1-Oleyl-lysophosphatidic acid (LPA) promotes polarization of BV-2 and primary murine microglia towards an M1-like phenotype

Abstract

BackgroundMicroglia, the immunocompetent cells of the CNS, rapidly respond to brain injury and disease by altering their morphology and phenotype to adopt an activated state. Microglia can exist broadly between two different states, namely the classical (M1) and the alternative (M2) phenotype. The first is characterized by the production of pro-inflammatory cytokines/chemokines and reactive oxygen and/or nitrogen species. In contrast, alternatively activated microglia are typified by an anti-inflammatory phenotype supporting wound healing and debris clearance. The objective of the present study was to determine the outcome of lysophosphatidic acid (LPA)-mediated signaling events on microglia polarization.MethodsLPA receptor expression and cyto-/chemokine mRNA levels in BV-2 and primary murine microglia (PMM) were determined by qPCR. M1/M2 marker expression was analyzed by Western blotting, immunofluorescence microscopy, or flow cytometry. Cyto-/chemokine secretion was quantitated by ELISA.ResultsBV-2 cells express LPA receptor 2 (LPA2), 3, 5, and 6, whereas PMM express LPA1, 2, 4, 5, and 6. We show that LPA treatment of BV-2 and PMM leads to a shift towards a pro-inflammatory M1-like phenotype. LPA treatment increased CD40 and CD86 (M1 markers) and reduced CD206 (M2 marker) expression. LPA increased inducible nitric oxide synthase (iNOS) and COX-2 levels (both M1), while the M2 marker Arginase-1 was suppressed in BV-2 cells. Immunofluorescence studies (iNOS, COX-2, Arginase-1, and RELMα) extended these findings to PMM. Upregulation of M1 markers in BV-2 and PMM was accompanied by increased cyto-/chemokine transcription and secretion (IL-1β, TNFα, IL-6, CCL5, and CXCL2). The pharmacological LPA5 antagonist TCLPA5 blunted most of these pro-inflammatory responses.ConclusionsLPA drives BV-2 and PMM towards a pro-inflammatory M1-like phenotype. Suppression by TCLPA5 indicates that the LPA/LPA5 signaling axis could represent a potential pharmacological target to interfere with microglia polarization in disease.

LPA1, LPA2, LPA4, and LPA6 receptor expression during mouse brain development

“…Especially in microglia, LPA 6 receptor shows the highest expression of all LPA receptors. LPA exposure in primary murine microglia leads to a shift toward a proinflammatory M1‐like phenotype . The regulation of microglia polarization (eg, interference of the LPA signal transmission via LPA receptors) could represent a potential pharmacological target of neuroinflammation in the CNS.…”

Antagonizing peroxisome proliferator‐activated receptor γ facilitates M1‐to‐M2 shift of microglia by enhancing autophagy via the LKB1–AMPK signaling pathway

“…Under normal conditions, microglial cells not only provide surveillance of the CNS environment but also respond to danger signals (Crotti & Ransohoff, 2016; Perry & Teeling, 2013). Activated microglial cells undergo morphological transformation (increase in the size of cell bodies and thickness of proximal processes and decreased ramification of distal branches; Plastira et al., 2016; Walker et al., 2014) and secrete pro‐inflammatory cytokines, leading to self‐perpetuating damage to the neurons, also known as the classically activated M1 phenotype. However, an alternatively activated M2 phenotype can be neuroprotective and neurosupportive and can promote recovery.…”

Rosiglitazone polarizes microglia and protects against pilocarpine‐induced status epilepticus

“…Under normal circumstances, microglial cells not only perform immune surveillance but also react to danger signals owing to distinct microglial phenotypes, including proinflammatory M1 and antiinflammatory M2 phenotypes . Activated microglial cells undergo morphological transformation to the M1 phenotype and then secrete proinflammatory cytokines, resulting in self‐perpetuating injury to neurons . The other phenotype, the M2 phenotype, is neuroprotective and can promote recovery .…”

“…[18][19][20] Activated microglial cells undergo morphological transformation to the M1 phenotype and then secrete proinflammatory cytokines, resulting in self-perpetuating injury to neurons. 21,22 The other phenotype, the M2 phenotype, is neuroprotective and can promote recovery. [23][24][25] Microglia-mediated neuroinflammation has dual effects on various brain diseases, and the proinflammatory action of M1 is hypothesized to be the etiologic cause of epileptogenesis.…”