Tcap, also known as Telethonin/titin-cap, encodes a Z-disc protein. It plays crucial roles in sarcomere/T-tubule interactions, stretch-sensing and signaling, and is involved in the regulation of desmin cytoskeleton organization. The putative receptors for its associated peptides are the latrophilin (LPHN) family of adhesion G-protein coupled receptors, facilitating actions through G-proteins associated with cAMP and calcium-regulating signalling pathways. Tcap is phylogenetically ancient and likely serves primitive functions in cell adhesion and energy regulation, which have evolved for more complex roles in synaptogenesis in vertebrate nervous systems. Genetic models, such as knockout zebrafish and mice, are valuable for studying Tcap's functions [1,2,3].

In tcap gene knockout zebrafish, muscular dystrophy-like phenotypes, abnormal mitochondria in skeletal muscles, inhibited stretch-sensing ability, altered cardiac morphology and function, as well as increased reactive oxygen species (ROS) and mitophagy were observed. The cardiac regeneration and cardiomyocyte proliferation ability were also impaired, but could be rescued by ROS scavengers or autophagy inhibitors, demonstrating Tcap's essential roles in striated muscle function and heart regeneration [2]. In Tcap-deficient mice, which mimic limb-girdle muscular dystrophy R7, the absence of telethonin led to desmin cytoskeleton collapse, mitochondrial network disorganization, and dysfunction. However, adeno-associated virus (AAV)-mediated Tcap replacement improved muscle phenotype, pathology, CK levels, muscle magnetic resonance imaging, mitochondrial network organization, and function, suggesting AAV-mediated replacement therapy could be a treatment option for limb-girdle muscular dystrophy R7 [3].

In conclusion, Tcap is essential for striated muscle function and heart regeneration. Its deficiency is associated with muscular dystrophy and cardiomyopathy. The use of gene knockout models in zebrafish and mice has provided insights into the mechanisms underlying these diseases, highlighting the potential of targeting ROS and autophagy, as well as AAV-mediated replacement therapy, for treating related muscle and heart disorders.

References:

1. Dodsworth, Thomas L, Lovejoy, David A. 2022. Role of Teneurin C-Terminal Associated Peptides (TCAP) on Intercellular Adhesion and Communication. In Frontiers in neuroscience, 16, 868541. doi:10.3389/fnins.2022.868541. https://pubmed.ncbi.nlm.nih.gov/35585927/

2. Zhao, Yan, Liang, Jieling, Liu, Xuan, Du, Fen, Zhang, Ruilin. 2024. Tcap deficiency impedes striated muscle function and heart regeneration with elevated ROS and autophagy. In Biochimica et biophysica acta. Molecular basis of disease, 1870, 167485. doi:10.1016/j.bbadis.2024.167485. https://pubmed.ncbi.nlm.nih.gov/39226992/

3. Lv, Xiaoqing, Liu, Shuangwu, Li, Xi, Yan, Chuanzhu, Lin, Pengfei. 2024. AAV-based TCAP delivery rescues mitochondria dislocation in limb-girdle muscular dystrophy R7. In Brain : a journal of neurology, , . doi:10.1093/brain/awae351. https://pubmed.ncbi.nlm.nih.gov/39468783/