Cell differentiation in cardiac myxomas: confocal microscopy and gene expression analysis after laser capture microdissection

RNA-seq profiling reveals different pathways between remodeled vessels and myocardium in hypertrophic cardiomyopathy

OBJECTIVE

Coronary microvascular dysfunction (CMD) is a key pathophysiological feature of hypertrophic cardiomyopathy (HCM), contributing to myocardial ischemia and representing a critical determinant of patients' adverse outcome. The molecular mechanisms underlying the morphological and functional changes of CMD are still unknown. Aim of this study was to obtain insights on the molecular pathways associated with microvessel remodeling in HCM.

METHODS

Interventricular septum myectomies from patients with obstructive HCM (n = 20) and donors' hearts (CTRL, discarded for technical reasons, n = 7) were collected. Remodeled intramyocardial arterioles and cardiomyocytes were microdissected by laser capture and next-generation sequencing was used to delineate the transcriptome profile.

RESULTS

We identified 720 exclusive differentially expressed genes (DEGs) in cardiomyocytes and 1315 exclusive DEGs in remodeled arterioles of HCM. Performing gene ontology and pathway enrichment analyses, we identified selectively altered pathways between remodeled arterioles and cardiomyocytes in HCM patients and controls.

CONCLUSIONS

We demonstrate the existence of distinctive pathways between remodeled arterioles and cardiomyocytes in HCM patients and controls at the transcriptome level.

miRNAs in Cardiac Myxoma: New Pathologic Findings for Potential Therapeutic Opportunities

MicroRNAs (miRNAs) regulate gene expression at the post-transcriptional level, contributing to all major cellular processes. The importance of miRNAs in cardiac development, heart function, and valvular heart disease has been shown in recent years, and aberrant expression of miRNA has been reported in various malignancies, such as gastric cancer and breast cancer. Different from other fields of investigation, the role of miRNAs in cardiac tumors still remains difficult to interpret due to the scarcity publications and a lack of narrative focus on this topic. In this article, we summarize the available evidence on miRNAs and cardiac myxomas and propose new pathways for future research. miRNAs play a part in modifying the expression of cardiac transcription factors (miR-335-5p), increasing cell cycle trigger factors (miR-126-3p), interfering with ceramide synthesis (miR-320a), inducing apoptosis (miR-634 and miR-122), suppressing production of interleukins (miR-217), and reducing cell proliferation (miR-218). As such, they have complex and interconnected roles. At present, the study of the complete mechanistic control of miRNA remains a crucial issue, as proper understanding of signaling pathways is essential for the forecasting of therapeutic implications. Other types of cardiac tumors still lack adequate investigation with regard to miRNA. Further research should aim at investigating the causal relationship between different miRNAs and cell overgrowth, considering both myxoma and other histological types of cardiac tumors. We hope that this review will help in understanding this fascinating molecular approach.

Atrial myxomas arise from multipotent cardiac stem cells

Aims

Cardiac myxomas usually develop in the atria and consist of an acid-mucopolysaccharide-rich myxoid matrix with polygonal stromal cells scattered throughout. These human benign tumours are a valuable research model because of the rarity of cardiac tumours, their clinical presentation and uncertain origin. Here, we assessed whether multipotent cardiac stem/progenitor cells (CSCs) give rise to atrial myxoma tissue.

Methods and results

Twenty-three myxomas were collected and analysed for the presence of multipotent CSCs. We detected myxoma cells positive for c-kit (c-kit^pos) but very rare Isl-1 positive cells. Most of the c-kit^pos cells were blood lineage-committed CD45^pos/CD31^pos cells. However, c-kit^pos/CD45^neg/CD31^neg cardiac myxoma cells expressed stemness and cardiac progenitor cell transcription factors. Approximately ≤10% of the c-kit^pos/CD45^neg/CD31^neg myxoma cells also expressed calretinin, a characteristic of myxoma stromal cells. In vitro, the c-kit^pos/CD45^neg/CD31^neg myxoma cells secrete chondroitin-6-sulfate and hyaluronic acid, which are the main components of gelatinous myxoma matrix in vivo. In vitro, c-kit^pos/CD45^neg/CD31^neg myxoma cells have stem cell properties being clonogenic, self-renewing, and sphere forming while exhibiting an abortive cardiac differentiation potential. Myxoma-derived CSCs possess a mRNA and microRNA transcriptome overall similar to normal myocardium-derived c-kit^pos/CD45^neg/CD31^negCSCs , yet showing a relatively small and relevant fraction of dysregulated mRNA/miRNAs (miR-126-3p and miR-335-5p, in particular). Importantly, myxoma-derived CSCs but not normal myocardium-derived CSCs, seed human myxoma tumours in xenograft’s in immunodeficient NOD/SCID mice.

Conclusion

Myxoma-derived c-kit^pos/CD45^neg/CD31^neg CSCs fulfill the criteria expected of atrial myxoma-initiating stem cells. The transcriptome of these cells indicates that they belong to or are derived from the same lineage as the atrial multipotent c-kit^pos/CD45^neg/CD31^neg CSCs. Taken together the data presented here suggest that human myxomas could be the first-described CSC-related human heart disease.