Cytosolic TDP-43 expression following axotomy is associated with caspase 3 activation in NFL-/- mice: support for a role for TDP-43 in the physiological response to neuronal injury.
TAR DNA binding protein (TDP-43) mislocalization has been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). We have recently reported that TDP-43 and PGRN expression is altered in response to axotomy in C57BL6 mice and that normal expression is restored following recovery. We have performed axotomies in two different presymptomatic models of motor neuron degeneration, low molecular weight neurofilament knockout (NFL(-/-)) mice and mutant SOD1(G93A) transgenic (mtSOD1(G93A)) mice aged 6 weeks, and observed TDP-43 and PGRN expression patterns in axotomized spinal motor neurons over 28 days. In contrast to both C57BL6 mice and mtSOD1(G93A) mice, behavioural deficits in NFL(-/-) mice were sustained. We did not observe differences in TDP-43 or PGRN expression between C57BL6 mice and mtSOD1(G93A) mice throughout the observation period. However, compared to C57BL6 mice and mtSOD1(G93A) mice, NFL(-/-) mice exhibited late upregulation of cytosolic TDP-43 expression and persistent downregulation of neuronal PGRN expression accompanied by caspase 3 activation on post-injury day 28. By post-injury day 42, no cytosolic TDP-43-positive neurons remained in NFL(-/-) mice, suggesting that they had undergone apoptotic cell death. These findings suggest that whereas TDP-43 expression is normally upregulated transiently following axotomy, in the absence of NFL this response is delayed and associated with caspase 3 activation and neuronal death. These results further support that TDP-43 is involved in neurofilament mRNA metabolism and transport, and provide insight into the pathogenesis of motor neuron death in ALS in which NFL mRNA levels are selectively suppressed.
Moisse
Katie
K
Molecular Brain Research Group, Robarts Research Institute, PO Box 5015, 100 Perth Drive, London ON, Canada.
Mepham
Jennifer
J
Volkening
Kathryn
K
Welch
Ian
I
Hill
Tracy
T
Strong
Michael J
MJ
D000818:Animals; D019771:Axotomy; D053148:Caspase 3 / Q000378:metabolism*; D016923:Cell Death / Q000502:physiology; D003600:Cytosol / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004195:Disease Models, Animal; D005260:Female; D000077155:Granulins; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D016472:Motor Neuron Disease / Q000503:physiopathology; D009046:Motor Neurons / Q000502:physiology*; D009410:Nerve Degeneration / Q000503:physiopathology; D016900:Neurofilament Proteins / Q000235:genetics / Q000378:metabolism*; D000077153:Progranulins; D012333:RNA, Messenger / Q000378:metabolism; D013116:Spinal Cord / Q000503:physiopathology; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism; D000072105:Superoxide Dismutase-1
D004268:DNA-Binding Proteins; D000077155:Granulins; C120204:Grn protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D016900:Neurofilament Proteins; D000077153:Progranulins; D012333:RNA, Messenger; C044882:neurofilament protein L; C000606291:Sod1 protein, mouse; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1; C505409:Casp3 protein, mouse; D053148:Caspase 3