned medium was investigated. Cell death and changes in neurite morphology were partly reduced when NO production was inhibited by nitric oxide synthase inhibitors. The results suggest that even in the absence of significant cell death, inflammatory processes, which are partly transmitted via NO metabolites, may affect intrinsic functions of neurons such as neurite extension that are essential components of neuronal morphology and thus may contribute to degenerative changes in Alzheimer's disease.

(−)‐Epigallocatechin gallate inhibits lipopolysaccharide‐induced microglial activation and protects against inflammation‐mediated dopaminergic neuronal injury

“…Activated microglia release a number of molecules, including free oxygen radicals, NO, and proinflammatory cytokines, such as TNF-␣ and interleukin-1␤, which can synergistically impair neurons (Jeohn et al, 1998). It has been reported that CM from the LPS-or advanced glycation end products (AGEs)-activated microglia caused neuronal cell death and retraction of neurite extension in the differentiated neuroblastoma cell line Neuro2a (Munch et al, 2003). In our study, SH-SY5Y cell injury induced by CM from activated microglia may not be mediated by the LPS in the media, insofar as high concentrations of LPS did not cause detectable cell death (Fig.…”

“…AGEs (Munch et al, 2003), rotenone (Sherer et al, 2003), and many others are potent microglial activators. Very similarly to LPS, these agents induce microglia from a resting to an activated state, resulting in increased generation of free radicals, NO and elevated proinflammatory factors, leading to the neuronal injury and death.…”

SRY-box containing gene 11 (Sox11) transcription factor is required for neuron survival and neurite growth

“…Differentiated Neuro2a cells were quantified using criteria similar to those described in Munch et al (2003). Cells with at least two neurites extending from the soma or one neurite longer than the diameter of the soma were considered differentiated.…”

“…They are easily propagated, they can be stimulated to differentiate by addition of 20μM retinoic acid (RA) and upon differentiation stop dividing and extend neurites (Shea et al, 1985, Sajithlal et al, 2002, Munch et al, 2003, Noguchi et al, 2003. Under culture conditions without RA, Neuro2a cells appear as amoeboid neuroblasts that begin to extend neurites after 1-3d in culture.…”

Cytokine toxicity to oligodendrocyte precursors is mediated by iron

“…Inflammatory processes play a key role in the pathogenesis of the degenerative changes associated with disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS) (Torreilles and Touchon, 2002;Munch et al, 2003). This is particularly well documented for AD and MS (LeVine, 1997), in which inflammatory reactions are associated with glial activation, complement proteins, and other indicators of inflammatory responses (Torreilles et al, 1999;Hoozemans et al, 2002).…”