Translating TNFR signalling into neuroprotective strategies: Proof of concept in acute in vivo models of neurodegeneration using humanized TNFR mice

Abstract

TNF is involved in several degenerative brain diseases including stroke, Multiple Sclerosis, Parkinson's disease and Alzheimer's disease (AD). It became apparent in recent years that TNFR1 and TNFR2 signalling diverges with respect to its involvement in neurodegeneration and neuroprotection, respectively (Fontaine et al., 2002; Marchetti et al., 2004; Dolga et al., 2008; 2009; Fischer et al., 2011; Naudé et al., 2012; Maier et al., 2013). Under chronic stimulation TNFR2 mediated signalling counteracts TNFR1 mediated pro‐apoptotic pathways by the activation of a PI3K, PKB/Akt dependent NF‐kB signalling pathway. This allows neuronal survival despite exposure to lethal concentrations of neurotoxins such as glutamate (NMDA) or oligomeric forms of Amyloid beta. Both agents are known to be involved in neuronal cell loss in the course of Alzheimer's disease.Consequently in recent years new compounds have been developed that – instead of targeting TNF itself – selectively target TNFR1 or TNFR2 as potential therapeutics in human neurodegenerative diseases. Here we show the results of blocking either human TNFR1 or activating human TNFR2 in a mouse model with humanized TNFRs. For generating humanized TNFR mice we used gene targeting to replace the extracellular domains of the mouse TNFR genes by their human counterpart.Loss of cholinergic innervation is one of the earliest hallmarks in AD, which leads to severe cognitive impairment. Cholinergic neurons project their fibres from the Nucleus Basalis of Meynert (NBM) into the hippocampus and prefrontal cortex. Therefore loss of neurons in the NBM will reduce fibre density in the hippocampus and prefrontal cortex and lead to memory and learning deficits. We have established the NBM lesion model in humanized TNFR mice to investigate in vivo the potential therapeutic role of either TNFR1 antagonists or TNFR2 agonists. By using optical density measurements of stained cholinergic fibres and microglial activation in brain sections we were able to quantify the amount of neuronal cell loss eight days upon delivery of a toxic dose of NMDA into the Nucleus basalis via stereotactic injection. Controlateral NBM damage was used as internal standard. Behavioural testing was performed to assess cognitive function. Our results suggest that both, blocking TNFR1 or activating TNFR2, results in neuroprotection in this acute lesioning model, which serves as a paradigm for neuronal loss in chronic neurodegenerative diseases such as AD.Support or Funding InformationParts of this work was funded by EU FP6 NeuroproMiSe, ZonMW Deltaplan Dementie Memorabel Program, Internationale Stichting Alzheimer Onderzoek, Netherlands, Carl‐Zeiss‐Stiftung, Hertie Stiftung, BMBF, Germany.