Analysis of Neurogenesis during Experimental Autoimmune Encephalomyelitis Reveals Pitfalls of Bioluminescence Imaging

Abstract

Bioluminescence imaging is a sensitive approach for longitudinal neuroimaging. Transgenic mice expressing luciferase under the promoter of doublecortin (DCX-luc), a specific marker of neuronal progenitor cells (NPC), allow monitoring of neurogenesis in living mice. Since the extent and time course of neurogenesis during autoimmune brain inflammation are controversial, we investigated neurogenesis in MOG-peptide induced experimental allergic encephalomyelitis (EAE) using DCX-luc reporter mice. We observed a marked, 2- to 4-fold increase of the bioluminescence signal intensity 10 days after EAE induction and a gradual decline 1–2 weeks thereafter. In contrast, immunostaining for DCX revealed no differences between EAE and control mice 2 and 4 weeks after immunization in zones of adult murine neurogenesis such as the dentate gyrus. Ex vivo bioluminescence imaging showed similar luciferase expression in brain homogenates of EAE and control animals. Apart from complete immunization including MOG-peptide also incomplete immunization with complete Freund´s adjuvant and pertussis toxin resulted in a rapid increase of the in vivo bioluminescence signal. Blood-brain barrier (BBB) leakage was demonstrated 10 days after both complete and incomplete immunization and might explain the increased bioluminescence signal in vivo. We conclude, that acute autoimmune inflammation in EAE does not alter neurogenesis, at least at the stage of DCX-expressing NPC. Effects of immunization on the BBB integrity must be considered when luciferase is used as a reporter within the CNS during the active stage of EAE. Models with stable CNS-restricted luciferase expression could serve as technically convenient way to evaluate BBB integrity in a longitudinal manner.

Long‐term effects of autoimmune CNS inflammation on adult hippocampal neurogenesis

“…We have previously shown that at the acute phase, the absolute number of DCX 1 cells was not different between EAE and control animals in the dorsal DG (Giannakopoulou et al, 2013), a finding that has already been addressed by others (Ayzenberg et al, 2015). However, in the present study we found that the DCX 1 cells increased in EAE mice during the recovery phase.…”

Animal models of multiple sclerosis: Focus on experimental autoimmune encephalomyelitis

“…This model was proposed to be a functional and valuable tool for monitoring whole‐body in vivo inflammation in various disease models including EAE (Hayashi et al, ; Li et al, ; Yang et al, ). Moreover, bioluminescence imaging was used to track the transplanted human embryonic stem cell–derived oligodendrocyte progenitors and neural stem cells during EAE (Ayzenberg et al, ; Stefferl, Brehm, et al, ). By expressing firefly luciferase under the IL‐6 promoter, Hayashi et al were able to show bioluminescence in the spinal cord and brain in the EAE mice (Hayashi et al, ).…”

“…Although bioluminescence imaging in EAE was recently proposed to have its shortcomings (Ayzenberg et al, ), it may be a valuable tool in animal model research of MS, especially when validated by other tools like magnetic resonance imaging and histology (Guglielmetti et al, ).…”

In vivo bioluminescence imaging of neurogenesis – the role of the blood brain barrier in an experimental model of Parkinson's disease

“…A study using an Experimental Autoimmune Encephalomyelitis (EAE) model in Dcx‐Luc mice already described an increase in BLI signal unrelated to neurogenesis, which followed the same temporal pattern as the opening of the BBB (Ayzenberg et al ., ). Nevertheless, more research is needed to determine the impact of BBB alterations on substrate/tracer availability in different models and diseases.…”