DNA Methylation Status of the Estrogen Receptor α Gene in Canine Mammary Tumors

Exploring the role of microRNAs as diagnostic and prognostic biomarkers in canine mammary tumors

Canine mammary tumors (CMTs) represent a significant health concern in dogs, with a high incidence among intact female dogs. CMTs are a promising comparative model for human breast cancer, due to sharing several pathophysiological features. Additionally, CMTs have a strong genetic correlation with their human counterpart, including the expression of microRNAs (miRNAs). MiRNAs are a class of non-coding RNAs that play important roles in post-translational regulation of gene expression, being implicated in carcinogenesis, tumor progression, and metastasis. Moreover, miRNAs hold promise as diagnostic, prognostic, and metastatic biomarkers. Understanding the molecular mechanisms underlying CMTs is crucial for improving diagnosis, prognosis, and monitoring of treatments. Herein, we provide a comprehensive overview of the current knowledge on miRNAs in CMTs, highlighting their roles in carcinogenesis and their potential as biomarkers. Additionally, we highlight the current limitations and critically discuss the overarching challenges in this field, emphasizing the need for future research to translate miRNA findings into veterinary clinical practice.

Profiling canine mammary tumors: A potential model for studying human breast cancer

Despite all clinical progress recorded in the last decades, human breast cancer (HBC) remains a major challenge worldwide both in terms of its incidence and its management. Canine mammary tumors (CMTs) share similarities with HBC and represent an alternative model for HBC. The utility of the canine model in studying HBC relies on their common features, include spontaneous development, subtype classification, mutational profile, alterations in gene expression profile, and incidence/prevalence. This review describes the similarities between CMTs and HBC regarding genomic landscape, microRNA expression alteration, methylation, and metabolomic changes occurring during mammary gland carcinogenesis. The primary purpose of this review is to highlight the advantages of using the canine model as a translational animal model for HBC research and to investigate the challenges and limitations of this approach.

Epigenetics in Canine Mammary Tumors: Upregulation of miR-18a and miR-18b Oncogenes Is Associated with Decreased ERS1 Target mRNA Expression and ERα Immunoexpression in Highly Proliferating Carcinomas

The expression of miRNAs is one of the main epigenetic mechanisms responsible for the regulation of gene expression in mammals, and in cancer, miRNAs participate by regulating the expression of protein-coding cancer-associated genes. In canine mammary tumors (CMTs), the ESR1 gene encodes for ERα, and represents a major target gene for miR-18a and miR-18b, previously found to be overexpressed in mammary carcinomas. A loss in ERα expression in CMTs is commonly associated with poor prognosis, and it is noteworthy that the downregulation of the ESR1 would appear to be more epigenetic than genetic in nature. In this study, the expression of ESR1 mRNA in formalin-fixed, paraffin-embedded (FFPE) canine mammary tumors (CMTs) was evaluated and compared with the expression levels of miR18a and miR18b, both assessed via RT-qPCR. Furthermore, the possible correlation between the miRNA expression data and the immunohistochemical prognostic factors (ERα immunoexpression; Ki67 proliferative index) was explored. A total of twenty-six FFPE mammary samples were used, including 22 CMTs (7 benign; 15 malignant) and four control samples (three normal mammary glands and one case of lobular hyperplasia). The obtained results demonstrate that miR-18a and miR-18b are upregulated in malignant CMTs, negatively correlating with the expression of target ESR1 mRNA. Of note, the upregulation of miRNAs strictly reflects the progressive loss of ERα immunoexpression and increased tumor cell proliferation as measured using the Ki67 index. The results suggest a central role of miR-18a and miR-18b in the pathophysiology of canine mammary tumors as potential epigenetic mechanisms involved in ERα downregulation. Moreover, as miRNA expression reflects ERα protein status and a high proliferative index, miR-18a and miR-18b may represent promising biomarkers with prognostic value. More detailed investigations on a larger number of cases are needed to better understand the influence of these miRNAs in canine mammary tumors.

A Systematic Review of Apicomplexa Looking into Epigenetic Pathways and the Opportunity for Novel Therapies

Interest in host epigenetic changes during apicomplexan infections increased in the last decade, mainly due to the emergence of new therapies directed to these alterations. This review aims to carry out a bibliometric analysis of the publications related to host epigenetic changes during apicomplexan infections and to summarize the main studied pathways in this context, pointing out those that represent putative drug targets. We used four databases for the article search. After screening, 116 studies were included. The bibliometric analysis revealed that the USA and China had the highest number of relevant publications. The evaluation of the selected studies revealed that Toxoplasma gondii was considered in most of the studies, non-coding RNA was the most frequently reported epigenetic event, and host defense was the most explored pathway. These findings were reinforced by an analysis of the co-occurrence of keywords. Even though we present putative targets for repurposing epidrugs and ncRNA-based drugs in apicomplexan infections, we understand that more detailed knowledge of the hosts' epigenetic pathways is still needed before establishing a definitive drug target.

Integrated analyses of the methylome and transcriptome to unravel sex differences in the perirenal fat from suckling lambs

In sheep, differences were observed regarding fat accumulation and fatty acid (FA) composition between males and females, which may impact the quality and organoleptic characteristics of the meat. The integration of different omics technologies is a relevant approach for investigating biological and genetic mechanisms associated with complex traits. Here, the perirenal tissue of six male and six female Assaf suckling lambs was evaluated using RNA sequencing and whole-genome bisulfite sequencing (WGBS). A multiomic discriminant analysis using multiblock (s)PLS-DA allowed the identification of 314 genes and 627 differentially methylated regions (within these genes), which perfectly discriminate between males and females. These candidate genes overlapped with previously reported QTLs for carcass fat volume and percentage of different FAs in milk and meat from sheep. Additionally, differentially coexpressed (DcoExp) modules of genes between males (nine) and females (three) were identified that harbour 22 of these selected genes. Interestingly, these DcoExp were significantly correlated with fat percentage in different deposits (renal, pelvic, subcutaneous and intramuscular) and were associated with relevant biological processes for adipogenesis, adipocyte differentiation, fat volume and FA composition. Consequently, these genes may potentially impact adiposity and meat quality traits in a sex-specific manner, such as juiciness, tenderness and flavour.

Epigenetic alterations in canine mammary cancer

In dogs, mammary cancer is the most common tumor type, especially in unspayed females. As in humans, this type of cancer has spontaneous development and is influenced by several risk factors, such as age and hormonal exposure in addition to genetic and epigenetic factors. Epigenetic mechanisms are responsible for gene expression modulation without alterations in the DNA sequence and include but are not limited to DNA methylation, histone modifications, and noncoding RNAs. Epigenetic patterns are known to influence a variety of biological mechanisms, such as cellular differentiation and development, and dysregulations of those patterns may result in several diseases, such as cancer. In this respect, this review summarizes the main findings concerning epigenetic alterations in canine mammary cancer, their relationship with the carcinogenic process, and their use as diagnostic and prognostic markers.

Hormonal Homologies between Canine Mammary Cancer and Human Breast Cancer in a Series of Cases

Simple Summary

There is worldwide interest in understanding the cancerous diseases that are causing increasing deaths in humans. In recent years, interest has grown in finding suitable models of different types of cancer in animals to lead the scientific community to a better understanding of the disease, in order to win the battle against cancer. The aim of this investigation was to compare breast cancer samples and canine mammary tumors from a hormonal point of view to validate the canine species as a model to study human breast cancer. There was a close similarity between premenopausal human breast cancer and canine mammary cancer in terms of hormonal receptors. In both species, all hormones assayed were increased in tumors compared to normal mammary gland samples. This research not only further supports canine mammary cancer as a spontaneous model for the study of human breast cancer but is also important in providing a deeper understanding of the hormonal pathogenesis of breast/mammary cancer in each independent species.

Abstract

The validity of spontaneous canine mammary cancer (CMC) as a natural model for the study of human breast cancer (HBC) from a hormonal point of view has never been thoroughly investigated. In this study, we analyzed the immunohistochemical expression of aromatase (Arom) and steroid receptors [estrogen receptor α (ER α), estrogen receptor β (ER β), progesterone receptor (PR) and androgen receptor (AR)] and intratumor steroid hormone levels of 17β-estradiol (E2), estrone sulfate (SO4E1), progesterone (P4), androstenedione (A4), dehydroepiandrosterone (DHEA), and testosterone (T) in 78 samples of mammary cancer—51 human breast cancer (HBC) and 27 canine mammary cancer (CMC)—and corresponding controls. Frequency of tumors expressing Arom, ERβ, PR, and AR was similar in both species, whereas ERα+ tumors were less frequent in the canine species. There was a closer similarity between premenopausal HBC and CMC. In HBC and CMC, all hormones assayed were increased in tumors compared to control samples. Intratumor androgen levels were similar in the two species, although levels of progesterone and estrogens were higher in the HBC samples than the CMC samples. Statistical associations among Arom, receptors, and hormones analyzed suggest that the major hormonal influence in both species is estrogenic through the ER, being the α isoform predominant in the human samples. Our findings further support CMC as a spontaneous model for the study of HBC, especially premenopausal HBC, although several differences, such as the more prevalent ERα immunoexpression and higher intratumor levels of estrogens and P4 in HBC, should be taken into account in comparative hormonal studies.

Mammary carcinoma arising in an adenoma in a ewe

A large, firm, multi-cystic mammary gland mass grew slowly over 4 y in a 12-y-old, female Finn-Shetland cross sheep. A diagnosis of epithelial malignancy was suspected following fine-needle aspiration cytology at 30 mo after initial observation. The sheep was euthanized when the flock was downsized 18 mo later. A field postmortem examination revealed a large mammary mass, but an absence of metastases to internal organs. Imprint cytology of the mammary tissue supported a benign proliferative process. Histologically, mammary tissue was obliterated by cystic, tubular, and papillary adenomatous arrangements of mammary epithelium, with an anaplastic component, consistent with mammary carcinoma arising in an adenoma. IHC showed strong nuclear positivity to the antibody against progesterone receptor and minimal positivity to the antibody against estrogen receptor alpha expression. Intrinsic subtyping for basal or luminal epithelial origin was attempted through adaptation of companion animal IHC classification panels; high- and low-molecular-weight cytokeratins (CK5, CK8, CK18) failed to stain, but p63 expression for basal epithelium was positive.

Hormonal Carcinogenesis in Canine Mammary Cancer: Molecular Mechanisms of Estradiol Involved in Malignant Progression

Mammary cancer is a frequent neoplasia in female dogs, in which most important risk factors are hormonal. Sexual hormones as estradiol play an important role in mammary carcinogenesis, being able to induce carcinogenic initiation, promotion and progression. However, the molecular mechanisms involved are incompletely understood. Estradiol is synthesized mainly in the ovaries, nevertheless, high concentrations of estradiol and some of its hormonal precursors have also been described in malignant mammary tumor tissue. The mechanisms of action of estradiol include the classic genomic effects that modulate gene transcription, and non-genomic effects, which trigger quick effects after estradiol binds to its specific receptors. These responses modulate various intracellular signaling pathways, triggering post-translational modification of several proteins. This review will discuss the well-known underlying mechanisms associated with the action of estradiol in the malignant progression of canine mammary tumors.

Quantification of Global DNA Methylation in Canine Mammary Gland Tumors via Immunostaining of 5-Methylcytosine: Histopathological and Clinical Correlations

Mammary tumors are the most prevalent neoplasms in non-neutered female dogs, with genetic and epigenetic alterations contributing to canine mammary carcinogenesis. This study quantified global DNA methylation in 5-methylcytosine (5mC)-immunostained canine mammary tumor samples and established histopathological and clinical correlations. A total of 91 formalin-fixed paraffin-embedded mammary tumor samples from female dogs were retrospectively selected and subjected to immunohistochemistry using an anti-5mC mouse monoclonal antibody. We evaluated 5mC+ stained nuclei of neoplastic epithelial cells in canine mammary glands to obtain semiquantitative histoscores based on staining intensity. Survival rates were estimated based on owners' or veterinary records. Histological samples comprised 28 and 63 benign and malignant canine mammary gland tumors, respectively. Results revealed significant differences between global DNA methylation patterns when mammary samples were categorized as benign or malignant (p = 0.024), with hypomethylated patterns more prevalent in malignant tumors and those with higher relapse behavior (p = 0.011). Of note, large diameter (>5 cm) tumors revealed a lower methylation pattern (p = 0.028). Additionally, we found non-statistically significant differences when tumors were grouped by histopathological characteristics, clinical parameters, or survival. These findings propose global DNA methylation assessment as a promising tool for detecting canine mammary tumors with relapse propensity.

ANK2 Hypermethylation in Canine Mammary Tumors and Human Breast Cancer

Canine mammary tumors (CMT) constitute the most common tumor types found in female dogs. Understanding this cancer through extensive research is important not only for clinical veterinary applications, but also in the scope of comparative oncology. The use of DNA methylation as a biomarker has been noted for numerous cancers in the form of both tissue and liquid biopsies, yet the study of methylation in CMT has been limited. By analyzing our canine methyl-binding domain sequencing (MBD-seq) data, we identified intron regions of canine ANK2 and EPAS1 as differentially methylated regions (DMGs) in CMT. Subsequently, we established quantitative methylation specific PCR (qMSP) of ANK2 and EPAS1 to validate the target hypermethylation in CMT tissue, as well as cell free DNA (cfDNA) from CMT plasma. Both ANK2 and EPAS1 were hypermethylated in CMT and highlighted as potential tissue biomarkers in CMT. ANK2 additionally showed significant hypermethylation in the plasma cfDNA of CMT, indicating that it could be a potential liquid biopsy biomarker as well. A similar trend towards hypermethylation was indicated in HBC at a specific CpG of the ANK2 target on the orthologous human region, which validates the comparative approach using aberrant methylation in CMT.

Epigenetic Mechanisms in Canine Cancer

A plethora of data has highlighted the role of epigenetics in the development of cancer. Initiation and progression of different cancer types are associated with a variety of changes of epigenetic mechanisms, including aberrant DNA methylation, histone modifications, and miRNA expression. At the same time, advances in the available epigenetic tools allow to investigate and reverse these epigenetic changes and form the basis for the development of anticancer drugs in human oncology. Although human and canine cancer shares several common features, only recently that studies emerged investigating the epigenetic landscape in canine cancer and applying epigenetic modulators to canine cancer. This review focuses on the existing studies involving epigenetic changes in different types of canine cancer and the use of small-molecule inhibitors in canine cancer cells.

Genome-wide DNA methylation analysis identifies promoter hypermethylation in canine malignant melanoma

Canine malignant melanoma is a common cancer with a high mortality rate. Although previous studies have evaluated various aspects of this tumour, the exact mechanism of tumourigenesis remains unknown. Epigenetic mechanisms, such as DNA methylation, have recently gained attention as aetiological factors for neoplasia in humans. This study aimed to analyse genome-wide DNA methylation patterns in canine malignant melanoma based on next-generation sequencing data. A total of 76,213 CpG sites, including 29,482 sites in CpG islands (CGIs), were analysed using next-generation sequencing of methylation-specific signatures, obtained by sequential digestion with enzymes, to compare normal oral mucosal samples from four healthy dogs, four canine melanoma cell lines (3 oral cavity and 1 skin), and five clinical samples of oral canine melanoma. Malignant melanoma showed increased methylation at thousands of normally unmethylated CpG sites in CGIs and decreased methylation at normally methylated CpG sites in non-CGIs. Interestingly, the promoter regions of 81-393 genes were hypermethylated; 23 of these genes were present in all melanoma cell lines and melanoma clinical samples. Among these 23 genes, six genes with "sequence-specific DNA binding" annotation were significantly enriched, including three Homeobox genes-HMX2, TLX2, and HOXA9-that may be involved in the tumourigenesis of canine malignant melanoma. This study revealed widespread alterations in DNA methylation and a large number of hypermethylated genes in canine malignant melanoma.

Analysis of DNA methylation and TP53 mutational status for differentiating feline oral squamous cell carcinoma from non-neoplastic mucosa: A preliminary study

Feline oral squamous cell carcinoma (FOSCC) is characterized by high local invasiveness and early bone lysis. The late diagnosis largely limits the efficacy of therapy and increases treatment-related morbidity. The aim of this exploratory study was to assess the methylation pattern of 10 candidate genes and TP53 mutational status in histologic samples of FOSCC. Results were compared with normal oral mucosa and oral inflammatory lesions, in order to establish a gene panel for FOSCC detection. For 10 cats, the above analyses were also performed on oral brushing samples, in order to explore the utility of these methods for screening purposes. Thirty-one FOSCC, 25 chronic inflammatory lesions and 12 controls were included. TP53 mutations were significantly more frequent in the FOSCC (68%) than in the non-neoplastic oral mucosa (3%; P <.001). Based on lasso regression analysis, a step-wise algorithm including TP53, FLI1, MiR124-1, KIF1A and MAGEC2 was proposed. The algorithm allowed to differentiate FOSCC with 94% sensitivity and 100% specificity (accuracy, 97%). When applying the proposed algorithm on 10 brushing samples, accuracy decreased to 80%. These results indicate that the altered DNA methylation of specific genes is present in FOSCC, together with a significant proportion of TP53 mutations. Such alterations are infrequent in normal oral mucosa and chronic stomatitis in cats, suggesting their involvement in feline oral carcinogenesis and their utility as diagnostic biomarkers. Further studies on a high number of brushing samples will be needed to assess the utility of a screening test for the early detection of FOSCC.

Histopathological and Immunohistochemical Characteristics of Thyroid Carcinoma in the Dog

Thyroid carcinomas are a common form of endocrine neoplasia in dogs. In the present study, we combined histopathology with immunohistochemistry (IHC) to search for the presence of oestrogen receptor alpha (ORα), Cox-2 and Ki67 in canine thyroid carcinomas. Forty-eight thyroid carcinomas were diagnosed throughout the study period. Thyroglobulin and calcitonin IHC distinguished between thyroid tumours with a follicular and medullary (C-cell) origin, respectively. IHC-based diagnosis showed that 42 (87.50%) of the cases were follicular cell carcinoma. In these cases, the follicular-compact pattern was the most frequent (n = 20/42; 47.62%) and six cases (12.5%) were medullary cell (C-cell) carcinomas. Both medullary (C-cell) and follicular carcinomas expressed Ki67 and Cox-2. No differences were observed between medullary and follicular carcinomas with respect to expression of Ki67 (P = 0.34) and Cox-2 (P = 0.9523) markers. A total of 4.17% (n = 2/48) of thyroid carcinomas showed positive nuclear labelling for ORα, suggesting that oestrogen does not directly participate in the pathogenesis of canine thyroid neoplasia.

DNA methylation landscape of triple-negative ductal carcinoma in situ (DCIS) progressing to the invasive stage in canine breast cancer

Triple-negative breast cancer (TNBC) is a subtype of breast cancer unresponsive to traditional receptor-targeted treatments, leading to a disproportionate number of deaths. Invasive breast cancer is believed to evolve from non-invasive ductal carcinoma in situ (DCIS). Detection of triple-negative DCIS (TN-DCIS) is challenging, therefore strategies to study molecular events governing progression of pre-invasive TN-DCIS to invasive TNBC are needed. Here, we study a canine TN-DCIS progression and investigate the DNA methylation landscape of normal breast tissue, atypical ductal hyperplasia (ADH), DCIS and invasive breast cancer. We report hypo- and hypermethylation of genes within functional categories related to cancer such as transcriptional regulation, apoptosis, signal transduction, and cell migration. DNA methylation changes associated with cancer-related genes become more pronounced at invasive breast cancer stage. Importantly, we identify invasive-only and DCIS-specific DNA methylation alterations that could potentially determine which lesions progress to invasive cancer and which could remain as pre-invasive DCIS. Changes in DNA methylation during TN-DCIS progression in this canine model correspond with gene expression patterns in human breast tissues. This study provides evidence for utilizing methylation status of gene candidates to define late-stage (DCIS and invasive), invasive stage only or DCIS stage only of TN-DCIS progression.