Musculoskeletal defects associated with myosin heavy chain‐embryonic loss of function are mediated by the YAP signaling pathway

• Published in: EMBO molecular medicine 2023-09, Vol.15 (9), p.e17187-21
• Main Authors: Bharadwaj, Anushree, Sharma, Jaydeep, Singh, Jagriti, Kumari, Mahima, Dargar, Tanushri, Kalita, Bhargab, Mathew, Sam J
• Format: Article
• Language: English
• Subjects: Biomedicine; Body weight; Congenital diseases; Cytoskeleton; Dysostosis; EMBO16; EMBO25; Embryos; Fibrosis; Homeostasis; Kinases; Mice; Molecular Medicine; Muscle contraction; Muscle function; Musculoskeletal diseases; Musculoskeletal system; Mutation; Myosin; Myosin heavy chain‐embryonic; Phenotypes; Proteins; Satellite cells; Scoliosis; Signal transduction; Skeletal muscle; Spondylocarpotarsal synostosis; Vertebrae; YAP; Yes-associated protein
• ISSN: 1757-4676; 1757-4684; 1757-4684
• DOI: 10.15252/emmm.202217187

Mutations in MYH3 , the gene encoding the developmental myosin heavy chain‐embryonic (MyHC‐embryonic) skeletal muscle‐specific contractile protein, cause several congenital contracture syndromes. Among these, recessive loss‐of‐function MYH3 mutations lead to spondylocarpotarsal synostosis (SCTS), characterized by vertebral fusions and scoliosis. We find that Myh3 germline knockout adult mice display SCTS phenotypes such as scoliosis and vertebral fusion, in addition to reduced body weight, muscle weight, myofiber size, and grip strength. Myh3 knockout mice also exhibit changes in muscle fiber type, altered satellite cell numbers and increased muscle fibrosis. A mass spectrometric analysis of embryonic skeletal muscle from Myh3 knockouts identified integrin signaling and cytoskeletal regulation as the most affected pathways. These pathways are closely connected to the mechanosensing Yes‐associated protein (YAP) transcriptional regulator, which we found to be significantly activated in the skeletal muscle of Myh3 knockout mice. To test whether increased YAP signaling might underlie the musculoskeletal defects in Myh3 knockout mice, we treated these mice with CA3, a small molecule inhibitor of YAP signaling. This led to increased muscle fiber size, rescue of most muscle fiber type alterations, normalization of the satellite cell marker Pax7 levels, increased grip strength, reduced fibrosis, and decline in scoliosis in Myh3 knockout mice. Thus, increased YAP activation underlies the musculoskeletal defects seen in Myh3 knockout mice, indicating its significance as a key pathway to target in SCTS and other MYH3 ‐related congenital syndromes. Synopsis In a mouse model for the MYH3‐associated spondylocarpotarsal synostosis (SCTS), altered mechanotransduction resulting from loss of MyHC‐embryonic leads to elevated Yes‐associated protein (YAP) signaling. Developing sarcomeres express MyHC‐embryonic, resulting in normal contractility and mechanical cues, leading to activation of the Hippo pathway kinases which phosphorylate YAP, causing cytoplasmic retention or degradation of YAP. Absence of MyHC‐embryonic in the Myh3 knockout mice leads to impaired contractility, mechanical cues and integrin signaling, resulting in inhibition of the Hippo pathway and lack of YAP phosphorylation. Unphosphorylated YAP gets stabilized, translocates to the nucleus, and activates downstream targets such as CTGF and CYR61, leading to musculoskeletal defects. The YAP pathway inhibitor CA3