Activation of the JNK–c‐Jun pathway during the early phase of neuronal apoptosis induced by PrP106–126 and prion infection

Abstract

Prion diseases are neurodegenerative pathologies characterized by apoptotic neuronal death. Although the late execution phase of neuronal apoptosis is beginning to be characterized, the sequence of events occurring during the early decision phase is not yet well known. In murine cortical neurons in primary culture, apoptosis was first induced by exposure to a synthetic peptide homologous to residues 106-126 of the human prion protein (PrP), PrP106-126. Exposure to its aggregated form induced a massive neuronal death within 24 h. Apoptosis was characterized by nuclear fragmentation, neuritic retraction and fragmentation and activation of caspase-3. During the early decision phase, reactive oxygen species were detected after 3 h. Using immunocytochemistry, we showed a peak of phosphorylated c-Jun-N-terminal kinase (JNK) translocation into the nucleus after 8 h, along with the activation of the nuclear c-Jun transcription factor. Both pharmacological inhibition of JNK by SP600125 and overexpression of a dominant negative form of c-Jun significantly reduced neuronal death, while the MAPK p38 inhibitor SB203580 had no effect. Apoptosis was also studied after exposure of tg338 cortical neurons in primary culture to sheep scrapie agent. In this model, prion-induced neuronal apoptosis gradually increased with time and induced a 40% cell death after 2 weeks exposure. Immunocytochemical analysis showed early c-Jun activation after 7 days. In summary, the JNK-c-Jun pathway plays an important role in neuronal apoptosis induced by PrP106-126. This pathway is also activated during scrapie infection and may be involved in prion-induced neuronal death. Pharmacological blockade of early pathways opens new therapeutic prospects for scrapie PrP-based pathologies.

Cellular pathogenesis in prion diseases

“…Misfolded monomers or oligomeric intermediates appear to be the more probable toxic species. This is consistent with recent data indicating that smaller subfibrillar particles with a mass equivalent to [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] PrP molecules are the most infectious moiety and may be much more toxic than larger amyloid fibrils or plaques [113].…”

Induction of ligand-specific PrPCsignaling in human neuronal cells

“…Specifically, the dual requirement for conversion to PrP Sc , as well as the association with lipid rafts suggest a subversion of the normal function of PrP C upon misfolding to PrP Sc that involves distortion of signaling events. 12 Subsequent investigations of PrP C and PrP Sc from the perspective of signaling analysis have implicated a number of intracellular kinases and signaling pathways including: Sarcoma (Src), 13 mitogen activated protein kinase (MAPK), 14,15 phosphoinositide-3 kinase (PI3K)/RAC-α series/threonine protein kinase (Akt), 16 c-Jun N-terminal kinase (JNK), 17 and extracellular signal-regulated kinase (Erk). 18 While these investigations strongly indicate that PrP influences the intracellular kinase environment there is no consensus on the specific mechanism and consequences.…”

“…A central challenge to understanding the molecular basis of TSEs is determining whether the The PrP 106-126 peptide fragment has been widely utilized as an experimental ligand to model prion effects and this made it an ideal stimulant of PrP C signaling. 17,[20][21][22][23][24] In addition, 6H4 is a well-characterized, commercially-available monoclonal antibody for PrP C . Prion protein specific antibody has been utilized to "activate" PrP C through direct binding for investigations of PrP C function.…”

Comparison of abnormal isoform of prion protein in prion-infected cell lines and primary-cultured neurons by PrPSc-specific immunostaining

“…In the previous reports using prion-infected primary cultured neurons, antimitotics were used throughout the culture period to suppress the growth of astrocytes (Carimalo et al, 2005;Cronier et al, 2007;Hannaoui et al, 2013), and some of them confirmed the neuronal predominance with astrocytes at 4 -5 % of the cellular composition at an early stage (Cronier et al, 2004). However, antimitotics will be harmful to neurons depending on concentrations and the period of treatment.…”