Abstract
Scrapie infection, which converts cellular prion protein (PrPC) into the pathological and infectious isoform (PrPSc), leads to neuronal cell death, glial cell activation and PrPSc accumulation. Previous studies reported that PrPC regulates RhoA/Rho-associated kinase (ROCK) signaling and that connexin 43 (Cx43) expression is upregulated in in vitro and in vivo prion-infected models. However, whether there is a link between RhoA/ROCK and Cx43 in prion disease pathogenesis is uncertain. Here, we investigated the role of RhoA/ROCK signaling and Cx43 in prion diseases using in vitro and in vivo models. Scrapie infection induced RhoA activation, accompanied by increased phosphorylation of LIM kinase 1/2 (LIMK1/2) at Thr508/Thr505 and cofilin at Ser3 and reduced phosphorylation of RhoA at Ser188 in hippocampal neuronal cells and brains of mice. Scrapie infection-induced RhoA activation also resulted in PrPSc accumulation followed by a reduction in the interaction between RhoA and p190RhoGAP (a GTPase-activating protein). Interestingly, scrapie infection significantly enhanced the interaction between RhoA and Cx43. Moreover, RhoA and Cx43 colocalization was more visible in both the membrane and cytoplasm of scrapie-infected hippocampal neuronal cells than in controls. Finally, RhoA and ROCK inhibition reduced PrPSc accumulation and the RhoA/Cx43 interaction, leading to decreased Cx43 hemichannel activity in scrapie-infected hippocampal neuronal cells. These findings suggest that RhoA/ROCK regulates Cx43 activity, which may have an important role in the pathogenesis of prion disease.
Highlights
Prion disease, a form of transmissible spongiform encephalopathy, is characterized by progressive neuronal degeneration caused by conformational changes in the cellular prion protein (PrPC) into a misfolded and aggregated form (PrPSc), which accumulates in the brain [1,2,3,4]
RhoA and Rho-associated kinase (ROCK) inhibition reduced PrPSc accumulation and the RhoA/connexin 43 (Cx43) interaction, leading to decreased Cx43 hemichannel activity in scrapie-infected hippocampal neuronal cells. These findings suggest that RhoA/ROCK regulates Cx43 activity, which may have an important role in the pathogenesis of prion disease
PrPC has been reported to contribute to neuronal differentiation in various neuronal cell lines by promoting neurite sprouting, extension, stability, and plasticity of neuronal polarity [7], which may depend on interactions with various proteins, including neural cell adhesion molecules (NCAMs) [8,9], heparan sulfate proteoglycans (HSPGs) [10,11], stress-inducible protein-1 (STI1) [12], growth factor receptor-bound protein 2 (Grb2) [13], caveolin [14], extracellular matrix (ECM) proteins [15,16], and RhoA [17,18]
Summary
A form of transmissible spongiform encephalopathy, is characterized by progressive neuronal degeneration caused by conformational changes in the cellular prion protein (PrPC) into a misfolded and aggregated form (PrPSc), which accumulates in the brain [1,2,3,4]. The pathological symptoms of prion disease are distinguished by its transmissibility, characteristic spongiform changes associated with synapse dysfunction, axon retraction and loss of neuronal polarity preceding neuronal cell loss, astrocytosis and amyloid plaque formation, and the prolonged incubation period between exposure and symptom onset. These changes lead to the release of inflammatory molecules, including proinflammatory cytokines, reactive oxygen species, proteases, and complement proteins that induce neuronal damage and removal of damaged cells [5,6]. ROCK activation and ROCK-3-phosphoinositide-dependent kinase 1 (PDK1) complex formation contribute to the regulation of neuronal polarity and the generation of pathogenic prions [6]
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