The Emerging Role of Nerves and Glia in Colorectal Cancer

Neuroscience in peripheral cancers: tumors hijacking nerves and neuroimmune crosstalk

Cancer neuroscience is an emerging field that investigates the intricate relationship between the nervous system and cancer, gaining increasing recognition for its importance. The central nervous system governs the development of the nervous system and directly affects brain tumors, and the peripheral nervous system (PNS) shapes the tumor microenvironment (TME) of peripheral tumors. Both systems are crucial in cancer initiation and progression, with recent studies revealing a more intricate role of the PNS within the TME. Tumors not only invade nerves but also persuade them through remodeling to further promote malignancy, creating a bidirectional interaction between nerves and cancers. Notably, immune cells also contribute to this communication, forming a triangular relationship that influences protumor inflammation and the effectiveness of immunotherapy. This review delves into the intricate mechanisms connecting the PNS and tumors, focusing on how various immune cell types influence nerve‒tumor interactions, emphasizing the clinical relevance of nerve‒tumor and nerve‒immune dynamics. By deepening our understanding of the interplay between nerves, cancer, and immune cells, this review has the potential to reshape tumor biology insights, inspire innovative therapies, and improve clinical outcomes for cancer patients.

Neuronal Distribution in Colorectal Cancer: Associations With Clinicopathological Parameters and Survival

Over the past years, insights in the cancer neuroscience field increased rapidly, and a potential role for neurons in colorectal carcinogenesis has been recognized. However, knowledge on the neuronal distribution, subtypes, origin, and associations with clinicopathological characteristics in human studies is sparse. In this study, colorectal tumor tissues from the Netherlands Cohort Study on diet and cancer (n = 490) and an in-cohort validation population (n = 529) were immunohistochemically stained for the pan-neuronal markers neurofilament (NF) and protein gene product 9.5 (PGP9.5) to study the association between neuronal marker expression and clinicopathological characteristics. In addition, tumor and healthy colon tissues were stained for neuronal subtype markers, and their immunoreactivity in colorectal cancer (CRC) stroma was analyzed. NF-positive and PGP9.5-positive nerve fibers were found within the tumor stroma and mostly characterized by the neuronal subtype markers vasoactive intestinal peptide and neuronal nitric oxide synthase, suggesting that inhibitory neurons are the most prominent neuronal subtype in CRC. NF and PGP9.5 protein expression were not consistently associated with tumor stage, sublocation, differentiation grade, and median survival. NF immunoreactivity was associated with a worse CRC-specific survival in the study cohort (P = .025) independent of other prognostic factors (hazard ratio, 2.31; 95% CI, 1.33-4.03; P = .003), but these results were not observed in the in-cohort validation group. PGP9.5, in contrast, was associated with a worse CRC-specific survival in the in-cohort validation (P = .046) but not in the study population. This effect disappeared in multivariate analyses (hazard ratio, 0.81; 95% CI, 0.50-1.32; P = .393), indicating that this effect was dependent on other prognostic factors. This study demonstrates that the tumor stroma of CRC patients mainly harbors inhibitory neurons and that NF as a single marker is significantly associated with a poorer CRC-specific survival in the study cohort but necessitates future validation.

Schwann cells and enteric glial cells: Emerging stars in colorectal cancer

Cancer neuroscience, a promising field dedicated to exploring interactions between cancer and the nervous system, has attracted growing attention. The gastrointestinal tracts exhibit extensive innervation, notably characterized by intrinsic innervation. The gut harbors a substantial population of glial cells, including Schwann cells wrapping axons of neurons in the peripheral nervous system and enteric glial cells intricately associated with intrinsic innervation. Glial cells play a crucial role in maintaining the physiological functions of the intestine, encompassing nutrient absorption, barrier integrity, and immune modulation. Nevertheless, it has only been in recent times that the significance of glial cells within colorectal cancer (CRC) has begun to receive considerable attention. Emerging data suggests that glial cells in the gut contribute to the progression and metastasis of CRC, by interacting with cancer cells, influencing inflammation, and modulating the tumor microenvironment. Here, we summarize the significant roles of glial cells in the development and progression of CRC and discuss the latest technologies that can be integrated into this field for in-depth exploration, as well as potential specific targeted strategies for future exploration to benefit patients.

Neurotransmitters: Impressive regulators of tumor progression

In contemporary times, tumors have emerged as the primary cause of mortality in the global population. Ongoing research has shed light on the significance of neurotransmitters in the regulation of tumors. It has been established that neurotransmitters play a pivotal role in tumor cell angiogenesis by triggering the transformation of stromal cells into tumor cells, modulating receptors on tumor stem cells, and even inducing immunosuppression. These actions ultimately foster the proliferation and metastasis of tumor cells. Several major neurotransmitters have been found to exert modulatory effects on tumor cells, including the ability to restrict emergency hematopoiesis and bind to receptors on the postsynaptic membrane, thereby inhibiting malignant progression. The abnormal secretion of neurotransmitters is closely associated with tumor progression, suggesting that focusing on neurotransmitters may yield unexpected breakthroughs in tumor therapy. This article presents an analysis and outlook on the potential of targeting neurotransmitters in tumor therapy.

Ginsenosides: an immunomodulator for the treatment of colorectal cancer

Ginsenosides, the primary bioactive ingredients derived from the root of Panax ginseng, are eagerly in demand for tumor patients as a complementary and alternative drug. Ginsenosides have increasingly become a "hot topic" in recent years due to their multifunctional role in treating colorectal cancer (CRC) and regulating tumor microenvironment (TME). Emerging experimental research on ginsenosides in the treatment and immune regulation of CRC has been published, while no review sums up its specific role in the CRC microenvironment. Therefore, this paper systematically introduces how ginsenosides affect the TME, specifically by enhancing immune response, inhibiting the activation of stromal cells, and altering the hallmarks of CRC cells. In addition, we discuss their impact on the physicochemical properties of the tumor microenvironment. Furthermore, we discuss the application of ginsenosides in clinical treatment as their efficacy in enhancing tumor patient immunity and prolonging survival. The future perspectives of ginsenoside as a complementary and alternative drug of CRC are also provided. This review hopes to open up a new horizon for the cancer treatment of Traditional Chinese Medicine monomers.

Perineural invasion in colorectal cancer: mechanisms of action and clinical relevance

BACKGROUND

In recent years, the significance of the nervous system in the tumor microenvironment has gained increasing attention. The bidirectional communication between nerves and cancer cells plays a critical role in tumor initiation and progression. Perineural invasion (PNI) occurs when tumor cells invade the nerve sheath and/or encircle more than 33% of the nerve circumference. PNI is a common feature in various malignancies and is associated with tumor invasion, metastasis, cancer-related pain, and unfavorable clinical outcomes. The colon and rectum are highly innervated organs, and accumulating studies support PNI as a histopathologic feature of colorectal cancer (CRC). Therefore, it is essential to investigate the role of nerves in CRC and comprehend the mechanisms of PNI to impede tumor progression and improve patient survival.

CONCLUSION

This review elucidates the clinical significance of PNI, summarizes the underlying cellular and molecular mechanisms, introduces various experimental models suitable for studying PNI, and discusses the therapeutic potential of targeting this phenomenon. By delving into the intricate interactions between nerves and tumor cells, we hope this review can provide valuable insights for the future development of CRC treatments.

Chromosome 1p deletion in colorectal cancer and lower grade glioma: possible relationship with the enteric nervous system

Background

Enteric neurons and enteric glial cells are a part of the enteric nervous system, which is sometimes referred to as the "second brain" of the body. This complex network of neurons controls various functions of the gastrointestinal tract, including motility, secretion, and blood flow. Research has shown that there is a connection between enteric neurons and the development of colorectal cancer, although the exact mechanisms are still being studied.

Methods

Because of the potential influence of chromosome mutations that may be common to both gliomas and colorectal cancer, we used the Cancer Genome Atlas (TCGA) to examine these mutations.

Results

166 of 506 lower grade gliomas had the 1p 19q co-deletion. 150 of 616 colorectal cancers had a 1p deletion but no 19q deletion.

Conclusion

Colorectal cancer cells adhere to and migrate along the neurons of the enteric nervous system. Therefore, cancer cells might be expected to pick up mutations from neurons and enteric glial cells during recombination events. We hypothesize that the chromosome 1p deletion in colorectal cancer above is not a chance event and instead was acquired from adjacent enteric glial cells. Chromosome 1p co-deletion may confer better survival in patients with lower grade glioma in part because of loss of the MycBP oncogene, which is important in glioma development. Enteric glia might have the chromosome 1p deletion but lack the chromosome 19q deletion of CNS gliomas, making them much less vulnerable to malignant transformation than CNS gliomas. Indeed, evidence exists for a tumor suppressor gene on chromosome 19q associated with human astrocytomas, oligodendrogliomas, and mixed gliomas.

β-adrenergic signaling triggers enteric glial reactivity and acute enteric gliosis during surgery

BACKGROUND

Enteric glia contribute to the pathophysiology of various intestinal immune-driven diseases, such as postoperative ileus (POI), a motility disorder and common complication after abdominal surgery. Enteric gliosis of the intestinal muscularis externa (ME) has been identified as part of POI development. However, the glia-restricted responses and activation mechanisms are poorly understood. The sympathetic nervous system becomes rapidly activated by abdominal surgery. It modulates intestinal immunity, innervates all intestinal layers, and directly interfaces with enteric glia. We hypothesized that sympathetic innervation controls enteric glia reactivity in response to surgical trauma.

METHODS

Sox10iCreERT2/Rpl22HA/+ mice were subjected to a mouse model of laparotomy or intestinal manipulation to induce POI. Histological, protein, and transcriptomic analyses were performed to analyze glia-specific responses. Interactions between the sympathetic nervous system and enteric glia were studied in mice chemically depleted of TH+ sympathetic neurons and glial-restricted Sox10iCreERT2/JellyOPfl/+/Rpl22HA/+ mice, allowing optogenetic stimulation of β-adrenergic downstream signaling and glial-specific transcriptome analyses. A laparotomy model was used to study the effect of sympathetic signaling on enteric glia in the absence of intestinal manipulation. Mechanistic studies included adrenergic receptor expression profiling in vivo and in vitro and adrenergic agonism treatments of primary enteric glial cell cultures to elucidate the role of sympathetic signaling in acute enteric gliosis and POI.

RESULTS

With ~ 4000 differentially expressed genes, the most substantial enteric glia response occurs early after intestinal manipulation. During POI, enteric glia switch into a reactive state and continuously shape their microenvironment by releasing inflammatory and migratory factors. Sympathetic denervation reduced the inflammatory response of enteric glia in the early postoperative phase. Optogenetic and pharmacological stimulation of β-adrenergic downstream signaling triggered enteric glial reactivity. Finally, distinct adrenergic agonists revealed β-1/2 adrenoceptors as the molecular targets of sympathetic-driven enteric glial reactivity.

CONCLUSIONS

Enteric glia act as early responders during post-traumatic intestinal injury and inflammation. Intact sympathetic innervation and active β-adrenergic receptor signaling in enteric glia is a trigger of the immediate glial postoperative inflammatory response. With immune-activating cues originating from the sympathetic nervous system as early as the initial surgical incision, adrenergic signaling in enteric glia presents a promising target for preventing POI development.

Enteric neuro-immune interactions in intestinal health and disease

The enteric nervous system is an autonomous neuronal circuit that regulates many processes far beyond the peristalsis in the gastro-intestinal tract. This circuit, consisting of enteric neurons and enteric glial cells, can engage in many intercellular interactions shaping the homeostatic microenvironment in the gut. Perhaps the most well documented interactions taking place, are the intestinal neuro-immune interactions which are essential for the fine-tuning of oral tolerance. In the context of intestinal disease, compelling evidence demonstrates both protective and detrimental roles for this bidirectional neuro-immune signaling. This review discusses the different immune cell types that are recognized to engage in neuronal crosstalk during intestinal health and disease. Highlighting the molecular pathways involved in the neuro-immune interactions might inspire novel strategies to target intestinal disease.

Identification of disulfidptosis-related subtypes, characterization of tumor microenvironment infiltration, and development of a prognosis model in colorectal cancer

BACKGROUND

Colorectal cancer is the second leading cause of cancer-related deaths, which imposes a significant societal burden. Regular screening and emerging molecular tumor markers have important implications for detecting the progression and development of colorectal cancer. Disulfidptosis is a newly defined type of programmed cell death triggered by abnormal accumulation of disulfide compounds in cells that stimulate disulfide stress. Currently, there is no relevant discussion on this mechanism and colorectal cancer.

METHODS

We classified the disulfidptosis-related subtypes of colorectal cancer using bioinformatics methods. Through secondary clustering of differentially expressed genes between subtypes, we identified characteristic genes of the disulfidptosis subtype, constructed a prognostic model, and searched for potential biomarkers through clinical validation.

RESULTS

Using disulfidptosis-related genes collected from the literature, we classified colorectal cancer patients from public databases into three subtypes. The differentially expressed genes between subtypes were clustered into three gene subtypes, and eight characteristic genes were screened to construct a prognostic model.

CONCLUSION

The disulfidptosis mechanism has important value in the classification of colorectal cancer patients, and characteristic genes selected based on this mechanism can serve as a new potential biological marker for colorectal cancer.

Mini-Review: Enteric glia of the tumor microenvironment: An affair of corruption

The tumor microenvironment corresponds to a complex mixture of bioactive products released by local and recruited cells whose normal functions have been "corrupted" by cues originating from the tumor, mostly to favor cancer growth, dissemination and resistance to therapies. While the immune and the mesenchymal cellular components of the tumor microenvironment in colon cancer have been under intense scrutiny over the last two decades, the influence of the resident neural cells of the gut on colon carcinogenesis has only very recently begun to draw attention. The vast majority of the resident neural cells of the gastrointestinal tract belong to the enteric nervous system and correspond to enteric neurons and enteric glial cells, both of which have been understudied in the context of colon cancer development and progression. In this review, we especially discuss available evidence on enteric glia impact on colon carcinogenesis. To highlight "corrupted" functioning in enteric glial cells of the tumor microenvironment and its repercussion on tumorigenesis, we first review the main regulatory effects of enteric glial cells on the intestinal epithelium in homeostatic conditions and we next present current knowledge on enteric glia influence on colon tumorigenesis. We particularly examine how enteric glial cell heterogeneity and plasticity require further appreciation to better understand the distinct regulatory interactions enteric glial cell subtypes engage with the various cell types of the tumor, and to identify novel biological targets to block enteric glia pro-carcinogenic signaling.

Biglycan regulated colorectal cancer progress by modulating enteric neuron-derived IL-10 and abundance of Bacteroides thetaiotaomicron

Biglycan (BGN) is a proteoglycan with branch chains and highly expressed in enteric neurons in the tumor tissue of colorectal cancer (CRC), which is negatively associated with survival rates in patients with CRC. However, how the proteoglycan promotes the progress of CRC through interacting with bacteria and regulating the immune response of enteric neurons remains largely unknown. In the present study, we found that biglycan deficiency changed tumor distribution in a colitis-associated colon cancer model. Furthermore, we revealed that BGN deficiency inhibits tumor growth in an allograft tumor model and the migration of cancer cell by upregulating interleukin-10 expression in enteric neurons. Significantly, we demonstrated that biglycan deficiency enriched the abundance of Bacteroides thetaiotaomicron through competing with it for chondroitin sulfate to inhibit CRC progress. Our work provided new insights into the interaction between host proteoglycan and gut microbiota as well as the role of enteric neurons in the tumor microenvironment.

Unravelling the Complexity of Colorectal Cancer: Heterogeneity, Clonal Evolution, and Clinical Implications

Colorectal cancer (CRC) is a global health concern and a leading cause of death worldwide. The disease's course and response to treatment are significantly influenced by its heterogeneity, both within a single lesion and between primary and metastatic sites. Biomarkers, such as mutations in KRAS, NRAS, and BRAF, provide valuable guidance for treatment decisions in patients with metastatic CRC. While high concordance exists between mutational status in primary and metastatic lesions, some heterogeneity may be present. Circulating tumor DNA (ctDNA) analysis has proven invaluable in identifying genetic heterogeneity and predicting prognosis in RAS-mutated metastatic CRC patients. Tumor heterogeneity can arise from genetic and non-genetic factors, affecting tumor development and response to therapy. To comprehend and address clonal evolution and intratumoral heterogeneity, comprehensive genomic studies employing techniques such as next-generation sequencing and computational analysis are essential. Liquid biopsy, notably through analysis of ctDNA, enables real-time clonal evolution and treatment response monitoring. However, challenges remain in standardizing procedures and accurately characterizing tumor subpopulations. Various models elucidate the origin of CRC heterogeneity, highlighting the intricate molecular pathways involved. This review focuses on intrapatient cancer heterogeneity and genetic clonal evolution in metastatic CRC, with an emphasis on clinical applications.

The enteric nervous system

Of all the organ systems in the body, the gastrointestinal tract is the most complicated in terms of the numbers of structures involved, each with different functions, and the numbers and types of signaling molecules utilized. The digestion of food and absorption of nutrients, electrolytes, and water occurs in a hostile luminal environment that contains a large and diverse microbiota. At the core of regulatory control of the digestive and defensive functions of the gastrointestinal tract is the enteric nervous system (ENS), a complex system of neurons and glia in the gut wall. In this review, we discuss 1) the intrinsic neural control of gut functions involved in digestion and 2) how the ENS interacts with the immune system, gut microbiota, and epithelium to maintain mucosal defense and barrier function. We highlight developments that have revolutionized our understanding of the physiology and pathophysiology of enteric neural control. These include a new understanding of the molecular architecture of the ENS, the organization and function of enteric motor circuits, and the roles of enteric glia. We explore the transduction of luminal stimuli by enteroendocrine cells, the regulation of intestinal barrier function by enteric neurons and glia, local immune control by the ENS, and the role of the gut microbiota in regulating the structure and function of the ENS. Multifunctional enteric neurons work together with enteric glial cells, macrophages, interstitial cells, and enteroendocrine cells integrating an array of signals to initiate outputs that are precisely regulated in space and time to control digestion and intestinal homeostasis.

A CRISPR/Cas9-Based Assay for High-Throughput Studies of Cancer-Induced Innervation

The aggressive nature of certain cancers and their adverse effects on patient outcomes have been linked to cancer innervation, where neurons infiltrate and differentiate within the cancer stroma. Recently we demonstrated how cancer plasticity and TGFβ signaling could promote breast cancer innervation that is associated with increased cancer aggressivity. Despite the promising potential of cancer innervation as a target for anti-cancer therapies, there is currently a significant lack of effective methods to study cancer-induced neuronal differentiation, hindering the development of high-throughput approaches for identifying new targets or pharmacological inhibitors against cancer innervation. To overcome this challenge, we used CRISPR-based endogenous labeling of the neuronal marker β3-tubulin in neuronal precursors to investigate cancer-induced neuronal differentiation in nerve-cancer cocultures and provide a tool that allows for better standardization and reproducibility of studies about cancer-induced innervation. Our approach demonstrated that β3-tubulin gene editing did not affect neuronal behavior and enabled accurate reporting of cancer-induced neuronal differentiation dynamics in high-throughput settings, which makes this approach suitable for screening large cohorts of cells or testing various biological contexts. In a more context-based approach, by combining this method with a cell model of breast cancer epithelial-mesenchymal transition, we revealed the role of cancer cell plasticity in promoting neuronal differentiation, suggesting that cancer innervation represents an underexplored path for epithelial-mesenchymal transition-mediated cancer aggressivity.

Nerves in gastrointestinal cancer: from mechanism to modulations

Maintenance of gastrointestinal health is challenging as it requires balancing multifaceted processes within the highly complex and dynamic ecosystem of the gastrointestinal tract. Disturbances within this vibrant environment can have detrimental consequences, including the onset of gastrointestinal cancers. Globally, gastrointestinal cancers account for ~19% of all cancer cases and ~22.5% of all cancer-related deaths. Developing new ways to more readily detect and more efficiently target these malignancies are urgently needed. Whereas members of the tumour microenvironment, such as immune cells and fibroblasts, have already been in the spotlight as key players of cancer initiation and progression, the importance of the nervous system in gastrointestinal cancers has only been highlighted in the past few years. Although extrinsic innervations modulate gastrointestinal cancers, cells and signals from the gut's intrinsic innervation also have the ability to do so. Here, we shed light on this thriving field and discuss neural influences during gastrointestinal carcinogenesis. We focus on the interactions between neurons and components of the gastrointestinal tract and tumour microenvironment, on the neural signalling pathways involved, and how these factors affect the cancer hallmarks, and discuss the neural signatures in gastrointestinal cancers. Finally, we highlight neural-related therapies that have potential for the management of gastrointestinal cancers.

Schwann cells promote the migration and invasion of colorectal cancer cells via the activated NF-κB/IL-8 axis in the tumor microenvironment

BACKGROUND

Evidence has shown neurons and glial cells were closely related to tumor progression. As the predominant glial cells in the external innervated nerves of the gastrointestinal, the role of Schwann cells (SCs) in colorectal cancer (CRC) has not been well explored.

METHODS

HCT-116 and HT-29 CRC cells were treated with conditioned medium (CM) from SCs, and the cells' proliferative and migrating capacities were examined. Cytokine array analysis was used to identify the tumor-promoting-cytokines from SCs-CM. Molecular changes from SCs after being co-cultured with tumor cells were detected by ELISA and reverse transcription-quantitative PCR. The activation of the nuclear factor kappa B (NF-κB) signaling pathway in SCs was demonstrated by immunofluorescence staining. Neutralizing antibody was used to verify the tumor-promoting effects of key cytokine.

RESULTS

Migration and invasion of CRC cells were markedly aided by CM from SCs in vitro. Interleukin-8 (IL-8) was identified as an effective factor. SCs co-cultured with CRC cells upregulated IL-8 expression, which may be related to its activated NF-κB signaling pathway. Neutralization of IL-8 attenuated the tumor-promoting effect of SCs.

CONCLUSION

The present study identified a new mechanism of tumor-neuroglia interaction, enriching the concept of the tumor-neural axis in the tumor microenvironment of CRC, which also inspired potential targets for anti-cancer therapies.

Emerging Roles of the Nervous System in Gastrointestinal Cancer Development

Simple Summary

Nerve–cancer cross-talk has increasingly become a focus of the oncology field, particularly in gastrointestinal (GI) cancers. The indispensable roles of the nervous system in GI tumorigenesis and malignancy have been dissected by epidemiological, experimental animal and mechanistic data. Herein, we review and integrate recent discoveries linking the nervous system to GI cancer initiation and progression, and focus on the molecular mechanisms by which nerves and neural receptor pathways drive GI malignancy.

Abstract

Our understanding of the fascinating connection between nervous system and gastrointestinal (GI) tumorigenesis has expanded greatly in recent years. Recent studies revealed that neurogenesis plays an active part in GI tumor initiation and progression. Tumor-driven neurogenesis, as well as neurite outgrowth of the pre-existing peripheral nervous system (PNS), may fuel GI tumor progression via facilitating cancer cell proliferation, chemoresistance, invasion and immune escape. Neurotransmitters and neuropeptides drive the activation of various oncogenic pathways downstream of neural receptors within cancer cells, underscoring the importance of neural signaling pathways in GI tumor malignancy. In addition, neural infiltration also plays an integral role in tumor microenvironments, and contributes to an environment in favor of tumor angiogenesis, immune evasion and invasion. Blockade of tumor innervation via denervation or pharmacological agents may serve as a promising therapeutic strategy against GI tumors. In this review, we summarize recent findings linking the nervous system to GI tumor progression, set the spotlight on the molecular mechanisms by which neural signaling fuels cancer aggressiveness, and highlight the importance of targeting neural mechanisms in GI tumor therapy.

Identification of a neural development gene expression signature in colon cancer stem cells reveals a role for EGR2 in tumorigenesis

Recent evidence demonstrates that colon cancer stem cells (CSCs) can generate neurons that synapse with tumor innervating fibers required for tumorigenesis and disease progression. Greater understanding of the mechanisms that regulate CSC driven tumor neurogenesis may therefore lead to more effective treatments. RNA-sequencing analyses of ALDHPositive CSCs from colon cancer patient-derived organoids (PDOs) and xenografts (PDXs) showed CSCs to be enriched for neural development genes. Functional analyses of genes differentially expressed in CSCs from PDO and PDX models demonstrated the neural crest stem cell (NCSC) regulator EGR2 to be required for tumor growth and to control expression of homebox superfamily embryonic master transcriptional regulator HOX genes and the neural stem cell and master cell fate regulator SOX2. These data support CSCs as the source of tumor neurogenesis and suggest that targeting EGR2 may provide a therapeutic differentiation strategy to eliminate CSCs and block nervous system driven disease progression.

Regulation of Carcinogenesis by Sensory Neurons and Neuromediators

Interactions between the immune system and the nervous system are crucial in maintaining homeostasis, and disturbances of these neuro-immune interactions may participate in carcinogenesis and metastasis. Nerve endings have been identified within solid tumors in humans and experimental animals. Although the involvement of the efferent sympathetic and parasympathetic innervation in carcinogenesis has been extensively investigated, the role of the afferent sensory neurons and the neuropeptides in tumor development, growth, and progression is recently appreciated. Similarly, current findings point to the significant role of Schwann cells as part of neuro-immune interactions. Hence, in this review, we mainly focus on local and systemic effects of sensory nerve activity as well as Schwann cells in carcinogenesis and metastasis. Specific denervation of vagal sensory nerve fibers, or vagotomy, in animal models, has been reported to markedly increase lung metastases of breast carcinoma as well as pancreatic and gastric tumor growth, with the formation of liver metastases demonstrating the protective role of vagal sensory fibers against cancer. Clinical studies have revealed that patients with gastric ulcers who have undergone a vagotomy have a greater risk of stomach, colorectal, biliary tract, and lung cancers. Protective effects of vagal activity have also been documented by epidemiological studies demonstrating that high vagal activity predicts longer survival rates in patients with colon, non-small cell lung, prostate, and breast cancers. However, several studies have reported that inhibition of sensory neuronal activity reduces the development of solid tumors, including prostate, gastric, pancreatic, head and neck, cervical, ovarian, and skin cancers. These contradictory findings are likely to be due to the post-nerve injury-induced activation of systemic sensory fibers, the level of aggressiveness of the tumor model used, and the local heterogeneity of sensory fibers. As the aggressiveness of the tumor model and the level of the inflammatory response increase, the protective role of sensory nerve fibers is apparent and might be mostly due to systemic alterations in the neuro-immune response. Hence, more insights into inductive and permissive mechanisms, such as systemic, cellular neuro-immunological mechanisms of carcinogenesis and metastasis formation, are needed to understand the role of sensory neurons in tumor growth and spread.

Exploring the Role of Metabolites in Cancer and the Associated Nerve Crosstalk

Since Otto Warburg's first report on the increased uptake of glucose and lactate release by cancer cells, dysregulated metabolism has been acknowledged as a hallmark of cancer that promotes proliferation and metastasis. Over the last century, studies have shown that cancer metabolism is complex, and by-products of glucose and glutamine catabolism induce a cascade of both pro- and antitumorigenic processes. Some vitamins, which have traditionally been praised for preventing and inhibiting the proliferation of cancer cells, have also been proven to cause cancer progression in a dose-dependent manner. Importantly, recent findings have shown that the nervous system is a key player in tumor growth and metastasis via perineural invasion and tumor innervation. However, the link between cancer-nerve crosstalk and tumor metabolism remains unclear. Here, we discuss the roles of relatively underappreciated metabolites in cancer-nerve crosstalk, including lactate, vitamins, and amino acids, and propose the investigation of nutrients in cancer-nerve crosstalk based on their tumorigenicity and neuroregulatory capabilities. Continued research into the metabolic regulation of cancer-nerve crosstalk will provide a more comprehensive understanding of tumor mechanisms and may lead to the identification of potential targets for future cancer therapies.

Prognostic value and biological function of LRRN4 in colorectal cancer

Background

Several nervous and nerve-related biomarkers have been detected in colorectal cancer (CRC) and can contribute to the progression of CRC. However, the role of leucine-rich repeat neuronal 4 (LRRN4), a recently identified neurogenic marker, in CRC remains unclear.

Methods

We examined the expression and clinical outcomes of LRRN4 in CRC from TCGA-COREAD mRNA-sequencing datasets and immunohistochemistry in a Chinese cohort. Furthermore, colony formation, flow cytometry, wound healing assays and mouse xenograft models were used to investigate the biological significance of LRRN4 in CRC cell lines with LRRN4 knockdown or overexpression in vitro and in vivo. In addition, weighted coexpression network analysis, DAVID and western blot analysis were used to explore the potential molecular mechanism.

Results

We provide the first evidence that LRRN4 expression, at both the mRNA and protein levels, was remarkably high in CRC compared to controls and positively correlated with the clinical outcome of CRC patients. Specifically, LRRN4 was an independent prognostic factor for progression-free survival and overall survival in CRC patients. Further functional experiments showed that LRRN4 promoted cell proliferation, cell DNA synthesis and cell migration and inhibited apoptosis. Knockdown of LRRN4 can correspondingly decrease these effects in vitro and can significantly suppress the growth of xenografts. Several biological functions and signaling pathways were regulated by LRRN4, including proteoglycans in cancer, glutamatergic synapse, Ras, MAPK and PI3K. LRRN4 knockdown resulted in downregulation of Akt, p-Akt, ERK1/2 and p-ERK1/2, the downstream of the Ras/MAPK signaling pathway, overexpression of LRRN4 leaded to the upregulation of these proteins.

Conclusions

Our results suggest that LRRN4 could be a biological and molecular determinant to stratify CRC patients into distinct risk categories, and mechanistically, this is likely attributable to LRRN4 regulating several malignant phenotypes of neoplastic cells via RAS/MAPK signal pathways.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02579-x.

Cancer Evolution in Precision Medicine Era

Recent advances in our understanding of cancer, driven mainly by the emergence of new technologies have highlighted that heterogeneity shapes not only the genetic profile of tumors but also their epigenetic and gene expression profile [...]

Mast Cell–Tumor Interactions: Molecular Mechanisms of Recruitment, Intratumoral Communication and Potential Therapeutic Targets for Tumor Growth

Mast cells (MCs) are tissue-resident immune cells that are important players in diseases associated with chronic inflammation such as cancer. Since MCs can infiltrate solid tumors and promote or limit tumor growth, a possible polarization of MCs to pro-tumoral or anti-tumoral phenotypes has been proposed and remains as a challenging research field. Here, we review the recent evidence regarding the complex relationship between MCs and tumor cells. In particular, we consider: (1) the multifaceted role of MCs on tumor growth suggested by histological analysis of tumor biopsies and studies performed in MC-deficient animal models; (2) the signaling pathways triggered by tumor-derived chemotactic mediators and bioactive lipids that promote MC migration and modulate their function inside tumors; (3) the possible phenotypic changes on MCs triggered by prevalent conditions in the tumor microenvironment (TME) such as hypoxia; (4) the signaling pathways that specifically lead to the production of angiogenic factors, mainly VEGF; and (5) the possible role of MCs on tumor fibrosis and metastasis. Finally, we discuss the novel literature on the molecular mechanisms potentially related to phenotypic changes that MCs undergo into the TME and some therapeutic strategies targeting MC activation to limit tumor growth.

Parasympathetic, but not sympathetic denervation, suppressed colorectal cancer progression

Disruption in the nerve-tumor interaction is now considered as a possible anticancer strategy for treating various cancer types, particularly colorectal cancer. However, the underlying mechanisms are not still fully understood. Therefore, the present study aimed to evaluate the effects of sympathetic and parasympathetic denervation on the inhibition of colorectal cancer progression in early and late phases and assess the involvement of nerve growth factor in denervation mediated anticancer effects. One-hundred and fifty male Wistar rats were assigned into 15 groups. Seven groups comprising the control group, 1,2-dimethylhydrazine (DMH) group, sympathetic denervation group (celiac-mesenteric ganglionectomy and guanethidine sulphate administration), parasympathetic denervation group (vagotomy and atropine administration), and combination group were used in the early-stage protocol. For the late-stage protocol, eight groups comprising the control, DMH, surgical and pharmacological sympathetic and parasympathetic denervation groups, combination group, and 5-flourouracil group were considered. After 8 weeks, sympathetic and parasympathetic denervation significantly reduced ACF numbers in rats receiving DMH. On the other hand, in the late stages, parasympathetic but not sympathetic denervation resulted in significant reductions in tumor incidence, tumor volume and weight, cell proliferation (indicated by reduced immunostaining of PCNA and ki-67), and angiogenesis (indicated by reduced immunostaining of CD31 and VEGF expression levels), and downregulated NGF, β2 adrenergic, and M3 receptors. It can be concluded that parasympathetic denervation may be of high importance in colon carcinogenesis and suggested as a possible therapeutic modality in late stages of colorectal cancer.

Non-immune Cell Components in the Gastrointestinal Tumor Microenvironment Influencing Tumor Immunotherapy

Interactions of genetic susceptibility factors, immune microenvironment, and microbial factors contribute to gastrointestinal tumorigenesis. The suppressive immune microenvironment reshaped by the tumors during gastrointestinal tumorigenesis directly contributes to T-cell depletion in tumor immunotherapy. Soluble factors secreted by tumor cells or stromal cells collectively shape the suppressive immune environment. Here, we reviewed the key factors in the gastrointestinal tumor microenvironment that influence tumor immunotherapy, focusing on the effects of fibroblasts, neuronal cells, soluble cytokines, exosomes, and the microbiome in tumor microenvironment. Research in this field has helped to identify more precise and effective biomarkers and therapeutic targets in the era of tumor immunotherapy.

The inflammatory pathogenesis of colorectal cancer

The mutational landscape of colorectal cancer (CRC) does not enable predictions to be made about the survival of patients or their response to therapy. Instead, studying the polarization and activation profiles of immune cells and stromal cells in the tumour microenvironment has been shown to be more informative, thus making CRC a prototypical example of the importance of an inflammatory microenvironment for tumorigenesis. Here, we review our current understanding of how colon cancer cells interact with their microenvironment, comprised of immune cells, stromal cells and the intestinal microbiome, to suppress or escape immune responses and how inflammatory processes shape the immune pathogenesis of CRC.

The enteric nervous system in gastrointestinal disease etiology

A highly conserved but convoluted network of neurons and glial cells, the enteric nervous system (ENS), is positioned along the wall of the gut to coordinate digestive processes and gastrointestinal homeostasis. Because ENS components are in charge of the autonomous regulation of gut function, it is inevitable that their dysfunction is central to the pathophysiology and symptom generation of gastrointestinal disease. While for neurodevelopmental disorders such as Hirschsprung, ENS pathogenesis appears to be clear-cut, the role for impaired ENS activity in the etiology of other gastrointestinal disorders is less established and is often deemed secondary to other insults like intestinal inflammation. However, mounting experimental evidence in recent years indicates that gastrointestinal homeostasis hinges on multifaceted connections between the ENS, and other cellular networks such as the intestinal epithelium, the immune system, and the intestinal microbiome. Derangement of these interactions could underlie gastrointestinal disease onset and elicit variable degrees of abnormal gut function, pinpointing, perhaps unexpectedly, the ENS as a diligent participant in idiopathic but also in inflammatory and cancerous diseases of the gut. In this review, we discuss the latest evidence on the role of the ENS in the pathogenesis of enteric neuropathies, disorders of gut-brain interaction, inflammatory bowel diseases, and colorectal cancer.