Cthrc1 is Involved in the Activation of Adult Stem Cells in Skeletal Muscle

Abstract

Collagen triple helix repeat containing‐1 (Cthrc1) is a novel protein highly expressed after vascular injury, however the global functionality of the protein remains largely unknown. To determine the role of Cthrc1 in skeletal muscle we have characterized the skeletal muscle phenotype in Cthrc1 overexpressing transgenic (Tg15), knock out (KO) and wildtype (WT) mice. Preliminary characterization of the tibials anterior from KO and WT 12‐week old males identified a reduction in Type I muscle fiber size (KO vs. WT) with no change in distribution of Type I and Type II muscle fibers (as shown by cytochrome oxidase staining). Immunohistochemistry of the gastrocnemius from Tg15 and WT animals showed colocalization of activated Pax7+ satellite cells with both Cthrc1 and myogenin expression, suggesting that Cthrc1 correlates with stem cell activation. Tg15 muscles showed signs of active fiber regeneration, both basophilic cytoplasm and nuclear chains, possibly as a result of increased Cthrc1 expression leading to an increased number of activated stem cells within the tissue. Muscle stem cell populations dual‐labeled for Sca‐1 and CD31 were evaluated by flow cytometry; KO animals showed a significant reduction in the Sca‐1+/CD31− cell population when compared to wildtype animals. C2C12 myoblasts cultured in Cthrc1 conditioned media show increased transcript levels of muscle regulatory factors (MRF) Myf5 and myogenin when compared to controls; consistent with our animal data. The difference between Sca‐1+ MSCs, coupled with the influence of Cthrc1 on MRF expression suggests that Cthrc1 may affect MSC activation as well as proliferation. Cthrc1's potential to act as an MSC activator suggests it may play a significant role in skeletal muscle repair and regeneration offering new therapeutic approaches to fibrotic and muscle wasting diseases.