BMP Signaling in Development, Stem Cells, and Diseases of the Gastrointestinal Tract

Jag1/2 maintain esophageal homeostasis and suppress foregut tumorigenesis by restricting the basal progenitor cell pool

Basal progenitor cells are crucial for maintaining foregut (the esophagus and forestomach) homeostasis. When their function is dysregulated, it can promote inflammation and tumorigenesis. However, the mechanisms underlying these processes remain largely unclear. Here, we employ genetic mouse models to reveal that Jag1/2 regulate esophageal homeostasis and foregut tumorigenesis by modulating the function of basal progenitor cells. Deletion of Jag1/2 in mice disrupts esophageal and forestomach epithelial homeostasis. Mechanistically, Jag1/2 deficiency impairs activation of Notch signaling, leading to reduced squamous epithelial differentiation and expansion of basal progenitor cells. Moreover, Jag1/2 deficiency exacerbates the deoxycholic acid (DCA)-induced squamous epithelial injury and accelerates the initiation of squamous cell carcinoma (SCC) in the forestomach. Importantly, expression levels of JAG1/2 are lower in the early stages of human esophageal squamous cell carcinoma (ESCC) carcinogenesis. Collectively, our study demonstrates that Jag1/2 are important for maintaining esophageal and forestomach homeostasis and the onset of foregut SCC.

A Natural Peptide from A Traditional Chinese Medicine Has the Potential to Treat Chronic Atrophic Gastritis by Activating Gastric Stem Cells

Chronic atrophic gastritis (AG) is initiated mainly by Helicobacter pylori infection, which may progress to stomach cancer following the Correa's cascade. The current treatment regimen is H. pylori eradication, yet evidence is lacking that this treatment is effective on later stages of AG especially gastric gland atrophy. Here, using AG mouse model, patient samples, gastric organoids, and lineage tracing, this study unraveled gastric stem cell (GSC) defect as a crucial pathogenic factor in AG in mouse and human. Moreover, a natural peptide is isolated from a traditional Chinese medicine that activated GSCs to regenerate gastric epithelia in experimental AG models and revitalized the atrophic gastric organoids derived from patients. It is further shown that the peptide exerts its functions by stabilizing the EGF-EGFR complex and specifically activating the downstream ERK and Stat1 signaling. Overall, these findings advance the understanding of AG pathogenesis and open a new avenue for AG treatment.

Vitamin D opposes multilineage cell differentiation induced by Notch inhibition and BMP4 pathway activation in human colon organoids

Understanding the mechanisms involved in colonic epithelial differentiation is key to unraveling the alterations causing inflammatory conditions and cancer. Organoid cultures provide an unique tool to address these questions but studies are scarce. We report a differentiation system toward enterocytes and goblet cells, the two major colonic epithelial cell lineages, using colon organoids generated from healthy tissue of colorectal cancer patients. Culture of these organoids in medium lacking stemness agents resulted in a modest ultrastructural differentiation phenotype with low-level expression of enterocyte (KLF4, KRT20, CA1, FABP2) and goblet cell (TFF2, TFF3, AGR2) lineage markers. BMP pathway activation through depletion of Noggin and addition of BMP4 resulted in enterocyte-biased differentiation. Contrarily, blockade of the Notch pathway using the γ-secretase inhibitor dibenzazepine (DBZ) favored goblet cell differentiation. Combination treatment with BMP4 and DBZ caused a balanced strong induction of both lineages. In contrast, colon tumor organoids responded poorly to BMP4 showing only weak signals of cell differentiation, and were unresponsive to DBZ. We also investigated the effects of 1α,25-dihydroxyvitamin D3 (calcitriol) on differentiation. Calcitriol attenuated the effects of BMP4 and DBZ on colon normal organoids, with reduced expression of differentiation genes and phenotype. Consistently, in normal organoids, calcitriol inhibited early signaling by BMP4 as assessed by reduction of the level of phospho-SMAD1/5/8. Our results show that BMP and Notch signaling play key roles in human colon stem cell differentiation to the enterocytic and goblet cell lineages and that calcitriol modulates these processes favoring stemness features.

Epithelial-mesenchymal interaction protects normal colonocytes from 4-HNE-induced phenotypic transformation

INTRODUCTION

Recent studies have shown that epithelial-stromal interactions could play a role in the development of colorectal cancer. Here, we investigated the role of fibroblasts in the transformation of normal colonocytes induced by 4-HNE.

METHODS

Normal Co colonocytes and nF fibroblasts from the same mouse colon were exposed, in monoculture (m) or coculture (c), to 4-HNE (5 μM) twice weekly for 3 weeks. Gene expression was then analysed and the ability of Co colonocytes to grow in anchorage-independent conditions was tested in soft agar. Fibroblasts previously treated or not with 4-HNE were also seeded in culture inserts positioned above the agar layers to allow paracrine exchanges with colonocytes.

RESULTS

First, 60% of the genes studied were modulated by coculture in Co colonocytes, with notably increased expression of BMP receptors. Furthermore, while 4-HNE increased the ability of monoculture-treated Co colonocytes to form colonies, this effect was not observed in coculture-treated Co colonocytes. Adding a selective BMPR1 inhibitor during the treatment phase abolished the protective effect of coculture. Conversely, addition of a BMP4 agonist to the medium of monoculture-treated Co colonocytes prevented phenotypic transformation by 4-HNE. Second, the presence of nF(m)-HNE fibroblasts during the soft agar assay increased the number and size of Co(m) colonocyte colonies, regardless of whether these cells had been previously treated with 4-HNE in monoculture. For soft agar assays performed with nF(c) and Co(c) cells initially treated in coculture, only the reassociation between Co(c)-HNE and nF(c)-HNE resulted in a small increase in the number of colonies.

CONCLUSIONS

During the exposure phase, the epithelial-mesenchymal interaction protected colonocytes from 4-HNE-induced phenotypic transformation via activation of the BMP pathway. This intercellular dialogue also limited the ability of fibroblasts to subsequently promote colonocyte-anchorage-independent growth. In contrast, fibroblasts pre-exposed to 4-HNE in monoculture strongly increased the ability of Co(m) colonocytes to form colonies.

Gastric intestinal metaplasia: progress and remaining challenges

Most gastric cancers arise in the setting of chronic inflammation which alters gland organization, such that acid-pumping parietal cells are lost, and remaining cells undergo metaplastic change in differentiation patterns. From a basic science perspective, recent progress has been made in understanding how atrophy and initial pyloric metaplasia occur. However, pathologists and cancer biologists have long been focused on the development of intestinal metaplasia patterns in this setting. Arguably, much less progress has been made in understanding the mechanisms that lead to the intestinalization seen in chronic atrophic gastritis and pyloric metaplasia. One plausible explanation for this disparity lies in the notable absence of reliable and reproducible small animal models within the field, which would facilitate the investigation of the mechanisms underlying the development of gastric intestinal metaplasia (GIM). This review offers an in-depth exploration of the current state of research in GIM, shedding light on its pivotal role in tumorigenesis. We delve into the histological subtypes of GIM and explore their respective associations with tumor formation. We present the current repertoire of biomarkers utilized to delineate the origins and progression of GIM and provide a comprehensive survey of the available, albeit limited, mouse lines employed for modeling GIM and engage in a discussion regarding potential cell lineages that serve as the origins of GIM. Finally, we expound upon the myriad signaling pathways recognized for their activity in GIM and posit on their potential overlap and interactions that contribute to the ultimate manifestation of the disease phenotype. Through our exhaustive review of the progression from gastric disease to GIM, we aim to establish the groundwork for future research endeavors dedicated to elucidating the etiology of GIM and developing strategies for its prevention and treatment, considering its potential precancerous nature.

The zinc finger protein CG12744 regulates intestinal stem cells in aged Drosophila through the EGFR and BMP pathways

AIM

Aging is a process characterized by a time-dependent decline in the functionality of adult stem cells and is closely associated with age-related diseases. However, understanding how aging promotes disease and its underlying causes is critical for combating aging.

MAIN METHODS

The offspring of UAS-Gal4 and CG12744RNAiDrosophila were cultured for 33 days to evaluate the role of CG12744 in the aging intestine. Immunofluorescence was performed to detect specific cell type markers for assessing proliferation and differentiation. qRT-PCR was used to observe the changes in signaling regulating intestinal homeostasis in the aging intestine after CG12744 knockdown. 16S rRNA-seq analysis was also conducted to elucidate the role of gut microbes in CG12744-mediated intestinal dysfunction.

KEY FINDINGS

The mRNA levels of CG12744 were significantly increased in the aged midguts. Knockdown of CG12744 in progenitor cells further exacerbates the age-related intestinal hyperplasia and dysfunction. In particular, upon depletion of CG12744 in progenitors, enteroblasts (EBs) exhibited an increased propensity to differentiate along the enteroendocrine cell (EE) lineage. In contrast, the overexpression of CG12744 in progenitor cells restrained age-related gut hyperplasia in Drosophila. Moreover, CG12744 prevented age-related intestinal stem cell (ISC) overproliferation and differentiation by modulating the EGFR, JNK, and BMP pathways. In addition, the inhibition of CG12744 resulted in a significant increase in the gut microbial composition in aging flies.

SIGNIFICANCE

This study established a role for the CG12744 in regulating the proliferation and differentiation of adult stem cells, thereby identifying a potential therapeutic target for diseases caused by age-related dysfunction stem cell dysfunction.

Opsin-Free Activation of Bmp Receptors by a Femtosecond Laser

Bone morphogenetic protein (BMP) signaling plays a vital role in differentiation, organogenesis, and various cell processes. As a member of TGF-β superfamily, the BMP initiation usually accompanies crosstalk with other signaling pathways and simultaneously activates some of them. It is quite challenging to solely initiate an individual pathway. In this study, an opsin-free optical method to specifically activate BMP receptors (BMPR) and subsequent pSmad1/5/8 cascades by a single-time scan of a tightly-focused femtosecond laser in the near infrared range is reported. Via transient two-photon excitation to intrinsic local flavins near the cell membrane, the photoactivation drives conformational changes of preformed BMPR complexes to enable their bonding and phosphorylation of the GS domain in BMPR-I by BMPR-II. The pSmad1/5/8 signaling is initiated by this method, while p38 and pSmad2 are rarely perturbed. Based on a microscopic system, primary adipose-derived stem cells in an area of 420  × 420 µm2 are photoactivated by a single-time laser scanning for 1.5 s and exhibit pSmad1/5/8 upregulation and osteoblastic differentiation after 21 days. Hence, an opsin-free, specific, and noninvasive optical method to initiate BMP signaling, easily accomplished by a two-photon microscope system is reported.

Vibrio cholerae arrests intestinal epithelial proliferation through T6SS-dependent activation of the bone morphogenetic protein pathway

To maintain an effective barrier, intestinal progenitor cells must divide at a rate that matches the loss of dead and dying cells. Otherwise, epithelial breaches expose the host to systemic infection by gut-resident microbes. Unlike most pathogens, Vibrio cholerae blocks tissue repair by arresting progenitor proliferation in the Drosophila model. At present, we do not understand how V. cholerae circumvents such a critical antibacterial defense. We find that V. cholerae blocks epithelial repair by activating the growth inhibitor bone morphogenetic protein (BMP) pathway in progenitors. Specifically, we show that interactions between V. cholerae and gut commensals initiate BMP signaling via host innate immune defenses. Notably, we find that V. cholerae also activates BMP and arrests proliferation in zebrafish intestines, indicating an evolutionarily conserved link between infection and failure in tissue repair. Our study highlights how enteric pathogens engage host immune and growth regulatory pathways to disrupt intestinal epithelial repair.

Death receptor 5 is required for intestinal stem cell activity during intestinal epithelial renewal at homoeostasis

Intestinal epithelial renewal, which depends on the proliferation and differentiation of intestinal stem cells (ISCs), is essential for epithelial homoeostasis. Understanding the mechanism controlling ISC activity is important. We found that death receptor 5 (DR5) gene deletion (DR5-/-) mice had impaired epithelial absorption and barrier function, resulting in delayed weight gain, which might be related to the general reduction of differentiated epithelial cells. In DR5-/- mice, the expression of ISC marker genes, the number of Olfm4+ ISCs, and the number of Ki67+ and BrdU+ cells in crypt were reduced. Furthermore, DR5 deletion inhibited the expression of lineage differentiation genes driving ISC differentiation into enterocytes, goblet cells, enteroendocrine cells, and Paneth cells. Therefore, DR5 gene loss may inhibit the intestinal epithelial renewal by dampening ISC activity. The ability of crypts from DR5-/- mice to form organoids decreased, and selective DR5 activation by Bioymifi promoted organoid growth and the expression of ISC and intestinal epithelial cell marker genes. Silencing of endogenous DR5 ligand TRAIL in organoids down-regulated the expression of ISC and intestinal epithelial cell marker genes. So, DR5 expressed in intestinal crypts was involved in the regulation of ISC activity. DR5 deletion in vivo or activation in organoids inhibited or enhanced the activity of Wnt, Notch, and BMP signalling through regulating the production of Paneth cell-derived ISC niche factors. DR5 gene deletion caused apoptosis and DNA damage in transit amplifying cells by inhibiting ERK1/2 activity in intestinal crypts. Inhibition of ERK1/2 with PD0325901 dampened the ISC activity and epithelial regeneration. In organoids, when Bioymifi's effect in activating ERK1/2 activity was completely blocked by PD0325901, its role in stimulating ISC activity and promoting epithelial regeneration was also eliminated. In summary, DR5 in intestinal crypts is essential for ISC activity during epithelial renewal under homoeostasis.

Ischemia-reperfusion injury: molecular mechanisms and therapeutic targets

Ischemia-reperfusion (I/R) injury paradoxically occurs during reperfusion following ischemia, exacerbating the initial tissue damage. The limited understanding of the intricate mechanisms underlying I/R injury hinders the development of effective therapeutic interventions. The Wnt signaling pathway exhibits extensive crosstalk with various other pathways, forming a network system of signaling pathways involved in I/R injury. This review article elucidates the underlying mechanisms involved in Wnt signaling, as well as the complex interplay between Wnt and other pathways, including Notch, phosphatidylinositol 3-kinase/protein kinase B, transforming growth factor-β, nuclear factor kappa, bone morphogenetic protein, N-methyl-D-aspartic acid receptor-Ca2+-Activin A, Hippo-Yes-associated protein, toll-like receptor 4/toll-interleukine-1 receptor domain-containing adapter-inducing interferon-β, and hepatocyte growth factor/mesenchymal-epithelial transition factor. In particular, we delve into their respective contributions to key pathological processes, including apoptosis, the inflammatory response, oxidative stress, extracellular matrix remodeling, angiogenesis, cell hypertrophy, fibrosis, ferroptosis, neurogenesis, and blood-brain barrier damage during I/R injury. Our comprehensive analysis of the mechanisms involved in Wnt signaling during I/R reveals that activation of the canonical Wnt pathway promotes organ recovery, while activation of the non-canonical Wnt pathways exacerbates injury. Moreover, we explore novel therapeutic approaches based on these mechanistic findings, incorporating evidence from animal experiments, current standards, and clinical trials. The objective of this review is to provide deeper insights into the roles of Wnt and its crosstalk signaling pathways in I/R-mediated processes and organ dysfunction, to facilitate the development of innovative therapeutic agents for I/R injury.

The MuSK-BMP pathway maintains myofiber size in slow muscle through regulation of Akt-mTOR signaling

Myofiber size regulation is critical in health, disease, and aging. MuSK (muscle-specific kinase) is a BMP (bone morphogenetic protein) co-receptor that promotes and shapes BMP signaling. MuSK is expressed at all neuromuscular junctions and is also present extrasynaptically in the mouse soleus, whose predominantly oxidative fiber composition is akin to that of human muscle. To investigate the role of the MuSK-BMP pathway in vivo, we generated mice lacking the BMP-binding MuSK Ig3 domain. These ∆Ig3-MuSK mice are viable and fertile with innervation levels comparable to wild type. In 3-month-old mice, myofibers are smaller in the slow soleus, but not in the fast tibialis anterior (TA). Transcriptomic analysis revealed soleus-selective decreases in RNA metabolism and protein synthesis pathways as well as dysregulation of IGF1-Akt-mTOR pathway components. Biochemical analysis showed that Akt-mTOR signaling is reduced in soleus but not TA. We propose that the MuSK-BMP pathway acts extrasynaptically to maintain myofiber size in slow muscle by promoting protein synthetic pathways including IGF1-Akt-mTOR signaling. These results reveal a novel mechanism for regulating myofiber size in slow muscle and introduce the MuSK-BMP pathway as a target for promoting muscle growth and combatting atrophy.

Agaricus bisporus-Derived Glucosamine Hydrochloride Regulates VEGF through BMP Signaling to Promote Zebrafish Vascular Development and Impairment Repair

Glucosamine hydrochloride (GAH) is a natural component of glycoproteins present in almost all human tissues and participates in the construction of human tissues and cell membranes. GAH has a wide range of biological activities, particularly in anti-inflammatory and osteogenic damage repair. At present, little is known about how GAH functions in angiogenesis. To determine the role of GAH on vascular development and impairment repair, we used the inhibitors VRI, DMH1, and dorsomorphin (DM) to construct vascular-impaired models in Tg(kdrl: mCherry) transgenic zebrafish. We then treated with GAH and measured its repair effects on vascular impairment through fluorescence intensity, mRNA, and protein expression levels of vascular-specific markers. Our results indicate that GAH promotes vascular development and repairs impairment by regulating the vascular endothelial growth factor (VEGF) signaling pathway through modulation of bone morphogenetic protein (BMP) signaling. This study provides an experimental basis for the development of GAH as a drug to repair vascular diseases.

BMP signaling in cancer stemness and differentiation

The BMP (Bone morphogenetic protein) signaling pathway plays a central role in metazoan biology, intricately shaping embryonic development, maintaining tissue homeostasis, and influencing disease progression. In the context of cancer, BMP signaling exhibits context-dependent dynamics, spanning from tumor suppression to promotion. Cancer stem cells (CSCs), a modest subset of neoplastic cells with stem-like attributes, exert substantial influence by steering tumor growth, orchestrating therapy resistance, and contributing to relapse. A comprehensive grasp of the intricate interplay between CSCs and their microenvironment is pivotal for effective therapeutic strategies. Among the web of signaling pathways orchestrating cellular dynamics within CSCs, BMP signaling emerges as a vital conductor, overseeing CSC self-renewal, differentiation dynamics, and the intricate symphony within the tumor microenvironment. Moreover, BMP signaling's influence in cancer extends beyond CSCs, intricately regulating cellular migration, invasion, and metastasis. This multifaceted role underscores the imperative of comprehending BMP signaling's contributions to cancer, serving as the foundation for crafting precise therapies to navigate multifaceted challenges posed not only by CSCs but also by various dimensions of cancer progression. This article succinctly encapsulates the diverse roles of the BMP signaling pathway across different cancers, spanning glioblastoma multiforme (GBM), diffuse intrinsic pontine glioma (DIPG), colorectal cancer, acute myeloid leukemia (AML), lung cancer, prostate cancer, and osteosarcoma. It underscores the necessity of unraveling underlying mechanisms and molecular interactions. By delving into the intricate tapestry of BMP signaling's engagement in cancers, researchers pave the way for meticulously tailored therapies, adroitly leveraging its dualistic aspects-whether as a suppressor or promoter-to effectively counter the relentless march of tumor progression.

Reduced LHFPL3-AS2 lncRNA expression is linked to altered epithelial polarity and proliferation, and to ileal ulceration in Crohn disease

Disruption of intestinal epithelial functions is linked to Crohn disease (CD) pathogenesis. We identified a widespread reduction in the expression of long non-coding RNAs (lncRNAs) including LHFPL3-AS2 in the treatment-naïve CD ileum of the RISK pediatric cohort. We validated the reduction of LHFPL3-AS2 in adult CD and noted a further reduction in patients with more severe CD from the RISK cohort. LHFPL3-AS2 knockdown in Caco-2 cells robustly affected epithelial monolayer morphogenesis with markedly reduced confluency and spreading, showing atypical rounding, and clumping. mRNA-seq analysis of LHFPL3-AS2 knockdown cells highlighted the reduction of genes and pathways linked with apical polarity, actin bundles, morphogenesis, and the b-catenin-TCF4 complex. LHFPL3-AS2 knockdown significantly reduced the ability of cells to form an internal lumen within the 3-dimensional (3D) cyst model, with mislocalization of actin and adherent and tight junction proteins, affecting epithelial polarity. LHFPL3-AS2 knockdown also resulted in defective mitotic spindle formation and consequent reduction in epithelial proliferation. Altogether, we show that LHFPL3-AS2 reduction affects epithelial morphogenesis, polarity, mitotic spindle formation, and proliferation, which are key processes in maintaining epithelial homeostasis in CD. Reduced expression of LHFPL3-AS2 in CD patients and its further reduction with ileal ulceration outcome, emphasizes its significance in this context.

Essential Role of BMP4 Signaling in the Avian Ceca in Colorectal Enteric Nervous System Development

The enteric nervous system (ENS) is principally derived from vagal neural crest cells that migrate caudally along the entire length of the gastrointestinal tract, giving rise to neurons and glial cells in two ganglionated plexuses. Incomplete migration of enteric neural crest-derived cells (ENCDC) leads to Hirschsprung disease, a congenital disorder characterized by the absence of enteric ganglia along variable lengths of the colorectum. Our previous work strongly supported the essential role of the avian ceca, present at the junction of the midgut and hindgut, in hindgut ENS development, since ablation of the cecal buds led to incomplete ENCDC colonization of the hindgut. In situ hybridization shows bone morphogenetic protein-4 (BMP4) is highly expressed in the cecal mesenchyme, leading us to hypothesize that cecal BMP4 is required for hindgut ENS development. To test this, we modulated BMP4 activity using embryonic intestinal organ culture techniques and retroviral infection. We show that overexpression or inhibition of BMP4 in the ceca disrupts hindgut ENS development, with GDNF playing an important regulatory role. Our results suggest that these two important signaling pathways are required for normal ENCDC migration and enteric ganglion formation in the developing hindgut ENS.

Skin-type-dependent development of murine mechanosensory neurons

Mechanosensory neurons innervating the skin underlie our sense of touch. Fast-conducting, rapidly adapting mechanoreceptors innervating glabrous (non-hairy) skin form Meissner corpuscles, while in hairy skin, they associate with hair follicles, forming longitudinal lanceolate endings. How mechanoreceptors develop axonal endings appropriate for their skin targets is unknown. We report that mechanoreceptor morphologies across different skin regions are indistinguishable during early development but diverge post-natally, in parallel with skin maturation. Neurons terminating along the glabrous and hairy skin border exhibit hybrid morphologies, forming both Meissner corpuscles and lanceolate endings. Additionally, molecular profiles of neonatal glabrous and hairy skin-innervating neurons largely overlap. In mouse mutants with ectopic glabrous skin, mechanosensory neurons form end-organs appropriate for the altered skin type. Finally, BMP5 and BMP7 are enriched in glabrous skin, and signaling through type I bone morphogenetic protein (BMP) receptors in neurons is critical for Meissner corpuscle morphology. Thus, mechanoreceptor morphogenesis is flexibly instructed by target tissues.

BMP signaling in the development and regeneration of tooth roots: from mechanisms to applications

Short root anomaly (SRA), along with caries, periodontitis, and trauma, can cause tooth loss, affecting the physical and mental health of patients. Dental implants have become widely utilized for tooth restoration; however, they exhibit certain limitations compared to natural tooth roots. Tissue engineering-mediated root regeneration offers a strategy to sustain a tooth with a physiologically more natural function by regenerating the bioengineered tooth root (bio-root) based on the bionic principle. While the process of tooth root development has been reported in previous studies, the specific molecular mechanisms remain unclear. The Bone Morphogenetic Proteins (BMPs) family is an essential factor regulating cellular activities and is involved in almost all tissue development. Recent studies have focused on exploring the mechanism of BMP signaling in tooth root development by using transgenic animal models and developing better tissue engineering strategies for bio-root regeneration. This article reviews the unique roles of BMP signaling in tooth root development and regeneration.

Recent developments on BMPs and their antagonists in inflammatory bowel diseases

Inflammatory bowel diseases (IBDs), including ulcerative colitis, and Crohn's disease, are intestinal disorders characterized by chronic relapsing inflammation. A large proportion of patients with IBD will progress to develop colitis-associated colorectal cancer due to the chronic intestinal inflammation. Biologic agents that target tumour necrosis factor-α, integrin α4β7, and interleukin (IL)12/23p40 have been more successful than conventional therapies in treating IBD. However, drug intolerance and loss of response are serious drawbacks of current biologics, necessitating the development of novel drugs that target specific pathways in IBD pathogenesis. One promising group of candidate molecules are bone morphogenetic proteins (BMPs), members of the TGF-β family involved in regulating morphogenesis, homeostasis, stemness, and inflammatory responses in the gastrointestinal tract. Also worth examining are BMP antagonists, major regulators of these proteins. Evidence has shown that BMPs (especially BMP4/6/7) and BMP antagonists (especially Gremlin1 and follistatin-like protein 1) play essential roles in IBD pathogenesis. In this review, we provide an updated overview on the involvement of BMPs and BMP antagonists in IBD pathogenesis and in regulating the fate of intestinal stem cells. We also described the expression patterns of BMPs and BMP antagonists along the intestinal crypt-villus axis. Lastly, we synthesized available research on negative regulators of BMP signalling. This review summarizes recent developments on BMPs and BMP antagonists in IBD pathogenesis, which provides novel insights into future therapeutic strategies.

Establishment of gastrointestinal assembloids to study the interplay between epithelial crypts and their mesenchymal niche

The cellular organization of gastrointestinal crypts is orchestrated by different cells of the stromal niche but available in vitro models fail to fully recapitulate the interplay between epithelium and stroma. Here, we establish a colon assembloid system comprising the epithelium and diverse stromal cell subtypes. These assembloids recapitulate the development of mature crypts resembling in vivo cellular diversity and organization, including maintenance of a stem/progenitor cell compartment in the base and their maturation into secretory/absorptive cell types. This process is supported by self-organizing stromal cells around the crypts that resemble in vivo organization, with cell types that support stem cell turnover adjacent to the stem cell compartment. Assembloids that lack BMP receptors either in epithelial or stromal cells fail to undergo proper crypt formation. Our data highlight the crucial role of bidirectional signaling between epithelium and stroma, with BMP as a central determinant of compartmentalization along the crypt axis.

The MuSK-BMP pathway maintains myofiber size in slow muscle through regulation of Akt- mTOR signaling

Myofiber size regulation is critical in health, disease, and aging. MuSK (muscle-specific kinase) is a BMP (bone morphogenetic protein) co-receptor that promotes and shapes BMP signaling. MuSK is expressed at all neuromuscular junctions and is also present extrasynaptically in the slow soleus muscle. To investigate the role of the MuSK-BMP pathway in vivo we generated mice lacking the BMP-binding MuSK Ig3 domain. These ΔIg3-MuSKmice are viable and fertile with innervation levels comparable to wild type. In 3-month-old mice myofibers are smaller in the slow soleus, but not in the fast tibialis anterior (TA). Transcriptomic analysis revealed soleus-selective decreases in RNA metabolism and protein synthesis pathways as well as dysregulation of IGF1-Akt-mTOR pathway components. Biochemical analysis showed that Akt-mTOR signaling is reduced in soleus but not TA. We propose that the MuSK-BMP pathway acts extrasynaptically to maintain myofiber size in slow muscle by promoting protein synthetic pathways including IGF1-Akt-mTOR signaling. These results reveal a novel mechanism for regulating myofiber size in slow muscle and introduce the MuSK-BMP pathway as a target for promoting muscle growth and combatting atrophy.

Osteoarthritis: pathogenic signaling pathways and therapeutic targets

Osteoarthritis (OA) is a chronic degenerative joint disorder that leads to disability and affects more than 500 million population worldwide. OA was believed to be caused by the wearing and tearing of articular cartilage, but it is now more commonly referred to as a chronic whole-joint disorder that is initiated with biochemical and cellular alterations in the synovial joint tissues, which leads to the histological and structural changes of the joint and ends up with the whole tissue dysfunction. Currently, there is no cure for OA, partly due to a lack of comprehensive understanding of the pathological mechanism of the initiation and progression of the disease. Therefore, a better understanding of pathological signaling pathways and key molecules involved in OA pathogenesis is crucial for therapeutic target design and drug development. In this review, we first summarize the epidemiology of OA, including its prevalence, incidence and burdens, and OA risk factors. We then focus on the roles and regulation of the pathological signaling pathways, such as Wnt/β-catenin, NF-κB, focal adhesion, HIFs, TGFβ/ΒΜP and FGF signaling pathways, and key regulators AMPK, mTOR, and RUNX2 in the onset and development of OA. In addition, the roles of factors associated with OA, including MMPs, ADAMTS/ADAMs, and PRG4, are discussed in detail. Finally, we provide updates on the current clinical therapies and clinical trials of biological treatments and drugs for OA. Research advances in basic knowledge of articular cartilage biology and OA pathogenesis will have a significant impact and translational value in developing OA therapeutic strategies.

Insights into bone morphogenetic proteins in cardiovascular diseases

Bone morphogenetic proteins (BMPs) are secretory proteins belonging to the transforming growth factor-β (TGF-β) superfamily. These proteins play important roles in embryogenesis, bone morphogenesis, blood vessel remodeling and the development of various organs. In recent years, as research has progressed, BMPs have been found to be closely related to cardiovascular diseases, especially atherosclerosis, vascular calcification, cardiac remodeling, pulmonary arterial hypertension (PAH) and hereditary hemorrhagic telangiectasia (HHT). In this review, we summarized the potential roles and related mechanisms of the BMP family in the cardiovascular system and focused on atherosclerosis and PAH.

In Silico Study and Effects of BDMC33 on TNBS-Induced BMP Gene Expressions in Zebrafish Gut Inflammation-Associated Arthritis

The bone morphogenic protein (BMP) family is a member of the TGF-beta superfamily and plays a crucial role during the onset of gut inflammation and arthritis diseases. Recent studies have reported a connection with the gut-joint axis; however, the genetic players are still less explored. Meanwhile, BDMC33 is a newly synthesized anti-inflammatory drug candidate. Therefore, in our present study, we analysed the genome-wide features of the BMP family as well as the role of BMP members in gut-associated arthritis in an inflammatory state and the ability of BDMC33 to attenuate this inflammation. Firstly, genome-wide analyses were performed on the BMP family in the zebrafish genome, employing several in silico techniques. Afterwards, the effects of curcumin analogues on BMP gene expression in zebrafish larvae induced with TNBS (0.78 mg/mL) were determined using real time-qPCR. A total of 38 identified BMP proteins were revealed to be clustered in five major clades and contain TGF beta and TGF beta pro peptide domains. Furthermore, BDMC33 suppressed the expression of four selected BMP genes in the TNBS-induced larvae, where the highest gene suppression was in the BMP2a gene (an eight-fold decrement), followed by BMP7b (four-fold decrement), BMP4 (four-fold decrement), and BMP6 (three-fold decrement). Therefore, this study reveals the role of BMPs in gut-associated arthritis and proves the ability of BDMC33 to act as a potential anti-inflammatory drug for suppressing TNBS-induced BMP genes in zebrafish larvae.

Advancing intestinal organoid technology to decipher nano-intestine interactions and treat intestinal disease

With research burgeoning in nanoscience and nanotechnology, there is an urgent need to develop new biological models that can simulate native structure, function, and genetic properties of tissues to evaluate the adverse or beneficial effects of nanomaterials on a host. Among the current biological models, three-dimensional (3D) organoids have developed as powerful tools in the study of nanomaterial-biology (nano-bio) interactions, since these models can overcome many of the limitations of cell and animal models. A deep understanding of organoid techniques will facilitate the development of more efficient nanomedicines and further the fields of tissue engineering and personalized medicine. Herein, we summarize the recent progress in intestinal organoids culture systems with a focus on our understanding of the nature and influencing factors of intestinal organoid growth. We also discuss biomimetic extracellular matrices (ECMs) coupled with nanotechnology. In particular, we analyze the application prospects for intestinal organoids in investigating nano-intestine interactions. By integrating nanotechnology and organoid technology, this recently developed model will fill the gaps left due to the deficiencies of traditional cell and animal models, thus accelerating both our understanding of intestine-related nanotoxicity and the development of nanomedicines.

BMP2 inhibits cell proliferation by downregulating EZH2 in gastric cancer

Gastric cancer is among the most common gastrointestinal malignancies. Recent studies have suggested that bone morphogenetic protein-2 (BMP2) is related to the development and progression of various cancers. Meanwhile, evidence suggests that BMP2 might lead to epigenetic changes in gastric cancer. Thus, we investigated whether BMP2 plays a role in the development of gastric cancer via epigenetic regulation. Cell viability, colony formation, and cell cycle assays were performed to assess the effect of recombinant human BMP2 (rhBMP2) in gastric cancer cells. LDN-193189 and Noggins were used as antagonists of the canonical BMP-SMAD signaling pathway. The protein levels were determined using a western blot analysis. Lentiviral vectors with EZH2 shRNA or EZH2 overexpression were used to mediate the role of EZH2 and the relationship between BMP2 and EZH2 in gastric cancer. We found that rhBMP2 inhibits cell proliferation by arresting the cell cycle in HGC-27 and SNU-216 gastric cancer cells. Neither LDN-193189 nor Noggins, antagonists of the canonical BMP-SMAD signaling pathway, can reverse the effect of rhBMP2 on gastric cancer. Molecularly, rhBMP2 downregulates the expression of EZH2 and H3K27me3, leading to increases in P16 and P21 and decreases in CDK2, CDK4, and CDK6. Altogether, in this study, we demonstrate that BMP2 serves as a tumor suppressor in gastric cancer cells by downregulating EZH2 and H3K27me3 through the non-SMAD BMP pathway, suggesting that BMP2 might be a new therapeutic target for gastric cancer treatment. Abbreviations: BMP: bone morphogenetic protein; TGF-β: transforming growth factor-beta; EZH2: enhancer of zeste homolog 2; H3K27me3: trimethylation histone H3 lysine 27; HRECs: human retinal endothelial cells; PcG: polycomb group; PRC: polycomb repressive complexes.

Elevated Protein Kinase A Activity in Stomach Mesenchyme Disrupts Mesenchymal-epithelial Crosstalk and Induces Preneoplasia

BACKGROUND & AIMS

Mesenchymal-epithelial crosstalk (MEC) in the stomach is executed by pathways such as bone morphogenetic protein (BMP) and extracellular signal-regulated kinase (ERK). Mis-regulation of MEC disrupts gastric homeostasis and causes tumorigenesis. Protein Kinase A (PKA) crosstalks with BMP and ERK signaling; however, PKA function(s) in stomach development and homeostasis remains undefined.

METHODS

We generated a novel Six2-Cre^+/-PKAcαR^fl/wt (CA-PKA) mouse in which expression of constitutive-active PKAcαR was induced in gastric mesenchyme progenitors. Lineage tracing determined spatiotemporal activity of Six2-Cre in the stomach. For phenotyping CA-PKA mice histological, co-immunofluorescence, immunoblotting, mRNA sequencing, and bioinformatics analyses were performed.

RESULTS

Lineage tracing showed that Six2-Cre activity in the stomach is restricted to the mesenchymal compartment. CA-PKA mice showed disruption of gastric homeostasis characterized by aberrant mucosal development and epithelial hyperproliferation; ultimately developing multiple features of gastric corpus preneoplasia including decreased parietal cells, mucous cell hyperplasia, spasmolytic peptide expressing metaplasia with intestinal characteristics, and dysplastic and invasive cystic glands. Furthermore, mutant corpus showed marked chronic inflammation characterized by infiltration of lymphocytes and myeloid-derived suppressor cells along with the upregulation of innate and adaptive immune system components. Striking upregulation of inflammatory mediators and STAT3 activation was observed. Mechanistically, we determined there is an activation of ERK1/2 and downregulation of BMP/SMAD signaling characterized by marked upregulation of BMP inhibitor gremlin 1.

CONCLUSIONS

We report a novel role of PKA signaling in gastric MEC execution and show that PKA activation in the gastric mesenchyme drives preneoplasia by creating a proinflammatory and proproliferative microenvironment associated with the downregulation of BMP/SMAD signaling and activation of ERK1/2.

Regulatory mechanisms of cytoneme-based morphogen transport

During development and tissue homeostasis, cells must communicate with their neighbors to ensure coordinated responses to instructional cues. Cues such as morphogens and growth factors signal at both short and long ranges in temporal- and tissue-specific manners to guide cell fate determination, provide positional information, and to activate growth and survival responses. The precise mechanisms by which such signals traverse the extracellular environment to ensure reliable delivery to their intended cellular targets are not yet clear. One model for how this occurs suggests that specialized filopodia called cytonemes extend between signal-producing and -receiving cells to function as membrane-bound highways along which information flows. A growing body of evidence supports a crucial role for cytonemes in cell-to-cell communication. Despite this, the molecular mechanisms by which cytonemes are initiated, how they grow, and how they deliver specific signals are only starting to be revealed. Herein, we discuss recent advances toward improved understanding of cytoneme biology. We discuss similarities and differences between cytonemes and other types of cellular extensions, summarize what is known about how they originate, and discuss molecular mechanisms by which their activity may be controlled in development and tissue homeostasis. We conclude by highlighting important open questions regarding cytoneme biology, and comment on how a clear understanding of their function may provide opportunities for treating or preventing disease.

Uncoupling the BMP receptor antagonist function from the WNT agonist function of R-spondin 2 using the inhibitory peptide dendrimer RWd

Signaling by bone morphogenetic proteins (BMPs) plays pivotal roles in embryogenesis, adult tissue homeostasis, and disease. Recent studies revealed that the well-established WNT agonist R-spondin 2 (RSPO2) is also a BMP receptor (BMP receptor type 1A) antagonist, with roles in early Xenopus embryogenesis and human acute myeloid leukemia (AML). To uncouple the BMP antagonist function from the WNT agonist function and to promote development of AML therapeutics, here we identified a 10-mer peptide (RW) derived from the thrombospondin 1 domain of RSPO2, which specifically prevents binding between RSPO2 and BMP receptor type 1A without altering WNT signaling. We also show that a corresponding RW dendrimer (RW^d) exhibiting improved half-life relieves inhibition of BMP receptor signaling by RSPO2 in human AML cells, reduces cell growth, and induces differentiation. Moreover, microinjection of RW^d in Xenopus embryos ventralizes the dorsoventral embryonic patterning by upregulating BMP signaling without affecting WNT signaling. Our study corroborates the function of RSPO2 as a BMP receptor antagonist and provides a proof of concept for pharmacologically uncoupling BMP antagonist from WNT agonist functions of RSPO2 using the inhibitor peptide RW^d with enhanced target selectivity and limited side effects.

Bone Morphogenetic Protein 4 Alleviates DSS-Induced Ulcerative Colitis Through Activating Intestinal Stem Cell by Target ID3

Damage to intestinal epithelial cell proliferation or intestinal stem cell (ISC) maintenance may trigger inflammatory bowel disease (IBD), and protecting the ISCs is critical for IBD treatment. Here, we found that in the dextran sulfate sodium (DSS)-induced ulcerative colitis mice model, colon epithelium and Lgr5⁺ intestinal stem cells (ISCs) renew quickly during the first 3 days. We also found that during this renewing period, SMAD4 and bone morphogenetic protein 4 (BMP4) expression were significantly upregulated. An extra BMP4 treatment could preserve the Lgr5⁺ ISCs and the colon epithelium turnover, and could significantly decrease colon mucosal damage. Moreover, we found that BMP4 regulated ID3 expression in the colon epithelium. Depletion of ID3 could significantly reduce the epithelium renewal and ratio of Lgr5⁺ ISCs at the base of crypts. In conclusion, the present study showed that BMP4 could maintain epithelium cellular proliferation and the ISCs function through ID3 in mice with DSS-induced colitis. The administration of exogenous BMP4 supplement could alleviate DSS-induced colitis by restoring epithelium cellular proliferation and ISC function, suggesting the possible therapeutic function of BMP4 for ulcerative colitis.

αSMA+ fibroblasts suppress Lgr5+ cancer stem cells and restrain colorectal cancer progression

The development and progression of solid tumors is dependent on cancer cell autonomous drivers and the tumor microenvironment (TME). Cancer-associated fibroblasts (CAFs) in the TME possess both tumor-promoting and tumor-restraining functions. In the current study, we interrogated the role of αSMA⁺ CAFs in a genetic mouse model of metastatic colorectal cancer (CRC). Selective depletion of αSMA⁺ CAFs resulted in increased tumor invasiveness, lymph node metastasis, and reduced overall survival. Depletion of αSMA⁺ CAFs reduced BMP4 and increased TGFβ1 secretion from stromal cells, and was associated with increased Lgr5⁺ cancer stem-like cells (CSCs) and the generation of an immunosuppressive TME with increased frequency of Foxp3⁺ regulatory T cells and suppression of CD8⁺ T cells. This study demonstrates that αSMA⁺ CAFs in CRC exert tumor-restraining functions via BMP4/TGFβ1 paracrine signaling that serves to suppress Lgr5⁺ CSCs and promote anti-tumor immunity, ultimately limiting CRC progression.

Obesity and intestinal stem cell susceptibility to carcinogenesis

Background

Obesity is a top public health problem associated with an increase in colorectal cancer incidence. Stem cells are the chief cells in tissue homeostasis that self-renew and differentiate into other cells to regenerate the organ. It is speculated that an increase in stem cell pool makes cells susceptible to carcinogenesis. In this review, we looked at the recent investigations linking obesity/high-fat diet-induced obesity to intestinal carcinogenesis with regard to intestinal stem cells and their niche.

Findings

High-fat diet-induced obesity may rise intestinal carcinogenesis by increased Intestinal stem cells (ISC)/progenitor’s population, stemness, and niche independence through activation of PPAR-δ with fatty acids, hormonal alterations related to obesity, and low-grade inflammation. However, these effects may possibly relate to the interaction between fats and carbohydrates, and not a fatty acid per se. Nonetheless, literature studies are inconsistency in their results, probably due to the differences in the diet components and limitations of genetic models used.

Conclusion

High-fat diet-induced obesity affects carcinogenesis by changing ISC proliferation and function. However, a well-matched diet and the reliable colorectal cancer models that mimic human carcinogenesis is necessary to clearly elucidate the influence of high-fat diet-induced obesity on ISC behavior.

Stem cell and niche regulation in human short bowel syndrome

Loss of functional small bowel surface area following surgical resection for disorders such as Crohn’s disease, intestinal ischemic injury, radiation enteritis, and in children, necrotizing enterocolitis, atresia, and gastroschisis, may result in short bowel syndrome, with attendant high morbidity, mortality, and health care costs in the United States. Following resection, the remaining small bowel epithelium mounts an adaptive response, resulting in increased crypt cell proliferation, increased villus height, increased crypt depth, and enhanced nutrient and electrolyte absorption. Although these morphologic and functional changes are well described in animal models, the adaptive response in humans is less well understood. Clinically the response is unpredictable and often inadequate. Here we address the hypotheses that human intestinal stem cell populations are expanded and that the stem cell niche is regulated following massive gut resection in short bowel syndrome (SBS). We use intestinal enteroid cultures from patients with SBS to show that the magnitude and phenotype of the adaptive stem cell response are both regulated by stromal niche cells, including intestinal subepithelial myofibroblasts, which are activated by intestinal resection to enhance epithelial stem and proliferative cell responses. Our data suggest that myofibroblast regulation of bone morphogenetic protein signaling pathways plays a role in the gut adaptive response after resection.

LGR5+ stem cells are expanded and BMP signaling regulates the stem cell niche in human short bowel syndrome.

Altered BMP-Smad4 signaling causes complete cleft palate by disturbing osteogenesis in palatal mesenchyme

As the major receptor mediated BMP signaling in craniofacial development, Bmpr1a expression was detected in the anterior palatal shelves from E13.5 and the posterior palatal shelves from E14.5. However, inactivating BMP receptor in the mesenchyme only leads to anterior cleft palate or submucous cleft palate. The role of BMP signaling in posterior palatal mesenchyme and palatal osteogenesis is still unknown. In this study, a secreted BMP antagonist, Noggin was over-expressed by Osr2-cre^KI to suppress BMP signaling intensively in mouse palatal mesenchyme, which made the newborn mouse displaying complete cleft palate, a phenotype much severer than the anterior or submucous cleft palate. Immunohistochemical analysis indicated that in the anterior and posterior palatal mesenchyme, the canonical BMP-Smad4 signaling was dramatically down-regulated, while the non-canonical BMP signaling pathways were altered little. Although cell proliferation was reduced only in the anterior palatal mesenchyme, the osteogenic condensation and Osterix distribution were remarkably repressed in the posterior palatal mesenchyme by Noggin over-expression. These findings suggested that BMP-Smad4 signaling was essential for the cell proliferation in the anterior palatal mesenchyme, and for the osteogenesis in the posterior palatal mesenchyme. Interestingly, the constitutive activation of Bmpr1a in palatal mesenchyme also caused the complete cleft palate, in which the enhanced BMP-Smad4 signaling resulted in the premature osteogenic differentiation in palatal mesenchyme. Moreover, neither the Noggin over-expression nor Bmpr1a activation disrupted the elevation of palatal shelves. Our study not only suggested that BMP signaling played the differential roles in the anterior and posterior palatal mesenchyme, but also indicated that BMP-Smad4 signaling was required to be finely tuned for the osteogenesis of palatal mesenchyme.

R-spondins are BMP receptor antagonists in Xenopus early embryonic development

BMP signaling plays key roles in development, stem cells, adult tissue homeostasis, and disease. How BMP receptors are extracellularly modulated and in which physiological context, is therefore of prime importance. R-spondins (RSPOs) are a small family of secreted proteins that co-activate WNT signaling and function as potent stem cell effectors and oncogenes. Evidence is mounting that RSPOs act WNT-independently but how and in which physiological processes remains enigmatic. Here we show that RSPO2 and RSPO3 also act as BMP antagonists. RSPO2 is a high affinity ligand for the type I BMP receptor BMPR1A/ALK3, and it engages ZNRF3 to trigger internalization and degradation of BMPR1A. In early Xenopus embryos, Rspo2 is a negative feedback inhibitor in the BMP4 synexpression group and regulates dorsoventral axis formation. We conclude that R-spondins are bifunctional ligands, which activate WNT- and inhibit BMP signaling via ZNRF3, with implications for development and cancer.

R-spondins are known modulators of Wnt signaling. Here, the authors demonstrate that R-spondins function in Xenopus embryonic development as BMP antagonists by targeting BMP receptor 1A for degradation.

Prevention of tumor risk associated with the reprogramming of human pluripotent stem cells

Human pluripotent embryonic stem cells have two special features: self-renewal and pluripotency. It is important to understand the properties of pluripotent stem cells and reprogrammed stem cells. One of the major problems is the risk of reprogrammed stem cells developing into tumors. To understand the process of differentiation through which stem cells develop into cancer cells, investigators have attempted to identify the key factors that generate tumors in humans. The most effective method for the prevention of tumorigenesis is the exclusion of cancer cells during cell reprogramming. The risk of cancer formation is dependent on mutations of oncogenes and tumor suppressor genes during the conversion of stem cells to cancer cells and on the environmental effects of pluripotent stem cells. Dissecting the processes of epigenetic regulation and chromatin regulation may be helpful for achieving correct cell reprogramming without inducing tumor formation and for developing new drugs for cancer treatment. This review focuses on the risk of tumor formation by human pluripotent stem cells, and on the possible treatment options if it occurs. Potential new techniques that target epigenetic processes and chromatin regulation provide opportunities for human cancer modeling and clinical applications of regenerative medicine.