Risk-Predictive and Diagnostic Biomarkers for Colorectal Cancer; a Systematic Review of Studies Using Pre-Diagnostic Blood Samples Collected in Prospective Cohorts and Screening Settings

5-Hydroxymethylated Biomarkers in Cell-Free DNA Predict Occult Colorectal Cancer up to 36 Months Before Diagnosis in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial

PURPOSE

Using the prostate, lung, colorectal, and ovarian (PLCO) Cancer Screening Trial samples, we identified cell-free DNA (cfDNA) candidate biomarkers bearing the epigenetic mark 5-hydroxymethylcytosine (5hmC) that detected occult colorectal cancer (CRC) up to 36 months before clinical diagnosis.

MATERIALS AND METHODS

We performed the 5hmC-seal assay and sequencing on ≤8 ng cfDNA extracted from PLCO study participant plasma samples, including n = 201 cases (diagnosed with CRC within 36 months of blood collection) and n = 401 controls (no cancer diagnosis on follow-up). We conducted association studies and machine learning modeling to analyze the genome-wide 5hmC profiles within training and validation groups that were randomly selected at a 2:1 ratio.

RESULTS

We successfully obtained 5hmC profiles from these decades-old samples. A weighted Cox model of 32 5hmC-modified gene bodies showed a predictive detection value for CRC as early as 36 months before overt tumor diagnosis (training set AUC, 77.1% [95% CI, 72.2 to 81.9] and validation set AUC, 72.8% [95% CI, 65.8 to 79.7]). Notably, the 5hmC-based predictive model showed comparable performance regardless of sex and race/ethnicity, and significantly outperformed risk factors such as age and obesity (assessed as BMI). Finally, when splitting cases at median weighted prediction scores, Kaplan-Meier analyses showed significant risk stratification for CRC occurrence in both the training set (hazard ratio, [HR], 3.3 [95% CI, 2.6 to 5.8]) and validation set (HR, 3.1 [95% CI, 1.8 to 5.8]).

CONCLUSION

Candidate 5hmC biomarkers and a scoring algorithm have the potential to predict CRC occurrence despite the absence of clinical symptoms and effective predictors. Developing a minimally invasive clinical assay that detects 5hmC-modified biomarkers holds promise for improving early CRC detection and ultimately patient outcomes.

Proteome of plasma extracellular vesicles as a source of colorectal cancer biomarkers

The search for minimally invasive methods for diagnostics of colorectal cancer (CRC) is the most important task for early diagnostics of the disease and subsequent successful treatment. Human plasma represents the main type of biological material used in the clinical practice; however, the complex dynamic range of substances circulating in it complicates determination of CRC protein markers by the mass spectrometric (MS) method. Studying the proteome of extracellular vesicles (EVs) isolated from human plasma represents an attractive approach for the discovery of tissue-secreted CRC markers. We performed shotgun mass spectrometry analysis of EV samples obtained from plasma of CRC patients and healthy volunteers. This MS analysis resulted in identification of 370 proteins (which were registered by at least two peptides). Stable isotope-free relative quantitation identified 55 proteins with altered abundance in EV samples obtained from plasma samples of CRC patients as compared to healthy controls. Among the EV proteins isolated from blood plasma we found components involved in cell adhesion and the VEGFA-VEGFR2 signaling pathway (TLN1, HSPA8, VCL, MYH9, and others), as well as proteins expressed predominantly by gastrointestinal tissues (polymeric immunoglobulin receptor, PIGR). The data obtained using the shotgun proteomic profiling may be added to the panel for targeted MS analysis of EV-associated protein markers, previously developed using CRC cell models.

UKLF/PCBP2 axis governs the colorectal cancer development by transcriptionally activating SLC39A4

Colorectal cancer (CRC) is one of the most prevalent malignant tumors with limited treatment options. Therefore, there is an urgent need to investigate new therapeutic targets against CRC. Ubiquitous Kruppel-like factor (UKLF) is involved in various cancer processes, but its effect and detailed molecular mechanism in CRC are not yet fully understood. Here, this study aimed to investigate the function and mechanism of UKLF in the development of CRC. The results showed that UKLF was highly expressed in CRC tissues from clinical patients and its high expression was related to poor prognosis. UKLF promoted cell proliferation, migration and invasion, and inhibited cell apoptosis. The promotion effect of UKLF on tumor growth was further confirmed in vivo. As far as the mechanism was concerned, poly (C) binding protein 2 (PCBP2) was verified to bind to the 3'-UTR of UKLF mRNA and enhance its mRNA stability. Moreover, UKLF modulated the expression of solute carrier family 39 member 4 (SLC39A4) at the transcriptional level. Taken together, these findings elucidated the regulatory mechanism of UKLF and uncovered the importance of the PCBP2/UKLF/SLC39A4 pathway. The targeting of UKLF may be a novel direction for molecular-targeted CRC therapy.

The Association between Blood Test Trends and Undiagnosed Cancer: A Systematic Review and Critical Appraisal

Clinical guidelines include monitoring blood test abnormalities to identify patients at increased risk of undiagnosed cancer. Noting blood test changes over time may improve cancer risk stratification by considering a patient's individual baseline and important changes within the normal range. We aimed to review the published literature to understand the association between blood test trends and undiagnosed cancer. MEDLINE and EMBASE were searched until 15 May 2023 for studies assessing the association between blood test trends and undiagnosed cancer. We used descriptive summaries and narratively synthesised studies. We included 29 articles. Common blood tests were haemoglobin (24%, n = 7), C-reactive protein (17%, n = 5), and fasting blood glucose (17%, n = 5), and common cancers were pancreatic (29%, n = 8) and colorectal (17%, n = 5). Of the 30 blood tests studied, an increasing trend in eight (27%) was associated with eight cancer types, and a decreasing trend in 17 (57%) with 10 cancer types. No association was reported between trends in 11 (37%) tests and breast, bile duct, glioma, haematological combined, liver, prostate, or thyroid cancers. Our review highlights trends in blood tests that could facilitate the identification of individuals at increased risk of undiagnosed cancer. For most possible combinations of tests and cancers, there was limited or no evidence.

Untargeted plasma metabolomics and risk of colorectal cancer-an analysis nested within a large-scale prospective cohort

BACKGROUND

Colorectal cancer (CRC) is a leading cause of cancer-related death worldwide, but if discovered at an early stage, the survival rate is high. The aim of this study was to identify novel markers predictive of future CRC risk using untargeted metabolomics.

METHODS

This study included prospectively collected plasma samples from 902 CRC cases and 902 matched cancer-free control participants from the population-based Northern Sweden Health and Disease Study (NSHDS), which were obtained up to 26 years prior to CRC diagnosis. Using reverse-phase liquid chromatography-mass spectrometry (LC-MS), data comprising 5015 metabolic features were obtained. Conditional logistic regression was applied to identify potentially important metabolic features associated with CRC risk. In addition, we investigated if previously reported metabolite biomarkers of CRC risk could be validated in this study population.

RESULTS

In the univariable analysis, seven metabolic features were associated with CRC risk (using a false discovery rate cutoff of 0.25). Two of these could be annotated, one as pyroglutamic acid (odds ratio per one standard deviation increase = 0.79, 95% confidence interval, 0.70-0.89) and another as hydroxytigecycline (odds ratio per one standard deviation increase = 0.77, 95% confidence interval, 0.67-0.89). Associations with CRC risk were also found for six previously reported metabolic biomarkers of prevalent and/or incident CRC: sebacic acid (inverse association) and L-tryptophan, 3-hydroxybutyric acid, 9,12,13-TriHOME, valine, and 13-OxoODE (positive associations).

CONCLUSIONS

These findings suggest that although the circulating metabolome may provide new etiological insights into the underlying causes of CRC development, its potential application for the identification of individuals at higher risk of developing CRC is limited.

Effect of Vitamin D Supplements on Relapse or Death in a p53-Immunoreactive Subgroup With Digestive Tract Cancer: Post Hoc Analysis of the AMATERASU Randomized Clinical Trial

Importance

Recent meta-analyses of randomized clinical trials found that daily vitamin D3 supplementation had beneficial effects on cancer mortality, although the results are still controversial.

Objective

To examine whether vitamin D supplementation reduces the risk of relapse or death in a supgroup of patients with digestive tract cancer who were p53 immunoreactive.

Design, Setting, and Participants

This was a post hoc subgroup analysis of the AMATERASU randomized, double-blind, placebo-controlled clinical trial. This trial included patients at a single university hospital in Japan with digestive tract cancers between January 2010 and February 2018 followed up for a median (IQR) of 3.5 (2.5-5.3) years to compare the effects of vitamin D supplementation with placebo and was reported in 2019. Patients from among 417 participants in the AMATERASU trial whose residual serum samples were available were included. Data were analyzed from October 20 to November 24, 2022.

Interventions

Vitamin D3 (2000 IU/d) supplementation or placebo.

Main Outcomes and Measures

The primary outcome was 5-year relapse or death. The subgroup of patients who were p53 immunoreactive was defined by positivity for anti-p53 antibodies in serum and nuclear accumulation of p53 oncosuppressor protein in more than 99% of cancer cells, which is considered a biomarker for p53 missense mutations. Anti-p53 antibody levels were measured using chemiluminescent enzyme immune assay. Immunohistochemical staining data of p53 protein in cancer tissue in pathologic specimens were obtained from a previous study and divided into 4 grades.

Results

Among 392 patients with digestive tract cancer (mean [SD] age, 66 [10.7] years; 260 males [66.3%]), there were 37 patients with esophageal cancer (9.4%), 170 patients with gastric cancer (43.4%), 2 patients with small bowel cancer (0.5%), and 183 patients with colorectal cancer (46.7%). Serum anti-p53 antibody was detectable in 142 patients (36.2%), and p53-immunohistochemistry grade showed a positive association with serum anti-p53 antibody levels (coefficient = 0.19; P < .001). In the p53-immunoreactive subgroup (80 patients), relapse or death occurred in 9 of 54 patients (16.7%) in the vitamin D group and 14 of 26 patients (53.8%) in the placebo group; 5-year relapse-free survival (RFS) was significantly higher in the vitamin D group (13 patients [80.9%]) than the placebo group (1 patient [30.6%]; hazard ratio [HR], 0.27; 95% CI, 0.11-0.61; P = .002). This was significantly different from 272 patients in the non-p53 immunoreactive subgroup, in which vitamin D had no effect on 5-year RFS (vitamin D: 35 of 158 patients [22.2%] vs placebo: 24 of 114 patients [21.1%]; HR, 1.09; 95% CI, 0.65-1.84) (P for interaction = .005).

Conclusions and Relevance

This study found that vitamin D supplementation reduced the risk of relapse or death in the subgroup of patients with digestive tract cancer who were p53 immunoreactive.

Trial Registration

Identifier: UMIN000001977.

Joint Asian Pacific Association of Gastroenterology (APAGE)-Asian Pacific Society of Digestive Endoscopy (APSDE) clinical practice guidelines on the use of non-invasive biomarkers for diagnosis of colorectal neoplasia

Screening for colorectal cancer (CRC) is effective in reducing CRC related mortality. Current screening methods include endoscopy based and biomarker based approaches. This guideline is a joint official statement of the Asian Pacific Association of Gastroenterology (APAGE) and the Asian Pacific Society of Digestive Endoscopy (APSDE), developed in response to the increasing use of, and accumulating supportive evidence for the role of, non-invasive biomarkers for the diagnosis of CRC and its precursor lesions. A systematic review of 678 publications and a two stage Delphi consensus process involving 16 clinicians in various disciplines was undertaken to develop 32 evidence based and expert opinion based recommendations for the use of faecal immunochemical tests, faecal based tumour biomarkers or microbial biomarkers, and blood based tumour biomarkers for the detection of CRC and adenoma. Comprehensive up-to-date guidance is provided on indications, patient selection and strengths and limitations of each screening tool. Future research to inform clinical applications are discussed alongside objective measurement of research priorities. This joint APAGE-APSDE practice guideline is intended to provide an up-to-date guide to assist clinicians worldwide in utilising non-invasive biomarkers for CRC screening; it has particular salience for clinicians in the Asia-Pacific region.

NCR, an Inflammation and Nutrition Related Blood-Based Marker in Colon Cancer Patients: A New Promising Biomarker to Predict Outcome

Background: Colorectal carcinoma (CRC) is a heterogeneous disease, and differences in outcomes have been reported among patients diagnosed with the same disease stage. Prognostic and predictive biomarkers provide information for patient risk stratification and guide treatment selection. Although numerous studies have analyzed the effects of systemic inflammatory factors on CRC outcomes, clinical significance remains to be elucidated. In particular, the treatment strategy of colon cancer patients is different from that of rectal cancer due to outcome and recurrence differences. The identification of patients with a poor prognosis who might benefit from intensive treatment approaches is clinically necessary. Methods: This study aimed to evaluate the value of different blood-based markers and assess the significance of our newly developed inflammatory-nutrition-related biomarker (NCR = BMI × albumin/CRP) in patients with colon cancer. A two-stage design was used with 212 patients with colon cancer (CC) in the discovery cohort (n = 159) and in an external validation cohort (n = 53). Results: A lower preoperative NCR level was significantly correlated with a worse prognosis, sidedness, undifferentiated histology, nodal involvement, and advanced UICC stage. We compared the NCR with other established prognostic indices and showed that the NCR is a more reliable indicator of a poor prognosis for patients with CC. Patients with low NCR levels experienced a significantly shorter Overall Survival (OS) than patients with high levels. Multivariate analysis confirmed preoperative NCR levels as an independent predictor for overall survival with a hazard ratio of 3.3 (95% confidence interval 1.628−6.709, p < 0.001). Finally, we confirmed the predictive value of the NCR in an independent validation cohort and confirmed NCR as an independent prognostic factor for OS. Conclusion: Taken together, we discovered a new prognostic index (NCR) based on BMI, albumin, and CRP levels as an independent prognostic predictor of OS in patients with colon cancer. In all UICC stages, our newly developed NCR marker is able to distinguish patients with better and worse prognoses. We, therefore, propose that NCR may serve as a supplement to the TNM staging system to optimize the risk stratification in CC patients towards personalized oncology. In particular, NCR can be used in clinical trials to stratify patients with UICC II and III tumors and help better select patients who might benefit from adjuvant treatment.

Pan-cancer analysis of pre-diagnostic blood metabolite concentrations in the European Prospective Investigation into Cancer and Nutrition

BACKGROUND

Epidemiological studies of associations between metabolites and cancer risk have typically focused on specific cancer types separately. Here, we designed a multivariate pan-cancer analysis to identify metabolites potentially associated with multiple cancer types, while also allowing the investigation of cancer type-specific associations.

METHODS

We analysed targeted metabolomics data available for 5828 matched case-control pairs from cancer-specific case-control studies on breast, colorectal, endometrial, gallbladder, kidney, localized and advanced prostate cancer, and hepatocellular carcinoma nested within the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. From pre-diagnostic blood levels of an initial set of 117 metabolites, 33 cluster representatives of strongly correlated metabolites and 17 single metabolites were derived by hierarchical clustering. The mutually adjusted associations of the resulting 50 metabolites with cancer risk were examined in penalized conditional logistic regression models adjusted for body mass index, using the data-shared lasso penalty.

RESULTS

Out of the 50 studied metabolites, (i) six were inversely associated with the risk of most cancer types: glutamine, butyrylcarnitine, lysophosphatidylcholine a C18:2, and three clusters of phosphatidylcholines (PCs); (ii) three were positively associated with most cancer types: proline, decanoylcarnitine, and one cluster of PCs; and (iii) 10 were specifically associated with particular cancer types, including histidine that was inversely associated with colorectal cancer risk and one cluster of sphingomyelins that was inversely associated with risk of hepatocellular carcinoma and positively with endometrial cancer risk.

CONCLUSIONS

These results could provide novel insights for the identification of pathways for cancer development, in particular those shared across different cancer types.

Presurgery Adhesion Molecules and Angiogenesis Biomarkers Are Differently Associated with Outcomes in Colon and Rectal Cancer: Results from the ColoCare Study

BACKGROUND

Cell-to-cell adhesion and angiogenesis are hallmarks of cancer. No studies have examined associations of adhesion molecules and angiogenesis biomarkers with clinical outcomes in colorectal cancer.

METHODS

In presurgery serum from n = 426 patients with colorectal cancer (stage I-III), we investigated associations of CRP, SAA, adhesion molecules (sICAM-1, sVCAM-1), and angiogenesis markers (VEGF-A and VEGF-D) with overall survival (OS), disease-free survival (DFS), and risk of recurrence. We computed HRs and 95% confidence intervals; adjusted for age, sex, BMI, stage, site, and study site, stratified by tumor site in exploratory analyses.

RESULTS

N = 65 (15%) were deceased, and 39 patients (14%) had a recurrence after a median follow-up of 31 months. We observed significant associations of biomarkers with OS, DFS, and risk of recurrence on a continuous scale and comparing top to bottom tertile, with HRs ranging between 1.19 and 13.92. CRP was associated with risk of death and recurrence in patients in the top tertile compared with patients in the bottom tertile, for example, risk of recurrence HRQ3-Q1: 13.92 (1.72-112.56). Significant heterogeneity between biomarkers and clinical outcomes was observed in stratified analysis by tumor site for CRP, SAA, sICAM-1, sVCAM-1, and VEGF-D. VEGF-D was associated with a 3-fold increase in risk of death for rectal cancer (HRlog2: 3.26; 95% CI, 1.58-6.70) compared with no association for colon cancer (HRlog2: 0.78; 95% CI, 0.35-1.73; Pheterogenity = 0.01).

CONCLUSIONS

Adhesion molecules and angiogenesis biomarkers are independent prognostic markers for colorectal cancer, with differences by tumor site.

IMPACT

There is need for tailored treatment for colon and rectal cancer.

Cancer as microenvironmental, systemic and environmental diseases: opportunity for transdisciplinary microbiomics science

Cancer is generally regarded as a localised disease, with the well-established role of the tumour microenvironment. However, the realm of cancer goes beyond the tumour microenvironment, and cancer should also be regarded as a systemic and environmental disease. The exposome (ie, the totality of exposures), which encompasses diets, supplements, smoking, alcohol, other lifestyle factors, medications, etc, likely alters the microbiome (inclusive of bacteria, viruses, archaea, fungi, parasites, etc) and immune system in various body sites and influences tumour phenotypes. The systemic metabolic/inflammatory status, which is likely influenced by exposures and intestinal physiological changes, may affect tissue microenvironment of colorectum and any other organs. Germline genomic factors can modify disease phenotypes via gene-by-environment interactions. Although challenges exist, it is crucial to advance not only basic experimental research that can analyse the effects of exposures, microorganisms and microenvironmental components on tumour evolution but also interdisciplinary human population research that can dissect the complex pathogenic roles of the exposome, microbiome and immunome. Metagenomic, metatranscriptomic and metabolomic analyses should be integrated into well-designed population research combined with advanced methodologies of artificial intelligence and molecular pathological epidemiology. Ideally, a prospective cohort study design that enables biospecimen (such as stool) collection before disease detection should be considered to address reverse causation and recall biases. Robust experimental and observational research together can provide insights into dynamic interactions between environmental exposures, microbiota, tumour and immunity during carcinogenesis processes, thereby helping us develop precision prevention and therapeutic strategies to ultimately reduce the cancer burden.

Prospective Proteomic Study Identifies Potential Circulating Protein Biomarkers for Colorectal Cancer Risk

BACKGROUND

Proteomics-based technologies are emerging tools used for cancer biomarker discovery. Limited prospective studies have been conducted to evaluate the role of circulating proteins in colorectal cancer (CRC) development.

METHODS

A two-stage case-control proteomics study nested in the Shanghai Women's Health Study was conducted. A total of 1104 circulating proteins were measured in the discovery phase, consisting of 100 incident CRC cases and 100 individually matched controls. An additional 60 case-control pairs were selected for validation. Protein profiling at both stages was completed using the Olink platforms. Conditional logistic regression was used to evaluate the associations between circulating proteins and CRC risk. The elastic net method was employed to develop a protein score for CRC risk.

RESULTS

In the discovery set, 27 proteins showed a nominally significant association with CRC risk, among which 22 were positively and 5 were inversely associated. Six of the 27 protein markers were significantly associated with CRC risk in the validation set. In the analysis of pooled discovery and validation sets, odds ratios (ORs) per standard deviation (SD) increase in levels of these proteins were 1.54 (95% confidence interval (CI): 1.15-2.06) for CD79B; 1.71 (95% CI: 1.24-2.34) for DDR1; 2.04 (95% CI: 1.39-3.01) for EFNA4; 1.54 (95% CI: 1.16-2.02) for FLRT2; 2.09 (95% CI: 1.47-2.98) for LTA4H and 1.88 (95% CI: 1.35-2.62) for NCR1. Sensitivity analyses showed consistent associations for all proteins with the exclusion of cases diagnosed within the first two years after the cohort enrollment, except for CD79B. Furthermore, a five-protein score was developed based on the six proteins identified and showed significant associations with CRC risk in both discovery and validation sets (Discovery: OR1-SD = 2.46, 95% CI: 1.53-3.95; validation: OR1-SD = 4.16, 95% CI: 1.92-8.99).

CONCLUSIONS

A panel of five protein markers was identified as potential biomarkers for CRC risk. Our findings provide novel insights into the etiology of CRC and may facilitate the risk assessment of the malignancy.

Role of the Ghrelin System in Colorectal Cancer

The ghrelin system contains several components (e.g., ghrelin with growing number of alternative peptides, growth hormone secretagogue receptors (GHS-Rs), and ghrelin-O-acyl-transferase (GOAT) and participates in regulation of a number of key processes of gastrointestinal (GI) tract cancer progression, including cell proliferation, migration, invasion, apoptosis, inflammation, and angiogenesis. However, its exact role in promoting or inhibiting cancer progression is still unclear. Colorectal cancer (CRC) is one of the most common human malignancies worldwide. Molecular studies suggest an autocrine/paracrine mechanism for the secretion of ghrelin in colorectal carcinogenesis and its contribution to its initial stages. However, the signalling pathways of CRC development involving the ghrelin system are poorly understood. Potential mechanisms of colon carcinogenesis involving components of the ghrelin system were previously described in an animal model and in in vitro studies. However, the diagnostic–prognostic role of serum ghrelin concentrations, tissue expression, or genetic changes of this system in various stages of CRC progression remains an open case. Thus, the aim of this study is to discuss the role of the ghrelin system in colon carcinogenesis, diagnostics and CRC prognostics, as well as the results of studies on the use of ghrelin and its analogues in the therapy of CRC-related syndromes (e.g., cachexia and sarcopenia).

hsa_circ_0001955 Promotes Colorectal Cancer Progression by Regulating miR-583/FGF21 Axis

Objective

Hsa_circ_0001955 presents significant upregulation in colorectal cancer (CRC) tissues. However, its role in CRC remains unclear. Thus, we attempted to clarify functions of hsa_circ_0001955 on CRC.

Methods

qRT-PCR was performed to examine hsa_circ_0001955, miR-583, and FGF21 levels. Western blotting was conducted to measure FGF21 protein expression. CCK-8, flow cytometry, and Ki-67 immunohistochemical staining and TUNEL assays were conducted to assess proliferation and apoptosis in vitro and in vivo, respectively. Cell invasion and migration were assessed by Transwell assay. Tumor-bearing mouse model and HE staining were used to assess inflammatory injury. Luciferase reporter system and RNA pull-down were conducted to evaluate the regulation between miR-583 and hsa_circ_0001955 or FGF21.

Results

We found that hsa_circ_0001955 showed characteristics of upregulated circRNA in CRC. Further analysis indicated that hsa_circ_0001955 elevation facilitated CRC cell malignancy in vitro and promoted tumor growth in vivo. Furthermore, hsa_circ_0001955 was a miR-583 sponge and FGF21 was directly targeted by miR-583. In addition, we found that downregulation of miR-583 promoted hsa_circ_0001955-mediated CRC cell malignancy in vitro. In contrast, FGF21 elevation promoted miR-583-regulated CRC cell malignancy in vitro.

Conclusion

We demonstrated that hsa_circ_0001955 facilitated CRC progression via miR-583/FGF21 axis, suggesting that hsa_circ_0001955 may provide a novel insight for therapy of CRC.

Research Progress on Leucine-Rich Alpha-2 Glycoprotein 1: A Review

Leucine-rich alpha⁃2 glycoprotein 1 (LRG1) is an important member of the leucine-rich repetitive sequence protein family. LRG1 was mainly involved in normal physiological activities of the nervous system, such as synapse formation, synapse growth, the development of nerve processes, neurotransmitter transfer and release, and cell adhesion molecules or ligand-binding proteins. Also, LRG1 affected the development of respiratory diseases, hematological diseases, endocrine diseases, tumor diseases, eye diseases, cardiovascular diseases, rheumatic immune diseases, infectious diseases, etc. LRG1 was a newly discovered important upstream signaling molecule of transforming growth factor⁃β (TGF⁃β) that affected various pathological processes through the TGF⁃β signaling pathway. However, research on LRG1 and its involvement in the occurrence and development of diseases was still in its infancy and the current studies were mainly focused on proteomic detection and basic animal experimental reports. We could reasonably predict that LRG1 might act as a new direction and strategy for the treatment of many diseases.

Single nuclei RNA sequencing of the rat AP and NTS following GDF15 treatment

Objective

Growth differentiation factor 15 (GDF15) is known to play a role in feeding, nausea, and body weight, with action through the GFRAL-RET receptor complex in the area postrema (AP) and nucleus tractus solitarius (NTS). To further elucidate the underlying cell type-specific molecular mechanisms downstream of GDF15 signaling, we used a single nuclei RNA sequencing (snRNAseq) approach to profile AP and NTS cellular subtype-specific transcriptomes after systemic GDF15 treatment.

Methods

AP and NTS micropunches were used for snRNAseq from Sprague Dawley rats 6 h following GDF15 or saline injection, and Seurat was used to identify cellular subtypes and cell type-specific alterations in gene expression that were due to the direct and secondary effects of systemic GDF15 treatment.

Results

Using the transcriptome profile of ∼35,000 individual AP/NTS nuclei, we identified 19 transcriptomically distinct cellular subtypes, including a single population Gfral and Ret positive excitatory neurons, representing the primary site of action for GDF15. A total of ∼600 cell type-specific differential expression events were identified in neurons and glia, including the identification of transcriptome alterations specific to the direct effects of GDF15 in the Gfral-Ret positive excitatory neurons and shared transcriptome alterations across neuronal and glial cell types. Downstream analyses identified shared and cell type-specific alterations in signaling pathways and upstream regulatory mechanisms of the observed transcriptome alterations.

Conclusions

These data provide a considerable advance in our understanding of AP and NTS cell type-specific molecular mechanisms associated with GDF15 signaling. The identified cellular subtype-specific regulatory mechanism and signaling pathways likely represent important targets for future pharmacotherapies.

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GDF15 directly alters transcription in Gfral- and Ret-positive excitatory neurons.

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GDF15 indirectly alters transcription in other neuronal and glial populations.

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Cell type-specific expression changes identify regulatory and signaling mechanisms.