A team at the Centro Nacional de Investigaciones Cardiovasculares (CNIC), led by Jorge Alegre-Cebollada, has developed an innovative method, called TEVs-TTN, for studying the specific mechanical functions of proteins through their controlled cleavage, a process that renders the proteins unable to sense and transmit mechanical force. The study results extend knowledge about the development of muscular diseases.
The study, published in Nature Biomedical Engineering, demonstrates that interrupting mechanical transmission by the protein titin precipitates muscular diseases. This finding opens new routes to understanding muscular dystrophies and other diseases associated with the protein titin.
Titin, named after the titans of Greek mythology, is the largest protein in animals and plays a critical role as the structural linchpin of sarcomeres, the contractile units of muscle cells. Mutations in the titin gene (TTN) are a leading cause of congenital muscular diseases and cardiomyopathies, explains first author Dr. Roberto Silva-Rojas: "Many of these mutations generate a prematurely truncated form of the protein, impeding its correct anchoring in the sarcomeres and disrupting muscle function."
Through controlled cleavage of titin with TEVs-TTN, the CNIC team was able to replicate the sarcomere disorganization typical of patients with titin mutations. As Silva-Rojas explains, muscles with cleaved titin show similar defects to those observed in patients, including cell-volume reduction, nuclear internalization, mitochondrial aggregation, and interstitial fibrosis.
"In the absence of experimental animal models with titin-cleavage mutations, our approach allows a structured and targeted analysis of the impact of these types of alterations. This makes TEVs-TTN an ideal tool for testing therapies designed to mitigate the effects of impaired sarcomere integrity."
One intriguing finding of the study is that titin cleavage caused complete disintegration of sarcomeres over the course of a few days, leaving muscle cells devoid of their basic functional unit. Nevertheless, these cells survived, suggesting that similar processes might operate in other situations, such as muscle tears, heart failure, or cardiotoxicity associated with chemotherapy.
The methodology developed at the CNIC marks a milestone in the study of how protein mechanics contribute to tissue and organ physiology. Just as titin is critical for force transmission in sarcomeres, other proteins, such as dystrophin, dystroglycan complexes, integrins, and lamins, play critical roles in extracellular matrix regulation and cell membrane integrity.
The new tool will enable the research team to confirm or refute hypotheses about the functioning of these proteins. These advances, in turn, could pave the way to the development of new therapeutic strategies for many diseases beyond those affecting muscle.
The study was funded mainly by the European Research Council through the ProtMechanics-Life Consolidator Grant (101002927) and a postdoctoral fellowship from the European Molecular Biology Organization to Dr. Silva-Rojas (EMBO ALTF 417-2022).
The CNIC is an affiliate center of the Carlos III Health Institute (ISCIII), an executive agency of the Spanish Ministry of Science, Innovation, and Universities. Directed by Dr. Valentín Fuster, the CNIC is dedicated to cardiovascular research and the translation of the knowledge gained into real benefits for patients. The CNIC has been recognized by the Spanish government as a Severo Ochoa center of excellence (award CEX2020-001041-S, funded by MICIN/AEI/10.13039/501100011033). The center is financed through a pioneering public-private partnership between the government (through the ISCIII) and the Pro-CNIC Foundation, which brings together 11 of the most important Spanish private companies.
