Differential expression of death receptors, their ligands and adaptors as molecular signatures of neuropathologies in a mouse model of prion disease

Abstract

Background Prion diseases are transmissible and fatal neurodegenerative diseases characterized by accumulation of a misfolded form of a host-encoded protein (PrPSc), astrocytosis, microgliosis, spongiosis, and extensive neuron loss. Elevated levels of cell membrane associated PrPSc protein and inflammatory cytokines hint towards the activation of death receptor (DR) pathway/s in prion diseases. However, it is unclear whether prion disease is associated with the alteration of all major death receptors, their ligands and adaptors. Methods C57BL/6J mice were infected with RML scrapie mouse prion strain. Progression of prion disease was evaluated by observing clinical symptoms like motor deficits. Key neuropathologies like PrPSc accumulation and astrocytosis were evaluated by brain blot, western blot and immunofluorohistochemical analysis. To examine the expression of proteins involved in DR pathways, all major death receptors (TNFR1, Fas, DR3, DR5, DR6, p75NTR), their ligands (TNFα, FasL, TL1A, TRAIL and NGF), and adaptors (TRADD, FADD, TRAF2 and RIPK1) were studied by western blot analysis. Glycosylation of DRs was studied by PNGase F treatment followed by western blot analysis. Results Prion infected mice developed motor deficits like plastic tail, frequent circling, hind limb twitching and neuropathologies like prion protein accumulation and astrocytosis similar to other prion diseases. The prion-diseased mice brains exhibit significant increased expression of TNFR1, Fas and p75NTR but reduced ectodomain shedding of TNFR1 and Fas. Results show reduced expression of DR3 and DR5. All DR ligands like TNFα, TL1A, TRAIL, FasL and PrPSc exhibit increased expression except NGF. DR adaptors like TRADD and TRAF2 that primarily regulate pro-survival pathways show reduced expression whereas, FADD expression remained unchanged. The results from RIPK1 demonstrate its increased expression and proteolysis in mouse prion disease. Conclusions The findings from the present study provide evidence towards the involvement of DR3, DR5, DR6, TL1A, TRAIL, TRADD, TRAF2, FADD and RIPK1 for the first time, along with a mechanistic insight into the significance of differential expression of these death receptor factors towards neuropathologies like neurodegeneration, astrocytosis and microgliosis seen in prion diseases.