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Hypertrophic cardiomyopathy (HCM) is the most common inherited heart muscle disease, with a prevalence of at least 1 in 500 in the general population. The disease is pleiotropic and is characterized by an increased stiffness of the myocardium, partly due to changes in the extracellular matrix (ECM), with elevated levels of interstitial fibrosis. Myocardial fibrosis is linked to impaired diastolic function and possibly phenotypic heterogeneity of HCM. The ECM consists of a very large number of proteins, which actively interact with each other as well as with myocardial cells. The role of other multiple components of the ECM in HCM has not been defined. Fibulin-2 is a glycoprotein component of the ECM, which plays an important role during embryogenesis of the heart; however, its role in adult myocardium has not been adequately studied. We here describe, for the first time, abnormal expression of fibulin-2 in the myocardium in patients with HCM as compared to normal controls. This abnormal expression was localized in the cytoplasm of myocardial cells and in the interstitial fibroblasts. In addition, fibulin-2 levels, measured by ELISA, were significantly elevated in the serum of patients with HCM as compared to normal controls.

Introduction: Cardiac fibroblasts (CFs) have a crucial role in ECM remodeling as well as influencing contractility through crosstalk with the cardiomyocytes. There is accumulating evidence that the phenotype of CFs is disease specific. We here investigate the transcriptome signature of CFs in HCM patients and their functional significance. Methods: Primary CFs were isolated from the myectomy specimens of 12 clinically phenotyped HCM patients and 3 controls. RNA library was prepared from the cell isolates, and whole transcriptome sequencing was performed. Differential expression analysis was carried out using the Tuxedo pipeline. Pathway, Gene Ontology (GO) enrichment, and gene network analyses were performed using Ingenuity Pathways Analysis (IPA) and Gprofiler, respectively. Expression of candidate genes was validated using real time PCR, ICC, immunohistochemistry, cytokines profiling and western blotting. Results: Whole transcriptome analysis identified 292 significant differentially expressed genes (DEGs) (pvalue <0.05 threshold) in HCM fibroblasts compared to controls. The DEGs identified with the highest significance were associated with the “Cardiovascular System development and Function” network (1.55e-27 <pvalue< 3.10e-08). The most significant GO terms identified were associated with ECM remodeling, collagen binding, signal receptor binding, circulatory system development and biological adhesion and other relevant processes. The DEGs encompassed gene families such as collagens ( COL7A1, COL17A1, COL21A1, COL15A1 and COL5A3 ), proteases ( MMP9, MMP12, ABI13BP and ADAM19 ), fibulins (FBLN1 and FBLN5), inflammatory and signaling cytokines ( IL6, CCL2, CCL4, CCL11, IGF2, CSF1, FGF16 and FGF2 ), integrins and signaling receptors ( ITGA4, ITGA7, NRP2, SULF2, ADORA2B, CXCR4, FOLR2, PLXNA4 and TREM2 ) and kinases ( DDR1, EFNB2, RGCC, MAPK11, CDKN2B, PTK7, MARCKSL1, ROCK2, MET, TYROBP and KSR1 ). Assessment of candidate genes was further performed by studying their expression patterns in patients’ samples (CFs extracts and tissue sections). Conclusion: Transcriptome signature of CFs derived from HCM identifies new candidate genes and pathways for ECM remodeling, collagen binding and pro-inflammatory signaling.