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2012 ; 61
(9
): 1269-1278
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Induction of dsRNA-activated protein kinase links mitochondrial unfolded protein
response to the pathogenesis of intestinal inflammation
#MMPMID21997551
Rath E
; Berger E
; Messlik A
; Nunes T
; Liu B
; Kim SC
; Hoogenraad N
; Sans M
; Sartor RB
; Haller D
Gut
2012[Sep]; 61
(9
): 1269-1278
PMID21997551
show ga
OBJECTIVE: Inflammatory bowel diseases (IBDs) feature multiple cellular stress
responses, including endoplasmic reticulum (ER) unfolded protein responses
(UPRs). UPRs represent autoregulatory pathways that adjust organelle capacity to
cellular demand. A similar mechanism, mitochondrial UPR (mtUPR), has been
described for mitochondria. ER UPR in intestinal epithelial cells (IECs)
contributes to the development of intestinal inflammation, and since
mitochondrial alterations and dysfunction are implicated in the pathogenesis of
IBDs, the authors characterised mtUPR in the context of intestinal inflammation.
METHODS: Truncated ornithine transcarbamylase was used to selectively induce
mtUPR in a murine IEC line. Dextran sodium sulphate (DSS) was administered to PKR
(double-stranded-RNA-activated protein kinase) knockout mice to induce IEC stress
in vivo and to test for their susceptibility to DSS-induced colitis. Expression
levels of the mitochondrial chaperone chaperonin 60 (CPN60) and PKR were
quantified in IECs from patients with IBDs and from murine models of colitis
using immunohistochemistry and Western blot analysis. RESULTS: Selective mtUPR
induction by truncated ornithine transcarbamylase transfection triggered the
phosphorylation of eukaryotic translation initiation factor (eIF) 2? and cJun
through the recruitment of PKR. Using pharmacological inhibitors and small
inhibitory RNA, the authors identified mtUPR-induced eIF2? phosphorylation and
transcription factor activation (cJun/AP1) as being dependent on the activities
of the mitochondrial protease ClpP and the cytoplasmic kinase PKR. Pkr(-/-) mice
failed to induce CPN60 in IECs upon DSS treatment at early time points and
subsequently showed an almost complete resistance to DSS-induced colitis. Under
inflammatory conditions, primary IECs from patients with IBDs and two murine
models of colitis exhibited a strong induction of the mtUPR marker protein CPN60
associated with enhanced expression of PKR. CONCLUSION: PKR integrates mtUPR into
the disease-relevant ER UPR via eIF2? phosphorylation and AP1 activation.
Induction of mtUPR and PKR was observed in IECs from murine models and patients
with IBDs. The authors' results indicate that PKR might link mitochondrial stress
to intestinal inflammation.