The insulin-like growth factors IGF-I and IGF-II—as well as their binding proteins (IGFBPs), which regulate their bioavailability—are involved in many pathological and physiological processes in cardiac tissue. Pregnancy-associated plasma protein A (PAPP-A) is a metalloprotease that preferentially cleaves IGFBP-4, releasing IGF and activating its biological activity. Previous studies have shown that PAPP-A-specific IGFBP-4 proteolysis is involved in the pathogenesis of cardiovascular diseases, such as ischemia, heart failure, and acute coronary syndrome. However, it remains unclear whether PAPP-A-specific IGFBP-4 proteolysis participates in human normal cardiomyocytes. Here, we report PAPP-A-specific IGFBP-4 proteolysis occurring in human cardiomyocytes derived from two independent induced pluripotent cell lines (hiPSC-CMs), detected both on the cell surface and in the cell secretome. PAPP-A was measured by fluoroimmune analysis (FIA) in a conditioned medium of hiPSC-CMs and was detected in concentrations of up to 4.3 ± 1.33 ng/mL and 3.8 ± 1.1 ng/mL. The level of PAPP-A-specific IGFBP-4 proteolysis was determined as the concentration of NT-IGFBP-4 proteolytic fragments using FIA for a proteolytic neo-epitope-specific assay. We showed that PAPP-A-specific IGFBP-4 proteolysis is IGF-dependent and inhibited by EDTA and 1,10-phenanthroline. Therefore, it may be concluded that PAPP-A-specific IGFBP-4 proteolysis functions in human normal cardiomyocytes, and hiPSC-CMs contain membrane-bound and secreted forms of proteolytically active PAPP-A.

Multiple endocrine neoplasia type 1 (MEN1) is a rare tumor syndrome that manifests differently among various patients. Despite the mutations in the MEN1 gene that commonly predispose tumor development, there are no obvious phenotype–genotype correlations. The existing animal and in vitro models do not allow for studies of the molecular genetics of the disease in a human-specific context. We aimed to create a new human cell-based model, which would consider the variability in genetic or environmental factors that cause the complexity of MEN1 syndrome. Here, we generated patient-specific induced pluripotent stem cell lines carrying the mutation c.1252G>T, D418Y in the MEN1 gene. To reduce the genetically determined variability of the existing cellular models, we created an isogenic cell system by modifying the target allele through CRISPR/Cas9 editing with great specificity and efficiency. The high potential of these cell lines to differentiate into the endodermal lineage in defined conditions ensures the next steps in the development of more specialized cells that are commonly affected in MEN1 patients, such as parathyroid or pancreatic islet cells. We anticipate that this isogenic system will be broadly useful to comprehensively study MEN1 gene function across different contexts, including in vitro modeling of MEN1 syndrome.

Filamin C (FLNC) is a member of a high-molecular weight protein family, which bind actin filaments in the cytoskeleton of various cells. In human genome FLNC is encoded by the FLNC gene located on chromosome 7 and is expressed predominantly in striated skeletal and cardiac muscle cells. Filamin C is involved in organization and stabilization of thin actin filaments three-dimensional network in sarcomeres, and is supposed to play a role of mechanosensor transferring mechanical signals to different protein targets. Under mechanical stress FLNC can undergo unfolding that increases the risk of its aggregation. FLNC molecules with an impaired native structure could be eliminated by the BAG3-mediated chaperone-assisted selective autophagy. Mutations in the FLNC gene could be accompanied by the changes in FLNC interaction with its protein partners and could lead to formation of aggregates, which overload the autophagy and proteasome protein degradation systems, thus facilitating development of various pathological processes. Molecular mechanisms of the FLNC-associated congenital disorders, called filaminopathies, remain poorly understood. This review is devoted to analysis of the structure and mechanisms of filamin C function in muscle and heart cells in normal state and in the FLNC-associated pathologies. The presented data summarize the results of research at the molecular, cellular, and tissue levels and allow us to outline promising ways for further investigation of pathogenetic mechanisms in filaminopathies.

Human induced pluripotent stem cell-derived cardiomyocytes (iCMs) provide a powerful platform for investigating cardiac biology. However, structural, metabolic, and electrophysiological immaturity of iCMs limits their capacity to model adult cardiomyocytes. Currently, no universally accepted criteria or protocols for effective iCMs maturation exist. This study aimed to identify practical culture conditions that promote iCMs maturation, thereby generating more physiologically relevant in vitro cardiac models. We evaluated the effects of short- and long-term culture in media supplemented with various stimulatory compounds under 2D conditions, focusing on intracellular content and localization of slow skeletal troponin I (ssTnI) and cardiac troponin I (cTnI) isoforms. Our findings demonstrate that the multicomponent metabolic maturation medium (MM-1) effectively enhances the transition toward a more mature iCM phenotype, as evidenced by increased cTnI expression and formation of cross-striated myofibrils. iCMs cultured in MM-1 more closely resemble adult cardiomyocytes and are compatible with high-resolution single-cell techniques such as electron microscopy and patch-clamp electrophysiology. This work provides a practical and scalable approach for advancing the maturation of iPSC-derived cardiac models, with applications in disease modeling and drug screening.

Restrictive cardiomyopathy (RCM) is an orphan heart disease, which is characterized by an increase in myocardial stiffness and restriction of ventricular filling with blood in the diastole. Familial forms of RCM are associated with mutations in genes encoding sarcomeric and cytoskeletal proteins. One of them is the FLNC gene encoding the actin-binding protein of Z-disks filamin C (Brodehl et al., 2016). To study the pathogenetic mechanisms of FLNC-associated RCM at the cellular level, the authors generated iPSCs (RCPCMi011-A) from fibroblasts of a patient with RCM caused by the c.7416_7418delGAA/p.Glu2472_Asn2473delAsp mutation in the FLNC gene. The pluripotent state of RCPCMi011-A iPSCs was confirmed by typical stem cell morphology, normal male karyotype maintenance, expression of pluripotency markers, and the ability to differentiate into three germ layers.

Despite recent advances in genomics and the discovery of numerous genes involved in carcinogenesis, the mechanisms of malignant transformation of different tissues remain poorly understood in...