PKCε induces astrocyte stellation by modulating multiple cytoskeletal proteins and interacting with Rho A signalling pathways: implications for neuroinflammation

Abstract

Despite the importance of stellation to maintain astrocyte functionality, the intracellular signals controlling morphology in these cells are poorly characterized. Our goal was to examine the implication of protein kinase C epsilon (PKCepsilon) in astrocyte stellation. We found that the morphological transformation of astrocytes induced by exposure to the pro-inflammatory agent lipopolysaccharide is enhanced by adenoviral expression of wild-type PKCepsilon, and that activation of PKCepsilon is sufficient to trigger a dramatic stellation. Such an effect is mediated by the rearrangement of microtubules and filaments of glial fibrillary acidic protein, disorganization of stress fibres, and formation of new actin filaments within growing cellular processes. Furthermore, PKCepsilon regulates actin-interacting elements such as non-muscle myosin and proteins of the ezrin/radixin/moesin family. We also observed that at least part of the actions of PKCepsilon depend on its catalytic activity. Finally, stellation by PKCepsilon could be blocked by the expression of a constitutively active form of Rho A implicated in the stability of the flat astrocytic morphology. In summary, PKCepsilon stands out as a key intracellular regulator of morphological plasticity in astrocytes, affecting a large range of cytoskeletal elements and inactivating Rho A-dependent pathways. These morphological effects of PKCepsilon may play essential roles during the course of neuroinflammation.

Astrocytic GAP43 Induced by the TLR4/NF-κB/STAT3 Axis Attenuates Astrogliosis-Mediated Microglial Activation and Neurotoxicity

“…RhoA, another actin polymerization mediator that mediates LPS-induced astrocyte migration (Sato et al, 2011) and MKL1 activation in various cell types (Smith et al, 2013), was also found to affect Slc1a2 gene transcription in a transcriptome analysis of RhoA kinase inhibitor-treated astrocytes . On the contrary, the activation of astrocytic RhoA with injury or chemical insults has been shown to play an adverse role in suppressing astrocyte stellation (Burgos et al, 2007) and exacerbating the inflammatory response (Dusaban et al, 2013) in addition to increasing astrocyte apoptosis (Miñambres et al, 2006). In the present study, astrocytic GAP43 appears to modulate astrogliosis toward beneficial features in various aspects.…”

“…Astrocytic GAP43 knockdown augmented astrogliosisinduced microgliosis and inhibited axonal plasticity Next, we investigated the role of astrocytic GAP43 on the microgliosis and neuronal plasticity, as the actin reorganization is known to be involved in the reactive astrocyte-regulated immune response, synaptic plasticity, and neuronal survival (Tancredi et al, 2000;Haber et al, 2006;Burgos et al, 2007;Strehl et al, 2014). We applied ACM derived from LPS-treated primary astrocytes transfected with Scr or Gap43 siRNA onto primary rat microglia and cortical neurons (Fig.…”

Lipocalin-2 Is an Autocrine Mediator of Reactive Astrocytosis

“…Previously, it was demonstrated that RhoA negatively regulated astrocyte stellation (Suidan et al, 1997;Abe and Misawa, 2003;Chen et al, 2006;Burgos et al, 2007), migration (Höltje et al, 2005), and the IL-1␤-induced reactive astroglial phenotype (John et al, 2004). RhoA activation was, however, required for Thy-1-induced morphological changes in astrocytes that resembled those in brain injuries (Avalos et al, 2004).…”

Protein kinase C as a stress sensor

“…A pro-inflammatory agent lipopolysaccharide (LPS) that induces astrocyte stellation has enhanced activity in the presence of PKCε. This effect is blocked by expression of constitutively active Rho A, demonstrating that PKC activity is important for inactivating Rho A dependent pathways [21]. LPS signaling mechanisms are unclear but recently it was shown that TRAM (Toll-like receptor 4 adaptor molecule) is directly phosphorylated by PKCε on Ser 16 .…”