for aerobic respiration under microaerophilic
conditions, there was no benefit provided by aerobic respiration to S. Typhimurium in wild-type
mice. Hence, depletion of Tregs was not sufficient
for increasing oxygen bioavailability. In contrast,
depletion of Tregs increased oxygen bioavailability
in mice lacking epithelial PPAR-g signaling but not
in wild-type littermate control mice (Fig. 4C and
fig. S6H). Genetic ablation of PPAR-g signaling
combined with Treg depletion phenocopied the effects of streptomycin treatment on the recovery of
avirulent S. Typhimurium strains proficient or deficient for aerobic respiration under microaerophilic conditions (Fig. 4D). Depletion of Tregs
increased epithelial oxygenation in mice lacking
epithelial PPAR-g signaling but not in littermate
control mice (Fig. 3, G and H). Consistent with
metabolic reprogramming toward anaerobic glycolysis, Treg depletion increased intracellular lactate
levels and lowered ATP concentrations in colonocyte preparations from mice lacking epithelial
PPAR-g signaling but not from littermate controls
(Fig. 4, E and F). Measurement of mitochondrial
cytochrome c oxidase activity revealed that Treg
depletion caused a significant (P < 0.001) reduction in oxygen consumption in colonocyte preparations of mice lacking epithelial PPAR-g signaling
but not in littermate control animals (Fig. 4G).
To further study how colonic Tregs and PPAR-g
signaling cooperate to limit respiratory growth
of facultative anaerobic bacteria, mice lacking
epithelial PPAR-g signaling were treated with anti-
CD25 antibody and infected with a 1:1 mixture of
wild-type E. coli and a mutant lacking cytochrome
bd oxidase and nitrate reductases (cydAB napA
narG narZ mutant). The competitive index was
~1000 times greater (P < 0.01) in anti-CD25–
treated mice lacking epithelial PPAR-g compared
with wild-type littermate control animals (Fig. 4H).
Similar results were obtained when mice were
infected with individual bacterial strains (fig. S6I).
The emerging picture is that epithelial hypoxia
maintains anaerobiosis in the colon to drive the
microbial community toward a dominance of
obligate anaerobes, which produce short-chain
fatty acids. In turn, short-chain fatty acids sus-
tain Tregs and epithelial PPAR-g signaling, which
cooperatively drives the energy metabolism of
colonocytes toward b-oxidation of microbiota-
derived butyrate to preserve epithelial hypoxia,
thereby closing a virtuous cycle maintaining ho-
meostasis of a healthy gut. PPAR-g signaling also
activates expression of b-defensins, which might
contribute to shaping the intestinal environment
(25). An antibiotic-induced lack of epithelial
PPAR-g signaling and a contraction of the Treg
pool cooperatively drive a metabolic reorienta-
tion of colonocytes toward anaerobic glycolysis,
thereby increasing epithelial oxygenation and
consequently elevating oxygen bioavailability to
promote an expansion of Enterobacteriaceae
(fig. S1), a common marker of dysbiosis (1). Thus,
an expansion of Enterobacteriaceae in the gut-
associated microbial community is a microbial
signature of epithelial dysfunction, which has
important ramifications for targeting PPAR-g
signaling as a potential intervention strategy.
REFERENCES AND NOTES
1. N. R. Shin, T. W. Whon, J. W. Bae, Trends Biotechnol. 33,
2. A. M. Spees et al., mBio 4, e00430-13 (2013).
3. F. Rivera-Chávez et al., Cell Host Microbe 19, 443–454
4. S. E. Winter et al., Science 339, 708–711 (2013).
5. D. R. Donohoe et al., Cell Metab. 13, 517–526 (2011).
6. R. Marion-Letellier, M. Butler, P. Déchelotte, R. J. Playford,
S. Ghosh, Am. J. Clin. Nutr. 87, 939–948 (2008).
7. M. Lefebvre et al., J. Endocrinol. 162, 331–340 (1999).
8. S. Alex et al., Mol. Cell. Biol. 33, 1303–1316 (2013).
9. M. Vital, A. C. Howe, J. M. Tiedje, mBio 5, e00889-14
10. K. Atarashi et al., Nature 500, 232–236 (2013).
11. C. J. Kelly et al., Cell Host Microbe 17, 662–671
12. G. T. Furuta et al., J. Exp. Med. 193, 1027–1034
13. M. N. Xavier et al., Cell Host Microbe 14, 159–170
14. N. Terada, N. Ohno, S. Saitoh, S. Ohno, Histochem. Cell Biol.
128, 253–261 (2007).
15. S. Kizaka-Kondoh, H. Konse-Nagasawa, Cancer Sci. 100,
16. K. M. Maslowski et al., Nature 461, 1282–1286 (2009).
574 11 AUGUST 2017 • VOL 357 ISSUE 6351 sciencemag.org SCIENCE
Fig. 4. Microbiota-induced PPAR-g
signaling and Tregs
cooperate to limit the
oxygen in the colon.
(A and B) Groups of mice
(N = 4) were treated
with streptomycin (A) or
with anti-CD25 antibody
(B), and CD3+-enriched
live colonic cells were
analyzed for expression of
CD4 and FOXP3 by flow
cytometry. (C) Groups
of mice (N = 6) were
treated with anti-CD25
antibody or isotype
control and, 10 days later,
were inoculated with a 1:1
mixture of an avirulent
Salmonella strain (invA
spiB mutant) and an
strain lacking cytochrome
bdII oxidase (invA spiB
cyxA mutant). (D) Groups
(N = 6) of streptomycin-treated or mock-treated
mice were inoculated with Salmonella indicator strains and received supplementation with tributyrin or a community of 17 human Clostridia isolates (C17).
(C and D). The CI was determined 4 days after inoculation. (E to G) Groups of
mice (N = 6) were treated with anti-CD25 antibody or isotype control antibody,
and colonocytes were isolated to measure intracellular concentrations of lactate
(E), ATP (F), or mitochondrial cytochrome c oxidase activity (G). (G) The width of
the box shows the interquartile range, the horizontal line shows the median, and the
top and bottom lines show the highest and lowest values, respectively. (H) Groups
(N = 6) of anti-CD25–treated mice lacking epithelial PPAR-g signaling or
untreated wild-type mice (WT) were infected with a 1:1 mixture of the indicated
E. coli strains. The CI was determined 4 days after inoculation. (A, B, E, and F) Bars
represent geometric means ± SE. (C, D, and H) Each circle represents data
from an individual animal, and black bars represent geometric means. *P < 0.05;
**P < 0.01; ***P < 0.001; ns, not statistically significantly different.