Molecular characterization of the neprilysin-mediated hydrolysis of SERCA regulatory micropeptides

• Applicant: Dr. Heiko Harten
• Subject Area: Cell Biology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 550193937

The contraction of muscle fibers requires the coordinated interplay of well-characterized molecular processes, with the concentration of free cytosolic calcium ions being a crucial parameter. This concentration is largely governed by the activity of the sarcoplasmic and endoplasmic reticulum Ca2+ ATPase (SERCA), an enzyme that transports Ca2+ from the cytosol into the sarcoplasmic reticulum. The resulting reduction in cytosolic Ca2+ levels initiates the muscle relaxation phase. Accordingly, precise regulation of SERCA activity is essential for the proper function of muscle tissue and a high physiological relevance of SERCA in heart and muscle disease has been proven. Both in vertebrates and in Drosophila melanogaster, the activity of SERCA is controlled by SR membrane integral peptides that bind to the enzyme and inhibit its activity. In vertebrate hearts, Phospholamban (PLB) and Sarcolipin (SLN) have been identified as such regulatory peptides, while Sarcolamban A and B (SCLA, SCLB) represent homologous peptides in Drosophila. Vertebrate and fly loss-of-function mutants for corresponding peptides exhibit impaired Ca2+ transients in heart cells as well as severe heart arrhythmia. Until recently, mechanisms that regulate the amount or the turnover of any of the SERCA-regulatory micropeptides were completely unknown. In a recent study, we found that the endopeptidase Neprilysin 4 (Nep4) cleaves the Sarcolamban peptides and thus acts as an essential regulator of peptide homeostasis and SERCA activity in Drosophila. In addition, we provided initial evidence that this mechanism is also relevant in the human heart and that the neprilysin-mediated control of micropeptide abundance represents an evolutionarily conserved means to ensure proper SERCA regulation and heart function. Based on these results, the proposed project will address the following objectives: 1) How does neprilysin-mediated SCL / SLN cleavage affect the ability of the peptides to interact with SERCA? 2) Is neprilysin-mediated cleavage a general mechanism to control the amount and activity of SERCA-regulatory micropeptides? 3) How conserved is the identified regulatory mechanism in human cardiomyocytes? Addressing these questions has significant potential to advance the current understanding of muscle physiology and functionality, and may represent the basis for the development of innovative therapies against predominant heart and muscle diseases.

• DFG Programme: Research Grants