The Translational Landscape of the Human Heart.

Gene expression in human tissue has primarily been studied on the transcriptional level, largely neglecting translational regulation. Here, we analyze the translatomes of 80 human hearts to identify new translation events and quantify the effect of translational regulation. We show extensive translational control of cardiac gene expression, which is orchestrated in a process-specific manner. Translation downstream of predicted disease-causing protein-truncating variants appears to be frequent, suggesting inefficient translation termination. We identify hundreds of previously undetected microproteins, expressed from lncRNAs and circRNAs, for which we validate the protein products in vivo. The translation of microproteins is not restricted to the heart and prominent in the translatomes of human kidney and liver. We associate these microproteins with diverse cellular processes and compartments and find that many locate to the mitochondria. Importantly, dozens of microproteins are translated from lncRNAs with well-characterized noncoding functions, indicating previously unrecognized biology.

Mutant Phosphodiesterase 3A Protects From Hypertension-Induced Cardiac Damage.

BACKGROUND: Phosphodiesterase 3A (PDE3A) gain-of-function mutations cause hypertension with brachydactyly (HTNB) and lead to stroke. Increased peripheral vascular resistance, rather than salt retention, is responsible. It is surprising that the few patients with HTNB examined so far did not develop cardiac hypertrophy or heart failure. We hypothesized that, in the heart, PDE3A mutations could be protective. METHODS: We studied new patients. CRISPR-Cas9-engineered rat HTNB models were phenotyped by telemetric blood pressure measurements, echocardiography, microcomputed tomography, RNA-sequencing, and single nuclei RNA-sequencing. Human induced pluripotent stem cells carrying PDE3A mutations were established, differentiated to cardiomyocytes, and analyzed by Ca2+ imaging. We used Förster resonance energy transfer and biochemical assays. RESULTS: We identified a new PDE3A mutation in a family with HTNB. It maps to exon 13 encoding the enzyme's catalytic domain. All hitherto identified HTNB PDE3A mutations cluster in exon 4 encoding a region N-terminally from the catalytic domain of the enzyme. The mutations were recapitulated in rat models. Both exon 4 and 13 mutations led to aberrant phosphorylation, hyperactivity, and increased PDE3A enzyme self-assembly. The left ventricles of our patients with HTNB and the rat models were normal despite preexisting hypertension. A catecholamine challenge elicited cardiac hypertrophy in HTNB rats only to the level of wild-type rats and improved the contractility of the mutant hearts, compared with wild-type rats. The ß-adrenergic system, phosphodiesterase activity, and cAMP levels in the mutant hearts resembled wild-type hearts, whereas phospholamban phosphorylation was decreased in the mutants. In our induced pluripotent stem cell cardiomyocyte models, the PDE3A mutations caused adaptive changes of Ca2+ cycling. RNA-sequencing and single nuclei RNA-sequencing identified differences in mRNA expression between wild-type and mutants, affecting, among others, metabolism and protein folding. CONCLUSIONS: Although in vascular smooth muscle, PDE3A mutations cause hypertension, they confer protection against hypertension-induced cardiac damage in hearts. Nonselective PDE3A inhibition is a final, short-term option in heart failure treatment to increase cardiac cAMP and improve contractility. Our data argue that mimicking the effect of PDE3A mutations in the heart rather than nonselective PDE3 inhibition is cardioprotective in the long term. Our findings could facilitate the search for new treatments to prevent hypertension-induced cardiac damage.