Our knowledge of pluripotent stem cell (PSC) biology has advanced to the point where we now can generate most cells of the human body in the laboratory. PSC-derived cardiomyocytes can be generated routinely with high yield and purity for disease research and drug development, and these cells are now gradually entering the clinical research phase for the testing of heart regeneration therapies. However, a major hurdle for their applications is the immature state of these cardiomyocytes. In this Review, we describe the structural and functional properties of cardiomyocytes and present the current approaches to mature PSC-derived cardiomyocytes. To date, the greatest success in maturation of PSC-derived cardiomyocytes has been with transplantation into the heart in animal models and the engineering of 3D heart tissues with electromechanical conditioning. In conventional 2D cell culture, biophysical stimuli such as mechanical loading, electrical stimulation and nanotopology cues all induce substantial maturation, particularly of the contractile cytoskeleton. Metabolism has emerged as a potent means to control maturation with unexpected effects on electrical and mechanical function. Different interventions induce distinct facets of maturation, suggesting that activating multiple signalling networks might lead to increased maturation. Despite considerable progress, we are still far from being able to generate PSC-derived cardiomyocytes with adult-like phenotypes in vitro. Future progress will come from identifying the developmental drivers of maturation and leveraging them to create more mature cardiomyocytes for research and regenerative medicine.

COVID-19 patients often develop severe cardiovascular complications, but it remains unclear if these are caused directly by viral infection or are secondary to a systemic response. Here we examine the cardiac tropism of SARS-CoV-2 in human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) and smooth muscle cells (hPSC-SMCs). We find that that SARS-CoV-2 selectively infects hPSC-CMs through the viral receptor ACE2, whereas in hPSC-SMCs there is minimal viral entry or replication. After entry into cardiomyocytes, SARS-CoV-2 is assembled in lysosome-like vesicles and egresses via bulk exocytosis. The viral transcripts become a large fraction of cellular mRNA while host gene expression shifts from oxidative to glycolytic metabolism and up-regulates chromatin modification and RNA splicing pathways. Most importantly, viral infection of hPSC-CMs progressively impairs both their electrophysiological and contractile function, and causes widespread cell death. These data support the hypothesis that COVID-19-related cardiac symptoms can result from a direct cardiotoxic effect of SARS-CoV-2.

Proprotein convertase subtilisin kexin type 9 (PCSK9) is a keyregulator of hepatic low-density lipoprotein-receptor (LDLR). PCSK9 is expressed in cultured smooth muscle cells (SMCs) and co-localizes with SMCs in human carotid atherosclerotic plaques. The present study aimed at comparing the neointimal lesions induced by periadventitial carotid placement of a non-occlusive collar in PCSK9 knock-out (PCSK9-/-) and wild type (WT) littermate (PCSK9+/+) mice. Collared carotids of the PCSK9-/-mice showed less intimal thickening compared to WT mice (p<0.05), a decreased intimal media ratio (p<0.02) and tendency to higher lumen area. When compared with PCSK9-/-, carotid lesions of WT mice had a higher content of SMCs (p<0.05) and collagen (p<0.05). No difference in macrophage content was detected between the two groups. SMCs freshly isolated from PCSK9-/-, when compared to PCSK9+/+ cells, showed higher levels of the contractile markers α-smooth muscle actin (α-SMA; 2.24±0.36 fold; p<0.01) and myosin heavy chain II (MHC-II; 8.65±1.55 fold; p<0.01), and decreased levels of synthetic markers caldesmon (-54±14%; p<0.01). PCSK9-/-cells also showed in response to platelet-derived growth factor-BB (PDGF-BB) a slower proliferation rate, and impaired migratory capacity and G1/S progression of the cell cycle. The reconstitution of PCSK9 expression, by retroviral infection of PCSK9-/-SMCs, led to a downregulation of α-SMA (-56±2%; p<0.01) and significant induction of caldesmon (1.46±0.3 fold; p<0.05). Proliferation rate of SMCs PCSK9-/-was significantly lower compared to PCSK9 reconstituted cells. Taken together, the present results suggest that by sustaining SMC synthetic phenotype, proliferation and migration PCSK9 may play a pro-atherogenic role in the arterial wall. HighlightsIn response to perivascular manipulation, the neointimal formation is reduced in PCSK9 -/-mice PCSK9 directly regulates smooth muscle cell differentiation, proliferation and migrationThe reconstitution of PCSK9 expression in SMCs PCSK9 -/-determines a switch towards a synthetic phenotype and rescue the impaired proliferation and migration capacities of SMCs PCSK9 -/-SMCs PCSK9 -/-respond less efficiently to the proliferative and chemotactic action of PDGF-BB 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 AbstractProprotein convertase subtilisin kexin type 9 (PCSK9) is a key-regulator of hepatic low-density lipoprotein-receptor (LDLR). PCSK9 is expressed in cultured smooth muscle cells (SMCs) and colocalizes with SMCs in human carotid atherosclerotic plaques. The present study aimed at comparing the neointimal lesions induced by periadventitial carotid placement of a non-occlusive collar in PCSK9 knock-out (PCSK9 -/-) and wild type (WT) littermate (PCSK9 +/+ ) mice. Collared carotids of the PCSK9 -/-mice showed less intimal thickening compared...

BackgroundProprotein convertase subtilisin/kexin type 9 (PCSK9) circulating levels are significantly associated with an increased risk of cardiovascular events. This study aimed to evaluate the relationship between circulating levels of PCSK9 and arterial stiffness, an early instrumental biomarker of cardiovascular disease risk, in a large sample of overall healthy participants.Methods and ResultsFrom the historical cohort of the Brisighella Heart Study, after exclusion of active smokers, participants in secondary prevention for cardiovascular disease, and patients in treatment with statins or vasodilating agents, we selected 227 premenopausal women and 193 age‐matched men and 460 postmenopausal women and 416 age‐matched men. In these participants, we evaluated the correlation between PCSK9 plasma circulating levels and pulse wave velocity. Postmenopausal women showed higher PCSK9 levels (309.9±84.1 ng/mL) compared with the other groups (P<0.001). Older men had significant higher levels than younger men (283.2±75.6 versus 260.9±80.4 ng/mL; P=0.008). In the whole sample, pulse wave velocity was predicted mainly by age (B=0.116, 95% CI 0.96–0.127, P<0.001), PCSK9 (B=0.014, 95% CI 0.011–0.016, P<0.001), and serum uric acid (B=0.313, 95% CI 0.024–0.391, P=0.026). Physical activity, low‐density lipoprotein cholesterol, high‐density lipoprotein cholesterol, and estimated glomerular filtration rate were not associated with pulse wave velocity (P>0.05).By considering the subgroups described, age and PCSK9 levels were mainly associated with pulse wave velocity, which also correlated with serum uric acid in postmenopausal women.ConclusionsIn the Brisighella Heart Study cohort, circulating PCSK9 is significantly related to arterial stiffness, independent of sex and menopausal status in women.

Human pluripotent stem cells (hPSCs) offer a multifaceted platform to study cardiac developmental biology, understand disease mechanisms, and develop novel therapies. Remarkable progress over the last two decades has led to methods to obtain highly pure hPSC-derived cardiomyocytes (hPSC-CMs) with reasonable ease and scalability. Nevertheless, a major bottleneck for the translational application of hPSC-CMs is their immature phenotype, resembling that of early fetal cardiomyocytes. Overall, bona fide maturation of hPSC-CMs represents one of the most significant goals facing the field today. Developmental biology studies have been pivotal in understanding the mechanisms to differentiate hPSC-CMs. Similarly, evaluation of developmental cues such as electrical and mechanical activities or neurohormonal and metabolic stimulations revealed the importance of these pathways in cardiomyocyte physiological maturation. Those signals cooperate and dictate the size and the performance of the developing heart. Likewise, this orchestra of stimuli is important in promoting hPSC-CM maturation, as demonstrated by current in vitro maturation approaches. Different shades of adult-like phenotype are achieved by prolonging the time in culture, electromechanical stimulation, patterned substrates, microRNA manipulation, neurohormonal or metabolic stimulation, and generation of human-engineered heart tissue (hEHT). However, mirroring this extremely dynamic environment is challenging, and reproducibility and scalability of these approaches represent the major obstacles for an efficient production of mature hPSC-CMs. For this reason, understanding the pattern behind the mechanisms elicited during the late gestational and early postnatal stages not only will provide new insights into postnatal development but also potentially offer new scalable and efficient approaches to mature hPSC-CMs.

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Summary Heart failure remains a significant cause of morbidity and mortality following myocardial infarction. Cardiac remuscularization with transplantation of human pluripotent stem cell-derived cardiomyocytes is a promising preclinical therapy to restore function. Recent large animal data, however, have revealed a significant risk of engraftment arrhythmia (EA). Although transient, the risk posed by EA presents a barrier to clinical translation. We hypothesized that clinically approved antiarrhythmic drugs can prevent EA-related mortality as well as suppress tachycardia and arrhythmia burden. This study uses a porcine model to provide proof-of-concept evidence that a combination of amiodarone and ivabradine can effectively suppress EA. None of the nine treated subjects experienced the primary endpoint of cardiac death, unstable EA, or heart failure compared with five out of eight (62.5%) in the control cohort (hazard ratio = 0.00; 95% confidence interval: 0–0.297; p = 0.002). Pharmacologic treatment of EA may be a viable strategy to improve safety and allow further clinical development of cardiac remuscularization therapy.

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