Deficiency in p38β MAPK Fails to Inhibit Cytokine Production or Protect Neurons against Inflammatory Insult in In Vitro and In Vivo Mouse Models

Bin Xing,Adam D Bachstetter,Linda J Van Eldik

doi:10.1371/journal.pone.0056852

Abstract

The p38 MAPK pathway plays a key role in regulating the production of proinflammatory cytokines, such as TNFα and IL-1β, in peripheral inflammatory disorders. There are four major isoforms of p38 MAPK (p38α, β, δ, γ), with p38α and p38β the targets of most p38 MAPK inhibitor drugs. Our previous studies demonstrated that the p38α MAPK isoform is an important contributor to stressor-induced proinflammatory cytokine up-regulation and neurotoxicity in the brain. However, the potential role of the p38β MAPK isoform in CNS proinflammatory cytokine overproduction and neurotoxicity is poorly understood. In the current studies, we used primary microglia from wild type (WT) and p38β knockout (KO) mice in co-culture with WT neurons, and measured proinflammatory cytokines and neuron death after LPS insult. We also measured neuroinflammatory responses in vivo in WT and p38β KO mice after administration of LPS by intraperitoneal or intracerebroventricular injection. WT and p38β KO microglia/neuron co-cultures showed similar levels of TNFα and IL-1β production in response to LPS treatment, and no differences in LPS-induced neurotoxicity. The in vitro results were confirmed in vivo, where levels of TNFα and IL-1β in the CNS were not significantly different between WT or p38β KO mice after LPS insult. Our results suggest that, similar to peripheral inflammation, p38α is critical but p38β MAPK is dispensable in the brain in regards to proinflammatory cytokine production and neurotoxicity induced by LPS inflammatory insult.

Highlights

Neuroinflammation and overproduction of proinflammatory cytokines are implicated in the pathological process of chronic neurodegenerative disorders such as Alzheimer’s disease (AD) and acute trauma such as spinal cord injury
Verification of p38b KO in microglia and brain As a control for our studies, it was important to confirm the deletion of p38b mitogen activated protein kinase (MAPK) in both the microglia cultures and the mouse brain tissue, and determine that significant compensatory changes in the other p38 isoforms were not present
RNA was prepared from primary microglia cultures derived from wild type (WT) or p38b KO mice (Figure 1A), and from lysates of WT and p38b KO mouse cortical tissue (Figure 1B), and the expression levels of the four p38 MAPK isoforms (p38a, p38b, p38d, p38c) were determined by qPCR

Summary

Introduction

Neuroinflammation and overproduction of proinflammatory cytokines are implicated in the pathological process of chronic neurodegenerative disorders such as Alzheimer’s disease (AD) (for recent review see: [1]) and acute trauma such as spinal cord injury (for recent review see: [2]). In terms of inflammatory pathways, the p38a isoform plays a major role in cytokine up-regulation in both CNS inflammatory disorders and peripheral inflammatory diseases [8,9]. Pharmacological inhibition of p38a MAPK in an AD mouse model decreases brain proinflammatory cytokine production, and attenuates synaptic protein loss [10]. Our more recent study further demonstrated that the deficiency of microglial p38a MAPK rescues neurons and reduces synaptic protein loss via suppressing LPS-induced TNFa overproduction [11]. These data demonstrated that microglia p38a MAPK-mediated cytokine overproduction is critical to inflammation-induced neurotoxicity. The role of p38b MAPK in CNS proinflammatory cytokine production and neurotoxicity is poorly understood

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