ComEA-mCherry protein, which is indicative of
DNA translocation into the periplasm ( 6) of a predator cell (Fig. 4 and figs. S13 and S14). Similar gene-transfer events were never or only rarely observed
in the T6SS-negative strain; in the presence of
extracellular deoxyribonuclease; if the predator
lacked the outer membrane secretin protein PilQ,
which is required for efficient DNA uptake ( 5, 6);
or in the absence of any prey (figs. S14 and S15).
Our findings indicated that the T6SS of V.
cholerae is part of the competence regulon and
is induced on chitinous surfaces in a TfoX-,
HapR-, and QstR-dependent manner, thereby
enhancing HGT (Fig. 5). HGT plays a major
role in bacterial evolution and contributes to
the spread of antibiotic resistance cassettes and
pathogenicity islands. Moreover, because chitinous
zooplankton are thought to play an important
role in cholera transmission in endemic regions (1),
chitin-induced expression of the T6SS might also
enhance the virulence potential of the pathogen
due to the killing of commensal bacteria within
the human gut.
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We thank A. Boehm, M. Miller, members of the Institut National
de Recherche Biomédicale of the Democratic Republic of the
Congo, and M. Lo Scrudato for providing V. cholerae strains.
We also acknowledge the service provided by Microsynth and
members of the Blokesch laboratory for scientific discussions.
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Materials and Methods
Figs. S1 to S15
Tables S1 to S5
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15 August 2014; accepted 1 December 2014
Dermal adipocytes protect against
invasive Staphylococcus aureus
Ling-juan Zhang,1 Christian F. Guerrero-Juarez,2, 3 Tissa Hata,1 Sagar P. Bapat, 4
Raul Ramos,2, 3 Maksim V. Plikus,2, 3 Richard L. Gallo1*
Adipocytes have been suggested to be immunologically active, but their role in host
defense is unclear. We observed rapid proliferation of preadipocytes and expansion of
the dermal fat layer after infection of the skin by Staphylococcus aureus. Impaired
adipogenesis resulted in increased infection as seen in Zfp423nur12 mice or in mice given
inhibitors of peroxisome proliferator–activated receptor g. This host defense function
was mediated through the production of cathelicidin antimicrobial peptide from adipocytes
because cathelicidin expression was decreased by inhibition of adipogenesis, and
adipocytes from Camp−/− mice lost the capacity to inhibit bacterial growth. Together, these
findings show that the production of an antimicrobial peptide by adipocytes is an
important element for protection against S. aureus infection of the skin.
Host defense against microbial infection in- volves the participation of several cell types. Owing to the rapid doubling time of many microbes, immediate protection provided by local resident cells—such as epithelial
cells, mast cells, and resident leukocytes—is essential to restrict the spread of infection during
the lag period before recruitment of additional
cells, such as neutrophils and monocytes (1, 2).
The production of antimicrobial peptides (AMPs)
by local resident cells and recruited leukocytes is
a key mechanism to limit pathogen growth ( 3–5).
Staphylococcus aureus is a major cause of skin
and soft-tissue infections in humans, causing both
local and systemic disease ( 6, 7). We observed that
a large and previously unrecognized expansion
of the subcutaneous adipose layer was evident
during the early response to S. aureus skin in-
fection (Fig. 1A). The response to infection was
confirmed with quantification of the abundance
of adipocytes (Fig. 1B and fig. S1A), observations
of an increase in lipid staining (fig. S1B), and
increased activation of the adiponectin promoter
as measured in AdipoQcre;R26R mice (Fig. 1C)
( 8). Adipocytes progressively increased in size
after S. aureus infection (Fig. 1B), suggesting that
the expansion of dermal adipose tissue occurs at
least in part through hypertrophy of mature ad-
ipocytes. PREF1 and ZFP423 mark committed
preadipocytes required for adipose tissue de-
velopment and expansion ( 9–11). Proliferation
of these preadipocytes at the site of infection
was further confirmed with colocalization of
PREF1 and ZFP423 with proliferation markers
BrdU (Fig. 1D and fig. S1C) and Ki67 (fig. S1D).
Additionally, dermal cells isolated from S. aureus–
infected skin exhibited greater adipogenic po-
tential than that of cells isolated from the same
amount of uninfected skin, as indicated by lipid
production and induction of adipocyte markers
Adipoq and Fabp4 in response to adipocyte dif-
ferentiation medium (Fig. 1E and fig. S1E). Also
supporting the conclusion that infection results
in an increase of cells within the dermis with the
potential to differentiate into adipocytes were
observations of an increase of mRNA and protein
for transcription factors driving preadipocyte
differentiation, including Cebpb, Pparg, and Cebpa
(Fig. 1F and fig. S1, D and F) ( 12, 13). Peroxisome
proliferator–activated receptor–g (PPARg)–positive
cells at the infected sites were negative for CD11b
(fig. S1G), confirming that they were not myeloid
cells. To test that cell proliferation was associated
with adipocyte formation, we examined BrdU
1Division of Dermatology, University of California, San Diego
(UCSD), La Jolla, CA 92093, USA. 2Department of
Developmental and Cell Biology, Sue and Bill Gross Stem
Cell Research Center, University of California, Irvine, Irvine,
CA 92697, USA. 3Center for Complex Biological Systems,
University of California, Irvine, Irvine, CA 92697, USA.
4Nomis Foundation Laboratories for Immunobiology and
Microbial Pathogenesis, The Salk Institute for Biological
Studies, San Diego, La Jolla, CA 92037, USA.
*Corresponding author. E-mail: email@example.com