Biology subjects

Kontaridis, M. I.

Publications and source records attributed to Kontaridis, M. I..

4 recordsLinked to original sources

bioRxiv2025

MYRF is Essential for Epicardial Development

Myelin Regulatory Factor (MYRF) is a transcription factor previously known for myelination of neurons in the central nervous system. Accumulating evidence has recently implicated MYRF mutations in the pathogenesis of cardiac urogenital syndrome (CUGS), in which patients exhibit a range of cardiac abnormalities, including atrial septal defect (ASD), ventricular septal defect (VSD), and hypoplastic left heart syndrome (HLHS). However, the mechanisms by which MYRF deficiency leads to cardiac anomalies remain poorly defined. Moreover, in part due to the lack of cell-type specific loss-of-function models, it is unclear which cardiac cell types contribute to the defects observed in MYRF-related CUGS. To address these questions, we examined the expression pattern of MYRF in the heart and found that it is most highly expressed in epicardial cells (EPCs) among all cardiac cell types. Importantly, Myrf global knockout (KO) mice displayed impeded epicardial development, with markedly reduced epicardial coverage of the myocardial surface. Furthermore, specifically deleting MYRF in EPCs results in severely degenerated epicardium, dramatically reduced epicardial derived cells (EPDCs), and thin myocardial wall. Conversely, ablating MYRF in cardiomyocytes (CMs) did not lead to any overt cardiac phenotypes, indicating that MYRF is dispensable for the developing CMs. Taken together, our findings suggest that compromised function of MYRF in EPCs may contribute to the pathogenesis of MYRF-related CUGS. To our knowledge, this is the first study to link impaired epicardial development to this disease.

developmental biology↗

bioRxiv2024

Rigosertib reverses hypertrophic cardiomyopathy in RAF1-associated Noonan syndrome

BackgroundRASopathies constitute a group of rare genetic disorders caused by mutations in genes that reside along the canonical Ras/MAPK signaling pathway, affecting cell growth and differentiation. These syndromes, which include conditions like Noonan syndrome (NS), are characterized by developmental delays, distinctive facial dysmorphia, and a variety of cardiac defects, notably hypertrophic cardiomyopathy (HCM). Despite their prevalence and impact, therapeutic options for RASopathies remain limited. Rigosertib, a novel dual Ras/MAPK and PI3K/AKT pathway inhibitor, is currently in clinical trials for treatment of melanoma and recessive dystrophic epidermolysis bullosa. Here, we identify rigosertib as a candidate therapy for RAF1-associated HCM. Methods and ResultsOur Drosophila screen of clinically relevant drugs and compounds identified rigosertib as broadly effective across a panel of transgenic RASopathy fly transgenic models, indicating that rigosertib may be effective against multiple disease isoforms. Analysis of a Drosophila model targeting a RAF1L613V transgene to the heart found that rigosertib reduced aspects of cardiac hypertrophy. Rigosertib treatment prevented or regressed cellular hypertrophy in human induced pluripotent stem cell-(iPSC-) derived cardiomyocytes homozygous for the NS-associated RAF1S257L allele. We extended these findings to a mammalian model, using Raf1L613V/+ KI mice to explore the therapeutic implications of rigosertib on RAF1-driven HCM. Longitudinal six-week treatment with rigosertib in these mice resulted in significant improvement in left ventricular chamber dimension and posterior wall thickness, total heart mass, size of individual cardiomyocytes (CMs), as well as reversal of cardiac hypertrophy. Rigosertib treatment also led to normalized fetal gene expression and inhibition of ERK and AKT pathway activities in primary CMs isolated from Raf1L613V/+ mice. Cardiac function, as assessed by echocardiography, showed significant improvement in ejection fraction and fractional shortening, with molecular studies confirming downregulation of hypertrophic markers and signaling pathways. Together with the Drosophila data, these mammalian results support the potential and use for rigosertib to reverse pathological hypertrophy in NS through targeted pathway inhibition in patients. Moreover, in addition to its effects in the heart, rigosertib treatment in mice also significantly improved other NS-associated syndromic features, including increasing bone growth and correcting craniofacial abnormalities. ConclusionsTaken together, our findings suggest rigosertib effectively normalizes and reverses RASopathy-associated HCM as well as other NS-associated syndromic features, supporting its potential for development as a promising treatment for RAF1-associated HCM and, potentially, other RASopathies-dependent pathologies. This study not only highlights the therapeutic potential of rigosertib but also demonstrates the utility of an integrated approach using Drosophila, iPSC and mammalian models to elucidate drug effects across complex biological systems.

molecular biology↗

bioRxiv2023

Cardiomyocyte-specific deletion of PTP1B protects against HFD-induced cardiomyopathy through direct regulation of cardiac metabolic signaling

BackgroundHeart failure is the number one cause of death worldwide and mortality is directly correlated with the high incidence of obesity and diabetes. Indeed, the epidemic phenomenon of obesity was projected to reach 50% in the US by the year 2030. However, the mechanisms linking metabolic dysfunction with heart disease are not clear. Protein Tyrosine Phosphatase 1B (PTP1B), a negative regulator of insulin signaling, is considered to be an emerging therapeutic target against the development of obesity, insulin resistance, and diabetes. Increased PTP1B levels and activity have been observed in brain, muscle and adipose tissues isolated from obese and/or diabetic animals, as well as in human obese human patients. Its role, however, and the mechanisms by which it modulates metabolic processes in the heart remain unknown. Method and ResultsWe generated cardiomyocyte (CM)-specific PTP1B knock-out (PTP1Bfl/fl::MHCCre/+) mice to investigate the cardiomyocyte-specific role of PTP1B in response to high fat diet (HFD)-induced cardiac dysfunction. While we did not observe any physiological or functional cardiac differences at baseline, in response to HFD, we found that PTP1Bfl/fl::MHCCre/+ mice were protected against development of cardiac hypertrophy, mitochondrial dysfunction, and diminished cardiac steatosis. Metabolomics data revealed that hearts with CM-specific deletion of PTP1B had increased fatty acid oxidation and NAD+ metabolism, but reduced glucose metabolism; we further validated these findings by real-time qPCR analysis. Mechanistically, we identified a novel PTP1B PKM2-AMPK axis in the heart, which acts as a molecular switch to promote fatty acid oxidation. In this regard, we identified that hearts from PTP1Bfl/fl::MHCCre/+ mice had upregulated levels of nicotinamide adenine dinucleotide (NAD+) and NAD phosphate (NADPH), leading to higher levels of nicotinamide phosphoribosyl transferase (NAMPT), the rate-limiting step of the NAD+ salvage pathway and an enzyme associated with obesity and diabetes. ConclusionsTogether, these results suggest that CM-specific deletion of PTP1B mediates a substrate switch from glucose to fatty acid metabolism, protecting hearts against development of HFD-induced cardiac hypertrophy and dysfunction through mechanisms involving a novel PTP1B/PKM2/AMPK axis that is critical for the regulation of NAMPT and NAD+ biosynthesis.

molecular biology↗

bioRxiv2021

Distinct stress-dependent signatures of cellular and extracellular tRNA-derived small RNAs (tDRs)

The cellular response to stress is an important determinant of disease pathogenesis. Uncovering the molecular fingerprints of distinct stress responses may yield novel biomarkers for different diseases, and potentially identify key signaling pathways important for disease progression. tRNAs and tRNA-derived small RNAs (tDRs) comprise one of the most abundant RNA species in cells and have been associated with cellular stress responses. The presence of RNA modifications on tDRs has been an obstacle for accurately identifying tDRs with conventional small RNA sequencing. Here, we use AlkB-facilitated methylation sequencing (ARM-seq) to uncover a comprehensive landscape of cellular and extracellular tDR expression in a variety of human and rat cells during common stress responses, including nutritional deprivation, hypoxia, and oxidative stress. We found that extracellular tDRs have a distinct fragmentation signature with a predominant length of 31-33 nts and a highly specific termination position when compared with intracellular tDRs. Importantly, we found these signatures are better discriminators of different cellular stress responses compared to extracellular miRNAs. Distinct extracellular tDR signatures for each profiled stressor are elucidated in four different types of cells. This distinct extracellular tDR fragmentation pattern is also noted in plasma extracellular RNAs from patients on cardiopulmonary bypass. The observed overlap of these patient tDR signatures with the signatures of nutritional deprivation and oxidative stress in our cellular models provides preliminary in vivo corroboration of our findings and demonstrates the potential to establish novel extracellular tDR biomarkers in human disease models.

cell biology↗