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PHYSIOLOGY 27: 148 –155, 2012; doi:10.1152/physiol.00003.2012
Hedgehog Signaling and Maintenance
of Homeostasis in the Intestinal Epithelium
Homeostasis of the rapidly renewing intestinal epithelium depends on a
balance between cell proliferation and loss. Indian hedgehog (Ihh) acts as a
Nikè V. J. A. Büller,
Sanne L. Rosekrans,
Jessica Westerlund,
and Gijs R. van den Brink
Tytgat Institute for Liver and Intestinal Research, Department of
Gastroenterology & Hepatology, Academic Medical Center,
Amsterdam, The Netherlands
[email protected]
negative feedback signal in this dynamic equilibrium. We discuss recent
evidence that Ihh may be one of the key epithelial signals that indicates
epithelial integrity to the underlying mesenchyme.
148
negative feedback signal to the underlying mesenchyme. Loss of this signal not only activates an
epithelial proliferative response but also activates a
mesenchymal immune response.
The Hedgehog Pathway
Three Hedgehog genes exist in mouse and man,
Sonic hedgehog (Shh), Indian hedgehog (Ihh),
and Desert hedgehog (Dhh) (10). Hedgehog proteins are produced as a 45-kDa precursor protein, which is cleaved and lipid modified to
generate an active 19-kDa NH2-terminal fragment that is responsible for all signaling (5, 18,
26). Dispatched (Disp) is required for release of
Hedgehog from the cell membrane (6, 14, 20).
Once released, Hedgehogs bind to Patched
(Ptch) (7, 22, 27), a 12-transmembrane receptor
that does not convey the Hedgehog signal to the
intracellular components of the pathway itself
like a conventional receptor. Rather, binding of
Hedgehog to Ptch alleviates the inhibitory effect
of Ptch on another membrane receptor, the seven-transmembrane protein Smo (FIGURE 2) (1,
28, 34). Cdo, Boc, and Gas1 are co-receptors that
interact with Ptch, facilitate binding, and positively regulate signaling (30, 40, 43). All aspects of
Hedgehog signaling are mediated via the glioblastoma (Gli) transcription factors Gli1, Gli2,
and Gli3 (2). Processing of Gli2 and Gli3 from
repressor to activator is believed to occur in the
primary cilium, although the mechanism has not
been entirely resolved. Gli2 acts mainly as a transcriptional activator, whereas Gli3 can also be
processed into a transcriptional repressor (25,
38). In the context of gut development, however,
both Gli2 and Gli3 seem to act mainly as an
activator since Gli2 and Gli3 are the main mediators of the Hedgehog signal (15, 23, 24). Several
transcriptional targets of the Hedgehog pathway
are more or less universal and independent of
the tissue or target cell type. Ptch1, Ptch2, Gli1,
and Hedgehog-interacting protein (Hhip) can be
used as readouts of pathway activity.
1548-9213/12 ©2012 Int. Union Physiol. Sci./Am. Physiol. Soc.
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The intestinal epithelium consists of a single layer
of highly specialized cells (FIGURE 1) that serve to
digest our food and absorb water and nutrients. At
the same time, this thin layer is the major barrier
that separates us from the large variety of microorganisms present in the lumen of the gut. Under
homeostatic conditions, there is a remarkable stability in the turnover time of the differentiated
epithelial cells. However, the balance between the
two compartments of differentiated and proliferating cells is a dynamic equilibrium. In conditions of
inflammation or epithelial damage, the compartment of proliferating cells can rapidly expand, and
the rate of epithelial proliferation is substantially
increased. For a large part, this proliferative response probably serves to rapidly replace damaged
epithelial cells. However, it has also been shown
that the increased proliferation in response to inflammatory mediators may serve to expulse parasites that attempt to colonize the intestinal
epithelium (8).
Dynamic equilibria between different compartments exist by virtue of the presence of negative
feedback loops. Such signaling circuits must exist
in rapidly regenerating homeostatic tissues such as
the epithelia of the gastrointestinal tract and the
skin. This would mean that differentiated cells secrete signals that negatively regulate the size of the
precursor cell compartment, the rate of proliferation, or both. If differentiated cells are lost by damage or infection, the signal is diminished and
proliferation is enhanced to regenerate the epithelium. As the differentiated cells increase again in
numbers, so does the negative feedback signal
that will restore proliferation in the precursor
cell compartment to its normal rate. This line of
reasoning predicts that wound healing responses
are controlled by the size of the differentiated
cell compartment and the negative feedback signals that are normally secreted from this
compartment.
Here, we will review the role of Hedgehog signaling in the adult intestine. We will discuss recent
evidence demonstrating that Indian hedgehog
(Ihh) derived from the superficial epithelium is a
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Hedgehog Signaling Is From
Epithelium to Mesenchyme in the
Adult Intestine
Ihh is the main Hedgehog expressed in the small
intestine (3, 35) and colon (32, 36). Low levels of
Shh may be expressed at the base of the small
intestinal and colonic crypts (33, 36, 37). These
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levels are difficult to detect; therefore, it is not clear
whether any protein is expressed, and the role of
Shh in adult intestinal homeostasis (if any) remains to be determined. Careful analysis of Hedgehog targets Ptch1 and Gli1 by in situ hybridization
(3, 16, 35, 36) and using various reporter mice (16)
has shown that Hedgehog signaling is exclusively
paracrine in the adult intestine, from the epithelium to the mesenchyme. These studies have
shown that Hedgehog responsive cells consist
mainly of smooth muscle precursor cells, differentiated smooth muscle cells, myofibroblast-like
cells, and pericytes. In addition, it was found that
there are also LacZ-positive Cd11b and Cd11c cells
(16), suggesting that intestinal macrophages and
dendritic cells may directly respond to Hedgehog
signaling. Thus mesenchymal cells such as smooth
muscle cells and myofibroblast-like cells are the
main Hedgehog responsive cells, but the innate
immune system is a potential alternative target of
the pathway.
Hedgehog Signaling Regulates
Homeostasis of Intestinal
Mesenchymal Cells
FIGURE 1. Crypt-villus compartment
In the adult intestine, stem cells reside in the bottom of
the crypt and give rise to transit amplifying cells. These
cells either move downward to form Paneth cells (only
in the small intestine) or upward to form the other intestinal cell lineages.
Hedgehog signaling regulates the growth and specification of the gut tube mesenchyme during development (31). Several experiments have shown
that Hedgehog signaling is also a key factor in the
homeostasis of mesenchymal cells in the adult intestine. Accumulation of mesenchymal cells resulted when Hedgehog signaling was increased
using two different strategies. One approach used
Rosa26CreERT2-Ptch1fl/fl mice in which the Hedgehog pathway can be conditionally activated in a
body-wide fashion upon injection of tamoxifen
(36). In these mice, an accumulation of ␣-Sma
positive cells was observed in the mesenchyme.
For another approach, Villin-Ihh transgenic mice
were made, in which Ihh was overexpressed under
the control of a 12.4-kBa intestine-specific villin promoter. These mice displayed an accumulation of
smooth muscle precursors (desmin⫹, ␣-Sma⫺), differentiated smooth muscle cells (desmin⫹, ␣Sma⫹),
and myofibroblast-like cells (desmin⫺, ␣Sma⫹) (42).
Experiments in which Hedgehog signaling was
conditionally lost in the adult intestine have shown
that Hedgehog signaling is not only sufficient to
expand mesenchymal cells but also required to
maintain the existing smooth muscle cells and
myofibroblast-like cells. One model combined two
different 12.4-kBa villin promoter transgenes, the
Villin-Cre and a Villin-LacZfl/fl-Hhip⌬TM (41, 42).
In this latter mouse model, Cre-mediated removal
of the LacZ cassette results in a frame shift leading
to the translation of the soluble Hedgehog inhibitor Hhip. Although the Villin-Cre is active from
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precursor cells and complete loss of the villus
core support structure.
Hedgehog Signaling Regulates the
Size of the Crypt Compartment
Ihh is produced by differentiated cells in the adult
colon (32, 36) and small intestine (35). Several lines
of evidence indicate that Ihh acts as a negative
feedback signal to the proliferating cells in the
crypt (FIGURE 3). The first experiments with blocking Hedgehog signaling were performed using anti-Hedgehog monoclonal antibody 5E1 (39) or by
overexpression of Hhip under control of the 12.4kBa villin promoter in developing mice (21). In
both experiments, this resulted in a substantial
expansion of the proliferating cell compartment
and aberrant localization of crypt-like foci of proliferating cells on the small intestinal villi at birth.
This indicated that Hedgehog signaling might negatively regulate epithelial proliferation and crypt
size in adult mice. The question remained, however, which Hedgehog was being blocked, since
both 5E1 and Hhip block all Hedgehogs. We found
that in Ihh⫺/⫺ mice, which survived until embryonic day 16.5, the epithelium of the colon failed to
organize into crypts with superficial non-proliferating cells but remained a multilayered proliferating epithelium (32). An analysis of later time points
in development could be performed in Villin-CreIhhfl/fl mice in which Ihh was specifically deleted
FIGURE 2. Hedgehog pathway
A model of interaction between receptors Smo and Ptch. A: in the absence of Hedgehog Ptch functions to inhibit
the signaling receptor Smo. B: binding of Hedgehog to Ptch alleviates the suppression of Smo and results in activation of the pathway.
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embryonic day 12.5, the combination of the transgenes reportedly leads to delayed induction of
Hhip expression, and mice are born without apparent histological abnormalities. In the double
transgenic Hhip⌬TM mouse, a progressive loss of
smooth muscle cells and an accumulation of
smooth muscle precursor cells were found (42).
When the same authors cultured embryonic day
18.5 mesenchyme in the absence of Hedgehog
(which is derived from the epithelium and therefore absent from cultured mesenchyme), they observed an accumulation of smooth muscle precursor
cells. These precursor cells differentiated into
smooth muscle cells and myofibroblast-like cells after treatment with recombinant Hedgehog (42).
A similar observation was made in Cyp1a1CreIhhfl/fl mice that we generated (35). In these mice,
Ihh was conditionally deleted from the intestinal
epithelium in adult mice. In a time series after
deletion, we found that 2 wk after loss of Ihh both
desmin and ␣-Sma-positive cells changed their
elongated appearance to adopt a spherical shape.
We subsequently observed a sequential loss of first
␣-Sma (at 2 wk) and then desmin expression (between 2 and 4 mo) from the villus core.
In conclusion, Hedgehog signaling is both sufficient for the expansion of intestinal mesenchymal cells and necessary to maintain their
homeostasis. The analysis of Ihh mutant mice
suggests that prolonged loss of Ihh signaling ultimately also results in loss of smooth muscle
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from the intestinal epithelium during intestinal development (17). This resulted in the same phenotype as the 5E1 anti-Hedgehog antibody treated
and Villin-Hhip mice, showing that Ihh is mainly
responsible for the negative regulation of the size
of the crypt compartment.
To examine the role of Hedgehog signaling in
crypt size compartment regulation in adult animals, we initially treated adult rats with the Smo
antagonist cyclopamine. In these rats, we found an
expansion of BrdU-positive proliferating cells (32).
We later used a conditional genetic approach to
confirm this negative regulation of the precursor
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cell compartment in adult mice. We used both the
Rosa26CreERT2-Ptch1fl/fl mice in which Hedgehog
signaling can be activated and Cyp1a1Cre-Ihhfl/fl
mice in which Ihh signaling can be lost conditionally. Analysis of these mice confirmed the role of
Ihh signaling in the negative regulation of the size
of the crypt compartment in adult mice under
homeostatic conditions. Interestingly, when studying different time points after recombination in
Ihh mutant mice, we observed progressive lengthening of crypts. On the other hand, we found that
crypt fissioning, a mechanism of crypt multiplication through budding and elongation, was only
transiently induced at 2 wk after recombination.
The crypt fissioning stopped when the crypts had
reached an increased density at 1 mo after recombination (35). This indicates that, in addition to
restraining crypt proliferation and length, Ihh controls a signal that maintains crypt spacing and
prevents crypt fissioning under homeostatic conditions. A second, Ihh-independent signal must be
present to prevent further crypt fissioning when
crypt spacing is progressively reduced.
One of the situations in which expansion of the
intestinal precursor cell compartment is induced is
in case of a massive small bowel resection. These
resections induce both crypt lengthening and fissioning in the remainder of the intestine via an
unknown mechanism. Interestingly, it was shown
that massive small bowel resection results in a
remarkable reduction in the expression of Ihh and
almost complete loss of Hedgehog signaling as
measured by the expression of Hedgehog targets in
the remaining intestine (29). Given the fact that it
has been demonstrated in Ihh mutant mice that
loss of Ihh induces epithelial changes very similar
to those observed after massive small bowel resection, it may well be that loss of Ihh expression is
responsible for the adaptive response to intestinal
resection.
In conclusion, Ihh is a signal that limits the
size of the precursor cell compartment in the
crypt. Ihh also prevents crypt fissioning under
homeostatic conditions, but there are additional
unidentified levels of regulation of the rate of
crypt fissioning that stop fissioning when crypt
spacing is reduced.
Hedgehog Induced Mesenchymal
Signals That Control Epithelial
Proliferation
FIGURE 3. Link between Hedgehog and Wnt
signaling
Proposed model of negative feedback signaling in the
intestinal epithelial crypt. Ihh secreted by differentiated
epithelial cells acts on mesenchymal cells, which secrete factors that subsequently negatively regulate
stem cells at the base of the crypt, possibly through
Bmp and Activin signaling.
Since Hedgehog signaling is exclusively from the
epithelium to the mesenchyme, this implies that a
mesenchymal derived factor controls epithelial
proliferation and stem cells in response to Hedgehog signaling.
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Hedgehog Signaling Suppresses a
Lamina Propria Immune Response
Polymorphisms in the GLI1 gene have been associated with the risk to develop inflammatory
bowel disease (IBD) (19). The rs2228226C to G
variant associated with the development of IBD
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is a missense mutation, which encodes a change
from glutamine to glutamic acid (Q1100E) in the
COOH terminus of GLI1 near the transactivation
domain and is present in 30% of healthy controls.
Odds ratios for the homozygous presence of the
Q1100E variant were 1.56, 1.79, and 1.41 for all IBD,
Crohn’s disease, and ulcerative colitis, respectively.
It should be noted, however, that the association
with this SNP has not subsequently been replicated
in the various genome-wide association screens
(GWAS), nor has any other component of the
Hedgehog pathway been associated with IBD in
these screens.
It was shown that Q1100E is a hypomorphic
variant as it shows lower transcriptional activity
than the more prevalent allele. In addition to
studying the association of GLI1 with human IBD,
the authors used Gli1 mutant mice in an experimental model of colitis (19). Gli1 heterozygous or
even homozygous mutant mice have no evident
phenotype. The authors then exposed Gli1⫹/lacZ
heterozygous animals to dextrane sodium sulfate
(DSS), a chemical that activates an innate immune
response by causing damage to the epithelial barrier. They found that DSS-treated Gli1 heterozygotes show more severe colitis and an exaggerated
cytokine response. Since the animals had a LacZ
inserted into the Gli1 knockout allele, the cells
responding to Hedgehog signaling in the uninflamed and DSS-treated intestine could be identified by their LacZ positivity. The authors observed
LacZ positivity in both Cd11b- and Cd11c-positive
cells, suggesting that macrophages and/or dendritic cells may respond directly to Hedgehog
signaling.
In an elegant follow-up study (41), the Gumucio
laboratory found further evidence for the important role of Ihh derived from the epithelium in
suppressing an inflammatory response of the mesenchyme. When primary mesenchymal cells were
cultured for 48 h in the absence of epithelium, a
loss of Hedgehog signaling was observed. When
these cultures were then retreated with Hedgehog,
the major class of downregulated genes were proinflammatory cytokines such as Il-1␤, Il-6, and a
variety of chemokines. These data clearly indicated
that epithelium-derived Ihh is required to continuously repress a proinflammatory response of the
underlying mesenchyme.
In conclusion, signaling by epithelium-derived
Ihh is required to suppress an inflammatory response by the underlying mesenchyme. Reduced
signaling by Gli1 may be associated with human
IBD, exaggerates the immune response, and aggravates disease in the DSS model of intestinal epithelial damage.
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Bone morphogenetic proteins (Bmp) and activins are part of the Tgf-␤ family. In the normal
colon, Bmp signaling acts mainly on the differentiated enterocytes in the upper half of the crypt
(12). We found that activation of Hedgehog signaling in the Rosa26CreERT2-Ptch1fl/fl mouse resulted
in increased expression of Bmps in the mesenchyme and expanded the range of Bmp signaling
from the top toward the base of the crypt (36).
Since Bmps negatively regulate intestinal epithelial
proliferation (12) and seem to restrict the number
of stem cells in the crypt (11, 13), this could be one
of the important Hedgehog-regulated signals that
controls the size and activity of the epithelial precursor cell compartment. However, since Bmp signaling occurs mainly in the differentiated cells
under homeostatic conditions, it is difficult to understand how loss of Ihh could result in increased
proliferation. We therefore examined the expression pattern of the phosphorylated form of Smads2
and 3 that acts downstream of Tgf-␤/activin signaling. We found that pSmad1,5,8 and pSmad2,3
are expressed in remarkable, non-overlapping patterns in the small intestine, with pSmad2,3 being
expressed specifically in the proliferating cells in
the crypts (35). Both pSmad1,5,8 and pSmad2,3
expression were almost completely lost in Ihh
mutant animals, suggesting that they depend on
Ihh-regulated mesenchymal factors. We found
that loss of pSmad2,3 did not correlate with loss
of Tgf-␤ expression but with loss of activin expression (35). These data suggest that Ihh may
control the expression of both Bmps and activins
in the intestinal mesenchyme and that both contribute to the negative regulation of intestinal
precursor cells. It should be noted, however, that
the cell types expressing the different activin
subunits have not been carefully mapped in the
intestine and that the role of activin signaling in
the intestinal epithelium has not been studied in
vivo. Also, it is clear that additional Ihh controlled mesenchymal factors are likely to exist
that have not yet been identified.
In conclusion, pSmad2,3 and pSmad1,5,8 display non-overlapping expression patterns in the
intestinal epithelium and are both dependent on
Ihh-regulated mesenchymal factors. Bmps control
the activity of Smad1,5,8, and activins are important candidate intermediates in the regulation of
Smad2,3 phosphorylation.
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Does Loss of Hedgehog Signaling
Result in a Celiac Disease Like
Phenotype?
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Both Ihh conditional mutant mice and Hhip overexpressing mice showed crypt hyperplasia, villous
atrophy, and mucosal inflammation, which are
hallmarks of the histopathology of celiac disease
(FIGURE 4). In patients with celiac disease, T cells
respond aberrantly to gliadins, resulting in a rapid
destruction of the villi of the small intestine with
subsequent crypt hyperplasia to replace the damaged surface epithelium. However, studies in human volunteers with celiac disease have shown
that villus atrophy occurs within hours of a gluten
challenge and that damage to the villus epithelial
cells is the primary event, with a secondary compensatory increase of crypt size and proliferation
(4, 9). On the other hand, in both Ihh mutant and
Hhip-overexpressing mice, the proliferative response preceded the development of villous atrophy, and villous atrophy took several months to
develop. Also, one of the hallmarks of celiac disease and diagnostic criteria is the presence of increased numbers of intraepithelial T cells. In
contrast, in Ihh mutant animals, we observed a loss
of intraepithelial T cells. On the basis of these
essential differences, we would therefore conclude
that, although there is some superficial similarity
between the histopathology of Hh mutant intestine
and celiac disease, the underlying pathophysiological mechanism is completely different.
It remains remarkable, however, that Hhip overexpressing mice frequently developed dermatitis
with IgA deposits (41). This is similar to the dermatitis herpetiformis that is observed in patients
with celiac disease and could suggest that such
dermatitis is the result of a breech in the duodenal
mucosal barrier and not specific to celiac disease.
Thus, although the histological image several
months after loss of Hedgehog signaling is in some
aspects reminiscent of celiac disease, we feel that it
has a very different etiology and is most likely the
result of loss of mesenchymal cells from the villus
core, which seem to be required to anchor villi to
the intestinal tube. In our hands, the overt influx of
inflammatory cells follows the loss of villi and,
therefore, seems to be a consequence and not a
cause of villous atrophy.
crypt fissioning. The epithelial phenotype observed
after loss of Ihh is highly similar to the epithelial
response to wound healing. Indeed, in addition to
the epithelial remodeling, we observed a marked influx of both macrophages and fibroblasts, the two
major mesenchymal cell types that are recruited during a wound-healing response, 2 wk after recombination (35). Together, these data suggest that loss of
Ihh is sufficient to activate major aspects of a woundhealing response such as activation of an immune
response, epithelial remodeling, and recruitment of
fibroblasts and macrophages in the absence of any
damage to the epithelial layer. Thus the loss of Ihh
expression, which results from damage or dysfunction of the superficial epithelial layer, may be one of
the major mechanisms that triggers a wound-healing
response in the underlying mesenchyme. Ihh may
therefore serve as a major signal to indicate superficial epithelial integrity to the underlying mesenchyme.
Conclusions
Research over the past years has clearly established
that the role of Hedgehog signaling is not restricted
to intestinal development but that it is an important factor in the maintenance of homeostasis of
the adult small intestine and colon. Ihh is produced by the superficial epithelium and signals to
the underlying mesenchyme where it targets
smooth muscle cells, myofibroblast-like cells, and
possibly also myeloid cells. Ihh seems to be a key
signal emitted by the superficial epithelium to indicate its integrity. Loss of this signal is in itself
sufficient to trigger not only a wound-healing response with activation of an epithelial repair program and influx of fibroblast and macrophages but
also activates a mesenchymal immune response.
Several key questions remain. What are the factors
that drive Ihh expression and why is its expression
almost completely lost upon massive small bowel
resection? What is the exact nature of the mesenchymal factors that activate the epithelial repair
Loss of Ihh Activates Multiple
Aspects of a Wound Healing
Response
As discussed above, Ihh is produced by the superficial epithelium, suppresses a lamina propria immune response, and controls mesenchymal factors
that negatively regulate epithelial proliferation and
FIGURE 4. Loss of Ihh leads to inflammation and villous atrophy
Compared with wild-type animals, the duodenum of Ihh mutant mice shows severe
enteritis with infiltrating immune cells and blunting of villi. Crypts showed increased
length and crypt fissioning.
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No conflicts of interest, financial or otherwise, are declared by the author(s).
Author contributions: N.V.B., S.L.R., and G.R.V.D.B.
prepared figures; N.V.B., J.W., and G.R.V.D.B. drafted
the manuscript; N.V.B., S.L.R., J.W., and G.R.V.D.B. edited and revised the manuscript; N.V.B., S.L.R., J.W.,
and G.R.V.D.B. approved the final version of the
manuscript.
References
1.
Alcedo J, Ayzenzon M, Von OT, Noll M, Hooper JE. The
Drosophila smoothened gene encodes a seven-pass membrane protein, a putative receptor for the hedgehog signal.
Cell 86: 221–232, 1996.
2.
Altaba A. Gli proteins encode context-dependent positive
and negative functions: implications for development and
disease. Development 126: 3205–3216, 1999.
3.
Batts LE, Polk DB, Dubois RN, Kulessa H. Bmp signaling is
required for intestinal growth and morphogenesis. Dev Dyn
235: 1563–1570, 2006.
4.
Bramble MG, Zucoloto S, Wright NA, Record CO. Acute
gluten challenge in treated adult coeliac disease: a morphometric and enzymatic study. Gut 26: 169 –174, 1985.
5.
Bumcrot DA, Takada R, McMahon AP. Proteolytic processing
yields two secreted forms of sonic hedgehog. Mol Cell Biol
15: 2294 –2303, 1995.
6.
Caspary T, Garcia-Garcia MJ, Huangfu D, Eggenschwiler JT,
Wyler MR, Rakeman AS, Alcorn HL, Anderson KV. Mouse
dispatched homolog1 is required for long-range, but not
juxtacrine, Hh signaling. Curr Biol 12: 1628 –32, 2002.
7.
Chen Y, Struhl G. Dual roles for patched in sequestering and
transducing hedgehog. Cell 87: 553–563, 1996.
8.
Cliffe LJ, Humphreys NE, Lane TE, Potten CS, Booth C,
Grencis RK. Accelerated intestinal epithelial cell turnover: a
new mechanism of parasite expulsion. Science 308: 1463–
1465, 2005.
9.
Dissanayake AS, Jerrome DW, Offord RE, Truelove SC,
Whitehead R. Identifying toxic fractions of wheat gluten and
their effect on the jejunal mucosa in coeliac disease. Gut 15:
931–946, 1974.
10. Echelard Y, Epstein DJ, St-Jacques B, Shen L, Mohler J,
McMahon JA, McMahon AP. Sonic hedgehog, a member of a
family of putative signaling molecules, is implicated in the
regulation of CNS polarity. Cell 75: 1417–1430, 1993.
11. Haramis AP, Begthel H, van den Born M, van Es J, Jonkheer
S, Offerhaus GJ, Clevers H. De novo crypt formation and
juvenile polyposis on BMP inhibition in mouse intestine. Science 303: 1684 –1686, 2004.
154
PHYSIOLOGY • Volume 27 • June 2012 • www.physiologyonline.org
12. Hardwick JC, Van Den Brink GR, Bleuming SA, Ballester I,
Van Den Brande JM, Keller JJ, Offerhaus GJ, Van Deventer
SJ, Peppelenbosch MP. Bone morphogenetic protein 2 is
expressed by, and acts upon, mature epithelial cells in the
colon. Gastroenterology 126: 111–121, 2004.
13. He XC, Zhang J, Tong WG, Tawfik O, Ross J, Scoville DH,
Tian Q, Zeng X, He X, Wiedemann LM, Mishina Y, Li L. BMP
signaling inhibits intestinal stem cell self-renewal through
suppression of Wnt-beta-catenin signaling. Nat Genet 36:
1117–1121, 2004.
14. Kawakami T, Kawcak T, Li YJ, Zhang W, Hu Y, Chuang PT.
Mouse dispatched mutants fail to distribute hedgehog proteins and are defective in hedgehog signaling. Development
129: 5753–5765, 2002.
15. Kim JH, Huang Z, Mo R. Gli3 null mice display glandular
overgrowth of the developing stomach. Dev Dyn 234: 984 –
991, 2005.
16. Kolterud A, Grosse AS, Zacharias WJ, Walton KD, Kretovich
KE, Madison BB, Waghray M, Ferris JE, Hu C, Merchant JL,
Dlugosz AA, Kottmann AH, Gumucio DL. Paracrine hedgehog signaling in stomach and intestine: new roles for hedgehog in gastrointestinal patterning. Gastroenterology 137:
618 – 628, 2009.
17. Kosinski C, Stange DE, Xu C, Chan AS, Ho C, Yuen ST,
Mifflin RC, Powell DW, Clevers H, Leung SY, Chen X. Indian
hedgehog regulates intestinal stem cell fate through epithelial-mesenchymal interactions during development.
Gastroenterology 139: 893–903, 2010.
18. Lee JJ, Ekker SC, von Kessler DP, Porter JA, Sun BI, Beachy
PA. Autoproteolysis in hedgehog protein biogenesis. Science
266: 1528 –1537, 1994.
19. Lees CW, Zacharias WJ, Tremelling M, Noble CL, Nimmo ER,
Tenesa A, Cornelius J, Torkvist L, Kao J, Farrington S, Drummond HE, Ho GT, Arnott ID, Appelman HD, Diehl L, Campbell H, Dunlop MG, Parkes M, Howie SE, Gumucio DL,
Satsangi J. Analysis of germline GLI1 variation implicates
hedgehog signalling in the regulation of intestinal inflammatory pathways. PLos Med 5: e239, 2008.
20. Ma Y, Erkner A, Gong R, Yao S, Taipale J, Basler K, Beachy
PA. Hedgehog-mediated patterning of the mammalian embryo requires transporter-like function of dispatched. Cell
111: 63–75, 2002.
21. Madison BB, Braunstein K, Kuizon E, Portman K, Qiao XT,
Gumucio DL. Epithelial hedgehog signals pattern the intestinal crypt-villus axis. Development 132: 279 –289, 2005.
22. Marigo V, Davey RA, Zuo Y, Cunningham JM, Tabin CJ.
Biochemical evidence that patched is the hedgehog receptor. Nature 384: 176 –179, 1996.
23. Mo R, Kim JH, Zhang J, Chiang C, Hui CC, Kim PC. Anorectal
malformations caused by defects in sonic hedgehog signaling. Am J Pathol 159: 765–774, 2001.
24. Motoyama J, Liu J, Mo R, Ding Q, Post M, Hui CC. Essential
function of Gli2 and Gli3 in the formation of lung, trachea and
oesophagus. Nat Genet 20: 54 –57, 1998.
25. Pan Y, Bai CB, Joyner AL, Wang B. Sonic hedgehog signaling regulates Gli2 transcriptional activity by suppressing its processing and degradation. Mol Cell Biol 26: 3365–
3377, 2006.
26. Porter JA, von Kessler DP, Ekker SC, Young KE, Lee JJ,
Moses K, Beachy PA. The product of hedgehog autoproteolytic cleavage active in local and long-range signalling. Nature 374: 363–366, 1995.
27. Stone DM, Hynes M, Armanini M, Swanson TA, Gu Q,
Johnson RL, Scott MP, Pennica D, Goddard A, Phillips H,
Noll M, Hooper JE, de SF, Rosenthal A. The tumoursuppressor gene patched encodes a candidate receptor
for Sonic hedgehog. Nature 384: 129 –134, 1996.
28. Taipale J, Cooper MK, Maiti T, Beachy PA. Patched acts
catalytically to suppress the activity of Smoothened. Nature
418: 892– 897, 2002.
29. Tang Y, Swietlicki EA, Jiang S, Buhman KK, Davidson NO,
Burkly LC, Levin MS, Rubin DC. Increased apoptosis and
accelerated epithelial migration following inhibition of
hedgehog signaling in adaptive small bowel postresection.
Am J Physiol Gastrointest Liver Physiol 290: G1280 –G1288,
2006.
Downloaded from http://physiologyonline.physiology.org/ by 10.220.33.6 on June 16, 2017
program once Ihh expression is lost? Does the
Hedgehog pathway control the mesenchymal immune response directly in myeloid cells or is this
mediated via Hedgehog responsive smooth muscle
cells or myofibroblast-like cells? To answer these
questions, it seems important to specifically isolate
the different Hedgehog responsive target cells individually and generate specific knockout mice
that target Smo in the different mesenchymal cell
types.
Thus, although many important aspects of the
role of Hedgehog signaling in the adult intestine
have been revealed over the past few years, important questions remain. Research into the role of the
pathway in intestinal homeostasis is likely to make
further important contributions to understanding
intestinal physiology. 䡲
REVIEWS
30. Tenzen T, Allen BL, Cole F, Kang JS, Krauss RS, McMahon AP. The cell surface membrane proteins
Cdo and Boc are components and targets of the
Hedgehog signaling pathway and feedback network in mice. Dev Cell 10: 647– 656, 2006.
31. Van Den Brink GR. Hedgehog signaling in development and homeostasis of the gastrointestinal tract. Physiol Rev 87: 1343–1375, 2007.
32. Van Den Brink GR, Bleuming SA, Hardwick JC,
Schepman BL, Offerhaus GJ, Keller JJ, Nielsen C,
Gaffield W, Van Deventer SJ, Roberts DJ, Peppelenbosch MP. Indian Hedgehog is an antagonist of Wnt signaling in colonic epithelial cell
differentiation. Nat Genet 36: 277–282, 2004.
33. Van Den Brink GR, Hardwick JC, Nielsen C, Xu C,
ten Kate FJ, Glickman J, Van Deventer SJ, Roberts
DJ, Peppelenbosch MP. Sonic hedgehog expression correlates with fundic gland differentiation in
the adult gastrointestinal tract. Gut 51: 628 – 633,
2002.
36. Van dop WA, Uhmann A, Wijgerde M, Sleddens-Linkels E, Heijmans J, Offerhaus GJ, van
den Bergh Weerman MA, Boeckxstaens GE,
Hommes DW, Hardwick JC, Hahn H, Van Den
Brink GR. Depletion of the colonic epithelial
precursor cell compartment upon conditional
activation of the hedgehog pathway. Gastroenterology 136: 2195–2203, 2009.
37. Varnat F, Zacchetti G, Altaba A. Hedgehog pathway activity is required for the lethality and intestinal phenotypes of mice with hyperactive
Wnt signaling. Mech Dev 127: 73– 81, 2010.
38. Wang B, Fallon JF, Beachy PA. Hedgehogregulated processing of Gli3 produces an anterior/posterior repressor gradient in the
developing vertebrate limb. Cell 100: 423– 434,
2000.
39. Wang LC, Nassir F, Liu ZY, Ling L, Kuo F, Crowell
T, Olson D, Davidson NO, Burkly LC. Disruption
of hedgehog signaling reveals a novel role in
intestinal morphogenesis and intestinal-specific
lipid metabolism in mice. Gastroenterology 122:
469 – 482, 2002.
40. Yao S, Lum L, Beachy P. The ihog cell-surface
proteins bind Hedgehog and mediate pathway
activation. Cell 125: 343–357, 2006.
41. Zacharias WJ, Li X, Madison BB, Kretovich K, Kao
JY, Merchant JL, Gumucio DL. Hedgehog is an
anti-inflammatory epithelial signal for the intestinal lamina propria. Gastroenterology 138: 2368 –
2377, 2010.
42. Zacharias WJ, Madison BB, Kretovich KE, Walton
KD, Richards N, Udager AM, Li X, Gumucio DL.
Hedgehog signaling controls homeostasis of
adult intestinal smooth muscle. Dev Biol 355:
152–162, 2011.
43. Zhang W, Kang JS, Cole F, Yi MJ, Krauss RS. Cdo
functions at multiple points in the Sonic Hedgehog pathway, and Cdo-deficient mice accurately
model human holoprosencephaly. Dev Cell 10:
657– 665, 2006.
PHYSIOLOGY • Volume 27 • June 2012 • www.physiologyonline.org
155
Downloaded from http://physiologyonline.physiology.org/ by 10.220.33.6 on June 16, 2017
34. van den Heuvel M, Ingham PW. Smoothened encodes a receptor-like serpentine protein required for hedgehog signalling. Nature 382: 547–
551, 1996.
35. Van dop WA, Heijmans J, Buller NV, Snoek SA,
Rosekrans SL, Wassenberg EA, van den Bergh
Weerman MA, Lanske B, Clarke AR, Winton DJ,
Wijgerde M, Offerhaus GJ, Hommes DW, Hardwick JC, de Jonge WJ, Biemond I, Van Den Brink
GR. Loss of Indian Hedgehog activates multiple
aspects of a wound healing response in the
mouse intestine. Gastroenterology 139: 1665–
1676, 1676, 2010.