Altered cell signaling linked to neurodegeneration : Studies on scrapie-infected neuroblastoma cells and activated microglia 

Prion diseases are neurodegenerative disorders that can affect humans and animals. The underlying event is a conformational change of the normal cellular prion protein (PrPC) into an aberrant isoform termed PrP-scrapie (PrPSc). PrPSc is thought to lead to neurodegeneration and activation of glial cells. Scrapie infection of neuroblastoma cells was shown to increase the expression of insulin receptor (IR). Additionally, a marked reduction of 125I-insulin binding sites was observed. Insulin stimulation showed alteration in both IR β-subunit tyrosine phosphorylation and extracellular signal regulated kinase-2 (ERK2) activity. Furthermore, scrapie infection was shown to increase insulin-like growth factor-1(IGF-1) receptor (IGF-1R) expression, although the number of 125I-IGF-1-binding sites was reduced. Also binding affinity of 125I-IGF-1 to its receptor was reduced, and tyrosine phosphorylation of IGF-1R-β-subunit in response to IGF-1 was altered. The increased levels of neurotrophic receptors might represent a neuroprotective response to prion infection. However, scrapie infection instead leads to decreased function, decreased levels of functional receptors, or both, which could promote neurodegeneration in prion diseases, through attenuated neurotrophic support. In BV-2 microglial cells, LPS-induced iNOS (inducible nitric oxide synthase) expression and subsequent NO production were mainly mediated through c-Jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) pathway. Antioxidant treatment indicates that oxidative suppressing mechanism(s) acts on JNK pathway possibly as a regulatory mechanism controlling the NO levels. The JNK pathway was also shown to play an important role in the survival of BV-2 cells. We show that BV-2 cells are protected from ongoing apoptosis by pro-survival activity mediated both by the JNK and p38 MAPK pathway during LPS-induced inflammation. This is very interesting findings since it is important for microglia to respond properly to a pathogen, without themselves being affected and undergo apoptosis