Identification of GM-CSF in Paneth cells using single-cell RT-PCR

Unraveling the Complexities of Myeloid-Derived Suppressor Cells in Inflammatory Bowel Disease

Myeloid-derived suppressor cells (MDSCs) regulate immune responses in many pathological conditions, one of which is inflammatory bowel disease (IBD), an incurable chronic disorder of the digestive tract and beyond. The pathophysiology of IBD remains unclear, likely involving aberrant innate and adaptive immunity. Studies have reported altered population of MDSCs in patients with IBD. However, their distribution varies among patients and different preclinical models of IBD. The expansion and activation of MDSCs are likely driven by various stimuli during intestinal inflammation, but the in-depth mechanisms remain poorly understood. The role of MDSCs in the pathogenesis of IBD appears to be paradoxical. In addition to intestinal inflammation, suppressive MDSCs may promote colitis-to-colon cancer transition. In this Review, we summarize recent progresses on the features, activation, and roles of MDSCs in the development of IBD and IBD-associated colon cancer.

Macrophage niche imprinting as a determinant of macrophage identity and function

Macrophage niches are the anatomical locations within organs or tissues consisting of various cells, intercellular and extracellular matrix, transcription factors, and signaling molecules that interact to influence macrophage self-maintenance, phenotype, and behavior. The niche, besides physically supporting macrophages, imposes a tissue- and organ-specific identity on the residing and infiltrating monocytes and macrophages. In this review, we give examples of macrophage niches and the modes of communication between macrophages and surrounding cells. We also describe how macrophages, acting against their immune defensive nature, can create a hospitable niche for pathogens and cancer cells.

Sargramostim for Prophylactic Management of Gastrointestinal Immune-Related Adverse Events of Immune Checkpoint Inhibitor Therapy for Cancer

Immune checkpoint inhibitor (ICI) therapy improves outcomes in several cancers. Unfortunately, many patients experience grade 3-4 treatment-related adverse events, including gastrointestinal (GI) toxicities which are common. These GI immune-related adverse events (irAEs) induced by ICIs present significant clinical challenges, require prompt intervention, and result in treatment delays or discontinuations. The treatment for these potentially severe and even fatal GI irAEs which include enterocolitis, severe diarrhea, and hepatitis may interfere with the anti-cancer approach. Sargramostim (glycosylated, yeast-derived, recombinant human GM-CSF) is an agent that has been used in clinical practice for more than 30 years with a well-recognized safety profile and has been studied in many therapeutic areas. The mechanism of action of sargramostim may treat moderate-to-severe GI irAEs without impairing the anti-cancer therapy. Some early data also suggest a potential survival benefit. Through the differentiation/maturation of monocytes, macrophages, and neutrophils and induction of anti-inflammatory T cell responses, GM-CSF aids in GI homeostasis, mucosal healing, and mucosal immunity. GM-CSF knockout mice are susceptible to severe colitis which was prevented with murine GM-CSF administration. For some patients with GI mucosa and immune cell function impairment, e.g., Crohn's disease, sargramostim reduces disease severity. In a prospective, randomized study (ECOG 1608), advanced melanoma patients had a reduction in grade 3-5 GI irAEs and less frequent colonic perforation in the sargramostim plus ipilimumab arm compared to ipilimumab alone. Sargramostim continues to be studied with ICIs for the prophylactic management of irAEs while also potentially providing a survival benefit.

Neutrophil Homeostasis and Emergency Granulopoiesis: The Example of Systemic Juvenile Idiopathic Arthritis

Neutrophils are key pathogen exterminators of the innate immune system endowed with oxidative and non-oxidative defense mechanisms. More recently, a more complex role for neutrophils as decision shaping cells that instruct other leukocytes to fine-tune innate and adaptive immune responses has come into view. Under homeostatic conditions, neutrophils are short-lived cells that are continuously released from the bone marrow. Their development starts with undifferentiated hematopoietic stem cells that pass through different immature subtypes to eventually become fully equipped, mature neutrophils capable of launching fast and robust immune responses. During severe (systemic) inflammation, there is an increased need for neutrophils. The hematopoietic system rapidly adapts to this increased demand by switching from steady-state blood cell production to emergency granulopoiesis. During emergency granulopoiesis, the de novo production of neutrophils by the bone marrow and at extramedullary sites is augmented, while additional mature neutrophils are rapidly released from the marginated pools. Although neutrophils are indispensable for host protection against microorganisms, excessive activation causes tissue damage in neutrophil-rich diseases. Therefore, tight regulation of neutrophil homeostasis is imperative. In this review, we discuss the kinetics of neutrophil ontogenesis in homeostatic conditions and during emergency myelopoiesis and provide an overview of the different molecular players involved in this regulation. We substantiate this review with the example of an autoinflammatory disease, i.e. systemic juvenile idiopathic arthritis.

Sargramostim (rhu GM-CSF) as Cancer Therapy (Systematic Review) and An Immunomodulator. A Drug Before Its Time?

BACKGROUND

Sargramostim [recombinant human granulocyte-macrophage colony-stimulating factor (rhu GM-CSF)] was approved by US FDA in 1991 to accelerate bone marrow recovery in diverse settings of bone marrow failure and is designated on the list of FDA Essential Medicines, Medical Countermeasures, and Critical Inputs. Other important biological activities including accelerating tissue repair and modulating host immunity to infection and cancer via the innate and adaptive immune systems are reported in pre-clinical models but incompletely studied in humans.

OBJECTIVE

Assess safety and efficacy of sargramostim in cancer and other diverse experimental and clinical settings.

METHODS AND RESULTS

We systematically reviewed PubMed, Cochrane and TRIP databases for clinical data on sargramostim in cancer. In a variety of settings, sargramostim after exposure to bone marrow-suppressing agents accelerated hematologic recovery resulting in fewer infections, less therapy-related toxicity and sometimes improved survival. As an immune modulator, sargramostim also enhanced anti-cancer responses in solid cancers when combined with conventional therapies, for example with immune checkpoint inhibitors and monoclonal antibodies.

CONCLUSIONS

Sargramostim accelerates hematologic recovery in diverse clinical settings and enhances anti-cancer responses with a favorable safety profile. Uses other than in hematologic recovery are less-well studied; more data are needed on immune-enhancing benefits. We envision significantly expanded use of sargramostim in varied immune settings. Sargramostim has the potential to reverse the immune suppression associated with sepsis, trauma, acute respiratory distress syndrome (ARDS) and COVID-19. Further, sargramostim therapy has been promising in the adjuvant setting with vaccines and for anti-microbial-resistant infections and treating autoimmune pulmonary alveolar proteinosis and gastrointestinal, peripheral arterial and neuro-inflammatory diseases. It also may be useful as an adjuvant in anti-cancer immunotherapy.

Macrophage Deficiency Makes Intestinal Epithelial Cells Susceptible to NSAID-Induced Damage

Objectives

In Crohn's disease (CD), the mechanisms underlying the regulation by granulocyte-macrophage colony-stimulating factor (GM-CSF) of mucosal barrier function in the ileum are unclear. We analyzed the molecular mechanisms underlying the regulation by GM-CSF of the mucosal barrier function.

Methods

We examined the role of GM-CSF in the intestinal barrier function in CD at the molecular-, cellular-, and animal-model levels.

Results

Macrophages directly secreted GM-CSF, promoting intestinal epithelial proliferation and inhibiting apoptosis, which maintained intestinal barrier function. Macrophages were absent in NSAID-induced ileitis, causing GM-CSF deficiency, increasing the apoptosis rate, decreasing the proliferation rate, increasing inter- and paracellular permeabilities, decreasing the TJP levels, and reducing the numbers of mesenteric lymph nodes, memory T cells, and regulatory T cells in Csf1^op/op transgenic mice.

Conclusions

GM-CSF is required for the maintenance of intestinal barrier function. Macrophages directly secrete GM-CSF, promoting intestinal epithelial proliferation and inhibiting apoptosis.

Attenuation of NF-κB in Intestinal Epithelial Cells Is Sufficient to Mitigate the Bone Loss Comorbidity of Experimental Mouse Colitis

Skeletal abnormalities are common comorbidities of inflammatory bowel disease (IBD). Patients suffering from IBD, including ulcerative colitis and Crohn's disease, present with skeletal complications. However, the mechanism underpinning IBD-associated bone loss remains vague. Intestinal inflammation generates an inflammatory milieu at the intestinal epithelium that leads to dysregulation of mucosal immunity through gut-residing innate lymphoid cells (ILCs) and other cell types. ILCs are recently identified mucosal cells considered as the gatekeeper of gut immunity and their function is regulated by intestinal epithelial cell (IEC)-secreted cytokines in response to the inflammatory microenvironment. We first demonstrate that serum as well as IECs collected from the intestine of dextran sulfate sodium (DSS)-induced colitis mice contain high levels of inflammatory and osteoclastogenic cytokines. Mechanistically, heightened inflammatory response of IECs was associated with significant intrinsic activation of NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) in IECs and increased frequency of ILC1, ILC3, and myeloid osteoclast progenitors. Validating the central role of IEC-specific NF-κB activation in this phenomenon, conditional expression of constitutively active inhibitor kappa B kinase 2 (IKK2) in IECs in mice recapitulates the majority of the cellular, inflammatory, and osteolytic phenotypes observed in the chemically induced colitis. Furthermore, conditional deletion of IKK2 from IECs significantly attenuated inflammation and bone loss in DSS-induced colitis. Finally, using the DSS-induced colitis model, pharmacologic inhibition of IKK2 was effective in reducing frequency of ILC1 and ILC3 cells, attenuated circulating levels of inflammatory cytokines, and halted colitis-associated bone loss. Our findings identify IKK2 in IECs as viable therapeutic target for colitis-associated osteopenia.

Mist1 Expression Is Required for Paneth Cell Maturation

BACKGROUND

Paneth cells are professional secretory cells found within the small intestinal crypt epithelium. Although their role as part of the innate immune complex providing antimicrobial secretory products is well-known, the mechanisms that control secretory capacity are not well-understood. MIST1 is a scaling factor that is thought to control secretory capacity of exocrine cells.

METHODS

Mist1+/+ and Mist1-/- mice were used to evaluate the function of MIST1 in small intestinal Paneth cells. We used histologic and immunofluorescence staining to evaluate small intestinal tissue for proliferation and lineage allocation. Total RNA was isolated to evaluate gene expression. Enteroid culture was used to evaluate the impact of the absence of MIST1 expression on intestinal stem cell function.

RESULTS

Absence of MIST1 resulted in increased numbers of Paneth cells exhibiting an intermediate cell phenotype but otherwise did not alter overall epithelial cell lineage allocation. Muc2 and lysozyme staining confirmed the presence of intermediate cells at the crypt base of Mist1-/- mice. These changes were not associated with changes in mRNA expression of transcription factors associated with lineage allocation, and they were not abrogated by inhibition of Notch signaling. However, the absence of MIST1 expression was associated with alterations in Paneth cell morphology including decreased granule size and distended rough endoplasmic reticulum. Absence of MIST1 was associated with increased budding of enteroid cultures; however, there was no evidence of increased intestinal stem cell numbers in vivo.

CONCLUSIONS

MIST1 plays an important role in organization of the Paneth cell secretory apparatus and managing endoplasmic reticulum stress. This role occurs downstream of Paneth cell lineage allocation.

Controlling Gut Inflammation by Restoring Anti-Inflammatory Pathways in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is caused by a dysregulated immune response against normal components of the intestinal microflora combined with defective functioning of anti-inflammatory pathways. Currently, all therapies approved for IBD manipulate the immune system by inhibiting pro-inflammatory mechanisms, such as tumor necrosis factor-α, gut-homing α4β7 integrin, interleukin-12/interleukin-23, and Janus kinases. However, some IBD patients are non-responders to these drugs, which are also associated with serious side effects. Thus, it has been hypothesized that therapies aimed at restoring anti-inflammatory signals, by exploiting the tolerogenic potential of cytokines (interleukin-10, transforming growth factor-β, granulocyte macrophage colony-stimulating factor), immune cells (regulatory T cells, tolerogenic dendritic cells), or mesenchymal stem cells, might offer promising results in terms of clinical efficacy with fewer side effects. In this review, we provide new insights into putative novel treatments aimed at restoring anti-inflammatory signaling pathways in IBD.

A platform of genetically engineered bacteria as vehicles for localized delivery of therapeutics: Toward applications for Crohn's disease

For therapies targeting diseases of the gastrointestinal tract, we and others envision probiotic bacteria that synthesize and excrete biotherapeutics at disease sites. Toward this goal, we have engineered commensal E. coli that selectively synthesize and secrete a model biotherapeutic in the presence of nitric oxide (NO), an intestinal biomarker for Crohn's disease (CD). This is accomplished by co‐expressing the pore forming protein TolAIII with the biologic, granulocyte macrophage‐colony stimulating factor (GM‐CSF). We have additionally engineered these bacteria to accumulate at sites of elevated NO by engineering their motility circuits and controlling pseudotaxis. Importantly, because we have focused on in vitro test beds, motility and biotherapeutics production are spatiotemporally characterized. Together, the targeted recognition, synthesis, and biomolecule delivery comprises a “smart” probiotics platform that may have utility in the treatment of CD. Further, this platform could be modified to accommodate other pursuits by swapping the promoter and therapeutic gene to reflect other disease biomarkers and treatments, respectively.

GM-CSF and GM-CSF receptor have regulatory role in transforming rat mesenteric mesothelial cells into macrophage-like cells

OBJECTIVE AND DESIGN

During peritonitis, mesothelial cells assume macrophage characteristics, expressing macrophage markers, indicating that they might differentiate into macrophage-like cells.

MATERIALS AND SUBJECTS

Twenty-five male rats were used for in vivo experiments. For in vitro experiments, a primary mesentery culture model was developed. The mesothelial cell to macrophage-like cell transition was followed by studying ED1 expression.

TREATMENTS

In vitro primary mesenteric culture was treated with granulocyte-macrophage colony-stimulating factor (GM-CSF, 1 ng/ml). Blocking internalization of receptor-ligand complex, Dynasore (80 µM) was used. Acute peritonitis was induced by Freund's adjuvant's (1 ml) intraperitoneal injection.

RESULTS

Immunohistochemistry: GM-CSF in vitro treatment resulted in a prominent ED1 expression in transformed mesothelial cells. Blocking the internalization, ED1 expression could not be detected. GM-CSF receptor (both α and β) was expressed in mesothelial cells in vitro (even if the GM-CSF was not present) and in vivo. Inflammation resulted in an increasing GM-CSF and GM-CSF-receptor level in the lysate of mesothelial cells.

CONCLUSIONS

Mesothelial cells can differentiate into macrophage-like cells, and GM-CSF, produced by the mesothelial cells, has probably an autocrine regulatory role in this transition. Our results provide new data about the plasticity of mesothelial cell and support the idea that during inflammation macrophages can derive from non-hematopoietic sources as well.

Transmissible Plasmid Containing Salmonella enterica Heidelberg Isolates Modulate Cytokine Production During Early Stage of Interaction with Intestinal Epithelial Cells

The variation in cytokine production during bacterial invasion of human intestinal epithelial cells (IECs) is a contributing factor for progression of the infection. A few Salmonella enterica Heidelberg strains isolated from poultry products harbor transmissible plasmids (TPs), including those that encode a type-IV secretion system. Earlier, we showed that these TPs are responsible for increased virulence during infection. This study examines the potential role of these TPs in cytokine production in IECs. This study showed that S. Heidelberg strains containing TPs (we refer as virulent strains) caused decreased interleukin (IL)-10 production in IECs after 1 h infection. The virulent strains induced a high level of tumor necrosis factor-α production under identical conditions. The virulent strains of S. Heidelberg also altered the production of IL-2, IL-17, and granulocyte macrophage colony-stimulating factor compared to an avirulent strain. As a part of infection, bacteria cross the epithelial barrier and encounter intestinal macrophages. Hence, we examined the cytotoxic mechanism of strains of S. Heidelberg in macrophages. Scanning electron microscopy showed cell necrosis occurs during the early stage of infection. In conclusion, virulent S. Heidelberg strains were able to modify the host cytokine profile during the early stages of infection and also caused necrosis in macrophages.

Pivotal roles of GM-CSF in autoimmunity and inflammation

Granulocyte macrophage-colony stimulating factor (GM-CSF) is a hematopoietic growth factor, which stimulates the proliferation of granulocytes and macrophages from bone marrow precursor cells. In autoimmune and inflammatory diseases, Th17 cells have been considered as strong inducers of tissue inflammation. However, recent evidence indicates that GM-CSF has prominent proinflammatory functions and that this growth factor (not IL-17) is critical for the pathogenicity of CD4⁺ T cells. Therefore, the mechanism of GM-CSF-producing CD4⁺ T cell differentiation and the role of GM-CSF in the development of autoimmune and inflammatory diseases are gaining increasing attention. This review summarizes the latest knowledge of GM-CSF and its relationship with autoimmune and inflammatory diseases. The potential therapies targeting GM-CSF as well as their possible side effects have also been addressed in this review.

STAT5 programs a distinct subset of GM-CSF-producing T helper cells that is essential for autoimmune neuroinflammation

T helper (T_H)-cell subsets, such as T_H1 and T_H17, mediate inflammation in both peripheral tissues and central nervous system. Here we show that STAT5 is required for T helper-cell pathogenicity in autoimmune neuroinflammation but not in experimental colitis. Although STAT5 promotes regulatory T cell generation and immune suppression, loss of STAT5 in CD4⁺ T cells resulted in diminished development of experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. Our results showed that loss of encephalitogenic activity of STAT5-deficient autoreactive CD4⁺ T cells was independent of IFN-γ or interleukin 17 (IL-17) production, but was due to the impaired expression of granulocyte-macrophage colony-stimulating factor (GM-CSF), a crucial mediator of T-cell pathogenicity. We further showed that IL-7-activated STAT5 promotes the generation of GM-CSF-producing CD4⁺ T cells, which were preferentially able to induce more severe EAE than T_H17 or T_H1 cells. Consistent with GM-CSF-producing cells being a distinct subset of T_H cells, the differentiation program of these cells was distinct from that of T_H17 or T_H1 cells. We further found that IL-3 was secreted in a similar pattern as GM-CSF in this subset of T_H cells. In conclusion, the IL-7-STAT5 axis promotes the generation of GM-CSF/IL-3-producing T_H cells. These cells display a distinct transcriptional profile and may represent a novel subset of T helper cells which we designate as T_H-GM.

Ipilimumab plus sargramostim vs ipilimumab alone for treatment of metastatic melanoma: a randomized clinical trial

IMPORTANCE

Cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) blockade with ipilimumab prolongs survival in patients with metastatic melanoma. CTLA-4 blockade and granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting tumor vaccine combinations demonstrate therapeutic synergy in preclinical models. A key unanswered question is whether systemic GM-CSF (sargramostim) enhances CTLA-4 blockade.

OBJECTIVE

To compare the effect of ipilimumab plus sargramostim vs ipilimumab alone on overall survival (OS) in patients with metastatic melanoma.

DESIGN, SETTING, AND PARTICIPANTS

The Eastern Cooperative Oncology Group (ECOG) conducted a US-based phase 2 randomized clinical trial from December 28, 2010, until July 28, 2011, of patients (N = 245) with unresectable stage III or IV melanoma, at least 1 prior therapy, no central nervous system metastases, and ECOG performance status of 0 or 1.

INTERVENTIONS

Patients were randomized to receive ipilimumab, 10 mg/kg, intravenously on day 1 plus sargramostim, 250 μg subcutaneously, on days 1 to 14 of a 21-day cycle (n = 123) vs ipilimumab alone (n = 122). Ipilimumab treatment included induction for 4 cycles followed by maintenance every fourth cycle.

MAIN OUTCOMES AND MEASURES

Primary end point: comparison of length of OS. Secondary end point: progression-free survival (PFS), response rate, safety, and tolerability.

RESULTS

Median follow-up was 13.3 months (range, 0.03-19.9). Median OS as of December 2012 for ipilimumab plus sargramostim was 17.5 months (95% CI, 14.9-not reached) vs 12.7 months (95% CI, 10.0-not reached) for ipilimumab. The 1-year survival rate for ipilimumab plus sargramostim was 68.9% (95% CI, 60.6%-85.5%) compared to 52.9% (95% CI, 43.6%-62.2%) for ipilimumab alone (stratified log-rank 1-sided P = .01; mortality hazard ratio 0.64 [1-sided 90% repeated CI, not applicable-0.90]). A planned interim analysis was conducted at 69.8% of expected events (104 observed with 149 expected deaths). Planned interim analysis using the O'Brien-Fleming boundary was crossed for improvement in OS. There was no difference in PFS. Median PFS for ipilimumab plus sargramostim was 3.1 months (95% CI, 2.9-4.6) vs 3.1 months (95% CI, 2.9-4.0) for ipilimumab alone. Grade 3 to 5 adverse events occurred in 44.9% (95% CI; 35.8%-54.4%) of patients in the ipilimumab plus sargramostim group vs 58.3% (95% CI, 49.0%-67.2%) of patients in the ipilimumab-alone group (2-sided P = .04).

CONCLUSION AND RELEVANCE

Among patients with unresectable stage III or IV melanoma, treatment with ipilimumab plus sargramostim vs ipilimumab alone resulted in longer OS and lower toxicity, but no difference in PFS. These findings require confirmation in larger studies with longer follow-up.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01134614.

Retinoic acid and GM-CSF coordinately induce retinal dehydrogenase 2 (RALDH2) expression through cooperation between the RAR/RXR complex and Sp1 in dendritic cells

Retinoic acid (RA)-producing dendritic cells (DCs) play critical roles in gut immunity. Retinal dehydrogenase 2 (RALDH2) encoded by Aldh1a2 is a key enzyme for generating RA in DCs. Granulocyte–macrophage colony-stimulating factor (GM-CSF) potently induces RALDH2 expression in DCs in an RA-dependent manner, and RA alone weakly induces the expression. However, how GM-CSF and RA induce RALDH2 expression remains unclear. Here, we show that GM-CSF-induced activation of the transcription factor Sp1 and RA-dependent signaling via the RA receptor (RAR)/retinoid X receptor (RXR) complex contribute to Aldh1a2 expression. The RAR antagonist LE540 and the Sp1 inhibitor mithramycin A inhibited GM-CSF-induced Aldh1a2 expression in fms-related tyrosine kinase 3 ligand-generated bone marrow-derived DCs (BM-DCs). ERK and p38 MAPK inhibitors suppressed GM-CSF-induced nuclear translocation of Sp1 and Aldh1a2 expression. Sp1 and the RARα/RXRα complex bound to GC-rich Sp1-binding sites and an RA response element (RARE) half-site, respectively, near the TATA box in the mouse Aldh1a2 promoter. The DNA sequences around these sites were highly conserved among different species. In the presence of RA, ectopic expression of RARα/RXRα and Sp1 synergistically enhanced Aldh1a2 promoter-reporter activity. GM-CSF did not significantly induce Aldh1a2 expression in plasmacytoid DCs, peritoneal macrophages, or T cells, and the Aldh1a2 promoter in these cells was mostly unmethylated. These results suggest that GM-CSF/RA-induced RALDH2 expression in DCs requires cooperative binding of Sp1 and the RAR/RXR complex to the Aldh1a2 promoter, and can be regulated by a DNA methylation-independent mechanism.

Microbiota-dependent crosstalk between macrophages and ILC3 promotes intestinal homeostasis

The intestinal microbiota and tissue-resident myeloid cells promote immune responses that maintain intestinal homeostasis in the host. However, the cellular cues that translate microbial signals into intestinal homeostasis remain unclear. Here, we show that deficient granulocyte-macrophage colony-stimulating factor (GM-CSF) production altered mononuclear phagocyte effector functions and led to reduced regulatory T cell (T(reg)) numbers and impaired oral tolerance. We observed that RORγt(+) innate lymphoid cells (ILCs) are the primary source of GM-CSF in the gut and that ILC-driven GM-CSF production was dependent on the ability of macrophages to sense microbial signals and produce interleukin-1β. Our findings reveal that commensal microbes promote a crosstalk between innate myeloid and lymphoid cells that leads to immune homeostasis in the intestine.

Paneth cells expand from newly created and preexisting cells during repair after doxorubicin-induced damage

Paneth cell numbers increase following intestinal damage, but mechanisms driving this process are not understood. We hypothesized that the increase in Paneth cell numbers is due to recruitment of cells from a preexisting pool of secretory progenitors. Mice were given a single injection of doxorubicin (Dox), and intestinal tissue was collected 0-168 h after treatment. Paneth, goblet, and intermediate cells were counted and evaluated for cell morphology. Quantitative RT-PCR was used to measure expression of various genes associated with Paneth cell allocation and maturation. Paneth cells were birth dated using incorporation of thymidine analogs given before or after Dox. Staining revealed "intermediate" cells, which were rarely observed in control crypts but increased significantly in number 96 and 120 h after Dox treatment. Birth dating of intermediate cells 5 days after Dox treatment revealed that 24% of these cells took up thymidine analog given prior to Dox treatment and 36% took up thymidine analog given after Dox treatment. Quantitative RT-PCR demonstrated a significant increase in Spdef, Atoh1, Sox9, EphB3, Mist, Wnt5a, FGF-9, and FGF-18 mRNAs and a significant decrease in Indian hedgehog mRNA. Expansion of the Paneth cell compartment after Dox treatment is due to generation of new cells and recruitment of cells from an existing pool. These cells express Paneth and goblet biomarkers and are found only during repair. Expansion of these cells correlates temporally with reduced Indian hedgehog and increased FGF and Wnt mRNA. These findings are significant, as they provide a first step in understanding mechanisms of Paneth cell expansion during mucosal repair.

GM-CSF produced by nonhematopoietic cells is required for early epithelial cell proliferation and repair of injured colonic mucosa

GM-CSF is a growth factor that promotes the survival and activation of macrophages and granulocytes, as well as dendritic cell differentiation and survival in vitro. The mechanism by which exogenous GM-CSF ameliorates the severity of Crohn's disease in humans and colitis in murine models has mainly been considered to reflect its activity on myeloid cells. We used GM-CSF-deficient (GM-CSF(-/-)) mice to probe the functional role of endogenous host-produced GM-CSF in a colitis model induced after injury to the colon epithelium. Dextran sodium sulfate (DSS), at doses that resulted in little epithelial damage and mucosal ulceration in wild type mice, caused marked colon ulceration and delayed ulcer healing in GM-CSF(-/-) mice. Colon crypt epithelial cell proliferation in vivo was significantly decreased in GM-CSF(-/-) mice at early times after DSS injury. This was paralleled by decreased expression of crypt epithelial cell genes involved in cell cycle, proliferation, and wound healing. Decreased crypt cell proliferation and delayed ulcer healing in GM-CSF(-/-) mice were rescued by exogenous GM-CSF, indicating the lack of a developmental abnormality in the epithelial cell proliferative response in those mice. Nonhematopoietic cells, and not myeloid cells, produced the GM-CSF important for colon epithelial proliferation after DSS-induced injury, as revealed by bone marrow chimera and dendritic cell-depletion experiments, with colon epithelial cells being the cellular source of GM-CSF. Endogenous epithelial cell-produced GM-CSF has a novel nonredundant role in facilitating epithelial cell proliferation and ulcer healing in response to injury of the colon crypt epithelium.

Activation of two distinct Sox9-EGFP-expressing intestinal stem cell populations during crypt regeneration after irradiation

Recent identification of intestinal epithelial stem cell (ISC) markers and development of ISC reporter mice permit visualization and isolation of regenerating ISCs after radiation to define their functional and molecular phenotypes. Previous studies in uninjured intestine of Sox9-EGFP reporter mice demonstrate that ISCs express low levels of Sox9-EGFP (Sox9-EGFP Low), whereas enteroendocrine cells (EEC) express high levels of Sox9-EGFP (Sox9-EGFP High). We hypothesized that Sox9-EGFP Low ISCs would expand after radiation, exhibit enhanced proliferative capacities, and adopt a distinct gene expression profile associated with rapid proliferation. Sox9-EGFP mice were given 14 Gy abdominal radiation and studied between days 3 and 9 postradiation. Radiation-induced changes in number, growth, and transcriptome of the different Sox9-EGFP cell populations were determined by histology, flow cytometry, in vitro culture assays, and microarray. Microarray confirmed that nonirradiated Sox9-EGFP Low cells are enriched for Lgr5 mRNA and mRNAs enriched in Lgr5-ISCs and identified additional putative ISC markers. Sox9-EGFP High cells were enriched for EEC markers, as well as Bmi1 and Hopx, which are putative markers of quiescent ISCs. Irradiation caused complete crypt loss, followed by expansion and hyperproliferation of Sox9-EGFP Low cells. From nonirradiated intestine, only Sox9-EGFP Low cells exhibited ISC characteristics of forming organoids in culture, whereas during regeneration both Sox9-EGFP Low and High cells formed organoids. Microarray demonstrated that regenerating Sox9-EGFP High cells exhibited transcriptomic changes linked to p53-signaling and ISC-like functions including DNA repair and reduced oxidative metabolism. These findings support a model in which Sox9-EGFP Low cells represent active ISCs, Sox9-EGFP High cells contain radiation-activatable cells with ISC characteristics, and both participate in crypt regeneration.

Role of resveratrol-induced CD11b(+) Gr-1(+) myeloid derived suppressor cells (MDSCs) in the reduction of CXCR3(+) T cells and amelioration of chronic colitis in IL-10(-/-) mice

Resveratrol, a naturally occurring polyphenol has received significant attention as a potent anti-inflammatory agent. Inflammatory bowel disease (IBD) is a chronic intestinal inflammation caused by hyperactivated effector immune cells that produce proinflammatory cytokines. Myeloid derived suppressor cells (MDSCs) are a heterogeneous population characterized by the co-expression of CD11b(+) and Gr-1(+) and have long been known for their immunosuppressive function. We report that resveratrol effectively attenuated overall clinical scores as well as various pathological markers of colitis in IL-10(-/-) mice by down regulating Th1 responses. Resveratrol lessened the colitis-associated decrease in body weight and increased levels of serum amyloid A (SAA), CXCL10 and colon TNF-α, IL-6, RANTES, IL-12 and IL-1β concentrations. After resveratrol treatment, the percentage of CXCR3 expressing T cells was decreased in the spleen, mesenteric lymph nodes (MLN), and intestinal lamina propria (LP). However, the percentage and absolute numbers of CD11b(+) and Gr-1(+)cells in the lamina propria (LP) and spleen were increased after resveratrol treatment as compared with the vehicle treatment. Co-culture of resveratrol-induced CD11b(+) Gr-1(+) cells with T cells, attenuated T cell proliferation, and most importantly reduced IFN-γ and GM-CSF production by LP derived T cells from vehicle treated IL-10(-/-) mice with chronic colitis. The current study suggests that administration of resveratrol into IL-10(-/-) mice induces immunosuppressive CD11b(+) Gr-1(+) MDSCs in the colon, which correlates with reversal of established chronic colitis, and down regulation of mucosal and systemic CXCR3(+) expressing effector T cells as well as inflammatory cytokines in the colon. The induction of immunosuppressive CD11b(+) Gr-1(+) cells by resveratrol during colitis is unique, and suggests an as-yet-unidentified mode of anti-inflammatory action of this plant polyphenol.

Treatment of Crohn's disease with colony-stimulating factors: An overview

Current treatments for Crohn's disease are aimed at suppressing excessive immune activation in the bowel walls. However, alternative strategies can be drawn. These involve the augmentation of the innate immune response, in the hypothesis that patients affected with Crohn's disease are characterized by a relative immunodeficiency, with failure of the defensive barrier to luminal microbes and microbial products, resulting in a chronic inflammatory process sustained by T-cells. Alternatively, therapy could act by enhancing the number or the activity of subpopulations of T regulatory cells, able to reduce T-cell activation. Colony-stimulating factors are substances that could be efficacious in these settings. In fact, besides in vitro and animal studies, some human studies have been conducted in recent years with both granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor, the results of which are reported here.

Intestinal growth factors: potential use in the treatment of inflammatory bowel disease and their role in mucosal healing

BACKGROUND

A key feature of inflammatory bowel disease (IBD) is impaired epithelial repair. Human growth factors comprise an array of signaling molecules that lead to ligand-specific signal transduction. Their downstream effects are associated with several cellular functions including epithelial healing in response to injury. Several studies have described specific growth factor deficiencies in patients with IBD, implicating their role in disease pathophysiology. The aim of this review was to describe currently known enterocyte-targeted growth factors, their mechanisms of action, and their potential therapeutic utility.

METHODS

The National Library of Medicine (http://www.pubmed.gov) and meeting abstracts were searched using the following terms: growth factor, intestine, colon, inflammatory bowel disease, Crohn's disease, ulcerative colitis, colitis, animal model, transforming growth factor, bone morphogenetic protein, activins, growth hormone, fibroblast growth factor, epidermal growth factor (EGF), keratinocyte growth factor (KGF), glucagon-like peptide II, granulocyte macrophage colony-stimulating factor (GM-CSF), granulocyte colony-stimulating factor (G-CSF), vascular endothelial growth factor (VEGF) inhibitors, and trefoil factors.

RESULTS

Several growth factors are therapeutic candidates in IBD. Growth hormone, KGF, EGF, teduglutide, GM-CSF/G-CSF have entered early clinical trials, whereas others are currently in preclinical evaluation.

CONCLUSIONS

There are several growth factors responsible for epithelial repair. Preliminary studies using recombinant growth factors seem promising in IBD preclinical and clinical trials.

GM-CSF: a role in immune and inflammatory reactions in the intestine

Granulocyte macrophage colony-stimulating factor (GM-CSF) is a cytokine that promotes myeloid cell development and maturation, and dendritic cell differentiation and survival in vitro. Growing evidence supports the notion that GM-CSF has a major role in some inflammatory and autoimmune reactions and in the host's response to pulmonary infection, but few studies have addressed its functions and importance in the GI tract. Recent studies demonstrated that administration of GM-CSF can result in clinical improvement in patients with Crohn's disease. Mice deficient in GM-CSF (GM-CSF(-/-) ) developed more severe intestinal and systemic infection after an enteric infection, and more severe colitis in response to enteric exposure to dextran sodium sulfate. Both the severity of infection and colitis were largely prevented by GM-CSF administration. Such studies indicate that GM-CSF has an important role in the regulation of intestinal immune and inflammatory responses.

Regeneration of intestinal stem/progenitor cells following doxorubicin treatment of mice

The intestinal epithelium is in a constant state of renewal. The rapid turnover of cells is fed by a hierarchy of transit amplifying and stem/progenitor cells destined to give rise to the four differentiated epithelial lineages of the small intestine. Doxorubicin (Dox) is a commonly used chemotherapeutic agent that preferentially induces apoptosis in the intestinal stem cell zone (SCZ). We hypothesized that Dox treatment would initially decrease "+4" intestinal stem cell numbers with a subsequent expansion during mucosal repair. Temporal assessment following Dox treatment demonstrated rapid induction of apoptosis in the SCZ leading to a decrease in the number of intestinal stem/progenitor cells as determined by flow cytometry for CD45(-) SP cells, and immunohistochemistry of cells positive for putative +4 stem cell markers beta-cat(Ser552) and DCAMKL1. Between 96 and 168 h postinjection, overall proliferation in the crypts increased concomitant with increases in both absolute and relative numbers of goblet, Paneth, and enteroendocrine cells. This regeneration phase was also associated with increases of CD45(-) SP cells, beta-cat(Ser552)-positive cells, crypt fission, and crypt number. We used Lgr5-lacZ mice to assess behavior of Lgr5-positive stem cells following Dox and found no change in this cell population. Lgr5 mRNA level was also measured and showed no change immediately after Dox but decreased during the regeneration phase. Together these data suggest that, following Dox-induced injury, expansion of intestinal stem cells occurs during mucosal repair. On the basis of available markers this expansion appears to be predominantly the +4 stem cell population rather than those of the crypt base.

Sargramostim in patients with Crohn's disease: results of a phase 1-2 study

BACKGROUND

We aimed to assess the tolerability, pharmacokinetics, safety, and efficacy of sargramostim in Japanese patients with active Crohn's disease (CD).

METHODS

Patients with moderately to severely active CD were enrolled. Step 1 was an open-label, phase 1 study of 2 microg/kg per day sargramostim administered subcutaneously (SC) for 4 weeks, with an optional 8-week extension with 6 microg/kg per day. Step 2 was an open-label, phase 1-2 study of the tolerability and pharmacokinetics of SC sargramostim 6 microg/kg per day over 4 weeks and of 8-week efficacy and safety. Efficacy variables were the proportion of patients achieving a clinical response [> or =100-point decrease from baseline in the CD activity index (CDAI)] and the proportion achieving clinical remission (CDAI < or = 150 points).

RESULTS

Six patients participated in Step 1; five in Step 2. Serum concentrations of sargramostim peaked within 1 h of administration; mean terminal half-life was 2 h. Maximal serum concentrations increased with the dose. Mean accumulation ratios were 0.998 in Step 1 and 0.673 in Step 2. One of the six patients in the Step-1 extension and none of the five in Step 2 achieved a clinical response. Clinical remission was reported in one patient in each step. A notable decrease in median CDAI scores was observed in the extension and Step 2. In responders, improvement tended to be maintained through the 30-day follow-up. Drug-related adverse events included injection-site reaction, pyrexia, back pain, and bone pain.

CONCLUSION

The systemic exposure of sargramostim increased dose-dependently. No accumulation in systemic exposure was associated with the repeated once-daily administration. SC sargramostim at 6 microg/kg per day improved median CDAI scores. A minority of patients experienced clinical remission or clinical response.

Toll-like receptor-induced granulocyte-macrophage colony-stimulating factor secretion is impaired in Crohn's disease by nucleotide oligomerization domain 2-dependent and -independent pathways

Pattern recognition receptors (PRRs) are an integral part of the innate immune system and govern the early control of foreign microorganisms. Single nucleotide polymorphisms (SNPs) in the intracellular pattern recognition receptor nucleotide-binding oligomerization domain-containing protein (NOD2, nucleotide oligomerization domain 2) are associated with Crohn's disease (CD). We investigated the impact of NOD2 polymorphisms on cytokine secretion and proliferation of peripheral blood mononuclear cells (PBMCs) in response to Toll-like receptor (TLR) and NOD2 ligands. Based on NOD2 SNP analyses, 41 CD patients and 12 healthy controls were studied. PBMCs were stimulated with NOD2 and TLR ligands. After 18 h culture supernatants were measured using multiplex assays for the presence of human cytokines granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-1 beta and tumour necrosis factor (TNF)-alpha. In CD patients, TLR-induced GM-CSF secretion was impaired by both NOD2-dependent and -independent mechanisms. Moreover, TNF-alpha production was induced by a TLR-2 ligand, but a down-regulatory function by the NOD2 ligand, muramyl dipeptide, was impaired significantly in CD patients. Intracellular TLR ligands had minimal effect on GM-CSF, TNF-alpha and IL-1beta secretion. CD patients with NOD2 mutations were able to secrete TNF-alpha, but not GM-CSF, upon stimulation with NOD2 and TLR-7 ligands. CD patients have impaired GM-CSF secretion via NOD2-dependent and -independent pathways and display an impaired NOD2-dependent down-regulation of TNF-alpha secretion. The defect in GM-CSF secretion suggests a hitherto unknown role of NOD2 in the pathogenesis of CD and is consistent with the hypothesis that impaired GM-CSF secretion in part constitutes a NOD2-dependent disease risk factor.

Myeloid-derived suppressor cells in inflammatory bowel disease: a new immunoregulatory pathway

BACKGROUND & AIMS

CD11b(+)Gr-1(+) myeloid-derived suppressor cells (MDSCs) have been shown to cause T-cell tolerance in tumor-bearing mice; however, little is known about the role of MDSCs in chronic inflammation. Here, for the first time, we have identified and analyzed their role in inflammatory bowel disease (IBD).

METHODS

Repetitive adoptive transfer of clone 4/T-cell receptor (CL4-TCR) transgenic CD8(+) T cells into VILLIN-hemagglutinin (HA) transgenic mice was performed on days 1, 12, and 27. Recipient mice were analyzed for immunopathology, HA-specific CD8(+) T-cell responses, and CD11b(+)Gr-1(+) MDSCs (frequency, phenotype, expression analysis, and in vitro as well as in vivo function). In addition, peripheral blood from patients with active Crohn's disease and ulcerative colitis was examined for the presence and function of human MDSCs denoted as CD14(+)HLA-DR(-/low) cells.

RESULTS

Repetitive transfer of HA-specific CD8(+) T cells prevented VILLIN-HA recipient mice from development of severe enterocolitis, which is seen after a single transfer of T cells. Repeated transfer of antigen-specific T cells led to an increase in the frequency of nitric oxide synthase 2 and arginase-expressing CD11b(+)Gr-1(+) MDSCs in spleen and intestine of VILLIN-HA mice with immunosuppressive function. Cotransfer of MDSCs with HA-specific CD8(+) T cells into naive VILLIN-HA mice ameliorated enterocolitis, indicating a direct immune regulatory effect of MDSCs on induction of IBD by antigen-specific T cells. Finally, an increase in the frequency of human MDSCs with suppressor function was observed in peripheral blood from patients with IBD.

CONCLUSIONS

These results identify MDSCs as a new immune regulatory pathway in IBD.

Granulocyte macrophage colony-stimulating factor ameliorates DSS-induced experimental colitis

BACKGROUND

Sargramostim, granulocyte macrophage colony-stimulating factor (GM-CSF), a hematopoietic growth factor, stimulates cells of the intestinal innate immune system. Clinical trials show that sargramostim induces clinical response and remission in patients with active Crohn's disease. To study the mechanism, we examined the effects of GM-CSF in the dextran sulfate sodium (DSS)-induced acute colitis model. We hypothesized that GM-CSF may work through effects on dendritic cells (DCs).

METHODS

Acute colitis was induced in Balb/c mice by administration of DSS in drinking water. Mice were treated with daily GM-CSF or phosphate-buffered saline (PBS). To probe the role of plasmacytoid DCs (pDCs) in the response to GM-CSF, we further examined the effects of monoclonal antibody 440c, which is specific for a sialic acid-binding immunoglobulin (Ig)-like lectin expressed on pDCs.

RESULTS

GM-CSF ameliorates acute DSS-induced colitis, resulting in significantly improved clinical parameters and histology. Microarray analysis showed reduced expression of proinflammatory genes including TNF-alpha and IL1-beta; the results were further confirmed by real-time reverse-transcriptase polymerase chain reaction and serum Bio-plex analysis. GM-CSF treatment significantly expands pDCs and type 1 IFN production. Administration of mAb 440c completely blocked the therapeutic effect of GM-CSF. GM-CSF is also effective in RAG1(-/-) mice, demonstrating activity-independent effects on T and B cells. IFN-beta administration mimics the therapeutic effect of GM-CSF in DSS-treated mice. GM-CSF increases systemic and mucosal type 1 IFN expression and exhibits synergy with pDC activators, such as microbial cytosine-phosphate-guanosine (CpG) DNA.

CONCLUSIONS

GM-CSF is effective in the treatment of DSS colitis in a mechanism involving the 440c(+) pDC population.

Intestine-specific ablation of mouse atonal homolog 1 (Math1) reveals a role in cellular homeostasis

BACKGROUND & AIMS

Math1 (Atoh1) is a basic helix-loop-helix transcription factor important for intestinal secretory cell differentiation. We hypothesized that Math1 is important in cell fate commitment, and therefore mediates proliferative homeostasis and the adaptive response following intestinal resection in the adult intestine.

METHODS

We generated mice with an intestine-specific mosaic deletion of Math1 (Math1(Delta intestine)) using the Cre/loxP system. Histologic analysis in adult Math1(Delta intestine) and wild-type littermates at baseline and following small bowel resection or sham surgery was performed.

RESULTS

We observed loss of Paneth, goblet, and enteroendocrine cells in Math1-null crypts. In addition, aberrant activation of the Math1 promoter occurred in absorptive enterocytes derived from Math1-null crypts, suggesting a change in cell fate. Proliferation was increased but apoptosis unchanged in Math1-mutant crypts compared to adjacent wild-type crypts. Math1(Delta intestine) mice and wild-type littermates displayed similar physiologic adaptive responses to small bowel resection as measured by changes in body weight and ileal wet weight. In contrast, Math1-mutant crypts displayed a blunted adaptive response compared to adjacent wild-type crypts.

CONCLUSIONS

We show that Math1 is essential for adult intestinal secretory cell production, and in its absence cells destined to a secretory phenotype instead adopt an absorptive phenotype. Subtle abnormalities of proliferation within Math1-null crypts in Math1(Delta intestine) mice were identified, together with a substantial defect in the adaptive response of Math1-null crypts following small bowel resection. Our results suggest that Math1 is critical for both cell fate determination within the intestinal epithelium and for regulation of the response to intestinal resection.

Innovative therapeutics for inflammatory bowel disease

Inflammatory bowel diseases (IBD) are chronic inflammatory conditions of the gastrointestinal tract, which clinically present as one of two disorders, Crohn’s disease or ulcerative colitis. Mainstays of drug treatments for IBD include aminosalicylates, corticosteroids and immunosuppressants such as azathioprine, methotrexate and cyclosporin. Advances in basic research of the pathophysiological process in IBD have been applied to generate a variety of new therapeutics targeting at different levels of the inflammatory processes. New therapies are classified as: (1) Anti-TNFα antibodies; (2) Recombinant cytokines; (3) Selective adhesion blockade; (4) Growth factors; (5) Innate immunostimulation; (6) Nucleic acid based therapies; (7) Gene therapy; (8) Autologous bone-marrow transplantation; (9) Helminths and (10) Extracorporeal immunomodulation. All treatments have the potential to provide more effective and safe treatment for IBD.

Rapid expansion of intestinal secretory lineages following a massive small bowel resection in mice

Following massive small bowel resection (SBR) in mice, there are sustained increases in crypt depth and villus height, resulting in enhanced mucosal surface area. The early mechanisms responsible for resetting and sustaining this increase are presently not understood. We hypothesized that expansion of secretory lineages is an early and sustained component of the adaptive response. This was assessed in the ileum by quantitative morphometry at 12 h, 36 h, 7 days, and 28 days and by quantitative RT-PCR of marker mRNAs for proliferation and differentiated goblet, Paneth cell, and enterocyte genes at 12 h after 50% SBR or sham operation. As predicted, SBR elicited increases of both crypt and villus epithelial cells, which were sustained though the 28 days of the experiment. Significant increases in the overall number and percentage of both Paneth and goblet cells within intestinal epithelium occurred by 12 h and were sustained up to 28 days after SBR. The increases of goblet cells after SBR were initially observed within villi at 12 h, with marked increases occurring in crypts at 36 h and 7 days. Consistent with this finding, qRT-PCR demonstrated significant increases in the expression of mRNAs associated with proliferation (c-myc) and differentiated goblet cells (Tff3, Muc2) and Paneth cells (lysozyme), whereas mRNA associated with differentiated enterocytes (sucrase-isomaltase) remained unchanged. From these data, we speculate that early expansion of intestinal secretory lineages within the epithelium of the ileum occurs following SBR, possibly serving to amplify the signal responsible for initiating and sustaining intestinal adaptation.

Crohn’s disease: Innate immunodeficiency?

In the past, Crohn’s disease (CD) has been understood primarily as an immunologic disorder characterized by an abnormal T-cell response. Recent in vitro and in vivo data suggests that CD may instead be precipitated by innate immune dysfunction resulting from a combination of genetic and environmental factors. Some reports have demonstrated a defective immune response in a variety of other cellular components, including neutrophils, monocytes and dendritic cells. Recent studies of granulocyte-macrophage colony-stimulating factor (GM-CSF) in CD, aiming to stimulate the innate immune system with the conception that an innate immune defect underlies the development of the disease, have been demonstrated a clinical benefit and reinforce this evolving understanding of the disease.

Growth factors as treatment options for intestinal inflammation

On the basis of several studies that have been completed to date, some growth factors appear promising for the treatment of inflammatory bowel disease: keratinocyte-like growth factor-2 (KGF-2), epidermal growth factor (EGF) enemas used in combination with oral mesalamine, somatropin (human growth hormone), and sargramostim (recombinant human GM-CSF). The results of these studies are highlighted and suggest that new insights into the regulation of intestinal immunity may provide effective synergistic or single-agent treatment alternatives to immunosuppression for inflammatory bowel disease. These data focus on the reparative components of mucosal homeostasis.

Paneth cells and the innate immune response

PURPOSE OF REVIEW

To review recently published studies presenting novel and relevant information on Paneth cells and their function.

RECENT FINDINGS

Paneth cells are secretory epithelial cells which are predominantly found in the small-intestinal crypts of Lieberkühn. Their most abundant products are alpha-defensins, which are endogenous antibiotics with activity against gram-negative and gram-positive bacteria, fungi, viruses and protozoa. The differentiation from stem-cell progenitors to Paneth cells is regulated by Wnt signalling via a complex gene programme, terminally including defensins. A disturbance of Paneth-cell differentiation and function may predispose to intestinal infections and appears to be a critical factor in the pathogenesis of ileal Crohn's disease, an inflammatory disease of the intestinal tract.

SUMMARY

It is conceivable that these recent findings together with a better understanding of underlying mechanisms involved in the regulation and biology of Paneth cells will open up new therapeutic avenues for preventing infection as well as for causally treating inflammatory bowel diseases.

PPARbeta/delta regulates paneth cell differentiation via controlling the hedgehog signaling pathway

BACKGROUND & AIMS

All 4 differentiated epithelial cell types found in the intestinal epithelium derive from the intestinal epithelial stem cells present in the crypt unit, in a process whose molecular clues are intensely scrutinized. Peroxisome proliferator-activated receptor beta (PPARbeta) is a nuclear hormone receptor activated by fatty acids and is highly expressed in the digestive tract. However, its function in intestinal epithelium homeostasis is understood poorly.

METHODS

To assess the role of PPARbeta in the small intestinal epithelium, we combined various cellular and molecular approaches in wild-type and PPARbeta-mutant mice.

RESULTS

We show that the expression of PPARbeta is particularly remarkable at the bottom of the crypt of the small intestine where Paneth cells reside. These cells, which have an important role in the innate immunity, are strikingly affected in PPARbeta-null mice. We then show that Indian hedgehog (Ihh) is a signal sent by mature Paneth cells to their precursors, negatively regulating their differentiation. Importantly, PPARbeta acts on Paneth cell homeostasis by down-regulating the expression of Ihh, an effect that can be mimicked by cyclopamine, a known inhibitor of the hedgehog signaling pathway.

CONCLUSIONS

We unraveled the Ihh-dependent regulatory loop that controls mature Paneth cell homeostasis and its modulation by PPARbeta. PPARbeta currently is being assessed as a drug target for metabolic diseases; these results reveal some important clues with respect to the signals controlling epithelial cell fate in the small intestine.

Sargramostim for active Crohn's disease

BACKGROUND

Sargramostim, granulocyte-macrophage colony-stimulating factor, a hematopoietic growth factor, stimulates cells of the intestinal innate immune system. Preliminary studies suggest sargramostim may have activity in Crohn's disease. To evaluate this novel therapeutic approach, we conducted a randomized, placebo-controlled trial.

METHODS

Using a 2:1 ratio, we randomly assigned 124 patients with moderate-to-severe active Crohn's disease to receive 6 mug of sargramostim per kilogram per day or placebo subcutaneously for 56 days. Antibiotics and aminosalicylates were allowed; immunosuppressants and glucocorticoids were prohibited. The primary end point was a clinical response, defined by a decrease from baseline of at least 70 points in the Crohn's Disease Activity Index (CDAI) at the end of treatment (day 57). Other end points included changes in disease severity and the health-related quality of life and adverse events.

RESULTS

There was no significant difference in the rate of the primary end point of a clinical response defined by a decrease of at least 70 points in the CDAI score on day 57 between the sargramostim and placebo groups (54 percent vs. 44 percent, P=0.28). However, significantly more patients in the sargramostim group than in the placebo group reached the secondary end points of a clinical response defined by a decrease from baseline of at least 100 points in the CDAI score on day 57 (48 percent vs. 26 percent, P=0.01) and of remission, defined by a CDAI score of 150 points or less on day 57 (40 percent vs. 19 percent, P=0.01). The rates of either type of clinical response and of remission were significantly higher in the sargramostim group than in the placebo group on day 29 of treatment and 30 days after treatment. The sargramostim group also had significant improvements in the quality of life. Mild-to-moderate injection-site reactions and bone pain were more common in the sargramostim group, and three patients in this group had serious adverse events possibly or probably related to treatment.

CONCLUSIONS

This study was negative for the primary end point, but findings for the secondary end points suggest that sargramostim therapy decreased disease severity and improved the quality of life in patients with active Crohn's disease.

Altered epithelial cell lineage allocation and global expansion of the crypt epithelial stem cell population are associated with ileitis in SAMP1/YitFc mice

Crohn's disease is characterized by cycles of mucosal injury and ulceration followed by epithelial regeneration and restoration of normal epithelial function. In this study, we examined whether ileitis in SAMP1/YitFc mice, a recombinant-inbred line that spontaneously develops ileitis resembling human Crohn's disease, was associated with alterations in normal patterns of epithelial differentiation or changes in epithelial regeneration after experimental injury. Increased numbers of Paneth, goblet, and intermediate cells were present focally in the ileum of SAMP1/YitFc mice by 4 weeks of age, before any histological evidence of acute or chronic inflammation. This increase in secretory cells became more pronounced at sites of ileitis with increasing age and inflammation. Additionally, there was mispositioning of Paneth and intermediate cells along the crypt-to-villus unit. A concomitant reduction in the number of absorptive enterocytes was observed. In contrast to the ileal-specific changes in lineage allocation, crypt stem cell numbers began to increase in both the ileum and proximal jejunum at the onset of inflammation in SAMP1/YitFc mice. These data suggest that the alterations in epithelial cell differentiation and increases in the size of the crypt stem cell population observed in SAMP1/YitFc mice are regulated by distinct mechanisms. We speculate that these epithelial alterations may play a role in the pathogenesis of ileitis in this murine model of Crohn's disease.