Download contributes to protein aggregation and age

Dysregulation of tissue transglutaminase (TG2) contributes to protein
aggregation and age-related neurodegeneration
Professor M. Griffin (http://www.aston.ac.uk/lhs/staff/az-index/griffinm/)
Dr Russell Collighan (http://www.aston.ac.uk/lhs/staff/az-index/collighr/)
Abstract
Neurodegeneration increases in incidence with age and is related to the accumulation, either
intracellular or extracellular, of insoluble protein aggregates that resist the normal cellular
proteolytic degradation pathways. The protein cross-linking enzyme tissue transglutaminase (TG2)
has been implicated in the formation of aggregates, which contain the unique cross-links
chararcteristic of transglutaminase action[1]. TG2 also acts as a regulatory protein, activating the
transcription factor NF-κB by neutralising its cytosolic binding partner through cross-linking. NF-κB
is an early factor in the initiation of many inflammatory responses and also upregulates expression
of the inflammatory cytokine TGFβ, which, in turn, upregulates TG2. This cycle of events can lead
to stabilisation of protein aggregates and ultimately, neuronal cell death. This project will elucidate
the mechanism of TG2 involvement in this process.
Background
The mechanisms underlying the extensive protein cross-linking observed during normal brain
ageing is still not fully understood but the Ca2+ activated protein crosslinking enzyme, tissue
transglutaminase (TG2) has been implicated in this process[2]. Many stressors may contribute to
TG2 upregulation including mild hypoxia and pro-inflammatory states, which are evident during
normal ageing. TG2 is then thought to activate the transcriptional activator nuclear factor NF-κB by
a mechanism involving polymerisation of the inhibitory NF-κB binding protein, I-kB alpha. This
polymerisation results in dissociation of NF-κB and its translocation to the nucleus where it is
capable of eliciting the expression of a host of genes thought to be involved in the inflammatory
response. NF-κB can also elicit expression of TGFBeta1, a pleiotropic cytokine involved in the
maintenance of the nervous system. TGFBeta1 can also elicit further upregulation of TG2
ultimately leading to protein aggregate formation in the traumatised cell propagating a cascade of
events finally leading to neuronal cell death.
Plan of Work
In this project the student will 1) examine the direct involvement of TG2 in the proposed
mechanism of NF-κB activation using both gel shift and reporter assays. The student will use the
neuroblastoma cell line SH-SY5Y in the first instance. Cells will be stressed either by hypoxic
conditions or by excitotoxic agents as model systems consistent with the ageing process, to
confirm TG2 involvement in NF-κB activation using both site directed-TG2 inhibitors and analysis
of TG2 crosslinked products. 2) The student will then confirm the increased expression and
activation of TGFBeta1 by NF-κB and the subsequent increased expression of TG2 by TGFBeta1.
References
1.
Bailey C, Tucholski J, Johnson G 2005. Transglutaminases in Neurodegenerative
Disorders. In ‘Transglutaminases’, Mehta K, Eckert R (eds). Prog Exp Tum Res. Basel, Karger, vol
38, pp 139-157
2.
Ientile, R; Caccamo, D; Griffin, M. 2007. Tissue transglutaminase and the stress response.
Amino Acids 33 (2): 385-394