Lipin1 plays complementary roles in myofiber stability and regeneration in dystrophic muscles.

Duchenne muscular dystrophy (DMD) is a severe muscle wasting disorder caused by dystrophin mutation, leading to the loss of sarcolemmal integrity and resulting in progressive myofiber necrosis and impaired muscle function. Our previous studies suggest that lipin1 is important for skeletal muscle regeneration and myofiber integrity. Additionally, we discovered that mRNA expression levels of lipin1 were significantly reduced in skeletal muscle of DMD patients and mdx mouse model. To understand the role of lipin1 in dystrophic muscle, we generated dystrophin/lipin1 double knockout (DKO) mice, and compared the limb muscle pathology and function of wild-type B10, muscle-specific lipin1 deficient (lipin1 Myf5cKO ), mdx and DKO mice. We found that further knockout of lipin1 in dystrophic muscle exhibited a more severe phenotype characterized by increased necroptosis, fibrosis and exacerbated membrane damage in DKO compared to mdx mice. In BaCl 2 -induced muscle injury, both lipin1 Myf5cKO and DKO showed prolonged regeneration at day 14 post-injection, suggesting that lipin1 is critical for muscle regeneration. In situ contractile function assays showed that lipin1 deficiency in dystrophic muscle led to reduced specific force production. Using cell culture system, we found that lipin1 deficiency led to elevated expression levels of necroptotic markers and medium creatine kinase which could be due to sarcolemmal damage. Most importantly, restoration of lipin1 inhibited the elevation of necroptotic markers in differentiated primary lipin1-deficient myoblasts. Overall, our data suggest that lipin1 plays complementary roles in myofiber stability and muscle function in dystrophic muscles, and overexpression of lipin1 may serve as a potential therapeutic strategy for dystrophic muscles. We identified that lipin1 mRNA expression levels are significantly reduced in skeletal muscles of DMD patients and mdx mice. We found that further depletion of lipin1 in skeletal muscles of mdx mice induces more severe dystrophic phenotypes including enhanced myofiber sarcolemma damage, muscle necroptosis, inflammation, fibrosis, and reduced specific force production. Lipin1 deficiency leads to elevated expression levels of necroptotic markers while restoration of lipin1 inhibits their expression. Our results suggest that lipin1 is functionally complementary to dystrophin in muscle membrane integrity and muscle regeneration. Abstract figure legend Lipin1 plays complementary roles in myofiber stability and muscle function in dystrophic muscles. Further knockout of lipin1 in dystrophic muscle exhibited increased necroptosis, inflammation, fibrosis, sarcolemma damage, and reduced force production (Figure is created with BioRender.com). This article is protected by copyright. All rights reserved.