download report - Istituto Pasteur

P a r t i c i p a n t s :
Luigi Lembo-Fazio, Giulia Nigro, Laura Curcuru’,
Valeria Liparoti, PhD students.
C o l l a b o r a t i o n s :
Department of Immunology, University of Toronto, Toronto,
Canada (Prof. Dana J. Philpott); Facoltà di Medicina Veterinaria,
Università di Camerino (Prof. Giacomo Rossi); Dipartimento di
Chimica Organica e Biochimica, Università di Napoli “Federico II”
(Prof. Antonio Molinaro).
Report of activity
The purpose of this project was to contribute to the
knowledge of the mechanisms relative to PAMP-
PRM recognition and subsequent signaling. In particular,
we planned to investigate on the interaction
of the PRR Nods with their agonist PAMP, peptidoglycan
(PGN). Our aim was to understand how to
modulate the immune response triggered by the
PAMPs of the enteropathogen Shigella in order to
reduce inflammation.
Results and perspectives
A certain number of invariant bacterial structures,
so-called pathogen-associated molecular patterns
(PAMPs), are selectively recognized by the host via
pattern recognition molecules (PRMs), like Toll-like
receptors (TLRs) and nucleotide-binding oligomerization
domain (Nod) molecules (Inohara N, Núñez
G, Nat Rev Immunol. 2003, 3:371-82). Upon interaction
between a specific PAMP and its cognate PRM,
the innate immune system is alerted essentially
through NF-κB activation and subsequent cytokine
production.
Nod proteins are intracellular PRMs that recognize
pathogens in the cytosol through sensing PGN
motifs. In particular, Nod1 recognizes the core
dipeptide structure, (iE-DAP), contained in the
Pathogenetic mechanisms of microbially associated diseases - AREA 2
Role of Shigella surface components in immunomodulation
of the inflammatory response
Principal investigator: Maria Lina Bernardini
Researcher in Cellular Microbiology
Dipartimento di Biologia Cellulare e dello Sviluppo
Tel: (+39) 06 49917850; Fax: (+39) 06 49917994
marialina.bernardini@uniroma1.it
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PGN of Gram-negative bacteria (Girardin SE et al.,
Science 2003, 300:1584-87) and Nod2 recognizes
muramyldipeptide present on PGN of both Gramnegative
and Gram-positive bacteria (Girardin SE et
al., J Biol Chem. 2003, 278:8869-72). Genetic variants
of Nod proteins are associated with inflammatory
disorders, thus reinforcing the link between
bacterial sensing and inflammation.
Dramatic colonic inflammation is the feature of
shigellosis, a human infectious disease caused by the
infection of as few as 100 bacteria of the enteroinvasive
pathogen Shigella spp. Shigellae penetrate the
baso-lateral pole of intestinal epithelial cells (IEC)
through injection of Ipa proteins via a type III secretion
system (TTSS) (Tran Van Nhieu G et al., Cell
Microbiol. 2000, 2:187-93). In IEC, shigellae stimulate
NF-κB activation (Philpott DJ et al., J Immunol.
2000, 165:903-14) upon recognition of iE-DAP by
Nod1 (Girardin SE et al., Science 2003, 300:1584-87).
Following this step, inflammation mounts via the
production of pro-inflammatory cytokines, primarily
IL-8 that stimulates polymorphonuclear leukocyte
recruitment (Philpott DJ et al., J Immunol. 2000,
165:903-14).
However, despite the great number of studies focused
on the interaction of PRMs with PAMPs, it is still
unclear how in epithelial cells, which are not normally
committed to ingest and digest pathogens, Nod1
could physically interact in vivo with PGN, a structure
internal to Gram-negative bacteria envelope.
Several studies have detailed that following PGN
remodeling around 40-50% of PGN is released during
each bacterial generation and approximately
90% of this material accumulates in the periplasm,
from where it is re-imported into the cytoplasm for
recycling.
This project started from the hypothesis that this
process, leading to the release of minimal PGN
products, could contribute to pathogen recognition
by Nod1 during natural infection.
In order to assess the biological role of these PGN