ERK1/2 and p38 MAP kinases control prion protein fragment 90–231‐induced astrocyte proliferation and microglia activation

Abstract

Astrogliosis and microglial activation are a common feature during prion diseases, causing the release of chemoattractant and proinflammatory factors as well as reactive free radicals, involved in neuronal degeneration. The recombinant protease-resistant domain of the prion protein (PrP90-231) displays in vitro neurotoxic properties when refolded in a beta-sheet-rich conformer. Here, we report that PrP90-231 induces the secretion of several cytokines, chemokines, and nitric oxide (NO) release, in both type I astrocytes and microglial cells. PrP90-231 elicited in both cell types the activation of ERK1/2 MAP kinase that displays, in astrocytes, a rapid kinetics and a proliferative response. Conversely, in microglia, PrP90-231-dependent MAP kinase activation was delayed and long lasting, inducing functional activation and growth arrest. In microglial cells, NO release, dependent on the expression of the inducible NO synthase (iNOS), and the secretion of the chemokine CCL5 were Ca(2+) dependent and under the control of the MAP kinases ERK1/2 and p38: ERK1/2 inhibition, using PD98059, reduced iNOS expression, while p38 blockade by PD169316 inhibited CCL5 release. In summary, we demonstrate that glial cells are activated by extracellular misfolded PrP90-231 resulting in a proliferative/secretive response of astrocytes and functional activation of microglia, both dependent on MAP kinase activation. In particular, in microglia, PrP90-231 activated a complex signalling cascade involved in the regulation of NO and chemokine release. These data argue in favor of a causal role for misfolded prion protein in sustaining glial activation and, possibly, glia-mediated neuronal death.

Dual Modulation of ERK1/2 and p38 MAP Kinase Activities Induced by Minocycline Reverses the Neurotoxic Effects of the Prion Protein Fragment 90–231

“…Cell viability assays support the hypothesis of a causal role of p38 activation in hPrP90-231-induced cell death, since cell pre-treatment with p38 inhibitor SB203580 abolished hPrP90-231 toxicity. A similar antagonistic activity of ERK1/2 on p38 activation in response to hPrP90-231 was also identified in rat astrocytes and microglia (Thellung et al 2007b;Thellung et al 2007a), possibly representing a common feature by which different brain cell populations respond to abnormally folded, toxic PrP molecules.…”

“…The toxic effects of hPrP90-231 were related to the internalization of the peptide and mediated by b-rich monomers or small oligomers but not by macro-aggregates or amyloid fibrils ). Noteworthy, this peptide was also able to reproduce the PrP Sc effects on astrocytes (proliferation) and microglia (activation), inducing both brain cell populations to release a number of proinflammatory cytokines and chemokines and high levels of NO, which are all known in vivo contributors to the neurodegenerative process (Thellung et al 2007b;Thellung et al 2007a). …”

HIV-1 Nef Induces CCL5 production in astrocytes through p38-MAPK and PI3K/Akt pathway and utilizes NF-kB, CEBP and AP-1 transcription factors

“…The p38MAPK pathway has been demonstrated to mediate the induction of CCL5 in brain cells in response to stimuli as rabies virus56, West Nile Virus57 and the protease-resistant domain of prion protein58. In addition, Nef has been demonstrated to activate p38 in as diverse macrophages59.…”

Cellular prion protein controls stem cell-like properties of human glioblastoma tumor-initiating cells

“…PrP C is considered at the basis of the pathogenesis of prion diseases, in which the fundamental event is its misfolding into a protease-insensitive, amyloidogenic isoform (PrP Sc ) [1]. Misfolded PrP C accumulates in intra- and extracellular deposits as insoluble protein aggregates [2, 3] responsible of neurotoxicity and astrogliosis [4–8]. The conversion of PrP C into PrP Sc consists in a radical modification of its three-dimensional structure and, consequently, of its biochemical and biological properties [9–11].…”