Functions of Peptidoglycan Recognition Proteins (Pglyrps) at the Ocular Surface: Bacterial Keratitis in Gene-Targeted Mice Deficient in Pglyrp-2, -3 and -4.
OBJECTIVE
Functions of antimicrobial peptidoglycan recognition proteins (Pglyrp1-4) at the ocular surface are poorly understood. Earlier, we reported an antibacterial role for Pglyrp-1 in Pseudomonas aeruginosa keratitis. Here we investigated functions of three other related genes Pglyrp-2, -3 and -4 in a mouse model of P. aeruginosa keratitis.


METHODS
Wild type (WT) and each of the Pglyrp-null genotypes were challenged with P. aeruginosa keratitis. The eyes were scored in a blinded manner 24 and 48h post infection. Viable bacterial counts and inflammatory factors (IL-12, TNF-α, IFN-γ, CCL2, IL-6 and IL-10) were measured in whole eye homogenates using cytometric bead arrays. Expressions of Pglyrp-1-4, mouse beta defensins (mBD)-2,-3, cathelicidin-related antimicrobial peptide (CRAMP) were determined by qRTPCR in total RNA extracts of uninfected and infected eyes of WT and each of the Pglyrp-null mouse types.


RESULTS
The Pglyrp-2-/- mice showed reduced disease and lower induction of pro-inflammatory TNF-α (p = 0.02) than WT or the other Pglyrp null mice. Viable bacterial yield was significantly lower in the Pglyrp-2-/- (p = 0.0007) and the Pglyrp-4-/- (p = 0.098) mice. With regards to expression of these antimicrobial genes, Pglyrp-2 expression was induced after infection in WT mice. Pglyrp-3 expression was low before and after infection in WT mice, while Pglyrp-4 expression was slightly elevated after infection in WT, Pglyrp-2 and -3 null mice. Pglyrp-1 expression was slightly elevated after infection in all genotypes without statistical significance. Transcripts for antimicrobial peptides mBD2, mBD3 and CRAMP were elevated in infected Pglyrp-2-/- males without statistical significance.


CONCLUSIONS
Efficient resolution of keratitis in the Pglyrp-2-/- mice may be due to a reduced pro-inflammatory microenvironment and synergistic antibacterial activities of defensins, CRAMP and Pglyrp-1. Therefore, in ocular infections the pro-inflammatory functions of Pglyrp-2 must be regulated to benefit the host.
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
Ranjita N
RN
Gowda
The Ocular Surface Institute, College of Optometry, University of Houston, Houston, TX, United States of America.
Rachel
R
Redfern
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
Jihane
J
Frikeche
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
Sudarshan
S
Pinglay
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
James William
JW
Foster
The Ocular Surface Institute, College of Optometry, University of Houston, Houston, TX, United States of America.
Carolina
C
Lema
Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
Leslie
L
Cope
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, United States of America; Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD, United States of America; Department of Ophthalmology, Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
Shukti
S
Chakravarti
D000818:Animals; D001424:Bacterial Infections / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D016207:Cytokines / Q000378:metabolism; D019573:Epithelium, Corneal / Q000378:metabolism*; D015870:Gene Expression; D018390:Gene Targeting; D018836:Inflammation Mediators / Q000378:metabolism; D007634:Keratitis / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000235:genetics / Q000378:metabolism*
D002352:Carrier Proteins; D016207:Cytokines; D018836:Inflammation Mediators; C000607986:Pglyrp3 protein, mouse; C000607987:Pglyrp4 protein, mouse; D009238:N-Acetylmuramoyl-L-alanine Amidase; C416533:Pglyrp2 protein, mouse