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

Duchenne muscular dystrophy (DMD) is a severe muscle wasting disorder caused by dystrophin mutations, leading to the loss of sarcolemmal integrity, and resulting in progressive myofibre necrosis and impaired muscle function. Our previous studies suggest that lipin1 is important for skeletal muscle regeneration and myofibre integrity. Additionally, we discovered that mRNA expression levels of lipin1 were significantly reduced in skeletal muscle of DMD patients and the 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 (lipin1Myf5cKO ), 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 barium chloride-induced muscle injury, both lipin1Myf5cKO 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 a cell culture system, we found that lipin1 deficiency led to elevated expression levels of necroptotic markers and medium creatine kinase, which could be a result of sarcolemmal damage. Most importantly, restoration of lipin1 inhibited the elevation of necroptotic markers in differentiated primary lipin1-deficient myoblasts. Overall, our data suggests that lipin1 plays complementary roles in myofibre stability and muscle function in dystrophic muscles, and overexpression of lipin1 may serve as a potential therapeutic strategy for dystrophic muscles. KEY POINTS: We identified that lipin1 mRNA expression levels are significantly reduced in skeletal muscles of Duchenne muscular dystrophy patients and mdx mice. We found that further depletion of lipin1 in skeletal muscles of mdx mice induces more severe dystrophic phenotypes, including enhanced myofibre sarcolemma damage, muscle necroptosis, inflammation, fibrosis and reduced specific force production. Lipin1 deficiency leads to elevated expression levels of necroptotic markers, whereas restoration of lipin1 inhibits their expression. Our results suggest that lipin1 is functionally complementary to dystrophin in muscle membrane integrity and muscle regeneration.

Automated Image Analysis Pipeline Development to Monitor Disease Progression in Muscular Dystrophy Using Cell Profiler.

Muscular dystrophies are inherited disorders that are characterized by progressive muscle degeneration. These disorders are caused by mutations in the genes encoding structural elements within the muscle, which leads to increased vulnerability to mechanical stress and sarcolemma damage. Although myofibers have the capacity to regenerate, the newly formed myofibers still harbor genetic mutation, which induces continuous cycles of muscle fiber death and regeneration. This repeated cycling is accompanied by an inflammatory response which eventually provokes excessive fibrotic deposition. The histopathological changes in skeletal muscle tissue are central to the disease pathogenesis. Analysis of muscle histopathology is the gold standard for monitoring muscle health and disease progression. However, manual, or semi-manual quantification methods, are not only immensely tedious but can be subjective. Here, we present four image analysis pipelines built in CellProfiler which enable users without a background in computer vision or programming to quantitatively analyze biological images. These image analysis pipelines are designed to quantify skeletal muscle histopathological staining for membrane damage, the abundance and size distribution of regenerating muscle fibers, inflammation via quantification of CD68+ M1 macrophages, and collagen deposition. Additionally, we discuss methods to address common errors associated with the quantification of microscopy images. These automated tools can not only improve workflow efficiency but can provide a better understanding of the histopathological progression of muscular dystrophy.