Tumor necrosis factor alpha triggers proliferation of adult neural stem cells via IKK/NF-kappaB signaling.
BACKGROUND
Brain inflammation has been recognized as a complex phenomenon with numerous related aspects. In addition to the very well-described neurodegenerative effect of inflammation, several studies suggest that inflammatory signals exert a potentially positive influence on neural stem cell proliferation, migration and differentiation. Tumor necrosis factor alpha (TNF-alpha) is one of the best-characterized mediators of inflammation. To date, conclusions about the action of TNF on neural stem or progenitor cells (NSCs, NPCs) have been conflicting. TNF seems to activate NSC proliferation and to inhibit their differentiation into NPCs. The purpose of the present study was to analyze the molecular signal transduction mechanisms induced by TNF and resulting in NSC proliferation.


RESULTS
Here we describe for the first time the TNF-mediated signal transduction cascade in neural stem cells (NSCs) that results in increased proliferation. Moreover, we demonstrate IKK-alpha/beta-dependent proliferation and markedly up-regulated cyclin D1 expression after TNF treatment. The significant increase in proliferation in TNF-treated cells was indicated by increased neurosphere volume, increased bromodeoxyuridin (BrdU) incorporation and a higher total cell number. Furthermore, TNF strongly activated nuclear factor-kappa B (NF-kappaB) as measured by reporter gene assays and by an activity-specific antibody. Proliferation of control and TNF-treated NSCs was strongly inhibited by expression of the NF-kappaB super-repressor IkappaB-AA1. Pharmacological blockade of IkappaB ubiquitin ligase activity led to comparable decreases in NF-kappaB activity and proliferation. In addition, IKK-beta gene product knock-down via siRNA led to diminished NF-kappaB activity, attenuated cyclin D1 expression and finally decreased proliferation. In contrast, TGFbeta-activated kinase 1 (TAK-1) is partially dispensable for TNF-mediated and endogenous proliferation. Understanding stem cell proliferation is crucial for future regenerative and anti-tumor medicine.


CONCLUSIONS
TNF-mediated activation of IKK-beta resulted in activation of NF-kappaB and was followed by up-regulation of the bona-fide target gene cyclin D1. Activation of the canonical NF-kappaB pathway resulted in strongly increased proliferation of NSCs.
Widera
Darius
D
University of Witten/Herdecke, Stockumer Str, 10, 58448 Witten, Germany. darius.widera@uni-wh.de
Mikenberg
Ilja
I
Elvers
Margitta
M
Kaltschmidt
Christian
C
Kaltschmidt
Barbara
B
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D001973:Bromodeoxyuridine / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D002552:Cerebral Ventricles / Q000166:cytology; D019938:Cyclin D1 / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D020868:Gene Silencing / Q000187:drug effects / Q000502:physiology; D051550:I-kappa B Kinase / Q000235:genetics / Q000378:metabolism*; D007150:Immunohistochemistry / Q000379:methods; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D009457:Neuroglia / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015398:Signal Transduction / Q000187:drug effects*; D013234:Stem Cells / Q000187:drug effects*; D014162:Transfection / Q000379:methods; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D016328:NF-kappa B; D034741:RNA, Small Interfering; D014409:Tumor Necrosis Factor-alpha; D019938:Cyclin D1; D051550:I-kappa B Kinase; D001973:Bromodeoxyuridine